Optical pickup device and optical disk device

1. Field of the Invention

The present invention relates to an optical pickup device used for recording and reproducing information on a high density recording disk such as a DVD and information on a low density recording disk such as a compact disk and the like. More particularly, the present invention relates to an optical pickup device in which a tilt caused by a lens shift is self-canceled so that a radial tilt can be conducted. The present invention also relates to an optical disk device on which the optical pickup device is mounted.

2. Description of the Related Art

In the case of a conventional optical pickup device, it has been known that an objective lens is inclined, which is referred to as a tilt hereinafter, due to the structure of a magnetic circuit when a focusing motion and a tracking motion are simultaneously conducted which is referred to as a lens shift hereinafter. In order to prevent the occurrence of the above problems, there is proposed an optical pickup device in which the structure of the magnetic circuit is devised so that no tilt is caused even when the lens is shifted. For example, refer to JP-A-10-031829 (pages 3 to 4, FIGS. 4, 5 and 6).

Since the high density recording disk such as a DVD has widely spread, there is a demand for an optical disk device by which information on the high density recording disk can be reproduced and recorded in the same manner as that of the conventional optical disk device for recording and reproducing information on the low density recording disk.

However, in the case of the high density recording disk, the recording density is so high that the tolerance (tilt margin) with respect to an inclination angle of the objective lens is far narrow. Therefore, it is demanded to the optical disk device that reproducing and recording can be conducted even when the optical disk is warped.

It is an object of the present invention to provide an optical pickup device capable of self-canceling a tilt caused by a lens shift and generating a twisting tilt in the radial direction, by adding a controlled tilt as an optical pickup device in which the tilt can be self-canceled.

The present invention provides an optical pickup device comprising: a movable portion having an objective lens, a lens holder for holding the objective lens and a drive means for driving the lens holder; and a fixing portion having an elastic member for elastically supporting the movable portion, a suspension holder for supporting and fixing one end of the elastic member and a yoke for supporting the suspension holder and composing a portion of a magnetic circuit of the drive means, wherein the yoke composes a first and a second vertical portion for forming the magnetic circuit, the first vertical portion disposes a first and a second magnet, the second vertical portion branches to two vertical yokes in which a third and a fourth magnet are respectively arranged, the first to the fourth magnet are arranged so that a magnetic flux connecting the first magnet with the third magnet, which are opposed to each other, and a magnetic flux connecting the second magnet with the fourth magnet, which are opposed to each other, can be opposite to each other, the driving means has a focus coil for conducting a focusing motion and a tracking coil for conducting a tracking motion, the focus coil has a first and a second focus coil which are respectively wound round the two vertical yokes, and the tracking coil has a first tracking coil wound round the first and the second magnet, a second tracking coil, the winding side of 1 of which is arranged in the first magnet, and a third tracking coil, the winding side of 1 of which is arranged in the second magnet.

FIG. 1 is a perspective view of an optical disk device on which an optical pickup device of an embodiment of the present invention is mounted.

FIG. 2 is a perspective view of an optical pickup device of an embodiment of the present invention.

FIG. 3 is an exploded perspective view of FIG. 2 .

FIG. 4 is a view for explaining a magnetic circuit portion of FIG. 2 .

FIG. 5 is a view for explaining a motion of the magnetic circuit portion of FIG. 2 .

FIG. 1 is a perspective view of an optical disk device on which an optical pickup device of an embodiment of the present invention is mounted.

In FIG. 1 , reference numeral 21 is a housing. The housing 21 is composed of an upper housing portion and a lower housing portion 21 a which are combined with each other. In FIG. 1 , the upper housing portion is omitted because of the convenience of explanations. In this connection, the upper housing portion and the lower housing portion 21 a are fixed to each other with screws or the like. Reference numeral 22 is a retractable tray, reference numeral 23 is a spindle motor provided on the tray 22 , and reference numeral 24 is an optical pickup device of an embodiment of the present invention. At least a light source not shown and each optical component are mounted on the optical pickup device 24 . When the optical pickup device 24 irradiates light to the optical disk, at least one of the information writing motion and the information reading motion is conducted on the optical disk. Reference numeral 25 is a bezel arranged on the front end face of the tray 22 . When the tray 22 is accommodated into the housing 21 , the bezel 25 closes an opening for retraction of the tray 22 . Reference numerals 26 and 27 are rails slidably attached to both the tray 22 and the housing 21 . These rails 26 and 27 are arranged on both side portions of the tray 22 . By these rails 26 and 27 , the tray 22 is attached to the housing 21 so that the tray 22 can be freely retracted from the housing 21 . Reference numeral 28 is a circuit board fixed at an inner portion of the housing 21 . On the circuit board 28 , IC of the signal processing system and the electric power supply circuit are mounted. Reference numeral 29 is a flexible printed board for electrically connecting a circuit board not shown provided on the tray 22 with the circuit board 28 . This printed board 29 is formed into a substantial U-shape. Reference numeral 30 is an external connector, which is connected with an electric power supply/signal line provided in an electronic apparatus such as a computer. Electric power is supplied to the optical disk device via this external connector 30 . Further, an electric signal sent from the outside is guided into the optical disk device via this external connector 30 . Furthermore, electric signals generated in the optical disk device are sent out to the electronic apparatus via this external connector 30 .

The bezel 25 arranged on the front end face of the tray 22 is provided with an eject button 31 . When this eject button 31 is pressed, an engaging portion (not shown) arranged in the housing 21 and an engaging portion (not shown) arranged on the tray 22 are released from each other.

Reference numeral 32 is a push sheet metal movably held on the tray 22 . The push sheet metal 32 is pushed in the direction of arrow R shown in FIG. 1 by an elastic means such as a spring not shown.

When the tray 22 is manually inserted into the housing 21 , the forward end portion 32 a of the push sheet metal 32 comes into contact with the inner portion 21 c of the housing 21 . When the tray 22 is further inserted into the housing 21 , the push sheet metal 32 is pushed to the tray 22 side. When the tray 22 is furthermore inserted into the housing 21 by a predetermined distance, while resisting an elastic force of an elastic means arranged on the push sheet metal 32 , the aforementioned engaging portions are engaged with each other, so that the tray 22 can be accommodated in the housing 21 and the tray 22 can not jump out from the housing 21 by an external force because the tray 22 is held in the housing 21 .

Next, when the eject button 31 is pressed down and the above engaging portions are released from each other, the push sheet metal 32 pushes the inner portion 21 c and the tray 22 is protruded from the housing 21 by a distance not less than a predetermined value. After that, the tray 22 is manually drawn out and the optical disk or the like is attached to the spindle motor.

When the optical pickup device 24 of the present invention, which will be explained below, is mounted on a thin type optical disk device, it is possible to obtain a sufficiently high recording or reproducing characteristic even if the device is made thin.

Referring to FIG. 2 , the optical pickup device 24 of an embodiment of the present invention will be explained in detail as follows.

In FIG. 2 , reference numeral 1 is an objective lens. Light emergent from a light source not shown is incident on this objective lens 1 via optical parts not shown in the drawing, and the objective lens 1 stops down the incident light, so that the light can be condensed upon an optical disk not shown and information can be recorded on the disk. Reflected light of the light condensed upon the optical disk is incident on the objective lens 1 and then the light is incident on a light receiving element via optical components not shown. The light incident on the light receiving element is converted into an electric signal. The thus obtained electric signal is used for acquiring data and servo control. In this connection, in this embodiment, the objective lens 1 is used as a light condensing means. However, as long as it is possible to condense light to the optical disk, any optical component can be used. (For example, a hologram light condensing member or a diffraction grating condensing member.)

Reference numeral 2 is a lens holder for attaching the objective lens 1 . In a portion of the lens holder 2 to which the objective lens 1 is attached, the through-hole 2 a (circular or elliptical through-hole) is formed. The objective lens 1 is attached to the through-hole 2 a with adhesive in such a manner that this through-hole 2 a is closed by the objective lens 1 . Except for the through-hole 2 a to which the objective lens 1 is attached, the square through-hole 2 b , the corners of which are round, are provided. On the side of the through-hole 2 b on which the objective lens 1 of the lens holder 2 is arranged, the protruding portion 2 c , which extends to the center side of the through-hole 2 b , is provided being formed into a substantial C-shape so that the diameter of the through-hole 2 b can be smaller than that of the other portion. At the end portion of this protruding portion 2 c , a pair of cutout portions 2 d , 2 e are provided so that a portion of the protruding portion 2 c can be cut out.

In this connection, it is preferable that the lens holder 2 is made of insulating resin material. When the lens holder 2 is made of resin material, it becomes easy to manufacture the lens holder 2 , and further the weight can be reduced. Epoxy resin, liquid crystal polymer and the like are preferably used as the resin material. In the case of the very thin optical pickup device of the present invention, when the lens holder 2 is made of resin material, the thickness of the lens holder is reduced and the mechanical strength is lowered, however, when the protruding portion 2 c is provided as described above, it is possible to provide a somewhat high mechanical strength.

Reference numeral 3 is a suspension wire. Three suspension wires are respectively arranged on both side portions of the lens holder 2 . One end portion of each suspension wire 3 is embedded in the lens holder. Further, the end portions 3 a to 3 f of the suspension wires 3 protrude out again from the suspension holder 2 . In this connection, in this embodiment, three suspension wires 3 are respectively arranged on both sides, however, the number of the suspension wires may be not less than four and not more than six. Alternatively, the number of the suspension wires may be two. When the number of the suspension wires is not less than six on one side, it becomes difficult to reduce the thickness. In this connection, the suspension wires 3 are made of elastic conductive material. For example, the suspension wires 3 are composed of linear bodies or flat-plate-shaped bodies made of iron alloy or copper alloy (for example, copper-beryllium alloy).

The suspension wires 3 provided on one side of the lens holder 2 are arranged in the thickness direction of the lens holder at relatively regular intervals. However, according to the specification, the intervals of arranging the suspension wires 3 may not be regular.

Reference numeral 4 is a suspension holder. In the suspension holder 4 , the other end portion of each suspension wire 3 is embedded. That is, the suspension holder 4 elastically supports the lens holder 2 via the suspension wires 3 by the cantilever method so that the lens holder 2 can be displaced. A circuit board not shown such as a flexible printed board is attached to the suspension holder 4 or a circuit board not shown such as a flexible printed board is arranged close to the suspension holder 4 . This circuit board and the suspension wires 3 are electrically connected with each other. The through-hole 4 a is formed in the suspension holder 4 .

The suspension holder 4 is made of insulating material. It is preferable that the suspension holder 4 is made of resin, ceramics or the like. Especially, in the case where the suspension holder 4 is made of resin material, it is advantageous to use liquid crystal polymer or epoxy resin from the viewpoints of mechanical strength, weight and easiness of machining.

Reference numeral 5 is a yoke on which the suspension holder 4 is mounted. The yoke 5 is made of magnetic material such as Fe alloy. In this embodiment, the yoke 5 was formed by bending a metal plate made of Fe alloy. A Ni film or Ni alloy film is provided on the surface of the yoke 5 . The yoke 5 includes: side vertical portions 5 a , 5 b , vertical yoke portions 5 c , 5 d , 5 e , a front end vertical portion 5 f and a rear end vertical portion 5 g which are bent to the same side. The vertical yoke portion 5 c and the vertical yoke portions 5 d , 5 e are arranged being opposed to each other. On the surface of the vertical yoke portion 5 c on the vertical yoke portion 5 d , 5 e side, there are provided a pair of magnets 9 a , 9 b . On the surfaces of the vertical yoke portions 5 d , 5 e on the vertical yoke 5 c side, there are provided a pair of magnets 10 a , 10 b . In this case, each vertical yoke portion and each magnet are bonded to each other by ultraviolet-ray-setting adhesive or thermo-setting resin. As an example of the method of attaching each magnet to each vertical yoke portion, since each vertical yoke portion is made of magnetic material, each magnet is attracted to each vertical yoke portion by a magnetic force. Under this condition, ultraviolet-ray-setting adhesive is coated and irradiated with ultraviolet rays so as to fix each magnet to each vertical yoke portion. In this connection, it is preferable that the magnets of the substantially same size and same characteristic are used. That is, when the magnets of the substantially same size and same characteristic are used, it is sufficient to prepare the magnets of one type. Therefore, it is unnecessary to select the magnet in the case of attaching it to each vertical yoke portion. When parts are commonly used as described above, it is possible to enhance the productivity. According to the specification, magnets of different sizes and characteristics can be used. In this embodiment, the two magnets 9 a , 9 b are attached to the vertical yoke portion 5 c , however, one magnet, the width of which is large, may be used, and the direction of the magnetic force may be changed on both sides. Each magnet is composed of a permanent magnet containing Nd and Fe. On the surface of each magnet, there is provided a coat of plating of Ni or Ni alloy, the thickness of which is 10 to 20 μm. In the corner of each magnet, there is provided a chamfered portion or a tapered portion so that each corner can not be damaged.

Reference numerals 6 a , 6 b are focus coils. Each focus coil 6 a , 6 b is composed in such a manner that a conductive electric wire made of copper or copper alloy is wound into a square shape, the corners of which are formed round. Further, an insulating coat is provided on the surface of the conductive electric wire. Therefore, even if the conductive electric wire is wound, the conductive electric wires, which are adjacent to each other, are not electrically communicated with each other. Side portions of the focus coils 6 a , 6 b are bonded to each other by at least one of the thermo-setting adhesive or the ultraviolet-ray-setting resin so that the winding axes of the focus coils 6 a , 6 b can become substantially parallel to each other.

Reference numerals 7 , 8 a , 8 b are tracking coils. On both sides of the tracking coil 7 , the tracking coils 8 a , 8 b are closely arranged. Alternatively, on both sides of the tracking coil 7 , the tracking coils 8 a , 8 b are arranged leaving a gap. At this time, the winding axes of the tracking coils 7 , 8 a , 8 b are arranged so that they can be substantially parallel to each other. The tracking coils 7 , 8 a , 8 b are bonded to the side portion of an assembled body, in which the focus coils 6 a , 6 b are joined to each other, by at least one of thermo-setting adhesive and the ultraviolet-ray-setting resin in such a manner that the winding axes of the tracking coils 7 , 8 a , 8 b and the winding axes of the focus coils 6 a , 6 b are not parallel to each other, preferably in such a manner that the winding axes of the tracking coils 7 , 8 a , 8 b and the winding axes of the focus coils 6 a , 6 b are perpendicular to each other. The tracking coils 7 , 8 a , 8 b are electrically joined to each other, that is, the tracking coils 7 , 8 a , 8 b are composed of the same electric wire and integrated into one body. In this case, the tracking coils 7 , 8 a , 8 b are connected in series to each other. Each tracking coil 7 , 8 a , 8 b is composed in such a manner that a conductive electric wire made of copper or copper alloy is wound into a square shape, the corners of which are formed round. Further, an insulating coat is provided on the surface of the conductive electric wire. Therefore, even if the conductive electric wire is wound, the conductive electric wires, which are adjacent to each other, are not electrically communicated with each other.

Each focus coil 6 a , 6 b is wound into a shape, the cross section of which is square, and each tracking coil 7 , 8 a , 8 b is wound into a shape, the cross section of which is rectangular. The tracking coils 8 a , 8 b are respectively attached to the focus coils 6 a , 6 b so that the long sides of the tracking coils 8 a , 8 b can be substantially parallel with the winding axes of the focus coils 6 a , 6 b . The tracking coil 7 is attached to the focus coils 6 a , 6 b so that the long side of the tracking coil 7 can be substantially perpendicular to the winding axes of the focus coils 6 a , 6 b.

A coil composition body in which the focus coils 6 a , 6 b and the tracking coils 7 , 8 a , 8 b are combined with each other is attached to the lens holder 2 . At this time, the coil composition body is inserted from the side opposite to the side on which the protruding portion 2 c of the through-hole 2 b is provided. Outer circumferential portions of the focus coils 6 a , 6 b of the coil composition body, which has been inserted, come into contact with this protruding portion 2 c and are held in the through-hole 2 b of the lens holder 2 . At this time, the outer circumferential portions of the tracking coils 8 a , 8 b enters the cutout portions 2 e , 2 d , and the upper faces of the tracking coils 8 a , 8 b protrude out from the protruding portion 2 c . The coil composition body is fixed to the lens holder 2 with thermo-setting adhesive such as thermo-setting epoxy resin.

After the coil composition body has been fixed to the lens holder 2 , the suspension holder 4 is fixed to the yoke 5 with at least one of the thermo-setting adhesive and the ultraviolet ray-setting resin. At this time, the rear end vertical portion 5 g is inserted into the through-hole 4 a of the suspension holder 4 , and the vertical yoke portions 5 c , 5 d , 5 e and the magnets 9 a , 9 b , 10 a , 10 b are inserted into the through-hole 2 b of the lens holder 2 . The vertical yoke portion 5 d and the magnet 10 a are inserted into the focus coil 6 a , and the vertical yoke portion 5 e and the magnet 10 b are inserted into the focus coil 6 b . Between the vertical yoke portion 5 c and the vertical yoke portions 5 d , 5 e , the focus coils 6 a , 6 b , to which the tracking coils 7 , 8 a , 8 b are attached, are arranged.

Although not shown in the drawing, both end portions of the focus coil 6 a are respectively wound round the end portions 3 f , 3 e of the suspension wire 3 and joined with solder or the like. Both end portions of the focus coil 6 b are respectively wound round the end portions 3 c , 3 b of the suspension wire 3 and joined with solder or the like. Both end portions of the tracking coils 7 , 8 a , 8 b are respectively wound round the end portions 3 a , 3 d and joined with solder or the like. In this connection, in this embodiment, the focus coils 6 a , 6 b are separately composed. However, when the focus coils 6 a , 6 b are connected in series to each other in the same manner as the tracking coils 7 , 8 a , 8 b , the end portion of the focus coil 6 a is connected to the end portion 3 f , and the end portion of the focus coil 6 b is connected to the end portion 3 c . At this time, the end portions 3 b , 3 e are not electrically connected to the coils.

Accordingly, at least one of the information recording and the information reproducing can be positively conducted as follows. When an electric current is selectively made to flow in each suspension wire 3 , the electric current is made to flow in each coil. In the magnetic circuit composed of the magnetic field generated by each coil and the magnetic field generated by the magnets 9 a , 9 b , 10 a , 10 b , the lens holder 2 is moved in the direction having at least one of the focusing direction component and the tracking direction component. For example, according to a servo signal generated by the reflected light on an optical disk, the objective lens 1 is moved in the focusing direction or the tracking direction, so that the light is condensed to a data track formed on the optical disk. In this way, at least one of the information recording and the information reproducing can be positively conducted.

In FIG. 4 , FIG. 4( a ) is a plan view showing a primary portion of the magnetic circuit portion of FIG. 2 , FIG. 4( b ) is a side view of FIG. 4( a ), and FIG. 4( c ) is a view taken on line A—A in FIG. 4( a ). As shown in FIG. 4( a ), the direction of the magnetic field of the magnets 9 a , 10 a opposed to each other is shown by arrow Ja, and the direction of the magnetic field of the magnets 9 b , 10 b opposed to each other is shown by arrow Jb. As shown by arrows Ja and Jb, the magnetic fluxes proceed in the opposite direction to each other. That is, on the surfaces of the magnets 9 a , 9 b , N-pole and S-pole are respectively formed. On the surfaces of the magnets 10 a , 10 b , S-pole and N-pole are respectively formed.

As shown in FIG. 4( c ), gap P 1 between the focus coils 7 and 8 a and gap P 2 between the focus coils 7 and 8 b are respectively set in the range from 0 to 1.5 mm. Gaps P 1 and P 2 may be different from each other in this range. Alternatively, gaps P 1 and P 2 may be the same with each other in this range. In the case of P 1 , P 2 =0, the side portions of the focus coils 7 , 8 a , 8 b are closely contacted with each other. In this case, it is difficult for the tracking coils 8 a , 8 b to be disconnected from the magnetic field composed by the magnets. When gaps P 1 and P 2 are larger than 0 mm, a gap is substantially generated between the tracking coils 7 , 8 a , 8 b . Therefore, when the coil composition body is composed, it is possible to pour adhesive into this gap. Accordingly, it is possible to obtain a strong coil composition body.

In FIG. 4( c ), heights P 3 of the tracking coils 7 , 8 a , 8 b are the same. However, according to the specification, only height P 3 of the tracking coil 7 may be made to be larger than that of the other coils. Alternatively, the height of at least one of the tracking coils 8 a , 8 b is made to be larger than that of the other coils. Further, the winding numbers of the tracking coils 8 a , 8 b may be the same. Furthermore, the winding numbers of the tracking coils 8 a , 8 b may be in the range of ±25%. For example, in the case where the winding number of the tracking coil 8 a is 20, the winding number of the tracking coil 8 b is determined in the range from 15 to 25. Furthermore, the winding number of the tracking coil 7 may be at least not less than one. In this embodiment, the winding numbers of the tracking coils 8 a and 8 b were respectively set at 18, and the winding number of the tracking coil 7 was set at 32.

Further, as shown in FIG. 4( b ), it is composed that heights P 3 of the tracking coils 7 , 8 a , 8 b are larger than the height of the focus coils 6 a , 6 b . Furthermore, in the upper and the lower portion, the tracking coils 7 , 8 a , 8 b are respectively protruded by the heights of P 4 and P 5 . The reason is that the heights of the tracking coils 7 , 8 a , 8 b are increased as large as possible so as to increase the driving force. The reason why gap P 4 in the upper portion is larger than gap P 5 is that the protruding portion 2 c of the lens holder 2 enters this gap P 4 . That is, when the thickness of the protruding portion 2 c is increased, even if the pickup is made thin, the rigidity of the lens holder 2 can be enhanced. Although it is possible to make gap P 5 larger than gap P 4 , when gap P 5 is made larger than P 4 , the yoke 5 comes into contact with the tracking coils 7 , 8 a , 8 b . Therefore, it is not preferable.

In FIG. 5 , FIG. 5( a ) is a view taken on line A—A in FIG. 4( a ). FIG. 5( a ) shows a state in which the tracking coil 7 and the tracking coils 8 a , 8 b are located at the neutral positions. FIG. 5( b ) shows a state in which focus shifting is conducted in FIG. 5( a ). FIG. 5( c ) shows a state in which tracking shift is further conducted in FIG. 5( b ).

The focus coils 6 a , 6 b and the tracking coils 7 , 8 a , 8 b are arranged so that they are incorporated into the magnetic circuit composed of the magnets 9 a , 9 b , 10 a , 10 b . When an electric current is made to flow in the focus coils 6 a , 6 b and the tracking coils 7 , 8 a , Bb, according to the Fleming's left-hand rule, it is possible to drive the lens holder 2 in the focusing direction and the tracking direction.

In this case, when the two focus coils 6 a , 6 b are wired in series to each other, only a motion in the focusing direction is conducted. When the two focus coils 6 a , 6 b are wired in parallel to each other, that is, when an electric current is independently supplied to the two focus coils 6 a , 6 b , an independent motion in the focusing direction can be conducted. Since a difference can be made between the driving forces in the focusing direction, it is possible to generate a twisting tilt in the radial direction.

In this connection, since the behavior of the lens holder 2 can be shown by the focusing coils 6 a , 6 b and the tracking coils 7 , 8 a , 8 b , the objective lens 1 and the lens holder 2 are omitted in FIGS. 4 and 5 . As shown in FIG. 4( c ), the upper and lower horizontal portions of the tracking coils 7 , 8 a , 8 b overlap the end portions of the upper and lower horizontal portions of the magnets 9 a , 9 b , 10 a , 10 b.

Operation of the optical pickup device of the present invention composed as described above will be explained below. As shown in FIG. 4( a ), the magnetic poles of the magnets 9 a , 9 b , 10 a , 10 b are arranged in the yoke 5 , and the magnetic field proceeds in the directions of arrows Ja and Jb. At this time, for example, when the focusing coils 6 a , 6 b are electrified as shown by arrow If in FIG. 4( a ), the focus coils 6 a , 6 b are given a force of arrow Ff in FIG. 5( a ) by the Fleming's left-hand rule. Therefore, the lens holder 2 is moved upward in the drawing as shown in FIG. 5( b ).

In the same manner, for example, as shown by arrow It in FIG. 5( b ), when the tracking coils 7 , 8 a , 8 b are energized, according to the Fleming's left-hand rule, the tracking coils 7 , 8 a , 8 b are given a force of arrow Ft, and the lens holder 2 is moved to the left in the drawing as shown in FIG. 5( c ). As a result of energizing the tracking coils 7 , 8 a , 8 b , the lens holder 2 is given a composite force in which forces Ff and Ft are compounded with each other. Therefore, the lens holder 2 is moved to the position shown in FIG. 5( c ).

As a result, in the same manner as that of the conventional device, under the condition that the coil composition body, which is composed of the focus coils 6 a , 6 b and the tracking coils 7 , 8 a , 8 b , is offset to the left in FIG. 5( c ), force Ff in the focusing direction is given. Therefore, as shown by the arrow in the drawing, the lens holder 2 is given a counterclockwise angular moment (Mccw)Mf.

On the other hand, portions of the tracking coils 7 , 8 a , 8 b , in which electric current It flows so that the portions are related to the magnets 9 a , 9 b , 10 a , 10 b , are horizontal portions shown by the net pattern in the drawing. Therefore, as shown by arrow Mta in the drawing, by the net pattern horizontal portion overlapping the tracking coil 7 , the lens holder 2 is given a counterclockwise angular moment (Mccw). By the net pattern horizontal portions overlapping the tracking coils 8 a , 8 b , as shown by arrow Mtb in the drawing, the lens holder 2 is given a clockwise angular moment (Mcw).

In this way, angular moment Mf, Mta and Mtb are generated in the lens holder 2 . The positional relations between the tracking coils 7 , 8 a , 8 b and the magnets 9 a , 9 b , 10 a , 10 b are set so that the angular moment can satisfy the following equation.

Mf+Mta=Mtb

Due to the foregoing, while the lens holder 2 is maintaining its original posture, the lens holder 2 moves in the focusing and the tracking direction so that no inclination is caused.

In this connection, in the example of operation explained above, when either the directions of electric currents flowing in the focus coils 6 a , 6 b and the tracking coils 7 , 8 a , 8 b or the directions of the magnetic fields of the magnets 9 a , 9 b , 10 a , 10 b are opposite, the moving direction of the lens holder 2 shown in FIG. 5( c ) becomes opposite. However, even in this case, the same effect can be provided by the same operation principle. Therefore, the redundant explanations are omitted here.