JPH1031828A - Focus servo device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a focus servo device capable of stabilizing focus lead-in by keeping constant the open-loop gain of a servo system. SOLUTION: The amplitude of an S curve is measured from a focus error signal S preliminarily with an S curve amplitude detecting circuit 7 prior to a focus lead-in; and the amplitude of the S curve is kept constant at the input point of the focus servo loop filter 9, by varying the gain of a variable gain amplifier 6 in accordance with the measured result. Consequently, even if an optical pickup 3 is driven by impressing a triangular wave voltage to a focus coil 12, the focus error signal S is provided with an amplitude equal to the maximum voltage (or the absolute value of the minimum voltage) while the open-loop gain of the servo system is kept constant; the focus servo is actuated when the focus position comes close to the face of a disk 1 with a voltage becoming zero; therefore, the focus lead-in can be stably carried out.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a CD (Compact).
The present invention relates to a focus servo device applied to an optical disc recording / reproducing system such as a disc (Disc) player and an MD (Mini Disc) player.

[0002]

2. Description of the Related Art In an optical disk recording / reproducing apparatus such as a CD player and an MD player, a laser beam is focused on pits arranged in a spiral from the inner circumference to the outer circumference of a disk.
A digital signal is read by detecting the reflected light with an optical head. At this time, the converged spot of the laser light on the recording surface of the disk needs to be about 1 to 2 μm. If there is a slight error in the distance between the disk and the optical head, a reading error occurs. Therefore, conventionally, while controlling the optical system by applying a triangular wave voltage or the like to the focus coil, a focus error signal is generated based on the light reflected on the disk surface, the focus is pulled in, and then the focus servo is performed. A multiplying focus servo device is known (for example, Japanese Patent Publication No. Hei 7-19381). In addition, among such focus servo devices, there are also known focus servo devices which perform an automatic adjustment for measuring and compensating a loop gain of the servo system by injecting a disturbance or the like into the servo system in a state where the servo is applied, if necessary. (For example, JP-A-4-49530). In these conventional focus servo devices, the peak value of the S curve of the focus error signal is detected at the time of focus pull-in, and a so-called pull-in possible range between the peaks is recognized.

[0003]

However, in the above-described conventional focus servo device, the loop gain of the servo system changes due to a change in the amount of light of the laser diode, a change in the reflectivity of the disk, and the like, and the peak value of the S curve. Is not always constant. For this reason, there is a problem that the peak value is not detected, or even if the peak value is detected, the detection level is low, so that the control operation cannot be performed in time and the focus pull-in after the peak detection fails. Also, even if the focus pull-in succeeds, if the loop characteristics are different from the preset characteristics, the servo may not be stable, and the servo may be deviated during the subsequent automatic adjustment. In order to prevent the servo from coming off during automatic adjustment, it is necessary to anticipate fluctuations in the loop gain of the servo system in advance.Therefore, it is not possible to increase the disturbance to be injected. There is also a problem that it takes time and the compensation accuracy is deteriorated.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and stabilizes a focus pull-in, shortens a gain measurement time, improves compensation accuracy by making a loop gain of a servo system constant. It is another object of the present invention to provide a focus servo device capable of stabilizing automatic adjustment.

[0005]

A focus servo device according to the present invention receives a light radiated from a light source and reflected on a disk surface to generate a focus error signal, and generates the focus error signal based on the focus error signal. In a focus servo device for controlling an optical system so that light emitted from the optical disc is focused on the disk surface, amplitude detecting means for measuring the amplitude of the S curve of the focus error signal prior to focusing, and Variable gain means for controlling the gain so that the loop gain of the servo system becomes a predetermined value in accordance with the measurement result of the detection means, wherein the focus is adjusted after the loop gain of the servo system is adjusted to the predetermined value. A pull-in operation is performed.

According to the focus servo device of the present invention, the amplitude of the S-curve of the focus error signal is measured by the amplitude detecting means before the focus is pulled in,
By changing the gain of the variable gain means according to the measurement result, the loop gain of the servo system is set to a predetermined value. For this reason, the peak value of the S curve at the time of focus pull-in can always be a constant value, and focus pull-in can be performed stably. Further, according to the present invention, since the peak value of the S curve of the focus error signal becomes constant, it is possible to inject an optimal disturbance into the servo system within a range not exceeding the peak value, and to reduce the gain measurement time. Shortening, improvement of compensation accuracy, and stabilization of automatic adjustment can be achieved.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a focus servo device according to one embodiment of the present invention.

The disk 1 is driven to rotate by a disk motor 2 in the direction of the arrow in the figure. The optical pickup 3 is arranged to face the disk 1.
The laser light emitted from the optical pickup 3 is focused on a minute spot and enters the disk 1, and a part (main laser light) is provided for focus servo.

The main laser light reflected from the disk 1 is converted into an electric signal by the optical head 3 and supplied to a focus error signal generation circuit 4, where a focus error signal S is generated. The focus error signal S is
The signals are supplied to an S-curve amplitude detection circuit 7, an in-focus detection circuit 8, and a focus servo loop filter 9 via an adder 5 and a variable gain amplifier 6, respectively. The S-curve amplitude detection circuit 7 detects the amplitude of the S-curve of the focus error signal S prior to focusing. When the focus detection circuit 8 detects that the optical pickup 3 is at an appropriate position with respect to the disk 1 based on the focus error signal S at the time of pulling in the focus, it outputs a switching signal and switches the switch 10 from the a side to the b side. Switch to.

The focus error signal S is a signal for driving the focus coil 12 via the switch 10 and the driver 11 after the phase is compensated by the focus servo loop filter 9. Thereby, the focus coil 1
2 drives the optical pickup 3 in the direction perpendicular to the disk 1. Further, the disturbance signal generation circuit 13 adds a disturbance signal such as a sine wave or a square wave having one or more frequencies to the focus error signal S by the adder 5 during the focus servo operation. The gain adjustment circuit 14 measures the loop gain of the servo system based on the added output,
This is automatically adjusted.

FIG. 2 is a block diagram showing an example of a main configuration of the optical head 3 and the focus error signal generating circuit 4. The optical head 3 includes four photodetectors 21, 22, and 2 for detecting main laser light reflected from the disk 1.
3 and 24 are provided. Each photodetector 21, 22,
23 and 24 are detection signals A, B, and
C and D are supplied to the focus error signal generation circuit 4.
The focus error signal generation circuit 4 includes, for example, the adder 3
1 and 32 and a differential amplifier 33. The adder 31 adds the detection signals A and C from the photodetectors 21 and 23 and supplies the obtained signal (A + C) to the positive input terminal of the differential amplifier 33. Further, the adder 32 includes the photodetector 2
The detection signals B and D from 2 and 24 are added, and the obtained signal (B + D) is supplied to the negative input terminal of the differential amplifier 33. The differential amplifier 33 generates and outputs a focus error signal S based on (A + C)-(B + D).

FIG. 3 is a waveform diagram showing an example of the focus error signal S. If the focus position is not appropriate, that is, if the optical pickup 3 is not at an appropriate position with respect to the disk 1, the main laser beam spot has a long axis in the AC direction indicated by L1 in FIG. 2, for example. It becomes an ellipse, and (A + C)-(B + D) = S> 0. When the ellipse has a major axis in the BD direction, (A + C)-
(B + D) = S <0. On the other hand, when the focus position is appropriate, that is, when the optical pickup 3 is at an appropriate position with respect to the disk 1, the spot of the main laser light has a circular shape indicated by L2 in FIG. (B
+ D) = S = 0.

Next, the operation of the focus servo device will be described. At the time of focus pull-in before the focus servo is applied, the switch 10 is set to the a side, and the triangular wave from the triangular wave generation circuit 15 is supplied to the focus coil 12 via the driver 11. Thus, the optical pickup 3 is moved by the focus coil 12 to the disc 1.
Are reciprocated in the vertical direction. At this time, the focus error signal S output from the focus error signal generation circuit 4 is a signal that reciprocates on the S curve in FIG.

The amplitude of the focus error signal S is S
It is measured by the curve amplitude detection circuit 7. For example, when the triangular wave voltage is applied a plurality of times by the triangular wave generating circuit 15, the S curve amplitude detection circuit 7 performs a comparison process between the measurement result and the preset amplitude until a preset amplitude is obtained. When the measurement result is large, as indicated by H in FIG. 3, the gain of the variable gain amplifier 6 is decreased. When the measurement result is small, as indicated by L in FIG. 3, the gain of the variable gain amplifier 6 is decreased. What is necessary is just to comprise so that it may enlarge.
In this configuration, it is necessary to supply the output of the variable gain amplifier 6 to the S-curve amplitude detection circuit 7. However, since the measurement result is compared with a preset amplitude, a proper loop gain can be obtained.

When the loop gain of the servo system is set to an appropriate value, the triangular wave from the triangular wave generating circuit 15 is supplied again to the focus coil 12 via the driver 11, and the same focus search as in the prior art is performed. As a result, when the in-focus state is detected by the in-focus detection circuit 8, the switch 10 is switched to the b side by the in-focus detection circuit 8. Thereafter, the focus servo is applied.

When a gain is adjusted by adding a disturbance signal from the disturbance signal generation circuit 13 as necessary, the disturbance signal has an amplitude value of about 70% of the peak value of the adjusted S curve shown in FIG. A signal can be added. Thereby, the adjustment speed and the adjustment accuracy are improved.

According to this embodiment, the amplitude of the S-curve is measured from the focus error signal S by the S-curve amplitude detection circuit 7 before the focus pull-in, and the gain of the variable gain amplifier 6 is adjusted in accordance with the measurement result. By changing it, S at the input point of the focus servo loop filter 9 is changed.
The amplitude of the curve becomes constant. For this reason, even if the optical pickup 3 is driven by applying a triangular wave voltage to the focus coil 12, the focus error signal S remains at the maximum voltage (or the absolute value of the minimum voltage) while keeping the loop gain of the servo system constant. Since the focus servo is applied when the focus position approaches the surface of the disk 1 and the voltage becomes 0, focus pull-in can be stably performed. In addition, since the loop gain of the servo system is constant, it is possible to inject an optimal disturbance into the servo system, shorten the gain measurement time, improve the compensation accuracy,
In addition, the automatic adjustment can be stabilized.

In the above-described embodiment, the focus servo loop filter 9 which forms a single loop of the servo system is used.
And a variable gain amplifier 6 is provided in the preceding stage of the focus detection circuit 8 for switching and outputting the same, and an S-curve amplitude detecting circuit 7 is provided in the subsequent stage to control the gain of the variable gain amplifier 6 to converge to a set value. , Without such control,
A triangular wave voltage is applied only once by the triangular wave generating circuit 15,
An S-curve amplitude detection circuit 7 having a peak hold function detects a peak value of the S-curve, and obtains a predetermined amplitude based on a transfer function of another circuit constituting a servo system and a measurement result. Thus, the gain to be set by the variable gain amplifier 6 may be calculated, and the gain of the variable gain amplifier 6 may be controlled based on the calculated value.
In this case, it is not always necessary to supply the output of the variable gain amplifier 6 to the S-curve amplitude detection circuit 7;
The variable gain amplifier 6 is provided immediately before the input point of the focus servo loop filter 9 as shown in FIG. 5, or the variable gain amplifier 6 is provided immediately after the input point of the S curve amplitude detection circuit 7 as shown in FIG. It may be.

[0019]

As described above, according to the present invention,
Prior to the focus pull-in, the amplitude of the S curve of the focus error signal is measured in advance by the amplitude detection means, and the gain of the variable gain means is changed in accordance with the measurement result, so that the peak value of the S curve at the time of the focus pull-in is obtained. The value can always be constant, and the focus pull-in can be performed stably. According to the invention,
Since the peak value of the S curve of the focus error signal is constant, it is possible to inject an optimal disturbance into the servo system within a range not exceeding the peak value, thereby shortening the gain measurement time, improving the compensation accuracy, and The automatic adjustment can be stabilized.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a focus servo device according to one embodiment of the present invention.

FIG. 2 is a block diagram illustrating an example of a main configuration of an optical head and a focus error signal generation circuit.

FIG. 3 is a waveform diagram illustrating an example of a focus error signal.

FIG. 4 is a block diagram showing a configuration of a focus servo device according to another embodiment of the present invention.

FIG. 5 is a block diagram showing a configuration of a focus servo device according to still another embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Disc, 2 ... Disk motor, 3 ... Optical pick-up, 4 ... Focus error signal generation circuit, 5 ... Adder, 6 ... Variable gain amplifier, 7 ... S-curve amplitude detection circuit, 8 ... In-focus detection circuit, 9 ... Focus servo loop filter, 10 switch, 11 driver, 12 focus coil, 13 disturbance signal generation circuit, 14 gain adjustment circuit, 15 triangular wave generation circuit.

Claims (1)

[Claims] And a focus error signal generated by receiving light emitted from the light source and reflected on the disk surface, and focusing the light emitted from the light source on the disk surface based on the focus error signal. A focus servo device for controlling an optical system such that the amplitude of the S-curve of the focus error signal is measured prior to focusing, and a loop of the servo system according to the measurement result of the amplitude detection device. Variable gain means for controlling the gain so that the gain becomes a predetermined value, wherein the focus pull-in operation is performed after the loop gain of the servo system is adjusted to the predetermined value. Servo device.