JPH06251404A - Tilt detecting device for optical pickup - Google Patents

Abstract

PURPOSE:To accurately and stably detect a tilt in a circumferential direction by detecting the tilt of an optical disk in the circumferential direction in a relative tilt between an optical pickup and the optical disk by means of an AC component of a signal corresponding to the output of a multi divided photodetector. CONSTITUTION:A bisected photodetector 1A is divided into two photodetectors E, F by a dividing line N, the respective out-puts (e), (f) are impressed to AC amplifiers 2, 3, the outputs of the amplifiers 2, 3 are impressed to multipliers 4, 5 so as to be squared, respectively, the outputs are impressed to a subtracter 6 and the difference is impressed to an LPF 7. The high frequency signal component is cut off in the LPF 7 and a tangential tilt signal is outputted. The received light quantities of the detectors E, F change by the recording mark on an information track, however, when the tangential tilt is present, the difference is generated between the signals (e), (f) and is detected as the tangential tilt signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tilt detecting device for an optical pickup used in an optical disc device, and more particularly to a device for detecting a component of a relative tilt between the optical pickup and the surface of the optical disc in a circumferential direction of the optical disc. It is about.

[0002]

2. Description of the Related Art In reproducing an optical disc, when the optical axis of the optical pickup is not orthogonal to the surface of the optical disc (hereinafter, also referred to as the inclination of the optical pickup), that is, When there is a relative inclination with respect to the normal line of the optical disk surface, the reproduced waveform tends to be distorted. Particularly in reproducing a high-density optical disc, it is necessary to increase the numerical aperture NA of the objective lens for converging the laser light, but the coma aberration of the reproduced signal is proportional to the cube of the numerical aperture NA. Since the number of optical pickups increases, the inclination of the optical pickup allowed in the reproducing apparatus becomes extremely small.
However, it is difficult to make the optical axis of the optical pickup and the surface of the optical disc always perpendicular to each other due to the movement of the optical pickup, the surface wobbling of the optical disc, and the like, and the objective lens is tilted according to the inclination of the optical pickup. It is necessary to take measures such as correcting the axis or correcting the reproduced signal with a waveform equalizer.

For this reason, a device for detecting the tilt of the optical pickup by dividing it into a radial component (hereinafter also referred to as a radial tilt) and a circumferential component (hereinafter also referred to as a tangential tilt) of the optical disk is used. Have been proposed by. The present invention aims to provide an apparatus for detecting a component (tangential tilt) in the circumferential direction of an optical disc with a high degree of accuracy among the inclinations of an optical pickup. Hereinafter, a conventional tilt detection device for an optical pickup will be described with reference to FIGS. 8 and 9. FIG. 8 is a diagram showing a general optical pickup and an optical disc. In the figure, 20
Is an optical disk provided with a number of information tracks in a circular shape, 41 is a light source such as a semiconductor laser, 42 is the light source
A collimating lens for collimating the light flux from 1 into a parallel light flux, 43
Is a beam splitter for separating the irradiation light from the light source 41 such as the semiconductor laser and the reflected light from the optical disk 20.

The laser light from the light source 41 is condensed by the objective lens 44 to form a light spot on the recording surface of the optical disk 20. Reference numeral 47 is an actuator for moving or tilting the objective lens 44, 45 is a condensing lens for condensing the reflected light from the beam splitter 43, and 1 is a light beam from the condensing lens 45 for photoelectric conversion. It is a multi-segment photodetector for performing. The optical pickup 40 is provided with an optical system (not shown) for obtaining an RF signal, a tracking error signal, a focus error signal, and a radial tilt signal in addition to the optical system.
That is, the reflected light from the optical disk is split into two light beams, one of which is used to obtain an RF signal, a tracking error signal, a focus error signal, and a radial tilt signal, and the other light beam is used by the optical pickup 40. It is used to detect the inclination between the optical disc 20 and the optical disc 20.

In FIG. 8, the display of the optical system related to only the one light beam is omitted, and the optical pickup 4 is shown.
The optical system associated with the other light beam for detecting the tilt between 0 and the optical disc 20 is shown. Information tracks are concentrically or spirally formed on the recording surface of the optical disk 20, and a large number of recording marks (hereinafter also referred to as information pits) are concavely formed on the information tracks. In FIG. 8, the direction of the information track of the optical disk is shown as the vertical direction of the figure. Figure 9
FIG. 8 is a diagram showing a conventional example of a tilt detection device for an optical pickup. In FIG. 9, a two-divided photodetector 1C is used as an example of the photodetector 1 shown in FIG. Light detector 1C
Is divided into a photodetector G and a photodetector H by a dividing line K corresponding to the radial direction (direction orthogonal to the circumferential direction) of the optical disc 20. The arrow shown in the figure indicates the circumferential direction of the optical disc and also indicates the relative movement direction of the photodetector 1C with respect to the rotating optical disc. That is, the photodetector 1C is actually stopped, and the recording mark on the optical disk 20 moves in the direction opposite to the arrow.

In the following description, the side with the photodetector G for detecting a signal is described as the front side in the track direction, and the side with the photodetector H for detecting a signal as a rear side is described as the rear side in the track direction. The reflected light from the optical disc 20 is condensed by the condenser lens 45 and guided to the photodetector 1C. The outputs g and h of the photodetectors G and H are amplified by the amplifiers 51 and 52 for amplifying the DC component and the AC component, respectively, and then subtracted by the subtractor 6, and the output of the subtractor 6 is obtained by the low-pass filter 7. The high frequency component is removed and the tangential tilt signal representing the tangential tilt is output.

In the tilt detecting device for the optical pickup shown in FIG. 9, when there is a tangential tilt, the tangential tilt signal is obtained because the light receiving amounts of the two photodetectors G and H are different from each other. Since g and h are amplified and calculated with the DC component still included, a pseudo signal is superimposed on the tangential tilt signal due to the dark current of the photodetector 1C and the temperature dependence of this dark current, and an error occurs. An error also occurs in the tangential tilt signal due to the DC offset of the amplifiers 51 and 52 and its temperature dependence.

[0008]

As described above, in the conventional tilt detecting device for an optical pickup, since the output of the photodetector is amplified and calculated while including the DC component, a pseudo signal is generated in the tangential tilt signal. Therefore, there is a problem that the tangential tilt correction cannot be performed with high accuracy. The present invention has been made in view of the above problems, and an object thereof is to accurately and stably detect the circumferential direction component of an optical disc within the relative inclination between the optical axis of the optical pickup and the normal line of the optical disc surface. It is an object of the present invention to provide a tilt detecting device for an optical pickup.

[0009]

A tilt detecting device for an optical pickup according to the present invention calculates substantially only those AC components based on a signal corresponding to an output of a multi-division photodetector, and accurately calculates the AC components. The tangential tilt is detected. A first optical pickup tilt detecting apparatus according to the present invention is a laser light source, an objective lens that collects a light beam from the light source and irradiates the optical disk, and multi-division that photoelectrically converts reflected light from the optical disk. In an optical disc device for reproducing an optical disc by using an optical pickup including a photodetector, one division line of the multi-division photodetector is made to correspond to a radial direction of the optical disc, and the optical pickup and the optical disc Is a tilt detecting device of an optical pickup for detecting the tilt in the circumferential direction of the optical disc among the tilts relative to and from the AC component of the signal according to the output of the multi-division photodetector.

A second optical pickup tilt detecting device according to the present invention is the same as the first optical pickup tilt detecting device, wherein the multi-division photodetector is associated with the optical disc in the radial direction. A tilt detecting device for an optical pickup, comprising: a multiplier for squaring the AC component of the output of the photodetector on each side of one dividing line; and a subtractor for obtaining the difference between the outputs of the multipliers. .

A third optical pickup tilt detecting device according to the present invention is the first optical pickup tilt detecting device according to the first embodiment, wherein the multi-division photodetector is associated with the optical disc in the radial direction. Inclination detection of an optical pickup provided with a double-wave rectifier for double-wave rectifying the alternating current component of the output of the photodetector on each side of one dividing line, and a subtractor for obtaining the difference between the outputs of the double-wave rectifier It is a device.

According to a fourth aspect of the present invention, there is provided a tilt detecting device for an optical pickup according to the first tilt detecting device for an optical pickup, wherein the multi-division photodetector is arranged in a radial direction of the optical disc and in the information track. Outputs of two photodetectors which are divided into four by a first dividing line and a second dividing line of the multi-divided photodetector corresponding to a center line, and which belong to the same side of the first divided line. A tilt detecting device for an optical pickup, comprising two multipliers for multiplying each other and a subtracter for obtaining a difference between outputs of the two multipliers.

A fifth optical pickup tilt detecting apparatus according to the present invention is the same as the first optical pickup tilt detecting apparatus, wherein the multi-division photodetector is arranged in a radial direction of the optical disk and in the information track. Outputs of two photodetectors which are divided into four by a first dividing line and a second dividing line of the multi-divided photodetector corresponding to a center line, and which belong to the same side of the first divided line. An inclination detecting device for an optical pickup, comprising: two adders for adding each other and a multiplier for multiplying a result of addition and subtraction of outputs of the two adders.

A sixth optical pickup tilt detecting device according to the present invention is the tilt detecting device of the first optical pickup, wherein the multi-division photodetector is the radial direction of the optical disc and the center of the information track. Line is divided into four by a first dividing line and a second dividing line of the multi-divided photodetector, and outputs of two photodetectors belonging to the same side of the second dividing line are divided. A first adder and a second adder for adding, and a third adder and a fourth adder for adding outputs of two photodetectors that do not belong to the same side with respect to the first dividing line and the second dividing line. A subtractor for subtracting the outputs of the first and second adders, a subtractor for subtracting the outputs of the third and fourth adders, and the outputs of the two subtractors. Optical pickup tilt detection device having a multiplier for multiplying It is.

[0015]

One of the division lines of the multi-division photo detector for reading the reproduction signal of the optical disc is arranged so as to correspond to the radial direction of the optical disc, and the signal corresponding to the output of the multi-division photo detector has its direct current component cut off. After that, the signal is multiplied by the multiplier, or the direct current component is cut, and then the double-wave rectifier performs double-wave rectification, and a signal corresponding to the output of the multiplier or the double-wave rectifier is extracted as a tangential tilt signal. The extracted signal does not include a pseudo signal due to the dark current of the photodetector or the DC offset of the DC amplifier.

[0016]

Embodiments of the present invention will be described below with reference to FIGS. 1 to 5 and 9, corresponding components are designated by the same reference numerals. The tilt detection device for an optical pickup according to the present invention is used in a reproducing apparatus for an optical disc, and the optical pickup of this reproducing apparatus is a general one as shown in FIG. Information pit) is an optical pickup 4
Read by 0. As described above, in the optical head 40, the detection and the description of the RF signal, the tracking error signal, the focus error signal, and the radial tilt signal are omitted. Here, the tangential tilt signal according to the present invention is detected. A description will be given of particularly related parts.

In the optical pickup tilt detecting device of the present invention, a two-division or four-division photodetector is used as the photodetector for receiving the reflected light from the optical disk. In the first and second embodiments of the present invention described below, a two-division photodetector is used as the photodetector, and in the third to fifth embodiments, a four-division photodetector is used. However, the dividing line N of the 2-split photodetector and one dividing line L of the 4-split photodetector are arranged so as to correspond to the radial direction of the optical disc 20, that is, the direction orthogonal to the information track of the optical disc 20. There is. FIG. 7 is a diagram showing corresponding positions of the information tracks of the optical disc and the photodetectors. In FIG. 7, one division line L of a four-division photodetector 1B described later corresponds to the radial direction of the optical disk, the other division line M corresponds to the circumferential direction, and the information pits are arrows. Move in the opposite direction. Further, since the light spot formed on the optical disc is irradiated on the substantially center line of the information track by the tracking control,
The center of the two-division photodetector or the four-division photodetector also corresponds to the approximate center line of the 20 information tracks of the optical disc.

FIG. 1 is a diagram showing a first embodiment of a tilt detecting device for an optical pickup according to the present invention. In the tilt detecting device for an optical pickup of the present invention shown in FIG. 1, the dividing line N of the two-divided photodetector 1A is arranged in correspondence with the radial direction of the optical disc. The arrow in the figure indicates the direction of the information track, that is, the circumferential direction of the optical disc.
The rotation direction of 0 is the opposite direction of the arrow. The photodetector 1A is divided into two photodetectors E and F by the dividing line N, and respective outputs e and f are applied to an AC amplifier (hereinafter also referred to as an AC amplifier) 2 and 3, respectively. The outputs of the AC amplifiers 2 and 3 are applied to the multipliers 4 and 5, respectively, and are squared. The outputs of the AC amplifiers 2 and 3 are applied to the subtractor 6, and the difference is applied to the low-pass filter 7.

In the low pass filter 7, the high frequency signal component is cut and the tangential tilt signal is output. The amount of light received by the photodetectors e and f changes according to the recording mark on the information track, but if there is a tangential tilt, a difference occurs between the signals e and f, and this is detected as a tangential tilt signal. As is clear from the figure, since the DC components of the output signals e and f of the photodetector are discarded before being multiplied, the influence of the DC component contained in the output signals e and f of the photodetector is affected. Does not reach the tangential tilt signal. FIG. 6 is a diagram showing the output characteristics of the tilt detection device for an optical pickup according to the present invention. Similar output characteristics can be obtained in the second to fifth embodiments of the present invention described later.

FIG. 2 is a diagram showing a second embodiment of the tilt detecting device for an optical pickup according to the present invention. In FIG. 2, the outputs e and f of the photodetector are amplified by the AC amplifiers 2 and 3, respectively, and are double-wave rectified by the double-wave rectifiers 8 and 9, respectively. The outputs of the two full-wave rectifiers are applied to the subtractor 6, and the difference between them is applied to the low-pass filter 7. The output of the low pass filter 7 is output as a tangential tilt signal. As is clear from the figure, since the DC components of the output signals e and f of the photodetector are discarded before the two-wave rectification, the DC components contained in the output signals e and f of the photodetector are discarded. Does not affect the tangential tilt signal.

FIG. 3 is a diagram showing a third embodiment of the tilt detecting device for an optical pickup according to the present invention. The relative positional relationship between the photodetector 1B and the optical disc shown in FIG. 3 is, as described in FIG. 7, one division line L of the four-division photodetector 1B corresponds to the radial direction of the optical disc, and the other division line M is It is arranged corresponding to the circumferential direction of the optical disc. The photodetector 1B is divided into four photodetectors A, B, C and D by the two dividing lines L and M. That is, the photodetectors A and D are formed on one side of the dividing line L and the photodetectors B and C are formed on the other side, and one side of the dividing line M (inner side of the optical disc). Photodetectors A and B are formed on the other side, and photodetectors D and C are formed on the other side. The arrow in the figure shows the direction of the information track, that is, the circumferential direction of the optical disc, but the moving direction of the recording mark of the optical disc 20 is the opposite direction of the arrow.

The output signals a, b, c, d of the photodetectors A, B, C, D are applied to AC amplifiers 11, 12, 13, 14 respectively, and the output signals of the AC amplifiers 11, 14 are multiplied. To the AC amplifier 1
The output signals of 2 and 13 are respectively applied to the multiplier 16,
The outputs of the multipliers 15 and 16 are applied to the subtractor 6, and the difference is output as a tangential tilt signal via the low pass filter 7. As is clear from the figure, since the DC components of the output signals a, b, c, d of the photodetector are discarded before being multiplied, the DC components contained in the output signal of the photodetector are discarded. The influence does not affect the tangential tilt signal.

FIG. 4 is a diagram showing a fourth embodiment of the tilt detecting device for an optical pickup according to the present invention. In FIG. 4, 4
The division mode of the divided photodetector 1B and the relative position relationship with the optical disc are the same as those described in the description of FIGS. The output signals a of the photodetectors A and D,
d is applied to the adder 21, and the output signals b and c of the photodetectors B and C are applied to the adder 22. The outputs of the adders 21 and 22 are added by the adder 23 and subtracted by the subtractor 24. The outputs of the adder 23 and the subtractor 24 are supplied to the multiplier 2 via AC amplifiers 25 and 26, respectively.
7 and the output of the multiplier 27 is output as a tangential tilt signal via the low pass filter 7.

The output signals a, b, c, d of the photodetector may be added after being amplified by the amplifier. Also, as is clear from the figure, the output signals a, b, c,
d is added or subtracted and then multiplied before the AC amplifier 2
Since the DC component of the signal is discarded at 5 and 26, the influence of the DC component contained in the output signal of the photodetector does not affect the tangential tilt signal.

FIG. 5 is a diagram showing a fifth embodiment of the tilt detecting device for an optical pickup according to the present invention. In FIG. 5, 4
The division mode of the divided photodetector 1B and the relative position relationship with the optical disc are the same as those described in the description of FIGS. The output signals a of the photodetectors A and B,
b is added by the adder 31, and the output signals c and d of the photodetectors C and D are added by the adder 32. The signals a and c are added by the adder 33, and the signals b and d are added by the adder 34. The outputs of the adders 31 and 32 are subtracted by a subtractor 35, and the outputs of the adders 33 and 34 are subtracted by a subtractor 36. And the subtractor 35,
The output signals of the subtractor 36 are AC amplifiers 25 and 26, respectively.
Is multiplied by the multiplier 27, and the output of the multiplier 27 is output as a tangential tilt signal via the low pass filter 7.

Further, as is apparent from the figure, the output signals a, b, c, d of the photodetector are added or subtracted, and thereafter, the DC components of the signals are discarded by the AC amplifiers 37, 38 before being multiplied. Therefore, the influence of the direct current component included in the output signal of the photodetector does not affect the tangential tilt signal. The output signals a, b, c, and d of the photodetector are amplified by individual amplifiers and then added by adders 31, 32, 33, and
There is no problem even if it is applied to 34. In this case, the AC amplifiers 25 and 26 may be amplifiers that also amplify the DC component, or the amplifiers 25 and 26 may not be provided. Further, when the four-division photodetector is used as the photodetector as in the third to fifth embodiments, the reflected light from the optical disk is not divided into two and is separated by a single beam. RF signal, tracking error signal, focus error signal, radial tilt signal,
It is also possible to obtain a tangential tilt signal.

[0027]

As described above, according to the present invention, since it is not affected by the dark current of the photodetector or the DC offset of the amplifier, the optical axis of the optical pickup is inclined with respect to the normal line of the surface of the optical disc. The tangential tilt, which is a component in the circumferential direction of the optical disc, can be detected with high accuracy.

[Brief description of drawings]

FIG. 1 is a first embodiment of a tilt detection device for an optical pickup according to the present invention.
It is a figure which shows an Example.

FIG. 2 is a second part of the tilt detection device for an optical pickup according to the present invention.
It is a figure which shows an Example.

FIG. 3 is a third part of a tilt detecting device for an optical pickup according to the present invention.
It is a figure which shows an Example.

FIG. 4 is a fourth embodiment of the tilt detection device for an optical pickup according to the present invention.
It is a figure which shows an Example.

FIG. 5 is a fifth part of a tilt detecting device for an optical pickup according to the present invention.
It is a figure which shows an Example.

FIG. 6 is a diagram showing output characteristics of the tilt detection device for an optical pickup according to the present invention.

FIG. 7 is a diagram showing corresponding positions of an information track of an optical disc and a photodetector.

FIG. 8 is a diagram showing a general optical pickup and an optical disc.

FIG. 9 is a diagram showing an example of a conventional tilt detection device for an optical pickup.

[Explanation of symbols]

 1A 2-division photodetector 1B 4-division photodetector 2, 3, 11, 12, 13, 14, 25, 26 AC amplifier 4, 5, 15, 16, 27 Multiplier 6, 24, 35, 36 Subtractor 8 , 9 Double wave rectifiers 21-23, 31-34 Adder 20 Optical disc 40 Optical pickup 41 Laser light source 44 Objective lens

Claims (6)

[Claims] 1. An optical pickup comprising a laser light source, an objective lens for converging a light beam from the light source and irradiating the optical disc, and a multi-segment photodetector for photoelectrically converting reflected light from the optical disc. In an optical disc device for reproducing an optical disc using the optical disc, one division line of the multi-division photodetector is made to correspond to a radial direction of the optical disc, and an optical disc within a relative inclination between the optical pickup and the optical disc. The inclination detecting device for an optical pickup, wherein the inclination in the circumferential direction of the optical pickup is detected from the AC component of the signal corresponding to the output of the multi-division photodetector. 2. The tilt detecting device for an optical pickup according to claim 1, wherein the photodetector on each side of one division line of the multi-division photodetector corresponding to the radial direction of the optical disc. An inclination detecting device for an optical pickup, comprising: a multiplier for squaring an AC component of an output; and a subtractor for obtaining a difference between outputs of the multiplier. 3. The tilt detection device for an optical pickup according to claim 1, wherein the photodetector on each side of one division line of the multi-division photodetector corresponding to the radial direction of the optical disc. A tilt detecting device for an optical pickup, comprising: a double-wave rectifier for double-wave rectifying an AC component of an output, and a subtractor for obtaining a difference between outputs of the double-wave rectifier. 4. The tilt detection device for an optical pickup according to claim 1, wherein the multi-division photo detectors correspond to the radial direction of the optical disc and the center line of the information track, respectively. Is divided into four by a first dividing line and a second dividing line of the detector, and two multipliers for multiplying outputs of two photodetectors belonging to the same side of the first dividing line, and the two A tilt detector for an optical pickup, comprising: a subtractor for obtaining a difference between outputs of a multiplier. 5. The tilt detection device for an optical pickup according to claim 1, wherein the multi-division light detector is arranged to correspond to a radial direction of an optical disc and a center line of the information track. Is divided into four by a first dividing line and a second dividing line, and two adders for adding outputs of two photodetectors belonging to the same side of the first dividing line; A tilt detector for an optical pickup, comprising: a multiplier that multiplies the result of addition and subtraction of the output of the adder. 6. The optical pickup tilt detecting apparatus according to claim 1, wherein the multi-segment photo detectors correspond to the radial direction of the optical disc and the center line of the information track. A first adder and a second adder for adding outputs of two photodetectors which are divided into four by a first dividing line and a second dividing line of the detector and which belong to the same side of the second dividing line. A third adder and a fourth adder for adding outputs of two photodetectors that do not belong to the same side with respect to the first dividing line and the second dividing line, the first adder and the second adder And a subtractor that subtracts the outputs of the third adder and the fourth adder, and a multiplier that multiplies the outputs of the two subtracters. Optical pickup tilt detector.