JPH10233020A - Optical disk drive - Google Patents

Abstract

(57) [Problem] In the conventional technology, it is necessary to add a dedicated sensor for detecting the displacement of the tracking actuator from the center of the optical axis in the direction crossing the track, which increases the product cost. Had become. In addition, there is a problem that a deviation from the center of the optical axis caused by a DC offset component included in the output signals of these sensors causes a new vibration. According to the present invention, a signal processing circuit including a differential amplifier or the like is added by diverting a part of a signal output from a light detection unit originally provided for focus error detection by an astigmatism method. The displacement amount of the objective lens from the center of the optical axis can be detected only by the above. In addition, even when a DC offset component is included in the displacement signal, a filter unit for reducing or removing the DC offset component is provided so that a deviation does not occur when the feedback control is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an access control method for an optical disk drive, and more particularly to a tracking actuator generated by a reaction caused by moving a slider on which an optical pickup is mounted during a seek operation in which the tracking actuator is not controlled. The present invention relates to a technology for suppressing the vibration of the data, shortening the tracking pull-in time and shortening the access time.

[0002]

2. Description of the Related Art In a conventional optical disk device, in order to suppress the vibration of a tracking actuator during a seek operation in which the tracking actuator is not controlled and to shorten an access time, for example, a light amount, a capacitance, a magnetic resistance, a vortex, etc. A dedicated sensor is added to detect the displacement of the tracking actuator from the optical axis center based on changes in current, etc., and signals are used to perform feedback control on the deviation of the tracking actuator from the optical axis center for tracking. 2. Description of the Related Art Vibration of an actuator is suppressed. One example of this method is disclosed in
6331, JP-A-59-71138, JP-A-61-187131, and the like.

[0003]

Among the vibration preventing methods described in the preceding paragraph, the methods described in JP-A-58-26331 and JP-A-59-71138 are based on the optical axis center in the direction crossing the track of the tracking actuator. It is necessary to add a dedicated sensor for detecting the displacement from the device, which has caused an increase in product cost. In each of the methods cited in the previous section, the effect of the deviation from the center of the optical axis in the direction crossing the track of the tracking actuator caused by the DC offset component which is unavoidable to be included in the output signals of these sensors is examined. There was a problem that was not.

[0004]

According to the present invention, a special sensor for detecting the displacement from the center of the optical axis in the direction crossing the track of the tracking actuator as in the above-mentioned prior art is not used. As described in JP-A-61-187131, a part of the signal output from the light detection means originally provided for focus error detection by the astigmatism method is diverted, and includes an operational amplifier and the like. The above-described displacement can be detected only by adding a signal processing circuit. Further, a filter means for reducing or removing the DC offset component is provided so that a deviation does not occur when the feedback control is performed even when the displacement amount signal includes the DC offset component.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a functional block diagram of a portion related to a function of suppressing an objective lens vibration during a seek in the optical disc device according to the first embodiment of the present invention.

The light reflected from the optical disk forms a light spot 9 on the photodetector 1, and the photodetector 1 has four divided light beams.
It outputs a current proportional to the amount of light applied to the areas 1a, 1b, 1c, 1d. The current-voltage converter 2 converts an output signal current from each region of the photodetector 1 into a voltage signal. Adder
3a is a photodetector 1b among the output signals of the current-voltage converter 2.
And the two signals corresponding to 1c are added and output. Adder
3b is a photodetector 1a of the output signal of the current-voltage converter 2.
And two signals corresponding to 1d are added and output. The subtractor 4 subtracts the output signals of the adders 3a and 3b and outputs the result. As a result, the output signal of the subtractor 4 becomes (1b + 1c)-(1a + 1d), which becomes the objective lens displacement signal 11. The high-pass filter 5 has a high-pass characteristic, and outputs a vibration component signal 13 by reducing or removing a DC component from the objective lens displacement signal 11. The changeover switch 6 performs tracking servo by controlling the position of the objective lens with a tracking error signal 10 generated by a normal method (for example, a three-spot method or a DPD method) in a steady state, and generates a signal by a method described in the present invention during a seek. This is for switching the tracking actuator drive signal so as to control the objective lens position by the vibration component signal 13 and to suppress the vibration of the objective lens. The switching operation is performed by the vibration suppression control signal 12. The tracking actuator drive circuit 7 performs power amplification, phase compensation, and the like necessary for driving the tracking actuator with the signal selected by the changeover switch 6. The tracking actuator 8 displaces the objective lens in a direction crossing the track on the optical disk by a signal from the tracking actuator drive circuit 7.

Here, the behavior of the light spot 9 during a seek will be described. When a slider on which an optical pickup is mounted is moved in a direction crossing a track in order to move a reproduction position to a target track on an optical disc, a reaction force is generated in the objective lens due to a reaction reaction of the slider.
The objective lens is displaced in the direction opposite to the movement of the slider by the acceleration generated by this reaction force. Next, when the acceleration of the movement of the slider decreases, the energy which has been accumulated as the displacement of the spring of the tracking actuator acts as a restoring force of the spring, and displaces the objective lens in the same direction as the movement of the slider. As a result, the objective lens causes free vibration in the moving direction of the slider.

When the slider is stationary, the tracking actuator is located at the center of the optical axis. Therefore, the light spot 9 is also located substantially at the center of the photodetector 1 divided into four parts.
When the objective lens moves in the direction of movement of the slider, that is, in the direction traversing the track, it moves in a direction perpendicular to the direction in which the track is projected. Therefore, when the objective lens vibrates in the moving direction of the slider as described above, the light spot 9 applied to the photodetector 1 also vibrates in a direction perpendicular to the direction in which the track is projected. Therefore, the displacement due to this vibration is detected,
By performing feedback control so as to suppress this vibration, it is possible in principle to suppress the vibration of the objective lens. The above-described method of detecting the displacement of the objective lens is similar to a conventionally known push-pull method, and is described in Japanese Patent Application Laid-Open No. 61-187131.

Now, in actually performing the feedback control, there are the following problems. That is, in the above-described method of detecting the position of the objective lens, a signal for detecting a focus error by the astigmatism method is used. Originally, only the operation guaranteed by the pickup, such as tracking error detection by the three-spot method or the like, is performed, and this method is naturally not considered at all. Therefore, when the objective lens displacement signal 11 is observed with an actual pickup, a DC offset component may be superimposed. As described above, when the tracking actuator control signal is switched by the changeover switch in a state where the DC offset component is superimposed on the feedback control signal for suppressing vibration, a step response occurs in the tracking actuator due to the DC offset component, and the tracking actuator is originally suppressed. The step vibration at this time will generate the power vibration. Therefore, in the present invention, the high-pass filter 5 is used to reduce or remove the DC offset component included in the objective lens displacement signal 11, and the objective lens position is determined by the vibration component signal 13 in which the DC offset component is reduced to a level that does not cause a problem. The above problem is avoided by controlling the vibration. High pass filter 5
In order to remove the DC offset component, the low frequency cutoff frequency may be set to, for example, several Hz.

Next, a description will be given of the vibration suppression control signal 12 for switching the changeover switch 6 to actually suppress the vibration of the tracking actuator by the vibration component signal 13 described above. FIG. 2 is a timing chart schematically showing the vibration suppression control signal 12 and the timing related thereto. As described above, since the movement of the slider is caused by the movement of the objective lens, the timing 14 at which the changeover switch 6 is switched from the steady reproduction side 6-1 to the vibration suppression side 6-2 occurs before the acceleration due to the movement of the slider is applied to the objective lens. And it is sufficient. Conversely, from the vibration suppression side 6-2 to the steady regeneration side 6-1
The timing 15 may be set after the acceleration due to the movement of the slider is not applied to the objective lens and the vibration of the tracking actuator is suppressed. Therefore, more specifically, the timing 14 may be the same as the slider driving start timing. Timing 15
May be between the end of driving of the slider and the start of tracking servo at the time of steady reproduction.

Next, a second embodiment of the present invention will be described. Since the present embodiment is the same as the first embodiment except for the characteristics of the high-pass filter 5, only the characteristics of the high-pass filter 5 will be described here, and the description of the same parts as those of the first embodiment will be omitted. I do.

FIG. 3 is a schematic diagram of the frequency characteristic for explaining the frequency characteristic of the high-pass filter 5 in the optical disk device according to the second embodiment of the present invention in relation to the frequency characteristic of the tracking actuator.

In this embodiment, the low cutoff frequency of the high-pass filter 5 (hereinafter referred to as fcl1) and the free vibration frequency of the tracking actuator (hereinafter referred to as f0).
And fcl1 ≦ f0. The reason for this is that the vibration of the tracking actuator caused by the acceleration of the slider is concentrated at frequencies near f0, and f0
This is because components other than the vicinity are relatively small. That is, by providing the relationship of fcl1 ≦ f0, the component of the frequency f0 at which the objective lens freely vibrates can pass through the high-pass filter 5 as in the first embodiment.
The vibration near f0 can be suppressed, but the frequency components lower than fcl1 cannot pass, so the frequency components lower than fcl1 of the objective lens displacement signal 11 due to the non-uniformity of the resin constituting the optical disc and the like. This is because an effect of preventing unnecessary displacement of the tracking actuator due to the above can be expected.

Next, a third embodiment of the present invention will be described. The present embodiment is the same as the first embodiment except that the high-pass filter 5 of the first embodiment is replaced by a band-pass filter. Therefore, only the characteristics of the band-pass filter are described here, and the same as the first embodiment. The description of the parts will be omitted.

FIG. 4 is a schematic diagram of the frequency characteristic for explaining the frequency characteristic of the band-pass filter in the optical disk device according to the third embodiment of the present invention in relation to the frequency characteristic of the tracking actuator.

In this embodiment, fcl2 ≦ f0 is set between the low cut-off frequency of the band-pass filter (hereinafter referred to as fcl2) and the free vibration frequency f0 of the tracking actuator.
/ M1 and the relationship between the high-frequency cutoff frequency of the band-pass filter (hereinafter referred to as fch2) and the free vibration frequency f0 of the tracking actuator is f0 × M2 ≦ fch2.
And set 1 <M1, M2 ≦ 10. The reason for this is that, as described in the second embodiment, the vibration of the tracking actuator caused by the acceleration of the slider is concentrated on the frequency near f0, and the components other than f0 are relatively small. In other words, by providing the above relationship, it becomes impossible to pass the frequency components other than the frequency f0 near the frequency at which the objective lens freely vibrates, so that unnecessary displacement of the tracking actuator due to the frequency components other than the frequency f0 is prevented. Is expected.

Next, a fourth embodiment of the present invention will be described. The present embodiment is the same as the first embodiment except that the high-pass filter 5 of the first embodiment is replaced by a band-pass filter. Therefore, only the characteristics of the band-pass filter are described here, and the same as the first embodiment. The description of the parts will be omitted.

FIG. 5 is a schematic diagram of the frequency characteristic for explaining the frequency characteristic of the high-pass filter in the optical disk device according to the fourth embodiment of the present invention in relation to the frequency characteristic of the tracking actuator.

In this embodiment, a relationship of f0 ≦ fch3 is provided between the low-pass cutoff frequency of the high-pass filter (hereinafter referred to as fch3) and the free vibration frequency f0 of the tracking actuator. The reason for this is that the sensitivity of the tracking actuator decreases by approximately -40 dB / decade at frequencies above f0, so that the gain increases at frequencies above f0 to compensate for this sensitivity change. Set. By providing the above relationship, it is possible to compensate for a decrease in the response of the objective lens in a high frequency range, so that it is possible to effectively suppress vibration at frequencies near and above the frequency f0.

[0021]

As described above, according to the present invention, a feedback control is performed by adding a simple circuit to the circuit of the conventional optical disk apparatus without adding a new objective lens position sensor, and a seek control at the time of seeking or the like is performed. Vibration of the objective lens generated when the slider is moved can be effectively reduced, and the access time can be reduced.

[Brief description of the drawings]

FIG. 1 is a functional block diagram of a part related to a function of suppressing an objective lens vibration during a seek in an optical disc device according to a first embodiment of the present invention.

FIG. 2 is a timing chart schematically showing a seek control signal and a timing related thereto in the optical disc device according to the first embodiment of the present invention.

FIG. 3 is a schematic diagram of a frequency characteristic of a high-pass filter in an optical disc device according to a second embodiment of the present invention.

FIG. 4 is a schematic diagram of a frequency characteristic of a band-pass filter in an optical disc device according to a third embodiment of the present invention.

FIG. 5 is a schematic diagram of a frequency characteristic of a high-pass filter in an optical disc device according to a fourth embodiment of the present invention.

[Explanation of symbols]

1 photodetector, 2 current-voltage converter, 3 adder, 4
... Subtractor, 5 ... High-pass filter, 6 ... Switch, 7 ... Tracking actuator drive circuit, 8 ... Tracking actuator, 9 ... Light spot, 10 ... Tracking error signal in steady state, 11 ... Object lens displacement signal, 12 ... Vibration Suppression control signal, 13: vibration component signal,
14: Start timing of the vibration suppression control signal, 15: End timing of the vibration suppression control signal.

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[Procedure amendment]

[Submission date] June 16, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

[Correction contents]

Next, a fourth embodiment of the present invention will be described. Since the present embodiment is the same as the first embodiment except for the characteristics of the high-pass filter 5 , only the characteristics of the high- pass filter will be described here, and the same parts as those of the first embodiment will be described. Is omitted.

Claims (6)

[Claims] 1. A laser beam converged by an objective lens onto a disc-shaped information recording medium on which information is recorded along a concentric or spiral track, and a reflected light from the information storage medium is received. An optical disc device for optically reproducing information by means of a photodetector means for detecting reflected light from the information recording medium having an area divided into two or more areas; Differential detection means for obtaining a difference between detection outputs, displacement amount detection means for detecting a displacement of a light spot irradiated on the information recording medium in a direction crossing a track from an output of the differential detection means, A filter means for performing a filter process on an output of the detection means, and a tracking servo actuator driven by the output from the filter means to move the light spot to the optical disc. Tracking servo control signal switching means for forming a negative feedback loop so as to control the optical axis in the direction transverse to the track of the optical system. An optical disk device, wherein feedback control is performed such that the light spot is located at the center of an optical axis in a direction crossing a track of an optical system of the optical disk device by an output from a means. 2. An optical disk apparatus according to claim 1, wherein said filter processing means has a filter characteristic for reducing or removing a DC component. 3. The filter processing means according to claim 1, which has a high-pass filter characteristic, and a low-pass cutoff frequency (hereinafter, referred to as fcl1) of the high-pass filter is substantially a free vibration frequency (hereinafter, referred to as f0) of the tracking actuator. An optical disk device characterized by having a relationship of fcl1 ≦ f0 4. The filter processing means according to claim 1, which has a high-pass filter characteristic, and a low-frequency cutoff frequency (hereinafter, referred to as fcl1) of the high-pass filter is substantially a free vibration frequency (hereinafter, referred to as f0) of the tracking actuator. ) And f1 / N ≦ fcl1 ≦ f0, and 1 <N ≦ 10. 5. The filter processing means according to claim 1, wherein the band-pass filter has a band-pass filter characteristic, and a low-pass cutoff frequency (hereinafter, fcl2) of the band-pass filter is substantially equal to a free vibration frequency f0 of the tracking actuator. Fcl2 ≤
There is a relationship of f0 / M1, and f0 × M2 ≦ fch2 between the high-frequency cutoff frequency (hereinafter, referred to as fch2) of the band-pass filter and the free vibration frequency f0 of the substantially tracking actuator.
An optical disc device characterized in that 1 <M1 and M2 ≦ 10. 6. The filter processing means according to claim 1, which has a high-pass filter characteristic, and a low cut-off frequency (hereinafter, referred to as fcl3) of the high-pass filter is substantially a free vibration frequency (hereinafter, referred to as f0) of the tracking actuator. An optical disc device characterized by having a relationship of fcl3> f0