JPH097200A - Optical disk device - Google Patents

Abstract

PURPOSE: To effectively eliminate an error due to offset of tracking error signal accompanying tracking control, etc., by providing a BPF, an LPF and a subtraction circuit, etc., corresponding to sensor elements. CONSTITUTION: Output signals from the LPFs 13A, 13D are subtracted by a subtracter circuit 14, and an offset component is detected to be amplified by an amplifier circuit 15, and after a signal level is corrected, the signal is subtracted from a push-pull signal by the subtracter circuit 8, and thus, a tracking error signal TE canceling the offset by the subtracter circuit 8 is generated. Thus, a signal component changing by the meandering of a pregroove is extracted from the sensor outputs SA and SD of the sensor elements A and D arranged in the radial direction of a magneto-optical disk 2, and the signal component is detected, and the push-pull signal level is corrected. Thus, the offset of the tracking error signal is evaded effectively, and tracking precision is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk device for tracking control using a pregroove formed on a disk-shaped recording medium.

[0002]

2. Description of the Related Art Conventionally, in an optical disk device such as a magneto-optical disk device, a so-called pre-groove, which is formed on the optical disk so as to undulate in the horizontal direction, is used to perform a tracking control so as to surely obtain a desired value. The data of can be recorded and reproduced.

That is, in this type of magneto-optical disk, a magnetic film is formed on a transparent substrate such as polycarbonate by vapor deposition, and the magnetic film is covered with a protective film. The magneto-optical disk is irradiated with a light beam, a modulation magnetic field is applied to the irradiation position of the light beam, and a thermomagnetic recording method is applied to record desired data. At the time of reproduction, the magnetization polarity of the light beam irradiation position is detected by detecting a change in the polarization plane of the return light from the magneto-optical disk, and thus the recorded data is reproduced by utilizing the Kerr effect.

That is, on such a magneto-optical disk, so-called pre-grooves, which function as guide grooves for the light beam, are formed in a wavy manner. With respect to the pregroove, in the magneto-optical disk device, a light-receiving element whose light-receiving surface is divided is arranged in a direction corresponding to the radial direction of the magneto-optical disk, and the light-receiving element receives the return light of the light beam.

Such a magneto-optical disk device detects a change in the amount of return light in the radial direction of the magneto-optical disk from the output signal of each light-receiving surface of the light-receiving element, and thus applies the so-called push-pull method. Generate a tracking error signal. That is, in a light receiving element whose light receiving surface is divided in a direction corresponding to the radial direction of the magneto-optical disk, an objective lens for converging a light beam is placed so that the beam center of return light is located at the center of the divided light receiving surface. Tracking control is performed by moving in the radial direction of the magneto-optical disk.

Further, the magneto-optical disk device detects a light amount component (wobble signal) which changes due to the meandering of the pre-groove from the change of the light amount of the return light, and the fluctuation frequency of this light amount component becomes a predetermined frequency of 22.05 kHz. The magneto-optical disk is rotationally driven, and the position information of the light beam irradiation position is detected based on the position information obtained from this light amount component.

[0007]

However, in the magneto-optical disk device to which such push-pull method is applied, when the optical axis of the objective lens is displaced from the center of the divided light-receiving surface, or when the magneto-optical disk is deviated. In that case, there is a problem that an offset occurs in the tracking error signal and an error occurs in the tracking error signal.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an optical disk device capable of effectively avoiding an offset of a tracking error signal due to tracking control or the like.

[0009]

In the present invention, the above object is to record desired data on a disk-shaped recording medium having a meandering groove and / or to the disk-shaped recording medium. In an optical disc device for reproducing recorded data, a laser light source that emits the light beam, and the light beam emitted from the laser light source is focused on the disc-shaped recording medium and returned from the disc-shaped recording medium. An objective lens for condensing light and a light-receiving surface divided in the radial direction of the disk-shaped recording medium are received, and the return light condensed by the objective lens is received, and an output signal of each divided light-receiving surface. , A subtracting circuit for generating a tracking error signal by taking a difference signal between the output signals of the divided light receiving surfaces, and the output signal of the divided light receiving surfaces. , A band-pass filter for extracting respectively the signal component that varies with the meandering of the groove, the signal component extracted by the band-pass filter, an envelope detection circuit for detecting the end base rope respectively,
From the subtraction circuit that generates a subtraction signal based on the detection result of the envelope detection circuit, the tracking error signal correction circuit that corrects the signal level of the tracking error signal with the output signal of the subtraction circuit, and the tracking error signal correction circuit Objective lens moving means for moving the objective lens in the radial direction of the disc-shaped recording medium so that the output tracking error signal becomes 0 level, and the envelope detection circuit has a band of the disc-shaped recording medium. This is achieved by an optical disc device in which the frequency is set higher than the rotation frequency of the recording medium.

[0010]

According to the above structure, the offset component of the tracking error signal can be canceled by correcting the tracking error signal with the signal component that changes due to the meandering of the groove. In this case, the band of the envelope detection circuit can be set to a frequency higher than the rotation frequency of the disc-shaped recording medium to cancel the error component due to the eccentricity of the magneto-optical disc during on-track.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described below in detail with reference to the accompanying drawings. The examples described below are
Since it is a preferred specific example of the present invention, various technically preferable limitations are attached, but the scope of the present invention is, unless otherwise stated to limit the present invention, in the following description.
It is not limited to these modes.

1 and 2 show an embodiment of a magneto-optical disk device according to the present invention. In FIG. 1, a magneto-optical disk device 1 records desired data on a magneto-optical disk 2 and reproduces the data recorded on the magneto-optical disk 2.

The magneto-optical disk 2 is formed by forming a magnetic film on a transparent substrate such as polycarbonate by vapor deposition and covering the magnetic film with a protective film. Further, in the magneto-optical disk 2, a groove meandering horizontally in a wavy manner is formed on this transparent substrate, and a pre-groove is formed by this groove. As a result, desired data is recorded on the magneto-optical disk 2 by applying the thermomagnetic recording method, and the recorded data is reproduced by utilizing the Kerr effect. At this time, the recording / reproducing position is detected by performing tracking control using the pre-groove of the magneto-optical disk 2.

The optical pickup 3 emits a light beam of a predetermined polarization plane from a built-in semiconductor laser, and the light beam is passed through an objective lens held by a so-called biaxial actuator so as to move vertically and horizontally. Two
Focus on. Then, at the time of recording, the light quantity of this light beam is intermittently increased, and a modulation magnetic field is applied to the irradiation position of this light beam, whereby desired data is recorded.

Further, the optical pickup 3 collects the returning light from the magneto-optical disk 2 by the objective lens, and the returning light is received by the photodetectors as a plurality of light receiving elements via respective predetermined optical systems. Therefore, the output signals of the plurality of photodetectors are subjected to addition / subtraction processing, the change of the polarization plane of the return light is detected, the recorded data is reproduced, and the focus error signal is generated to perform the focus control.

Further, in the optical pickup 3, one photodetector 4 among the plurality of photodetectors is used.
For example, as shown in FIG. 2, the light receiving surface is divided into four to form sensor elements A to D in the direction corresponding to the radial direction of the magneto-optical disk 2, and the output signals of the sensor elements A to D are formed. Is output. These sensor elements A to D
Corresponding to the above, the magneto-optical disk device 1 processes the output signals of the sensor elements A to D after current-voltage conversion by the current-voltage conversion circuit.

In FIG. 2, for convenience of explanation, only the sensor elements A and D of the photodetector arranged on the outer side are subjected to the current-voltage conversion circuit (IV).
5A and 5D, and the rest of the current-voltage conversion circuit and the output signal processing circuit of this current-voltage conversion circuit are omitted. In addition, this photo detector 4
By utilizing this and a sensor output (not shown), the beam diameter of the light beam can be detected. As a result, the sensor output is processed together with other photo detectors arranged to detect the focus error described above.

The sensor outputs SA and AD of the sensor elements A and D obtained through the current-voltage conversion circuits (IV) 5A and 5D are input to the inverting input terminal and the non-inverting input terminal of the subtraction circuit 6, respectively. , These two sensor outputs S
The subtraction signal of A and AD is output. As a result, the subtraction circuit 6 receives the tracking error signal (hereinafter referred to as push-pull signal) by the push-pull method from the sensor outputs SA and SD of the two sensor elements A and D arranged in the direction corresponding to the radial direction of the magneto-optical disk 2. Call) and outputs this push-pull signal.

The phase compensating circuit 7 receives the output signal of the subtracting circuit 6 through the subtracting circuit 8, limits the band, and compensates the phase and outputs the result. The driver 9 drives the coil 10 of the biaxial actuator based on the output signal of the phase compensating circuit 7 so that the output signal of the phase compensating circuit 7 becomes 0 level. The objective lens is moved to the position (1), so that the magneto-optical disk device 1 forms a servo loop for tracking control.

Bandpass filters BPF 11A and 11
D has a pass band selected to a frequency of 19 to 35 kHz, and extracts a signal component that changes due to meandering of the pre-groove from the sensor outputs SA and SD. As a result, in the magneto-optical disk device 1, the bandpass filter 11
A wobble signal is generated by subtracting the output signals of A and 11D by a subtraction circuit, and the spindle motor is driven so that the carrier frequency of this wobble signal becomes 22.05 kHz. As a result, in the magneto-optical disk device 1, a servo loop is formed as a whole, and the magneto-optical disk 2 is rotationally driven under the condition of constant linear velocity.

Further, in the magneto-optical disk device 1, the wobble signal is demodulated by the FM demodulation circuit, and the position information of the light beam irradiation position is detected from the demodulation result. As a result, in the magneto-optical disk device 1, the optical pickup 3 is sought based on the detection result, and the recording / reproducing operation is controlled.

The full-wave rectifier circuits 12A and 12D detect the envelope of the signal component that changes due to the meandering of the pregroove by full-wave rectifying and outputting the output signals of the bandpass filters 11A and 11D. The result is output to the low pass filters (LPF) 13A and 13D. The low-pass filters 13A and 13D band-limit the envelope detection result and output it.

The subtraction circuit 14 uses the low-pass filter 1
The output signals of 3A and 13D are subtracted and output, and the amplification circuit 15 amplifies the output signal of the subtraction circuit 14 by a predetermined gain K and outputs it. The subtraction circuit 8 corrects the signal level of the push-pull signal by subtracting the output signal of the amplification circuit 15 from the push-pull signal output from the subtraction circuit 6 to generate the tracking error signal TE.

As a result, the magneto-optical disk device 1 detects the change in the wobble signal component from the sensor outputs SA and SB, corrects the signal level of the push-pull signal based on the detection result, and generates the tracking error signal TE. , The signal level of this tracking error signal TE is 0
By driving the objective lens to reach the level,
It is designed to control tracking.

That is, in this embodiment, the beam spot SP (FIG. 2) of the return light formed on the sensor elements A to D is separated from the sensor element B or C from the division line dividing the sensor elements B and C. When the signal level of the push-pull signal does not change in proportion to the displacement amount of the beam spot SP when displaced in the direction, an offset of the tracking error signal due to tracking control or the like is observed. This is because the signal levels of the sensor outputs SA and SB of the sensor elements A and D do not change complementarily to the displacement amount of the beam spot SP, that is, the sensor output SD corresponds to the change of the signal level of the sensor output SA. It means that the signal level of does not change.

On the other hand, the signal component due to the meandering of the pre-groove is generated by the displacement of the pre-groove side with respect to the light beam held at a fixed position, and is represented as a change in the signal level of the sensor outputs SA and SB. To be observed. As a result, the signal component due to the meandering of the pre-groove observed as a change in the signal level of the sensor outputs SA and SB is amplitude-modulated by the offset component, and the envelope is detected as in this embodiment. If the difference is obtained, only the offset component can be extracted.

Thus, in the magneto-optical disk device 1, the subtraction circuit 8 can subtract the offset component from the push-pull signal to effectively avoid the error in the tracking error signal. Thus, the amplifier circuit 15
The gain K is formed to be variable, and the offset K contained in the push-pull signal can be completely canceled by adjusting the gain K on the manufacturing line.

By the way, in the case of detecting the envelope in this way, if the cut-off frequency of the low-pass filters 13A and 13D is set to a low range, the DC offset can be reduced, but it is synchronized with the rotation of the magneto-optical disk 2. Offset, that is, magneto-optical disk 2
It is difficult to reduce the offset and the like generated by tracking control following the eccentricity.

Therefore, as shown in FIG. 3, in this embodiment, the cut-off frequency fc of the low-pass filters 13A and 13D is selected to be 200 Hz. On the other hand, since the magneto-optical disk 2 is rotationally driven under the condition that the linear velocity is constant, the rotational frequency becomes highest when the innermost circumference is irradiated with the light beam, and this frequency fd is selected to be 15 Hz. It has become so. As a result, the magneto-optical disk device 1 can completely remove the offset synchronized with the rotation of the magneto-optical disk 2.

The magneto-optical disk device 1 according to this embodiment is configured as described above, and the light beam emitted from the optical pickup 3 is applied to the magneto-optical disk 2, and the return light obtained as a result thereof is returned to the optical pickup. The photodetector 3 receives the light, and a focus error signal and a reproduction signal are generated.

Of these, the return light received by the photodetector 4 is detected in quantity by sensor elements A to D formed by dividing the light receiving surface in the radial direction of the magneto-optical disk 2, and of these sensor elements A and D. The sensor output of 1 is subtracted by the subtraction circuit 6 to form a push-pull signal. Further, in the sensor outputs of the sensor elements A and D, after the signal components that change due to the meandering of the pregrooves are extracted in the bandpass filters 11A and 11D, the signal components are respectively received by the full-wave rectifier circuits 12A and 12D. After being rectified, the band is limited by the low-pass filters 13A and 13D,
The envelope of the signal component that changes due to the meandering of the pregroove is detected.

The output signals of the low-pass filters 13A and 13D are subtracted by a subtraction circuit 14 to detect an offset component, amplified by an amplification circuit 15 to correct the signal level, and then pushed by a subtraction circuit 8. The pull signal is subtracted from the pull signal, and the subtraction circuit 8 cancels the offset to generate the tracking error signal TE.
As a result, in the magneto-optical disk device 1, the objective lens is moved based on the tracking error signal TE, and tracking control is performed.

Thus, according to the magneto-optical disk device of this embodiment, the signal components which change due to the meandering of the pre-groove are extracted from the sensor outputs SA and AD of the sensor elements A and D arranged in the radial direction of the magneto-optical disk 2. Then, by detecting the offset component from the envelope of this signal component and correcting the signal level of the push-pull signal,
The offset of the tracking error signal can be effectively avoided, and the accuracy of tracking control can be improved. At this time, by setting the envelope detection band to a frequency sufficiently higher than the rotation frequency of the magneto-optical disk 2, it is possible to cancel the offset that changes in synchronization with the rotation of the magneto-optical disk 2.

In the above embodiment, the case where the tracking error signal and the wobble signal are detected by using the photodetector whose light receiving surface is divided into four in the radial direction of the magneto-optical disk 2 has been described. However, the present invention is not limited to this, and can be widely applied to a case where a tracking error signal is generated by the push-pull method using a light receiving element whose light receiving surface is divided in a direction corresponding to the radial direction of the disk-shaped recording medium.

Further, in the above-mentioned embodiment, the case where the magneto-optical disk is rotationally driven under the condition of constant linear velocity has been described, but the present invention is not limited to this, and when it is driven under the condition of constant angular velocity, further zoning. The magneto-optical disk can be widely applied when it is driven under the condition that the angular velocity is constant for each zone.

Further, in the above-mentioned embodiment, the case where the present invention is applied to the magneto-optical disk device has been described.
The present invention is not limited to this, and can be widely applied to various optical disc devices such as a so-called write-once type optical disc device that irradiates a disc-shaped recording medium with a light beam to record and / or reproduce desired data.

[0037]

As described above, according to the optical disk device of the present invention, the error due to the offset of the tracking error signal due to the tracking control or the like can be effectively removed.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a configuration of an embodiment of an optical disc device according to the present invention.

FIG. 2 is a plan view showing the photodetector of FIG.

3 is a characteristic curve diagram showing a frequency characteristic of envelope detection of the optical disk device of FIG.

[Explanation of symbols]

 1 Magneto-optical disk device 2 Magneto-optical disk 3 Optical pickup 4 Photo detector 6 Subtractor circuit 8 Subtractor circuit 14 Subtractor circuit 11A Bandpass filter 11D Bandpass filter 12A Full-wave rectifier circuit 12D Full-wave rectifier circuit 13A Low-pass filter 13D Low-pass filter

Claims (4)

[Claims] 1. An optical disk device for recording desired data on a disk-shaped recording medium having a meandering groove and / or reproducing the data recorded on the disk-shaped recording medium, wherein the light beam is emitted. A laser light source, an objective lens that collects the light beam emitted from the laser light source on the disk-shaped recording medium, and collects return light from the disk-shaped recording medium; A light-receiving element that has a light-receiving surface divided in the radial direction, receives the return light condensed by the objective lens, and outputs an output signal of each divided light-receiving surface, and an output of each divided light-receiving surface A subtraction circuit that generates a tracking error signal by taking a difference signal between the signals, and a signal component that changes due to meandering of the groove from the output signal of each of the divided light receiving surfaces. A band pass filter for extracting Re respectively, the signal component extracted by the band-pass filter,
An envelope detection circuit that detects an envelope, a subtraction circuit that generates a subtraction signal based on the detection result of the envelope detection circuit, and a tracking error that corrects the signal level of the tracking error signal by the output signal of the subtraction circuit. A signal correction circuit and an objective lens moving means for moving the objective lens in the radial direction of the disk-shaped recording medium so that the tracking error signal output from the tracking error signal correction circuit becomes 0 level. The optical disc device, wherein the envelope detection circuit has a band set to a frequency higher than a rotation frequency of the disc-shaped recording medium. 2. The disk-shaped recording medium is rotationally driven under a condition of a constant linear velocity, and the band of the envelope detection circuit is the one when the light beam is irradiated to the innermost circumference of the disk-shaped recording medium. The optical disk device according to claim 1, wherein the frequency is set to be higher than the rotation speed of the disk-shaped recording medium. 3. The envelope detection circuit is formed by a rectifier circuit that rectifies the signal component extracted by the bandpass filter, and a lowpass filter that limits the output signal of the rectifier circuit. The band of the envelope detection circuit is set to a frequency higher than the rotation frequency of the disk-shaped recording medium, whereby the band of the envelope detection circuit is set to a frequency higher than the rotation frequency of the disk-shaped recording medium. The optical disk device described in 1. 4. The tracking error signal correction circuit is formed of an amplification circuit that amplifies the output signal of the subtraction circuit with a predetermined gain, and a subtraction circuit that subtracts the output signal of the amplification circuit from the tracking error signal. 2. The optical disk device according to claim 1, wherein the gain of the amplifier circuit is selected so as to cancel the offset of the tracking error signal.