JPH0452530B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an apparatus for reproducing information recorded on an optical disc, which is a recording medium for a video disc or a digital audio disc, and particularly for reproducing information. The present invention relates to a feed servo circuit for an optical head for maintaining a proper tracking state of an optical pickup.

[Background technology and its problems]

In a device that arranges video and audio signals in a spiral shape on the recording surface of an optical disk as concave and convex pit information, irradiates the optical disk with a laser beam and reads out the video and audio signals from the reflected light, the optical It is essential to apply tracking servo so that the pickup device moves while accurately tracing the spirally formed recording track.

Fig. 1 shows a block diagram for applying such a tracking servo, in which numeral 1 shows a rotating optical disk disk, numeral 2 irradiates the optical disk disk 1 with a laser beam, and simultaneously irradiates the optical disk disk 1 with a laser beam. 3 is an operational amplifier circuit for detecting a tracking error signal from the reflected light; and 4 is for driving a tracking coil provided in the optical pickup device 2. This is the drive circuit.

Note that the tracking coil usually drives an objective lens or a reflection mirror to control the laser beam so that it is accurately irradiated onto the recording track of the optical disc 1.

Reference numeral 5 indicates an integrator circuit that detects the DC component from the tracking error signal, and the output of this integrator circuit is power-amplified by a power amplifier 6, and then a thread feed motor 7 that moves the entire optical pickup device 2 in the radial direction. , or supplied to a linear motor.

Note that 8 is a spindle motor that rotates the turntable, and 9 is a feed screw.

In such a tracking servo mechanism, the tracking coil is controlled by the tracking error signal output from the optical pickup device 2.
For example, it is possible to irradiate a laser beam while accurately following the recording track even when there is a tracking error on the optical disc 1, an error in the roundness of the track, etc. Since it is controlled by the level,
The radial position of the recording track being read and the moving distance of the optical pickup device 2 can also be kept constant.

However, when shock-like vibrations are applied from the outside during playback, or immediately after the optical pickup device 2 is jumped by an access signal in order to read a particular piece of music, tracking is significantly disrupted.

This is a waveform diagram of the tracking error signal similar to that shown in FIG. 2, where A is the tracking error signal in a normal reproduction state. In this case, the signal waveform is approximately sinusoidal with a period T equal to one revolution of the optical disk, and its amplitude is not very large. However, if the optical pickup is moved by a large amount due to a jump command, or if shock-related disturbances are applied to the device, the relative positions of the optical disk and the optical pickup will change rapidly, and a large number of recording tracks will be removed from the optical pickup device 2. A traverse signal is generated as shown in B when jumping over.

This traverse signal B also has a high amplitude level, and when this is supplied to the tracking coil as tracking error, the two-axis tracking servo becomes unstable and at the same time various variations in the optical system are added. This results in an asymmetrical signal output in both positive and negative directions. Therefore, when such a signal is input to the integrating circuit 5, a low-frequency AC component as shown in C is generated, and this erroneous feed servo signal drives the optical pickup device 2. becomes increasingly unstable, and thereafter a phenomenon occurs in which stable tracking servo is not applied for a long time.

[Purpose of the invention]

The present invention provides an optical head feed servo circuit for the purpose of eliminating unstable tracking conditions caused by external shock vibrations, optical pickup jumps, or the like.

[Summary of the invention]

In this invention, a limiter circuit is inserted on the input side of a servo circuit that drives a feed mechanism that moves an optical pickup device to limit the amplitude at constant positive and negative levels centering on the O level of a tracking error signal. It is. Therefore, even if the tracking signal becomes unstable, the limiter circuit keeps its amplitude constant in both positive and negative directions, and the servo signal obtained by integrating this signal is not affected by disturbances in the tracking signal.

〔Example〕

FIG. 3 is a block diagram showing an embodiment of the present invention, and the same reference numerals as in FIG. 1 indicate the same parts.
In this figure, 10 is a signal limiting circuit placed before the integrating circuit 5 (low-pass filter).

This signal control circuit 10 includes, for example, diodes D ₁ , which are connected inversely to each other as shown in FIG.
_D2 and a unit amplifier G.

As is well known, these reversely connected diodes D ₁ and D ₂ conduct at approximately 0.5V, so as mentioned above, the large amplitude traverse signal B
When input, as shown by the dashed line in FIG. 2, signals of approximately ±0.5V or more are short-circuited, and signals of a certain level or more, centered around the O level, are not output from the unit amplifier G.

Therefore, only signals of constant positive and negative levels are input to the integrating circuit 5, and unstable alternating current signal components do not occur in the feed servo signal as described above. However, the tracking error signal in the normal reproduction state is supplied to the integrating circuit 5 without being short-circuited by the diodes _D1 and _D2 , and is sent to the thread feed motor 7 as a feed servo signal to move the optical pickup device 2 in the radial direction. Supplied.

As the signal limiting circuit 10, Zener diodes may be used in place of the diodes _D1 and _D2 , and it goes without saying that other active elements such as transistors can also be used as limiters.

〔Effect of the invention〕

As explained above, in the optical head feed servo circuit of the present invention, a limiter circuit is inserted at the inlet side of the servo circuit, and the limiter circuit can be used even when an asymmetric signal such as a traverse signal when the optical pickup is moved is input. Since the envelope is made vertically symmetrical by the limiter action and is input to the integrating circuit, the feed mechanism will not operate due to an erroneous feed servo signal. Therefore, even if there is a jump or disturbance vibration in the optical pickup, the tracking servo will recover in a short time, and the advantage is that the phenomenon in which the optical pickup device greatly jumps over the recorded track and unstable tracking conditions can be reduced. There is.

[Brief explanation of drawings]

Fig. 1 is a block diagram for explaining the tracking servo mechanism, Fig. 2 is a waveform diagram of a tracking error signal and a sending servo signal, Fig. 3 is a block diagram showing an embodiment of the present invention, and Fig. 4 FIG. 2 is a circuit diagram showing a specific example of a signal limiting circuit. In the figure, 3 is an operational amplifier circuit, 4 is a drive circuit,
5 is an integrating circuit, 6 is a power amplifier, 7 is a thread feed motor, and 10 is a signal limiting circuit.

Claims (1)

[Claims] 1. A feed servo circuit for an optical head, characterized in that a limiter is inserted on the input side of the feed servo circuit to limit the amplitude at a constant positive and negative level centered on the O level of a tracking error signal.