JP2007018650A - Optical disk drive and method for controlling optical disk drive - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To allow a light spot exactly follow the track center of an optical disk by eliminating the offset generated in a tracking error signal due to focus offset adjustment. <P>SOLUTION: The optical disk inspection apparatus displaces an objective lens 25 in the optical axis direction of a laser beam while stopping tracking servo control and detects a tracking offset correction coefficient as a tracking deviation relation from an amount of change in the tracking error signal with respect to the amount of deviation of the light spot from the recording surface in the optical disk DK. An amount of correction is calculated by multiplying the amount-of-deviation detection signal indicating the amount of deviation of the light spot from the recording surface of the optical disk DK by a coefficient of tracking offset correction and the tracking servo of the objective lens 50 is controlled by superposing the calculated amount of the tracking correction on the tracking servo signal. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical disc apparatus for recording a signal on an optical disc such as a CD and a DVD, or reproducing a signal recorded on the optical disc, and a control method for the optical disc apparatus.

  2. Description of the Related Art Conventionally, in an optical disc apparatus that records a signal on an optical disc such as a CD or a DVD or reproduces a signal recorded on the optical disc, an objective lens is recorded on the optical disc when the signal is recorded on the optical disc or the signal is reproduced from the optical disc. A light spot is formed on the track of the optical disc by irradiating the laser beam through the optical disc. In this case, tracking servo control of the objective lens is performed to accurately follow the light spot with the track, and focus servo control of the objective lens is performed to accurately position the light spot on the recording surface of the optical disc.

  Among these, in tracking servo control, a DPD (Differential Phase Detection) method may be used as a method of detecting the amount of deviation of the light spot from the track center. In the DPD method, reflected light from an optical disk is collected on a four-divided photodetector, and the phase difference of two signals obtained from the diagonal sum of the four light-receiving elements of the four-divided photodetector is shifted from the track center of the light spot. It is detected as a quantity. In this case, a perfectly circular light spot is always formed on the four-divided photodetector by focus servo control. In tracking servo control, the phase difference of the diagonal sum of the light spots formed in the perfect circle shape is calculated. The position of the objective lens (the radial position of the optical disk) is controlled so as to be “0”.

  In this tracking servo control, due to variations in the depth of the recording pits formed on the optical disc, the objectivity of the light spot formed on the quadrant photodetector with respect to the optical axis collapses, thereby causing the light spot from the track center. A tracking offset occurs in a signal representing the amount of deviation, that is, a tracking error signal. For this reason, tracking offset adjustment is performed in which the phase difference between two signals obtained from the diagonal sum of the four light receiving elements of the four-divided photodetector is adjusted to remove the tracking offset from the tracking error signal.

  On the other hand, in the focus servo control, an astigmatism method may be used as a method for detecting the amount of deviation of the light spot from the recording surface of the optical disk. In the astigmatism method, the reflected light from the optical disc is condensed on a quadrant photodetector through a cylindrical lens, and the intensity difference between the two signals obtained from the diagonal sum of the four light receiving elements of the quadrant photodetector is converted into light. This is detected as the amount of deviation of the spot from the recording surface of the optical disk. In this case, a light spot having a perfect circle shape or an ellipse shape is formed on the quadrant photodetector in accordance with the amount of deviation of the light spot from the recording surface of the optical disk. Therefore, in the focus servo control, the intensity difference between the two signals obtained from the diagonal sum of the four light receiving elements of the four-divided photodetector is “0”, that is, the shape of the light spot formed on the four-divided photodetector is The position of the objective lens (the position in the optical axis direction of the laser beam) is controlled so as to have a perfect circular shape.

In this focus servo control, the position of the objective lens where the shape of the light spot formed on the quadrant photodetector is a perfect circle and the position of the objective lens where the evaluation value of the signal reproduced from the optical disk is the best Since it is slightly different, the signal representing the amount of deviation of the light spot from the recording surface of the optical disk, that is, the evaluation value of the signal reproduced from the optical disk by superimposing a predetermined focus offset on the focus error signal, specifically, the jitter is the best Focus offset adjustment is performed so that the objective lens is positioned at a position where In this case, as shown in Patent Document 1 below, after performing the focus offset adjustment, the tracking offset adjustment is performed, and the objective lens is placed at the position where the jitter of the signal reproduced from the optical disc is best. Tracking offset adjustment is performed in the positioned state.
JP 2000-76668 A

  However, when this focus offset adjustment is performed, the shape of the light spot formed on the quadrant photodetector is deformed from a perfect circle shape to a slightly elliptical shape. For this reason, an offset caused by focus offset adjustment different from the tracking offset occurs in the tracking error signal, and the optical spot follows in a state of being slightly shifted from the track center of the optical disc. As a result, there is a problem that the accuracy of recording a signal on the optical disc or reproducing the signal recorded on the optical disc deteriorates. In particular, in a narrow track pitch optical disc such as a DVD and a Blu-ray Disc, a more severe optical spot tracking accuracy is required, and this deterioration of signal recording and reproduction accuracy is a serious problem. is there.

  The present invention has been made to cope with the above-described problem, and an object of the present invention is to remove the offset generated in the tracking error signal due to the focus offset adjustment and cause the optical spot to accurately follow the track center of the optical disc. It is an object of the present invention to provide an optical disc apparatus and a control method for the optical disc apparatus that can improve the recording and reproduction accuracy of signals.

  In order to achieve the above object, the present invention is characterized by a laser light source that emits laser light toward an optical disc, an objective lens that collects the emitted laser light to form a light spot on the optical disc, and is reflected by the optical disc. A photodetector that receives the received laser light and outputs a received light signal, a tracking actuator that displaces the objective lens in the radial direction of the optical disk, and an optical pickup that has a focus actuator that displaces the objective lens in the optical axis direction of the emitted laser light; Based on the received light signal output from the photodetector, a tracking error signal generation circuit that generates a tracking error signal indicating the amount of deviation of the light spot from the track center, and a tracking servo signal based on the tracking error signal is output to the tracking actuator The tracking servo control circuit that feedback-controls the tracking actuator so that the light spot follows the track of the optical disk, and the focus that represents the amount of deviation of the light spot from the recording surface on the optical disk based on the light reception signal output from the photodetector A focus error signal generation circuit that generates an error signal, and a focus servo control circuit that outputs a focus servo signal based on the focus error signal to the focus actuator and feedback-controls the focus actuator so that the light spot follows the recording surface of the optical disk Focus correction amount for positioning the objective lens at the position where the evaluation value for evaluating the received light signal output from the photodetector is the best A focus correction signal for correcting a focus error signal or a focus servo signal with a focus correction signal, and a tracking correction signal for correcting a tracking error signal or a tracking servo signal with a tracking correction signal representing an amount of change in a tracking error signal caused by the focus correction device. And a correction means.

  In this case, the focus correction means controls the focus actuator to displace the objective lens in the direction of the optical axis of the laser beam, so that the objective value is evaluated at the position where the evaluation value for evaluating the received light signal output from the photodetector is the best. Focus correction amount detecting means for detecting a focus correction amount for positioning the lens, and focus correction for superimposing a focus correction signal representing the focus correction amount detected by the focus correction amount detecting means on the focus error signal or the focus servo signal It is good to comprise with quantity superimposition means. Alternatively, the focus correction means stores in advance a focus correction amount for positioning the objective lens at a position where the evaluation value for evaluating the light reception signal output from the photodetector is the best. You may comprise a memory | storage means and the focus correction amount superimposing means which superimposes the focus correction signal showing the focus correction amount memorize | stored in the focus correction amount memory | storage means on a focus error signal or a focus servo signal.

  The tracking correction means controls the focus actuator in a state where the tracking servo control by the tracking servo control circuit is stopped to displace the objective lens in the optical axis direction of the laser beam, so that the recording surface of the optical spot on the optical disc A relationship detection means for detecting the relationship between the amount of change in the tracking error signal generated by the tracking error signal generation circuit and the amount representing the deviation from the tracking error, and the amount representing the deviation of the light spot from the recording surface of the optical disc , And a tracking correction amount for canceling the amount of change in the tracking error signal caused by the focus correction means is calculated based on the input amount representing the deviation and the tracking deviation relationship detected by the relation detection means. Tracking correction amount calculation means It may be configured by the tracking correction amount superimposing means for superimposing a tracking correction signal representative of the tracking correction amount calculated by the tracking correction amount calculating means to the tracking error signal or a tracking servo signal. In this case, the relationship detecting means controls the focus actuator to displace the objective lens in the optical axis direction, and a tracking offset for calculating a change amount of the tracking error signal with respect to the displacement amount of the objective lens. Coefficient correction means for calculating a correction coefficient, and the tracking correction amount calculation means sets the tracking offset correction coefficient calculated by the coefficient calculation means to an amount representing the deviation of the input light spot from the recording surface of the optical disk. It is preferable to calculate the tracking correction amount by multiplication. In these cases, the tracking correction amount calculation means may calculate the tracking correction amount by inputting a focus correction signal instead of the amount representing the deviation of the light spot from the recording surface of the optical disk.

  According to the feature of the present invention configured as described above, an evaluation value for evaluating the received light signal output from the photodetector by correcting the focus error signal or the focus servo signal with the focus correction signal by the focus correction unit, for example, the same value. The objective lens is positioned at a position where the jitter of the received light signal is the best, and the tracking correction signal changes due to the correction by the focus correction signal by the tracking correction means. For this reason, even if the light spot is deviated from the recording surface of the optical disk by correcting the focus error signal or the focus servo signal by the focus correction signal, the light spot is always maintained by the tracking correction amount corresponding to the deviation amount. Follow the center of the track. As a result, the offset generated in the tracking error signal due to the focus offset adjustment can be removed, and the optical spot can be made to accurately follow the track center of the optical disk to improve the recording and reproduction accuracy of the signal with respect to the optical disk.

  Another feature of the present invention is that the tracking correction means in the optical disc apparatus according to the present invention stores a tracking correction amount storage means for preliminarily storing a tracking correction amount for canceling a change amount of the tracking error signal caused by the focus correction means. And a tracking correction amount superimposing means for superimposing a tracking correction signal representing the tracking correction amount stored in the tracking correction amount storage means on the tracking error signal or the tracking servo signal.

  According to another feature of the present invention configured as described above, if the tracking correction amount is known, for example, the tracking correction amount calculated by the relation detecting unit and the tracking correction amount detecting unit is used as the tracking correction amount storing unit. , The tracking error signal or the tracking servo signal can be corrected by the tracking correction amount superimposing means. As a result, the same effect as described above can be expected even in an optical disc apparatus that does not have a configuration for calculating the tracking correction amount, such as the relationship detection unit and the tracking correction amount detection unit.

  Another feature of the present invention is that the tracking correction means in the optical disc apparatus according to the present invention is characterized in that the relationship between the amount of change of the tracking error signal and the amount representing the deviation of the light spot from the recording surface of the optical disc is a tracking deviation relationship. The relation storage means to be stored in advance and the amount representing the deviation of the light spot from the recording surface of the optical disk are input, and the tracking correction amount for canceling the change amount of the tracking error signal caused by the focus correction means is the input deviation. Tracking correction amount calculation means for calculating based on the amount representing the tracking deviation relationship stored in the relationship storage means, and a tracking correction signal representing the tracking correction amount calculated by the tracking correction amount calculation means as the tracking error Signal or tracking It lies in the structure by the tracking correction amount superimposed superimposed on turbo signal.

  In this case, the relation storage unit stores a tracking offset correction coefficient for calculating a change amount of the tracking error signal with respect to an amount representing a deviation of the light spot from the recording surface of the optical disc, and the tracking correction amount calculation unit includes: The tracking correction amount may be calculated by multiplying the amount representing the deviation of the input light spot from the recording surface of the optical disk by the tracking offset correction coefficient stored in the relation storage means. In these cases, the tracking correction amount calculation means may calculate the tracking correction amount by inputting a focus correction signal instead of the amount representing the deviation of the light spot from the recording surface of the optical disk.

  According to another feature of the present invention configured as described above, if the tracking deviation relation is known, for example, the tracking deviation relation detected by the relation detecting means may be stored in the relation storage means in advance. The tracking correction amount is calculated by the tracking correction amount calculating means using the tracking deviation relationship, and the tracking error signal or the tracking servo signal can be corrected by the tracking correction amount superimposing means. As a result, the same effect as described above can be expected even in an optical disc apparatus that does not have a configuration for detecting a tracking deviation relationship such as the relationship detecting means described above.

  The present invention can be implemented not only as an apparatus invention but also as a method invention.

  Hereinafter, an embodiment of an optical disk device according to the present invention will be described with reference to the drawings. FIG. 1 is an overall schematic diagram of an optical disc inspection apparatus for inspecting an optical disc DK such as a CD or a DVD. This optical disk inspection apparatus includes a rotation drive device 10 that rotates and drives an optical disk DK, and an optical pickup 20 that irradiates the optical disk DK with laser light and receives reflected light from the optical disk DK.

  The rotational drive device 10 includes a spindle motor 11 for rotationally driving the optical disk DK and a feed motor 12 for moving the optical disk DK in the radial direction. A turntable 13 is fixed to a rotating shaft 11b of the spindle motor 11, and an optical disk DK is detachably assembled on the turntable 13.

The spindle motor 11 incorporates an encoder 11a that detects the rotation of the spindle motor 11, that is, the rotation of the turntable 13 (optical disk DK) and outputs a rotation detection signal indicating the rotation. This rotation detection signal repeats a high level and a low level by a predetermined minute rotation angle and a z-phase signal φ _Z generated every time the rotation position of the turntable 13 (optical disc DK) reaches one reference rotation position. It consists of a pulse train signal and an A phase signal φ _A and a B phase signal φ _B that are shifted in phase by π / 2. These rotation detection signals φ _Z , φ _A , and φ _B are output to the spindle motor control circuit 14, and are used by the spindle motor control circuit 14 to detect the rotation speed of the spindle motor 11, that is, the optical disc DK.

  The rotation of the spindle motor 11 is controlled by a spindle motor control circuit 14. The spindle motor control circuit 14 uses the rotation detection signal output from the encoder 11a and the wobble signal output from the wobble signal extraction circuit 53 described later, so that the light spot on the optical disk DK is always kept on the optical disk DK at a constant linear velocity. The rotational speed of the spindle motor 11 is controlled so as to move with respect to it. Specifically, when tracking servo control of the objective lens 25 described later is not performed, the rotation speed of the optical disk DK is detected using a rotation detection signal output from the encoder 11a, and the controller 70 described later detects the radius of the light spot. The rotation speed of the spindle motor 11 is servo-controlled so that the rotation speed is calculated and instructed based on the position. When tracking servo control of the objective lens 25 is performed, the rotational speed of the spindle motor 11 is servo-controlled so that the wobble signal output from the wobble signal extraction circuit 53 has a standardized frequency. Thereby, the linear velocity with respect to the optical pickup 20 of the optical disk DK at the position where the light spot is formed is kept constant.

  The feed motor 12 is connected via a screw rod 15 to a support member 16 that fixedly supports the spindle motor 11 and is allowed only to move in the radial direction of the optical disk DK. The screw rod 15 is connected to one end of the screw rod 15 so as to rotate integrally with the rotation shaft of the feed motor 12, and is screwed to a nut (not shown) fixed to the support member 16 at the other end. Therefore, when the feed motor 12 rotates, the spindle motor 11, the turntable 13, and the support member 16 are displaced in the radial direction of the optical disc DK by the screw feed mechanism including the screw rod 15 and the nut.

Also incorporated in the feed motor 12 is an encoder 12a that detects the rotation of the feed motor 12 and outputs rotation detection signals φ _Z , φ _A , and φ _B similar to those of the encoder 11a. The rotation detection signals φ _Z , φ _A and φ _B from the encoder 12 a are output to the feed motor control circuit 17. The feed motor control circuit 17 controls the rotation of the feed motor 12 using a position detection signal output from an objective lens position detector 33 described later in addition to the rotation detection signals φ _Z , φ _A , and φ _B. The displacement of the spindle motor 11, the turntable 13, and the support member 16 in the radial direction of the optical disk DK is controlled. Specifically, a signal representing the radial position on the optical disc DK of the light spot designated by the input device 71 is input from the controller 70, and the rotation detection signals φ _Z , φ _A , and φ _B from the encoder 12a are used. Then, the light spot is moved to the designated radial position, and the position detection signal output from the objective lens position detector 33 is used to control the light spot to follow the track of the optical disc DK. .

  The optical pickup 20 includes a laser light source 21, a collimating lens 22, a polarizing beam splitter 23, a ¼ wavelength plate 24, an objective lens 25, a convex lens 26, a cylindrical lens 27, and a photodetector 28. In this optical pickup 20, the laser light from the laser light source 21 is condensed on the optical disk DK via the collimating lens 22, the polarization beam splitter 23, the quarter wavelength plate 24 and the objective lens 25, and is collected on the optical disk DK. A light spot is formed. The reflected light from the light spot formed on the optical disk DK is guided to the photodetector 28 through the objective lens 25, the quarter wavelength plate 24, the polarization beam splitter 23, the convex lens 26, and the cylindrical lens 27, and received. Is done. The photodetector 28 is composed of four divided light receiving elements composed of four light receiving elements having the same square shape divided by dividing lines, and each light receiving element receives detection signals A, B, C, and D proportional to the amount of received light. Output as a received light signal. The detection signals A, B, C, and D represent the amount of light received by each light receiving element arranged clockwise from the upper left.

  The optical pickup 20 also includes a focus actuator 31, a tracking actuator 32, and an objective lens position detector 33. The focus actuator 31 drives the objective lens 25 in the optical axis direction of the laser light (perpendicular to the disk surface of the optical disc DK) to finely move the light spot in the optical axis direction. The tracking actuator 32 drives the objective lens 25 in the radial direction of the optical disc DK to finely move the light spot in the radial direction of the optical disc DK. The objective lens position detector 33 detects a displacement amount from the reference position (neutral position) of the objective lens 25 in the radial direction of the optical disk DK, and outputs a position detection signal representing the displacement amount to the feed motor control circuit 17. A laser driving circuit 41 is connected to the laser light source 21 of the optical pickup 20 in order to control the operation of the laser light source 21.

  An HF signal amplifier circuit 42 is connected to the photodetector 28. The HF signal amplifying circuit 42 amplifies the detection signals A to D output from the photodetector 28, and supplies them to the focus error signal generation circuit 43, tracking error signal generation circuit 47, deviation amount detection circuit 54 and reproduction signal generation circuit 56. Output each.

  The focus error signal generation circuit 43 uses the detection signals A to D from the photodetector 28 via the HF signal amplification circuit 42 (specifically, (A + C) − (B + D) calculation by the astigmatism method). Thus, a focus error signal is generated and output to the focus servo circuit 44. In this case, the focus error signal (A + C) − (B + D) represents the amount of deviation of the light spot from the recording surface of the optical disk DK. The focus servo circuit 44 is controlled by the controller 70, generates a focus servo signal based on the focus error signal, and outputs the focus servo signal to the adder 45. The adder 45 superimposes a first focus offset signal, a second focus offset signal, or a third focus offset signal output from a focus offset signal generation circuit 62, which will be described later, on the focus servo signal and outputs the superimposed signal to the drive circuit 46. The drive circuit 46 drives and controls the focus actuator 31 in accordance with the focus servo signal on which the first focus offset signal, the second focus offset signal, or the third focus offset signal is superimposed, thereby moving the objective lens 25 in the optical axis direction. Displace the focus servo control.

  As shown in FIG. 2, the tracking error signal generation circuit 47 includes phase adjusters 47a and 47b, addition circuits 47c and 47d, binarization circuits 47e and 47f, a phase comparator 47g, and an integration circuit 47h. A tracking error signal is generated by calculation using the detection signals A to D from the photodetector 28 via the HF signal amplification circuit 42 (specifically, calculation of (A + C) − (B + D) by the DPD method), Output to the offset cancel circuit 48. Specifically, the detection signals A and D output from the phase adjusters 47a and 47b and the detection signals C and B are added by the addition circuits 47c and 47d, respectively, and (A + C) and (B + D). Calculate The calculated (A + C) and (B + D) are binarized by the binarization circuits 47e and 47f, respectively, and then the phase difference between (A + C) and (B + D) is calculated by the phase comparator 47g, that is, (A + C) − (B + D) is calculated, and the calculated value (A + C) − (B + D) is low-pass processed by the integrating circuit 47h and output as a tracking error signal. That is, this tracking error signal (A + C)-(B + D) represents the amount of deviation of the light spot from the track center.

  As shown in FIG. 2, the offset cancel circuit 48 includes a buffer amplifier 48a, a gain adjuster 48b, and an adder circuit 48c. The offset cancel circuit 48 superimposes the tracking correction amount on the tracking error signal and outputs the tracking correction signal to the tracking servo circuit 49. Specifically, the tracking correction amount output from the gain adjuster 48b is added to the tracking error signal output via the buffer amplifier 48a by the adding circuit 48c, and then output. In this case, the tracking offset correction coefficient is output from the controller 70 to the gain adjuster 48b, and the gain adjuster 48b multiplies the shift amount detection signal output from the shift amount detection circuit 54 by the tracking offset correction coefficient. The tracking correction amount is output to the adding circuit 48c.

  The tracking servo circuit 49 is controlled by the controller 70, generates a tracking servo signal based on the tracking error signal, and outputs the tracking servo signal to the drive circuit 51. The drive circuit 51 drives and controls the tracking actuator 32 according to the tracking servo signal, and performs tracking servo control by displacing the objective lens 25 in the radial direction of the optical disk DK.

  The tracking error signal output from the tracking error signal generation circuit 47 is also output to the tracking deviation amount calculation circuit 52 and the wobble signal extraction circuit 53. The tracking deviation amount calculation circuit 52 samples the tracking error signal at a predetermined sampling period, and outputs an average value of the sampled values to the controller 70 as a tracking deviation amount. The predetermined sampling period is a period that equally divides one rotation of the optical disk DK into a plurality of parts, and is 500 equals in this embodiment. In this case, instead of the average value of the sampled values, the median value of the sampled values may be used. The wobble signal extraction circuit 53 is composed of a bandpass filter, and is controlled by the controller 70 to extract the wobble signal from the tracking error signal and output it to the spindle motor control circuit 14. As described above, this wobble signal is used in the spindle motor control circuit 14 to rotate the optical disk DK at a constant linear velocity.

  As shown in FIG. 2, the deviation amount detection circuit 54 includes a difference circuit 54 a, and uses the detection signals A and D from the photodetector 28 via the HF signal amplification circuit 42 (specifically, (D-A)), a deviation amount detection signal is generated and output to the offset cancellation circuit 48 and the focus deviation amount calculation circuit 55, respectively. This deviation amount detection signal is equivalent to the focus error signal (A + C) − (B + D), and represents the amount of deviation of the light spot from the recording surface of the optical disc DK. Therefore, the deviation amount detection signal output from the deviation amount detection circuit 54 may be generated by calculation using the detection signals B and C (specifically, calculation of (C−B)). Alternatively, it may be generated by calculation using the detection signals A to D (specifically, calculation of (A + C) − (B + D)).

  The focus shift amount calculation circuit 55 samples the shift amount detection signal at a predetermined sampling period, and outputs an average value of the sampled values to the controller 70 as a focus shift amount. Note that the predetermined sampling period in this case is also a period that divides one rotation of the optical disk DK into 500 equal parts as described above. In this case, instead of the average value of the sampled values, the median value of the sampled values may be used.

  Based on the detection signals A to D from the HF signal amplification circuit 42, the reproduction signal generation circuit 56 generates a reproduction signal (SUM signal composed of the sum signal A + B + C + D of the detection signals A to D from the photodetector 28). This reproduced signal is output to a waveform equivalent circuit 57 constituted by an equalize circuit, and its amplitude is corrected according to the frequency. The output of the waveform equivalent circuit 57 is converted into a binarized signal, that is, a digital signal by the binarizing circuit 59 and output to the jitter meter 61. The jitter meter 61 measures the jitter of the reproduction signal. The jitter measured by the jitter meter 61 is an evaluation value for evaluating the received light signal according to the present invention. Further, the reproduction signal output from the reproduction signal generation circuit 56 is also output to a waveform evaluation device 58 configured with a digital oscilloscope. The waveform evaluation device 58 evaluates the waveform of the reproduction signal, such as the symmetry of the reproduction signal and the amplitude ratio for each recording mark length. The waveform evaluation device 58 and the jitter meter 61 output an evaluation result regarding the reproduction signal to the controller 70 under the control of the controller 70. Therefore, the controller 70 inspects the optical disc DK using these evaluation results.

  The focus offset signal generation circuit 62 is controlled by the controller 70 to output the first focus offset signal, the second focus offset signal, or the third focus offset signal to the drive circuit 46 via the adder 45, and at the same time the second focus offset signal A signal is output to the controller 70. The first focus offset signal is a predetermined amount (for example, in the direction in which the objective lens 25 is brought closer to the optical disc DK (plus direction) and the direction in which the objective lens 25 is moved away from the optical disc DK (minus direction) within the range in which the objective lens 25 can be displaced in the optical axis direction. It is a signal for positioning at a position displaced by 0.3 to 0.5 μm). The second focus offset signal is a signal for continuously displacing the objective lens 25 in the plus direction and the minus direction within the range in which the objective lens 25 can be displaced in the optical axis direction. The third focus offset signal is a signal for displacing the objective lens 25 by a certain amount in the plus direction or the minus direction within the range in which the objective lens 25 can be displaced in the optical axis direction. The fixed amount represented by the third focus offset signal is a focus correction amount calculated by the controller 70 in focus offset adjustment described later.

  Therefore, when the first focus offset signal is superimposed on the focus servo signal, the objective lens 25 is positioned at a position displaced by a predetermined amount in the plus direction and the minus direction from the reference position (neutral position). When the second focus offset signal is superimposed on the focus servo signal, the objective lens 25 is continuously displaced in the plus direction and the minus direction from the reference position (neutral position). Further, when the third focus offset signal is superimposed on the focus servo signal, the objective lens 25 is positioned at a position displaced from the reference position (neutral position) by the focus correction amount in the plus or minus direction. The second focus offset signal is also output to the controller 70 and used for focus offset adjustment.

  The controller 70 is configured by a microcomputer including a CPU, ROM, RAM, hard disk, and the like, and inspects the optical disk DK by executing a program (not shown) according to instructions from the input device 71 including a keyboard and a mouse. The execution process and execution result of the inspection are appropriately displayed on the output device 72 including a CRT (or liquid crystal display), a printer, and the like. In addition, the controller 70 calculates a tracking offset correction coefficient using a tracking deviation amount output from the tracking deviation amount calculation circuit 52 and a focus deviation amount output from the focus deviation amount calculation circuit 55 by executing a program (not shown). Then, the tracking offset correction coefficient is output to the offset cancel circuit 48. A storage area for temporarily storing the tracking deviation amount and the focus deviation amount is prepared in a RAM, a hard disk or the like built in the controller 70, and this storage area is hereinafter referred to as a memory 70a.

  Further, the controller 70 executes a program (not shown) to adjust the focus offset of the objective lens 25, calculates the focus correction amount, and sets the focus correction amount in the focus offset signal generation circuit 62. This focus offset adjustment will be described later. The controller 70 includes a spindle motor control circuit 14, a feed motor control circuit 17, a laser drive circuit 41, a focus servo circuit 44, a tracking servo circuit 49, a wobble signal extraction circuit 53, a waveform evaluation device 58, a jitter meter 61, and a focus. An offset signal generation circuit 62 is connected for each operation control.

  The operation of the embodiment configured as described above will be described. The operator starts operation of various circuits of the optical disc inspection apparatus including the controller 70 by turning on a power switch (not shown). Then, the optical disc DK to be inspected is placed on the turntable 13 and the optical disc DK is fixed on the turntable 13. In this case, a signal for inspection of the optical disk DK is recorded in a part of the recording area of the optical disk DK to be inspected. Next, the operator operates the input device 71 to instruct the controller 70 to calculate the tracking offset correction coefficient. In response to this instruction, the controller 70 starts calculation of the tracking offset correction coefficient by executing a program (not shown).

  First, the controller 70 operates the spindle motor control circuit 14 to rotate the optical disk DK at the rotation speed instructed from the controller 70, and operates the feed motor control circuit 17 to move the optical disk DK to a predetermined radial position. . The predetermined radial position is a radial position of the optical disc DK that forms a light spot on the track on which the recording signal is recorded in the recording area of the optical disc DK. Next, the controller 70 starts the operation of the laser drive circuit 41 to emit laser light from the laser light source 21 toward the optical disk DK, and starts the operation of the focus servo circuit 44 to control the focus servo of the objective lens 25. To start. In this case, the controller 70 stops the operation of the tracking servo circuit 49 and does not perform the tracking servo control of the objective lens 25. In this case, the controller 70 also stops the operations of the offset cancel circuit 48, the waveform evaluation device 58, the jitter meter 61, and the focus offset signal generation circuit 62.

The laser light emitted from the laser light source 21 is reflected by the optical disk DK and received by the photodetector 28. The photodetector 28 sends detection signals A to D corresponding to the amount of received light to the focus error signal generation circuit 43, tracking error signal generation circuit 47, deviation amount detection circuit 54, and reproduction signal generation circuit 56 via the HF signal amplification circuit 42, respectively. Output.
Among these, the detection signals A to D output to the focus error signal generation circuit 43 are used for focus servo control of the objective lens 25 by the focus error signal generation circuit 43, the focus servo circuit 44, and the drive circuit 46. In this case, since the operation of the focus offset signal generation circuit 62 is stopped, the objective lens 25 performs focus servo control with a focus servo signal on which the first focus offset signal, the second focus offset signal, and the third focus offset signal are not superimposed. Then, it is controlled to a position (just focus position) where the light spot is focused on the recording surface of the optical disc DK. In this case, as shown in FIG. 3A, the light spot formed on the photodetector 28 by the reflected light from the optical disk DK is formed in a substantially circular shape. FIG. 3A shows the shape of the light spot formed on the photodetector 28 when the light spot is located on the track center. However, FIG. 3A shows the case where the light spot is off the track center. Even if it exists, the shape of the light spot formed on the photo-detector 28 becomes a substantially perfect circle shape.

  The detection signals A to D output to the tracking error signal generation circuit 47 are converted into tracking error signals and output to the offset cancellation circuit 48, the tracking deviation amount calculation circuit 52, and the wobble signal extraction circuit 53, respectively. In this case, since the operation of the offset cancel circuit 48 and the wobble signal extraction circuit 53 is stopped by the controller 70, the output of the tracking error signal is ignored. The tracking error signal output to the tracking deviation amount calculation circuit 52 is sampled at a predetermined sampling period (period in which one rotation of the optical disk DK is divided into 500 equal parts), and an average value of the sampled values is calculated. Is output to the controller 70 as a tracking deviation amount.

  The detection signals A to D output to the shift amount detection circuit 54 are converted into shift amount detection signals and output to the focus shift amount calculation circuit 55. The shift amount detection signal output to the focus shift amount calculation circuit 55 is sampled at the same sampling period as described above, and the average value of the sampled values is calculated and output to the controller 70 as the focus shift amount. . The detection signals A to D output to the reproduction signal generation circuit 56 are converted into reproduction signals and then output to the waveform evaluation device 58 and the jitter meter 61. The waveform evaluation device 58 and the jitter meter 61 are controllers. Since the operation is stopped by 70, the output of the reproduction signal is ignored.

  The controller 70 stores the tracking shift amount output from the tracking shift amount calculation circuit 52 in the memory 70 a in correspondence with the focus shift amount output from the focus shift amount calculation circuit 55. In this case, the focus shift amount is substantially “0” because none of the first focus offset signal, the second focus offset signal, and the third focus offset signal is superimposed on the focus servo signal. Therefore, the memory 70a stores the average value of the tracking error signal when the focus shift amount is “0”, that is, when the objective lens 25 is at the just focus position.

  Next, the controller 70 instructs the focus offset signal generation circuit 62 to output the first focus offset signal. In response to this instruction, the focus offset signal generation circuit 62 outputs the first focus offset signal to the adder 45. The adder 45 superimposes the first focus offset signal on the focus servo signal output from the focus servo circuit 44 and outputs it to the drive circuit 46. Thereby, the objective lens 25 is positioned at a position displaced in the plus direction by a predetermined amount from the just focus position. In this case, as shown in FIG. 3B, the light spot formed by the reflected light formed on the photodetector 28 has an elliptical shape inclined to the right side in the figure, and the photodetector 28 corresponds to the light spot formed in the same elliptical shape. Detection signals A to D are output. Note that the shape of the light spot shown in FIG. 3B is exaggerated to clarify the difference from the shape of the light spot shown in FIG.

  The tracking error signal generation circuit 47 outputs a tracking error signal corresponding to the detection signals A to D to the tracking deviation amount calculation circuit 52, and the tracking deviation amount calculation circuit 52 calculates the average value of the tracking error signal in the same manner as described above. Is calculated and output to the controller 70 as a tracking deviation amount. In this case, since tracking servo control of the objective lens 25 is stopped, the calculated tracking deviation amount changes corresponding to the change in the shape of the light spot formed on the photodetector 28. Further, the shift amount detection circuit 54 outputs a shift amount detection signal corresponding to the detection signals A to D to the focus shift amount calculation circuit 55, and the focus shift amount calculation circuit 55 sets the shift amount detection signal in the same manner as described above. The average value is calculated and output to the controller 70 as the amount of focus deviation. In this case, the amount of focus shift changes corresponding to the change in shape of the light spot formed on the photodetector 28. That is, the focus shift amount represents a position displaced by a predetermined amount in the plus direction with the just focus position of the objective lens 25 as a reference position.

  In the same manner as described above, the controller 70 stores the tracking deviation amount in the memory 70a in correspondence with the focus deviation amount. In this case, the memory 70a stores the average value of the tracking error signal at a position where the objective lens 25 is displaced in the plus direction by a predetermined amount from the just focus position. Then, the focus offset signal generation circuit 62 outputs a first focus offset signal for displacing the objective lens 25 by a predetermined amount in the minus direction following the plus direction to the adder 45. Thereby, the objective lens 25 is positioned at a position displaced in the minus direction by a predetermined amount from the just focus position. In this case, as shown in FIG. 3C, the light spot formed by the reflected light formed on the photodetector 28 has an elliptical shape inclined to the left in the figure, and the photodetector 28 is a light spot formed in the same elliptical shape. The detection signals A to D corresponding to are output. Note that the shape of the light spot shown in FIG. 3C is also exaggerated to clarify the difference from the shape of the light spot shown in FIG.

  The detection signals A to D output from the photodetector 28 at a position where the objective lens 25 is displaced in the minus direction by a predetermined amount from the just focus position are used to displace the objective lens 25 in the plus direction by a predetermined amount from the just focus position. In the same manner as in the case of the above, the tracking error signal generation circuit 54, the tracking deviation amount calculation circuit 52, the deviation amount detection circuit 54, and the focus deviation amount detection circuit 55 are processed and output to the controller 70, respectively. That is, the controller 70 stores the average value of the tracking error signal at the position where the objective lens 25 is displaced in the minus direction by a predetermined amount from the just focus position in the memory 70a. As a result, the memory 70a stores the tracking error signal corresponding to each displacement amount in the plus direction and minus direction from the just focus position of the objective lens 25, in other words, each displacement amount in the plus direction and minus direction from the just focus position. Each change amount is stored.

  Next, the controller 70 calculates a tracking offset correction coefficient using the amount of change in the tracking error signal with respect to the amount of displacement of the objective lens 25 stored in the memory 70a. The tracking offset correction coefficient is a coefficient for calculating the amount of change in the tracking error signal by multiplying the deviation amount of the objective lens 25 from the just focus position, and is the same as the three positions of the objective lens 25 in the optical axis direction. It is a proportionality constant between the average values of the tracking error signals that change corresponding to the three positions. The controller 70 sets the amount of change in the tracking error signal corresponding to two positions displaced from the just focus position of the objective lens 25, that is, positions shifted from the just focus position in the plus and minus directions, respectively. After the tracking offset correction coefficient is calculated by the least square method, the tracking offset correction coefficient is output to the offset cancel circuit 48. The offset cancel circuit 48 stores the tracking offset correction coefficient output from the controller 70. Then, the controller 70 stops the operation of various circuits in the optical disc inspection apparatus and ends the calculation of the tracking offset correction coefficient. The tracking offset correction coefficient representing the relationship between each deviation amount of the objective lens 25 from the just focus position and the change amount of the tracking error signal is the tracking deviation relationship according to the present invention.

  Next, the operator operates the input device 71 to instruct the controller 70 to adjust the focus offset. As shown in FIG. 4, this focus offset adjustment is performed by adjusting the position of the objective lens 25 in the optical axis direction where the shape of the light spot formed on the photodetector 28 is a perfect circle, that is, the just focus position (the horizontal axis “0” in the figure). ) And the position of the objective lens 25 in the optical axis direction where the jitter of the signal reproduced from the optical disk DK is the best (minimum), the amount of deviation of the light spot from the recording surface of the optical disk DK. The objective lens 25 is positioned at a position where the jitter of the reproduction signal reproduced from the optical disk DK is best by superimposing a predetermined focus correction amount on the signal representing the error, that is, the focus error signal.

  In response to the instruction for focus offset adjustment, the controller 70 starts focus offset adjustment by executing a program (not shown). First, the controller 70 operates the spindle motor control circuit 14 to rotate the optical disk DK at a constant linear velocity, and operates the feed motor control circuit 17 to move the optical disk DK to a predetermined radial position. The predetermined radial position is the position of the optical disc DK that forms a light spot on the track on which the recording signal is recorded in the recording area of the optical disc DK. Next, the controller 70 starts the operation of the laser drive circuit 41 to emit laser light from the laser light source 21 toward the optical disk DK, and starts the operation of the jitter meter 61. Further, the focus servo circuit 44 is started to start the focus servo control of the objective lens 25, and the offset cancel circuit 48 and the tracking servo circuit 49 are operated to start the tracking servo control of the objective lens 25.

The laser light emitted from the laser light source 21 is reflected by the optical disk DK and received by the photodetector 28. The photodetector 28 sends detection signals A to D corresponding to the amount of received light to the focus error signal generation circuit 43, tracking error signal generation circuit 47, deviation amount detection circuit 54, and reproduction signal generation circuit 56 via the HF signal amplification circuit 42, respectively. Output.
Among these, the detection signals A to D output to the focus error signal generation circuit 43 are used for focus servo control of the objective lens 25 by the focus error signal generation circuit 43, the focus servo circuit 44, and the drive circuit 46. Is controlled to the just focus position.

  The detection signals A to D output to the tracking error signal generation circuit 47 are converted into tracking error signals and output to the offset cancellation circuit 48. A shift amount detection signal is output from the shift amount detection circuit 54 to the offset cancel circuit 48, and the offset cancel circuit 48 tracks the shift amount from the just focus position of the objective lens 25 indicated by the shift amount detection signal. The amount of change in the tracking error signal corresponding to the amount of deviation is calculated as the tracking correction amount by multiplying the correction coefficient. Then, the offset cancel circuit 48 superimposes the tracking correction amount on the tracking error signal and outputs it to the tracking servo circuit 49. That is, the tracking correction amount is a correction amount that cancels out the amount of change in the tracking error signal caused by the deviation of the objective lens 25 from the just focus position, in other words, the deviation of the light spot from the recording surface of the optical disk DK.

  The tracking servo circuit 49 generates a tracking servo signal based on the tracking error signal on which the tracking correction amount is superimposed and outputs the tracking servo signal to the drive circuit 51. The drive circuit 51 drives the tracking actuator 32 according to the tracking servo signal. The objective lens 25 is subjected to tracking servo control. That is, the tracking servo control of the objective lens 25 is performed while correcting the change amount of the tracking error signal that changes in accordance with the deviation amount of the objective lens 25 from the just focus position. As a result, the light spot formed on the track always follows the center of the track accurately regardless of the shape of the light spot formed by the reflected light formed on the photodetector 28.

  The detection signals A to D output to the reproduction signal generation circuit 56 are converted into reproduction signals, and then output to the jitter meter 61 via the waveform equivalent circuit 57 and the binarization circuit 59. The jitter meter 61 measures the jitter of the reproduction signal and outputs the measurement result to the controller 70. Note that the reproduction signal is also output from the reproduction signal generation circuit 56 via the waveform equivalent circuit 57 to the waveform evaluation device 58. However, since the operation of the waveform evaluation device 58 is stopped by the controller 70, the reproduction signal is output. Is ignored.

  Next, the controller 70 detects the focus correction amount. The focus correction amount is detected by continuously displacing the objective lens 25 from the plus direction to the minus direction in the optical axis direction to detect the position of the objective lens 25 at which the jitter of the reproduction signal output from the jitter meter 61 is minimized. . Specifically, the controller 70 instructs the focus offset signal generation circuit 62 to output the second focus offset signal. In response to this instruction, the focus offset signal generation circuit 62 outputs the second focus offset signal to the adder 45 and the controller 70, respectively.

  The adder 45 superimposes the second focus offset signal on the focus servo signal output from the focus servo circuit 44 and outputs the superimposed signal to the drive circuit 46. Thereby, the objective lens 25 is continuously displaced in the plus direction and the minus direction from the just focus position. In this case, the controller 70 detects the value of the second focus offset signal that provides the best (minimum) jitter of the reproduction signal that changes according to the displacement of the objective lens 25 as the focus correction amount, and the detected focus correction amount. Is output to the focus offset signal generation circuit 62. The focus offset signal generation circuit 62 stores the focus correction amount output from the controller 70. This focus correction amount is the amount of displacement from the just focus position of the objective lens 25 for making the jitter of the reproduction signal reproduced from the optical disc DK best (minimum), and the third focus offset signal at the time of inspection of the optical disc DK. Is output to the adder 45. Then, the controller 70 stops the operation of various circuits in the optical disc inspection apparatus and ends the focus offset adjustment.

  Next, the worker moves to the inspection work of the optical disk DK which is the original role of the optical disk inspection apparatus. In this inspection operation, the inspection signal recorded in advance on the optical disc DK is reproduced as described above, and the evaluation of the reproduction signal waveform and the measurement of the jitter of the reproduction signal are performed. First, the operator operates the input device 71 to instruct the controller 70 to inspect the optical disk DK. In response to this instruction, the controller 70 starts inspection of the optical disc DK by executing a program (not shown).

  First, the controller 70 operates the spindle motor control circuit 14 to rotate the optical disk DK at a constant linear velocity, and operates the feed motor control circuit 17 to move the optical disk DK to a predetermined radial position. The predetermined radial position is the position of the optical disc DK that forms a light spot on the track on which the recording signal is recorded in the recording area of the optical disc DK. Next, the controller 70 starts the operation of the laser drive circuit 41 to emit laser light from the laser light source 21 toward the optical disc DK, and starts the operation of the waveform evaluation device 58. Further, the focus servo circuit 44 and the focus offset signal generation circuit 62 are started to start the focus servo control of the objective lens 25, and the offset cancel circuit 48 and the tracking servo circuit 49 are started to operate the tracking servo of the objective lens 25. Start control. In this case, the focus offset signal generation circuit 62 is instructed to output the third focus offset signal.

  The laser light emitted from the laser light source 21 is reflected by the optical disk DK and received by the photodetector 28. The photodetector 28 sends detection signals A to D corresponding to the amount of received light to the focus error signal generation circuit 43, tracking error signal generation circuit 47, deviation amount detection circuit 54, and reproduction signal generation circuit 56 via the HF signal amplification circuit 42, respectively. Output.

  Among these, the detection signals A to D output to the focus error signal generation circuit 43 are converted into focus servo signals via the focus error signal generation circuit 43 and the focus servo circuit 44 and output to the adder 45. The adder 45 outputs the third focus offset signal from the focus offset signal generation circuit 62, and the adder 45 superimposes the third focus offset signal on the focus servo signal and outputs it to the drive circuit 46. Thereby, the objective lens 25 is controlled to a position shifted from the just focus position by the focus correction amount represented by the third focus offset signal. That is, the objective lens 25 is controlled to the position in the optical axis direction where the jitter of the reproduction signal reproduced from the optical disk DK is the best. In this case, the shape of the light spot formed by the reflected light formed on the photodetector 28 is an elliptical shape as shown in FIGS.

  The detection signals A to D output to the tracking error signal generation circuit 47 are converted into tracking error signals and output to the offset cancellation circuit 48. A shift amount detection signal is output from the shift amount detection circuit 54 to the offset cancel circuit 48, and the offset cancel circuit 48 tracks the shift amount from the just focus position of the objective lens 25 indicated by the shift amount detection signal. The amount of change in the tracking error signal corresponding to the amount of deviation is calculated as the tracking correction amount by multiplying the correction coefficient. Then, the offset cancel circuit 48 superimposes the tracking correction amount on the tracking error signal and outputs it to the tracking servo circuit 49. The tracking servo circuit 49 generates a tracking servo signal based on the tracking error signal on which the tracking correction amount is superimposed and outputs the tracking servo signal to the drive circuit 51. The drive circuit 51 drives the tracking actuator 32 according to the tracking servo signal. The objective lens 25 is subjected to tracking servo control.

  That is, the tracking servo control of the objective lens 25 is performed while correcting the change amount of the tracking error signal that changes in accordance with the deviation amount of the objective lens 25 from the just focus position, similarly to the above-described focus offset adjustment. In this case, the objective lens 25 is controlled to a position shifted from the just focus position by the focus correction amount represented by the third focus offset signal, as described above, and is calculated by the offset cancel circuit 48 and used as a tracking error signal. The tracking correction amount to be superimposed corresponds to the amount of change in the tracking error signal caused by the focus correction amount, that is, the amount that cancels the amount of change in the tracking error signal. Thereby, the light spot is controlled to always follow the track center of the optical disk DK.

  The detection signals A to D output to the reproduction signal generation circuit 56 are converted into reproduction signals, and then output to the waveform evaluation device 58 via the waveform equivalent circuit 57. The waveform evaluation device 58 performs an evaluation on the waveform of the reproduction signal and outputs the evaluation result to the controller 70. The controller 70 inspects the optical disc DK using this evaluation result. Then, when the inspection of the optical disk DK by the optical disk inspection apparatus is completed, the operator removes the optical disk DK from the turntable 13. Thereby, the inspection work of the optical disk DK is completed. Further, when inspecting another optical disk DK, a new optical disk DK is placed and fixed on the turntable 13, and the new optical disk DK is inspected in the same manner as described above. In this case, the operator does not need to calculate the tracking offset correction coefficient and adjust the focus offset again, and continues to perform the inspection work using the tracking offset correction coefficient and the focus correction amount calculated in each of the above works.

  As can be understood from the above description of the operation, according to the above embodiment, the objective lens 25 is displaced in the optical axis direction of the laser light while tracking servo control is stopped, and the objective lens 25 is moved from the just focus position. The amount of deviation, that is, the amount of change in the tracking error signal relative to the amount of deviation of the optical spot from the recording surface of the optical disc DK is detected, and the amount of change in the tracking error signal corresponding to the amount of deviation of the optical spot from the recording surface in the optical disc DK Is used to calculate the tracking correction amount as a tracking deviation relationship. The tracking correction amount is superimposed on the tracking servo signal by the adder 45 to perform tracking servo control of the objective lens 25. For this reason, even if the light spot is deviated from the recording surface of the optical disc DK by the third focus offset signal output from the focus offset signal generation circuit 62, the light spot is always maintained by the tracking correction amount corresponding to the deviation amount. Follow the track center of the optical disc DK. As a result, the offset generated in the tracking error signal due to the focus offset adjustment is removed, and the optical spot is accurately followed by the track center of the optical disc DK to improve the recording and reproduction accuracy of the signal with respect to the optical disc DK. it can.

  Furthermore, in carrying out the present invention, the present invention is not limited to the above embodiment, and various modifications can be made without departing from the object of the present invention.

  In the above embodiment, the focus correction amount is detected by causing the controller 70 to execute focus offset adjustment by a program (not shown). However, once this focus correction amount is detected, it is not necessary to detect the focus correction amount again unless the optical pickup 20 is replaced. In this case, the detected focus correction amount may be stored in the memory 70a of the controller 70, and the focus correction amount stored in the focus offset signal generation circuit 62 may be input every time the optical disc inspection apparatus is operated. . Thereby, the working efficiency of the inspection process of the optical disk can be improved.

  In the above embodiment, the tracking offset correction coefficient is calculated as the tracking deviation relationship using the tracking deviation amount and the focus deviation amount output from the tracking deviation amount calculation circuit 52 and the focus deviation amount calculation circuit 55, respectively. The tracking offset correction coefficient thus set is set in the offset cancel circuit 48. However, if the tracking deviation relationship is detected by an external device connected to the optical disc inspection apparatus, a configuration for detecting the tracking deviation relationship, specifically, the tracking deviation amount calculation circuit 52 and the focus deviation amount calculation circuit. Even in an optical disc inspection apparatus that does not have 55 or the like, the same effect as in the above embodiment can be expected. That is, the tracking deviation relationship detected by the external device, specifically, the tracking offset correction coefficient may be stored in the memory 70a of the controller 70, and the tracking offset correction coefficient may be set in the offset cancel circuit 48.

  According to this, when a large number of optical disk inspection devices are arranged as in an optical disk production line, an external device is connected to each optical disk inspection device to detect a tracking deviation relationship and store it in the memory 70a. Thus, the cost for the optical disk inspection apparatus can be reduced.

  In the above embodiment, the offset cancel circuit 48 is configured to calculate the tracking correction amount by multiplying the shift amount detection signal output from the shift amount detection circuit 54 by the tracking offset correction coefficient. However, the tracking correction amount may be an amount that cancels the third focus offset signal superimposed on the focus servo signal, that is, the amount of change in the tracking error signal caused by the focus correction amount. Therefore, the third focus offset signal output from the focus offset signal generation circuit 62 may be input to the offset cancel circuit 48 instead of the shift amount detection signal output from the shift amount detection circuit 54. . In this case, since the third focus offset signal is always a constant value, the calculated tracking correction amount is always a constant value, and the tracking error signal is corrected corresponding to the focus correction amount.

  Further, when the tracking correction amount is a constant value as described above, the tracking correction amount having the same constant value is set in the offset cancellation circuit 48, and the tracking correction amount is superimposed on the tracking error signal. Also good. According to this, the configuration for setting the tracking offset correction coefficient in the offset cancel circuit 48 is unnecessary, and the circuit configuration can be simplified. In addition, when a large number of optical disk inspection devices are arranged, the third focus offset signal detected for each optical disk inspection device is detected by connecting an external device to each optical disk inspection device as described above to detect the tracking deviation relationship. That is, if the tracking correction amount is calculated by multiplying by the focus correction amount and stored in the offset cancel circuit 48, the cost of the optical disc inspection apparatus can be reduced as described above.

  In the above embodiment, the shift amount detection signal output from the shift amount detection circuit 54 is output to the offset cancel circuit 48 and the focus shift amount calculation circuit 55, respectively. However, the present invention is not limited to this. Absent. The shift amount detection signal output from the shift amount detection circuit 54 represents the shift amount of the light spot from the recording surface of the optical disc DK, and as described above, the focus error signal output from the focus error signal generation circuit 43 and the focus error signal. It is an equivalent signal. Therefore, the same effect as described above can be expected even when the focus error signal is output to the offset cancel circuit 48 and the focus shift amount calculation circuit 55 instead of the shift amount detection signal.

  When detecting the tracking deviation relationship, the first focus offset signal output from the focus offset signal generation circuit 62 is equivalent to the deviation amount detection signal output from the deviation amount detection circuit 54. For this reason, instead of the shift amount detection signal, the first focus offset signal may be output to the focus shift amount calculation circuit 55 to detect the tracking shift relationship. Also by this, the same effect as the above can be expected.

  In the above-described embodiment, the objective lens 25 is displaced by a predetermined amount from the just focus position in the plus direction and the minus direction by the first focus offset signal in order to detect the tracking deviation relationship. Although the amount of change in the tracking error signal is detected at the three positions in FIG. 3, the present invention is not limited to this as long as the tracking offset correction coefficient can be calculated from the amount of change in the tracking error signal with respect to the amount of displacement of the objective lens 25. For example, the objective lens 25 is displaced from the just focus position in one of the plus direction and the minus direction by a predetermined amount, and the amount of change in the tracking error signal is detected at two positions of the displaced position and the just focus position. You may do it. According to this, the change amount of the tracking error signal with respect to the displacement amount of the objective lens 25 and the tracking offset correction coefficient can be calculated efficiently. Further, the change amount of the tracking error signal may be detected at four or more positions in the optical axis direction of the objective lens 25. According to this, the tracking offset correction coefficient can be calculated with higher accuracy.

  In the above embodiment, the tracking offset correction coefficient is set in the offset cancel circuit 48 as a tracking deviation relationship, and the deviation detection signal output from the deviation detection circuit 54 is multiplied by the tracking offset correction coefficient to perform tracking correction. Although configured to calculate the quantity, the present invention is not limited to this. For example, by using a tracking offset correction coefficient calculated from the tracking deviation amount and the focus deviation amount, the deviation amount detection signal is a tracking corresponding to the deviation amount of the light spot represented by the deviation amount detection signal from the recording surface of the optical disc DK. A tracking correction amount conversion table to be converted into a correction amount is generated, and the tracking offset correction conversion table is set in the offset cancel circuit 48 as a tracking deviation relationship. The deviation amount detection signal output from the deviation amount detection circuit 54 may be converted into a tracking correction amount using a tracking correction amount conversion table. Also by this, the same effect as the above-mentioned embodiment can be expected.

  In the embodiment and the first modification, the present invention is applied to the optical disk inspection apparatus for inspecting the optical disk DK. However, the present invention records a signal on the optical disk DK or records on the optical disk DK. The present invention can also be widely applied to an optical disk apparatus that reproduces a signal that has been recorded.

1 is a block diagram schematically showing an entire optical disc inspection apparatus according to an embodiment of the present invention. FIG. 2 is a detailed block diagram of a tracking error signal generation circuit, an offset cancellation circuit, and a deviation amount detection circuit in the optical disc inspection apparatus of FIG. 1. (A)-(C) is explanatory drawing which shows the shape of the light spot by the reflected light formed on a photodetector for every position with respect to the recording surface in the optical disk of an optical spot, (A) is a recording surface in an optical disk. (B) shows the case where the light spot is located in the plus direction with respect to the recording surface of the optical disc, and (C) shows the minus direction with respect to the recording surface of the optical disc. The case where it is located is shown. It is explanatory drawing which shows the relationship between jitter amount and focus correction amount.

Explanation of symbols

DK: optical disk, 10: rotational drive device, 11: spindle motor, 12: feed motor, 20 ... optical pickup, 21 ... laser light source, 25 ... objective lens, 28 ... photo detector, 31 ... focus actuator, 32 ... tracking actuator, 43 ... focus error signal generation circuit, 44 ... focus servo circuit, 45 ... adder, 47 ... tracking error signal generation circuit, 48 ... offset cancel circuit, 49 ... tracking servo circuit, 52 tracking deviation amount calculation circuit, 54 ... deviation amount detection Circuit 55... Defocus amount calculation circuit 61. Jitter meter 62. Focus offset signal generation circuit 70 controller

Claims (20)

A laser light source that emits laser light toward an optical disc, an objective lens that collects the emitted laser light to form a light spot on the optical disc, and receives a laser beam reflected by the optical disc and outputs a received light signal An optical pickup having a photodetector, a tracking actuator for displacing the objective lens in the radial direction of the optical disc, and a focus actuator for displacing the objective lens in the optical axis direction of the emitted laser light;
A tracking error signal generation circuit that generates a tracking error signal that represents the amount of deviation of the light spot from the track center, based on the light reception signal output from the photodetector;
A tracking servo control circuit that outputs a tracking servo signal based on the tracking error signal to the tracking actuator and feedback-controls the tracking actuator so that the light spot follows a track of an optical disc;
A focus error signal generation circuit that generates a focus error signal that represents the amount of deviation of the light spot from the recording surface of the optical disk, based on the light reception signal output from the photodetector;
A focus servo control circuit that outputs a focus servo signal based on the focus error signal to the focus actuator and feedback-controls the focus actuator so that the light spot follows a recording surface of the optical disc;
The focus error signal or the focus servo signal is corrected with a focus correction signal representing a focus correction amount for positioning the objective lens at a position where the evaluation value for evaluating the light reception signal output from the photodetector is the best. Focus correction means for
An optical disc apparatus comprising: a tracking correction signal that corrects the tracking error signal or the tracking servo signal with a tracking correction signal that represents a change amount of the tracking error signal generated by the focus correction unit. The optical disc apparatus according to claim 1,
The focus correction means includes
To control the focus actuator to displace the objective lens in the optical axis direction of the laser beam and position the objective lens at a position where the evaluation value for evaluating the light reception signal output from the photodetector is the best Focus correction amount detection means for detecting the focus correction amount of
An optical disc apparatus comprising: a focus correction amount superimposing unit that superimposes a focus correction signal representing the focus correction amount detected by the focus correction amount detecting unit on the focus error signal or the focus servo signal. The optical disc apparatus according to claim 1,
The focus correction means includes
A focus correction amount storage means for preliminarily storing a focus correction amount for positioning the objective lens at a position where the evaluation value for evaluating the light reception signal output from the photodetector is the best;
An optical disc apparatus comprising: a focus correction amount superimposing unit that superimposes a focus correction signal representing a focus correction amount stored in the focus correction amount storage unit on the focus error signal or the focus servo signal. The optical disc apparatus according to any one of claims 1 to 3, wherein
The tracking correction means includes
In a state where tracking servo control by the tracking servo control circuit is stopped, the focus actuator is controlled to displace the objective lens in the optical axis direction of the laser beam, so that the light spot is displaced from the recording surface of the optical disk. Relationship detecting means for detecting the relationship between the amount of change in the tracking error signal generated by the tracking error signal generating circuit and the amount representing the tracking deviation relationship;
By inputting an amount representing the deviation of the light spot from the recording surface of the optical disk, the tracking correction amount for canceling the amount of change in the tracking error signal caused by the focus correction means is the relationship between the input amount representing the deviation and the relationship. Tracking correction amount calculating means for calculating based on the tracking deviation relationship detected by the detecting means;
An optical disc apparatus comprising: a tracking correction amount superimposing unit that superimposes a tracking correction signal representing the tracking correction amount calculated by the tracking correction amount calculating unit on the tracking error signal or the tracking servo signal. The optical disk apparatus according to claim 4, wherein
The relationship detecting means includes
Objective lens displacement means for controlling the focus actuator to displace the objective lens in the optical axis direction;
Coefficient calculating means for calculating a tracking offset correction coefficient for calculating a change amount of the tracking error signal with respect to a displacement amount of the objective lens;
The tracking correction amount calculating means includes
An optical disc apparatus for calculating a tracking correction amount by multiplying an amount representing a deviation of the input light spot from a recording surface of an optical disc by a tracking offset correction coefficient calculated by the coefficient calculating means. In the optical disc device according to claim 4 or 5,
The tracking correction amount calculating means includes
An optical disc apparatus that calculates a tracking correction amount by inputting the focus correction signal instead of an amount representing a deviation of the light spot from the recording surface of the optical disc. The optical disc apparatus according to any one of claims 1 to 3, wherein
The tracking correction means includes
Tracking correction amount storage means for preliminarily storing a tracking correction amount for canceling a change amount of the tracking error signal generated by the focus correction means;
An optical disk apparatus comprising: a tracking correction amount superimposing unit that superimposes a tracking correction signal representing a tracking correction amount stored in the tracking correction amount storage unit on the tracking error signal or the tracking servo signal. The optical disc apparatus according to any one of claims 1 to 3, wherein
The tracking correction means includes
Relationship storage means for preliminarily storing the relationship of the amount of change in the tracking error signal with respect to the amount representing the displacement of the light spot from the recording surface of the optical disc as a tracking displacement relationship;
By inputting an amount representing the deviation of the light spot from the recording surface of the optical disk, the tracking correction amount for canceling the amount of change in the tracking error signal caused by the focus correction means is the relationship between the input amount representing the deviation and the relationship. Tracking correction amount calculating means for calculating based on the tracking deviation relationship stored in the storage means;
An optical disc apparatus comprising: a tracking correction amount superimposing unit that superimposes a tracking correction signal representing the tracking correction amount calculated by the tracking correction amount calculating unit on the tracking error signal or the tracking servo signal. The optical disc apparatus according to claim 8, wherein
The relationship storage means
Storing a tracking offset correction coefficient for calculating a change amount of the tracking error signal with respect to an amount representing a deviation of the light spot from the recording surface of the optical disc;
The tracking correction amount calculating means includes
An optical disc apparatus for calculating a tracking correction amount by multiplying an amount representing a deviation of the input light spot from a recording surface on an optical disc by a tracking offset correction coefficient stored in the relation storage means. In the optical disc apparatus according to claim 8 or 9,
The tracking correction amount calculating means includes
An optical disc apparatus that calculates a tracking correction amount by inputting the focus correction signal instead of an amount representing a deviation of the light spot from the recording surface of the optical disc. A laser light source that emits laser light toward an optical disc, an objective lens that collects the emitted laser light to form a light spot on the optical disc, and receives a laser beam reflected by the optical disc and outputs a received light signal An optical pickup having a photodetector, a tracking actuator for displacing the objective lens in the radial direction of the optical disc, and a focus actuator for displacing the objective lens in the optical axis direction of the emitted laser light;
A tracking error signal generation circuit that generates a tracking error signal that represents the amount of deviation of the light spot from the track center, based on the light reception signal output from the photodetector;
A tracking servo control circuit that outputs a tracking servo signal based on the tracking error signal to the tracking actuator and feedback-controls the tracking actuator so that the light spot follows a track of an optical disc;
A focus error signal generation circuit that generates a focus error signal that represents the amount of deviation of the light spot from the recording surface of the optical disk, based on the light reception signal output from the photodetector;
A focus servo signal based on the focus error signal is output to the focus actuator, and is applied to an optical disc apparatus including a focus servo control circuit that feedback-controls the focus actuator so that the light spot follows a recording surface of the optical disc. In the control method of the optical disc apparatus to be performed,
The focus error signal or the focus servo signal is corrected with a focus correction signal representing a focus correction amount for positioning the objective lens at a position where the evaluation value for evaluating the light reception signal output from the photodetector is the best. Focus correction step to
And a tracking correction step of correcting the tracking error signal or the tracking servo signal with a tracking correction signal representing a change amount of the tracking error signal generated by the focus correction step. In the control method of the optical disc device according to claim 11,
The focus correction step includes
To control the focus actuator to displace the objective lens in the optical axis direction of the laser beam and position the objective lens at a position where the evaluation value for evaluating the light reception signal output from the photodetector is the best A focus correction amount detection step for detecting the focus correction amount of
A control method for an optical disc apparatus, comprising: a focus correction amount superimposing step of superimposing a focus correction signal representing the focus correction amount detected in the focus correction amount detecting step on the focus error signal or the focus servo signal. In the control method of the optical disc device according to claim 11,
The focus correction step includes
A focus correction amount storage step for preliminarily storing a focus correction amount for positioning the objective lens at a position where an evaluation value for evaluating the light reception signal output from the photodetector is the best;
A control method for an optical disc apparatus, comprising: a focus correction amount superimposing step of superimposing a focus correction signal representing the focus correction amount stored in the focus correction amount storing step on the focus error signal or the focus servo signal. 14. The method for controlling an optical disc device according to claim 11, wherein:
The tracking correction step includes
In a state where tracking servo control by the tracking servo control circuit is stopped, the focus actuator is controlled to displace the objective lens in the optical axis direction of the laser beam, so that the light spot is displaced from the recording surface of the optical disk. A relationship detecting step of detecting a relationship between the amount of change in the tracking error signal generated by the tracking error signal generation circuit and the amount representing the tracking deviation relationship;
By inputting an amount representing the deviation of the light spot from the recording surface of the optical disk, the tracking correction amount for canceling the amount of change in the tracking error signal caused by the focus correction step is the relationship between the input amount representing the deviation and the relationship. A tracking correction amount calculating step for calculating based on the tracking deviation relationship detected in the detecting step;
A method of controlling an optical disc apparatus, comprising: a tracking correction amount superimposing step of superimposing a tracking correction signal representing the tracking correction amount calculated in the tracking correction amount calculating step on the tracking error signal or the tracking servo signal. The method of controlling an optical disc device according to claim 14,
The relationship detecting step includes:
An objective lens displacement step of controlling the focus actuator to displace the objective lens in the optical axis direction;
A coefficient calculating step of calculating a tracking offset correction coefficient for calculating a change amount of the tracking error signal with respect to a displacement amount of the objective lens;
The tracking correction amount calculating step includes:
A control method for an optical disc apparatus, wherein a tracking correction amount is calculated by multiplying an amount representing a deviation of the input light spot from a recording surface of an optical disc by a tracking offset correction coefficient calculated in the coefficient calculation step. In the control method of the optical disc device according to claim 14 or 15,
The tracking correction amount calculating step includes:
A control method for an optical disc apparatus, wherein the tracking correction amount is calculated by inputting the focus correction signal instead of the amount representing the deviation of the light spot from the recording surface of the optical disc. 14. The method for controlling an optical disc device according to claim 11, wherein:
The tracking correction step includes
A tracking correction amount storing step for storing in advance a tracking correction amount for canceling the amount of change in the tracking error signal caused by the focus correction step;
A method for controlling an optical disc apparatus, comprising: a tracking correction amount superimposing step of superimposing a tracking correction signal representing the tracking correction amount stored in the tracking correction amount storing step on the tracking error signal or the tracking servo signal. 14. The method for controlling an optical disc device according to claim 11, wherein:
The tracking correction step includes
A relationship storage step for storing in advance the relationship of the amount of change in the tracking error signal with respect to the amount representing the displacement of the light spot from the recording surface of the optical disc as a tracking displacement relationship;
By inputting an amount representing the deviation of the light spot from the recording surface of the optical disk, the tracking correction amount for canceling the amount of change in the tracking error signal caused by the focus correction step is the relationship between the input amount representing the deviation and the relationship. A tracking correction amount calculating step for calculating based on the tracking deviation relationship stored in the storing step;
A method of controlling an optical disc apparatus, comprising: a tracking correction amount superimposing step of superimposing a tracking correction signal representing the tracking correction amount calculated in the tracking correction amount calculating step on the tracking error signal or the tracking servo signal. The method of controlling an optical disc device according to claim 18,
The relation storing step includes
Storing a tracking offset correction coefficient for calculating a change amount of the tracking error signal with respect to an amount representing a deviation of the light spot from the recording surface of the optical disc;
The tracking correction amount calculating step includes:
A control method for an optical disc apparatus, wherein a tracking correction amount is calculated by multiplying an amount representing a deviation of the input light spot from a recording surface on an optical disc by a tracking offset correction coefficient stored in the relation storage step. In the control method of the optical disc device according to claim 18 or 19,
The tracking correction amount calculating step includes:
A control method for an optical disc apparatus, wherein the tracking correction amount is calculated by inputting the focus correction signal instead of the amount representing the deviation of the light spot from the recording surface of the optical disc.

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