JPS5830264Y2 - Focus control device for optical disc player - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focus control device for an optical disc player.

Optical discs, such as video discs, are densely recorded and require a laser beam diameter of 1 to 2 μm for signal reading, so the objective lens for signal reading must be placed very close to the disc ( It is usually placed around the 2nd floor.

When playing a disc, it is common for the vertical fluctuation amplitude of the disc to be larger in a transient state below a constant rotation speed, such as when starting or braking, than when the disc is rotating at a constant speed, and the average position of the disc also differs. be.

Such unstable fluctuations may cause the disk and the lens portion disposed close to the disk to come into contact with each other, causing damage to the disk and/or the lens.

Therefore, general players need to detect changes in the relative distance between the disc and the lens relative to the appropriate distance.1.
A focus control device is provided that controls the lens so that the relative distance matches the appropriate distance based on the detection signal.

However, even with this device, there is a risk that the disc and lens may come into contact if the disc is out of the focus control range due to scratches on the disc or attached dust during playback operation.

The present invention aims to eliminate this drawback and furthermore provide a device that can automatically return the control system to the control range.

The present invention will be explained below with reference to its embodiments.

As shown in the circuit block diagram of FIG. 1, the disk 1 is rotated by the motor 2 at 1800 revolutions per minute when reproducing an NTSC video signal.

The laser beam is irradiated with a diameter of 1 to 2 μm onto the effective recording portion of the disk by an objective lens (not shown) built into the voice coil 3.

After the reflected light passes through the lens in the voice coil again, it is converted into an electrical signal by a photoelectric converter with a fast response speed, such as a PIN photodiode, and its output is sent to the preamplifier 4, signal processing circuit 5, and television signal converter. It is led out via circuit 6 to an empty channel of the television receiver.

Normally, in order to keep the laser beam at a spot of 1 to 2 .mu.m, it is considered necessary to maintain the relative distance between the lens and the disk within an error of ±2 .mu.m or less with respect to the appropriate distance.

For this purpose, the above-mentioned focus control device is used, and the voice coil is controlled in a direction that cancels the vertical fluctuation of the disc, so that the relative distance between the lens and the disc matches the appropriate distance. There is.

Although various methods are already known as specific focus control methods, an example of an optical method will be described here.

A portion of the laser beam reflected from the disk 1 is incident on the sensors 7a and 7b, and when the laser beam hits the signal recording area of the disk with a beam diameter of 1 to 2 μm, both sensors The amount of light incident on is equal,
The optical system is designed so that as the lens approaches the disk, the amount of light incident on the sensor 7a increases and the amount of light incident on the sensor 7b decreases, and conversely, as the lens moves away from the disk, the amount of light incident on the sensor is reversed. In the assembled optical system, when the outputs of the sensors 7a and 7b are calculated by the differential amplifier 8, a signal as shown in FIG. 2 is obtained at the output.

The horizontal axis in the figure represents the relative distance between the disk and the lens with respect to the proper distance, and the right side thereof indicates the direction in which the lens is closer to the disk, while the left side thereof indicates the opposite direction.

The region indicated by symbol A in the figure is the operating range of the control system, and this operating range (lock range) is usually about ±100 to 200 μm.

Even in such a narrow operating range, if the control system operates normally and the button is pressed, focus control is possible even if the disc changes by nearly one peak.

However, when the disk starts up, the variation in the relative distance tends to be too large and the control system does not operate correctly.
Further, outside this operating range, as can be seen from the tendency shown in FIG. 2, the control system becomes as if it were subjected to positive feedback, and the lens suddenly deviates from its normal state.

When such a state occurs, it will not be possible to return to the original state unless the operation of the control system is stopped.

If the lens comes off toward the disk, there is a risk that the two will come into contact and be damaged.

This is a drawback of the conventional device, and in order to prevent this, the device of the present invention includes a nonlinear circuit 9 in the control system.

This circuit has the output characteristics of the control system as shown in Figure 3, that is, the output voltage remains constant for inputs above or below a certain value (inputs exceeding a certain value). An output signal conforming to its characteristics is derived to the terminal 10.

This rotation causes another output terminal 11 to derive an output that exhibits a high level when there is an input exceeding the above-mentioned certain value.

A circuit having such a function can be composed of a comparator with two threshold values and an operational amplifier.

When a high-level signal appears at the output terminal 11, it means that the lens has abnormally approached or moved away from the disk, that is, the control system has become unlocked.This is detected and the oscillation circuit 12 is configured to be driven.

This oscillation circuit oscillates at a frequency of several Hz, and when this output is added to the differential amplifier 13 and calculated with the output of the nonlinear circuit 9, the output of the latter circuit 9 is fixed at a constant level, so the voice The coil 3 will move up and down depending on the output of the oscillation circuit.

At this time, by appropriately selecting the output level of the oscillation circuit, the oscillation output will necessarily fall within the operating range A shown in FIG. Therefore, the output of its output terminal 11 also becomes low.

Then, the operation of the oscillation circuit is stopped and the control system resumes normal operation.

The above operation would be carried out without problems if it was guaranteed that the control system would always maintain a predetermined level as shown in the flat section in Figure 3 outside its operating range, but in reality it would be far outside the operating range. In that case, as can be seen from the illustrated characteristics, it becomes impossible to distinguish between what is inside the operating range and what is outside the operating range.

Therefore, it is preferable that the device of the present invention has the following auxiliary functions.

That is, the output signal of the preamplifier 4 is rectified by the rectifier circuit 14, the output thereof is inputted to the level determination circuit 15, and the oscillation circuit 12 is also connected to the output of the rectifier circuit 14.

This determination circuit maintains the output terminal at a high level if the output of the preamplifier is above a certain level, and is constructed of, for example, a Schmitt trigger circuit.

Since the output signal of the preamplifier is detected from the disk only when the laser beam is properly focused on the disk, the output of the judgment circuit becomes ``elevated'' because the output voltage of the differential amplifier 8 is Only when in the operating range.

That is, the output of the determination circuit cannot reach a high level outside the operating range.

Therefore, if the oscillation circuit is driven even with the negative output of this determination circuit, the control system will be locked only when it is in the operating range, and otherwise operate to find the operating range using the output of the oscillation circuit. It turns out.

Therefore, the disk and lens do not come into abnormal proximity or come into contact with each other, and furthermore, even if the control system goes out of its operating range due to dirt, dust, etc. during playback, it can automatically return to its normal state.

The switching circuit 16 is used when focus control is not required (for example, until the disc reaches a certain speed and when the disc is stopped).
In addition, the voice coil is moved back so that no extra signal component is added to the voice coil and contact between the lens and the disk never occurs, and a constant voltage v is supplied to the differential amplifier 13 through this switching circuit. That's what I do.

This switching circuit switches between the oscillation circuit 12 and the differential amplifier 13 when the rotational speed of the motor 2 reaches a predetermined level, for example.
Tachometer 1 connected to motor 2 so as to connect
The rotation speed detection circuit 18 is controlled by a rotation speed detection circuit 18 to which the output of No. 7 is input.

The addition of this configuration allows the control system to operate only when the disk rotates at a constant rate, that is, after the fluctuation of the disk becomes small, so the operating range of the voice coil can be made that much smaller, and the control system can work just as much. It is lightweight and eliminates the possibility of contact between the disc and lens.

[Brief explanation of the drawing]

FIG. 1 shows a block diagram of one embodiment of the device of the present invention, FIG. 2 shows an output characteristic diagram of a differential amplifier, and FIG. 3 shows an output characteristic diagram of a nonlinear circuit. 1... Disc, 2... Motor, 3... Voice coil, 4... Preamplifier, 5... Signal processing circuit, 6
...Signal conversion circuit, 7a, 7b...Sensor, 8.
... Differential amplifier, A... Operating range, 9... Nonlinear circuit (detection means), 12... Oscillation circuit, 13... Differential amplifier, 14... Rectifier circuit, 15... Level judgment circuit, 16... switching circuit, 17... tachometer, 18...
・Rotation speed detection circuit.

Claims (1)

[Scope of utility model registration request] Focus control for an optical disc player, wherein a change in the relative distance between a disc and a lens with respect to an appropriate distance is detected, and the lens is controlled based on the detection signal so that the relative distance matches the appropriate distance. In the apparatus, the control system further includes a detection means for deriving an output signal when the level of the detection signal exceeds a certain value, and a detection means for deriving an output signal when the level of the reproduced output signal becomes below a certain value. and a detection means for causing the rain detection means to forcibly vibrate the lens when an output signal is generated from at least one of the rain detection means, so that the level of the detection signal is kept within the certain value. Focus control device for optical disc players.