JPH06150353A - On-track adjusting method for optical pickup device - Google Patents

Abstract

PURPOSE:To realize the on-track adjustment of each beam by means of an automatic machine by detecting a specialized signal having the same pattern and periodically existing on a disk by means of respective detected outputs obtained from two beams. CONSTITUTION:If each sub-beam becomes to be in an off-track state, the number of times of detection counted by a counter 18 in a fixed period determined by an on-track discriminating circuit 17 is extremely smaller value compared with the number of times of detection at the time of on-track even when erroneous detection occurs. Consequently, only at the time of on-track, the condition in which the on-track discriminating circuit 17 generates the on-track is satisfied. A diffraction grating rotating device 19 continues rotating operation until an on-track signal is supplied. Also, a main beam is arranged at the center of a straight line (t) connecting the respective sub-beams. Consequently, by that the arranged angles of the respective light beams of an optical pickup device are displaced, the on-track adjustment of the light beam is automatically performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an on-track adjustment method for placing each beam on the same signal track in an optical pickup device which performs tracking servo by the three-beam method.

[0002]

2. Description of the Related Art There is known an optical pickup device which performs a tracking servo for causing a light beam to follow a signal track of a disk by a three-beam method. An optical pickup device that employs such a three-beam method for tracking servo is usually a main unit for reading or writing a signal by diffracting a light beam generated from a light source such as a laser diode using a diffraction grating. In addition to the beam (zero-order light), the preceding and following sub-beams (± first-order light) arranged before and after it are created. Then, the optical pickup device determines the degree to which the light spot of each of the sub-beams is relatively applied to the signal track by detecting the difference in the amount of reflected light of each of the sub-beams, thereby detecting the tracking error with respect to the signal track of the main beam. It is made to be done.

By the way, in the optical pickup device which employs the tracking servo of the three-beam method, it is necessary to perform on-track adjustment so that each beam is correctly placed on the same signal track of the disk, and this on-track adjustment is an assembly work. It is incorporated in one item.

For the on-track adjustment, the diffraction grating is rotated to change the angle of the grating arrangement direction, and as shown in the schematic view of FIG. 2, the light spot 2 of the preceding sub-beam and the light spot of the rear sub-beam. It is necessary to shift 3 and 3 in the left and right opposite directions so that the same signal track 4 is half-split, and the light spot 1 of the main beam is adjusted to be in the center of the same signal track 4.

[0005]

Conventionally, in the above-mentioned on-track adjustment, the waveform showing the tracking error between each sub-beam and the signal track is observed by an oscilloscope by detecting the reflected light of each sub-beam on the disc, and This was done by manually rotating the diffraction grating while observing. That is, in the conventional on-track adjustment, it is necessary to rely on a person who observes the oscilloscope, and automation cannot be promoted, and there is a problem in workability.

[0006]

In view of the above-mentioned problems, the present invention is such that on-track adjustment can be performed by an automatic machine. The detection output obtained from at least two beams among the three beams makes it possible to perform the same on the disc periodically. Along with detecting the specific signal of the pattern, the passage time difference of the specific signal detected by each beam is detected, and the time difference is set in advance at a time corresponding to the dimension of the interval difference of the light spot positions on the disk of each beam. The on-track adjustment of each beam is performed by detecting the presence.

[0007]

1 is a circuit block diagram showing an example for achieving an on-track adjusting method for an optical pickup device according to the present invention, which is suitable for a compact disc (CD). In the figure, the first light receiving element 5 receives the reflected light of the preceding sub-beam on the disk, and the light receiving output obtained from the first light receiving element 5 is converted from a current signal to a voltage signal by the first current / voltage conversion amplifier 6. After the conversion, the digital signal recorded on the disc is taken out as an RF signal (high frequency signal) through the first low pass filter 7. The RF signal is subjected to waveform shaping by the first waveform shaping circuit 8 to be binarized and becomes one input signal input to the input switching circuit 9.

On the other hand, the second light receiving element 10 receives the reflected light of the subsequent sub-beam on the disk, and the light receiving output obtained from the second light receiving element 10 is converted into a voltage from the current signal by the second current / voltage conversion amplifier 11. After being converted to a signal,
The digital signal recorded on the disc through the second low-pass filter 12 is taken out as an RF signal. That R
The F signal is waveform shaped by the second waveform shaping circuit 13
The other input signal is digitized and input to the input switching circuit 9.

The input switching circuit 9 includes a switching control circuit 14
The switching is controlled by the switching control circuit 14, and the input signal supplied to the subsequent stage is switched under the control of the switching control circuit 14.

The input signal supplied through the input switching circuit 9 is input to the synchronizing signal detecting circuit 15 and whether the input signal corresponds to the frame synchronizing signal recorded in the disc by the synchronizing signal detecting circuit 15. It is determined whether or not.

By the way, as is well known, on the CD, a frame synchronization signal indicating the beginning of the frame is recorded for each frame in which data of 6 samples of the left and right channels are grouped together. The frame synchronization signal has a special pattern (11T-11T; “0”) that does not exist in the data.
And “1” are arranged in an array of 11 each). Therefore, the frame sync signal is detected by detecting the special pattern by the sync signal detection circuit 15.

When the frame sync signal is detected by the sync signal detection circuit 15 and a detection output indicating that is generated, whether or not the next detection output is generated within a predetermined time set with a certain width. Accordingly, the time difference detection circuit 16 detects whether or not the detection output generation interval is within a predetermined time range. Here, the predetermined time is determined in correspondence with a trace time difference at the same position when the disc is rotated, which is caused by a distance difference size of each light spot position on the signal surface of the disc of the preceding and following sub beams. Therefore, when the time difference detection circuit 16 detects that the generation interval of the detection output from the synchronization signal detection circuit 15 is within the predetermined time range, both the preceding and succeeding sub-beams trace the same signal track. You can judge that there is.

When the sync signal detection circuit 15 detects a frame sync signal, the switching control circuit 14 operates by the detection output to that effect, and the input switching circuit 9 switches the input. Therefore, each time the sync signal detection circuit 15 detects the frame sync signal, the input switching circuit 9 switches the input.

Further, the time difference detection circuit 16 is reset every time the input switching circuit 9 is switched and controlled by the switching control circuit 14 so that the signal from the first waveform shaping circuit 8 is selected, and then the synchronizing signal detection circuit 16 is reset. A detection output when the frame synchronization signal is detected by 15 is used as a trigger.

When the time difference detection circuit 16 detects that the generation interval of the detection output from the synchronization signal detection circuit 15 is within a predetermined time range, the on-track discrimination circuit 17 is provided each time the detection is performed. The number of times is counted by the counter 18 which is configured to be reset at regular time intervals. Then, the on-track discrimination circuit 17
Generates an on-track signal indicating that each beam from the optical pickup device is on-track when the number of times counted by the counter 18 reaches a predetermined number within the fixed time.

The on-track signal is generated by rotating a diffraction grating (not shown) incorporated in the optical pickup device using a motor to change the arrangement angle of each light beam of the optical pickup device. It becomes a stop signal to stop.

Next, an on-track adjustment method for each light beam of the optical pickup device will be described with reference to FIG.

During the on-track adjustment, the diffraction grating rotating device 19 is operated and the diffraction grating is rotated slowly.

The first and second light receiving elements 5 and 10 receive the reflected light from the disc of the preceding and following sub-beams which are displaced by the rotation of the diffraction grating. 2 The amount of reflected light received by each of the light receiving elements 5 and 10 changes as the diffraction grating rotates.

The received light output obtained from the first light receiving element 5 is
First current / voltage conversion amplifier 6, first low-pass filter 7
And is binarized via the first waveform shaping circuit 8 and supplied to the input switching circuit 9 as a digital signal, while the light reception output obtained from the second light receiving element 10 is the second current / voltage conversion amplifier 11, It is binarized through the two low-pass filter 12 and the second waveform shaping circuit 13, and is supplied to the input switching circuit 9 as a digital signal. Therefore, the input switching circuit 9 is configured to selectively input two systems of digital signals whose signal waveforms change according to the trace states of the preceding and following sub-beams in the rotational displacement state of the diffraction grating. Become.

Here, the input switching circuit 9 is switched by the switching control circuit 14 so as to select the digital signal from the first waveform shaping circuit 8 which is a read signal obtained by tracing the preceding sub-beam. The digital signal is input to the sync signal detection circuit 15. Therefore, the first digital signal obtained by tracing the preceding sub-beam is the synchronization signal detection circuit 1
The frame sync signal is detected by 5.

When the sync signal detection circuit 15 detects the frame sync signal from the first digital signal, the time difference detection circuit 16 operates at the detection end timing and the switching control circuit 14 causes the input switching circuit 9 to follow. The digital signal from the second waveform shaping circuit 13, which is the read signal obtained by tracing the sub-beams, is switched to be selected. Therefore, the synchronization signal detection circuit 1
5, the frame sync signal is now detected from the second digital signal obtained by the tracing of the subsequent sub-beam, and the generation interval of the frame sync signal detected by the sync signal detection circuit 15 is time difference. The detection circuit 16 detects whether the time is within a predetermined time range.

The sync signal detection circuit 15 detects the frame sync signal from the second digital signal, and the time difference detection circuit 16 detects the frame sync signal from each of the first and second digital signals. When the range is detected, the on-track discrimination circuit 1
The counter 18 of 7 counts the number of detections during a certain period.

Here, the switching control circuit 14 operates each time the time difference detection circuit 16 detects whether or not the time difference of the generation intervals of the frame synchronization signals detected by the respective sub-beams of the optical pickup device is within a predetermined time range. The input switching circuit 9 is switched to the first waveform shaping circuit 8 side so as to select the read signal obtained by tracing the preceding sub beam. Therefore, the time difference detection circuit 16 repeatedly detects whether or not the time difference between the generation intervals of the frame synchronization signals detected by the respective sub-beams is within the predetermined time range.

As described above, when each sub-beam of the optical pickup device traces on the same track, the generation interval of the frame sync signal detected by each sub-beam is within a predetermined time range determined by the time difference detection circuit 16. Will be inside. Therefore, when each sub-beam enters the on-track state, the number of times of detection counted by the counter 18 in a certain period set by the on-track discrimination circuit 17 becomes a predetermined value or more. On the other hand, when the sub-beams are not traced on the same track, the generation intervals of the frame synchronization signals detected by the sub-beams are not constant and are outside the predetermined time range defined by the time difference detection circuit 16. Therefore, when each sub-beam is in the off-track state, even if an erroneous detection or the like occurs, the counter 18 remains in the fixed period defined by the on-track discrimination circuit 17.
The number of detections counted by means of the number becomes significantly smaller than the number of detections counted during on-track.

Therefore, the condition for the on-track discrimination circuit 17 to generate an on-track signal is satisfied only during on-track. Then, the diffraction grating rotating device 19 continues the operation of rotating the diffraction grating until the on-track signal is supplied.

Further, the main beam is arranged at the center of a straight line connecting the sub-beams.

Therefore, on-track adjustment of each light beam is automatically performed by changing the arrangement angle of each light beam of the optical pickup device.

Further, in particular, in the above-described embodiment, since the frame synchronization signal recorded in a special pattern which does not exist in the data is used, the on-track discrimination of each light beam is surely detected. Have advantages.

The on-track of each sub-beam referred to in the specification means a state in which the light spot of each sub-beam hangs on the signal track by half, as shown in FIG.

[0031]

As described above, according to the present invention, the specific signal is detected by at least two of the three beams, and the passage time difference between the specific signals detected by the respective beams is detected, and the time difference is detected. Since it is possible to detect the on-track state of each beam by detecting that it is the time corresponding to the interval difference size of the light spot positions on the disc of each beam set in advance, Track adjustment can be performed using an automatic machine.

[Brief description of drawings]

FIG. 1 is a circuit block diagram showing an example for achieving an on-track adjustment method according to the present invention.

FIG. 2 is a schematic diagram showing a state of each light spot on a disc in an optical pickup device which performs tracking servo by a three-beam method.

[Explanation of symbols]

 9 input switching circuit 14 switching control circuit 15 sync signal detection circuit 16 time difference detection circuit 17 on-track discrimination circuit

Claims (1)

[Claims] 1. The main beam is obtained by irradiating a disc with three beams of a main beam and preceding and following sub beams arranged before and after the main beam, and detecting a difference in reflected light amount reflected by the disc of each of the sub beams. In the optical pickup device configured to detect a tracking error with respect to the signal track, the specific signals of the same pattern periodically present on the disk are detected by the detection outputs obtained from at least two beams of the three beams. , By detecting the transit time difference of the specific signal detected by each beam, and by detecting that the time difference is a time corresponding to the interval difference dimension of the light spot positions on the disc of each beam set in advance Perform on-track adjustment to place the beam on the same signal track of the disc. On-track adjustment method for optical pickup device.