JP2008097719A - Optical disk unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical disk unit which can increase reliability in operation. <P>SOLUTION: An offset specifying circuit 71 specifies an offset Teost_max for minimizing a jitter at the maximum voltage of a voltage V1 (Vfo_max), and an offset Teofst_min for minimizing the jitter at the minimum voltage (Vfo_min) of the voltage V1. An offset supplying circuit 73 determines the offset Teofst based on the values, and gives the offset Teofst to a tracking servo circuit 61 so that the tracking servo circuit 61 can control tracking to minimize the jitter of reproducing signal. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical disc apparatus, and more particularly to a technique for controlling a light spot on an optical disc.

  In an optical disc device such as a CD (Compact Disc) playback device or a DVD (Digital Versatile Disc) playback device, the laser beam emitted from the optical pickup is focused on the signal surface of the disc, and the reflected light from the signal surface is reflected by the optical pickup. Data is read by detection. In order for the light emitted from the optical pickup to be reflected by the signal surface of the disk and return to the optical pickup, the optical axis of the light emitted from the optical pickup needs to be perpendicular to the signal surface.

  However, the disc may be warped depending on the state of manufacture or storage of the disc. It is also conceivable that the disk is inclined with respect to the rotating shaft of the motor that rotates the disk. In these cases, when the disk is rotated at a high speed, so-called “surface vibration” occurs, and the distance between the optical pickup and the surface of the disk fluctuates periodically. For this reason, there arises a problem that the laser beam is defocused, or that the reflected light travels in a different direction from the original direction. These problems cause a read error when the disc is played back.

  Japanese Patent Application Laid-Open No. 11-232676 (Patent Document 1) discloses an optical disk control apparatus capable of expanding the tolerance of a reproduction signal with respect to the inclination of the optical disk in the radial direction. This optical disk control device includes a measurement circuit that measures the jitter amount of a reproduction signal, an arithmetic circuit that generates an offset signal that minimizes the jitter amount based on the measurement result, a tracking error signal and an offset signal from an optical pickup, And a tracking servo circuit that performs tracking control using the.

  On the other hand, Japanese Patent Application Laid-Open No. 2004-127454 (Patent Document 2) discloses an optical disc apparatus that corrects the tilt of the optical disc. This optical disk apparatus calculates the inclination of the disk with respect to the optical axis of the optical pickup based on the focal positions of the optical pickup at the first and second positions along the radial direction of the optical disk. Then, the optical disk apparatus corrects the angle of the disk with respect to the optical axis of the optical pickup by tilting the optical pickup based on the calculation result.

  Japanese Patent Laying-Open No. 2005-327425 (Patent Document 3) discloses a focus control method for solving the problem that focus control does not function effectively when a disk with a large amount of change in surface shake is reproduced. According to this method, the surface shake change amount during one rotation of the optical disc is approximated to a sine wave to calculate the surface shake amount in advance, and focus control is performed based on the calculation result.

  Japanese Patent Laying-Open No. 2005-166088 (Patent Document 4) discloses an optical disc apparatus capable of stable focus control by suppressing the influence of surface deflection of the optical disc. The optical disc apparatus includes a surface shake detection unit that detects a surface shake amount based on an output signal (focus error signal) of a focus error detection unit at a low recording speed (linear velocity), and a bias is applied based on the surface shake amount. A controller that determines the amount, a bias applying unit that outputs a bias signal corresponding to the amount of bias applied to the focus control unit, and a signal generated by applying a bias signal to a drive signal of a normal optical pickup is output to the optical pickup A focus control unit. As a result, even when recording is performed at a high linear velocity, the positional relationship between the converging lens of the optical pickup and the optical disc enables accurate focus servo while maintaining a constant distance.

Japanese Patent Laid-Open No. 2000-20967 (Patent Document 5) can perform a track jump and a focus jump without causing off-track or defocus even in the presence of disc eccentricity or surface runout. An optical disc device is disclosed. This optical disc apparatus includes a jump signal generation circuit that generates a jump signal for moving a light detection circuit, a storage circuit that stores a rotation angle and an eccentricity (or surface shake) component of the optical disc in association with each other, and an optical disc at the time of a jump. Is provided with an arithmetic circuit that extracts information from the storage circuit according to the rotation angle and adds the information and the jump signal, and a drive circuit that moves the photodetection circuit based on the calculation result of the arithmetic circuit.
JP-A-11-232676 JP 2004-127454 A JP 2005-327425 A JP 2005-166088 A JP 2000-20967 A

  In the case of an optical disk control device disclosed in Japanese Patent Laid-Open No. 11-232676 (Patent Document 1), an offset amount for minimizing the jitter amount is determined for an entire track (a row of marks for one round of the disk). Is done. Therefore, the jitter amount may not be minimized in a certain portion of the track.

  Further, according to the disclosure of Japanese Patent Application Laid-Open No. 2004-127454 (Patent Document 2), it is necessary to provide a mechanism for tilting the optical pickup, so that the structure of the optical disc apparatus becomes complicated.

  Further, according to the disclosures of Japanese Patent Application Laid-Open No. 2005-327425 (Patent Document 3), Japanese Patent Application Laid-Open No. 2005-166088 (Patent Document 4), and Japanese Patent Application Laid-Open No. 2000-20967 (Patent Document 5). Although focus control at the time of reproduction (or recording) can be performed by obtaining the amount, that is, the magnitude of the vibration of the disk that occurs when the disk rotates, tracking error is not taken into consideration, so reading errors (or It is assumed that a recording error) occurs.

  SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an optical disc apparatus capable of improving reliability during operation.

  In summary, the present invention is an optical disc apparatus, which includes a light source, an objective lens, an objective lens driving device, a signal processing unit, a focus control circuit, a tracking control circuit, a detection circuit, and an offset amount specifying circuit. And an offset amount supply circuit. The light source irradiates the signal recording surface of the optical disc with laser light. The objective lens collects laser light. The objective lens driving device receives the first and second control voltages and moves the objective lens in the optical axis direction of the laser light and in the direction perpendicular to the optical axis direction of the laser light. The signal processing unit outputs a focus error signal and a tracking error signal based on the reflected light generated by the reflection of the laser beam on the signal recording surface, and information recorded on the signal recording surface based on the reflected light Is generated, and the amount of jitter included in the reproduction signal is detected and output. The focus control circuit changes the first control voltage based on the focus error signal. The tracking control circuit changes the second control voltage based on the tracking error signal and the offset amount. The detection circuit detects that the optical disk is tilted in the radial direction of the optical disk based on the change in the first control voltage. When receiving the detection result of the detection circuit, the offset amount specifying circuit changes the offset amount based on the first control voltage and the jitter amount, and the jitter amount is minimized at the maximum value of the first control voltage. The first offset amount and the second offset amount that minimizes the jitter amount at the minimum value of the first control voltage are specified. The offset amount supply circuit determines a function for associating the first control voltage with the offset amount based on the first and second offset amounts. The offset amount supply circuit calculates the offset amount by substituting the value of the first control voltage acquired from the focus control circuit into the function. The offset amount supply circuit supplies the calculated offset amount to the tracking control circuit.

  According to another aspect of the present invention, there is provided an optical disc apparatus that includes a light source, an objective lens, an objective lens driving device, a signal processing unit, a focus control circuit, a detection circuit, an offset amount specifying circuit, and an offset amount. And a supply circuit. The light source irradiates the signal recording surface of the optical disc with laser light. The objective lens collects laser light. The objective lens driving device receives the control voltage and moves the objective lens in the optical axis direction of the laser light. The signal processing unit outputs a focus error signal based on the reflected light generated by the reflection of the laser light on the signal recording surface, and generates a reproduction signal including information recorded on the signal recording surface based on the reflected light. Then, the jitter amount included in the reproduction signal is detected and output. The focus control circuit changes the control voltage based on the focus error signal and the offset amount. The detection circuit detects that the optical disk is tilted in the radial direction of the optical disk based on the change in the control voltage. When receiving the detection result of the detection circuit, the offset amount specifying circuit changes the offset amount based on the control voltage and the jitter amount, and the first offset amount that minimizes the jitter amount at the maximum value of the control voltage. And the second offset amount that minimizes the jitter amount at the minimum value of the control voltage. The offset amount supply circuit supplies the focus control circuit with a value determined based on the control voltage from the focus control circuit, the maximum and minimum values of the control voltage, and the first and second offset amounts as an offset amount.

  According to still another aspect of the present invention, an optical disc apparatus includes a light source, an objective lens, an objective lens driving device, a signal processing unit, a focus control circuit, an offset output circuit, and a tracking control circuit. . The light source irradiates the signal recording surface of the optical disc with laser light. The objective lens collects laser light. The objective lens driving device receives the first and second control voltages and moves the objective lens in the optical axis direction of the laser light and in the direction perpendicular to the optical axis direction of the laser light. The signal processing unit outputs a focus error signal and a tracking error signal based on the reflected light generated by reflecting the laser beam on the signal recording surface. The focus control circuit changes the first control voltage based on the focus error signal. The offset output circuit determines whether the optical disk is tilted based on the first control voltage. When detecting that the optical disc is tilted, the offset output circuit calculates an offset amount of the tracking error signal accompanying the tilt of the optical disc based on the first control voltage. The offset output circuit outputs the calculated offset amount. The tracking control circuit changes the second control voltage based on the tracking error signal and the offset amount.

  Preferably, the signal processing unit generates a reproduction signal including information recorded on the signal recording surface based on the reflected light, and detects and outputs a jitter amount included in the reproduction signal.

  The offset output circuit includes an offset amount specifying circuit and an offset amount calculating circuit. The offset amount specifying circuit changes the offset amount based on the first control voltage and the jitter amount. The offset amount specifying circuit specifies the first and second offset amounts that minimize the amount of jitter, respectively, at predetermined first and second voltage values of the first control voltage. The offset amount calculation circuit determines a function for associating the first control voltage with the offset amount based on the first and second offset amounts. The offset amount calculation circuit calculates the offset amount by substituting the value of the first control voltage acquired from the focus control circuit into the function.

  More preferably, the predetermined first and second voltage values are a maximum value and a minimum value of the first control voltage, respectively.

  According to still another aspect of the present invention, an optical disc apparatus includes a light source, an objective lens, an objective lens driving device, a signal processing unit, an offset output circuit, and a focus control circuit. The light source irradiates the signal recording surface of the optical disc with laser light. The objective lens collects laser light. The objective lens driving device receives the control voltage and moves the objective lens in the optical axis direction of the laser light. The signal processing unit outputs a focus error signal based on the reflected light generated by reflecting the laser beam on the signal recording surface. The offset output circuit determines whether or not the optical disk is tilted based on the control voltage. When detecting that the optical disk is tilted, the offset output circuit calculates an offset amount of the focus error signal accompanying the tilt of the optical disk based on the control voltage. The offset output circuit outputs the calculated offset amount. The focus control circuit changes the control voltage based on the focus error signal and the offset amount.

  Preferably, the signal processing unit generates a reproduction signal including information recorded on the signal recording surface based on the reflected light, and detects and outputs a jitter amount included in the reproduction signal.

  The offset output circuit includes an offset amount specifying circuit and an offset amount calculating circuit. The offset amount specifying circuit changes the offset amount based on the control voltage and the jitter amount. The offset amount specifying circuit specifies the first and second offset amounts that minimize the amount of jitter, respectively, at predetermined first and second voltage values of the control voltage. The offset amount calculation circuit determines a function for associating the first control voltage with the offset amount based on the first and second offset amounts. The offset amount calculation circuit calculates the offset amount by substituting the value of the first control voltage acquired from the focus control circuit into the function.

  More preferably, the predetermined first and second voltage values are a maximum value and a minimum value of the first control voltage, respectively.

  According to the present invention, it is possible to improve reliability during operation of the optical disc apparatus.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

[Embodiment 1]
FIG. 1 is a schematic configuration diagram of an optical disc apparatus 100 according to the first embodiment. Specifically, the optical disc apparatus 100 is a disc playback apparatus.

  Referring to FIG. 1, an optical disk device 100 includes a motor 1, a disk drive controller 2, a head access control unit 3, a guide 50, a pickup device 10, a signal processing unit 4, a tracking servo circuit 61, A focus servo circuit 62 and an offset output circuit 70 are provided.

  The motor 1 receives the control signal from the disk drive controller 2 and rotates the optical disk 20 at a predetermined rotational speed. The optical disk 20 is, for example, a DVD or a CD. There are various types of DVD and CD, but the type of the optical disc 20 is not particularly limited. In the following, it is assumed that the optical disk 20 is a DVD-RAM.

  The pickup device 10 is driven in the radial direction of the optical disc 20 along the guide 50 by the head access control unit 3. The pickup device 10 condenses the laser beam LA on the signal recording surface of the optical disc 20 and the semiconductor laser 13 that irradiates the laser beam LA on the signal recording surface of the optical disc and the laser beam LA output from the semiconductor laser 13. The objective lens 11 into which the reflected light LB from the signal recording surface is incident and the objective lens driving device 12 that drives the objective lens 11 are provided.

  The objective lens driving device 12 includes a magnet and a coil. When the objective lens driving device 12 receives the voltage V1 from the focus servo circuit 62, it sends a current to the focus coil placed in the magnetic field generated from the magnet, and drives the objective lens 11 in the focus direction. The “focus direction” is the optical axis direction (direction R1) of the laser light LA.

  Further, when the objective lens driving device 12 receives the voltage V2 from the tracking servo circuit 61, the objective lens driving device 12 drives the objective lens 11 in the tracking direction by passing a current through a tracking coil placed in a magnetic field generated from the magnet. The “tracking direction” is a direction (direction R2) perpendicular to the optical axis direction of the laser beam LA.

  The signal processing unit 4 includes a photodetector 14, a reproduction circuit 30, an error detection circuit 40, and a jitter amount measurement circuit 43.

  The photodetector 14 detects reflected light incident on the objective lens 11 and outputs a light reception signal. The reproduction circuit 30 generates a reproduction signal including information recorded on the signal recording surface based on the light reception signal from the photodetector 14.

  The jitter amount measurement circuit 43 measures the jitter amount of the reproduction signal output from the reproduction circuit 30.

  The error detection circuit 40 includes a tracking error detection circuit 41 and a focus error detection circuit 42.

  The tracking error detection circuit 41 calculates a light reception signal from the photodetector 14 according to the push-pull method and generates a tracking error signal TE. The tracking error signal TE indicates a deviation of the objective lens 11 in the tracking direction.

  The focus error detection circuit 42 calculates the received light signal from the photodetector 14 according to the astigmatism method and generates a focus error signal FE. The focus error signal FE indicates a shift in the focus direction of the objective lens 11.

  The tracking servo circuit 61 changes the voltage V <b> 2 according to the sum of the tracking error signal TE sent from the tracking error detection circuit 41 and the offset amount Teofst (offset voltage) sent from the offset output circuit 70. The objective lens driving device 12 receives the voltage V2 and moves the objective lens 11 in the tracking direction.

  The focus servo circuit 62 changes the voltage V <b> 1 according to the focus error signal FE sent from the focus error detection circuit 42. The objective lens driving device 12 receives the voltage V1 and moves the objective lens 11 in the focus direction.

  The offset output circuit 70 determines whether the optical disk 20 is tilted based on the voltage V1. When the offset output circuit 70 detects that the optical disc 20 is tilted, the offset output circuit 70 calculates the offset amount Teofst of the tracking error signal TE accompanying the tilt of the optical disc 20 based on the voltage V1. Then, the offset output circuit 70 outputs the calculated offset amount Teofst.

  The offset output circuit 70 includes an offset amount specifying circuit 71, an offset amount supply circuit 73, a memory 75, and a detection circuit 76.

  The offset amount specifying circuit 71 receives the voltage V1 from the focus servo circuit 62 and the jitter amount of the reproduction signal from the jitter amount measuring circuit 43. When the detection circuit 76 detects that the optical disc 20 is tilted, the offset amount specifying circuit 71 changes the offset amount based on the voltage V1 and the jitter amount.

  The offset amount specifying circuit 71 specifies the first offset amount that minimizes the jitter amount when the voltage V1 is maximum, and the second offset amount that minimizes the jitter amount when the voltage V1 is minimum. . These offset amounts are stored in the memory 75 in association with the value of the voltage V1.

  The offset amount supply circuit 73 determines a function for associating the voltage V1 with the offset amount based on the first and second offset amounts. Then, the offset amount supply circuit 73 calculates the offset amount by substituting the value of the voltage V1 acquired from the focus servo circuit 62 into the function. More specifically, the offset amount supply circuit 73 receives the voltage V 1 from the focus servo circuit 62. Further, the offset amount supply circuit 73 reads out from the memory 75 the maximum value and minimum value of the voltage V1 and two offset amounts respectively corresponding to the maximum value and the minimum value. Then, the offset amount supply circuit 73 gives the value calculated based on the voltage V1, the maximum value and minimum value of the voltage V1, and the two offset amounts to the tracking servo circuit 61 as an offset amount.

  The detection circuit 76 detects the tilt of the optical disc 20 based on the voltage V1. When the optical disc 20 is tilted, when the optical disc 20 is rotated, the signal recording surface of the optical disc 20 vibrates. In this case, the focus servo circuit 62 changes the voltage V1 so that the laser beam LA is focused on the signal recording surface of the optical disc 20. The detection circuit 76 determines that the optical disk is tilted when the change amount of the voltage V1 is larger than a predetermined threshold value.

  During focus servo, the voltage V1 changes at high speed in order to focus the laser beam on the optical disk 20. On the other hand, the voltage V1 changes slowly according to the surface shake of the optical disc 20. That is, the signal output from the focus servo circuit includes a high frequency component and a low frequency component.

  Due to the influence of this high-frequency component, the detection circuit 76 may erroneously detect the presence of surface vibration despite the fact that the disk does not actually have surface vibration. In order to prevent such a problem from occurring, the detection circuit 76 includes a low-pass filter therein. As a result, the detection circuit 76 can extract only the low-frequency component of the signal output from the focus servo circuit 62, so that it is possible to detect the disk runout based on the fluctuation of the voltage V1.

The detection circuit 76 may be included in the offset amount specifying circuit 71.
FIG. 2 is a view showing a state in which the optical disk 20 of FIG. 1 is inclined with respect to the rotation axis of the motor 1.

  Referring to FIG. 2, when the optical disc 20 is tilted with respect to the rotation axis of the motor 1, the incident angle of the laser beam LA from the semiconductor laser 13 changes on the recording surface of the optical disc 20. For example, when the laser light LA is incident on the optical disk 20 indicated by a solid line, the reflected light LB1 proceeds to the inner peripheral side of the optical disk 20, but when the laser light LA is incident on the optical disk 20 indicated by a broken line, the reflected light LB1 is the optical disk. Proceed to the outer peripheral side of 20.

FIG. 3 is a diagram showing a state in which the outer peripheral portion of the optical disc 20 in FIG. 1 is warped.
Referring to FIG. 3, when the optical disk 20 is flat (solid line), when the laser light LA is incident on the optical disk 20, the reflected light LB3 travels toward the semiconductor laser 13, whereas the warp of the optical disk 20 indicated by a broken line is shown. If it occurs, the reflected light LB4 travels to the outer peripheral side of the optical disc 20.

  In the following, the tilt of the optical disc 20 when the optical disc 20 as shown in FIGS. 2 and 3 is in the reference state perpendicular to the laser beam LA is referred to as “radial tilt” or “rad skew”. To do. Hereinafter, the amount of fluctuation in the position of the signal recording surface of the optical disk in the optical axis direction of the laser beam LA is referred to as “surface deflection amount”.

  FIG. 4 is a diagram for explaining the light spots formed on the light receiving surface of the photodetector 14 when the optical disk 20 shown in FIG. 2 is irradiated with the laser light LA.

  Referring to FIG. 4, the light receiving surface of photodetector 14 is divided into two regions 14A and 14B. When the reflected light LB shown in FIG. 1 enters the light receiving surface, a light spot SP is formed on the light receiving surface. When the light beam moves on the same track, the traveling direction of the reflected light changes, so that the light spot SP moves in the direction from the region 14A to the region 14B (and the reverse direction).

  From the areas 14A and 14B, light reception signals SA and SB corresponding to the amount of light received are output, respectively. The tracking error detection circuit 41 of FIG. 1 generates a tracking error signal TE by performing an operation of TE = (SA−SB) (push-pull method).

  In such a push-pull method, crosstalk components from adjacent tracks increase due to the inclination of the optical disk in the radial direction. Therefore, even if the light spot accurately traces the center of the track on the optical disk, the quality of the reproduction signal is deteriorated.

  In order to prevent this problem, not only the tracking error signal TE but also the offset amount is input to the tracking servo circuit 61 of FIG. The tracking servo circuit 61 controls the driving of the objective lens 11 by the objective lens driving device 12 by outputting a voltage V2 corresponding to the sum of the tracking error signal TE and the offset amount. In this case, the amount of jitter can be minimized by slightly shifting the position of the light spot from the track center on the optical disk. Therefore, it is possible to prevent the quality of the reproduction signal from being deteriorated.

  However, for example, when the light spot SP is close to the region 14A, the offset amount is determined so as to minimize the jitter amount, and the offset amount is not changed. In this case, when the light spot SP is shifted from the region 14A side to the region 14B side, the jitter amount of the reproduction signal may not be minimized.

  In the present embodiment, the offset amount is changed according to the inclination of the optical disk in the radial direction. As a result, it is possible to prevent the above-described problem from occurring, so that information can be accurately read from the optical disk (or information can be correctly written to the optical disk). Therefore, it is possible to improve the reliability during operation of the optical disc apparatus.

FIG. 5 is a diagram for explaining the fluctuation of the voltage V1 when the optical disk 20 of FIG. 1 is rotated.
5 and 1, when the voltage V1 is Vfo_max, the objective lens 11 is in the position closest to the optical disc 20 in the movable range, and when the voltage V1 is Vfo_min, the objective lens 11 is the optical disc in the movable range. It is the farthest position from 20.

  At time t_max, the voltage V1 is Vfo_max. During the period from time t_max to t_max + T (T is the disk rotation period), the voltage V1 decreases from Vfo_max to Vfo_min, and then returns to Vfo_max. In the period from time t_max + T to t_max + 2T and the period thereafter, the voltage V1 changes as described above.

  Vfo_c is an intermediate voltage between Vfo_max and Vfo_min. At this time, the radial gradient (rad skew) is zero.

  FIG. 6 is a diagram for explaining the relationship between the voltage V1 and the inclination (rad skew) of the optical disc 20 in the radial direction.

  Referring to FIG. 6, the vertical axis of the graph indicates the amount of change in the distance between the objective lens 11 and the optical disc when the optical disc is rotated with the position of the objective lens 11 in the focus direction fixed. rs_max and rs_min respectively indicate the inclination in the radial direction of the optical disc 20 when the distance of the optical disc with respect to the objective lens 11 is maximum and minimum. The magnitude of the surface shake amount is | rs_max−rs_min |. When the magnitude of the inclination of the optical disk 20 in the radial direction is rs_max and rs_min, the voltage V1 is Vfo_max and Vfo_min, respectively. As shown in FIG. 6, the voltage V1 and the inclination of the optical disc 20 in the radial direction are in a proportional relationship.

  FIG. 7 is a diagram for explaining the relationship between the radial tilt (rad skew) of the optical disc 20 and the offset amount of the tracking error signal TE that can minimize the jitter amount.

  Referring to FIG. 7, when the inclination of the optical disc 20 in the radial direction is rs_max, the offset amount is the maximum value (Teofst_max). On the other hand, when the inclination of the optical disk 20 in the radial direction is rs_min, the offset amount is the minimum value (Teofst_min). When the radial tilt of the optical disc 20 changes in the range from rs_max to rs_min, the offset amount also changes in the range from Teofst_max to Teofst_min. As shown in FIG. 7, the radial tilt of the optical disc 20 and the offset amount of the tracking error signal TE are in a proportional relationship.

  FIG. 8 is a diagram for explaining the relationship between the offset amount and the jitter amount when the inclination of the optical disk 20 in the radial direction is a fixed value.

  Referring to FIG. 8, curves A and C indicate changes in the jitter amount with respect to changes in the offset amount when the radial inclination of the optical disc 20 is rs_min and rs_max, respectively. A curve B shows a change in the jitter amount with respect to a change in the offset amount when the inclination of the optical disc 20 in the radial direction is zero.

  Each of the curves A to C indicates that there is an offset amount for minimizing the jitter amount. Note that the offset amounts for minimizing the jitter amount in the curves A and C are respectively Teofst_min and Teofst_max.

  From FIG. 6 and FIG. 7, it is derived that the voltage V1 and the offset amount are in a proportional relationship. That is, if the offset amount is determined according to the voltage V1, even if the inclination of the optical disk 20 in the radial direction changes, the offset amount according to the change can be determined. In the first embodiment, since the offset amount is determined using such a relationship, the offset amount for minimizing the jitter amount can be determined regardless of the inclination of the optical disc 20 in the radial direction.

  FIG. 9 is a diagram for explaining processing in which the offset amount specifying circuit 71 in FIG. 1 specifies the offset amount.

  With reference to FIG. 9 and FIG. 1, voltage V1 changes periodically between Vfo_max and Vfo_min. On the other hand, the offset amount specifying circuit 71 receives the jitter amount of the reproduction signal from the jitter amount measuring circuit 43 by sequentially changing the offset amount (TE offset) as Te1, Te2, Te3, Te4, and Te5.

  The period during which the offset amount specifying circuit 71 outputs each of the offset amounts Te1 to Te5 is equal to the disk rotation period T shown in FIG. Further, the offset amount specifying circuit 71 determines the timing for outputting the offset amounts Te1 to Te5 so that the voltage V1 becomes Vfo_max and Vfo_min within the period in which each offset amount is output.

  In the curve indicating the jitter waveform, a circular symbol and a triangular symbol indicate the amounts of jitter when the voltage V1 reaches Vfo_max and Vfo_min, respectively. Focusing only on the circular symbol, the jitter amount becomes the smallest when the offset amount is Te2 (time t1). Therefore, the offset amount specifying circuit 71 specifies the value of the offset amount Tofst_max as Te2 when the voltage V1 is Vfo_max, that is, when the inclination in the radial direction of the optical disc is maximum.

  Similarly, when focusing only on the triangular symbol, the jitter amount becomes the smallest when the offset amount is Te4 (time t2). Therefore, the offset amount specifying circuit 71 specifies the value of the offset amount Tofst_min as Te4 when the voltage V1 is Vfo_min, that is, when the inclination of the optical disk in the radial direction is minimum.

FIG. 10 is a flowchart for explaining the processing of the offset amount specifying circuit 71 of FIG.
Referring to FIG. 10 and FIG. 1, when the process is started, the disk drive controller 2 rotates the motor 1 in step S1. As a result, the optical disk 20 rotates.

  In step S2, the disk drive controller 2 and the head access controller 3 move the pickup device 10 to a predetermined track position.

  Subsequently, in step S3, the focus servo circuit 62 starts a focus control operation (the focus servo is turned on). As a result, the focus servo circuit 62 changes the voltage V1 in accordance with the focus error signal FE.

  Subsequently, in step S4, the detection circuit 76 determines whether or not vibration (surface vibration) has occurred in the optical disc 20. The detection circuit 76 acquires the maximum value (Vfo_max) and the minimum value (Vfo_min) of the voltage V1, and if the difference between the maximum value and the minimum value (Vfo) is larger than a predetermined value, the optical disc 20 has a surface shake. judge.

  When the detection circuit 76 detects vibration of the optical disc 20 that is larger than the predetermined shake amount (YES in step S4), the tracking servo circuit 61 starts a tracking control operation (turns on the tracking servo) in step S5. On the other hand, when the magnitude of vibration of the optical disc 20 is smaller than the predetermined shake amount (NO in step S4), the entire process ends.

  In step S <b> 6, the offset amount specifying circuit 71 receives the detection result from the detection circuit 76. Then, the offset amount specifying circuit 71 specifies the tracking offset amount (offset amount Teofst_max, Teofst_min) that minimizes the jitter amount in each case where the voltage V1 is Vfo_max and the voltage V1 is Vfo_min.

  In step S <b> 7, the offset amount specifying circuit 71 stores the offset amounts Teofst_max and Teofst_min in the memory 75. When the process of step S7 ends, the entire process ends.

  FIG. 11 is a flowchart for explaining the processing of the offset amount supply circuit 73 in FIG. The process shown in FIG. 11 is performed at the time of reproducing the optical disk.

  When the processing is started with reference to FIGS. 11 and 1, the offset amount supply circuit 73 acquires the voltage V <b> 1 from the focus servo circuit 62 in step S <b> 11. Next, in step S <b> 12, the offset amount supply circuit 73 acquires voltage values Vfo_min and Vfo_max and offset amounts Teofst_max and Teofst_min from the memory 75.

  Subsequently, in step S13, the offset amount supply circuit 73 determines the offset amount Teofst by linear interpolation. Specifically, the offset amount supply circuit 73 calculates the offset amount Teofst by substituting the value of the voltage V1 acquired from the focus servo circuit 62 into the function shown in the following equation (1).

Teofst = (Teofst_max−Teofst_min) / (Vfo_max−Vfo_min) × (V1−Vfo_min) + Teofst_min (1)
In step S <b> 14, the offset amount supply circuit 73 supplies the offset amount Teofst to the tracking servo circuit 61. When the process of step S14 ends, the entire process returns to step S11.

  Note that the process shown in FIG. 10 may be performed for all tracks before reproduction, or may be performed prior to the process shown in FIG. However, when the processing shown in FIGS. 10 and 11 is performed on each track during reproduction, the information of the offset amounts Teofst_max and Teofst_min and the voltage values Vfo_max and Vfo_min stored in the memory 75 is only required for one track. Therefore, even when the memory capacity is small, the processes of FIGS. 10 and 11 can be executed.

FIG. 12 is a diagram for explaining the operation according to the comparative example of the first embodiment.
Referring to FIG. 12, in the case of the operation according to the comparative example, the value of the tracking error offset amount is constant regardless of the change in voltage V1. As shown in FIG. 8, the offset amount Teofst_min when the jitter amount is minimized in the curve A is different from the offset amount when the jitter amount is minimized in the curves B and C. That is, as shown in FIG. 12, when the value of the tracking error offset amount is fixed regardless of the change in the voltage V1, the jitter amount is minimized at a certain portion of the track, but the jitter amount is increased at the other portion. Therefore, there is a possibility that the quality of the reproduction signal is lowered.

FIG. 13 is a diagram for explaining the operation of the optical disk device according to the first embodiment.
Referring to FIG. 13, offset amount Teofst changes in synchronization with voltage V1. Thereby, even if the inclination of the optical disk in the radial direction changes, the offset amount Teofst corresponding to the change can be generated. As a result, it is possible to control the jitter to be minimized during the reproduction of the optical disc, so that the quality of the reproduction signal can be improved.

  As described above, according to the first embodiment, the offset amount specifying circuit 71 includes the offset amount Teofst_max that minimizes the jitter amount at the maximum value (Vfo_max) of the voltage V1 and the jitter amount at the minimum value (Vfo_min) of the voltage V1. Is specified as an offset amount Teofst_min that minimizes. Based on these values, the offset amount supply circuit 73 determines the offset amount Teofst and gives the offset amount Teofst to the tracking servo circuit 61. As a result, the tracking servo circuit 61 can perform tracking control so that the amount of jitter of the reproduction signal is minimized, so that the reliability of the operation of the optical disc apparatus can be improved.

[Embodiment 2]
In the first embodiment, tracking control is performed by changing the offset amount added to the tracking error signal TE in accordance with the change in the voltage V1 input to the objective lens driving circuit. On the other hand, in the second embodiment, the focus control is performed by changing the offset amount added to the focus error signal FE in accordance with the change of the voltage V1.

FIG. 14 is a schematic configuration diagram of an optical disc device 100A according to the second embodiment.
Referring to FIGS. 14 and 1, optical disc apparatus 100A is different from optical disc apparatus 100 in that it includes an offset output circuit 70A instead of offset output circuit 70. The offset output circuit 70A is different from the offset output circuit 70 in that the offset amount Feofst is output to the focus servo circuit 62.

  The offset output circuit 70A determines whether the optical disc 20 is tilted based on the voltage V1. When the offset output circuit 70A detects that the optical disc 20 is tilted, the offset output circuit 70A calculates an offset amount Feofst of the focus error signal FE accompanying the tilt of the optical disc 20 based on the voltage V1. The offset output circuit 70A outputs the calculated offset amount Feofst.

  The offset output circuit 70 </ b> A includes an offset amount specifying circuit 71, an offset amount supply circuit 73, a memory 75, and a detection circuit 76.

  The offset amount specifying circuit 71 receives the voltage V1 from the focus servo circuit 62 and the jitter amount of the reproduction signal from the jitter amount measuring circuit 43. When the detection circuit 76 detects the tilt of the optical disc 20, the offset amount specifying circuit 71 changes the offset amount Feofst based on the voltage V1 and the jitter amount.

  The offset amount specifying circuit 71 specifies the first offset amount that minimizes the jitter amount when the voltage V1 is maximum, and the second offset amount that minimizes the jitter amount when the voltage V1 is minimum. . These offset amounts are stored in the memory 75 in association with the value of the voltage V1.

  The offset amount supply circuit 73 determines a function for associating the voltage V1 with the offset amount based on the first and second offset amounts. Then, the offset amount supply circuit 73 calculates the offset amount by substituting the value of the voltage V1 acquired from the focus servo circuit 62 into the function. More specifically, the offset amount supply circuit 73 receives the voltage V 1 from the focus servo circuit 62. Further, the offset amount supply circuit 73 reads out from the memory 75 the maximum value and minimum value of the voltage V1 and two offset amounts respectively corresponding to the maximum value and the minimum value. Then, the offset amount supply circuit 73 gives the value calculated based on the voltage V1, the maximum value and minimum value of the voltage V1, and the two offset amounts to the focus servo circuit 62 as an offset amount.

  14 has the same function as that of memory 75 and detection circuit 76 shown in FIG. 1, and therefore, description thereof will not be repeated.

FIG. 15 is a diagram for explaining a general focus error detection method.
Referring to FIG. 15, the light receiving surface of the photodetector is divided into four regions, and light incident on each of the four regions is converted into electric signals A, B, C, and D. The focus error circuit that receives the electrical signals A to D performs arithmetic processing on the electrical signals A, B, C, and D, and outputs (A + C) − (B + D) as the focus error signal FE.

  First, a change (solid line) in the focus error signal FE in the case where no surface shake has occurred on the optical disc will be described. When the optical disc is at the focal position (focusing point), a circular light spot is formed at the center of the photodetector. In this case, the level of the focus error signal FE becomes zero. When defocusing occurs due to the large distance between the optical disk and the objective lens, an elliptical light spot spreading horizontally is formed. In this case, the level of the focus error signal FE is lower than zero. In addition, when a focus shift occurs due to a small distance between the optical disk and the objective lens, an elliptical light spot extending vertically is formed. In this case, the level of the focus error signal FE becomes higher than zero.

  When the optical disc has a radial inclination, the level of the focus error signal FE fluctuates up and down within the range indicated by the broken line. For this reason, the jitter amount of the reproduction signal also varies. In order to prevent this problem, as in the first embodiment, not only the focus error signal FE but also the offset amount is input to the focus servo circuit 62 in FIG. The focus servo circuit 62 outputs a voltage V1 corresponding to the sum of the focus error signal FE and the offset amount.

  Next, the operation of the optical disk apparatus according to the second embodiment will be described. In summary, the operation of the optical disc apparatus of the second embodiment is the same as that of the optical disc apparatus of the first embodiment in which the tracking offset is replaced with the focus offset.

  FIG. 16 is a diagram for explaining the relationship between the radial inclination (rad skew) of the optical disc 20 and the offset amount of the focus error signal FE that can minimize the jitter amount.

  Referring to FIG. 16, when the inclination of the optical disc 20 in the radial direction is rs_max, the offset amount becomes the maximum value (Feofst_max). On the other hand, when the inclination of the optical disk 20 in the radial direction is rs_min, the offset amount is the minimum value (Feofst_min). As shown in FIG. 16, the radial tilt of the optical disc 20 and the offset amount of the focus error signal FE are in a proportional relationship.

  As described above, from FIG. 6, the voltage V1 and the inclination of the optical disk 20 in the radial direction are in a proportional relationship. Therefore, it is derived from FIGS. 16 and 6 that the voltage V1 and the offset amount are in a proportional relationship.

  As a result, as in the first embodiment, if the focus offset amount is determined according to the voltage V1, even if the radial tilt of the optical disc 20 changes, the offset amount according to the change can be determined. In the second embodiment, since the offset amount is determined using such a relationship, the offset amount for minimizing the jitter amount can be determined regardless of the inclination of the optical disc 20 in the radial direction.

  FIG. 17 is a diagram for explaining the relationship between the offset amount and the jitter amount when the radial tilt of the optical disc 20 is fixed at a certain size.

  Referring to FIG. 17, curves A1 and C1 indicate changes in the jitter amount with respect to changes in the offset amount when the radial inclination of the optical disc 20 is rs_min and rs_max, respectively. A curve B1 shows a change in the jitter amount with respect to a change in the offset amount when the radial inclination of the optical disc 20 is zero.

  Each of the curves A1 to C1 indicates that there is an offset amount for minimizing the jitter amount. In the curves A1 and C1, the offset amounts for minimizing the jitter amount are Feofst_min and Feofst_max, respectively.

  FIG. 18 is a diagram for explaining processing in which the offset amount specifying circuit 71 in FIG. 1 specifies the offset amount.

  18 and 14, the offset amount specifying circuit 71 receives the jitter amount of the reproduction signal from the jitter amount measuring circuit 43 by sequentially changing the offset amount (FE offset) as Fe1, Fe2, Fe3, Fe4, and Fe5. .

  18 and 9, also in the second embodiment, the period during which offset amount specifying circuit 71 outputs each of offset amounts Fe1 to Fe5 is equal to disk rotation period T. Further, the offset amount specifying circuit 71 determines the timing for outputting the offset amounts Fe1 to Fe5 so that the voltage V1 becomes Vfo_max and Vfo_min within the period in which each offset amount is output.

  In the curve indicating the jitter waveform, a circular symbol and a triangular symbol indicate the amount of jitter when the voltage V1 reaches Vfo_max and Vfo_min, respectively. Similarly to the change in the jitter amount shown in FIG. 9, when the voltage V1 is Vfo_max, the jitter amount becomes the smallest when the offset amount is Fe2 (time t1). On the other hand, when the voltage V1 is Vfo_min, the jitter amount becomes the smallest when the offset amount is Fe4 (time t2). Thereby, the offset amount specifying circuit 71 specifies the offset amounts Feofst_max and Feofst_min as Fe2 and Fe4, respectively.

  FIG. 19 is a flowchart for explaining the processing flow of the offset amount specifying circuit 71 of FIG. Note that the processing shown in FIG. 19 is processing at the time of reproducing an optical disc.

  Referring to FIG. 19 and FIG. 10, the processing of the second embodiment is that the processing of step S5 is not executed, and the processing of steps S6A and S7A is executed instead of the processing of steps S6 and S7. This is different from the first process. The process of steps S1 to S4 shown in FIG. 19 is the same as the process of steps S1 to S4 shown in FIG. Therefore, below, the process of step S6, 7A is demonstrated.

  Referring to FIGS. 19 and 14, when the magnitude of vibration of the optical disk detected by detection circuit 76 is larger than a predetermined value (YES in step S4), in step S6A, offset amount specifying circuit 71 has voltage V1 at Vfo_max. In each case, and in each case where the voltage V1 is Vfo_min, the focus offset amount that minimizes the jitter amount (specifies the offset amounts Feofst_max and Feofst_min). In step S <b> 7 </ b> A, the offset amount specifying circuit 71 stores the offset amounts Feofst_max and Feofst_min in the memory 75. When the process of step S7A ends, the entire process ends.

  FIG. 20 is a flowchart for explaining the processing of the offset amount supply circuit 73 in FIG.

  Referring to FIGS. 20 and 11, the process of the second embodiment is different from the process of the first embodiment in that the processes of steps S12A, S13A, and S14A are executed instead of the processes of steps S12 to S14.

  When the processing is started with reference to FIGS. 20 and 14, the offset amount supply circuit 73 acquires the voltage V <b> 1 from the focus servo circuit 62 in step S <b> 11. Next, in step S12A, the offset amount supply circuit 73 acquires the offset amounts Feofst_max and Feofst_min from the memory 75.

  Subsequently, in step S13A, the offset amount supply circuit 73 determines the offset amount Feofst by linear interpolation. Specifically, the offset amount supply circuit 73 calculates the offset amount Feofst by substituting the value of the voltage V1 acquired from the focus servo circuit 62 into the function shown in the following equation (2).

Feofst = (Feofst_max−Feofst_min) / (Vfo_max−Vfo_min) × (V1−Vfo_min) + Feofst_min (2)
In step S14A, the offset amount supply circuit 73 supplies the offset amount Feofst to the focus servo circuit 62. When the process of step S14A ends, the entire process returns to step S11.

  The process shown in FIG. 20 may be performed before reproduction, or may be performed prior to the process shown in FIG. 19 during reproduction. However, by executing the processing of FIG. 20 and the processing of FIG. 19 at the time of reproduction, it is possible to obtain an effect that it can be executed even if the memory capacity is small.

FIG. 21 is a diagram for explaining the operation according to the comparative example of the second embodiment.
Referring to FIG. 21, in the case of the operation according to the comparative example, the value of the focus error offset amount is constant regardless of the change in voltage V1. In this case, as shown in FIG. 17, the offset amount Feofst_min when the jitter amount is minimized in the curve A1 is different from the offset amount when the jitter amount is minimized in the curves B1 and C1. That is, as shown in FIG. 21, when the value of the focus error offset amount is fixed regardless of the change in the voltage V1, the quality of the reproduction signal may be reduced due to an increase in the jitter amount.

FIG. 22 is a diagram for explaining the operation of the optical disk device according to the second embodiment.
Referring to FIG. 22, offset amount Feofst changes in synchronization with voltage V1. Thereby, the optimum offset amount Feofst can be generated with respect to the inclination of the optical disk in the radial direction. This makes it possible to set the focus offset amount so that the jitter amount is always minimized during reproduction of the optical disc.

  As described above, according to the second embodiment, the offset amount specifying circuit 71 performs jitter at the offset amount Feofst_max that minimizes the jitter amount at the maximum value (Vfo_max) of the voltage V1 and at the minimum value (Vfo_min) of the voltage V1. An offset amount Feofst_min that minimizes the amount is specified. Based on these values, the offset amount supply circuit 73 determines the offset amount Feofst and gives the offset amount Feofst to the focus servo circuit 62. As a result, the focus servo circuit 62 can always perform the focus control so that the amount of jitter of the reproduction signal is minimized, so that the reliability of the operation of the optical disc apparatus can be improved.

  In the above description, the offset amount for minimizing the jitter amount at the maximum value and the minimum value of the voltage V1 is specified. However, the value of the voltage V1 for specifying the offset amount is not limited to the maximum value and the minimum value, and may be two different values.

  In the first and second embodiments, an offset amount for minimizing the jitter amount is determined for one of tracking control and focus control. However, in the present invention, it is also possible to obtain both the tracking error signal offset amount and the focus error signal offset amount. In this case, the optical disk apparatus calculates the offset amount in the order of the offset amount of the tracking error signal and the offset amount of the focus error signal, for example.

  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.

1 is a schematic configuration diagram of an optical disc apparatus 100 according to Embodiment 1. FIG. FIG. 2 is a diagram showing a state in which the optical disc 20 of FIG. It is a figure which shows the state which the curvature has produced in the outer peripheral part of the optical disk 20 of FIG. It is a figure explaining the light spot formed in the light-receiving surface of the photodetector 14, when the optical disk 20 shown in FIG. 2 is irradiated with the laser beam LA. It is a figure explaining the fluctuation | variation of the voltage V1 at the time of rotation of the optical disk 20 of FIG. FIG. 6 is a diagram for explaining a relationship between a voltage V1 and a radial gradient (rad skew) of the optical disc 20; FIG. 7 is a diagram for explaining the relationship between the radial tilt of the optical disc 20 and the offset amount of the tracking error signal TE that can minimize the jitter amount. FIG. 10 is a diagram for explaining the relationship between the offset amount and the jitter amount when the magnitude of the inclination in the radial direction of the optical disc 20 is a fixed value. It is a figure for demonstrating the process which the offset amount specific circuit 71 of FIG. 1 specifies offset amount. 7 is a flowchart for explaining processing of an offset amount specifying circuit 71 in FIG. 1. It is a flowchart explaining the process of the offset amount supply circuit 73 of FIG. 6 is a diagram for explaining an operation according to a comparative example of the first embodiment. FIG. FIG. 6 is a diagram for explaining the operation of the optical disc device according to the first embodiment. 5 is a schematic configuration diagram of an optical disc device 100A according to Embodiment 2. FIG. It is a figure explaining the detection method of a general focus error. FIG. 10 is a diagram for explaining the relationship between the radial tilt of the optical disc 20 and the offset amount of the focus error signal FE that can minimize the jitter amount. FIG. 10 is a diagram for explaining a relationship between an offset amount and a jitter amount when the optical disc 20 is fixed at a certain radial inclination. It is a figure for demonstrating the process which the offset amount specific circuit 71 of FIG. 1 specifies offset amount. It is a flowchart explaining the flow of a process of the offset amount specific circuit 71 of FIG. It is a flowchart explaining the process of the offset amount supply circuit 73 of FIG. FIG. 10 is a diagram for explaining an operation according to a comparative example of the second embodiment. FIG. 10 is a diagram for explaining the operation of the optical disc device according to the second embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Motor, 2 Disk drive controller, 3 Head access control part, 4 Signal processing part, 10 Pickup apparatus, 11 Objective lens, 12 Objective lens drive device, 13 Semiconductor laser, 14 Photodetector, 14A, 14B area | region, 20 Optical disk, 30 reproduction circuit, 40 error detection circuit, 41 tracking error detection circuit, 42 focus error detection circuit, 43 jitter amount measurement circuit, 50 guide, 61 tracking servo circuit, 62 focus servo circuit, 70 offset output circuit, 71 offset amount specifying circuit 73, offset amount supply circuit, 75 memory, 76 detection circuit, 100, 100A optical disk device, LA laser light, LB, LB1, LB3, LB4 reflected light, R1, R2 direction, SP light spot.

Claims (8)

A light source for irradiating a laser beam onto the signal recording surface of the optical disc;
An objective lens for condensing the laser beam;
An objective lens driving device that receives the first and second control voltages and moves the objective lens in the optical axis direction of the laser light and in the direction perpendicular to the optical axis direction of the laser light;
A focus error signal and a tracking error signal are output based on the reflected light generated by reflecting the laser beam on the signal recording surface, and information recorded on the signal recording surface based on the reflected light is output. A signal processing unit that generates a reproduction signal including, detects and outputs a jitter amount included in the reproduction signal;
A focus control circuit that changes the first control voltage based on the focus error signal;
A tracking control circuit that changes the second control voltage based on the tracking error signal and an offset amount;
A detection circuit for detecting that the optical disk is tilted in a radial direction of the optical disk based on a change in the first control voltage;
When the detection result of the detection circuit is received, the offset amount is changed based on the first control voltage and the jitter amount, and the jitter amount is minimized at the maximum value of the first control voltage. An offset amount specifying circuit that specifies a first offset amount and a second offset amount that minimizes the jitter amount at the minimum value of the first control voltage;
A function for associating the first control voltage with the offset amount is determined based on the first and second offset amounts, and the value of the first control voltage acquired from the focus control circuit is substituted into the function. An offset amount supply circuit that calculates the offset amount and supplies the calculated offset amount to the tracking control circuit. A light source for irradiating a laser beam onto the signal recording surface of the optical disc;
An objective lens for condensing the laser beam;
An objective lens driving device that receives a control voltage and moves the objective lens in the optical axis direction of the laser beam;
A focus error signal is output based on the reflected light generated by the reflection of the laser beam on the signal recording surface, and a reproduction signal including information recorded on the signal recording surface is generated based on the reflected light. A signal processing unit that detects and outputs a jitter amount included in the reproduction signal;
A focus control circuit that changes the control voltage based on the focus error signal and an offset amount;
A detection circuit for detecting that the optical disc is tilted in a radial direction of the optical disc based on a change in the control voltage;
When the detection result of the detection circuit is received, the offset amount is changed based on the control voltage and the jitter amount, and the first offset amount that minimizes the jitter amount at the maximum value of the control voltage And an offset amount specifying circuit that specifies a second offset amount that minimizes the jitter amount at the minimum value of the control voltage;
An offset to be given to the focus control circuit as the offset amount based on the control voltage from the focus control circuit, the maximum and minimum values of the control voltage, and the first and second offset amounts. An optical disc device comprising a quantity supply circuit. A light source for irradiating a laser beam onto the signal recording surface of the optical disc;
An objective lens for condensing the laser beam;
An objective lens driving device that receives the first and second control voltages and moves the objective lens in the optical axis direction of the laser light and in the direction perpendicular to the optical axis direction of the laser light;
A signal processing unit that outputs a focus error signal and a tracking error signal based on reflected light generated by reflecting the laser beam on the signal recording surface;
A focus control circuit that changes the first control voltage based on the focus error signal;
The presence or absence of tilt of the optical disc is determined based on the first control voltage, and if the optical disc is detected to be tilted, the tracking error signal associated with the tilt of the optical disc is detected based on the first control voltage. An offset output circuit that calculates an offset amount and outputs the calculated offset amount;
An optical disc apparatus comprising: a tracking control circuit that changes the second control voltage based on the tracking error signal and the offset amount. The signal processing unit generates a reproduction signal including information recorded on the signal recording surface based on the reflected light, detects and outputs a jitter amount included in the reproduction signal,
The offset output circuit is
The offset amount is changed based on the first control voltage and the jitter amount, and the jitter amount is minimized at predetermined first and second voltage values of the first control voltage. An offset amount specifying circuit for specifying the first and second offset amounts;
A function for associating the first control voltage with the offset amount is determined based on the first and second offset amounts, and the value of the first control voltage acquired from the focus control circuit is substituted into the function. The optical disk apparatus according to claim 3, further comprising an offset amount calculation circuit that calculates the offset amount.   The optical disc apparatus according to claim 4, wherein the predetermined first and second voltage values are a maximum value and a minimum value of the first control voltage, respectively. A light source for irradiating a laser beam onto the signal recording surface of the optical disc;
An objective lens for condensing the laser beam;
An objective lens driving device that receives a control voltage and moves the objective lens in the optical axis direction of the laser beam;
A signal processing unit that outputs a focus error signal based on reflected light generated by reflecting the laser beam on the signal recording surface;
The presence or absence of tilt of the optical disc is determined based on the control voltage, and when the optical disc is detected to be tilted, the offset amount of the focus error signal accompanying the tilt of the optical disc is calculated based on the control voltage. An offset output circuit for outputting the calculated offset amount;
An optical disc apparatus comprising: a focus control circuit that changes the control voltage based on the focus error signal and an offset amount. The signal processing unit generates a reproduction signal including information recorded on the signal recording surface based on the reflected light, detects and outputs a jitter amount included in the reproduction signal,
The offset output circuit is
First and second offsets that minimize the jitter amount at predetermined first and second voltage values of the control voltage by changing the offset amount based on the control voltage and the jitter amount, respectively. An offset amount specifying circuit for specifying the amount;
A function for associating the first control voltage with the offset amount is determined based on the first and second offset amounts, and the value of the first control voltage acquired from the focus control circuit is substituted into the function. And an offset amount calculation circuit for calculating the offset amount.   8. The optical disc apparatus according to claim 7, wherein the predetermined first and second voltage values are a maximum value and a minimum value of the first control voltage, respectively.

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