JPH0640393B2 - Tracking control circuit and optical disk device using the same - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a control circuit of a track following device used for an optical information recording / reproducing device such as an optical disk and for making an optical spot follow an information track.

[Background of the Invention]

The reading of information recorded at a high density poses a difficult technical problem in terms of accuracy. Therefore, various track-tracking devices are used for the purpose of relatively correctly positioning the read light spot and the track. Proposed. However, in such a device, when the light spot is moved for tracking control, the light quantity of the light beam incident on the photodetector also changes, so that the amplitude of the tracking error signal changes. Therefore, there is a drawback that the gain of the tracking control circuit fluctuates and tracking control becomes unstable. This will be described below with reference to the drawings.

FIG. 1 is a diagram showing the configuration of an optical track following device utilizing diffracted light. Such a device is disclosed in Japanese Patent Laid-Open No. 49-6070.
No. 2 or JP-A No. 52-62037. A light beam emitted from a light source, for example, a semiconductor laser 1 is collimated by a lens 2, passes through a prism 3 and a focusing lens 4, and is converged on the surface of the disk 5 in a spot shape of about 1 μmφ. On the surface of the disc 5, information tracks 51 are provided in which information is arranged in the form of irregularities (pits). When the light spot is located in the track, a diffracted light pattern containing information is generated in the light reflected from the track. This reflected light is again focused on the lens 4 and the prism 3.
Through the condenser lens 6 and two photodetectors 7a, 7a
The light is received by b. These photodetectors 7a and 7b are arranged so as to sandwich the track 51 to the left and right. When the light spot of the reflected diffracted light deviates from the center of the track, asymmetry occurs due to the edge of the track groove. Therefore, the relative position (deviation amount) between the light spot and the track can be detected by detecting the output difference between both detectors. 2 from photodetectors 7a, 7b
The two outputs are differentiated by the differential amplifier 8 and the tracking error signal is detected. As shown in FIG. 2, this signal becomes an S-shaped curve due to the deviation of the light spot from the track center. The tracking error signal is passed through the phase compensation circuit 9 to the drive circuit 1 of the tracking actuator 11.
Supplied to zero. The actuator 11 is mounted around the aperture lens 4 and finely moves the lens 4 in the track width direction (the direction of the arrow in the figure) so as to reduce the above-mentioned deviation according to the output of the drive circuit 10. Thus, the tracking control system is constructed so that the light spot follows the center of the track. However, when the focusing lens 4 starts to move to follow the track, the light beam also moves on the detector surface as the optical axis moves, and the amount of light incident on the photodetector changes. For this reason, the amplitude of the tracking error signal obtained by differentially fluctuates, and the gain of the tracking control system fluctuates. The gain of the control system is the sensitivity of the tracking error signal at the track center, that is, S shown in FIG.
Corresponds to the inclination of the curve in the track center. As described above, the movement of the light beam is indispensable for the tracking control, but in the tracking control system, the control gain fluctuates, which causes the control to be unstable.

[Object of the Invention]

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a tracking control circuit that can compensate for fluctuations in control gain based on track following and thereby achieve more stable control.

[Outline of Invention]

In order to achieve such an object, the present invention is characterized in that a variable gain circuit is provided between the tracking error detection circuit and the tracking drive circuit and the gain is varied so that the tracking control gain does not change. And The specific configuration of the present invention is as follows.

The tracking control circuit of the present invention is a tracking error detection circuit that detects a deviation between a focused spot and a track from the output of a photodetector that detects the return light of a light beam that is irradiated as a focused spot on a track provided on a recording surface. When,
It has a drive circuit for controlling the moving means for moving the convergent spot in the track width direction based on the output of the tracking error detection circuit, and the position of the convergent spot on the recording surface so that the moving means reduces the displacement by the drive circuit. Is a tracking control circuit for controlling a tracking error detection circuit in a state where tracking control is not performed, and a storage circuit that stores the peak value of the output, and a tracking circuit that receives the output of the storage circuit as a control input. And a variable gain circuit for controlling the control gain.

Further, the optical disc apparatus includes an optical system that forms a light spot on a track provided on the optical disc, a photodetector that detects return light from the optical disc, and a tracking that indicates the deviation between the light spot and the track from the output of the photodetector. A tracking error detection circuit that forms an error signal, a moving unit that moves the light spot in the optical disc radial direction based on the tracking error signal, and a drive circuit that drives the moving unit are provided so that the moving unit reduces the deviation. At the optical disc position that controls the position of the light spot on the recording surface, the storage circuit that stores the peak value of the tracking error signal when the tracking control is open, and the gain of the tracking error signal by the output of the storage circuit And a variable gain circuit for controlling.

With such a configuration, first, the peak value of the output signal in the state where tracking is not performed is detected, and the amplitude of the tracking control signal peculiar to the disk is stored based on this signal. By controlling the variable gain circuit based on the stored amplitude, the tracking control gain does not vary even if disks having different characteristics are used, and stable tracking control can be performed.

Example of Invention

Embodiments of the present invention will be described below with reference to the drawings. FIG. 3 is a block diagram showing an embodiment of the tracking control circuit according to the present invention. In the figure, 12 is a variable gain circuit,
It is inserted between the differential amplifier 8 which is a tracking error detection circuit and the phase compensation circuit 9, and the output of the actuator equivalent circuit 13 is input as a gain control signal. When the level of this input becomes large (small), Correspondingly functions to increase (decrease) the gain. The output of the drive circuit 10 is input to the actuator equivalent circuit 13. As the equivalent circuit 13, a filter having a characteristic equivalent to that of the actuator 11 is used. That is, the characteristic of the actuator 11 is generally a secondary system, and the displacement with respect to the current has the resonance frequency fo and the resonance sharpness Q. Therefore, as shown in FIG. 4, the cutoff frequencies fo and f
When a low-pass filter having a resonance peak Q at o is used and the drive current of the actuator 11 is input to this filter, its output becomes a signal corresponding to the movement amount of the lens 4, that is, the movement amount of the light spot. Therefore, as the equivalent circuit 13, a low-pass filter having the characteristics shown in FIG. 4 is used, and the absolute value voltage of the signal corresponding to the movement amount of the light spot is extracted as the output of the equivalent circuit.

With the above configuration, since the amplitude variation due to the movement of the light spot based on the tracking control of the tracking error signal is reduced, the control gain variation due to the amplitude variation is reduced,
Therefore, stable tracking control is performed.

In the above description, the control gain fluctuation in the case of using one disc is described. However, when the disc is changed, it is shown in FIG. 2 due to the variation of the depth of the pits recorded in the track of the disc. In addition, there is also a problem that the S-shaped curve fluctuates significantly, which causes the control gain to fluctuate and the control to become unstable. The problem is that the amplitude of the tracking error signal in the state where the tracking control is not performed is stored every time the disc is changed, and the gain of the variable gain circuit provided in the control circuit is determined by the magnitude thereof. , Is solved by starting the tracking control.

This embodiment will be described with reference to FIG. In the figure, 1
4 is a switch inserted between the drive circuit 10 and the actuator 11, and when the switch 9 is open,
The tracking control is released, and the tracking error signal output from the differential amplifier 8 repeats the S-shaped curve shown in FIG. The control gain, that is, the slope of the curve at the track center is proportional to the peak voltage V _E of the S-shaped curve. Therefore, when the disk is changed, the switch 14 is first opened and the peak value V _E of the S-shaped curve is detected and stored in the memory circuit 15. The output of the memory circuit 15 is input to the variable gain circuit 12 as a gain control signal, and when the level of this input increases (decreases), it functions to decrease (increase) the gain correspondingly, and the peak value of the S-shaped curve. Correct for changes in V _E. Next, by closing the switch 4, the output of the differential amplifier 8 is corrected to a constant gain by the variable gain circuit 12, and the phase compensation circuit 9 and the drive circuit 1 are corrected.
0, drive the actuator 11 through the switch 14,
Tracking control is performed. When the disk is replaced, the above operation is repeated according to a command from the control circuit 16.

With the above configuration, fluctuations in the tracking control gain due to variations in the disk are eliminated, and stable control is maintained.

In the present invention, the tracking error signal is detected by utilizing the asymmetry of the diffracted light, but the tracking error signal is detected by the tracking error signal due to the light vignetting or the optical axis shift. Therefore, the present invention can be applied when the amount of light varies.

〔The invention's effect〕

According to the present invention, it is possible to obtain a control circuit in which fluctuations in control gain are small, and more stable tracking control can be realized.

[Brief description of drawings]

FIG. 1 is a block diagram showing a conventional example of an optical track following device, FIG. 2 is a diagram showing characteristics of a track error signal, and FIG.
FIG. 4 is a block diagram showing an embodiment of a tracking circuit according to the present invention, FIG. 4 is a diagram showing an example of characteristics of an actuator price circuit, and FIG. 5 is a block diagram showing another embodiment of the present invention.

Claims (5)

[Claims] 1. A tracking error detection circuit for detecting a deviation between the converged spot and the track from an output of a photodetector for detecting return light of a light beam irradiated as a convergent spot on a track provided on a recording surface. A driving circuit for controlling a moving means for moving the converged spot in the width direction of the track based on an output of the tracking error detection circuit, and the driving circuit reduces the deviation by the moving means. In a tracking control circuit for controlling the position of the converged spot on the recording surface, a storage circuit which is supplied with the output of the tracking error detection circuit in the state where tracking control is not performed, and stores the peak value of the output, and the storage circuit. Gain control circuit and a variable gain circuit for controlling the tracking control gain. Control circuit. 2. An optical system for forming a light spot on a track provided on an optical disc, a photodetector for detecting return light from the optical disc, and an output of the photodetector for detecting the light spot and the track. A tracking error detection circuit for forming a tracking error signal indicating a shift, a moving means for moving the light spot in the optical disc radial direction based on the tracking error signal, and a drive circuit for driving the moving means, A storage circuit for storing the peak value of the tracking error signal in the state where the tracking control is opened at the optical disc position where the moving means controls the position of the light spot on the recording surface so as to reduce the deviation. An optical disc having a variable gain circuit that controls the gain of the tracking error signal by the output of the storage circuit. Apparatus. 3. The photodetector is a two-part photodetector,
The tracking error detection circuit is a differential amplifier that makes a difference between two outputs of the photodetector divided into two, and the variable gain circuit is at a stage subsequent to the differential amplifier, and a part of the output of the differential amplifier. 3. The optical disk device according to claim 2, wherein is input to the storage circuit. 4. The optical disc according to claim 2 or 3, wherein a phase compensation circuit is provided at a stage subsequent to the variable gain circuit, and an output of the phase compensation circuit is input to the drive circuit. apparatus. 5. A state in which a switching means arranged between the drive circuit and the moving means and a control circuit for controlling the switching means and the storage circuit are provided, and the tracking control is opened by the control of the control circuit. The optical disk device according to any one of claims 2 to 4, which stores the peak value of the tracking error signal in the above item.