JPS5830263Y2 - Automatic focusing device for optical disc player - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of an automatic focus search device for an optical video disk player.

When playing back an optical video disc, a servo loop as shown in FIG. 1, for example, is used to keep the relative distance between the video disc and the objective lens constant within a necessary range.

It incorporates an objective lens 1 into an electrodynamic converter 2, and detects fluctuations in the video disc 3 using two sensors SA y S.
B detects the output, and the arithmetic unit 4 controls the converter 2 so that the outputs of both sensors are constant. The straight line part At of the character characteristic is used.

However, there are usually large fluctuations in the disk outside this straight line, especially at the time of startup, and the average position of the reflective surface of the disk often differs between startup and constant speed rotation.

Therefore, if this servo system is activated at the same time as the video disk is driven, there is a possibility that the servo system will be locked at a position other than the straight line portion of the figure-8 characteristic.

Furthermore, even if a device is devised to operate the servo after the rotation of the disk reaches a constant speed, normal servo control will not occur if the disk changes significantly or if the above relative distance is not located near the focal position. There is a risk of not being locked into the loop.

The present invention aims to provide a device that can prevent such malfunctions and automatically lead to a control loop.

That is, when the objective lens for the video disk is placed outside the control range of the servo loop, the vertical vibrator, which is an electrodynamic transducer equipped with the objective lens, is removed from the loop and forced to vibrate, thereby causing the objective lens to vibrate. It is an object of the present invention to provide a device that activates a servo loop when a lens enters a control range.

Next, the present invention will be explained according to illustrated embodiments.

FIG. 3 is a block diagram of the main configuration, and FIG. 4 is a waveform diagram for explaining its operation.

Reference numeral 5 denotes a sine wave oscillator which operates when the disk starts to be driven.

This does not necessarily have to be a sine wave, but may be any waveform that can cause the vertical vibrator to reciprocate.

This output is passed through a suitable amplifier circuit 6 to a switching means 7.
is input on one side.

A common output terminal of this switching means is connected to the vertical vibrator 2.

Further, SA and SB are sensors, and their outputs are inputted to an AND circuit 12 through integration circuits 8 and 9, comparators 10 and 11 with appropriate hysteresis, respectively.
The output is inputted to the switching means 7 as a switching signal.

The outputs of the sensors SA, S, and B are also respectively input to an arithmetic circuit 4, and are connected to other input terminals of the switching means via a necessary amplifier circuit 13.

Now, when the reflective surface of the disk is at an arbitrary position (of course, a certain degree of mechanical position is ensured so that the reflective surface is within the movable range of the vertical vibrator), the vertical vibrator is forcibly driven with a sine wave. The waveform detected by sensor S A ISB when
Explaining in terms of the half cycle between the farthest point and the nearest point of the drive amplitude, the outputs of the sensors SA and SB after passing through the integrating circuits 8 and 9 due to the vibration process of the vertical vibrator are as shown in Fig. 4A. Illustrated.

Here, the potential of the output of the sensor sA side applied to the peak position of the output of the sensor sB side is v1 (or the potential of the output of the sensor SB side applied to the peak position of the output of the sensor SA side is kVx), and the output of the sensor SA side and the sensor If the potential at the point where the SB side output intersects at the center position is 2, then the sensors SA, SB
The side comparator level Vcp is set to V 1<VcP<V
When an arbitrary position of 2 is selected, each comparator output on each sensor side is outputted as shown in FIG.

Therefore, the AND output is output as shown in FIG. 4-2.

The AND output output in this manner is always output only on the straight line portion of the above-mentioned 8-character characteristic.

When this AND output exists, the switching means is controlled, and the output of the arithmetic circuit is supplied to the vertical vibrator 2 instead of the oscillator output, thereby forming a servo loop.

After this, the fluctuation of the disc is automatically controlled by the control circuit that is calculated based on the output of the sensor as described above, and the distance between the disc and the objective lens is maintained at a constant interval, and the focus is controlled as necessary for normal playback. will be carried out.

As described above, with the device of the present invention, the control loop is correctly locked in the straight line portion of the figure 8 characteristic, and no malfunction occurs.

Furthermore, in the present invention, if the disc is damaged, for example, if there is a missing reflective surface that exceeds the time constant in the integrating circuit, the logical product output will no longer be output, and the switching means will switch to simultaneously perform the search. Once the reflecting surface is recovered again, the above-mentioned operation leads to the correct focus control loop again, and the normal function is subsequently restored.

Furthermore, according to the present invention, it is possible to reduce the accuracy of the mechanical positional relationship between the vertical vibrator and the disk reflective surface for forcing the focus position to be searched for the focus position or button.

[Brief explanation of the drawing]

Figure 1 is a schematic configuration diagram of a conventional servo loop.
The figure is a diagram showing the output characteristics of the arithmetic unit therein. FIG. 3 is a block diagram of the main structure of the device of the present invention, and FIG. 4 is a waveform diagram for explaining its operation. 3...Video display 1...Objective lens, 2...
- Vibrator, 5... Oscillator, SA, SB, 4... Control means (sensor, arithmetic circuit), 7... Switch circuit, S
A, SB. 8.9, 10, 11, 12...Switching means (sensor, integration circuit, comparator, AND circuit).

Claims (1)

[Scope of utility model registration request] A vibrator that displaces an objective lens placed opposite to a disk record in the optical axis direction, a pair of sensors that receive reflected beam light, and a focus control circuit that issues a focus control signal so that the output levels of both sensors match. an oscillator that generates a sine wave signal that forces the objective lens to vibrate; a pair of comparators that generate an output when each of the sensor outputs reaches a predetermined level or higher; and a logical product that inputs the outputs of both the comparators. and a switching circuit for supplying the focus control signal to the vibrator in place of the sine wave signal using the AND output.