Optical disk apparatus having a reduced size

Abstract: An optical disk apparatus characterized in that the apparatus comprises: a spindle motor (14) for rotating a mounted optical disk (17); and a swing-motion type optical head apparatus (15) for scanning the optical disk in a radial direction of the optical disk by moving the objective lens (50), the head apparatus being made to swing about a swing axis in a plane parallel to a recording surface (17a) of the mounted optical disk (17), the swing-motion type optical head apparatus comprising: a head main body (20) supported by bearing device (23) so as to be enabled to swing about the axis; and an electromagnetic driving device (40) for driving the head main body to swing, wherein the bearing device and the electromagnetic driving device are provided at a location outside of the mounted optical disk when viewed in a direction perpendicular to the recording surface, so that the mounted optical disk has a level within the height of the bearing device (23) and the electromagnetic driving device (40).

Description: The present invention generally relates to optical storage of information, and more particularly to an optical disk apparatus that uses a flexible and removable recording medium for recording information. In the information storage devices for storing information, there has been a continuous demand for reducing the size of the device. In addition, there is a persisting demand for an increased storage capacity of information in any types of optical storage devices. Conventionally, various storage devices are proposed and used for storing information. For example, use of a semiconductor memory device configured such as a so-called IC card device is proposed. In the IC card devices, one can form the device with a very small size particularly with respect to the thickness. However, the IC card devices generally have a drawback of small storage capacity of information. As the means for storing information, floppy disk devices are used also commonly. Particularly, compact floppy disk devices of the 3.5 inch size are used commonly. However, the device is still bulky and provides only a limited storage capacity. Under such a situation, there is a proposal to construct an optical disk device that is capable of replacing the recording medium. According to the optical disk device of such a construction, a large storage capacity is guaranteed as a result of use of the optical recording and reproducing technique. For example, Japanese Laid-Open Patent Publication 63-20732 describes a compact optical disk device that uses a detachable rotary optical recording disk and an optical head held on a swing arm, wherein the swing arm swings about an axis such that the optical head held at a tip end of the swing arm scans the recording surface of the rotary optical disk with the swinging motion of the arm. More specifically, the swing arm provides a hollow passage for an optical beam, and the optical head provided at the tip end of the arm includes a mirror for deflecting the optical beam in the direction perpendicular to the recording surface of the optical disk and a lens for focusing the optical beam thus deflected on the recording surface of the optical beam. In addition, there is provided an optical device in the swing arm in correspondence to the swing axis of the arm. In order to accommodate the optical device in alignment with the axis of the swinging motion, the arm is held rotatably to the base of the optical disk device by upper and lower shafts separated from each other by a gap, and the detection device is accommodated into a space that is formed in correspondence to such a gap. In other words, the swing arm accommodates therein the optical device at the end that is opposite to the end at which the optical head is provided. According to the construction of the device of the reference, one can record and reproduce information signals on and from the rotary optical recording medium by means of the optical head while swinging the arm about the axis. On the other hand, the device has a problem, associated with the feature of providing the optical device at the space formed in correspondence to the gap between the upper and lower shafts, namely that a substantial part of the arm as well as a substantial part of the electromagnetic driving mechanism are located under the region that is covered by the optical disk when viewed in the direction perpendicular to the optical disk. Thereby, because of the thickness of the axial part of the arm as well as the thickness of the electromagnetic driving mechanism, the optical disk has to be mounted at a level above these bulky portions of the arm and the electromagnetic driving mechanism. Thereby, the device of the reference inevitably becomes thick and bulky, contrary to the requirement to reduce the size of the device. Further, the device of the reference has a problem, associated with the fact that the arm is formed to be elastic for effecting the focusing control and the fact that the mirror for deflecting the optical beam is fixed on the elastic arm, in that the focusing adjustment of the lens tends to cause various aberrations and decrease of luminosity due to the deviation of the optical path. According to the present invention there is provided optical disk apparatus for recording and/or reproducing information on and from a recording surface provided on an optical disk, which apparatus comprises: optical disk support means for supporting such an optical disk at a desired location within the apparatus, which means include a spindle motor for causing such an optical disk to rotate during use; and a swing-motion type optical head apparatus, for radially scanning the said optical disk using light transmitted through an objective lens, which apparatus comprises: a head main body having an arm carrying the said objective lens, such that the lens faces the said recording surface of the mounted optical disk, and a supporting member for supporting the said arm, the said head main body being supported by bearing means for enabling the head main body to swing about a swing axis in a plane parallel to the recording surface of the said mounted optical disk; and electromagnetic driving means connected to drive the said head main body to swing about the said swing axis; the said optical disk support means and swing-motion type optical head apparatus being mounted on a base of the optical disk apparatus relative to one another such that, if viewed in a direction perpendicular to the said plane, neither the said supporting member nor the said electromagnetic driving means would appear to lie above or below an optical disk supported by the said optical disk support means; characterised in that the said optical disk support means and the said head main body are constructed and arranged such that when the apparatus is in use an optical disk is supported by the said optical disk support means at a position relative to the said base which is lower than that of the highest point of the said head main body. Thus, since the vertical position of the optical disk is not dependent on the bearings or the electromagnetic driving means, the thickness of the optical disk does not add to the height of the swing-motion type optical head apparatus. In this way the height of the optical disk apparatus is not determined by the result of an addition of the height of the optical head to the thickness of the optical disk, but essentially by the height of the optical head only. Thereby the apparatus can be made thinner than conventional apparatus. EP-A-0400570 reflecting the preamble of claim 1 discloses optical disk apparatus for recording and/or reproducing information on and from a recording surface provided on an optical disk, which apparatus comprises: optical disk support means for supporting such an optical disk at a desired location within the apparatus, which means include a spindle motor for causing such an optical disk to rotate during use; and a swing-motion type optical head apparatus, for radially scanning the said optical disk using light transmitted through an objective lens, which apparatus comprises: a head main body having an arm carrying the said objective lens, such that the lens faces the said recording surface of the mounted optical disk, and a supporting member for supporting the said arm, the said head main body being supported by bearing means for enabling the head main body to swing about a swing axis in a plane parallel to the recording surface of the said mounted optical disk; and electromagnetic driving means connected to drive the said head main body to swing about the said swing axis; the said optical disk support means and swing-motion type optical head apparatus being mounted on a base of the optical disk apparatus relative to one another such that, if viewed in a direction perpendicular to the said plane, neither the said supporting member nor the said electromagnetic driving means would appear to lie above or below an optical disk supported by the said optical disk support means. However, in such apparatus the optical disk is supported at a higher position than the head main body. Reference will now be made, by way of example, to the accompanying drawings, in which:- Fig. 1 shows an interior perspective view illustrating optical disk apparatus embodying the present invention; Fig. 2 shows a side view of the apparatus of Fig. 1; Fig. 3 shows a perspective view of part of the apparatus of Fig. 1; Fig. 4 illustrates a portion of the part shown in Fig. 3; Fig. 5 shows a partially broken-away view of part of the apparatus of Fig. 1; Fig. 6 shows a cross-sectional view taken along the line VI - VI of Fig. 5; Fig. 7 shows a view of part of the apparatus of Fig. 1; Figs. 8 and 9 illustrate further parts of the apparatus of Fig. 1; Figs. 10(A), 10(B), 11, 12, 13, 14, 15 and 16 further illustrate the part shown in Fig. 9; Fig. 17 shows a partially cut-away perspective view of another optical disk apparatus embodying the present invention; Fig. 18 shows a side view of the apparatus of Fig. 17; Fig. 19 shows a top view of part of the apparatus of Fig. 17; Fig. 20 shows a cross-sectional view taken along the line LX-LX of Fig. 19; Fig. 21 schematically illustrates how part of the apparatus of Fig. 17 is supported; Fig. 22 illustrates a first variation of part of the apparatus of Fig. 17; Fig. 23 schematically illustrates how the part shown in Fig. 22 is supported; Fig. 24 illustrates a variation of a portion of the apparatus of Fig. 17; Fig. 25 illustrates a second variation of part of the apparatus of Fig. 17; Fig. 26 shows a cross-sectional view taken along the line LXVI-LXVI of Fig. 25; Fig. 27 schematically illustrates how the part shown in Fig. 25 is supported; and Fig. 28 illustrates a variation of part of the apparatus of Fig. 25. Figs. 1 and 2 illustrate an overall configuration of an optical disk apparatus 10 embodying the present invention. The optical disk apparatus 10 is configured such that a spindle motor 14 and a swing motion type optical head apparatus 15 are assembled in a frame 13 consisting of a bottom cover 11 and a top cover 12. A write-enabled phase-transition type optical disk 17 is attracted, at a metal hub 18 portion thereof, by a permanent magnet provided on a turntable so that the disk is detachably mounted on the turntable. This optical disk 17 has a diameter D of 46 mm (1.8 inches) and a thickness t of 0.3 mm. Alternatively two of such disks are adhesively attached to each other, resulting in a thickness of 0.6 mm. This small and thin optical disk apparatus 10 has a length L of 75 mm, a width W of 48 mm, and a height H 3 of 5 mm, meaning that it is substantially smaller than an IC memory card. A description will be given next of the swing motion type optical head apparatus 15, which contributes to realizing a thin-type optical disk apparatus 10. As shown in FIG.3, 20 indicates a head main body, which main body consists of a disk portion 21 having a radius R 1 (about 7 mm) and an arm portion 22 that extends therefrom. The head main body is made of a hollow and hermetically sealed structure. This head main body 20 is supported, in a way described below, by a bearing 23 at a side 21a of the disk portion 21, so that the main body can swing. The side 21a is fitted with arc-shaped rails 24 and 25 each having a V-shaped groove, which rails serve as a movable inner ring portion of the bearing 23. The bottom cover 11 is fitted, in positions opposite to the above-mentioned rails 24 and 25, with respective arc-shaped rails 26 and 27 each having a V-shaped groove, which rails serve as a stationary outer ring portion of the bearing 23. As shown in FIG.4, a plurality of steel balls 28 each having a small diameter and being separated from each other by retainers 29 placed between them are engaged to V-shaped grooves 24a and 26a provided opposite to each other in the rails 24 and 26, respectively. Likewise, balls 28 are engaged to V-shaped grooves 25a and 27a provided opposite to each other in the rails 25 and 27, respectively. The head main body 20 is thus supported by the above-mentioned bearing structure 23, so that the body is capable of swinging in directions 32 and 33 shown by arrows in FIG.1 on a swing motion center axle 31, which is designated as a Z axis passing through a center 30 of the disk portion 21. The head main body 20 swings on a plane parallel to a recording face 17a of the mounted optical disk 17; an objective lens 50 described later moves in a radial direction of the mounted optical disk 17. As shown in FIG.4, the bearing 23 is of a thin type where a height H 4 thereof has a dimension corresponding to a thickness t 2 of the rail 24. Since the aforementioned radius R 1 of the disk portion is as large as about 7 mm, angular rigidity of the bearing 23 is great, so that a precise positioning of the optical head apparatus 15 is possible. Further, the bearing 23 is located at a certain horizontal distance from the mounted optical disk 17; and the whole of the disk portion 21 is located at a distance from a region 34 created when the mounted optical disk 17 is projected on the bottom cover 11. As shown in FIG.2, the disk portion 21 and the optical disk 17 are disposed such that the optical disk 17 has a height from the bottom of the apparatus shorter than a height H 5 of the disk portion 21. Since a height H 3 of the optical disk apparatus 10 is determined by the height H 5 of the disk portion 21 and not by a thickness t 1 of the optical disk 17, the optical disk apparatus 10 is thinner than conventional apparatuses. The above-mentioned rails 24 and 25 can be provided in one block integral with the lateral face of the disk portion 21. This arrangement can decrease the radial size of the bearing 23, and can further contribute to a downsizing of the optical disk apparatus 10. As described later, a plurality of optical parts are built inside the above-mentioned disk portion 21. The arm portion 22 is provided to extend from the disk portion 21 of the main body 20 and underneath the mounted optical disk 17. 35 indicates a flexible cable, which is provided in order to prevent a swinging motion of the head main body 20 from being suppressed. A description of an electromagnetic driving apparatus 40 for making the head main body 20 swing is given below with reference to FIGS.5 and 6. The electromagnetic driving apparatus 40 is a permanent magnet motor provided on the side of the swing motion center axle 31 opposite to the objective lens 50 (described later), and positioned at a distance from the region 34 as in the case of the above-mentioned disk portion 21. 41 and 42 indicate permanent magnet plates adhesively attached to the disk portion 21. The magnet plates extend away from the arm portion 22, and are arranged along a peripheral direction of the disk portion 21. The permanent magnet plate 41 is polarized in the positive direction of the Z axis, while the permanent magnet plate 42 is polarized in the negative direction thereof. 43 indicates a stationary yoke, which is fixed to the bottom cover 11. 44 indicates a driving coil, which is adhesively attached inside the stationary yoke 43, and is opposite to the permanent magnet plates 41 and 42. As shown in FIG.6, a magnetic flux  flows through a magnetic circuit consisting of the permanent magnet plates 41 and 42, and the stationary yoke 43. When the driving coil 44 conducts, a force acts, in an X direction shown by an arrow, on the permanent magnet plates 41 and 42, due to interaction between magnetic flux and electric current. This action makes the head main body 20 swing, and causes the objective lens, described later, to be positioned above a desired track on the optical disk 17. The electromagnetic driving apparatus 40 is not provided underneath the optical disk 17 but at a distance from the optical disk 17, with the result that a height H 6 of the driving apparatus can be determined irrespective of the thickness of the optical disk 17, and that the height H 6 can be great enough for the electromagnetic driving apparatus 40 to be installed, which apparatus generates satisfactory driving force and has an excellent driving characteristic. The above apparatus 40 is of a structure such that the permanent magnet plates 41 and 42 are movable and the driving coil 44 is stationary. This structure has an advantage in that the apparatus can be made thinner as compared with a structure where permanent magnets are stationary and a driving coil is movable. A description will be given next of an inside structure of the head main body 20 with reference to FIGS.7, 8, and 9. The head main body 20 is configured such that a case 49 accommodates a variety of optical parts built therein, as described below, the case consisting of: a case main body 47 composed of a bottom plate 45 and a peripheral wall 46 rising from a periphery of the bottom plate; and a top board 48 covering the case main body 47. The case main body 47 and the top board 48 may be made of an aluminum alloy, a ceramic, or a fiber reinforced resin, and are both light. 50 indicates an objective lens and 63 indicates a perpendicularly reflecting mirror. Both are provided at an end 12 of the arm portion 22. The objective lens 50 is a single lens having non-spherical surfaces, and is thinner than a conventional objective lens assembly consisting of a plurality of lenses. As will be described later, optical parts other than the objective lens 50 and the reflecting mirror 63 are all accommodated in the disk portion 21, and are provided near the swing motion center axle 31. 51 indicates a semiconductor laser chip adhesively attached to a silicon substrate 52. This silicon substrate 52 is mounted on a copper heat sink 53, and the heat sink 53 is adhesively attached to the bottom plate 45. The semiconductor laser chip 51 is not packaged. A height from the substrate 54 to the semiconductor chip 51 is adjusted to be smaller than a height when the chip is packaged. 55 indicates a collimator lens embodied by a single lens having non-spherical surfaces. 56 indicates a complex optical element having a structure where a beam shaping prism 57, a deflected beam-splitter 58, a prism 59, and a 1/4 wavelength plate 60 are integrated. 61 and 62 indicate photodetectors. 65 is a tracking actuator disposed in a base portion of the arm portion 22. A reflecting mirror 66 having the shape of a triangular pole is supported by a blade spring 67. A detailed description of the actuator will be given later. As shown in FIG.9, a movable portion 71 of a focusing actuator 70 is provided at the end of the arm portion 22. Referring to FIG.7, a laser light beam 80 emitted from the semiconductor laser chip 51 is allowed to pass through the lens 55 so as to be turned into a parallel light beam 81, which parallel light beam is then allowed to enter the prism 57 so as to be shaped into a completely round shape. Thereafter, the light is allowed to pass through the deflecting beam-splitter 58 and the 1/4 wavelength plate 60 before reaching the tracking actuator 65, is reflected by the reflecting mirror 66, and advances toward the end of the arm portion 22, as indicated by an arrow 82. As shown in FIG.9, the light is then reflected perpendicularly by the reflecting mirror 63, converged by the objective lens 50, and then converged on the optical disk 17. The laser light reflected by the optical disk 17 and returned to the deflecting beam-splitter 58 follows the same path as the light converged on the disk, but it is then reflected by the deflecting beam-splitter 58 and reaches the photodetectors 61 and 62 as shown by an arrow 83. Outputs from the photodetectors 61 and 62 are subjected to logical operations, so that a reproduction signal, a tracking control signal, and a focus control signal are obtained. Since, as shown in FIG.7, the heat sink 53, the complex optical element 56, and the tracking actuator 65 are disposed near the swing motion center axle 31, a moment of inertia of the head main body 21 is small, the moment of inertia being measured around the swing motion center axle 31, so that an access to the desired track is achieved at a high speed. Moreover, since there is no axle piercing the disk portion, a high flexibility in the arrangement of parts, including the above-mentioned complex optical element 56, is made possible. Parts including the complex optical element 56 are arranged such that they are close to the swing motion center axle 31. This arrangement also ensures that a moment of inertia of the head main body 21 around the swing motion center axle 31 is maintained to be small, so that access can be achieved at a high speed. Although the semiconductor chip 51 is not packaged but is instead a bare part, the reliability of the semiconductor chip 51 is guaranteed because the head main body 20 is made of a hermetically sealed structure. Although the head main body 20 is made of a hermetically sealed structure, heat generated by the semiconductor chip 51 is conducted through the heat sink 53 to the bottom plate 45 so as to be effectively radiated out of the head main body 20. A description will be given next of the above-mentioned tracking actuator 65 with reference to FIG.8, particularly. An L-shaped holder 90 is fitted with the reflecting mirror 66 having a shape of a triangular pole, and with the driving coil 91. The holder 90 is supported by the wall of the head main body 20 through the blade spring 67. The head main body 20 is fitted with a magnetic circuit structure 95 consisting of permanent magnets 92 and 93 and a yoke 94. The driving coil 91 is provided with a gap 96 for this magnetic circuit structure 95. When a tracking control current is fed to the driving coil 91, a force Fa in a Y direction is generated in the coil 91; the reflecting mirror 66 then rotates on a Z axis, causing a deflection of the blade spring 67, so that the light is deflected on an X-Y plane. Tracking control is achieved in the following manner: a spot, on the optical disk 17, limited by the objective lens 50 follows a minute displacement of a track. The tracking actuator 65 is configured such that the above-mentioned force Fa operates on a node of a secondary-deflection-mode resonance of the blade spring 67, by positioning the driving coil 91. The above arrangement ensures that the secondary-deflection-mode resonance of the blade spring 67 is suppressed, and that the tracking actuator 65 has an excellent mechanical oscillation characteristic. In correspondence with a swinging motion of the head main body 21, two forces operate in a movable portion of the tracking actuator 65: a centrifugal force Fc; and an inertia force Fi along a circumference of a circle created by a swinging motion of the head main body 21. These forces Fc and Fi act as disturbance. In the case of a swinging motion, generally, Fi > Fc. The blade spring 67 is disposed such that its longitudinal direction, along which direction its rigidity is great, is aligned with circumferential directions 32 and 33 of the head main body 21 swinging motion. This arrangement ensures that even when the force Fi operates, a deformation of the blade spring 67 is small. Therefore the tracking actuator 65 operates normally and a tracking control is effected with precision. A description will be given next of the focusing actuator 70 with reference to FIGS.9 and 10. As shown in FIGS.9 and 10(A), the objective lens 50 is attached to an L-shaped holder 100. The holder 100 is fixed at ends of two identically-shaped blade springs 101 and 102, which springs are disposed parallel to each other. As shown in FIG.10(B), the blade springs 101 and 102 are both constituted such that one of the two sides of a spring metal plate 109a has, on its entire surface, a damper 109b made of a silicon-gum visco-elastic body, the damper having thereon a thin, soft resin film 109c. Referring to the same figure, thickness t 11 is 30µm, thickness t 12 is 50µm, and thickness t 13 is 10µm. In this structure, the damper 109b suppresses sharp main mechanical resonance generated with a frequency of the order of 10 to 100 Hz, which range is characteristic of a metal blade spring. The damper also acts to suppress a peak value of higher mechanical resonance. The resin film 109c prevents adherence of dust due to the viscosity of the damper 109b. Base portions of the blade springs 101 and 102 are fixed to a portion 103 of the arm portion 22 of the head main body 20. An interval a between the blade springs 101 and 102 is adjusted to be smaller than a thickness of the objective lens 50. The driving coil 104 is fixed to a perpendicular portion of the holder 100, and is opposite to an opening 105 at the end of the arm portion 22. 106 indicates a thin resin film that covers an opening 105 at the end of the arm portion 22. As will be described later, this resin film 106 allows magnetic flux to pass through but does not allow dust to pass through it. An opening 107 surrounding the objective lens 50 is covered by a soft resin film 108. The soft resin film 108 does not limit a displacement of the objective lens 50, which lens is provided for focus control, but it does prevent invasion of dust. 110 indicates a stationary magnetic circuit having a long and narrow shape assembled onto the bottom cover 11 in such a manner that the magnetic circuit extends, at a short distance from the end of the arm portion 22, along the movement track of the end of the arm portion 22, the track being created when the head main body 20 is made to swing. As shown in FIG.11, the stationary magnetic circuit 110 consists of two permanent magnets 111 and 112 and a yoke 113. The permanent magnets 111 and 112 are disposed such that their polarities are opposite to each other, and such that a magnetic flux  f flows as shown in FIG.11. The magnetic flux  f passes through the resin film 106 and reaches the driving coil 104. The magnetic flux  f flows out from the entire front face of the stationary magnetic circuit 110, and exerts itself on the driving coil 104 no matter what position the head main body 20 is at during its rotation. When the driving coil 104 is supplied with a focus control current, this current interacts with the magnetic flux  f and a force Fb in the Z axis direction is generated in the driving coil 104. This way the objective lens 50 is displaced in the Z axis direction while causing the blade springs 101 and 102 to deflect, so that a focus control is achieved. Since the magnetic circuit 110, having a comparatively heavy weight, is assembled onto the bottom cover 11, the end of the arm portion 22 is small by comparison, so that a moment of inertia of the head main body 20 measured around the swing motion center axle 31 is small. The focusing actuator 70 is provided with dynamic vibration absorbers 120 and 121, as shown in FIG.12. The dynamic vibration absorber 120 consists of a blade spring 122, which extends in the Z direction so that its upper end is fixed onto a part of the holder 100, and a minute movable weight 123 fixed to a free lower end of the blade spring 122. The other dynamic vibration absorber 121 also consists of a blade spring 124 and a minute movable weight 125. The dynamic vibration absorbers 120 and 121 are provided on both sides of the holder 100. The main resonance frequency of each of these dynamic vibration absorbers is set to be the same as the higher mechanical vibration frequency, described later, of the movable part of the focus actuator 70. A description will be given next of the operation and effect of the above-mentioned dynamic vibration absorbers 120 and 121. As shown in FIG.13, the center of gravity of the movable part of the focusing actuator 70 resides approximately on the optical axis of the objective lens 50. An inertia force Fd caused by the movement of the movable part acts along the optical axis 50a of the objective lens 50. The driving force Fb, on the other hand, acts on the coil 104, meaning that the driving force Fb and the inertia force Fd act on points that are horizontally apart. This way a couple of force M around the X axis acts on the holder 100, generating a higher mechanical resonance in the focusing actuator 70. This resonance mode is manifested as a rotational mode oscillation around the X axis, as shown in FIG.14. When the above-mentioned higher mechanical resonance occurs, an inclination oscillation of the optical axis of the objective lens is generated, so that a focus control is disturbed. A measurement was made of a characteristic of an oscillation, around the X axis, of the optical axis 50a of the objective lens 50 of a focusing actuator not equipped with dynamic vibration absorbers, in which measurement angular displacement, around the X axis, caused by the driving force Fb was measured. The gain obtained is indicated by a line I in FIG.15(A), and the phase obtained is indicated by a line II in FIG.15(B). A peak 126 of the gain occurred at a frequency of about 3 kHz, at which frequency a 180 degree phase shift is seen. This means that a focus control beyond the frequency of 3 kHz is rendered impossible. However, when the actuator is equipped with the dynamic vibration absorbers 120 and 121 as shown in FIG.12, a higher resonance generated in the movable part of the focusing actuator 70 is suppressed because the dynamic vibration absorbers 120 and 121 resonate in a phase opposite to the phase of the higher resonance. A line III in FIG.16(A) shows again of oscillation, around the X axis, of the optical axis 50a of the objective lens 50. As can be seen from the same figure, the peak 126, which occurred at the frequency of 3 kHz, is suppressed, as shown by a line 127. The phase obtained is shown by a line IV in FIG.16(B). As can be seen from the same figure, phase variation is small as shown by a line 128, and no phase reversal is observed. This way a focus control is effected in a stable manner across a satisfactorily wide frequency range. Finally, for the sake of clarity configurations incorporated in the optical disk apparatus 10 will be listed, i.e., 1 ○ configurations which make it possible to make an apparatus thin 2 ○ main configurations which make it possible to decrease, for speedy access, a moment of inertia, around the swing motion center axle 31, of the head main body 20. (1) Configurations which make it possible to make an apparatus thin. 1 ○ a configuration in which the optical head apparatus 15 is of a swing motion type, and in which the disk portion 21 and the electromagnetic driving apparatus 40 are disposed at a distance from the projection region 34 of the optical disk. (FIGS.1 and 2) 2 ○ the bearing 23 supporting the circumference of the disk portion 21. (FIG.3) 3 ○ a single-lens configuration of the objective lens 50. (FIG.9) 4 ○ a packageless configuration of the semiconductor laser. (FIG.7) (2) Configurations which make it possible to decrease a moment of inertia of the head main body. 1 ○ a configuration in which the swing motion center resides on the disk portion 21, in which portion are provided optical parts. (FIG.7) 2 ○ the magnetic circuit 110 of the focusing actuator 70 is fixed to the bottom cover 11, and is not mounted on the head main body 20. (FIG.1) An optical disk apparatus 420 shown in FIGS.17 and 18 is of the same size as a so-called IC card, and has a height (thickness) of about 5 mm. 421 indicates a bottom cover and 422 indicates a top cover. The optical disk 17 is caused to rotate at a substantially great speed by means of a spindle motor 424 provided on the bottom cover 421. A swing-motion type head apparatus 425 is supported as described below, and, by being driven by a motor 429 consisting of a yoke 426, a permanent magnet 427, and a coil 428, is made to swing around a swing motion center stationary axle 430 in a direction shown by an arrow 431. When the swing-motion type head apparatus 425 is made to swing in the direction shown by the arrow 431, an optical head 432 is made to move underneath the optical disk 17 in a radial direction thereof. A description of the swing-motion type head apparatus 425 will be given with reference to FIGS. 19 and 20. 440 indicates a head main body consisting of a disk portion 441 having a diameter D 1 of approximately 20 mm, and an arm portion 442 extending from the disk portion. The optical head 432 is provided at the end of the arm portion 442. 443 indicates a single ball bearing fixed to the above-mentioned axle 430, and secured at the center of the disk portion 441 by being embedded therein. A peripheral side 444 of the disk portion 441 stands on a circle 449 having a diameter R 1 of 10 mm, the center of the circle being the axle 430. 445-1 and 445-4 indicate rolling bearings such as a ball bearing or a roller bearing. The bearings are assembled with axles 446-1 through 446-4 provided on the peripheral side 444 at equal intervals, and are separated from each other by 90° along a circumference of the disk portion 441. 447 and 448 are arc-shaped rails fixed to the bottom cover 421 so as to support outer rings 445-1a - 445-4a of the rolling bearings 445-1 - 445-4. The height H 1 of the disk portion 441 is configured to be slightly greater than the height H 2 of the ball bearing 443. The rolling bearings 445-1 - 445-4 roughly fit within the vertical range limited by a horizontal plane 450 extended from a topside 443a of the ball bearing 443 and a horizontal plane extended from an underside 443b thereof. The above ensures that the height of the head main body 440 including the rolling bearings 445-1 - 445-4 is less than half that of the conventional technology. A description will be given next of angular rigidity of the above-mentioned swing-motion type head apparatus 420. The swing-motion type head apparatus 420 is made to swing around the axle 430 as the outer rings 445-1a - 445-4a roll on the rails 447 and 448. The rails 447 and 448 are configured to have dimensions such that the rails give the rolling bearings 445-1 - 445-4 an upward thrust. That is, the rails are made to be several µm higher than the height at which preload begins to exert itself on the ball bearing 443. This mechanism ensures that the rails 447 and 448 presses the rolling bearings 445-1 - 445-4 with a force F 1 , and, as a result, the ball bearing 443 receives a preload of the force F 1 . FIG. 21, which schematically illustrates how the swing-motion type head apparatus 420 is supported while being made to swing at a substantially great speed, shows that the apparatus is supported by the axle 430 via a spring 455 having a spring constant k 1 , and is also supported by the rails 447 and 448 via a spring 456 having a spring constant k 2 . The head main body 440 has a satisfactorily great angular rigidity because a dimension L 1 , measured from a center 457 of angular displacement of the head main body 440 to the above-mentioned spring 456, is substantially great, and because the spring constant k 2 of the spring 456 is made to be substantially large due to the above-mentioned force F 1 . A preload supplied to the ball bearing 443 causes the spring constant k 1 of the spring 455 to be large. This has an effect of increasing radial rigidity of the head main body 440. Accordingly, the head main body 440 can be made to swing in a stable manner, and the optical head 432 can be positioned with precision. A description will be given next of a first variation of the above-mentioned swing-motion type head apparatus, with reference to FIG. 22. Rails 447A and 448A are configured such that surfaces 447Aa and 448Aa thereof are an equivalent of a slope 463 of an inverse cone having an apex at a point 462 on a center line 461 of the axle 430, and an apex angle of . The rolling bearings 445-1 - 445-4 are fitted diagonally so as to roll on the above-mentioned surfaces 447Aa and 448Aa. The rails 447A and 448A are configured to have dimensions such that the rails give the rolling bearings 445-1 - 445-4 an upward thrust. The above mechanism ensures that the rails 447A and 448A press the rolling bearings 445-1 - 445-4 with a force F 2 , and, as a result, the ball bearing 443 receives a preload of a force F 3 operating in a thrust direction of the bearing. FIG. 23 schematically illustrates how a swing-motion type head apparatus 425A of the above configuration is supported during operation. The head main body 440 is supported by the axle 430 via the spring 456 having the spring constant k 1 , and is also supported by the rails 447A and 448A via a spring 456A having the spring constant k 2 . The spring 456A is inclined, with respect to a vertical line, at an angle given by the formula below. The spring 456A suppresses angular displacement of the head main body 440 as well as suppressing radial displacement of the head main body. Accordingly, the head main body 440 is supported with a satisfactorily great angular rigidity and a radial rigidity. FIG.24 illustrates a variation of a preload mechanism. This variation is configured such that a holder 470 for holding an axle 446-1 is assembled with the head main body 440 via a blade spring 471 having an appropriate spring constant. The blade spring 471 is caused to bend slightly in a direction shown by an arrow 472 so that a preload is supplied to the bearing due to a spring force of the blade spring 471. This configuration does not require a high precision in the dimensions of the rails 447 and 448. A description will be given of a swing-motion type head apparatus 480 of the second variation with reference to FIGS. 25 and 26. First V-shaped grooves 481 and 482 are formed along a circumference of the peripheral side 444 of a disk portion 441A of a head main body 440A. 483 and 484 indicate arc-shaped fixed rails fixed on the bottom cover to be opposite to the above-mentioned peripheral side 444. Second V-shaped grooves 485 and 486 are formed on the rails 483 and 484. The grooves 481 and 485 are opposite to each other, and the grooves 482 and 486 are opposite to each other, so that they form a rhombus. Steel balls 487 and 488, separated from each other by a retainer 489, are engaged between the groove 481 and the groove 485. Likewise, steel balls 490 and 491, separated from each other by a retainer 492, are engaged between the groove 482 and the groove 486. The positions of the rails 483 and 484 are controlled so as to supply preload to the steel balls 487, 488, 490, and 491. The head main body 440A is caused to swing at a substantially great speed on a center 493 of the disk portion 441 in the direction shown by the arrow 431, as the steel balls 487, 488, 490, and 491 roll. As is schematically shown in FIG. 27, the head main body 440A (the disk portion 441A) is supported by springs 495, 496, 497, and 498 having a spring constant k 10 . The springs 495 and 496 serve to improve angular rigidity of the head main body 440A. This embodiment enables flexible arrangement of optical parts since it does not have the swing motion center stationary axle, and is thus less restrictive in the arrangement of optical parts in the head main body than the embodiments shown in FIGS. 17 to 22. As shown in FIG.28 cylindrical rollers 500 and 501 can be used in place of the above-mentioned steel balls 487, for example. The cylindrical rollers 500 and 501 are disposed such that they are alternately inclined at one of the two angles. The end face of the cylindrical rollers 500 and 501 are provided with a cone-shaped depression so that a contact area between the end face and the V-shaped groove is small. The contact between the cylindrical rollers 500 and 501 and the V-shaped grooves 481 and 485 is not a point contact but a line contact, thereby increasing a spring constant of each of the springs 495 - 498 in FIG.27. Therefore, angular rigidity and radial rigidity of the head main body 440A is greater than that of the head main body shown in FIG. 25.

Claims: Optical disk apparatus (10) for recording and/or reproducing information on and from a recording surface (17a) provided on an optical disk (17), which apparatus (10) comprises: optical disk support means for supporting such an optical disk (17) at a desired location within the apparatus, which means include a spindle motor (14) for causing such an optical disk (17) to rotate during use; and a swing-motion type optical head apparatus (15), for radially scanning the said optical disk (17) using light transmitted through an objective lens (50), which apparatus (15) comprises: a head main body (20) having an arm (22) carrying the said objective lens (50), such that the lens (50) faces the said recording surface (17a) of the mounted optical disk (17), and a supporting member (21) for supporting the said arm (22), the said head main body (20) being supported by bearing means (23) for enabling the head main body (20) to swing about a swing axis (31) in a plane parallel to the recording surface (17a) of the said mounted optical disk (17); and electromagnetic driving means (40) connected to drive the said head main body (20) to swing about the said swing axis (31); the said optical disk support means and swing-motion type optical head apparatus (15) being mounted on a base (11) of the optical disk apparatus (10) relative to one another such that, if viewed in a direction perpendicular to the said plane, neither the said supporting member (21) nor the said electromagnetic driving means (40) would appear to lie above or below an optical disk (17) supported by the said optical disk support means; characterised in that the said optical disk support means and the said head main body (20) are constructed and arranged such that when the apparatus is in use an optical disk (17) is supported by the said optical disk support means at a position relative to the said base (11) which is lower than that of the highest point of the said head main body (20). Apparatus as claimed in claim 1, suitable for use with an optical disk (17) having an outer diameter of about 46mm (1.8 inches). Apparatus as claimed in claim 1 or 2, suitable for use with an optical disk (17) having a disk base thickness of between 0.2 and 0.5 mm. Apparatus as claimed in any preceding claim, wherein the said supporting member (21) is approximately circular and contains optical apparatus (55, 56) for use in transmitting the light to the said objective lens (50). Apparatus as claimed in claim 4, wherein the said head main body (20) comprises a hermetically-sealed case (49). Apparatus as claimed in any preceding claim, wherein the said swing-motion type optical head apparatus (15) comprises a focusing actuator (70) including: the said objective lens (50), which is provided displaceably on the said head main body (20) ; a driving coil (104); and a magnetic circuit (110) mounted outside the head main body (20) so as to generate magnetic flux for influencing the said driving coil (104). Apparatus as claimed in claim 6, wherein the said head main body (20) is further provided with a nonmagnetic thin film (106) for preventing the said driving coil (104) from being contacted by the said magnetic circuit (110). Apparatus as claimed in claim 6 or 7, wherein the said focusing actuator (70) is further provided with dynamic vibration absorbers (120, 121). Apparatus as claimed in claim 6, 7 or 8, wherein the said focusing actuator (70) comprises two parallel blade springs (101, 102) of the same shape, each of said two blade springs carrying, on the entire surface of one side thereof, a damper (109b) made of a visco-elastic body. Apparatus as claimed in claim 4, wherein the said bearing means (23) comprise stationary outer rings (26, 27), mounted on the said base (11), and movable inner rings (24, 25), connected to the side edge of the said supporting member (21). Apparatus as claimed in any preceding claim, wherein the said electromagnetic driving means (40) comprise permanent magnets (41, 42), which are fixed onto the said head main body (20), and a driving coil (44), which is fixed onto a yoke (43). Apparatus as claimed in claim 1, wherein the said bearing means comprise: a swing-motion-center stationary axle (430) mounted on the said base (421); a single ball bearing (443) assembled with said swing-motion-center stationary axle (430) so as to support a swing-motion center of the said head main body (440) ; arc-shaped rails (447, 448) mounted on the said base (421); and a plurality of rolling bearings (445-1 - 445-4) assembled with an arc-shaped peripheral side (444) of the said head main body (440), which side (444) stands on a circle having a predetermined radius (R 1 ) and a center at the said swing-motion center, said bearings (445-1 - 445-4) supporting a peripheral portion of the said swing-motion center of the said head main body (440) by being in contact with the said rails (447, 448) in such a manner that the said single ball bearing (443) is provided with preload. Apparatus as claimed in claim 12, wherein surfaces (447Aa, 448Aa) of the said rails (447, 448), on which surfaces said rolling bearings (445-1 - 445-4) roll, are equivalent to a slope (463) of an inverse cone having an apex at a point on an axis of the said swing-motion center. Apparatus as claimed in claim 1, wherein the said bearing means comprise: first V-shaped grooves (481, 482) formed along a circumference of an arc-shaped peripheral side of the said head main body (440A), the center of the arc being at a swing motion center (493); arc-shaped rails (483, 484) on which second V-shaped grooves (485, 486) are formed, the said rails (483, 484) being mounted on the said base so that the said second V-shaped grooves (485, 486) are opposite to the said first V-shaped grooves (481, 482) ; and steel balls (487, 488, 490, 491) engaged between the said mutually-opposite first and second V-shaped grooves (481, 482; 485, 486). Apparatus as claimed in claim 1, wherein the said bearing means comprise: first V-shaped grooves (481, 482) formed along a circumference of an arc-shaped peripheral side of the said head main body (440A), the center of the arc being at a swing-motion center; arc-shaped rails (483, 484) on which second V-shaped grooves (485, 486) are formed, the said rails (483, 484) being mounted on the said base so that the said second V-shaped grooves (485, 486) are opposite to the said first V-shaped grooves (481, 482); and cylindrical rollers (500, 501) engaged between the said mutually-opposite first and second V-shaped grooves (481, 482; 485, 486).

Inventors: ICHIHARA JUNICHI, MAKITA AKIHIKO, OGAWA KOICHI, ICHIHARA, JUNICHI, MAKITA, AKIHIKO, OGAWA, KOICHI, Ichihara, Junichi, c/o Fujitsu Limited, Makita, Akihiko, c/o Fujitsu Limited, Ogawa, Koichi, c/o Fujitsu Limited
Applicants: FUJITSU LTD, FUJITSU LIMITED
Application year: 1992
Main classification: G11B7
IPC codes: G11B7, G11B17, G11B33, G11B25, G11B5