JPH0518183B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a focus pull-in method for an optical disk device equipped with a focus servo mechanism.

2. Description of the Related Art In recent years, the amount of information processed by computers has continued to increase, and in order to record and reproduce this increased amount of information, optical disk devices that can record a large amount of data have attracted attention, and the technology has improved at a remarkable rate. Since the information recorded or to be recorded on the recording medium in an optical disk device is minute pits of 1 μm or less, the laser beam is focused to a minute spot light with a diameter of about 1 μm, and the laser beam is always focused regardless of the surface wobbling of the recording medium. A focus servo mechanism that illuminates the medium surface is essential, and the development of highly accurate servo functions is desired.

[Conventional technology]

FIG. 4 shows a configuration diagram of an optical disk device equipped with a conventional focus servo mechanism. In the figure,
1 is a semiconductor laser which is a light source; 2 is a collimating lens that converts the light beam emitted from the semiconductor laser 1 into parallel light; 3 and 4 are optical elements for separating the light beams, including a polarizing beam splitter and 1/2 Four
A wavelength plate, 5 is a condenser lens equipped with a focus servo mechanism for irradiating a light beam onto a recording medium 6, 7 is a reflecting mirror for dividing the reflected light from the recording medium into two parts, 8 and 9 are focal points A condensing lens and a 2-split photodiode for detecting an error signal (hereinafter referred to as focus error signal), also 1
0 and 11 are a condenser lens and a two-split photodiode for detecting a track error signal (hereinafter abbreviated as track error signal).

When the recording medium 6 rotates, the surface of the recording medium moves up and down due to surface deflection, and FIG. become that way.

12 shows the situation when the distance X between the condenser lens 5 and the recording medium becomes longer than the focal length of the condenser lens 5, 13 shows the situation when it matches the focal length, and 14 shows the situation when it becomes shorter than the focal length. . Therefore, a focus error signal is obtained from the differential signal A-B of the two-split detector 9.

The focus error signal at this time is shown in FIG. In this figure, the vertical axis is the focus error signal V, and the horizontal axis is the distance X between the condenser lens 5 and the recording medium 6 in FIG. 16 is a just focus point, and the value of the focus error signal V crosses zero on the line of distance X. This point 16
It would be good if stable control could be performed within the range of the linearity change portion 19 centered on A plurality of points (in this example, points 15, 17, and 18) appear as shown in the figure.

If the focus servo system is closed at the wrong time, it will become stable at other zero cross points 15, 17, and 18, and in the worst case, the condensing lens will get too close to the recording medium, damaging the recording medium or the condensing lens. In some cases, this may result in

[Problem that the invention seeks to solve]

Conventionally, the timing for closing the focus servo system used a signal obtained by differentiating the sum signal or difference signal obtained from the two-split photodiode 9 or the two-split photodiode 11.
All of them had the disadvantage of poor stability, and their operation became unstable even with slight changes in external conditions.

SUMMARY OF THE INVENTION In view of the above-mentioned drawbacks of the conventional art, it is an object of the present invention to provide a focus pull-in method for stably performing focus servo at a normal just-focus point.

[Means for solving problems]

The purpose of this is to irradiate a light spot onto the recording medium surface through a condensing lens, and use the reflected light to generate a focus error signal necessary for driving the focus servo mechanism of the condensing lens and to drive the track servo mechanism. In an optical disk device comprising a detector for detecting each of the necessary track error signals, a detector for detecting the envelope waveform of the track error signal above a required threshold is provided, and the condenser lens is moved in the optical axis direction. This is achieved by providing the focus pull-in method of the present invention, characterized in that the timing for starting the drive of the focus servo mechanism is determined by the output of the detector that appears during the forced initial movement of the focus servo mechanism. Ru.

[Effect]

That is, the present invention provides means for reliably detecting the timing to close the focus servo system by utilizing the fact that the track error signal obtained from the reflected light of the recording medium is obtained only from the vicinity of the just focus point. It is.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.
Note that, in order to make the explanation of the configuration and operation easier to understand, the same parts are given the same reference numerals throughout all the figures, and repeated explanation thereof will be omitted.

FIG. 1 shows a diagram explaining the principle of the present invention. Waveform a shows the focus error signal explained in FIG. 6, waveform b shows the track error signal and its envelope waveform (hereinafter abbreviated as envelope), and waveform c shows the timing signal for closing the focus servo system. be. In the figure, 21 is a track error signal;
22 is the envelope signal, 23 is the threshold value Vr for detecting a desired constant value or more, and 24 is the focus servo ON'' signal. From this, the focus servo ON'' signal is output only at a normal just focus point. I can see that

FIG. 2 shows a block diagram of the focus pull-in method according to the present invention. In the figure, 28 is a signal generation circuit for initially driving the condenser lens 5;
26 is a switching circuit for switching the signal for driving the condenser lens from the initial drive to the focus error signal; 25 is a focus servo drive circuit;
7 is a focus error signal compensation circuit, 29 is a circuit for detecting the envelope of the track error signal, and 30 is a detector (comparator) for determining whether the envelope has exceeded the threshold value Vr.

FIG. 3 shows a time chart of the operation of each part in FIG. 2. In the figure, waveform d represents an initial drive signal, waveform e represents a track error signal, waveform f represents a focus scan signal, and waveform g represents a switch changeover signal.

First, when an initial drive signal is applied to bring the condensing lens 5 close to the recording medium 6 from a distance, a track error signal begins to appear near the just focus. Circuit 29 for detecting the envelope of this signal
When the comparator 30 detects the threshold value Vr or more at time T ₁ via It will be drawn into the focus servo system by the focus error signal.

〔Effect of the invention〕

As explained in detail above, according to the focus pull-in method of the present invention, the timing to close the focus servo can be accurately detected, so the focus servo will not be activated at an erroneous stable point, and the recording medium and condensing lens It has the effect of preventing damage to the skin.

[Brief explanation of the drawing]

Fig. 1 is a diagram explaining the principle of the present invention, Fig. 2 is a block diagram of the focus pull-in method according to the present invention,
Figure 3 is a time chart of the operation of each part in Figure 2, Figure 4 is a configuration diagram of an optical disk device equipped with a conventional focus servo mechanism, and Figure 5 is a diagram of the reflected light on the focus error signal detector. Diagram showing shape change,
FIG. 6 shows a focus error signal waveform diagram near the just focus point. In the figure, 5 is a condenser lens, 6 is a recording medium,
9 is a two-divided photodiode for detecting a focus error signal, 11 is a two-divided photodiode for detecting a tracking error signal, 22 is an envelope waveform, 30 is a detector, and Vr is a threshold value.

Claims (1)

[Claims] 1. A light spot is irradiated onto the recording medium surface through a condensing lens, and from the reflected light, a focus error signal necessary for driving the focus servo mechanism of the condensing lens and a track error necessary for driving the track servo mechanism are obtained. In an optical disk device comprising a detector for detecting each signal, a detector for detecting the envelope waveform of the track error signal above a required threshold is provided, and the condenser lens is forcibly moved in the direction of the optical axis. A focus pull-in method, characterized in that the timing for starting drive of the focus servo mechanism is determined by the output of the detector that appears during initial movement.