JPS62140247A - Tracking servo controller - Google Patents

Abstract

PURPOSE:To execute a stable tracking servo without malfunction with respect to the reproduction of a recording medium with distortion by forming a sine signal corresponding to track crossing executed on the basis of the 4D signal of error information used for following surface vibration and inhibiting the servo following from being switched until the wave number attains the prescribed value. CONSTITUTION:A tracking error from a terminal 1 is supplied through a loop switch 3 and an amplifier 4, and the tracking servo is executed through a tracking drive device 5. On the other hand, a differentiator 7 and a detector 8 process the 4D signal from a terminal 6 to generate a sine wave over a threshold level corresponding to the track crossing, and a counter 9 counts the said wave. Unless the counted value reaches the prescribed Grade 5 value value during a fixed period, an n-time detection latch circuit 10 outputting a signal changing over the switch 3 never outputs the signal, and the changeover of the servo following to the surface vibration following is inhibited. Accordingly the stable tracking servo without malfunction, etc., caused by the surface vibration following can be executed with respect to the recording medium containing distortion.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an optical reading device, and particularly to a control device that performs stable tracking servo.

[Background of the invention]

As described in Japanese Unexamined Patent Publication No. 54-33724, the conventional device differentiates a 4D sum signal, which is a low frequency component of the sum of detection signals for detecting an error signal for surface runout, so that the light beam can track the track. The switching part of the transfer function at the positive feedback slope of the racking error to 1 is changed depending on the speed of crossing the .

This means that the stabilization effect increases as the track is displaced due to disturbances and the moving speed is high, that is, the 1-racking error and the frequency of the 4D sum signal increases.

This stabilizing effect is required at frequencies of approximately 3 KHz or higher, at which the tracking ability of the tracking servo decreases. General recording media have various track distortions.

FIG. 2 shows a 1-racking error waveform (a) and a 4D sum signal (b) when a recording medium with track distortion is reproduced by a tracking servo that is not controlled by the 4D sum signal. The main frequency component of the tracking error at this time is 3 kHz to 4 kHz, and the tracking servo follows this distortion. Here, if the 4D sum signal is detected at the limit voltage vth and the tracking servo is not controlled, the tracking servo will not follow this distortion and the track will be misaligned. As described above, switching the tracking servo transfer function using the 4D sum signal is effective for stable pull-in due to track deviation due to disturbance, but produces undesirable results in normal playback of a distorted recording medium.

[Purpose of the invention]

The present invention eliminates the above-mentioned drawbacks and has stable normal playback and stable pull-in against track deviation caused by disturbance.
The present invention aims to provide a racking servo control device.

[Summary of the invention]

In order to achieve the above object, the present invention prevents the tracking servo from being inactivated from one to five times after the first detection of the 4D sum signal within a certain period of time within one rotation of a rotating recording medium. It is.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG.

A tracking error signal for tracking 1 to 6 of the recording medium is input to terminal 1. During normal playback, this signal obtains the transfer characteristics necessary for the servo with phase compensation 2,
The loop switch 3 is closed, and the signal is amplified by the amplifier 4 and applied to the tracking drive coil 5 to perform tracking.

Further, a 4D sum signal obtained by removing the information signal of the sum signal of the error signal detector for tracking the vibration using a low-pass filter is input to the terminal 6.

Now, as shown in FIG. 3, time t. This is the waveform when the light beam crosses the track due to disturbances. Figure 3 (
3(a) is a tracking error signal inputted to terminal 1, and FIG. 3(b) is a 4D sum signal inputted to terminal 6. During normal playback, time t.

The 4D sum signal before was V. DC level.

Next, time t. The subsequent 4D sum signal is V between tracks. is detected. This 4D sum signal has a level V by removing the DC component in a differentiator 7. becomes a sinusoidal waveform of ov,
The signal is input to the detector 8 and output as a time pulse exceeding the limit value vth. This pulse is input to counter 9 and becomes 0
The n-th pulse is outputted by the pulse detection latch 10, and when this latch signal and the pulse of the detector 8 match in the determination circuit 11, this output opens the loop switch 3 and makes the tracking servo uncontrolled. Also.

The pulse from the detector 8 causes the latch 13 to output a latch signal to put the counter 14 into the operating state, and while the detector 8 is outputting the pulse, the counter 14 is put into the reset state. When the pulse of the detector 8 disappears, the counter 14 starts to operate and the fixed time detection circuit 12 resets the counter 9.0 times detection latch 10 and latch 13 after a certain period of time.
4 and return to the initial state.

As shown in Fig. 3(b), the 4D sum signal is
When the input signal exceeds th, the counter 14 is reset by the pulse from the detector 8, and thus detection is performed for a fixed period of time from the fall of the last pulse. FIG. 3(c) is an example in which the 0-time detection latch 10 detects the fourth time, and the tracking servo is rendered uncontrolled on the fourth and fifth times when the 4D sum signal exceeds vth.

By having the circuit configuration as explained above, vth
Stable normal reproduction is possible even on a recording medium with distortion that generates a 4D sum signal exceeding .

Furthermore, even if the track is misaligned due to disturbance and the light beam quickly crosses the track, the tracking servo will be uncontrolled after the second to sixth positive return slope of the tracking error where the 4D sum signal is generated. Stable retraction is possible.

〔Effect of the invention〕

According to the present invention, there is an effect that stable I-racking servo can be performed without malfunction even when reproducing a distorted recording medium.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2(a) is a 1-ranking error waveform diagram, FIG. 2(b) is a 4D sum signal waveform diagram, and FIG. 3(a) is a 4D sum signal waveform diagram. Tracking error waveform diagram, Figure 3(b) is 4D sum signal waveform diagram, Figure 3(c)
) is a servo loop switch signal waveform diagram. 3... Loop switch, 5... 1 to racking drive device coil, 9, 13... Counter, 10... n times detection latch circuit, 12... Fixed time detection circuit.

Claims (1)

[Claims] 1. An optical device that focuses a light beam on the recording surface of a rotating recording medium, a first detector that detects an error signal for surface wobbling, and a focus control device in response to the detection signal. a first control circuit that detects an error signal for tracking the recording track; a second control circuit that performs tracking control in response to the signal; The third signal detects the low frequency component of the total signal and obtains a sinusoidal signal while crossing the tracks, and when the light beam is positioned between the tracks, the third signal detects the low frequency component of the total signal. In a tracking servo control device for an optical reader in which the control circuit is inactive, the second signal is detected from one to five times after the first detection of the third signal within a certain period of time within one rotation.
Tracking servo control device that does not disable the control circuit. 2. The fixed time period is sequentially extended by the second and subsequent third signals detected within a fixed time period after the first detection of the third signal. Tracking servo control device.