JP3247121B2 - Tracking error detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tracking error detecting apparatus, and more particularly to an offset of a tracking error signal generated when an objective lens is moved in a radial direction of a disk-shaped recording medium, and a separation type light. The present invention relates to a tracking error detection device capable of effectively removing an offset of a tracking error signal caused by a tilt of a movable axis of a movable portion with respect to an optical axis of a fixed portion in a pickup device.

[0002]

2. Description of the Related Art In an optical information recording / reproducing apparatus, information is recorded and / or reproduced by irradiating an information recording medium with a light beam using an optical pickup device. Recently, so-called separation type optical pickup devices have begun to spread under the demand for high-speed access.

The optical pickup device is divided into a fixed portion having a light source and a movable portion having an objective lens for irradiating a predetermined position on an information recording medium with a light beam emitted from the light source. is there. Since the optical system including the light source is fixed, the assembling and adjustment of the light source unit become easy, and the objective lens and the reflecting member incorporated in the movable unit are moved and adjusted, and / or the entire movable unit is moved and adjusted. Accordingly, tracking control can be performed with higher accuracy.

Further, when a light beam is largely moved across a track formed on an information recording medium at the time of seeking or the like, it is easily performed by moving the entire movable portion via a slider structure or the like. be able to.

[0005]

In such a separation type optical pickup device, there are cases where the movable axis of the movable section is inclined with respect to the optical axis of the light emitted from the fixed section, and mechanical errors. The tracking error signal is generated when the displacement of the movable part occurs due to the position of the movable part in the radial direction of the disk, or when the optical axis shift occurs due to the thermal characteristics of each element in the optical information recording / reproducing device. Offset occurs.

Also, in an integrated pickup device in which the movable part and the fixed part are not separated, the tracking control is performed by moving the objective lens in the radial direction of the disk with respect to the light beam incident from the light source. As in the case of the separation type optical pickup device, an offset is generated in the tracking error signal due to a mechanical error or the influence of the thermal characteristics of each element.

FIG. 11 shows an example of a state in which such an optical axis shift occurs in the separation type optical pickup device. As shown in FIG. 11, when the movable axis of the movable portion 21 has a certain inclination error with respect to the light beam A emitted from the fixed portion 22, when the movable portion 21 is located on the inner peripheral portion of the disk, Is moved and positioned at the outer peripheral portion of the disk (indicated by a broken line in FIG. 11), the light beam A emitted from the movable shaft of the movable portion 21 and the fixed portion 22 becomes δ in the track direction.
It is clear that the deviation is only. In FIG. 11, reference numeral 23 indicates the position of the rotating shaft of the spindle motor for rotating the disk.

Japanese Patent Application Laid-Open No. Sho 61-1986 discloses a means for solving such an optical axis shift between the fixed portion and the movable portion of the separation type pickup.
182640, detecting a change in the incident angle of light incident on the reflective member provided in the movable portion, based on the detection result, adjust the position of the reflective member to cancel the change in the incident angle, There is disclosed an optical axis shift correction method for correcting a change in a relative position between a fixed portion and a movable portion due to yawing or the like.

However, in this method, it is necessary to provide the movable section with a two-segment photodetector for detecting the optical axis shift and a beam splitter for guiding the light beam to the two-segment photodetector, and the weight of the movable section is reduced. However, there is a problem that the seek characteristics deteriorate.

Japanese Unexamined Patent Publication (Kokai) No. 61-148630 discloses that incident light entering an actuator is split into two beams, one of which is used as a beam for normal recording, reproduction, and erasing.
The other is reflected in the actuator, this reflected light and the reflected light from the disk are passed through the same optical path again, and both reflected beams are separated in the fixed optical system, and the light spot control detected from the latter reflected beam An optical pickup in which a signal is corrected to remove the influence of an optical axis shift is disclosed. However, also in this method, it is necessary to provide a beam splitter, a λ / 4 plate, and a mirror for detecting an optical axis shift in the movable portion, which increases the weight of the movable portion and deteriorates seek characteristics. In addition, since the beam splitter for guiding the light beam to the optical axis shift detector is provided in the fixed portion, there is a problem that the P-polarized light component returning to the laser is large.

The present invention is proposed to solve the above-mentioned problem, and provides a tracking error detecting device which is provided with detecting means for detecting only an offset value and can correct a tracking error including the offset value. It is intended to do so.

[0012]

According to the first aspect of the present invention, there is provided a pickup device for recording or reproducing information by irradiating an information recording medium with a light beam through an objective lens. A tracking error detection device for detecting a tracking error signal including an offset value based on a reflected beam from the information recording medium; and the offset value based on a reflected beam from the information recording medium. A second detection unit for detecting only the first and second detection units, and a unit for performing a differential operation on outputs of the first and second detection units, wherein the second detection unit includes:
A light beam separating means for separating the reflected beam into at least three light beams, and a width approximately one-fourth of a beam diameter so as to receive the at least three light beams separated by the light beam separating means. And a photodetector having at least two light receiving areas divided by a dividing line parallel to the direction of the track on the information recording medium, wherein the at least three light beams are orthogonal to the direction of the track. The beam is incident on the photodetector so as to be shifted by approximately half a beam in the direction and intersect with the division line.

As described above, in the tracking error detecting device of the present invention, the first detecting means for detecting the tracking error signal including the offset value based on the reflected beam from the information recording medium, and detecting only the offset value. A second detecting means for detecting a tracking error signal from which an offset value has been removed by differentially calculating an output from the detecting means; Therefore, it is possible to obtain a tracking error signal in which the optical axis shift is corrected.

[0014]

FIG. 1 is a diagram showing the entire configuration of a separation type optical pickup device using a tracking error detection device according to a first embodiment of the present invention. The disk 1 is rotated by the spindle motor 2, and the movable part 3 of the separation type optical pickup is arranged below the disk 1. This movable part 3
Is provided with a reflecting member 4 for reflecting light from a light source and an objective lens 5 for condensing the light on the surface of the disk 1. The entire movable section 3 and / or the objective lens 5
The tracking control is performed by moving in the radial direction.

A fixed portion 6 is provided for the movable portion 3,
The movable section 3 and the fixed section 6 constitute a separation optical system. The fixed section 6 is provided with a laser diode 7 as a light source, and a light beam emitted from the laser diode 7 enters a first beam splitter 9 as a parallel light beam via a collimating lens 8. Here, most of the light beams pass through the first beam splitter 9 and move to the movable portion 3.
And is reflected toward the objective lens 5 by the reflecting member 4 provided on the movable section 3, and is condensed and irradiated on the surface of the disk 1 via the objective lens 5.

The reflected light from the recording layer provided on the disk 1 is condensed by the objective lens 5 and becomes a substantially parallel light flux.
After being reflected by the reflecting member 4, the light enters the first beam splitter 9. Here, a part of the light is reflected by the reflection surface 9a of the beam splitter 9 and guided to the detection system. A second beam splitter 10 is arranged on the optical path of the light reflected by the beam splitter 9, and separates the reflected light in two directions. One of the separated light beams enters the critical angle prism 11, is reflected by the prism surface of the critical angle prism 11, and is received by the first photodetector 12. The first photodetector 12 comprises a four-division photodiode (PD), and is configured to detect a focus error signal and a tracking error signal from its output.

On the other hand, the other light beam split by the second beam splitter 10 is separated by a grating 13 formed in the beam splitter 10 and having a pitch substantially parallel to the tangential direction into 0-order light and ± 1 order light. After being separated into light, the light is condensed by a lens 14 and the second photodetector 15
Is received at.

The grating 13 is attached to the beam splitter 10 by rotating the ± first-order light separated by the grating 13 on the photodetector 15 so as to be shifted by a half spot in the radial direction with respect to the zero-order light.

The intensity of the spots of the zero-order light and the ± first-order lights changes asymmetrically in the radial direction when the light beam incident on the disk 1 crosses the groove formed on the disk 1. Therefore, the AC component of the tracking error signal can be substantially canceled by receiving the ± first-order light by half a spot shifted in the radial direction with respect to the zero-order light.

FIG. 2 is a diagram showing a configuration of the second photodetector 15 used in the first embodiment of the tracking error detection device of the present invention. As shown in FIG. 2, the second photodetector 15 is composed of photodiodes 15a and 15b radially divided by a dividing line parallel to the track direction of the disk 1 into two parts with a width of about 1/4 of the spot diameter. And a spot of 0-order light divided by the grating 13 (see FIG. 1), +1
The intensities of the next light spot and the minus first light spot are made substantially equal, and these spots are received by the photodiodes 15a and 15b, and a difference signal is obtained, whereby the movable part 3 and the fixed part 6 in FIG. And a DC offset component caused by disturbance when a spot moves on the photodiode can be obtained.

That is, the first photodetector detects a tracking error signal including an offset amount, and the second photodetector does not detect the tracking error signal. By detecting the difference between the distributions and taking the difference signal between the outputs of the photodetectors, a tracking error signal in which the offset component has been corrected is obtained. Note that the condenser lens 14 is not always necessary.

FIG. 3 shows the operation of such a tracking error signal detecting device.

First, a tracking error signal is detected by performing a differential operation on the output of the first photodetector 12 in the radial direction. The tracking error signal is a signal including an offset due to optical axis deviation or the like. .

On the other hand, the output of the second photodetector 15 is subjected to a differential calculation in the radial direction to detect only an offset signal due to an optical axis shift or the like.

The differential signal of the photodetector 12 and the photodetector 15
By further performing a differential operation on the differential signal with the above, a tracking error signal from which an offset due to an optical axis shift or the like has been removed can be obtained. Further, the photodetector 12 and the photodetector
The second photodetector 15 is used to correct the imbalance in the amount of light received at 15, the difference in the shape of the photodiode, and the difference in sensitivity.
A sufficient effect can be exhibited by performing an operation of subtracting a value obtained by multiplying the optical axis deviation signal obtained from the above by a constant G1.

FIG. 4 is a diagram showing a modification of the second photodetector 15 used in the first embodiment shown in FIG. 1 of FIG.
In the embodiment, the tracking error signal including the offset is obtained from the output of the first photodetector 12. However, as shown in FIG.
The photodiodes 15c and 15d are arranged beside the photodiodes 15a and 15b so as to receive the left half and the right half of the primary light spot, respectively.
A tracking error signal including an offset may be obtained by obtaining a differential signal of d.

Further, as shown in FIG.
Photodiodes 15e and 15f are arranged beside the central part of the 15 photodiodes 15a and 15b where the zero-order light spot is formed to receive the left and right ends of the zero-order light spot. A 15f differential signal may be obtained to obtain a tracking error signal including an offset.

FIG. 5 is a diagram showing a second photodetector 15 used in a second embodiment of the tracking error detecting device according to the present invention. In the second embodiment, a hologram element is used in place of the grating 13 provided in the second beam splitter 10 in the first embodiment shown in FIG.

The photodetector 15 is a six-divided photodiode 15
g, 15h, 15i, 15j, 15k, 15l, ± 1st-order light is arranged side by side on photodiodes 15i, 15l, and 0th-order light is arranged so as to cover photodiodes 15g, 15h, 15j, 15k. .

The offset due to the optical axis shift in the track direction between the movable unit 3 and the fixed unit 4 is (g + h + i)-(j + k +
1), and the offset due to the optical axis shift in the focus direction is obtained by (g + j)-(h + k).

These offset values are converted to the first photodetector 12
The error signal from which the offset has been removed can be generated by subtracting from the tracking error signal and the focusing error signal including the offset obtained from the above.

In this example, the hologram element is formed on the second beam splitter 10, but the condensing lens 14 may have the same hologram effect.

FIG. 6 is a diagram showing a configuration of the second photodetector 16 used in a development example developed simultaneously with the present invention. In this development example, the grating 13 of the detection system shown in FIG. 1 is removed, and the second photodetector 15 is replaced with the grating shown in FIG.
A split photodetector 16 is used. The photodetector 16 is divided into six parts in the radial direction by dividing lines parallel to the track direction of the disk 1.

The principle of tracking error detection is as follows. Light receiving area of the second photodetector shown in FIG.
FIG. 6B shows a configuration in which each of 15a and 15b is divided into three in the track direction. That is, the light receiving areas 15a and 15b of the photodetector 15 shown in FIG.
c, d, e, and f, and these areas are shown in FIG.
Correspond to the light receiving areas a, b, c, d, e, and f of the photodetector 16, respectively.

In the photodetector shown in FIG.
15a, that is, the sum of the outputs of the regions b, d, and f
The offset correction signal can be obtained by subtracting 15b, that is, the sum of the outputs of the areas a, c, and e. In the photodetector 16 shown in FIG. 6A, an offset correction signal is obtained from a similar operation, that is, (b + d + f)-(a + c + e). Therefore, FIG.
The photodetector shown in FIG. 6A and FIG. 6B or FIG.
It can be said that the photodetector 16 shown in FIG.

The tracking error signal including the offset value is obtained from (a + b + c)-(d + e + f), and the offset correction signal is multiplied by G1 to subtract the offset correction signal from the track error signal including the offset. A corrected track error signal can be obtained.

According to this development example, there is no need to provide a beam splitting means such as a grating to separate the light beams.
With one beam, it is possible to obtain a tracking error signal whose offset has been corrected to the same extent as in the first and second embodiments. Therefore, it is possible to reduce the number of parts of the apparatus, reduce the size, and reduce the number of adjustment steps. Further, since the configuration is simple, the combination with the focus detection can be easily performed.

FIG. 7 shows a photodetector 16 used in the above development example.
It is a figure which shows the modification of. As shown in FIG. 7, this modification is a four-divided photodetector 17 excluding the light receiving areas c and f on both outer sides of the photodetector 16 shown in FIG. Even with such a four-divided detector, a certain amount of offset correction signal can be obtained. Of course, the tracking error signal including the offset is supplied to the first photodetector 12 shown in FIG.
Get more. The photodetector 16 of FIG. 6 or the photodetector 17 of FIG.
Is approximately 1/4 of the beam diameter
The degree is sufficient and is not strictly specified.

FIG. 8 is a diagram showing another modified example of the photodetector used in the above development example. In this modification, each light receiving area is formed by a pattern, and the light receiving areas a, c, and e shown in FIG. 6A correspond to the pattern 18b, and the light receiving areas b, d, and f correspond to the pattern 18a, respectively. . The offset correction signal is obtained from the differential of the output from each pattern, so that it is not necessary to perform an addition operation for each light receiving area.

FIG. 9 is a graph showing the shift amount of the objective lens with respect to the optical axis and the light beam obtained by performing a simulation by setting a constant G1 by which the offset signal obtained from the second photodetector is multiplied to G1 = 3. 5 is a graph showing a relationship between the off-track amount and the off-track amount. The result of the simulation of the tracking operation using the tracking error detection device of the present invention is indicated by a solid line, and the result of the simulation of the tracking operation using the conventional tracking error detection device is indicated by a broken line. The NA of the objective lens is 0.53, the track pitch of the tracks on the recording medium is 1.6 μm, and the pupil diameter of the objective lens is 4
mm.

According to the results obtained by setting the conventional apparatus, when the objective lens is shifted by 0.3 mm or more from the reference position, the tracking error signal does not cross zero and the tracking operation cannot be performed. On the other hand, in the result obtained by setting the device of the present invention,
Since the offset of the tracking error signal has been corrected, the offset amount of the light beam when the objective lens is shifted by 0.3 mm from the reference position is very small at 0.03 μm, and when the objective lens is shifted from the optical axis. However, a good tracking operation could be performed.

In addition, the tracking error detection device of the above-mentioned development example can be combined with a focus detection system.

FIG. 10A is a diagram showing a configuration of a photodetector used for a combination of the focusing error detection by the astigmatism method and the tracking error detection of the above-mentioned development example. The photodetector 19 has a light receiving area 16a, 16b, 16
c, 16d, 16e, 16f divided into 6 parts, the lower half is the light receiving area
The one divided into 16g and 16h is used. The tracking error signal including the offset is (gh) / (g + h) or And the offset correction signal is Obtained from By subtracting a value obtained by multiplying the offset correction signal by G1 from the tracking error signal including the offset, a tracking error signal in which the offset has been corrected can be obtained. The focus error signal is Is calculated.

FIG. 10B is a diagram showing a configuration of a photodetector used for a combination of the detection of a focusing error by the beam size method and the detection of a tracking error of the above-mentioned development example. The photodetector 20 has two light receiving elements 20-1 and 20-2.
Consists of The light receiving elements 20-1 and 20-2 are each divided into three by a dividing line orthogonal to the track direction.
The light receiving area at the center of -2 is divided into six light receiving areas 18a, 18b, 18c, 18d, 18e and 18f by dividing lines parallel to the track direction. The tracking error signal including the offset is obtained from {(a + b + c)-(d + e + f)} / (a + b + c + d + e + f), and the offset correction signal is obtained from {(b + d + f)-(a + c + e)} / (a + b + c + d + e + f). The tracking signal from which the offset has been removed is obtained by subtracting the value obtained by multiplying the offset correction signal by G1 from the tracking error signal including the offset. The focus error signal is obtained from {(j + g + h)-(i + k + a + b + c + d + e + f)} / (a + b + c + d + e + f + g + h + i + j + k).

FIG. 10C is a diagram showing a photodetector used for a combination of the focusing error detection by the knife edge method and the tracking error detection of the above-mentioned developed example. The configuration of the photodetector 21 is the same as that used for the astigmatism method shown in FIG. The photodetector 21 is a photodetector 21
Are arranged in such a manner that the dividing line dividing the vertical direction is parallel to the chord of the light beam spot. The tracking error signal including the offset is obtained from TE = {(a + b + c)-(d + e + f)} / (a + b + c + d + e + f), and the offset correction signal is obtained from {(b + d + f)-(a + c + e)} / (a + b + c + d + e + f). The tracking error signal corrected as the offset is obtained by subtracting the offset correction signal multiplied by G1 from the tracking error signal including the offset. The focus error signal is obtained from {(a + b + c + d + e + f) -g} / (a + b + c + d + e + f + g).

As shown in FIGS. 10 (a), 10 (b), and 10 (c), when the focusing error detection and the tracking error detection of the above-described development example are combined, the first photodetector becomes unnecessary. Further, the number of steps for adjusting the number of parts can be reduced.

In the above-described embodiment, the separation type pickup device has been described as an example. However, even in the case of an integrated type pickup device, it can be generated when the objective lens is moved in the radial direction by using the tracking error detecting device of the present invention. Offset on the photodetector can be similarly corrected.

[0048]

As described above in detail, according to the tracking error detecting device of the present invention, in the optical pickup device, the optical axis of the light emitted from the fixed portion with respect to the movable axis of the movable portion is inclined in the radial direction. When the movable portion has a radial displacement due to the position on the disk radius of the movable portion, when the radial displacement occurs due to the influence of the thermal characteristics of the components in the pickup device, When the tilt angle in the radial direction of the disc varies depending on the radial position, etc., the tracking offset is detected with high sensitivity and high accuracy, including the case where the offset amount changes depending on the radial position of the disc when tracking. It can be canceled without lowering the modulation of the error signal, and stable information recording, reproduction, To, it is possible seek.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an optical pickup device using a tracking error detection system of the present invention.

FIG. 2 is a diagram showing a first embodiment of the present invention.

FIG. 3 is a diagram showing the operation of the tracking error signal detection system of the present invention.

FIG. 4 is a diagram showing a modification of the first embodiment of the present invention.

FIG. 5 is a diagram showing a second embodiment of the present invention.

FIG. 6 is a diagram showing a development example of a tracking error detection device developed simultaneously with the present invention.

FIG. 7 is a diagram showing a modification of the development example of FIG. 6;

FIG. 8 is a diagram showing another modified example.

FIG. 9 is a diagram illustrating a relationship between a shift amount of an objective lens and an off-track amount of a light beam by simulation.

FIG. 10 is a diagram for explaining a combination of focus error detection and tracking error detection according to the above development example.

FIG. 11 is a diagram showing a state of displacement between a fixed part and a movable part in the separation type pickup device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Disc 2 Spindle motor 3 Movable part 4 Reflecting member 5 Objective lens 6 Fixed part 7 Light source 8 Collimator lens 9 First beam splitter 10 Second beam splitter 11 Critical angle prism 12 First photodetector 13 Grating 14 Condensing lens 15, 16, 17, 18, 19, 20, 21 Second photodetector

Claims (1)

(57) [Claims] A tracking error detection device provided in a pickup device for recording or reproducing information by irradiating an information recording medium with a light beam through an objective lens, wherein the offset is determined based on a reflected beam from the information recording medium. First detecting means for detecting a tracking error signal including a value, second detecting means for detecting only the offset value based on a reflected beam from the information recording medium, and first and second detections Means for performing a differential operation on the output of the means, wherein the second detecting means detects the reflected beam by at least 3
A light beam separating means for separating the light beam into three light beams; and a light beam separating means for receiving the at least three light beams separated by the light beam separating means, having a width of about 1/4 of a beam diameter on the information recording medium. And a photodetector having at least two light receiving areas divided by a dividing line parallel to the direction of the track, wherein the at least three light beams are substantially half beams in a direction orthogonal to the direction of the track. A tracking error detection device, wherein the tracking error detection device is configured to be incident on the photodetector so as to be shifted and intersect with the division line.