GB2366625A

GB2366625A - Galvano mirror unit with biassing member

Info

Publication number: GB2366625A
Application number: GB0122266A
Authority: GB
Inventors: Toshio Nakagishi; Suguru Takishima; Hiroshi Yamamoto
Original assignee: Asahi Kogaku Kogyo Co Ltd
Current assignee: Pentax Corp
Priority date: 1997-06-27
Filing date: 1998-06-29
Publication date: 2002-03-13
Anticipated expiration: 2018-06-29
Also published as: GB2365538A; GB2365538B; GB0122285D0; GB2365537B; GB0122266D0; GB2366625B; GB0122280D0; GB0122282D0; GB2367382B; GB2365536A; GB2366626B; GB2366626A; GB0122279D0; GB2365536B; GB0122264D0; GB2365537A; GB2367382A

Abstract

A galvano mirror unit comprises a galvano mirror (26), a rotor (70) to which said galvano mirror is mounted, a stator (80) that rotatably supports said rotor about a rotation axis, first and second center pins (71, 72) provided to said stator, first and second receive meters (73, 74) provided to said rotor, which respectively receive said first and second center pins, and a biassing meter (82) provided to said stator which biases said first center pin to said first receive member thereby to eliminate backlash between said first center pin and said first receive member and between said second center pin and said second receive member.

Description

2366625 GALVANO MIRROR UNIT This invention relates to an optical disk

drive.

Generally, an optical disk drive writes and reads data 5 onto an optical disk by means of a laser beam. The optical disk drive includes a light source module that emits the laser beam, and an optical head carrying an object lens that converges the laser beam to a small light spot on the optical disk.

10 The tracking operation of the optical disk drive includes (1) a rough tracking operation and (2) a fine tracking- operation. The rough tracking operation is accomplished by moving the optical head across the tracks of the optical disk. The fine tracking operation is 15 accomplished by minutely moving the light spot on the optical disk. For this purpose, a galvano mirror is provided in a light path between the light source module and the object lens. By rotating the galvano mirror, the angle of incidence of the laser beam incident on the object lens is 20 changed so that the light spot on the optical disk is moved.

Fig. I is a perspective view of a conventional galvano mirror unit disclosed in Japanese Patent Laid-Open Publication No. 64-2105. A galvano mirror 41 is supported by a pair of elongate plate springs 42. The plate springs 42 25 extend from opposing side ends of the galvano mirror 41 in 2 such a manner that center lines of the plate springs 42 are aligned with each other. Distal ends of the plate springs 42 are fixed to a base 43. The plate springs 42 are deformable so that the plate springs 42 can be twisted about an axis 5 42A defined by the center lines of the plate springs 42. Due to the ability to twist (elastic deformation) of the plate springs 42, rotation of the galvano mirror 41 about an axis 42A can take place.

In order to actuate the galvano mirror 41, coils 45 and 10 46 are fixed to the galvano mirror 41. Further, a yoke 44 is provided on the base 43, which has a pair of magnets (not shown) generating a magnetic field in which the coils 45 and

46 are positioned. The galvano mirror 41 is rotated by the electromagnetic induction caused by the current flow in the 15 coils 45 and 46 and the magnetic field caused by the magnets of the yoke 44.

However, since the rotation of the galvano mirror 41 causes elastic deformation of the plate springs 42, there exists a primary resonance frequency that causes an unstable 20 rotation of the galvano mirror 41.

In order to lower the primary resonance frequency, it is necessary to increase the deformability of the plate springs 42. For that purpose, it is necessary to increase the axial length of the plate springs 42, which may increase 25 the total size of the galvano mirror unit. Thus, a compact galvano mirror unit that enables a stable tracking operation is desired.

It is therefore an object of the present invention to provide a compact galvano mirror unit that enables a stable 5 tracking operation.

According to one aspect of the present invention there is provided a galvano marror unit including a galvano mirror, a rotor to which the galvano mirror is mounted, a stator that rotatably supports the rotor about a rotation axis, a pair of center pins provided to one of the rotor and the stator, and a pair of receive members provided to the other of the rotor and the stator. The receiving members respectively receive the center pins. The rotor is pivoted by the engagement of the center pin and the receive member.

is Since the rotor is pivoted by the center pins and the receive members, there is no primary resonance frequency (which generates in a conventional galvano mirror) that causes an unstable rotation of the galvano mirror. Thus, it is possible to obtain a stable tracking operation.

20 In the conventional spring-supported galvano mirror, it is necessary to lengthen the spring member in order to lower the primary resonance frequency. However, according to the above-described arrangement, it is not necessary to increase the size of the galvano mirror unit (since there is no primary resonance frequency). Accordingly, the size of the galvano mirror unit can be compact.

In a particular arrangement, the galvano mirror unit further includes a pair of driving coils provided to one of the rotor and the stator, and a pair of driving magnets 5 provided to the other of the rotor and the stator. By allowing current to flow in the driving coils, the rotor can be rotated about the rotation axis.

It is preferable that the center pins have curved projections. In such case, the receive members have conical 10 surfaces. Further, the conical surfaces of the receive members respectively contact the curved projections of the center pins.

According to another aspect of the present invention, there is provided a galvano mirror unit including a galvano 15 mirror, a rotor to which the galvano mirror is mounted, a stator that rotatably supports the rotor about a rotation axis, first and second center pins provided to the stator, first and second receive members (which respectively receive the first and second center pins) provided to the rotor, and 20 a biassing member provided to the stator. The biassing member is arranged to bias the first center pin to the first receive member.

As constructed above, due to the biassing member, it is possible to eliminate the backlash between the first center 25 pin and the first receive member and between the second center pin and the second receive member.

In a particular arrangement, the biassing member includes a plate spring. Further, the first center pin and the plate spring are mechanically coupled with each other.

5 With such an arrangement, the inclination of the upper center pin is prevented. Therefore, the rotation of the galvano mirror is stabilized.

According to further aspect of the present invention, there is provided a galvano mirror unit including a galvano 10 mirror, a rotor to which the galvano mirror is mounted, a stator that rotatably supports the rotor about a rotation axis, first and second center pins provided to the stator, first and second receive members (respectively receiving the first and second center pins) provided to the rotor, and an 15 offset member provided to the stator. The first center pin is provided in a hole of the stator so that the first center pin is movable in the direction of the rotation axis. The offset member urges the first center pin so that the center pin is inclined in a predetermined direction in the hole.

With such an arrangement, since the first center pin is inclined in a predetermined direction, the deviation of the inclination of the first center pin is prevented. Therefore, the rotation of the galvano mirror is stabilized.

According to other aspect of the present invention, there is provided a galvano mirror unit including a galvano - 6 mirror, a rotor to which the galvano mirror is mounted, a stator that rotatably supports the rotor about a rotation axis, first and second center pins provided to the stator, first and second receive members (respectively receiving the 5 first and second center pins) provided to the rotor, and a plate spring provided to the stator. The plate spring biases the first center pin to the first receive member. The first center pin is fixed to the plate spring.

With such an arrangement, since the first center pin is 10 fixed to the plate spring, the inclination of the rotation axis of the rotor is prevented. Therefore, the rotation of the galvano mirror is stabilized.

According to still further aspect of the present invention, there is provided a galvano mirror unit including 15 a galvano mirror, a rotor to which the galvano mirror is mounted, a stator that rotatably supports the rotor about a rotation axis, a pair of center pins provided to one of the rotor and the stator, a pair of receive members (respectively receiving the center pins) provided to the 20 other of the rotor and the stator, a pair of driving magnets provided at opposing ends of the rotor, and a pair of driving coils provided to the stator. The driving coils are faced with the driving magnets respectively.

With such an arrangement, since the driving coils are 25 not provided to the rotor but provided to the stator, the 7 arrangement for electrical connection (for supplying electricity to the driving coils) becomes simple.

According to still yet further aspect of the present invention, there is provided a galvano mirror unit including 5 a galvano mirror, a rotor to which the galvano mirror is mounted, a stator that rotatably supports the rotor about a rotation axis, a pair of center pins provided to one of the rotor and the stator, a pair of receive members (respectively receiving the center pins) provided to the 10 other of the rotor and the stator, and first and second driving coils provided to the stator. The rotor has first and second sides that are respectively faced with the first and second coils. The first and second sides being magnetized.

15 With such an arrangement, since it is not necessary to provide separate driving magnets to the rotor, the structure of the mirror holder can be simplified.

According to yet further aspect of the present invention, there is provided a galvano mirror unit including 20 a galvano mirror block having a mirror surface, a stator that rotatably supports the galvano mirror block about a rotation axis, first and second center pins provided to the stator, and first and second receive portions provided to the galvano mirror block. The first and second receive 2S portions respectively receive the first and second center 8 pins.

With such an arrangement, since it is not necessary to provide a mirror holder or the like for holding the galvano mirror, the structure of the galvano mirror unit can be 5 simplified.

According to still other aspect of the present invention, there is provided a galvano mirror unit including a galvano mirror, a rotor to which the galvano mirror is mounted, a stator that rotatably supports the rotor about a 10 rotation axis, first and second center pins provided to the stator, first and second receive members (respectively receiving the first and second center pins) provided to the rotor, a biassing magnet provided to the stator so that the biassing magnet is located around the first center pin, and 15 a magnetic chip provided to a predetermined portion of the first center pin. Due to the magnetic force generated by the biassing magnet and the magnetic chip, the first center pin is biassed to the first receive member.

With such an arrangement, since the biassing force can 20 be obtained by the biassing magnet and the magnet chip, it is not necessary to provide a separate spring member for biassing the first center pin. Thus, the structure of the galvano mirror unit can be simplified.

According to still another aspect of the present 25 invention, there is provided a galvano mirror unit including 1.

- 9 a galvano mirror, a rotor to which the galvano mirror is mounted, a stator that rotatably supports the rotor about a rotation axis, first and second center pins provided to the stator, first and second receive members (respectively 5 receiving the first and second center pins) provided to the rotor, a biassing coil provided to the stator, and a magnetic chip provided to a predetermined portion of the first center pin. By allowing current to flow in the biassing coil, the first center pin is biassed to the first 10 receive member.

With such an arrangement, since the biassing force can be obtained by the biassing coil and the first center pin, it is not necessary to provide a separate spring member for biassing the upper center pin. Thus, the structure of the 15 galvano mirror unit can be simplified. Further, since the biassing force can be adjusted by varying the current flow in the biassing coil, the friction produced when the mirror holder is rotated can be adjusted.

According to still another aspect of the present 20 invention, there is provided a galvano mirror unit including a galvano mirror, a rotor to which the galvano mirror is mounted, a stator that rotatably supports the rotor about a rotation axis, first and second center pins provided to the stator. The first center pin is made of a magnetized member.

25 The first center pin is provided in a hole of the stator so - 10 that the first center pin is movable in the direction of the rotation axis. The galvano mirror unit further includes first and second receive members (respectively receiving the first and second center pins) provided to the rotor, and an 5 offset magnet provided to the stator. The offset magnet attracts the first center pin in a predetermined direction, thereby to prevent the deviation of the inclination of the first center pin in the hole.

With such an arrangement, since the offset magnet urges 10 the first center pin in a predetermined direction, the deviation of the inclination of the first center pin is prevented. Thus, the rotation of the galvano mirror is stabilized.

According to still another aspect of the present 15 invention, there is provided a galvano mirror unit including a galvano mirror, a rotor to which the galvano mirror is mounted, a stator that rotatably supports the rotor about a rotation axis, first and second center pins provided to the stator, first and second receive members (respectively 20 receiving the first and second center pins) provided to the rotor, first positioning magnet provided to the rotor, and second positioning magnet provided to the stator. Each of the first and second positioning magnets including a portion of N-pole and a portion of S-pole. A neutral position of the 25 rotor is obtained by the attraction of the first and second positioning magnets.

With such an arrangement, the galvano mirror is urged to its rotational neutral position without providing a separate spring member.

According to still another aspect of the present invention, there is a galvano mirror unit comprising, a galvano mirror, a rotor to which the galvano mirror is mounted, a stator that rotatably supports the rotor about a rotation axis, first and second center pins provided to the 10 stator, first and second receive members (respectively receiving the first and second center pins) provided to the rotor, and positioning magnet provided to the stator. The first center pin includes a portion of N-pole and a portion of S-pole. The positioning magnet includes a portion of 15 N-pole and a portion of S-pole. A neutral position of the rotor is obtained by the attraction of the first center pin and the positioning magnet.

With such an arrangement, the gaivano mirror is urged to its rotational neutral position without providing a 20 separate spring member.

Examples of the present invention will now be described with reference to the accompanying drawings, in which:

Fig. 1 is a perspective view of a conventional galvano mirror unit; 25 Fig. 2 is a perspective view of an optical disk drive to which the various embodiments of the present invention can be applied; Fig. 3 is an enlarged view of a floating head of the optical disk of Fig. 2; 5 Fig. 4 is an enlarged view of a tip of a rotary arm of the optical disk drive of Fig. 2; Fig. 5 is a plan view of the rotary arm of the optical disk drive of Fig. 2; Fig. 6 is a longitudinal sectional view of the rotary arm of the optical disk drive of Fig. 2; Fig. 7 is an exploded perspective view of a galvano mirror unit of a first embodiment of the invention; Fig. 8 is a horizontal sectional view of a galvano mirror unit of the first embodiment of Fig. 7; is Fig. 9 is a longitudinal sectional view of the galvano mirror unit of the first embodiment of Fig. 7; Fig. 10 is an enlarged view illustrating a center pin and a receive member of the first embodiment of Fig. 7; Figs. 11A and 11B are Bode diagrams showing examples of amplitude/frequency characteristics and phase/frequency characteristics of the galvano mirror unit of the first embodiment; Fig. 12 is a perspective view of a galvano mirror unit of a second embodiment of the invention; Fig. 13 is a longitudinal sectional view of the galvano - 13 mirror unit of the second embodiment of Fig. 12; Fig. 14 is an enlarged view illustrating a center pin and a receive member of the second embodiment of Fig.12; Fig. 15 is a plan view of a plate spring for use in the 5 second embodiment of Fig. 12; Fig. 16 is a longitudinal sectional view of a galvano mirror unit of a first modification of the second embodiment of the invention; Fig. 17 is a longitudinal sectional view of a galvano 10 mirror unit of a second modification of the second embodiment of the invention; Fig.- 18 is a longitudinal sectional view of a galvano mirror unit of a third embodiment of the invention; Fig. 19 is an enlarged view illustrating a center pin 15 and a receive member of the third embodiment of Fig. 18; Fig. 20 is a plan view of a plate spring for use in the third embodiment of Fig. 18; Fig. 21 is a longitudinal sectional view of a galvano mirror unit of a first modification of the third embodiment; 20 Fig. 22 is a perspective view showing a center pin and a plate spring of a second modification of the third embodiment; Fig. 23 is a longitudinal sectional view of a galvano mirror unit of a fourth embodiment of the invention; 25 Fig. 24 is a longitudinal sectional view of a galvano - 14 mirror unit of a modification of the fourth embodiment; Fig. 25 is a perspective view of a galvano mirror unit of a fifth embodiment of the invention; Fig. 26 is a longitudinal sectional view of the galvano 5 mirror unit of the fifth embodiment of Fig. 25; Fig. 27 is an exploded perspective view of a galvano mirror unit of a sixth embodiment of the invention; Fig. 28 is a horizontal view of the galvano mirror unit of the sixth embodiment of Fig. 27; 10 Fig. 29 is an exploded perspective view illustrating a modification of the sixth embodiment; Fig. 30 is an exploded perspective view of a galvano mirror unit of a seventh embodiment of the present invention; 15 Fig. 31 is a horizontal sectional view of the galvano mirror unit of the seventh embodiment of Fig. 30; Fig. 32 is an exploded perspective view of a galvano mirror unit of an eighth embodiment of the invention; Fig. 33 is a longitudinal sectional view of the galvano mirror unit of the eighth embodiment of Fig. 32; Fig. 34 is a perspective view of the galvano mirror of the eighth embodiment of Fig. 32; Fig. 35 is an exploded perspective view of a galvano mirror unit of a modification of the eighth embodiment; 25 Fig. 36 is a longitudinal sectional view of a galvano I - 15 mirror unit of a ninth embodiment of the invention; Fig. 37 is a perspective view of a center pin and a magnet ring of the galvano mirror unit shown in Fig. 36; Fig. 38 is a longitudinal sectional view of the center 5 pin and the magnet ring of Fig. 37; Fig. 39 is a longitudinal sectional view of a galvano mirror of a modification of the ninth embodiment; Fig. 40 is a perspective view of a center pin and magnet rings of the galvano mirror unit shown in Fig. 39; 10 Fig. 41 is a longitudinal sectional view of the center pin and magnet rings of Fig. 40; Fig. 42 is a longitudinal sectional view of a galvano mirror unit of a tenth embodiment of the invention; Fig. 43 is a perspective view of a center pin and a coil of the galvano mirror unit shown in Fig. 42; Fig. 44 is longitudinal sectional view of the center pin and the coil of Fig. 42; Fig. 4S is a longitudinal sectional view showing a galvano mirror unit of a modification of the tenth 2 0 embodiment; Fig. 46 is a perspective view of a center pin and coils of the galvano mirror unit shown in Fig. 45; Fig. 47 is a longitudinal sectional view of the center pin and coils of Fig. 46; 25 Fig. 48 is a longitudinal sectional view of a galvano - 16 mirror unit of an eleventh embodiment of the invention; Fig. 49 is a perspective view of a center pin and an offset magnet of the galvano mirror unit shown in Fig. 48; Fig. 50 is a longitudinal sectional view of the center 5 pin and the offset magnet of Fig. 49; Fig. 51 is a longitudinal sectional view of a galvano mirror unit of a modification of the eleventh embodiment; Fig. 52 is a perspective view of magnets and a center pin of the galvano mirror unit shown in Fig. 51; 10 Fig. 53 is a longitudinal sectional view of the magnets and the center pin of Fig. 52; Fig. 54 is a perspective view of a galvano mirror unit of a twelfth embodiment of the invention; Fig. 55 is a longitudinal sectional view of the galvano mirror unit of the twelfth embodiment of Fig. 54; Fig. 56 is a perspective view of magnet rings of the galvano mirror unit of Fig. 55; Fig. 57 is a longitudinal sectional view of a galvano mirror unit of a thirteenth embodiment of the invention; 20 Fig. 58 is a perspective view of a center pin and a magnet ring of the galvano mirror unit shown in Fig. 57; Figs. 59A and S93 are a plan view and a longitudinal sectional view of the center pin and the magnet ring of Fig.

58; 25 Fig. 60 is a perspective view showing a center pin and - 17 a magnet ring of a modification of thirteenth embodiment; and Figs. 61A and 62B are a plan view and a longitudinal sectional view of the center pin and the magnet ring of Fig. 5 60.

First, an optical disk drive to which the first to fourteenth embodiments of the present invention can be applied is described.

Fig. 2 is a perspective view of an optical disk drive 10 (hereinafter, the disk drive 1). The disk drive 1 is arranged to write and read data on an optical disk 2 by means of - a so-called Near Field Recording (NFR) technology.

In the disk drive 1, the optical disk 2 is mounted to a rotating shaft 2a of a spindle motor (not-shown). The disk 15 drive 1 includes a rotary arm 3 extending in parallel to the surface of the optical disk 2, which is rotatably supported by a shaft 5. A floating head 6 that carries an optical lens (described later) is provided to a tip of the rotary arm 3. When the rotary arm 3 is rotated, the floating head 6 moves 20 across tracks formed on the optical disk 2. The rotary arm 3 is further provided with a light source module 7 in the vicinity of the shaft 5.

Fig. 3 is an enlarged view of the floating head 6. Fig. 4 is an enlarged view of the tip of the rotary arm 3. As 25 shown in Fig. 4, the floating head 6 is mounted to the - 18 rotary arm 3 via a flexure beam B. One end of the flexure beam 8 is fixed to the bottom of the rotary arm 3, while the floating head 6 is fixed to the other end of the flexure beam 8. When the optical disk 2 rotates, the floating head 5 6 is lifted upward by air flow generated between the spinning optical disk 2 and the floating head 6. When the floating head 6 is lifted upward, the flexure beam 8 is elastically deformed, which urges the floating head 6 downward. With this, the floating amount of the floating 10 head 6 is kept constant, due to the balance of the upward force (caused by the air flow) and the downward force (caused by the deformation of the flexure beam 8).

As shown in Fig. 3, the floating head 6 includes an objective lens 10 and a solid immersion lens (SIL) 11. A 15 reflecting mirror 31 is provided on the rotary arm 3, which reflects a laser beam 13 emitted from the light source module 7 (Fig. 4) to the objective lens 10. The objective lens 10 converges the laser beam 13. The solid immersion lens 11 is a hemispherical lens and the plane surface 20 thereof lla faces the optical disk 2. Further, a focal point of the objective lens 10 is positioned on the plane surface of the solid immersion lens 11. That is, the laser beam 13 is converged onto the plane surface lla of the solid immersion lens 11.

25 Since the clearance of the optical disk and the plane - 19 surface lla of the solid immersion lens 11 is less than 1 gm, the converged laser beam is converted to a so-called evanescent beam (which propagates across a small gap between closely disposed surfaces) and reaches the optical disk 2.

5 Since the beam diameter of the evanescent beam is smaller than the converged laser beam, the data storage capacity can be remarkably increased. Application of the solid immersion lens and the evanescent beam in a data recording device is described in detail by B. D. Terris, H. J. Manin, and D.

10 Rugar, "Near-field optical data storage", Appl. Phys. Lett. 68,.141143 (1996).

In. order to apply a magnetic field on the surface of the optical disk 2, a coil 12 is provided around the solid immersion lens 11. A current flow in the coil 12 generates

15 a magnetic field in the part of the optical disk 2 at which the floating head is positioned. Data writing is performed by the evanescent beam from the solid immersion lens 11 and the magnetic field generated by the coil 12.

Figs. 5 and 6 are a plan view and a longitudinal 20 sectional view of the rotary arm 3. As shown in Figs. 5 and 6, the rotary arm 3 is provided with a driving coil 16 at the opposite end to the floating head 6. The driving coil 16 is inserted into a magnetic circuit (not shown). The driving coil 16 and the magnetic circuit constitute a voice coil 25 motor 4 (Fig. 2). The rotary arm 3 is supported by the shaft 5 via bearings 17. When current flows in the driving coil 16, the rotary arm 3 is rotated about the axis 5 due to the electromagnetic induction.

As shown in Figs. 5 and 6, the light source module 7 includes a semiconductor laser 18, a laser drive circuit 19, 5 a collimator lens 20 and a composite prism assembly 21. Further, the light source module 7 includes a laser power monitor sensor 22, a reflection prism 23, a data sensor 24 and a tracking detection sensor 25. A divergent laser beam emitted from the semiconductor laser 18 is converted to a 10 parallel laser beam by the collimator lens 20. Due to the characteristics of the semiconductor laser 18, the sectional shape of the laser beam is elongated. In order to correct the sectional shape of the laser beam, an incident surface 21a of the composite prism assembly 21 is inclined with 15 respect to the incident laser beam. When the laser beam is refracted by the incident surface 21a of the composite prism assembly 21, the sectional shape of the laser beam becomes a circle. The laser beam is then incident on a first half mirror surface 21b. With the first half mirror surface 21b, 20 the laser beam is partially reflected to the laser power monitor sensor 22. The laser power monitor sensor 22 detects the intensity of the incident laser beam. The output from the laser power monitor sensor 22 is sent to a power control circuit (not shown) so as to stabilize the power of the 25 semiconductor laser 18.

The tracking operation includes two steps: (1) a rough tracking and (2) a fine tracking. The rough tracking is accomplished by the rotation of the rotary arm 3. The fine tracking operationAs accomplished by minutely moving the 5 light spot on the optical disk 2. For this purpose, a galvano mirror 26 is provided in a light path between the light source module 7 and the objective lens 10. In particular, the galvano mirror 26 is located so that the laser beam 13 emitted from the laser source module 7 is 10 fully incident thereon. The laser beam 13 reflected by the galvano mirror 26 proceeds to the reflection mirror 31 and is reflected by the reflection mirror 31 to the floating head 6. Then, the laser beam 13 is converged and made incident on the optical disk 2. By rotating the galvano 1S mirror 26, the incident angle of the laser beam 13 incident on the objective lens 10 is changed so that the light spot on the optical disk 2 is moved. The rotation angle of the galvano mirror 26 is detected by a galvano mirror positioning sensor 28 located in the vicinity of the galvano 20 mirror 26.

When the galvano mirror 26 rotates to change the incident angle of the laser beam 13 incident on the objective lens 10, there is a possibility that the laser beam 13 partially fails to enter the objective lens 10. In 25 order to solve this problem, first and second relay lenses --22 - 29 and 30 are provided between the galvano mirror 26 and the objective lens 10 to obtain a conjugate relationship between a principal plane of the objective lens 10 and the center of the mirror surface of the galvano mirror 26 (in the vicinity 5 of the rotation axis thereof). In this way,the laser beam 13 reflected by the galvano mirror 26 is made to be surely incident on the objective lens 10 irrespective of the rotation of the galvano mirror 26.

The laser beam 13 that has returned from the surface of 10 the optical disk 2 travels through the floating head 6, the relay lenses 30 and 29 and the galvano mirror 26. Then, the return laser beam 13 enters the composite prism assembly 21 and is reflected by the first half mirror surface 21b to a second half mirror surface 21c. The return laser beam that 15 has passed through the second half mirror surface 21c is directed to the tracking detection sensor 25. The tracking detection sensor 25 outputs a track error signal based on the incident laser beam. The laser beam that has been reflected by the second half mirror surface 21c is split by 20 a Wollaston polarizing prism 32 to generate two polarized beams. The polarized beams are converged by a converging lens 33 onto the data detection sensor 24 via the reflection prism 23. The data detection sensor 24 has two light receiving portions which respectively receive two polarized 25 beams. Thus, the data detection sensor 24 reads data recorded on the optical disk 2. In particular, a data signal from the tracking detection sensor 25 and data detection sensor 24 are amplified by an amplifier circuit (not-shown) and sent to a control circuit (not-shown).

5 Hereinafter, the various embodiments of the present invention will be described. In the various embodimentst common reference numerals have been used for common components where appropriate.

First Embodiment 10 Fig. 7 is an exploded perspective view of a galvano mirror unit of the first embodiment. The galvano mirror 26 is mounted to a mirror holder (rotor) 50 that is supported by a stator 60 (Fig. 9) so that the mirror holder 50 is rotatable about a rotation axis Z. Hereinafter, the 15 direction in parallel to the rotation axis Z is referred to as a vertical direction. Further, a plane that is perpendicular to the rotation axis Z is referred to as a horizontal plane. Further, the galvano mirror 26 side of the mirror holder 50 is referred to as 'front', while the 20 opposite side of the mirror holder 50 is referred to as 'rear'.

Figs. 8 and 9 are a horizontal sectional view and a longitudinal sectional view of the galvano mirror unit of Fig. 7. The galvano mirror 26 is rectangular shaped and has 25 a certain width W and a height H. The rotation axis Z of the galvano mirror 26 is in parallel to the height H of the galvano mirror 26. Further, the rotation axis Z is at the center of the width W of the galvano mirror 26.

As shown in Fig. 8, a pair of driving coils 58 and 59 are provided to lateral side ends of the mirror holder 50.

5 Further, respective pairs of driving magnets 63 and 64 are provided to the stator 60 (Fig. 9) so that the driving magnets 63 and 64 face the driving coils 58 and 59, respectively. The driving magnets 63 and 64 generates a magnetic field in which the driving coils 58 and 59 are

10 located. The driving coils 58 and S9 are connected to lead wires (not shown) for supplying electricity to the driving coils 58 and 59. When current flows in driving coils 58 and 59, the mirror holder 50 is rotated about the rotation axis Z due to the electromagnetic induction caused by the current 1S and the magnetic field. With such an arrangement, the galvano mirror 26 can be rotated thereby to change the direction of the laser beam reflected by the galvano mirror 26.

As shown in Fig. 9, in order to rotatably support the 20 mirror holder 50, a pair of center pins 51 and 52 are provided to the stator 60 so that the center pins 51 and 52 vertically sandwich the mirror holder 50. The center pins 51 and 52 are aligned on a line defining the rotation axis Z of the mirror holder SO. A pair of receive members 53 and 54 25 are provided at the top and the bottom of the mirror holder 50, which receive the center pins 51 and 52, respectively.

Fig. 10 is an enlarged view illustrating the upper center pin 51 and the upper receive member 53. The upper center pin 51has a conical bottom portion 51A and a rounded 5 top portion. The apex 51B of the conical bottom portion 51A is rounded. The receive member 53 has a recess 53A having a conical surface. The rounded apex 51B of the upper center pin 51 contacts the conical surface of the recess 53A. In this way, the upper center pin 51 is received by the 10 receive member 53 so that the receive member 53 is rotatable with respective to the upper center pin 51. Preferably, the apex angle of the conical surface of the recess 53A is set from 80' to 115'. The lower center pin 52 and the lower receive member 54 contact in a similar manner to the upper 15 center pin 51 and the upper receive member 53. As shown in Fig. 9, the center pins 51 and 52 fit into holes 61 and 62 of the stator 60. The lower center pin 52 has a flange portion 52A for determining the axial position of the lower center pin 52 when the lower center pin 52 fits into the 20 hole 62.

Preferably, the receive members 53 and 54 are made of ruby or sapphire. Since ruby and sapphire have a low coefficient of friction, the driving force for rotating the mirror holder 50 is relatively small. Further, since ruby 25 and sapphire have a high wear resistance, the rotation of 26 the mirror holder 50 is stable for a long time.

Fig. 11A and 11B are Bode diagrams respectively showing examples of the amplitude/ frequency characteristics and the phase/frequency characteristics of the galvano mirror unit 5 of the first embodiment. Figs. 11A and 11B are obtained by measuring responses (by means of a laser-Doppler vibration meter) of the galvano mirror 26 with respect to the frequency of the current in the driving coils 58 and 59. As seen from Figs. 11A and 11B, there is no primary resonance 10 frequency that causes an unstable rotation of the galvano mirror 26.

As constructed above, with the first embodiment of the invention, the galvano mirror 26 is pivoted by the center pins 51 and 52 and the receive members 53 and 54. Thus, 15 unlike a conventional galvano mirror in which a galvano mirror is supported by a spring mechanism (Fig. 1), there is no primary resonance frequency that causes an unstable rotation of the galvano mirror 26. Thus, it is possible to obtain a stable tracking operation.

20 Further, in the conventional spring-supported galvano mirror (Fig. 1), in order to lower the primary resonance frequency, it is necessary to lengthen the spring member and this may increase the size of the galvano mirror unit.

However, with this embodiment, it is not necessary to 25 increase the size of the galvano mirror unit, since there is - 27 no primary resonance frequency.

Second Embodiment Figs. 12 and 13 are a perspective view and a longitudinal sectional view of a galvano mirror unit of a 5 second embodiment of the invention. As shown in Figs. 12 and 13, the galvano mirror 26 is mounted to a mirror holder 70 that is rotatably supported by a stator 80.

As shown in Fig. 13, in order to rotatably support the mirror holder 70, a pair of center pins 71 and 72 are 10 provided to the stator 80 so that the center pins 71 and 72 vertically sandwich the mirror holder 70. The center pins 71 and 72 are aligned on a line defining the rotation axis Z of the mirror holder 70. A pair of receive members 73 and 74 are provided at the top and the bottom of the mirror holder 15 70, which receive the center pins 71 and 72, respectively.

Fig. 14 is an enlarged view illustrating the upper center pin 71 and the upper receive member 73. The center pin 71 contacts the receive member 73 in a similar manner that the center pin 51 contacts the receive member 53 in the 20 first embodiment, as illustrated in Fig. 10. The lower center pin 72 and the lower receive member 74 contact in a similar manner to the upper center pin 71 and the upper receive member 73.

As shown in Fig. 13, the lower center pin 72 fits into 25 a hole 80B formed at the bottom of the stator 80. The lower - 28 center pin 72 has a flange portion 72A for determining the axial position of the lower center pin 72. The upper center pin 71 is inserted, via a bushing 75, into a hole 80A formed on the top of the stator 80. The bushing 75 has a center 5 hole 75A through which the upper center pin 71 is inserted. The outer diameter of the upper center pin 71 is smaller than the inner diameter of the hole 75A of the bushing 75 so that the upper center pin 71 is axially movable in the bushing 75.

10 A plate spring 82 is provided at the top of the stator 80, which urges the upper center pin 71 downward. one end of the plate spring 82 is fixed to the stator 80 by means of a fixing screw 83, while the other end of the plate spring 82 is placed on the upper center pin 71. Due to the biassing by 1S the plate spring 82, backlash between the center pins 71 and 72 and their respective receive members 73 and 74 can be eliminated. Fig. 15 shows a plate spring 82 which has a first engaging hole 82A through which the fixing screw 83 is inserted and a second engaging hole 82B described below.

20 In order to prevent inclination of the upper center pin 71, the upper center pin 71 is provided with a projection 71C at the top thereof. The protrusion 71C engages the second engaging hole 82B. Due to the engagement of the projection 71C and the second engaging hole 82B, inclination of the upper center pin 71 in the hole 75A of the bushing 75 29 - is prevented.

In the second embodiment, the arrangement of driving coils and driving magnets for actuating the galvano mirror 26 is the same as in the first embodiment (Fig. 7).

5 With the second embodiment, due to the biassing by the plate spring 82, backlash between the center pins 71 and 72 and their respective receive members 73 and 74 can be eliminated. Further, since the projection 71C of the upper center pin 71 engages the second engaging hole 82B of the 10 plate spring 82, inclination of the upper center pin 71 in the hole 75A of the bushing 75 is prevented. Therefore, rotation of the galvano mirror 26 is stabilized.

A first modification of the setond embodiment of the invention will now be described. Fig. 16 is a longitudinal 15 sectional view of a galvano mirror unit of the first modification of the second embodiment. In this modification, the upper center pin 71 is biassed by a pair of plate springs 84 and 85 that are facing each other. The pair of plate springs 84 and 85 have one end fixed to the top of the 20 stator 80 (via the fixing screw 83), while their other end is placed on the upper center pin 71. Spacers 86 and 87 are sandwiched between the plate springs 84 and 85, so that the plate springs 84 and 85 are in parallel with each other. The spacers 86 and 87 are adhered to the plate springs 84 and 25 85. The lower plate spring 84 is similar to the plate spring 82 of the second embodiment (Fig. 15) and has an engaging hole which engages the projection 71C of the upper center pin 71. The upper plate 85 is different from the plate spring 82 in that the upper plate 85 has no engaging hole 5 which engages the projection of the upper center pin 71. In this way, the plate springs 84 and 85 act as integrally formed spring member.

With the first modification of the second embodiment, since two plate springs 84 and 8S are used as a biassing 10 member for biassing of the upper center pin 71, the rigidity of the biassing member is relatively high. Alternatively, it is possible to provide three or more plate springs.

A second modification of the second embodiment will now be described. Fig. 17 is a longitudinal sectional view of a 15 galvano mirror unit of the second modification of the second embodiment. In the second modification, an upper center pin 76 has a conical bottom portion 71A and a rounded top surface. The lower center pin 72 and the receive members 73 and 74 are the same as in the second embodiment (Fig. 13).

20 A plate spring 88 is mounted to the top of the stator via the screw 83 so that the plate spring 88 is inclined with respect to the rotation axis Z of the galvano mirror 26. There is a gap 89 between the round top surface of the upper center pin 76 and the distal end of the plate spring 25 88. An adhesive agent is appliGd to the gap between the - 31 upper center pin 76 and the plate spring 88 so that the upper center pins 76 is adhered to the plate spring 88.

It is possible to use the plate spring 82 of the second embodiment (Fig. 15) instead of the plate spring 88. In that 5 case, it is also possible to supply adhesive through the engaging hole 82A of the plate spring 82.

With the second modification of the second embodiment, since the upper center pin 76 is adhered to the plate spring 88, deviation of the inclination of the upper center pin 76 10 in the bushing 75 is prevented. Therefore, rotation of the galvano mirror 26 is stabilized.

Third Embodiment Fig. 18 is a longitudinal sectional view of a galvano mirror unit of a third embodiment of the invention. Fig. 19 15 is an enlarged view of an upper center pin 78 of the third embodiment. As shown in Fig. 19, the upper center pin 78 has a rounded top portion 78C and a conical bottom portion 78A.

An apex 78B of the conical bottom portion 78A is rounded. As shown in Fig. 18, the upper center pin 78 is inserted into 20 the bushing 75 mounted to the stator 80. The bushing 75 is the same as in the second embodiment (Fig. 13), and has the hole in which the upper center pin 78 is movably supported therein. The center pin 78 contacts the receive member 73 in a similar manner that the center pin 51 contacts the receive member 53 in the first embodiment (Fig. 10). The lower center pin 72 and the lower receive member 74 contact in a similar manner to the upper center pin 78 and the upper receive member 73.

A plate spring 90 is provided at the top of the stator 5 80, which biases the upper center pin 78 downward. One end of the plate spring 90 is fixed to the stator 80 by the fixing screw 83, while the other end of the plate spring 90 is bent upward to form a bent portion 91. The bent portion 91 contacts the front periphery of the top portion 78C of 10 the upper center pin 78. In this way, the plate spring 90 urges the upper center pin 78 diagonally downward as shown by an arrow in Fig. 19. Due to the diagonally downward force, the upper center pin 78 is inclined in a direction in which the top portion 78C of the upper center pin 78 is 15 moved rearward. Fig. 20 is a plan view of the plate spring 90. As shown in Fig. 20, a screw hole 90A through which the fixing screw 83 is inserted is formed at one end of the plate spring 90, and the bent portion 91 is formed on the other end of the plate spring 90.

With the third embodiment, the arrangement of driving coils and driving magnets for actuating the galvano mirror 26 is the same as in the first embodiment (Fig. 7).

With the third embodiment, due to the biassing of the plate spring 90, backlash between the center pins 78 and 72 and their respective receive members 73 and 74 can be - 33 eliminated. Further, since the plate spring 90 biases the upper center pin 78 diagonally downward, the upper center pin 78 is inclined in a certain direction. Accordingly, the direction in which the upper center pin 78 is inclined in 5 the bushing 75 can be definite. Thus, deviation of the inclination of the upper center pin 78 is prevented. Therefore, rotation of the galvano mirror 26 is stabilized.

A first modification of the third embodiment will now be described. Fig. 21 is a longitudinal sectional view of 10 the galvano mirror unit of the first modification of the third embodiment. Unlike the plate spring 90 of the third embodiment, a plate spring 92 of the first modification has no bent portion. In order to incline the upper center pin 78, the plate spring 92 biases the periphery of the rounded 15 top portion 78C of the upper center pin 78.

Accordingly, the direction in which the upper center pin 78 is inclined can be definite. Thus, deviation of the inclination of the upper center pin 78 is prevented.

Therefore, rotation of the galvano, mirror 26 is stabilized.

20 A second modification of the third embodiment will now be described. Fig. 22 shows the upper center pin 78 and the plate spring 92 of the second modification. In this second modification, the upper center pin 78 is provided with a flat portion 79 on the rounded top portion. The plate spring 25 92 abuts with the flat portion 79 of the upper center pin 78 34 in face-to-face contact.

With such an arrangement, since the plate spring 92 abuts with the flat portion 79 by face-to-face contact, the upper center pin 78 is surely inclined. Thus, the contact of 5 the plate spring 92 and the upper center pin 78 is further stabilized.

Fourth Embodiment Fig. 23 is a sectional view of a galvano mirror unit of a fourth embodiment of the invention. The galvano mirror 26 10 is mounted to a mirror holder 100 that is supported by a stator 110 so that the mirror holder 100 is rotatable about the rotation axis Z. In order to rotatably support the mirror holder 100, a pair of center pins 101 and 102 are provided to the stator 110 so that the center pins 101 and 15 102 vertically sandwich the mirror holder 100. The center pins 101 and 102 are aligned on a line defining the rotation axis Z of the mirror holder 100. A pair of receive members 103 and 104 are provided at the top and the bottom of the mirror holder 100, which respectively receive the center 20 pins 101 and 102.

The lower center pin 102 fits into a hole formed in the bottom of the stator 110. The lower center pin 102 includes a conical upper portion, with an apex thereof being rounded. The lower receive member 104 has a conical recess. The 25 rounded apex of the lower center pin 102 contacts the - 35 conical recess of the lower receive member 104. The upper center pin 101 is unitarily formed with a plate spring 112 provided at the top of the stator 110. The plate spring 112 is fixed to the stator 110 via a fixing screw 113 at an end 5 thereof, and the upper center pin 101 is formed on the other end of the plate spring 112.

The upper center pin 101 has a cylindrical shape, a bottom portion thereof being rounded. The rounded bottom portion of the upper center pin 101 contacts a conical 10 surface of the upper receive member 103. In this way, the mirror holder 100 is pivoted by the center pins 101 and 102 and the receive members 103 and 104.

With the fourth embodiment, the arrangement of the driving coils and driving magnets for actuating the galvano 15 mirror 26 is the same as in the first embodiment (Fig. 7).

With the fourth embodiment, due to the elastic force of the plate spring 112, backlash between the center pins 101 and 102 and their respective receive members 103 and 104 can be eliminated. Further, since the upper center pin 101 is 20 unitarily formed with the plate spring 112, the number of parts can be reduced. Furthermore, since the upper center pin 101 is movable only in the Z axis direction, inclination of the mirror holder 100 is prevented. Therefore, rotation of the galvano mirror 26 is stabilized.

25 Fig. 24 is a longitudinal sectional view of a galvano - 36 mirror unit of a modification of the fourth embodiment. In this modification, an upper center pin 10S is fixed to the top of the mirror holder 100 and projects upward. The top portion of the upper center pin 105 is rounded. A plate 5 spring 114 is provided at the top of the stator 110, which has an indentation 115 that receives the top portion of the upper center pin 105. The indentation 115 has a conical surface, and the rounded top portion of the upper center pin 105 contacts the conical surface of the indentation 115. The 10 lower center pin 102 and the lower receive member 104 are the same as in the fourth embodiment. In this way, the mirror holder 100 is pivoted by the center pins 105 and 102, the indentation 115 of the plate spring 114 and the receive member 104.

15 With such an arrangement, since the upper center pin is received by the indentation 11S of the plate spring 114, it is not necessary to provide a further receive member that receives the upper center pin 105. Thus, the number of parts can be reduced. Further, inclination of the mirror holder 100 is prevented.

Fifth Embodiment Figs. 25 and 26 are a perspective view and a longitudinal sectional view of a galvano mirror unit of a fifth embodiment of the invention. The galvano mirror 26 is mounted to a mirror holder 120 that is supported by a stator e- I so that the mirror holder 120 is rotatable about the rotation axis Z. In order to rotatably support the mirror holder 120, a pair of center pins 121 and 122 are provided at the top and bottom of the mirror holder 120. The center 5 pins 121 and 122 are aligned on a line defining the rotation axis Z. The center pins lil and 122 are' received by receive members 123 and 124 provided at the top and the bottom of the stator 130. The lower receive member 124 is fitted into a hole formed in the bottom of the stator 130, while the 10 upper receive member 123 is fixed to a plate spring 132 provided at the top of the stator 130. Each of the center pins 121'and 122 has a conical portion with an apex being rounded. Each of the receive members 123 and 124 has a recess with a conical surface. The rounded apex of the upper center pin 121 contacts the conical surface of the receive member 123, and the rounded apex of the lower center pin 122 contacts the conical surface of the receive member 124. In this way, the center pins 121 and 122 are received by the receive members 123 and 124. Due to the elastic force of the plate spring 132, backlash between the center pins 121 and 123 and their respective receive members 122 and 124 can be eliminated.

With the fifth embodiment, the arrangement of the driving coils and driving magnets for actuating the galvano mirror 26 is the same as in the first embodiment (Fig. 7).

With the fifth embodiment, since the upper receive member 123 is fixed to the plate spring 132, inclination of the mirror holder 120 is prevented. Therefore, rotation of the galvano mirror 26 is stabilized.

5 Sixth Embodiment Fig. 27 is an exploded perspective view of a galvano mirror unit of a sixth embodiment of the invention. The galvano mirror 26 is mounted to a mirror holder 140 that is rotatable about the rotation axis Z. The mirror holder 140 10 is pivoted about center pins 141 and 142 and receive members 143 and 144 (receive member 144 is not shown) in a similar manner to the second embodiment (Fig. 13). The structure of the stator is the same as the stator 80 (Fig. 13) of the second embodiment. In the sixth embodiment, driving coils 15 146 and 147 are provided to the stator (not shown) and driving magnets 148 and 149 are provided to the mirror holder 140.

Fig. 28 is a horizontal sectional view of the galvano mirror unit of the fifth embodiment of Fig. 27. The driving 20 magnet 148 includes front and rear segments 148A and 148B.

The segments 148A and 148B of the driving magnet 148 are located so that their magnetization is in the opposite direction to each other. In particular, the N-pole of the front segment 148A faces the driving coil 146, while the 25S-pole of the rear segment 148B faces the driving coil 146.

Similarly, the driving magnet 149 includes front and rear segments 149A and 149B. The S-pole of the front segment 149A faces the driving coil 147, while the N-pole of the rear segment 149B faces the driving coil 147.

5 With the sixth embodiment, since the driving coils 146 and 147 are not provided to the mirror holder 140 but provided to the stator (not shown), the arrangement for electrical connection for supplying electricity to the driving coils 146 and 147 becomes simpler.

10 Fig. 29 shows an exploded perspective view of a galvano mirror unit of a modification of the sixth embodiment. In this modification, the galvano mirror 26 is mounted to the mirror holder 140 that is rotatable about the rotation axis Z. The mirror holder 140 is pivoted by center pins 151 and 15 152 (center pin 152 is not shown) and the receive members 153 and 154 in a similar manner to the fifth embodiment (Fig. 25). The structure of the stator is the same as the stator 130 (Fig. 26) of the fifth embodiment. The center pins 151 and 152 are provided to the top and the bottom of 20 the mirror holder 140, while receive members 153 and 154 are provided to the stator (not shown). The center pins 151 and 152 contact their respective receive members 153 and 154 in a similar manner to the fifth embodiment (Fig. 26).

With such an arrangement, like the sixth embodiment, 25 the arrangement for electrical connection for supplying electricity to the driving coils 146 and 147 becomes simpler.

Seventh Embodiment Fig. 30 is an exploded perspective view of a galvano 5 mirror unit of a seventh embodiment of the invention. The galvano mirror 26 is mounted to a mirror holder 155 that is made of a plastic magnet and is rotatable about the rotation axis Z. The mirror holder 15S is rotatably supported by a stator (not shown)via center pins 141 and 142 and receive 10 members 143 and 144 (receive member 144 is not shown) in a similar manner to the second embodiment (Fig. 13). The structure of the stator is same as that of the second embodiment (Fig. 13). A pair of driving coils 158 and 159 are provided to the stator so that the driving coils 158 and 15 159 face the lateral side ends of the mirror holder 155.

Fig. 31 is a horizontal sectional view of the galvano mirror unit 155. The mirror holder 155 includes front and rear sections 156 and 157. The sections 1S6 and 157 are magnetized in the opposite direction to each other. That is, 20 the N-pole of the front section 156 and the S-pole of the rear section 157 face the driving coil 158, while the S-pole of the front section 156 and the N-pole of the rear section 157 face the driving coil 159. In this way, when current flows in the driving coils 158 and 159, the mirror holder 25 155 is rotated by the electromagnetic induction generated by the magnetic field of the mirror holder 155 and the current flow in driving coils 158 and 159.

With the seventh embodiment, since it is not necessary to provide separate magnets to the mirror holder 155, the 5 structure of the mirror holder 155 can be simplified.

Eicfhth Embodiment Figs. 32 and 33 are an exploded perspective view and a longitudinal sectional view of a galvano mirror unit of an eighth embodiment of the invention, whilst Fig. 34 is a perspective view of the galvano mirror shown in Fig. 32. As shown in Fig. 34, in the eighth embodiment, a galvano mirror is cubic-shaped, one surface thereof being a mirror surface 160A. As shown in Fig. 33, center pins 161 and 162 are provided to a stator 170 so that the galvano mirror 160 is sandwiched between the center pins 161 and 162. The center pins 161 and 162 are aligned on a line defining the rotation axis Z. As shown in Fig. 33, the center pins 161 and 162 are received by conical recesses 163 and 164 formed at the top and the bottom of the galvano, mirror 160. Each of the center pins 161 and 162 has a conical portion with a rounded apex. The rounded apexes of the center pins 161 and 162 respectively contact the conical surfaces of the recesses 163 and 164.

As shown in Fig. 32, driving magnets 176 and 177 are provided to the stator 170 (Fig. 33). Driving coils 166 and 167 are provided to the lateral side ends of the galvano mirror 160 so that the driving coils 166 and 167 face the driving magnets 176 and 177. In this way, when current flows in the driving coils 166 and 167, the galvano mirror 160 is 5 rotated by the electromagnetic induction generated by the magnetic field of the driving magnets 176 and 177 and the current flow in driving coils 166 and 167.

With the eighth embodiment, since it is not necessary to provide a mirror holder for holding the galvano mirror, the structure of the galvano mirror unit can be simplified.

Fig. 35 is an exploded perspective view of a galvano mirrorunit of a modification of the eighth embodiment. In this modification, driving magnets 168 and 169 are provided to the lateral side ends of the galvano,mirror 160. Driving 15coils 178 and 179 are provided to the stator (not shown) so that the driving coils 178 and 179 face the driving magnets 168 and 169.

With such an arrangement, since the driving coils 178 and 179 are not provided to the galvano mirror 160 but are provided to the stator, the arrangement for electrical connection for supplying electricity to the driving coils 178 and 179 becomes simpler. Accordingly, the structure of the galvano mirror unit can be further simplified.

Ninth Embodiment 25 Fig. 36 is a sectional view of a galvano mirror unit of a ninth embodiment of the invention. The galvano mirror 26 is mounted to a mirror holder 200 that is rotatably supported by a stator 210. Center pins 201 and 202 are provided so that the mirror holder 200 is sandwiched by the 5 center pins 201 and 202. The center pins 201 and 202 are aligned on a line defining the rotation axis Z. The center pins 201 and 202 are received by respective receive members 203 and 204 provided to the mirror holder 200. The upper center pin 201 is inserted into a bushing 20S provided to 10 the top of the stator 210 so that the upper center pin 201 is axially movable in the bushing 20S. The bushing 20S is provided-with a biassing magnet 206 at the inner surface thereof.

Figs. 37 and 38 are a perspective view and a sectional 15 view of the upper center pin 201 and the biassing magnet 206.

The biassing magnet 206 has the shape of a ring. The upper center pin 201 is made of nonmagnetic material such as nonmagnetic stainless steel or nonmagnetic ceramics.

20 Further, the upper center pin 201 is provided with a magnet chip 207 at the top portion thereof. The magnet chip 207 is magnetized so that the top surface is a N-pole and the bottom surface is a S-pole. The biassing magnet 206 includes two half rings 206A and 206B. Each of the half rings 206A 25 and 206B is magnetized so that inner surface thereof is the N-pole and the outer surface thereof is the S-pole. As shown in Fig. 38, the S-pole of the magnet chip 207 is attracted by the N-pole of inner surface of the biassing magnet 206. In this way, the upper center pin 201 is urged downward.

S Thus, backlash between the center pins 201 and 202 and their respective receive members 203 and 204 can be eliminated.

With the ninth embodiment, the arrangement of the driving coils and driving magnets for actuating the galvano mirror 26 is the same as in the first embodiment (Fig. 7).

10 With the ninth embodiment, since a biassing force can be obtained by the biassing magnet 206 and the magnet chip 207, it is not necessary to provide a separate spring member for biassing the upper center pin 201. Thus, the structure of the galvano mirror unit can be simplified. Alternatively, 1S the magnet chip 207 can be made of ferromagnetic material.

Fig. 39 is a longitudinal sectional view showing a modification of the ninth embodiment. An upper center pin 221 of this modification is provided with a disk shaped magnet chip 222 at an axially intermediate portion thereof.

20 Further, two biassing magnets 223 and 224 are provided to the bushing 20S so that the magnet chip 222 is positioned between the biassing magnets 223 and 224.

Figs. 40 and 41 are a perspective view and a sectional view of the upper center pin 221 and the biassing magnets 25223 and 224. As shown in Fig. 40, the upper biassing magnet 223 has the shape of a ring and includes two half rings 223A and 223B. Each of the half rings 223A and 223B is magnetized so that the inner surface thereof is a N-pole and the outer surface thereof is a S-pole. The structure of the lower 5 biassing magnet 224 is the same as the biassing magnet 223.

As shown in Fig. 41, the magnet chip 222 is magnetized so that the top surface thereof is a N-pole and the bottom surface thereof is a S-pole. In this way, the magnet chip 222 is repulsed by the upper biassing magnet 223 and is attracted by the lower biassing magnet 224. That is, the upper center pin 221 is urged downward. Thus, backlash between the center pins 221 and 202 and their respective receive members 203 and 204 can be eliminated.

With such an arrangement, since a biassing force can be 15 obtained by the biassing magnets 223 and 224 and the disk shaped magnet chip 222, a relatively large biassing force can be obtained. Alternatively, the magnet chip 222 can be made of ferromagnetic material.

Tenth Embodiment 20 Fig. 42 is a sectional view of a galvano mirror unit of a tenth embodiment of the invention. In the tenth embodiment, a biassing coil 235 is employed for biassing an upper center pin 231 downward instead of the biassing magnet 206 of the ninth embodiment. The mirror holder 200 and the stator 210 are the same as in the ninth embodiment (Fig.

-- 46 - 36). The mirror holder 200 is rotatably supported by the stator 210 via the center-pins 231 and 202 and the receive member 203 and 204. The upper center pin 231 is supported by the bushing 205 mounted at the top of the stator 210, so 5 that the upper center pin 231 is axially movable therein.

Figs. 43 and 44 are a perspective view and a sectional view of the upper center pin 231 and the biassing coil 235. The upper center pin 231 is made from a nonmagnetic material such as nonmagnetic stainless steel or nonmagnetic ceramics.

10 Further, the upper center pin 231 is provided with a magnet chip 232 at the top portion thereof. The magnet chip 232 is magnetized so that the top surface thereof is a N-pole and the bottom surface thereof is a S- pole. The biassing coil 235 is provided to the bushing 205 (Fig. 42) so that the 15 biassing coil 235 surrounds the upper center pin 231. The biassing coil 235 has lead wires 235A and 235B electrically connected to a circuit (not shown). As shown in Fig. 44, when current flows in the biassing coil 235, a magnetic field (directed downward) is generated in the upper center

20 pin 231. Due to the magnetic field directed downward, the

S-pole of the magnet chip 232 is attracted downward. That is, the upper center pin 231 is biassed downward. Therefore, backlash between the center pins 231 and 202 and their respective receive members 203 and 204 can be eliminated.

25 With the tenth embodiment, the arrangement of the - 47 driving coils and driving magnets for actuating the galvano mirror 26 is the same as in the first embodiment (Fig. 7).

With the tenth embodiment, since a biassing force can be obtained by the biassing coil 235 and the upper center 5 pin 231, it is not necessary to provide a separate spring member for biassing the upper center pin 231. Thus, the structure of the galvano mirror unit can be simplified. Further, since the biassing force can be adjusted by varying the current flow in the biassing coil 235, the friction 10 produced when the mirror holder 200 is rotated can be adjusted after assembling the galvano motor unit.

Fig-. 45 is a longitudinal sectional view of a galvano mirror unit of a modification of the tenth embodiment. An upper center pin 241 of this modification is provided with 15 a magnet chip 242 at an axially intermediate portion thereof. Further, two biassing coils 245 and 246 are provided to the bushing 205 so that the magnet chip 242 is positioned between the biassing coils 245 and 246. The magnet chip 242 is magnetized so that the top surface 20 thereof is a N-pole and the bottom surface thereof is a S-pole.

Figs. 46 and 47 are a perspective view and a sectional view of the upper center pin 241 and the biassing coils 245 and 246. The biassing coils 245 and 246 have respective lead 25 wires 245A, 245B and 246A, 246B (only one of each is shown) I - 48 electrically connected to a circuit (not shown) When current flows in the biassing coils 245 and 246 in the same direction, a magnetic field (directed downward) is generated in the upper center pin 241. Due to the magnetic field being

5 directed downward, the S-pole of the magnet chip 242 is repulsed by the upper magnetic field caused by the current in the biassing coil 245 and is attracted by the lower magnetic field caused by the current in the biassing coil 246. That is, the upper center pin 241 is urged downward.

10 Thus, backlash between the center pins 241 and 202 and their respective receive members 203 and 204 can be eliminated.

With such an arrangement, since a biassing force can be obtained by the biassing coils 245 and 246 and the upper center pin 241, it is not necessary to provide a separate 15 spring member. Thus, the structure of the galvano mirror unit can be simplified. Further, the friction produced when the mirror holder 200 is rotated can be adjusted after assembling the galvano motor unit.

Eleventh Embodiment 20 Fig. 48 is a sectional view of a galvano mirror unit of an eleventh embodiment of the invention. The galvano mirror 26 is mounted to a mirror holder 250 that is rotatably supported by a stator 260. Center pins 251 and 252 are provided to the stator 260 so that the center pins 251 and 25 252 vertically sandwich the mirror holder 250. The center -- 49 - pins 251 and 252 are aligned on a line defining the rotation axis Z. The center pins 251 and 252 are received by respective receive members 253 and 254 provided at the top and the bottom of the mirror holder 250. The upper center 5 pin 251 is inserted into a bushing 255 provided to the top of the stator 250 so that the upper center pin 251 is axially movable in the bushing 255. Further, a plate spring 262 is provided to the stator 260, which urges the upper center pin 251 downward. one end of the plate spring 262 is 10 fixed to the front end of the stator 260, while the other end-of the plate spring 262 contacts the top portion of the upper center pin 251. In this way, the upper center pin 251 is rotatably supported by the stator 260 via the center pins 251 and 252 and the receive members 253 and 254.

15 In order to prevent deviation of the inclination of the upper center pin 251 in the bushing 255, an offset magnet 256 is provided to the rear side of the bushing 255. Figs.

49 and 50 are a perspective view and a sectional view of the upper center pin 251 and the offset magnet 256. The offset 20 magnet 256 is a magnet having the shape of an arc. The upper center pin 251 is made of ferromagnetic material (such as ferromagnetic stainless steel). Due to the offset magnet 256, the upper center pin 251 is attracted rearward. With such an arrangement, since the center pin 251 is biassed 25 downward by the plate spring 262, backlash between the -.50 center pin 251 (252) and the receive member 253 (254) can be eliminated. Further, the upper center pin 251 is urged rearward by the offset magnet 256 so that the direction of the inclination of the upper center pin 251 (in the bushing 5 255) is definite.

In the eleventh embodiment, the arrangement of the driving coils and driving magnets for actuating the galvano mirror 26 is the same as in the first embodiment (Fig. 7).

With the eleventh embodiment, since the offset magnet 10 256 and the plate spring 262 urge the upper center pin 251 rearward, deviation of the inclination of the upper center pin 251 is prevented. Thus, rotation of the galvano mirror 26 is stabilized.

Fig. 51 is a longitudinal sectional view of a galvano 15 mirror unit of a modification of the eleventh embodiment. In this modification, an upper center pin 265 is made of magnet. Further, front and rear offset magnets 266 and 267 are provided at the front and rear sides of the bushing 255.

Figs. 52 and 53 are a perspective view and a sectional 20 view of the offset magnets 266 and 267 and the upper center pin 265. The upper center pin 265 includes front and rear sections 265A and 265B divided by a plane 265C including the axis of the upper center pin 265. The front and rear sections 265A and 265B are a S-pole and a N-pole. Each of 25 the front and rear offset magnets 266 and 267 has a shape of - 51 an arc. Further, each of the front and rear offset magnets 266 and 267 is magnetized so that the inner surface thereof is a S-pole and the outer surface thereof is a N-pole. As shown in Fig. 53, the N-pole of the upper center pin 265 5 faces the S-pole of the rear offset magnet 267, while the S-pole of the upper center pin 265 faces the S-pole of the front offset magnet 266. Accordingly, the upper center pin 265 is repulsed by the front offset magnet 267 and attracted by the rear offset magnet 266 so that the upper center pin 10 265 is urged rearward. Thus, deviation of the inclination of the mirror holder 100 is prevented so that rotation of the galvano mirror 26 is stabilized.

Twelfth Embodiment Figs. 54 and 55 are a perspective view and a 15 longitudinal sectional view of a galvano mirror unit of a twelfth embodiment of the invention. In the twelfth embodiment, the galvano mirror 26 is mounted to a mirror holder 250. The mirror holder 250 is rotatably supported by a stator 260 via the center pins 251 and 252 and the receive 20 members 253 and 254 that are the same as in the eleventh embodiment (Fig. 48).

In order to urge the mirror holder 250 to a neutral position, two positioning magnets 271 and 272 are respectively provided around the lower receive member 254 2S and the lower center pin 252. Each of the positioning - 52 magnets 271 and 272 has the shape of a ring. The positioning magnet 271 is provided to the mirror holder 250 and the positioning magnet 272 is provided to the stator 260 so that the positioning magnets 271 and 272 face each other. Fig. 56 5 is a perspective view of the positioning magnets 271 and 272. The positioning magnet 271 includes two front and rear sections 271A and 271B which are a S-pole and a N-pole, respectively. The positioning magnet 272 includes front and rear sections 272A and 272B which are a N-pole and a S- pole, 10 respectively.

In this way, a rotational neutral position of the mirror holder 250 is obtained when the N-pole of the positioning magnet 271 faces the S-pole of the lower positioning magnet 272 and the S-pole of the upper 15 positioning magnet 271 faces the N-pole of the lower positioning magnet 272. When the mirror holder 250 rotates from the neutral position, the N-pole of the positioning magnet 271 partially faces the N-pole of the positioning magnet 272 and the S-pole of the positioning magnet 271 20 partially faces the S-pole of the positioning magnet 272. This causes a repulsive force that urges the mirror holder 2SO to return to the neutral position.

With the twelfth embodiment, the arrangement of the driving coils and driving magnets for actuating the galvano 25 mirror 26 is the same as in the first embodiment (Fig. 7).

With the twelfth embodiment, the galvano mirror is urged to a rotational neut.ral position without providing a separate spring member.

Thirteenth Embodiment 5 Figs. 57 and 58 are a perspective view and a sectional view of a galvano mirror unit of a thirteenth embodiment of the invention. The galvano mirror 26 is mounted to a mirror holder 300 that is supported by a stator 310. In order to rotatably support the mirror holder 300, a pair of center 10 pins 301 and 302 are provided at the top and bottom of the mirror holder 300. The center pins 301 and 302 are received by receive members 303 and 304 provided at the top and the bottom of the stator 310. The lower receive member 304 is fitted into a hole in the stator 310, while the upper 15 receive member 303 is fixed to a plate spring 312 provided at the top of the stator 310. In order to urge the mirror holder 300 to its neutral position, a positioning magnet 305 is provided around the lower center pin 302.

Fig. 58 is a perspective view of the lower center pin 20 302 and the lower positioning magnet 305. Figs. 59A and 59B are a plan view and a longitudinal sectional view of the lower center pin 302 and the positioning magnet 305. The lower center pin 302 includes front and rear sections 302A and 302B divided by a plane 302C including the center axis of the lower center pin 302. The front and rear sections 302A and 302B are respectively a S-pole and a N-pole. The positioning magnet 305 has- the shape of a ring and includes front and rear half- rings 305A and 305B. The front half-ring 305A is magnetized so that the inner surface thereof is a 5 N-pole and the outer surface thereof is a S-pole, while the rear halfring 305B is magnetized so that the inner surface thereof is a S-pole and the outer surface thereof is a N-pole.

In this way, a rotational neutral position of the 10 mirror holder 300 is obtained when the N-pole of the lower center pin 302 faces the S-pole of the positioning magnet 305 and the S-pole of the lower center pin 302 faces the N-pole of the positioning magnet 305. When the mirror holder 300 rotates from this neutral position, the N-pole of the 15 lower center pin 302 partially faces the N-pole of the positioning magnet 305 and the S-pole of the lower center pin 302 partially faces the S-pole of the positioning magnet 305). This causes a repulsive force that urges the mirror holder 300 to return to the neutral position.

With the thirteenth embodiment, the arrangement of the driving coils and driving magnets for actuating the galvano mirror 26 is the same as in the first embodiment (Fig. 7).

With the thirteenth embodiment, the galvano mirror is urged to its rotational neutral position without providing a separate spring member.

Fig. 60 is a perspective view showing a center pin and a magnet ring of a modification of thirteenth embodiment. In the modification, a lower center pin 306 includes four sections divided by two planes that perpendicularly cross 5 with each other at the axis of the lower center pin 306. The four sections are a S-pole, a N-pole, a S-pole and a N-pole, as taken along the circumference of the lower center pin 306. A positioning magnet 307 has the shape of a ring and includes four arc-shaped portions 307A, 307B, 307C and 307D, 10 a center angle of each arc-shaped portion being 90 degrees.

In this way, a rotational neutral position of the mirror holder 300 is obtained when the N-poles of the lower center pin 306 face the S-poles of the positioning magnet 307 and the S-poles of the lower center pin 306 face the 15 N-poles of the positioning magnet 307. When the mirror holder 300 rotates from this neutral position, the N-poles of the lower center pin 306 partially face the N-poles of the positioning magnet 307 and the S- poles of the lower center pin 306 partially face the S-poles of the positioning 20 magnet 307). This causes a repulsive force that urges the mirror holder 300 to the neutral position.

With such an arrangement, the galvano mirror is urged to the rotational neutral position without providing a separate spring member.

25 Although the structure and operation of agalvano - 56 mirror unit is described herein with respect to the preferred embodiments, many modifications and changes can be made without departing from the scope of the invention. For example, whilst pins have been described for the purpose of 5 rotationally mounting the rotor to the stator, it will be appreciated that other rotational mountings can be employed. In this respect, the pins can be replaced by balls, needles or other elements whereby the rotor is pivoted by the engagement of said rotation mounting or element and some 10 form of receiving member or locating member provided on the stator. Of course, the mountings on the stator and rotor can be reversed.

Furthermore, the embodiments can be embodied in any kind of optical disk drive and are not limited to an optical 15 disk drive using the Near Field Recording technology.

Claims

1. A galvano mirror unit comprising:

a galvano mirror; a rotor to which said galvano mirror is mounted; a stator that rotatably supports said rotor about a rotation axis; first and second center pins provided to said stator; first and second receive members provided to said rotor, which respectively receive said first and second center pins; and a biassing member provided to said stator which biases said first center pin to said first receive member thereby to eliminate backlash between said first center pin and said 15 first receive member and between said second center pin and said second receive member.

2. A galvano mirror unit according to claim 1 wherein said biassing member comprises a plate spring.

3. A galvano mirror unit according to claim 2 wherein said first center pin and said plate spring are mechanically coupled with each other thereby to prevent deviation of the inclination of said first center pin.

- 58 4. A galvano mirror unit according to claim 2 or 3 wherein said plate spring has an engaging hole, and said first center pin has a protrusion that fits into said engaging hole. 5 S. A galvano mirror unit according to claim 2 or 3 wherein said first center pin and said plate spring are adhered with each other.

10 6. A galvano mirror unit according to claim 1 wherein said biassing member comprises a plurality of plate springs, said plurality of plate springs being arranged in the direction of said rotation axis.

15 7. A galvano mirror unit comprising:- a galvano mirror; a rotor to which said galvano mirror is mounted; a stator that rotatably supports said rotor about a rotation axis; 20 first and second center pins provided to said stator; first and second receive members provided to said rotor, said first and second receive members respectively receiving said first and second center pins; a biassing magnet provided to said stator so that said 25 biassing magnet is located around said first center pin; and S9 a magnetic chip provided to a predetermined portion of said first center pin, wherein the magnetic force generated between said biassing magnet and said magnetic chip biases said first S center pin towards said first receive member.

8. A galvano mirror unit according to claim 7 wherein said biassing magnet comprises a ring-shaped magnet.

9. A galvano mirror unit according to claim 7 or 8 wherein said biassing magnet is located between said magnetic chip and said first receive member in the direction of said rotation axis; and wherein said biassing magnet attracts said magnetic 1S chip thereby to bias said first center pin.

10. A galvano mirror unit according to claim 7 wherein said biassing magnet comprises two ring-shaped magnets disposed in the direction of said rotation axis.

11. A galvano mirror unit according to claim 10 wherein said magnetic chip is located between said two ring-shaped magnets in the direction of said rotation axis.

2S 12. A galvano mirror unit according to claim 11 wherein - 60 said biassing magnet attracts one of said ring-shaped magnets and repulses the other of said ring-shaped magnets.

13. A galvano mirror unit comprising:

5 a galvano mirror; a rotor to which said galvano mirror is mounted; a stator that rotatably supports said rotor about a rotation axis; first and second center pins provided to said stator; 10 first and second receive members provided to said rotor, said first and second receive members respectively receiving said first and second center pins; a biassing coil provided to said stator, said biassing coil being arranged to surround said first center pin; and is a magnetic chip provided to a predetermined portion of said first center pin, wherein during current to flow in said biassing coil, said first center pin is biassed to said first receive member.

14. A galvano mirror unit according to claim 13 wherein said biassing coil is located between said magnetic chip and said first receive member in the direction of said rotation axis.

- 61 15. A galvano mirror unit according to claim 13 or 14 wherein a biassing force can be adjusted by varying current flow in said biassing coil.

5 16. A galvano mirror unit according to any one of claims 13 to 15 wherein said first center pin is made of non-magnetized material.

17. A galvano mirror unit comprising:- 10 a galvano mirror; a rotor to which said galvano-mirror is mounted; a 'stator that rotatably supports said rotor about a rotation axis; first and second center pins provided to said stator; is first and second receive members provided to said rotor, said first and second receive members respectively receiving said first and second center pins; two biassing coils provided to said stator, said biassing coils being arranged to surround said first center pin; and a magnetic chip provided to a predetermined portion of said first center pin, wherein during current flow in said biassing coils, said first center pin is biassed to said first receive member.

- 62 18. A galvano mirror unit according to claim 17 wherein said magnetic chip is located between said two biassing coils.

5 19. A galvano mirror unit substantially as herein described with reference to figures 2 to 61B of the accompanying drawings.

(1-1 Amendments to the claims have been filed as follows 1. A gaivano mirror unit comprising:

4. A galvano mirror unit according to claim 2 or 3 wherein said plate spring has an- engaging hole, and said first center pin has a protrusion that fits into said engaging hole.

S S. A galvano mirror unit according to claim 2 or 3 wherein said first center pin and said plate spring are adhered with each other.

15 7. A galvano mirror unit comprising:- a galvano mirror; A rotor to which said galvano mirror is mounted; a stator that rotatably supports said rotor about a rotation axis; 20 first and second center pins provided to said stator; first and second receive members provided to said rotor, said first and second receive members respectively receiving said first and second center pins; a biassing magnet provided to said stator so that said 25 biassing magnet is located around said first center pin; and - (05 - a magnetic chip provided to a predetermined portion of said first center pin, - wherein the magnetic force generated between said biassing magnet and said magnetic dhip biases said first 5 center pin towards said first receive member.

10 9. A galvano mirror unit according to claim 7 or 8 wherein said biassing magnet is located between said magnetic chip and said first receive member in the direction of said rotation axis; and wherein said biassing magnet attracts said magnetic 15 chip thereby to bias said first center pin.

12. A galvano mirror unit according to claim 11 wherein - loko said biassing magnet attracts one of said ring-shaped magnets and repulses the other of said ring-shaped magnets.

13. A galvano mirror unit comprising:

15. A galvano mirror unit according to claim 13 or 14,wherein a biassing force can be adjusted by varying current flow in said biassing coil.

174 A galvano mirror unit comprising:- 10 a galvano mirror; a rotor to which said galvano-mirror is mounted; a stator that rotatably supports said rotor about a rotation axis; first and second center pins provided to said stator; is first and second receive members provided to said rotor, said first and second receive member s respectively receiving said first and second center pins; two biassing coils provided to said stator, said biassing coils being arranged to surround said first center 2 0 pin; and a magnetic chip provided to a predetermined portion of said first center pin, wherein during current flow in said biassing coils, said first center pin is biassed to said first receive member.

-.4- 18. A galvano mirror unit according to claim 17 wherein said magnetic chip is located between said two biassing coils.

19. A galvano mirror unit substantially as herein described with reference to figures 12 to 23 and 36 to 56 of the accompanying drawings.