JPH06103590A - Device for detecting speed for optical disk - Google Patents

Abstract

PURPOSE:To control a speed by using a speed signal by the frequency of the binarization output of a track traverse difference signal. CONSTITUTION:The track traverse difference signal is binarized by a binarization circuit 9, and a counter output is generated by a periodic counter 11. By a period/speed converter 13, a constant is divided by respective count values of the counter output and outputted as a speed signal value. By a speed difference detection part, the difference between the speed signal value and the last time value, that is, a speed difference signal is outputted. The signal is compared with a prescribed reference value showing a normal range level, and when it has not exceeded the normal range level, a comparator is inactive, and the speed signal from the converter 13 is outputted as a detected speed signal as it is through a D/A converter 17 and a lowpass filter 19. By such a manner, erroneous speed detection is prevented even when a noise occurs in the track traverse signal, etc., in a light beam, and seek control is performed stably and accurately.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a speed detecting device for an optical disk, and more particularly to a speed detecting device for an optical disk which obtains a moving speed of a light beam from a track crossing signal of the light beam to prevent an abnormal speed detection due to noise and to accurately perform the detection. The present invention relates to a technique for performing a seek operation.

[0002]

2. Description of the Related Art Conventionally, in an optical disk device, a track crossing signal detected when a light beam crosses a track has been used to allow an optical head to access a desired track on the disk. That is, the counter measures the period of the track crossing signal of the light beam, calculates the period signal obtained from the measured value to obtain the velocity signal, and uses the velocity signal to detect the velocity of the light beam and the optical head. Speed control, that is, seek control. See, for example, JP-A-63-173230.

[0003]

However, in such a conventional apparatus, when measuring the period of the transverse signal of the light beam, for example, by using preformed pits (prepits) of a preformatted optical disk, etc. Noise may be generated in the track crossing signal, or electrical noise may be generated around a circuit including a counter for counting the period of the track crossing signal. When such noise occurs, the track crossing cycle of the light beam cannot be correctly measured, and thus the track crossing speed of the light beam may be erroneously detected.
If the track crossing speed is erroneously detected, the speed control of the optical head, that is, the seek control is not accurately performed, and a desired track cannot be quickly accessed or cannot be accessed.

In view of the problems in the above-mentioned conventional apparatus, it is an object of the present invention to make an erroneous speed detection in an optical disk speed detecting apparatus even if noise occurs in a track crossing signal of a light beam. It is to prevent the seek control from being performed stably and accurately.

[0005]

In order to achieve the above object, according to the present invention, an optical disk is used for an optical disk in which a moving speed of a light beam is obtained from a measured value of a period or a frequency of a track crossing signal of the light beam. A speed detecting device is provided, and the speed detecting device for an optical disc is

A cycle or frequency-to-speed conversion means for sequentially generating a speed signal from a measured value of the cycle or frequency of the light beam cross-track signal, and a speed memory means for sequentially storing the value of the speed signal as a previous value, Speed difference detecting means for obtaining a difference between the speed signal and a previous value stored in the speed memory means, and comparing means for detecting whether or not the speed difference obtained by the speed difference detecting means is larger than a predetermined value. A selection to output the previous speed signal value stored in the speed memory means or the corrected speed signal value predicted from the previous speed signal value when the speed difference detected based on the output of the comparison means is larger than a predetermined value And means.

[0007]

In the above structure, the period or frequency-to-velocity converting means sequentially generates velocity signals from the measured values of the period or frequency of the track crossing signal of the light beam. This speed signal is sequentially stored as the previous value in the speed memory means. Then, the speed difference detecting means obtains a difference between the speed signal output from the period or frequency-to-speed converting means and the previous value stored in the speed memory means, and the difference is given by the comparing means as a predetermined value. Compare with. If the detected speed difference is larger than a predetermined value based on the comparison by the comparing means, the selecting means stores the previous speed signal value stored in the speed memory means or the corrected speed predicted from the previous speed signal value. Output the signal value. Therefore, even if the original speed signal was not output properly due to noise, an abnormal speed signal that would cause the seek operation to fail will not be output, and a serious malfunction such as inability to access the desired track will occur. It will not occur.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic structure of an optical disc speed detecting apparatus according to an embodiment of the present invention. The device in the figure is
An optical head 3 for irradiating the optical disc 1 with a light beam, a servo light detection system 5 for detecting servo light from the optical head 3,
A low-pass filter 7 connected to the servo light detection system 5,
A binarization circuit 9 and a period counter 11 for counting using a clock signal of a predetermined frequency, for example, 10 MHz.
And a data processor 15 including a period / speed converter,
It is composed of a D / A converter 17, another low-pass filter 19, a subtracter 21, a current driver 23, and the like.

In the apparatus shown in FIG. 1, the servo light detection system 5
Detects servo light output when the optical head 3 moves a track of the optical disc 1 in a radial direction, for example, and generates a track crossing difference signal of a light beam in a known manner. This track crossing difference signal is converted into a binary signal by a binarizing circuit 9 after removing noise through a low pass filter 7. 2A and 2B show the cross-track difference signal and the binarized signal after passing through the low-pass filter 7, respectively. In FIG. 2, the speed at which the light beam traverses the track is assumed to be constant.

The binarized signal output from the binarization circuit 9 is input to the cycle counter 11, and the cycle is measured as the number of 10 MHz clocks that can be counted within the cycle time. The period of the binarized signal is measured as the time from one rising edge to the next rising edge of the binarized signal or the time from a certain falling edge to the next falling edge.

The cycle data measured in this manner is taken in by the data processor 15 as a 12-bit signal, for example, and the cycle is converted into a speed by the division V = K / T. Here, V represents speed data, T represents cycle data, and K represents a constant. The velocity data thus obtained is further inputted to the D / A converter 17 in the data processor 15 after the large fluctuation due to noise is removed, as will be described later in detail. The speed signal converted into an analog signal by the D / A converter 17 passes through another low-pass filter 19 for smoothing, and then is input to the subtractor 21 as a detected speed signal. The reference speed signal is applied to the other input of the subtractor 21, so that the subtractor 21 generates a difference between the detected speed signal and the reference speed signal, and the difference is the current driver 23.
Entered in. Then, the current driver 23 drives the optical head 3 in a known manner to perform the seek operation of the light beam.

Next, the speed detecting operation in the apparatus according to the present invention will be described with reference to FIG. 3 and FIG. FIG. 3 shows a detailed configuration near the data processor 15 shown in FIG. In FIG. 3, the same parts as those in FIG. 1 are designated by the same reference numerals. As shown in FIG. 3, the data processor 15 includes, in addition to the cycle / speed converter 13 that converts the cycle signal input from the cycle counter 11 into a speed signal, the immediately preceding speed memory 25, the speed difference detection unit 27, and the comparator. Two
9 and a changeover switch 31 and the like. The immediately preceding speed memory 25 sequentially stores the speed data sequentially output from the cycle / speed converter 13 as a previous value.
The speed difference detector 27 subtracts the speed signal from the cycle / speed converter 13 and the speed signal corresponding to the previous speed data read from the immediately preceding speed memory 25 to obtain the difference between them. . Further, the comparator 29 compares the difference signal from the speed difference detector 27 with a reference signal indicating a normal range level. Furthermore, the changeover switch 31
On the basis of the output of the comparator 29, switching between the output data of the immediately preceding speed memory 25 and the speed signal from the cycle / speed converter 13 is performed.

In the apparatus having the above-mentioned configuration, the track crossing difference signal as shown in FIG. 2A is binarized by the binarizing circuit 9 and the binary signal as shown in FIG. Output is generated. Such a binarized output is
In the cycle counter 11, the cycle is counted by a clock having a frequency of, for example, 10 MHz, and (c)
The output shown in is generated. Although the output of the cycle counter has a triangular waveform in FIG. 2C, the cycle counter output actually increases in a stepwise manner.

The cycle / speed converter 13 in the processor 15 detects each count value of the output (c) of the cycle counter 11, that is, from the rising edge of the binarized output (b) to the next rising edge. The count value N of the period is taken out, the constant K is divided by this count value N to obtain K / N, and this is output as the speed signal value (d). The speed signal value (d) is stored in the immediately preceding speed memory 25 and is also supplied to the speed difference detection unit 27 and the changeover switch 31.

Therefore, the speed difference detecting section 27 subtracts such a speed signal value from the previous value stored in the immediately preceding speed memory 25, and outputs the difference between them, that is, the speed difference signal. This speed difference signal is compared with a predetermined reference value indicating the normal range level in the comparator 29, and it is determined whether or not the speed difference signal exceeds the level of the normal range. If the speed difference signal does not exceed the normal range level, the comparator 29
Becomes inactive, for example, and the changeover switch 31 remains in the position shown. Therefore, the speed signal (d) from the cycle / speed converter 13 is directly applied to the D / A converter 17
And is output as a detected speed signal via the low-pass filter 19.

However, for example, when noise that cannot be removed by the low-pass filter 7 as shown in the central portion of the waveform of FIG. 2A remains in the track crossing difference signal, the binarization circuit. The output of 9 has a signal "0" portion corresponding to the noise portion as shown in (b). Therefore, the output of the cycle counter 11 is also as shown in (c).
A value smaller than the actual cycle count value such as M is output as the cycle count value. Therefore, the speed signal output from the cycle / speed converter 13 has a value K / M that is very different from the actual speed, as shown in (d).

However, according to the present invention, in this case, the speed difference signal output from the speed difference detector 27 becomes very large, and the comparator 29 determines that the speed difference signal exceeds the normal range level. It Therefore, the comparator 29 gives a signal indicating an abnormal state, that is, an abnormal signal to the changeover switch 31, and the changeover switch 31 is changed over to the position shown by the dotted line in FIG. Therefore, D /
As the speed signal supplied to the A converter 17, not the output of the cycle / speed converter 13, but the speed data immediately before stored in the speed memory 25 immediately before is used. As a result, as the detected speed signal (e), the same value K / N as the previous time is output, and the output of the abnormal speed signal due to noise is blocked.

In the embodiment shown in FIG. 3, the comparator 2
When 9 outputs an abnormal signal, the previous speed data stored in the immediately preceding speed memory 25 is output.
Instead of outputting the previous value of the speed data, it is possible to output the predicted speed data using the previous value or the like.

[0019]

As described above, according to the present invention, with a relatively simple structure, it is possible to accurately determine that an abnormal speed signal is output due to a track crossing difference signal or noise around the period counter in the optical disk device. Can be prevented. Therefore, for example, the stability of the direct seek operation in the optical disk device can be improved, and a desired track can be accessed quickly and accurately.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a speed detecting device for an optical disk according to an embodiment of the present invention.

FIG. 2 is a signal waveform diagram for explaining the operation of the device of FIG.

3 is a block diagram showing a detailed configuration of a speed signal processing unit including a period / speed converter in the apparatus of FIG.

[Explanation of symbols]

 1 Optical Disc 3 Optical Head 5 Servo Light Detection System 7, 19 Low Pass Filter 9 Binarization Circuit 11 Period Counter 13 Period / Speed Converter 15 Data Processor 17 D / A Converter 21 Subtractor 23 Current Driver 25 Immediate Speed Memory 27 Speed Difference detection unit 29 Comparator 31 Changeover switch

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kikuji Kato 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (1)

[Claims] 1. A velocity detecting device for an optical disc, wherein a moving velocity of a light beam in an optical disc device is obtained from a measured value of a period or frequency of a cross-track signal of the light beam, wherein a period of the cross-track signal of the light beam or A cycle or frequency-to-speed conversion means for sequentially generating a speed signal from the measured value of frequency, a speed memory means for sequentially storing the value of the speed signal as a previous value, a previous time stored in the speed signal and the speed memory means. A speed difference detecting means for obtaining a difference with the value, a comparing means for detecting whether or not the speed difference obtained by the speed difference detecting means is larger than a predetermined value, and a detected speed difference based on the output of the comparing means. Is larger than a predetermined value, the previous speed signal value stored in the speed memory means or the corrected speed signal value predicted from the previous speed signal value is calculated. Optical disk speed detecting apparatus characterized by comprising selecting means for force, the.