JPH08190723A - Servo controller - Google Patents

Abstract

PURPOSE: To enhance the reliability of a servo system by correcting the leakage of an optical or electric signal from a tracking error signal owing to a focusing error signal. CONSTITUTION: This controller is equipped with a detector 4 for generating the focusing error signal and the tracking error signal, an A/D converter 7 of a digital processing circuit being a sampling means for sampling the amplitude level of the focusing error signal from this detector 4 at prescribed time intervals, a digital signal processor 8 being a correcting means for obtaining a frequency characteristic of the amplitude sampled by the sampling means 7, compairing this frequency characteristic with a preset frequency characteristic, correcting it, and obtaining the amplitude level corresponding to the prescribed time from the corrected frequency characteristic, a D/A converter 9 for converting the amplitude level obtained by the correcting means 8 at the prescribed time intervals into an analog signal and outputting this signal, and a driving means 10 for driving an actuator 11 for focusing based on the output of this converter 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a servo controller used for an optical disk device or the like.

[0002]

2. Description of the Related Art For example, a servo system of a magneto-optical disk device includes a servo system for performing focusing servo and tracking servo. Focusing servo mainly includes methods such as an astigmatism method and knife edge method, and tracking servo includes methods such as push-pull method and three-beam method.

[0003]

In the prior art as described above, the leakage of the optical and electrical signals from the tracking error signal to the focusing error signal (hereinafter referred to as crosstalk) is a focusing and tracking detector. Was happening in. Crosstalk has occurred in the digital control circuit from the focusing and tracking detection circuit through the analog processing circuit, and it has been very difficult to completely remove it.

The present invention has been made in view of the above problems, and an object thereof is to provide a servo control device capable of correcting crosstalk.

[0005]

[Means for Solving the Problems] In order to solve the above problems,
The servo control device of the present invention is a detector for generating a focusing error signal and a tracking error signal, and a sampling means for sampling the amplitude level of the focusing error signal from the detector at predetermined intervals.
Correction means for obtaining a frequency characteristic of the amplitude level sampled by the sampling means, correcting the frequency characteristic by comparing it with a preset frequency characteristic, and obtaining an amplitude level corresponding to time from the corrected frequency characteristic; A D / A converter that converts the amplitude level for each time obtained by the correction unit into an analog signal and outputs the analog signal, and a drive that drives an actuator for focusing according to the output from the D / A converter. And a structure including means.

[0006]

According to the present invention, by obtaining the frequency characteristic of the amplitude level of the sampled focusing error signal and correcting it, a focusing error signal with crosstalk removed can be generated.

[0007]

1 is a block diagram showing the configuration of a servo controller according to an embodiment of the present invention. The focusing / tracking detector 4 is composed of a four-division photo detector. In this embodiment, the magneto-optical disk having the track groove is irradiated with the light beam emitted from the magneto-optical head 1, and the reflected light is received by the detector 4 provided in the magneto-optical head 1. , Performs focusing servo and tracking servo. Then, the light beam is converged on the track, and the track is controlled so as to continue following the track while the light beam is irradiated on the track. The case where the astigmatism method is used for the focusing servo and the push-pull method is used for the tracking servo is shown.

In addition to the detector 4, the magneto-optical head 1 is provided with current-voltage conversion amplifiers 5a and 5b, an adder circuit 12, an actuator driver 10, an actuator 11 and the like. FIG. 2 is a diagram showing the arrangement of photodetectors of the detector 4. The detector 4 has four photo detectors A, B, C and D arranged as shown in FIG.
In FIG. 2, a portion indicated by reference symbol E is a spot shape of the reflected light when the convergence point of the light beam is on the track, that is, in the focused state. Further, the portion indicated by the symbol F is the spot shape of the reflected light when the light beam is irradiated directly above the track. The four photodetectors output currents of levels corresponding to the amounts of incident light.

The photodetector A of the four-division detector 4,
If the currents flowing through B, C, and D are a, b, c, and d, the focusing error signal used for focusing servo is expressed by (a + d)-(b + c), and the tracking error signal used for tracking servo is , (A +
It is represented by b)-(c + d). In FIG. 1, (a + d) is input to the current-voltage conversion amplifier 5a, and (b + c) is input to the current-voltage conversion amplifier 5b. Then, the adder circuit 12 inputs the voltages corresponding to (a + d) and (b + c), respectively, and outputs the voltage corresponding to (a + d)-(b + c). Therefore, the output from the adder circuit 12 is the focusing error signal.

Further, in order to obtain the tracking error signal, the voltage corresponding to (a + b)-(c + d) may be obtained by using the current-voltage conversion amplifier and the addition circuit as in the above. Photoelectric conversion is performed on each of the detection surfaces of the photodetectors A, B, C, and D of the detector 4. The focusing error signal generated as a result of this is a leakage of optical and electrical signals from the tracking error signal. (Hereinafter referred to as crosstalk) occurs.

FIGS. 3A and 3B are views for explaining crosstalk. FIG. 3A is a diagram showing the waveform of the tracking error signal (TE). FE of FIG. 3 (b)
Is a waveform of the focusing error signal when crosstalk does not occur. The actual focusing error signal becomes a signal in which a tracking error signal as shown by FE ′ in FIG. 3B leaks due to crosstalk. Such a focusing error signal is added to the adder 12 of FIG.
Output from

The focusing error signal FE 'is input to the analog processing circuit 2 including the error detection amplifier 6, amplified, and sent to the digital processing circuit 3. In the digital processing circuit 3, the focusing error signal from the adder 12 is processed in the procedure shown in FIG. In the A / D converter 7 of the digital processing circuit, the amplitude level of the focusing error signal is sampled at every predetermined time, and the sampled amplitude level is converted into a digital value (step 1 in FIG. 4). FIG. 3C is a diagram showing each amplitude level sampled in this way.

A digital signal processor (DSP) 8 of the digital processing circuit 3
Then, the following procedure is executed. Figure 3 now
If the signal amplitude of the tracking error signal is TE and the signal amplitude of the focusing error signal in the absence of crosstalk is FE in (a) and (b), the focusing error actually observed after the current-voltage conversion amplifier 5 will be described. Signal F
E ′ is expressed as FE ′ = FE + αt · TE (1). Here, αt is a coefficient when the change in the amplitude of the focusing error signal is viewed as a function of time, as shown in FIG. 3C, and is called a crosstalk coefficient in the time signal band. After these amplitude values are sampled, they are replaced with the relationship between the amplitude level and the frequency as shown in FIG. That is, the so-called Z transform (discrete Laplace transform) is performed on the focusing error signal (step 2 in FIG. 4). If the amplitudes in the frequency band are FEs' (actual amplitude of the focus error signal), FEs (amplitude of the focus error signal when there is no crosstalk), and TEs (amplitude of the tracking error signal), then equation (1) is obtained. Similarly, FEs ′ = FEs + αs · TEs (2) Here, αs is a coefficient that changes depending on the frequency of the focusing error signal, and will be referred to as a crosstalk coefficient in the frequency signal band.

FIG. 3D shows ideal frequency characteristics of the focusing error signal and the tracking error signal. That is, it is the frequency characteristic when there is no crosstalk. Such frequency characteristics are determined by characteristics of electric circuits and mechanical parts. Reference numeral FEf indicates the frequency characteristic of the focusing error signal, and reference numeral TEf indicates the frequency characteristic of the tracking error signal.

In the digital signal processor 8, .alpha.s is corrected according to the frequency band so that FES 'in the equation (2) approaches the frequency characteristic of the gain indicated by FEf in FIG. 3D (step 3 in FIG. 4). . FIG. 3 (f) shows the corrected FE
It is a figure which shows S '. FIG. 3F shows the relationship between the gain and the frequency, which is converted into the time signal band (converted into the relationship between time and amplitude) as shown in Expression (1). That is, Z inverse transformation is performed (step 4 in FIG. 4). Then, the amplitude level at each time is sequentially output from the digital signal processor 8. The D / A converter 9 then converts the output (digital value) from the digital signal processor 8 into an analog signal and outputs it (step 5 in FIG. 4).
The output from the D / A converter 9 becomes a focusing error signal in which crosstalk is corrected. That is, the signal is cross-talk corrected so that FE ′ = FE (3).

The crosstalk-corrected focusing error signal output from the D / A converter 9 is input to the actuator driver 10. The actuator driver 10 drives the actuator according to the level of the focusing error signal, and controls so that the focusing error signal becomes zero. Focus control is generally performed by driving the objective lens of the head. The actuator here is a drive unit for the objective lens.

For example, the analog filter and the digital filter which have been conventionally used cannot realize the arithmetic processing as shown in the equation (2), but the digital signal processor 8 is used as in the present embodiment. This enables high-speed arithmetic processing. Furthermore, equation (1),
Z conversion (discrete Laplace transform) shown in (2), (3) and FIG. 4, crosstalk correction in the frequency band, and Z inverse transform (discrete inverse Laplace transform) are possible.

Incidentally, since the focusing error signal has a signal period which is about four times as long as that of the tracking error signal, the sampling frequency at the time of A / D conversion in the A / D converter 7 is set to the signal frequency of the tracking signal. If it is set to be sufficiently large, F which is crosstalk corrected from FE '
It is possible to obtain E. In this embodiment, only the gain is mentioned in the frequency band, but it goes without saying that the phase is also improved.

Further, since the focusing and tracking quality of the servo system are improved by performing the crosstalk correction of this embodiment, the individual optical, magneto-optical head,
It is also possible to improve the variation in electrical machine difference. As described above, adjustment and phase compensation according to the frequency band of the gain of the crosstalk signal, which were very difficult with the analog processing circuit, are simplified by this embodiment, and the magneto-optical head of the magneto-optical disk device is also provided. Since it is also possible to easily absorb the individual machine-difference variations in the above, it is possible to further improve the reliability of the servo system of the magneto-optical disk device.

In this embodiment, an apparatus using a magneto-optical disk has been described, but it goes without saying that it can be applied to an apparatus using another recording medium (reproduction-only optical disk, write-once optical disk, etc.). .

[0021]

As described above, according to the present invention, it is possible to correct the leakage of the optical or electrical signal from the tracking error signal, which has been caused by the focusing error signal, and to improve the reliability of the servo system. Can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a servo control device according to an embodiment of the present invention.

FIG. 2 is a diagram showing an arrangement of photodetectors of a tracking / focusing detector of the servo controller according to the embodiment of the present invention.

FIG. 3 is a diagram for explaining correction of crosstalk occurring in a focusing error signal in the servo controller according to the embodiment of the present invention. 3A is a waveform of a tracking error signal, FIG. 3B is a waveform of a focusing error signal (FE ′) including crosstalk, and FIG. 3C is a focusing error signal including sampled crosstalk.
3D is an ideal frequency characteristic of the focusing error signal and the tracking error signal, FIG. 3E is a frequency characteristic of the focusing error signal including Z-converted crosstalk, and FIG. 3F is crosstalk correction. FIG. 6 is a diagram showing frequency characteristics of a focusing error signal obtained by performing

FIG. 4 is a diagram showing a processing procedure in a digital processing circuit of the servo controller according to the embodiment of the present invention.

[Explanation of symbols]

 1 magneto-optical head, 2 analog processing circuit, 3 digital control circuit, 4 focusing, tracking detector, 5 current-voltage conversion amplifier, 6 error detection amplifier, 7 A / D converter, 8 digital signal processor, 9 D / A conversion Vessel, 10 actuator driver, 11 actuator, 12 addition circuit.

Claims (1)

[Claims] 1. A detector for generating a focusing error signal and a tracking error signal, sampling means for sampling the amplitude level of the focusing error signal from the detector at predetermined time intervals, and sampling by the sampling means. The frequency characteristic of the amplitude level is obtained, the frequency characteristic is compared with a preset frequency characteristic and the frequency characteristic is corrected, and the amplitude level corresponding to time is calculated from the corrected frequency characteristic. A D / A converter that converts an amplitude level for each time into an analog signal and outputs the analog signal, and a driving unit that drives an actuator for focusing according to an output from the D / A converter are provided. Characteristic servo control device.