JP2520393B2 - Optical head device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head device used for a CD player, an optical disc player, a magneto-optical disc breaker or the like for optically reproducing information or recording / reproducing information.

2. Description of the Related Art Optical head devices consist of a forward optical system that guides the light emitted from a laser light source to an objective lens facing the disk and focuses it on the disk, and a return optical system that deflects the return light from the disk and guides it to a photodetector. And an objective lens actuator that supports the objective lens and performs servo in the focus and tracking directions. An optical head device incorporating the forward and backward optical systems and an objective lens actuator is supported by a linear feed mechanism, and linearly feeds a stroke from the innermost periphery to the outermost periphery of a programmed disc in the disc radial direction.

This type of optical head device adopts a configuration in which optical components constituting the forward and backward optical systems are arranged on a horizontal plane parallel to the disk surface, deflected 90 ° through a 45 ° mirror, and guided to an objective lens. In general, the optical head device is made thinner. In this type of optical head device, in order to achieve further miniaturization and compactness, the horizontal center axis of the objective lens actuator is set to the horizontal optical axis from the semiconductor laser of the forward optical system to the 45-degree mirror. 15 ° to 45 degrees toward the disc center on a horizontal plane
There is a bent type in which the main body of the optical head device is tilted by about a degree and bent into a substantially V shape. As a result, the movement space associated with the reciprocating movement of the optical head device is reduced, and the amount of protrusion of the optical head device outside the space corresponding to the disc surface (disc radius range) is reduced to reduce the size of the player body. There is.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in the conventionally proposed vent type optical head device, the optical system forming the forward path and the backward path of the laser light and the objective lens actuator are placed on the left and right opposite sides with the objective lens as the center. One of the forward path optical system and the backward path optical system has a main body shape that largely projects from the bifurcation point of the two in the center of the objective lens.

Therefore, even if the optical head device is bent type,
It is necessary to devise so that the protruding part on one side does not reach the disk drive motor etc., and the protruding part largely protrudes from the disk radius range and linear feed system, and the moving space of the optical head device is correspondingly large. Therefore, there is a limit to downsizing the player body.

Generally, the optical head device is roughly classified into a one-beam system and a three-bit system, but the three-beam system has higher tracking characteristics than the one-beam system. However, in the three-beam type optical head device, the optical system is complicated due to structurally requiring parts such as a diffraction grating, and the light beam is branched when the return light from the disk is guided to the photodetector. Therefore, an enlarging optical system is required, and the entire optical path length is likely to increase as compared with the one-beam method. Therefore, most of the optical head devices of this type have a limit because of the large optical path length even if an attempt is made to reduce the size to a vent type, and as a result of the above-mentioned protrusion amount being further increased, the player body There was an unavoidable major limitation in achieving further miniaturization. For this reason. In order to further reduce the size of the player main body, it is necessary to use the one-beam type optical head device and further improve the tracking characteristics.

However, in the conventional head structure, the center axis of the objective lens and the optical axis of the backward optical system are easily misaligned during tracking servo, which is a factor that deteriorates the tracking characteristics, and some improvement measures are indispensable. Since both the system and the return path optical system are included in the objects to be driven by the tracking servo or the focus servo, there is a problem that the weight load of the servo mechanism is large and the weight load adversely affects the servo performance.

Further, in JP-A-61-57049 "Optical pickup", a biaxial attitude control of an objective lens holding portion is carried out on an optical table having an outward optical system for guiding laser light emitted from a semiconductor laser to an outward path toward a disk. There is disclosed an optical head device in which a return path optical system for guiding reflected light to a photodetector is provided in the objective lens holding portion, which is assembled so as to be vertically movable and rotatable through a mechanism.

However, this is an optical element incorporated in the rotary shaft by utilizing the hollow portion of the rotary shaft supported by the bearings provided on the optical base as the forward path from the semiconductor laser arranged on the lower surface side of the optical base. The light reflected in the horizontal direction by is further reflected to the objective lens side to irradiate the disc,
For this reason, the configuration of the outward optical system is very complicated, and in particular, the assembly adjustment of the irradiation light reflection and reflection light transmission optical elements arranged in the rotation axis is complicated, and workability in the assembly process is improved. It had the problem of being bad.
Further, since there is no damper member that connects the optical base and the objective lens holding portion, the objective lens holding portion cannot be kept in the tracking neutral position when the tracking coil is not energized. However, there is a problem in that it often takes time to shift to a stable state in the initial stage, and the tracking accuracy cannot be maintained in the initial stage of driving or when a shocking external force is applied. Furthermore, if a semiconductor laser and a collimator lens are provided inside the rotary shaft, the overall size of the device can be made compact, but since these optical elements increase the weight of the servo, deterioration of the servo performance cannot be denied. However, there were problems such as the necessity of reviewing the coil design.

The present invention has been made in view of the above points, and it is an object of the present invention to further reduce the size of an optical head device and further improve the tracking characteristics even though it is a one-beam system.

Means for Solving the Problems The present invention, in order to achieve the above-mentioned object, includes a main base that holds a laser light source and a forward optical system that guides laser light emitted by the laser light source to a forward path toward a disk. A two-axis attitude control mechanism for focus control and tracking control arranged on the main base, and a two-axis attitude control mechanism mounted on the main base via the two-axis attitude control mechanism so as to be vertically movable and rotatable. An objective lens holder that is formed outside the attitude control mechanism and holds an objective lens on the forward path, and a return path that is disposed on the objective lens holder and that branches the return light of the laser light from the disc from the middle of the forward path. And a photodetector located at the end of the return path for receiving the return light, and the forward path horizontal part of the forward path optical system is provided with respect to the return path horizontal part of the return path optical system. From 45
It is characterized by the oblique arrangement in the range of °.

Further, according to the present invention, the two-axis attitude control mechanism is erected on the main base and supports the objective lens holder so as to be vertically movable and rotatable, and the main shaft surrounding the support shaft. A substantially cylindrical permanent magnet fixed on the base, and assembled into the objective lens holder in a substantially cylindrical shape,
A focus coil and a tracking coil loosely fitted to the permanent magnet are provided, or the objective lens holder and the main base are interconnected via a damper member that biases the objective lens holder to a tracking neutral position. Another feature is that the photodetector is a four-division photosensor that outputs a focus error detection signal based on the astigmatism method and a tracking error detection signal based on the push-pull method. It is a thing.

Effect According to the present invention, the backward optical system is arranged in the objective lens holder that holds the objective lens, and the forward optical system arranged in the main base is excluded from the control target of the biaxial attitude control mechanism. The weight of the posture control mechanism is reduced and at the same time the controllability is improved, enabling stable focus control and tracking control.

Embodiments Embodiments of the present invention will be described below with reference to the drawings. 1 is a perspective view showing an embodiment of the optical head device of the present invention, FIG. 2 is an exploded perspective view of the optical head device shown in FIG. 1, and FIG. 3 is shown in FIG. FIG. 4 is a plan view showing a state where the optical head device is incorporated in the player main body, and FIG. 4 is a schematic diagram showing a signal detecting operation of the optical head device shown in FIG.

The optical head device shown in FIGS. 1 to 3 holds an objective lens 33 and a return optical system on a main base 10 holding a reciprocating optical system via an objective lens actuator 20 as a biaxial attitude control mechanism. The objective lens holder 21 is combined. By arranging the return path optical system in the objective lens holder that holds the objective lens, the burden weight related to the forward path optical system from the objective lens actuator 20 is reduced, the focus control performance and the tracking control performance are improved, and the return path optical system is achieved. By being integrated with the objective lens 33, it is possible to eliminate the deterioration of tracking characteristics due to the deviation of the lens center axis.

The main base 10 is formed in a bent shape in the middle part, which is bent at a predetermined angle θ within a range of 15 ° to 45 °. This angle θ is set to 30 degrees, for example. Main base 10
The laser diode 30, the collimator lens 31, and the 45-degree mirror 32 are arranged in this order from one end to the other end, forming a forward optical system. An objective lens actuator 20 is arranged at a position slightly closer to the right of the center of the main base 10 and close to the 45-degree mirror 32.

The objective lens actuator 20 supports an objective lens holder 21 holding an objective lens 33 at one end on a main base so as to be vertically movable and rotatable, and a focus control excitation coil 22 and a tracking coil provided below the holder 21. It is configured by combining a control exciting coil 23 and a magnetic circuit 26 including a yoke body 24 and a permanent magnet 25 provided on the main base 10. The yoke body 24 is formed in an annular shape having a cylindrical rising inner wall 241 and a pair of arc-shaped rising outer walls 242, 242 opposed to each other outside the cylindrical inner wall 241 at intervals. On the inner side surfaces of the outer walls 242, 242 of the yoke body 24, a pair of permanent magnets 25, 25 obtained by equally dividing a cylindrical magnet into several pieces in the circumferential direction are attached. Between the outer peripheral surface of the inner wall 241 of the yoke body 24 and the permanent magnets 25, 25, gaps are formed at regular intervals. A magnetic circuit is formed by the inner and outer walls 241, 242, 242 of the yoke body 24 and the permanent magnets 25, 25. A support shaft 27 that supports the objective lens holder 21 is provided upright at the center of the annular yoke body 24. The objective lens holder 21 is mounted on the support shaft 27 so as to be vertically movable and rotatable.

The objective lens holder 21 is formed in a flat plate shape. At one end of the holder 21, a mounting hole 21 for mounting the objective lens 33
1 is formed. The objective lens 33 is fastened to the mounting hole 211. At the center of the lower surface of the holder 21, a cylindrical bearing portion 212 is formed so as to project downward. The bearing 212 is fitted and supported on the support shaft 27 so as to be vertically movable and rotatable. The holder 21 is formed with an annular coil attachment portion 213 centered on the bearing portion 212. A focus control exciting coil 22 wound in a cylindrical shape is attached to the attaching portion 213. On the outer peripheral surface of the focus control exciting coil 22, a pair of tracking control exciting coils 23, 23 wound in the shape of a flat bar are attached at intervals of 180 degrees. The focus and tracking control exciting coils 22, 23 (23) are incorporated in the gap formed between the yoke inner wall 241 of the magnetic circuit 26 and the permanent magnets 25, 25. Note that the tracking control exciting coils 23, 23 are magnetic circuit 26 only in approximately half including one rising portion wound in a frame shape.
It is provided so as to cover the gap. In addition, the holder
At the other end of 21, a pin 214 is provided so as to project downward, and a damper member 28 made of a substantially annular rubber material or the like is provided between this pin 214 and the pin 101 standingly provided at the end of the main base 10. It is installed. The objective lens holder 21 is a damper member.
Always held in neutral position by 28.

A half mirror 34 is attached to the lower surface of the objective lens holder 21 corresponding to the objective lens 33. The half mirror 34 is arranged so as to deflect the return light from the disk in the horizontal direction orthogonal to the rotation center axis of the objective lens holder 21. In addition, the angle θ with the horizontal part of the forward optical system described above.
To form a return path for returning light that extends in the opposite direction, a 45 degree mirror 35,
Convergent convex lens 36, magnifying concave lens 37, cylindrical lens
A return optical system composed of 38 is provided, and the return path is terminated by a four-division optical sensor 39 held at the end of the objective lens holder 21. The half mirrors 34, 45-degree mirrors 35 are made of a plate-like material to reduce the weight, which contributes to reducing the weight load of the objective lens actuator 20.

The objective lens rudder 21 is formed such that the center of gravity is located on the center axis of rotation with the coil and the optical components attached, and unnecessary portions are cut out to reduce the weight as much as possible. The optical components, the coil, and the like are attached to the objective lens holder 21 by adhesion and fixing with an adhesive so as to avoid an increase in weight due to parts such as screws and screws. Although the parts are attached to the main base 10 by adhesive fixing with an adhesive, this itself affects the behavior characteristics of the main base 10 and is directly related to reducing the load on the objective lens actuator 20. There is no.

The optical head device configured as described above is covered and sealed by the external cover 11 except for the part of the objective lens 33. Bearings 12, 12 are formed on the cover 11. The optical head device is slidably mounted on a pair of parallel shafts 13 and 14 supported by the player body. The optical head device is linearly fed back and forth in the disk radial direction along the shafts 13 and 14 via a linear feed system (not shown). In this optical head device, the laser diode 30
The optical axis of the outward optical system from the center of the objective lens 33 to the center of the objective lens 33 through the collimator lens 31 and the 45-degree mirror 32, and the central axis connecting the rotation center axis of the objective lens holder 21 and the center of the objective lens are the center of the disc. It is inclined at an angle θ with respect to. The optical axis of the backward optical system from the center of the objective lens 33 to the four-divided sensor 39 through the 45-degree mirror 32 is also tilted toward the disc center at an angle θ with the optical axis of the forward optical system. As a result, a bent type optical head device is formed which is bent in a substantially V shape. The optical head device is linearly fed back and forth from a direction inclined at an angle θ with respect to the conventional orthogonal direction. Therefore, when this is incorporated into the player main body, it is arranged at a position closer to the center of the disc, and reciprocating linear feed is performed in a minimum moving space. Further, the amount of protrusion from the outer circumference of the disk when it is moved to the outermost track is suppressed to the minimum.

In the backward optical system as described above, the tracking error is detected by the push-pull method, and the focus error is detected by the astigmatism method. Detection of these error signals and reproduced RF signals is performed by one photodetector using the four-division photosensor 39.

When the objective lens actuator 20 is driven by driving the electromagnetic drive system in the above structure, the attitude of the objective lens 33 is controlled in the radial direction of the disk or in the vertical direction. As a result, the spot of the laser beam emitted from the objective lens 33 to the disc is controlled to follow the recording track correctly. At that time, since the backward optical component is mounted on the objective lens holder 21, the backward optical system moves integrally in accordance with the servo of the objective lens, and its optical axis is always aligned with the center of the objective lens 33. Be drunk Therefore,
The optical axis of the return light passing through the return path always coincides with the central axis of the objective lens 33 not only during the focus servo but also during the tracking servo. Therefore, even when the head structure of the one-beam system as in the embodiment in which the tracking error detection is performed by the push-pull method and the focus error detection is performed by the astigmatism method, the three-beam system using the expansion optical system is used. Stable tracking characteristics equal to or higher than that can be obtained. As a result, the tracking characteristics of the one-beam method are improved while taking advantage of the one-beam method.

Next, the outline of the signal detection operation will be described with reference to FIGS.

The reproduction RF signal is detected by the light receiving parts A, B, and
It is performed by the sum (A + B + C + D) of the detection outputs of C and D. The tracking error signal is detected by taking the difference between the detection outputs of the light receiving section (A + B) and the light receiving section (C + D). Focus error signal detection is
The sum (A + D) of the detection outputs of the light receiving parts A and D at the diagonal position of the four-division sensor 39 and the sum (B +) of the detection outputs of the light receiving parts B and C.
It is done by taking the difference of C).

In addition, as a method of detecting the tracking error signal,
As shown in the figure, the RF signal is compared and converted into a pulse signal, and the rising and falling edges switch the signals obtained by the differential output by switching, and sample-hold each signal to extract the differential output. You may make it perform the signal processing by a heterodyne method.

EFFECTS OF THE INVENTION As described above, according to the optical head device of the present invention, the backward optical system is arranged in the objective lens holder for holding the objective lens, and the forward optical system arranged in the main base is biaxially posture controlled. Since it is excluded from the control target of the mechanism, the weight load of the two-axis posture control mechanism is reduced and at the same time the controllability is improved, stable focus control and tracking control are possible, and the return path optical system is arranged on the objective lens holder. With the provision, the central axis of the objective lens and the optical axis of the return path optical system can be made to always coincide with each other, and the optical axis of the returning light does not shift, so that the tracking error can be detected stably. As a result, even when the 1-beam method is adopted, stable tracking servo equivalent to or higher than that of the 3-beam method is possible, and further, it is formed outside the 2-axis attitude control mechanism. Since the laser light is guided to the objective lens along the outward path, a complicated manufacturing process such as incorporating an optical element inside the biaxial attitude control mechanism is unnecessary, and the optical path arrangement bypassing the biaxial attitude control mechanism is unnecessary. For optimum design, the forward horizontal part of the forward optical system is obliquely arranged in the range of 15 ° to 45 ° with respect to the horizontal return part of the backward optical system, so the optical head unit moves even when tracking the outermost circumference of the disc. The space can be contained within the disk radius range,
Since there is almost no protrusion of the optical head device from the disc, for example, when adopting a configuration in which the optical head device is tracking-driven in the diagonal direction of the player main body to maximize the space inside the player main body, Unlike other optical head devices in which the forward horizontal part of the optical system and the return horizontal part of the optical system are linearly arranged, the part protruding outside the radius of the disk does not hinder the downsizing of the player main body. Therefore, there is an excellent effect that the space saving merit of the moving space of the optical head device can be directly utilized for downsizing of the player main body.

Further, according to the present invention, a two-axis attitude control mechanism is erected on the main base and supports the objective lens holder so as to be vertically movable and rotatable, and is fixed on the main base by surrounding the support shaft. Since the permanent magnet having a substantially cylindrical shape and the focus coil and the tracking coil which are assembled into the objective lens holder in a substantially cylindrical shape and are loosely fitted to the permanent magnet are provided, the heavy permanent magnet is disposed on the main base. By reducing the weight of the objective lens holder and by assembling the cylindrical focus coil and tracking coil that loosely fit in the permanent magnet to the objective lens holder, it is possible to realize focus servo and tracking servo with excellent dynamic characteristics. Play.

Furthermore, since the objective lens holder and the main base are interconnected via a damper member that urges the objective lens holder to the tracking neutral position, the tracking coil is not energized and the servo is not applied. Also, the objective lens holder and the main base can be kept in the tracking neutral position by the urging force of the damper member, and thus, the stability or the settling property is sufficiently maintained at the initial stage of the tracking servo or when a shocking external force is applied. Even if the damper member exerts a viscous resistance proportional to the displacement speed in the tracking direction, it does not adversely affect the tracking servo or focusing servo, and the initial position of the tracking servo is stable. Promises a good servo history It is an effect such as can.

Furthermore, by configuring the photodetector with a 4-division optical sensor that outputs a focus error detection signal based on the astigmatism method and a tracking error detection signal based on the push-pull method, a single 4-division optical sensor is used. The signal reproduction, the focus servo, and the tracking servo can be effectively performed.

[Brief description of drawings]

1 is a perspective view showing an embodiment of the optical head device of the present invention, FIG. 2 is an exploded perspective view of the optical head device shown in FIG. 1, and FIG. 3 is shown in FIG. FIG. 4 is a plan view showing a state where the optical head device is incorporated in the player main body.
FIG. 5 is a schematic diagram showing a signal detecting operation of the optical head device shown in FIG. 3, and FIG. 5 is a circuit diagram showing another embodiment of the tracking error signal detecting method. 10 …… Main base 20 …… Objective lens actuator 21 …… Objective lens holder 22,23 …… Excitation coil 26 …… Magnetic circuit 30 …… Laser diode 33 …… Objective lens 39 …… Quarantine optical sensor

Claims (4)

(57) [Claims] 1. A main base for holding a laser light source and a forward optical system for guiding a laser beam emitted by the laser light source to a forward path toward a disk, and a focus control and a tracking control disposed on the main base. A two-axis attitude control mechanism and an objective lens mounted on the main base via the two-axis attitude control mechanism so as to be vertically movable and rotatable, and on the forward path formed outside the two-axis attitude control mechanism. An objective lens holder that holds the return lens, a return optical system that is disposed in the objective lens guide and guides the return light of the laser light from the disc to a return path that branches from the middle of the return path, and the return path located at the end of the return path. A photodetector for receiving light, wherein the forward horizontal part of the forward optical system is obliquely arranged in the range of 15 ° to 45 ° with respect to the backward horizontal part of the backward optical system. De devices. 2. The two-axis attitude control mechanism is erected on the main base, and supports a support shaft that supports the objective lens holder so as to be vertically movable and rotatable, and the main base surrounding the support shaft. A substantially cylindrical permanent magnet fixed on the upper side, and a focus coil and a tracking coil which are assembled into the objective lens holder in a substantially cylindrical shape and are loosely fitted to the permanent magnet. The optical head device according to item 1. 3. The objective lens holder and the main base are interconnected via a damper member for urging the objective lens holder to a tracking neutral position. The optical head device according to item 2. 4. The photodetector comprises a four-division photosensor that outputs a focus error detection signal based on the astigmatism method and a tracking error detection signal based on the push-pull method. First to third
The optical head device according to any one of items.