JPS62141636A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To make it possible to start a defective light pickup for automatic focusing by exciting a focusing coil by ramp shaped waveform on which high frequency signals are superposed and bringing an objective lens close to a disk face. CONSTITUTION:When a focus search instruction is inputted to input of a ramp waveform generating circuit 11, an electronic switch 12 becomes open, and output of the ramp waveform generating circuit 11 and signals of a high frequency superposition signal generating circuit 13 are composed in an adder 14, and a power amplifier 4 is excited by the signal. Frictional force of focusing direction existing in the movable part including an objective lens is reduced by output signals of the high frequency superposition signal generating signal 13, and the objective lens can be brought close to the disk face smoothly by signals of the ramp waveform generating circuit 11. When the focus search instruction is made off, the electronic switch is shunted, and accordingly, signals in which high frequency signals are superposed on ramp wave are not transmitted to the power amplifier 4.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention is directed to a device that reads information by projecting a light spot onto an information track on a recording medium recorded in a spiral or concentric manner. The present invention relates to an autofocus device that swings a lens greatly in a vertical direction facing an ErH recording medium, detects a focal point position, and applies focus servo.

(Prior Art) Conventionally, an autofocus device has been designed as shown in FIG. In the figure, 1 is a four-part photodetector that receives reflected light from the disk, 2 is a focus error detection circuit, 3 is a compensation circuit, and 4 is a power amplifier that drives the focus coil 5.

For autofocus N'fth, first turn on the electronic switch 6 to shunt the focus error signal generated from 2 so as not to transmit it to the compensation circuit 8 and beyond. next,
By giving a focus search command to the ramp wave generation circuit 7, the focus coil 5 is excited and the objective lens is gradually brought closer to the disk surface. At the moment when the on-focus state detection circuit 8 detects the presence of the objective lens near the focal point and the zero-cross detection circuit 9 detects the zero-crossing point of the focus error signal, the focus search command is turned off and the electronic switch 6t is opened. If you give a command to do this, the focus servo will be applied constantly. The ramp wave generation circuit 7 is, for example, as shown in the third factor. When an IJOW level command is input from the left side of 7, the electronic switch 10 closes and the +V power supply becomes stepped KR.
It is input to the O-integrator circuit and a ramp-shaped waveform is output. ■
If the command is at the GH level, the electronic switch 10 is opened and r:r is turned on, thereby discharging the electric charge charged in the capacitor CK.

Such an autofocus device is known, for example, in the document Mitsubishi Electric Wave Layer (■ol, 58, 110.11.1984).
．． P3 to P12) etc.

(Problem to be solved by the invention) However, if you wish to use an optical pickup that has a considerable amount of frictional force in the focusing direction, even if you try to start it with a conventional autofocus device, it will fail. There is a high probability that

In a steady servo state, some optical pickups with no defects in optical or servo performance cannot be driven by autofocus due to initial movement failure due to frictional force, and are therefore included in the group of defective products.

An object of the present invention is to remedy the optical pickup which causes poor autofocus due to the uneven movement in the focus direction as described above.

If an optical pickup, which has no problems as long as it is used in a steady servo system, can be repaired, the yield of optical pickup manufacturing will improve, which will greatly contribute to reducing product costs.

In order to solve the above problems, this invention excites the focusing coil with a ramp-shaped waveform superimposed with a nuisance wave signal to move the objective lens to the disk when performing autofocus. I tried to bring it closer to the surface.

(Function) Using the autofocus device configured as above,
When an optical pickup whose initial movement in the focus direction is not smooth is driven for autofocus, the friction f in the focus direction is reduced by the action of the high-frequency signal superimposed on the ramp waveform, allowing the objective lens to move smoothly. If it can be moved smoothly, it will be possible to activate the autofocus function of the optical pickup, which was considered defective in the past.

〔Example〕

Embodiments of the present invention will be described below based on the drawings. In FIG. 1, autofocus driving is performed as follows.

As described above, the output of the focus error detection circuit p'fr2 is shunted so as not to be transmitted to the compensation circuit 8 and beyond by keeping the electronic switch 6 on. next,
When a focus search command is input to the input of the ramp waveform generation circuit 11, the electronic switch 12 is opened.
The output of the ramp wave generation circuit 11 and the signal of the high frequency superimposed signal generation circuit 13 are combined in an adder 14, and the power amplifier 4 is excited with this signal. In this way, the output signal of the high-frequency superimposed signal generation circuit 13 reduces the frictional force in the focus direction that exists in the movable part including the objective lens, and the signal of the ramp waveform generation circuit 11 causes the objective lens to move smoothly. can be brought close to the disk surface. Here, the on-focus state detection circuit 8 detects that the objective lens approaches the focal point, and the focus search command is turned off at the moment when the zero-crossing point of the focus error signal is detected by the zero-crossing detection circuit 9. Since the electronic switch 12 is shunted when the focus search command is turned off,
The signal in which the high frequency signal is superimposed on the ramp wave is no longer transmitted to the power amplifier 4. Further, if the electronic switch 6 is opened at the same time as the focus search command is turned off, the focus servo can be constantly applied.

[Effects of the Invention] As explained above, this invention provides this remedy for optical pickups that suffer from poor autofocus as a result of the frictional force in the focus direction and the failure of normal focus search to make a smooth initial movement. This will provide an effective means to do so. That is, as a result of the frictional force being reduced by the superimposed high-frequency signal, the movement in the focusing direction becomes smooth, and the optical pickup, which had a poor initial movement, can reliably autofocus.

[Brief explanation of drawings]

FIG. 1 is a circuit block diagram showing an autofocus device according to the present invention together with a servo device. FIG. 2 is a circuit block diagram showing a conventionally used autofocus device together with a servo device. FIG. 3 is an example of a ramp wave generation circuit. 1. 4-segment photodetector, 20. Focus error detection circuit, 80. Compensation circuit, 40. power amplifier 50
．． Focus coil, 6. ．． 11 Switch 7. . Ramp wave generation circuit, 86. On-focus state detection circuit, 9
1. Zero cross detection circuit 10. , 'l child switch, 1
1. , Ramp waveform generation circuit, 120. Electronic switch, 13. , high frequency superimposed signal generation circuit, 140. Katana Ω calculator. that's all

Claims (1)

[Claims] a) a ramp waveform generation circuit for gradually bringing a movable part including an objective lens closer to the disk surface; b) a high frequency superimposed signal generation circuit for superimposing a high frequency signal on the ramp waveform; c) ) an adder for adding the output of the ramp waveform generation circuit and the output of the high-frequency superimposed signal generation circuit; d) an electronic switch for shunt at the input stage of the adder; and e) a high-frequency signal superimposed on the ramp waveform. With a signal,
An autofocus device characterized by bringing a movable part including an objective lens close to a disk surface and pulling it into focus.