JPH0877582A - Optical disk device - Google Patents

Abstract

PURPOSE: To perform tracking without largely deviating the center of an objective lens from the center of a light beam by detecting a driving current of the objective lens and correcting a tracking error signal based on the driving current. CONSTITUTION: A low frequency component of the driving current of a tracking actuator 12 of an objective lens driving part 9 is detected by an objective lens driving current detecting circuit 14. Subsequently, the tracking error signal is corrected by subtracting the driving current from the tracking error signal from a differential amplifier 8 by an arithmetic circuit 15. The driving part 9 is controlled by a high frequency component of eccentricity of the corrected tracking error signal, while an optical head driving part 13 is controlled by a low frequency component. By this method, an offset of the tracking error signal due to movement of the objective lens at the time of following a track can be corrected, and a regenerative RF signal is prevented from deteriorating due to deviation of a spot from the track.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tracking servo for an optical disk device including a magneto-optical disk device.

[0002]

2. Description of the Related Art In recent years, optical disc devices such as CD players and magneto-optical disc devices such as MD players have been commercialized as information recording / reproducing devices capable of erasing, recording, and reproducing with a large capacity, and the development thereof is still active. It is being appreciated. Generally, in this type of device, a light beam emitted from a semiconductor laser is focused on a disk surface through an objective lens to record information, or information is read from the reflected light. Since the track of the disc is eccentric due to the eccentricity of the center hole of the optical disc, the eccentricity of the track, or the axial vibration of the rotary shaft of the turntable, the optical head body is driven in the radial direction of the optical disc to follow the track. An optical head drive unit and an objective lens drive unit that drives the objective lens alone are required.

One of the methods of following the track is a one-beam push-pull method (for example, Japanese Patent Laid-Open No. 63-20697).
6), which is a method of detecting the track deviation by taking out the light reflected and diffracted by the guide groove on the disk as the output difference of the two-divided sensor symmetrically arranged with respect to the center of the track. That is, when the spot of the light beam incident on the objective lens irradiates the center of the track, symmetrical reflected diffracted light is obtained, and when the spot deviates from the center of the track, the left and right intensities can be different. Therefore, if a sensor divided into two is used, a tracking error signal can be obtained from the difference between the left and right. By sending this signal to the tracking actuator and controlling so that the left-right difference is always 0, the center of the track can be tracked.

[0004]

However, as shown in FIG. 2, the light intensity of the light beam used is not uniform, and has a substantially Gaussian distribution (17) in which the light intensity gradually decreases with distance from the peak position. ing. For this reason, when the objective lens (6) is largely moved by the tracking actuator (12), the incident light does not move, and the center of the objective lens (6) and the peak position of the incident light deviate by L. . Therefore, even if the center of the objective lens (6) coincides with the center of the track (16), the center of the light intensity is located at a position deviated from the center of the two-divided sensor (7) as shown in FIG. Even if two semicircles (18) and (19) are formed, the light intensities are not equal. For example, objective lens (6)
Is moved by 50 μm, an offset, which is a deviation between the center of the track and the center of the objective lens (6), is generated by about 7% with respect to the amplitude of the error signal. When the tracking servo is applied in this state, the spot at the center of the track moves to a position slightly deviated from the center, and there is a problem that the signal at the time of recording / reproducing deteriorates.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and is characterized by a current detection unit for detecting a drive current of an objective lens drive unit and a tracking error signal corrected by the drive current. And an arithmetic circuit for performing the operation.

[0006]

When the light beam is made to follow one track,
Tracking is performed so that the center of the objective lens does not largely deviate from the center of the light beam.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the main part of the structure of a track servo. Reference numeral (1) is an optical head including a laser (2), a collimator lens (3), a polarization beam splitter (4),
It has a reflection mirror (5), an objective lens (6), a two-divided sensor (7), a differential amplifier (8), and an objective lens driving section (9). The laser (2) emits a light beam, and the collimator lens (3) narrows this light beam. The polarization beam splitter (4) has a polarization film and is polarized by an optical disc (1
The light beam reflected from 0) does not return to the laser (2). The reflection mirror (5) reflects the light beam from the laser (2) toward the objective lens (6). The objective lens (6) converges the light beam to the optical disc (10) or guides the light beam reflected by the optical disc (10) to the polarization beam splitter (4). The two-divided sensor (7) has two light-receiving surfaces (11) and (11) divided from each other.
And convert the received light beams into electric signals. The differential amplifier (8) includes the respective light receiving surfaces (11) (1
The difference between the signals converted in 1) is output. The objective lens driving section (9) has a tracking actuator (12) and moves the objective lens (6) in the radial direction of the optical disc (10) based on the high frequency component of the tracking error signal. Reference numeral (13) is an optical head drive unit, which moves the optical head (1) in the radial direction of the optical disc (10) based on the low frequency component of the tracking error signal. (14)
Is an objective lens drive current detection circuit, which detects a low frequency component of the drive current of the objective lens drive section (9). (15)
Is an arithmetic circuit, which performs an arithmetic operation for correcting the signal from the differential amplifier (8) by the drive current from the objective lens drive current detection circuit (14) and outputs the high frequency component to the objective lens drive section (9). The frequency component is output to the optical head drive unit (13) as each tracking error signal.

The operation of the above configuration will be described. First,
The light beam emitted from the laser (2) is applied to the track of the optical disk through the collimator lens (3), the polarization beam splitter (4), the reflection mirror (5) and the objective lens (6). Then, the light beam reflected by the track is irradiated onto the two-divided sensor (7) through the objective lens (6) and the polarization beam splitter (4) and is converted into two electric signals. The difference between the two signals is output by the differential amplifier (8). Here, when the center of the objective lens (6) and the center of the light beam (the center of the Gaussian distribution) match, when the center of the signal track and the center of the objective lens (6) match, the light beam is divided into two sensors. The two light receiving surfaces (11) and (11) of (7) are equally irradiated, and the tracking error signal becomes zero. If the center of the signal track deviates from the center of the objective lens (6), the two light receiving surfaces (11)
A difference occurs in the light amount of (11), and the tracking error signal has a value according to the deviation.

Next, the offset correction will be described. The offset occurs due to the displacement of the center of the objective lens (6) and the center of the light beam (the center of the Gaussian distribution) due to the movement of the objective lens (6) by the tracking actuator (12). That is, when the tracking error signal is large as a result of, for example, a large movement of the optical head, the objective lens drive unit (9) drives the objective lens (6) with a large drive current, whereby the objective lens (6) is moved. The center of the light beam is largely moved and deviated from the center of the objective lens (6). In this case, the drive current and the amount of movement of the objective lens (6), the amount of movement of the objective lens (6) and the deviation of the center of the light beam, and the deviation of the center of the light beam and the magnitude of the offset are respectively proportional. The present invention focuses on this proportional relationship and corrects the tracking error signal by the drive current. The objective lens drive current detection circuit (14) detects the low frequency component of the drive current of the tracking actuator (12) of the objective lens drive unit (9).
Detect with. The tracking error signal is corrected by subtracting the drive current from the objective lens drive current detection circuit (14) from the tracking error signal from the differential amplifier (8) in the arithmetic circuit (15). The high frequency component of the eccentricity of the corrected tracking error signal controls the objective lens drive section (9), and the low frequency component of the optical head drive section (13).
Control.

The gain of the current obtained by the drive current detection circuit (14) is adjusted so that the lens comes to the center of the track when the tracking servo is applied using the corrected tracking error signal.

Next, a second embodiment will be described with reference to the block diagram of FIG. The second embodiment is the objective lens drive current detection circuit (14) and the arithmetic circuit (15) in the first embodiment.
1 is performed by the control circuit (20), and the components corresponding to those in FIG. 1 are denoted by the same reference numerals. That is, the control circuit (20) detects the current from the objective lens drive section (9), and tracking is performed due to the deviation between the center of the intensity of the laser beam and the center of the objective lens (6) which is proportional to this current value as described above. Calculate the error in the error signal. Then, the error of the tracking error signal from the differential amplifier (8) is corrected, and the objective lens drive unit (9) and the optical head drive unit (13) are controlled. In this way, the control circuit (20) controls so that the center of the intensity of the laser light and the center of the objective lens (6) substantially coincide with each other.

In the present embodiment, the two-division sensor in the one-beam push-pull method has been described, but the present invention can be applied to the three-beam method or the four-division sensor.

[0013]

According to the above invention, when the track is followed, the offset of the tracking error signal due to the movement of the objective lens can be corrected, and the reproduction RF signal due to the track deviation of the spot can be prevented from deteriorating.

[Brief description of drawings]

FIG. 1 is a block diagram of a first embodiment of the present invention.

FIG. 2 is a diagram showing a light reception intensity of a two-divided sensor when an objective lens moves.

FIG. 3 is a block diagram of a second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical head 6 Objective lens 7 2 division sensor 9 Objective lens drive part 10 Optical disk 12 Tracking actuator 14 Objective lens drive current detection circuit 15 Arithmetic circuit 16 Track 20 Control circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hirohide Otani 3-201 Minamiyoshikata, Tottori City, Tottori Prefecture Tottori Sanyo Electric Co., Ltd.

Claims (2)

[Claims] 1. An optical head for irradiating a light beam on a signal track recorded on a recording medium through an objective lens, and a sensor for detecting a deviation amount between the signal track and the light beam and outputting a tracking error signal. In an optical disc device having an objective lens drive unit that moves the objective lens in the radial direction of the recording medium based on the tracking error signal, a current detection unit that detects a drive current of the objective lens drive unit, and the drive current An optical disc device comprising: an arithmetic circuit that corrects the tracking error signal. 2. An optical head for irradiating a light beam on a signal track recorded on a recording medium through an objective lens, and a sensor for detecting a deviation amount between the signal track and the light beam and outputting a tracking error signal. In an optical disc device having an objective lens drive section that moves the objective lens in the radial direction of the recording medium based on the tracking error signal, a laser beam is detected by detecting a drive current of the objective lens drive section based on the tracking error signal. An optical disk device comprising a control means for making the intensity center of the optical axis and the center of the objective lens substantially coincide with each other.