JPS60242524A - Optical pickup - Google Patents

Abstract

PURPOSE:To eliminate oscillating the whole pickup at highspeed and to detect a track on push-pull basis by providing a means which detects deviation when a lens system is moved and to correct DC deviation due to the movement. CONSTITUTION:When the lens system rocks in a direction B-B, a shutter 5 varies the quantity of light incident on the photodetecting element 6a of a photointerrupter and the output of a detector 6a as a photodetecting element varies. This output is so applied as to cancel the deviation of the output E of push-pull amplification as to outputs of photodiodes PD1 and PD2, obtaining a correct signal EE. Then, the output of the detector 6a is inputted to a differential amplifier A3 in order to cancel the DC component of the detector 6a and then compared with a reference voltage VREF for DC cancellation; and the amplifier A3 outputs an inverse voltage equal to the signal E about the center position of the lens system as 0V and a mixing circuit A2 cancels the DC component, thereby obtaining the correct push-pull signal EE.

Description

[Detailed Description of the Invention] Technical Field B to which the Invention Pertains The present invention relates to an optical pickup for detecting information on an optical disc such as a compact disc, and in particular has four detection means for detecting displacement of a lens system. Shiba regarding J-4 optical pickup.

Background of the Technology In the original pickup of optical discs such as video discs and digital audio discs, it is necessary to perform tracking servo in addition to focus servo, and sometimes it is necessary to perform minute tracking with an accuracy of, for example, 0.1 μ. To detect this track deviation, there is a so-called 23-beam method that uses three laser beams using a diffraction grating, etc., but the pickup is complicated and adjustment is difficult. I'm wanted.

Prior Art and Its Problems In response to the above-mentioned requirements, a push-pull method as shown in FIG. 4 has been proposed as a detection method.

That is, in FIG. 4, the laser beam from the laser diode LD is semi-transparent f! The pit portion of the disk D8 is irradiated through the A mirror M and the information reading lens Lk, and the reflected light is sent to the semi-transparent mirror M and the two 7. j) Diode PD, , PD.

When the disk bit is shallower than λ/4 (λ is the recording wavelength of the laser), the amplifier A extracts it as a υ push-pull signal. 4o With this configuration, the entire lens is used for tracking. When moving in the track direction, the reflected light entering the photodiodes PD1 and PD of both detectors is shifted from the center, and as shown in Figure 5, the output voltage E corresponding to each track TH of the disk is centered at the lens system. A correct error signal is obtained only in the track TR near the off point P, and 4 has the disadvantage that the push-pull method cannot be used for discs with large eccentricity.

For this reason, it was necessary to move the entire pickup in the direction of the track, and the drive device for tracking was large and required a large amount of electric power.

OBJECTS OF THE INVENTION The present invention was developed in view of the above-mentioned drawbacks, and uses a push-pull detection method that uses sound to accurately obtain error signals for each track even if only the lens system is moved in all track directions.4 Simple detection means outputs 4 lights. This is a device whose purpose is to provide a full pick-up system.40 The structure of the present invention is configured to perform full correction of direct current deviation by moving the lens using the detection means. One embodiment will be described in detail with reference to Figures 1 to 3.

FIG. 1 (() is a perspective view of the main parts of the optical pickup of the present invention,
Figure 1 (b) is an enlarged plane quotient of the main part of the detection means in Figure 1 (a), Figure 2 is a circuit diagram of the optical pickup of the present invention, and Figure 3 is a waveform explanatory diagram of the original pickup of the present invention. be.

In Figure 1 (a), the objective lens l is the lens mounting plate 1a.
A plate spring 2.2 is attached to the lower part of the mounting portion, and is coupled to the vertical drive coil portion 3a, so that it moves up and down integrally with the coil 3. On the other hand, in the track direction B--B, the lens mounting plate 1a containing the objective lens 1't- is swung by the leaf spring 2.2 (4o) toward the rack.

The oscillation is caused by an external coil (not shown in FIG. 1(a)) and a magnet 4 attached to the bottom of the lens mounting plate 1a.
It is carried out by Here, the shutter 5 is attached to the plate spring 2 of the lens system, and the z0 lens system has a 7-oto-interrupter consisting of the light emitting element 6 and the light receiving element 6a attached to the vertical drive coil part. When the photointerrupter swings in the -B direction, the amount of light incident on the light receiving element 6a of the photointerrupter changes due to the shutter 5, as shown in FIG. 1 (b). For this reason, the output of the photo detector 6a changes. By adding this output to the photodiode PD shown in FIG. 4, as shown in FIG.
] As shown in c, you can get the correct signal.

Here is the DC component 6a of photodetector a'? , the output of the detector 6a is input into a differential amplifier 80 for cancellation and compared with the reference voltage VREf for canceling the DC component 6a', the output of the differential amplifier A is zero volts at the center position of the lens system. As a result, a voltage equal to and opposite to the DC fluctuation of the push-pull signal E is generated and canceled by the mix circuit A, and the output is the correct push-pull signal EIc.

Although the above embodiment has been explained using a push-pull signal, it is clear that direct current deviation occurs due to movement of the lens system in 3 beams and other systems as well, but it is obvious that this can also be corrected. As shown in Fig. 2, the entire original pickup is oscillated at high speed because a detection means is provided to detect all movement of the lens system.
Push-pull type track detection is possible without the need for track detection, and the circuit and optical pickup are both simple and stable servos can be obtained. Furthermore, the output of the detection means indicates the movement of the lens system, and if velocity feedback is performed on the lens system without depending on the track information of the disk, damping can be applied to the path of the disk without being affected by 4, and is even more effective as it can provide strong optical pickup against track errors due to scratches and external vibrations.

[Brief explanation of the drawing]

FIG. 1(A) is a perspective view of the lens system of the present invention, FIG. 1(B) is a partially enlarged plan view of the shutter and photo interface 2 portions of FIG. 1, and FIG. 2 is a detection circuit of the present invention. 3 is a waveform explanatory diagram of the present invention, FIG. 4 is a diagram showing an optical system and detection means showing a conventional data detection method, and FIG. 5 is a waveform explanatory diagram of FIG. 4.・Lens 2・Fist・Plate blade 3a・・・・Vertical drive coil part 3・・Meeting coil 4・・
-Magnet 5...Shutter 6...Light emitting element 6
a...Fist light receiving element PD, PD...Photo interrupter DS...Disk LD...Laser M life...
Semi-transparent mirror Loo, lens (in (o) Figure 1 Figure 3

Claims (1)

[Claims] (11) For soft high-frequency components such as eccentricity of the information track, track servo is fully executed by swinging the lens system of the optical pickup, and for low-frequency components such as track feeding. The original pickup is characterized in that the original pickup body is moved, and a means for detecting the displacement of the lens system is provided for the original pickup body, which is configured to move the entire original pickup body and perform full z-track servo operation. The optical pickup 0 according to claim 1, wherein the detection means fully corrects the direct current deviation of the z-track error signal due to the displacement of the lens system.