CA1219073A - Optical focus position control in an optical memory system - Google Patents
Optical focus position control in an optical memory systemInfo
- Publication number
- CA1219073A CA1219073A CA000451907A CA451907A CA1219073A CA 1219073 A CA1219073 A CA 1219073A CA 000451907 A CA000451907 A CA 000451907A CA 451907 A CA451907 A CA 451907A CA 1219073 A CA1219073 A CA 1219073A
- Authority
- CA
- Canada
- Prior art keywords
- optical
- tracking
- control device
- focus position
- holder
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B11/00—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor
- G11B11/10—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field
- G11B11/105—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing
- G11B11/1055—Disposition or mounting of transducers relative to record carriers
- G11B11/10576—Disposition or mounting of transducers relative to record carriers with provision for moving the transducers for maintaining alignment or spacing relative to the carrier
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B11/00—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor
- G11B11/10—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field
- G11B11/105—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B11/00—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor
- G11B11/10—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field
- G11B11/105—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing
- G11B11/10502—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing characterised by the transducing operation to be executed
- G11B11/10504—Recording
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B11/00—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor
- G11B11/10—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field
- G11B11/105—Recording on or reproducing from the same record carrier wherein for these two operations the methods are covered by different main groups of groups G11B3/00 - G11B7/00 or by different subgroups of group G11B9/00; Record carriers therefor using recording by magnetic means or other means for magnetisation or demagnetisation of a record carrier, e.g. light induced spin magnetisation; Demagnetisation by thermal or stress means in the presence or not of an orienting magnetic field using a beam of light or a magnetic field for recording by change of magnetisation and a beam of light for reproducing, i.e. magneto-optical, e.g. light-induced thermomagnetic recording, spin magnetisation recording, Kerr or Faraday effect reproducing
- G11B11/10532—Heads
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
- G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
- G11B7/0925—Electromechanical actuators for lens positioning
- G11B7/093—Electromechanical actuators for lens positioning for focusing and tracking
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
- G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
- G11B7/0925—Electromechanical actuators for lens positioning
- G11B7/0932—Details of sprung supports
Landscapes
- Optical Recording Or Reproduction (AREA)
- Automatic Focus Adjustment (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
An optical focus position control system for an optomagnetic disc apparatus avoids magnetic leakage to the disc and includes a tracking control device and a focus control device. The tracking control device includes an intermediate holder, a tracking parallel spring which con-nects an objective lens-mirror cylinder to the intermediate holder while ensuring movement of the objective lens-mirror cylinder in the radial direction of the optomagnetic disc, and a tracking drive mechanism to shift the objective lens-mirror cylinder in the radial direction within the inter-mediate holder. The focus control device includes a stationary holder, a focusing parallel spring which con-nects the intermediate holder to the stationary holder while ensuring movement of the intermediate holder in the direction of the optical axis of laser beams emitted through the optical focus position control system, and a focusing drive mechanism to shift the intermediate holder in the optical axis direction within the stationary holder.
An optical focus position control system for an optomagnetic disc apparatus avoids magnetic leakage to the disc and includes a tracking control device and a focus control device. The tracking control device includes an intermediate holder, a tracking parallel spring which con-nects an objective lens-mirror cylinder to the intermediate holder while ensuring movement of the objective lens-mirror cylinder in the radial direction of the optomagnetic disc, and a tracking drive mechanism to shift the objective lens-mirror cylinder in the radial direction within the inter-mediate holder. The focus control device includes a stationary holder, a focusing parallel spring which con-nects the intermediate holder to the stationary holder while ensuring movement of the intermediate holder in the direction of the optical axis of laser beams emitted through the optical focus position control system, and a focusing drive mechanism to shift the intermediate holder in the optical axis direction within the stationary holder.
Description
The present invention relates to an optical focus position control device of an optical disc apparatus that records, plays back, and erases a variety of information by irradiating optical beams such as laser beams onto a recording medium. The present invention relates, more par-ticularly, to an optical focus position control device in an optomagnetic disc apparatus which records, plays back, and erases a variety of information by irradiating optical beams such as laser beams onto a recording medium inclu-ding a magnetic film.
The conventional optical discs existing hithertohave surfaces which can easily be caused to vibrate during rotation, and as a result, recording tracks on the discs are displaced in the direction of the optical axis of the incident laser beams that irradiate the disc surfaces. Also, being adversely affected by any deviation between the center position of such a disc and the motor shaft that drives the disc, the recording tracks of such a disc are displaced in the direction of the disc radius (hereinafter called the radial direction). To prevent the recording tracks from being displaced, a device is provided such that the laser beam focus position can be correctly adjusted within the optical head mechanism to enable the incident laser beam spot to correctly match the recording tracks of a disc.
Such a device is referred to as an optical focus position control in the following description.
Using any of the existing optical disc appara-tuses such as one that only plays back information and does not employ a magnetic film recording medium, or one that can record additional information, in order to effect fine ad-justment of the focus position of the incident laser beams (hereinafter referred to as focus control) to counteract the disc displacement in the direction of the optical axis of the incident laser beams, a device that can vary the position of the objective lens by means of electromagnetism is well known by now. On the other hand, to effect fine adjustment of the focus position of the incident laser beam (hereinafter called the tracking controller) to counteract the disc displacement in the radial direction, a variety of mechanisms that can finely adjust the focus position of the incident laser beams via a rotary mirror which re-flects incident laser beams in any optimum direction havebeen introduced. The above-mentioned tracking control is not practical because the incident laser beams inevitably incline from the perpendicular direction of the disc.
Accordingly, a new proposal has been introduced quite recently, which provides a mechanism capable of jointly performing both the focus and tracking controls mentioned above by varying the position of the objective lens via electromagnetic force. Basically, this mechanism comprises a coil that can be moved integrally with the ob-jective lens and a stationary permanent magnet, thus causing the objective lens to be displaced by a current flowing through said coil.
However, this mechanism involves the following problem.
For example, a mechanism may be employed which incorporates an objective lens-mirror cylinder which is supported by rubber material whose one end is secured to a stationary holder, while the objective lens-mirror cy-linder can be driven by electromagnetic force existing between a coil secured to the objective lens-mirror cylinder and a magnetic circuit secured to the stationary cylinder.
Since the resilient rubber material supports the objective lens-mirror cylinder, it cannot fully resist the tilting force of the objective lens-mirror cylinder, and as a result, accidental force may be generated when the drive force generated by the electromagnetic force cannot be applied to the center of gravity of the objective lens-mirror cy-linder, thus causing the cylinder eventually to undergo a rotary movement. This will cause the optical axis of the beam to tilt relative to the central axis of the ob-jective lens, and so either off-axis astigmatism or coma aberration will adversely affect the disc tracks containing ~...
lZl~;~73 information, causing beams to focus poorly on them, and as a result, the quality of the recorded information will be degraded significantly.
Furthermore, if such an already known mechanism, capable of jointly performing both the focus and tracking controls by varying the position of the objective lens via the electromagnetic force, is actually applied to an optical disc apparatus, it will easily create problems described below.
Since the proposed mechanism uses magnetism generated by a permanent magnet, a leakage magnetism or flux will occur in portions peripheral to the disc.
Nevertheless, since the disc uses magnetic film as the recording medium, if such leakage adversely affects the magnetic film, the following problems will arise.
(1) When the laser beams are irradiated onto an optical magnetic disc to cause the temperature to rise, and simultaneously an information is recorded on the disc via an external magnetism, if a leakage of magnetism from the optical focus position control affects the disc, then the quality of the recorded information will be degraded significantly.
The conventional optical discs existing hithertohave surfaces which can easily be caused to vibrate during rotation, and as a result, recording tracks on the discs are displaced in the direction of the optical axis of the incident laser beams that irradiate the disc surfaces. Also, being adversely affected by any deviation between the center position of such a disc and the motor shaft that drives the disc, the recording tracks of such a disc are displaced in the direction of the disc radius (hereinafter called the radial direction). To prevent the recording tracks from being displaced, a device is provided such that the laser beam focus position can be correctly adjusted within the optical head mechanism to enable the incident laser beam spot to correctly match the recording tracks of a disc.
Such a device is referred to as an optical focus position control in the following description.
Using any of the existing optical disc appara-tuses such as one that only plays back information and does not employ a magnetic film recording medium, or one that can record additional information, in order to effect fine ad-justment of the focus position of the incident laser beams (hereinafter referred to as focus control) to counteract the disc displacement in the direction of the optical axis of the incident laser beams, a device that can vary the position of the objective lens by means of electromagnetism is well known by now. On the other hand, to effect fine adjustment of the focus position of the incident laser beam (hereinafter called the tracking controller) to counteract the disc displacement in the radial direction, a variety of mechanisms that can finely adjust the focus position of the incident laser beams via a rotary mirror which re-flects incident laser beams in any optimum direction havebeen introduced. The above-mentioned tracking control is not practical because the incident laser beams inevitably incline from the perpendicular direction of the disc.
Accordingly, a new proposal has been introduced quite recently, which provides a mechanism capable of jointly performing both the focus and tracking controls mentioned above by varying the position of the objective lens via electromagnetic force. Basically, this mechanism comprises a coil that can be moved integrally with the ob-jective lens and a stationary permanent magnet, thus causing the objective lens to be displaced by a current flowing through said coil.
However, this mechanism involves the following problem.
For example, a mechanism may be employed which incorporates an objective lens-mirror cylinder which is supported by rubber material whose one end is secured to a stationary holder, while the objective lens-mirror cy-linder can be driven by electromagnetic force existing between a coil secured to the objective lens-mirror cylinder and a magnetic circuit secured to the stationary cylinder.
Since the resilient rubber material supports the objective lens-mirror cylinder, it cannot fully resist the tilting force of the objective lens-mirror cylinder, and as a result, accidental force may be generated when the drive force generated by the electromagnetic force cannot be applied to the center of gravity of the objective lens-mirror cy-linder, thus causing the cylinder eventually to undergo a rotary movement. This will cause the optical axis of the beam to tilt relative to the central axis of the ob-jective lens, and so either off-axis astigmatism or coma aberration will adversely affect the disc tracks containing ~...
lZl~;~73 information, causing beams to focus poorly on them, and as a result, the quality of the recorded information will be degraded significantly.
Furthermore, if such an already known mechanism, capable of jointly performing both the focus and tracking controls by varying the position of the objective lens via the electromagnetic force, is actually applied to an optical disc apparatus, it will easily create problems described below.
Since the proposed mechanism uses magnetism generated by a permanent magnet, a leakage magnetism or flux will occur in portions peripheral to the disc.
Nevertheless, since the disc uses magnetic film as the recording medium, if such leakage adversely affects the magnetic film, the following problems will arise.
(1) When the laser beams are irradiated onto an optical magnetic disc to cause the temperature to rise, and simultaneously an information is recorded on the disc via an external magnetism, if a leakage of magnetism from the optical focus position control affects the disc, then the quality of the recorded information will be degraded significantly.
(2) When playing back the recorded information via the magnetic-optical effect by irradiating laser beams onto the optical magnetic disc, leakage flux from the optical focus position control may adversely affect the disc, thus causing the recorded information to be easily erased.
In the light of these potential disadvantages, if an optical disc apparatùs is used, it is necessary to prevent completely even the slightest leakage of flux from the optical focus position control from seriously affect-ing the optical disc. In addition, there are still further problems to solve.
Acc~rdingly, it is an object of the present in-vention to provide an improved optical focus position con-trol device which counteracts the magnetic leakage to the ~, optical disc.
The present invention provides an optical focus position control device for controlling the optical focus position of an optical beam in an optical disc apparatus, the optical focus position control device comprises a stationary holder, tracking control means for shifting a mirror cylinder containing an objective lens in the radial direction of an optical disc, the tracking control device includes an intermediate holder, tracking parallel spring means connecting the mirror cylinder to the inter-mediate holder in such a manner that the objective lens and the mirror cylinder are movable in the radial direction with respect to the intermedaite holder, and electro-magnetic tracking drive means for shifting the objective lens and the mirror cylinder in the radial direction within the intermediate holder for displacing the optical beams radially of the optical disc, and focus control means for shifting the tracking control device in the direction of the optical axis of the optical beam, the focus control device includes focusing parallel spring means connecting the intermediate holder to the stationary holder in such a manner that the intermediate holder is movable in the direction of the optical axis, and electromagnetic focus drive means for shifting the intermediate holder in the direction of the optical axis.
The present invention will become more readily apparent from the detailed description given hereinafter.
It should be understood, however, that the detai]ed description and specific examples, while indicating pre-ferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
An embodiment of the present invention is illus-trated in the accompanying drawings, which is given by way of example only, and thus is not limitative of the , ~.
~ . .
~2~
present invention and wherein:
Figure 1 is a schematic block diagram of an optical disc apparatus;
Figure 2 is a sectional view of an embodiment of an optical focus position control system embodying the present invention included in the optical disc apparatus of Figure l;
Figure 3 is a plan view of parallel springs in-cluded in the optical focus position control system of Figure 2;
Figures 4(A) and 4~B) are sectional views for explaining an operational mode of a focus control unit included in the optical focus position control system of Figure 2 and Figures 5(A), 5(B) and 5(C) are sectional views for explaining an operational mode of a tracking control unit included in the optical focus position control system of Figure 2.
Figure 1 shows a simplified block diagram of an optical disc apparatus as a preferred embodiment of the present invention. In Figure 1, symbol 1 denotes a laser beam source that emits laser beams 2. Symbol 3 denotes a mirror, and symbol 4 denotes an objective lens that causes the laser beams 2 to be focussed onto the re-cording medium surface of a disc. Symbol 5 denotes anoptical focus position control device that causes the optical focus position to be accurately dir~cted onto the tracks of the recording medium of the disc by driving the objective lens 4 in the vertical (up/down) and horizontal (left/right) directions. Symbol 6 denotes an optical head that contains all the optical devices mentioned above.
Symbol 7 denotes a recording~erasing coil that provides the surface of the disc recording medium with magnetism while either recording or erasing information. Symbol 8 denotes the optical disc, which incorporates a disc re-cording medium 8', and symbol 9 denotes a motor that causes the optical disc to rotate.
~Z~ 3 The focus control to be performed by the optical focus position control ~evice 5, i.e. a fine aajustment o~ the incident laser beam focus position relative to the disc displacement in the direction of the incident laser beam axis, can be achieved by causing the objective lens 4 to move in the direction of the thickness of the optical disc 8. On the other hand, the tracking control to be performed by the optical focus position control device 5, i.e. a fine adjustment of the incident laser beam focus position for counteracting the disc displacement in the radial direction, can be performed by causing the objective lens 4 to move in the radial direction of the optical disc 8.
Figure 2 shows a detailed construction of the optical focus position control system 5. First, the track-ing control device will be described. An objective lens-mirror cylinder 10 supports the objective lens 4. The lens-mirror cylinder 10 is supported by a movable inter-mediate support member 11 via parallel springs 12 so that the lens-mirror cylinder 10 is movable in the radial (leftlright), tracking direction with respect to the inter-mediate support member 11. A tracking permanent magnet 13, a tracking yoke plate 14 and a tracking yoke 15 are secured to the intermédiate support member 11 and form, in combination, a closed magnetic circuit. A tracking magnetic gap 16 is provided between the tracking yoke plate 14 and the tracking yoke 15. A tracking drive coil 17 is secured to the lens-mirror cylinder 10 and extends into the tracking magnetic gap 16. When the tracking control current is fed to the tracking drive coil 17, magnetism will be generated in the tracking drive coil 17, and as a result, due to a combined effect with the other magne-tism generated by the tracking permanent magnet 13, the tracking drive coil 17, the lens-mirror cylinder 10, the ob-jective lens 4, and a counterbalance 18 are all displaced inthe radial direction. The counterbalance 18 is secured to the bottom of the lens-mirror cylinder 10 so that the tracking ~2~
drive force is applied to the center of gravity of the movable tracking elements.
The focus control device will b~ described below.
A focussing permanent magnet 19, a focussing yoke plate 20, and a focussing yoke 21 form, in combination, a closed magnetic circuit. These elements are securely installed in a stationary holder 25 which supports the entire optical focus position control device. A focussing magnetic gap 22 is formed between the focussing yoke plate 20 and the focussing yoke 21. A focus drive coil 23 is secured to the movable intermediate support member 11 and extends into the focussing magnetic gap 22. The movable inter-mediate support member ll is supported by the stationary holder 25 via parallel springs 24 so that the movable in-termediat~ support member 11 is movable in the verticaldirection, i.e. in the direction of the incident laser beam a~is with respect to the stationary holder 25. When the focus control current is fed to the focus drive coil 23, magnetism is generated in the focus drive coil 23, and as a result, due to a combined effect with the other magnetism generated by the focussing permanent magnet l9, the tracking control device supported by the movable inter-mediate support member 11 is displaced in the focus direction (i.e. the direction of the incident laser beam axis).
Next, the movement characteristics of both the focussing and tracking controllers of the objective lens-mirror cylinder 10 are described below.
(I) Movement characteristics of the tracking controller As shown in Figure 2, the tracking controller is driven by the electromagnetic effect that interacts between the tracking closed magnetic circuit secured to the intermediate support member 11 and the tracking drive coil 17 secured to the objective lens-mirror cylinder lO.
~he intermediate support member 11 and the objective lens-mirror cylinder 10 are connected to each other via elastic material that is workable only to the left and to the right ? J
~z~
by moving in the radial direction, i.e. via parallel springs 12 that move in the direction of the disc radius. Assuming that the weight of the units movable in the tracking direction (the objective lens 4, the objective lens-mirror cylinder 10, and the tracking drive coil 17) is MT and the spring constant of the parallel springs 12 moving in the direction of the disc radius is KT, then the objective lens-mirror cylinder 10 will have a resonance frequency fT which is represented by the formula fT = 12~ ~ when the objective lens-mirror cylinder 10 moves to the left and to the right. When the tracking drive force FT is generated by the interacting electromagnetic force men-tioned above with a frequency denoted by fHz, the movement phase delay caused by the displacement XT of the objective lens-mirror cylinder 10 in the tracking direction is 0 through 90 when 0 < f < fT, or 90 through 180 when fT < f, or near 180 when fT f. When the tracking drive force FT is gen~rated, the delay in the movement phase caused by the displacement XT of the objective lens-mirror cylinder 10 moving to the tracking target position YT should remain below 180 throughout the frequency bands of the tracking control signal. When a phase advancing compensa-tion circuit is used to advance the phase of the track-ing drive signal FT, the phase delay is properly maintained below 180. This ensures a stable tracking control.
(II) Movement characteristics of the focussing controller As shown in Figure 2, the focussing controller is driven by the electromagnetic effect that interacts between the focussing closed magnetic circuit secured to the stationary holder 25 and the focussing drive coil 23 secured to the intermediate support member 11. The inter-mediate support member 11 and the stationary holder 25 are connected to each other via the parallel springs 24 which are workable only in the vertical direction by moving in the direction of focussing. Assuming that the weight of the parts movable in the direction of focussing, inclu-ding the tracking control device, is MF, whereas the spring ~l~Z~$1~'7~
constant of the parallel springs 24 moving in the direction of focussing is KF, then the objective lens-mirror cylinder lO will be provided with a resonance frequency which is represented by the formula fF = l2~ ~ (hereinafter called the primary resonance frequency) when performing vertical (up/down) movements. The interim holder 11 and the ob-jective lens-mirror cylinder 10 are connected to each other via the parallel springs 12 movable in the tracking di-rection. When the focus driving force is applied to the device, the parallel springs 12 move slightly in the ver-tical direction due to their elasticity. Thus, assuming that the spring constant in the focus-direction of the parallel springs 12 is KT', the objective lens-mirror cylinder 10 will have a resonance frequency (hereinafter called the secondary resonance frequency) represented as flF - 1 ~
2~ ~ MT -As described above, whenever the objective lens-mirror cylinder 10 moves upward and downward, both the primary and secondary resonance frequencles exist. Note that the spring constant KT' in the vertical direction of the parallel spring 12 is substantial or KT' >> KF.
This means that the secondary resonance frequency f'F is significantly higher than the primary resonance frequency fF, the relationship of which is denoted by f'F > fF. As soon as a driving force FF for the focussing operation is given by the interacting electromagnetic force, the movement phase delay in the displacement XF caused by the objective lens-mirror 10 in the focussing direction can be represented to be 0 through 90 when 0 < f < fF, where f (Hz) represents a frequency, whereas such a delay in the movement phase can be represented to be 90 through 270 when fF < f < f'F, and it will be 270 through 360 when f'F < f. When the focussing drive force FF is gen-erated, the delay in the movement phase caused by the dis-placement XF of the objective lens-mirror cylinder 10 moving to the focussing target position YF should remain below 180 throughout the frequency bands of the focussing con-~Z~
trol signal. As described earlier, even if the phase ad-vancing compensation circuit is used to advance the phase of the focussing drive signal FF, since there is a certain limit for advancing the phase amount, the phase cannot be compensated for in order that it can exceed 180 signi-ficantly. To properly compensate for the phase delay, the second resonance frequency fF shou]d be set at an op-timum level higher than the frequency band o the focus-sing control signal. Although frequency bands available for the focussing control signal are variable according to uses, generally, an optical disc apparatus uses 1 through 4 K~z of the frequency bands. As a result, the secondary resonance frequency f'F should be set at a level above 7 KHz.
Means for designing a construction that fully satisfies the above conditions are described below.
As described above, the secondary resonance fre-quency f'F can be determined by the spring constant KT' of the parallel tracking springs 12 when they move in the focussing direction and by the weight MT of the moving parts in the tracking direction. The secondary resonance frequency f'F becomes large as the spring constant KT' becomes large and as the weight MT becomes small.
Nevertheless, since there is a certain limit in the means for decreasing the weight MT of the objective lens 4 and the lens-mirror cylinder 10, the weight MT of the parts moving in the tracking direction cannot be decreased signi-ficantly. (Normally, the weight MT is designed in a range from 0.5 to 10 grams). The inventors, carried out ex-periments by increasing the spring constant KT' of thetracking parallel springs 12 during movement in the ver-tical direction. The spring constant KT' was found to be KT'~KT = (XT/YT) 2 when the tracking parallel springs 12 had a length XT in the focus direction YT. As a result, it is clear that the spring constant KT' in the vertical direction (upldown) can be increased by increasing the length XT and decreasing the thickness YT of the parallel .
~lZ~73 springs 12. In the light of the relationship denoted by ffTF = ~ , the secondary resonance frequency f'F can be obtained by an equation f'F = yT.fT. It was eventually made clear that the tracking parallel springs 12 should be designed so that they have a thickness YT of 20 through 50 microns and an actual length that is from 100 to 500 times the thickness YT. If the tracking parallel springs 12 can be correctly designed in accordance with the find-ings described above, the delay in the movement phase caused by the displacement XF of the objective lens 4 against the focussing target position can be decreased below 180 within the frequency bands available for the focussing control signal. It is important that the phase advancing compensation circuit be used for correctly com-pensating for the movement phase.
According to the results of the trials carriedout by the inventors, very stable focussing and tracking controls were achieved in practice by using tracking parallel springs 12 made from beryllium-copper alloy having a th~ckness of 30 through 50 microns.
(III) Damping Characteristics Improvement in the Tracking Control Device and the Focus Control Device As discussed above in the sections ~I) and (II), there are two kinds of resonance frequencies fF and fT
when the tracking control device and the focus control device are operated. If the damping characteristics in the directions of focussing and tracking control remain negligible, the multiple resonance factor in the resonance frequencies fF and fT will grow, thus causing interference vibration to easily occur during either the focussing or tracking control operation. Also, when a certain frequency above the resonance frequency level is applied, the phase in response to the displacement of the movable parts will be extremely delayed to a point very close to 180, which will result in an extremely unstable optical focus position control opera-tion. To prevent this and ensure satisfactory damping ~Z~73 characteristics, the following means may be effectively employed.
(III-a) Structure of the primary means The primary improvement includes a latexed damp-ing member painted on the focussing parallel spring and/orthe tracking parallel spring. (A plate rubber attached to the metal spring by an adhesive is not suitable for the device, because the spring constant becomes high due to the adhesive). To make up the damping material, viscose-elastic materials such as silicon rubberr butyl rubber, silicon-butyl rubber, and acrylic-ethylene rubber, foaming synthetic resin such as foamed polyurethane, and viscose fluid such as silicon grease, can be made available.
(III-b) Structure of the second means Figure 3 shows a plan view of one of the focus-sing parallel springs 24. Each focussing parallel spring 24 has a structure that connects two concentric circles, where two flat sheet springs, each being connected to four arms at the edges, are provided at the upper and lower ZO positions. The parallel springs 24, moving in the di-rection of focus, permit movement of the intermediate holder 11 in the vertical direction with respect to the stationary holder 25 (see Figure 2). Damping material 26 is bonded to the portion C of the surface of the focus-sing parallel springs 24, where the largest amount of rela-tive displacement exists, thus resulting in greater damping characteristics in the direction of focus. To make up the damping material 26, viscose-elastic materials such as silicon-rubber, butyl rubber, silicon-butyl rubber, and acrylic-ethylene rubber, and foaming synthetic resin such as foamed polyurethane, can be made available.
(III-c) Structure of the third means The third improvement is to form the focussing parallel springs and/or the tracking parallel springs from a vibration-proof alloy such as manganese-copper alloy, ferro-aluminum alloy, nickel-titanium alloy or magnesium alloy.
~Z~ 73 The structures of (III-a), ~ b) and (III-c) can be effectively combined with each other to signifi-cantly enhance the damping characteristics~
(IV) Improvement relating to the application of the pre-sent optical focus position controlling device to an optomagnetic disc apparatus A variety of means may be employed for effec-tively preventing the optical focus position control device from causing its magnetic leakage to adversely affect the recording medium 8' of the optical disc ~. Such effective means are described below.
(IV-a) Details of means related to the focus controller Figure 4(A) shows a sectional view of a focus controller incorporating an improved means as a preferred embodiment of the present invention, whereas Figure 3(B) shows a sectional view of another focus controller not incorporating any improved means. Symbols N and S res-pectively denote the north and south poles. As shown in Figure 3(A), the focus controller provides a magnetic gap 22 for the focussing operation in an area close to the optical disc. This construction minimizes magnetic leakage that otherwise adversely affects the recording medium 8' of the optical disc. In other words, magnetic leakage will significantly affect the surface of the re-cording medium 8' of the optical disc if the magnetic gap22' for the focussing operation is provided in an area remote from the optical disc as shown in Figure 3(B). The lengths of the arrows in Figures 3(A) and 3(B) denote the intensities of the leakage magnetism at the respective positions, while the direction of the magnetic leakage is also indicated by the arrows.
(IV-B) Details of means related to the tracking controller Figure 5(A) shows a sectional view of the track-ing controller incorporating an improved means as a pre-ferred embodiment of the present invention, whereas Figures5(B) and 5~C) show sectional views of another tracking controller without any such improved means. The tracking ~2~ 3 controller incorporating an improved means provides the permanent magnet 13 available for the tracking operation in the center position of the closed magnetic circuit.
This construction minimizes magnetic leakage that other-wise adversely affects the recording medium 8' of theoptical disc. In other words, in such a construction where the permanent magnet 13' available for the tracking opera-tion is provided encircling the closed magnetic circuit as shown in Figure 5(B), or in such a construction wnere the open magnetic circuit faces the optical disc as shown in Figure 5(C), if the magnitude of magnetism that functions in the magnetic gap 16' or 16'' is designed to be equal to that in the magnetic gap 16 of Figure 5(A) available for the tracking operation, magnetic leakage will signi-ficantly affect the surface of the recording medium 8'of the optical disc.
(IV-c) Details of means for supporting the tracking con-trol device Whèn the magnetic field in the tracking magnetic space is selected at a fixed value, the magnetic leakage ~ncreases as the tracking magnetic gap increases. Thus, it is preferable for the tracking magnetic gap to be made as narrow as possible. The objective lens must be movable in two dimensions, i.e. up/down and leftlright. If both the tracking control magnetic circuit and the focus con-trol magnetic circuit are supported by the stationary holder, the tracking coil must be movable in the two dimensions within the tracking magnetic gap. This requires a wide magnetic gap.
In accordance with the present embodiment, the tracking magnetic circuit is supported by the movable in-termediate holder 11. By this construction, the tracking drive coil 17 is required to move only in the left/right direction within the tracking magnetic gap 16. This will effectively minimize the tracking magnetic gap 16 and the magnetic leakage.
An embodiment of the invention being thus ,,, described, it will be obvious that the invention may be varied in many ways. Such variations are not to be re-garded as a departure from the spirit and scope of the in~ention, and all such modifications are intended to be included within the scope of the following claims~
In the light of these potential disadvantages, if an optical disc apparatùs is used, it is necessary to prevent completely even the slightest leakage of flux from the optical focus position control from seriously affect-ing the optical disc. In addition, there are still further problems to solve.
Acc~rdingly, it is an object of the present in-vention to provide an improved optical focus position con-trol device which counteracts the magnetic leakage to the ~, optical disc.
The present invention provides an optical focus position control device for controlling the optical focus position of an optical beam in an optical disc apparatus, the optical focus position control device comprises a stationary holder, tracking control means for shifting a mirror cylinder containing an objective lens in the radial direction of an optical disc, the tracking control device includes an intermediate holder, tracking parallel spring means connecting the mirror cylinder to the inter-mediate holder in such a manner that the objective lens and the mirror cylinder are movable in the radial direction with respect to the intermedaite holder, and electro-magnetic tracking drive means for shifting the objective lens and the mirror cylinder in the radial direction within the intermediate holder for displacing the optical beams radially of the optical disc, and focus control means for shifting the tracking control device in the direction of the optical axis of the optical beam, the focus control device includes focusing parallel spring means connecting the intermediate holder to the stationary holder in such a manner that the intermediate holder is movable in the direction of the optical axis, and electromagnetic focus drive means for shifting the intermediate holder in the direction of the optical axis.
The present invention will become more readily apparent from the detailed description given hereinafter.
It should be understood, however, that the detai]ed description and specific examples, while indicating pre-ferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
An embodiment of the present invention is illus-trated in the accompanying drawings, which is given by way of example only, and thus is not limitative of the , ~.
~ . .
~2~
present invention and wherein:
Figure 1 is a schematic block diagram of an optical disc apparatus;
Figure 2 is a sectional view of an embodiment of an optical focus position control system embodying the present invention included in the optical disc apparatus of Figure l;
Figure 3 is a plan view of parallel springs in-cluded in the optical focus position control system of Figure 2;
Figures 4(A) and 4~B) are sectional views for explaining an operational mode of a focus control unit included in the optical focus position control system of Figure 2 and Figures 5(A), 5(B) and 5(C) are sectional views for explaining an operational mode of a tracking control unit included in the optical focus position control system of Figure 2.
Figure 1 shows a simplified block diagram of an optical disc apparatus as a preferred embodiment of the present invention. In Figure 1, symbol 1 denotes a laser beam source that emits laser beams 2. Symbol 3 denotes a mirror, and symbol 4 denotes an objective lens that causes the laser beams 2 to be focussed onto the re-cording medium surface of a disc. Symbol 5 denotes anoptical focus position control device that causes the optical focus position to be accurately dir~cted onto the tracks of the recording medium of the disc by driving the objective lens 4 in the vertical (up/down) and horizontal (left/right) directions. Symbol 6 denotes an optical head that contains all the optical devices mentioned above.
Symbol 7 denotes a recording~erasing coil that provides the surface of the disc recording medium with magnetism while either recording or erasing information. Symbol 8 denotes the optical disc, which incorporates a disc re-cording medium 8', and symbol 9 denotes a motor that causes the optical disc to rotate.
~Z~ 3 The focus control to be performed by the optical focus position control ~evice 5, i.e. a fine aajustment o~ the incident laser beam focus position relative to the disc displacement in the direction of the incident laser beam axis, can be achieved by causing the objective lens 4 to move in the direction of the thickness of the optical disc 8. On the other hand, the tracking control to be performed by the optical focus position control device 5, i.e. a fine adjustment of the incident laser beam focus position for counteracting the disc displacement in the radial direction, can be performed by causing the objective lens 4 to move in the radial direction of the optical disc 8.
Figure 2 shows a detailed construction of the optical focus position control system 5. First, the track-ing control device will be described. An objective lens-mirror cylinder 10 supports the objective lens 4. The lens-mirror cylinder 10 is supported by a movable inter-mediate support member 11 via parallel springs 12 so that the lens-mirror cylinder 10 is movable in the radial (leftlright), tracking direction with respect to the inter-mediate support member 11. A tracking permanent magnet 13, a tracking yoke plate 14 and a tracking yoke 15 are secured to the intermédiate support member 11 and form, in combination, a closed magnetic circuit. A tracking magnetic gap 16 is provided between the tracking yoke plate 14 and the tracking yoke 15. A tracking drive coil 17 is secured to the lens-mirror cylinder 10 and extends into the tracking magnetic gap 16. When the tracking control current is fed to the tracking drive coil 17, magnetism will be generated in the tracking drive coil 17, and as a result, due to a combined effect with the other magne-tism generated by the tracking permanent magnet 13, the tracking drive coil 17, the lens-mirror cylinder 10, the ob-jective lens 4, and a counterbalance 18 are all displaced inthe radial direction. The counterbalance 18 is secured to the bottom of the lens-mirror cylinder 10 so that the tracking ~2~
drive force is applied to the center of gravity of the movable tracking elements.
The focus control device will b~ described below.
A focussing permanent magnet 19, a focussing yoke plate 20, and a focussing yoke 21 form, in combination, a closed magnetic circuit. These elements are securely installed in a stationary holder 25 which supports the entire optical focus position control device. A focussing magnetic gap 22 is formed between the focussing yoke plate 20 and the focussing yoke 21. A focus drive coil 23 is secured to the movable intermediate support member 11 and extends into the focussing magnetic gap 22. The movable inter-mediate support member ll is supported by the stationary holder 25 via parallel springs 24 so that the movable in-termediat~ support member 11 is movable in the verticaldirection, i.e. in the direction of the incident laser beam a~is with respect to the stationary holder 25. When the focus control current is fed to the focus drive coil 23, magnetism is generated in the focus drive coil 23, and as a result, due to a combined effect with the other magnetism generated by the focussing permanent magnet l9, the tracking control device supported by the movable inter-mediate support member 11 is displaced in the focus direction (i.e. the direction of the incident laser beam axis).
Next, the movement characteristics of both the focussing and tracking controllers of the objective lens-mirror cylinder 10 are described below.
(I) Movement characteristics of the tracking controller As shown in Figure 2, the tracking controller is driven by the electromagnetic effect that interacts between the tracking closed magnetic circuit secured to the intermediate support member 11 and the tracking drive coil 17 secured to the objective lens-mirror cylinder lO.
~he intermediate support member 11 and the objective lens-mirror cylinder 10 are connected to each other via elastic material that is workable only to the left and to the right ? J
~z~
by moving in the radial direction, i.e. via parallel springs 12 that move in the direction of the disc radius. Assuming that the weight of the units movable in the tracking direction (the objective lens 4, the objective lens-mirror cylinder 10, and the tracking drive coil 17) is MT and the spring constant of the parallel springs 12 moving in the direction of the disc radius is KT, then the objective lens-mirror cylinder 10 will have a resonance frequency fT which is represented by the formula fT = 12~ ~ when the objective lens-mirror cylinder 10 moves to the left and to the right. When the tracking drive force FT is generated by the interacting electromagnetic force men-tioned above with a frequency denoted by fHz, the movement phase delay caused by the displacement XT of the objective lens-mirror cylinder 10 in the tracking direction is 0 through 90 when 0 < f < fT, or 90 through 180 when fT < f, or near 180 when fT f. When the tracking drive force FT is gen~rated, the delay in the movement phase caused by the displacement XT of the objective lens-mirror cylinder 10 moving to the tracking target position YT should remain below 180 throughout the frequency bands of the tracking control signal. When a phase advancing compensa-tion circuit is used to advance the phase of the track-ing drive signal FT, the phase delay is properly maintained below 180. This ensures a stable tracking control.
(II) Movement characteristics of the focussing controller As shown in Figure 2, the focussing controller is driven by the electromagnetic effect that interacts between the focussing closed magnetic circuit secured to the stationary holder 25 and the focussing drive coil 23 secured to the intermediate support member 11. The inter-mediate support member 11 and the stationary holder 25 are connected to each other via the parallel springs 24 which are workable only in the vertical direction by moving in the direction of focussing. Assuming that the weight of the parts movable in the direction of focussing, inclu-ding the tracking control device, is MF, whereas the spring ~l~Z~$1~'7~
constant of the parallel springs 24 moving in the direction of focussing is KF, then the objective lens-mirror cylinder lO will be provided with a resonance frequency which is represented by the formula fF = l2~ ~ (hereinafter called the primary resonance frequency) when performing vertical (up/down) movements. The interim holder 11 and the ob-jective lens-mirror cylinder 10 are connected to each other via the parallel springs 12 movable in the tracking di-rection. When the focus driving force is applied to the device, the parallel springs 12 move slightly in the ver-tical direction due to their elasticity. Thus, assuming that the spring constant in the focus-direction of the parallel springs 12 is KT', the objective lens-mirror cylinder 10 will have a resonance frequency (hereinafter called the secondary resonance frequency) represented as flF - 1 ~
2~ ~ MT -As described above, whenever the objective lens-mirror cylinder 10 moves upward and downward, both the primary and secondary resonance frequencles exist. Note that the spring constant KT' in the vertical direction of the parallel spring 12 is substantial or KT' >> KF.
This means that the secondary resonance frequency f'F is significantly higher than the primary resonance frequency fF, the relationship of which is denoted by f'F > fF. As soon as a driving force FF for the focussing operation is given by the interacting electromagnetic force, the movement phase delay in the displacement XF caused by the objective lens-mirror 10 in the focussing direction can be represented to be 0 through 90 when 0 < f < fF, where f (Hz) represents a frequency, whereas such a delay in the movement phase can be represented to be 90 through 270 when fF < f < f'F, and it will be 270 through 360 when f'F < f. When the focussing drive force FF is gen-erated, the delay in the movement phase caused by the dis-placement XF of the objective lens-mirror cylinder 10 moving to the focussing target position YF should remain below 180 throughout the frequency bands of the focussing con-~Z~
trol signal. As described earlier, even if the phase ad-vancing compensation circuit is used to advance the phase of the focussing drive signal FF, since there is a certain limit for advancing the phase amount, the phase cannot be compensated for in order that it can exceed 180 signi-ficantly. To properly compensate for the phase delay, the second resonance frequency fF shou]d be set at an op-timum level higher than the frequency band o the focus-sing control signal. Although frequency bands available for the focussing control signal are variable according to uses, generally, an optical disc apparatus uses 1 through 4 K~z of the frequency bands. As a result, the secondary resonance frequency f'F should be set at a level above 7 KHz.
Means for designing a construction that fully satisfies the above conditions are described below.
As described above, the secondary resonance fre-quency f'F can be determined by the spring constant KT' of the parallel tracking springs 12 when they move in the focussing direction and by the weight MT of the moving parts in the tracking direction. The secondary resonance frequency f'F becomes large as the spring constant KT' becomes large and as the weight MT becomes small.
Nevertheless, since there is a certain limit in the means for decreasing the weight MT of the objective lens 4 and the lens-mirror cylinder 10, the weight MT of the parts moving in the tracking direction cannot be decreased signi-ficantly. (Normally, the weight MT is designed in a range from 0.5 to 10 grams). The inventors, carried out ex-periments by increasing the spring constant KT' of thetracking parallel springs 12 during movement in the ver-tical direction. The spring constant KT' was found to be KT'~KT = (XT/YT) 2 when the tracking parallel springs 12 had a length XT in the focus direction YT. As a result, it is clear that the spring constant KT' in the vertical direction (upldown) can be increased by increasing the length XT and decreasing the thickness YT of the parallel .
~lZ~73 springs 12. In the light of the relationship denoted by ffTF = ~ , the secondary resonance frequency f'F can be obtained by an equation f'F = yT.fT. It was eventually made clear that the tracking parallel springs 12 should be designed so that they have a thickness YT of 20 through 50 microns and an actual length that is from 100 to 500 times the thickness YT. If the tracking parallel springs 12 can be correctly designed in accordance with the find-ings described above, the delay in the movement phase caused by the displacement XF of the objective lens 4 against the focussing target position can be decreased below 180 within the frequency bands available for the focussing control signal. It is important that the phase advancing compensation circuit be used for correctly com-pensating for the movement phase.
According to the results of the trials carriedout by the inventors, very stable focussing and tracking controls were achieved in practice by using tracking parallel springs 12 made from beryllium-copper alloy having a th~ckness of 30 through 50 microns.
(III) Damping Characteristics Improvement in the Tracking Control Device and the Focus Control Device As discussed above in the sections ~I) and (II), there are two kinds of resonance frequencies fF and fT
when the tracking control device and the focus control device are operated. If the damping characteristics in the directions of focussing and tracking control remain negligible, the multiple resonance factor in the resonance frequencies fF and fT will grow, thus causing interference vibration to easily occur during either the focussing or tracking control operation. Also, when a certain frequency above the resonance frequency level is applied, the phase in response to the displacement of the movable parts will be extremely delayed to a point very close to 180, which will result in an extremely unstable optical focus position control opera-tion. To prevent this and ensure satisfactory damping ~Z~73 characteristics, the following means may be effectively employed.
(III-a) Structure of the primary means The primary improvement includes a latexed damp-ing member painted on the focussing parallel spring and/orthe tracking parallel spring. (A plate rubber attached to the metal spring by an adhesive is not suitable for the device, because the spring constant becomes high due to the adhesive). To make up the damping material, viscose-elastic materials such as silicon rubberr butyl rubber, silicon-butyl rubber, and acrylic-ethylene rubber, foaming synthetic resin such as foamed polyurethane, and viscose fluid such as silicon grease, can be made available.
(III-b) Structure of the second means Figure 3 shows a plan view of one of the focus-sing parallel springs 24. Each focussing parallel spring 24 has a structure that connects two concentric circles, where two flat sheet springs, each being connected to four arms at the edges, are provided at the upper and lower ZO positions. The parallel springs 24, moving in the di-rection of focus, permit movement of the intermediate holder 11 in the vertical direction with respect to the stationary holder 25 (see Figure 2). Damping material 26 is bonded to the portion C of the surface of the focus-sing parallel springs 24, where the largest amount of rela-tive displacement exists, thus resulting in greater damping characteristics in the direction of focus. To make up the damping material 26, viscose-elastic materials such as silicon-rubber, butyl rubber, silicon-butyl rubber, and acrylic-ethylene rubber, and foaming synthetic resin such as foamed polyurethane, can be made available.
(III-c) Structure of the third means The third improvement is to form the focussing parallel springs and/or the tracking parallel springs from a vibration-proof alloy such as manganese-copper alloy, ferro-aluminum alloy, nickel-titanium alloy or magnesium alloy.
~Z~ 73 The structures of (III-a), ~ b) and (III-c) can be effectively combined with each other to signifi-cantly enhance the damping characteristics~
(IV) Improvement relating to the application of the pre-sent optical focus position controlling device to an optomagnetic disc apparatus A variety of means may be employed for effec-tively preventing the optical focus position control device from causing its magnetic leakage to adversely affect the recording medium 8' of the optical disc ~. Such effective means are described below.
(IV-a) Details of means related to the focus controller Figure 4(A) shows a sectional view of a focus controller incorporating an improved means as a preferred embodiment of the present invention, whereas Figure 3(B) shows a sectional view of another focus controller not incorporating any improved means. Symbols N and S res-pectively denote the north and south poles. As shown in Figure 3(A), the focus controller provides a magnetic gap 22 for the focussing operation in an area close to the optical disc. This construction minimizes magnetic leakage that otherwise adversely affects the recording medium 8' of the optical disc. In other words, magnetic leakage will significantly affect the surface of the re-cording medium 8' of the optical disc if the magnetic gap22' for the focussing operation is provided in an area remote from the optical disc as shown in Figure 3(B). The lengths of the arrows in Figures 3(A) and 3(B) denote the intensities of the leakage magnetism at the respective positions, while the direction of the magnetic leakage is also indicated by the arrows.
(IV-B) Details of means related to the tracking controller Figure 5(A) shows a sectional view of the track-ing controller incorporating an improved means as a pre-ferred embodiment of the present invention, whereas Figures5(B) and 5~C) show sectional views of another tracking controller without any such improved means. The tracking ~2~ 3 controller incorporating an improved means provides the permanent magnet 13 available for the tracking operation in the center position of the closed magnetic circuit.
This construction minimizes magnetic leakage that other-wise adversely affects the recording medium 8' of theoptical disc. In other words, in such a construction where the permanent magnet 13' available for the tracking opera-tion is provided encircling the closed magnetic circuit as shown in Figure 5(B), or in such a construction wnere the open magnetic circuit faces the optical disc as shown in Figure 5(C), if the magnitude of magnetism that functions in the magnetic gap 16' or 16'' is designed to be equal to that in the magnetic gap 16 of Figure 5(A) available for the tracking operation, magnetic leakage will signi-ficantly affect the surface of the recording medium 8'of the optical disc.
(IV-c) Details of means for supporting the tracking con-trol device Whèn the magnetic field in the tracking magnetic space is selected at a fixed value, the magnetic leakage ~ncreases as the tracking magnetic gap increases. Thus, it is preferable for the tracking magnetic gap to be made as narrow as possible. The objective lens must be movable in two dimensions, i.e. up/down and leftlright. If both the tracking control magnetic circuit and the focus con-trol magnetic circuit are supported by the stationary holder, the tracking coil must be movable in the two dimensions within the tracking magnetic gap. This requires a wide magnetic gap.
In accordance with the present embodiment, the tracking magnetic circuit is supported by the movable in-termediate holder 11. By this construction, the tracking drive coil 17 is required to move only in the left/right direction within the tracking magnetic gap 16. This will effectively minimize the tracking magnetic gap 16 and the magnetic leakage.
An embodiment of the invention being thus ,,, described, it will be obvious that the invention may be varied in many ways. Such variations are not to be re-garded as a departure from the spirit and scope of the in~ention, and all such modifications are intended to be included within the scope of the following claims~
Claims (37)
1. An optical focus position control device for controlling the optical focus position of an optical beam in an optical disc apparatus, the optical focus posi-tion control device comprising:
a stationary holder;
tracking control means for shifting a mirror cylinder containing an objective lens in the radial di-rection of an optical disc, the tracking control device including:
an intermediate holder;
tracking parallel spring means connecting said mirror cylinder to said intermediate holder in such a manner that said objective lens and said mirror cylinder are movable in said radial direction with respect to said intermediate holder; and electromagnetic tracking drive means for shifting said objective lens and said mirror cylinder in said radial direction within said intermediate holder for displacing said optical beam radially of said optical disc; and focus control means for shifting said tracking control device in the direction of the optical axis of said optical beam, said focus control device including:
focusing parallel spring means connecting said intermediate holder to said stationary holder in such a manner that said intermediate holder is movable in the direction of said optical axis; and electromagnetic focus drive means for shifting said intermediate holder in the direction of said optical axis.
a stationary holder;
tracking control means for shifting a mirror cylinder containing an objective lens in the radial di-rection of an optical disc, the tracking control device including:
an intermediate holder;
tracking parallel spring means connecting said mirror cylinder to said intermediate holder in such a manner that said objective lens and said mirror cylinder are movable in said radial direction with respect to said intermediate holder; and electromagnetic tracking drive means for shifting said objective lens and said mirror cylinder in said radial direction within said intermediate holder for displacing said optical beam radially of said optical disc; and focus control means for shifting said tracking control device in the direction of the optical axis of said optical beam, said focus control device including:
focusing parallel spring means connecting said intermediate holder to said stationary holder in such a manner that said intermediate holder is movable in the direction of said optical axis; and electromagnetic focus drive means for shifting said intermediate holder in the direction of said optical axis.
2. The optical focus position control device of claim 1, wherein said tracking parallel spring means includes a parallel spring which has a length XT in said optical axis direction, and a thickness YT, which satisfy the condition:
3. The optical focus position control device of claim 1, wherein said tracking parallel spring means includes:
a parallel metal spring; and an acrylic-ethylene rubber attached to the surface of said parallel metal spring.
a parallel metal spring; and an acrylic-ethylene rubber attached to the surface of said parallel metal spring.
4. The optical focus position control device of claim 1, whereio said tracking parallel spring means includes:
a parallel metal spring; and a latexed rubber attached to the surface of said parallel metal spring.
a parallel metal spring; and a latexed rubber attached to the surface of said parallel metal spring.
5. The optical focus position control device of claim 4, wherein said latexed rubber is a latexed acrylic-ethylene rubber.
6. The optical focus position control device of claim 1, 2 or 3, wherein said tracking parallel spring means includes a parallel spring made of vibration-proof alloy.
7. The optical focus position control device of claim 1, 2 or 3, wherein said focussing parallel spring means includes:
a parallel metal spring; and an acrylic-ethylene rubber attached to the surface of said parallel metal spring.
a parallel metal spring; and an acrylic-ethylene rubber attached to the surface of said parallel metal spring.
8. The optical focus position control device of claim 1, wherein said focussing parallel spring means includes:
a parallel metal spring; and a latexed rubber attached to the surface of said parallel metal spring.
a parallel metal spring; and a latexed rubber attached to the surface of said parallel metal spring.
9. The optical focus position control device of claim 8, wherein said latexed rubber is a latexed acrylic-ethylene rubber.
10. The optical focus position control device of claim 1, 2 or 3, wherein said focussing parallel spring means includes a parallel spring made of vibration-proof alloy.
11. The optical focus position control device of claim 1, said electromagnetic tracking drive means com-prising:
a tracking permanent magnet forming a closed magnetic circuit;
a tracking yoke plate;
a tracking yoke;
a tracking magnetic gap formed between said track-ing yoke plate and said tracking yoke; and a radial drive coil disposed in said tracking magnetic gap.
a tracking permanent magnet forming a closed magnetic circuit;
a tracking yoke plate;
a tracking yoke;
a tracking magnetic gap formed between said track-ing yoke plate and said tracking yoke; and a radial drive coil disposed in said tracking magnetic gap.
12. The optical focus position control device of claim 11, wherein said tracking permanent magnet is disposed in a central position of said closed magnetic circuit.
13. The optical focus position control device of claim 11, wherein said tracking parallel spring means includes:
a parallel metal spring; and a latexed acrylic-ethylene rubber attached to the surface of said parallel metal spring.
a parallel metal spring; and a latexed acrylic-ethylene rubber attached to the surface of said parallel metal spring.
14. The optical focus position control device of claim 13, wherein said parallel metal spring has a length XT in said optical axis direction, and a thickness YT, which satisfy the condition:
15. The optical focus position control device of claim 1, said electromagnetic focus drive means com-prising:
a focussing permanent magnet forming a closed magnetic circuit;
a focussing yoke plate;
a focussing yoke;
a focussing magnetic gap formed between said focussing yoke plate and said focussing yoke; and a focussing drive coil disposed in said focus-sing magnetic gap.
a focussing permanent magnet forming a closed magnetic circuit;
a focussing yoke plate;
a focussing yoke;
a focussing magnetic gap formed between said focussing yoke plate and said focussing yoke; and a focussing drive coil disposed in said focus-sing magnetic gap.
16. The optical focus position control device of claim 15, wherein said focussing magnetic gap is located close to a position for the installation of an optical disc in said optical disc apparatus.
17. The optical focus position control device of claim 16, wherein said focussing parallel spring means includes:
a parallel metal spring; and a latexed acrylic-ethylene rubber attached to the surface of said parallel metal spring.
a parallel metal spring; and a latexed acrylic-ethylene rubber attached to the surface of said parallel metal spring.
18. An optical focus and positioning control device for controlling the optical focus and position of an optical beam such as a laser beam in an optical disc apparatus, the optical focus position control device comprising:
an objective lens;
lens support means for supporting said objective lens;
a stationary holder;
tracking control means for shifting said lens support means in the radial direction of the optical disc, said tracking control means including, a movable intermediate holder, tracking parallel spring means for connecting said lens support means to said intermediate holder in a manner to allow said lens support means to move in with respect to said intermediate holder in the radial direction of the optical disc, and electromagnetic tracking drive means, having a closed magnetic circuit mounted for movement with said intermediate holder, for shifting said lens support means in said radial direction within said intermediate holder, said closed magnetic circuit minimizing flux leakage therefrom; and focus control means for shifting said tracking control means in the direction of the optical axis of said optical beam, said focus control means including, focussing parallel spring means for connecting said intermediate holder to said stationary holder in a manner to allow said intermediate holder to move with respect to said stationary holder in said optical axis direction and electromagnetic focus drive means for shifting said intermediate holder in said optical axis direction within said stationary holder, said electromagnetic focus drive means including a closed magnetic circuit to minimize flux leakage therefrom.
an objective lens;
lens support means for supporting said objective lens;
a stationary holder;
tracking control means for shifting said lens support means in the radial direction of the optical disc, said tracking control means including, a movable intermediate holder, tracking parallel spring means for connecting said lens support means to said intermediate holder in a manner to allow said lens support means to move in with respect to said intermediate holder in the radial direction of the optical disc, and electromagnetic tracking drive means, having a closed magnetic circuit mounted for movement with said intermediate holder, for shifting said lens support means in said radial direction within said intermediate holder, said closed magnetic circuit minimizing flux leakage therefrom; and focus control means for shifting said tracking control means in the direction of the optical axis of said optical beam, said focus control means including, focussing parallel spring means for connecting said intermediate holder to said stationary holder in a manner to allow said intermediate holder to move with respect to said stationary holder in said optical axis direction and electromagnetic focus drive means for shifting said intermediate holder in said optical axis direction within said stationary holder, said electromagnetic focus drive means including a closed magnetic circuit to minimize flux leakage therefrom.
19. The optical focus position control device of claim 18, said electromagnetic tracking drive means comprising:
a tracking permanent magnet creating said closed magnetic circuit;
a tracking yoke plate supporting said tracking permanent magnet;
a tracking yoke mounted on said intermediate holder and supplying said tracking yoke plate a tracking magnetic space formed between said tracking yoke plate and said tracking yoke; and a radial drive coil disposed in said tracking magnetic space so as to cross said tracking magnetic space.
a tracking permanent magnet creating said closed magnetic circuit;
a tracking yoke plate supporting said tracking permanent magnet;
a tracking yoke mounted on said intermediate holder and supplying said tracking yoke plate a tracking magnetic space formed between said tracking yoke plate and said tracking yoke; and a radial drive coil disposed in said tracking magnetic space so as to cross said tracking magnetic space.
20. The optical focus position control device of claim 19, wherein said tracking parallel spring means includes, a parallel metal spring; and a latexed acrylic-ethylene rubber attached to the surface of said parallel metal spring.
21. The optical focus position control device of claim 18, said electromagnetic focus drive means comprising:
a focusing permanent magnet creating said closed magnetic circuit;
a focusing yoke plate supporting said focusing permanent magnet;
a focusing yoke mounted on said stationary holder and supporting said focusing yoke plate;
a focusing magnetic space formed between said focusing yoke plate and said focusing yoke; and a focusing drive coil disposed in said focusing magnetic space so as to cross said focusing magnetic space.
a focusing permanent magnet creating said closed magnetic circuit;
a focusing yoke plate supporting said focusing permanent magnet;
a focusing yoke mounted on said stationary holder and supporting said focusing yoke plate;
a focusing magnetic space formed between said focusing yoke plate and said focusing yoke; and a focusing drive coil disposed in said focusing magnetic space so as to cross said focusing magnetic space.
22. The optical focus position control device of claim 21, wherein said focusing magnetic space is located close to an optical disc when installed in said optical disc apparatus.
23. The optical focus position control device of claim 19, wherein said tracking permanent magnet is disposed in the central position of said closed magnetic circuit.
24. The optical focus position control device of claim 19, wherein said tracking parallel spring means includes:
a parallel metal spring; and a latexed acrylic-ethylene rubber attached to the surface of said parallel metal spring.
a parallel metal spring; and a latexed acrylic-ethylene rubber attached to the surface of said parallel metal spring.
25. The optical focus position control device of claim 24, wherein said parallel metal spring has a length XT in said optical axis direction, and a thickness YT, which satisfy the condition:
26. An optical focus and positioning control device for controlling the optical focus and position of an optical beam such as a laser beam in an optical disc apparatus, the optical focus position control device comprising:
an objective lens;
lens support means for supporting said objective lens;
a stationary holder;
tracking control means for shifting said lens support means in the radial direction of the optical disc, said tracking control means including, an intermediate holder, tracking parallel spring means for connecting said lens support means to said intermediate holder in a manner to allow said lens support means to move in with respect to said intermediate holder in the radial airection of the optical disc, said tracking parallel spring means including, a parallel metal spring, and a viscose-elastic material attached to the surface of said parallel metal spring, and electromagnetic tracking drive means for shifting said lens support means in said radial direction within said intermediate holder; and focus control means for shifting said tracking control means in the direction of the optical axis of said optical beam, said focus control means including, focusing parallel spring means for connecting said intermediate holder to said stationary holder in a manner to allow said intermediate holder to move with respect to said stationary holder in said optical axis direction; and electromagnetic focus drive means for shifting said intermediate holder in said optical axis direction within said stationary holder.
an objective lens;
lens support means for supporting said objective lens;
a stationary holder;
tracking control means for shifting said lens support means in the radial direction of the optical disc, said tracking control means including, an intermediate holder, tracking parallel spring means for connecting said lens support means to said intermediate holder in a manner to allow said lens support means to move in with respect to said intermediate holder in the radial airection of the optical disc, said tracking parallel spring means including, a parallel metal spring, and a viscose-elastic material attached to the surface of said parallel metal spring, and electromagnetic tracking drive means for shifting said lens support means in said radial direction within said intermediate holder; and focus control means for shifting said tracking control means in the direction of the optical axis of said optical beam, said focus control means including, focusing parallel spring means for connecting said intermediate holder to said stationary holder in a manner to allow said intermediate holder to move with respect to said stationary holder in said optical axis direction; and electromagnetic focus drive means for shifting said intermediate holder in said optical axis direction within said stationary holder.
27. The optical focus position control device of claim 26, wherein said parallel spring has a length XT
in said optical axis direction, and a thickness YT, which satisfy the condition:
in said optical axis direction, and a thickness YT, which satisfy the condition:
28. The optical focus position control device of claim 26, wherein said viscose-elastic material is an acrylic-ethylene rubber.
29. The optical focus position control device of claim 28, wherein said viscose-elastic material is a latexed rubber.
30. The optical focus position control device of claim 29, wherein said latexed rubber is a latexed acrylic-ethylene rubber.
31. An optical focus and positioning control device for controlling the optical focus and position of an optical beam such as a laser beam in an optical disc apparatus, the optical focus position control device comprising:
an objective lens;
lens support means for supporting said objective lens a stationary holder tracking control means for shifting said lens support means in the radial direction of the optical disc, said tracking control means including, an intermediate holder, tracking parallel spring means for connecting said lens support means to said intermediate holder in a manner to allow said lens support means to move in with respect to said intermediate holder in the radial direction of the optical disc, said tracking parallel spring means including a parallel spring formed of a vibration-proof alloy, and electromagnetic tracking drive means for shifting said lens support means in said radial direction within said intermediate holder, and focus control means for shifting said tracking control means in the direction of the optical axis of said optical beam, said focus control means including, focusing parallel spring means for connecting said intermediate holder to said stationary holder in a manner to allow said intermediate holder to move with respect to said stationary holder in said optical axis direction, and electromagnetic focus drive means for shifting said intermediate holder in said optical axis direction within said stationary holder.
an objective lens;
lens support means for supporting said objective lens a stationary holder tracking control means for shifting said lens support means in the radial direction of the optical disc, said tracking control means including, an intermediate holder, tracking parallel spring means for connecting said lens support means to said intermediate holder in a manner to allow said lens support means to move in with respect to said intermediate holder in the radial direction of the optical disc, said tracking parallel spring means including a parallel spring formed of a vibration-proof alloy, and electromagnetic tracking drive means for shifting said lens support means in said radial direction within said intermediate holder, and focus control means for shifting said tracking control means in the direction of the optical axis of said optical beam, said focus control means including, focusing parallel spring means for connecting said intermediate holder to said stationary holder in a manner to allow said intermediate holder to move with respect to said stationary holder in said optical axis direction, and electromagnetic focus drive means for shifting said intermediate holder in said optical axis direction within said stationary holder.
32. An optical focus and positioning control device for controlling the optical focus and position of an optical beam such as a laser beam in an optical disc apparatus, the optical focus position control device comprising:
an objective lens lens support means for supporting said objective lens;
a stationary holder;
tracking control means for shifting said lens support means in the radial direction of the optical disc, said tracking control means including, an intermediate holder, tracking parallel spring means for connecting said lens support means to said intermediate holder in a manner to allow said lens support means to move in with respect to said intermediate holder in the radial direction of the optical disc, and electromagnetic tracking drive means for shifting said lens support means in said radial direction within said intermediate holder; and focus control means for shifting said tracking control means in the direction of the optical axis of said optical beam, said focus control means including, focusing parallel spring means for connecting said intermediate holder to said stationary holder in a manner to allow said intermediate holder to move with respect to said stationary holder in said optical axis direction, said focusing parallel spring means including, a parallel metal spring, and a viscose-elastic material attached to the surface of said parallel metal spring, and electromagnetic focus drive means for shifting said intermediate holder in said optical axis direction within said statutory holder.
an objective lens lens support means for supporting said objective lens;
a stationary holder;
tracking control means for shifting said lens support means in the radial direction of the optical disc, said tracking control means including, an intermediate holder, tracking parallel spring means for connecting said lens support means to said intermediate holder in a manner to allow said lens support means to move in with respect to said intermediate holder in the radial direction of the optical disc, and electromagnetic tracking drive means for shifting said lens support means in said radial direction within said intermediate holder; and focus control means for shifting said tracking control means in the direction of the optical axis of said optical beam, said focus control means including, focusing parallel spring means for connecting said intermediate holder to said stationary holder in a manner to allow said intermediate holder to move with respect to said stationary holder in said optical axis direction, said focusing parallel spring means including, a parallel metal spring, and a viscose-elastic material attached to the surface of said parallel metal spring, and electromagnetic focus drive means for shifting said intermediate holder in said optical axis direction within said statutory holder.
33. The optical focus position control device of claim 32, wherein said viscose-elastic material is an acrylic-ethylene rubber.
34. The optical focus position control device of claim 32, wherein said viscose-elastic material is a latexed rubber.
35. The optical focus position control device of claim 34, wherein said latexed rubber is a latexed acrylic-ethylene rubber.
36. The optical focus position control device of claim 29, wherein said parallel metal spring is made of a vibration-proof alloy.
37. An optical focus and positioning device for adjusting the optical focus and position of an optical beam such as a laser beam of an optical disc apparatus for communicating information with an optical disc when located in a disc mounting position comprising:
an objective lens;
an objective lens support;
support position adjustment means for shifting said lens support with respect to an optical disc mounted in said disc mounting position device, said tracking adjustment means including closed magnetic circuit means for applying a shifting force to said lens support, said closed magnetic circuit means further minimizing the presence of leakage flux adjacent said disc mounting position.
an objective lens;
an objective lens support;
support position adjustment means for shifting said lens support with respect to an optical disc mounted in said disc mounting position device, said tracking adjustment means including closed magnetic circuit means for applying a shifting force to said lens support, said closed magnetic circuit means further minimizing the presence of leakage flux adjacent said disc mounting position.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP58-68771 | 1983-04-18 | ||
| JP6877183A JPS59193552A (en) | 1983-04-18 | 1983-04-18 | Controller for light focusing position |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1219073A true CA1219073A (en) | 1987-03-10 |
Family
ID=13383325
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000451907A Expired CA1219073A (en) | 1983-04-18 | 1984-04-12 | Optical focus position control in an optical memory system |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JPS59193552A (en) |
| CA (1) | CA1219073A (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS634433A (en) * | 1986-06-24 | 1988-01-09 | Sharp Corp | Objective lens driver |
| JPH02270150A (en) * | 1989-04-12 | 1990-11-05 | Olympus Optical Co Ltd | Optical information recording and reproducing device |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5679820A (en) * | 1979-11-30 | 1981-06-30 | Matsushita Electric Works Ltd | Delayed distinguishing switch |
| JPS56117338A (en) * | 1980-02-16 | 1981-09-14 | Olympus Optical Co Ltd | Driving device for objective lens |
| JPS6217Y2 (en) * | 1980-07-04 | 1987-01-06 |
-
1983
- 1983-04-18 JP JP6877183A patent/JPS59193552A/en active Granted
-
1984
- 1984-04-12 CA CA000451907A patent/CA1219073A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| JPS59193552A (en) | 1984-11-02 |
| JPH0516091B2 (en) | 1993-03-03 |
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| MKEX | Expiry |