JP3858897B2 - Optical disc apparatus and objective lens driving method - Google Patents

Description

The present invention relates to an access control method for an optical disk apparatus, suppress the vibration of the tracking actuators occurring in particular reaction force produced by moving the slider the optical pickup is mounted at seek the tracking servo is not applied or the like to the tracking actuator Thus, the present invention relates to a technique for shortening access time by shortening tracking pull-in time.

  In the conventional optical disk apparatus, in order to reduce the access time by suppressing the vibration of the tracking actuator at the time of seeking when the tracking actuator is not controlled, for example, from the change in light quantity, capacitance, magnetic resistance, eddy current, etc. A dedicated sensor that detects the displacement of the tracking actuator from the center of the optical axis is added, and the signals from these sensors are used to control the tracking actuator's deviation from the center of the optical axis to control the tracking actuator's vibration. To be done. An example of this method is disclosed in Patent Documents 1, 2, and 3.

JP 58-26331 A

JP 59-71138 A JP-A-61-187131

  Of the vibration prevention methods described in the previous section, the methods described in Patent Documents 1 and 2 require the addition of a dedicated sensor for detecting the displacement from the center of the optical axis in the direction crossing the track of the tracking actuator. , Which was causing the product cost to rise. In addition, any of the methods cited in the previous section examines the effect of deviation from the center of the optical axis in the direction crossing the track of the tracking actuator caused by the DC offset component that is unavoidable to be included in the output signals of these sensors. There was a problem that was not done.

In the present invention, the drive control for suppressing the objective lens vibration of the objective lens, and started in response to the drive start before or slider acceleration by the movement of the slider is applied to the objective lens, even after the drive-end of the slider tracking The process ends before the control unit starts controlling the position of the objective lens.

According to the present invention as described above it is possible to effectively reduce the vibration of the Ku pair objective lens such that adding a new objective lens position sensor, it is possible to shorten the access time.

  Embodiments 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 objective lens vibration when a tracking servo is not applied to a tracking actuator at the time of seeking or the like in the optical disc apparatus according to the first embodiment of the present invention.

The reflected light from the optical disk creates a light spot 9 on the photodetector 1, and the photodetector 1 outputs a current proportional to the amount of light irradiated to each of the divided four regions 1a, 1b, 1c, 1d. The current-voltage converter 2 converts the output signal current from each region of the photodetector 1 into a voltage signal. The adder 3a adds two signals corresponding to the photodetectors 1b and 1c among the output signals of the current-voltage converter 2 and outputs the result. The adder 3b adds two signals corresponding to the photodetectors 1a and 1d among the output signals of the current-voltage converter 2 and outputs the result. The subtracter 4 subtracts the output signals of the adders 3a and 3b and outputs the result. As a result, the output signal of the subtracter 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 direct current component with respect to the objective lens displacement signal 11. Changeover switch 6, the steady-state controls the objective lens position performs tracking servo by a tracking error signal 10 generated in the usual way (for example, three spot method or DPD method), the tracking servo to the tracking actuator such as during a seek When not applied , the tracking actuator drive signal is switched so as to control the objective lens position with the vibration component signal 13 to suppress the vibration of the objective lens, and the switching operation is performed with the vibration suppression control signal 12. . The tracking actuator drive circuit 7 performs power amplification, phase compensation, etc. 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 when the tracking servo is not applied to the tracking actuator during seeking or the like will be described. When the slider on which the optical pickup is mounted is moved in the direction crossing the track in order to move the reproduction position to the target track on the optical disc, a reaction force is generated in the objective lens due to the reaction of the slider movement. The objective lens is displaced in the direction opposite to the movement of the slider by the acceleration generated by the reaction force. Next, when the acceleration of the movement of the slider decreases, the energy accumulated until then as the displacement of the spring of the tracking actuator acts as a restoring force of the spring, and the objective lens is displaced 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.

Now, when the slider is stationary, the tracking actuator is at the center of the optical axis, so the light spot 9 is also almost in the center of the photodetector 1 divided into four parts, but the objective lens crosses the moving direction of the slider, that is, across the track. When moving in the direction to move, the track moves in a direction perpendicular to the projected direction. 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, it is possible in principle to suppress the vibration of the objective lens by detecting the displacement due to the vibration and performing feedback control so as to suppress the vibration. The method for detecting the displacement of the objective lens described above is similar to the conventionally known push-pull method, and is described in JP-A-61-187131. In the present embodiment, the photodetector is described as being divided into four parts. However, if the displacement in the direction crossing the track of the light spot can be detected by differential detection of the divided areas, the photodetector is divided into two or more. An optical detector may be used.

When actually performing feedback control, there are the following problems. In other words, the objective lens position detection method described above uses a signal for focus error detection by the astigmatism method, but in an ordinary optical pickup, adjustment performed after manufacture is performed by the focus error detection method by the astigmatism method. The tracking error detection by the three-spot method and the like are performed only for the operation guaranteed by the pickup, 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 the vibration, a step response is generated in the tracking actuator due to the DC offset component, which is inherently suppressed. The step response at this time will generate the power vibration. For this reason, in this method , 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 problem-free level. Occurrence of the above problem is avoided by controlling and suppressing vibration. If the characteristic of the high-pass filter 5 is to remove the DC offset component, the low-frequency cut-off frequency may be several Hz, for example.

Next, the vibration suppression control signal 12 for switching the changeover switch 6 to actually suppress the vibration of the tracking actuator with the above-described vibration component signal 13 will be described. FIG. 2 is a timing chart schematically showing the vibration suppression control signal 12 and the timing related thereto. As described above, the cause of the objective lens vibration is the movement of the slider when the tracking servo is not applied to the tracking actuator at the time of seek or the like. Therefore, the changeover switch 6 is changed from the steady reproduction side 6-1 to the vibration suppression side 6-2. The timing 14 to be performed may be before the acceleration due to the movement of the slider when the tracking servo is not applied to the tracking actuator at the time of seeking or the like is applied to the objective lens. Conversely, the timing 15 from the vibration suppression side 6-2 to the steady reproduction side 6-1 may be 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 simultaneous with the drive start timing of the slider. Further, the timing 15 may be from the end of driving of the slider to the start of tracking servo during steady reproduction.

  Next, a second embodiment of the present invention will be described. Since this 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. To do.

  FIG. 3 is a schematic diagram of frequency characteristics for explaining the frequency characteristics of the high-pass filter 5 in association with the frequency characteristics of the tracking actuator in the optical disc apparatus according to the second embodiment of the present invention.

  In this embodiment, a relationship of fcl1 ≦ f0 is provided between the low-pass cutoff frequency (hereinafter referred to as fcl1) of the high-pass filter 5 and the free vibration frequency (hereinafter referred to as f0) of the tracking actuator. This is because 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 the vicinity of f0 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, so that the vibration near f0 is suppressed. However, since the frequency component lower than fcl1 cannot pass, unnecessary displacement of the tracking actuator due to the frequency component lower than fcl1 of the objective lens displacement signal 11 due to the non-uniformity of the resin constituting the optical disk, etc. It is because the effect which prevents this can be expected.

  Next, a third embodiment of the present invention will be described. Since the present embodiment is the same except that the high-pass filter 5 of the first embodiment is replaced with a bandpass filter, only the characteristics of the bandpass filter will be described here and the same as the first embodiment. The description about the part is omitted.

  FIG. 4 is a schematic diagram of frequency characteristics for explaining the frequency characteristics of the bandpass filter in the optical disk apparatus according to the third embodiment of the present invention in relation to the frequency characteristics of the tracking actuator.

  In this embodiment, a relationship of fcl2 ≦ f0 / M1 is provided between the low-pass cutoff frequency (hereinafter referred to as fcl2) of the bandpass filter and the free vibration frequency f0 of the tracking actuator, and the high-pass of the bandpass filter. A relationship of f0 × M2 ≦ fch2 is established between the cutoff frequency (hereinafter referred to as fch2) and the free vibration frequency f0 of the tracking actuator, and 1 <M1, M2 ≦ 10 is set. This is because, 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 near f0 are relatively small. In other words, by providing the above relationship, it becomes impossible for the objective lens to pass other than the frequency component in the vicinity of the frequency f0 at which the objective lens vibrates freely. Therefore, it is possible to prevent unnecessary displacement of the tracking actuator due to the frequency component other than in the vicinity of f0. Because it can be expected.

Next, a fourth embodiment of the present invention will be described. For this embodiment, except the characteristics of the high-pass filter 5 of the first embodiment is the same, be described here and the characteristics of the high-pass filter, a description of the same parts as the first embodiment is omitted To do.

  FIG. 5 is a schematic diagram of frequency characteristics for explaining the frequency characteristics of the high-pass filter in association with the frequency characteristics of the tracking actuator in the optical disc apparatus according to the fourth embodiment of the present invention.

  In this embodiment, a relationship of f0 ≦ fch3 is provided between the low-pass cutoff frequency (hereinafter referred to as fch3) of the high-pass filter and the free vibration frequency f0 of the tracking actuator. The reason for this is that the sensitivity of the tracking actuator decreases at approximately -40 dB / decade at frequencies above f0, so the low-pass cutoff frequency of the high-pass filter increases the gain 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 the high frequency range, so that vibration suppression in the vicinity of the frequency f0 and higher frequencies can be effectively performed.

The functional block diagram of the part in connection with the function which suppresses the objective lens vibration at the time of the seek in the optical disc apparatus of the 1st Example of this invention. 2 is a timing chart schematically showing a seek control signal and timing related thereto in the optical disc apparatus according to the first embodiment of the present invention. The schematic diagram of the frequency characteristic of the high-pass filter in the optical disk apparatus of the 2nd Example of this invention. The schematic diagram of the frequency characteristic of the band pass filter in the optical disk apparatus of the 3rd Example of this invention. The schematic diagram of the frequency characteristic of the high-pass filter in the optical disk apparatus of the 4th Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photodetector 2 Current-voltage converter 3 Adder 4 Subtractor 5 High pass filter 6 Changeover switch 7 Tracking actuator drive circuit 8 Tracking actuator 9 Light spot 10 Constant tracking error signal 11 Objective lens displacement signal 12 Vibration suppression control signal 13 Vibration component signal 14 Start timing of vibration suppression control signal 15 End timing of vibration suppression control signal

Claims (8)

An optical pickup having an objective lens for irradiating a laser beam onto an information recording medium having a track;
A signal processing circuit that outputs a vibration component signal of the objective lens based on an output signal from the optical pickup;
A slider capable of moving the optical pickup in a transverse direction of the track;
Tracking control means for controlling the position of the objective lens so that the laser beam is irradiated along the track based on the output signal;
Control means for performing drive control of the objective lens that suppresses vibration of the objective lens based on the vibration component signal, and the control means performs drive control of the objective lens, and acceleration caused by movement of the slider is An optical disc apparatus, which starts before being applied to an objective lens, and ends after the end of driving of the slider and before the start of position control of the objective lens by the tracking control means.   2. The optical disc apparatus according to claim 1, wherein the position control of the objective lens by the tracking control unit is terminated when the control unit starts driving control of the objective lens. An optical pickup having an objective lens for irradiating a laser beam onto an information recording medium having a track;
A signal processing circuit that outputs a vibration component signal of the objective lens based on an output signal from the optical pickup;
A slider capable of moving the optical pickup in a transverse direction of the track;
Tracking control means for controlling the position of the objective lens so that the laser beam is irradiated along the track of the information recording medium based on the displacement signal;
Control means for performing drive control of the objective lens that suppresses vibration of the objective lens by the vibration component signal, and the control means starts drive control of the objective lens in response to the start of driving of the slider. An optical disc apparatus that ends after the end of driving of the slider and before the start of position control of the objective lens by the tracking control means.   4. The optical disc apparatus according to claim 3, wherein the position control of the objective lens by the tracking control unit is terminated when the control unit starts driving control of the objective lens. An optical pickup having an objective lens for irradiating a laser beam onto an information recording medium having a track;
A signal processing circuit that outputs a vibration component signal of the objective lens based on an output signal from the optical pickup;
A slider capable of moving the optical pickup in a transverse direction of the track, and controlling the position of the objective lens so that the laser light is irradiated along the track based on an output signal from the optical pickup. An objective lens driving method for an optical disc apparatus for performing
Based on the vibration component signal, drive control of the objective lens to suppress the vibration of the objective lens,
The drive control of the objective lens is started before acceleration due to the movement of the slider is applied to the objective lens, and is ended after the drive of the slider is finished and before the position control of the objective lens is started by the tracking control means. An objective lens driving method for an optical disk device, characterized in that:   6. The objective lens driving method for an optical disc apparatus according to claim 5, wherein the position control of the objective lens is terminated when the objective lens drive control is started. An optical pickup having an objective lens for irradiating a laser beam onto an information recording medium having a track;
A signal processing circuit that outputs a vibration component signal of the objective lens based on an output signal from the optical pickup;
A slider capable of moving the optical pickup in a transverse direction of the track, and controlling the position of the objective lens so that the laser light is irradiated along the track based on an output signal from the optical pickup. An objective lens driving method for an optical disc apparatus for performing
Based on the vibration component signal, drive control of the objective lens to suppress the vibration of the objective lens,
An objective lens drive control method for an optical disc apparatus, wherein the objective lens drive control is started in response to the start of driving of the slider, and is ended after the end of driving of the slider and before the start of position control of the objective lens .   8. The objective lens driving method for an optical disc apparatus according to claim 7, wherein the position control of the objective lens is terminated when the objective lens drive control is started.

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