JPH0638294B2 - Optical disk tracking controller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention uses an actuator to track an objective lens for condensing a light beam so that an optical 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 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 Laid-Open No. 59-28253. In FIG. An optical disk to be reproduced, (2) is an actuator, which causes the light beam (a) to follow a predetermined track of the optical disk (1). (3) is an objective lens that focuses the light beam (a). (4) is an actuator coil, which supplies a 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 which distributes the output of the laser oscillator (5) to the optical disc (1) and the reflected light from the optical disc (1) to the photodetector (7). Photo detector above
(7) converts the quantity of light reflected from the optical disk (1) into electricity. (8) is a tracking error signal generating circuit, which converts the position of the focusing spot of the light beam with respect to the tracking guide groove in the optical disc (1) into an electric signal by the signal from the photo detector (7) and outputs it. A tracking sensor is constituted by the beam splitter (6), the photo detector (7), and the tracking error signal generation circuit (8).

(9) is a phase compensating circuit, which works to secure predetermined control performance such as stability when the control loop is closed. An amplifier circuit (10) 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 described.

The reflected light from the optical disk (1) enters the photodetector (7) via the beam splitter (6), and the incident light quantity is electrically converted, and then the optical disk in the tracking error signal generation circuit (8). The position of the focusing spot of the light beam (a) with respect to the tracking guide groove in (1) is detected, and an electric signal corresponding to it is output. The output signal is converted into a drive current and supplied to the actuator coil (4), whereby the actuator (2) is operated. Along with this, the objective lens (3) is moved by the driving force generated by the actuator coil (4), and the optical spot on the optical disc (1) is moved so as to follow the tracking guide groove. It will be.

In the above tracking control operation, when the control loop is closed, the operation of the phase compensation circuit (9) ensures the control stability, quick response, etc., and performs the tracking control operation as specified.

However, if the tracking error signal is detected by push-pull detection, the optical axis of the reflected light from the optical disc (1) to the photodetector (7) is shown in FIG. 5 as the objective lens (3) moves. As described above, the movement moves from (x) to (x1), so that the tracking offset (C) with respect to the lens shift amount is generated in proportion to the lens shift amount as shown in FIG.

[Problems to be Solved by the Invention] Since the conventional tracking control device for an optical disc is configured as described above, a tracking offset proportional to the movement of the objective lens is generated as the objective lens moves.
There was a problem that the tracking control could not be performed as specified. Therefore, it is necessary to limit the moving range of the objective lens in order to keep the tracking offset small.

The present invention has been made to solve the above problems, and it is possible to automatically correct the tracking offset generated as the objective lens moves.
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 disc according to the present invention includes an objective lens that forms a light spot on a track of an optical disc, an actuator that moves the objective lens in a tracking direction, and the optical disc. Tracking of an optical disk including a tracking sensor that receives reflected light from a spot and generates a tracking error signal, and a control unit that drives the actuator based on the output of the tracking sensor and causes the light spot to follow the track. In the control device, a sum signal generating means for detecting the absolute incident light amount of the reflected light received by the tracking sensor, and a sensor output by holding the output of the tracking sensor at the detection timing of the peak output of the sum signal generating means. Detect foot amount Holding means and offset storage means for detecting the displacement amount of the objective lens and storing the sensor offset amount corresponding to the displacement amount, and the output of the tracking sensor and the offset storage means are provided. The actuator is driven by a difference output from the stored corresponding sensor offset amount.

[Operation] According to the present invention, since the sensor offset amount is obtained by holding the output of the tracking sensor at the detection timing of the peak output of the sum signal generating means, a highly accurate sensor offset amount can be obtained. Since the sensor offset amount is stored in association with the displacement amount of the objective lens obtained based on the drive current of the actuator, a tracking detection signal without offset can be obtained.

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a configuration of a tracking control device for an optical disk according to an example of the present invention. In FIG. 1, (1) to (7) have the same configuration as the conventional example shown in FIG. Therefore, the same reference numerals are given and their description is omitted.

In FIG. 1, (11) is a driver, and this driver (11)
Is the actuator coil in the actuator (2) (4)
Drive current is supplied to. Reference numerals (12a) and (12b) are current-voltage conversion circuits (hereinafter referred to as IV conversion circuits).
The conversion circuits (12a) and (12b) convert the detection current of the photodetector (7) into a voltage. (13) is a sum signal generation circuit,
The outputs of the four I-V conversion circuits (12a) and (12b) are added to generate a signal proportional to the amount of light received by the photodetector (7). (14) is an error signal generation circuit, which subtracts the outputs of the two I-V conversion circuits (12a) and (12b) to generate a tracking sensor signal.

A peak detection circuit (15) detects the peak of the voltage of the sum signal output from the sum signal generation circuit (13). A hold circuit (16) holds the output of the difference signal generation circuit (14) at the timing of the peak detection circuit (15). An amplifier (17) amplifies the output of the hold circuit (16). (1
8) is an A / D converter which converts the analog information signal of the amplifier (17) into a digital information signal. Reference numeral (19) is a semiconductor-based memory circuit which stores the digital information signal output from the A / D converter (18) in accordance with an instruction from the address controller (23). Reference numeral (20) is a D / A converter, which is used from the memory circuit (19) to the address controller (23).
The digital information signal output in accordance with the instruction of 1 is converted 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, which converts the output of the actuator equivalent circuit (21) into a digital signal. (twenty four)
Is a ramp function generating circuit, which generates a ramp-shaped voltage.
(25) is a timing circuit, the ramp function generating circuit (24)
And the operation timing of the address controller (23).

Reference numeral (26) is an automatic gain control circuit (hereinafter referred to as AGC circuit). The AGC circuit (26) keeps the difference signal level constant with respect to changes in laser power. (27) is a subtraction circuit, which converts the output of the AGC circuit (26) into a D / A converter (2
Subtract the output of 0). Reference numeral (28) is a control circuit for phase compensation and gain compensation, which controls the actuator (2) by the output of the subtraction circuit (27).

FIG. 2 is a voltage output waveform of each part at the time of sensor offsetting / teaching before the tracking operation of the tracking controller, and FIG. 2 (a) is a tracking sum signal output voltage output from the sum signal generation circuit (13). (e) and the tracking difference signal output voltage that is the output of the difference signal generation circuit (14)
(d) is shown, (b) shows the offset detection voltage which is the output of the hold circuit (16), and (c) shows the ramp voltage output of the ramp function generating circuit (24).

Further, FIG. 3 is a voltage output waveform of each part during the tracking operation of the tracking control device, FIG. 3 (a) shows the actuator drive current, and FIG. 3 (b) shows the sensor of the D / A converter (20). Indicates the offset output voltage.

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

When the optical disk (1) is inserted into the optical disk device (not shown), focus control is performed and then the timing circuit (2
The ramp function generation circuit (24) is shown in Fig. 2 according to the instruction from 5).
It outputs the lamp voltage as shown in (c). When the lamp voltage is input to the driver (11), the actuator (2) is driven and the objective lens (3) moves in the tracking direction. At this time, since the guide grooves for tracking are present at a constant pitch in the optical disk (1), the sum signal generation circuit (13) and the difference signal generation circuit are accompanied by the movement of the objective lens (3) by the actuator (2). (25) is Fig. 2 (a)
The signal voltages shown in (e) and (d) are generated respectively. Here, since the peak of the tracking sum signal voltage (e) represents the center between the tracking guide grooves of the optical disk (1), the value of the difference signal voltage (d) at the peak of this tracking sum signal voltage (e) is When held, the sensor offset amount for the movement of the actuator (2) in the tracking direction can be taken out. This sensor offset amount corresponds to the amount of movement of the objective lens (3) by the actuator (2), so the drive current when the actuator (2) is driven is detected and the same frequency characteristics as the frequency characteristic of the actuator (2) are detected. The equivalent actuator displacement is detected by an actuator equivalent circuit (21) having characteristics. The sensor offset voltage is stored in the memory circuit (19) using the equivalent actuator displacement as address information.

Next, when the optical disk device performs a predetermined tracking operation, a drive current as shown in FIG. 3 (a) flows through the coil (4) of the actuator (2). This indicates that the optical spot follows the eccentricity of the optical disc (1).

An equivalent actuator displacement is generated in the actuator equivalent circuit (21) by the drive current, and a sensor offset corresponding to this equivalent actuator displacement is called from the memory circuit (19) to obtain a sensor as shown in FIG. 3 (b). The offset output voltage is obtained. This sensor offset output voltage corresponds to the sensor offset amount during the tracking operation. By subtracting such a sensor offset amount as a reverse offset amount from the actual control loop tracking error signal, a tracking error signal not including the sensor offset can be obtained. The above-described correction is performed after the AGC circuit (26) in which the gain is constant with respect to the change in laser power.

According to the tracking control device that operates as described above,
Even if the sensor offset of the push-pull sensor in the head is changed, such as when the optical disk (1) is replaced, the sensor offset can be corrected accordingly. Even if the state of the sensor offset changes due to the head, the sensor offset can be similarly corrected.

EFFECTS OF THE INVENTION As described above, according to the present invention, an objective lens that forms a light spot on a track of an optical disc, an actuator that moves the objective lens in the tracking direction, and a reflected light from the light spot are provided. The tracking control device for an optical disc, comprising: a tracking sensor that receives light and generates a tracking error signal; and a control means that drives the actuator based on the output of the tracking sensor to cause the light spot to follow the track. Sum signal generating means for detecting the absolute incident light amount of the reflected light received by the sensor, and holding means for detecting the sensor offset amount by holding the output of the tracking sensor at the detection timing of the peak output of the sum signal generating means. And the objective lens An offset storage unit that detects the displacement amount and stores the sensor offset amount corresponding to the displacement amount, and outputs the tracking sensor and the corresponding sensor offset amount stored in the offset storage unit. Since the actuator is driven by the differential output of, there is an effect that a highly accurate sensor offset amount can be obtained. Further, since the displacement amount of the objective lens is detected based on the drive current of the actuator, a tracking detection signal having no offset can be obtained, which allows tracking control with no or very little tracking offset. It can be performed.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a tracking control device for an optical disk according to an embodiment of the present invention, and FIG. 2 is (a).
~ (C) is the voltage output waveform diagram of each part during sensor offset teaching, Fig. 3 (a), (b) is the voltage output waveform diagram of each part during tracking operation, and Fig. 4 is the conventional optical disc. FIG. 5 is a block diagram showing the configuration of the tracking control device, FIG. 5 is a diagram for explaining the movement of the reflection optical axis along with the movement of the objective lens, and FIG. 6 is a diagram showing the relationship between the lens shift amount and the tracking offset. . (1) …… optical disk, (2) …… actuator, (3) ……
Objective lens, (4) …… Actuator coil, (6) …… Beam splitter, (7) …… Photo detector, (11) ……
Driver, (12) ... IV conversion circuit, (13) ... sum signal generation circuit, (14) ... difference signal generation circuit, (15) ... peak detection circuit, (16) ... hold circuit, (19) …… Memory circuit, (2
3) ... address controller, (24) ... ramp function generating circuit, (27) ... subtraction circuit, (28) ... phase compensation and gain compensation control circuit. The same reference numerals in the drawings indicate the same or corresponding parts.

Claims (2)

[Claims] 1. An objective lens that forms a light spot on a track of an optical disc, an actuator that moves the objective lens in a tracking direction, and a tracking sensor that receives reflected light from the light spot and generates a tracking error signal. And a control means for driving the actuator based on the output of the tracking sensor to cause the light spot to follow the track, the absolute incident light amount of the reflected light received by the tracking sensor. Detecting means for detecting the sensor offset amount by holding the output of the tracking sensor at the peak output detection timing of the sum signal generating means, and detecting the displacement amount of the objective lens. Together with the displacement Offset storage means for storing the sensor offset amount corresponding to the above, and the actuator is driven by a difference output between the output of the tracking sensor and the corresponding sensor offset amount stored in the offset storage means. An optical disc tracking control device. 2. The tracking control device for an optical disk according to claim 1, wherein the displacement amount of the objective lens is detected by the offset storage means based on a drive current of the actuator.