II 1111111111111
`
`United States Patent [19]
`Futagawa et al.
`
`[11]
`
`[45]
`
`US005719834A
`Patent Number:
`Date of Patent:
`
`5,719,834
`Feb. 17, 1998
`
`[54] OBJECTIVE LENS DRIVING APPARATUS
`AND METHOD INCLUDING VISCO(cid:173)
`ELASTIC SUPPORT FOR A MAGNETIC
`CIRCUIT WHICH ALLOWS TRANSLATION
`OF THE MAGNETIC CIRCUIT WITHOUT
`PIVOTING OR ROTATING THERE OF
`
`[75]
`
`Inventors: Masayaso Futagawa; Keiji Sakai. both
`of Nara; Toshiyuki Tanaka, Moriguchi,
`all of Japan
`
`[73] Assignee: Sharp Kabosbiki Kaisba, Osaka, Japan
`
`[21] AppL No.: 671,510
`Jun. 27, 1996
`
`[22] Filed:
`
`Related U.S. AppHcation Data
`
`[63] Conlinuatiou of Ser. No. 315,349, Sep. 30, 1994, Pat No.
`5,602,808.
`Foreign AppHcation Priority Data
`
`[30]
`
`Oct. 1, 1993
`Japan .................................... S-247215
`[JP]
`Int. CL 6 ..................................................... G 118 7/085
`[51]
`[52] U.S. Cl ....... - ............................ 369144.14; 369/44.15;
`369/44.16; 359/823
`[58] Field of Search .............................. 369/44.14, 44.15,
`369/44.16, 44.21. 44.22; 3591813, 814,
`823,824
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`S,o70,489 12/1991 Perry et al ........................... 369/44.16
`5,164,936 1U1992 Kagami ................................ 369/44.15
`7/1993 Matsuzaki et al ................... 369/44.16
`5,228,017
`5,463,612 1011995 Date ..................................... 369/44.16
`
`FOREIGN PATENT DOCUMENTS
`
`432035
`4245033
`
`2/1992
`9/1992
`
`Japan.
`Japan .
`
`Primary &aminer-Thang V. Tran
`ABSTRACT
`
`[57]
`
`An objective lens driving apparatus includes a base. an
`objective lens for converging an optical beam on an optical
`disc while 1he optical disc is rotating. and a holding member
`for holding the objective lens. A first supporting mechanism
`elastically supports 1he holding member on 1he base in such
`a manner as to allow 1he holding member to be translated in
`a focusing direction which is substantially perpendicular to
`a surface of the optical disc and in a tracking direction which
`is substantially perpendicular to the focusing direction and
`parallel to a radial direction of the optical disc. A moving
`mechanism including a coil and a magnetic circuit for
`translates the holding member in the focusing direction and
`the tracking direction by a driving force generated by the
`coil and the magnetic circuit. A second supporting mecha(cid:173)
`nism for visco-elastically supports the magnetic circuit on
`the base in such a manner as to translate the magnetic circuit
`in the focusing direction. The magnetic circuit is translated
`in an opposite direction to the translation direction of the
`holding member by a driving force acting oppositely to the
`driving force for translating the holding member in the
`focusing direction.
`
`4,615,585 10/1986 Van Sluys et al ............ - .... 369/44.16
`
`24 Claims, 14 Drawing Sheets
`
`Focusing direction
`
`31c
`
`LG Electronics, Inc. et al.
`EXHIBIT 1009
`IPR Petition for
`U.S. Patent No. 6,785,065
`
`

`
`U.S. Patent
`
`Feb. 17, 1998
`
`Sheet 1 of 14
`
`5,719,834
`
`FIG.1
`
`Focusing direction
`
`31
`
`31c
`
`31b
`
`Tracking direction
`
`21
`
`23 23
`
`31a
`
`

`
`U.S. Patent
`
`Feb. 17, 1998
`
`Sheet 2 of 14
`
`5,719,834
`
`FIG.2
`
`25
`
`-
`31 - t-
`31c
`
`- r
`
`22
`\
`
`1s
`
`~
`
`12b 12 12a
`14 I
`\
`I
`.-.,\
`
`J
`
`I
`
`I
`I
`22
`
`\
`\
`\
`
`I J -
`I
`} l
`~
`23 31b
`21
`~
`26
`
`I
`
`I
`1
`J
`10
`
`1
`I
`
`13
`)
`
`1?
`
`-r-
`
`31a
`
`

`
`U.S. Patent
`
`Feb. 17, 1998
`
`Sheet 3 of 14
`
`5,719,834
`
`FIG.3
`
`122
`
`31c
`
`Focusing direction
`
`Tracking direction
`
`2
`
`/
`
`31b
`
`

`
`U.S. Patent
`
`Feb. 17, 1998
`
`Sheet 4 of 14
`
`5,719,834
`
`FIG.4
`
`Focusing direction
`
`Tracking direction
`
`13
`
`

`
`U.S. Patent
`
`Feb. 17, 1998
`
`Sheet 5 of 14
`
`5,719,834
`
`FIG.5
`222
`a
`\
`
`~
`
`31c
`
`-...
`t-
`
`I II'"
`
`21 23
`I
`222
`i
`I
`l
`I
`222b
`
`12
`\
`\' .\ ~ I
`I_
`
`3
`J
`-
`
`-r-
`
`31a
`
`13
`I
`
`13
`(
`
`I
`
`I
`
`14
`
`L
`
`j
`
`15
`
`I
`10
`
`

`
`U.S. Patent
`
`Feb. 17, 1998
`
`Sheet 6 of 14
`
`5,719,834
`
`FIG.6
`
`322
`21
`23
`
`31
`
`

`
`U.S. Patent
`
`Feb. 17, 1998
`
`Sheet 7 of 14
`
`5,719,834
`
`FIG.7
`
`Focusing direction
`
`Tracking direction
`
`31c
`
`14
`
`10
`
`13
`
`31a
`
`

`
`U.S. Patent
`
`Feb. 17, 1998
`
`Sheet 8 of 14
`
`5,719,834
`
`FIG.B
`
`54
`
`31c
`
`52 50 15 14
`
`12
`
`31a
`
`31b
`
`10
`
`

`
`U.S. Patent
`
`Feb. 17, 1998
`
`Sheet 9 of 14
`
`5,719,834
`
`FIG.9
`
`34
`
`61
`
`Tracking
`direction
`
`31 c,
`
`62
`
`63
`
`

`
`U.S. Patent
`
`Feb. 17, 1998
`
`Sheet 10 of 14
`
`5,719,834
`
`FIG. tO
`
`21
`
`22
`
`22
`
`32
`
`7
`
`/
`
`31a"
`
`36
`
`

`
`U.S. Patent
`
`Feb. 17, 1998
`
`Sheet 11 of 14
`
`5,719,834
`
`FIG.11
`
`..,.......,
`
`-- .......
`--I-"'
`~ __.,..
`---
`
`p
`
`I
`1'\1
`'i
`f'\:
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`71
`r1
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`_.,;
`v
`
`\.
`
`v "
`"
`'
`'
`'
`
`........
`
`.... _
`' ..........._
`
`........
`
`""'t--..
`
`-"-
`
`10d8
`
`.........
`
`........
`
`]"-...
`
`10
`
`100
`
`t-
`
`Conventional
`
`Present
`invention
`
`F'j.,..
`1K
`(Hz)
`
`

`
`U.S. Patent
`
`Feb. 17, 1998
`
`Sheet 12 of 14
`
`5,719,834
`
`FIG.12
`
`-.-
`
`~
`
`10
`
`1\
`
`I
`
`/'-
`
`..... _
`
`""" .........
`
`v
`
`...........
`
`10d8
`
`100
`
`I
`I
`I
`I
`I
`
`./ \
`
`I"-- -1--.
`
`~
`t-1-
`I"'
`
`Conventional
`Present
`invention
`
`i
`
`1K
`(Hz)
`
`

`
`U.S. Patent
`
`Feb. 17, 1998
`
`Sheet 13 of 14
`
`5,719,834
`
`FIG.13
`PRIOR ART
`
`31
`
`Focusing direction
`
`Tracking direction
`
`100
`
`/
`
`13
`
`

`
`U.S. Patent
`
`Feb. 17, 1998
`
`Sheet 14 of 14
`
`5,719,834
`
`FIG.14
`PRIOR ART
`
`Ft
`
`12
`_\
`
`J
`
`100
`/
`
`.-
`
`1(
`
`13
`)
`
`I
`
`I
`
`Q 14
`15
`/r-fl
`v/~ 1 I -
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`r---
`
`31 -....... 1-
`
`.-I--
`
`_I_
`
`/ I I
`1 11
`21 23
`
`,.
`
`

`
`5,719,834
`
`1
`OBJECTIVE LENS DRIVING APPARATUS
`AND METHOD INCLUDING VISCO(cid:173)
`ELASTIC SUPPORT FOR A MAGNETIC
`CIRCUIT WHICH ALLOWS TRANSLATION
`OF THE MAGNETIC CIRCUIT WITHOUT
`PIVOTING OR ROTATING THERE OF
`
`5
`
`This is a continuation of application Ser. No. 08/315349,
`filed on Sep. 30. 1994, now U.S. Pat. No. 5,602,808, the
`entire contents of which are hereby incorporated by refer- 10
`ence.
`
`BACKGROUND OF THE INVENTION
`
`2
`focusing direction and is conveyed to the carriage 31 via the
`springs 13, thereby vibrating the carriage 31. The driving
`force F2 vibrates the yoke 21 of the magnetic circuit 26 and
`the carriage 31 on which the yoke 21 is fixed.
`The vibration of the carriage 31 caused by the driving
`forces F1 and F2 is conveyed to the optical disc through the
`guiding mechanism and the driving mechanism. If such a
`path for conveying the vibration has a specific resonance
`point. focusing servo control is impossible. Such a problem.
`which occurs more easily and more frequently today when
`less rigid components are used in the optical disc drives in
`order to reduce the size and weight of the drives, is a barrier
`against further reduction in the size and weight of the drives.
`Japanese Laid-Open Patent Publication No. 4-32035
`15 proposes, as one of the solutions of such a problem. insertion
`of a visco-elastic body such as rubber or a spring into the
`conveying path of the vibration in order to damp the
`vibration. Such a method has problems in that, for example,
`positioning precision of the components of the objective lens
`20 driving apparatus is lowered. Especially the method.
`described in the above-mentioned publication, of visco(cid:173)
`elastically supporting the magnetic circuit by rubber or a
`cantilever spring tends to present problems in that sufficient
`damping is not obtained, and in that the magnetic circuit is
`25 inclined by the movement of the objective lens holder and
`thus contacts the coil.
`Japanese Laid-Open Patent Publication No. 4-245033
`proposes provision of a device for generating a vibration
`30 having the same magnitude with and the opposite phase to
`the vibration generated by the movement of the objective
`lens holder in order to counteract the vibration. Provision of
`such a device increases the number of the components and
`the size of the apparatus.
`
`~
`
`1. Field of the Invention
`The present invention relates to an objective lens driving
`apparatus, and in particular to an objective lens driving
`apparatus for use in an optical disc drive for recording on an
`optical disc or reproducing data from the optical disc while
`the optical disc is rotating.
`2. Description of the Related Art
`The above-described type of optical disc drives are pro(cid:173)
`vided with an objective lens driving apparatus for moving an
`objective lens in a focusing direction and a tracking direc(cid:173)
`tion. In this specification, the focusing direction refers to the
`direction perpendicular to a surface of the optical disc, and
`the tracking direction refers to a direction horizontal and
`parallel to the radial direction of the optical disc.
`Briefly referring to FIGS. 13 and 14, a conventional
`objective lens driving apparatus 100 will be described. FIG.
`13 is a perspective view of the objective lens driving
`apparatus 100, and FIG. 14 is a side view of the objective
`lens driving apparatus 100. In this specification, the focusing
`direction and the tracking direction are set as shown in FIG.
`l l
`As is illustrated in FIGS. 13 and 14, an objective lens 11
`is supported by an objective lens holder 12 in a state where
`the optical axis thereof is perpendicular to the surface of an
`optical disc (not shown). In such a state, the objective lens
`11 converges an optical beam on the optical disc. The
`objective lens holder 12 is attached to a carriage 31 via four
`springs 13. The four springs 13 support the objective lens
`holder 12 in such a manner that the objective lens holder 12
`is movable in the focusing direction and the tracking direc-
`tion. To the objective lens holder 12, a focusing coil 14 and
`a tracking coil lS are attached as well as the objective lens
`11. The focusing coil 14, the tracking coil IS, and a pair of
`magnets 23 are included in an actuator for moving the
`objective lens holder 12 in the focusing direction and the
`tracking direction. The magnets 23 are attached to a yoke 21
`which is fixed to the carriage 31. The magnets 23 and the
`yoke 21 are included in a magnetic circuit 26.
`The objective lens driving apparatus 100 having the
`above-described structure operates in the following manner. 55
`While the data is recorded on the optical disc or the data
`is reproduced from the optical disc, appropriate focusing
`servo control and tracking servo control are performed on
`the actuator. The carriage 31 moves in the tracking direction
`by a guiding mechanism and a driving mechanism (not 60
`shown), for example, a chassis or a spindle motor.
`When a driving current flows through the focusing coil
`14, driving forces F1 and F2 (FIG. 14) are generated and act
`on the focusing coil 14 and the magnetic circuit 26, respec(cid:173)
`tively. The driving forces Fl and F2 have the same magni- 65
`tude and act in opposite directions from each other. The
`driving force F1 moves the objective lens holder 12 in the
`
`50
`
`40
`
`45
`
`SUMMARY OF THE INVENTION
`One aspect of the present invention relates to an objective
`lens driving apparatus including a base; an objective lens for
`converging an optical beam on an optical disc while the
`optical disc is rotating; a holding member for holding the
`objective lens; a first supporting mechanism for elastically
`supporting the holding member on the base in such a manner
`as to allow the holding member to be translated in a focusing
`direction which is substantially perpendicular to a surface of
`the optical disc and in a tracking direction which is sub(cid:173)
`stantially perpendicular to the focusing direction and parallel
`to a radial direction of the optical disc; a moving mechanism
`including a coil and a magnetic circuit for translating the
`holding member in the focusing direction and the tracking
`direction by a driving force generated by the coil and the
`magnetic circuit; and a second supporting mechanism for
`visco-elastically supporting the magnetic circuit on the base
`in such a manner as to translate the magnetic circuit in the
`focusing direction. The magnetic circuit is translated in an
`opposite direction to the translation direction of the holding
`member by a driving force acting oppositely to the driving
`force for translating the holding member in the focusing
`direction.
`Another aspect of the present invention relates to an
`objective lens driving apparatus including a base; an objec(cid:173)
`tive lens for converging an optical beam on an optical disc
`while the optical disc is rotating; a holding member for
`holding the objective lens; a first supporting mechanism for
`elastically supporting the holding member on the base in
`such a manner as to allow the holding member to be
`translated in a focusing direction which is substantially
`perpendicular to a surface of the optical disc and in a
`
`

`
`5,719,834
`
`4
`FIG. 13 is a perspective view of a conventional objective
`lens driving apparatus; and
`FIG. 14 is a side view of the conventional objective lens
`driving apparatus shown in FIG. 13.
`
`DESCRIPITON OF THE PREFERRED
`EMBODIMENTS
`
`Hereinafter, the present invention will be described by
`way of illustrative examples with reference to the accom-
`10 panying drawings.
`
`3
`tracking direction which is substantially perpendicular to the
`focusing direction and parallel to a radial direction of the
`optical disc; a moving mechanism including a coil and a
`magnetic circuit for translating the holding member in the
`focusing direction and the tracking direction by a driving 5
`force generated by the coil and the magnetic circuit; and a
`second supporting mechanism for visco-elastically support(cid:173)
`ing the magnetic circuit on the base in such a manner as to
`vibrate the magnetic circuit in the focusing direction at the
`lowest resonance frequency thereof. The magnetic circuit is
`translated in an opposite direction to the translation direction
`of the holding member by a driving force acting oppositely
`to the driving force for translating the holding member in the
`focusing direction.
`Thus, the invention described herein makes possible an 15
`advantage of providing an objective lens driving apparatus
`in which vibration generated by the movement of an objec(cid:173)
`tive lens holder in the focusing direction and the tracking
`direction can be effectively restricted without causing a
`magnetic circuit to contact a coil, or without increasing the 20
`number of components or the size of the objective lens
`driving apparatus.
`This and other advantages of the present invention will
`become apparent to those skilled in the art upon reading and
`understanding the following detailed description with refer- 25
`ence to the accompanying figures.
`The present invention will become more fully understood
`from the detailed description given hereinbelow and the
`accompanying drawings which are given by way of illus-
`tration only, and thus are not limitative of the present
`invention, and wherein.
`
`30
`
`(Example 1)
`With reference to FIGS. 1 and 2, an objective lens driving
`apparatus 1 in a first exemplary embodiment of the present
`invention will be described. FIG. 1 is a perspective view of
`the objective lens driving apparatus 1, and FIG. 2 is a side
`view of the objective lens driving apparatus 1.
`As is illustrated in FIGS. 1 and 2, an objective lens 11 is
`supported by an objective lens holder 12 in a state where the
`optical axis thereof is perpendicular to a surface of an q_:~tical
`disc (not shown). In such a state, the objective lens 11
`converges an optical beam onto the optical disc. The objec(cid:173)
`tive lens holder 12 is attached to a carriage 31 acting as a
`base via four springs 13 acting as first supporting means
`each formed of an elastic wire. The four springs 13 allow the
`objective lens holder 12 to move mainly in the focusing
`direction and the tracking direction. The carriage 31 includes
`a horizontal portion 31b and vertical portions 31a and 31c
`each extended perpendicularly from the respective ends of
`the horizontal portion 3lb. Thus, the carriage 31 has a
`substantially C-shaped vertical cross section. The four
`springs 13 are each fixed at both ends thereof to the surface
`of the vertical portion 31a opposed to the vertical portion
`31c and a vertical portion 12b (FIG. 2) of the objective lens
`holder 12. A mirror 10 for guiding the optical beam emitted
`from an optical source (not shown) to be incident on the
`objective lens 11 is located on the horizontal portion 31b.
`As is shown in FIG. 2, the objective lens holder 12
`40 includes a lens retaining portion 12a in which the objective
`lens 12 is fixed and the vertical portion 12b. A focusing coil
`14 is fixed on a surface of the vertical portion l2b opposed
`to the vertical portion 31c, and a tracking coil15 is fixed on
`the focusing coil 14. The focusing coil 14, the tracking coil
`45 15 and the objective lens holder 12 are included in a
`movable section 25. The focusing coil 14, the tracking coil
`15 and a magnetic circuit 26 are included in an actuator for
`moving the objective lens holder 12 in the focusing direction
`and the tracking direction.
`The magnetic circuit 26 includes a pair of magnets 23
`located so as to interpose the tracking coil 15 and also
`includes a yoke 21 on which the magnets 23 are fixed. One
`of the magnets 23 is inserted into the focusing coil 14. The
`yoke 21 is visco-elastically supported on the carriage 31 by
`55 a pair of leaf springs 22 acting as second supporting means.
`The leaf springs 22 are fixed at both ends thereof to the
`vertical portion 31c and the yoke 21 in the state where main
`surfaces thereof are horizontal and parallel to each other in
`the focusing direction. The leaf springs 22 are attached to a
`60 top end and a bottom end of the yoke 21. respectively.
`Preferably, the leaf springs 22 are attached to the magnetic
`circuit 26 in such a manner that the supporting center of the
`leaf springs 22 corresponds with the center of gravity of the
`magnetic circuit 26. The leaf springs 22 have substantially
`65 the same elastic constant.
`The objective lens driving apparatus 1 having the above(cid:173)
`described structure operates in the following manner.
`
`35
`
`50
`
`BRIEF DESCRII'I10N OF TilE DRAWINGS
`FIG. 1 is a perspective view of an objective lens driving
`apparatus in a first exemplary embodiment of the present
`invention;
`FIG. 2 is a side view of the objective lens driving
`apparatus shown in FIG. 1;
`FIG. 3 is a perspective view of an objective lens driving
`apparatus in a second exempalary embodiment of the
`present invention;
`FIG. 4 is a perspective view of an objective lens driving
`apparatus in a third exemplary embodiment of the present
`invention;
`FIG. 5 is a side view of the objective lens driving
`apparatus shown in FIG. 4;
`FIG. 6 is a perspective view of an objective lens driving
`apparatus in a fourth exemplary embodiment of the present
`invention;
`FIG. 7 is a perspective view of an objective lens driving
`apparatus in a fifth exemplary embodiment of the present
`invention;
`FIG. 8 is a side view of the objective lens driving
`apparatus shown in FIG. 7;
`FIG. 9 is a partial top view of an objective lens driving
`apparatus in a sixth exemplary embodiment of the present
`invention;
`FIG. 10 is an exploded perspective view of an objective
`lens driving apparatus in a seventh exemplary embodiment
`of the present invention;
`FIGS. 11 and 12 are each a graph illustrating the transfer
`function of the vibration of a mounting plate with respect to
`the vibration of an objective lens holder in the objective lens
`driving apparatus shown in FIG. 10 and in a conventional
`objective lens driving apparatus;
`
`

`
`5
`When a driving current flows through the focusing coil
`14, a driving force F1 acting in the focusing direction is
`generated. The driving force F1 translates the objective lens
`holder 12 in the focusing direction. Simultaneously. a driv(cid:173)
`ing force F2 equal in magnitude with and opposjte in acting 5
`direction to the driving force F1 is generated. The driving
`force F2 translates the magnetic circuit 26 in the opposite
`direction to the translation direction of the objective lens
`holder 12 without pivoting the magnetic circuit 26 toward
`the vertical portion 31c. The pivoting movement of the 10
`magnetic circuit 26 is substantially prohibited by the leaf
`springs 22 arranged parallel to each other in the focusing
`direction.
`The translation of the magnetic circuit 26 in the opposite
`direction to the translation direction of the objective lens 15
`holder 12 counteracts the vibration generated by the move(cid:173)
`ment of the objective lens holder 12 in the focusing direc(cid:173)
`tion. Accordingly, the vibration caused by the movement of
`the objective lens holder 12 in the focusing direction can be
`significantly reduced. As a result, a stable focusing servo 20
`control can be realized.
`Further, as is described above, the leaf springs 22 are
`arranged parallel to each other in the focusing direction. As
`a result, the magnetic circuit 26 is substantially prohibited
`from pivoting toward the vertical portion 31c while being
`translated oppositely to the objective lens holder 12 in the
`focusing direction. For this reason, the yoke 21 and the
`magnets 23 are kept out of contact with the focusing coil14
`and the tracking coil 15. Accordingly, the distance between
`the magnetic circuit 26 and each of the coils 14 and 15 can
`be set at a minimum possible distance. Such a short distance
`is advantageous in reducing the total size of the objective
`lens driving apparatus 1.
`The leaf springs 22 are formed of, for example, phospho(cid:173)
`rus bronze, beryllium bronze, or stainless steel. Phosphorus
`bronze is less expensive than the other materials. Beryllium
`bronze and stainless steel are high in resistance against
`wearing and corrosion, respectively. The leaf springs 22
`formed of one of the above-mentioned materials are strong
`against deformation during assembly of the objective lens
`driving apparatus 1, and the characteristics thereof are not
`changed much in accordance with the temperature.
`As is described above, the leaf springs 22 are preferably
`located in such a position that the supporting center of the
`leaf springs 22 corresponds with the center of gravity of the
`magnetic circuit 26. Even if the supporting center of the leaf
`springs 22 is offset from the center of gravity of the magnetic
`circuit 26, the vibration conveyed to the carriage 31 for the
`lack of counteraction due to such positional offset presents
`no problem as long as the vibration is too small to cause any
`trouble in performing focusing servo control.
`In the first example, a pair of leaf springs 22 are provided
`for visco-elastically supporting the magnetic circuit 26 in the
`state where the main surfaces thereof are arranged parallel to
`each other in the focusing direction. In such a structure,
`since the leaf springs 22 are highly rigid against deformation
`in all directions except for the direction perpendicular to the
`main surfaces thereof, namely. the focusing direction, the
`leaf springs 22 are untwisted even when exposed to the
`driving force F2. In other words, the magnetic circuit 26
`vibrates at the lowest resonance frequency thereof in the
`focusing direction. Thus, the magnetic circuit 26 is not
`inclined in any direction. Accordingly, the magnetic circuit
`26 is kept out of contact with the coils 14 and 15, which
`allows the distance between the magnetic circuit 26 and each
`of the coils 14 and 15 to be set at a minimum possible
`
`40
`
`35
`
`5,719,834
`
`6
`distance. This is advantageous in reducing the total size of
`the objective lens driving apparatus 1.
`
`(Example 2)
`
`With reference to FIG. 3, an objective lens driving appa(cid:173)
`ratus 2 in a second exemplary embodiment of the present
`invention will be described. FIG. 3 is a perspective view of
`the objective lens driving apparatus 2. Identical elements
`with those in the first example will bear identical reference
`numerals therewith, and explanation thereof will be omitted.
`In the second example, a pair of hinges 122 are provided
`for visco-elastically supporting the magnetic circuit 26
`instead of the pair of leaf springs 22. The hinges 122 are
`each a plate having two V-shaped grooves on a main surface
`thereof. The hinges 122 are attached to the vertical portion
`31c in the state where the surfaces thereof having the
`V-grooves are horizontal and parallel to each other one
`above the other. Further, the surfaces of the hinges 122
`having the V-shaped grooves are opposed to each other.
`Since the hinges 122 function in the same way as the leaf
`springs 22, the objective lens driving apparatus 2 operates in
`the same manner as the objective lens driving apparatus 1.
`Thus, the vibration caused by the movement of the objective
`lens holder 12 in the focusing direction is significantly
`25 reduced by counteraction.
`As is described above, the surfaces of the hinges 122
`having the V-shaped grooves are arranged parallel to each
`other one above the other. By such arrangement, the reaction
`30 force of the hinges 122 is generated in the focusing direc(cid:173)
`tion. Accordingly, the magnetic circuit 26 is prohibited from
`pivoting toward the vertical portion 31c while being trans(cid:173)
`lated oppositely to the objective lens holder 12. For this
`reason, the yoke 21 and the magnets 23 are kept out of
`contact with the focusing coil 14 and the tracking coil 15.
`This allows the distance between the magnetic circuit 26 and
`each of the coils 14 and 15 to be set at a minimum possible
`distance. As a result, the objective lens driving apparatus 2
`can be reduced in size, while greatly reducing the vibration
`of the carriage 31 caused by the movement of the objective
`lens holder 12 in the focusing direction.
`The hinges 122 are formed of. for example, a resin such
`as thermoplastic polyester elastomer, which is high in resis(cid:173)
`tance against wearing. The hinges 122 formed of a resin.
`45 which can be produced by molding, are easy to mass(cid:173)
`produce. The hinges 122 formed of a resin can be molded
`integrally with the vertical portion 31c or a member for
`attaching the hinges 122 to the yoke 21. Since there is little
`possibility that the hinges 122 formed of a resin might be
`50 deformed during the assembly, the assembly of the objective
`lens driving apparatus 2 can be performed more easily and
`at a higher yield.
`As in the first example, the hinges 122 are preferably
`located in such a manner that the supporting center of the
`55 hinges 122 corresponds with the center of gravity of the
`magnetic circuit 26. Such correspondence is not absolutely
`necessary as long as the vibration conveyed to the carriage
`31 for the lack of counteraction due to such positional offset
`is too small to cause any trouble in performing focusing
`60 servo control.
`In the second example. a pair of hinges 122 are provided
`for visco-elastically supporting the magnetic circuit 26 in the
`state where the surfaces thereof having the V-shape grooves
`are parallel to each other one above the other. In such a
`65 structure, since the hinges 122 are highly rigid against
`deformation in all directions except for the direction per(cid:173)
`pendicular to the surfaces thereof having the V-shaped
`
`

`
`5,719,834
`
`7
`grooves, namely. the focusing direction, the hinges U2 are
`untwisted even when exposed to the driving force F2. In
`other words. the magnetic circuit 26 vibrates at the lowest
`resonance frequency thereof in the focusing direction. Thus,
`the magnetic circuit 26 is not inclined in any direction.
`Accordingly, the magnetic circuit 26 is kept out of contact
`with the coils 14 and 15, which allows the distance between
`the magnetic circuit 26 and each of the coils 14 and 15 to be
`set at a minimum possible distance. This is advantageous in
`reducing the total size of the objective lens driving apparatus 10
`2.
`
`8
`tion. In other words, the magnetic circuit 26 vibrates at the
`lowest resonance frequency thereof in the focusing direc(cid:173)
`tion. Accordingly. the magnetic circuit 26 is not inclined in
`any direction. Thus, the magnetic circuit 26 is kept out of
`5 contact with the coils 14 and 15, which allows the distance
`between the magnetic circuit 26 and each of the coils 14 and
`15 to be set at a minimum possible distance. As a result, the
`total size of the objective lens driving apparatus 3 can be
`reduced.
`
`(Example 4)
`
`(Example 3)
`
`With reference to FIGS. 4 and 5, an objective lens driving
`apparatus 3 in a third examplary embodiment of the present
`invention will be described. FIG. 4 is a perspective view of
`the objective lens driving apparatus 3, and FIG. 5 is a side
`view of the objective lens driving apparatus 3. Identical
`elements with those in the first example will bear identical
`reference numerals therewith, and explanation thereof will
`be omitted.
`In the third example, two pairs of elastic wires 222a and
`222b are provided for visco-elastically supporting the mag(cid:173)
`netic circuit 26. The upper pair of wires 222a are attached to
`top corners of the yoke 21, and the lower pair of wires 222b
`(only one wire is shown in FIG. 4) are attached to the bottom
`corners of the yoke 21. All the four wires 222a and 222b are
`horizontal The distance between the wires 222a and the
`distance between the wires 222b are each expanded from the
`yoke 21 toward the vertical portion 31c of the carriage 31.
`Since the pairs of wires 222a and 222b function in the same
`manner as the leaf springs 22, the objective lens driving
`apparatus 3 operates in the same way as the objective lens
`driving apparatus 1. Thus, the vibration caused by the
`movement of the objective lens holder 12 in the focusing
`direction is significantly reduced by counteraction.
`As is appreciated from FIGS. 4 and 5, the elastic wires
`222a and 222b are located in such a manner that the reaction
`force of the elastic wires 222a and 222b is generated in the 40
`focusing direction. Accordingly, the magnetic circuit 26 is
`substantially prohibited from pivoting toward the vertical
`portion 31c while being translated oppositely to the objec(cid:173)
`tive lens holder 12 in the focusing direction. For this reason,
`the yoke 21 and the magnets 23 are kept out of contact with 45
`the focusing coil14 and the tracking coil15. This allows the
`distance between the magnetic circuit 26 and each of the
`coils 14 and 15 to be set at a minimum possible distance. As
`a result, the objective lens driving apparatus 3 can be
`reduced in size.
`The elastic wires 222a and 222b are preferably formed of,
`for example, phosphorus bronze, beryllium bronze, or stain(cid:173)
`less steel. By using one of such materials, the magnetic
`circuit can be easily designed to vibrate in the focusing
`direction at a lower resonance frequency. The elastic wires 55
`222a and 222b formed of one of such materials are advan(cid:173)
`tageous in being less infiuenced by temperature as well as in
`effectively absorbing the vibration.
`In the third example, two pairs of elastic wires 222a and
`222b are provided for visco-elastically supporting the mag- 60
`netic circuit 26. In such a structure, the assembly of the
`elastic wires 222a and 222b is highly rigid against defor(cid:173)
`mation in all directions except for the direction perpendicu-
`lar to a plane defined by the elastic wires 222a and a plane
`defined by the elastic wires 222b. Namely, the assembly of 65
`the elastic wires 222a and 222b is highly rigid against
`deformation in all directions except for the focusing direc-
`
`15
`
`With reference to FIG. 6, an objective lens driving appa(cid:173)
`ratus 4 in a fourth exemplary embodiment of the present
`invention will be described. FIG. 6 is a perspective view of
`the objective lens driving apparatus 4. Identical elements
`with those in the first example will bear identical reference
`numerals therewith, and explanation thereof will be omitted.
`In the fourth example, two pairs of elastic wires 322 for
`20 visco-elastically supporting the magnetic circuit 26 are
`provided parallel to one another. Due to such a structure, the
`magnetic circuit 26 is translated in the tracking direction as
`well as in the focusing direction with no pivoting movement.
`Accordingly, the vibration caused by the movement of the
`25 objective lens holder 12 in the focusing direction and also
`the vibration caused by the movement of the objective lens
`holder 12 in the tracking direction can be counteracted by
`the vibration of the magnetic circuit 26, thereby significantly
`reducing both types of vibration.
`The elastic wires 322 are preferably formed of, for
`example, phosphorus bronze, beryllium bronze, or stainless
`steel. By using one of such materials, the magnetic c