JPH0817061A - Optical pickup device - Google Patents

Abstract

PURPOSE:To improve the quality of tracking error signals in the optical pickup device which detects tracking error signals by the push-pull system. CONSTITUTION:The photodetecting surface of a photodetector 7 is divided into four sections 7d to 7g by the separating lines 7a to 7c along the track of an optical disk and these photodetecting sections 7d to 7g are grouped into two-left and right-photodetecting groups in accordance with the positions of beam spots 8 formed on the detecting surface. The grouping of the photodetecting sections is conducted to minimize the output difference between the two photodetecting section groups. The output difference between the two photodetecting section groups ultimately determined after such grouping is repeated allows to obtain the tracking error signal for applying tracking servo.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device for irradiating a recording medium such as an optical disc or a magneto-optical disc with a light beam to optically read information recorded on the recording medium, and particularly to a tracking device. The present invention relates to an optical pickup device that detects an error signal by a push-pull method.

[0002]

2. Description of the Related Art When information is read from a recording medium, a track of the recording medium becomes meandering due to eccentricity or surface wobbling of the recording medium, and a beam spot deviates from the meandering track. When the light beam cannot trace the track accurately,
There is a problem that the information on the recording medium cannot be accurately reproduced. Therefore, conventionally, the amount of positional deviation (tracking error signal) between the track and the beam spot is detected, and the position of the objective lens is moved in the direction substantially orthogonal to the track based on this amount of deviation, thereby A control called tracking servo is performed to follow the track.

Conventionally, as a method for detecting such a tracking error signal, there is a method called, for example, a push-pull method. The principle of the push-pull method will be described with reference to FIG. In FIG. 5, when the recording surface of the optical disc 51, which is a recording medium, is irradiated with a light beam, the reflected light from the optical disc 51 is diffracted by the pits of the track 51a, and the 0th-order diffracted light 52 and the ± 1st-order diffracted lights 53 and 54 are formed. Each part passes through the objective lens 55 and is incident on the photodetection surface of the photodetector 56 to form a beam spot 57. The portions 57a and 57b of the beam spot 57 are the overlapping regions of the 0th-order diffracted light and the ± 1st-order diffracted lights. The photodetector 56 has two photodetectors 56b and 56c divided by a separating line 56a along the track direction, and the overlapping regions 57a and 57b of the diffracted light are respectively photodetectors 56.
b, 56c.

When the beam spot is accurately located on the track 51a of the optical disk 1, the ± 1st-order diffracted lights are symmetrical, the light amount distributions on the photodetection portions 56b and 56c are equal, and the photodetection surfaces 56b and 56c are the same. The received light amounts of are the same. On the other hand, when the beam spot deviates from the track 1a, the ± 1st-order diffracted lights become asymmetric, and the light amount distributions on the photodetectors 56b and 56c are different, that is, the distributions of the overlapping regions 57a and 57b are different, and the photodetector 56 is detected.
A difference occurs in the amount of light received by b and 56c.

Therefore, the difference between the outputs of the photodetectors 56b and 56c is obtained by the subtractor 58, the difference between the outputs is detected as a tracking error signal, and tracking servo is applied based on this error signal to make the objective lens 55 orthogonal to the track. The beam spot is moved back to the track 51a on the track 51a, and the tracking servo allows the light beam to follow the meandering of the track and accurately trace the track.

[0006]

In the optical pickup device which detects the tracking error signal by the push-pull method, the light quantity distribution of the beam spot formed on the photodetection surface of the photodetector 56 is shown in FIG. ), As shown in FIG.
The positional relationship between the photodetector, the objective lens, and other optical parts is adjusted in advance.

However, when the above adjustment is performed before the product is shipped, there is a concern that the beam spot on the photodetector 56 may be displaced due to environmental changes such as temperature during actual use. Particularly, in the case where the objective lens is movably supported in the focus direction and the tracking direction by using a parallel link mechanism made of a resin molded product (see, for example, Japanese Patent Application Laid-Open No. 2-227833), between the parallel links. There is a concern that the expansion and contraction of the thin hinge may cause the positional relationship between the photodetector and the objective lens to shift. In such a case, as shown in FIG.
As shown in (b) and (c), the beam spot formed on the photodetection surface of the photodetector 56 is biased to the left or right, which causes the output difference between the photodetectors 56b and 56c. An offset appears in the tracking error signal obtained by the above, which leads to a deterioration in the quality of the tracking error signal, which causes a problem that an accurate tracking servo cannot be performed and an accurate information cannot be read.

However, the present invention provides an optical pickup device which improves the reading accuracy of information by automatically suppressing the occurrence of offset regardless of the position of the beam spot.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, and in an optical pickup device for detecting a tracking error signal by a push-pull method, a light detection surface on which reflected light from a recording medium is incident is provided. Have,
Further, a photodetector formed by dividing this photodetection surface into at least four photodetection sections by a separation line along the track direction, and a connection relationship between the photodetection sections are switched to select two groups of left and right photodetection sections. Switching means for grouping into two groups, a comparison calculation means for comparing the outputs of the two left and right photodetector groups grouped by the switching means to obtain the difference, and an output difference obtained by the comparison calculation means. On the basis of this, a grouping change command signal for each photodetecting section is output to the switching means so that the output difference between the two photodetecting section groups becomes small, and control means for determining the grouping of each photodetecting section. Then, a tracking error signal is obtained from the output difference of the two photodetector groups determined by the control means.

Further, according to the present invention, in the photodetector, the width of the photodetection section near the center separation line is smaller than the width of the photodetection section distant from the center separation line. Still further, according to the present invention, the photodetection surface of the photodetector has a bilaterally symmetrical shape with respect to the center separation line.

[0011]

In the above structure, the photodetector surface of the photodetector is divided into at least four photodetector sections, and these photodetector sections are divided into two groups of left and right photodetector sections. Based on the output difference of the subgroups, the groups are rearranged so that the difference becomes the smallest, and the above operation is executed again. By repeating such an operation, the two photodetector groups having the smallest output difference are divided into groups.
Such an operation is performed by turning the power on when using the device.
It is programmed to execute each time N times, and the settings of the two photodetector groups determined by the above operation are maintained until the power is turned off next time. A tracking error signal can be obtained from the output difference of the photodetection unit group to perform tracking servo.

Therefore, when the beam spot formed on the photodetection surface of the photodetector is misaligned, the grouping described above is performed to minimize the offset appearing in the tracking error signal. It can be stopped and the quality of the tracking error signal is improved.

Also, in the photodetector, the width of the photodetector near the center separation line is made small, so that the photodetector can be divided into groups more finely and accurately according to the position of the beam spot. , The quality of the tracking error signal is further improved.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention shown in FIGS. 1 to 3 will be described below in detail. 1A to 1C are explanatory views showing the relationship between the photodetector and the beam spot used in the optical pickup device according to the embodiment of the present invention, and FIG.
FIG. 3 is a control block diagram for grouping the photodetection units of the photodetector, and FIG. 3 is a configuration explanatory view showing an outline of the optical pickup device.

First, referring to FIG. 3, a schematic structure of the optical pickup device will be described. 1 is a semiconductor laser as a light source, 2 is a collimator lens, 3 is a beam splitter, and 4 is a beam splitter.
Is an objective lens, 5 is an optical disk as a recording medium, 6 is a focusing lens, and 7 is a photodetector. The laser light emitted from the semiconductor laser 1 is collimated by the collimator lens 2 and transmitted through the beam splitter 3. And reaches the objective lens 4, and is focused by the objective lens 4 to illuminate the optical disc 5. On the other hand, the reflected light from the optical disk 5 is diffracted by the pits of the track, and each part of the 0th-order diffracted light and the ± 1st-order diffracted light is transmitted through the objective lens 4 and then reflected at a right angle by the beam splitter 3 to be reflected by the focusing lens 6. The beam spot is formed by being incident on the light detection surface of the detector 7.

As shown in FIG. 1, the photodetector 7 used in the present embodiment has four photodetection portions (light receiving parts) on the photodetection surface by three separating lines 7a to 7c along the track direction of the optical disk 1. Element) 7d to 7g, and the widths of the inner photodetection portions 7e and 7f near the center separation line 7b are formed smaller than the widths of the outer photodetection portions 7d and 7g. Thus, the beam spot 8 is formed on the split detection surface of the photodetector 7 by the reflected light from the optical disc 1 as described above, and the beam spot 8 is equal to the 0th-order diffracted light. A portion indicated by reference numeral 8a is formed by a part of the first-order diffracted light and is an overlapping region of the 0th-order diffracted light and the ± first-order diffracted light.

Next, the grouping of the photodetectors 7d to 7g will be described with reference to FIG.

In FIG. 2, 9 to 12 are terminals for receiving output signals from the photodetection sections 7d to 7g, and 13 and 14 are connected to the terminals 9 to 12 respectively, and the photodetection sections 7d to 7g are divided into groups. The input switching circuit for performing the above, and the switching means in the present invention is constituted by the both input switching circuits. 1
Reference numerals 5 and 16 denote adders for adding outputs of one or a plurality of photodetection units connected via the input switching circuits 13 and 14, and 1
Reference numerals 7 and 18 are low-pass filters for extracting DC components from the outputs of the adders 15 and 16 and inputting them to a comparison operation circuit (comparison operation means) 19 in the subsequent stage. Reference numeral 20 is an input switching circuit 13 based on the operation result of the comparison operation circuit 19. , 14 show input control circuits (control means) for outputting grouping change command signals.

The grouping operation of the photodetectors 7d to 7g will be described below. Now, when the power source of the device is turned on, the laser light emitted from the semiconductor laser 1 passes through the collimator lens 2 and the beam splitter 3 and is focused on the recording surface of the optical disc 1 by the objective lens 4, and the reflected light from this optical disc 1 is reflected. Based on the above, a conventionally known focusing servo is performed to obtain a focused state, and then the grouping operation of each of the photodetectors 7d to 7g is executed.

First, the input switching circuit 13 includes the photodetector 7d,
7e as one group and these are added to one adder 15
In addition, the input switching circuit 14 connects the photodetectors 7f and 7g to the other adder 16 as another group. Then, the comparison calculation circuit 19 compares the total output of the photodetectors 7d and 7e with the total output of the photodetectors 7f and 7g.

Now, on the light detecting surface of the light detector 7, FIG.
When the beam spot 8 is formed at the correct position as shown in (a), the light amount distribution of the beam spot 8 is bilaterally symmetric with respect to the separation line 7b, and the calculation result at this time is zero output difference. . However, the input control circuit 20 to which the calculation result is input determines that the current grouping is correct and sets the state as it is.

On the other hand, the beam spot 8 is shown in FIG.
When the position is deviated as shown in (c), an output difference is generated as a result of the above calculation, and the input control circuit 20 to which the calculation result is input switches the input based on the calculation result. A grouping change command signal is output to the circuits 13 and 14. When the beam spot 8 is displaced as shown in FIG. 1 (b), the input switching circuit 13 includes the photodetection unit 7d as one group in the adder 15, and the input switching circuit 14 includes the photodetection unit. 7e to 7g are connected to the adder 16 as the other group, and the above operation is repeated based on the outputs of both groups. At this time, the light quantity distribution of the beam spot 8 is bilaterally symmetric with respect to the separation line 7a, and the calculation result is an output difference of zero, and finally the photodetector 7
The grouping of d and the photodetectors 7e to 7g is determined.

When the beam spot 8 is displaced as shown in FIG. 1C, the input switching circuit 13 groups the photodetectors 7d to 7f as one group into the adder 15,
The input switching circuit 14 connects the photodetector 7g to the adder 16 as the other group, and repeats the above operation again based on the outputs of both groups. At this time, the light quantity distribution of the beam spot 8 is bilaterally symmetric with respect to the separation line 7c, and the operation result is an output difference of zero, and finally the photodetection unit 7
The grouping of d and the photodetectors 7e to 7g is determined.

With such an operation, each photodetector 7d ...
The grouping of 7 g is determined, the output of each group is guided to the tracking servo circuit via the terminals 21 and 22, and a tracking error signal is obtained by this output difference, and an offset does not appear in this tracking error signal. Instead, tracking servo is performed based on a high quality tracking error signal. As a result, when information is read, the track meanders due to eccentricity or surface contact of the optical disk 5, but the light beam follows the track and traces the track accurately. Reading accuracy is improved.

Further, since such an operation is executed every time the power source of the apparatus is turned on, high precision is not required for the position adjustment of the beam spot in the assembly stage, and the adjustment can be performed relatively roughly, which results in productivity. Will also be preferred.

In the above embodiment, the photodetection surface of the photodetector 7 is divided into four photodetection portions by the separating line along the track direction, but it may be divided into a larger number. As the number of divisions of the photodetection surface is increased to make the width of the photodetection section near the center separation line smaller than the width of the photodetection section far away from the center separation line, Grouping of the photodetectors can be performed more finely and accurately, and the quality of the obtained tracking error signal is further improved. As an example thereof, FIG. 4 shows an example of six divisions, and the photodetector 7 has six photodetection portions 7m with five separation lines 7h to 7l along the track on the photodetection surface.
To 7r, and the photodetection portions 7n to 7q are formed to be narrower than the outer photodetection portions 7m and 7r.

Further, in the above-mentioned embodiment, if the circuit parts of the control system for grouping the photodetector units are incorporated in the same package as the photodetector, the number of external terminals of the optical pickup device can be increased. It can be expected to be effective in that it can be prevented and handled easily.

[0028]

As described above, according to the present invention, in the optical pickup device which detects the tracking error signal by the push-pull method, the beam spot formed on the photodetection surface of the photodetector is displaced. By the way, the positional deviation can be effectively dealt with by grouping the photodetection sections, the offset appearing in the tracking error signal can be minimized, the quality of the signal can be improved, and the track can be accurately tracked by the tracking servo. Accurate traces can be expected, and improvement in information reading accuracy can be expected.

Further, in the photodetector, the width of the photodetection section near the central separation line is made smaller than the width of the outer photodetection section, so that the photodetection sections are grouped with respect to the positional deviation of the light beam. This can be performed with high accuracy, and the quality of the tracking error signal can be further improved.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a relationship between a photodetector and a beam spot used in an optical pickup device according to an embodiment of the present invention.

FIG. 2 is a control block diagram for grouping photodetection units of the photodetector.

FIG. 3 is a structural explanatory view showing an outline of the optical pickup device.

FIG. 4 is an explanatory diagram showing a relationship between a photodetector and a beam spot used in an optical pickup device according to another embodiment of the present invention.

FIG. 5 is a diagram for explaining the principle of detecting a tracking error signal by the push-pull method.

FIG. 6 is an explanatory diagram showing a relationship between a photodetector and a beam spot used in a conventional optical pickup device.

[Description of Reference Signs] 1 semiconductor laser 3 beam splitter 4 objective lens 5 optical disk (recording medium) 7 photodetectors 7a to 7c separation line 7d to 7g photodetector 8 beam spots 13 and 14 input switching circuit (switching means) 15, 16 adder 17, 18 low-pass filter 19 comparison operation circuit (comparison operation means) 20 input control circuit (control means)

Claims (3)

[Claims] 1. An optical pickup device for detecting a tracking error signal by a push-pull method, which has a photodetection surface on which reflected light from a recording medium is incident, and which is a separation line along the track direction. A photodetector divided into at least four or more photodetector sections, switching means for switching the connection relationship of the photodetector sections to group into two left and right photodetector groups, and the switching means. By comparing the outputs of the two left and right photodetector groups divided by the group and calculating the difference between them, and the output difference between the two photodetector groups is small based on the output difference obtained by the comparison calculating means. And a control means for outputting a grouping change command signal for each photodetector to the switching means so as to determine the grouping for each photodetector. Optical pickup apparatus characterized by obtaining a tracking error signal by the output difference of the constant is two photodetection unit group. 2. The photodetector is characterized in that the width of the photodetector near the center separation line is smaller than the width of the photodetector far away from the center separation line. Optical pickup device. 3. The optical pickup device according to claim 2, wherein the photodetection surface of the photodetector has a bilaterally symmetric shape with respect to the center separation line.