JP2718052B2 - Tracking servo gain adjustment device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tracking servo gain adjusting device for an optical disk player that reproduces information recorded on a disk using a light beam.

2. Description of the Related Art In an optical disk player that reproduces an information signal recorded on a spiral or concentric track of a disk by a light beam of an optical pickup, light incident on the disk to reproduce the information signal is used. A tracking servo and a focus servo are required to make the beam scan the center of the track and focus on the disk information surface.

The tracking servo detects the deviation of the spot of the light beam incident on the disk from the track, that is, the so-called tracking error, and moves the focus lens of the optical pickup or the entire optical pickup to the radius of the disc according to the tracking error signal output from the tracking error signal. Thus, the tracking error is reduced to zero.

The focus servo detects a deviation of the focal point of the light beam from the recording surface of the disk, a so-called focus error, and moves the focus lens of the optical pickup in a direction perpendicular to the recording surface of the disk by a focus error signal output from the focus error. Is set to zero.

By the way, the tracking servo gain adjustment
This is performed by applying a disturbance of a specific frequency to the servo loop from outside. FIG. 3 shows the configuration of a conventional tracking servo gain adjustment method. In FIG. 3, reference numeral 10 denotes an optical disk on which an information signal is recorded, and reference numeral 11 denotes an optical pickup, and a light beam 12 is incident on the optical disk 10. An error signal generating circuit 13 receives the output 111 of the optical pickup 11 and generates a tracking error signal. Reference numeral 19 denotes a frequency response analyzer having a disturbance oscillator 20 and a gain detector 21 therein, and adding a sine-wave-like disturbance signal S corresponding to a desired gain intersection frequency from the disturbance oscillator 20 to the adder.
Output to 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 tracking servo loop filter 14. 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 15 whose gain is controlled by the output 211 of the gain detector 21, and the output 151 is input to the actuator drive circuit 16, power-amplified, and focused by the output 161. It drives an actuator 17 for moving the lens or the entire optical pickup. 26 is disk 10
It is a turntable for mounting and rotating.

In the tracking servo gain adjusting device configured as described above, the portion other than the adder 18 and the frequency response analyzer 19 is a conventional optical disc player itself, and therefore description thereof is omitted. The tracking servo of an optical disc player is described in many documents (for example, "Compact Disc Reader", pp. 133-138, Ohmsha, 1982). Here, a description will be given of a conventional tracking servo gain adjustment method using a frequency response analyzer.

Focusing on the output disturbance signal S of the disturbance oscillator 20 shown in FIG. 3, the signal is applied to the tracking servo loop via the adder 18 and returns to the input of the adder 18 through the loop.
Therefore, if the ratio between the output X of the adder 18 and the input Y is taken, it is apparent that the gain is the tracking servo loop at the frequency of the disturbance signal S.

Here, the frequency response analyzer 19 will be described with reference to FIGS. In FIG. 4, reference numeral 20 denotes the disturbance oscillator. The input Y of the adder 18 is Y
Output X is connected to input amplifier 22 and output X is connected to Y input amplifier 23. The outputs of the Y input amplifier 22 and the X input amplifier 23 are Fourier-transformed by the microcomputer 24 and output. When the ratio of each output is obtained by the comparator 25, the gain of the tracking servo loop at the frequency of the disturbance signal S is obtained (for example, MODEL S-5720, S-5730 FREQUENCY RESPONSE A, NF Circuit Design Block Co., Ltd.).
NALYZER Instruction Manual page 1-5). The variable gain amplifier 15 is controlled by the output 211 of the comparator 25 to adjust the gain of the tracking servo loop.

However, in the above configuration, the gain of the tracking servo loop cannot be correctly adjusted unless the output level of the disturbance oscillator is set appropriately. The reason is that optical discs such as compact discs (CDs) have large optical variations due to the discs, and furthermore, optical variations in the pickup of the optical player itself, so that the level (that is, the voltage value) of the disturbance signal is reduced. Even if it is constant, the shake amount of the focus lens or the shake amount of the entire optical pickup (that is, the physical dimension in which the lens actually moves) differs. For this reason, if the level of the disturbance signal is too high, the servo becomes unstable, and in the worst case, the servo is disconnected. Also, if the level of the disturbance signal is too small, the level of X, Y which is the input signal to the frequency response analyzer becomes small, and the S / N of the measurement system deteriorates,
There was a problem that the adjustment could not be performed correctly.

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

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

Operation In the present invention, the level of the disturbance applied to the tracking servo loop is appropriately set by the above-described configuration, and the gain can be correctly adjusted irrespective of the optical variation of the disk or the pickup.

Embodiment Hereinafter, a tracking servo gain adjusting device according to an embodiment of the present invention will be described with reference to the drawings. First
FIG. 1 shows the configuration of a tracking servo gain adjusting device according to an embodiment of the present invention. In FIG.
An error signal level detector 30 detects the level of the output Y of the error signal generation circuit 13. The output 301 controls the level of the disturbance signal S output from the disturbance oscillator 20. 31
Is an oscillator, the output 311 of which is input to the actuator drive circuit 16 via the switch 32. Other configurations are the same as the conventional one.

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

First, the switch 32 is connected to the A side, and the output 311 of the oscillator 31 is output.
Drives the focus lens or the entire optical pickup in the tracking direction (radial direction of the disk). When the disk 10 is rotated by the turntable 26, the output Y of the error signal generating circuit 13 continuously draws an S-shaped curve each time the light beam crosses a track on which information is recorded on the recording surface of the disk. (The peak value of the S-shaped curve reflects the optical variation of the disk or pickup as a voltage value E (v), but the optical distance is constant, for example, 0.75 μm in FIG. 2). The peak value of the S-shaped curve is detected by the error signal level detector 30. A so-called peak hold circuit is used as the error signal level detector. The disturbance oscillator 20 is controlled so that the output 301 (E (v)) becomes an output S having a beam value of E / 5. As a result, the level of the disturbance applied to the tracking servo loop can be set to 0.15 μm irrespective of the optical variation of the disk or pickup.

Next, by connecting the switch 32 to the B side, the tracking servo loop is closed to perform tracking pull-in. Although there are various methods for the tracking pull-in operation, they are well known and will not be described. Next, while the output level of the disturbance oscillator 20 is kept at E / 5, the gain is adjusted by the same method as in the related art.

As described above, according to the present embodiment, the switch 32 is connected to the A side, the level of the tracking error signal in the open state of the tracking servo loop is detected by the error signal level detector 30, and the output E thereof is used as the disturbance oscillator. By setting the output of E20 to E / 5, the disturbance level can be set to 0.15μm regardless of the optical variation of the disk and pickup, and 0.15μm is sufficiently smaller than 0.75μm which is the D range of the tracking servo. Since it does not come off and the S / N of the measurement system is sufficient, correct gain adjustment can be performed using a frequency response analyzer.

In this embodiment, the error signal level detector 30 is a peak hold circuit. However, the output Y of the error signal generation circuit 13 is A / D (analog / digital) converted and its peak to
The output level of the disturbance oscillator 20 may be controlled based on the eak value obtained. Further, since the eccentricity of the disk cannot be practically reduced to zero, the oscillator 31 may not be necessary in some cases.

Effect of the Invention As described above, the present invention provides a means for detecting the level of a tracking servo error signal when the tracking servo loop is in an open state, and a means for controlling the level of disturbance applied based on the level of the tracking error signal. Thus, the tracking servo gain can be stably adjusted irrespective of the optical variation of the optical disk or the pickup.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a tracking servo gain adjusting device according to an embodiment of the present invention, FIG. 2 is a waveform diagram for explaining an S-shaped curve of a tracking error signal, and FIG. FIG. 4 is a block diagram of a servo gain adjusting device, and FIG. 4 is a block diagram for explaining a 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, 30 error signal level detector, 31 oscillator.

Claims (1)

(57) [Claims] 1. A gain adjusting device for applying a disturbance of a specific frequency to a tracking servo loop of an optical disc player to adjust a loop gain thereof, wherein the level of a tracking error signal is set when the tracking servo loop is open. And a means for controlling the level of disturbance applied based on the level of the tracking error signal.