JPS59217239A - Track tracing device for disk - Google Patents

Abstract

PURPOSE:To prevent a track jump even if a light spot strikes a flaw or stain part to cuase the disorder of a tracking error signal, by detecting the level of envelopes of a high frequency signal reproduced from a disk, and substituting it with a signal which is held at a potential in an envelope level drop. CONSTITUTION:The tracking error signal 12 is supplied to a phase compensating circuit 13 through the 2nd analog switch 24b to put a tracking servo system in operation. When, however, the envelope 18 of the high frequency signal 17 detected on a track drops below a preset value Vref, the 1st and the 2nd switches 24a and 24b are changed over for a specific period determined by a pulse signal 30. The mean value of the tracking error signal right after the envelope drop is supplied from a holding circuit 25 and a phase compensating circuit output having a specific level based upon the input signal is generated, so that a tracking actuator 15 keeps on holding the position.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a track tracking device for a disc, and more particularly, to a track tracking device for tracking information on a disc used in, for example, an optical digital audio disc player or an optical video disc player.

FIG. 1 is a schematic block diagram showing a tracking device of a conventional optical digital audio disc player, FIG. 2 is a diagram showing the positional relationship of three light spots that illuminate the tracks of the disc, and The figure is a waveform diagram of a tracking error signal and a high frequency signal obtained when a light spot traverses the disk.

First, in FIG. 1, a laser beam 2 output from a laser light source 1 is divided into three laser beams by a diffraction grating 3, passes through a beam splitter 4°λ/4 plate 5,
The light is collected by an objective lens 6 and focused on an information track 8 on a disk 7 . At this time, if track tracking is performed at the correct position, as shown in Figure 2 (m
), three light spots 16a to 16G
appear in line at positions inclined at a predetermined angle with respect to the direction of the information track 8. On the other hand, the three laser beams reflected by the information track 8 of the disk 7 follow the opposite course to the above explanation and are sent to the beam splitter 4.
photodetectors 9a, 9b.

It is bent towards 9C. The central photodetector 9b among the three photodetectors is used for reading the high frequency signal 17 recorded on the information track 8 and for focus servo for focusing the light spot. Furthermore, the two outer photodetectors ga and gc are used for tracking servo.

As shown in FIG. 2(m), if the three light spots 16a to 16C are properly positioned on the track 8, the amount of light incident on the photodetectors 9a and 90 on both sides will be equal; The tracking error signal 12, which is the output signal of the differential amplifier 11, has a zero potential. In addition, as shown in FIG. 2 (k) and (n), three light spots 16a
160 is at a position shifted from the information track 8, the amount of light incident on the photodetectors 9a and 90 will be different, so the tracking error signal 12, which is the output of the differential amplifier 11, will be positive or negative. The potential is . In FIG. 1, preamplifiers 10a, 10b, and 10C are connected to photodetectors 9a, 9b, and 9° to amplify minute currents and convert them into voltages.

In an actual disk device, the information tracks 8 are arranged very closely, so the tracking error signal 12 is output in the form shown in FIG. 3(a), and one track consisting of -(, A dragging servo is applied to follow it.In addition, when the optical spot 16b is located at the center of the information track 8, the reproduction high-frequency signal @17 shows that when the optical spot 16b is located at the center of the information track 8, the tracking error signal 12 has an upward slope to the right (third (in the case shown in the figure), the amplitude of the envelope 18 of the reproduced high-frequency signal 17 becomes maximum.The deviation of the laser beam from the center of the track is detected by the principle described above, and the tracking error signal 12 is O
the tracking actuator 15 via the power amplifier 14 through the phase compensation circuit '13 so that the potential is
moves the objective lens 6 in the radial direction of the disk 7, and a tracking operation is performed.

Conventional tracking devices follow the information track 8 on the disk 7 based on the principle explained above, but this only applies if the information track 8 on the disk 7 is accurately recorded and the recording surface is This assumes that the disc protective film that protects the disc is free from scratches and dirt.

If there are scratches on the recording surface or protective film of the disk, or if there is dirt on the surface, the reflected light from the disk 7 will not enter the photodetectors 9a to 9C normally. A tracking error signal 12 as shown in a) is no longer obtained. As a result, it becomes impossible to follow the track, and in the worst case, the track may jump.
You end up stuck in a pause state where you keep following the same track, or you end up in a fast-forward or reverse-forward state.

Therefore, the main purpose of this invention is to improve the problem that conventional tracking devices are invulnerable to scratches and dirt on the disk, and to solve the problem of a tracking error signal being disturbed when a light spot enters the scratched or dirty part. To provide a tracking device that does not cause track skipping even if the track jump occurs.

The above objects and other objects and features of the invention will become more apparent from the following detailed description with reference to the drawings.

To summarize the invention, the reflected light from the disk is incident on a photodetector, a tracking error signal is formed from the light intensity of the reflected light spot, and the level of the envelope of the high frequency signal reproduced from the disk is detected. When the level of this envelope drops below a predetermined value, the tracking error signal that is input to the phase compensation circuit for controlling the tracking actuator for a certain period of time is changed to the signal held at the potential just before the envelope level drops. Replace. If the envelope recovers after a certain period of time, that is, if an accurate tracking error signal can be obtained, the tracking error signal is again input to the subsequent phase compensation circuit. In this way, even if the tracking error signal is disturbed during the envelope drop time, it will not be output to the subsequent stage, and the potential just before the envelope drop will be transmitted as is, allowing the tracking operation to be performed. .

FIG. 4 is a schematic block diagram of an embodiment of the present invention,
FIG. 5 is a waveform diagram of each part of FIG. 4.

First, in FIG. 4, from the laser light source 1 to the λ/4 plate 5,
is the same as in FIG. 1 above. A high frequency signal @17 which is an output signal of the preamplifier 10b connected to the central photodetector 9b is input to an information reading circuit (not shown) and also to a comparator 19. A reference voltage V ref is applied in advance to the other terminal of the comparator 19, and the envelope 18 of the high frequency signal 17 and the reference voltage Vref are compared. When the envelope 118 falls below the reference voltage Vref, the comparator 19 outputs, for example, a high level signal @26 (see waveform 26 in FIG. 5), and when the envelope 18 does not fall, it outputs a low level signal. do.

A low-pass filter 20 is connected to the next stage of the comparator 19. This is because the tracking servo system can continue to operate without much disturbance for cases where the envelope fall period is relatively short. .3m5ec), and the output 27 of the low-pass filter 20 is fed to the next stage buffer 21 for waveform shaping. The output signal 28 of the Barafun 21 is input to one side of the OR circuit 23 and is also input to the monostable multivibrator 22 . The monostable multivibrator 22 outputs a constant length pulse triggered by the fall of the output signal 28 of the buffer 21, as shown by the signal 29 in FIG. This pulse signal is applied to the other input terminal of the OR circuit 23. The output of the OR circuit (pulse width of g30 is the standard value (approximately 0.3 m
sec ) becomes shorter than J, the output 1 of the OR circuit 23
On August 30, the first analog switch 24a etc.
Controls analog switch 24b. Here, the first analog switch 24a outputs the tracking error signal 12.
The output terminal of the differential amplifier 11 and the hold circuit 25 forming the
inserted between. When the output signal 30 of the OR circuit 23 is at a high level, the first analog switch 24a is in an off state, that is, the tracking error signal 12 is not input to the hold circuit 25, and the hold circuit 25 maintains the previous state. In addition, the second analog switch 24
b serves to switch the input terminal of the phase compensation circuit 13 between selecting the tracking error signal 12 which is the output of the differential amplifier 11 or the holding output signal 31 of the hold circuit 25. When the output signal 30 of the OR circuit is at a high level, the first analog switch 24a is turned off and the second analog switch 24b is connected to the hold circuit 25. That is, the envelope 118
During the period when the differential amplifier 11 is decreasing and for a certain period after recovery, the tracking error signal 12 which is the output of the differential amplifier 11 is not transmitted to the phase compensation circuit 13 in the subsequent stage, and the hold circuit 2
5 output signal 31 is transmitted. Note that the hold circuit 25 is constituted by a time constant circuit that sufficiently responds to the disk rotation frequency component included in the tracking error signal 12, but does not respond to the high frequency component. As a result, the average of the tracking 1 and 1 signals is held without holding the erroneous tracking error signal caused by noise or the like.

In the circuit configured as described above, in the case of normal track tracking operation, the tracking error signal 12 is
phase compensation circuit 13 through the analog switch 24b.
The 1-racking servo system is activated. However, when the envelope 18 of the high frequency signal 17 detected from the track becomes less than the preset value V ref,
The first and second periods given by the pulse signal 30
The switches 24a and 2'llb are switched, and the signal shown in the waveform 32 of diagram M5 is input to the phase compensation circuit 13. During the envelope drop period and for a certain period after recovery, the average value of the tracking error signal immediately after the envelope drop outputted from the hold circuit 25 is given, and a phase compensation circuit output of a certain level is formed based on this human signal. The tracking actuator 15 continues to maintain its position. Next, when a certain period of time set by the monostable multivibrator 22 etc. has elapsed,
The connection states of the first and second analog switches 24a and 24b are switched, respectively. At the time when this switching is performed, since an accurate tracking error signal has already been obtained, track following according to the 1-racking error signal is promptly resumed.

Although the above-mentioned embodiment has been explained using a tracking device, it is clear that the present invention can also be applied to a focusing device that focuses on a disk, and the same effect can be achieved by using a held signal. Furthermore, although the above embodiments have been described with reference to optical audio or video disc players, the present invention can also be applied to devices that perform similar track tracking.

As described above, according to the present invention, the recording surface of the disc,
If the reflected light does not return to normal due to scratches on the protective film or dirt on the disc surface, and the envelope of the reproduced high-frequency signal decreases, making it impossible to obtain an accurate tracking error signal, the envelope may be on the verge of decreasing. By holding the average value of the tracking error signal and transmitting the held potential to the subsequent stage, it is possible to stop the occurrence of abnormal vibrations of the tracking actuator due to abnormal changes in the envelope. Normal tracking can be carried out without the problem of track skipping that occurs in the case of conventional methods.

[Brief explanation of the drawing]

Figure 1 shows the RI! of a conventional tracking device. 8 block diagram. FIG. 2 is a diagram showing the positional relationship of three light spots that illuminate the tracks of the disk. FIG. 3 is a waveform diagram of a tracking error signal and a high frequency signal obtained when the optical spot traverses the disk. FIG. 4 is a schematic block diagram of an embodiment of the present invention. FIG. 5 shows six diagrams of signal waveforms at each part in FIG. 4. In the figure, 1 is a light source, 2 is a laser beam, 7 is a disk, 8 is an information track, 9a to 9G are photodetectors, 1
1 is a differential amplifier and 13 is a phase? ili compensation circuit, 15 is a tracking actuator, 19 is a comparator, 20
is a low-pass filter, 22 is a monostable multi-bi break, 23 is an OR circuit, 24a is a first analog switch,
24b is a second analog switch, and 25 is a hold circuit. Agent: Masuo Oiwa Procedural amendment (voluntary) August 25, 1958 2. Title of invention: disk track tracking device; 3. Relationship with old cases to be amended
No. 12 No. 3 Name (601) - Nisubishi Electric Co., Ltd. Representative Hitoshi Katayama 4, Agent fJ Yu Address No. 3, 2-2 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Electric Co., Ltd. 56 Subject of amendment Me Column 6 of the Detailed Description of the Invention, page 10, lines 10 to 13 of the Specification of Contents of the Amendment [OR circuit output signal...J is corrected to the following sentence so as to make it shorter. The pulse width of the above-mentioned pulse No. 1g is based on the standard #i (approximately 0°3m5), which requires the envelope drop time to be cleared.
ec) is set to be shorter than

Claims (5)

[Claims] (1) A track tracking device for tracking a track on which information is recorded on an information recording medium in an optical reproducing device that optically reproduces information from an information recording medium, the track tracking device comprising: a reproduction signal from the information recording medium; a circuit that forms a tracking error signal for tracking the track; a hold circuit that holds the tracking error signal for a certain period of time; and a hold circuit that detects a reproduction signal from the information recording medium and controls the tracking based on the detection result. A disc comprising: a selection circuit that selects either an error signal or a hold circuit output; and a tracking servo that receives the selected signal and controls the relative position of the information recording medium and the light beam. track tracking device. (2) The selection circuit comprises: voltage comparison means for comparing the envelope of the reproduced signal from the information recording medium with a reference voltage; a low-pass filter for removing the output signal of the voltage comparison means and high-frequency components; and the low-pass filter. a buffer amplifier that shapes the waveform of an output signal; a pulse generating means that is triggered by the output signal of the buffer amplifier and generates a pulse of a constant length; and a gate circuit that receives the output signal of the buffer amplifier and the output of the pulse generating means. and a switch circuit that performs a switching operation according to the output of the gate circuit and passes either the tracking error signal or the output of the hold circuit. (3) The low-pass filter is configured to block those whose envelope drop time caused by defects in the information recording medium to be reproduced is smaller than a standard value that must be cleared, and to allow those exceeding the standard value to pass through. A disc track tracking device according to claim 2, wherein (4) The low-pass filter is configured to set the output pulse width from the pulse generating means to be shorter than a standard value that must be cleared by an envelope drop time caused by a defect in the information recording medium. A disk track tracking device according to scope 2. (5) The disk track tracking device according to claim 1 or 2, wherein the hold circuit is set to a time constant that sufficiently responds to the rotation frequency of the information recording medium.