JPS63244321A - Automatic focus draw-in adjusting device - Google Patents

Abstract

PURPOSE:To stably draw-in a focus by holding the peak value of a focus error signal, and closing a focus servo loop at the time of obtaining a draw detection signal when the focus error signal comes to or below the peak value, at the time of controlling focus draw-in. CONSTITUTION:A focus start signal is inputted, and a diaphragm lens 11 approaches to the signal recording surface of a disk, and the focus error signal FE is obtained. The said focus error signal FE and a slice signal that the peak value of the focus error signal, inputted and held in a peak value holder 1, is divided by an attenuator 2, are compared by a comparator 3, and the draw-in detection signal is outputted to a counter circuit 4. The counter circuit 4 outputs an ON signal to a gate circuit 5, and closes the focus servo loop, and at the same time, stops the output of a lamp signal generation circuit 7. Thus, a focus draw-in point can be stably detected through the use of a simple constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an automatic focus pull-in control device used in an optical information recording/reproducing device.

2. Description of the Related Art In recent years, optical information recording and reproducing apparatuses have been developed that use laser light to record information signals on disks or to reproduce information signals from disks.

This information recording/reproducing device is equipped with a focus servo technology that focuses a light beam that has been narrowed down to a diameter of about 1 μm by an optical pickup optical system on the signal recording surface of the disk while following the surface runout of the disk. It is essential.

FIG. 2 shows the relationship between the focus error signal and the distance between the aperture lens and the signal recording surface of the disk. The distance between the aperture lens 11 and the signal recording surface 12 of the disk is d.
1 If the focus error signal is FIC, dl in Figure 2 a
, d2 , d3 , d4゜d6 are dl in Figure 2
, d2+d3 +d4, and d5. The range from point d2 to point d4 in FIG. 2 is the pull-in range of the focus loop, and the focus servo is activated by closing the focus loop when the aperture lens 11 enters the pull-in range.

FIG. 3 shows an example of a method for detecting that the aperture shift/shift has entered the focus loop pull-in range, in which the focus error signal FE and a constant slice signal are compared in a comparator 13, and as shown in FIG. A commonly used technique is to close the switch 15 by changing the polarity of the gate signal to operate the focus servo. (For example, JP-A-60-5
(No. 0633 Publication) Problems to be Solved by the Invention With such conventional techniques, focus errors may occur depending on the location even on the same disc using a recording material in which the recorded and unrecorded areas have different reflectances. If the amplitude of the signal changes, the detection timing of the pull-in range varies, or the light transmission efficiency decreases due to dust, etc., there is a problem that the pull-in point cannot be detected in areas with low reflectance.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an automatic focus pull-in control device that stably detects a focus pull-in point with a simple configuration.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention maintains the peak value of the focus error signal, and performs the pull-in when the focus error signal becomes equal to or less than the peak value during focus pull-in control. The focus servo loop is closed by obtaining a detection signal.

In addition, to avoid false detection of peak values due to disc scratches, etc., move the aperture lens close to the signal recording surface of the disk to hold the peak, then move the aperture lens away from the disk recording surface, and then move the aperture lens again to record the signal on the disk. bring it close to the surface,
The held peak value is used to obtain a pull-in detection signal.

Effect of the Invention The present invention uses the above-described configuration to detect a peak value every time the device operates and obtain a slice signal, thereby stably obtaining a pull-in detection signal even when there is a difference in reflectance of the disk or a change in optical transmission efficiency. be able to.

Embodiment FIG. 1 is a block diagram showing an automatic focus pull-in control device according to an embodiment of the present invention. The automatic focus pull-in control device in FIG. 1 includes a peak holder 1 that holds the peak of a focus error signal FIE sent from a photodetector;
An attenuator 2 that reduces the peak value held by the peak holder to one to several fractions, a comparator 3 that compares the output from the attenuator with the focus error signal FW, and a change in the polarity of the output signal of the comparator. A counter circuit 4 that counts the polarity and outputs a gate signal when the polarity changes a preset number of times, a switch 5 that is turned on and off according to the output of the counter circuit, and a phase compensation of the focus error signal yz. A ramp signal generating circuit T generates a predetermined ramp signal in response to a focus start signal, and an adder circuit 8 adds the ramp signal to a drive circuit 9 that drives the aperture lens drive device 10. ing.

The operation of the automatic focus pull-in control device according to the present invention configured as described above will be explained.

First, the ramp signal generation circuit 7 generates a predetermined ramp signal in response to a focus start signal.

At this time, the gate circuit 5 is turned off. The ramp signal is added to an adder circuit 8, and its output is sent to an aperture lens driving device 10 through a drive circuit 9 for drive control, so that the aperture lens 11 approaches the signal recording surface 12 of the disk at a constant speed.

Thereafter, the focus error signal FIC detected by the photodetector is input to the peak holder 1, where the peak of the focus error signal FE is held, and a slice signal obtained by dividing the peak value by an attenuator is output to the comparator 3. .

On the other hand, the focus error signal FIC is also input to the comparator 3, which compares it with this slice signal and outputs a focus pull-in detection signal to the counter circuit 4. The counter circuit 4 counts how many times the focus pull-in detection signal is input, and when the count is 1, it resets the ramp signal generation circuit 7 without outputting an on signal to the gate circuit 5, and sets the ramp signal to the initial value. Make it.

This allows the aperture lens 11 to
Move away from 2.

Next, the focus start signal is input again, and the diaphragm lens 11 approaches the signal recording surface 12 of the disk in the same way as before, and the focus error signal FE is obtained. This focus error signal FIC is compared with a slice signal obtained by dividing the peak value of the focus error signal FE input and held in the peak holder 1 by an attenuator 2 in a comparator 3, and outputs a pull-in detection signal to a counter circuit 4. . Since the count number is 2 this time, the counter circuit 4 outputs an on signal to the gate circuit 6, and simultaneously closes the focus servo loop and stops the output of the ramp signal generation circuit.

In this way, this device retains the peak of the focus error signal and uses a signal obtained by dividing the peak value by an attenuator as a slice signal, and when the diaphragm lens approaches the signal recording surface of the disk once, the focus error signal is reduced. It is characterized by reliably holding the peak of the signal and closing the focus loop after the second time to eliminate false detections due to disc scratches, etc.
The above methods are not limited to the above methods.

Effects of the Invention As described above, according to the present invention, the focus can be drawn in stably and reliably without false detection due to scratches on the disk, etc., with an extremely simple circuit configuration, and is extremely useful in practice. be.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an automatic focus pull-in control device in an embodiment of the present invention, Fig. 2 is a characteristic diagram showing a focus error signal with respect to the distance between the signal recording surface of the disk and the aperture lens, and Fig. 3 is a conventional example. FIG. 4 is a block diagram showing a general automatic focus pull-in control device, and FIG. 4 is a waveform diagram showing a gate signal for a slice signal and a focus error signal. 1... Peak holder, 2... Attenuator, 3... Comparator, 4... Counter circuit, 6... Switch, 6 ...Phase compensation circuit, a...Ramp signal generation circuit, 8...
... Addition circuit, 9... Drive circuit, 10.
...Aperture lens drive device, 11...Aperture lens, 12...Signal recording surface of disk, 13
... Comparator, 14 ... Phase compensation circuit,
15...Switch. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 3
Figure 4

Claims (2)

[Claims] (1) A drive device that drives an aperture lens that converges a focus error signal obtained by detecting reflected light from a disk and a light beam onto a signal recording surface of the disk, and the aperture lens drives the signal recording surface of the disk. means for generating an aperture lens drive signal that brings the aperture lens closer to the surface; An automatic focus pull-in control device comprising means for closing a focus servo loop when the focus servo loop reaches a peak value or less than the peak value. (2) Bring the diaphragm lens close to the signal recording surface, hold the peak value of the focus error signal, move the diaphragm lens away from the signal recording surface, and bring the diaphragm lens close to the signal recording surface again, so that the focus error signal becomes the focus error signal. 2. The automatic focus pull-in control device according to claim 1, wherein the focus servo loop is closed when the focus servo loop becomes at or below a peak value.