JPH0281327A - Seek system for optical disk - Google Patents

Abstract

PURPOSE:To allow positioning with high accuracy by driving only the rough moving mechanism to move the greater part of a seek operation and simultaneously driving both the fine moving mechanism and simultaneously driving both the fine moving mechanism and rough moving mechanisms upon attainment of the speed at which a light spot decelerates and movement can be made by a two-stage servo system. CONSTITUTION:Mode selecting switches 10, 12 are held connected to a C side before a seek error 106 attains a preset value N and, therefore, a linear motor driver 20 drives a linear motor 14 at a relative speed by a signal 116 and a linear motor control signal 118. The mode selecting switches 10, 12 are selected to the D side when the light spot moves and the seek error 106 falls to the preset value N or below. The relative speed error 114 is then made into a galvanomirror control signal 120 and a galvanomirror driver 22 begins to drive a galvanomirror 16. The seek operation is thus executed at the high speed with the high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a seek method for positioning a recording/reproducing light spot of an optical disc device on a target track.

[Conventional technology]

The seek method, which positions the recording/reproducing light spot on the target track by counting cross-track pulses, uses a two-stage method that drives only the coarse movement mechanism, and the two-stage method that drives both the fine movement mechanism and the coarse movement mechanism simultaneously. The Bo method is known.

Incidentally, related devices of this type include, for example, Japanese Patent Application Laid-Open No. 58-91536.

[Problem to be solved by the invention]

Since the track pitch of optical discs is extremely small,
In order to perform positioning without being affected by external vibrations or optical disk eccentricity, it is necessary to construct a positioning servo system with high gain and high bandwidth. However, in the method in which only the coarse movement mechanism is driven, it is difficult to construct a high gain, high band servo system because the mechanical resonance frequency of the coarse movement mechanism is low, and highly accurate positioning is not possible.

On the other hand, in the two-stage servo system in which both the fine movement mechanism and the coarse movement mechanism are driven simultaneously, the resonant frequency of the fine movement mechanism determines the band of the entire servo system. Since this resonant frequency is sufficiently high, it is possible to construct a positioning servo system with high gain and high band. However, in the two-stage thrust system, the precision detection mechanism first follows the slight displacement, and the overall movement speed is approximately proportional to the displacement of the precision detection mechanism, but due to optical limitations, The displacement of the fine inspection mechanism cannot be made too large,
There was a problem with slow seek speed.

[Means to solve the problem]

In the present invention, most of the seek operation is performed by driving only the coarse movement mechanism, and when the light spot decelerates to a speed that can be moved in a two-step speed mode, both the fine movement mechanism and the coarse movement mechanism are activated. are simultaneously driven to position the target track.

[Effect]

High-precision positioning is required only immediately before track pull-in, and most seek operations focus only on movement speed, and do not require extremely high servo bandwidth.
During this period, only the coarse movement mechanism is controlled and driven in a low servo band. It is important that the process from settling operation to track retraction is not affected by track eccentricity or external vibration.
Movement speed does not have to be very high. Therefore, during this period, both the fine detection mechanism and the coarse movement mechanism are driven at the same time and controlled in a high servo band to ensure tracking accuracy.

〔Example〕

Embodiment 1 of the present invention will be described in detail with reference to FIG.

Number of cross tracks from the light spot to the target track: 10
0 is set in error counter 2.

The error counter 2 is counted down by the cross-track pulse 104 generated by the cross-track pulse generation circuit 4 from the track deviation error signal 102. The seek error 106, which is the value of the error counter 2, is determined by the nonlinear D/
The A converter 6 generates a speed command 108. Also, the seek error 106 is input to the comparator 8, and the output 110 of the comparator 8 connects the mode changeover switches 10 and 12 to the C side when the seek error 106 is larger than the preset value N. When the value is N or less, the mode changeover switches 10 and 12 are connected to the D side. As will be described in detail below, when the mode changeover switches 1o and 12 are connected to the C side, the linear motor 14, which is a coarse movement mechanism for the light spot, is driven independently, and the mode changeover switch 1o and 12 are connected to the C side. and 12
When is connected to the D side, the galvanometer mirror 16 and the linear motor 14, which are the precision movement mechanism of the optical switch, perform double servo operation.

The differential amplifier 18 determines a relative velocity error 114, which is the difference between the relative velocity 112 between the optical disc track and the optical spot and the velocity command 108. The mode selector switch 10.12 is pressed until the seek error 106 reaches the preset value N.
is connected to the C side, so the linear motor driver 20 drives the linear motor 14 at a relative speed via the signal 116 and the linear motor control signal 118.

The light spot moves and the seek error 106 becomes the preset value N.
When the following happens, the mode selector switch 10.12 is switched to the D side, the relative velocity error 114 becomes the galvano mirror control signal 120, and the galvano mirror driver 22 starts driving the galvano mirror 16. The deflection angle of the galvano mirror 16 is detected by a deflection angle detector 24, and its output becomes a linear motor speed command 122. Various optical sensors are known for galvano mirror deflection angle detectors. The difference between the linear motor speed command 122 and the recording/reproducing head absolute continuity 124 based on the optical disk device base is the difference between the differential amplifier 2
6, this absolute speed error 126 becomes the linear motor control signal 118, and the linear motor driver 20 wears out the linear motor so as to reduce the deflection angle of the galvano mirror. As a result, the speed of the light spot is controlled relative to the track of the optical disk, and the absolute speed of the recording/reproducing head is controlled so that the deflection angle of the galvano mirror 16 becomes small.

In the present invention, the absolute speed 124 of the recording/reproducing head with respect to the base of the optical disc device is detected by a conventionally known electromagnetic tachometer or electronic tachometer.

Example 2 of the present invention will be described using FIG. 2.

In the second embodiment, absolute speed control is performed during movement using only the coarse movement mechanism. Since the speed during this movement is fast, there is almost no effect of eccentricity of the optical disk, and no problem occurs even if control is performed using absolute speed without using relative speed.

Number of cross tracks from the light spot to the target track: 10
0 is set in error counter 2.

The error counter 2 is counted down by the cross-track pulse 104 generated by the cross-track pulse generation circuit 4 from the track deviation error signal 102. The seek error 106, which is the value of the error counter 2, is determined by the nonlinear D/
A speed command 108 is generated by the A converter 6. Also, the seek error 106 is input to the comparator 8, and the output 110 of the comparator 8 connects the mode changeover switches 11 and 12 to the C side when the seek error 106 is larger than the preset value N. When the value is less than N, mode changeover switches 11 and 12 are connected to the D side. As will be explained in detail below, when the mode changeover switches 11 and 12 are connected to the C side, the linear motor 14, which is the coarse movement mechanism for the light spot, is driven independently; 12 is connected to the D side, the galvanometer mirror 16, which is a mechanism for finely inspecting the light spot, and the linear motor 14 perform double servo operation.

Until the seek error 106 reaches the preset value N, the mode selector switch 11.12 is connected to the C side, so the speed command 108 becomes the signal 109.

A difference signal 117 between the absolute speed 124 of the recording and reproducing head with respect to the base of the optical disk device as a reference is obtained by the differential amplifier 19, and becomes a linear motor control signal 118 via the mode changeover switch 12. is the absolute speed error.

The light spot moves and the seek error 106 becomes the preset value N.
When the following happens, the mode selector switches 11 and 12 are switched to the D side, the speed command 108 becomes the signal 111, the differential amplifier 21 calculates the difference signal 121 between the relative speed 112 of the optical disc track and the optical spot, and the galvanometer The mirror driver 22 starts driving the galvano mirror 16. The deflection angle of the galvano mirror 16 is detected by a deflection angle detector 24, and its output becomes a linear motor speed command 122.

The difference between the linear motor speed command 122 and the recording/reproducing head absolute speed 124 with respect to the optical disk device base is determined by the differential amplifier 26, and this absolute speed error 126 is sent to the linear motor control signal 1 via the mode changeover switch 12.
18, and the linear motor driver 20 drives the linear motor 14 so as to reduce the deflection angle of the galvano mirror 16. As a result, the speed of the light spot is controlled relative to the track of the optical disk, and the absolute speed of the recording/reproducing head is controlled so that the deflection angle of the galvano mirror 16 becomes small.

FIG. 3 shows a method for determining the relative velocity between the optical disc track and the optical spot used in the present invention.

The cross-track pulse 104 is transmitted through the frequency/voltage converter 3o.
The polarity becomes the quantized position differential signal 300 with positive polarity, and the polarity becomes the quantized position differential signal 300 with negative polarity after passing through the inverter 32
It becomes 02. Linear motor current detection signal 304 passes through amplifier 34 and becomes linear motor current signal 306. The galvano-mirror current detection signal 308 passes through the filter 36 and becomes a linear motor conversion current signal 310. Here, the transfer function G (S) of the filter is G (S) = KS''/ (5 for JS'' + BS +), where J is the moment of inertia of the galvano mirror, B is the viscous drag coefficient, Ks is the spring constant, and K is a suitable gain constant.

This filter G(S) converts the current of the galvano mirror into the current of the near motor.

When the seek direction signal 314 is positive, the recording/reproducing head and the optical spot are driven toward the outer circumference of the optical disk, and the linear motor current signal 306 and the linear motor conversion current signal 310 are driven.
is configured so that it is positive. At this time, the polarity changeover switch 38 is connected to the positive quantized position differential signal 300 side by the seek direction signal 314, and its output 3
12 is added to the linear motor current signal 306 and the linear motor converted current signal 310 by the adder 40 to obtain an addition signal 31.
4, which passes through the first-order low-pass filter 42 which also serves as an integrator, and becomes a positive relative velocity signal 112. When the seek direction signal 314 is negative, the linear motor current signal 306 and linear motor conversion current signal 310 are negative, the polarity changeover switch 38 is connected to the negative quantized position differential signal 302 side, and the relative speed signal 112 is becomes negative.

The pass band of the first-order low-pass filter 42 is set to be equal to or lower than the rotational frequency of the optical disk, and the low-frequency components of the relative velocity including the effects of eccentricity etc. can be obtained from the output 312, so that the relative velocity The high-frequency component of
It can be obtained by integrating by 2.

〔Effect of the invention〕

As described above, according to the present invention, when counting and seeking cross-track pulses, the mechanical resonance frequency of the coarse movement mechanism is not affected, and both the fine movement mechanism and the coarse movement mechanism are simultaneously driven. This solves the problem of slow seek speed in the step-by-step method and achieves high-speed, high-precision seek operations.

[Brief explanation of the drawing]

FIG. 1 is a diagram explaining Embodiment 1 of the present invention, and FIG.
FIG. 3 is a diagram illustrating a second embodiment of the present invention, and is a diagram illustrating a method for determining the relative velocity between a track of an optical disc and a light spot. 3ρ-・-F/r history 32-A to °゛-evening 3t--・7a ulta 3♂----70,000-position Δtsuke 3θ--・-Caro thickness a gu 2-・-7 support IJ'F-

Claims (1)

[Claims] 1. From at least one of the track deviation error signal and the total reflected light amount signal, a cross-track pulse is generated that is output every time the optical spot crosses a track on the optical disk, and this is counted to move the optical spot to the target track. In the optical disc seek method for positioning, the relative movement speed between the optical disc track and the optical spot, or the absolute speed of the recording/reproducing head relative to the base of the optical disc device, during the period until the optical spot reaches a very short distance from the target track. Movement is performed by applying the feedback of the relative movement speed between the optical disc track and the optical spot to the fine movement mechanism, and then applying the feedback of the relative movement speed between the optical disc track and the optical spot to the fine movement mechanism to drive only the coarse movement mechanism. An optical disc seek method in which the absolute velocity of the recording/reproducing head is fed back to the coarse movement mechanism to drive both the fine movement mechanism and the coarse movement mechanism.