JPH0237581A - Digital servo device for optical head - Google Patents

Abstract

PURPOSE:To prevent sound jump due to track jump from being generated by making a servo error signal into a digital signal, limiting a change quantity between adjacent samples to a value by which no track jump is generated, and applying it on a servo loop. CONSTITUTION:A detected tracking error signal is converted to the digital signal by an A/D converter 24, and difference between the present sampling value X(n) obtained via a digital low-pass filter 26 and a digital phase correction circuit 28 and a sample delayed sampling value X(n-1) just before is computed by a subtractor 36. A comparator 38 performs the switching of a switch 30, and outputs X(n) when a subtraction value [X(n)-X(n-1)] is set within a value + or -X and X(n-1)+ or -X when it exceeds + or -X, and an output digital signal is converted to an analog signal at a D/A converter 40, and is applied on a tracking actuator in an optical head via a driver 42.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention is applicable to CD (compact disc) players, L
Regarding the servo device of the optical head in an optical disc playback device such as a V (laser vision disc) player, the servo error signal is digitally processed to prevent skipping due to discontinuous parts such as scratches and black spots on the disc surface. It is.

[Conventional technology]

In optical disc playback devices such as CD players and LV players, servo control such as tracking servo and focus servo is performed on the optical head. In this case, if there are discontinuous parts such as scratches, black spots, or air bubbles on the disc surface, noise as shown in Figure 2 will occur in the tracking error signal, causing the tracking actuator to swing significantly, causing track jumps and skipping. Even if it does not result in a track jump, noise may be generated due to playback errors or the like.

Conventionally, in order to solve such problems, the noise component in the servo error signal is detected, and the gain or frequency characteristics of the servo loop are changed (loop gain reduction, high frequency cut), or the servo loop is turned off. This prevents the actuator from swinging too much.

[Problem to be solved by the invention]

The method of switching the gain or frequency characteristics of the servo loose or cutting the loop has the disadvantage that it greatly affects the loop characteristics in terms of ensuring stability due to variable gain. In addition, depending on the type of scratch, the rise and fall of the noise component in the servo error signal may be extremely rapid, and controlling the preset loop response alone may not be effective enough to cause the actuator to swing significantly, resulting in skipped sounds. Sometimes it caused noise.

This invention solves the drawbacks of the conventional technology, does not significantly affect the loop characteristics against normal servo errors due to disk misalignment, etc., has excellent responsiveness, and prevents the actuator from swinging greatly regardless of the type of scratch. The present invention aims to provide a digital servo device for an optical head that can prevent sound skipping and noise generation.

[Means to solve the problem]

The present invention includes an A/D conversion means for converting an analog servo error signal into a digital signal, a current sample value x (n>) output from the A/D conversion means, and a previous sample value x ( x (n) -x (n
-1) is within ±X (X is a value greater than the maximum amount of change between adjacent samples of the servo error signal in the normal playback state and less than or equal to the minimum amount of change between adjacent samples that causes a track jump) a correction servo error signal output means that outputs x(n) and outputs x(n-1)±X when larger than ±X, and converts the output digital signal of the correction servo error signal output means into an analog signal. I)/
A converting means, and driving means for driving a servo actuator based on the output analog signal of the D/A converting means, and the subtracting means converts the output signal of the corrected servo error signal output means into It is characterized in that it is used as the immediately preceding sample value x(ni) in the calculation.

[For production]

According to this invention, the analog servo error signal is
After being converted into a digital signal by the conversion conversion stage, the subtraction means calculates the difference between the sample and the previous output sample. The correction servo error signal output means outputs x (n) when this subtraction value is within ±X, and outputs x (n) when it is larger than ±X.
x(n-1>±X) instead of x (n-1>±X).The output digital signal of the correction servo error signal output means is converted into an analog signal by the D/A conversion means, and the servo actuator is driven via the drive means. .

When the servo error signal passes through a discontinuous portion such as a scratch or a black spot, noise is generated as shown in FIG. 2 above. In this noise part, the level of the servo error signal changes rapidly, causing the servo actuator to swing significantly. Therefore, by limiting the amount of change between V4# samples to a maximum of ±X as in the present invention, the level change of the servo error signal becomes gradual in the discontinuous portion, and the servo actuator is prevented from swinging greatly. - Prevents skipping caused by track jumps.

〔Example〕

An embodiment in which the present invention is applied to a tracking servo is shown in FIG. 1. An optical disc 10 such as a CD or LV is rotationally driven by a disc motor 12. As shown in FIG.

The optical disk 10 is irradiated with a laser beam from the optical head 14, and the reflected light is received by a three-split photodetector 16 within the optical head 14. The light reception signals output from the tracking error detection photodiodes 18 and 20 of the photodetector 16 are subtracted by a subtracter 22 to detect a tracking error signal.

The detected tracking error signal is converted into a digital signal by an A/D converter 24 whose sampling frequency is set to about 30 to 50 Hz, for example 44.1KH7, and then a low frequency gain of about 20 to 100112 is converted to a digital signal. The current sample (ax(n) is obtained through the lifting digital low-pass filter 26 and the digital phase correction circuit 28 for ensuring a phase margin near the gain of 1, and is input to the contact a of the switch 30.The switch 30 outputs the current sample (ax(n)). The sample value is delayed by one sample in a register to obtain the previous sample value x(n 1).

A constant X is added to the previous sample value x<n-1) by an adder 34 to create x(n-1)+X, which is input to the terminal C of the switch 30. Also, the immediately preceding sample value x<n
1> is x(n-1)- after the constant X is subtracted by the subtracter 36
X is created and input to the terminal of switch 30. The comparator 38 compares x(n)-x(n-1) and X to switch the switch 30, that is, -X≦x(n
> When −x(n-1)≦X, switch 30 is connected to terminal a
to output the sample x (n) and x (n)
When -x(n-1)>X, the switch 30 is connected to contact C to output x(n-1)+X, and x(n)-x (
n-1) <-X, connect the switch 30 to the contact point and output x(n-1)-X.

The output of the switch 30 is converted into an analog signal by a D/A converter 40 and applied to a tracking actuator in the optical head 14 via a driver 42 to perform tracking control.

In the above configuration, the constant
Therefore, the maximum amount of change can be determined based on the relationship between a value based on this and the sampling period of the A/D converter 24. ) and less than the minimum amount of change between adjacent samples that is noise on the tracking error signal due to discontinuous parts such as scratches and black dots and causes track jumps. In this way, in the normal playback state, the amount of change between adjacent samples is within ± will be carried out. Furthermore, when passing through a discontinuous part such as a scratch or a black spot, noise is generated at is connected to contact S or C, so the output of switch 30 is
It is limited to (n-1)±X and becomes as shown in FIG. 3(b).

Therefore, if X is set to exactly the minimum amount of change between adjacent samples that causes a track jump, skips due to track jumps will be prevented, and if set to a value smaller than that, skips will occur in addition to skips due to track jumps. It is also possible to prevent the generation of noise due to playback errors caused by vibration, even if it is not so bad.

[Example of change]

In the above embodiment, the present invention was applied to a tracking servo, but it can also be applied to various servos of an optical head such as a focus servo.

〔Effect of the invention〕

As explained above, according to the present invention, a servo error signal is converted into a digital signal, and when the amount of change between adjacent samples is large enough to cause a track jump, the amount of change is converted into a value X that does not cause a track jump. Since the signal is applied to the servo loop with a limit of 100 kHz, it is possible to prevent sound skipping and noise generation due to track jumps even when passing through a discontinuous portion such as a scratch or a black spot. Furthermore, this is not due to gain variation but to replacement of data samples, and in normal playback conditions where the amount of change between adjacent samples is small, the servo error signal is output as is, so it does not have any effect on normal servo. Moreover, since it is a digital signal processing system, changes between samples can be accurately grasped. Therefore, if the sampling frequency is increased, the rise of the noise component in the servo error signal,
Since it can handle even extremely sudden falls, it is possible to prevent sound skipping due to track jumps, etc., regardless of the type of scratches.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment in which the present invention is applied to a tracking servo. FIG. 2 is a waveform diagram showing a tracking error signal when passing through a scratch or a sunspot. FIG. 3 shows the sample x (n) in FIG. FIG. 3 is a waveform diagram showing an analog version of x(n-1). Engineering O...Optical disk, 14...Optical head, 16...
- Photodetector, 24... A/D converter, 38... Comparator, 40... D/A converter, 42... Driver. Third

Claims (1)

[Claims] A/D conversion means for converting an analog servo error signal into a digital signal, and a current sample value x(n
) and the previous sample x value (n-1) output just before that
and a subtraction means for calculating the difference between x and
(n) - x (n - 1) is ± a correction servo error signal output means that outputs x(n) when the value is within the value of ±X, and outputs x(n-1)±X when it is greater than ±X; D/A converting means for converting a digital signal into an analog signal; and driving means for driving a servo actuator based on an output analog signal of the D/A converting means, and the subtracting means is adapted to perform the correction. In the next calculation, the output signal of the servo error signal output means is calculated using the immediately preceding sample value x(n
-1) A digital servo device for an optical head, characterized in that it is used as: