JPH08235800A - Tracking servo - Google Patents

Abstract

PURPOSE: To provide a tracking servo device which can perform quick pull-in of a light spot to a track. CONSTITUTION: This device is provided with a speed servo means which controls relative speed of a light spot for a track through a speed arithmetic means 41 and the like of a signal processor 4. And when an OFF state of a tracking servo is shifted to an ON state in a search operation, after a frequency of a tracking error signal is lowered by performing speed servo, a tracking servo loop is closed.

Description

Detailed Description of the Invention

[0001]

[0001]

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tracking servo device for an information recording disk.

[0003]

[0002]

[0004]

2. Description of the Related Art An optical spot is irradiated onto an information recording disk (hereinafter referred to as a disk) on which information such as video and audio signals is recorded on concentric circles or spiral tracks, and its reflected light or transmitted light is used. There is an information reproducing device for reproducing recorded information. In such an information reproducing device, the light spot should be accurately traced on the track.

In addition, so-called tracking servo is performed based on the tracking error signal indicating the deviation between the track and the light spot. An example of such tracking servo is, for example, one using three beams.
Japanese Patent Laid-Open No. 49954/1975 uses one beam.
No. 60702.

[0006]

[0003]

[0007]

By the way, since there is usually a deviation, that is, an eccentricity, between the center of the disc rotation of the apparatus and the center of the disc to be reproduced, in the state where the tracking servo is not performed. The light spot will cross the track. As a result, the tracking error signal undergoes frequency modulation, and when the amount of eccentricity is large, the frequency modulation received by the tracking error signal reaches several KHz to several tens KHz. On the other hand, the response frequency of the tracking servo system is 2 KHz to 3 KH.
Since it is about z, when the tracking servo is operated in such a state, there is a problem that it takes time for the tracking servo to reach a stable state (this is called pull-in).

[0008]

Accordingly, it is an object of the present invention to provide a tracking servo device which enables a light spot to be quickly drawn into a track.

[0009]

[0005]

[0010]

In order to solve the above problems, a spindle servo apparatus according to a first aspect of the present invention moves an information reading point of a pickup toward a target recording track of an information recording disk in response to a jump command signal. And a tracking error detection means for obtaining a tracking error signal according to the deviation amount of the information reading point with respect to the recording track in the radial direction of the disk based on the reflected light from the information recording disk, and the information recording disk. A speed detection means for obtaining a speed signal proportional to the relative speed of the information reading point with respect to the recording track based on the reflected light from the information reading point and the pickup moving means bring the information reading point to the vicinity of the target recording track. At times, the relative speed of the information reading point depends on the speed signal. It is characterized in that the control so as to reduce, and a subsequent control means for controlling the position of said information reading point so allowed to reduce the bias amount of the information reading point in response to the tracking error signal.

[0011]

A spindle servo apparatus according to a second aspect is
The spindle servo apparatus according to claim 1, wherein the speed detecting means obtains the speed signal based on a cycle of the tracking error signal.

[0012]

[0007]

[0013]

In the tracking servo device of the present invention,
In order to suppress the increase in the frequency of the tracking error signal, speed servo means for controlling the relative speed in the radial direction of the light spot on the disk is provided, and when the tracking servo is switched from the off state to the on state in a search operation, first, After performing the speed servo for a predetermined time to reduce the frequency of the tracking error signal, the tracking servo is started.

[0014]

[0008]

[0015]

Embodiments of the present invention will be described below. First, the overall configuration will be described with reference to the block diagrams shown in FIGS. 1 (A) and 1 (B). The reflected light of two tracking light beams (not shown) is received and
A tracking error signal (hereinafter referred to as a TE signal) which is converted into two electric signals and obtained as a difference signal of these signals is supplied to the zero-cross detection circuit 1 and the A / D converter 5. The output of the A / D converter 5 is supplied to the signal processor 4 as a signal for tracking servo. The TAB signal obtained as the sum signal of the above two signals is supplied to the light quantity comparator 2. Zero cross detection circuit 1
Generates a TZ signal that inverts the output when the level of the TE signal becomes the center level of the AC vibration, and measures the width of the waveform of this signal (between zero cross points) by the period detection counter 3 and the direction detection circuit. Supply to 6. The cycle detection counter 3 obtains a T signal indicating the cycle of the TZ signal by counting a clock signal of a constant cycle using the TZ signal as a timing control signal, and supplies this to the speed calculation means 41 of the signal processor 4. . As shown in FIG. 1 (B), the speed calculation means 41 is composed of a reciprocal calculation circuit 41a, a positive / negative sign addition circuit 41b, and an equalizer calculation circuit 41c. The reciprocal arithmetic circuit 41a obtains an F signal representing the reciprocal of the cycle, that is, the frequency, by a predetermined arithmetic operation, and supplies this to the positive / negative sign addition circuit 41b. This F
The signal will represent the absolute value of the velocity error amount of the light spot.

[0016]

On the other hand, the TAB signal is waveform-shaped by the light quantity comparator to become a TL signal, which is supplied to the direction detection circuit 6. As described above, the TE signal is separately supplied to the direction detection circuit 6, and based on these signals, it is determined in which direction the optical spot on the disk is moving in the radial direction. The FWD / REV signal, which has a high level when the spot moves from the center of the disc toward the outer peripheral direction and has a low level when the spot moves from the outer peripheral direction toward the center, is sent to the positive / negative sign adding circuit 41b. Supply. The plus / minus sign adding circuit 41b
Based on the FWD / REV signal, positive or negative information is added to the value of the F signal to obtain a v1 signal, and the tracking actuator 10 described later operates so as to reduce the relative speed of the light spot. This v1 signal is supplied to the equalizer arithmetic circuit 7. The equalizer arithmetic circuit 7 corrects the value of the v1 signal so that the value of the v1 signal falls within an appropriate value for control of the tracking actuator, and uses the corrected value as the v2 signal of one of the signal switching circuits (not shown) of the control means 42. Supply to the input end. The output of the A / D converter 5 is supplied to the other input terminal of the signal switching circuit. The signal switcher is controlled by the control means 42. The control means 42 stops the servo operation by cutting off the data output to the D / A converter 8 in response to a jump command signal supplied from a control circuit (not shown) during a search operation, for example. Then, the slider servo system 100 is operated to roughly adjust the pickup position.
The slider 103 as a pickup moving means moves to bring the light spot to the vicinity of the target position, and the speed information of the slider 103 obtained from the low-frequency component of the tracking error signal changes the output level to the D / A converter 101. When the control means 42 detects that the moving speed of the slider 103 becomes equal to or less than a predetermined value, or when a certain time elapses based on the address difference between the jump address and the current address represented by the command signal,
The v2 signal is relayed to the D / A converter 8 for controlling the signal switching circuit to perform speed servo, for example, for a predetermined time, and then for position servo, that is, tracking servo. The signal supplied to the D / A converter is converted into a voltage signal having a level corresponding to its value and supplied to the drive circuit 9 to become a TD signal. This TD
The pickup tracking actuator 10 is driven by the signal, the light beam is deflected in the disk radial direction, and the position of the light spot is controlled. Thus, the velocity servo system and the tracking servo system are constructed. In addition,
Even if the signal switching circuit is used as an adding circuit, a certain effect can be obtained.

[0017]

Next, concrete circuit examples of the zero-cross detection circuit 1, the light quantity comparator 2 and the direction detection circuit 6 will be described with reference to FIGS. 2 (A), (B) and (C). The reflected lights of the three light beam spots S1 to S3 irradiated on the track enter the light receiving elements P1 to P3. Light receiving element P
The optical signal incident on 2 is converted into an electric signal and supplied to a video demodulation circuit (not shown). The outputs of the light receiving elements P1 and P3 are supplied to the adder circuit 11 and the subtractor circuit 12, respectively. The output of the adder circuit 11 is supplied as a TAB signal to the light quantity comparator 2, where it is waveform-shaped and supplied to the D input of the D flip-flop 13. The output of the subtraction circuit 12 is T
It is supplied to the zero-cross comparator 1 as an E signal and T
A TZ signal whose output is inverted every half cycle of the E signal is obtained. This TZ signal is supplied to the clock (hereinafter referred to as CK) input terminal of the flip-flop 13. The flip-flop 13 takes in the level of the TL signal as the Q output in response to the rise of the signal supplied to the CK input terminal. As a result, the Q output of the flip-flop 13 becomes as shown in FIG. 2 (B).
The light spot has a low level when moving in the FWD direction, and has a high level when moving in the REV direction. The Q output of the flip-flop 13 becomes the FWD / REV signal. Here, the flip-flop 13 corresponds to the direction detection circuit 6.

[0018]

Direction detection circuit 6 is shown in FIGS. 3 (A) and 3 (B).
Another configuration example of is shown. In the case of this example, since the moving direction of the spot is detected at both the rising and falling edges of the TZ signal, there is an advantage that the accuracy is improved accordingly.
That is, in the case of the direction detection circuit shown in FIG. 2 (A), the movement direction of the spot is detected every one cycle of the TE signal, but in the case of this example, it is detected every half cycle. Therefore, as a result that the period for speed detection can be shortened,
The speed servo accuracy is improved.

[0019]

In the circuit shown in FIG. 3 (A), the CK signal supplied from a clock oscillator (not shown) is, for example, a 220 KHz pulse, and passes through the CK input terminal of the D flip-flop 61 and the inverter 62. , CK input terminals of the D flip-flops 63 and 64. The TZ signal is supplied to the D input terminal of the flip-flop 61, the Q1 signal flip-flop 63 of the Q output, one input terminal of the exclusive OR 65, and the switching control input terminal of the selector 66. The Q output of the flip-flop 63 is supplied to the other input terminal of the exclusive OR 65 as the Q2 signal. The output of this exclusive OR65 is D as the R signal.
It is supplied to the CK input terminal of the flip-flop 67. The TL signal is supplied to the D input terminal of the flip-flop 67,
The Q3 signal which is the Q output thereof and the bar Q3 signal which is the bar Q output thereof are supplied to the 1C0 and 1C1 input terminals of the selector 66, respectively. The selector 66 selects the bar Q3 signal when the Q1 signal is at the high level and outputs it to the flip-flop 6
4 to the D input terminal, and when the Q1 signal is low level, Q
Three signals are selected and supplied to the D input terminal of the flip-flop 64. F to the Q output of the flip-flop 64
The WD / REV signal is obtained. An example of the waveform of each signal when the light spot moves in the FWD direction is shown in FIG. Similarly, movement in the REV direction is also detected.

[0020]

A specific circuit example of the cycle detection counter 3 will be described with reference to FIGS. 4 (A) and 4 (B). The TZ signal from the zero-cross detection circuit 1 and the CK signal from an oscillator (for example, 220 KHz) not shown are supplied to the D input terminal and the CK input terminal of the D flip-flop 31, respectively. The Q output of the flip-flop 31 is supplied to the D input terminal of the D flip-flop 32 and one input terminal of the exclusive OR 33 as the TZDP signal. CK of flip-flop 32
The inverted CK signal, the output of which is inverted by the inverter 34, is supplied to the input end, and its Q output is used as the TZDN signal, the other input end of the exclusive OR 33, one input end of the exclusive OR 35, and the D flip-flop 36. It is supplied to the input terminal. CK is applied to the CK input terminal of the flip-flop 36
Signal and its Q output is provided as the TZDP1 signal to the other input of exclusive OR 35. The output of the exclusive OR 35 is inverted by the inverter 37 to obtain C
It becomes the LR signal and is supplied to the clear input terminal of the counter 38. The counter 38 counts the pulses of the inverted CK signal and supplies the count value to the latch circuit 39, while C
The count value is reset according to the LR signal. Since the CLR signal is generated approximately every half cycle of the TZ signal, the counter 38
Updates the count value for each zero-cross section of the TE signal. The latch circuit is formed by a series of D flip-flops, and takes in the above-mentioned count value supplied to the D input in response to the ZE signal supplied to the CK input terminals thereof, and uses it as the T signal in the speed calculation circuit 41 described above. Supply. The ZE signal is the output of the exclusive OR 33, which is generated immediately before the CLR signal and holds the count value for approximately a half cycle of the TZ signal. The waveform of each signal is as shown in FIG.

In this way, the cycle detection counter 3 detects the half cycle value of the tracking error signal.

[0022]

A specific circuit of the reciprocal arithmetic circuit 41a will be described with reference to FIG. The reciprocal arithmetic circuit 41a is composed of a numerical arithmetic processor (not shown),
An arithmetic expression is selected according to the value of the input x, and the value of the reciprocal y is obtained by the approximate value calculation. In the example of FIG. 5, the reciprocal numbers are obtained by using five linear approximation formulas, but the calculation characteristics of these are appropriately set as necessary.

[0023]

A sixth configuration example of the equalizer arithmetic circuit 41c
Description will be made with reference to the drawings. The v1 signal from the plus / minus sign adding circuit 41b is supplied to the coefficient circuit 411. Coefficient circuit 4
11, the coefficient K is set to 0.0625, and the current value v1 (n) of the v1 signal is multiplied by the coefficient K to obtain a value K · v1 (n), which is one of the input terminals of the adder circuit 412. Is supplied to. The output of the previous value calculation circuit including the delay circuit 413 and the coefficient circuit 414 is supplied to the other input terminal of the addition circuit 412. Output v of this arithmetic circuit 412
2 (n) is supplied to the coefficient circuit 414. Coefficient circuit 41
The coefficient Ko of 4 is set to 0.935, for example,
The value Ko · v2 (n) is supplied to the delay circuit 413.
The delay circuit 413 delays this value for a predetermined time to obtain the previous value Ko · v2 (n−1), and its delay time characteristic Z is expressed as exp (s · T). Here, T is a sampling period, for example, a horizontal synchronization period 63.5.
The half cycle of μSec is set to 31.778 μSec. Therefore, v1 supplied to this equalizer arithmetic circuit
The signal is v2 (n) = K · v1 (n) + Ko · v2 (n
-1) is processed into a v2 signal, and D / A
It is supplied to the converter 8.

[0024]

The difference between the operation of the tracking servo device of the present invention and the operation of the conventional tracking servo device will be described with reference to FIGS. 7 (A) and 7 (B). First,
FIG. 7 (A) shows an example of a conventional apparatus. When the tracking servo is turned on at the final stage of the search from the state where the tracking servo is turned off and the search is performed, the high frequency component of the TE signal is the tracking position. As a result of exceeding the response frequency of the servo, the convergence of the TD signal that drives the tracking actuator is slow, and it takes time (t1) to pull in the track.

[0025]

FIG. 7B shows an example of the apparatus of the present invention. When the tracking servo and the velocity servo are turned off and the search is performed, the search reaches the final stage.
The control means 42 first performs speed servo until the speed servo is turned on for a predetermined time or until the relative speed of the spot becomes a predetermined value or less. Due to this speed servo, the frequency of the TE signal drops below the response frequency of the tracking servo system. After that, the tracking servo is switched to the tracking-in state in a short time (t2).

Thus, even when the tracking error signal has a high frequency due to eccentricity or vibration of the disk. The velocity is accurately detected for each half cycle of the tracking error signal and based on this half cycle, and an appropriate servo is applied to the tracking actuator by this velocity.

[0027]

When the speed is detected, the differential signal of the tracking error signal can be used as the speed information, but such a method has a problem that the level of the speed information changes due to a change in the reflectance of the disk surface or a scratch. is there. On the other hand, according to the present invention, since the speed is detected based on the cycle of the tracking error signal, such a problem can be reduced.

[0028]

It is possible to improve the position control accuracy of the pickup by using the detected speed servo signal as a control signal for the carriage servo in the search operation.

[0029]

In the embodiment, the tracking error signal is obtained by three beams, but the same tracking error signal can be obtained by one beam.

[0030]

[0021]

[0031]

As described above, in the tracking servo apparatus of the present invention, when the loop of the tracking servo is closed, the speed servo is performed in advance to reduce the relative speed of the optical spot in the disk radial direction for tracking. Since the frequency of the error signal is lowered and then the tracking servo loop is closed, the track lead-in time at the information reading point can be shortened.

[Brief description of drawings]

FIG. 1 is a block circuit diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration example of a zero-cross detection circuit 1, a light amount comparator 2, and a direction detection circuit 6, and signal waveforms of respective parts thereof.

FIG. 3 is a diagram showing another configuration example of the direction detection circuit 6 and signal waveforms of respective parts thereof.

FIG. 4 is a diagram showing a configuration example of a cycle detection counter 3 and a signal waveform of each part thereof.

FIG. 5 is a diagram showing output characteristics of an inverse arithmetic circuit 41a.

FIG. 6 is a block circuit diagram showing a configuration example of an equalizer arithmetic circuit 41c.

FIG. 7 is a waveform diagram for explaining the difference in operation between the conventional device and the device of the present invention.

[Explanation of symbols for main parts]

 DESCRIPTION OF SYMBOLS 1 zero cross detection circuit 2 light quantity comparator 3 synchronization detection counter 4 signal processor 41 speed calculation means 41a reciprocal calculation circuit 41b positive / negative sign addition circuit 41c equalizer calculation circuit 42 control means 6 direction detection circuit 10 tracking actuator 103 slider

Claims (2)

[Claims] 1. A pickup moving means for moving an information reading point of a pickup toward a target recording track of an information recording disk in response to a jump command signal, and a recording track with respect to a recording track based on reflected light from the information recording disk. Tracking error detecting means for obtaining a tracking error signal according to the deviation amount of the information reading point in the disc radial direction; and proportional to the relative speed of the information reading point with respect to the recording track based on the reflected light from the information recording disc. When the information reading point reaches the vicinity of the target recording track by the speed detecting means for obtaining the speed signal and the pickup moving means, the relative speed of the information reading point is controlled so as to be reduced according to the speed signal. , Then read the information according to the tracking error signal A tracking servo device, comprising: a control unit that controls the position of the information reading point so as to reduce the deviation amount of the jump point. 2. The tracking servo device according to claim 1, wherein the speed detecting means obtains the speed signal based on a cycle of the tracking error signal.