JP2002092914A - Method for automatically adjusting servo of optical disk drive - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably control a servo or the like even in a pickup whose characteristics deteriorate when its lens is shifted in a tracking direction. SOLUTION: In the automatic adjustment of the optical disk drive, the adjustment is performed after shifting the objective lens of the optical pickup in the tracking direction, and then adjustment values are stored (Step S2). The measurement of sigmoid characteristic of a focus is included in the adjustment. A servo operation or the like in the optical pickup is controlled by using these adjustment values.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk drive, and more particularly, to an automatic adjustment performed when an optical disk is inserted into the apparatus.

[0002]

2. Description of the Related Art To accurately and stably operate an optical disk drive, it is very important to adjust the offset and balance of various signals such as a tracking error signal and a focus error signal. To make various adjustments accurately,
It is necessary to accurately supplement the characteristics of the pickup used.

In the conventional optical disk drive, the average level and amplitude of the reflected light beam greatly change depending on the use environment temperature and the disk (media) used, and the optimum point such as focus changes accordingly.
Therefore, the position of the objective lens and the signal amplifier are adjusted to the optimum points by automatic adjustment performed when the optical disk is inserted into the apparatus. However, this adjustment is performed without moving the lens in the tracking direction, that is, at a neutral position in the tracking direction. No consideration is given to characteristics when the lens is moved in the tracking direction, that is, when the lens is shifted. That is, on the assumption that the characteristics do not change even when the lens is shifted, the conventional adjustment method performs the automatic adjustment without shifting the objective lens of the optical pickup.

[0004]

The characteristics of some optical pickups change significantly when the lens is shifted in the tracking direction. Originally, a pickup whose characteristics change due to a lens shift should be regarded as a defective product, but must be actively used due to restrictions on development time and cost.

For example, it has been actually confirmed that there is a pickup in which the symmetry of the S-shaped characteristic of the focus deteriorates when the lens is shifted. When the lens is gradually brought closer to the optical disk, the amplitude of the focus error signal becomes S
It changes like a letter. The S-shaped focus specification indicates the amplitude change characteristic of the focus error signal.

In the case of such a pickup in which the S-shaped characteristic changes due to the lens shift, the range in which the focus servo operation can be performed at the time of access changes, and the servo deviates, making it difficult to control.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an automatic adjustment method in which a servo or the like can be stably controlled even in a pickup in which various characteristics are degraded when a lens is shifted in a pickup of an optical disk drive. .

[0008]

The servo can be prevented from coming off if the change of the S-shaped characteristic when the lens is shifted is grasped in advance and controlled so that the servo can follow the change.

That is, the servo automatic adjustment method of the present invention
At the time of automatic adjustment performed when the optical disk is inserted into the device, performing adjustment by shifting the objective lens of the optical pickup in the tracking direction, and storing the adjustment value,
Controlling the optical pickup using the stored adjustment value. Further, the adjustment includes measurement of the S-shaped characteristic of the focus.

[0010] By grasping the lens shift characteristics of the optical pickup at the time of adjustment, it is possible to optimize the servo and the equalizer so that a pickup head having poor lens shift characteristics can be used effectively.

[0011]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a block diagram showing a configuration of an optical disk apparatus to which the present invention is applied. The optical disk 1 is rotated by a motor 3 at a constant linear velocity, for example. Recording and reproduction of information on and from the optical disc 1 are performed by an optical pickup 5.
Done by The optical pickup 5 is fixed to a drive coil 7 constituting a movable part of a linear motor 6,
This drive coil 7 is controlled by a linear motor control circuit 8.

The linear motor control circuit 8 includes a speed detection circuit 9
The speed signal of the optical pickup 5 detected by the speed detection circuit 9 is sent to the linear motor control circuit 8. A permanent magnet (not shown) is provided at a fixed portion of the linear motor 6. When the drive coil 7 is excited by the linear motor control circuit 8, the optical pickup 5 is moved in the radial direction of the optical disc 1.

The optical pickup 5 is provided with an objective lens 10 supported by a wire or a leaf spring (not shown). The objective lens 10 can be moved in the focusing direction (the direction of the optical axis of the lens) by driving the drive coil 12, and can be moved in the tracking direction (the direction orthogonal to the optical axis of the lens) by driving the drive coil 11. Is possible.

A light beam is emitted from the semiconductor laser oscillator 9 by drive control of the laser control circuit 13. The light beam emitted from the semiconductor laser oscillator 19 is irradiated on the optical disc 1 via the collimator lens 20, the half prism 21, and the objective lens 10. The reflected light from the optical disc 1 is guided to a photodetector 24 via an objective lens 10, a half prism 21, a condenser lens 22, and a cylindrical lens 23.

The photodetector 24 includes a four-divided photodetector cell 24.
a, 24b, 24c and 24d. The output signal of the photodetector cell 24a is supplied to one end of an adder 26a via a current / voltage conversion amplifier 25a. The output signal of the light detection cell 24b is supplied to one end of an adder 26b via an amplifier 25b. The output signal of the light detection cell 24c is supplied to the other end of the adder 26a via the amplifier 25c. The output signal of the light detection cell 24d is
It is supplied to the other end of the adder 26b via d.

Further, the output signal of the light detection cell 24a is:
The signal is supplied to one end of the adder 26c via the amplifier 25a. The output signal of the light detection cell 24b is supplied to one end of an adder 26d via an amplifier 25b. Photodetection cell 24
The output signal of c is supplied to the other end of the adder 26d via the amplifier 25c. The output signal of the light detection cell 24d is supplied to the other end of the adder 26c via the amplifier 25d.

The output signal of the adder 26a is a differential amplifier OP
2, and the output signal of the adder 26b is supplied to the non-inverting input terminal of the differential amplifier OP2. The differential amplifier OP2 outputs a signal corresponding to the difference between the two output signals of the adders 26a and 26b, that is, a focus error signal. This signal is supplied to the focusing control circuit 27. The output signal of the focusing control circuit 27 is supplied to the focusing drive coil 12. Thus, control is performed such that the laser beam is always just focused on the optical disc 1.

The output signal of the adder 26c is a differential amplifier OP
1, and the output signal of the adder 26d is supplied to the non-inverting input terminal of the differential amplifier OP1. The differential amplifier OP1 outputs a signal corresponding to the difference between the two output signals of the adders 26c and 26d, that is, a track error signal. This signal is supplied to the tracking control circuit 28. The tracking control circuit 28 creates a track drive signal according to the track error signal from the differential amplifier OP1.

When seeking a target track on an optical disk, the linear motor control circuit 8
Is moved to the target track position. Further, the tracking control circuit 28 drives the drive coil 11 to control the position of the objective lens 10 in the tracking direction so that the focus point of the objective lens 10 is accurately on the target track.

The track drive signal output from the tracking control circuit 28 is applied to the drive coil 1 in the tracking direction.
1 is supplied. The track drive signal used in the tracking control circuit 28 is
Supplied to

By performing the focusing control and the tracking control, the sum signal of the output signals of the photodetection cells 24a to 24d of the photodetector 24, that is, the addition signal for adding both output signals of the adders 26c and 26d. The change in the reflectance from the bits formed on the tracks of the optical disc 1 corresponding to the recorded information is reflected in the output signal of the optical unit 26e. This signal is supplied to the data reproducing circuit 18. The data reproduction circuit 18 reproduces recorded data based on a reproduction clock signal from the PLL circuit 16.

The motor control circuit 4, the linear motor control circuit 8, the laser control circuit 15, the PLL circuit 16, the data reproduction circuit 18, the focusing control circuit 27, the tracking control circuit 28, the error correction circuit 32 and the like are connected via a bus 29. It is controlled by the CPU 30. The CPU 30 performs a predetermined operation according to a program recorded in the memory 2.

FIG. 2 is a diagram showing an S-shaped characteristic of focus. 2A shows the output signal waveform of the differential amplifier OP2, and FIG. 2B shows the distance from the surface of the optical disc 1 to the objective lens 10.

As shown by the straight line C2 in FIG. 2B, when the drive current of the focus drive coil 12 is gradually changed and the distance from the optical disk 1 to the objective lens 10 is reduced, FIG. As shown by the curve C1 in a), the differential amplifier OP2 outputs an S-shaped waveform signal as a focus error signal. This S-shaped waveform is the S-shaped characteristic of the focus. The curve C1 showing the ideal S-shaped characteristic is point-symmetric with respect to the point d. As described above, the amplitude center point d of the S-shaped waveform is referred to as a servo pull-in point. The amplitude A of the curve C1 is an operation range during focus servo. In general, an optical pickup having a point-symmetric S-characteristic such as a curve C1 in a state where the objective lens 10 does not move in the tracking direction, that is, does not shift the lens, is used as a good product. Conventional automatic adjustment is performed based on the S-shaped characteristic when the servo pull-in point and the operating range are not shifted.

This S-shaped characteristic is not generally measured when the lens is shifted. This is because it is generally considered that the S-shaped characteristic does not change even if the lens shifts. However, depending on the pickup,
As shown by the curve C3 in (a), there is a case where the S-shaped characteristic changes when the lens shifts. The S-characteristic shown in the curve C3 has a lower point symmetry than the characteristic of the curve C1, the pull-in point changes from d to g, and the operating range decreases from A to B. As described above, when the lens is shifted in the tracking direction and the S-shaped characteristic is degraded, the servo controllable range is reduced (A> B), and the servo is deviated.

Therefore, if the S-shaped characteristic when the lens is shifted can be grasped, the servo can be prevented from coming off by changing the servo pull-in point when the lens is shifted.

FIG. 3 is a flowchart showing a servo automatic adjustment method for an optical disk drive according to the present invention.
Items adjusted during automatic adjustment are the differential amplifier OP1 and OP
Although there are a number of offsets, a balance between a tracking error signal and a focus error signal, and the like, here, the determination of each adjustment value relating to the S-shaped characteristic of focus will be described.

First, adjustment is performed without shifting the lens as in the prior art (step S1). For example, this step S1
Includes the measurement of the S-characteristic of the focus. In this measurement, as shown in FIG. 2, the current flowing through the focus direction drive coil 12 is gradually changed, and the output voltage of the differential amplifier OP2 is measured. Then, the pull-in point d and the amplitude A of the curve C1 indicating the S-shaped characteristic are measured. The pull-in point d and the amplitude A obtained by this measurement are stored in the memory 2.

Next, adjustment is performed by shifting the lens (step S2). For example, in step S2, the S-shaped characteristic of the focus is measured by shifting the lens. In this measurement, as in step S1, the pull-in point g and the amplitude B of the curve C3 indicating the S-shaped characteristic are measured, and the obtained data is stored in the memory 2. As described above, the S-shaped characteristic of focus usually does not change even when the lens is shifted, but some pickups change as shown by a curve C3 in FIG. 2B. In such a pickup, when the lens is shifted and the servo of the focus is applied, if the optical disk has undulation or warpage, the servo is easily released. In the present invention, the characteristics when the lens is shifted are also measured, and the measured data is used during actual focus servo.

In step S3, the S-shaped characteristic is compared with the case where the lens shift is performed and the case where the lens shift is not performed, and the change is grasped.

In step 4, each adjustment value is determined according to the change when the lens is shifted. For example, in this step S4, each adjustment value at the time of focus servo is determined according to the change when the lens is shifted. For example, FIG.
A limit value is set for the tracking direction control amount so that the focus error signal of the differential amplifier OP2 as shown in FIG. That is, a limit value is provided for the current flowing through the tracking direction drive coil 11. In addition, the pull-in point when performing the focus servo by shifting the lens is set to a point g as shown in FIG. 2A (the driving current of the focus drive coil 12 corresponding to the distance f is set as the pull-in point). Alternatively, the maximum control width in the focus direction when the lens is shifted is set to a value smaller than that in the case of the curve C1.

The actual focus servo is performed based on the adjustment values measured and set as described above. That is, the focus servo is performed by limiting the lens shift amount, that is, the tracking direction control amount, to the limit value. or,
When the lens is shifted, focus servo is performed around the disc-lens distance f corresponding to the pull-in point g. Alternatively, the control width in the focus direction when the lens is shifted is limited to the maximum control width in the focus direction so that the servo does not come off.

Although the above description has been given of the case where the present invention is applied to automatic focus adjustment, it is apparent that the present invention can be similarly applied to automatic tracking adjustment.

[0035]

According to the present invention, a pickup which is originally defective can be positively used.
Further, even if the S-shaped characteristic changes when the lens shifts for some reason after entering the market, it can be adapted. If the S-shaped waveform changes due to the lens shift, in the worst case, the focus loop may come off and the lens may come into contact with the disk and damage the disk. The method is effective.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an optical disk drive device to which the present invention is applied.

FIG. 2 is a diagram showing an S-shaped characteristic of focus.

FIG. 3 is a flowchart showing a servo automatic adjustment method of the optical disk drive device according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Optical disk 3 ... Motor 10 ... Objective lens 11, 12 ... Driving coil 20 ... Collimator lens 21 ... Half prism 22 ... Condensing lens 23 ... Cylindrical lens 24a-24d ... Photodetection cell 25a-25d ... Current / voltage conversion amplifier 26a ~ 26d ... Adder

Claims (2)

[Claims] A step of shifting an objective lens of an optical pickup in a tracking direction to perform adjustment, and storing the adjustment value, in the automatic adjustment performed when the optical disk is inserted into the apparatus; Controlling the optical pickup using a value of the optical pickup. 2. The automatic adjustment method according to claim 1, wherein said adjustment includes measuring an S-shaped characteristic of focus.