Ultrasonic actuator

The present invention relates to an ultrasonic actuator which includes a piezoelectric element.

Conventionally, an ultrasonic actuator is known which includes a piezoelectric element (electromechanical conversion element) for use in various electric devices and other types of devices (e.g., see Patent Document 1). This piezoelectric element is formed by alternately stacking piezoelectric bodies and electrodes. In the ultrasonic actuator, voltages are applied to the electrodes to cause the piezoelectric element to vibrate, whereby a movable element is moved.

Another ultrasonic actuator is known in which the piezoelectric element is energized to generate the first vertical vibration in a driving direction and the second bending direction in a direction perpendicular to the driving direction so that a vibrator provided in the piezoelectric element make an orbital movement which is a synthesis of the vertical vibration and the bending vibration, whereby a movable element is moved (e.g., see Patent Document 2).

To apply voltages to the electrodes of the piezoelectric element, the electrodes are connected to conductive members.

Patent Document 1: Japanese Laid-Open PCT National-Phase Publication No. 2003-501988

Patent Document 2: Japanese Laid-Open Patent Publication No. 2000-295876

In the piezoelectric element described in Patent Document 1, the electrodes and the conductive members are connected in a plane which is perpendicular to a surface of a piezoelectric body provided with the electrodes and which is parallel to the long sides of the surface of the piezoelectric body provided with the electrodes. Vibration of the piezoelectric element deforms the connection face and generates a stress therein. As a result, the connected portion between the electrodes and the conductive members is subjected to a stress, and there is a probability that peeling of the connection face occurs.

In the piezoelectric element described in Patent Document 2, the electrodes and the conductive members are connected on a surface of the piezoelectric element on which the electrodes are provided. Vibration of the piezoelectric element deforms the connection face and generates a stress therein. As a result, the connected portion between the electrodes and the conductive members is subjected to a stress, and there is a probability that peeling of the connection face occurs.

An object of the disclosed technology may be to provide an ultrasonic actuator in which generation of a stress is prevented in the connection face of the piezoelectric element between the electrodes and the conductive members.

The above-described object is accomplished by an ultrasonic actuator which includes the following elements. The ultrasonic actuator includes a piezoelectric element and an electric connection member electrically connected to the piezoelectric element. The piezoelectric element includes: a plurality of generally rectangular piezoelectric layers; a power supply electrode provided on a principal surface of at least one of the plurality of piezoelectric layers; a counter electrode provided to face the power supply electrode with the piezoelectric layer interposed therebetween; a power supply external electrode provided on one of external surfaces of the piezoelectric element which is perpendicular to the principal surface of the piezoelectric layer and which is parallel to short sides of the principal surface, the power supply external electrode being electrically coupled to the power supply electrode; and a counter external electrode provided on one of the external surfaces of the piezoelectric element which is perpendicular to the principal surface of the piezoelectric layer and which is parallel to the short sides of the principal surface, the counter external electrode being electrically coupled to the counter electrode. The electric connection member includes a power supply conductive member electrically connected to the power supply external electrode, and a counter conductive member electrically connected to the counter external electrode.

The disclosed technology may provide an ultrasonic actuator in which generation of a stress is prevented in the connection face of the piezoelectric element between the electrodes and the conductive members.

FIG. 1 is a general perspective view of an ultrasonic actuator according to embodiment 1.

FIG. 2 is an orthographic developed view of a piezoelectric element P 1 according to embodiment 1.

FIG. 3 shows the layers of the piezoelectric element of embodiment 1 which are seen in the layer stacking direction.

FIG. 4 illustrates the four regions over a principal surface of a piezoelectric layer.

FIG. 5 shows the positional relationship for connection of flexible cables F 1 and short-side surfaces of the piezoelectric element P 1 .

FIG. 6 is a concept diagram illustrating the displacement of the first mode stretching vibration of the ultrasonic actuator.

FIG. 7 is a concept diagram illustrating the displacement of the second mode bending vibration of the ultrasonic actuator.

FIG. 8 is a concept diagram illustrating the operation of the ultrasonic actuator.

FIG. 9 is an orthographic developed view of the piezoelectric element P 2 according to embodiment 2.

FIG. 10 shows the layers of the piezoelectric element P 2 of embodiment 2 which are seen in the layer stacking direction.

FIG. 11 shows the positional relationship for connection of flexible cables F 2 and short-side surfaces of the piezoelectric element P 2 .

FIG. 12 is an orthographic developed view of the piezoelectric element P 3 according to embodiment 3.

FIG. 13 shows the layers of the piezoelectric element P 3 of embodiment 3 which are seen in the layer stacking direction.

FIG. 14 shows the positional relationship for connection of flexible cables F 2 and short-side surfaces of the piezoelectric element P 3 .

FIG. 15 is an orthographic developed view of the piezoelectric element P 4 according to embodiment 4.

FIG. 16 shows the layers of the piezoelectric element P 4 of embodiment 4 which are seen in the layer stacking direction.

FIG. 17 shows the positional relationship for connection of flexible cables F 4 and short-side surfaces of the piezoelectric element P 4 .

FIG. 18 is an orthographic developed view of the piezoelectric element P 5 according to embodiment 5.

FIG. 19 shows the layers of the piezoelectric element P 5 of embodiment 5 which are seen in the layer stacking direction.

FIG. 20 shows the positional relationship for connection of flexible cables F 5 and short-side surfaces of the piezoelectric element P 5 .

FIG. 21 shows another ultrasonic actuator embodiment.

FIG. 22 shows still another ultrasonic actuator embodiment.

P 1 , P 2 , P 3 , P 4 , P 5 piezoelectric element

F 1 , F 2 , F 4 , F 5 flexible cable (electrical connection member)

F 11 , F 21 , F 41 , F 51 first flexible cable (first electrical connection member)

F 12 , F 22 , F 42 , F 52 second flexible cable (second electrical connection member)

1 piezoelectric layer

2 power supply electrode

2 A first power supply electrode

2 B second power supply electrode

2 a first power supply lead electrode

2 b second power supply lead electrode

3 counter electrode

3 g counter lead electrode

3 A first counter electrode

3 B first counter electrode

3 a first counter lead electrode

3 b second counter lead electrode

4 power supply external electrode

4 A first power supply external electrode

4 B second power supply external electrode

5 counter external electrode

5 A first counter external electrode

5 B second counter external electrode

6 electric line (power supply conductive member)

6 A electric line (first power supply conductive member)

6 B electric line (second power supply conductive member)

7 electric line (counter conductive member)

7 A electric line (first counter conductive member)

7 B electric line (second counter conductive member)

8 driver element

9 movable element

J 1 first connection electrode

J 2 second connection electrode

J 3 third connection electrode

J 4 fourth connection electrode

10 A first connection external electrode

10 B second connection external electrode

10 C third connection external electrode

10 D fourth connection external electrode

11 case

13 a , 13 b , 13 c supporting portion

Hereinafter, embodiments are described in detail with reference to the drawings. Note that, in the description of the embodiments, elements with the same reference character are identical elements. The description of the elements provided with the same reference character is sometimes omitted.

FIG. 1 is a general perspective view of a drive unit according to this embodiment. The drive unit of this embodiment includes an ultrasonic actuator, a movable element 9 which is actuated in a predetermined movable direction by the ultrasonic actuator, and a drive power supply (not shown) configured to control the ultrasonic actuator.

<1.1: General Configuration of Ultrasonic Actuator>

The ultrasonic actuator of this embodiment includes a piezoelectric element P 1 , driver elements 8 provided to the piezoelectric element P 1 , a case 11 containing the piezoelectric element P 1 , supporting portions 13 a - 13 c supporting the piezoelectric element P 1 on the case 11 , and flexible cables F 1 for powering the piezoelectric element P 1 . Generation of stretching vibration and bending vibration in the piezoelectric element P 1 causes generation of relative driving force between the piezoelectric element P 1 and the movable element 9 .

As shown in FIG. 1 , the ultrasonic actuator includes the piezoelectric element P 1 which is in the shape of a generally rectangular parallelepiped (for example, length 6.0 mm×width 1.7 mm×thickness 2.0 mm). The piezoelectric element P 1 includes piezoelectric layers and electrode layers which are stacked in the direction perpendicular to the plane of FIG. 1 . In FIG. 1 , the anterior surface of the piezoelectric element P 1 in the drawing sheet is a principal surface of the piezoelectric layer 1 . Hereinafter, a pair of opposite principal surfaces of the piezoelectric layer are referred to as “principal surfaces”. A pair of opposite surfaces which are perpendicular to the principal surfaces and which are parallel to the long sides of the principal surfaces are referred to as “long-side surfaces”. A pair of opposite surfaces which are perpendicular to the principal surfaces and which are parallel to the short sides of the principal surfaces are referred to as “short-side surfaces”. The principal surfaces, the long-side surfaces and the short-side surfaces constitute the outer surfaces of the piezoelectric element P 1 . The long-side surfaces and the short-side surfaces constitute the circumferential surfaces of the piezoelectric element P 1 . In this embodiment, among the principal surfaces, the long-side surfaces and the short-side surfaces, the principal surfaces have the largest area. In this embodiment, the piezoelectric element P 1 forms a vibrator.

The piezoelectric element P 1 is contained in the case 11 which is a supporting body. The piezoelectric element P 1 is supported on the case 11 via three supporting portions 13 a , 13 b and 13 c . All of the three supporting portions 13 a , 13 b and 13 c are elastic. The supporting portions 13 a and 13 c are compressed in the gaps between the two short-side surfaces and the case 11 . In this way, the piezoelectric element P 1 is supported by the supporting portions 13 a and 13 c in the long-side direction of the principal surface.

The two short-side surfaces of the piezoelectric element P 1 are electrically connected to electrical connection members.

One of the long-side surfaces of the piezoelectric element P 1 is provided with the driver elements 8 , and the driver elements 8 are in contact with the movable element 9 which is in the shape of a flat plate. Specifically, the driver elements 8 are fixed to part of the piezoelectric element P 1 near the antinode of the second mode bending vibration, which will be described later. The driver elements 8 are in the shape of a circular pole and are in line contact with the piezoelectric element P 1 . The driver elements 8 and the piezoelectric element P 1 are fixed together by an adhesive. The adhesive used is softer than the piezoelectric layer 1 and the driver elements 8 . The softness can be compared by, for example, the modulus of elasticity. The driver elements 8 and part of the movable element 9 which is in contact with the driver elements 8 are formed of a ceramic material containing, e.g., zirconia, alumina, silicon nitride as main constituents, or a resin material.

The supporting portion 13 b is provided between the other long-side surface of the piezoelectric element P 1 , i.e., a long-side surface opposite to the long-side surface on which the driver elements 8 are provided, and the case 11 . The supporting portion 13 b is compressed along a direction toward the movable element 9 (the lateral direction of the piezoelectric element P 1 ). The supporting portion 13 b pushes the piezoelectric element P 1 against the movable element 9 due to its reaction force. This increases the frictional force between the tips of the driver elements 8 and the movable element 9 so that the driving force produced by the vibration of the piezoelectric element P 1 is effectively transmitted to the movable element 9 via the driver elements 8 .

<1.2: Piezoelectric Element P 1 >

The piezoelectric element P 1 of this embodiment is in the shape of a generally rectangular parallelepiped. The piezoelectric element P 1 includes a plurality of generally rectangular piezoelectric layers 1 , which are piezoelectric, and internal electrode layers interposed between the piezoelectric layers 1 . The piezoelectric element P 1 is configured in such a manner that the piezoelectric layers and the electrode layers are stacked in a direction from front to back of the drawing sheet of FIG. 1 (hereinafter, sometimes referred to as thickness direction).

FIG. 2 is an orthographic developed view of the piezoelectric element P 1 of this embodiment. In FIG. 2 , a portion at the center represents the principal surface, portions on the right and left sides of the principal surface are the short-side surfaces, and portions on the upper and lower sides of the principal surface are the long-side surfaces. The internal electrode layers are located behind the principal surface, and thus cannot be seen. The positions of the internal electrode layers projected over the principal surface are represented by broken lines. FIG. 3 shows the respective layers of the piezoelectric element P 1 of this embodiment which are seen in the stacking direction.

As shown in FIG. 2 , the piezoelectric element P 1 is in the shape of a generally rectangular parallelepiped, which is formed by alternately stacking the generally rectangular piezoelectric layers 1 and the internal electrode layers. The piezoelectric layer 1 is an insulation layer formed of, for example, a ceramic material, such as lead zirconate titanate. The internal electrode layers are formed of power supply electrodes 2 and counter electrodes 3 which are alternately provided in the stacking direction (thickness direction of the piezoelectric element P 1 ) with the piezoelectric layers 1 interposed therebetween. The internal electrode layers are electrode layers which are formed of a metal containing, for example, silver and palladium as main constituents and which are provided on the principal surface of the piezoelectric layer 1 .

As shown in FIG. 2 , power supply external electrodes 4 and counter external electrodes 5 are provided on the short-side surfaces of the piezoelectric element P 1 . Specifically, the power supply external electrodes 4 include two first power supply external electrodes 4 A and two second power supply external electrodes 4 B which are mutually separate. The first power supply external electrodes 4 A are provided on respective one of the two short-side surfaces of the piezoelectric element P 1 at one lateral end of the piezoelectric element P 1 . The second power supply external electrodes 4 B are provided on respective one of the two short-side surfaces of the piezoelectric element P 1 at the other lateral end of the piezoelectric element P 1 (i.e., the lateral end opposite to the first power supply external electrode 4 A). The piezoelectric element P 1 includes the two counter external electrodes 5 . The counter external electrodes 5 are provided respectively on the two short-side surfaces of the piezoelectric element P 1 at the lateral center of the piezoelectric element P 1 (i.e., between the first power supply external electrode 4 A and the second power supply external electrodes 4 B). These electrodes 4 A, 4 B and 5 are mutually insulated. In other words, the electrodes 4 A, 4 B and 5 are not electrically coupled to one another.

The power supply electrodes 2 are provided on a principal surface of at least one of the plurality of piezoelectric layers 1 as shown in FIG. 3(B) .

Specifically, the power supply electrodes 2 include, on the same principal surface of the piezoelectric layer 1 , two first power supply electrodes 2 A and two second power supply electrodes 2 B which are not electrically coupled to the first power supply electrodes 2 A. The first power supply electrodes 2 A and the second power supply electrodes 2 B are rectangular electrodes.

Among four divisional regions A 1 -A 4 (see FIG. 4 ) of the principal surface of the piezoelectric layer 1 which are defined by halving the principal surface with respect to both longitudinal direction L and lateral direction S, the first power supply electrodes 2 A are provided in two of the four divisional regions which are aligned in the first diagonal direction D 1 of the principal surface of the piezoelectric layer 1 , i.e., in the divisional regions A 2 and A 4 . The second power supply electrodes 2 B are provided in the other two of the four divisional regions A 1 -A 4 which are aligned in the second diagonal direction D 2 of the principal surface of the piezoelectric layer 1 , i.e., in the divisional regions A 1 and A 3 .

Each of the first power supply electrodes 2 A includes a first power supply lead electrode 2 a extending to the first power supply external electrode 4 A which is provided on a closer one of the two short-side surfaces of the piezoelectric element P 1 . In this way, the first power supply electrode 2 A is electrically coupled to the first power supply external electrode 4 A via the first power supply lead electrode 2 a . The first power supply electrodes 2 A which are provided in the same region (A 2 or A 4 ) on the principal surfaces of different piezoelectric layers 1 are electrically coupled to each other via the first power supply lead electrodes 2 a and the first power supply external electrode 4 A.

Each of the second power supply electrodes 2 B includes a second power supply lead electrode 2 b extending to the second power supply external electrode 4 B which is provided on a closer one of the two short-side surfaces of the piezoelectric element P 1 . In this way, the second power supply electrode 2 B is electrically coupled to the second power supply external electrode 4 B via the second power supply lead electrode 2 b . The second power supply electrodes 2 B which are provided in the same region (A 1 or A 3 ) on the principal surfaces of different piezoelectric layers 1 are electrically coupled to each other via the second power supply lead electrodes 2 b and the second power supply external electrode 4 B.

The counter electrode 3 is provided over substantially the entire surface of the piezoelectric layer 1 as shown in FIG. 3(D) . Specifically, the counter electrode 3 is not provided in a circumferential region of the principal surface of the piezoelectric layer 1 but is provided over substantially the entirety of a region inside the circumferential region. The counter electrode 3 includes counter lead electrodes 3 g which extend from its lateral center to the counter external electrodes 5 which are provided on both short-side surfaces of the piezoelectric element P 1 . In this way, the counter electrode 3 is electrically coupled to the counter external electrodes 5 via the counter lead electrodes 3 g . The counter electrodes 3 provided on different piezoelectric layers 1 are electrically coupled to each other via the counter lead electrodes 3 g and the counter external electrodes 5 .

The piezoelectric element P 1 is formed by stacking the piezoelectric layers 1 provided with the power supply electrodes 2 or the counter electrode 3 on the principal surfaces as described above. Specifically, the plurality of piezoelectric layers 1 are sequentially stacked in the order of the piezoelectric layer 1 provided with the power supply electrodes 2 , the piezoelectric layer 1 provided with the counter electrode 3 , the piezoelectric layer 1 provided with the power supply electrodes 2 , . . . . The piezoelectric layers 1 are stacked such that the principal surfaces provided with the power supply electrodes 2 or the counter electrode 3 are oriented in the same direction, i.e., such that the principal surface of one of the piezoelectric layers 1 on which the power supply electrodes 2 or the counter electrode 3 is provided face the principal surface of another one of the piezoelectric layers 1 on which none of the power supply electrodes 2 and the counter electrode 3 is provided. Note that, the first and/or last of the stacked layers are the piezoelectric layers 1 which are not provided with the power supply electrodes 2 or the counter electrode 3 such that the power supply electrodes 2 or the counter electrode 3 would not be exposed.

As a result of stacking the piezoelectric layers 1 , the power supply electrodes 2 and the counter electrode 3 , each of the piezoelectric layers 1 is sandwiched by the power supply electrodes 2 (specifically, the first power supply electrode 2 A and the second power supply electrode 2 B) and the counter electrode 3 . Here, each of the piezoelectric layers 1 is polarized from the power supply electrode 2 side to the counter electrode 3 side.

In the thus-stacked structure, the power supply electrodes 2 and the counter electrode 3 are overlapping with each other with the piezoelectric layer 1 interposed therebetween when seen in the stacking direction. However, the piezoelectric layers 1 include a region in which the power supply electrodes 2 and the counter electrode 3 are not overlapping when seen in the stacking direction (see FIG. 2 ). For example, the first power supply lead electrode 2 a , the second power supply lead electrode 2 b , and the counter lead electrodes 3 g are not overlapping with the counter electrode 3 or the power supply electrodes 2 when seen in the stacking direction. In part of the piezoelectric layers 1 corresponding to the non-overlapping region, no electric field occurs. In other words, this part of the piezoelectric layers 1 is piezoelectrically inactive. Specifically, in part of the piezoelectric layers 1 near the short-side surfaces, the power supply electrodes 2 and the counter electrode 3 are not overlapping when seen in the stacking direction. This part of the piezoelectric layers 1 is piezoelectrically inactive.

The resonance frequency of the stretching vibration and the resonance frequency of the bending vibration of the piezoelectric element P 1 , which will be described later, depend on the material, the shape, etc., of the piezoelectric element P 1 . The material, the shape, etc., of the piezoelectric element P 1 are determined such that the resonance frequency of the stretching vibration and the resonance frequency of the bending vibration are approximately equal to each other.

<1.3: Electrical Connection Member>

In this embodiment, flexible cables F 1 are used as the electrical connection member. The flexible cables F 1 include a first flexible cable F 11 and a second flexible cable F 12 . As shown in FIG. 1 , the first flexible cable F 11 and the second flexible cable F 12 are electrically connected to the respective short-side surfaces of the piezoelectric element P 1 . The first flexible cable F 11 and the second flexible cable F 12 are electrically coupled to the piezoelectric element P 1 . The first flexible cable F 11 and the second flexible cable F 12 have substantially the same shape.

FIG. 5 shows the positional relationship in connection between the first and second flexible cables F 11 and F 12 and the lateral surfaces of the piezoelectric element P 1 . As shown in FIG. 5 , the first and second flexible cables F 11 and F 12 include a plurality of electric wires formed by printing copper over an insulative resin substrate. The electric wires are mutually insulated.

The first flexible cable F 11 is connected to one of the short-side surfaces of the piezoelectric element P 1 . The second flexible cable F 12 is connected to the other one of the short-side surfaces of the piezoelectric element P 1 . The first flexible cable F 11 and the second flexible cable F 12 each have electric lines 6 which are connected to the power supply external electrodes 4 and an electric line 7 which is connected to the counter external electrodes 5 . Specifically, the first flexible cable F 11 and the second flexible cable F 12 each have an electric line 6 A which is coupled to the first power supply external electrode 4 A, an electric line 6 B which is coupled to the second power supply external electrode 4 B, and an electric line 7 which is coupled to the counter external electrodes 5 . In the first flexible cable F 11 , the electric line 6 A, the electric line 7 and the electric line 6 B are sequentially arranged from one lateral end to the other lateral end of the piezoelectric element P 1 . In the second flexible cable F 12 , the electric line 6 B, the electric line 7 and the electric line 6 A are sequentially arranged from the one lateral end to the other lateral end of the piezoelectric element P 1 . The electric lines 6 constitute the power supply conductive member. The electric line 7 constitutes the counter conductive member. More specifically, the electric line 6 A constitutes the first power supply conductive member, and the electric line 6 B constitutes the second power supply conductive member.

The first flexible cable F 11 has a shape symmetrical about a plane which passes through the midpoints of the short sides of the principal plane of the piezoelectric layer 1 and which is perpendicular to the short-side surfaces. The second flexible cable F 12 also has a shape symmetrical about the plane which passes through the midpoints of the short sides of the principal plane of the piezoelectric layer 1 and which is perpendicular to the short-side surfaces as does the first flexible cable F 11 . The first flexible cable F 11 and the second flexible cable F 12 have a shape symmetrical about a plane which passes through the midpoints of the long sides of the principal plane of the piezoelectric layer 1 and which is perpendicular to the principal surface. A connecting portion of the first flexible cable F 11 which is connected to the piezoelectric element P 1 has a shape symmetrical about the plane which passes through the midpoints of the short sides of the principal plane of the piezoelectric layer 1 and which is perpendicular to the short-side surfaces. Also, a connecting portion of the second flexible cable F 12 which is connected to the piezoelectric element P 1 has a shape symmetrical about the plane which passes through the midpoints of the short sides of the principal plane of the piezoelectric layer 1 and which is parallel to the long-side surfaces. The connecting portion of the first flexible cable F 11 which is connected to the piezoelectric element P 1 , and the connecting portion of the second flexible cable F 12 which is connected to the piezoelectric element P 1 have a shape symmetrical about the plane which passes through the midpoints of the long sides of the principal plane of the piezoelectric layer 1 and which is parallel to the short-side surface.

In the connecting portions of the first and second flexible cables F 11 and F 12 , and a connecting portion of the piezoelectric element P 1 , these elements are electrically connected and adhered using an anisotropic conductive adhesion sheet. The anisotropic conductive adhesion sheet is prepared by molding a resin containing electrically conductive particles dispersed therein into the form of a sheet, respectively. The anisotropic conductive adhesion sheet has an electric conductivity in the adhesion direction, i.e., in the sheet thickness direction, but lacks electric conductivity in the in-plane directions. Therefore, the plurality of electrodes provided over the short-side surfaces of the piezoelectric element P 1 can be electrically connected to the respective electric lines of the first and second flexible cables F 11 and F 12 by a single anisotropic conductive adhesion sheet with the electrodes being mutually insulated. In the first step of the connection method, an anisotropic conductive sheet is sandwiched between the first and second flexible cables F 11 and F 12 made of polyimide and the piezoelectric element P 1 . Then, the first and second flexible cables F 11 and F 12 are pressed against the piezoelectric element P 1 using a heated flat iron. As a result, the first and second flexible cables F 11 and F 12 and the piezoelectric element P 1 are electrically coupled by the electrically conductive particles and adhered by the effect of the resin of the anisotropic conductive adhesion sheet.

The connection portions of the first and second flexible cables F 11 and F 12 and the piezoelectric element P 1 are respectively interposed between the supporting portion 13 a and the piezoelectric element P 1 and between the supporting portion 13 c and the piezoelectric element P 1 . Specifically, the first flexible cable F 11 is pressed by the supporting portion 13 a against the piezoelectric element P 1 . The second flexible cable F 12 is pressed by the supporting portion 13 c against the piezoelectric element P 1 .

The electric lines 6 connected to the power supply external electrodes 4 are an example of the power supply conductive member. The electric line 6 A connected to the first power supply external electrode 4 A is an example of the first power supply conductive member. The electric line 6 B connected to the second power supply external electrode 4 B is an example of the second power supply conductive member. The electric lines 7 connected to the counter external electrodes 5 are an example of the counter conductive member. The first flexible cable F 11 is an example of the first electrical connection member. The second flexible cable F 12 is an example of the second electrical connection member.

The first and second flexible cables F 11 and F 12 are coupled to a power supply (not shown). A driving voltage from the power supply is applied to the piezoelectric element P 1 via the first and second flexible cables F 11 and F 12 such that vibration is generated in the piezoelectric element P 1 .

<1.4: Operation of Ultrasonic Actuator>

Hereinafter, an operation of the ultrasonic actuator is described. FIG. 6 is a concept diagram illustrating the displacement of the first-order stretching vibration according to this embodiment. FIG. 7 is a concept diagram illustrating the displacement of the second-order bending vibration of the ultrasonic actuator. FIG. 8 is a concept diagram illustrating the operation of the piezoelectric element P 1 . Note that, in FIGS. 6-8 , the principal surface of the piezoelectric element P 1 is parallel to the surfaces of the sheets of the drawings.

The electric lines 7 of the flexible cables F 11 and F 12 are coupled to the ground. The power supply applies a sinusoidal driving voltage of a predetermined frequency, as the first driving voltage, to the first power supply electrode 2 A of the principal surface of the piezoelectric layer 1 via the electric line 6 A and the first power supply external electrode 4 A. Also, the power supply also applies a sinusoidal second driving voltage to the second power supply electrode 2 B via the electric line 6 B and the second power supply external electrode 4 B. The amplitude and frequency of the second driving voltage are substantially equal to those of the first driving voltage. The frequencies of the first and second driving voltages are set near the resonance frequency of the stretching vibration and the resonance frequency of the bending vibration of the piezoelectric element P 1 which are substantially equal to each other.

When the phase difference between the first driving voltage applied to the first power supply electrode 2 A and the second driving voltage applied to the second power supply electrode 2 B is 0°, the first-order stretching vibration is induced in the piezoelectric element P 1 as shown in FIG. 6 . When the phase difference is 180°, the second-order bending vibration is induced in the piezoelectric element P 1 as shown in FIG. 7 .

When the phase difference between the first driving voltage applied to the first power supply electrode 2 A and the second driving voltage applied to the second power supply electrode 2 B is generally 90° or −90°, the first-order stretching vibration and the second-order bending vibration are harmonically induced in the piezoelectric element P 1 as shown in FIG. 8 . As a result, the piezoelectric element P 1 vibrates with its shape being sequentially deformed in the order of FIG. 8(A) , FIG. 8(B) , FIG. 8(C) , and FIG. 8(D) . The driver elements 8 provided on the piezoelectric element P 1 make a revolutionary movement, specifically a generally-elliptic movement, when seen in the direction perpendicular to the surface of the sheet of FIG. 8 . In other words, the composite vibration of the stretching vibration and bending vibration of the piezoelectric element P 1 causes the driver elements 8 to make an elliptic movement. Due to this elliptic movement, the movable element 9 on which the driver elements 8 abut moves relative to the piezoelectric element P 1 .

The piezoelectric element P 1 is arranged such that the longitudinal direction of its principal surface is equal to the movable direction of the movable element 9 , and that the lateral direction of its principal surface is equal to the direction in which the piezoelectric element P 1 is biased by the supporting portion 13 b toward the movable element 9 . The stretching direction of the stretching vibration of the piezoelectric element P 1 is equal to the movable direction of the movable element 9 , and the vibration direction of the bending vibration is equal to the direction in which the driver elements 8 are pressed against the movable element 9 . Note that the stacking direction of the piezoelectric element P 1 is perpendicular to both the stretching direction of the stretching vibration and the vibration direction of the bending vibration.

The short-side surfaces of the piezoelectric element P 1 are far away from a stress-concentrated part of the stretching vibration and therefore create only a small stress. Since the short-side surfaces are free ends of the piezoelectric element P 1 , only a small stress is created even in the case of the bending vibration. In this embodiment, the first and second flexible cables F 11 and F 12 are connected to the short-side surfaces. Therefore, the stress created in the connection faces (connection portions) by vibration of the piezoelectric element is reduced. Thus, occurrence of peeling at the connection faces can be prevented. In this embodiment, the connection faces of the piezoelectric element P 1 and the first and second flexible cables F 11 and F 12 include connection faces of the piezoelectric element P 1 and the anisotropic conductive adhesion sheets and connection faces of the anisotropic conductive adhesion sheets and the first and second flexible cables F 11 and F 12 .

<1.5: Advantages of Embodiment>

In this embodiment, the short-side surfaces of the piezoelectric element P 1 are far away from a stress-concentrated part of the first mode stretching vibration and therefore create only a small stress. Since the lateral surfaces are free ends of the piezoelectric element, only a small stress is created even in the case of the second mode bending vibration. In view of such circumstances, the flexible cables F 1 , which are the electrical connection members, are connected to the short-side surfaces of the piezoelectric element P 1 , so that the stress created in the connection faces of the flexible cables F 1 and the piezoelectric element P 1 by vibration of the piezoelectric element P 1 is reduced. Thus, occurrence of peeling at the connection faces of the piezoelectric element P 1 and the flexible cables F 1 can be prevented. In other words, the electrical connection members are connected to the short-side surfaces of the piezoelectric element P 1 which maintain themselves substantially flat even in the first mode stretching vibration and in the second mode bending vibration, whereby stress is unlikely to occur in the planes of the electrical connection members, and stable connection can be realized.

When seen in a direction perpendicular to the principal surface of the piezoelectric element P 1 , an area of the power supply electrodes 2 and an area of the counter electrode 3 are not overlapping in regions near the short sides of the principal surface of the piezoelectric layer 1 . Therefore, part of the piezoelectric layer 1 near the short sides of its principal surface is piezoelectrically inactive, and occurrence of strain due to electrostrictive effect is reduced. Since the stress created in the connection faces of the electrical connection members and the piezoelectric element P 1 by vibration of the piezoelectric element is reduced by connecting the electrical connection members to the short-side surfaces of the piezoelectric element P 1 , occurrence of peeling at the connection faces can be prevented. When the piezoelectric element P 1 and the electrical connection members are connected by heating, such heating can result in reduced polarization of the piezoelectric layer 1 near the short-side surfaces of the piezoelectric element P 1 . Collapse of the balance of polarization near the two short-side surfaces leads to collapse of the vibration balance. However, since the part of the piezoelectric element P 1 near the short-side surfaces piezoelectrically inactive as described above, collapse of the balance of vibration of the piezoelectric element P 1 can be prevented even if the state of polarization of the piezoelectric layer 1 is altered by the heat applied for connection of the electrical connection members. Examples of the thermal connection of the piezoelectric element P 1 and the electrical connection members by heating include connection with an anisotropic conductive adhesive sheet as in the above-described embodiment as well as connection with a conductive adhesive, a low-melting metal, etc.

The electrical connection members include the first electrical connection member and the second electrical connection member. The first electrical connection member is electrically connected to the piezoelectric element P 1 at one of the two short-side surfaces which are perpendicular to the principal surface of the piezoelectric layer 1 and which are parallel to the short sides of the principal surface. The second electrical connection member is electrically connected to the piezoelectric element P 1 at the other short-side surface. The shape of the first electrical connection member is symmetrical about a plane which passes through the midpoints of the short sides of the principal surface of the piezoelectric layer 1 and which is perpendicular to the one of the two lateral surfaces. The shape of the second electrical connection member is symmetrical about a plane which passes through the midpoints of the short sides of the principal surface of the piezoelectric layer 1 and which is perpendicular to the other one of the two lateral surfaces. In this configuration, the influence of the connection of the electrical connection members on vibration is symmetrical about a plane which passes through the midpoints of the short sides of the principal surface of the piezoelectric layer and which is perpendicular to the short-side surfaces. The influence of the connection of the electrical connection members on the symmetry of vibration can be reduced. As a result, the vibration balance of the piezoelectric element can be improved.

The first electrical connection member and the second electrical connection member are shaped symmetrical about a plane which passes through the midpoints of the long sides of the principal surface of the piezoelectric layer 1 and which is perpendicular to the principal surface. In this configuration, the influence of the connection of the electrical connection members on vibration is symmetrical about a plane which passes through the midpoints of the long sides of the principal surface of the piezoelectric layer 1 and which is perpendicular to the principal surface. The influence of the connection of the electrical connection members on the symmetry of vibration can be reduced.

Since the driver elements 8 and the piezoelectric element P 1 are fixedly in point contact or line contact with each other, interference with the bending vibration of the piezoelectric element P 1 can be reduced, and the efficiency of the bending vibration can be improved.

An ultrasonic actuator according to embodiment 2 of the present invention is now described. Note that elements equivalent to those described in the above embodiment are denoted by the same reference characters, and the description thereof is herein omitted. The ultrasonic actuator of embodiment 2 is different from embodiment 1 in the configurations of the piezoelectric element and the flexible cables.

<2.1: Piezoelectric Element P 2 >

The piezoelectric element P 2 of this embodiment is in the shape of a generally rectangular parallelepiped. The piezoelectric element P 2 includes a plurality of generally rectangular piezoelectric layers 1 , and internal electrode layers interposed between the piezoelectric layers 1 . The piezoelectric element P 2 includes the piezoelectric layers and the electrode layers which are stacked in a direction from front to back of the drawing sheet of FIG. 1 .

FIG. 9 is an orthographic developed view of the piezoelectric element P 2 . FIG. 10 shows the respective layers of the piezoelectric element P 2 which are seen in the stacking direction.

As shown in FIG. 9 , the piezoelectric element P 2 is in the shape of a generally rectangular parallelepiped, which is formed by alternately stacking the generally rectangular piezoelectric layers 1 and the internal electrode layers. The piezoelectric layer 1 is an insulation layer formed of, for example, a ceramic material, such as lead zirconate titanate. The internal electrode layers are formed of power supply electrodes 2 and counter electrodes 3 which are alternately provided in the stacking direction (thickness direction of the piezoelectric element P 2 ) with the piezoelectric layers 1 interposed therebetween. In FIG. 9 , a portion at the center represents the principal surface, portions on the right and left sides of the principal surface are the short-side surfaces, and portions on the upper and lower sides of the principal surface are the long-side surfaces. The internal electrode layers are behind the principal surface and thus cannot be seen. The positions of the internal electrode layers projected over the principal surface are represented by broken lines.

As shown in FIG. 9 , power supply external electrodes 4 and counter external electrodes 5 are provided on the short-side surfaces of the piezoelectric element P 2 . Specifically, the power supply external electrodes 4 include a first power supply external electrode 4 A and a second power supply external electrode 4 B which are mutually separate. The first power supply external electrode 4 A and the second power supply external electrode 4 B are provided on one of the two short-side surfaces of the piezoelectric element P 2 . The piezoelectric element P 2 includes the two counter external electrodes 5 which are provided on the other one of the two short-side surfaces. These electrodes 4 A, 4 B and 5 are mutually insulated. In other words, the electrodes 4 A, 4 B and 5 are not electrically coupled to one another.

The power supply electrodes 2 are provided on the principal surface of at least one of the plurality of piezoelectric layers 1 as shown in FIG. 10(B) and FIG. 10(C) . Specifically, the power supply electrodes 2 are provided on the principal surface of at least one of the plurality of piezoelectric layers 1 in the first pattern as shown in FIG. 10(B) . On the principal surface of another one of the plurality of piezoelectric layers 1 different from the piezoelectric layer 1 on which the power supply electrodes 2 are provided in the first pattern, the power supply electrodes 2 are provided in the second pattern as shown in FIG. 10(C) which is different from the first pattern.

The power supply electrodes 2 include first power supply electrodes 2 A which are provided on the principal surface of one of the piezoelectric layers 1 and second power supply electrodes 2 B which are provided on the principal surface of another one of the plurality of piezoelectric layers 1 different from the piezoelectric layer 1 provided with the first power supply electrode 2 A. The first power supply electrodes 2 A and the second power supply electrodes 2 B are not electrically coupled to each other.

Specifically, among four divisional regions A 1 -A 4 (see FIG. 4 ) of the principal surface of the piezoelectric layer 1 which are defined by halving the principal surface with respect to both longitudinal direction L and lateral direction S, the first power supply electrodes 2 A are provided in two of the four divisional regions which are aligned in the first diagonal direction D 1 of the principal surface of the piezoelectric layer 1 , i.e., in the divisional regions A 2 and A 4 . Further, the power supply electrodes 2 include a first connection electrode J 1 extending in the lateral direction at the longitudinal center of the principal surface of the piezoelectric layer 1 . The first power supply electrodes 2 A provided in the two divisional regions A 2 and A 4 are electrically connected via the first connection electrode J 1 . The first power supply electrodes 2 A and the first connection electrode J 1 constitute the first pattern.

The second power supply electrodes 2 B are provided in the other two of the four divisional regions A 1 -A 4 (see FIG. 4 ) which are aligned in the second diagonal direction D 2 of the principal surface of the piezoelectric layer 1 , i.e., in the divisional regions A 1 and A 3 . Further, the power supply electrodes 2 include a second connection electrode J 2 extending in the lateral direction at the longitudinal center of the principal surface of the piezoelectric layer 1 . The second power supply electrodes 2 B provided in the two divisional regions A 1 and A 3 are electrically coupled via the second connection electrode J 2 . The second power supply electrodes 2 B and the second connection electrode J 2 constitute the second pattern.

Among the first power supply electrodes 2 A provided in the two divisional regions A 2 and A 4 , the first power supply electrode 2 A provided in the divisional region A 2 which is closer to the short-side surface that has the first power supply external electrode 4 A thereon includes a first power supply lead electrode 2 a extending to the first power supply external electrode 4 A. In this way, the first power supply electrode 2 A of the divisional region A 2 is electrically coupled to the first power supply external electrode 4 A via the first power supply lead electrode 2 a . The first power supply electrodes 2 A of different piezoelectric layers 1 are electrically coupled to each other via the first power supply external electrode 4 A, the first power supply lead electrodes 2 a , and the first connection electrodes J 1 .

In each of the first and second patterns, among the second power supply electrodes 2 B provided in the two divisional regions A 1 and A 3 , the second power supply electrode 2 B provided in the divisional region A 3 which is closer to the short-side surface that has the second power supply external electrode 4 B thereon includes a second power supply lead electrode 2 b extending to the second power supply external electrode 4 B. In this way, the second power supply electrode 2 B of the divisional region A 3 is electrically coupled to the second power supply external electrode 4 B via the second power supply lead electrode 2 b . The second power supply electrodes 2 B of different piezoelectric layers 1 are electrically coupled to each other via the second power supply external electrode 4 B, the second power supply lead electrodes 2 b , and the second connection electrodes J 2 .

The counter electrode 3 is provided over substantially the entire surface of the piezoelectric layer 1 as shown in FIG. 10(D) . Specifically, the counter electrode 3 is not provided in a circumferential region of the principal surface of the piezoelectric layer 1 but is provided over substantially the entirety of a region inside the circumferential region. The counter electrode 3 includes counter lead electrodes 3 g which extend from both ends of a short-side near the short-side surface that has the counter external electrodes 5 thereon toward the counter external electrodes 5 so as to be connected to the counter external electrodes 5 . In this way, the counter electrode 3 is electrically coupled to the counter external electrodes 5 via the counter lead electrodes 3 g . The counter electrodes 3 provided on different piezoelectric layers 1 are electrically coupled to each other via the counter lead electrodes 3 g and the counter external electrodes 5 .

The piezoelectric element P 2 is formed by stacking the piezoelectric layers 1 provided with the power supply electrodes 2 or the counter electrode 3 on the principal surfaces as described above. Specifically, the plurality of piezoelectric layers 1 are sequentially stacked in the order of the piezoelectric layer 1 provided with the first pattern power supply electrodes 2 (i.e., the first power supply electrodes 2 A), the piezoelectric layer 1 provided with the counter electrode 3 , the piezoelectric layer 1 provided with the second pattern power supply electrodes 2 (i.e., the second power supply electrodes 2 B), the piezoelectric layer 1 provided with the counter electrode 3 , the piezoelectric layer 1 provided with the first pattern power supply electrodes 2 , the piezoelectric layer 1 provided with the counter electrode 3 , . . . . The piezoelectric layers 1 are stacked such that the principal surfaces provided with the power supply electrodes 2 or the counter electrode 3 are oriented in the same direction, i.e., such that the principal surface of one of the piezoelectric layers 1 on which the power supply electrodes 2 or the counter electrode 3 is provided face the principal surface of another one of the piezoelectric layers 1 on which none of the power supply electrodes 2 and the counter electrode 3 is provided. Note that, the first and/or last of the stacked layers are the piezoelectric layers 1 which are not provided with the power supply electrodes 2 or the counter electrode 3 such that the power supply electrodes 2 or the counter electrode 3 would not be exposed.

As a result of stacking the piezoelectric layers 1 , the power supply electrodes 2 and the counter electrode 3 , each of the piezoelectric layers 1 is sandwiched by the power supply electrodes 2 (specifically, the first power supply electrode 2 A or the second power supply electrode 2 B) and the counter electrode 3 . Thus, when seen in the stacking direction, the power supply electrodes 2 and the counter electrode 3 are overlapping with each other with the piezoelectric layer 1 interposed therebetween. Here, each of the piezoelectric layers 1 is polarized from the power supply electrode 2 side to the counter electrode 3 side.

However, the piezoelectric layers 1 include a region in which the power supply electrodes 2 and the counter electrode 3 are not overlapping when seen in the stacking direction (see FIG. 9 ). For example, the first power supply lead electrode 2 a , the second power supply lead electrode 2 b , and the counter lead electrodes 3 g are not overlapping with the counter electrode 3 or the power supply electrodes 2 when seen in the stacking direction. In part of the piezoelectric layers 1 corresponding to the non-overlapping region, no electric field occurs. In other words, this part of the piezoelectric layers 1 is piezoelectrically inactive. Specifically, in part of the piezoelectric layers 1 near the short-side surfaces, the power supply electrodes 2 and the counter electrode 3 are not overlapping when seen in the stacking direction. This part of the piezoelectric layers 1 is piezoelectrically inactive.

The resonance frequency of the stretching vibration and the resonance frequency of the bending vibration of the piezoelectric element P 2 , which will be described later, depend on the material, the shape, etc., of the piezoelectric element P 2 . The material, the shape, etc., of the piezoelectric element P 2 are determined such that the resonance frequency of the stretching vibration and the resonance frequency of the bending vibration are approximately equal to each other.

<2.2: Electrical Connection Member>

In this embodiment, flexible cables F 2 are used as the electrical connection member. The flexible cables F 2 include a first flexible cable F 21 and a second flexible cable F 22 . As shown in FIG. 1 , the first flexible cable F 21 and the second flexible cable F 22 are electrically connected to the respective short-side surfaces of the piezoelectric element P 2 . The first flexible cable F 21 and the second flexible cable F 22 are electrically coupled to the piezoelectric element P 2 . The first flexible cable F 21 and the second flexible cable F 22 have substantially the same shape.

FIG. 11 shows the positional relationship in connection between the first and second flexible cables F 21 and F 22 and the lateral surfaces of the piezoelectric element P 2 . As shown in FIG. 11 , the first and second flexible cables F 21 and F 22 include a plurality of electric wires formed by printing copper over an insulative resin substrate. The electric wires are mutually insulated.

The first flexible cable F 21 is connected to one of the short-side surfaces of the piezoelectric element P 2 . The first flexible cable F 21 has electric lines 6 which are connected to the power supply external electrodes 4 . Specifically, the first flexible cable F 21 has an electric line 6 A connected to the first power supply external electrode 4 A and an electric line 6 B connected to the second power supply external electrode 4 B.

The second flexible cable F 22 is connected to the other one of the short-side surfaces of the piezoelectric element P 2 . The second flexible cable F 22 has electric lines 7 which are connected to the counter external electrodes 5 . Specifically, the second flexible cable F 22 has electric lines 7 connected to the counter external electrodes 5 .

The first flexible cable F 21 has a shape symmetrical about a plane which passes through the midpoints of the short sides of the principal plane of the piezoelectric layer 1 and which is perpendicular to the short-side surfaces. The second flexible cable F 22 also has a shape symmetrical about the plane which passes through the midpoints of the short sides of the principal plane of the piezoelectric layer 1 and which is perpendicular to the short-side surfaces. The first flexible cable F 21 and the second flexible cable F 22 have a shape symmetrical about a plane which passes through the midpoints of the long sides of the principal plane of the piezoelectric layer 1 and which is perpendicular to the principal surface. A connecting portion of the first flexible cable F 21 which is connected to the piezoelectric element P 2 has a shape symmetrical about the plane which passes through the midpoints of the short sides of the principal plane of the piezoelectric layer 1 and which is perpendicular to the short-side surfaces. A connecting portion of the second flexible cable F 22 which is connected to the piezoelectric element P 2 also has a shape symmetrical about the plane which passes through the midpoints of the short sides of the principal plane of the piezoelectric layer 1 and which is perpendicular to the short-side surfaces. The connecting portion of the first flexible cable F 21 which is connected to the piezoelectric element P 2 and the connecting portion of the second flexible cable F 22 which is connected to the piezoelectric element P 2 have a shape symmetrical about the plane which passes through the midpoints of the long sides of the principal plane of the piezoelectric layer 1 and which is perpendicular to the principal surface.

In the connecting portions of the first and second flexible cables F 21 and F 22 and a connecting portion of the piezoelectric element P 2 , these elements are electrically connected and adhered using an anisotropic conductive adhesion sheet. The anisotropic conductive adhesion sheet is prepared by molding a resin containing electrically conductive particles dispersed therein into the form of a sheet. The anisotropic conductive adhesion sheet has an electric conductivity in the adhesion direction, i.e., in the sheet thickness direction, but lacks electric conductivity in the in-plane directions of the adhesion surface. Therefore, the plurality of electrodes provided over the short-side surfaces of the piezoelectric element P 2 can be electrically connected to the respective electric lines of the first and second flexible cables F 21 and F 22 by a single anisotropic conductive adhesion sheet with the electrodes being mutually insulated. In the first step of the connection method, an anisotropic conductive sheet is sandwiched between the first and second flexible cables F 21 and F 22 made of polyimide and the piezoelectric element P 2 . Then, the first and second flexible cables F 21 and F 22 are pressed against the piezoelectric element P 2 using a heated planar cautery. As a result, the first and second flexible cables F 21 and F 22 and the piezoelectric element P 2 are electrically coupled by the electrically conductive particles and adhered by means of the resin of the anisotropic conductive adhesion sheet.

The connection portions of the first and second flexible cables F 21 and F 22 and the piezoelectric element P 2 are respectively interposed between the supporting portion 13 a and the piezoelectric element P 2 and between the supporting portion 13 c and the piezoelectric element P 2 . Specifically, the first flexible cable F 21 is pressed by the supporting portion 13 a against the piezoelectric element P 2 . The second flexible cable F 22 is pressed by the supporting portion 13 c against the piezoelectric element P 2 .

The electric lines 6 connected to the power supply external electrodes 4 are an example of the power supply conductive member. The electric line 6 A connected to the first power supply external electrode 4 A is an example of the first power supply conductive member. The electric line 6 B connected to the second power supply external electrode 4 B is an example of the second power supply conductive member. The electric lines 7 connected to the counter external electrodes 5 are an example of the counter conductive member. The first flexible cable F 21 is an example of the first electrical connection member. The second flexible cable F 22 is an example of the second electrical connection member.

The first and second flexible cables F 21 and F 22 are coupled to a power supply (not shown). A driving voltage from the power supply is applied to the piezoelectric element P 2 via the first and second flexible cables F 21 and F 22 such that vibration is generated in the piezoelectric element P 2 .

<2.3: Operation of Ultrasonic Actuator>

Hereinafter, an operation of the ultrasonic actuator is described. The operation of the ultrasonic actuator of this embodiment is basically the same as that of the ultrasonic actuator of embodiment 1. Specifically, a first driving voltage at a frequency near the substantially-matched resonance frequencies of the stretching vibration and the bending vibration of the piezoelectric element P 2 is applied to the first power supply electrode 2 A, and a second driving voltage which is approximately equal in amplitude and frequency to and different in phase by generally 90° or −90° from the first driving voltage is applied to the second power supply electrode 2 B, whereby the first-order stretching vibration and the second-order bending vibration are harmonically induced in the piezoelectric element P 2 . As a result, the piezoelectric element P 2 vibrates with its shape being sequentially deformed in the order of FIG. 8(A) , FIG. 8(B) , FIG. 8(C) , and FIG. 8(D) . The driver elements 8 provided on the piezoelectric element P 2 make an orbit movement, specifically a generally-elliptic movement, when seen in the direction perpendicular to the surface of the sheet of FIG. 8 . In other words, the composite vibration of the stretching vibration and bending vibration of the piezoelectric element P 2 causes the driver elements 8 to make an elliptic movement. Due to this elliptic movement, the movable element 9 on which the driver elements 8 abut moves relative to the piezoelectric element P 2 .

In this embodiment, the first power supply external electrode 4 A and the counter external electrodes 5 are provided at different short-side surfaces. The second power supply external electrode 4 B and the counter external electrodes 5 are provided at different short-side surfaces. Therefore, a sufficient distance can be ensured between the first power supply external electrode 4 A and the counter external electrodes 5 and between the second power supply external electrode 4 B and the counter external electrodes 5 . Accordingly, sufficient insulation can be ensured between the first power supply external electrode 4 A and the counter external electrodes 5 and between the second power supply external electrode 4 B and the counter external electrodes 5 .

<2.4: Advantages of Embodiment>

According to this embodiment, the first power supply external electrode 4 A and the counter external electrodes 5 are provided at different short-side surfaces. The second power supply external electrode 4 B and the counter external electrodes 5 are provided at different short-side surfaces. This configuration ensures a sufficient distance between the first power supply external electrode 4 A and the counter external electrodes 5 and between the second power supply external electrode 4 B and the counter external electrodes 5 . Accordingly, sufficient insulation can be ensured between the first power supply external electrode 4 A and the counter external electrodes 5 and between the second power supply external electrode 4 B and the counter external electrodes 5 .

The principal surface of the piezoelectric layer 1 on which the first power supply electrode is provided has the first connection electrode J 1 which provides electrical connection between the first power supply electrodes 2 A. The principal surface of another piezoelectric layer 1 , which is different from the principal surface that has the first connection electrode J 1 thereon, has the second connection electrode J 2 which provides electrical connection between the second power supply electrodes 2 B. This configuration enables reduction of the number of the first power supply external electrodes 4 A which are electrically coupled to the first power supply electrodes 2 A and the number of the second power supply external electrodes 4 B which are electrically coupled to the second power supply electrode 2 B. For example, a structure which has the first connection electrode J 1 and the second connection electrode J 2 requires only one piece of the first power supply external electrode 4 A and one piece of the second power supply external electrode 4 B whereas embodiment 1 which does not have the first connection electrode J 1 or the second connection electrode J 2 requires two pieces of the first power supply external electrodes 4 A and two pieces of the second power supply external electrodes 4 B. As a result, the number of connection points between the piezoelectric element P 2 and the electrical connection members can be reduced, and accordingly, the probability of occurrence of peeling at the connection faces between the piezoelectric element P 2 and the electrical connection members. Further, the factors of interference with the vibration of the piezoelectric element P 2 are decreased so that the efficiency of the vibration can be improved.

The longitudinal center of the piezoelectric layer 1 is the node of the first mode stretching vibration, i.e., a stress-concentrated part at which the stress caused by the stretching vibration concentrates. In this stress-concentrated part, electric charge concentrates due to the piezoelectric effect. In view of such, the first connection electrode J 1 and the second connection electrode J 2 have a shape elongated in the lateral direction at the longitudinal center of the principal surface of the piezoelectric layer 1 . Therefore, the power supply electrodes 2 can have an increased area at the longitudinal center of the piezoelectric layer 1 . By increasing the areas of the first connection electrode J 1 and the second connection electrode J 2 , large stretching vibration can be induced even when the size of the piezoelectric element P 2 is reduced. As a result, the efficiency of the ultrasonic actuator can be improved.

Embodiment 2 can also provide effects and advantages substantially equivalent to those of embodiment 1.

An ultrasonic actuator according to embodiment 3 of the present invention is now described. Note that elements equivalent to those described in the above embodiment are denoted by the same reference characters, and the description thereof is herein omitted. The ultrasonic actuator of embodiment 3 is different from embodiment 1 in the configurations of the piezoelectric element and the flexible cables.

<3.1: Piezoelectric Element P 3 >

The piezoelectric element P 3 of this embodiment is in the shape of a generally rectangular parallelepiped. The piezoelectric element P 3 includes a plurality of generally rectangular piezoelectric layers 1 , and internal electrode layers interposed between the piezoelectric layers 1 . The piezoelectric element P 3 includes the piezoelectric layers and the electrode layers which are stacked in a direction from front to back of the drawing sheet of FIG. 1 .

FIG. 12 is an orthographic developed view of the piezoelectric element P 3 . FIG. 13 shows the respective layers of the piezoelectric element P 3 which are seen in the layer stacking direction. In FIG. 12 , a portion at the center represents the principal surface, portions on the right and left sides of the principal surface are the short-side surfaces, and portions on the upper and lower sides of the principal surface are the long-side surfaces. The internal electrode layers are behind the principal surface and thus cannot be seen. The positions of the internal electrode layers projected over the principal surface are represented by broken lines.

As shown in FIG. 12 , power supply external electrodes 4 and counter external electrodes 5 are provided on the short-side surfaces of the piezoelectric element P 3 . Specifically, the power supply external electrodes 4 include a first power supply external electrode 4 A and a second power supply external electrode 4 B which are mutually separate. The first power supply external electrode 4 A and the second power supply external electrode 4 B are provided on one of the two short-side surfaces of the piezoelectric element P 3 . The piezoelectric element P 3 includes the two counter external electrodes 5 which are provided on the other one of the two short-side surfaces. These electrodes 4 A, 4 B and 5 are mutually insulated. In other words, the electrodes 4 A, 4 B and 5 are not electrically coupled to one another. One of the long-side surfaces of the piezoelectric element P 3 is provided with a first connection external electrode 10 A, and the other long-side surface is provided with a second connection external electrode 10 B. The first connection external electrode 10 A and the second connection external electrode 10 B are mutually insulated.

The power supply electrodes 2 are provided on the principal surface of at least one of the plurality of piezoelectric layers 1 as shown in FIG. 13(B) and FIG. 13(C) . Specifically, the power supply electrodes 2 are provided on the principal surface of at least one of the plurality of piezoelectric layers 1 in the first pattern as shown in FIG. 13(B) . On the principal surface of another one of the plurality of piezoelectric layers 1 different from the piezoelectric layer 1 on which the power supply electrodes 2 are provided in the first pattern, the power supply electrodes 2 are provided in the second pattern as shown in FIG. 13(C) which is different from the first pattern.

Specifically, the power supply electrodes 2 formed in the first pattern and in the second pattern each include first power supply electrodes 2 A and second power supply electrodes 2 B which are not electrically coupled to the first power supply electrodes 2 A.

In each of the first and second patterns, among four divisional regions A 1 -A 4 (see FIG. 4 ) of the principal surface of the piezoelectric layer 1 which are defined by halving the principal surface with respect to both longitudinal direction L and lateral direction S, the first power supply electrodes 2 A are provided in two of the four divisional regions A 1 -A 4 which are aligned in the first diagonal direction D 1 of the principal surface of the piezoelectric layer 1 , i.e., in the divisional regions A 2 and A 4 . The second power supply electrodes 2 B are provided in the other two of the four divisional regions A 1 -A 4 which are aligned in the second diagonal direction D 2 of the principal surface of the piezoelectric layer 1 , i.e., in the divisional regions A 1 and A 3 .

The first pattern power supply electrodes 2 include a first connection electrode J 1 extending in the lateral direction at the longitudinal center of the principal surface of the piezoelectric layer 1 . The first power supply electrodes 2 A provided in the two divisional regions A 2 and A 4 of the first pattern are mutually coupled via the first connection electrode J 1 . The second pattern power supply electrodes 2 include a second connection electrode J 2 extending in the lateral direction at the longitudinal center of the principal surface of the piezoelectric layer 1 . The second power supply electrodes 2 B provided in the two divisional regions A 1 and A 3 of the second pattern are mutually coupled via the second connection electrode J 2 .

In each of the first and second patterns, among the first power supply electrodes 2 A provided in the two divisional regions A 2 and A 4 , the first power supply electrode 2 A provided in the divisional region A 2 which is closer to the short-side surface that has the first power supply external electrode 4 A thereon includes a first power supply lead electrode 2 a extending to the first power supply external electrode 4 A. In this way, the first power supply electrode 2 A of the divisional region A 2 is electrically coupled to the first power supply external electrode 4 A via the first power supply lead electrode 2 a. Among the first power supply electrodes 2 A provided in the two divisional regions A 2 and A 4 , the first power supply electrode 2 A provided in the divisional region A 4 which is more distant from the short-side surface that has the first power supply external electrode 4 A thereon includes a first power supply lead electrode 2 a extending to the first connection external electrode 10 A provided on the long-side surface. In this way, the first power supply electrodes 2 A of the divisional region A 4 in the different piezoelectric layers 1 are electrically coupled to each other via the first connection external electrode 10 A. Since in the first pattern the first power supply electrode 2 A of the divisional region A 4 is electrically coupled to the first power supply electrode 2 A of the divisional region A 2 via the first connection electrode J 1 , the first power supply electrode 2 A of the divisional region A 4 of the second pattern, which is electrically coupled to the first power supply electrode 2 A of the divisional region A 4 of the first pattern via the first connection external electrode 10 A, is electrically coupled to the first power supply external electrode 4 A of the first pattern via the first connection electrode J 1 .

In each of the first and second patterns, among the second power supply electrodes 2 B provided in the two divisional regions A 1 and A 3 , the second power supply electrode 2 B provided in the divisional region A 3 which is closer to the short-side surface that has the second power supply external electrode 4 B thereon includes a second power supply lead electrode 2 b extending to the second power supply external electrode 4 B. In this way, the second power supply electrode 2 B of the divisional region A 3 is electrically coupled to the second power supply external electrode 4 B via the second power supply lead electrode 2 b . Among the second power supply electrodes 2 B provided in the two divisional regions A 1 and A 3 , the second power supply electrode 2 B provided in the divisional region A 1 which is more distant from the short-side surface that has the second power supply external electrode 4 B thereon includes a second power supply lead electrode 2 b extending to the second connection external electrode 10 B provided on the long-side surface. In this way, the second power supply electrodes 2 B of the divisional region A 1 in the different piezoelectric layers 1 are electrically coupled to each other via the second connection external electrode 10 B. Since in the second pattern the second power supply electrode 2 B of the divisional region A 1 is electrically coupled to the second power supply electrode 2 B of the divisional region A 3 via the second connection electrode J 2 , the second power supply electrode 2 B of the divisional region A 1 of the first pattern, which is electrically coupled to the second power supply electrode 2 B of the divisional region A 1 of the second pattern via the second connection external electrode 10 B, is electrically coupled to the second power supply external electrode 4 B via the second connection electrode J 2 of the second pattern.

The counter electrode 3 is provided over substantially the entire principal surface of the piezoelectric layer 1 as shown in FIG. 13(D) . Specifically, the counter electrode 3 is not provided in a circumferential region of the principal surface of the piezoelectric layer 1 but is provided over substantially the entirety of a region inside the circumferential region. The counter electrode 3 includes counter lead electrodes 3 g which extend from both ends of a short-side near the short-side surface on which the counter external electrodes 5 are provided toward the counter external electrodes 5 so as to be connected to the counter external electrodes 5 . In this way, the counter electrode 3 is electrically coupled to the counter external electrodes 5 via the counter lead electrodes 3 g . The counter electrodes 3 provided on different piezoelectric layers 1 are electrically coupled to each other via the counter lead electrodes 3 g and the counter external electrodes 5 .

The piezoelectric element P 3 is formed by stacking the piezoelectric layers 1 provided with the power supply electrodes 2 or the counter electrode 3 on the principal surfaces as described above. Specifically, the plurality of piezoelectric layers 1 are sequentially stacked in the order of the piezoelectric layer 1 provided with the first pattern power supply electrodes 2 , the piezoelectric layer 1 provided with the counter electrode 3 , the piezoelectric layer 1 provided with the second pattern power supply electrodes 2 , the piezoelectric layer 1 provided with the counter electrode 3 , the piezoelectric layer 1 provided with the first pattern power supply electrodes 2 , the piezoelectric layer 1 provided with the counter electrode 3 , . . . . The piezoelectric layers 1 are stacked such that the principal surfaces provided with the power supply electrodes 2 or the counter electrode 3 are oriented in the same direction, i.e., such that the principal surface of one of the piezoelectric layers 1 on which the power supply electrodes 2 or the counter electrode 3 is provided faces the principal surface of another one of the piezoelectric layers 1 on which none of the power supply electrodes 2 and the counter electrode 3 is provided. Note that, the first and/or last of the stacked layers are the piezoelectric layers 1 which are not provided with the power supply electrodes 2 or the counter electrode 3 such that the power supply electrodes 2 or the counter electrode 3 would not be exposed.

As a result of stacking the piezoelectric layers 1 , the power supply electrodes 2 and the counter electrode 3 , each of the piezoelectric layers 1 is sandwiched by the power supply electrodes 2 (specifically, the first power supply electrode 2 A and the second power supply electrode 2 B) and the counter electrode 3 . Thus, when seen in the stacking direction, the power supply electrodes 2 and the counter electrode 3 are overlapping with each other with the piezoelectric layer 1 interposed therebetween. Here, each of the piezoelectric layers 1 is polarized from the power supply electrode 2 side to the counter electrode 3 side.

However, the piezoelectric layers 1 include a region in which the power supply electrodes 2 and the counter electrode 3 are not overlapping when seen in the stacking direction (see FIG. 12 ). For example, the first power supply lead electrode 2 a , the second power supply lead electrode 2 b , and the counter lead electrodes 3 g are not overlapping with the counter electrode 3 or the power supply electrodes 2 when seen in the stacking direction. In part of the piezoelectric layers 1 corresponding to the non-overlapping region, no electric field occurs. In other words, this part of the piezoelectric layers 1 is piezoelectrically inactive. Specifically, in part of the piezoelectric layers 1 near the short-side surfaces, the power supply electrodes 2 and the counter electrode 3 are not overlapping when seen in the stacking direction. This part of the piezoelectric layers 1 is piezoelectrically inactive.

The resonance frequency of the stretching vibration and the resonance frequency of the bending vibration of the piezoelectric element P 3 , which will be described later, depend on the material, the shape, etc., of the piezoelectric element P 3 . The material, the shape, etc., of the piezoelectric element P 3 are determined such that the resonance frequency of the stretching vibration and the resonance frequency of the bending vibration are approximately equal to each other.

<3.2: Electrical Connection Member>

This embodiment uses the flexible cables F 2 of embodiment 2 as the electrical connection members. FIG. 14 shows the positional relationship in connection between the first and second flexible cables F 21 and F 22 and the short-side surfaces of the piezoelectric element P 3 .

The relationship between the first and second flexible cables F 21 and F 22 and the other elements is the same as that in embodiment 2. For example, the relationship between the first flexible cable F 21 and the piezoelectric element P 3 is the same as the relationship between the first flexible cable F 21 and the piezoelectric element P 2 in embodiment 2. Note that the description of the electrical connection members of embodiment 3 is provided by applying the description of the <2.2: Electrical Connection Member> section of embodiment 2 of this specification mutatis mutandis to this section with “piezoelectric element P 2 ” being replaced by “piezoelectric element P 3 ” and “FIG. 11 ” being replaced by “FIG. 14 ”.

Note that the first and second flexible cables F 21 and F 22 are not directly connected to the first connection external electrode 10 A or the second connection external electrode 10 B.

<3.3: Operation of Ultrasonic Actuator>

Hereinafter, an operation of the ultrasonic actuator is described. The operation of the ultrasonic actuator of this embodiment is basically the same as that of the ultrasonic actuator of embodiment 1. Specifically, a first driving voltage at a frequency near the substantially-matched resonance frequencies of the stretching vibration and the bending vibration of the piezoelectric element P 3 is applied to the first power supply electrode 2 A, and a second driving voltage which is approximately equal in amplitude and frequency to and different in phase by generally 90° or −90° from the first driving voltage is applied to the second power supply electrode 2 B, whereby the first-order stretching vibration and the second-order bending vibration are harmonically induced in the piezoelectric element P 3 . As a result, the piezoelectric element P 3 vibrates with its shape being sequentially deformed in the order of FIG. 8(A) , FIG. 8(B) , FIG. 8(C) , and FIG. 8(D) . The driver elements 8 provided on the piezoelectric element P 3 make a revolutionary movement, specifically a generally-elliptic movement, when seen in the direction perpendicular to the surface of the sheet of FIG. 8 . In other words, the composite vibration of the stretching vibration and bending vibration of the piezoelectric element P 3 causes the driver elements 8 to make an elliptic movement. Due to this elliptic movement, the movable element 9 on which the driver elements 8 abut moves relative to the piezoelectric element P 3 .

In this example, the first connection external electrode 10 A is provided on one of the two long-side surfaces of the piezoelectric element P 3 , and the second connection external electrode 10 B is provided on the other one of the two long-side surfaces. Alternatively, the first connection external electrode 10 A and the second connection external electrode 10 B may be provided on the same long-side surface. In this case, the first connection external electrode 10 A and the second connection external electrode 10 B may preferably be provided on a long-side surface other than the long-side surface provided with the driver elements 8 .

<3.4: Advantages of Embodiment>

According to this embodiment, as in embodiment 2, the first power supply external electrode 4 A and the counter external electrodes 5 are provided at different short-side surfaces, and the second power supply external electrode 4 B and the counter external electrodes 5 are provided at different short-side surfaces. This configuration ensures a sufficient distance between the first power supply external electrode 4 A and the counter external electrodes 5 and between the second power supply external electrode 4 B and the counter external electrodes 5 . Accordingly, sufficient insulation can be ensured between the first power supply external electrode 4 A and the counter external electrodes 5 and between the second power supply external electrode 4 B and the counter external electrodes 5 .

The first connection external electrode 10 A is provided on one of the two long-side surfaces of the piezoelectric element P 3 , and the second connection external electrode 10 B is provided on the other one of the two long-side surfaces. This configuration ensures sufficient insulation between the first connection external electrode 10 A and the second connection external electrode 10 B.

Embodiment 3 can also provide effects and advantages substantially equivalent to those of embodiments 1 and 2.

An ultrasonic actuator according to embodiment 4 of the present invention is now described. Note that elements equivalent to those described in the above embodiment are denoted by the same reference characters, and the description thereof is herein omitted. The ultrasonic actuator of embodiment 4 is different from embodiment 1 in the configurations of the piezoelectric element and the flexible cables.

<4.1: Piezoelectric Element P 4 >

The piezoelectric element P 4 of this embodiment is in the shape of a generally rectangular parallelepiped. The piezoelectric element P 4 includes a plurality of generally rectangular piezoelectric layers 1 , and internal electrode layers interposed between the piezoelectric layers 1 . The piezoelectric element P 4 includes the piezoelectric layers and the electrode layers which are stacked in a direction from front to back of the drawing sheet of FIG. 1 .

FIG. 15 is an orthographic developed view of the piezoelectric element P 4 . FIG. 16 shows the respective layers of the piezoelectric element P 4 which are seen in the layer stacking direction. In FIG. 15 , a portion at the center represents the principal surface, portions on the right and left sides of the principal surface are the short-side surfaces, and portions on the upper and lower sides of the principal surface are the long-side surfaces. The internal electrode layers are behind the principal surface and thus cannot be seen. The positions of the internal electrode layers projected over the principal surface are represented by broken lines.

As shown in FIG. 15 , power supply external electrodes 4 and counter external electrodes 5 are provided on the short-side surfaces of the piezoelectric element P 4 . Specifically, the power supply external electrodes 4 include a first power supply external electrode 4 A and a second power supply external electrode 4 B which are mutually separate. The first power supply external electrode 4 A is provided on one of the two short-side surfaces of the piezoelectric element P 4 . The second power supply external electrode 4 B is provided on the other one of the two short-side surfaces of the piezoelectric element P 4 . The piezoelectric element P 4 includes the two counter external electrodes 5 which are respectively provided on the two short-side surfaces in a one-to-one fashion. Specifically, on one of the short-side surfaces of the piezoelectric element P 4 , the counter external electrode 5 is provided at one lateral end of the piezoelectric element P 4 , and the first power supply external electrode 4 A is provided at the other lateral end. On the other one of the short-side surfaces of the piezoelectric element P 4 , the counter external electrode 5 is provided at one lateral end of the piezoelectric element P 4 , and the second power supply external electrode 4 B is provided at the other lateral end. These electrodes 4 A, 4 B and 5 are mutually insulated. In other words, the electrodes 4 A, 4 B and 5 are not electrically coupled to one another. On one of the long-side surfaces of the piezoelectric element P 4 , a second connection external electrode 10 B is provided at one longitudinal end of the piezoelectric element P 4 , and a first connection external electrode 10 A is provided at the other longitudinal end. The first connection external electrode 10 A and the second connection external electrode 10 B are mutually insulated.

The power supply electrodes 2 are provided on the principal surface of at least one of the plurality of piezoelectric layers 1 as shown in FIG. 16(B) and FIG. 16(C) . Specifically, the power supply electrodes 2 are provided on the principal surface of at least one of the plurality of piezoelectric layers 1 in the first pattern as shown in FIG. 16(B) . On the principal surface of another one of the plurality of piezoelectric layers 1 different from the piezoelectric layer 1 on which the power supply electrodes 2 are provided in the first pattern, the power supply electrodes 2 are provided in the second pattern as shown in FIG. 16(C) which is different from the first pattern.

Specifically, the power supply electrodes 2 formed in the first pattern and in the second pattern each include first power supply electrodes 2 A and second power supply electrodes 2 B which are not electrically coupled to the first power supply electrodes 2 A.

In each of the first and second patterns, among four divisional regions A 1 -A 4 (see FIG. 4 ) of the principal surface of the piezoelectric layer 1 which are defined by halving the principal surface with respect to both longitudinal direction L and lateral direction S, the first power supply electrodes 2 A are provided in two of the four divisional regions A 1 -A 4 which are aligned in the first diagonal direction D 1 of the principal surface of the piezoelectric layer 1 , i.e., in the divisional regions A 2 and A 4 . The second power supply electrodes 2 B are provided in the other two of the four divisional regions A 1 -A 4 which are aligned in the second diagonal direction D 2 of the principal surface of the piezoelectric layer 1 , i.e., in the divisional regions A 1 and A 3 .

The first pattern power supply electrodes 2 include a first connection electrode J 1 extending in the lateral direction at the longitudinal center of the principal surface of the piezoelectric layer 1 . The first power supply electrodes 2 A provided in the two divisional regions A 2 and A 4 of the first pattern are mutually coupled via the first connection electrode J 1 . The second pattern power supply electrodes 2 include a second connection electrode J 2 extending in the lateral direction at the longitudinal center of the principal surface of the piezoelectric layer 1 . The second power supply electrodes 2 B provided in the two divisional regions A 1 and A 3 of the second pattern are mutually coupled via the second connection electrode J 2 .

In each of the first and second patterns, among the first power supply electrodes 2 A provided in the two divisional regions A 2 and A 4 , the first power supply electrode 2 A provided in the divisional region A 2 which is closer to the short-side surface that has the first power supply external electrode 4 A thereon includes a first power supply lead electrode 2 a extending to the first power supply external electrode 4 A. In this way, the first power supply electrode 2 A of the divisional region A 2 is electrically coupled to the first power supply external electrode 4 A via the first power supply lead electrode 2 a. Among the first power supply electrodes 2 A provided in the two divisional regions A 2 and A 4 , the first power supply electrode 2 A provided in the divisional region A 4 which is more distant from the short-side surface that has the first power supply external electrode 4 A thereon includes a first power supply lead electrode 2 a extending to the first connection external electrode 10 A provided on the long-side surface. In this way, the first power supply electrodes 2 A of the divisional region A 4 in the different piezoelectric layers 1 are electrically coupled to each other via the first connection external electrode 10 A. Since in the first pattern the first power supply electrode 2 A of the divisional region A 4 is electrically coupled to the first power supply electrode 2 A of the divisional region A 2 via the first connection electrode J 1 , the first power supply electrode 2 A of the divisional region A 4 of the second pattern, which is electrically coupled to the first power supply electrode 2 A of the divisional region A 4 of the first pattern via the first connection external electrode 10 A, is electrically coupled to the first power supply external electrode 4 A of the first pattern via the first connection electrode J 1 .

In each of the first and second patterns, among the second power supply electrodes 2 B provided in the two divisional regions A 1 and A 3 , the second power supply electrode 2 B provided in the divisional region A 3 which is closer to the short-side surface that has the second power supply external electrode 4 B thereon includes a second power supply lead electrode 2 b extending to the second power supply external electrode 4 B. In this way, the second power supply electrode 2 B of the divisional region A 3 is electrically coupled to the second power supply external electrode 4 B via the second power supply lead electrode 2 b . Among the second power supply electrodes 2 B provided in the two divisional regions A 1 and A 3 , the second power supply electrode 2 B provided in the divisional region A 3 which is more distant from the short-side surface that has the second power supply external electrode 4 B thereon includes a second power supply lead electrode 2 b extending to the second connection external electrode 10 B provided on the long-side surface. In this way, the second power supply electrodes 2 B of the divisional region A 1 in the different piezoelectric layers 1 are electrically coupled to each other via the second connection external electrode 10 B. Since in the second pattern the second power supply electrode 2 B of the divisional region A 1 is electrically coupled to the second power supply electrode 2 B of the divisional region A 3 via the second connection electrode J 2 , the second power supply electrode 2 B of the divisional region A 1 of the first pattern, which is electrically coupled to the second power supply electrode 2 B of the divisional region A 1 of the second pattern via the second connection external electrode 10 B, is electrically coupled to the second power supply external electrode 4 B via the second connection electrode J 2 of the second pattern.

The counter electrode 3 is provided over substantially the entire surface of the piezoelectric layer 1 as shown in FIG. 16(D) . Specifically, the counter electrode 3 is not provided in a circumferential region of the principal surface of the piezoelectric layer 1 but is provided over substantially the entirety of a region inside the circumferential region. The counter electrode 3 includes counter lead electrodes 3 g which extend from one lateral end to the counter external electrodes 5 provided on both short-side surfaces of the piezoelectric element P 4 . In this way, the counter electrode 3 is electrically coupled to the counter external electrodes 5 via the counter lead electrodes 3 g . The counter electrodes 3 provided on different piezoelectric layers 1 are electrically coupled to each other via the counter lead electrodes 3 g and the counter external electrodes 5 .

The piezoelectric element P 4 is formed by stacking the piezoelectric layers 1 provided with the power supply electrodes 2 or the counter electrode 3 on the principal surfaces as described above. Specifically, the plurality of piezoelectric layers 1 are sequentially stacked in the order of the piezoelectric layer 1 provided with the first pattern power supply electrodes 2 , the piezoelectric layer 1 provided with the counter electrode 3 , the piezoelectric layer 1 provided with the second pattern power supply electrodes 2 , the piezoelectric layer 1 provided with the counter electrode 3 , the piezoelectric layer 1 provided with the first pattern power supply electrodes 2 , the piezoelectric layer 1 provided with the counter electrode 3 , . . . . The piezoelectric layers 1 are stacked such that the principal surfaces provided with the power supply electrodes 2 or the counter electrode 3 are oriented in the same direction, i.e., such that the principal surface of one of the piezoelectric layers 1 on which the power supply electrodes 2 or the counter electrode 3 is provided face the principal surface of another one of the piezoelectric layers 1 on which none of the power supply electrodes 2 and the counter electrode 3 is provided. Note that, the first and/or last of the stacked layers are the piezoelectric layers 1 which are not provided with the power supply electrodes 2 or the counter electrode 3 such that the power supply electrodes 2 or the counter electrode 3 would not be exposed.

As a result of stacking the piezoelectric layers 1 , the power supply electrodes 2 and the counter electrode 3 , each of the piezoelectric layers 1 is sandwiched by the power supply electrodes 2 (specifically, the first power supply electrode 2 A and the second power supply electrode 2 B) and the counter electrode 3 . Thus, when seen in the stacking direction, the power supply electrodes 2 and the counter electrode 3 are overlapping with each other with the piezoelectric layer 1 interposed therebetween. Here, each of the piezoelectric layers 1 is polarized from the power supply electrode 2 side to the counter electrode 3 side.

However, the piezoelectric layers 1 include a region in which the power supply electrodes 2 and the counter electrode 3 are not overlapping when seen in the stacking direction (see FIG. 15 ). For example, the first power supply lead electrode 2 a , the second power supply lead electrode 2 b , and the counter lead electrodes 3 g are not overlapping with the counter electrode 3 or the power supply electrodes 2 when seen in the stacking direction. In part of the piezoelectric layers 1 corresponding to the non-overlapping region, no electric field occurs. In other words, this part of the piezoelectric layers 1 is piezoelectrically inactive. Specifically, in part of the piezoelectric layers 1 near the short-side surfaces, the power supply electrodes 2 and the counter electrode 3 are not overlapping when seen in the stacking direction. This part of the piezoelectric layers 1 is piezoelectrically inactive.

The resonance frequency of the stretching vibration and the resonance frequency of the bending vibration of the piezoelectric element P 4 , which will be described later, depend on the material, the shape, etc., of the piezoelectric element P 4 . The material, the shape, etc., of the piezoelectric element P 4 are determined such that the resonance frequency of the stretching vibration and the resonance frequency of the bending vibration are approximately equal to each other.

<4.2: Electrical Connection Member>

In this embodiment, flexible cables F 4 are used as the electrical connection member. The flexible cables F 4 include a first flexible cable F 41 and a second flexible cable F 42 . As shown in FIG. 1 , the first flexible cable F 41 and the second flexible cable F 42 are electrically connected to the respective short-side surfaces of the piezoelectric element P 4 . The first flexible cable F 41 and the second flexible cable F 42 are electrically coupled to the piezoelectric element P 4 . The first flexible cable F 41 and the second flexible cable F 42 have substantially the same shape.

FIG. 17 shows the positional relationship in connection between the first and second flexible cables F 41 and F 42 and the short-side surfaces of the piezoelectric element P 4 . As shown in FIG. 17 , the first and second flexible cables F 41 and F 42 include a plurality of electric wires formed by printing copper over an insulative resin substrate. The electric wires are mutually insulated.

The first flexible cable F 41 is connected to one of the short-side surfaces of the piezoelectric element P 4 . The second flexible cable F 42 is connected to the other one of the short-side surfaces of the piezoelectric element P 4 . The first and second flexible cables F 41 and F 42 each include an electric line 6 connected to the power supply external electrode 4 and an electric line 7 connected to the counter external electrode 5 . Specifically, the first flexible cable F 41 has an electric line 6 A connected to the first power supply external electrode 4 A and an electric line 7 connected to the counter external electrode 5 . The second flexible cable F 42 has an electric line 6 B connected to the second power supply external electrode 4 B and an electric line 7 connected to the counter external electrode 5 .

Note that the flexible cables F 4 are not directly connected to the first connection external electrode 10 A or the second connection external electrode 10 B.

The first flexible cable F 41 has a shape symmetrical about a plane which passes through the midpoints of the short sides of the principal plane of the piezoelectric layer 1 and which is perpendicular to the short-side surfaces. The second flexible cable F 42 also has a shape symmetrical about the plane which passes through the midpoints of the short sides of the principal plane of the piezoelectric layer 1 and which is perpendicular to the short-side surfaces. The first flexible cable F 41 and the second flexible cable F 42 have a shape symmetrical about a plane which passes through the midpoints of the long sides of the principal plane of the piezoelectric layer 1 and which is perpendicular to the principal surface. A connecting portion of the first flexible cable F 41 which is connected to the piezoelectric element P 4 has a shape symmetrical about the plane which passes through the midpoints of the short sides of the principal plane of the piezoelectric layer 1 and which is perpendicular to the short-side surfaces. A connecting portion of the second flexible cable F 42 which is connected to the piezoelectric element P 4 also has a shape symmetrical about the plane which passes through the midpoints of the short sides of the principal plane of the piezoelectric layer 1 and which is perpendicular to the short-side surfaces. The connecting portion of the first flexible cable F 41 which is connected to the piezoelectric element P 4 and the connecting portion of the second flexible cable F 42 which is connected to the piezoelectric element P 4 have a shape symmetrical about the plane which passes through the midpoints of the long sides of the principal plane of the piezoelectric layer 1 and which is perpendicular to the principal surface.

In the connecting portions of the first and second flexible cables F 41 and F 42 and a connecting portion of the piezoelectric element P 4 , these elements are electrically connected and adhered using an anisotropic conductive adhesion sheet. The anisotropic conductive adhesion sheet is prepared by molding a resin containing electrically conductive particles dispersed therein into the form of a sheet. The anisotropic conductive adhesion sheet has an electric conductivity in the adhesion direction, i.e., in the sheet thickness direction, but lacks electric conductivity in the in-plane directions of the adhesion surface. Therefore, the plurality of electrodes provided over the short-side surfaces of the piezoelectric element P 4 can be electrically connected to the respective electric lines of the first and second flexible cables F 41 and F 42 by a single anisotropic conductive adhesion sheet with the electrodes being mutually insulated. In the first step of the connection method, an anisotropic conductive sheet is sandwiched between the first and second flexible cables F 41 and F 42 made of polyimide and the piezoelectric element P 4 . Then, the first and second flexible cables F 41 and F 42 are pressed against the piezoelectric element P 4 using a heated planar cautery. As a result, the first and second flexible cables F 41 and F 42 and the piezoelectric element P 4 are electrically coupled by the electrically conductive particles and adhered by means of the resin of the anisotropic conductive adhesion sheet.

The connection portions of the first and second flexible cables F 41 and F 42 and the piezoelectric element P 4 are respectively interposed between the supporting portion 13 a and the piezoelectric element P 4 and between the supporting portion 13 c and the piezoelectric element P 4 . Specifically, the first flexible cable F 41 is pressed by the supporting portion 13 a against the piezoelectric element P 4 . The second flexible cable F 42 is pressed by the supporting portion 13 c against the piezoelectric element P 4 .

The electric lines 6 connected to the power supply external electrodes 4 are an example of the power supply conductive member. The electric line 6 A connected to the first power supply external electrode 4 A is an example of the first power supply conductive member. The electric line 6 B connected to the second power supply external electrode 4 B is an example of the second power supply conductive member. The electric lines 7 connected to the counter external electrodes 5 are an example of the counter conductive member. The first flexible cable F 41 is an example of the first electrical connection member. The second flexible cable F 42 is an example of the second electrical connection member.

The first and second flexible cables F 41 and F 42 are coupled to a power supply (not shown). A driving voltage from the power supply is applied to the piezoelectric element P 4 via the first and second flexible cables F 41 and F 42 such that vibration is generated in the piezoelectric element P 4 .

<4.3: Operation of Ultrasonic Actuator>

Hereinafter, an operation of the ultrasonic actuator is described. The operation of the ultrasonic actuator of this embodiment is basically the same as that of the ultrasonic actuator of embodiment 1. Specifically, a first driving voltage at a frequency near the substantially-matched resonance frequencies of the stretching vibration and the bending vibration of the piezoelectric element P 4 is applied to the first power supply electrode 2 A, and a second driving voltage which is approximately equal in amplitude and frequency to and different in phase by generally 90° or −90° from the first driving voltage is applied to the second power supply electrode 2 B, whereby the first-order stretching vibration and the second-order bending vibration are harmonically induced in the piezoelectric element P 4 . As a result, the piezoelectric element P 4 vibrates with its shape being sequentially deformed in the order of FIG. 8(A) , FIG. 8(B) , FIG. 8(C) , and FIG. 8(D) . The driver elements 8 provided on the piezoelectric element P 4 make a revolutionary movement, specifically a generally-elliptic movement, when seen in the direction perpendicular to the surface of the sheet of FIG. 8 . In other words, the composite vibration of the stretching vibration and bending vibration of the piezoelectric element P 4 causes the driver elements 8 to make an elliptic movement. Due to this elliptic movement, the movable element 9 on which the driver elements 8 abut moves relative to the piezoelectric element P 4 .

In this example, the first connection external electrode 10 A and the second connection external electrode 10 B are provided on the same long-side surface. Alternatively, the first and second connection external electrodes 10 A and 10 B may be provided on different long-side surfaces of the piezoelectric element P 4 .

<4.4: Advantages of Embodiment>

According to this embodiment, the first connection external electrode 10 A and the second connection external electrode 10 B are provided on the same long-side surface. Specifically, the long-side surface which has the driving elements 8 is not provided with the first connection external electrode 10 A or the second connection external electrode 10 B, and the other long-side surface which is different from the long-side surface that has the driving elements 8 thereon is provided with the first connection external electrode 10 A and the second connection external electrode 10 B. This configuration improves the flexibility of arrangement of the driving elements 8 such that the driving elements 8 are fixed at positions other than the first connection external electrode 10 A or the second connection external electrode 10 B.

Embodiment 4 can also provide effects and advantages substantially equivalent to those of embodiments 1 and 2.

An ultrasonic actuator according to embodiment 5 of the present invention is now described. Note that elements equivalent to those described in the above embodiment are denoted by the same reference characters, and the description thereof is herein omitted. The ultrasonic actuator of embodiment 5 is different from embodiment 1 in the configurations of the piezoelectric element and the flexible cables.

<5.1: Piezoelectric Element P 5 >

The piezoelectric element P 5 of this embodiment is in the shape of a generally rectangular parallelepiped. The piezoelectric element P 5 includes a plurality of generally rectangular piezoelectric layers 1 , and internal electrode layers interposed between the piezoelectric layers 1 . The piezoelectric element P 5 includes the piezoelectric layers and the electrode layers which are stacked in a direction from front to back of the drawing sheet of FIG. 1 .

FIG. 18 is an orthographic developed view of the piezoelectric element P 5 . FIG. 19 shows the respective layers of the piezoelectric element P 5 which are seen in the layer stacking direction. In FIG. 18 , a portion at the center represents the principal surface, portions on the right and left sides of the principal surface are the short-side surfaces, and portions on the upper and lower sides of the principal surface are the long-side surfaces. The internal electrode layers are behind the principal surface and thus cannot be seen. The positions of the internal electrode layers projected over the principal surface are represented by broken lines.

As shown in FIG. 18 , power supply external electrodes 4 and counter external electrodes 5 are provided on the short-side surfaces of the piezoelectric element P 5 . Specifically, the power supply external electrodes 4 include a first power supply external electrode 4 A and a second power supply external electrode 4 B which are mutually separate. The first power supply external electrode 4 A and the second power supply external electrode 4 B are provided on one of the two short-side surfaces of the piezoelectric element P 5 . The counter external electrodes 5 include a first counter external electrode 5 A and a second counter external electrode 5 B. The first counter external electrode 5 A and the second counter external electrode 5 B are provided on the other one of the two short-side surfaces of the piezoelectric element P 5 . The piezoelectric element P 5 includes the two counter external electrodes 5 which are provided on the other one of the two short-side surfaces. These electrodes 4 A, 4 B, 5 A, and 5 B are mutually insulated. In other words, the electrodes 4 A, 4 B, 5 A, and 5 B are not electrically coupled to one another. A first connection external electrode 10 A and a fourth connection external electrode 10 D are provided on one of the long-side surfaces of the piezoelectric element P 5 . A second connection external electrode 10 B and a third connection external electrode 10 C are provided on the other one of the long-side surfaces of the piezoelectric element P 5 . The first through fourth connection external electrodes 10 A- 10 D are mutually insulated. In other words, the first through fourth connection external electrodes 10 A- 10 D are not electrically coupled to one another.

The power supply electrodes 2 are provided on the principal surface of at least one of the plurality of piezoelectric layers 1 as shown in FIG. 19(B) and FIG. 19(C) . Specifically, the power supply electrodes 2 are provided on the principal surface of at least one of the plurality of piezoelectric layers 1 in the first pattern as shown in FIG. 19(B) . On the principal surface of another one of the plurality of piezoelectric layers 1 different from the piezoelectric layer 1 on which the power supply electrodes 2 are provided in the first pattern, the power supply electrodes 2 are provided in the second pattern as shown in FIG. 19(C) which is different from the first pattern.

Specifically, the power supply electrodes 2 formed in the first pattern and in the second pattern each include first power supply electrodes 2 A and second power supply electrodes 2 B which are not electrically coupled to the first power supply electrodes 2 A.

In each of the first and second patterns, among four divisional regions A 1 -A 4 (see FIG. 4 ) of the principal surface of the piezoelectric layer 1 which are defined by halving the principal surface with respect to both longitudinal direction L and lateral direction S, the first power supply electrodes 2 A are provided in two of the four divisional regions A 1 -A 4 which are aligned in the first diagonal direction D 1 of the principal surface of the piezoelectric layer 1 , i.e., in the divisional regions A 2 and A 4 . The second power supply electrodes 2 B are provided in the other two of the four divisional regions A 1 -A 4 which are aligned in the second diagonal direction D 2 of the principal surface of the piezoelectric layer 1 , i.e., in the divisional regions A 1 and A 3 .

The first pattern power supply electrodes 2 include a first connection electrode J 1 extending in the lateral direction at the longitudinal center of the principal surface of the piezoelectric layer 1 . The first power supply electrodes 2 A provided in the two divisional regions A 2 and A 4 of the first pattern are mutually coupled via the first connection electrode J 1 . On the other hand, the second pattern power supply electrodes 2 include a second connection electrode J 2 extending in the lateral direction at the longitudinal center of the principal surface of the piezoelectric layer 1 . The second power supply electrodes 2 B provided in the two divisional regions A 1 and A 3 of the second pattern are mutually coupled via the second connection electrode J 2 .

In each of the first and second patterns, among the first power supply electrodes 2 A provided in the two divisional regions A 2 and A 4 , the first power supply electrode 2 A provided in the divisional region A 2 which is closer to the short-side surface that has the first power supply external electrode 4 A thereon includes a first power supply lead electrode 2 a extending to the first power supply external electrode 4 A. In this way, the first power supply electrode 2 A of the divisional region A 2 is electrically coupled to the first power supply external electrode 4 A via the first power supply lead electrode 2 a. Among the first power supply electrodes 2 A provided in the two divisional regions A 2 and A 4 , the first power supply electrode 2 A provided in the divisional region A 4 which is more distant from the short-side surface that has the first power supply external electrode 4 A thereon includes a first power supply lead electrode 2 a extending to the first connection external electrode 10 A provided on the long-side surface. In this way, the first power supply electrodes 2 A of the divisional region A 4 in the different piezoelectric layers 1 are electrically coupled to each other via the first connection external electrode 10 A. Since in the first pattern the first power supply electrode 2 A of the divisional region A 4 is electrically coupled to the first power supply electrode 2 A of the divisional region A 2 via the first connection electrode J 1 , the first power supply electrode 2 A of the divisional region A 4 of the second pattern, which is electrically coupled to the first power supply electrode 2 A of the divisional region A 4 of the first pattern via the first connection external electrode 10 A, is electrically coupled to the first power supply external electrode 4 A of the first pattern via the first connection electrode J 1 .

In each of the first and second patterns, among the second power supply electrodes 2 B provided in the two divisional regions A 1 and A 3 , the second power supply electrode 2 B provided in the divisional region A 3 which is closer to the short-side surface that has the second power supply external electrode 4 B thereon includes a second power supply lead electrode 2 b extending to the second power supply external electrode 4 B. In this way, the second power supply electrode 2 B of the divisional region A 3 is electrically coupled to the second power supply external electrode 4 B via the second power supply lead electrode 2 b . Among the second power supply electrodes 2 B provided in the two divisional regions A 1 and A 3 , the second power supply electrode 2 B provided in the divisional region A 1 which is more distant from the short-side surface that has the second power supply external electrode 4 B thereon includes a second power supply lead electrode 2 b extending to the second connection external electrode 10 B provided on the long-side surface. In this way, the second power supply electrodes 2 B of the divisional region A 1 in the different piezoelectric layers 1 are electrically coupled to each other via the second connection external electrode 10 B. Since in the second pattern the second power supply electrode 2 B of the divisional region A 1 is electrically coupled to the second power supply electrode 2 B of the divisional region A 3 via the second connection electrode J 2 , the second power supply electrode 2 B of the divisional region A 1 of the first pattern, which is electrically coupled to the second power supply electrode 2 B of the divisional region A 1 of the second pattern via the second connection external electrode 10 B, is electrically coupled to the second power supply external electrode 4 B via the second connection electrode J 2 of the second pattern.

The counter electrodes 3 are provided on the principal surface of at least one of the plurality of piezoelectric layers 1 on which the power supply electrodes 2 are not provided as shown in FIG. 19(D) and FIG. 19(E) . Specifically, the counter electrodes 3 are provided in the third pattern on the principal surface of at least one of the plurality of piezoelectric layers 1 on which the power supply electrodes 2 are not provided as shown in FIG. 19(D) . On the principal surface of another one of the plurality of piezoelectric layers 1 on which none of the power supply electrodes 2 and the third pattern counter electrodes 3 are provided, counter electrodes 3 are provided in the fourth pattern as shown in FIG. 19(E) which is different from the third pattern.

Specifically, the counter electrodes 3 formed in the third pattern and in the fourth pattern each include first counter electrodes 3 A and second counter electrodes 3 B which are not electrically coupled to the first counter electrodes 3 A.

In each of the third and fourth patterns, among four divisional regions A 1 -A 4 (see FIG. 4 ) of the principal surface of the piezoelectric layer 1 which are defined by halving the principal surface with respect to both longitudinal direction L and lateral direction S, the first counter electrodes 3 A are provided in two of the four divisional regions A 1 -A 4 which are aligned in the first diagonal direction D 1 of the principal surface of the piezoelectric layer 1 , i.e., in the divisional regions A 2 and A 4 . The second counter electrodes 3 B are provided in the other two of the four divisional regions A 1 -A 4 which are aligned in the second diagonal direction D 2 of the principal surface of the piezoelectric layer 1 , i.e., in the divisional regions A 1 and A 3 .

The third pattern counter electrodes 3 include a third connection electrode J 3 extending in the lateral direction at the longitudinal center of the principal surface of the piezoelectric layer 1 . The first counter electrodes 3 A provided in the two divisional regions A 2 and A 4 of the third pattern are electrically coupled to each other via the third connection electrode J 3 . On the other hand, the fourth pattern counter electrodes 3 include a fourth connection electrode J 4 extending in the lateral direction at the longitudinal center of the principal surface of the piezoelectric layer 1 . The second counter electrodes 3 B provided in the two divisional regions A 1 and A 3 of the fourth pattern are electrically coupled to each other via the fourth connection electrode J 4 .

In each of the third and fourth patterns, among the first counter electrodes 3 A provided in the two divisional regions A 2 and A 4 , the first counter electrodes 3 A provided in the divisional region A 4 which is closer to the short-side surface that has the first counter external electrode 5 A thereon includes a first counter lead electrode 3 a extending to the first counter external electrode 5 A. In this way, the first counter electrode 3 A of the divisional region A 4 is electrically coupled to the first counter external electrode 5 A via the first counter lead electrode 3 a . Among the first counter electrodes 3 A provided in the two divisional regions A 2 and A 4 , the first counter electrode 3 A provided in the divisional region A 2 which is more distant from the short-side surface that has the first counter external electrode 5 A thereon includes a first counter lead electrode 3 a extending to the third connection external electrode 10 C provided on the long-side surface. In this way, the first counter electrodes 3 A of the divisional region A 2 in the different piezoelectric layers 1 are electrically coupled to each other via the third connection external electrode 10 C. Since in the third pattern the first counter electrode 3 A of the divisional region A 2 is electrically coupled to the first counter electrode 3 A of the divisional region A 4 via the third connection electrode J 3 , the first counter electrode 3 A of the divisional region A 2 of the fourth pattern, which is electrically coupled to the first counter electrode 3 A of the divisional region A 2 of the third pattern via the third connection external electrode 10 C, is electrically coupled to the first counter external electrode 5 A via the third connection electrode J 3 of the third pattern.

In each of the third and fourth patterns, among the second counter electrodes 3 B provided in the two divisional regions A 1 and A 3 , the second counter electrode 3 B provided in the divisional region A 1 which is closer to the short-side surface that has the second counter external electrode 5 B thereon includes a second counter lead electrode 3 b extending to the second counter external electrode 5 B. In this way, the second counter electrodes 3 B of the divisional region A 1 is electrically coupled to the second counter external electrode 5 B via the second counter lead electrode 3 b . Among the second counter electrodes 3 B provided in the two divisional regions A 1 and A 3 , the second counter electrode 3 B provided in the divisional region A 3 which is more distant from the short-side surface that has the second counter external electrode 5 B thereon includes a second counter lead electrode 3 b extending to the fourth connection external electrode 10 D provided on the long-side surface. In this way, the second counter electrodes 3 B of the divisional region A 3 in the different piezoelectric layers 1 are electrically coupled to each other via the second connection external electrode 10 B. Since in the fourth pattern the second counter electrode 3 B of the divisional region A 3 is electrically coupled to the second counter electrode 3 B of the divisional region A 1 via the fourth connection electrode J 4 , the second counter electrodes 3 B of the divisional region A 3 of the third pattern, which is electrically coupled to the second counter electrode 3 B of the divisional region A 3 of the fourth pattern via the fourth connection external electrode 10 D, is electrically coupled to the second counter external electrode 5 B via the fourth connection electrode J 4 of the fourth pattern.

The piezoelectric element P 5 is formed by stacking the piezoelectric layers 1 provided with the power supply electrodes 2 or the counter electrodes 3 on the principal surfaces as described above. Specifically, the plurality of piezoelectric layers 1 are sequentially stacked in the order of the piezoelectric layer 1 provided with the first pattern power supply electrodes 2 , the piezoelectric layer 1 provided with the third pattern counter electrodes 3 , the piezoelectric layer 1 provided with the second pattern power supply electrodes 2 , the piezoelectric layer 1 provided with the fourth pattern counter electrodes 3 , the piezoelectric layer 1 provided with the first pattern power supply electrodes 2 , the piezoelectric layer 1 provided with the third pattern counter electrodes 3 , . . . . The piezoelectric layers 1 are stacked such that the principal surfaces provided with the power supply electrodes 2 or the counter electrodes 3 are oriented in the same direction, i.e., such that the principal surface of one of the piezoelectric layers 1 on which the power supply electrodes 2 or the counter electrodes 3 are provided face the principal surface of another one of the piezoelectric layers 1 on which none of the power supply electrodes 2 and the counter electrodes 3 is provided. Note that, the first and/or last of the stacked layers are the piezoelectric layers 1 which are not provided with the power supply electrodes 2 or the counter electrodes 3 such that the power supply electrodes 2 or the counter electrodes 3 would not be exposed.

As a result of stacking the piezoelectric layers 1 , the power supply electrodes 2 and the counter electrodes 3 , each of the piezoelectric layers 1 is sandwiched by the power supply electrodes 2 and the counter electrodes 3 . Thus, when seen in the stacking direction, the power supply electrodes 2 and the counter electrodes 3 are overlapping with each other with the piezoelectric layer 1 interposed therebetween. Here, each of the piezoelectric layers 1 is polarized from the power supply electrode 2 side to the counter electrode 3 side.

Specifically, the first power supply electrodes 2 A are overlapping with the first counter electrodes 3 A with the piezoelectric layer 1 interposed therebetween when seen in the stacking direction. The second power supply electrodes 2 B are overlapping with the second counter electrodes 3 B with the piezoelectric layer 1 interposed therebetween when seen in the stacking direction. The first connection electrode J 1 is overlapping with the third connection electrode J 3 with the piezoelectric layer 1 interposed therebetween when seen in the stacking direction. The second connection electrode J 2 is overlapping with the fourth connection electrode J 4 with the piezoelectric layer 1 interposed therebetween when seen in the stacking direction.

However, the piezoelectric layers 1 include a region in which the power supply electrodes 2 and the counter electrodes 3 are not overlapping when seen in the stacking direction (see FIG. 18 ). For example, the first and second power supply lead electrodes 2 a and 2 b and the counter lead electrodes 3 a and 3 b are not overlapping with the counter electrodes 3 or the power supply electrodes 2 when seen in the stacking direction. In part of the piezoelectric layers 1 corresponding to the non-overlapping region, no electric field occurs. In other words, this part of the piezoelectric layers 1 is piezoelectrically inactive. Specifically, in part of the piezoelectric layers 1 near the short-side surfaces, the power supply electrodes 2 and the counter electrodes 3 are not overlapping when seen in the stacking direction. This part of the piezoelectric layers 1 is piezoelectrically inactive.

The resonance frequency of the stretching vibration and the resonance frequency of the bending vibration of the piezoelectric element P 5 , which will be described later, depend on the material, the shape, etc., of the piezoelectric element P 5 . The material, the shape, etc., of the piezoelectric element P 5 are determined such that the resonance frequency of the stretching vibration and the resonance frequency of the bending vibration are approximately equal to each other.

<5.2: Electrical Connection Member>

In this embodiment, flexible cables F 5 are used as the electrical connection member. The flexible cables F 5 include a first flexible cable F 51 and a second flexible cable F 52 . As shown in FIG. 1 , the first flexible cable F 51 and the second flexible cable F 52 are electrically connected to the respective short-side surfaces of the piezoelectric element P 5 . The first flexible cable F 51 and the second flexible cable F 52 are electrically connected to the piezoelectric element P 5 . The first flexible cable F 51 and the second flexible cable F 52 have substantially the same shape.

FIG. 20 shows the positional relationship in connection between the first and second flexible cables F 51 and F 52 and the lateral surfaces of the piezoelectric element P 5 . As shown in FIG. 20 , the first and second flexible cables F 51 and F 52 include a plurality of electric wires formed by printing copper over an insulative resin substrate. The electric wires are mutually insulated.

The first flexible cable F 51 is connected to one of the short-side surfaces of the piezoelectric element P 5 . The first flexible cable F 51 includes electric lines 6 connected to the power supply external electrodes 4 . Specifically, the first flexible cable F 51 has an electric line 6 A connected to the first power supply external electrode 4 A and an electric line 6 B connected to the second power supply external electrode 4 B.

The second flexible cable F 52 is connected to the other one of the short-side surfaces of the piezoelectric element P 5 . The second flexible cable F 52 includes electric lines 7 connected to the counter external electrodes 5 . Specifically, the second flexible cable F 52 has an electric line 7 A connected to the first counter external electrode 5 A and an electric line 7 B connected to the second counter external electrode 5 B. The electric line 7 A constitutes the first counter conductive member, and the electric line 7 B constitutes the second counter conductive member.

Note that the flexible cables F 5 are not directly connected to the first through fourth connection external electrodes 10 A- 10 D.

The first flexible cable F 51 has a shape symmetrical about a plane which passes through the midpoints of the short sides of the principal plane of the piezoelectric layer 1 and which is perpendicular to the short-side surfaces. The second flexible cable F 52 also has a shape symmetrical about the plane which passes through the midpoints of the short sides of the principal plane of the piezoelectric layer 1 and which is perpendicular to the short-side surfaces. The first flexible cable F 51 and the second flexible cable F 52 have a shape symmetrical about a plane which passes through the midpoints of the long sides of the principal plane of the piezoelectric layer 1 and which is perpendicular to the principal surface. A connecting portion of the first flexible cable F 51 which is connected to the piezoelectric element P 5 has a shape symmetrical about the plane which passes through the midpoints of the short sides of the principal plane of the piezoelectric layer 1 and which is perpendicular to the short-side surfaces. A connecting portion of the second flexible cable F 52 which is connected to the piezoelectric element P 5 also has a shape symmetrical about the plane which passes through the midpoints of the short sides of the principal plane of the piezoelectric layer 1 and which is perpendicular to the short-side surfaces. The connecting portion of the first flexible cable F 51 which is connected to the piezoelectric element P 5 and the connecting portion of the second flexible cable F 52 which is connected to the piezoelectric element P 5 have a shape symmetrical about the plane which passes through the midpoints of the long sides of the principal plane of the piezoelectric layer 1 and which is perpendicular to the principal surface.

In the connecting portions of the first and second flexible cables F 51 and F 52 and a connecting portion of the piezoelectric element P 5 , these elements are electrically connected and adhered using an anisotropic conductive adhesion sheet. The anisotropic conductive adhesion sheet is prepared by molding a resin containing electrically conductive particles dispersed therein into the form of a sheet. The anisotropic conductive adhesion sheet has an electric conductivity in the adhesion direction, i.e., in the sheet thickness direction, but lacks electric conductivity in the in-plane directions of the adhesion surface. Therefore, the plurality of electrodes provided over the short-side surfaces of the piezoelectric element P 5 can be electrically connected to the respective electric lines of the first and second flexible cables F 51 and F 52 by a single anisotropic conductive adhesion sheet with the electrodes being mutually insulated. In the first step of the connection method, an anisotropic conductive sheet is sandwiched between the first and second flexible cables F 51 and F 52 made of polyimide and the piezoelectric element P 5 . Then, the first and second flexible cables F 51 and F 52 are pressed against the piezoelectric element P 5 using a heated planar cautery. As a result, the first and second flexible cables F 51 and F 52 and the piezoelectric element P 5 are electrically coupled by the electrically conductive particles and adhered by means of the resin of the anisotropic conductive adhesion sheet.

The connection portions of the first and second flexible cables F 51 and F 52 and the piezoelectric element P 5 are respectively interposed between the supporting portion 13 a and the piezoelectric element P 5 and between the supporting portion 13 c and the piezoelectric element P 5 . Specifically, the first flexible cable F 51 is pressed by the supporting portion 13 a against the piezoelectric element P 5 . The second flexible cable F 52 is pressed by the supporting portion 13 c against the piezoelectric element P 5 .

The electric lines 6 connected to the power supply external electrodes 4 are an example of the power supply conductive member. The electric line 6 A connected to the first power supply external electrode 4 A is an example of the first power supply conductive member. The electric line 6 B connected to the second power supply external electrode 4 B is an example of the second power supply conductive member. The electric lines 7 connected to the counter external electrodes 5 are an example of the counter conductive member. The electric line 7 A connected to the first counter external electrode 5 A is an example of the first power supply conductive member. The electric line 7 B connected to the second counter external electrode 5 B is an example of the second counter conductive member. The first flexible cable F 51 is an example of the first electrical connection member. The second flexible cable F 52 is an example of the second electrical connection member.

The first and second flexible cables F 51 and F 52 are coupled to a power supply (not shown). A driving voltage from the power supply is applied to the piezoelectric element P 5 via the first and second flexible cables F 51 and F 52 such that vibration is generated in the piezoelectric element P 5 .

<5.3: Operation of Ultrasonic Actuator>

Hereinafter, an operation of the ultrasonic actuator is described.

A first driving voltage at a frequency near the substantially-matched resonance frequencies of the stretching vibration and the bending vibration of the piezoelectric element P 5 is applied between the first power supply electrode 2 A and the first counter electrode 3 A, and a second driving voltage which is approximately equal in amplitude and frequency to and different in phase by generally 90° or −90° from the first driving voltage is applied between the second power supply electrode 2 B and the second counter electrode 3 B, whereby the first mode stretching vibration and the second mode bending vibration are harmonically induced in the piezoelectric element P 5 . As a result, the piezoelectric element P 5 vibrates with its shape being sequentially deformed in the order of FIG. 8(A) , FIG. 8(B) , FIG. 8(C) , and FIG. 8(D) . The driver elements 8 provided on the piezoelectric element P 5 make a revolutionary movement, specifically a generally-elliptic movement, when seen in the direction perpendicular to the surface of the sheet of FIG. 8 . In other words, the composite vibration of the stretching vibration and bending vibration of the piezoelectric element P 5 causes the driver elements 8 to make an elliptic movement. Due to this elliptic movement, the movable element 9 on which the driver elements 8 abut moves relative to the piezoelectric element P 5 .

In this embodiment, the power supply applies to the first counter electrode 3 A a voltage opposite in polarity to that applied to the first power supply electrode 2 A. The power supply applies to the second counter electrode 3 B a voltage opposite in polarity to that applied to the second power supply electrode 2 B. This power supply may be implemented using a full-bridge circuit, a push-pull circuit, or the like. This structure is possible because the counter electrodes 3 include the first counter electrodes 3 A and the second counter electrodes 3 B which are separate from each other.

Although the first power supply external electrode 4 A and the second power supply external electrode 4 B are provided on one of the two short-side surfaces of the piezoelectric element P 5 while the first counter external electrode 5 A and the second counter external electrode 5 B are provided on the other one of the two short-side surfaces, any combination of these electrodes may be possible. The structure in which the first power supply external electrode 4 A is provided on one of the two short-side surfaces of the piezoelectric element P 5 while the first counter external electrode 5 A is provided on the other one of the two short-side surfaces and in which the second power supply external electrode 4 B is provided on one of the two short-side surfaces of the piezoelectric element P 5 while the second counter external electrode 5 B is provided on the other one of the two short-side surfaces may be implemented by an alternative structure in which both the first power supply external electrode 4 A and the second counter external electrode 5 B are provided on one of the two short-side surfaces of the piezoelectric element P 5 while both the first counter external electrode 5 A and the second power supply external electrode 4 B are provided on the other one of the two short-side surfaces.

Both the first counter electrodes 3 A and the second counter electrodes 3 B may be coupled to the ground.

Although the above-described example uses one piece of the piezoelectric element P 5 which is coupled to the power supply, two or more pieces of the piezoelectric elements P 5 may be used and may be connected in series and coupled to the power supply. In this case, for example, the serial connection may be implemented by electrically coupling the second counter external electrode 5 B of the first piezoelectric element P 5 to the second power supply external electrode 4 B of the second piezoelectric element P 5 using an electrical connection member, such as a flexible, or the like, and electrically coupling the first counter external electrode 5 A of the first piezoelectric element P 5 to the first power supply external electrodes 4 A of the second piezoelectric element P 5 using an electrical connection member, such as a flexible, or the like.

<5.4: Advantages of Embodiment>

According to this embodiment, as in embodiment 2, the first power supply external electrode 4 A and the counter external electrodes 5 are provided at different short-side surfaces of the piezoelectric element P 5 , and the second power supply external electrode 4 B and the counter external electrodes 5 are provided at different short-side surfaces. This configuration ensures a sufficient distance between the first power supply external electrode 4 A and the counter external electrodes 5 and between the second power supply external electrode 4 B and the counter external electrodes 5 . Accordingly, sufficient insulation can be ensured between the first power supply external electrode 4 A and the counter external electrodes 5 and between the second power supply external electrode 4 B and the counter external electrodes 5 .

Since the counter electrodes 3 include the first counter electrodes 3 A and the second counter electrodes 3 B which are separate from each other, a voltage opposite in polarity to that applied to the first power supply electrodes 2 A can be applied to the first counter electrodes 3 A, and a voltage opposite in polarity to that applied to the second power supply electrodes 2 B can be applied to the second counter electrodes 3 B. Therefore, the voltage applied to the piezoelectric layer 1 can be twice that applied when the counter electrodes 3 are coupled to the ground. Further, due to this configuration, a plurality of pieces of the piezoelectric elements P 5 can be connected in series as described above.

The first power supply external electrode 4 A is provided on one of the two short-side surfaces of the piezoelectric element, and the first counter external electrode 5 A is provided on the other one of the two short-side surfaces which is different from that on which the first power supply external electrode 4 A is provided. This configuration ensures a large distance between the first power supply external electrode 4 A and the first counter external electrode 5 A. This configuration also improves insulation between the first power supply external electrode 4 A and the first counter external electrode 5 A. Likewise, the second power supply external electrode 4 B is provided on one of the two short-side surfaces of the piezoelectric element, and the second counter external electrode 5 B is provided on the other one of the two short-side surfaces which is different from that on which the second power supply external electrode 4 B is provided. This configuration ensures a large distance between the second power supply external electrode 4 B and the second counter external electrode 5 B. This configuration also improves insulation between the second power supply external electrode 4 B and the second counter external electrode 5 B.

The principal surface of the piezoelectric layer 1 on which the first counter electrodes 3 A are provided has the third connection electrode J 3 which provides electrical connection between the first counter electrodes 3 A. The principal surface of another piezoelectric layer 1 , which is different from the principal surface that has the third connection electrode J 3 thereon, has the fourth connection electrode J 4 which provides electrical connection between the second counter electrodes 3 B. This configuration enables reduction of the number of the first counter external electrodes 5 A which are electrically coupled to the first counter electrodes 3 A and the number of the second counter external electrodes 5 B which are electrically coupled to the second counter electrodes 3 B. As a result, the number of connection points between the piezoelectric element P 5 and the electrical connection members can be reduced, and accordingly, the probability of occurrence of peeling at the connection faces between the piezoelectric element P 5 and the electrical connection members. Further, the factors of interference with the vibration of the piezoelectric element P 5 are decreased so that the efficiency of the vibration can be improved.

The third and fourth connection electrodes J 3 and J 4 have a shape elongated in the lateral direction at the longitudinal center of the principal surface of the piezoelectric layer 1 . Therefore, the counter electrodes 3 can have an increased area at the longitudinal center of the piezoelectric layer 1 . By increasing the areas of the third and fourth connection electrodes J 3 and J 4 , large stretching vibration can be induced even when the size of the piezoelectric element P 5 is reduced. As a result, the efficiency of the ultrasonic actuator can be improved.

Embodiment 5 can also provide effects and advantages substantially equivalent to those of embodiments 1 and 2.

Other Embodiments

According to the present invention, the above-described embodiments may have different structures which are described below.

The shape of the driver elements 8 is not limited to the shape of a circular pole. It may be the shape of a sphere or a square pole. The driver elements preferably have a spherical shape because in this case the driver elements and the piezoelectric element P 1 are fixedly in point contact with each other.

The electrical connection members are not limited to the flexible cables. For example, wires, contact pins, conductive rubbers, etc., may be used. The above-described connection with the anisotropic conductive adhesive sheet may be replaced by a different electrical connection method, for example, connection with a low-melting metal, such as soldering, connection by wire bonding, connection with a non-anisotropic conductive adhesive sheet, connection with a conductive adhesive, such as a liquid adhesive, connection by pressing, etc. The conductive rubbers may have a layered structure which includes a supporting layer made of, for example, silicone rubber as a principal constituent, and a conductive layer containing silicone rubber and metal particles of silver, or the like, and may be anisotropic so that it is nonconducting in the stacking direction. One of the short-side surfaces of the piezoelectric element may be provided with one piece of the conductive rubber or may be provided with two pieces of the conductive rubber. In the case of using the conductive rubber, the conductive rubber may be used as the supporting portions 13 a and 13 c . In the case where one of the short-side surfaces of the piezoelectric element is provided with one piece of the conductive rubber, the non-conductive property of the conductive rubber in the stacking direction is utilized to provide insulation of the power supply external electrodes 4 and the counter external electrodes 5 , specifically insulation between the first power supply external electrode 4 A and the second power supply external electrode 4 B, and insulation between a first counter external electrode 5 A and a second counter external electrode 5 B. In this case, the respective conductive layers function as any of the first power supply conductive member 6 A, the second power supply conductive member 6 B, the first counter conductive member 7 A, and the second counter conductive member 7 B.

The first connection electrode J 1 and the second connection electrode J 2 are provided at the longitudinal center of the principal surface of the piezoelectric layer 1 and have a shape elongated in a direction generally perpendicular to the short sides of the principal surface of the piezoelectric layer 1 . More preferably, as for the dimensions in the direction of the long sides of the piezoelectric layer 1 , the width of the first connection electrode J 1 and the second connection electrode J 2 is preferably about 5% to 40% of the length of the long sides of the piezoelectric layer 1 . This is because, although a greater stretching vibration occurs as the electrode areas of the first connection electrode J 1 and the second connection electrode J 2 increase, the second mode bending vibration would be interrupted if the electrode areas are excessively large. On the other hand, as for the dimensions in the direction of the short sides of the piezoelectric layer 1 , the first connection electrode J 1 and the second connection electrode J 2 should ideally be provided over the entire short sides. However, if the first connection electrode J 1 and the second connection electrode J 2 reach the edges of the piezoelectric layer 1 at its lateral ends, it is difficult to provide insulation between the internal electrode layers. As such, the first connection electrode J 1 and the second connection electrode J 2 are preferably provided over the principal surface of the piezoelectric layer 1 except for the edges of the principal surface at its lateral ends. Specifically, the first connection electrode J 1 and the second connection electrode J 2 are desirably provided over the entire principal surface of the piezoelectric layer 1 except for a region extending from the respective edges of the principal surface of the piezoelectric layer 1 at its lateral ends toward the lateral center by the distance equal to the thickness of the piezoelectric layer 1 . This applies to the third connection electrode J 3 and the fourth connection electrode J 4 of embodiment 5.

The number of power supply electrodes 2 of the first pattern and the number of power supply electrodes 2 of the second pattern are preferably equal although they may not be equal. The power supply electrodes 2 of the first pattern and the power supply electrodes 2 of the second pattern are preferably alternately provided although they may not be alternately provided. In embodiment 5, the number of counter electrodes 3 of the third pattern and the number of counter electrodes 3 of the fourth pattern are preferably equal although they may not be equal. The counter electrodes 3 of the third pattern and the counter electrodes 3 of the fourth pattern are preferably alternately provided although they may not be alternately provided. This alternate arrangement improves the symmetry of vibration of the piezoelectric element. Also, the alternate arrangement prevents generation of excessive vibration in the piezoelectric element so that the energy loss can be greatly reduced.

The power supply electrodes 2 and counter electrodes 3 are preferably configured so as not to be exposed on the principal surface of the piezoelectric element although they may be exposed thereon. When the power supply electrodes 2 and counter electrodes 3 are not exposed on the principal surface of the piezoelectric element which has a larger area among the external surfaces of the piezoelectric element, the probability of occurrence of short circuits with peripheral metal parts decreases.

The region where the power supply electrodes 2 and the counter electrodes 3 are not overlapping when seen in the stacking direction is more preferably a region extending from the respective edges of the piezoelectric layer 1 at its longitudinal ends toward the longitudinal center by the distance equal to or greater than 10% of the longitudinal dimension of the piezoelectric layer 1 . The region where the power supply electrodes 2 and the counter electrodes 3 are not overlapping when seen in the stacking direction is preferably a region extending from the respective edges of the piezoelectric layer 1 at its longitudinal ends toward the longitudinal center by the distance equal to or greater than 20% of the longitudinal dimension of the piezoelectric layer 1 . In this case, near the edges of the piezoelectric layer 1 at its longitudinal ends, only a small stress is created under the first mode stretching vibration. Also, the connection between the short-side surfaces of the piezoelectric element and the electrical connection members can be less affected.

In the above-described embodiments, the movable element 9 which is driven by applying a driving force from the ultrasonic actuator is in the shape of a flat plate, to which the present invention is not limited. Any structure may be adopted as the structure of the movable element 9 . For example, as shown in FIG. 21 , the movable element may be a circular disk 9 which is rotatable around a predetermined axis X, with the driver elements 8 of the ultrasonic actuator abutting the circumferential surface 9 a of the circular disk 9 . In the case of this structure, when the ultrasonic actuator is driven, the driver elements 8 make a generally-elliptic movement, and accordingly, the circular disk 9 is rotated around the predetermined axis X. Part of the mechanism including the piezoelectric element may be stationary or may be movable.

In the above-described embodiments, the supporting body is formed by the case 11 but may be formed by any structure.

The voltage applied to the second power supply electrode 2 B is different in phase from the reference voltage applied to the first power supply electrode 2 A by generally +90 degrees or by generally −90 degrees, to which however the present invention is not limited. A voltage of a different phase difference from the reference voltage may be applied. Also, the voltage may be applied to only one of the first power supply electrode 2 A and the second power supply electrode 2 B.

In the above-described embodiments, the ultrasonic actuator is supported using the supporting portions 13 a , 13 b and 13 c . However, the present invention is not limited to this example. For example, as shown in FIG. 22 , only the supporting portion 13 b is provided on one of the two long-side surfaces of the piezoelectric element on which the driver elements are not provided. This supporting portion 13 b restricts the movement of the piezoelectric element in the driving direction (the long-side direction of the principal surface) and allows the movement of the driver elements in a direction in which the driver elements abut the movable element 9 (the short-side direction of the principal surface). The supporting portion 13 b generates a pressing force in a direction in which the driver elements abut the movable element and increases the frictional force between the driver elements and the movable element.

The present invention is not limited to the above-described embodiments and can be implemented in various other forms without departing from the spirit of the invention. The embodiments are merely exemplary in all aspects and should not be construed as limiting. The scope of the invention is defined only by claims and is not restricted by the specification. Variations and modifications equivalent to the claimed inventions are all within the scope of the present invention.

The present invention is applicable to a highly-reliable ultrasonic actuator, for example, a driving force generator which is for use in a variety of electronic devices and other types of devices.