United States Patent £191
`Getreuer et al.
`
`[75]
`
`[54] SEEK ACI'UATOR FOR OPTICAL
`RECORDING
`Inventors: Kurt W. Getreuer, Colorado Springs;
`Leonardus J. Grassens, Chipita Park,
`both of Colo.
`[73] Assignee: Applied Magnetics Corporation,
`Goleta, Calif.
`[21] Appl. No.: 657,155
`
`Feb. 15, 1991
`[22] Filed:
`Int. Cl.s ..................................... ; .......... G11B 7/00
`[51]
`[52] u.s. Cl ............................... 369/44.14; 369/44.21;
`369/249; 359/824; 359/813
`[58] Field of Search ............... 369/44.14, 44.15, 44.18,
`369/44.17, 44.21, 44.22, 44.35, 219, 249, 256;
`359/814, 813, 819, 824
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`4,449,213 S/1984 Kazuiaka .......................... 369/44.15
`4,504,935 3/1985 Jansen ................................. 369/249
`
`(List continued on next page.)
`
`FOREIGN PATENT DOCUMENTS
`18037 1/1982 Japan .
`64649 4/1983 Japan .
`115031 6/1985 Japan .
`·129937 7/1985 Japan .
`17230 1/1986 Japan .
`182642 8/1986 Japan .
`248241 11/1986 Japan .
`205540 9/1987 Japan .
`OTHER PUBLICATIONS
`G. Bouwhuis, et al., Principles of Optical Disc Systems,
`Adam Hilger Ltd., Bristol, 1985, pp. 147-153.
`Eguichi, Naoya, et al., An 86mm Magneto-Optical Disk
`Drive with a compact and fast-seek-time Optical Head,
`Optical Data Storage Conference, Vancouver, Mar.,
`1990.
`
`lllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllll
`US005265079A
`5,265,079
`[11] Patent Number:
`[45] Date of Patent: Nov. 23, 1993
`
`Primary Examiner-Aristotelis Psitos
`Assistant Examiner-Nabil Hindi
`Attorney, Agent, or Firm-Knobbe, Martens, Olson &
`:sear
`[57]
`ABSTRACf
`The present invention is an apparatus for optical read(cid:173)
`ing or recording information on an optical information
`medium, wherein as a result of the relative position of
`· the components of the apparatus and the magnitude and
`:application points of the forces exerted to track and
`focus, the objective lens through which information is
`read from the information medium, prevents the objec(cid:173)
`tive lens from being affected by most resonances, motor
`forces and reaction forces. This is critical in that in .
`optical recording, displacements of 0.02 micrometers
`can easily be picked up. Specifically, one aspect of the
`invention is an apparatus for optically reading or re(cid:173)
`cording information on an optical disk which is rotat(cid:173)
`able about an axis of rotation, wherein the apparatus
`includes a frame, a carriage, a carriage drive, an objec(cid:173)
`tive lens, an objective lens holder and a focus drive. The
`carriage drive (i.e., those portions of the carriage motor
`which move relative the frame) drives the carriage
`along a path radial to the axis of the rotation. The objec(cid:173)
`tive lens is mounted on the objective lens holder so that
`the optical axis of the objective lens is within 0.5 milli(cid:173)
`meters of intersecting the center of mass of the carriage
`mass. The holder is movable relative to the carriage so
`as to move the objective lens along its optical axis. This
`movement is controlled by a focus drive (i.e., those
`portions of the focus motor which move relative to the
`carriage) which drives the holder so as to move the
`objective lens along its optical axis. For purposes of this
`application including appended claims, the carriage and
`actuator assembly is considered to be broken down into
`two mass groupings. The first is the "fme motor mass"
`(i.e., the mass of all components suspended for freedom
`of movement from the carriage). The second is the
`"carriage mass" (i.e., the mass of all components which
`move with the carriage excluding the fme motor mass
`and any incidental connecting wiring not wholly sup(cid:173)
`ported by the carriage).
`
`(List continued on next page.)
`
`26 Claims, 35 Drawing Sheets
`
`LG Electronics, Inc. et al.
`EXHIBIT 1008
`IPR Petition for
`U.S. Patent No. 6,785,065
`
`

`
`5,265,079
`Page 2
`
`U.S. PATENT DOCUMENTS
`4,514,837 4/1985 Van Rosma1en ................... 369/219
`4,568,142 2/1986
`lguma .................................. 359/819
`4,571,026 2/1986 Maruta ............................. 369/44.17
`4,592,037 5/1986 Ohnuki ............................. 369/44.15
`4,596,444 6/1986 Ushida .............................. 369/44.15
`4,596,448 6/1986 Kikuchi ............................ 369/44.15
`4,643,522 2/1987 Takashima ....................... 369/44.17
`4,644,516 2/1987 Musha .: ................................. 369/43
`4,646,283 2/1987 Ito et al. .............................. 369/256
`4,669,073 5/1987 Wakabaya5hi eta!. ............. 369/111
`4,679,904 7/1987 Kurihara .......................... 369/44.15
`4,702,555 10/1987
`lguma eta!. ..................... 369/44.16
`4,740,946 4/1988 Yumura eta!. ..................... 369/219
`4,763,314 8/1988 McCaslin eta!. ................... 369/249
`4,794,586 12/1988 Korth .................................. 369/215
`4,811,320 3/1989 Kawasaki eta!. ............... 369/44.22
`4,823,336 4/1989 Inada eta!. ......................... 369/215
`4,842,392 6/1989 Nakamura eta!. .............. 369/44.14
`4,845,699 7/1989 Kawasaki et al. ............... 369/44.22
`4,922,477 5/1990 Miura .................................. 369/221
`
`OTHER PUBLICATIONS
`Hartmann, M., "Erasable Magneto-Optical Recording
`Media", IEEE Transactions on Magnetics, vol. Ma(cid:173)
`g-20, No. 5, Sep., 1984, pp. 1013-1018.
`Kobori, et a!., New Magneto optic Head With a Built-in
`Generator for a Bias Magnetic Field, Applied Optics, vol.
`27, No.4, Feb. 15, 1988, pp. 698-702.
`Kobori, Murakami, et al., "New Magneto-Optic Head
`with a Built-In Generator for a Bias Magnetic Field",
`:Optical Data Storage Conference, Technical Digest
`Series vol. 10, Mar. 11-13, 1987, pp. 186-189.
`Murakami et a!., "Magnetooptic erasable disk memory
`with two optical heads", Applied Optics, vol. 25, No.
`22, Nov. 15, 1986, pp. 3986-3989.
`Sander, 1., "Digital Magneto-Optic Storage System",
`:Topical Meeting on Optical Data Storage, Jan. 20, 1989,
`ipp. THA2-l-THA2-4.
`:Yoshizumi, Keiichi, et al., Fast Access Actuator for Opti(cid:173)
`.cal Disk Memory, SPIE, 1985.
`
`

`
`U.S. Patent
`
`Nov. 23, 1993
`
`Sheet 1 of 35
`
`5,265,079
`
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`
`U.S. Patent
`
`Nov. 23, 1993
`
`Sheet 2 of 35
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`5,265,079
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`

`
`U.S. Patent
`
`Nov. 23, 1993
`
`Sheet 3 of 35
`
`5,265,079
`
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`FIG. 3
`
`

`
`U.S. Patent
`
`Nov. 23, 1993
`
`Sheet 4 of 35
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`5,265,079
`
`

`
`U.S. Patent
`
`Nov. 23, 1993
`
`Sheet 5 of 35
`
`5,265,079
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`166
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`

`
`U.S. Patent
`
`Nov. 23, 1993
`
`Sheet 6 of 35
`
`5,265,079
`
`

`
`U.S. Patent
`
`Nov. 23, 1993
`
`Sheet 7 of 35
`
`5,265,079
`
`2!0
`
`FIG. 7
`
`

`
`U.S. Patent
`
`Nov. 23, 1993
`
`Sheet 8 of 35
`
`5,265,079
`
`250
`
`FIG.B
`
`

`
`U.S. Patent
`
`Nov. 23, 1993
`
`Sheet 9 of 35
`
`5,265,079
`
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`166
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`FIG. 9a
`
`

`
`U.S. Patent
`
`Nov. 23, 1993
`
`Sheet 10 of 35
`
`5,265,079
`
`

`
`U.S. Patent
`
`Nov. 23, 1993
`
`Sheet 11 of 35
`
`5,265,079
`
`190
`
`IJB
`
`FIG. lOa
`
`

`
`U.S. Patent
`
`Nov. 23, 1993
`
`Sheet 12 of 35
`
`5,265,079
`
`

`
`U.S. Patent
`
`Nov. 23, 1993
`
`Sheet 13 of 35
`
`5,265,079
`
`110
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`IJB
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`FIG. /Ia
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`

`
`U.S. Patent
`
`Nov. 23, 1993
`
`Sheet 14 of 35
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`5,265,079
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`U.S. Patent
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`Nov. 23, 1993
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`Sheet 15 of 35
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`5,265,079
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`U.S. Patent
`
`Nov. 23, 1993
`
`Sheet 16 of 35
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`Nov. 23, 1993
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`
`U.S. Patent
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`Nov. 23, 1993
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`Sheet 18 of 35
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`U.S. Patent
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`Nov. 23, 1993
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`Sheet 19 of 35
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`

`
`U.S. Patent
`
`Nov. 23, 1993
`
`Sheet 20 of 35
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`5,265,079
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`

`
`U.S. Patent
`
`Nov. 23, 1993
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`Sheet 21 of 35
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`U.S. Patent
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`Nov. 23, 1993
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`Sheet 22 of 35
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`5,265,079
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`1.90
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`FIG. 16a
`
`

`
`U.S. Patent
`
`Nov. 23, 1993
`
`Sheet 23 of 35
`
`5,265,079
`
`

`
`U.S. Patent
`
`Nov. 23, 1993
`
`Sheet 24 of 35
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`U.S. Patent
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`Nov. 23, 1993
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`Sheet 25 of 35
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`
`U.S. Patent
`
`Nov. 23, 1993
`
`Sheet 26 of 35
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`5,265,079
`
`

`
`U.S. Patent
`
`Nov. 23, 1993
`
`Sheet 27 of 35
`
`5,265,079
`
`166
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`260
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`
`

`
`U.S. Patent
`
`Nov. 23, 1993
`
`Sheet 28 of 35
`
`5,265,079
`
`fie
`
`FIG. 19b
`
`

`
`U.S. Patent
`
`Nov. 23, 1993
`
`Sheet 29 of 35
`
`5,265,079
`
`

`
`U.S. Patent
`
`Nov. 23, 1993
`
`Sheet 30 of 35
`
`5,265,079
`
`

`
`FREQ
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`FIG. 2/a
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`
`U.S. Patent
`
`Nov. 23, 1993
`
`Sheet 33 of 35
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`5,265,079
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`
`U.S. Patent
`
`Nov. 23, 1993
`
`Sheet 34 of 35
`
`5,265,079
`
`-~ -------
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`

`
`U.S. Patent
`
`Nov. 23, 1993
`
`Sheet 35 of 35
`
`5,265,079
`
`FIG.25
`
`z
`0
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`DIRECTION ~
`
`

`
`1
`
`5,265,079
`
`SEEK ACfUATOR FOR OPTICAL RECORDING
`
`FIELD OF THE INVENTION
`The invention relates to optical disc recording sys(cid:173)
`tems and, in particular, to an electromagnetic carriage
`and actuator assembly for focussing, tracking, and ran(cid:173)
`dom access in optical disc players and recorders.
`
`2
`direction), or pitch; rotation about the Z axis, referred
`to as yaw; rotation about the Y axis, called roll; and
`linear motion along the X axis, or tangential translation.
`Motion in these directions is often caused by motor and
`5 reaction forces acting on the carriage and/or actuator.
`These modes typically produce undesired movement
`during tracking or focussing operations which subse(cid:173)
`quently affects the alignment of the objective lens rela(cid:173)
`tive to the optical disc.
`
`10
`
`30
`
`BACKGROUND OF THE INVENTION
`SUMMARY OF THE INVENTION
`Optical data storage systems that utilize a focused
`laser beam to record and instantaneously playback in-
`The present invention overcomes the drawbacks of
`the prior art devices by providing an apparatus for
`formation are very attractive in the computer mass
`optical reading or recording information on an optical
`storage industry. Such optical data storage systems
`offer very high data rates with very high storage den- 15 information medium, wherein as a result of the relative
`sity and rapid random access to the data stored on the
`position of the components of the apparatus and the
`information medium, most commonly an optical disc. In
`magnitude and application points of the forces exerted
`these types of optical disc memory systems, reading and
`to track and focus, the objective lens through which
`writing data is often accomplished using a single laser
`information is read from the information medium, pre-
`source functioning at two respective intensities. During 20 vents the objective lens from being affected by most
`resonances, motor forces and reaction forces. This is
`either operation, light from the laser source passes
`through an objective lens which converges the light
`critical in that in optical recording, displacements of
`beam to a specific focal point on the optical disc. Dur-
`0.02 micrometers can easily be picked up.
`ing data retrieval, the laser light is focused on the re-
`Specifically, one aspect of the invention is an appara-
`cording medium and is altered by the information of the 25 tus for optically reading or recording information on an
`data storage medium. This light is then reflected ofT the
`optical disk which is rotatable about an axis of rotation,
`disc, back through the objective lens, to a photodetec-
`wherein the apparatus includes a frame, a carriage, a
`tor. It is this reflected signal that transmits the recorded
`carriage drive, an objective lens, an objective lens
`information. It is thus especially important that, when
`hold
`d
`d · Th
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`th
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`d f
`· ~
`t"
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`h
`precisely focused at the center of the correct track so
`rame dnves t e carriage along a path radial to the axis
`of .the. rotation. The objective lens ~s mou_nted on the
`that the information may be accurately written and
`retrieved.
`obJective lens holder so that the optical ax1s of the ob-
`ln order to attain a precise reading of the information 35 jective lens is within 0.5 ':llillimeters of intersect.ing the
`center of .mass of the ca~nage mass. The holder ~~ m<;>V-
`stored on the disc, it is necessary to be able to move the
`able relat!v.e to t~e car~age s~ as to move t.he obJective
`objective lens in both a focussing (i.e., perpendicular to
`lens along Its.optl~al ax1s. Th1s ~ovement 1s controlled
`the plane of the disc) or Z direction in order to focus the
`by ? focus dnve (!:e., those port1?ns of th~ focu~ motor
`laser beam to a small point of light on a precise location
`of the disc to write or retrieve information, and in a 40 wh1ch move relative to the carnage) wh1ch dnves the
`tracking (i.e., radial) or Y direction to position the beam
`holder so as to move the objective lens along its optical
`over the exact center of the desired information track
`axis. For purposes of this application including ap-
`on the disc. Focus and tracking corrections may be
`pended claims, the carriage and actuator assembly is
`effected by moving the objective lens in either the di-
`considered to be broken down into two mass groupings.
`rection of the optical axis of the lens for focussing, or in 45 The first is the "fine motor mass" (i.e., the mass of all
`a direction perpendicular to the optical axis for track-
`components suspended for freedom of movement from
`ing.
`.
`the carriage). The second is the "carriage mass" (i.e.,
`In these systems, the position of the objective lens in
`the mass of all components which move with the car-
`the focus and tracking directions is commonly adjusted
`riage excluding the fine motor mass and any incidental
`by control systems. Actuators support the objective so connecting wiring not wholly supported by the car-
`lens and convert position correction signals from the
`riage).
`feedback control systems into movement of the objec-
`Another aspect of the invention is an apparatus for
`tive lens. As will be appreciated, failure to focus the
`optically reading or recording information on an optical
`light on a small enough area of the medium will result in
`disk which is rotatable about an axis of rotation,
`too large a portion of the disc being used to store a 55 wherein the apparatus includes a fine tracking drive
`(i.e., those portions of the fme tracking motor which
`given amount of information, or in too broad of an area
`of the disc being read. Likewise, the failure to precisely
`move relative to the carriage) for driving the objective
`control the tracking of the laser light will result in the
`lens holder so as to make fine adjustments in the relative
`information being stored in the wrong location, or in
`position of the objective lens along a path radial to the
`60 axis of rotation of the optical disk. The fine motor mass
`information from the wrong location being read.
`In addition to translation along the Z axis to effect
`has a center of mass within 0.5 millimeters of a line
`parallel to the optical axis containing the center of mass
`focusing, and translation along the Y axis to effect
`tracking, there are at least four additional motion modes
`of the carriage mass.
`for the actuator, each of which reduces the accuracy of
`Another aspect of the invention is an apparatus for
`the reading and writing operations and is thus undesir- 65 optically reading or recording information on an optical
`able during normal operation of the system. These un-
`disk which is rotatable about an axis of rotation,
`desirable modes of motion are rotation about the X axis
`wherein the apparatus includes a frame, a carriage, a
`carriage drive, an objective lens, an objective lens
`(an axis orthogonal to both the X direction and the Z
`
`

`
`3
`holder, a focus drive and a fine tracking drive, wherein
`the carriage mass and the fine motor mass each have a
`center of mass within 0.5 millimeters of the optical axis.
`Preferably, the carriage mass and the fine motor mass
`have respective centers of gravity within 0.5 mm of one 5
`another.
`Another aspect of the present invention is an optical
`axis for optically reading or recording information on
`an optical disk which is rotatable about an axis of rota·
`tion having a frame, a carriage, a carriage drive, an 10
`objective lens, an objective lens holder, a focus drive
`and a fine tracking drive, wherein the net center of
`force exerted by the fine tracking drive is less than 0.2
`mm from the optical axis. Another aspect of the inven(cid:173)
`tion is an apparatus for optically reading or recording 15
`information on an optical disk having a frame, a car(cid:173)
`riage, a carriage drive, an objective lens, an objective
`lens holder, a focus drive and a fine tracking drive,
`wherein the center of force exerted by the coarse track-
`ing drive is less than 0.2 mm from said optical axis.
`Yet another aspect of the invention is an apparatus for
`optically reading or recording information on an optical
`disk having a frame, a carriage, a carriage drive, an
`objective lens, an objective lens holder, a focus drive
`and a fine tracking drive, wherein the carriage drive
`exerts a pair of forces on the carriage to drive the car(cid:173)
`riage along a radial path and the distance between the
`center of mass of the carriage and the point upon which
`one of the forces acts is within 0.2 millimeters of the 30
`distance between the center of mass of the carriage and
`the point upon which the other carriage drive force
`acts.
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`BRIEF DESCRIPTION OF THE ORA WINGS
`FIG. 1 schematically illustrates an exemplary optical
`read/write system in which the carriage and actuator
`assembly of the present invention may be used;
`FIG. 2 is a perspective view of the carriage and actu·
`ator assembly;
`FIG. 3 is an exploded view of the carriage and actua(cid:173)
`tor assembly;
`FIG. 4 is an exploded view of the actuator;
`FIG. 5 is a schematic top view illustrating the coarse
`tracking forces acting on the assembly;
`FIG. 6 is a side schematic view further illustrating the
`coarse tracking forces;
`FIG. 7 is an exploded view which illustrates the focus
`forces acting on the actuator;
`FIG. 8 is an exploded view which illustrates the fine so
`tracking forces acting on the actuator;
`FIG. 9a is a schematic top view illustrating the sym(cid:173)
`metry of coarse tracking forces in the horizontal plane;
`FIG. 9b is a schematic side view illustrating the sym(cid:173)
`metry of coarse tracking forces in the vertical plane;
`FIG. lOa is a schematic top view illustrating the sym(cid:173)
`metry of fine tracking forces in the horizontal plane;
`FIG. lOb ia a schematic end view illustrating the
`alignment of the net fine tracking force with the center
`of mass of the fine tracking motor;
`FIG. lla is a schematic top view illustrating the sym(cid:173)
`metry of fine tracking reaction forces in the horizontal
`plane;
`FIG. llb is a schematic end view illustrating the
`alignment of the net fine tracking reaction force with 65
`the center of mass of the fine tracking motor;
`FIG. 12a is a schematic side view illustrating the
`symmetry of focus forces in the horizontal plane;
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`FIG. 12b is a schematic end view of illustrating the
`alignment of the net focus force with the optical axis of
`the objective lens;
`FIG. 13a ia a schematic side view which illustrates
`the symmetry of focus reaction forces in the horizontal
`plane;
`FIG. 13b is a schematic end view which illustrates
`the alignment of the net focus reaction force with the
`optical axis of the objective lens;
`FIG. 14 is a schematic top view illustrating the flex(cid:173)
`ure forces and fme motor reaction forces generated in
`response to the flexure forces;
`FIG. lSa is a schematic side view which illustrates
`the symmetry of carriage suspension forces in the hori(cid:173)
`zontal plane;
`FIG. 15b is a schematic end view illustrating the
`alignment of the net carriage suspension force with the
`optical axis of the objective lens;
`FIG. 16a ia a schematic top view which illustrates the
`symmetry of friction forces in the horizontal plane;
`FIG. l6b is a schematic side view illustrating the
`alignment of the friction forces with the center of mass
`of the carriage;
`FIG. 17 ia a schematic end view which illustrates the
`net inertial forces acting at the center of mass of the fine
`motor and center of mass of the carriage in response to
`a vertical acceleration;
`FIG. 18a is a schematic side view illustrating the
`alignment of the net inertial force of the fine motor with
`the optical axis of the objective lens;
`FIG. 18b is a schematic side view illustrating the
`alignment of the net inertial force of the carriage with
`the optical axis of the objective lens;
`FIG. 19a is a schematic top view which illustrates the
`inertial forces acting on components of the carriage and
`actuator assembly for horizontal accelerations;
`FIG. 19b is a schematic top view illustrating the net
`inertial forces for horizontal accelerations;
`FIG. 20a is a schematic end view which illustrates
`the fine motor and carriage inertial forces for accelera(cid:173)
`tions above the flexure arm resonance frequency;
`FIG. 20b is a schematic end view which illustrates
`the fine motor and carriage inertial forces for accelera(cid:173)
`tions below the flexure arm resonance frequency;
`FIGS. 21a-21b a diagram illustrating the relationship
`between the fine tracking position versus fine motor
`current;
`FIGS. 22a-22c illustrate the effects of asymmetrical
`focus forces acting on the assembly;
`FIG. 23 illustrates an alternative embodiment of a
`carriage and actuator assembly;
`FIG. 24 illustrates the operation of the actuator to
`move the lens holder in a focusing direction;
`FIG. 25 illustrates the operation of the actuator to
`move the lens holder in a tracking direction.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENT
`FIG. 1 schematically illustrates the operation of an
`exemplary optical read/write system SO in reading data
`from a precise location 52 on an information storage
`medium, such as an optical disc 54. While the system SO
`illustrated is a write-once or WORM system, those
`skilled in the art will recognize that the carriage and
`actuator assembly of the present invention could also be
`used in magneto-optical erasable system. Information is
`transmitted to and read from the disc 54 utilizing a light
`beam 56 produced by a light source 58 which passes
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`the carriage moves. A beam of light 120 emitted from
`through a plurality of components including a cube-
`the light source 58 in the optics module 102 enters the
`shaped beamsplitter 60 which separates the light beam
`actuator 116 through a circular aperture 118 and is
`56 according to its polarization, a quarter wave plate 62
`reflected by a mirror contained inside the actuator
`which changes the polarization of the light beam 58, a
`collimator lens 64, and an objective lens 66, which, in 5 through an objective lens 122 defining an optical axis 0
`combination, direct the light beam 58 toward the de-
`to the surface of the disc. As will be appreciated, the
`sired location 52 on the disc 54.
`axis of rotation A of the disc is parallel to the optical
`In operation, the light source element 58, typically a
`axis 0 of the objective lens 122.
`The carriage 106 and actuator 116 carried thereon are
`laser diode, emits the light beam 56 toward the convex
`collimator lens 64. The collimator lens 64 converts this 10 moved horizontally along the rails 112, 114 in a tracking
`source beam 56 into a parallel, linearly S polarized light
`direction by a coarse tracking motor to access various
`beam 70 and conducts the beam 70 toward the beam-
`information tracks on the surface of the disc. The track-
`splitter 60. This cube-shaped beamsplitter 60 is formed
`ing motor includes two permanent magnets 130, 132
`by attaching two right angle prisms 72, 74 along their
`wherein each magnet is attached to a C-shaped outer
`respective hypotenuses and includes a polarization sen- 15 pole piece 134, 136, respectively. Two inner pole pieces
`138, 140 are positioned across the ends of the outer pole
`sitive coating forming a beamsplitting interface 76 be-
`tween the two hypotenuses. The beamsplitter 60 sepa-
`pieces 134, 136 so as to form a rectangular box around
`rates and/or combines light beams of differing polariza-
`the permanent magnets 130, 132. Two coarse coils 142,
`tion states, namely linear S polarization and linear P
`144 of equal length are affixed to the bearing surfaces
`polarization. Separation is accomplished in conjunction 20 108, 110 and surround the inner pole pieces 138, 140
`with the polarization sensitive coating which transmits
`with sufficient clearance to move over the pole pieces
`linearly P polarized light beams and reflects linearly
`138, 140 when the carriage 106 is moved in the tracking
`polarized S light beams. Light exiting the beamsplitter
`direction. In this embodiment, these coarse coils 142,
`60 passes through the quarter wave plate 62 which
`144 are the only portion of the course tracking motor
`converts the linearly polarized light beam 70 to a circu- 25 that are movable. As will be described in more detail
`below, the actuator 116 can also move the objective lens
`larly polarized light beam 78. Upon exiting the quarter
`122 closer to or farther away from the disc, thereby
`wave plate 62, the circularly polarized beam 78 enters
`an actuator 80.
`focussing the exiting light beam 120 upon the desired
`The actuator 80 includes a mirror 82 which orthogo-
`location on the surface of the disc.
`nally reflects the light beam 78 upward toward the 30
`FIG. 3 is an exploded view illustrating the carriage
`106 and actuator 116 in greater detail. The carriage 106
`objective lens 66. This objective lens 66 converges the
`circularly polarized beam 78 to the precise focal point
`includes a generally rectangular base 150 to which the
`52 on surface of the optical disc 54. Upon striking the
`actuator 116 is attached. The base 150 has a substan-
`disc 54, the circularly polarized light beam 78 is altered
`tially flat top surface 152 having a generally rectangular
`by the information stored on the disc 54 and is reflected 35 chamber 154 formed therein. The first bearing surface is
`as a divergent circularly polarized light beam 84 carry-
`cylindrical in shape, while the second bearing surface
`ing information identical to that encoded on the disc 54.
`110 consists oftwo elliptical bearing sections 160, 162 of
`This reflected circularly polarized light beam 84 re-
`approximately equal length which meet inside the base
`enters the objective lens 66 where it is collimated. The
`150. The spacing of the rails 112, 114 relative to the
`light beam 84 is again reflected from the mirror 82 and 40 optical axis 0 is selected such that each bearing surface
`108, 110 is subjected to the same amount of preload.
`re-enters the quarter wave plate 62. Upon exiting the
`quarter wave plate 62, the circularly polarized beam 84
`The bearing surfaces 108, 110 are further designed such
`is converted to a linearly P polarized light beam 86. As
`that both surfaces have substantially the same amount of
`linearly P polarized light beams are transmitted through
`surface area contacting the rails 112, 114. The length of
`the beamsplitter 60 without reflection at the splitting 45 the bearing sections comprising the second bearing
`surface is approximately equal to the length of the first
`interface, this light beam 86 continues to a photodetec-
`tor 88, which detects the data stored on the disc 54. In
`bearing surface, although minor variations in length
`addition, if the light beam 86 falling on the photodetec-
`may be necessary to account for wear.
`tor 88 is out of focus or misaligned, the amount of mis-
`Two vertical walls 156, 158 extend upwardly from
`alignment or defocusing is measured electronically and 50 the top surface 152 of the base 150 adjacent the ends of
`used as feedback for a servo system (not shown) which
`the chamber 154. The base 150 further includes two
`properly realigns the objective lens 66.
`platform regions 164, 166 formed at the ends of the base
`FIG. 2 illustrates an electromagnetic carriage and
`150 above the bearing surfaces 108, 110. A step 168 joins
`actuator assembly 100 constructed in accordance with
`the top surface 152 of the base 150 with the second
`the present invention. The assembly can be used with an 55 platform region 166. A first U-shaped notch 170 is
`optics module 102 to read and write data onto the sur-
`formed in the first platform region 164, and a second
`U-shaped notch 172 is formed in the second platform
`face of an optical disc as described above in connection
`with FIG. 1, wherein the light source 58, detector 88,
`region 166 and step 168.
`The coarse coils 142, 144 are attached to two vertical
`collimating lens 64, quarter wave plate 62, and beam-
`splitter 60 are all incorporated within the module 102. A 60 plates 174, 176 respectively. The plates 174, 176 are
`positioned in notches 180, 182 formed in the ends of the
`spindle motor 104 is located adjacent the assembly 100
`and rotates an optical disc (not shown) about an axis of
`base 150. The base 150 further includes a mass balancing
`rotation A above the assembly 100. The assembly 100
`plate 184 which is attached to a bottom surface 186 of
`includes a carriage 106 having first and second bearing
`the base 150 via a screw 188, and a mass balancing
`surfaces 108, 110 slidably mounted on first and second 65 projection 190 which extends outwardly from the base
`150 adjacent the first coarse coil 142. A circular aper-
`guide rails 112, 114, respectively, and an actuator 116
`which is mounted on the carriage 106. As will be appre-
`ture 192 is formed in a front side 194 of the base 150 and
`receives the light beam 120 emitted from the optics
`ciated, these rails 112, 114 provide a frame along which
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`pair of pole pieces 246. A ledge 294 is formed on each
`module 102 (FIG. 2). A bracket 196 having a circular
`aperture 198 therein is positioned between the second
`side of the notch 292 on the top and bottom surfaces of
`the support member 290. The crossbar sections 280 of
`vertical wall 158 and the first platform region 164 along
`the flexure arms 260, 262 are attached to these ledges
`the front side 194 of the base 150. The bracket 196 addi-
`tionally includes a notch 200 which receives a photode- 5 294, while flexure arms 264, 266 are connected to corre-
`sponding ledges on the bottom of the support member
`tector 202 such that the photodetector 202 is positioned
`between the bracket 196 and the first platform region
`290 so as to cooperatively suspend the lens holder 210
`164.
`from the support member 290. The support member 290
`further includes an aperture 296 for receiving a light
`The actuator 116, often referred to as a "2-D" actua-
`tor for 2 de