JPH0312829A - Tracking control mechanism for optical head - Google Patents

Abstract

PURPOSE:To reduce influence on an output value for tracking control owing to a flaw and stain on a track by averaging the sum of light-receiving quantity detection values by means of plural beams, thereby attaining tracking control. CONSTITUTION:When the flaw 15 exists in a part on the track 7, reflected light beams by auxiliary beams 9 going ahead of main beams 8 are converged as shown on a detection sensor 13 as an imaginary line, and a difference occurs in the detection signal values C and D of elements (c) and (d) on the right and left by a quantity corresponding to the flaw 15. Since the difference does not occur in the light-receiving quantity of the other amplifiers AP1 and AP3, respective output values (A-B) and (E-F) of the amplifiers AP1 and AP3 are '0'. The output value of an amplifier AP4 is obtained by averaging respective output values, and it becomes equal to one obtained by making the output value of an amplifier AP2 to be 1/3. Consequently, tracking control is executed by the output value of the amplifier AP4. Thus, much influence of the flaw 15 is eliminated and the main beams 8 are prevented from being unnecessarily stepped off from the track 7.

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention <Industrial Field of Application> The present invention relates to a tracking control mechanism for an optical head in an optical information recording/reproducing device such as an optical disc.

<Prior Art> Conventionally, there have been various devices for recording or reproducing optical information on optical disks, optical cards, and the like as optical recording media. In this optical information recording and reproducing device, it is necessary to perform tracking control to align the main beam with the information recording track. There is also a three-beam method using a main beam and a pair of sub-beams.

In the push-pull method described above, a detection sensor consisting of a two-part photodiode divided into left and right parts by a dividing line corresponding to the direction along the track direction calculates the difference in the amount of light received on the left and right sides due to the light reflected from the recording medium of the main beam. to detect tracking errors. In this case, if there is a scratch or dirt between the recording pits and in the irradiation range of the main beam, the scratch is determined to be the main beam coming off the track as it passes. - There is a possibility that racking control may not be performed and recording or playback cannot be performed reliably.

In addition, in the above three-beam method, a diffraction grating or the like is used to use the 0th-order light as the main beam, and a pair of sub-beams consisting of the 1st-order diffracted light are symmetrically irradiated to both edges of the track, so that the two split beams are separated from each other. Tracking errors are detected by calculating the difference in the amount of reflected light received from the recording medium. In this case, as well as above, if there are scratches or dirt on the edge of the track, the secondary beam will be affected, causing incorrect lubricating.
・There is a risk that racking control will be performed.

<Problems to be Solved by the Invention> In view of the problems of the prior art, the main object of the present invention is to provide a tracking control mechanism for an optical head that can suppress the influence of scratches, dirt, etc. on the track on tracking control. Our goal is to provide the following.

[Structure of the Invention] Means for Solving the Problems According to the present invention, an optical recording medium of a type that records or reproduces information on an optical recording medium using a main beam while detecting a tracking error is provided. The head tracking control mechanism includes means for generating a plurality of sub beams moving forward and backward with respect to the track direction of the main beam, and means for generating respective reflected lights of the main beam and the sub beam from the optical recording medium, respectively. An I-racking control mechanism for an optical head, characterized in that it has the same number of detection sensors as each of the beams for separate detection, and detects the tracking error based on an average value of each detection value by each of the detection sensors. Alternatively, in a tracking control mechanism for an optical head that records or reproduces information on an optical recording medium using a main beam while detecting tracking errors, means for generating a plurality of pairs of sub-beams, and the same number of detection sensors as the respective sub-beams for separately detecting each reflected light of each of the sub-beams from the optical recording medium; This is achieved by providing a tracking control mechanism for an optical head, characterized in that the tracking error is detected using the average value of each detection value from each detection sensor.

<Function> By doing this, even if the amount of light received by one sub-beam changes greatly if there are scratches or dirt in the irradiation range of the sub-beam, the reflected light from the optical recording medium of each beam will be reduced. Since the amount of received light is averaged, the influence of scratches on tracking control can be reduced.

<Embodiments> Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is an explanatory diagram schematically showing a tracking control mechanism for an optical head based on the present invention. Light emitted from a semiconductor laser 1 as a light source is separated by a diffraction grating 2 into three beams consisting of a zero-order light and a pair of first-order diffracted lights. These beams are irradiated onto, for example, an optical disk 6 as an optical recording medium via a beam splitter 3, a collimator lens 4, and an objective lens 5.

FIG. 2 shows a main beam 8 consisting of 0th-order light and a sub-beam 9 consisting of 1st-order diffracted light directed to the track 7 of the optical disk 6.
10, each of the sub beams 9 and 10 is irradiated onto a predetermined position on the track 7 before and after the main beam 8 with respect to the track direction, which is the horizontal direction in the drawing of the main beam 8. The reflected light from the optical card 6 of each of these beams 8 to 10 travels back to the beam splitter 3, and is directed downward by the reflecting surface 3a of the beam splitter 3 to 9 in FIG.
The beam is deflected by 0 degrees and focused on three detection sensors 12 to 1-4 via a cylindrical lens scope 1.

As shown in FIG. 3, the detection sensor 12 is composed of, for example, a quadrilateral photodiode shaped like a square, and each detection sensor 13, 14 is composed of a two-division photodiode.
Each of the beams 8 to 10 is divided into left and right by a dividing line corresponding to the direction along the track direction, and each of the beams 8 to 10 is condensed at the center with the center of its leading axis aligned with the dividing line ``2''. Each element a1, a2 of the detection sensor 12 of the main beam 8,
The received light amount detection signals from bl and b2 are input to the amplifier API by combining the signals divided into two on the left and right from the dividing line along the 1-herc direction, and the detection signals from the pair of elements a1 and a2 on the left side are inputted to the amplifier API by the amplifier AP1. The sum B of the detection signal values of the left pair of elements b1 and b2 is subtracted from the sum A of the values, and the resultant sum is input to the amplifier AP4. Note that the detection sensor 12 can detect focusing errors using a known astigmatism method, and can also read information signals by detecting the sum of the detection signal values A and H.

The received light amount detection signal values C and D by each element cSd of the detection sensor 13 of the sub beam 9 are input to the amplifier AP2, and the received light amount detection signal values E and F by each element e and f of the detection sensor 14 of the sub beam 10 are Manually powered by amplifier AP3, each amplifier A
At P2 and AP3, respectively ((, -D), (E-F)
It is subtracted so that it becomes, and it is input into amplifier AP4. Then, in amplifier AP4, the average value of the output values of each amplifier API to AP3 [(A-B) + (C-D) + (
EF)] /3 is calculated, and tracking control is performed using the average value.

For example, if there is a scratch 15 on a part of the track 7 as shown in FIG. The light is focused as shown by the line, and the detection signal values C and D of the left and right elements c and d differ by the amount corresponding to the scratch 15. Therefore, when the output value ((, -D) of the amplifier AP2 shows the travel time of each beam on the horizontal axis in FIG. 4, it has a waveform as shown in the upper part of the figure.Other amplifier APIs, Each output value (A, -B), (E-F) of AP3 is 0 because there is no difference in the amount of light received on the left and right sides.The output value of amplifier AP4 is the average of the two output values. As shown in the lower part of the figure, it is the same as the output value of amplifier AP2 reduced to 1/3, so since tracking control is performed using the output value of amplifier AP4, it is not affected by scratch 15 to that extent. Therefore, it is possible to prevent the main beam 8 from unnecessarily coming off the track 7.

Note that the separation means for generating a plurality of beams is not limited to the above-mentioned diffraction grating 2, but may also include, for example, a hologram optical element,
An LD array or multiple LDs can be used.

In addition to the main beam 16 in the conventional three-beam method and a pair of first sub-beams 17 and 18 that extend diagonally back and forth with respect to the track direction of the main beam 16, FIG.
FIG. 2 is a diagram similar to FIG. 2 showing a case where tracking control is performed in the same manner as described in - by using a pair of second sub-beams 19.20 that precede and parallel to the sub-beams 17.18 of FIG. The second sub-beam 19.20 is generated by a known separation means as mentioned above, and the second sub-beam 17.1
8 and both edges of track 7 are irradiated.

The reflected light from the optical disk 6 of each pair of sub-beams 17-20 is focused on each corresponding detection sensor 21-24'', and each element gShS i.

The received light amount detection values G, H1■, J by j are (G - H) (I - J
), and in the amplifier AP7,
Average value of output values of amplifiers AP5 and AP6 [(GH)+
(I-J)/2 is calculated, and tracking control is performed using the average value.

In this second embodiment as well, if there is a scratch 25 on the track 7''2 as shown in FIG. 5, the output value of the amplifier AP5 changes greatly as shown in the second row of FIG. , since the output value of the amplifier AP6 is 0 as shown in the middle part of the figure, the output value of the amplifier AP7, which is the average value of them, is a waveform in which the influence of the scratch 25 is halved as shown in the lower part of the figure. Therefore, it is possible to prevent tracking control that would cause the main beam 16 to unnecessarily deviate from the track 7.

Note that it is preferable to provide, for example, a low-pass filter before the amplifier that calculates the average value of the tracking control values of each detection sensor. In this case, the output value of the amplifier, which shows sudden changes due to scratches, etc., will be ignored by the filter, so the influence of the scratches 15 can be further reduced, and the effect of the scratches 15 can be further reduced. Suitable tracking control can be performed.

[Effects of the Invention] According to the present invention, since tracking control is performed by averaging the sum of detected values of the amount of light received by a plurality of beams, the detected value of the beam formed by scratches or dirt on the track may be affected. Even if the change causes a tracking error,
Since the influence on the output value for tracking control is small, unnecessary tracking errors of the main beam can be prevented from occurring.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an overview of a tracking control mechanism for an optical head based on the present invention. FIG. 2 is an explanatory diagram showing the relationship between the track and the track according to the tracking control mechanism according to the present invention. FIG. 3 is a schematic circuit diagram showing a method of detection by a detection sensor of a tracking control mechanism according to the present invention. FIG. 4 is an explanatory diagram showing a waveform when a flaw on a track is detected in the tracking control mechanism based on the present invention. FIG. 5 is an explanatory diagram showing the relationship between the beam and the track according to the second embodiment. FIG. 6 is a schematic circuit diagram showing the method of detection by the detection sensor in the second embodiment. FIG. 7 is an explanatory diagram showing a waveform when a flaw on the second track is detected in the second embodiment. 1-2 1... Semiconductor laser 2... Diffraction grating 3... Beam splitter 3a... Reflective surface 4... Collimator lens 5... Objective lens 6... Optical disk 7.
...Track 8...Main beam 9.10...
Sub-beam 11... Cylindrical lenses 12-14... Detection sensor 15... Scratch 16... Main beam 17.1
8...First sub beam 19.20...Second sub beam 21-24...Detection sensor 25...Flaw

Claims (2)

[Claims] (1) In a tracking control mechanism for an optical head that records or reproduces information on an optical recording medium using a main beam while detecting tracking errors, a plurality of sub-heads arranged in front and behind the track direction of the main beam are provided. a means for generating a beam, and a number of detection sensors equal to the number of the beams for separately detecting each reflected light of the main beam and the sub-beam from the optical recording medium, and each of the detection sensors A tracking control mechanism for an optical head, characterized in that the tracking error is detected using an average value of each detected value. (2) In a tracking control mechanism for an optical head that records or reproduces information on an optical recording medium using a main beam while detecting tracking errors, the mechanism moves back and forth in an oblique direction with respect to the track direction of the main beam. means for generating a plurality of pairs of sub-beams, and the same number of detection sensors as the respective sub-beams for separately detecting each reflected light of each of the sub-beams from the optical recording medium; A tracking control mechanism for an optical head, characterized in that the tracking error is detected using an average value of each detection value by a detection sensor.