JPH01125733A - Tracking controller for optical disk - Google Patents

Abstract

PURPOSE:To automatically correct a tracking offset generated according to the shift of an objective lens by storing a sensor offset quantity being generated by the shift of the objective lens in a memory circuit, and subtracting the sensor offset quantity stored in the memory circuit from a tracking error signal detected by a tracking sensor at the time of a tracking operation. CONSTITUTION:The sensor offset quantity is detected by shifting the objective lens 3 in a tracking direction via an actuator before the tracking operation, and a detected sensor offset quantity is stored in the memory circuit 19. In the following tracking operation, the sensor offset quantity stored in the memory circuit 19, that is, the tracking offset is subtracted from the tracking error signal detected by the tracking sensor. In such a way, it is possible to obtain a tracking detecting signal without generating the offset.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention provides an objective lens for condensing a light beam through an actuator so that a light spot on a track of an optical disk follows a predetermined track. The present invention relates to a tracking control device for an optical disc configured to control movement in a tracking direction.

[Prior Art] Fig. 4 is a block diagram showing a conventional tracking control device for an optical disc disclosed in, for example, Japanese Patent Application Laid-Open No. 59-28253. An actuator (2) causes the light beam (a) to follow a predetermined track on the optical disc (1). (3) is the objective lens, and the light beam (a)
Focus the light. (4) is an actuator coil that supplies driving force to the movable part of the actuator (2).

(5) is a laser oscillator, which is a light source of the light beam (a). (6) is a beam splitter, and the laser oscillator (5) is a beam splitter.
) to the optical disk (1), and the output from the optical disk (1) to the optical disk (1).
The reflected light is distributed to a photodetector (7). The photodetector (7) converts the amount of light reflected from the optical disk (1) into electricity. (8) is a tracking error signal generation circuit which converts the position of the focused spot of the light beam relative to the tracking guide groove on the optical disc (1) into an electrical signal based on the signal from the photodetector (7) and outputs the electrical signal. The beam splitter (6), photodetector (7), tracking error signal generation circuit (8)
) constitutes a tracking sensor.

(9) is a phase compensation circuit, which is designed to ensure predetermined control performance such as stability when the control loop is closed.
0) is an amplifier circuit that converts the control voltage from the phase compensation circuit (9) into a drive current and supplies the drive current to the actuator coil (4).

Next, the operation of the above configuration will be explained.

The reflected light from the optical disk (1) passes through the beam splitter (6
), the incident light beam is electrically converted by entering the photodetector (7), and then the tracking error signal generation circuit (8) converts the light beam (a) into a focused spot on the tracking guide groove in the optical disc (1). The position of is detected, and the corresponding electrical signal is output. The actuator (2) is actuated by converting this output signal into a drive current and supplying it to the actuator coil (4). Accordingly, the objective lens (3) is moved by the driving force generated by the actuator coil (4), and the light spot on the optical disk (1) is moved to follow the tracking guide groove.

In the tracking control operation as described above, when the control loop is closed, the phase compensation circuit (9) works to ensure control stability, coordination, etc., and perform the predetermined tracking control operation.

However, if the detection of the tracking error signal is push-pull detection, as the objective lens (3) moves, the optical disc (1) will be moved from the optical disc (1) to the photodetector (7).
As shown in Figure 5, the optical axis of the reflected light from (X) to (
Therefore, as shown in FIG. 6, a tracking offset (C) with respect to the lens shift amount occurs in proportion to the lens shift amount.

[Problem that the invention attempts to solve] Conventional optical disc tracking control device.

With the above configuration, there is a problem in that as the objective lens moves, a tracking offset occurs proportional to the movement of the objective lens, making it impossible to perform tracking control as specified. Therefore, it was necessary to limit the movement range of the objective lens in order to keep the tracking offset small.

This invention was made to solve the above problems, and it is possible to automatically correct the tracking offset that occurs due to the movement of the objective lens.
It is an object of the present invention to provide a tracking control device for an optical disc that can always perform tracking control as specified.

[Means for Solving the Problems] A tracking control device for an optical disk according to the present invention stores the sensor offset amount caused by the movement of the objective lens in a memory circuit, and stores the tracking error detected by the tracking sensor during tracking operation. The present invention is characterized in that the sensor offset amount stored in the memory circuit is subtracted from the signal.

[Operation] According to the present invention, the amount of sensor offset is detected by moving the objective lens in the tracking direction via the actuator before the tracking operation, and the detected amount of sensor offset is stored in the memory circuit. and,
During the subsequent tracking operation, a tracking detection signal without offset is obtained by subtracting the sensor offset amount stored in the memory circuit, that is, the tracking offset, from the tracking error signal detected by the tracking sensor.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described based on the drawings.

FIG. 1 is a block diagram showing the configuration of an optical disk tracking control device according to an embodiment of the present invention, and in the same figure, (1) to (7) are the same configuration as the conventional example shown in FIG. 4. Therefore, since they have the same reference numerals, their explanation will be omitted.

In FIG. 1, (11) is a driver, and this driver (11) supplies a drive current to an actuator coil (4) in an actuator (2). (+2a).

(12b) is a current-voltage conversion circuit (hereinafter referred to as an IV conversion circuit), and these IV conversion circuits (12a).

(12b) converts the detected current of the photodetector (7) into voltage. (13) is a sum signal generation circuit which adds the outputs of the two IV conversion circuits (12a) and (12b) to generate a signal proportional to the amount of light received by the photodetector (7). (14) is an error signal generation circuit that generates a tracking sensor signal by subtracting the outputs of the two IV conversion circuits (12a) and (12b).

(15) is a peak detection circuit, and the sum signal generation circuit (I
3) Detect the voltage peak of the sum signal output from.

(16) is a hold circuit, and the peak detection circuit (15) is a hold circuit.
), the output of the difference signal generation circuit (14) is held. (17) is an amplifier that amplifies the output of the hold circuit (16). (18) is an A/D converter which converts the analog information signal of the amplifier (17) into a digital information signal. (19) is a memory circuit using a semiconductor, which stores the digital information signal output from the A/D converter (18) according to instructions from the address controller (23). (20) is a D/A converter which converts the digital information signal outputted from the memory circuit (19) according to the instruction of the address controller (23) into an analog information signal.

(21) is an actuator equivalent circuit, and this actuator equivalent circuit (21) detects the actuator drive current in the driver (11) and converts it into an equivalent actuator displacement. (22) is an A/D converter,
The output of the actuator equivalent circuit (21) is converted into a digital signal. (24) is a ramp function generating circuit that generates a ramp-like voltage. A timing circuit (25) instructs the operation timing of the ramp function generation circuit (24) and address controller (23).

(26) is an auto gain control circuit (hereinafter referred to as AG
This AGC circuit (26), referred to as C circuit, keeps the difference signal level constant against changes in laser power. (27
) is a subtraction circuit, which extracts D from the output of the AGC circuit (26) above.
/A converter (20) output is subtracted. (28) is a control circuit for phase compensation and gain compensation, which controls the actuator (2) with the output of the subtraction circuit (27).

Figure 2 shows the voltage output waveforms of various parts during sensor offset teaching before the tracking operation of the tracking control device, and Figure 2 (a) shows the sum signal generation circuit (1).
The tracking sum signal output voltage (e) that is the output of 3) and the tracking difference signal output voltage (d) that is the output of the difference signal generation circuit (14) are shown in FIG. shows the offset detection voltage which is the output of
+51(c) indicates the ramp voltage output of the ramp function generating circuit (24).

Further, FIG. 3 shows voltage output waveforms of various parts during the tracking operation of the tracking control device, and FIG. 3(a) shows the actuator drive current.

FIG. 4B shows the sensor offset output voltage of the D/A converter (20).

Next, the operation of the above configuration will be explained.

When the optical disc (1) is inserted into an optical disc device (not shown), focus control is performed and then the ramp function generating circuit (24)
outputs a lamp voltage as shown in FIG. 2(c). When this lamp voltage is input to the driver (11), the actuator (2) is driven and the objective lens (3) is driven.
moves in the tracking direction. At this time, since the optical disk (1) has guide grooves for tracking at a constant pitch, the sum signal generation circuit (13) moves as the objective lens (3) is moved by the actuator (2).
and the difference signal generation circuit (25) as shown in (e) of FIG. 2(a).
And a signal voltage as shown in (d) is generated accordingly. Here, since the peak of the tracking sum signal voltage (e) represents the center between the tracking guide grooves of the optical disc (1), the value of the difference signal voltage (d) at the peak of this tracking sum signal voltage (e) is held. Then, the amount of sensor offset with respect to the movement of the actuator (2) in the tracking direction can be extracted. This sensor offset amount corresponds to the amount of movement of the objective lens (3) by the actuator (2), so the drive current when driving the actuator (2) is detected, and the frequency characteristic is the same as that of the actuator (2). The equivalent actuator displacement is detected by the actuator equivalent circuit (21) having the following. The above-mentioned sensor offset voltage is stored in the memory circuit (1g) using this equivalent actuator displacement as address information.

Next, when the optical disk device enters a predetermined tracking operation, the coil (4) of the actuator (2) is activated as shown in FIG.
A drive current as shown in a) flows. This indicates that the light spot follows the eccentricity of the optical disc (1).

The drive current generates an equivalent actuator displacement in the actuator equivalent circuit (21), and a sensor offset corresponding to this equivalent actuator displacement is read from the memory circuit (19), thereby creating a sensor offset as shown in FIG. 3(b). Output voltage is obtained. This sensor offset output voltage corresponds to the sensor offset amount during tracking operation. By subtracting such a sensor offset amount from the tracking error signal of the actual control loop as an inverse offset amount, a tracking error signal that does not include the sensor offset can be obtained.

Note that the above-described correction is performed at a subsequent stage of the AGC circuit (26) in which the gain is constant with respect to changes in laser power.

According to the tracking control device that operates as described above,
The sensor offset of the push-pull sensor in the head can be corrected in response to changes in status such as replacement of the optical disk (1). Furthermore, even if the state of the sensor offset changes depending on the head, the sensor offset can be corrected in the same way.

[Effects of the Invention] As described above, according to the present invention, the amount of sensor offset that occurs due to the movement of the objective lens is stored in the memory circuit, and the tracking detected by the tracking sensor during the actual tracking operation is performed. By subtracting the above-mentioned stored sensor offset layer from the error signal, a tracking detection signal without sensor offset can be obtained, thereby making it possible to perform tracking control without or with little tracking offset. Therefore, it is possible to automatically respond to changes in the sensor offset amount due to variations in the optical disk or the head, and to always perform tracking control reliably in a predetermined manner.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an optical disc tracking control device according to an embodiment of the present invention, and FIG. 2(a)
- (C) are voltage output waveform diagrams of each part during sensor offset teaching, Figures 3 (a) and (b) are voltage output waveform diagrams of various parts during tracking operation, and Figure 4 is conventional optical disc tracking control. A block diagram showing the configuration of the device,
FIG. 5 is a diagram illustrating the movement of the reflection optical axis due to the movement of the objective lens, and FIG. 6 is a diagram illustrating the relationship between the lens shift amount and the tracking offset. (1) --- Optical disk, (2) --- Actuator, (:)) --- Objective lens, (4) --- Actuator coil, (6) --- Beam splitter, (
7) , -... Photodetector, (11) -... Driver, (12) - I-V conversion circuit, (13)... Sum signal generation circuit, (14)... Difference signal generation circuit, (1
5)...Peak detection circuit, (16)...Hold circuit, (19)...Memory circuit, (23)...Address controller, (24)...Ramp function generation circuit,
(27)--Subtraction circuit, (28)--Control circuit for phase compensation and gain compensation. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (4)

[Claims] (1) An optical disc for recording and reproducing signals, a tracking sensor for detecting the position of a light spot on a track on this optical disc and outputting a tracking error signal, an actuator for moving an objective lens in the tracking direction, and the above-mentioned tracking sensor. A tracking control device for an optical disc comprising a control circuit that performs phase compensation and gain compensation via the actuator so that the light spot follows the track of the optical disc based on a tracking error signal output from the optical disc. and a subtraction circuit that subtracts the sensor offset amount, which is the output of the memory circuit, from the tracking error signal, which is the output of the tracking sensor. Tracking control device. (2) Before starting the tracking operation, operate the actuator in the tracking direction, provide a memory that stores the amount of sensor offset for the actuator drive current at this time, and offset the sensor by the information stored in the memory during the tracking operation. An optical disk tracking control device according to claim 1, which is configured to correct the amount. (3) An actuator equivalent circuit having frequency characteristics equal to the frequency characteristics of the above actuator is provided, and the actuator equivalent circuit converts the actuator drive current into an equivalent actuator displacement, and the sensor offset amount for the converted actuator displacement is stored in the above memory. An optical disk tracking control device according to claim 2, which is configured to store data. (4) A sum signal generation circuit that detects the absolute incident light amount of the tracking sensor and a hold circuit that holds the tracking error signal that is the output of the tracking sensor, tracking at the peak of the output voltage of the sum signal generation circuit. 3. The optical disk tracking control device according to claim 2, wherein the optical disk tracking control device is configured to detect the sensor offset amount when the actuator is operated by holding the error signal in the hold circuit.