Impact producing actuator and touch panel

The contents of the following Japanese patent application and International patent application are incorporated herein by reference,

Japanese Patent Application NO. 2014-138034 filed on Jul. 3, 2014, and

International Patent Application NO. PCT/JP2014/082184 filed on Nov. 28, 2014.

The present invention relates to an impact producing actuator and a touch panel, and, for example, an impact producing actuator and a touch panel using a shape memory alloy the shape of which varies by the passage of electric current therethrough.

There are conventionally known actuators using a shape memory alloy (hereinafter abbreviated as “SMA” as necessary), which expands and contracts depending on variations in temperature (refer to Patent Literature 1, for example).

Patent Literature

Patent Literature 1: Japanese Patent No. 4553725

Technical Problem

In the conventional actuators using the SMA, electric current passes through the SMA for a fixed period of time, in other words, the SMA is heated by a fixed amount of energy, and hence there is a possibility that the desired operation of the SMA cannot be obtained.

Thus, one of objects of the present invention is to provide a new and useful impact producing actuator and touch panel that can solve the above problem.

Solution to Problem

To solve the above problem, a first aspect of the present invention is, for example, an impact producing actuator including:

a drive signal generation unit for generating a drive signal based on a single pulse signal generated in response to an input operation, and outputting the drive signal;

a switching element whose switching operation is controlled by the drive signal; and

a shape memory alloy through which electric current passes for a period of time during which the switching element is turned on or off.

The impact producing actuator is configured such that the period of time during which the switching element is turned on or off varies depending on an ambient temperature.

A second aspect of the present invention is, for example, a touch panel including:

an input unit for receiving an input operation;

a signal generation unit for generating a single pulse signal in response to the input operation;

a drive signal generation unit for generating a drive signal based on the single pulse signal and outputting the drive signal;

a switching element whose switching operation is controlled by the drive signal; and

a shape memory alloy through which electric current passes for a period of time during which the switching element is turned on or off.

The touch panel is configured such that the period of time during which the switching element is turned on or off varies depending on an ambient temperature.

According to at least one of embodiments, energy (the amount of heat) to be applied to the SMA to heat the SMA by passing electric current through the SMA can be made variable.

FIG. 1 is a diagram showing an example of a configuration of a common actuator.

FIG. 2 is a graph for explaining the temperature characteristics of the common actuator.

FIG. 3 is a diagram for explaining an example of a measurement method for acceleration.

FIG. 4 is a diagram showing an example of a configuration of an actuator according to an embodiment of the present invention.

FIG. 5 is a diagram for explaining an example of a configuration of a drive signal generation unit.

FIG. 6 is a diagram for explaining an example of variation of a single pulse signal.

FIG. 7 is a graph for explaining an example of the relationship between a period of time during which the level of a drive signal is higher than a reference voltage and an ambient temperature.

FIG. 8A is a diagram for explaining an example of an effect according to the embodiment of the present invention.

FIG. 8B is a diagram for explaining an example of an effect according to the embodiment of the present invention.

FIG. 8C is a diagram for explaining an example of an effect according to the embodiment of the present invention.

FIG. 9 is a graph for explaining the example of the effect according to the embodiment of the present invention.

FIG. 10 is a diagram for explaining an example of the concrete configuration of the actuator according to the embodiment of the present invention.

FIG. 11A is a diagram for explaining an example of the concrete operation of the actuator according to the embodiment of the present invention.

FIG. 11B is a diagram for explaining an example of the concrete operation of the actuator according to the embodiment of the present invention.

FIG. 12 is a diagram for explaining a modification example.

FIG. 13 is a diagram for explaining a modification example.

FIG. 14 is a diagram for explaining a modification example.

FIG. 15 is a diagram for explaining a modification example.

FIG. 16 is a diagram for explaining a modification example.

FIG. 17 is a diagram for explaining a modification example.

An embodiment of the present invention will be described below with reference to the drawings. The description will be given in the following sequence:

1. Embodiment

2. Modification examples

The embodiment and the like described below are preferable concrete examples of the present invention, but do not limit the contents of the present invention. Moreover, the effects described below are just an example, and do not limit the contents of the present invention.

1. Embodiment

[Configuration of Common Actuator]

First, the configuration of a common actuator will be described for the purpose of ease of understanding of the present invention. It is noted that a configuration including an SMA, a drive circuit for switching the passage of electric current through the SMA, and the like is collectively called an actuator in the following description. FIG. 1 shows an example of the configuration of the common actuator (actuator 1 ). A voltage V 1 is supplied as a drive voltage to the actuator 1 . The voltage V 1 is applied to one end of a resistor R 1 , and the other end of the resistor R 1 is connected to an SMA 1 . One end of a capacitor C 1 is connected to a node between the resistor R 1 and the SMA 1 , while the other end of the capacitor C 1 is grounded.

A switching element is connected to the SMA 1 . The switching element is, for example, an N-channel type MOSFET (metal oxide field effect transistor). The drain (D) of the MOSFET 1 is connected to the SMA 1 , and the source (S) of the MOSFET 1 is grounded. To the gate (G) of the MOSFET 1 , a single pulse signal is inputted to control the switching operation of the MOSFET 1 . The MOSFET 1 is turned on when the single pulse signal is at a high level (for example, 5 V (volts) in terms of voltage), while the MOSFET 1 is turned off when the single pulse signal is at a low level (for example, 0 V in terms of voltage).

Turning on and off the MOSFET 1 is controlled to switch the passage of electric current through the SMA 1 . For example, for a period of time during of which the MOSFET 1 is turned on, the electric current passes through the SMA 1 by a discharge from the capacitor C 1 and thus the SMA 1 is heated. The heating by the passage of the electric current contracts the SMA 1 . For a period of time during of which the MOSFET 1 is turned off, the passage of the electric current through the SMA 1 is stopped to stop heating. Cooling with outside air expands the SMA 1 .

In the common actuator 1 shown in FIG. 1 , the period of time for the discharge from the capacitor C 1 , that is, a period of time during which the single pulse signal is at the high level is fixed, and hence energy to be applied to the SMA 1 is fixed. There is no problem if a temperature (hereinafter called ambient temperature as appropriate; the ambient temperature is also referred to as environmental temperature) around the SMA 1 is always kept constant, but the ambient temperature of the SMA 1 varies in general. Thus, provided that the duty ratio of the single pulse signal is set on the basis of a room temperature (for example, 25° C.), if the ambient temperature is lower than the room temperature, the time required to contract the SMA 1 may increase or the amount of contraction may decrease due to insufficient heating. On the other hand, if the ambient temperature is higher than the room temperature, the time required to contract the SMA 1 may decrease or excessive heating may occur.

FIG. 2 shows an example of the temperature characteristics of the common actuator. In FIG. 2 , a horizontal axis represents the ambient temperature, and a vertical axis represents acceleration (G). It is noted that the acceleration is expressed in an arbitrary unit based on, for example, an acceleration (being 100) at 25° C. A concrete method for measuring the acceleration will be described later. As shown in FIG. 2 , in the case of the common actuator, since the single pulse signal is at the high level for a fixed period of time, the acceleration tends to be smaller than a reference value at low temperatures, while the acceleration tends to be greater than the reference level at high temperatures. If the acceleration varies and the operation of the actuator varies depending on the ambient temperature as described above, the operation of equipment having the actuator also varies depending on the ambient temperature. Therefore, it is desirable that the acceleration be as constant as possible independent of the ambient temperature, or the difference between a maximum value and a minimum value of the acceleration be as small as possible. Considering the problem described above, the embodiment and the like according to the present invention will be hereinafter described in detail.

[Measurement Method for Acceleration]

First, an example of the measurement method for the acceleration in this description will be given with reference to FIG. 3 . Note that, the following measurement method for the acceleration considers equipment (for example, touch panel) to which the actuator is applied, but the measurement method for the acceleration is not limited to the method described below. The characteristics of the actuator may be defined by another parameter.

As shown in FIG. 3 , a brass plate 10 is put on a flat surface. The thickness of the brass plate 10 is set at, for example, 30 mm (millimeters). A rubber foot 11 is mounted on the top surface of the brass plate 10 . A PWB (printed wiring board) 12 is also mounted on the top surface of the brass plate 10 , and an actuator 13 is mounted on the PWB 12 . It is configured such that the thickness of the rubber foot 11 is the same as or similar to the sum of those of the PWB 12 and the actuator 13 , and the rubber foot 11 , the actuator 13 , etc. are configured to support end portions of a touch panel 14 . The thickness of the touch panel 14 is set at, for example, 0.7 mm.

A weight 15 is mounted on the touch panel 14 , and an acceleration sensor 16 is mounted on the weight 15 . The weight 15 is, for example, 100 g (grams). As the acceleration sensor 16 , a well-known sensor can be employed. The weight 15 and the acceleration sensor 16 are disposed such that the center lines of the actuator 13 , the weight 15 , and acceleration sensor 16 coincide or substantially coincide with each other. The acceleration is measured with such an acceleration measurement jig having the structure described above. More specifically, while varying the ambient temperature, an SMA in the actuator 13 is heated by passing electric current through the SMA. The acceleration sensor 16 measures the acceleration owing to the expansion and contraction of the SMA.

[Configuration of Actuator]

FIG. 4 shows an example of a configuration of an actuator (actuator 100 ) according to an embodiment of the present invention. The actuator 100 is applicable to, for example, a touch panel. Out of the configuration of the actuator 100 shown in FIG. 4 , part thereof enclosed with dashed lines 20 has the same configuration as the common actuator described above, and hence the repetitive description thereof will be omitted.

The actuator 100 has, for example, a signal generation unit 30 and a drive signal generation unit 40 in addition to the configuration enclosed by the dashed lines 20 . The signal generation unit 30 generates the single pulse signal in response to an operation signal, and outputs the generated single pulse signal to the drive signal generation unit 40 . The operation signal to be inputted to the signal generation unit 30 is, for example, a signal generated in response to a touch operation on the touch panel.

The drive signal generation unit 40 is composed of, for example, a differentiating circuit (high-pass filter) having a capacitor C 10 and a resistor R 10 (first resistor) the resistance of which varies depending on the ambient temperature. The resistor R 10 can be a thermistor with negative characteristic i.e. an NTC (negative temperature coefficient), the resistance of which decreases with increase in temperature.

FIG. 5 is a diagram that explains an example of the concrete configuration of the drive signal generation unit 40 . In FIG. 5 , the drive signal generation unit 40 is represented as a circuit having four terminals. The drive signal generation unit 40 has a pair of input terminals IN 1 and IN 2 and a pair of output terminals OUT 1 and OUT 2 . A common potential line is formed by applying a common potential (for example, ground potential) to the input terminal IN 2 and the output terminal OUT 2 . As shown in the drawing, the capacitor C 10 is connected between the input terminal IN 1 and the output terminal OUT 1 . An intermediate point between the capacitor C 10 and the output terminal OUT 1 is connected to the common potential line through the resistor R 10 .

The drive signal generation unit 40 generates a drive signal on the basis of the single pulse signal inputted from the signal generation unit 30 . Then, the drive signal generation unit 40 outputs the generated drive signal to the MOSFET 1 . The switching operation of the MOSFET 1 is controlled in accordance with the drive signal generated by and outputted from the drive signal generation unit 40 .

[Operation of Actuator]

Next, an example of the operation of the actuator 100 will be described. FIG. 6 is a diagram showing, as an input signal, an example of the single pulse signal generated by the signal generation unit 30 . Note that, a reference voltage Vref, which is indicated by a dashed line, represents a threshold value at which the MOSFET 1 is turned on. That is to say, the MOSFET 1 is turned on when a voltage higher than the reference voltage Vref is applied to the gate of the MOSFET 1 .

The single pulse signal is inputted to the drive signal generation unit 40 as the input signal. The drive signal is outputted from the drive signal generation unit 40 as an output signal. FIG. 6 schematically shows the waveform of the drive signal at temperatures (low temperatures) lower than the room temperature, and the waveform of the drive signal at temperatures (high temperatures) higher than the room temperature.

The resistor R 10 of the drive signal generation unit 40 has an increased resistance at the low temperatures. In other words, since a time constant τ represented by the product of the capacitance of the capacitor C 10 and the resistance of the resistor R 10 is increased, a falling edge of the drive signal becomes gentle. By making the falling edge of the drive signal gentle, a period of time Ams during which the level of the drive signal is higher than the reference voltage Vref can be made long. In other words, it is possible to elongate the period of time during which the MOSFET 1 is turned on, and the period of time during which the electric current is passed through the SMA 1 .

On the other hand, the resistor R 10 of the drive signal generation unit 40 has a decreased resistance at the high temperatures. In other words, since the time constant τ represented by the product of the capacitance of the capacitor C 10 and the resistance of the resistor R 10 decreases, the falling edge of the drive signal becomes sharp. By sharpening the falling edge of the drive signal, a period of time Bms during which the level of the drive signal is higher than the reference voltage Vref can be made short. In other words, it is possible to shorten the period of time during which the MOSFET 1 is turned on, and the period of time during which the electric current is passed through the SMA 1 . Therefore, it is possible to prevent lack of heating of the SMA 1 at the low temperatures and excessive heating of the SMA 1 at the high temperatures.

FIG. 7 is a diagram showing an example of the period of time during which the level of the drive signal is higher than the reference voltage Vref. In FIG. 7 , a vertical axis shows the period of time during which the level of the drive signal is higher than the reference voltage Vref (also the period of time during which the MOSFET 1 is turned on and the period of time during which the electric current is passed through the SMA 1 ), and a horizontal axis shows the ambient temperature. As shown in the drawing, the higher the ambient temperature, the shorter the period of time during which the level of the drive signal is higher than the reference voltage Vref can be made, and the shorter the period of time during which the electric current is passed through the SMA 1 can be made.

FIGS. 8A, 8B and 8C are diagrams showing an example of variations in the acceleration with time. FIG. 8A shows the example of the variations in the acceleration with time in a state that the ambient temperature is the room temperature (for example, 25° C.). FIG. 8B shows the example of the variations in the acceleration with time in a state that the ambient temperature is lower than the room temperature. FIG. 8C shows the example of the variations in the acceleration with time in a state that the ambient temperature is higher than the room temperature.

As described above, at the low temperatures, the period of time during which the electric current is passed through the SMA 1 can be made long, and therefore energy (the amount of heat) to be applied to the SMA 1 can be increased. Accordingly, as shown in FIG. 8B , the maximum value of the acceleration becomes higher than that in related case, to a level substantially equal to the maximum value of the acceleration at the room temperature. On the other hand, at the high temperatures, the period of time during which the electric current is passed through the SMA 1 can be made short, and therefore energy (the amount of heat) to be applied to the SMA 1 can be decreased. Thereby, as shown in FIG. 8C , the maximum value of the acceleration becomes lower than that in related case, to a level substantially equal to the maximum value of the acceleration at the room temperature.

FIG. 9 is a graph that explains an example of the effect according to the embodiment of the present invention. In FIG. 9 , a horizontal axis represents the ambient temperature, and a vertical axis represents the acceleration. In FIG. 9 , a line G 1 with rhombus symbols represents an example of the temperature characteristics of the common actuator, just as with FIG. 2 . A line G 2 with square symbols represents an example of the temperature characteristics of the actuator that is subjected to a correction process according to the embodiment of the present invention. As is apparent from the graph, in the actuator according to the embodiment of the present invention, the acceleration is substantially kept constant independent of increase or decrease in the ambient temperature, as compared with the common actuator. It is noted that in FIG. 9 , a decrease in the acceleration at 50° C. or higher is one of the characteristics of a Ti alloy, caused by the fact that the Ti alloy neither expand nor contract at a limit temperature or higher. This causes no practical problem if the actuator is not frequently used at 50° C. or higher.

[Concrete Form of Actuator]

Next, an example of the concrete form of the actuator will be described. Note that, the form of the actuator according to the present invention is not limited to a form described below. FIG. 10 shows the external appearance of the actuator 100 . The illustrated actuator 100 is in an initial state before a displacement occurs. The actuator 100 is formed on a top surface of a printed wiring board 22 .

The actuator 100 includes, for example, a movable member 25 , a fixed member 26 , two terminal fittings 27 , and the SMA 1 having the shape of, for example, a line. The movable member 25 and the fixed member 26 are both made of an insulating rigid material. The bottom surface of the movable member 25 and the top surface of the fixed member 26 are formed in the shape of waves fitted with each other, and the SMA 1 is disposed between the waveform surfaces. It is noted that the movable member 25 and the fixed member 26 may be made of a conductive metal material or the like. In this case, it is necessary to provide a structure to prevent shorts between the two terminal fittings 27 , such as insulating films provided on the respective surfaces of the movable member 25 and the fixed member 26 .

The SMA 1 is secured at both ends of the fixed member 26 by the terminal fittings 27 . The SMA 1 according to this embodiment is made of, for example, a nickel-titanium alloy as described above, and has a high conductivity, a relatively low resistance, and the shape of a flexible thread with an extremely narrow diameter in an environment around the room temperature. The passage of the electric current through the SMA 1 generates heat in the SMA 1 itself, and the heat hardens and contracts the SMA 1 itself. It is noted that the SMA 1 may be made of a metal or alloy, other than the nickel titanium alloy, as long as it has similar characteristics.

The terminal fittings 27 are fitted onto both the ends of the fixed member 26 together with the ends of the SMA 1 , so as to secure the ends of the SMA 1 with a strength sufficient to prevent the SMA 1 from being loose. The terminal fittings 27 are made of a conductive metal, and soldered to a land (not shown) in a predetermined shape provided on the printed wiring board 22 . Thus, the fixed member 26 is secured on the printed wiring board 22 .

The operation of the actuator 100 will be described with reference to FIGS. 11A and 11B . FIG. 11A shows a state in which there is no passage of the electric current through the SMA 1 , in other words, a state before the displacement occurs. In this state, the SMA 1 is soft and flexible. In this state, the movable member 25 and the fixed member 26 are in close proximity to each other with catching the SMA 1 therebetween by, for example, an attractive force of a not-shown magnet.

FIG. 11B shows a state in which there is the passage of the electric current through the SMA 1 , in other words, a state after the displacement of the actuator 100 occurs. In this state, the SMA 1 contracts, and in conjunction with this, the movable member 25 is vertically displaced in a direction away from the fixed member 26 against the attractive force of the magnet. If a cover member (not illustrated in the drawing) is put on the movable member 25 , the cover member is displaced together in the same direction.

When the passage of the electric current through the SMA 1 is stopped from the state shown in FIG. 11B , the SMA 1 is cooled by a temperature difference from the atmosphere and heat dissipation to the movable member 25 , the fixed member 26 , and the terminal fittings 27 . The SMA 1 thus returns to the same length as in the state in which there is no passage of the electric current therethrough, and quickly returns to the state shown in FIG. 11A by the action of the attractive force by the magnet.

For example, the actuator 100 is applied to the touch panel, and an input surface on which the touch operation is performed is formed on the movable member 25 . When the touch operation is detected, the single pulse signal is generated, and the input surface is displaced once in one direction from the state of FIG. 11A to the state of FIG. 11B in response to the drive signal based on the single pulse signal. Therefore, an impact (a click feeling) can be transmitted to a user of the touch panel in response to the touch operation, allowing the user to be sure that the input operation is performed.

Applying the actuator according to the present invention to the touch panel can prevent a change in the feeling (click feeling) of the user due to a change of the ambient temperature, for example. Also, it is possible to prevent that when the ambient temperature is high, an increase in the acceleration generates an excessive load in the SMA and breaks the configurations of the SMA and the vicinity thereof.

2. Modification Examples

The embodiment of the present invention has been concretely described above. The present invention is not limited to the above embodiment, but can be variously modified. A plurality of modification examples will be described below. The matters described in the embodiment can be applicable to the modification examples, except where specifically noted.

[Modification Example 1]

FIG. 12 is a diagram for explaining a modification example 1. FIG. 12 shows only the configuration of the drive signal generation unit, and the configuration of the other parts is omitted as appropriate. A drive signal generation unit 50 includes a resistor R 20 (second resistor) connected to the resistor R 10 in series, in addition to the configuration of the drive signal generation unit 40 . That is, the intermediate point between the capacitor C 10 and the output terminal OUT 1 is connected to the common potential line through the resistor R 10 and the resistor R 20 .

In the configuration having only the resistor R 10 , a pulse width (here, the period of time during which the level of the drive signal is higher than the reference voltage Vref) is adjusted using only the resistance of the resistor R 10 (for example, thermistor). Thus, it sometimes becomes difficult to generate the drive signal having the pulse width that is suitable for correcting the temperature characteristics of the actuator. Accordingly, the resistance R 20 is added as shown in FIG. 12 . When the resistance R 20 is added, the time constant τ of the drive signal generation unit 50 is represented by the product of the capacitance of the capacitor C 10 and the sum (combined resistance) of the resistances of the resistors R 10 and R 20 . Appropriately setting the resistance of the resistor R 20 varies the time constant τ, and thereby varies the degree of sharpness or gentleness of the falling edge of the drive signal. For example, the addition of the resistor R 20 increases the time constant τ and makes the falling edge of the drive signal gentle. In other words, it is possible to set the pulse width of the drive signal in an appropriate manner without depending only on the characteristics of the resistor R 10 .

[Modification Example 2]

FIG. 13 is a diagram for explaining a modification example 2. FIG. 13 shows only the configuration of the drive signal generation unit, and the configuration of the other parts is omitted as appropriate. A drive signal generation unit 51 includes a resistor R 30 (third resistor) connected in parallel with the resistors R 10 and R 20 , in addition to the configuration of the drive signal generation unit 50 . That is, the intermediate point between the capacitor C 10 and the output terminal OUT 1 is connected to the common potential line through the resistor R 30 , as well as through the resistors R 10 and R 20 .

According to the configuration of the drive signal generation unit 51 , just as with the drive signal generation unit 50 , it is possible to vary the time constant τ and thereby vary the degree of sharpness or gentleness of the falling edge of the drive signal. In other words, it is possible to set the pulse width of the drive signal in an appropriate manner without depending only on the characteristics of the resistor R 10 . Note that, the resistor R 30 is added to the configuration of the drive signal generation unit 50 in FIG. 13 , but the resistor R 30 may be added to the configuration of the drive signal generation unit 40 .

[Modification Example 3]

FIG. 14 is a diagram for explaining a modification example 3. FIG. 14 shows only the configuration of the drive signal generation unit, and the configuration of the other parts is omitted as appropriate. A drive signal generation unit 52 includes a diode D 10 , in addition to the configuration of the drive signal generation unit 40 . For example, an anode of the diode D 10 is connected to the capacitor C 10 , and a cathode of the diode D 10 is connected to the output terminal OUT 1 . The drive signal generation unit 52 may cut a negative waveform using the rectification (half-wave rectification) function of the diode D 10 , as well as changes the waveform of the single pulse signal. As shown in FIG. 15 , a diode D 20 may be added to the configuration of the drive signal generation unit 51 .

[Modification Example 4]

FIG. 16 is a diagram for explaining a modification example 4. An actuator (actuator 110 ) according to the modification example 4 has a microcomputer 60 . In the actuator 110 , the drive signal generation unit 40 has a variable resistor that is independent of temperature and has a resistance controllable by an electric signal from the outside, that is, a so-called digital potentiometer R 40 , instead of the resistor R 10 . The digital potentiometer R 40 is connected to the microcomputer 60 , so that the resistance of the digital potentiometer R 40 is arbitrarily settable by outputting a necessary signal from the microcomputer 60 .

The microcomputer 60 obtains temperature information indicating the ambient temperature. For example, the microcomputer 60 has a temperature sensor (not illustrated in the drawing), and the temperature information obtained by the temperature sensor is inputted to the microcomputer 60 . The temperature information may be inputted to the microcomputer 60 through a network such as the Internet or a LAN (local area network).

The microcomputer 60 has a storage device, such as ROM (read only memory) or RAM (random access memory), to store therein a table that provides the correspondences between the ambient temperature and the resistance of the digital potentiometer R 40 . The microcomputer 60 reads out of the table the resistance that corresponds to the ambient temperature indicated by the temperature information, and sets the resistance read out of the table as the resistance of the digital potentiometer R 40 . An element having a variable resistance, as described above, is not limited to the thermistor.

[Modification Example 5]

FIG. 17 is a diagram for explaining a modification example 5. An actuator (actuator 120 ) according to the modification example 5 has a microcomputer 70 . The microcomputer 70 generates the drive signal (single pulse signal) for controlling the switching operation of the MOSFET 1 , and outputs the drive signal to the gate of the MOSFET 1 . Temperature information indicating the ambient temperature is inputted to the microcomputer 70 .

The microcomputer 70 has a storage device such as ROM or RAM, to store therein a table that provides the correspondences between the ambient temperature and the duty ratio. The microcomputer 70 reads out of the table the duty ratio that corresponds to the ambient temperature indicated by the temperature information, and generates the single pulse signal having the read duty ratio. The single pulse signal generated by the microcomputer 70 is supplied to the MOSFET 1 as the drive signal, and the switching operation of the MOSFET 1 is controlled thereby. As described above, the microcomputer may be provided instead of the differentiating circuit, and the microcomputer may generate and output the single pulse signal the pulse width of which is controlled in an appropriate manner.

[Other Modification Examples]

The present invention can be variously modified, other than the modification examples described above. For example, the switching element is not limited to the N-channel type MOSFET, but a P-channel type MOSFET or a transistor may be used. Also, the configuration of a peripheral circuit may be modified as appropriate, such as that a portion to which the switching element is connected may be modified in accordance with the characteristics of the switching element.

In the embodiment described above, the electric current passes through the SMA for a period of time during which the switching element is turned on. However, the electric current may pass through the SMA for a period of time during which the switching element is turned off. The SMA is connected to a drive voltage source through the resistor and the capacitor in the above embodiment, but may be connected directly (capacitor-less) to the drive voltage source.

A plurality of capacitors may be mounted, and the amount of heat to be applied to the SMA may be varied by changing the number of the capacitors to be connected to the actuator (SMA) in accordance with the ambient temperature. A thermistor may be connected between the drive voltage source and the SMA. Also in this configuration, the electric current passing through the SMA can be controlled in accordance with the ambient temperature, resulting in stabilization in the acceleration of the actuator.

The configurations, methods, processes, forms, materials, values, and the like described in the above embodiment and modification examples are just examples, and configurations, methods, processes, forms, materials, values, and the like different from the above may be used as necessary. The configurations, methods, processes, forms, materials, values, and the like described in the above embodiment and modification examples may be combined with each other as long as no technical contradiction occurs.

Furthermore, the present invention can be embodied as, for example, a method, a program, or a recording medium having the program recorded therein, in addition to equipment.

30 . . . signal generation unit

40 . . . drive signal generation unit

100 . . . actuator

MSFET 1 . . . N-channel type MOSFET

SMA 1 . . . shape memory alloy