JPH0756700B2 - Optical disk device - Google Patents

Description

The present invention relates to an optical disk device for recording / reproducing information on / from an optical disk medium.

[Conventional technology]

The size of the push-pull signal obtained by irradiating the optical disc with laser light is the pre-groove of the optical disc or
It depends on the shape of the pit. However, the push-pull signal detection optical system of the optical head causes an offset in the push-pull signal when the lens deviates from the center. The lens shift occurs when the lens follows the eccentricity of the optical disk due to the tracking servo, or when the tracking of the optical head is delayed due to the deviation of the feed servo of the optical head.
The push-pull signal detection optical system generates an offset in the push-pull signal even when the optical disc is tilted.

[Problems to be Solved by the Invention]

The offset of the push-pull signal increases the tracking servo deviation during recording / reproduction. In the case of a disk having a large I push-pull signal of the push-pull signal waveform of FIG. 6, the offset of the I-b and I-c push-pull signals becomes a tracking servo deviation, which significantly deteriorates the recording / reproducing performance.

Further, in the worst case, tracking servo becomes impossible. In the case of a disc having a small push-pull signal II in the push-pull signal waveform of FIG. 6, II-b and II-
The offset of the push-pull signal of c reaches a level at which negative feedback as a tracking servo signal is not realized, and the tracking servo becomes unstable and may not be closed.

[Means for Solving the Problems]

The present invention relates to a push-pull signal detection circuit for detecting a push-pull signal of an optical head and a lens position detector for detecting a radial deviation of a lens of the optical head in an optical disc device for recording and reproducing information on an optical disc. A means for track servoing the optical head, a correction circuit for correcting the detection signal of the push-pull signal to obtain the push-pull signal, an offset detection circuit for detecting the DC offset and AC offset of the push-pull signal, and the detected AC
A means to AD convert the offset signal and input the data to the correction circuit via the digital signal processing means to variably control the output of the lens position detection circuit, to remove the AC offset from the push-pull signal detection signal, and the detected DC offset signal. To
An optical disk device for obtaining a push-pull signal, comprising means for AD-converting and storing data and means for inputting the stored data to the correction circuit to remove DC offset.

[Action]

The lens position detector that detects the lens shift and its position detection circuit have a proportional relationship between the lens shift position signal that detects the lens position and the offset AC component (eccentricity component) of the push-pull signal. , The phase ratio is controlled by the correction circuit from the value of the AC offset by making the phase opposite to the offset of the push-pull signal and added to the push-pull signal to cancel the offset. Since the DC component of the push-pull signal offset is proportional to the tilt angle of the disc, the DC component of the push-pull signal offset is detected, and the phase is reversed using a correction circuit and added to the push-pull signal to cancel the offset. . A microcomputer can be used for the correction control, the optimization control of the correction value, and the timing of the correction. Further, since the correction control and the optimization control of the correction value are performed on various discs having different push-pull signal magnitudes, push-pull signals are transmitted to various discs having different push-pull signal magnitudes. The tracking servo used can be realized.

〔Example〕

The process of correcting the push-pull signal will be described with reference to FIGS. 1, 2, and 3.

First, the correction of the AC offset of the push-pull signal will be described.

Lens 1a of optical pickup 1 by tracking servo
Follows the eccentricity of the disk 20, which causes the lens 1a to shift. The amount of deviation of the lesbian and the offset of the push-pull signal are in a proportional relationship. Therefore, the disc 20
When the same displacement as that of the eccentricity is applied to the lens 1a, a push-pull signal including an offset can be obtained. In this case, only the focus servo of the optical head is turned on.
If you subtract the lens position signal of the same magnitude as this offset from the push-pull signal that includes the offset,
A push-pull signal with offset removed is obtained.
First, a method for detecting an offset will be described, and then a method for obtaining a lens position signal having the same magnitude as the offset will be described.

First, the waveform of FIG. 3a (the same displacement signal as the maximum eccentricity of the disc) is input to the tracking servo amplifier 2 of FIG. 1 and the same displacement as the maximum eccentricity of the disc is applied to the lens 1a. The output of the push-pull signal detection circuit 3 has a waveform of b (push-pull signal including an offset). Here, when the correction circuit 4 is not operated, the waveform of b is directly input to the offset detection circuit 5. The waveform of b is input to the peak hold circuit 6 and the bottom hold circuit 7 of FIG. 2, which is a block diagram of the offset detection circuit 5, and the respective outputs are the peak-held waveform of c and the bottom-held waveform of d. Becomes By inputting the waveform of e into the HPF8 and removing the DC component, the waveform of f is obtained. The waveform of f is an AC offset component of the push-pull signal and is proportional to the lens displacement signal a given to the lens 1a. Further, the waveform of f is input to the peak hold circuit 9 to detect the magnitude of the AC offset component of the push-pull signal, and the waveform of g is obtained. This is input to the A / D converter 10, converted into 4-bit data, and taken into the microcomputer 11. Based on this data, the microcomputer 11 variably controls the magnitude of the output signal h of the lens position detection circuit 12 so that the amplification factor variable circuit 13
Control data is output to.

If the value of the lens position signal having the same magnitude as the offset is subtracted, a push-pull signal with the offset removed can be obtained, but the magnitude of the offset and the magnitude of the lens position signal differ depending on the disc. Therefore,
It is necessary to change the amplification factor of the amplification factor variable circuit 13 that variably controls the size of the output signal of the lens position detection circuit 12 so as to make the size of the offset equal to the size of the lens position signal, for each disc.

The amplification factor is set by appropriate control data of the microcomputer 11, and subtraction is performed from the waveform of b. In this way, the correction circuit 4 is operated, the offset detection circuit 5 performs the series of offset detection operations described above, the waveform of g is taken in through the A / D converter 10, and the control data of the amplification factor variable circuit 13 is 4 bits of data. Is controlled to be the minimum value. This optimization control is performed by the microcomputer 11. First, the optimization control algorithm
The 4-bit data is started from 1000 and is increased by 1 bit, and if the offset is increased, the data is decreased by 1 bit, and the control data of the amplification factor variable circuit 13 is optimized and controlled to minimize the offset. This optimization control is performed immediately after a new disc is mounted, and the correction operation is continuously performed thereafter.

The push-pull signal corrected as described above has a waveform of i, and the AC offset of the push-pull signal due to the displacement of the lens 1a that occurs when the disk is decentered is removed.

However, the waveform of i contains a DC offset, which must be removed.

Finally, the correction of the DC offset of the push-pull signal will be described.

The tilt angle of the disk 20 and the DC offset of the push-pull signal are in a proportional relationship. When the disc 20 is tilted, a push-pull signal including an offset is obtained. in this case,
Only the focus servo of the optical head is turned on. When the offset magnitude is stored in the memory and the read output is subtracted from the push-pull signal including the offset, the push-pull signal with the offset removed is obtained. First, the offset detection method will be described, and then the offset removal method will be described.

First, the waveform (a displacement signal equal to the maximum eccentricity of the disk) of FIG. 3 is input to the tracking servo amplifier 2 of FIG. 1 to give the lens the same displacement as the maximum eccentricity of the disk. The output of the push-pull signal detection circuit 3 has a waveform of b (push-pull signal including an offset). Here, when the correction circuit 4 is not operated, the waveform of b is directly input to the offset detection circuit 5. The waveform of b is input to the peak hold circuit 6 and the bottom hold circuit 7 of FIG. 2, which is a block diagram of the offset detection circuit 5, and the respective outputs are the peak-held waveform of c and the bottom-held waveform of d. Becomes By inputting the d waveform into the LPF 14 and removing the AC component, the waveform of j is obtained. The waveform of j is the DC offset component of the push-pull signal, and the tilt angle of the disk is proportional to the DC offset of the push-pull signal. This is input to the A / D converter 15 to be converted into 4-bit data and taken into the microcomputer 11. The microcomputer 11 stores this data in the memory and outputs the same data to the D / A converter 16.

By storing the magnitude of this offset in the memory and subtracting the read output from the push-pull signal containing the offset, the push-pull signal with the offset removed can be obtained. Depends on It also depends on the radial position of the disc. As shown in FIG. 4 showing an extreme example of the warp of the disc, the tilt angle of the disc may differ depending on the radial position. If the offset detection operation is performed each time a disc is newly mounted, it is possible to solve the problem that the disc is different. In addition, the number of locations where the disk offset is detected is determined at the radial positions of the disk, the DC offset is detected at each radial position, and the radial position and the magnitude of the detected offset are stored in the memory of the microcomputer 11. The radial position may be a time code or address corresponding to the radius. Every time a disc is newly mounted, the radial position and the magnitude of the detected offset are stored in the memory of the microcomputer 11. In the correction operation, the output of the D / A converter 16 is input to the correction circuit 4 and subtraction is performed from the push-pull signal pull signal including the DC offset. At this time, as the data output to the D / A converter 16, it is assumed that the data stored in the memory is read corresponding to the radial position.

The DC offset is detected after starting the AC offset correction operation, and the DC offset correction operation is continuously performed after the detection.

As described above, the corrected push-pull signal is i
, The AC offset of the push-pull signal due to the tilt angle of the disc is removed.

〔The invention's effect〕

According to the present invention, since the offset of the push-pull signal is digitally processed and removed, the offset can be corrected in accordance with the disk and the tracking servo with a small servo deviation can be performed.

[Brief description of drawings]

FIG. 1 is a block diagram for explaining the present invention, FIG. 2 is a block diagram of essential parts, FIG. 3 is a waveform diagram of each part, FIG. 4 is a diagram showing a warp of a disk, and FIG. 5 is a conventional example. FIG. 6 is a block diagram for explaining the above, and FIG. 6 is a diagram showing a push-pull signal waveform. 1 ... Optical pickup 1a ... Lens 2 ... Tracking servo amplifier 3 ... Push-pull signal detection circuit 4 ... Correction circuit 5 ... Offset detection circuit 6,9 ... Peak hold circuit 7 ... Bottom hold circuit 8 ... … High-pass filter 10 …… A / D converter 11 …… Microcomputer 12 …… Lens position detection circuit 13 …… Amplification factor variable circuit 14 …… Low-pass filter 15,16 …… D / A converter 20 …… Disk.

Claims (1)

[Claims] 1. An optical disc device for recording and reproducing information on and from an optical disc, wherein a push-pull signal detecting circuit for detecting a push-pull signal of an optical head and a lens position for detecting a radial shift of a lens of the optical head. A detector, means for tracking servo the optical head, a correction circuit for correcting the detection signal of the push-pull signal to obtain a push-pull signal, and the push-pull signal
An offset detection circuit that detects DC offset and AC offset, and AD-converts the detected AC offset signal and inputs data to the correction circuit through digital signal processing means to variably control the output of the lens position detection circuit. Means for removing the AC offset from the detection signal of the push-pull signal, means for AD converting the detected DC offset signal and storing the data, and means for inputting the stored data to the correction circuit to remove the DC offset An optical disk device comprising the: and obtaining a push-pull signal.