JPH01220231A - Gain controller for tracking servo - Google Patents

Abstract

PURPOSE:To stably perform the gain control of tracking servo by providing a means to detect the level of a tracking servo error signal and a means to control the level of disturbance to be impressed by the level of the tracking error signal. CONSTITUTION:The means 30 to detect the tracking error signal in the open state of a tracking servo loop, and the means 20 to control the level of the disturbance to be impressed by the level of the tracking error signal are provided. In other words, the level of the output disturbance signal S of a disturbance oscillator 20 is controlled by the output 301 of an error signal level detector 30 which detects the level of the output Y of an error signal generation circuit 13. Thereby, the level of the disturbance to be impressed on the tracking servo loop can be set appropriately. In such a way, it is possible to perform the gain control correctly not depending on the optical dispersion of a disk and a pickup.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a tracking servo gain adjustment device for an optical disc player that uses a light beam to reproduce information recorded on a disc.

BACKGROUND OF THE INVENTION In an optical disc player that reproduces information signals recorded on a spiral or concentric track of a disc using a light beam of an optical pickup,
A tracking servo and a focus servo are required to scan the light beam incident on the disk to the center of the track and focus on the information surface of the disk in order to reproduce the information signal.

Tracking servo detects the deviation of the spot of the light beam incident on the disk from the track, so-called tracking error, and uses the output tracking error signal to move the focus lens of the optical pickup or the entire optical pickup in the radial direction of the disk. This is to ensure that the tracking error is zero.

Focus servo detects the shift of the focus of the light beam relative to the recording surface of the disk, so-called focus error, and uses the output of the focus error signal to move the focus lens of the optical pickup in a direction perpendicular to the recording surface of the disk to focus. This is to ensure that the error is zero.

Incidentally, the gain of the tracking servo is adjusted by applying a disturbance of a specific frequency to the servo loop from the outside. FIG. 3 shows the configuration of a conventional tracking servo gain adjustment method. In FIG. 3, 1o is an optical disk on which an information signal is recorded, and 11 is an optical pickup that makes a light beam 12 enter the optical disk 10. In FIG. 13 is an error signal generation circuit which inputs the output 111 of the optical pickup 11 and generates a tracking error signal.

19 is a frequency response analyzer which has a disturbance oscillator 2o and a gain detector 21 inside.
A sinusoidal disturbance signal S corresponding to a desired gain intersection frequency is output from the disturbance oscillator 2o to the adder 18. The adder 18 adds the output Y of the error signal generation circuit 13 and the disturbance signal S, and outputs the output X to the loop filter 14 of the tracking servo. The loop filter 14 is for performing low frequency compensation and phase compensation of the servo loop. The output 141 of the loop filter 14 is input to the variable gain amplifier 16 whose gain is controlled by the output 211 of the gain detector 21, and the output 151 thereof is input to the actuator drive circuit 16, and the output 161 outputs the output 141 of the variable gain amplifier 16. The actuator 17 is driven to move the lens or the entire optical pickup. 26 is a turntable on which the disc 1o is placed and rotated.

Of the tracking servo gain adjustment device configured as described above, the parts other than the adder 18 and the frequency response analyzer 19 are the same as those of a conventional optical disc player, so a description thereof will be omitted. The tracking servo of optical disc players is described in many documents (for example, "Compact Disc Reader", pages 133 to 138, Ohmsha, 19
1982). Here, we will explain a conventional tracking servo gain adjustment method using a frequency response analyzer.

Focusing on the output disturbance signal S of the disturbance oscillator 2o in FIG. 3, it is applied to the tracking servo loop via the adder 18, goes around the loop, and returns to the input of the adder 18. Therefore, if we take the ratio between the output X of the adder 18 and the input Y, it is clear that this is the gain of the tracking servo loop at the frequency of the disturbance signal S.

Here, the frequency response analyzer 19 will be explained using FIGS. 3 and 4.

In FIG. 4, 2o is the above-mentioned disturbance oscillator.

The input Y of the adder 18 is sent to the Y amplifier 22, and the output
Connected to input amplifier 23. Y power amplifier 22 and X
The output of the input amplifier 23 is Fourier transformed by the microcomputer 24 and outputted. If the ratio of these respective outputs is determined by the comparator 26, the gain of the tracking servo loop at the frequency of the disturbance signal S can be determined (
For example, NF Circuit Design Block Co., Ltd. MODEL
S-5720, S-673o FRKQUEN
CYRESPONSg ANALYZER Instruction Manual 1-5 pages). Then, the output 211 of the comparator 26 controls the variable gain amplifier 16 to adjust the gain of the tracking servo loop.

Problems to be Solved by the Invention However, with the above configuration, the gain of the tracking servo loop cannot be adjusted correctly unless the output level of the disturbance oscillator is appropriately set. The reason for this is that optical discs such as compact discs (CDs) have large optical variations depending on the disc, and there are also optical variations in the optical player's pickup itself. Even if it is constant, the blur of the focus lens or the amount of shake of the entire optical pickup (that is, the physical dimension in which the lens actually moves) differs. Therefore, if the level of the disturbance signal is too large, the servo will become unstable, and in the worst case, the servo will become disconnected. In addition, there are problems such as excessive quilting, which reduces the level of the disturbance signal, and the levels of the X and Y input signals to the frequency response analyzer become small, resulting in poor S/N of the measurement system and the inability to make correct adjustments. It had

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a tracking servo gain adjustment device for an optical disc player that can perform stable gain adjustment regardless of optical variations in discs and pickups.

Means for Solving the Problems In order to solve the above problems, the tracking servo gain adjustment device of the present invention includes means for detecting a tracking error signal when the tracking servo loop is in an open state, and detecting a tracking error signal based on the level of the tracking error signal. and means for controlling the level of applied disturbance.

Effect of the Invention With the above-described configuration, the present invention can appropriately set the level of disturbance applied to the tracking servo loop, and can perform correct gain adjustment regardless of optical variations in the disk or pickup.

Embodiment Hereinafter, a tracking servo gain adjustment device according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows the configuration of a tracking servo gain adjustment device in an embodiment of the present invention. In Figure 1, 3
o is an error signal level detector that detects the level of the output Y of the error signal generation circuit 13. This output 301 controls the level of the output disturbance signal S of the disturbance oscillator 20. 31 is an oscillator, and its output 311 is input to the actuator drive circuit 16 via a switch 32. Other configurations are the same as before.

The operation of the tracking servo gain adjustment method configured as above will be described below with reference to FIGS. 1 and 2.

First, connect the switch 32 to the A side and output 3 of the oscillator 31.
11 drives the actuator 17 to move the focus lens or the entire optical pickup in the tracking direction (
(in the radial direction of the disc). When the disk 1o is rotated by the turntable 2e, the error signal generation circuit 13
The output Y continuously draws a figure-eight curve each time the light beam crosses a track on which information is recorded on the recording surface of the disk, as shown in Figure 2 (the peak value of this figure-eight curve is The optical variation of the pickup is the voltage value E
(v), but the optical distance is constant.

For example, in Fig. 2, it is 0.76 μm).

The peak value of this figure 8 curve is detected by the error signal level detector 3.
Detected by 0. A so-called peak hold circuit is used as the error signal level detector.

And for this output 301 (E(v)), E15 (7
) The disturbance oscillator 20 is controlled so that the output S has a peak value. As a result, the level of disturbance applied to the tracking servo loop can be set to 0.15 μm regardless of optical variations in the disk or pickup.

Next, by connecting the switch 32 to the B side, the tracking servo loop is closed and tracking is pulled in. There are various methods of tracking pull-in operation, but since they are well known, their explanation will be omitted.

Next, gain adjustment is performed in the same manner as in the conventional method while keeping the output level of the disturbance oscillator 2o at 15.

As described above, according to this embodiment, the level of the tracking error signal when the switch 32 is connected to the A side and the tracking servo loop is open is detected by the error signal level detector 3o, and the output E is used to detect the level of the tracking error signal. 2
By setting the o output to E15, the disturbance level can be reduced to 0.16 regardless of optical variations in the disc or pickup.
0.16 μm is smaller than the D range of the tracking servo, which is 0.76 μm, so the servo will not come off, and the S/N of the measurement system is sufficient, so a frequency response analyzer is used. correct gain adjustment.

In this embodiment, the error signal level detector 30 is a peak hold circuit, but the output Y of the error signal generation circuit 13 is A/D (analog-digital) converted and its pθ
t) The g to peak value may be determined and the output level of the disturbance oscillator 2o may be controlled using this value. Further, in reality, the oscillator 31 may not be necessary because the eccentricity of the disk cannot be made zero.

Effects of the Invention As described above, the present invention includes means for detecting the level of a tracking servo error signal when the tracking servo loop is open, and means for controlling the level of disturbance applied based on the level of this tracking error signal. This allows stable tracking servo gain adjustment regardless of optical variations in the optical disc or pickup.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the configuration of a tracking servo gain adjustment device in an embodiment of the present invention, Fig. 2 is a waveform diagram for explaining the figure-eight curve of the tracking error signal, and Fig. 3 is a conventional tracking FIG. 4 is a block diagram of the servo gain adjustment device. FIG. 4 is a block diagram for explaining the frequency response analyzer. 10... Optical disc, 11... Optical pickup, 13... Error signal generation circuit, 14... Loop filter, 15...
・Variable gain amplifier, 16...Actuator drive circuit, 17・Actuator, 18...
- Adder, 19... Frequency response analyzer, 20... Disturbance oscillator, 21...
...Gain detector, 26...Turntable, 3
0...Error signal level detector, 31...
...Oscillator.

Claims (1)

[Claims] A gain adjustment device that applies a disturbance of a specific frequency to a tracking servo loop of an optical disc player to adjust its open loop gain, the device detecting the level of a tracking error signal when the tracking servo loop is in an open state. A tracking servo gain adjustment device comprising: and means for controlling the level of applied disturbance based on the level of the tracking error signal.