JPH05314523A - Tracking offset correcting method for optical disk - Google Patents

Abstract

PURPOSE:To accurately correct a tracking offset by adding a second offset amt. to a second servo loop so that the first offset amt. of a tracking signal becomes small. CONSTITUTION:This method is provided with a first servo loop containing an optical axis drive means like an objective lens 3 driving the optical axis of a light spot according the tracking signal obtained from a track on a disk, and the second servo loop driving a carriage 2 containing the part perpendicular to the disk of the optical axis so as to reduce the drive amt. of the optical axis, and the second offset amt. is added to the second servo loop so that the first offset amt. of the tracking signal picked up from the first servo loop becomes small. Thus, a lens position is controlled accurately and the tracking offset is corrected further precisely.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of an offset correction method in a tracking servo device of an optical disk device, and more particularly, to a movable type even if it is an optical pickup having a track detector in a fixed part. The present invention relates to a tracking offset correction method for an optical disk device, which is capable of correcting an offset of a tracking signal due to a position variation of a part or the like.

[0002]

2. Description of the Related Art Conventionally, a method of correcting an offset in a tracking servo device of an optical disk device has been known. For example, in a separation type optical pickup including a movable optical system including an objective lens and a deflecting member and a fixed optical system including another optical system including a semiconductor laser, a movable portion is provided with a track detector to move the movable optical system. Even if the position of the part changes, the tracking signal is not offset (Japanese Patent Laid-Open No. 64-7345).

However, when the track detector is provided in the movable part, in practice, an electronic circuit such as a preamplifier is required to process the detection signal, which increases the weight of the movable part.
There is a problem that the control operation is hindered. By the way, the causes of the offset of the tracking signal are roughly classified into the movement of the objective lens, the inclination of the disk, the shape of the groove, etc. (Radio Technology Co., Ltd., 1989).
Issued May 10, "Optical Disk Technology", pp. 87-97).

As a measure against the "movement of the objective lens", a so-called two-stage servo is used in which a coarse movement motor equipped with a lens is driven according to the movement of the lens to suppress the movement of the lens relative to the coarse movement portion. The method is effective (the above-mentioned "Optical Disc Technology" pages 148 to 151). In addition, the two-stage servo system has the first lens position sensorless
Method and a second method with a lens position sensor.

However, only by adopting these two-stage servo systems, in the case of the separate type optical pickup in which the track detector is provided in the movable part as shown in the above publication, the movable part and the fixed part are relatively opposed to each other. It is not possible to reduce the offset of the tracking signal caused by the optical axis shift due to the position change. Furthermore, neither the separation type optical pickup in which the track detector is provided on the movable portion nor the two-stage servo system can correct the offset and the like due to the "disc tilt".

Although a method of improving the disk format with wobble pits or the like and taking special measures has been proposed, this method increases the manufacturing cost of the disk, the cost of the processing circuit of the optical disk device, and the like. There is an inconvenience. As described above, in the conventional optical disk device,
In an optical pickup which is a separate type and has a track detector on its fixed portion, there is a disadvantage in that it is not possible to correct offsets and the like due to positional fluctuations of the movable portion.

[0007]

In the present invention, it is needless to say that an optical pickup of a separate type having a track detector at a fixed portion solves such a problem in the conventional tracking offset correction method for an optical disk device. An object of the present invention is to provide a tracking offset correction method capable of correcting an offset caused by a tilt of a disc, an assembly error, and the like even in an integrated optical pickup in which the entire optical system is on a carriage.

[0008]

According to the present invention, firstly,
In a tracking offset correction method of a tracking servo device for causing a light spot to follow a track engraved on a record carrier such as a disc, an optical axis drive for driving the optical axis of the light spot according to a tracking signal obtained from the track of the disc A first servo loop including means, and a second servo loop that drives a carriage including a portion of the optical axis perpendicular to the disk so as to reduce the drive amount of the optical axis.
Tracking loop for adding a second offset amount to the second servo loop so that the first offset amount of the tracking signal extracted from the first servo loop is small. Is a correction method of.

Secondly, in the first tracking offset correction method, the optical axis driving means is a tracking offset correction method which is an objective lens forming a light spot.

Thirdly, in the first or second tracking offset correction method, the second servo loop is a tracking offset correction method having a position sensor for detecting the position of the objective lens with respect to the carriage.

Fourth, in the first to third tracking offset correction methods, the extraction of the first offset from the track signal is a tracking offset correction method performed when the first servo loop is open. ..

Fifth, in the above-mentioned first to third tracking offset correction methods, the first offset is extracted by a tracking offset correction method which is extracted from a tracking error signal of a portion of the disk where the tracking groove does not exist. is there.

Sixth, in the above first to fifth tracking offset correction methods, an offset storage means for storing second offset information at a plurality of points in the radial direction of the disk is provided, and when recording / reproducing information, The tracking offset correction method adds a new offset corresponding to the second offset information stored in the offset storage means to the second servo loop.

Seventh, in the sixth tracking offset correction method, the new offset is calculated from the information of the second offset stored in the offset storage means and the track address at the time of recording / reproducing the information. This is a method of correcting the tracking offset calculated by calculation.

[0015]

According to the tracking offset correction method of the present invention, the offset amount of the tracking signal TE is detected by calculating the difference between the positive peak amplitude and the negative peak amplitude of the tracking signal TE.
Focusing on the point that this difference signal (A-B) is not generated, the offset of the tracking signal TE is set to zero. Specifically, since the difference signal (A−B) may be set to A−B = 0,
By intentionally adding an offset voltage LPOFS to the output LP of the lens position sensor, the position of the objective lens 3 is moved (moved to a point b or a point c in FIG. 5 described later) to correct the offset of the tracking signal TE. I am trying to do it.

[0016]

Embodiments of the tracking offset correction method of the present invention will now be described in detail with reference to the drawings. This embodiment mainly corresponds to the invention of claim 1, but is also related to the inventions of claims 2 to 7.

FIG. 1 is a functional block diagram showing an example of the main configuration of an optical disk device suitable for carrying out the tracking offset correction method of the present invention.
In the figure, 1 is an optical disc, 2 is a carriage, 3 is an objective lens, 4 is a mirror, 5 is a lens position sensor, 6 is a linear motor, 7 is an objective lens actuator, 8 is a fixed optical system, 9 is a photodetector, and 10 is a photodetector. Is a differential amplifier, 11 is a first phase compensation circuit, 12 is a first switch (SW
1) and 13 are first power amplifiers, 14 is a second switch (SW2), 15 is a constant voltage DC power supply, and 16 is an A / D
Converter, 17 is a second power amplifier, 18 is a switching circuit, 19 is a second phase compensation circuit, 20 is an access circuit,
21 is an adder, 22 is a D / A converter, 23 is an MPU, TE is a tracking signal, LP is the output of the lens position sensor 5, LPOFS is the offset voltage for the lens position sensor 5 output LP, and TAD is the present Track address signal, arrow P indicates the moving direction of the carriage 2, and arrow Q indicates the moving direction of the objective lens 3.

Regarding the optical disk device shown in FIG. 1, the operation common to the conventional one will be described first. An objective lens 3 and a mirror 4 are mounted on a carriage 2 which is a movable part, and a relative position of the objective lens 3 with respect to the carriage 2 is detected by a lens position sensor 5.

The deviation of the light spot with respect to the track on the optical disk 1 is detected by the fixed optical system 8 and the differential amplifier 10 from the reflected beam guided by the mirror 4. The output of the differential amplifier 10 is the tracking signal TE, and during the tracking servo, the first switch 12 is turned on and the first phase compensation circuit 1
It is fed back to the objective lens actuator 7 via 1 and the first power amplifier 13 to perform the track following operation. The above operation is basically the same as that of the conventional optical disk device.

Here, the relationship between the position of the light beam irradiated on the photodetector 9 provided in the fixed optical system 8 and the tracking signal TE will be described. The photodetector 9 is, for example, a known push-pull type detector, and is divided into two in the direction parallel to the track in order to detect a tracking error.

FIG. 2 is a diagram for explaining the position of the light beam irradiated onto the photodetector. (1) shows the case where the light beam is located at the center of the dividing line, and (2) shows the deviation from the center of the dividing line. The case is shown. In the figure, 9a indicates a dividing line of the photodetector 9, and SP indicates a spot position of the light beam.

As shown in FIG. 2 (1), the light beam is
When located at the center of the dividing line 9a of the photodetector 9, as a matter of course, no offset occurs in the tracking signal TE. On the other hand, when the light beam is deviated from the center of the dividing line 9a of the photodetector 9 as shown in FIG. 2B, an offset occurs in the tracking signal TE.

The deviation of the light beam is caused by the deviation of the optical axis of the light beam from the reference position due to the movement of the carriage 2, the inclination of the disk, the mounting error, the movement of the objective lens 3, and the like. Therefore, the above-mentioned various factors are all equivalent in the sense of the deviation of the optical axis, and all of them cause the optical axis deviation and cause the offset in the tracking signal TE.

As described above, in the tracking offset correction method of the present invention, this optical axis shift is intentionally controlled, and in particular, the above three factors (carriage movement, carriage movement,
Offset of the tracking signal TE is canceled by canceling the deviation of the optical axis of the light beam from the reference position due to the tilt of the disc and mounting error, and shifting the light beam to the position shown in Fig. 2 (1). I am trying to correct. In FIG. 1 described above, the carriage 2 is movable in the disk radial direction (double-headed arrow P), and the output LP of the lens position sensor 5 is the adder 21, the second phase compensation circuit 19, the switching circuit 18, 2 power amplifier 1
It is fed back to the linear motor 6 through 7 and a so-called two-stage servo operation is performed.

At this time, the output LP of the lens position sensor 5
Is LP≈0, that is, the servo control is performed such that the movement of the objective lens 3 and the movement of the carriage 2 substantially match. Further, when the switching circuit 18 is connected to the access circuit 20 side, the objective lens 3 and the carriage 2 are largely moved in the disk radial direction, so that an arbitrary track on the disk 1 can be accessed. Since the access circuit 20 is publicly known, detailed description thereof will be omitted.

The tracking signal TE output from the differential amplifier 10 is converted into a digital signal by the A / D converter 16 and becomes a signal that can be read by the MPU (microprocessor) 23. Also, this MPU23
Through the D / A converter 22, the offset voltage LPOF with respect to the output LP of the lens position sensor 5.
S can be added.

The MPU 23 also has a function of controlling the switching of the first switch 12 and the second switch 14 at the same time. When the first switch 12 is "on" and the second switch 14 is "off", the tracking servo is closed and the tracking signal TE is
The objective lens 3 is driven so that TE≈0.

On the contrary, when the first switch 12 is "OFF" and the second switch 14 is "ON", the tracking servo is opened and the objective lens 3 is driven by the constant voltage DC power supply 15. A so-called track jump operation is performed.

By the way, when the track jump is performed, the positive and negative peak amplitudes of the tracking signal TE are obtained. When the MPU 23 calculates the difference between the positive peak amplitude and the negative peak amplitude of the tracking signal TE, the offset amount of the tracking signal TE is detected. According to the tracking offset correction method of the present invention, the tracking signal T
The offset of the tracking signal TE is corrected by intentionally giving an offset to the output LP of the lens position sensor 5 so that the offset of E becomes "0".

Next, the tracking offset correcting operation will be specifically described. In the circuit of FIG. 1, the differential amplifier 10
The offset voltage LPOFS is applied to the output LP of the lens position sensor 5 so that the offset amount of the tracking signal TE output from is 0.

FIG. 3 is a time chart showing an example of the relationship between the position on the track, the tracking signal TE and the tracking signal TE 'when there is an offset. The horizontal axis of the figure is the position on the track, the vertical axis A is the positive peak amplitude of the tracking signal TE, and B is the negative peak amplitude.
C is the center of the track, and δ is the amount of deviation from the track center C.

As shown in FIG. 3, the tracking signal TE has a positive peak amplitude A and a negative peak amplitude B, and A = B when there is no offset.
However, when the offset is generated, A ≠ B as shown by the waveform TE ', and when the tracking servo is applied in this state, as shown by δ, it is displaced from the track center C by δ. I will track. On the other hand, the output LP of the lens position sensor 5 is as shown in FIG.

FIG. 4 is a diagram showing the relationship between the lens position with respect to the carriage and the lens position sensor output LP. In the figure, the horizontal axis represents the lens position with respect to the carriage, the vertical axis represents the lens position sensor output, LP represents the sensor output of the lens position sensor 5, and LP 'represents the signal obtained by adding the offset voltage LPOFS.

In FIG. 4, the base point 0 indicates the reference position on the carriage 2. Then, when there is no offset, that is, when A = B, the output LP from the lens position sensor 5 coincides with the base point 0, as indicated by LP in FIG. In the tracking offset correction method of the present invention,
An offset (LPOFS) is intentionally applied to the output LP of the lens position sensor 5.

As a result, the offset voltage LPOFS is added to LP in FIG. 4 to obtain a signal as shown by LP '. In this way, the output LP of the lens position sensor 5
When the offset voltage LPOFS is added, a signal as shown by LP 'is obtained.

The signal LP 'added with the offset voltage LPOFS is such that when LPOFS ≠ 0 (when the lens position is a in FIG. 4), the sensor output LP is fed back to the carriage 2 so that LP = 0. Servo controlled to. That is, the position of the objective lens 3 with respect to the carriage 2 is controlled to be substantially 0 (reference position on the carriage 2).

As described above, the offset voltage LPOFS is added to the sensor output LP, and the signal LP 'becomes LP'.
Since the carriage 2 is servo-controlled so that = 0, the relative position of the objective lens 3 with respect to the carriage 2 is
As a result, it is displaced by a in FIG. In the tracking offset correction method of the present invention, the relative position of the objective lens 3 with respect to the carriage 2 can be variably controlled by varying the offset voltage LPOFS.

FIG. 5 is a diagram for explaining the relationship between the lens position with respect to the carriage and the offset amount of the tracking signal TE in the optical disk device. The horizontal axis of the figure is the lens position with respect to the carriage, and the vertical axis is the offset amount (A
-B), and X and Y respectively indicate characteristics corresponding to the movement of the carriage.

As described above with reference to FIG. 3, the carriage 2
When the position of the objective lens 3 with respect to changes, the difference A−B (offset amount) between the positive peak amplitude A and the negative peak amplitude B of the tracking signal TE changes. For example, when the position of the objective lens 3 with respect to the carriage 2 changes, the difference signal (A-B) of the tracking signal TE changes like straight lines X and Y shown in FIG. This point is the same as the conventional case.

When the carriage 2 moves and the optical axis with respect to the fixed optical system 8 deviates, the position of the light spot on the photodetector 9 deviates, and the difference signal (AB) also changes. Further, due to the assembling error of the optical disc device, the inclination of the disc, and the like, the light spot on the photodetector 9 is similarly displaced, and the difference signal (AB) is similarly changed.

The tracking offset correction method of the present invention is intended to prevent the difference signal (A-B) from occurring. Specifically, it is sufficient to set A-B = 0. As stated, the offset voltage L
By adding POFS, the position of the objective lens 3 is moved to the point b or the point c in FIG. Therefore, the objective lens 3 is moved to three points on the disk 1, for example, three points on the inner peripheral portion, the intermediate portion, and the outer peripheral portion, and the value of the offset voltage LPOFS corresponding to each is detected. Next, a flow for such control will be shown.

FIG. 6 shows the tracking offset correction method of the present invention in which the offset of the tracking signal TE is "0" at three points in the radial direction of the disk.
6 is a flowchart showing the main processing flow when determining the value of the offset voltage LPOFS that can be set. In the drawing, # 1 to # 13 indicate steps.

In step # 1, the known access circuit 20
Is used to move the carriage 2 in the inner circumferential direction. In the next step # 2, the tracking servo is turned on.
Specifically, control signal SW1 (tracking control ON / OFF signal for turning ON / OFF the first switch 12)
= ON, SW2 (access control ON / OFF signal for turning on / off the second switch 14) = OFF.

At step # 3, SW1 = OFF and SW2 = ON are set to perform the track jump. In the next step # 4, the positive and negative peak amplitudes A and B of the tracking signal TE are detected and stored in the memory.

In this case, A = tracking signal TE
And B = negative peak amplitude of the tracking signal TE. In step # 5, it is checked whether the difference signals A-B are equal to or smaller than the constant ε, that is, whether they are sufficiently small. In the flow, it is determined whether or not AB ≦ ε.

If the difference signal AB is large, the offset voltage LP is set so that the difference signal AB becomes a constant ε or less.
Change OFS. As a result of the judgment in step # 5, A-
If not B ≦ ε, in step # 6, the offset voltage L
The POFS is changed, the process returns to the previous step # 2, and the processes of steps # 2 to # 6 are repeated in the same manner.

By the processes of steps # 2 to # 6 described above, the value of the offset voltage LPOFS that can set the offset of the tracking signal TE at the inner peripheral portion to "0" is determined. Then, when it is detected in step # 5 that AB ≦ ε, the process proceeds to step # 7.

In step # 7, this offset voltage L
The value of POFS is stored in the memory as OFSIN (offset amount in the inner peripheral portion) = LPOFS. Next, in step # 8, the carriage 2 is moved in the outer peripheral direction and stopped at an intermediate position.

The next step # 9 is a process for determining the value of the offset voltage LPOFS which can set the offset of the tracking signal TE at the disk middle portion to "0", and the same process as the previous steps # 2 to # 6. To execute. When the value of the offset voltage LPOFS in the intermediate portion is determined, the process proceeds to step # 10, and OFSMID (offset amount in the intermediate portion) = LPOFS is stored in the memory.

Similarly, in step # 11, the carriage 2
Move toward the outer circumference. Next, in order to determine the value of the offset voltage LPOFS at the outer peripheral portion, step # 12
Then, the same processing as the previous steps # 2 to # 6 is executed again.

When the value of the offset voltage LPOFS at the outer peripheral portion is determined, the routine proceeds to step # 13, where OFSOU
T (offset amount at outer peripheral portion) = LPOFS is stored in the memory, and the flow of FIG. 6 ends. By the above processing of steps # 1 to # 13, the three values in the radial direction of the disk in the tracking offset correction method of the present invention are
The process of determining the value of the offset voltage LPOFS that can set the offset of the tracking signal TE for the point to “0” is completed, and each offset voltage LPOF
The value of S is stored in memory.

Offset voltage L at these three points
The POFS values are arranged on a substantially straight line as shown in FIG. 7, for example. FIG. 7 is a diagram showing an example of a change state of the offset voltage LPOFS corresponding to the track address. The horizontal axis of the figure shows the track address TAD, and the vertical axis shows the offset voltage LPOFS.

In FIG. 7, OFSIN (offset amount at the inner peripheral portion), OFSMID (offset amount at the intermediate portion) and OFSOUT (offset amount at the outer peripheral portion) are shown as the offset amounts at three points in the radial direction. ing. OF at the three points shown in FIG.
An offset voltage LPOFS corresponding to an arbitrary radial position on the disk, that is, at that point, from SIN (offset amount at the inner peripheral portion), OFSMID (offset amount at the intermediate portion), and OFSOUT (offset amount at the outer peripheral portion). It is extremely easy to calculate the value of the offset voltage LPOFS that can make the offset of the tracking signal TE "0".

In the circuit shown in FIG. 1, the address decoder is not shown, but in an optical disk device, the address decoder normally detects the current track address, that is, an amount corresponding to the radial direction of the disk. .. From the current track address thus obtained and the value of the offset voltage LPOFS at the three points arranged in a substantially straight line as shown in FIG. 7, the inside is appropriately adjusted to correspond to the current radial position. Offset voltage LPOF
The value of S should be calculated.

Here, a method of calculating the value of the offset voltage LPOFS during data read / write will be described.
FIG. 8 is a flowchart showing the flow of the main processing of the MPU at the time of reading / writing data. In the drawing, # 11 to # 12 indicate steps.

FIG. 8 shows the operation of the MPU 23 during normal data read / write. At the time of this normal read / write, in step # 11, the address decoder detects the current track address, that is, the amount corresponding to the radial direction of the disk.

Then, as described with reference to FIG. 7, the OFSI is set as the offset amount at the three points determined in advance.
An offset corresponding to the current radial position by performing an appropriate inner side calculation from each value of N (offset amount in inner circumference), OFSMID (offset amount in middle part), OFSOUT (offset amount in outer circumference) The voltage LPOFS is obtained, and the value is added to the output LP of the lens position sensor 5.

In the next step # 12, a data read (or write) operation is performed. In addition, in the inner edge calculation processing in step # 11, when linear as shown in FIG.

Further, even when it is not a straight line, the interpolation calculation may be performed by an approximate calculation of a polygonal line or a quadratic curve (the invention of claim 7). Known calculations can be used for these calculations.

As described above, according to the present invention, the first servo loop including the optical axis drive means for driving the optical axis of the light spot according to the tracking signal obtained from the track of the disk, and the drive of the optical axis. A second servo loop for driving a carriage including a portion of the optical axis perpendicular to the disk so as to reduce the amount, and a first offset amount of the tracking signal extracted from the first servo loop. The second offset amount is added to the second servo loop so that becomes smaller (the invention of claim 1). The optical axis driving means in this case is, for example, the objective lens 3 that forms the light spot in FIG. 1 (the invention of claim 2).

Further, the second servo loop is provided with, for example, a position sensor (lens position sensor 5) for detecting the position of the objective lens 3 with respect to the carriage 2 (claim 3).
Invention). Furthermore, the extraction of the first offset from the track signal is performed when the first servo loop is in the open state (in FIG. 1, the first switch 12 is “off” and the second switch 14 is “on”). When), it is performed (the invention of claim 4).

By the way, in the above description of the flow of FIG.
By jumping tracks and calculating the difference signal (A-B),
The case where the offset amount of the tracking signal TE is detected has been described. However, for example, 5 ″ 1/4 (5 inches 1
/ 4, ISO standard) disc, such as a disc having a part where the track groove is interrupted,
At that portion, only the offset of the tracking signal TE can be detected.

Therefore, when such a disc is used, A / D
The converter 16 allows the tracking signal TE to be read directly (invention of claim 5).

Further, in the above-mentioned embodiments, the description has been centered on the case where the offset voltage LPOFS at an arbitrary radial position is obtained from three points. However, the position where the offset voltage LPOFS is obtained is not limited to three points, and the offset voltage LPOFS obtained from an arbitrary number of points higher than that.
It is also possible to calculate based on FS (the invention of claim 6).

It should be noted that the offset of the tracking signal TE due to factors other than the movement of the carriage, for example, the offset due to factors such as the inclination of the disk and the assembling error, is sufficiently effective even if the offset voltage LPOFS of only one point is used. Therefore, it is needless to say that the tracking offset correction method of the present invention includes such a correction method.

[0066]

According to the first aspect of the present invention, in the case of the separation type pickup, the tracking offset caused by the beam optical axis shift on the tracking error detector caused by the carriage movement, the disc tilt, and the assembly error is accurately measured. Can be corrected to. Further, in the case of the integrated pickup, it is possible to correct the tracking offset caused by the deviation of the beam optical axis on the tracking error detector due to the disc tilt and the assembly error.

According to the invention of claim 2, in the invention of claim 1, it becomes possible to correct the tracking offset of the optical disk device for tracking by driving the objective lens. Therefore, it can be widely applied to general optical disk devices.

According to a third aspect of the invention, the lens position sensor is used in the first or second aspect of the invention. Therefore, the lens position can be controlled accurately, and the tracking offset can be corrected more accurately.

According to the invention of claim 4, in the inventions of claims 1 to 3, the tracking offset can be accurately extracted. Therefore, similarly, it becomes possible to more accurately correct the tracking offset.

According to the invention of claim 5, in the inventions of claims 1 to 3, the offset can be extracted while the tracking servo is still applied. Therefore, the circuit configuration is simplified and the cost is reduced.

According to the invention of claim 6, in the inventions of claims 1 to 5, since the offset correction results of a plurality of points in the radial direction are used, the offset can be corrected more accurately.

According to the seventh aspect of the invention, in the sixth aspect of the invention, since the inner circle calculation is further performed, the offset correction of an arbitrary radial position can be performed more accurately.

[Brief description of drawings]

FIG. 1 is a functional block diagram showing an example of a main part configuration of an optical disc device suitable for implementing a tracking offset correction method of the present invention.

FIG. 2 is a diagram illustrating a position of a light beam emitted onto a photodetector.

FIG. 3 is a time chart showing an example of a relationship between a position on a track, a tracking signal TE and a tracking signal TE ′ when there is an offset.

FIG. 4 is a diagram showing a relationship between a lens position with respect to a carriage and a lens position sensor output LP.

FIG. 5 is a diagram illustrating a relationship between a lens position with respect to a carriage and an offset amount of a tracking signal TE in an optical disc device.

FIG. 6 is a flowchart showing the main processing flow when determining the value of the offset voltage LPOFS that can set the offset of the tracking signal TE to “0” at three points in the radial direction of the disk in the tracking offset correction method of the present invention. Is.

FIG. 7 is an offset voltage L corresponding to a track address.
It is a figure which shows an example of the change state of POFS.

FIG. 8 is a flowchart showing a main processing flow of the MPU at the time of reading / writing data.

[Explanation of symbols]

 1 Optical Disc 2 Carriage 3 Objective Lens 4 Mirror 5 Lens Position Sensor 6 Linear Motor 7 Objective Lens Actuator 8 Fixed Optical System 9 Optical Detector 10 Differential Amplifier 11 First Phase Compensation Circuit 12 First Switch 13 First Power Amplifier 14 Second switch 15 Constant voltage direct current power supply 16 A / D converter 17 Second power amplifier 18 Switching circuit 19 Second phase compensation circuit 20 Access circuit 21 Adder 22 D / A converter 23 MPU

Claims (7)

[Claims] 1. A tracking offset correction method of a tracking servo device for causing a light spot to follow a track engraved on a record carrier such as a disc, wherein an optical axis of the light spot is set in accordance with a tracking signal obtained from the track of the disc. A first servo loop including an optical axis drive means for driving; and a second servo loop for driving a carriage including a portion of the optical axis perpendicular to the disk so as to reduce the drive amount of the optical axis. The tracking signal extracted from the first servo loop has a second offset so that the first offset amount is small.
Tracking offset correction method, characterized in that the second offset amount is added to the servo loop. 2. The tracking offset correction method according to claim 1, wherein the optical axis driving means is an objective lens that forms a light spot. 3. The tracking offset correction method according to claim 1 or 2, wherein the second servo loop includes a position sensor that detects a position of the objective lens with respect to the carriage. .. 4. The tracking offset correction method according to claim 1, wherein the extraction of the first offset from the track signal is performed when the first servo loop is in an open state. Method. 5. The tracking offset correction method according to any one of claims 1 to 3, wherein the first offset is extracted from a tracking error signal of a portion of the disc where the tracking groove does not exist. Correction method. 6. The tracking offset correction method according to any one of claims 1 to 5, further comprising offset storage means for storing information on second offsets at a plurality of points in a radial direction of the disk, wherein the information is recorded / reproduced when the information is recorded / reproduced. A tracking offset correction method, characterized in that a new offset corresponding to the information of the second offset stored in the offset storage means is added to the second servo loop. 7. The tracking offset correction method according to claim 6, wherein the new offset is calculated from the inner offset calculation from the second offset information stored in the offset storage means and the track address at the time of recording / reproducing the information. A tracking offset correction method characterized by calculating.