JPH0719391B2 - Optical recording / reproducing device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical information recording / reproducing apparatus for optically writing and / or reading information on a disc-shaped recording medium.

[Outline of Invention]

The present invention relates to an optical recording / reproducing apparatus using a separation type optical pickup, in which a fixed mirror is mounted on a moving optical system, and the reflecting surface of the movable mirror is tilted by 45 ° with respect to a rotating shaft of an optical scanning mirror device of the fixed optical system. By fixing and making the optical axis of the light beam entering the movable mirror from the light source approximately parallel to the rotation axis, we have realized a small and thin device that can obtain high-speed access, high-precision tracking, and high-quality signals. is there.

[Conventional technology]

An optical recording / reproducing apparatus using a conventional separation type optical pickup is described in JP-A-56-25241. The moving optical system is equipped with a focusing lens, a focusing actuator, and a galvano mirror for tracking, and the fixed optical system has two light sources (recording and reproducing), a photodetector, a piezoelectric element, and a microvibrating mirror and a recording beam. It is composed of an acousto-optic light modulator for turning on and off, an afocal optical magnifying system, a birefringent separator and the like.

In the conventional optical scanning mirror device, as in Japanese Utility Model Publication No. 57-1309, a mirror is held by an elastic body such as silicon rubber and electromagnetically driven.

FIG. 2 shows a perspective view of a conventional movable magnet type optical scanning mirror device. In this example, the permanent magnet 3 fixed to the mirror 1 is electromagnetically driven by the control magnetic field generated by the magnetic field control coil 2, and the mirror 1 is rotatably supported by the elastic material 4. The angle of the mirror 1 can be controlled.

Further, FIG. 3 shows a perspective view of a conventional example of a moving coil type, and FIG. 4 shows a longitudinal sectional view thereof. The control coil 2 is fixed to the mirror 1 and is arranged in the air gap of a magnetic circuit having an air gap made of the permanent magnet 3 and the magnetic material 6.
In FIG. 4, since the magnetic flux in the air gap is oriented laterally with respect to the paper surface and the two magnetic fluxes in the left and right air gaps have the same direction, the Lorentz force acting on the coil 2 is vertical with respect to the paper surface. The right side and the left side are in opposite directions, and therefore, the turning force indicated by the arrow is generated.

[Problems and Objectives to be Solved by the Invention]

In the conventional optical recording / reproducing apparatus described above, since the actuator for driving the mirror has to be mounted on the moving optical system, the weight of the moving optical system becomes heavy, and sufficient high speed access cannot be achieved. Further, the mirror of the fixed optical system is periodically vibrated by the piezoelectric element to generate a displacement of ± 0.1 μm on the surface of the recording medium, and the tracking error signal is obtained from the envelope of the reproduction signal. Then, the galvanometer mirror of the moving optical system is driven based on this error signal, and the light spot is positioned so that the center of the information track is located at the average position of the light spot that periodically oscillates, and tracking is performed. There is. Therefore, in this method, a tracking error of 0.1 μm at maximum occurs periodically. At present, the track pitch is about 1.6 μm, so when considering changes in external environmental conditions, changes over time, etc., this is a considerably large tracking error, which causes the quality of the reproduced signal to be considerably deteriorated. Further, since the piezoelectric element requires a high voltage, the driving circuit becomes large and complicated, which has been an obstacle to downsizing and thinning the device. Furthermore, since the direction in which the mirror of the fixed optical system is driven and the positional relationship with the light beam incident on this mirror are not clear, the light spot slightly moves in the tangential direction of the information track, which causes jitter in the time axis direction during reproduction. Which caused signal quality to deteriorate. For the same reason, there is a problem that the device becomes considerably large depending on how the light rays are arranged. Further, since two light sources are used, the device becomes large in size, which is disadvantageous in terms of cost.

In the conventional optical scanning mirror device described above, undesired vibration occurs at the resonance point determined by the mass of the mirror and the spring constant of the elastic body, and the vibration is damped by the damping constant of the elastic body or another damper. Was added. Therefore, it is necessary to pay attention to the elastic body design and the damper design, which leads to an increase in cost.

Further, the scanning control characteristics of the mirror in the high frequency region largely depend on the magnitude of the electromagnetic driving force, and the electromagnetic driving force depends on the magnitude of the magnetic flux density in the magnetic air gap where the coil is arranged and the magnitude of the current flowing through the coil. large. However, in order to increase the magnetic flux density, a large magnet is generally required.
Further, when using a rare earth magnet or the like, the cost is increased.
In addition, if the current flowing through the coil is increased, heat is generated, and the coil expands due to thermal expansion. In the worst case, the coil is burned.

Therefore, the present invention solves the above problems, and an object thereof is to achieve high-speed access and highly accurate tracking,
It is an object of the present invention to provide a small-sized thin film and inexpensive optical recording / reproducing device capable of high-quality recording / reproducing.

Another object of the present invention is to provide an optical scanning mirror device which can be applied to the optical recording / reproducing device of the present invention and which can eliminate the influence of resonance and can be controlled in a wide frequency range by a strong driving force.

[Means for solving problems]

The optical recording / reproducing apparatus of the present invention is an optical recording / reproducing apparatus in which an optical pickup is separated into a moving optical system and a fixed optical system, wherein the moving optical system is movable in a vertical direction of an information track of a recording medium, The moving optical system is equipped with at least a focusing lens and a fixed mirror, and the fixed optical system is composed of at least a light source, a light detecting means, and an optical scanning mirror device having a movable mirror rotatable about a rotation axis. The reflecting surface of the movable mirror is arranged at an angle of 45 ° with respect to the rotation axis, and the rotation axis is arranged parallel to the recording surface of the recording medium, and the light beam emitted from the light source is movable. The information track is irradiated through the mirror, the fixed mirror, and the focusing lens, and the reflected light from the information track is detected by the light detecting means, and the light source is Wherein the optical axis of the light beam incident on the movable mirror emits et is parallel to the pivot shaft.

Further, the optical axis of the light beam emitted from the light source and incident on the movable mirror coincides with the movable axis.

Further, a suitable optical scanning mirror device applied to the present invention is
It is characterized by comprising a magnetic circuit having an air gap and a movable coil arranged in the air gap to drive a movable mirror, and filling the remaining space in the air gap where the movable coil is arranged with a magnetic fluid.

[Action]

According to the above configuration of the present invention, since the fixed mirror is mounted on the moving optical system, an actuator for driving the mirror is not required, the moving optical system is lightened, and high-speed access is possible. In tracking, the moving optical system is moved to substantially follow the fluctuation of the information track, and the remaining minute tracking error is followed with high accuracy by the movable mirror of the fixed optical system, so that highly accurate tracking can be achieved.

The rotation axis is arranged parallel to the recording surface of the recording medium, the optical axis of the light beam incident on the movable mirror is parallel to the rotation axis, and the anti-slope surface of the movable mirror is inclined at 45 ° with respect to the rotation axis. With the arrangement, the light flux reflected by the movable mirror is deflected in a plane perpendicular to the recording surface of the recording medium. As a result, the light spot on the surface of the recording medium moves only in the vertical direction of the information track, and no jitter occurs in the time axis direction.

Further, each optical element of the fixed optical system can be arranged on the plane in the same plane as the optical scanning mirror, and the size and thickness of the device can be reduced. And because you can record and play with one light source,
The device can be made small, thin and inexpensive. Further, since the optical scanning mirror device does not use a piezoelectric element, the driving circuit can be made compact and simple.

According to the above-described configuration of the preferred optical scanning mirror device used in the present invention, the movable coil that drives the mirror moves in the magnetic fluid, so that the viscous force of the fluid acts and the vibration is damped. Also,
Since the magnetic fluid has a higher magnetic permeability than that of air, when filled in the air gap in the magnetic circuit, it lowers the magnetic resistance of the gap portion and increases the magnetic flux density. further,
Magnetic fluid is a dispersion of magnetic particles in a medium such as water.The thermal conductivity of these dispersion media is usually higher than that of air, so it is effective to place a coil in the magnetic fluid. A great heat dissipation effect can be obtained.

〔Example〕

FIG. 1 shows an optical scanning mirror device applied to the present invention, which has the same structure as the conventional example shown in FIG. When the coil 2 is arranged in the air gap of the magnetic circuit fixed to the frame 5 and composed of the permanent magnet 3 and the magnetic material 6, when the coil 2 is energized, the torque indicated by the arrow is generated by the Lorentz force. The space between the coil 2, the permanent magnet 3 and the magnetic material 6 is filled with the magnetic fluid 7. Since the magnetic resistance of the magnetic circuit is reduced by filling the air gap with the magnetic fluid, the magnetic flux density around the coil is increased. Further, since the coil has a plate-shaped cross section and the magnetic fluid is filled between the parallel flat plates, a viscous force acts on the coil due to the movement of the coil. This has an effective damping effect on the resonance of the coil. Furthermore, since the heat generated in the coil is transferred to the frame 5 through the magnetic fluid, the magnetic fluid also has the effect of cooling the coil.

Further, since the magnetic fluid is constrained by the magnetic field, unlike the other fluids, a shield for preventing scattering is not required.

5 (a) and 5 (b) show a suitable optical scanning mirror device applied to the optical recording / reproducing apparatus of the present invention. The mirror 1'has a shape obtained by cutting a cylinder at a plane inclined by 45 ° with respect to its axis, and its end face is a mirror surface. The mirror 1'is rotatably supported on the shaft by a shaft 9 and a bearing 10 about an axis indicated by a chain line. The mirror 1'is fixed to the coil 2 and is rotationally driven according to the same principle as in the example of FIG. Further, the shaft 9 is held at the neutral point by the leaf spring 8.
In designing the leaf spring 8, it is not necessary to consider vibration damping characteristics. That is, the vibration damping occurs because of the action of the magnetic fluid 7 in the air gap where the coil 2 is arranged.

FIG. 6 shows a longitudinal sectional view of the optical mirror device shown in FIGS. 5 (a) and 5 (b). The magnetic fluid 7 is filled in the air gap of the magnetic circuit composed of the permanent magnet 3 and the magnetic body 6,
The coil 2 is immersed in the magnetic fluid 7.

FIG. 7 shows an optical system of the optical recording / reproducing apparatus of the present invention to which the optical scanning mirror device shown in FIGS. 5 (a) and 5 (b) is applied. The laser beam emitted from the laser diode 11 becomes a parallel light beam by the collimator lens 12, passes through the polarization prism 13 and the quarter wavelength plate 14, and enters the optical scanning mirror 15. As shown in the figure, the rotation axis of the optical scanning mirror 15 is arranged so as to coincide with the incident optical axis, and the incident beam changes its direction by 90 ° and is reflected toward the rotation axis of the disk-shaped recording medium 18. The reflected beam of the optical scanning mirror 15 is incident on the mirror 16, and the reflected light travels substantially parallel to the rotation axis of the disc-shaped recording medium 18 and is focused on the disc-shaped recording medium 18 by the focusing lens 17. The beam incident on the disk-shaped recording medium 18 is reflected on the surface, traces the reverse path at the time of incidence, is reflected by the polarization beam splitter 13, passes through the cylindrical lens 19 and the condenser lens 20, and forms an image on the four-division photodiode 21. To do. In this optical system, tracking for tracking the recording track on the disc-shaped recording medium 18 is performed as follows. That is, coarse tracking is a mirror
16 and the focusing lens 17 as a unit, by moving in parallel in the radial direction of the disk-shaped recording medium 18,
Fine tracking is performed by using the optical scanning mirror 15 and controlling the incident angle of the laser beam incident on the focusing lens 17 with respect to the lens axis. According to the configuration of this optical system, conventionally, the entire optical system is integrated into a disc-shaped recording medium.
Compared to the case of moving in the radial direction of 18 or the case of moving the moving optical system equipped with the focusing lens and the galvano mirror in the separation type optical pickup, the mass of the movable part becomes smaller, so high-speed access will be possible. At the same time, it becomes stronger against vibration.

〔The invention's effect〕

As described above, according to the present invention, since the actuator for driving the mirror is not mounted on the moving optical system, the moving optical system can be reduced in weight and high speed access can be achieved. In addition, highly accurate tracking is achieved by the movement of the moving optical system and the two-step tracking method using the optical scanning mirror.

Moreover, the rotation axis is arranged parallel to the recording surface of the recording medium, the optical axis of the light beam incident on the movable mirror is parallel to the rotation axis, and the reflecting surface of the movable mirror is tilted 45 ° with respect to the rotation axis. The light flux reflected by the movable mirror is deflected in a plane perpendicular to the recording surface of the recording medium. As a result, since the light spot on the surface of the recording medium moves only in the vertical direction of the information track, jitter in the time axis direction is eliminated, and reliable recording and high quality signal reproduction can be achieved.

Further, each optical element of the fixed optical system can be arranged on the plane in the same plane as the optical scanning mirror, and the size and thickness of the device can be reduced. Further, since the fixed optical system can be arranged in the empty space where the mechanical system and the like are not arranged, the space in the device can be effectively utilized. Since recording and reproduction can be performed with one light source, there are great effects in reducing the size and thickness of the device and reducing the cost. Also, since the movable mirror is driven by an electromagnetic actuator, high voltage is not required unlike the piezoelectric element,
The drive circuit is small and simplified.

On the other hand, the actuator that drives the movable mirror of the optical scanning mirror device applied to the optical recording / reproducing apparatus of the present invention has an undesired vibration due to resonance due to an appropriate vibration damping effect, a high magnetic flux density in a magnetic air gap, and a high heat dissipation property. It is possible to control the optical scanning mirror device up to a high frequency by a strong electromagnetic driving force while eliminating the above.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view of an optical scanning mirror device applied to the present invention. FIG. 2 is a perspective view of a conventional movable magnet type optical scanning mirror device. FIG. 3 is a perspective view of a conventional moving coil type optical scanning mirror device. FIG. 4 is a vertical sectional view of a conventional moving coil type optical scanning mirror device. FIG. 5A is a plan view of an optical scanning mirror device that is rotatable about an incident optical axis. FIG. 5B is a front view of an optical scanning mirror device that is rotatable about an incident optical axis. FIG. 6 is a vertical cross-sectional view of an optical scanning mirror device that is rotatable about an incident optical axis. FIG. 7 is a schematic view of the optical system of the optical recording / reproducing apparatus of the present invention. 1: mirror, 1 ': mirror, 2: coil, 3: permanent magnet, 4: elastic material,
5: Frame, 6: Magnetic material, 7: Magnetic fluid, 8: Leaf spring, 9:
Axis, 10: Bearing, 11: Laser diode, 12: Collimating lens, 13: Polarizing prism, 14: 1/4 wavelength plate, 15: Optical scanning mirror, 16: Mirror, 17: Focusing lens, 18: Disc recording Medium, 19: Cylindrical lens, 20: Condensing lens, 21: 4
Split photodiode

Claims (3)

[Claims] 1. An optical recording / reproducing apparatus in which an optical pickup is separated into a moving optical system and a fixed optical system, wherein the moving optical system is movable in a vertical direction of an information track of a recording medium, Is equipped with at least a focusing lens and a fixed mirror, and the fixed optical system includes at least a light source, a light detection unit, and an optical scanning mirror device having a movable mirror rotatable about a rotation axis. A reflection surface of the recording medium is inclined by 45 ° with respect to the rotation axis, and the rotation axis is arranged in parallel with the recording surface of the recording medium. The information track is irradiated through the mirror and the focusing lens, the reflected light from the information track is detected by the light detecting means, and the light is emitted from the light source. Optical recording and reproducing apparatus, wherein the optical axis of the light beam incident on the mirror is parallel to the pivot shaft. 2. The optical recording / reproducing apparatus according to claim 1, wherein an optical axis of a light beam emitted from the light source and incident on the movable mirror coincides with the rotation axis. 3. A magnetic circuit having an air gap, and a movable coil arranged in the air gap for driving the movable mirror, wherein a magnetic field is present in the remaining space in the air gap where the movable coil is arranged. The optical recording / reproducing apparatus according to claim 1, wherein the optical scanning mirror device having a structure filled with a fluid is used.