JPH0714184A - Tracking control device - Google Patents

Abstract

PURPOSE:To perform tracking control with high accuracy by always performing the tracking control basing on an optical axis as a reference and correcting an offset of a galvanomirror. CONSTITUTION:The galvanomirror 19 for changing the direction of a light beam for irradiation of a disk 7 is turned by a driving circuit 26. A track deviation signal is obtained from an output of a photodetector 12 for detecting a deviation of an irradiating position, with the light beam from a track on the disk. A rotary angle at the time when the galvanomirror 19 is turned, is detected by a photosensor 21, and an offset due to the turning is canceled by this turning angle, so that a differential amplifier 13 for correcting the track deviation signal is equipped. At the time of retreaving a track on the disk 7, an output of a phase compensation circuit 24, where an added output of an output of a low-pass filter based on the output of the photodetector 12 and an output of a DC-cut filter based on the output of the photosensor 21 is phase- compensated, is negatively fed back to a driving input of the galvanomirror 19, and even in case of disturbance, the galvanomirror 19 is locked to make the center of a light spot coincide with the center of an optical axis of an optical system.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording / reproducing apparatus for optically recording or reproducing a signal on a recording medium using a light source such as a laser. The present invention relates to a tracking control device that controls a beam so as to accurately scan a track on a recording medium.

[0002]

2. Description of the Related Art Recently, in an optical recording / reproducing apparatus, in order to realize a thin device and a high-speed search, a part of the optical system is separated and placed in a movable part instead of moving the entire optical system. However, it is known to perform tracking by moving the movable part, that is, the optical head. further,
In order to reduce the weight of the movable part, a structure is known in which a galvano mirror is used as a tracking actuator and the galvano mirror is arranged on a fixed part.

A conventional tracking control device will be described below with reference to FIGS. 27 and 28.

FIG. 27 is a block diagram showing the structure of a conventional tracking control device. Light source 10 such as semiconductor laser
The emitted light 108 from the collimator lens 10
After being collimated by 2 the beam splitter 10
3 and is reflected by a galvanometer mirror 119 which is a tracking fine actuator. The light reflected by the galvano mirror 119 is further reflected by the mirror 104 arranged in the movable part, then converged by the objective lens 105, and irradiated on the rotating disk 107. A spindle motor 106 for rotating the disc 107 is connected to the disc 107.

Optical beam reflected by the disk 107
After passing through the objective lens 105, the beam is reflected by the mirror 104 and the galvanometer mirror 119 and then reflected by the beam splitter 103. The light beam incident on the beam splitter 103 is reflected toward the convex lens 109. The light beam passes through the convex lens 109, and the light beams 111 and 1 are transmitted by a cylindrical polarization beam splitter 110 (hereinafter, referred to as a cylindrical PBS).
It is divided into 15.

One of the split light beams 111 is focused on the split surface of the photodetector 112. Outputs A and B, which are output from the two-divided surface and correspond to the light amount of the condensed light beam, are input to each terminal of the differential amplifier 114. The differential amplifier 114 calculates the difference between the outputs A and B of the photodetector 112 to obtain the track shift signal. A method of detecting the track deviation signal as the output of the differential amplifier 114 in this manner is disclosed in, for example, Japanese Patent Laid-Open No. 49-6.
It is described in Japanese Patent No. 0702 and is known as a push-pull method.

The outputs A and B from the two-divided surface of the photodetector 112 are also input to the summing amplifier 116,
The sum of the outputs A and B is obtained by the summing amplifier 116, and the light quantity sum signal is obtained.

The track shift signal output from the differential amplifier 114 is input to the variable amplifier 117. The gain of the variable amplifier 117 is adjusted so that the amplitude of the track deviation signal at the output point a becomes substantially constant. The output from the variable amplifier 117 is input to the divider 118. The light quantity sum signal from the summing amplifier 116 is also input to the divider 118. By dividing the output from the variable amplifier 117 by the output from the summing amplifier 116, the light beam at the time of recording or erasing can be obtained. The amplitude of the track deviation signal is made substantially constant with respect to the change in the light amount or the change in the reflectance of the disk 107.

On the other hand, cylindrical P. B. S. 110
The other light beam 115 split by is focused on the four-divided surface of the photodetector 112. Based on the output from the four-divided surface, a focus shift signal for detecting that the light beam on the disk 107 has deviated from a predetermined converged state can be obtained. Here, the detection of the focus shift signal is performed by the known astigmatism method using the differential amplifier 113. By a known focus control that drives a focus actuator (not shown) based on the focus shift signal, the light beam is controlled to irradiate the disk 107 in a predetermined converged state. Since such focus control is not directly related to the present invention, detailed description thereof will be omitted.

Next, when the light beam converged by the objective lens 105 is controlled so as to be accurately irradiated onto the target track, that is, when the tracking control is performed, the entire optical system. The operation will be briefly described. In this tracking control, the galvano mirror 11 that is a tracking fine actuator is used at high frequencies.
9 is mainly driven, and the control is performed by mainly driving the linear motor 120 which is a tracking coarse actuator at low frequencies. In addition, a search for moving the light spot over a wide range over the entire area of the disk 107 is also performed by the linear motor 120.
Drive.

As described above, the track deviation signal whose amplitude is made substantially constant by the light intensity change of the light beam or the reflectance change of the disk 107 by the divider 118 is a tracking servo loop (hereinafter referred to as TR servo loop). .) To the phase compensation circuit 122. The output of the phase compensation circuit 122 of the TR servo loop is the disk 107.
A signal for selecting whether to perform tracking control in which the light spot irradiated on the disk 107 is controlled to follow a track on the disk 107 or to perform lock servo for fixing and controlling the galvanometer mirror 119 at a desired position. It is connected to one input terminal of the selection circuit 127. The output signal of the phase compensation circuit 128 for compensating the phase at the gain intersection of the lock servo loop is input to the other input terminal of the signal selection circuit. The output terminal of the signal selection circuit 127 is the drive circuit 12 for driving the galvano mirror 119.
It has been entered in 6. When the signal selection circuit 127 is selecting the signal from the phase compensation circuit 122 of the TR servo loop, the galvano mirror 119 is driven by the output from the drive circuit 126 according to the track deviation signal and rotates. The rotation of the galvanometer mirror 119 changes the direction in which the light beam is reflected, and the light spot moves in a direction that traverses the track on the disk 107 (hereinafter referred to as the tracking direction) so as to be located on the track.
In this way, the light spot is always controlled to be located at the center of the target track.

A mirror 104 and an objective lens 105 are mounted on a linear motor 120 capable of moving in the track direction from the inner circumference to the outer circumference of the disk 107.
This constitutes an optical head. Light spot
The disk 107 is moved along with the movement of the linear motor 120.
It moves in the tracking direction from the inner circumference to the outer circumference. When tracking control is performed, the output of the phase compensation circuit 122 of the TR servo loop is input to the phase compensation circuit 124 used for controlling the linear motor 120 via the equivalent filter circuit 123. Equivalent filter 1
Reference numeral 23 has an input / output characteristic of the galvanometer mirror 119 which is a tracking fine actuator, that is, a characteristic almost equal to the rotation characteristic with respect to the input. Phase compensation circuit 124
Is output to the drive circuit 125 that drives the linear motor 120, and this output causes the galvano mirror 119 to be in a natural state, that is, the optical axis center of the optical system and the optical axis of the light beam incident on the objective lens 105. The linear motor 120 is controlled so that the linear motor 120 can be rotated about the state in which

Next, when the tracking control is not performed, or when the linear motor 120 is performing a search operation in which the linear motor 120 moves in the tracking direction, the galvanometer mirror 119 arranged in the fixed portion vibrates due to disturbance. A lock servo for preventing the occurrence of the above and fixing the lock servo at a predetermined position will be described with reference to FIGS. 27 and 28. FIG. 28 is a block diagram of a conventional lock servo. Using FIG. 28,
The structure of the lock servo will be described. The signal detected by the reflection type optical sensor 121 for detecting the rotation angle of the galvano mirror 119 is the phase compensation circuit 128 of the lock servo loop.
And the galvano mirror 119 via the signal selection circuit 127.
Is input to the driving circuit 126 and is negatively fed back to the galvano mirror 119. The lock servo will be described again with reference to FIG. The rotation angle of the galvanometer mirror 119 is detected by the reflection type optical sensor 121, and is negatively fed back to the input of the galvanometer mirror 119 via the phase compensation circuit 128 that compensates the phase at the gain intersection of the lock servo. By performing the lock servo with the above-described configuration, the galvano mirror 119 can be fixed at a desired position according to the rotation angle detection signal from the reflective optical sensor 121.

[0014]

However, as shown in FIG.
In the conventional apparatus shown in (1), a galvanometer mirror 119 is used as a tracking fine actuator, and further, this galvanometer mirror 119 is arranged in a fixed portion, and the mirror 104 and the objective lens 105 are arranged on the linear motor 120 which is a coarse tracking actuator. Since the optical head is configured as a result, the optical path length from the galvano mirror 119 to the objective lens 105 via the mirror 104 becomes long.
When the optical path length becomes long, the galvano mirror 119 is in a non-controlled state in an initial state, that is, in a state in which the optical axis of the optical system and the center of the light beam coincide with each other. When it is changed in the receiving direction, a deviation easily occurs between the optical axis of the optical system and the center of the light beam. In this specification, such a deviation between the optical axis and the center of the light beam is referred to as an optical axis deviation. When the optical axis shift occurs, an offset occurs in the track shift signal.
This offset increases as the optical path length increases.

With reference to FIG. 29, the galvanometer mirror 1
The optical axis shift caused by the rotation of 19 will be described.
When the Galvano mirror 119 rotates as shown in FIG. 29, the above-mentioned optical axis shift occurs, and the track shift signal has an offset. That is, when the tracking control is performed, the optical axis shift occurs due to the rotation of the galvanometer mirror 119. Further, even when the tracking control is not performed, when the attitude change of the galvano mirror 119 described above occurs, the optical axis shifts in the rotation direction as in the case where the tracking control is performed. When the optical axis shift occurs in this way, a large offset occurs in the track shift signal due to spherical aberration of the objective lens 105, coma aberration of the light beam, vignetting of the lens frame, or the like. When the tracking control is performed in this state, the galvano mirror 119 is further rotated to increase the offset in a state where the offset has already occurred in the track deviation signal.

If the optical axis shift when the tracking control is not performed is large, the offset of the track shift signal also becomes large. Even if an attempt is made to remove such an offset in a circuit subsequent to the circuit in which the track deviation signal is detected, the offset may be too large and the circuit may not be removed. Further, the amplitude of the track deviation signal may be reduced due to vignetting of the lens frame, or the track deviation signal may not appear. When the track deviation signal disappears, the track deviation signal cannot appear even if the offset is removed by the circuit.

If the track shift signal has an offset during tracking control, the light spot on the disk 107 is positioned so as to be displaced from the center of the target track by the tracking control system. Controlled by. That is, the light spot on the disk 107 is controlled to be off-track.

When tracking control is being performed,
When the off-track as described above occurs due to the rotation of the galvanometer mirror 119, for example, the recording characteristics when recording information on the disk 107 or the reproducing characteristics when reproducing information are deteriorated, or the light spot is tracked. There is a problem that the tracking accuracy is lowered such that it is easily deviated from.

Furthermore, when the attitude of the galvano mirror 119 changes due to a change with time or a change in environmental temperature while tracking control is not performed, the center of the light beam deviates from the optical axis of the optical system, resulting in a track deviation signal. Offset occurs. When the optical axis shift occurs due to a change with time or a change in environmental temperature, a large offset of the track shift signal occurs or the track shift signal does not appear in some cases. If the offset of the track deviation signal is large or the track deviation signal disappears, the tracking control system cannot be pulled in stably. For this reason, there is a problem that the device cannot be started and the reliability is significantly reduced.

Further, as the rotation angle detector of the galvanometer mirror 119, the reflection type optical sensor 12 described in the conventional example is used.
When 1 is used, the output signal from the reflective photosensor 121 is a DC offset (hereinafter referred to as DC offset).
I have Furthermore, the detection characteristics of the reflective optical sensor 121 change due to temperature changes and changes over time, and the DC offset changes. When a DC offset occurs in the output of the reflective optical sensor 121 or the DC offset changes, the lock position of the galvano mirror 119 changes by the DC offset. When the lock position of the galvanometer mirror 119 changes, the optical axis of the optical system shifts. This optical axis shift causes a large offset of the track shift signal.

When the galvanometer mirror 119 is locked with the DC offset of the reflection type optical sensor 121 being large, the galvanometer mirror 119 is locked at a position where the optical axis shift occurs and an offset occurs in the track shift signal. Or, the amplitude of the track deviation signal becomes small. As a result, there is a problem that an incorrect count is likely to occur during retrieval.

In consideration of the above problems of the conventional tracking control device, the present invention corrects the deviation of the initial adjustment of the optical head and the deviation of the optical axis due to a change over time, so that the center of the optical axis of the optical system of the optical head is constantly adjusted. (EN) Provided is a highly reliable tracking control device capable of performing tracking control based on a reference, and performing an offset correction caused by rotation of a galvanometer mirror to perform accurate and highly accurate tracking control. With the goal.

[0023]

To achieve the above object, a tracking control device of the present invention receives a drive signal and a focusing means for focusing an optical beam on a recording medium, and receives the drive signal in response to the drive signal. A galvano-mirror that rotates a light beam direction with a moving unit that moves a convergence point of the light beam in a direction that traverses a track provided on the recording medium in a minute range, Coarse moving means for moving in a wide range, track deviation detecting means for generating a track deviation signal according to the position of the convergence point of the light beam with respect to the track, and the convergence of the light beam according to the track deviation signal. Generating a first driving signal for driving the moving means so that a point is located on the one of the tracks, and supplying the first driving signal as the driving signal to the moving means. A tracking control means, operation of said tracking control means, and means for switching the non-operation,
Drive means for generating a second drive signal for driving the moving means so that the convergence point of the light beam crosses a predetermined number of the tracks when the tracking control means is inactive; The rotation angle detecting means for detecting the rotation angle of the light beam, and the rotation angle detecting means obtained by driving the moving means by the second drive signal when the tracking control means is inactive A correction amount calculation means for calculating a correction amount for canceling the offset of the track deviation signal caused by the rotation of the light beam based on the angle signal, and an offset of the track deviation signal based on the obtained offset correction amount. And a correction unit that corrects the value to substantially zero.

Further, according to the present invention, a converging means for converging an optical beam on the recording medium, a drive signal, and a converging point of the light beam on the recording medium in response to the drive signal. A galvano-mirror that moves a light beam direction by a moving unit that moves in a direction traversing a track provided on the recording medium, a coarse moving unit that moves a wide range, and the light beam for the track. Of track deviation detecting means for generating a track deviation signal according to the position of the convergence point, a low pass filter for extracting a low frequency component of the output of the track deviation detecting means, and a rotation for detecting a rotation angle of the light beam. Angle detection means, a DC cut filter for cutting off the DC component of the rotation angle detection means, an addition means for adding the output of the low pass filter and the output of the DC cut filter, and A phase compensating circuit for compensating the phase of the output of the calculating means, and the galvano-mirror locking means for negatively feeding back the output of the phase compensating circuit to the galvano-mirror drive input; Switching between tracking control for driving the moving means so that the converging point of the light beam is located on the one of the tracks or locking of the galvano mirror according to the output of the rotation angle detecting means. And a second configuration including means.

Further, according to the present invention, a converging means for converging an optical beam on the recording medium and a drive signal are received, and the converging point of the light beam is set on the recording medium according to the drive signal. A galvano-mirror that moves a light beam direction by a moving unit that moves in a direction traversing a track provided on the recording medium, a coarse moving unit that moves a wide range, and the light beam for the track. Track deviation detecting means for generating a track deviation signal according to the position of the convergence point, and an equivalent filter having a transfer function substantially equal to that of the galvanometer mirror and extracting a low-frequency component of the output of the track deviation detecting means. A rotation angle detecting means for detecting a rotation angle of the light beam, a DC cut filter for cutting off a direct current component of the rotation angle detecting means, an output of the low pass filter and the DC filter. Filter for adding the output of the filter and a phase compensating circuit for compensating the phase of the output of the adding means, and the output of the phase compensating circuit is negatively fed back to the galvano mirror drive input. Output of the locking means and the tracking control or the rotation angle detecting means for driving the moving means so that the convergence point of the light beam is located on the one of the tracks in response to the track shift signal. And a means for switching whether to lock the galvano mirror according to the above.

Further, according to the present invention, a converging means for converging an optical beam on the recording medium, a drive signal, and a convergence point of the light beam on the recording medium according to the drive signal. A galvano-mirror that moves a light beam direction by a moving unit that moves in a direction traversing a track provided on the recording medium, a coarse moving unit that moves a wide range, and the light beam for the track. Track deviation detecting means for generating a track deviation signal according to the position of the convergence point, a low-pass filter for extracting a low-pass component of the output of the track deviation detecting means, and a phase of the output of the low-pass filter. And a phase compensating circuit for compensating the output of the phase compensating circuit, wherein the output of the phase compensating circuit is negatively fed back to the galvano mirror driving input. .

Further, according to the present invention, a converging means for converging an optical beam on the recording medium, a drive signal, and a converging point of the light beam on the recording medium according to the drive signal. A galvano-mirror that moves a light beam direction by a moving unit that moves in a direction traversing a track provided on the recording medium, a coarse moving unit that moves a wide range, and the light beam for the track. Track deviation detecting means for generating a track deviation signal according to the position of the convergence point, and an equivalent filter having a transfer function substantially equal to that of the galvanometer mirror and extracting a low-frequency component of the output of the track deviation detecting means. A phase compensation circuit for compensating the phase of the output of the low pass filter, wherein the output of the phase compensation circuit is negatively fed back to the galvanometer mirror drive input. Having a fifth structure with a mirror locking means.

[0028]

With the first structure, the offset of the track deviation signal generated by the rotation of the galvano mirror during tracking control can be corrected, accurate and highly accurate tracking control can be performed, and highly reliable recording / reproducing characteristics can be obtained. it can. By correcting the optical axis shift when the tracking is not controlled, the tracking control is always performed around the optical axis center of the optical system of the optical head, and accurate and highly accurate tracking control can be performed. Further, even if the optical system optical axis center is largely deviated due to a change with time and the offset of the track deviation signal is increased so that the track deviation signal does not appear, the optical axis deviation is corrected so that the track deviation signal appears. This makes it possible to prevent the apparatus from being unable to start due to the track deviation signal. Further, it becomes possible to stably bring in tracking control by adjusting the offset of the track deviation signal. Therefore, it becomes possible to secure stable control performance and search performance, prevent unavailability, and significantly improve the reliability of the device.

With the above-described second structure, when the search control of the track of the recording medium by the convergence point of the light beam is performed, the output of the low-pass filter based on the output of the track deviation detecting means and the DC based on the output of the detecting means. Even if the output of the phase compensation circuit that compensates the output of the cut filter and the output of the phase compensation circuit is negatively fed back to the drive of the galvanometer mirror and there is a disturbance in the device, the center of the convergence point of the light beam is always the optical axis of the optical system. The galvanometer mirror is locked so that the optical axis does not shift in line with the center.

According to the third configuration, when the search control of the track of the recording medium by the convergence point of the light beam is performed, the output of the equivalent filter based on the output of the track deviation detecting means and the DC cut filter based on the output of the detecting means. Even if the output of the phase compensation circuit that compensates the output of the output is negatively fed back to the drive of the galvanometer mirror and there is a disturbance in the device, the center of the convergence point of the light beam is always the center of the optical system optical axis. The galvanometer mirror is locked so that the optical axes do not coincide with each other.

With the above-described fourth structure, in the search control of the track of the recording medium by the converging point of the light beam, the phase compensating circuit which phase-compensates the output of the low pass filter based on the output of the track deviation detecting means. Even if the output is negatively fed back to the drive of the galvanometer mirror and there is a disturbance in the device, the galvanometer mirror is locked so that the center of the converging point of the light beam does not coincide with the optical axis center of the optical system and does not shift. To be done.

According to the fifth configuration, when the search control of the track of the recording medium by the convergent point of the light beam is performed, the output of the phase compensating circuit which phase-compensates the output of the equivalent filter based on the output of the track deviation detecting means is output. Even if there is a disturbance in the device due to negative feedback to the drive of the galvanometer mirror, always
The galvanometer mirror is locked so that the center of the convergence point of the light beam coincides with the center of the optical axis of the optical system and is not displaced.

[0033]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a tracking control device according to the present invention will be described below with reference to FIG.
~ It demonstrates with reference to FIG.

FIG. 1 is a block diagram showing the configuration of a first embodiment of a tracking control device according to the present invention. A light beam 8 emitted from a light source 1 such as a semiconductor laser is collimated by a collimator lens 2, passes through a beam splitter 3, and is reflected by a galvanometer mirror 19 of a tracking fine actuator. The reflected light is further reflected by the mirror 4 on the movable part, then converged by the objective lens 5, and irradiated on the rotating disk 7. A spindle motor 6 for rotating the disk 7 is connected to the disk 7.

The light beam reflected by the disk 7 passes through the objective lens 5, is reflected in the order of the mirror 4 and the galvanometer mirror 19 and enters the beam splitter 3. The light beam incident on the beam splitter 3 passes through the convex lens 9 and is then split into light beams 11 and 15 by a cylindrical polarization beam splitter 10 (hereinafter referred to as a cylindrical PBS). One of the split light beams is focused on the photodetector 12. Photo detector 1
The output of 2 has a plurality of detection surfaces, one of which is divided into two. The light beam 11 is condensed on this two-divided surface. Outputs A and B corresponding to the intensity of the light beam condensed on the two-divided surface are input to each terminal of the differential amplifier 14. By performing a calculation for obtaining the difference between the outputs A and B in the differential amplifier 14, a track shift signal can be obtained.

In this way, the track shift signal is obtained by the push-pull method. The outputs A and B from the two-divided surface of the photodetector 12 are also input to the summing amplifier 16, and the sum of the outputs A and B is obtained as a light quantity sum signal.

The track shift signal output from the differential amplifier 14 is input to the variable amplifier 17. Variable amplifier 1
The gain of No. 7 is adjusted so that the amplitude of the track deviation signal at the output point a becomes substantially constant. The output from the variable amplifier 17 is input to the divider 18. on the other hand,
The light amount sum signal output from the addition amplifier 16 is input to the divider 18. In the divider 18, the variable amplifier 1
By dividing the track deviation signal from No. 7 by the light quantity sum signal from the summing amplifier 16, the amplitude of the track deviation signal is almost constant with respect to the change of the light quantity of the light beam at the time of recording or erasing or the change of the reflectance of the disk 7. To be

Cylindrical P. B. S. The other light beam 15 divided by 10 is also a photodetector 12
Focused on top. The place where the light beam 15 is condensed is not the above-mentioned two-divided surface but another detection surface divided into four. Based on the output according to the intensity of the light beam condensed on the four-divided surface, a focus shift signal for detecting that the light beam on the disk 7 is deviated from a predetermined converged state is obtained. In this embodiment, the focus shift signal is detected by a known astigmatism method, and the light beam on the disk 7 is converged to a predetermined level by a known focus control that drives a focus actuator (not shown) based on the focus shift signal. The control is performed so as to be in the state. Since the focus control is not directly related to the present invention, detailed description will be omitted.

Next, the track shift signal detection by the push-pull method will be described with reference to FIGS. 4 and 5.

FIG. 4A shows the diffraction from the diffraction grating when the position of the light spot on the disk 7 is changed by regarding the track pit row (track) on the disk 7 as a one-dimensional diffraction grating. The interference pattern of 0th-order light and ± 1st-order light is shown. When the relative displacement of the center of the light spot with respect to the track center is u and the track pitch is q, the interference patterns at u = 0 and at u = q / 2 have the same shape on the left and right sides. However, u = q / 4, or u = -q /
In the interference pattern of 4, the shape of the pattern is reversed between the left side and the right side. Here, comparing the light intensities when the reflected lights from the interference patterns C, D, and E are condensed on the photodetector 12, the relationship is pattern C> pattern D> pattern E.

FIG. 4B shows a schematic view of the track deviation signal detection optical system. When the interference patterns C, D, and E have the above-described relationship, as shown in FIG. 4B, the dividing line of the two-divided surface of the photodetector 12 is arranged parallel to the track,
The difference between the center of the light spot and the track center can be detected by differentially detecting the output from the two-divided surface.

FIG. 5 shows an example of the track shift signal obtained by the push-pull method. When u = 0, the light spot is located at the center of the track, and the track shift signal matches the control reference for tracking control. u = q / 4
, The track deviation signal has a positive peak, and u =-
At q / 4, it has a negative peak. When u = q / 2, the light spot is located between the tracks. That is, when the outputs from the division planes A and B of the photodetector 12 when the light spot crosses the track on the disk 7 are calculated by the differential amplifier 14, a track deviation signal as shown in FIG. Obtainable. Further, the output from the two-divided surface of the photodetector 12 is input to the summing amplifier 16 as described above, and by the summing amplifier 16,
A light quantity sum signal corresponding to the reflected light quantity of the light beam from the disk 7 can be obtained.

Next, the operation of the entire optical system when the tracking control is performed will be described with reference to FIG. In tracking control, the galvanometer mirror 19 which is a fine actuator is mainly driven at a high frequency, and the linear motor 20 which is a coarse actuator is mainly driven at a low frequency. The linear motor 20 is also driven to perform a search for moving the light spot over a wide range over the entire area of the disk 7. Such tracking control is performed in a state in which the correction of the optical axis deviation, which will be described in detail later, and the adjustment of the gain for correcting the offset of the track deviation signal are completed. That is, in this embodiment, the tracking control is
The correction of the optical axis shift allows the galvano mirror 19 to rotate about the state where the optical axis of the optical system coincides with the center of the light beam, and the gain adjustment adjusts the track shift due to the rotation of the galvano mirror 19. It will be performed after the offset of the signal is canceled.

The track deviation signal whose amplitude is made substantially constant by the light quantity change of the light beam or the reflectance change of the disk 7 by the divider 18 is input to one input terminal of the differential amplifier 31. A signal obtained by adjusting the output of the sensor circuit to a predetermined gain by the gain adjusting circuit 30 is input to the other input terminal of the differential amplifier 31, and the output of the differential amplifier 31 is input to the phase compensation circuit 22. Phase compensation circuit 2
The output of 2 is input to the drive circuit 26 via the adder circuit 32. Therefore, the galvano mirror 19 is driven and rotated by the output from the drive circuit 26 according to the track shift signal. The rotation of the galvanometer mirror 19 causes the light spot to move in the direction traversing the track on the disk 7, that is, in the tracking direction. In this way, the light spot on the disk 7 is controlled so as to always be located at the track center.

A mirror 4 and an objective lens 5 are mounted on the linear motor 20. The mirror 4 and the objective lens 5 can be moved in the tracking direction from the inner circumference to the outer circumference of the disk 7 by moving the linear motor 20. Therefore, the light spot moves in the tracking direction from the inner circumference to the outer circumference of the disk 7 as the linear motor 20 moves. When tracking control is being performed, the output of the above-mentioned phase compensation circuit 22 is equivalent to the equivalent filter circuit 23 and the phase compensation circuit 2 of the linear motor control system.
4. The linear motor 20 is added to the linear motor 20 via the drive circuit 25 so that the galvanomirror 19 can rotate about the state where the optical axis of the optical system and the center of the light beam coincide. Controlling 20. Also,
The equivalent filter circuit 23 has an input / output characteristic of the galvanometer mirror 19, that is, a characteristic substantially equal to the rotation characteristic with respect to the input to the galvanometer mirror 19.

Next, the relationship between the optical axis shift and the offset of the track shift signal will be described with reference to FIGS.

The shape of the objective lens 5 is rotationally symmetric about one reference axis. The center of curvature of the spherical surface of the lens coincides with this axis. This reference axis is called the optical axis of the objective lens 5. The elements other than the objective lens 5 constituting the optical system are arranged so that the optical axis of the entire optical system coincides with the optical axis of the objective lens 5, and the entire optical system is rotated around this reference axis. However, the imaging relationship is completely the same.

FIG. 7 shows the optical axis of the entire optical system and the objective lens 5.
2 shows a cross section of the light beam perpendicular to the optical axis when the center of the light beam incident on is coincident with. That is, FIG. 7 shows the shape of the light spot on the disk 7 when the optical axis is not displaced. The spread of the light flux that actually passes through the optical system is limited by the diaphragm, the lens frame, and the like. Further, the influence of passing through the optical system differs depending on whether the image forming point is on the optical axis or not. If the optical system is rotationally symmetrical about the optical axis, the light flux is also rotationally symmetrical, and the center of the light flux and the optical axis coincide. At this time, the cross section perpendicular to the optical axis becomes circular as shown in FIG. However, if the center of the parallel light beam incident on the objective lens 5 deviates from the optical axis, the light beams will not converge at one point due to the spherical aberration of the objective lens 5. A case where the light beam is incident on the objective lens 5 obliquely with respect to the optical axis of the optical system will be described with reference to FIG. FIG. 8 shows a case where the light beam incident on the objective lens 5 enters obliquely with respect to the optical axis of the optical system.
It shows a cross section of a light beam perpendicular to the optical axis at the same position on the optical axis as. That is, FIG. 8 shows the shape of the spot on the disk 7 when the light beam incident on the objective lens 5 enters obliquely with respect to the optical axis of the optical system. At this time, the light beam is, so to speak, in a state where it obliquely passes through a thick round hole, and its cross section is not a circle. In addition, the cross-sectional area of the light beam is reduced due to vignetting of the lens frame. That is, when the light beam incident on the objective lens 5 enters obliquely with respect to the optical axis, the light beam is accompanied by coma aberration. Therefore, if the optical axis shift occurs,
The shape of the light spot on the disk 7 changes due to spherical aberration of the objective lens 5, coma aberration of the light beam, vignetting of the lens frame, and the like.

FIG. 6 is a diagram showing the relationship between the spot shape on the photodetector 12 and the optical axis shift when the light spot is located on the center of the track. 6A shows a state where there is no optical axis shift, FIG. 6B shows a state where the optical axis shift occurs on the outer peripheral side of the disk 7, and FIG. 6C shows a state where the optical axis shift occurs on the inner peripheral side of the disk 7. The shape of the light spot on the photodetector 12 when the light spot is located on the center of the track in the generated state is shown.

When the optical axis is not displaced, the shape of the light spot on the photodetector 12 is as shown in FIG. 6A, and the outputs A and B from the two-divided surface of the photodetector 12 are shown. Are equal. However, when the optical axis shift occurs, the photodetector 1
The shape of the light spot on No. 2 is as shown in FIG. 6 even though the light spot is located at the track center on the disk 7.
As shown in FIG. 6B or FIG. 6C, the photodetector 12
The outputs A and B from the two-divided plane are not equal. As a result, an offset occurs in the track shift signal.

FIG. 9 shows a state in which the optical axis shifts when the attitude of the galvanometer mirror 19 changes in the rotating direction of the galvanometer mirror 19. When the galvano mirror 19 is in the initial state when the optical axis is not displaced, when the galvano mirror 19 rotates counterclockwise (or clockwise), the center of the light beam deviates from the optical axis of the optical system.

The relationship between the optical path length from the galvano mirror 19 to the objective lens 5 and the rotation angle of the galvano mirror 19 and the optical axis shift will be described with reference to FIGS. FIG. 10 shows the rotation angle θ of the galvanometer mirror and the optical path length L,
The relationship between the amount of deviation of the center of the light beam from the optical axis of the optical system (hereinafter referred to as the amount of deviation of the optical axis) δx and the amount of movement x of the light spot on the disk 7 is shown. FIG. 11 shows the distance L1 from the galvanometer mirror 19 to the mirror 4, the distance L2 from the mirror 4 to the objective lens 5 and the optical path length L.

Relational expressions (1), (2), (3), (4) and (5) of the rotation angle θ of the galvanometer mirror 19, the optical path length L, the optical axis shift amount δx, and the movement amount x of the light spot. Is shown below.

L = L1 + L2 (1) In the equation (1), the distance L (optical path length) from the galvano mirror 19 to the objective lens 5 is from the galvano mirror 19 to the mirror 4.
It means that it is the sum of the distance L1 and the distance L2 from the mirror 4 to the objective lens 5.

F = 3 mm (2) Expression (2) represents the focal length f of the objective lens 5.

F · Sin (2θ) = x (3) Expression (3) is a relational expression of the focal length f of the objective lens 5, the rotation angle θ of the galvanometer mirror 19 and the movement amount x of the light spot.

2θ = ASin (x / f) (4) Equation (4) is obtained by converting Equation (3) into the rotation angle θ of the galvanometer mirror 19.
Is an expression developed for an angle 2θ that is twice as large as

Δx = Lmax · tan (2θ) (5) Equation (5) is a relational expression of the optical axis shift amount δx, the maximum optical path length Lmax, and the rotation angle θ of the galvano mirror 19. In the present embodiment, the maximum optical path length Lmax is 70 mm, and for example, the galvano mirror 19 has ± 0.0955 de.
When rotated by g, the light spot becomes ± from equations (2) and (3).
It will move on the 10 μm disk 7. At this time, the optical axis shift amount δx is ± 0.233 mm from the equation (5).

FIG. 12 shows a track shift signal when there is no optical axis shift, that is, a reference track shift signal and a track shift signal when the light spot moves on the disk 7 by 10 μm. When the amplitude of the track deviation signal is ± 1, when the center axis of the light beam is deviated by ± 0.233 mm from the optical axis, an offset of ± 0.6435 is generated in the track deviation signal. Offset of track deviation signal is ±
When 0.6435 occurs, the tracking control system controls the light spot so as to be located at a position displaced by ± 0.178 μm from the track center. Therefore, the maximum optical path length Lm from the galvanometer mirror 19 to the objective lens 5 is Lm.
It can be seen that as ax increases, the offset of the track deviation signal also increases.

Next, the optical sensor 21 for detecting the rotation angle of the galvanometer mirror 19 which is a fine actuator is shown in FIG.
This will be described with reference to FIGS.

FIG. 2 shows a galvanometer mirror 19 and an optical sensor 21.
FIG. In FIG. 2, the mirror 1 is provided on one surface (mirror surface) of the holder 19-2 of the galvano mirror 19.
9-1 is adhered. Further, a leaf spring 19-3 is adhered to the opposite side of the holder 19-2 from the mirror surface,
Further, a coil 19-4 is adhesively fixed on the leaf spring 19-3. The side of the leaf spring 19-3 opposite to the holder 19-2 is fixed to the fixed portion. During tracking control, a magnet (not shown) on the fixed portion side interacts with the magnetism due to the current flowing in the coil 19-4. The galvanometer mirror rotates,
Perform tracking operation. Holder 19-2 and mirror 1
A reflection member 19-5 is adhesively fixed to the side surface of 9-1. A sensor adjusted so as to obtain a desired signal in a state where the galvanometer mirror 19 is not controlled is fixed to the fixed portion side facing the reflecting member 19-5. This sensor has two photo reflectors (PR1, PR2)
21-1 and 21-3 and the LED 21-2.

FIG. 3 shows a drive circuit for the sensor LED 21-2 and photoreflectors (PR1, PR2) 21-1, 21.
-3 is a detection and differential amplifier circuit. LED 21-2
The Anode terminal of is connected to + 10V,
The hode terminal is connected to GND via a variable resistor (VR1) and a resistor R1. Adjust VR1 to LED
21-2 adjust the current flowing. The collector terminal of the photo reflector (PR1) 21-1 is connected to + 10V, and the emitter terminal is connected to GND via the resistor (RE1). Photo reflector (PR2) 21-3
Has a collector terminal connected to + 10V and an emitter terminal connected to GND through a resistor (RE2). The connection point between the photo reflector (PR1) 21-1 and RE1 is connected to the negative input terminal of the operational amplifier via the capacitor (C1) and the resistor (Ri1), and the photo reflector (PR1) is connected.
2) The connection point between 21-3 and RE2 is connected to the positive input terminal of the operational amplifier via the capacitor (C2) and the resistor (Ri2). The negative input terminal of the operational amplifier is connected to the output terminal of the operational amplifier via the resistor (Rf1),
Positive input terminal is + 5Vref via resistor (Rref)
It is connected to the. The light from the LED 21-2 is reflected by the reflecting member 19-5 fixed to the side surface of the mirror. The reflected light is received by the photo reflector (PR1) 21-1 and the photo reflector (PR2) 21-3, converted into light / voltage, and the direct current component is blocked by the capacitors (C1, C2).
Differentially amplified with an operational amplifier. As a result, a sensor detection signal corresponding to the amount of rotation of the galvanometer mirror 19 is obtained as the output of the operational amplifier.

FIG. 13 shows a sensor signal and a track deviation signal when the galvanometer mirror 19 is driven. FIG.
13A is a sensor signal waveform, FIG. 13B is a waveform of a track deviation signal before off-track correction, and FIG. 13C is a track deviation signal waveform after off-track correction. After adjusting the mounting position of the sensor 21 and setting the drive current of the LED 21-2, when the light spot moves on the disc 1 by ± 1 μm by the rotation of the galvano mirror 19, the sensor output is ±.
It changes by 100 mV. That is, the sensor sensitivity is 100 mV
/ Μm. When the galvano mirror 19 is driven by the sine wave signal from the drive signal generation circuit 33, the sensor signal waveform as shown in FIG.
The track deviation signal waveform is as shown in 3 (b). Looking at the track shift signal waveform in FIG. 13B, the track pitch crosses about ± 5 tracks, so the track pitch is 1.6.
Since it is μm, the movement amount of the light spot on the disk 7 is about 8 μm. Therefore, the sensor signal is ± 0.
It has changed by about 8V. Here, in order to reduce the influence of the eccentricity of the disk 7, it is preferable that the frequency of the sine wave signal from the drive signal generating circuit is about 1 KHz.

Next, the deviation between the optical axis of the optical system and the center of the light beam, that is, the deviation of the optical axis is detected, and the position of the light spot applied to the track on the disk 7 is detected based on the detected deviation of the optical axis. The deviation of the track position caused by the offset of the track deviation signal with respect to, that is, the off-track correction will be described with reference to FIGS.

When the center of the light beam deviates largely from the optical axis of the optical system due to the attitude change of the galvano mirror 19 and approaches the outer ring of the objective lens 5, the incident light on the disk 7 and the reflected light from the disk 7 are the objective. It is affected by the vignetting caused by the lens frame. Therefore, one of the outputs A and B from the two-divided surface of the photodetector 12 becomes dominant, and the track deviation signal hardly appears. In such a case, the tracking control cannot be pulled in and the device cannot be activated. Therefore, the off-track correction of the present invention is performed.

The circuit for off-track correction is the sensor 2
1, a sensor circuit 29, and a gain adjustment circuit 30, which are connected to the negative input terminal of the differential amplifier 31. As described above, when the galvanometer mirror 19 is rotationally driven,
An offset occurs in the track deviation signal output from the divider 18 according to the rotation angle of the galvanometer mirror 19 (or the amount of movement of the light spot on the disk 7). Therefore, by subtracting the gain-adjusted sensor output signal of the negative input terminal from the track deviation signal of the positive input terminal, the output of the differential amplifier 31 cancels the offset generated by the rotation of the galvano mirror 19. Can be obtained. Here, since the direct current component of the sensor 21 is blocked by the sensor circuit 29 in order to prevent the direct current component of the output of the sensor from changing due to the influence of the temperature drift of the sensor 21, the offset correction is performed by the capacitor of the sensor circuit 29. (C1) and photo reflector (PR1) 21-1, condenser (C2) and photo reflector (PR2) 21-
It is effective in the cutoff frequency (fc) determined by 3 and fc = 34 Hz or more.

FIG. 15 shows a Bode diagram of a servo loop (TR servo loop) for driving and controlling the galvanometer mirror 19.

FIG. 16 shows a Bode diagram of a servo loop (TRS servo loop) for controlling and driving the linear motor 20.

The gain intersection of the TR servo loop is 4 KH
The gain intersection of the z and TRS servo loops is 450 Hz. Linear motor 2 is mainly used at frequencies below 450 Hz.
0 works to perform tracking control. If the servo tolerance of the tracking system is ± 0.08 μm, the primary resonance frequency (fo) of the galvanometer mirror 19 is 200 Hz.
During tracking operation, the rotation of the galvano mirror 19 causes the light spot on the disk 7 to be ± 1 at maximum.
It will move about 0 μm. When the light spot on the disk 7 moves ± 10 μm during the tracking operation, the off-track characteristic causes the track deviation signal to be off-track ± 0.178 μm in terms of the light spot on the disk 7. However, by performing the off-track correction of the present invention, the off-track allowable range in the tracking servo system can be set to ± 0.02 μm or less. Further, when the tracking servo pull-in is performed, the light spot on the disk 7 moves by ± 10 μm or more, but the off-track correction is performed to cancel the offset of the track deviation signal due to the movement of the galvano mirror 19 to cancel the track center on the disk 7. Off-track tolerance range ± 0.0
The tracking servo system can be reliably pulled in so as to be 2 μm or less. Further, when tracking control is not performed, even if the galvano mirror 19 rotates, the symmetry of the track deviation signal does not deteriorate and the track deviation signal does not appear. Therefore, the track deviation signal is counted in the search operation. There is no mistake, and it is possible to accurately count the track shift signal for the target track.

Next, automatic adjustment of the off-track correction gain will be described with reference to FIGS. First, the off-track correction gain is adjusted with the focus servo on. In accordance with the sine wave signal output from the drive signal generator 33, the light spot on the disk 7 is ± 10 in the drive circuit that drives the galvano mirror 19 via the adder circuit 32.
The galvanometer mirror 19 is rotated so as to move about μm.
Differential amplifier 31 when the galvanometer mirror 19 is rotated
The track deviation signal output from the CPU is taken into the CPU 35 via the A / D converter 34. The CPU 35 performs a calculation for obtaining the maximum value and the minimum value of the track deviation signal fetched via the A / D converter 34, and detects the deviation of the symmetry of the track deviation signal. The CPU 35 adjusts the gain setting value of the gain adjusting circuit 30 via the D / A converter 136 so that the track shift signal output from the differential amplifier 31 becomes symmetrical. By adjusting the gain of the off-track correction in this way, the track deviation signal when the galvano mirror 19 is driven by the signal from the drive signal generation circuit 33 is changed from the waveform as shown in FIG. Thirteen
The waveform is as shown in (c).

As described above, it is possible to improve the tracking control accuracy during recording or reproduction of the apparatus by correcting the off-track generated by the rotation of the galvano mirror 19 during the tracking control. . Also,
At the time of pulling in the tracking servo, the off-track correction is performed to cancel the offset of the track deviation signal due to the movement of the galvano mirror 19 and the off-track allowable range ± 0.0 with respect to the track center on the disk 7.
The tracking servo can be reliably pulled in so that the thickness becomes 2 μm or less. Further, when the tracking control is not performed, even if the galvano mirror 19 rotates, the symmetry of the track deviation signal does not deteriorate and the track deviation signal does not appear. Therefore, the track deviation signal is counted in the search operation. There is no mistake, and it is possible to accurately count the track shift signal for the target track.

Further, the off-track correction gain is automatically adjusted so that the off-track allowable range of the track deviation signal output from the differential amplifier is not more than ± 0.02 μm. Even if there is, off-track correction can be reliably performed. In addition, since the sensor circuit 29 blocks the direct current component of 34 Hz or less in the configuration of the sensor 21, the off-track correction is not affected by the temperature drift of the sensor 21 or the like. In this way, the sensor 21
Since the configuration and adjustment are simple and the desired off-track correction effect can be obtained, the productivity is improved during mass production of the device.

In the above embodiment, the galvano mirror 19 is used as the light beam direction changing means. However, the invention is not limited to this, and if it is a system for changing the direction of the light beam, for example, a prism or the like. The one using is also applicable.

Further, although the linear motor 20 is used as the coarse actuator in the above-described embodiment, the invention is not limited to this, and it is also applicable to other types of devices such as a swing arm.

Further, in the above embodiment, in order to eliminate the deviation of the symmetry of the track deviation signal, the gain of the gain adjusting circuit 30 is adjusted to correct the correction amount. However, instead of this, the sensor 21 is used. Or the rotation angle signal of the output of the sensor circuit 29 may be modified. Alternatively, the track shift signal input to the differential amplifier may be modified.

Further, in the above embodiment, in order to eliminate the deviation of the symmetry of the track deviation signal, the gain adjusting circuit 30,
Although the A / D converter 34, the CPU 35, and the D / A converter 136 are provided in the configuration, these circuits may not be used.

Further, in the above embodiment, the CPU 35 or the like is used as the symmetry detecting means, but instead of this, dedicated hardware having the same function may be used.

Further, in the above embodiment, the correction means, the drive control means and the like are constituted by dedicated hardware, but instead of this, similar functions may be realized by software using a computer. (Second Embodiment) Next, a second embodiment of the tracking control device according to the present invention will be described with reference to FIGS. The tracking control in this embodiment is
The description is omitted here because it is performed in the same way as in the first embodiment.

First, the galvanometer mirror 1 in this embodiment.
The lock servo of No. 9 will be described with reference to FIGS.

FIG. 17 is a block diagram showing the configuration of the second embodiment. The same components as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted. FIG. 18 is a block diagram of the lock servo in the second embodiment.

As shown in FIGS. 17 to 18, in this embodiment, after the rotation angle of the galvano mirror 19 is detected by the reflection type optical sensor 21, the output signal of the reflection type optical sensor 21 is output by the DC cut filter of the sensor circuit 29. Block the DC component of.
Further, the track shift signal output from the divider 18 is input to the low pass filter 37, and the DC offset component of the track shift signal is extracted. The gain of the extracted DC offset component of the track shift signal is adjusted by the amplifier circuit 38. The gain of the amplifier circuit 38 is set to a gain that is just good for correcting the optical axis shift due to the rotation of the galvanometer mirror 19. The DC offset component and the rotation angle detection signal of the galvano-mirror 19 that have cut off the DC component of the track-shifted signal whose gain has been adjusted are added by the addition amplifier 36 as an addition means, and the galvano-mirror 19 is controlled to be fixed at a desired position. Phase compensation is performed by the phase compensation circuit 28 that compensates the phase at the gain intersection point of the lock servo. The phase-compensated signal is negatively fed back to the input terminal of the drive circuit 26 that drives the galvanometer mirror 19 via the signal selection circuit 27. When the lock servo is performed, the signal selection circuit 27 selects the output signal of the phase compensation circuit 28 of the lock servo.

As a modification of this embodiment, the output of the sensor circuit 29 may be directly input to the phase maintenance circuit 28 without using the summing amplifier 36.

The change in the locked state of the galvano mirror 19 will be described by taking the track shift signal waveform when the galvano mirror 19 is driven as an example. FIG. 19 shows a drive signal and a track shift signal waveform when the galvanometer mirror 19 is driven by a sinusoidal signal. Galvo mirror 19 Figure 19
When a signal like (a) is driven by a sinusoidal signal, FIG.
As shown in (b), the track shift signal also produces a sine wave undulation. That is, the track shift signal is offset in accordance with the rotation of the galvanometer mirror 19. FIG. 20 shows a drive signal and a track shift signal waveform when the galvano mirror 19 is driven by a DC signal. The galvanometer mirror 19 is shown in FIG.
When driven by a DC signal such as 0 (a), the track shift signal is offset according to the DC signal value as shown in FIGS. 20B shows a case where the DC drive value is relatively small, and FIG. 20C shows a case where the DC drive value is relatively large. When the DC drive value is large, not only the track deviation signal causes an offset, but also the amplitude of the track deviation signal becomes small. However, by carrying out the present invention, the galvano mirror 19 can be locked at a position where the track deviation signal does not cause offset. <Third Embodiment> Next, a third embodiment of the tracking control apparatus according to the present invention will be described with reference to FIGS. The tracking control in this embodiment is
The description is omitted here because it is performed in the same way as in the first embodiment.

First, the galvanometer mirror 1 in this embodiment.
The lock servo of No. 9 will be described with reference to FIGS.

FIG. 21 is a block diagram showing the structure of this embodiment. The same components as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted. FIG. 22 is a block diagram of the lock servo in the third embodiment.

The difference between the second embodiment and the third embodiment is the lock servo of the galvanometer mirror 19. As shown in FIG. 21, the low pass filter is used in the second embodiment to extract the DC offset component of the track deviation signal, but in the third embodiment, the equivalent filter 23 of the control loop of the linear motor 20 is used. Is used to extract the DC offset of the track deviation signal. Others are the same as in the second embodiment, and the gain of the DC offset component of the extracted track shift signal is adjusted by the amplifier circuit 38. The gain of the amplifier circuit 38 is set to a gain that is just good for correcting the optical axis shift due to the rotation of the galvanometer mirror 19. DC offset component and D of the track shift signal with gain adjustment
The rotation angle detection signal of the galvano mirror 19 with the C component cut off is added by the addition amplifier 36, phase-compensated by the phase compensation circuit 28, and then the drive circuit 26 for driving the galvano mirror 19 via the signal selection circuit 27. Negative feedback is given before. When the lock servo is performed, the signal selection circuit 27 selects the output signal of the phase compensation circuit 28 of the lock servo.

In the third embodiment, the equivalent filter of the control loop of the linear motor 20 is used instead of the low pass filter of the second embodiment to extract the low pass component of the track deviation signal. Since the low-pass filter can be omitted, the configuration can be simplified. <Fourth Embodiment> Next, a fourth embodiment of the tracking control apparatus according to the present invention will be described with reference to FIGS. The tracking control in this embodiment is
The description is omitted here because it is performed in the same way as in the first embodiment.

First, the galvanometer mirror 1 according to this embodiment.
The lock servo of No. 9 will be described with reference to FIGS.

FIG. 23 is a block diagram showing the structure of this embodiment. The same components as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted. FIG. 24 is a block diagram of the lock servo in the fourth embodiment.

As shown in FIG. 23, the track shift signal output from the divider 18 is input to the low pass filter 37, and the DC offset component of the track shift signal is extracted. The gain of the extracted DC offset component of the track shift signal is adjusted by the amplifier circuit 38. The gain of the amplifier circuit 38 is set to a gain that is just good for correcting the optical axis shift due to the rotation of the galvanometer mirror 19. The DC offset component of the gain-adjusted track deviation signal, that is, the output of the amplifier circuit 38 is phase-compensated by the phase compensation circuit 28 that compensates the phase at the gain intersection point of the lock servo, and the galvano mirror 19 is passed through the signal selection circuit 27. Negative feedback is performed before the driving circuit 26 for driving. When the lock servo is performed, the signal selection circuit 27 selects the output signal of the phase compensation circuit 28 of the lock servo.

In the fourth embodiment of the present invention, the second,
Compared to the third embodiment, the galvano mirror 19 is fixed around the position where the optical axis of the optical system coincides with the light beam center of the light spot, so that the lock servo characteristic at high frequencies is somewhat inferior, but the reflection type is used. The optical sensor 21 can be omitted and the lock servo can be configured. <Fifth Embodiment> Next, a fifth embodiment of the tracking control apparatus according to the present invention will be described with reference to FIGS. The tracking control in this embodiment is
The description is omitted here because it is performed in the same way as in the first embodiment.

First, the galvanometer mirror 1 according to this embodiment.
The lock servo of No. 9 will be described with reference to FIGS. 25 to 26.

FIG. 25 is a block diagram showing the structure of this embodiment. The same components as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted. FIG. 26 is a block diagram of the lock servo in the fifth embodiment.

The difference between the fourth embodiment and the fifth embodiment is the lock servo of the galvano mirror 19. As shown in FIG. 25, the low pass filter is used in the fourth embodiment to extract the DC offset component of the track deviation signal, but in the fifth embodiment, the equivalent filter 23 of the control loop of the linear motor 20 is used. Is used to extract the DC offset component of the track deviation signal. Others are the same as in the fourth embodiment, and the DC of the extracted track deviation signal
The gain of the offset component is adjusted by the amplifier circuit 38. The gain of the amplifier circuit 38 is set to a gain that is just good for correcting the optical axis shift due to the rotation of the galvanometer mirror 19. The DC offset component of the gain-adjusted track deviation signal is phase-compensated by the phase compensation circuit 28 that compensates the phase at the gain intersection of the lock servo, and is negatively fed back before the drive circuit 26 that drives the galvanometer mirror 19. When the lock servo is performed, the signal selection circuit 27 selects the output signal of the phase compensation circuit 28 of the lock servo.

In the fifth embodiment, the equivalent filter 23 of the control loop of the linear motor is used in place of the low pass filter of the fourth embodiment to extract the low pass component of the track deviation signal. Therefore, the reflection type optical sensor 21 and the low pass filter can be omitted.

[0096]

As described above, according to the present invention, tracking control is always performed with the optical axis center of the optical system of the optical head as a reference by correcting variations in the initial adjustment of the optical head and optical axis shift due to changes over time. Further, it is possible to perform the offset correction that occurs with the rotation of the galvanometer mirror, and it is possible to realize accurate and highly accurate tracking control.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a tracking control device for explaining a first embodiment of the present invention.

FIG. 2 is a perspective view showing a galvanometer mirror and a reflective optical sensor according to an embodiment of the present invention.

FIG. 3 is a circuit diagram showing a sensor circuit according to an embodiment of the present invention.

FIG. 4 is an explanatory view of a track deviation signal detection method. FIG. 4A is an explanatory view of the shapes of tracks and a light spot on the disk. FIG.

FIG. 5 is an explanatory diagram of a position of a light spot on a disc and a track shift signal waveform.

FIG. 6 is an explanatory diagram of an optical axis shift and a light spot on the photodetector. FIG. 6A is an explanation diagram of a light spot shape on the photodetector when the light spot is located on the track when there is no optical axis shift. Figure (b) is an illustration of the shape of the light spot on the photodetector when the light spot is located on the track with the optical axis deviation on the outer circumference side of the disk. (C) is the optical axis on the inner circumference side of the disk. Explanatory drawing of the shape of the light spot on the photodetector when the light spot is located on the track with misalignment

FIG. 7 is an explanatory diagram of a light spot shape when there is no optical axis shift.

FIG. 8 is an explanatory diagram of a change in shape of a light spot due to aberration or vignetting on a lens frame due to optical axis shift.

FIG. 9 is an explanatory diagram of an optical axis shift state due to a change in the galvano mirror state.

FIG. 10 is an explanatory diagram of rotation and optical axis shift of a galvano mirror in which the mirror 4 is omitted for explanation.

FIG. 11 is an explanatory diagram of an optical path length in the example.

FIG. 12 is an explanatory diagram of an amount of movement of a light spot on a disc and an offset of a track shift signal.

FIG. 13 is a waveform diagram of a sensor signal and a track deviation signal when the galvanomirror is driven by a sinusoidal drive signal from the drive signal generating means in the embodiment, and FIG. 13A is a waveform diagram of the galvanomirror driving signal generating means in the embodiment. (B) is a waveform diagram of the sensor signal when moved by the drive signal from (b) is a waveform diagram of the track deviation signal before off-track correction when the galvanomirror in the embodiment is moved by the drive signal from the drive signal generating means ( c) is a waveform diagram of a track deviation signal after off-track correction when the galvanomirror in the embodiment is moved by the drive signal from the drive signal generating means.

FIG. 14 is a characteristic diagram of the offset of the track deviation signal with respect to the moving distance of the light spot in the example.

FIG. 15 is a Bode diagram showing the open loop frequency characteristic of the TR servo of the embodiment.

FIG. 16 is a Bode diagram showing the open loop frequency characteristic of the TRS servo of the example.

FIG. 17 is a block diagram showing a configuration of a tracking control device for explaining a second embodiment of the present invention.

FIG. 18 is a block diagram for explaining a lock servo according to a second embodiment of the present invention.

FIG. 19 is a waveform diagram of a drive signal and a track deviation signal when the galvanomirror is driven by the sinusoidal drive signal from the drive signal generating means in the embodiment, and FIG. 19A is a waveform diagram of the drive signal generating means for the galvanomirror in the embodiment. (B) is a waveform diagram of a driving signal when the galvanomirror is driven by a driving signal from the driving signal generating means before the off-track correction.

FIG. 20 shows D from the drive signal generating means in the embodiment.
The waveform diagram of the drive signal and the track shift signal when the galvano mirror is driven by the C drive signal is shown in (a). The waveform diagram of the drive signal when the galvano mirror in the embodiment is driven by the drive signal from the drive signal generating means ( FIG. 7B is a waveform diagram of the track deviation signal before the off-track correction when the galvanomirror in the embodiment is moved by a relatively small DC drive signal from the drive signal generating means. FIG. 9C shows the galvanomirror in the embodiment. Waveform diagram of track deviation signal before off-track correction when moved by a relatively large DC drive signal from the signal generating means

FIG. 21 is a block diagram showing the configuration of a tracking control device for explaining a third embodiment of the present invention.

FIG. 22 is a block diagram for explaining a lock servo according to a third embodiment of the present invention.

FIG. 23 is a block diagram showing the configuration of a tracking control device for explaining a fourth embodiment of the present invention.

FIG. 24 is a block diagram for explaining a lock servo according to a fourth embodiment of the present invention.

FIG. 25 is a block diagram showing the configuration of a tracking control device for explaining a fifth embodiment of the present invention.

FIG. 26 is a block diagram for explaining a lock servo according to a fifth embodiment of the present invention.

FIG. 27 is a block diagram showing the configuration of a conventional tracking control device.

FIG. 28 is a block diagram for explaining a conventional lock servo.

FIG. 29 is an explanatory diagram of an optical axis shift state due to a change in state of the galvano mirror.

[Explanation of symbols]

 1 Light Source 2 Collimator Lens 3 Deflection Beam Splitter 4 Mirror 5 Objective Lens 6 Spindle Motor 7 Disk 8 Optical Beam 9 Convex Lens 10 Cylindrical P. B. S 11 Optical beam 12 Photodetector 13 Differential amplifier 14 Differential amplifier 15 Optical beam 16 Summing amplifier 17 Variable amplifier 18 Divider 19 Galvano mirror 20 Linear motor 21 Optical sensor 22 Phase compensation circuit 23 Equivalent filter 24 Phase compensation circuit 25 Drive circuit 26 Drive circuit 27 Signal selection circuit 28 Phase compensation circuit 29 Sensor circuit 30 Gain adjustment circuit 31 Differential amplifier 32 Adder circuit 33 Drive signal generation circuit 34 A / D converter 35 CPU 37 Low pass filter 38 Amplification circuit 136 D / A converter

Claims (9)

[Claims] 1. Converging means for converging a light beam on a recording medium, receiving a drive signal, and providing a converging point of the light beam on the recording medium according to the drive signal. Light beam direction changing means for rotating the light beam so as to move in a direction traversing the track, and track deviation detection for generating a track deviation signal according to the position of the convergence point of the light beam with respect to the track. Means, a rotation angle detecting means for detecting a rotation angle of the light beam, and a means for canceling an offset generated by the rotation of the light beam based on the rotation angle detected by the rotation angle detecting means. A correction amount calculation unit that calculates a correction amount, a correction unit that corrects the track deviation signal based on the correction amount calculated by the correction amount calculation unit, and a correction unit that is corrected by the track deviation signal correction unit. A tracking control device comprising: drive control means for driving and controlling a rotation angle of the light beam in accordance with a rack shift signal. 2. A symmetry detecting means for detecting a symmetry deviation of the corrected track deviation signal, and a symmetry deviation detected by the symmetry detecting means,
2. The tracking control device according to claim 1, further comprising a rotation angle detection signal correction means for correcting the rotation angle signal detected by the rotation angle detection means so as to eliminate the deviation of the symmetry. .. 3. A symmetry detecting means for detecting a symmetry deviation of the corrected track deviation signal, and a symmetry deviation detected by the symmetry detecting means,
The tracking control device according to claim 1, further comprising a correction amount correction unit that corrects the correction amount so as to eliminate the deviation of the symmetry. 4. A symmetry detecting means for detecting a symmetry deviation of the corrected track deviation signal, and a symmetry deviation detected by the symmetry detecting means,
2. The tracking control device according to claim 1, further comprising a track deviation signal correcting means for correcting the track deviation signal so that the symmetry deviation is eliminated. 5. Converging means for converging a light beam on a recording medium, receiving a drive signal, and providing a converging point of the light beam on the recording medium according to the drive signal. Light beam direction changing means for rotating the light beam so as to move in a direction traversing the track, and track deviation detection for generating a track deviation signal according to the position of the convergence point of the light beam with respect to the track. Means, a low-pass filter for extracting a low-pass component of the signal detected by the track shift detection means, a rotation angle detection means for detecting a rotation angle of the light beam, and a detection by the rotation angle detection means. A DC cut filter for cutting off the DC component of the generated signal, an addition means for adding the output of the low pass filter and the output of the DC cut filter, and a phase for compensating the phase of the output of the addition means Comprising a 償回 path, the tracking control device, characterized in that the negative feedback output of the phase compensation circuit to the drive input of the light beam direction change means. 6. Converging means for converging a light beam on a recording medium, receiving a drive signal, and providing a converging point of the light beam on the recording medium according to the drive signal. Light beam direction changing means for rotating the light beam so as to move in a direction traversing the track, and track deviation detection for generating a track deviation signal according to the position of the convergence point of the light beam with respect to the track. Means, an equivalent filter having a transfer function substantially equal to that of the light beam direction changing means, for extracting a low-frequency component of the signal detected by the track deviation detection means, and a rotation for detecting a rotation angle of the light beam. Angle detection means, a DC cut filter for cutting off the DC component of the signal detected by the rotation angle detection means, and an adder for adding the output of the equivalent filter and the output of the DC cut filter. And a phase compensating circuit for compensating the phase of the output of the adding means, wherein the output of the phase compensating circuit is negatively fed back to the drive input of the light beam direction changing means. 7. Converging means for converging a light beam on a recording medium, receiving a drive signal, and providing a converging point of the light beam on the recording medium according to the drive signal. Light beam direction changing means for rotating the light beam so as to move in a direction traversing the track, and track deviation detection for generating a track deviation signal according to the position of the convergence point of the light beam with respect to the track. Means, a low-pass filter for extracting a low-pass component of the signal detected by the track deviation detection means, and a phase compensation circuit for compensating for the phase of the output of the low-pass filter. A tracking control device, wherein an output is negatively fed back to a drive input of the light beam direction changing means. 8. Converging means for converging a light beam on a recording medium, receiving a drive signal, and providing a converging point of the light beam on the recording medium according to the drive signal. Light beam direction changing means for rotating the light beam so as to move in a direction traversing the track, and track deviation detection for generating a track deviation signal according to the position of the convergence point of the light beam with respect to the track. Means, an equivalent filter having a transfer function substantially equal to that of the light beam direction changing means, and extracting a low-frequency component of the signal detected by the track deviation detecting means, and a phase compensation for compensating the phase of the output of the equivalent filter. A tracking control device comprising: a circuit, wherein the output of the phase compensation circuit is negatively fed back to the drive input of the light beam direction changing means. 9. Converging means for converging a light beam on a recording medium, receiving a drive signal, and providing a converging point of the light beam on the recording medium according to the drive signal. Light beam direction changing means for rotating the light beam so as to move in a direction traversing the track, and track deviation detection for generating a track deviation signal according to the position of the convergence point of the light beam with respect to the track. Means, a turning angle detecting means for detecting a turning angle of the light beam, a DC cut filter for cutting off a DC component of a signal detected by the turning angle detecting means, and a phase of an output of the DC cut filter. A tracking control device comprising: a phase compensation circuit for compensating, wherein the output of the phase compensation circuit is negatively fed back to the drive input of the light beam direction changing means.