JP2005339635A - Focus control method in optical disk device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reasonably solve the problem, wherein an objective lens collides against a disk or the objective lens cannot reach the focusing point when curvature or a surface wobble exists in the optical disk, in an optical disk device. <P>SOLUTION: The focus search operation is executed when the optical disk is set. After the position of the focusing point of the objective lens is obtained at the innermost circumferential position, the focus servo condition at a low degree of quick response is set. The positions of the focusing points of the objective lens at a plurality of locations are obtained by oscillating the objective lens with respect to the up and down directions, in the process for moving the optical pickup in the radius direction of the optical disk, and the radius information and the focusing point positional information are saved in a memory. After the completion of the focus search operation, the discrete information in the memory is processed with interpolation, and the upper limit position of the objective lens is set, on the basis of the focusing point positional information processed with the interpolation. The focus servo is executed for the optical disk, with the condition of the upper limit condition for following the warpage or the surface wobble. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a focus control method in an optical disc apparatus, and more particularly to a focus control method characterized by a focus search operation that is executed to prevent an objective lens and an optical disc from colliding with each other due to warpage or surface wobbling of the optical disc.

In general, in an optical disc apparatus, focus servo is executed to record / reproduce information with respect to the optical disc. As a pre-processing for pulling in the focus servo, the objective lens of the optical pickup is in a direction orthogonal to the disc surface ( An operation (focus search) for searching for the focal position (in-focus point) of the objective lens by moving in the focus direction) is executed.
In optical disk devices, the distance from the neutral position of the objective lens to the focal point often varies depending on the warp or surface blur of the optical disk, the mounting accuracy of the lens actuator or disk motor, etc. This is because stable servo control cannot be performed unless the focus servo is pulled in after obtaining the actual in-focus position by largely moving in the focus direction.
In addition, the movement of the objective lens in the focus search is executed several times. This is because the output level of the focus error signal obtained during the focus search is a slight change in the reflectivity of the disk and the laser power. Further, it also varies with temperature changes.
With regard to the control device related to the focus search operation, many proposals have been made in relation to various problems in the following patent documents and the like.

Here, the focus search operation will be described with reference to FIG.
This figure is a graph showing the positional relationship between the disk surface and the tip of the objective lens during the focus search operation, and the trajectory of the objective lens shows an example in which a focal point for a low-density optical disk is obtained.
When the focus search operation is started, the objective lens approaches the disk surface from a neutral position far away from the disk surface, passes through the focal point for the low-density optical disk, and further approaches the disk surface. Is reversed from the surface of the disk, but in the meantime, the disk surface is irradiated with laser light through the objective lens and reflected by the disk surface, and the reflected light is detected by the photodetector and the focus error signal continues. Has been obtained.
Therefore, it can be confirmed from the focus error signal that the tip of the objective lens has passed the focal point for the low-density optical disc, and thereafter, focus servo is executed with reference to the focal point position.
Since the distance between the disc and the objective lens is large in the conventional low density optical disc, it is only necessary to move the objective lens up and down with a fixed width during the focus search operation.

By the way, the light spot formed on the information recording surface of the optical disc is determined by the NA (Numerical Aperture) of the objective lens and the wavelength of the laser beam, and the size of the light spot is proportional to (wavelength / NA). In order to increase the density of the optical disk, it is necessary to employ a laser beam having a short wavelength or increase the NA in order to obtain a minute light spot.
In addition, in order to reduce the influence of the tilt of the disc surface with respect to the optical axis of the objective lens, in the high-density optical disc, the thickness from the light incident surface to the information recording surface is reduced, and accordingly, from the tip of the objective lens. The working distance (WD), which is the distance to the disk surface, is also shortened.
For example, a DVD (Digital Versatile Disc) using a laser beam having a wavelength of 630 nm or 650 nm and using an objective lens having an NA of 0.6 has a WD of 1 mm or more, but employs a laser beam having a wavelength of 405 nm and has an NA of 0.3. When the 85 objective lens is used, the WD becomes very small, and when the NA is realized with two lenses, the WD is about 100 μm and when the NA is realized with two lenses, the WD becomes about 300 μm.
Therefore, when the fixed-width focus search is applied to a high-density optical disc, there is a high possibility that the objective lens and the optical disc collide on the outer peripheral side where the influence of warpage or surface blurring of the optical disc appears remarkably.

For this problem, the applicant of the present application has proposed the following focus control device in Japanese Patent Application No. 2003-062442.
The content of the proposal was set so that the objective lens would not collide with the optical disc in the direction in which the objective lens crossed the focal location and approached the recording surface of the optical disc, with the focus error signal at the in-focus location as a reference value. A focus error signal is set to the first threshold value, and the focus error signal is set so that the objective lens is in a direction away from the recording surface of the optical disc beyond the focal position and the objective lens is not too far from the optical disc. Two threshold values are set, and focus control is executed so that the focus error signal always falls between the first threshold value and the second threshold value, thereby preventing the objective lens from colliding with the optical disk.

JP-A-10-55546 JP-A-6-103584

In the case of the focus control device disclosed in Japanese Patent Application No. 2003-062442, the guard voltage (corresponding to the first threshold value) is set to prevent the objective lens from moving to the optical disc side beyond a certain level. However, there is a certain range for the setting level of the guard voltage, and a problem arises if it is too high or too low.
First, if the guard voltage is set high, the objective lens can reach the focal point even if the optical disc is warped or shaken, but if the focus error cannot be detected, the objective lens and the disc may collide. There is sex.
Here, as a case where the focus error cannot be detected, there are a case where light is not emitted due to a failure of the laser light source, a case where the amplitude of the focus error signal is lower than a threshold for signal detection, and the like. In the case of a high-density optical disk, as shown in FIG. 4, the time width of the S-shaped curve characteristic in the time axis direction of the focus error signal near the focal point tends to be difficult to detect.
On the other hand, if the guard voltage is set low, the possibility of collision between the objective lens and the optical disk can be eliminated even when a focus error cannot be detected. In some cases, the focal point may exceed the upper limit position by the guard voltage, and the objective lens cannot reach the focal point.

As described above, even when the focus servo based on the in-focus position set by the focus search or the focus servo using two thresholds according to Japanese Patent Application No. 2003-062442 is used, the objective lens is used when the optical disk is warped or shakes. And the possibility that the optical disc will collide cannot be eliminated.
Accordingly, the present invention provides a focus control that solves the above-described problems by setting a movement restriction range of the objective lens toward the optical disk side based on in-focus positions obtained at a plurality of radial positions of the optical disk in the focus search operation. It was created for the purpose of providing a method.

  The present invention relates to the objective lens for the optical disc by moving the objective lens with a constant amplitude in a direction perpendicular to the optical disc in a state in which laser light is irradiated onto the recording surface of the optical disc through the objective lens. After performing a focus search operation for obtaining the in-focus position, and setting a limit value for limiting the approach distance of the objective lens to the optical disk based on the in-focus position, a focus servo within a range not exceeding the limit value In the focus control method in the optical disc apparatus for executing the above, the focus search operation is performed by moving the optical pickup equipped with the objective lens to the innermost peripheral position of the optical disc, and the alignment of the objective lens obtained by the focus search operation is performed. Corresponding focus position information to the position information of the optical pickup The optical pickup is stored in the storage means and the radius of the optical disc is set in a state where focus servo with low speed response is applied with the in-focus position of the objective lens obtained in the first procedure as an initial position. The focus search operation is continuously performed while moving in the direction, and the focal point position of the objective lens at a plurality of positions in the radial direction is obtained and stored in the storage unit, and stored in the storage unit Based on the information, a third procedure for interpolating the in-focus position information of the objective lens between the positions of the optical pickup and storing the interpolation information in the storage means; and a third procedure in the storage means The limit value in the radial direction of the optical disc using the position information of the optical pickup after interpolation and the in-focus position information of the objective lens And a fourth procedure for storing each limit value in the storage means in association with each position information of the optical pickup, and thereafter, corresponding to each position information of the optical pickup in the storage means and the fourth procedure. Further, the present invention relates to a focus control method in an optical disc apparatus, wherein focus servo is executed while limiting an approach distance of the objective lens to the optical disc based on each limit value.

In the first procedure and the second procedure of the present invention, the in-focus position of the objective lens at the innermost peripheral position of the optical disk is obtained, and the optical pickup is set in the state where the focus servo with low speed response is applied with the initial position as the initial position. The focus search operation is continuously performed while moving in the radial direction of the optical disc, and the in-focus positions of the objective lens at a plurality of positions in the radial direction of the optical disc are obtained.
In this case, since it can be considered that there is no warping or surface blurring of the optical disk at the innermost circumferential position of the optical disk, the range of the focal point position of the objective lens can be predicted, and the range of the objective lens in the focus search operation can be set in advance. .
And since it is a focus servo with low speed response, the objective lens that follows the warp and surface shake of the optical disk without affecting the focus search operation, with the in-focus position of the objective lens obtained at the innermost circumference position as the initial value The in-focus position can be obtained.
Since the position information of the optical pickup and the in-focus position information of the objective lens obtained in the second procedure are discrete information, the third procedure is interpolated to form continuous information over the radial direction of the optical disc. In the fourth procedure, each limit value in the radial direction is set based on the information after the interpolation process.
Therefore, as described above, since the focal point position of the objective lens is obtained by following the warp and surface blurring in the radial direction of the optical disk, each focal point position set between each focal point position and the recording surface of the optical disk is determined. The limit value can also be given in the same following relationship, as in the case of the method of Japanese Patent Application No. 2003-062442, the state where the objective lens and the disk collide when the focus error cannot be detected, There is no situation in which the objective lens cannot reach the focal point because the warp or surface blur of the optical disk is large.

  According to the focus control method in the optical disc apparatus of the present invention, the limit value for limiting the approach distance of the objective lens to the optical disc can be set by following the warp or surface blur of the optical disc by the focus search operation, and is pulled into the focus servo. After that, it is possible to eliminate the problem that the objective lens collides with the optical disc or cannot reach the focal point with respect to the optical disc.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
First, FIG. 1 is a block circuit diagram relating to a disk rotation drive portion, an optical pickup portion, and a servo control portion in an optical disk apparatus, wherein 1 is an optical disk, 2 is a spindle motor, 3 is an optical pickup (PU), and 4 is a servo circuit. Show.

  Here, the optical pickup 3 includes an objective lens 3 a and an optical system (not shown) such as a polarizing prism and a photodetector (not shown). The objective lens 3 a is mounted on the optical disc 1 by a focusing actuator 31. The entire optical pickup 3 is moved in the radial direction of the optical disk 1 by the coarse movement actuator 32 and the tracking actuator 33.

For the focus servo system, a signal obtained by the photodetector of the optical pickup 3 is output to the focus error detection circuit 5, and the focus error detection circuit 5 generates a focus error signal, and the focus error signal is A / D converted. The signal is converted into a digital signal by the device 6 and input to the focus control unit 41 of the servo circuit 4.
The focus control unit 41 outputs a focus servo signal based on the focus error signal, and the focus servo signal is input to the actuator driver 8 via the D / A converter 7, and the actuator driver 8 drives the focusing actuator 31. Then, the focusing operation of the objective lens 3a is executed.

  For the coarse movement servo system of the optical pickup 3, the coarse movement control unit 42 of the servo circuit 4 outputs a coarse movement servo signal based on an instruction input signal from the system control system, and the coarse movement servo signal is D / A converted. Is input to the actuator driver 10 through the device 9, and the actuator driver 10 drives the coarse movement actuator 32 to coarsely move the entire optical pickup 3 in the radial direction of the optical disk 1, but the PU position detection constituted by a linear encoder or the like The position signal of the optical pickup 3 by the device 11 is input to the coarse motion control unit 42 of the servo circuit 4, and the coarse motion control unit 42 executes the coarse motion control based on the position information.

For the tracking servo system of the optical pickup 3, the tracking error detection circuit 12 generates a tracking error signal from the signal obtained by the optical detector of the optical pickup 3, and is converted into a digital signal by the A / D converter 13. Are input to the servo circuit 4, and the tracking servo signal output from the servo circuit 4 is input from the D / A converter 14 to the actuator driver 15. The actuator driver 15 drives the tracking actuator 33 and the optical pickup 3. Tracking servo for is executed.
However, since the tracking system is not related to the subject of this embodiment and is not directly related to the spindle system for executing the rotation control of the spindle motor 2, the servo circuit in FIG. The circuit configuration of those systems in 4 is omitted.

In the configuration of the optical disc apparatus described above, the feature of this embodiment is that the focus search mode is set prior to the recording / reproducing operation of the optical disc, and the in-focus position of the objective lens 3a and the in-focus position thereof in the radial direction of the optical disc. The upper limit position of the objective lens 3a following the above is obtained, and the upper limit position of the objective lens is limited at each position in the radial direction of the optical disk based on the upper limit position information.
For this purpose, the servo circuit 4 is provided with a memory 43 for storing each radial position of the optical disc 1 and the in-focus position and upper limit position of the objective lens 3a at each position, and is obtained in the focus search mode. A data processing unit 44 is provided for interpolating the obtained discrete information and obtaining the upper limit position of the objective lens 3a using the interpolated data.

Next, the execution procedure of the focus search mode and focus servo by this optical disc apparatus will be described with reference to the flowchart of FIG.
First, when the optical disc 1 is set, the spindle motor 2 is started and the focus search mode is set (S1).
In the focus search mode, first, the optical pickup 3 is moved to the innermost circumferential position in the radial direction of the optical disc 1, and the objective lens 3a is kept constant by changing the ramp voltage with respect to the actuator 31 in the vicinity of the focal position with respect to the optical disc 1. Is moved up and down with the amplitude of, and the actual focal position is obtained (S3, S4).
That is, the coarse motion control unit 42 controls the actuator 32 to move the optical pickup 3 to the innermost peripheral position, and the focus control unit 41 controls the actuator 31 to move the objective lens 3a in the vertical direction. Thus, the in-focus position is obtained based on the error signal detected by the focus error detector 5.
Further, the position information indicating the innermost peripheral position and the in-focus position information of the objective lens 3a are saved in the memory 43 (S5).
Incidentally, since the vicinity of the innermost circumference of the optical disk is generally less warped or deviated, the in-focus position of the objective lens 3a falls within a small error range, and the range in which the objective lens 3a is initially oscillated (the level at which the ramp voltage is changed). (Amplitude) can be set in advance.

Next, the focus control unit 41 sets a focus servo condition with low speed response as a control condition peculiar to the focus search mode (S6).
Then, the coarse motion control unit 42 moves the optical pickup 3 to the outside in the radial direction of the optical disc 1, and in this state, the focus control unit 41 controls the actuator 31 to reciprocate the objective lens 3a up and down with a constant amplitude. (S7, S8).
In this case, the initial level related to the reciprocation of the objective lens 3a is set to the vicinity of the in-focus position obtained in step S4.
Further, the speed response of the focus servo condition is a response characteristic sufficiently longer than the reciprocation period of the objective lens 3a, and the reciprocation of the objective lens 3a is hardly affected by the servo operation due to the low speed response. Thus, the center level of the reciprocating movement can be changed by following the change of the in-focus position of the objective lens 3a in the radial direction of the optical pickup 3.

In the above operating state, when the optical pickup 3 moves to the position of the radius: R0 + ΔR * i of the optical disc 1, the focus control unit 41 focuses on the objective lens 3a based on the focus error signal obtained from the focus error detection circuit 5. The position is obtained (S9, S10). However, R0 indicates the position information of the optical pickup 1 corresponding to the innermost peripheral position of the optical disk 1, ΔR indicates the interval in the radial direction of the optical disk 1 when the in-focus position of the objective lens 3a is obtained in the focus search mode, The in-focus position is obtained discretely for each ΔR.
The coarse motion control unit 42 performs movement control of the optical pickup 3 while obtaining the radial position information from the PU position detector 11, and confirms the position information of the optical pickup 3 at that time.
Then, in-focus position information of the objective lens 3a obtained in step S10 corresponding to the position information in the radial direction is saved in the memory 43 (S11).

  Thereafter, in this focus search mode, the procedure from step S8 to step S12 is repeated until the optical pickup 3 reaches the outermost peripheral position of the optical disc 1, and the focal point of the objective lens 3a is focused at intervals of ΔR in the radial direction of the optical disc 1. The position information and the position information in the radial direction of the optical pickup 1 are saved in the memory 43, and the focus search mode is canceled when the optical pickup 3 reaches the outermost peripheral position (S12, S13 → S8 to S11, S12 → S14).

At the stage when the focus search mode is released, the in-focus position information of the objective lens 3a and the radial position information of the optical pickup 1 are saved in the memory 43 as discrete information.
Therefore, in this embodiment, the data processor 44 interpolates the information in the memory 43 obtained at intervals of ΔR (S15).
This process is a process of interpolating in-focus position information between the radius: R0 + ΔR * i and the radius: R0 + ΔR * (i + 1) using the in-focus position information obtained at these radii. Approximate interpolation using the following function is possible.
For these interpolation functions, a method of using properly depending on the magnitude of ΔR, or a method of using properly depending on whether it is closer to the inner periphery or closer to the outer periphery may be applied.
Note that when ΔR is set large, the time required for the focus search mode can be shortened, but the accuracy of the in-focus position information by interpolation is reduced, and conversely, when ΔR is set small, the focus is reduced. Although the time required for the search mode becomes longer, the accuracy of the in-focus position information by interpolation becomes higher.

When the interpolation process is completed, the data processing unit 44, based on the radial direction information of the optical disc 1 after the interpolation process and the in-focus position information of the objective lens 3a, the upper limit position of the objective lens 3a corresponding to each radial direction position information. And the upper limit position information is saved in the memory 43 (S16).
Specifically, as shown in FIG. 3, when the information recording surface of the optical disc 1 is warped or shaken, the focal point position information of the objective lens 3a after the interpolation processing is shown in the one-dot chain line. 1 is obtained as information that substantially follows the change in the information recording surface, and therefore, as indicated by a broken line, a position that is closer to the information recording surface side of the optical disc 1 than the focal point position of the objective lens 3a by a certain distance If it is set as the upper limit position of the objective lens 3a, reasonable upper limit position information that follows the warp or surface wobbling of the optical disc 1 can be obtained.

Then, after the upper limit position of the objective lens 3a is obtained by the data processing unit 44 as described above, the objective lens 3a is pulled to the original focus servo, but the objective lens 3a is moved to the upper limit position or more at each radial position of the optical disc 1. The focus servo is executed by setting a guard voltage that gives a limiting condition of not (S17, S18).
In this case, as shown in FIG. 3, since the upper limit position of the objective lens 3a substantially follows the change in the information recording surface of the optical disc 1, the objective lens is not subject to the optical disc even if the optical disc 1 is warped or shakes. And the objective lens cannot be moved to the focal point with respect to the optical disc.

In the embodiment, in steps S9 and S10, the focal point position of the objective lens 3a is obtained when the optical pickup 3 is moved and reaches a predetermined radial position: R0 + ΔR * i. An average value of in-focus positions obtained in a fixed section before and after the position may be obtained and saved in the memory 43.
When the optical pickup 3 reaches the radial position: R0 + ΔR * i, the optical pickup 3 is temporarily stopped, and the objective lens 3a is reciprocated a plurality of times at that position to obtain a plurality of in-focus positions, and an average value thereof is obtained and saved in the memory 43. You may let them.

  The present invention provides an effective method for setting an approach limit position of an objective lens with respect to an optical disk in a rational procedure in an optical disk apparatus so that proper focus servo is always performed even if the optical disk is warped or shakes. provide.

1 is a block circuit diagram showing main components of an optical disc apparatus according to an embodiment of the present invention. 6 is a flowchart illustrating an operation procedure of the optical disc apparatus according to the embodiment. It is a schematic diagram which shows the relationship between the information recording surface of an optical disk, the focus position of an objective lens, and the upper limit position of an objective lens. It is a graph for demonstrating the focus search operation | movement in a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Optical disk, 2 ... Spindle motor, 3 ... Optical pick-up, 3a ... Objective lens, 4 ... Servo circuit, 5 ... Focus error detection circuit, 6, 13 ... A / D converter, 7, 9, 14 ... D / A Converter, 8, 10, 15 ... driver, 11 ... PU position detector, 12 ... tracking error detection circuit, 31 ... focusing actuator, 32 ... coarse actuator, 33 ... tracking actuator 33, 41 ... focus control unit, 42 ... Coarse motion control unit, 43 ... Memory, 44 ... Data processing unit.

Claims (1)

By moving the objective lens with a constant amplitude in a direction perpendicular to the optical disc while irradiating the recording surface of the optical disc with the laser beam through the objective lens, the focal point position of the objective lens with respect to the optical disc An optical disc that performs a focus search operation within a range that does not exceed the limit value after performing a focus search operation for obtaining the limit value and setting a limit value for limiting the approach distance of the objective lens to the optical disc based on the in-focus position In the focus control method in the apparatus,
The optical pickup equipped with the objective lens is moved to the innermost peripheral position of the optical disc to perform the focus search operation, and the in-focus position information of the objective lens obtained by the focus search operation is used as the position information of the optical pickup. A first procedure correspondingly stored in the storage means;
The focus search operation is continued while moving the optical pickup in the radial direction of the optical disc in a state where focus servo with low speed response is applied with the in-focus position of the objective lens obtained in the first procedure as an initial position. Performing a second step, obtaining a focal point position of the objective lens at a plurality of positions in the radial direction and storing it in the storage means;
A third procedure for interpolating in-focus position information of the objective lens between the positions of the optical pickup based on the information stored in the storage means, and storing the interpolation information in the storage means;
The limit value is set in the radial direction of the optical disc using the position information of the optical pickup after being interpolated in the third procedure in the storage means and the in-focus position information of the objective lens, and each limit value is set. And a fourth procedure for storing in the storage means corresponding to each position information of the optical pickup,
Thereafter, based on each position information of the optical pickup of the storage means and each limit value associated therewith, focus servo is executed while limiting the approach distance of the objective lens to the optical disk. Focus control method in apparatus.

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