JP2007042170A - Optical disk device and optimal radial tilt angle detection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical disk device capable of surely detecting the optimal radial tilt angle of an objective lens. <P>SOLUTION: According to the optical disk device, after an objective lens 11 is rotated from a reference position to the inside to detect the level of a high-frequency signal RF, the objective lens 11 is rotated from the reference position to the outside to detect the level of the signal RF, offset is corrected based on the difference of the level detection value of the signal RF when the objective lens 11 is set in the reference position, and an optimal radial tilt angle θ1 is obtained from an approximate expression indicating a relation between the radial tilt angle θ and the level detection value of the RF signal. Thus, the optimal radial tilt angle θ is accurately obtained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical disc device and an optimum radial tilt angle detection method, and more particularly to an optical disc device and an optimum radial tilt angle detection method for detecting a radial tilt angle of an objective lens at which the level of an output signal of an optical pickup is maximized.

  In an optical disc apparatus for reading / writing optical disc data such as DVD-R (Digital Versatile Disc-Recordable) and DVD-RW (Digital Versatile Disc-ReWritable), the radial tilt angle of the objective lens is corrected due to the specifications of the optical disc. Is essential.

  That is, in the optical disc apparatus, data is read / written by irradiating the optical disc with an optical beam from the optical pickup. Ideally, this light beam is irradiated perpendicularly to the surface of the optical disk. However, if there is a warp or the like on the optical disk, the angle between the surface of the optical disk and the optical axis of the objective lens of the optical pickup deviates from vertical, and aberration occurs in the light beam. When this aberration occurs, the recording mark is not properly formed on the optical disk when data is written, and the S / N of the reproduction signal deteriorates due to an increase in crosstalk or the like when data is read, resulting in jitter.

  Therefore, in such an optical disc apparatus, a tilt sensor using an infrared sensor or the like is provided in the optical pickup body, and the tilt sensor detects the warp of the optical disc, and corrects the radial tilt angle of the objective lens based on the detection result. Thus, the optical axis of the objective lens is set perpendicular to the surface of the optical disk.

Further, the radial tilt angle of the objective lens is changed within a predetermined range (for example, −0.8 degrees to +0.8 degrees) while irradiating the optical beam with the optical disk, and the high frequency signal or tracking error signal output from the optical pickup is changed. There is a method in which an optimum radial tilt angle at which the level is maximized is obtained, and an objective lens is set to the angle (see, for example, Patent Document 1).
JP 2005-85307 A

  However, the method of providing a tilt sensor in the optical pickup has a problem that the size of the optical pickup is increased by the amount of the tilt sensor and the cost is increased.

  In addition, in the method of obtaining the optimum radial tilt angle from the high frequency signal or tracking error signal, since the radial tilt angle of the objective lens is always changed within a predetermined range, there is a problem that the detection time of the optimum radial tilt angle becomes long. It was.

  SUMMARY OF THE INVENTION Therefore, a main object of the present invention is to provide an optical disc apparatus and an optimum radial tilt angle detection method capable of accurately and quickly detecting an optimum radial tilt angle with a small optical pickup size and low cost. It is.

  An optical disc apparatus according to the present invention includes an optical pickup that irradiates a rotating optical disc with a light beam and outputs an electric signal having a level corresponding to the intensity of the reflected light. This optical pickup includes a light source that emits a light beam, a photoelectric conversion unit that photoelectrically converts reflected light and outputs an electrical signal, and an objective that condenses the light beam on an optical disk and condenses the reflected light on the photoelectric conversion unit. A lens and a drive unit that rotates the objective lens in the radial tilt direction; The optical disc apparatus further includes a control unit that controls the drive unit to rotate the objective lens, detects the level of the electric signal, and obtains the optimum value of the radial tilt angle of the objective lens based on the detection result. This control unit detects the level of the electrical signal by setting the radial tilt angle to the reference value, and then detects the level of the electrical signal while rotating the objective lens to one side, and the level detection value of the electrical signal decreases. The first step of stopping the rotation of the objective lens in response to the tendency to become, the radial tilt angle is set again to the reference value, the level of the electric signal is detected, and then the objective lens is rotated to the other side. In the first step and the second step, the level of the electric signal is detected while moving, and the rotation of the objective lens is stopped according to the tendency that the level detection value of the electric signal tends to decrease. The difference in the level detection value of the electric signal when the radial tilt angle is set to the reference value is obtained, and the difference is subtracted from the level detection value of the electric signal in the first step, or the difference is subtracted from the second step. A third step of correcting the offset of the detected level of the electrical signal between the first and second steps by adding to the detected level of the level of the electrical signal, and the radial tilt angle and the detected level of the electrical signal. An approximate expression indicating the relationship with the correction value is calculated, and a fourth step is performed in which the radial tilt angle at which the level of the electric signal is maximized in the approximate expression is determined as the optimum value.

  Also, the optimum radial tilt angle detection method according to the present invention is an optical disc provided with an optical pickup that irradiates a rotating optical disc with a light beam via an objective lens and outputs an electric signal at a level corresponding to the intensity of the reflected light. In the apparatus, the level of an electric signal is detected while rotating the objective lens in the radial tilt direction, and the optimum value of the radial tilt angle of the objective lens is obtained based on the detection result. In this method, after the radial tilt angle is set to a reference value and the level of the electric signal is detected, the level of the electric signal is decreased by detecting the level of the electric signal while rotating the objective lens to one side. First step to stop the rotation of the objective lens in response to the tendency, and after setting the radial tilt angle to the reference value again and detecting the level of the electric signal, the objective lens is rotated to the other side A second step of detecting the level of the electric signal while stopping the rotation of the objective lens in response to the fact that the level detection value of the electric signal tends to decrease, and a radial in the first and second steps The offset of the level detection value of the electrical signal when the tilt angle is set to the reference value is used as an offset value to correct the offset of the level detection value of the electrical signal between the first and second steps. And calculating an approximate expression indicating the relationship between the radial tilt angle and the correction value of the level detection value of the electrical signal, and setting the radial tilt angle at which the level of the electrical signal is maximum to the optimum value in the approximate expression. Including a fourth step of determining.

  Preferably, in the third step, the offset value is subtracted from the level detection value of the electric signal in the first step, or the offset value is added to the level detection value of the electric signal in the second step. The offset of the level detection value of the electric signal between the second steps is corrected.

Preferably, the electrical signal is a high frequency signal.
Also preferably, the electrical signal is a tracking error signal.

  In the optical disk device and the optimum radial tilt angle detection method according to the present invention, the objective lens is rotated in one direction from the reference position, the level of the electrical signal is detected, and the level of the detected value of the electrical signal tends to decrease. Next, the objective lens is rotated in the other direction from the reference position and the level of the electric signal is detected. When the detected level of the electric signal tends to decrease, the rotation of the objective lens is stopped. Then, the optimum value of the radial tilt angle is obtained from an approximate expression showing the relationship between the radial tilt angle of the objective lens and the level detection value of the electric signal. Therefore, the rotation angle of the objective lens can be reduced compared with the conventional case where the objective lens is always rotated by a predetermined angle, and the detection time can be shortened.

  Further, the difference between the level detection values of the two electric signals when the objective lens is set at the reference position is used as an offset value, and the level detection value of the electric signal when the objective lens is rotated in one direction and the objective lens are the other. Since the offset with respect to the level detection value of the electric signal when rotated in the direction is corrected, the optimum value of the radial tilt angle can be accurately detected.

  In addition, since an electrical signal output from the optical pickup is used, the size of the apparatus can be reduced and the cost can be reduced as compared with the conventional case where a tilt sensor is separately provided.

  FIG. 1 is a block diagram showing a main part of an optical disc apparatus according to an embodiment of the present invention. In FIG. 1, the optical disk apparatus includes an optical pickup 1 and a servo block 2, and the servo block 2 includes a signal processing unit 3 and a driver 4.

  The optical pickup 1 is driven by a driver 4 to irradiate the surface of the optical disc 1 with a light beam, photoelectrically convert the reflected light, and output a high frequency signal RF, a tracking error signal TE, and the like.

  During normal operation, the signal processing unit 3 controls the optical pickup 1 via the driver 4 based on the tracking error signal TE and irradiates the light beam perpendicularly to the center of the track on the surface of the optical disc 5. In addition, when detecting the optimum radial tilt angle, the signal control unit 3 detects the level of the high-frequency signal RF while changing the radial tilt angle of the objective lens in the optical pickup 1, and the level detection value of the high-frequency signal RF is maximum. The optimal radial tilt angle is detected. The driver 4 drives the optical pickup 1 according to the control signal CNT output from the signal processing unit 3.

  FIG. 2 is a diagram illustrating a main part of the optical pickup 1. In FIG. 2, an optical pickup 1 includes a light source 10 such as a semiconductor laser, an objective lens 11 for condensing a light beam α emitted from the light source 10 on a signal surface of an optical disk 5, and the objective lens 10 in a radial tilt direction. And tilt coils 12 and 13 to be rotated. When a current is supplied from the driver 4 to the tilt coils 12 and 13, the radial tilt angle of the objective lens 10 is set to an angle corresponding to the current. The optical pickup 1 is also provided with a mechanism (not shown) for moving the objective lens 10 in the focus direction and the tracking direction.

  3A and 3B are diagrams for explaining the radial tilt angle. With reference to FIGS. 3A and 3B, the shaft 21 is a shaft of a spindle that rotates the optical disk 5. The axis 22 is an axis that intersects the axis 21 perpendicularly. Ideally, the surface of the optical disk 5 is positioned on the shaft 22, the angle between the surface of the optical disk 5 and the shaft 22 is 0 degree, and the optical disk 5 is mounted on the spindle. It intersects perpendicularly with the surface.

  However, when the optical disk 5 is warped, the surface of the optical disk 5 and the axis 22 intersect at an angle θ other than 0 degrees. That is, the angle between the shaft 23 and the shaft 22 in contact with the surface of the optical disk 5 is θ. In this case, the optical axis 25 of the objective lens 11 is in contact with the surface of the optical disk 5 in order for the light beam α irradiated from the light source 10 to the optical disk 5 via the objective lens 11 to intersect the surface of the optical disk 5 perpendicularly. 23 needs to be perpendicular. The optical axis 25 of the objective lens 11 intersects with an axis 24 parallel to the spindle axis 21 through θ through the position where the optical beam 5 is irradiated on the optical disk 5. This θ is referred to as a radial tilt angle of the objective lens 11.

  FIG. 4 is a block diagram showing a part of the optical pickup 1 related to the generation of the tracking error signal TE. In FIG. 4, tracks 30 are provided on the surface of the optical disk 5 at a predetermined interval. Information is recorded on the track 30. In the state where tracking is performed, the main beam 31 is irradiated onto the optical disc 5 so that the center thereof is positioned at the center of the track 30 being tracked. The preceding beam 32 is irradiated to a position on the optical disc 5 that is forward of the main beam 31 and shifted by +1/2 track. The trailing beam 33 is irradiated to a position behind the main beam 31 of the optical disc 5 and shifted by -1/2 track.

  The optical pickup 1 includes a detector 41 that converts the beam reflected from the optical disc 5 into the electrical signals A to D, and a detector that converts the beam reflected from the optical disc 5 into the electrical signals E and F. 42 and a detector 43 that converts the beam reflected from the optical disk 5 into the electrical signals G and H by the trailing beam 33.

  That is, the light receiving area of the detector 41 is divided into four. The main beam 31 detected by the light receiving areas on the front left side, front right side, rear right side, and rear left side in the scanning direction by the main beam 31 is converted into signals AD. The light receiving area of the detector 42 is divided into two. The preceding beam 32 detected by the left and right light receiving areas with respect to the scanning direction of the preceding beam 32 is converted into signals E and F, respectively. The light receiving area of the detector 43 is divided into two. The trailing beam 33 detected by the left and right light receiving areas with respect to the scanning direction of the trailing beam 33 is converted into signals G and H, respectively.

  The optical pickup 1 further includes differential amplifiers 44 to 46, 49 and amplifiers 47, 48. The differential amplifier 44 receives the output signals A to D of the detector 41, subtracts the sum B + C of the levels of the signals B and C from the sum A + D of the levels of the signals A and D, and shows the calculation result A + D− (B + C). Output a signal. The differential amplifier 45 receives the output signals E and F of the detector 42, subtracts the level of the signal F from the level of the signal E, and outputs a signal indicating the calculation result EF. The differential amplifier 46 receives the output signals G and H of the detector 43, subtracts the level of the signal H from the level of the signal G, and outputs a signal indicating the calculation result GH. The amplifiers 47 and 48 amplify the output signals of the differential amplifiers 45 and 46, respectively, with a predetermined gain K.

  The differential amplifier 49 subtracts the level of the output signal of the amplifiers 47 and 48 from the level of the output signal of the differential amplifier 44, and the operation result (A + D) − (B + C) −K [(E + G) − (F + H)]. Is output as a tracking error signal TE. The servo block 2 controls the position of the objective lens 11 in the tracking direction (direction orthogonal to the track 30) so that the main beam 31 passes through the center of the track 30 based on the tracking error signal TE.

  FIG. 5 is a block diagram showing a part related to generation of the high-frequency signal RF in the optical pickup 1. In FIG. 5, the optical pickup 1 further includes a differential amplifier 50. The differential amplifier 50 receives the output signals A to D of the detector 41, and outputs a signal indicating the sum A + B + C + D of the levels of the signals A to D as the high frequency signal RF. When detecting the optimum radial tilt angle, the servo block 2 detects the level of the high-frequency signal RF while changing the radial tilt angle θ of the objective lens 11, and the radial tilt angle θ1 that maximizes the level detection value of the high-frequency signal RF. Is detected. When the radial tilt angle θ of the objective lens 11 is set to θ1, the light beam α is irradiated substantially perpendicularly to the surface of the optical disc 5, and the aberration is minimized. The high frequency signal RF includes information recorded on the track 30, and the information recorded on the optical disc 5 is reproduced from the high frequency signal RF.

  Next, an optimum radial tilt angle detection method that is a feature of the optical disc apparatus will be described. FIG. 6 is a flowchart showing the optimum radial tilt angle detection operation of the optical disc apparatus, and FIG. 7 is a diagram illustrating the operation. During the optimum radial tilt angle detection operation, the desired optical disc 5 is set and rotated, and the optical pickup 1 is set at a predetermined position (for example, the center) in the radial direction of the optical disc 5.

  Referring to FIGS. 6 and 7, the signal processing unit 3 sets the radial tilt angle θ of the objective lens 11 to a reference value θ0 (for example, 0 degree) in step S1, and sets the signal level of the high-frequency signal RF in step S2. In step S3, the level detection value of the high-frequency signal RF is stored.

  In step S4, the signal processing unit 3 determines whether or not the detection end. Whether or not it is a detection end is determined by whether or not the level of the high-frequency signal RF tends to decrease. Specifically, whether or not it is the detection end is 1 / C of the detection value when the current detection value of the level of the high-frequency signal RF is θ = θ0 (where C is a positive constant). It may be determined based on whether or not the current detection value of the level of the high-frequency signal RF is smaller by a predetermined value than the detection value when θ = θ0. Further, whether or not it is the detection end may be determined by whether or not the level detection value of the high-frequency signal RF has continuously decreased a predetermined number of times, or simply whether or not it has become smaller than the previous detection value.

  If it is determined in step S4 that it is not the detection end, the radial tilt angle θ is shifted by a predetermined amount in step S5, and the process returns to step S2. The shift amount of θ in step S5 is set to a negative value when the objective lens 11 is rotated in the inner direction of the optical disc 5, and is set to a positive value when the objective lens 11 is rotated in the outer direction of the optical disc 5. Is set.

  If steps S2 to S5 are repeated and it is determined in step S4 that it is a detection end, it is determined in step S6 whether or not it is an outer end. If it is an outer end, the process proceeds to step S11. In step S7, the radial tilt angle θ of the objective lens 11 is set again to the reference value θ0, and in step S8, the level of the high-frequency signal RF is detected.

  Next, in step S9, the signal processing unit 3 determines whether or not the level of the high-frequency signal RF detected in step S8 is the same as the level of the high-frequency signal RF when initially detected as θ = θ0. Returning directly to S2, if not the same, proceed to step S10. In step S10, the difference between the level of the high-frequency signal RF when initially detected as θ = θ0 and the level of the high-frequency signal RF detected in step S8 is used as an offset value, and the offset value is used as each level detection value in the inner direction. And the offset of the detection in the inner direction and the detection in the outer direction is corrected, and the process returns to step S2.

  Steps S2 to S5 are repeated, and if it is determined in step S4 that it is a detection end, and if it is determined in step S6 that it is an outer end, then the corrected detection value in the inner direction and the detection value in the outer direction in step S11 Based on the above, an approximate expression is calculated, and a radial tilt angle θ1 at which the level of the high-frequency signal RF is maximum is calculated in the approximate expression.

  The above-described detection of the optimum radial tilt angle θ1 is performed at a plurality of positions in the radial direction of the optical disc 5. Θ1 at an arbitrary position is calculated from θ1 detected at a plurality of positions. The signal processing unit 3 sets the optimum radial tilt angle θ1 of the objective lens 11 according to the position of the optical pickup 1 in the radial direction of the optical disc 5. As a result, even when the optical disk 5 is warped, the light beam α emitted from the light source 10 is irradiated perpendicularly to the surface of the optical disk 5 through the objective lens 11, and the aberration of the light beam is eliminated. Therefore, a recording mark is appropriately formed on the optical disc when writing data, and a good reproduction signal free from jitter can be obtained when reading data.

  In this embodiment, the objective lens 11 is rotated inward from the reference position to detect the level of the high-frequency signal RF, and the rotation of the objective lens 11 is stopped when the level detection value of the high-frequency signal RF tends to decrease. Next, the objective lens 11 is rotated outward from the reference position to detect the level of the high-frequency signal RF. When the level detection value of the high-frequency signal RF tends to decrease, the rotation of the objective lens 11 is stopped. Then, the optimum value θ1 of the radial tilt angle θ is obtained from an approximate expression showing the relationship between the radial tilt angle θ and the level detection value of the high-frequency signal RF. Therefore, the rotation angle of the objective lens 11 can be reduced compared with the conventional case where the objective lens is always rotated by a predetermined angle, and the detection time can be shortened.

  Further, the difference between the level detection values of the two high-frequency signals RF when the objective lens 11 is set at the reference position is used as an offset value, and the level detection value of the high-frequency signal RF when the objective lens 11 is rotated inward. Since the offset from the level detection value of the high frequency signal RF when the objective lens 11 is rotated outward is corrected, the optimum value θ1 of the radial tilt angle θ can be accurately detected.

  Further, since the high-frequency signal RF output from the optical pickup 1 is used, the size of the apparatus can be reduced and the cost can be reduced as compared with the conventional case where a tilt sensor is separately provided.

  In this embodiment, the offset value is subtracted from the level detection value of the high-frequency signal RF when the objective lens 11 is rotated inward, but the high-frequency when the objective lens 11 is rotated outward. Needless to say, the same result can be obtained by adding the offset value to the level detection value of the signal RF.

  In this embodiment, the optimum radial tilt angle θ1 is detected using the level detection value of the high-frequency signal RF. However, the same result can be obtained even if the tracking error signal TE is used instead of the high-frequency signal RF. Needless to say.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a block diagram which shows the principal part of the optical disk device by one Embodiment of this invention. It is a figure which shows the light source, objective lens, and tilt coil which are contained in the optical pick-up shown in FIG. It is a figure for demonstrating the radial tilt angle of the objective lens shown in FIG. It is a block diagram which shows the part relevant to the production | generation of a tracking error signal among the optical pick-ups shown in FIG. It is a block diagram which shows the part relevant to the production | generation of the high frequency signal of the optical pick-up shown in FIG. 3 is a flowchart showing an optimum radial tilt angle detection operation of the optical disc apparatus shown in FIG. FIG. 6 is a diagram illustrating an example of an optimum radial tilt angle detection operation of the optical disc apparatus shown in FIG. 1.

Explanation of symbols

  1 optical pickup, 2 servo block, 3 signal processing unit, 4 driver, 10 light source, 11 objective lens, 12, 13 tilt coil, 21-24 axis, 25 optical axis, θ radial tilt angle, 30 tracks, 31 main beam, 32 Leading beam, 33 Trailing beam, 41 to 43 detector, 44 to 46, 49, 50 Differential amplifier, 47, 48 amplifier.

Claims (5)

An optical pickup that irradiates a rotating optical disk with a light beam and outputs an electric signal at a level corresponding to the intensity of the reflected light,
The optical pickup is
A light source that emits the light beam;
A photoelectric conversion unit that photoelectrically converts the reflected light and outputs the electrical signal;
An objective lens for condensing the light beam on the optical disc and condensing the reflected light on the photoelectric conversion unit;
A drive unit for rotating the objective lens in a radial tilt direction,
Furthermore, the control unit is configured to control the driving unit to rotate the objective lens and detect the level of the electric signal, and to obtain an optimum value of the radial tilt angle of the objective lens based on the detection result,
The controller is
After detecting the level of the electrical signal by setting the radial tilt angle as a reference value, the level of the electrical signal is decreased by detecting the level of the electrical signal while rotating the objective lens to one side. A first step of stopping the rotation of the objective lens in response to the tendency to
After the radial tilt angle is set to the reference value again and the level of the electrical signal is detected, the level of the electrical signal is detected while rotating the objective lens to the other side, and the level detection value of the electrical signal A second step of stopping the rotation of the objective lens in response to the tendency to decrease;
A difference in level detection value of the electric signal when the radial tilt angle is set to the reference value in the first and second steps is obtained, and the difference is obtained as a level detection value of the electric signal in the first step. Subtracting or adding the difference to the level detection value of the electrical signal in the second step to correct the offset of the level detection value of the electrical signal between the first and second steps And the steps
An approximate expression showing the relationship between the radial tilt angle and the correction value of the level detection value of the electric signal is calculated, and the radial tilt angle at which the electric signal level is maximum in the approximate expression is determined as the optimum value. 4. An optical disc apparatus characterized by executing four steps. In an optical disc apparatus equipped with an optical pickup that irradiates a rotating optical disc with a light beam through an objective lens and outputs an electric signal at a level corresponding to the intensity of the reflected light, the objective lens is rotated in a radial tilt direction. While detecting the level of the electrical signal, and obtaining the optimum value of the radial tilt angle of the objective lens based on the detection result,
After detecting the level of the electrical signal by setting the radial tilt angle as a reference value, the level of the electrical signal is decreased by detecting the level of the electrical signal while rotating the objective lens to one side. A first step of stopping the rotation of the objective lens in response to the tendency to
After the radial tilt angle is set to the reference value again and the level of the electrical signal is detected, the level of the electrical signal is detected while rotating the objective lens to the other side, and the level detection value of the electrical signal A second step of stopping the rotation of the objective lens in response to the tendency to decrease;
The difference between the level detection values of the electrical signal when the radial tilt angle is set to the reference value in the first and second steps is used as an offset value, and the electrical signal between the first and second steps is A third step of correcting the offset of the level detection value;
An approximate expression showing the relationship between the radial tilt angle and the correction value of the level detection value of the electric signal is calculated, and the radial tilt angle at which the electric signal level is maximum in the approximate expression is determined as the optimum value. 4. An optimal radial tilt angle detection method comprising four steps.   In the third step, the offset value is subtracted from the level detection value of the electrical signal in the first step, or the offset value is added to the level detection value of the electrical signal in the second step. The method for detecting the optimum radial tilt angle according to claim 2, wherein an offset of a level detection value of the electric signal between the first and second steps is corrected.   4. The optimal radial tilt angle detection method according to claim 2, wherein the electrical signal is a high-frequency signal.   4. The optimal radial tilt angle detection method according to claim 2, wherein the electrical signal is a tracking error signal.

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