JP2637243B2 - Track servo offset correction method for optical disk device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Table of Contents] Overview Industrial application field Conventional technology (Fig. 7) Problems to be solved by the invention Means for solving the problem (Fig. 1) Action Embodiment (a) One Description of the embodiment (FIGS. 2 to 5) (b) Description of another embodiment (FIG. 6) (c) Description of another embodiment [Summary] Light beam follows track of optical disk A method of correcting a track servo offset of a track servo control unit to be controlled is intended to remove an offset of a track error signal caused by characteristics of an optical disk or an optical head. , A track error signal creating means for creating a track error signal from a light receiving signal of the optical head, and an output from the track error signal creating means. A track servo control unit that controls a light beam of the optical head to follow a track based on a track error signal, wherein a positive and negative amplitude of the track error signal output from the track error signal creating unit is provided. Detecting the value and calculating the difference between the two; determining the offset correction amount in accordance with the determined difference; and providing the determined offset correction amount to the track error signal creating means. The method includes at least a step of performing signal offset correction and a step of repeating the above steps until there is no difference between the positive and negative amplitude values of the track error signal.

[Industrial applications]

The present invention relates to a method for correcting a track servo offset of a track servo control unit that controls a light beam to follow a track of an optical disk.

An optical disk device using an optical disk or a magneto-optical disk can be read / written by a light beam, so that the track interval can be set to several microns, and is attracting attention as a large-capacity storage device.

In this optical disc device, track servo control is used to control the light beam to follow the track.

In the track servo control, a track error signal is obtained by using diffraction of a guide groove (pre-group) of an optical disk medium, servo is applied, and a light beam follows the track (guide groove).

In such track servo control, the offset of the track error signal generated by various causes is removed,
There is a demand for stable track servo control.

[Conventional technology]

 FIG. 7 is an explanatory diagram of the prior art.

As shown in FIG. 7 (A), the optical disc device
The optical head 2 is moved and positioned in the radial direction of the optical disc 1 by a motor (not shown) with respect to the optical disc 1 rotating about the rotation axis by 1a, and the optical head 2 reads (reproduces) / writes (records) the optical disc 1. Done.

On the other hand, the optical head 2 guides the light emitted from the semiconductor laser 24 as a light source to the objective lens 20 via the lens 25 and the polarizing beam splitter 23, narrows down the beam spot BS by the objective lens 20, irradiates the optical disc 1 with the light, and The reflected light from the optical system is configured to enter the four-divided photodetector 26 from the polarizing beam splitter 23 via the objective lens 20.

In such an optical disk device, the optical disk 1
A large number of tracks or pits are formed at intervals of several microns in the radial direction of the optical disk 1. Even a slight eccentricity causes a large positional deviation of the track, and the undulation of the optical disk 1 causes a focal position deviation of the beam spot. Must follow a beam spot of 1 micron or less.

For this purpose, a focus actuator (focus coil) 22 for changing the focal position by moving the objective lens 20 of the optical head 2 in the vertical direction in the figure, and moving the irradiation position in the track direction by moving the objective lens 20 in the horizontal direction in the figure. Is provided with a track actuator (track coil) 21 for changing the position.

In response to this, the focus servo control unit 4 that generates the focus error signal FES from the light receiving signal of the light receiver 26 and drives the focus actuator 22 and the light receiver 26
The track servo control unit 3 that generates a track error signal TES from the received light signal and drives the track actuator 21 is provided.

By the way, it is desirable that the track error signal TES of the track servo controller 3 has no offset originally and is symmetrical about 0V.

However, due to the circuit-specific offset, the tilt of the optical disk, and the displacement of the head optical system, an offset occurs in the track error signal TES as shown in FIGS. 7B and 7C, and the track error signal TES becomes asymmetric around 0V. .

When an offset occurs in the track error signal TES, the beam spot is controlled to follow a position shifted from the center of the original track.

For this reason, if writing / reading is performed at this position, the track is deviated from the center of the track, so if it is used in a device having another offset, track crosstalk occurs, reading becomes impossible, and the compatibility of the device is lost.

For this reason, conventionally, no servo signal is output, that is,
The semiconductor laser 24 of the optical head 2 is turned off, the optical head 2 is moved to a position where there is no optical disk, and an offset correction voltage is applied to the track servo loop so that the track error signal TES becomes zero, thereby adjusting the circuit offset. Was being attempted.

[Problems to be solved by the invention]

Incidentally, the cause of the track offset is not only the offset on the circuit, but also the case where the parallelism between the optical head 2 seeking in the track direction and the spindle receiving surface for rotating the optical disk is not obtained. Offset occurs.

Also, the optical system of the optical head 2, that is, the semiconductor laser 24, the lens 25, the polarizing beam splitter 23, and the four-divided light receiver 26 are fixed, and the track and focus actuators are fixed.
In the configuration in which the objective lens 20 is movable and the objective lens 20 is movable, a slight offset of the optical axis with respect to the movement direction of the movable portion causes a track offset due to seek.

In the related art, there is a problem that even if the circuit offset can be removed, the track offset due to such a slight error of the mechanical system cannot be removed.

Accordingly, it is an object of the present invention to provide a track serve offset correction method for an optical disk device that can also remove an offset of a track error signal caused by characteristics of an optical disk or an optical head.

[Means for solving the problem]

 FIG. 1 is a diagram illustrating the principle of the present invention.

As shown in FIG. 1, the present invention relates to an optical head 2 for irradiating an optical disk 1 with a light beam and receiving light from the optical disk 1, and a track for generating a track error signal from a light receiving signal of the optical head 2. An optical disc apparatus comprising: an error signal generating unit; and a track servo control unit 3 that controls a track following of a light beam of the optical head 2 based on a track error signal output from the track error signal generating unit. Detecting the positive and negative amplitude values of the track error signal output from the generating means and calculating a difference between the two; and calculating an offset correction amount according to the determined difference. The step of giving the offset correction amount to the track error signal creating means to perform offset correction of the track error signal. And flop, in which at least a step of repeating the positive and the steps until the difference is eliminated the negative side of the amplitude value of the tracking error signal.

[Action]

According to the present invention, the positive and negative amplitudes of the actual track error signal TES are detected, and the offset is corrected based on the difference between the two amplitudes. Therefore, even if the cause of the offset is in the mechanical system, the offset of the track error signal can be removed.

〔Example〕

(A) Description of one embodiment FIG. 2 is a block diagram of one embodiment of the present invention, and FIG. 3 is a detailed circuit diagram of a main part thereof.

In the figure, the same components as those described in FIG. 1 and FIG. 7 are indicated by the same symbols.

Reference numeral 5 denotes a main control unit which is composed of a microprocessor, controls the servo operation of the track servo control unit 3 and the focus servo control unit 4 (see FIG. 7), and executes track servo offset correction control. And a memory 5a for storing an offset value OFS for each track range of the optical disc for offset correction.

Reference numeral 6 denotes a head circuit unit, and outputs a to
An RF generating circuit 60 for generating an RF signal RFS from the signal d. and an amplifier 61 for amplifying the outputs a to d of the four-divided photodetector 26 and outputting servo outputs SVa to SVd.

Reference numeral 30 denotes a TES creation circuit, which is a servo output SVa of the amplifier 61.
A circuit for generating a track error signal TES from SVd, 31 is an all signal generation circuit, which adds the servo outputs SVa to SVd to generate an all signal DSC which is a total reflection level, 32 is an AGC
(Automatic Gain Control) circuit that divides the track error signal TES by the total signal (total reflection level) DCS, and performs AGC with the total reflection level as a reference value, and corrects fluctuations in irradiation beam intensity and reflectance. Is what you do.

An amplifier 33 amplifies the track error signal TES when AGC is controlled.

34a is a zero cross detection value, and the track error signal T
The one that detects the zero cross point of ES and outputs the track zero cross signal TZC to the MPU5, 34b is an off-track detection circuit, and the track error signal TES is a fixed value + S in the plus direction.
A detector for detecting that the signal has reached L or less and a constant value −SL or less in the negative direction, that is, an off-track state and outputs an off-track signal TOS to the MPU 5, 35 is a phase compensation circuit, Differentiate the track error signal TES,
In addition to the proportion of the track error signal TES, the phase of the high frequency band is advanced.

Reference numeral 36 denotes a servo switch, which is closed when the servo-on signal SVS of the main control unit (hereinafter referred to as MPU) 5 is on, closes the servo loop, opens when off, and opens the servo loop, and 37 is an inverting amplifier. A power amplifier 38 amplifies the output of the inverting amplifier 37 and supplies the track drive current TDV to the track actuator 21.

Reference numeral 7a denotes an amplitude difference detection circuit, which detects the positive and negative amplitude values of the track error signal TES of the TES generation circuit 30 and calculates the difference as described later with reference to FIG. 3 (B). 7b is an analog / digital converter (hereinafter A /
D converter) and the ADC start signal AD of MPU5.
CSTART converts the analog amplitude difference of the amplitude difference detection circuit 7a into a digital value TESd,
Output to PU5.

7c is a digital / analog converter (hereinafter referred to as a D / A converter), which converts the offset value OFS from the MPU 5 into an analog quantity, and as described later with reference to FIG.
This is output to the input point of the TES creation circuit 30.

As shown in FIG. 3A, the TES generation circuit 30 includes input resistances R1, R2, and R4 of the outputs a, b, c, and d of the four-divided photodetector 26.
R3, R4 and offset value OFS from D / A converter 7c (=
α), an amplifier AMP for calculating (b + c) − (a + d + OFS) from the output of the quadrant photodetector 26 and the offset value OFS, and a track corrected by the offset value OFS. Outputs the error signal TES.

The amplitude difference detection circuit 7a has positive and negative side peak hold circuits 70 and 71 and a peak difference detection circuit 72.

The positive side peak hold circuit 70 outputs the track error signal TE
This is for performing peak hold on the positive side of S, and an amplifier AMP1 for comparing the track error signal TES with the peak hold level, a diode D1 in the positive direction, a capacitor C1 for positive peak hold, and a capacitor. It has a switch SW1 for discharging C1, an output field-effect transistor FET1, and an output resistor r1.

The negative-side peak hold circuit 71 is for performing a negative-side peak hold of the track error signal TES, and an amplifier AMP2 for comparing the track error signal TES with the peak hold level, and a diode D2 in the negative direction. , Capacitor C2 for negative peak hold, and capacitor
It has a switch SW2 for discharging C2, an output field-effect transistor FET2, and an output resistor r2.

Further, the peak difference detection circuit 72 calculates the peak difference between the positive peak hold level of the positive peak hold circuit 70 and the negative peak hold level of the negative peak hold circuit 71. Input resistance r3,
It includes an input resistor r5 for the negative peak hold and an inverting operational amplifier (op amp) AMP3 for adding the positive and negative peak hold levels via the resistors r3 and r5.

FIG. 4 is a processing flowchart of one embodiment of the present invention, and FIG. 5 is an explanatory diagram of the operation of one embodiment of the present invention.

The MPU 5 operates an optical head moving mechanism (not shown) to cause the optical head 2 to seek to n tracks.

Then, the focus servo control unit 4 is operated, the servo-on signal SVS is turned on, and the track servo is operated.

In this state, the track error signal TES is input to the amplitude difference detection circuit 7a, and as shown in FIG. 5, the positive side peak hold level in the positive side peak hold circuit 70 and the negative side peak hold level in the negative side peak hold circuit 71. The side peak hold level is detected, and the operational amplifier AMP3 of the peak difference detection circuit 72 outputs the peak difference (offset).

The MPU 5 synchronizes with the home pulse HOMEPSTN generated every one rotation of the optical disc 1 in FIG.
START is output to the A / D converter 7b, and the A / D converter 7b executes digital conversion of the peak difference.

The MPU 5 knows that the A / D conversion has ended by the ADC end signal ADCEND of the A / D converter 7b and obtains the A / D conversion value TESd.

Next, the MPU 5 checks whether the peak difference TESd is positive or negative.

If the peak difference TESd is positive, the MPU 5 converts the adjustment offset value DAC to (DAC + 1) to increase the adjustment offset on the negative side and increases the D / A
The offset adjustment value output to the converter 7c and given to the TES creation circuit 30 is changed.

In this state, similarly to the step, the MPU 5 converts the A / D conversion value TESd of the peak difference of the amplitude difference detection circuit 7a into an A / D converter.
Determine if the peak difference TESd is positive or negative, obtained by 7d.

If the peak difference TESd is not negative, the process returns to the beginning of the step. If the peak difference TESd becomes negative, the process proceeds to the step.

On the other hand, if it is determined in the step that the peak difference TESd is negative, there is a negative offset, so the MPU5
Changes the adjustment offset value DAC to (DAC-1) and sets the D / A
The output is output to the converter 7c, and the negative-side adjustment offset of the TES generation circuit 30 is reduced.

In this state, similarly to the step, the MPU 5 converts the A / D conversion value TESd of the peak difference of the amplitude difference detection circuit 7a into an A / D converter.
Determine if the peak difference TESd is positive or negative, obtained by 7b.

If the peak difference TESd is not positive, the process returns to the beginning of the step. If the peak difference TESd is positive, the process proceeds to the step.

When the offset adjustment of one track is completed in this way, the MPU 5 stores the offset adjustment value DAC in the register.

Then, the MPU 5 determines whether or not the last track has been exceeded.
Is changed to (n + m), and the process returns to the step. If the last track is exceeded, the process ends.

In this way, the TES creation circuit via the D / A converter 7c
While converting the offset adjustment value DAC given to 30, the detection peak difference TES via the amplitude difference detection circuit 7a and the A / D converter 7b
Monitor d.

That is, an offset adjustment value DAC that makes the detected peak difference TESd almost zero is obtained.

Such an offset adjustment value may replace all tracks with data of only one track, but is different for each track in the case of bending of the optical disk, bending of the optical head 2 or optical axis deviation.

Therefore, in this embodiment, the offset adjustment value DAC is measured every m tracks from the 0th track to obtain an offset distribution curve.

For example, if there are 40,000 tracks, measure the offset adjustment value every 1000 tracks, create an offset distribution curve for every 100 tracks using the MPU5 interpolation program,
Offset adjustment value OFS according to track range in memory 5a
Is stored.

Then, when performing a normal seek, the offset adjustment value OFS in the memory 5a corresponding to the track number to be sought is read, output as an offset correction value to the D / A converter 7c, and a track offset is input to the TES creation circuit 30. Inject DC voltage in the direction to turn off.

Such measurement of the offset adjustment value is performed when the power is turned on or when the optical disk is replaced.

(B) Another Embodiment FIG. 6 is an explanatory diagram of another embodiment of the present invention, and shows another configuration example of the amplitude difference detection circuit 7a.

6 (A) and 6 (B), the same components as those shown in FIG. 3 (B) are indicated by the same symbols.

6A, positive and negative envelope detectors 70-1 and 71-1 are used instead of the positive and negative peak hold circuits 70 and 71 in FIG. 3B. Things,
This can be realized by providing resistors r7 and r8 in parallel with the capacitors C1 and C2 in addition to the configuration of the peak hold circuit.

In FIG. 6B, the positive and negative integrators 70-2 and 71-2 are used instead of the positive and negative peak hold circuits 70 and 71, respectively. Resistors r7, r8 instead of switches SW1, SW2 in circuits 70, 71
This can be realized by providing.

As described above, the detection of the amplitude level can be realized by envelope detection or integration in addition to peak hold.

(C) Description of Another Embodiment In the above-described embodiment, the offset adjustment value is measured every m tracks. However, the offset adjustment value may be measured over all tracks. The output of the AGC circuit 32, the output of the amplifier 33, etc. may be used in addition to the output of the TES generation circuit 3.
The present invention is not limited to 0, and may be executed in the amplifier 33 or the like.

Furthermore, in the above-described embodiment, the correction is performed by the main control unit 5. However, the correction may be performed by a dedicated device or a route, and the description has been made with the optical disk, but the present invention may be applied to a magneto-optical disk.

Although the present invention has been described with reference to the embodiments, the present invention can be variously modified in accordance with the gist of the present invention, and these are not excluded from the present invention.

〔The invention's effect〕

As described above, according to the present invention, the difference in amplitude between the positive and negative sides of the track error signal is detected, and the offset correction amount is obtained and offset correction is performed. This has the effect of also removing the offset due to the above, and contributes to the improvement of the error rate due to the reduction in crosstalk between tracks.

In particular, the present invention detects the positive / negative amplitude of the track error signal of the track error signal generating means, checks whether the track error signal is biased to the positive side or the negative side, and outputs an offset value which is shifted to the opposite side from the biased direction. Feedback to the creation means, subsequently, the amplitude of the corrected TES is detected, and if offset to one side, the process of correcting by giving an offset value is repeated, and the positive / negative amplitude difference of the TES becomes An offset value that finally becomes 0 is determined.

Therefore, since an accurate offset value can be determined with high accuracy, it is possible to correct not only a track offset due to a variation in a circuit system but also a track offset due to eccentricity, waviness, etc. of an optical disk with high accuracy. become.

[Brief description of the drawings]

 1 is a principle diagram of the present invention, FIG. 2 is a block diagram of one embodiment of the present invention, FIG. 3 is a detailed circuit diagram of a main part of one embodiment of the present invention, and FIG. FIG. 5 is an explanatory diagram of the operation of one embodiment of the present invention, FIG. 6 is an explanatory diagram of another embodiment of the present invention, and FIG. 7 is an explanatory diagram of the prior art. In the figure, 1 ... optical disk, 2 ... optical head, 3 ... track servo control unit.

Claims (2)

(57) [Claims] An optical head for irradiating an optical disk with a light beam and receiving light from the optical disk; a track error signal generating means for generating a track error signal from a light receiving signal of the optical head; A track servo control unit for performing track following control of the light beam of the optical head based on the track error signal output from the means, the positive side of the track error signal output from the track error signal generating means. Detecting the amplitude value on the negative side and the negative side, and calculating the difference between the two; determining the offset correction amount in accordance with the determined difference; and providing the determined offset correction amount to the track error signal generating means. Performing an offset correction of the track error signal; Positive and track servo offset correction method of an optical disk device characterized by until the difference of the amplitude values of the negative side is eliminated it has at least the steps of: repeating said steps of. 2. The track servo offset correcting method for an optical disk device according to claim 1, further comprising the step of repeating the above steps for a plurality of tracks of the optical disk.