JP2002015441A - Optical focus drive assembly and method for detecting fluctuation in focus sensitivity - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stable focus controller which decreases the fluctuations in focus control by the fluctuations in the sensitivity of an error signal and to manufacture a stable pickup free of the fluctuations in the sensitivity by providing a method for detecting the fluctuations in the sensitivity of the error signal of the pickup to be used. SOLUTION: This device has a focus gain regulating circuit 115 which detects the gain of the focus control system and regulates the gain of the focus control system so as to make this gain constant, a focus gain regulating value memory circuit 117 which saves the focus gain regulating value of the output of the focus gain regulating circuit when the balance value in focus error detection is changed at prescribed intervals and a focus gain regulating value switching circuit 118 which changes over the focus gain regulating value according to the output of the focus gain regulating circuit 114. The factors for the fluctuations in the focus control by the fluctuations in the focus error signal of the pickup to be used are decreased, by which the focus control is stabilized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk device for reproducing or recording optical information using a laser beam or the like, particularly to a focus control device, and to a method for detecting a focus characteristic of an optical pickup.

[0002]

2. Description of the Related Art In recent years, various techniques for reproducing or recording high-density information using a laser beam have been proposed, and are mainly put to practical use as optical discs. In order to accurately reproduce or record data from the tracks on these optical discs, it is necessary to correct the deviation of the laser beam from the recording surface due to the fluctuation of the surface of the optical disk and the rotation of the rotation axis of the turntable. Focus control is required to accurately follow the focal point of the laser beam on the surface.

In order to perform focus control, it is necessary to detect a focus error (focus error). As a method of detecting the focus error, there are an SSD, an astigmatism method, and the like. In some cases, an offset may occur in the detection of a focus error depending on the reproduction and recording positions in one disc due to the mutual influence of each layer. This offset causes defocusing of the laser beam on the recording surface, which causes deterioration in the quality of the reproduction / recording signal. Therefore,
In addition to disturbance factors such as runout of the rotation axis of the turntable,
By resetting the focus balance so as to cancel the offset in the detection of the focus error according to the radial position of the disk to be reproduced or recorded, it is possible to improve the quality of the reproduced / recorded signal.

[0004]

FIG. 4A shows an ideal focus error signal when a laser beam from a converging lens moves up and down at a constant speed across a focal point on a recording surface of a disk. Is shown. As shown in FIG. 4A, the focus error signal is linear with respect to the in-focus position,
There is no change in focus sensitivity, and focus control can be performed with a constant focus gain. Therefore, usually, the pickup is also designed so that the sensitivity of the focus error signal does not change in the focus direction across the in-focus position.

However, due to variations in the components of the pickup and variations in the manufacturing of the optical system, the focus error signal may not be linear as shown in FIG. In this case, as described above, when the focus balance is reset, the change in the slope of the linearity of the focus error signal before and after the in-focus position becomes a change in the detection sensitivity of the focus error signal, and the loop gain of the focus control is substantially reduced. Will fluctuate. When the gain of the focus control tends to decrease, the residual of the focus control increases.
It has become a subject to be sensitive to disturbance elements such as dust, thereby reducing control stability and increasing control noise.

The present invention has been made in view of the above problems, and provides a stable focus control apparatus which reduces fluctuations in focus control by a disk due to fluctuations in sensitivity of a focus error signal. Furthermore, a method for detecting a sensitivity variation of a focus error signal of a pickup to be used is provided,
It is also possible to manufacture a stable pickup without fluctuation in sensitivity of the focus error signal.

[0007]

In order to solve the above-mentioned problems, the invention according to claim 1 of the present invention is directed to a disk-shaped optical disk on which tracks are arranged spirally or concentrically. A focus error signal detecting means for detecting an error in a focus direction between a recording surface of the optical disc and a laser focus point, and a focus error signal detection signal. Focus balance adjusting means for adjusting the balance amount of the focus, focus control means for performing focus control of the pickup based on the focus error signal, and focus control for detecting the gain of the focus control system so that the focus gain becomes constant. A focus gain adjusting means for adjusting a gain of the means, and a focus balance value at a predetermined interval. Focus gain adjustment value storage means for storing a focus gain adjustment value of the output of the focus gain adjustment means when changed; and focus gain adjustment stored in the adjustment value storage means according to the output of the focus balance adjustment means. And a focus gain adjustment value switching means for switching the value. When the focus balance is reset and the defocus in one disc is absorbed, an optimum focus gain according to the focus balance set again is obtained. It has the effect of resetting and eliminating the focus gain variation due to the sensitivity variation of the focus error signal.

[0008] The invention described in claim 2 of the present invention provides:
In an apparatus for reproducing or recording information by condensing a laser beam with an objective lens on an optical disk in which tracks are arranged spirally or concentrically in a disk shape, a recording surface of the optical disk and a laser focus point Focus error signal detecting means for detecting an error in the focus direction, focus balance adjusting means for adjusting the balance amount of the focus error signal detection signal, and focus control means for performing focus control of the pickup based on the focus error signal. Focus gain detection means for detecting the gain of the focus control system; focus gain storage means for storing the focus gain value of the output of the focus gain detection means when the focus balance value is changed at predetermined intervals; The output of the focus gain detection means will be constant A focus gain adjusting means for adjusting the gain of the focus control means; and a focus gain switching means for switching the focus gain according to the output of the focus balance adjusting means for adjusting the balance amount of the focus error signal detection signal. When the focus balance is reset and the defocus in one disc is absorbed, the optimum focus gain according to the set focus balance is also reset, and the focus gain fluctuation due to the sensitivity variation of the focus error signal. Has the effect of eliminating.

Further, the invention according to claim 3 of the present invention provides:
It has interpolation means for interpolating a focus gain value measured at a focus balance value at a predetermined interval, and sets a focus gain according to the focus balance value. By using this interpolation means, a focus error signal is obtained. This has the effect of eliminating the focus gain variation due to the sensitivity variation of the above with higher accuracy.

[0010] Further, on a disk-shaped optical disk in which tracks are arranged spirally or concentrically, a pickup for focusing and reproducing or recording a laser beam by an objective lens is used, and a recording surface of the optical disk and a laser beam are recorded. An error between the focus point and the focus direction is detected, a balance amount of the focus error signal detection signal is adjusted, and a focus control of the pickup is performed based on the focus error signal.
The gain of the focus control unit is measured, the gain of the focus control unit is adjusted by the focus gain measurement unit, and the output of the focus gain detection unit when the focus balance value is changed at a predetermined interval is stored. By calculating the ratio of the focus gain value measured with the focus balance value at a predetermined interval and detecting the change in the sensitivity of the focus error signal, the magnitude of the change in the detection sensitivity of the focus error signal can be known. This has the effect that it is possible to select a factor that reduces the precision of the image.

[0011]

(Embodiment 1) FIG. 1 is a block diagram of an optical focus driving apparatus according to Embodiment 1 of the present invention. In FIG.
Numeral 02 is a disk motor for driving the optical disk 101 to rotate, and 103 is an optical pickup for emitting laser light to the optical disk 101 and detecting reflected light. Optical disk 10
1 is attached to a rotating shaft of the disk motor 102 and is rotated at a predetermined rotation speed.

The optical pickup 103 includes a converging lens 104 for converging laser light emitted from a light source (omitted) onto the optical disk 101, an actuator 105 for moving the converging lens 104 in a direction perpendicular to the optical disk 101, And a photodetector 106 for detecting the reflected light of the laser light radiated to the optical disc. 10
Reference numeral 7 denotes a focus error signal detection circuit, which includes variable amplifiers 108 and 109 and a subtractor 110, and detects a position error in the focus direction between the recording surface of the optical disc 101 and the laser focal point. The converging lens 104 is attached to a movable part of an actuator 105, and the actuator 105 includes a focusing coil (not shown) provided on the movable part and a permanent magnet (not shown) attached to a fixed part. The convergent lens 104 is formed by an electromagnetic force applied to the coil when a current flows through the coil.
Moves in a direction perpendicular to the surface of the optical disk 101.

Reference numeral 111 denotes a focus control circuit, which ensures that the converging point of the light beam irradiating the converging lens 104 onto the optical disk 101 in accordance with the focus error signal (FE) is always positioned on the recording surface. And phase control is performed to control the position. A focus drive circuit 112 drives the actuator 105, and an adder 113 adds an output from the photodetector 106. Reference numeral 114 denotes a focus balance adjustment circuit, and the variable amplifiers 108 and 1 are configured to maximize the amplitude of a reproduction signal generated from the output of the adder 113.
09 to adjust the balance of the focus error signal. A focus gain adjustment circuit 115 detects a focus control gain controlled by the focus control circuit 111 and adjusts the focus control gain to a constant gain. The focus gain adjustment circuit 115 injects the disturbance signal S into the focus loop via the adder 116 in the focus loop,
Focus error signal FE that is fed back once
The disturbance signal component injected from the detector is detected, the gain change of the injected disturbance signal S is measured, and an adjustment value for adjusting the focus gain to a constant gain is output. A focus gain adjustment value storage circuit 117 stores the gain adjustment value. A focus gain adjustment value switching circuit 118 multiplies the stored focus gain adjustment value by the multiplier 1 according to the focus balance value (FBAL) adjusted by the focus balance adjustment circuit 114.
Control is performed to switch to 19. Reference numeral 120 denotes a microprocessor including a focus balance adjustment circuit 114, a focus gain adjustment value storage circuit 117, and a focus gain switching circuit 118.

FIG. 2 is a flowchart showing the operation of the microprocessor 120. Further, the first embodiment of the present invention will be described in detail with reference to FIG. First, in step S201, a focus balance adjustment is performed, and an optimum focus balance value FBAL at an initial radial position of the pickup 103 with respect to the optical disc 101 is set.
(0) is held. This focus balance value is a value set for the variable amplifiers 108 and 109 so that the amplitude of the reproduced signal generated from the adder 113 is maximized.
In S202, the loop variable I is initialized to -2, and in S20
3 is the focus balance value FBAL obtained in S201
For (0), the FBAL value obtained by adding the predetermined FBAL step size α and the product of the loop variable is reset, and the process proceeds to step S20.
At 4, the focus gain FOG (-2) at the time of executing the focus gain adjustment at that time is held. afterwards,
At S205, the loop variable I is incremented, and at S20
At S6, it is determined whether the loop variable I has been set within 5 points in the present embodiment, and S203, S204, S2
05 at FBAL step size α, 5 types of FBAL (F
A focus gain adjustment value FOG (FOG (0-4)) corresponding to BAL (0-4) is detected and held. S20
7, the pickup 1 for the optical disc 101 is again
Optimal focus balance value FB at initial radius position of 03
AL (0) and focus gain adjustment value FOG (0) are output, and reproduction or recording of the optical disk is started.

The radial position at the time of reproduction or recording of the optical disk changes, and the pickup 10
When defocus occurs for the initial radius position of 3,
The optimal focus balance adjustment at that position is executed. At this time, in S208, the focus balance value FBA
When L is reset, in S209, in S204, the focus gain adjustment values FOG (-2), (-1), (0), (1), and the focus gain adjustment value FBAL for the FBAL in α-width increments are set in advance.
An optimum focus gain adjustment value is selected from the five types (2), and a focus gain adjustment value corresponding to the reset focus balance value is set. In S210, FBAL and FOG are kept until the reproduction or recording process is completed.
Is determined to continue the resetting process.

That is, when the focus balance value is changed as shown in FIG. 5, the focus error signal changes from a solid line to a reference voltage for focus control as shown by a dotted line. Therefore, in the present embodiment, five focus gain adjustment values that are vertically symmetric from the initial adjustment position are stored. Focus balance value FBAL obtained as a result of performing focus balance readjustment on focus gain adjustment values FOG (1) to (5) corresponding to stored focus balance values FBAL (1) to (5).
Retrieves the FBAL closest to the values of FBAL (1) to (5) stored in advance, and calculates the focus gain adjustment value F corresponding to the retrieved focus balance value FBAL.
Switch to OG.

Although the physical characteristics of each optical disc are specified by the standard, there are actually manufacturing variations, and the optimum focus balance value (FBAL) at the radial position where reproduction is started is adjusted and set. However, depending on the combination of the fluctuation of the base material thickness of the disc at a radial position distant from the start of the reproduction and the optical characteristics of the pickup, the focus balance value initially set is not always the optimum correction value. Therefore, when the focus balance is readjusted to absorb the deviation of the focus balance during reproduction or recording of one disc, there is a non-linearity of the focus error signal as shown in FIG. Even if the focus sensitivity changes according to the change in the value and the actual focus system gain changes, as described in detail in the present embodiment, the optimal focus detected in advance according to the new focus balance value is changed. By switching to a gain value, it is possible to perform optimal focus control with respect to variations in the disc and variations in the characteristics of the optical pick.

FIG. 3 is a flowchart showing a detailed operation in the case where interpolation processing is performed in S209. S3
01, the initial value of the loop variable is set to I = 1, and S30
In steps 2, 3, and 4, the FBAL after readjustment is compared in magnitude with the preset FBAL (1) to (4), and a search is performed to find which area of the five-point focus balance corresponds. From the search result, linear interpolation is performed in S305 to calculate a focus gain adjustment value FOG suitable for the FBAL after readjustment, and outputs the result to the multiplier 119. By this interpolation processing, a more accurate focus gain adjustment value can be set for the five discrete focus balance values.

In the present embodiment, the case where the focus balance value is set to 5 points has been described. However, there is a limitation on setting the focus balance value to a plurality of points other than 5 points according to the defocus amount, the accuracy of the focus gain, and the like. And it is not limited to five points.

(Embodiment 2) Next, Embodiment 2 of the present invention will be described. FIG. 7 is a block diagram of the second embodiment.

In FIG. 7, the same components as those in FIG. 1 are denoted by the same reference numerals, and description thereof is omitted.
A focus gain detection circuit 701 detects a focus control gain controlled by the focus control circuit. The focus gain detection circuit 701 transmits a disturbance signal S into the focus loop via the adder 116 to the focus loop. The injected disturbance signal component is detected from the focus error signal FE that has been injected and fed back in a loop, and the gain change of the injected disturbance signal S is measured. 7
Reference numeral 02 denotes a focus gain storage circuit that stores the detected gain value. A focus gain adjustment value switching circuit 703 calculates a gain adjustment value for keeping the focus gain constant from the stored focus gain values according to the focus balance value (FBAL) adjusted by the focus balance adjustment circuit 114. And the multiplier 11
9 is output. Reference numeral 704 denotes a microprocessor, which forms the focus balance adjustment circuit 114, the focus gain storage circuit 702, and the focus gain adjustment value switching circuit 703.

The difference between the second embodiment and the first embodiment is that after the focus gain is detected by the focus gain detection circuit 701, the loop gain of the focus system becomes constant via the focus gain storage circuit 702. The configuration is such that a focus gain adjustment value representing a ratio to a predetermined reference gain is calculated and output by a focus gain adjustment value switching circuit 703, and the other configuration is the same as that of the first embodiment. Therefore, there is no significant difference in the target operation itself, and the optimum focus detected in advance according to the new focus balance value that has been readjusted to absorb the focus balance deviation during reproduction or recording of one disc. By switching to the gain value, there is nonlinearity of the focus error signal, and the focus sensitivity changes according to the change of the focus balance value,
Even if the actual focus system gain changes, optimum focus control can be performed with respect to variations in the disc and fluctuations in the characteristics of the optical pick.

Third Embodiment A third embodiment of the present invention will be described. FIG. 8 is a block diagram of the third embodiment. 8, the same components as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.
Reference numeral 800 denotes a microcomputer, which is the focus control circuit 111, the focus balance adjustment circuit 114, and the focus gain adjustment circuit 11 of FIG.
5, a configuration including a focus gain adjustment value storage circuit 117, a focus gain adjustment value switching circuit 118, an adder 116, and a multiplier 119 is also possible. It is sufficiently possible to adopt a configuration in which the above-described focus balance and focus gain calculation is performed simultaneously with the control. Embodiments 1 and 2 of the present invention are also possible.
However, the present invention is not limited to the configuration described above.

As described with reference to the flowchart of FIG. 2, the present invention detects a focus gain adjustment value corresponding to a change in focus balance. By calculating the ratio of the focus gain adjustment values at this time, it is possible to detect the inclination of the focus error signal near the in-focus position, that is, the change in sensitivity in actual operation. By introducing this method into a pickup manufacturing process or the like and providing a predetermined threshold value for the change in sensitivity, it is possible to select and exclude pickups with extremely large change in sensitivity.

[0025]

As described above, according to the present invention, the focus control residual due to the fluctuation of the sensitivity of the focus error signal of the pickup used increases, the control stability against disturbance elements such as scratches and dust is reduced, and the control noise is reduced. Instability factors such as an increase in the number of images can be reduced, and stable focus control can be performed.

Also, by measuring the focus gain in advance, when the focus balance is readjusted during reproduction or recording, no time is required for readjustment of the focus gain, and there is no restriction on the data reproduction and recording operations of the optical disk. The advantageous effect described above can be obtained.

Further, in the manufacturing process of the pickup, by using the focus sensitivity variation method of the present invention, it is possible to easily select only a pickup having a small focus sensitivity variation as a non-defective product in an inspection process suitable for actual operation. Is obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram of an optical focus driving device according to a first embodiment of the present invention.

FIG. 2 is a flowchart showing an operation of the microprocessor 120;

FIG. 3 is a flowchart showing a detailed operation when interpolation processing is used for S209 in the flowchart of FIG. 2;

FIG. 4A shows an ideal focus error signal when a laser beam from a converging lens moves up and down at a constant speed across a focal point on a recording surface of a disk; Diagram showing a non-linear focus error signal when the laser beam from above moves up and down at a constant speed across the focal point on the recording surface of the disk

FIG. 5 is a diagram showing the movement of a focus error signal due to focus balance adjustment.

FIG. 6 is a diagram showing a correspondence of a focus gain adjustment value to five focus balance values.

FIG. 7 is a block diagram of an optical focus driving device according to a second embodiment of the present invention.

FIG. 8 is a block diagram for realizing a focus sensitivity fluctuation detection method according to a third embodiment of the present invention;

[Explanation of symbols]

 Reference Signs List 101 optical disk 102 disk motor 103 optical pickup 104 converging lens 105 actuator 106 photodetector 107 focus error signal detection circuit 111 focus control circuit 112 focus drive circuit 114 focus balance adjustment circuit 115 focus gain adjustment circuit 117 focus gain adjustment value storage circuit 118 focus Gain adjustment value switching circuit 120, 704, 800 Microprocessor 701 Focus gain detection circuit 702 Focus gain storage circuit 703 Focus gain adjustment value switching circuit

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5D118 AA15 BA01 BF02 BF03 CA02 CB01 CD02 5D119 AA38 BA01 DA01 DA05 EA03 PA05

Claims (4)

[Claims] 1. An apparatus for reproducing or recording information by condensing a laser beam with an objective lens on an optical disk having a disk shape and tracks arranged spirally or concentrically, wherein the recording surface of the optical disk is Focus error signal detection means for detecting an error in the focus direction with respect to the focal point, focus balance adjustment means for adjusting the balance amount of the focus error signal detection signal, and focus control of the pickup based on the focus error signal. Focus control means for performing, a gain control means for detecting the gain of the focus control system, and adjusting the gain of the focus control means so that the focus gain becomes constant; and when the focus balance value is changed at predetermined intervals. Focus gain adjustment value of the output of the focus gain adjustment means And a focus gain adjustment value switching means for switching the focus gain adjustment value stored in the adjustment value storage means according to the output of the focus balance adjustment means. Optical focus drive. 2. An apparatus for reproducing or recording information by converging a laser beam with an objective lens on an optical disk in which tracks are arranged spirally or concentrically in a disk shape, wherein the recording surface of the optical disk is Focus error signal detection means for detecting an error in the focus direction with respect to the focal point, focus balance adjustment means for adjusting the balance amount of the focus error signal detection signal, and focus control of the pickup based on the focus error signal. Focus control means for performing, a focus gain detection means for detecting a gain of the focus control system, and a focus gain for storing a focus gain value of an output of the focus gain detection means when a focus balance value is changed at predetermined intervals. The output of the storage means and the focus gain detection means Focus gain adjustment means for adjusting the gain of the focus control means so as to be constant; and focus gain switching means for switching the focus gain according to the output of the focus balance adjustment means for adjusting the balance amount of the focus error signal detection signal. An optical focus drive device comprising: 3. Interpolation means for interpolating a focus gain value or a focus gain adjustment value detected at the focus balance value at the predetermined interval, and interpolating and setting a focus gain value according to the focus balance value. The optical focus driving device according to claim 1 or 2, wherein 4. A disk-shaped optical disk having tracks spirally or concentrically arranged on an optical disk, using a pickup for condensing a laser beam by an objective lens and reproducing or recording the laser light, and using a pickup surface of the optical disk and a laser. An error between the focus point and the focus direction is detected, the balance amount of the focus error signal detection signal is adjusted, the focus of the pickup is controlled based on the focus error signal, the focus gain is measured, and the focus gain is measured. A focus sensitivity fluctuation detection method that adjusts the gain so as to have a constant gain, calculates a focus gain ratio measured at a focus balance value at each of the predetermined intervals, and detects a change in sensitivity of a focus error signal.