JPH02265030A - Tracking servomechanism - Google Patents

Abstract

PURPOSE:To correct an error caused by a shift of an objective lens by estimating a real displacement of the objective lens from an actuator driving signal, and adding it to the actuating driving signal, in a tracking servomechanism. CONSTITUTION:A tracking error signal from a pickup 2 operates an actuator 21 through a tracking error signal detecting circuit 3, an AGC circuit 31, an adding circuit 32, and a drive amplifier 4, and also, inputted to a displacement estimating device 33. The estimating device 33 is constituted of a secondary active filter, etc., estimates a real displacement of an objective lens and outputs a voltage of the same frequency characteristic as that of the actuator 21. Subse quently, that which is obtained by multiplying an output of the estimating device 33 passing through an amplifier 34 by an error rate determined, based on dis placement of the actuator 21 and a characteristic of an error is added to the circuit 32. In such a way, an operating position of the actuator becomes a position in which an error caused by a shift of the lens is corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to improving the performance of a tracking servo mechanism in an optical disk drive.

<Conventional technology> In an optical disk drive, a light beam (
A tracking servo is used to make the laser beam (emitted from the laser diode) follow the optical disk guide groove. FIG. 4 is a diagram showing an example of a conventional servo circuit related to tracking control and radial movement of the pickup.
FIG. 5 is a block diagram thereof. A light beam is directed to the disc 1 based on the reflected beam obtained through the pickup 2.
The tracking error signal detection circuit 3 detects the deviation from the track of the drive amplifier 4 and performs phase compensation.
The objective lens (
(not shown).

In this way, the tracking servo corrects the position of the light beam by inputting the tracking error signal.

Now, there are several types of tracking error detection methods, one of which is push-pull (Pu5h-
There is a pull method.

FIG. 6 is a diagram explaining the principle of the push-pull method.

The light beam emitted from the semiconductor laser 11 passes through the beam splitter 12, becomes parallel light by the collimator lens 13, is focused by the objective lens 14, and is irradiated onto the surface of the optical disk 15. The light beam reflected by the optical disk 15 passes through the objective lens 14 and the collimator lens 13, is reflected by the beam splitter 12, and is split into two photodiodes 16.
incident on . The two-split photodiode is arranged in a direction perpendicular to the optical axis with the optical axis in between, and a voltage signal corresponding to the intensity of incident light is obtained. The differential amplifier 17 obtains the difference (+-racking error signal) between the voltage signals of the two photodiodes. When the light beam is on the track, the difference signal obtained from the amplifier is zero, but when the light beam is off the track, a positive or negative signal is output.

In an optical disk drive using such a push-pull method, it is known that an error occurs in principle when the racking actuator moves in the disk radial direction.

In order to reduce this error, typical drives are configured with a dual servo (also called cooperative servo) system consisting of a slide and an actuator that move to follow the large amplitude component of the disk's radial vibration.

<Problem to be solved by the invention> However, this cooperative system slide has relatively large inertia and has strong nonlinear elements such as friction.
It was necessary to be able to move it with I(z), which required the use of an expensive motor and slide movement guide mechanism, and the control system was also complicated and prone to instability.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a racking sabot mechanism capable of inexpensively and stably correcting errors caused by lens shift.

Means for Solving the Problems> In order to achieve the above objects, the present invention detects that the light beam deviates from the center of the track of the disk using a racking error signal detection circuit, and detects the detected signal. The output of the phase-compensated drive amplifier with input is used to drive the actuator installed in the pickup to move the objective lens so that the difference between the disk guide position and the displacement of the objective lens is always zero. A tracking servo mechanism that controls a light beam to follow a track includes a displacement estimator that uses the output of the drive amplifier as input to estimate the actual displacement of the objective lens, and a displacement estimator that estimates the actual displacement of the objective lens and an error that occurs according to the displacement of the actuator. The apparatus is equipped with an amplifier that converts the output of the displacement estimator with a gain based on the relationship, and by adding the error amount obtained from the amplifier to the input of the drive amplifier, the error due to the objective lens shift is corrected. It is characterized by

Effect> The conventional tracking servo mechanism is designed to estimate the actual displacement of the objective lens from the actuator drive signal and add it to the actuator drive signal. As a result, errors caused by objective lens shift 1~ are corrected.

<Example> The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a configuration diagram showing an embodiment of a tracking servo mechanism according to the present invention. In the figure, parts equivalent to those in FIG. 4 are given the same reference numerals.

Reference numeral 31 denotes an automatic gain control (AGC) circuit, which is provided to prevent the disc reflectance and the light emitting power of the laser diode from being affected. 32 is an addition circuit,
The output of the AGC circuit 31 and a displacement estimation amount, which will be described later, are added together.

The output of this summing circuit is input to a drive amplifier 4 which is subjected to phase compensation.

Reference numeral 33 denotes a displacement estimator for estimating the actual displacement of the objective lens, which receives the output of the drive amplifier 4 and outputs a voltage having the same frequency characteristics as the actuator 21, and is usually composed of a second-order active filter. 34 is an amplifier, the gain (magnification) K of which is determined from a conversion rate based on the characteristics of actuator displacement (that is, lens displacement) and error as shown in FIG. Note that the characteristics have a nearly linear relationship, so the gain may be fixed.

The output of amplifier 34 is fed back to summing circuit 32.

FIG. 2 is a block diagram of such a servo system.

The operation in such a configuration will be explained next.

■When the radial vibration of the disc enters the loop,
The actuator 21 operates in accordance with the main loop shown in FIG. 2 (the loop excluding the error correction loop).

(2) On the other hand, input signals entering the actuator are simultaneously given to the displacement estimator 33, and the output of the displacement estimator outputs a signal (converted to a voltage signal) substantially equal to the actual displacement of the actuator.

■ By adding the output of the displacement estimator multiplied by the error rate through the amplifier 34 to the middle of the loose circuit (to the output stage of the AGC circuit), the operating position of the actuator is corrected for errors caused by lens shift. It becomes something.

According to such a correction method, the AGC circuit makes it less dependent on the disk reflectance and the output optical power of the laser diode.

In the embodiment, the displacement estimator is a secondary active filter; however, the present invention is not limited to this, and may be, for example, a digital filter using a digital processor.

Furthermore, in the case of an actuator in which the lens position can be extracted as an output, it may be directly multiplied by an amplifier without using a displacement estimator.

<Effects of the Invention> As explained in detail above, according to the present invention, it is possible to correct errors in tracking servo caused by lens shift by simply adding a simple and inexpensive mechanism to the conventional tracking servo mechanism. It's effective.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the locking mechanism according to the present invention, FIG. 2 is a block diagram of the locking mechanism according to the present invention, and FIG. 3 is a displacement and error of the actuator. FIG. 4 is a diagram showing an example of a conventional servo circuit, FIG. 5 is a block diagram of the servo system shown in FIG. 4, and FIG. 6 is a diagram explaining the principle of the push-pull method. 1... Optical disc, 2... Pickup, 21...
- Actuator, 3... Tracking error signal detection circuit, 4... Drive amplifier, 31... AGC circuit, 32... Addition circuit, 33... Displacement estimator, 34... Amplifier.

Claims (1)

[Claims] A tracking error signal detection circuit detects that the optical beam deviates from the center of the track of the disk, and the detection signal is output from a phase-compensated drive amplifier that is installed in the pickup. The tracking servo mechanism controls the optical beam to follow the track by driving an actuator to move the objective lens so that the difference between the position of the disk guide groove and the displacement of the objective lens is always zero. A displacement estimator that uses the output as input to estimate the actual displacement of the objective lens, and an amplifier that converts the output of the displacement estimator with a gain based on the relationship between the error generated according to the displacement of the actuator and the displacement of the objective lens. . A tracking servo mechanism, wherein an error amount caused by an objective lens shift is corrected by adding an error amount obtained from the amplifier to an input of the drive amplifier.