JP3365574B2 - Offset adjustment device for optical disk device - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to relates to the offset adjustment equipment for adjusting the offset of the tracking error signal and a focus error signal obtained from the optical disk.

[0002]

2. Description of the Related Art Generally, MD (mini disk) and PC
In an information recording / reproducing apparatus as an optical disk apparatus for recording / reproducing data on / from a (phase change type) disk in a predetermined block time unit, a laser output power (hereinafter referred to as laser power) which gives a light beam spot to the disk at the time of recording. ) Is adjusted in multiple stages according to the wattage specified by the disc, and the laser power is made variable in multiple stages for several types of discs (pre-mastered and MO) with different reflectances during playback. The gain is switched to make the light proper, and the offset is adjusted each time this switching is performed. At this time, the offsets of the tracking error signal and the focus error signal must be adjusted accurately in consideration of compatibility with other devices.

In order to obtain an accurate tracking error signal or focus error signal, it is necessary to adjust the offset voltage by the circuit or the optical system in "there is no signal". As a conventional method of adjusting this offset, there is a method of canceling the offset of the tracking error signal or the focus error signal in this state when the state in which the focus coil and the tracking coil of the optical pickup are not energized is "no signal". Has been.

[0004]

However, in the above method, depending on how the optical disk device is placed on the ground, the state in which the focus coil and the tracking coil of the optical pickup are not energized is actually "no signal". Since there is no case, it is not possible to obtain an accurate tracking error signal or focus error signal, and therefore, there is the first problem that the best data signal cannot be obtained during reproduction or writing. Especially CD
In the case of MD and MD discs, the thickness from the disc signal surface to the disc surface is about 1.2 mm, and when the lens is lowered by about 1.2 mm from the disc due to the weight of the actuator, the reflected light from the disc signal surface returns. May be detected.

The thickness of the disk surface is 1.2 m.
If the optical pickup and the disc have a positional deviation of about 0.4 mm due to the fluctuation of m ± 0.1 mm, the fluctuation of the disc surface, or the play of the shaft of the spindle motor for fixing the disc. The offset cannot be adjusted accurately. Further, if the variation of the mechanism is increased in order to configure the apparatus at a low cost, or if the NA (numerical aperture) is increased in order to increase the recording density, the focal length becomes smaller, and it becomes more difficult to adjust at a fixed position.

A second problem is that the offset including the stray light component cannot be adjusted when the laser powers are different. For example, when the optical pickup generates the tracking error signal TE by the astigmatism method, the tracking error signal TE (= E
The signals E, F for detecting −F) are x as a function of laser power

[0007]

## EQU1 ## E = axsin ωt + b1 F = axsin (ωt + π) + b2 E−F = axsin ωt + b1- {axsin (ωt + π)
+ B2} = 2axsin ωt + b1-b2

Therefore, the constant term (b1-b2) is constant when the laser power is constant. However,
If the laser power is different

[0009]

[Equation 2]   E = axin ωt + b1x + c1   F = axsin (ωt + π) + b2x + c2   EF = axin ωt + b1x + c1                 -{Axsin (ωt + π) + b2x + c2}         = 2axsin ωt + (b1-b2) x + c1-c2 (1)

Therefore, there is a stray light component that is a function (b1-b2) x of x and a constant (c1-c2). The signals A, B, C, and D for detecting the focus error signal FE (= A + C−B−D) are

[0011]

## EQU3 ## A = axsin ωt + b1 B = axsin (ωt + π) + b2 C = axsin ωt + b3 D = axsin (ωt + π) + b4 A + C-B-D = 4axsin ωt + (b1 + b3-b2)
-B4)

And the above constant term (b1 + b3-b2-
b4) becomes constant when the laser power is constant. However, if the laser power is different,

[0013]

A = axsin ωt + b1x + c1 B = axsin (ωt + π) + b2x + c2 C = axsin ωt + b3x + c3 D = axsin (ωt + π) + b4x + c4 A + C-B-D = 4axsin ωt + (b1 + b3-b2)
-B4) x + c1 + c3-c2-c4

And the function of x (b1 + b3-b2-b
4) Stray light component of x and constant (c1 + c3-c2-c
4) exists. Further, this problem becomes remarkable when the optical pickup is a hologram type. In view of the above problems, it is possible to obtain an accurate tracking error signal and a focus error signal, thus, provide an offset adjustment equipment in an optical disk capable of obtaining the best data signals during playback or writing The purpose is to do.

[0015]

In order to achieve the above object, the present invention adjusts an offset at a focus position different from the first and second focus positions for the surface of an optical disk and the data recording surface in the optical disk, respectively. I am trying. That is, according to the present invention, the light from the optical disk is
Detection means for detecting the signal reproduced by the pickup
, Tracking error signal generation means, and focus error
Error signal generating means, tracking error signal and
Measure the offset of one or both of the cas-error signals
Offset measuring means and the tracking error signal
Offset of one or both of the focus error signals
And an optical pickup for correcting the offset,
In the focus direction with respect to the optical disc,
During this movement, the offset measuring means sequentially
Means for measuring the fuss and of the measured offset
Means for storing measurement results in relation to focus position
A means for comparing the measurement result with a predetermined threshold value,
From the comparison result, the surface of the optical disc and the inside of the optical disc
The first and second fobs corresponding to the respective data recording surfaces of
Means for detecting the focus position, and the first and second focus
The optical pick-up at a focus position different from the focus position.
The offset by the offset correction means.
Of an optical disk device having a control means for correcting
A set adjuster is provided.

[0016]

In the present invention, the offset is adjusted by the constant term of the signal detected at the laser power of at least two levels and the variable term due to the power change. That is, according to the present invention, a detection unit that detects a signal reproduced from the optical disc by the optical pickup, a tracking error signal generation unit, a focus error signal generation unit, and an offset of one or both of the tracking error signal and the focus error signal. Offset measuring means for measuring the offset error, offset correcting means for correcting one or both of the tracking error signal and the focus error signal, and means for changing the laser power of the optical pickup to at least two values to emit light. A means for measuring an offset in each of the laser power values by the offset measuring means,
Means for storing the measured measurement result of the offset in association with the respective laser power values, a constant offset component not related to the laser power value in the offset, and an offset due to a stray light component that changes due to laser power change There is provided an offset adjusting apparatus for an optical disk device, which has a unit for calculating a component and a control unit for correcting the offset by the offset correcting unit with each laser power value based on the calculated value .

[0018]

In the present invention, the offset is adjusted at the focus positions different from the first and second focus positions corresponding to the optical disk surface and the data recording surface, respectively. Is adjusted. Therefore, an accurate tracking error signal or focus error signal can be obtained, and as a result, the best data signal can be obtained at the time of reproduction or writing.

In the present invention, the laser diode
Since the offset is adjusted based on the maximum value or the minimum value of the signal detected when the amount of light that exits and returns to the optical pickup is the minimum, the offset by the circuit or the optical system is adjusted in the "no signal" state. Therefore, an accurate tracking error signal or focus error signal can be obtained, and as a result, the best data signal can be obtained at the time of reproduction or writing.

Further, in the present invention, since the offset is adjusted by the constant term (offset of the sensor and the circuit) of the signal detected by the laser power of at least two levels and the variable term (stray light component) due to the power change,
The offset can be adjusted even when the laser power is different, and therefore, an accurate tracking error signal or focus error signal can be obtained, and as a result,
The best data signal can be obtained during reproduction or writing.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. 1 is a block diagram showing an MD recording device as an optical disc device to which an offset adjusting device according to the present invention is applied, FIG. 2 is a block diagram showing the preamplifier of FIG. 1, and FIG. 3 is a focus current of the optical pickup of FIG. It is explanatory drawing which shows the amount of reflected light.

In FIG. 1, the optical pickup 2 optically records bibliographic information, audio information, and video information of a predetermined format on a track formed in a spiral shape on the disc 1 from the inner circumference to the outer circumference. Is played. This disc 1 is rotated at CLV (constant linear velocity) by a spindle motor 3 and a motor driver / tracking focus control circuit 4 based on a signal reproduced from the disc 1 by an optical pickup 2. The optical pickup 2 has a superposing device 5 and a traverse motor 6, and operates integrally with the magnetic field modulation head 7.

The optical pickup 2 also has a laser diode LD for emitting a laser beam to the disc 1, and outputs signals RF1 and RF2 which reproduce the optical information recorded on the disc 1 based on the reflected light. , The focus error signal detection signals A to D from the four-division sensor by the astigmatism method and the two types of tracking error signal detection signals E and F by the three-beam method are output. These signals RF
1, RF2, A to F are amplified by the head amplifier 8,
It is output to the preamplifier 9 that operates as a detection / adjustment means. Further, a signal for driving the laser diode LD in the optical pickup 2 is applied from the preamplifier 9 to the head amplifier 8.

The preamplifier 9 outputs the reproduced EFM signal, ADIP signal, focus error signal FEO, tracking error signal TEO, etc. to the EFM modulation / demodulation / error correction / ADIP (address implement groove) / servo circuit 10. The servo circuit of the circuit 10 is composed of, for example, a DSP (digital signal processor).

The EFM modulator / demodulator / error corrector / ADIP / servo circuit 10 encodes the record data at the time of recording and E
The signal is modulated into an FM signal and output to the head 7 via the driver 7a. The EFM modulation / demodulation / error correction / ADIP / servo circuit 10 also uses the EFM from the preamplifier 9 during reproduction.
The signal is demodulated and error-corrected and decoded, and the motor driver / tracking / focus control circuit 4 is arranged so that the optical pickup 2 tracks and focuses on the track of the disk 1 based on the focus error signal FEO and the tracking error signal TEO. Control through.

During writing, the microcomputer 11 moves the optical pickup 2 near the innermost circumference of the disk 1 (TOC: Tabl
e Of Contents and UTOC: User Table Of Content
s) and read out the necessary ID information.

The microcomputer 11 is an A / D converter 1 that takes in various signals A to F, FEO, TEO, etc. from the preamplifier 9.
1a, a laser diode LD in the optical pickup 2 for driving a laser diode LD with a signal corresponding to, for example, a 12-bit PWM signal to control the output power of the laser diode LD, and a RAM 11c for a work area or the like.
And a ROM 11d for programs and the like and a CPU 11e for performing control as will be described later.
11e is connected via a bus 11f. Also, R
The AM 11c has an area for storing measurement data and the like for the CPU 11e to perform offset adjustment described later. The PWM signal from the PWM unit 11b is converted into a DC voltage by the low pass filter (LPF) 12, and the laser diode LD in the optical pickup 2 is driven via the preamplifier 9 and the head amplifier 8.

Next, the preamplifier 9 will be described in detail with reference to FIG. First, the signals A to D for detecting the focus error signal FE of the four-division sensor (not shown) by the astigmatism method in the optical pickup 2 are output from the microcomputer 11 via the D / A converter 35, respectively. The respective balance adjustment values are added by the adders 31A to 31D to adjust the balance of the signals A to D and are I / V converted. Next, the output signals A to D of the adders 31A to 31D are applied to the arithmetic unit 32F, and the arithmetic expression (A + C
-BD), a focus error signal is generated on the basis of the focus error signal and the offset adjustment value output from the microcomputer 11 via the D / A converter 35 is added by the adder 33F. Is adjusted and output as a focus error signal FE.

Further, the balance adjustment values output from the microcomputer 11 via the D / A converter 35 are respectively applied to the signals E and F for detecting the tracking error signal TE by the three-beam method in the optical pickup 2. Are added by the adders 31E and 31F to adjust the balance of the signals E and F, and I / V converted. Next, the output signals E and F of the adders 31E and 31F are applied to the subtractor 32T to generate a tracking error signal based on the arithmetic expression (EF), and then this tracking error signal and D / The offset adjustment value output via the A converter 35 is added by the adder 33T to adjust the offset and output as the tracking error signal TE.

Further, the output signals A to F of the adders 31A to 31F and the eight signals of the focus error signal FE and the tracking error signal TE are converted into digital values by the A / D converter 11a, and the microcomputer 11 controls them. As will be described later, each balance and offset of the focus error signal FE and the tracking error signal TE are adjusted, and each adjustment value is added via the D / A converter 35 to the adders 31A to 31F, 3 and 3.
It is applied to 3F and 33T.

FIG. 3 shows the relationship between the distance between the optical pickup (PU) 2 and the disc 1 and the amount of reflected light, and shows that the optical pickup (PU) 2 approaches the disc 1 when the focus current increases. Position Z5 in FIG.
If the value measured at is the original offset only by the circuit and the optical system, the initial focus position is Z shown in FIG.
If there are variations such as 0, Z1 and Z2, the signal on the disk surface will be picked up at position Z1.
With 0, Z2, and Z4, the original measurement cannot be performed by focusing on the vicinity of the disk surface or the non-transparent portion between the polycarbonate resins of the disk 1.

Therefore, in this embodiment, before the spindle motor 3 is started, the focus actuator coil of the optical pickup 2 is set to an initial value of the current corresponding to any of the positions Z0, Z1 and Z2 shown in FIG. The focus current is gradually increased and applied in a direction approaching the disk.

Next, the offset adjustment in the first embodiment will be described. First, when there is no disc due to the detection signal of the disc detection switch, the optical pickup 2
Is placed at the initial position, each voltage of the focus error signal FE and the tracking error signal TE is measured, and the ROM
The offset value of the table written in 11d is output to the D / A converter 35 according to the measured voltage.

On the other hand, when there is a disk, the drive voltage is applied to the servo circuit 10 on the assumption that the initial position is on the left side of the position Z0 shown in FIG.
Increasing the focus current by increasing more built-in (not shown) D / A converter, successively takes in the voltage of the tracking error signal TE to every increase. Then, as shown in FIG. 3, when the surface of the disk, which is the first peak, is detected with a predetermined threshold value, D of the drive voltage at the time of this detection is detected.
/ A value (DA1) is stored, and then the second peak, the data recording surface in the disk, is detected at a predetermined threshold value,
The D / A value (DA2) at the time of this detection is stored.

Next, from these two values, (DA1 + DA
2) / 2 is calculated, this is output, and it is moved to the vicinity of the center position Z4 shown in FIG. 3 to adjust the offsets of the focus error signal FE and the tracking error signal TE.
It should be noted that the offset is adjusted by the focus error signal FE.
And tracking error signal TE, A, B, C, D,
This is performed by measuring the voltage of each of E and F and outputting the offset value previously written in the ROM 11d via the D / A converter 35 so that each voltage becomes the reference voltage. In the example shown in FIG. 3, the voltage at the position Z4 has a returning light component with respect to the original offset, but it is within the allowable range.

Next, the offset adjustment in the second to fifth embodiments of the present invention will be described. The operation of the second to fifth embodiments when there is no disk is the same as that of the first embodiment, and the description thereof is omitted. First, in the second embodiment,
When there is a disk, the drive voltage is set to the servo circuit 10 assuming that the initial position is on the left side of the position Z0 shown in FIG. 3, that is, the position far from the disk surface, as in the first embodiment.
Sequentially fetches the voltage of the tracking error signal TE for each of increasing focus current Te to the D / A converter (not shown) incorporated in, and a predetermined threshold disk surface is first peak as shown in FIG. 3 When detected by, the voltage DA1 of the D / A converter 35 at the time of this detection is stored and then the second DA
When the data recording surface which is the peak of is detected with a predetermined threshold value, the voltage DA2 of the D / A converter 35 at the time of this detection is stored.

Then, in the second embodiment, a predetermined offset, for example, DA2 + (DA2-) from these two values is located at a position closer to the data recording surface than the second peak shown in FIG.
DA1) / 2 is applied to move to the position Z5, and at the position Z5, the focus error signal FE, the tracking error signal TE, and the offsets of A, B, C, D, E, and F are adjusted. It should be noted that although the time and current required to move to the position Z5 shown in FIG. 3 increase, an accurate offset can be measured because of the position where no image is formed.

In the third embodiment, when the disc is present, it is not known which of the positions Z0, Z1 and Z2 the initial position is shown in FIG. 3, and the voltage of the tracking error signal TE is increased each time the focus current is increased. Are sequentially captured, the data recording surface is detected with a predetermined threshold value, and D at that position is detected.
When the A value is DA1, a predetermined offset a (a is a constant value) is added to a position closer to the disk than the data recording surface (= D
A1 + a) to move to the position Z5 and adjust each offset at this position Z5.

In the fourth embodiment, first, like the third embodiment, when the disc is present, it is not known which of the positions Z0, Z1 and Z2 the initial position is shown in FIG. The voltage of the tracking error signal TE is sequentially fetched each time the voltage increases. In the fourth embodiment, when the data recording surface is detected with a predetermined threshold value, a predetermined offset (-) is set at a position (DA1) farther from the data recording surface.
a) is added (= DA1-a) to move to the position Z4, and each offset is adjusted at this position Z4.

In the fifth embodiment, first, like the third and fourth embodiments, it is not known which of the positions Z0, Z1 and Z2 shown in FIG. 3 the initial position is when the disc is present. The focus current is gradually increased to sequentially capture the voltage of the tracking error signal TE. Then, in the fifth embodiment, the focus servo is turned on when the data recording surface is detected with a predetermined threshold in order to apply the servo at the center of the S curve of the focus error signal FE. And
When the focus error signal FE is positioned at the center of the S curve, the average value DA1 of the D / A values of the drive voltage at this position is obtained. Then, the focus servo is turned off to move to a position Z4 far from the data recording surface or a position Z5 close to the data recording surface (= DA1-a, or = DA1 + a), and each offset is adjusted at this position Z4 or Z5.

Therefore, according to the above-mentioned first to fifth embodiments, the position Z far from the data recording surface which is not the disk surface.
4 or close position Z5 to move to focus error signal F
E and tracking error signal TE, other A, B, C,
Since each offset of D, E, and F is adjusted, an accurate tracking error signal or focus error signal can be obtained, and therefore, the best data signal can be obtained at the time of reproduction or writing.

In the above adjustment operation, the laser power was kept constant, but in the case of MD as shown in FIG.
The offset changes each time the laser power changes, such as 0.25 mW when reproducing the OM region, and 0.5 mW and 5 mW when reproducing and recording the MO region, respectively.
The offset may be adjusted each time the laser power changes.

Next, a sixth embodiment of the present invention will be described. By the way, in FIG. 3, all of the detection signals A to F except the focus error signal FE and the tracking error signal TE have unnecessary offsets added in the + direction from the original offsets, so the minimum value is the desired offset. Become. In the circuit in which the signals A to F are inverted,
Since the unnecessary offset is added in the-direction from the offset that should be, the maximum value becomes the desired offset,
In other words, this minimum or maximum value is the laser diode L
It is the value when the light emitted from D and returning to the optical pickup is the least.

In the sixth embodiment, first, the operation when there is no disk is the same as in the first to fifth embodiments, so the description thereof will be omitted. If there is a disc, position Z shown in FIG.
The optical pickup 2 reciprocates in the range of positions Z0 to Z5 with a triangular waveform in which the focus current is linearly increased and then linearly decreased with the focus servo turned off, assuming that the position is 0 to Z5. Control as
Although signals A to F, TE, FE or circuits are not shown in the figure, A + C, B + D, etc. are A / D converters at a uniform sampling position of several positions to several tens of positions in a range of positions Z0 to Z5 at a constant sampling period. 11a is taken in and measured.

Then, the diagram shown in FIG.
0,2 linear current non drivers of the D / A converter
0, 40, 60, 80, 100, 120, 140, 16
It outputs at 10 points of 0 and 180 mA, and A, B, C, D, E, F, T at 0 mA at each current value position.
A / D conversion of E, FE, etc. in a short time, A1, B
1, C1, D1, E1, F1, TE1, FE1 are stored in RAM as one block, then set to 20 mA, and similarly A2, B2, C2, D2, E2, F2, TE2, FE2
Is stored in RAM as two blocks, and this is repeated up to 180 mA, and one block in which all the values of A, B, C, D, E, and F are the smallest among these blocks from this stored value Are extracted and compared with A, B,
Let C, D, E, F, TE, and FE be the target offsets. These A, B, C, D, E, F, TE, F
It is performed by outputting the D / A value corresponding to the value of E and determined by a table written in the ROM in advance so that the value becomes a predetermined reference voltage.

Therefore, in the sixth embodiment, the offset is adjusted by using the value when the light emitted from the laser diode LD and returned to the optical pickup is minimum , so that an accurate tracking error signal or focus error signal can be obtained. Therefore, the best data signal can be obtained at the time of reproduction or writing.

The offset referred to here is the offset of the optical sensor itself in the optical pickup 2, the offset of the circuit up to the measuring circuit as shown in FIG. 2, and the unnecessaryness from the laser diode LD in the optical pickup 2. The offset is included as stray light that is the return light. Therefore, as shown in FIG. 3, in the case of MD, the offset changes each time the laser power changes, such as 0.25 mW during reproduction in the ROM area and 0.5 mW and 5 mW during reproduction and recording in the MO area, respectively. The offset may be adjusted each time the laser power changes.

Next, a seventh embodiment of the present invention will be described. In the first to sixth embodiments, since the optical pickup 2 is moved in the focus direction, the optical pickup 2 may collide with the disc 1 due to the offset due to its own weight and damage the optical pickup 2 or the disc 1. By design, an image is formed on the data recording surface at the position Z6 shown in FIG. 3, but due to the weight of the optical pickup 2, it is far from the disc 1 when the optical pickup 2 is located below the disc 1 as shown in FIG. The position Z0 on one side becomes the image forming position, while the position Z7 near the disk 1 becomes the image forming position when the portable device is placed upside down. Therefore, in the former case (imaging at position Z0), there is no problem, but in the latter case (imaging at position Z7), the problem of collision occurs.

Therefore, in the seventh embodiment, the problem of the above collision is prevented by turning off the laser power or making it smaller than the normal reproduction power to adjust the offset. Explaining the specific operation, the optical pickup 2 is fixed to the initial position regardless of the disc detection signal, and the laser power is set to the minimum value, which is 1/5 of 0.25 mW when reproducing the ROM area of the disc 1. .05 mW or set to OFF, and signals A to F, TE, FE or A + C, B +
Repeat D etc. several tens of times at a fixed sampling cycle to obtain A /
The D converter 11a is taken in and measured.

Then, the average value of the measured values is calculated for each signal, and R is preset so that each voltage of the focus error signal FE and the tracking error signal TE becomes a reference voltage.
The offset value written in the OM 11d is output to the adders 31A to 31F, 33F and 33T for the signals A to F, TE and FE via the D / A converter 35.

The offset referred to herein is the offset of the optical sensor itself in the optical pickup 2 as described above, the offset of the circuit up to the measuring circuit as shown in FIG. 2, and the laser diode in the optical pickup 2. L
The offset as stray light cannot be measured in the second embodiment because the offset as stray light which is unnecessary return light from D is included, but the other two offsets are stably measured regardless of the direction of the optical pickup 2. can do. Further, in the optical pickup 2 having a sufficiently large offset with respect to stray light, it may be sufficient to correct the other two offsets. Furthermore, since this method is stable, there are cases where there is no measurement error compared to the first to sixth embodiments, and the accuracy can be improved, and the measurement time is significantly shorter, and the disk detection signal is further reduced. There is no need to judge.

Next, an eighth embodiment of the present invention will be described with reference to FIGS. First, when the laser powers are different as shown in FIG. 4, the detection signals A to F and A + C-
The levels of BD (FE) and EF (TE) are different, and tracking error signal TE is
Is a function of x (b1-b2) x is a stray light component and a constant (c
1-c2). In addition, as shown in FIG.
The b term shown in is proportional to the laser power x, and the c term is constant regardless of the laser power x.

Then, first, the MO of the MD (disc 1)
When reproducing the TOC area which is the area, the state where no current is passed through the focus coil is set as the initial position, the laser power x is set to 0.25 mW (= A), and the tracking offset Z1 is measured in this state. Remember.

[0054]

[Equation 5] EF = (b1-b2) A + c1-c2 = Z1 (measured value)

Next, when reproducing the data area which is the MO area, the laser power x is set to 0.5 mW (= B), and the tracking offset Z2 is measured and stored in this state.

[0056]

E−F = (b1−b2) B + c1−c2 = Z2 (measured value) From these two simultaneous equations, b1−b2 = (Z1−Z2) / (A−B) c1−c2 = (AZ2− BZ1) / (A-B), and by this formula, EF = (b1-b2) x + c1-c2 = (Z1-Z2) x / (A-B) + (AZ2-BZ1)
/ (AB)

It can be Therefore, when the laser power x is changed, the above values Z1 and Z2
The tracking offset can be calculated by measuring When adjusting this offset, the ROM 1 is set in advance so that the offset value becomes the reference value.
The offset value of the table written in 1d is output. Next, the case of adjusting the offset of the focus error signal FE will be described. First, like the tracking error signal TE

[0058]

A = axsin ωt + b1x + c1 B = axsin (ωt + π) + b2x + c2 C = axsin ωt + b3x + c3 D = axsin (ωt + π) + b4x + c4 A + C-B-D = 4axsin ωt + (b1 + b3-b2
-B4) x + c1 + c3-c2-c4

It is assumed that Then, first, when reproducing the TOC area which is the MO area of the MD, the state where no current is passed through the focus coil is set as the initial position, and the laser power x is set to 0.25 mW (= A). The focus offset Z1 is measured and stored.

[0060]

## EQU8 ## A + C-B-D = (b1 + b3-b2-b4)
A + c1 + c3-c2-c4 = Z1 (measured value)

Next, when reproducing the data area which is the MO area, the laser power x is set to 0.5 mW (= B), and the focus offset Z2 is measured and stored in this state.

[0062]

## EQU9 ## A + C-B-D = (b1 + b3-b2-b4)
B + c1 + c3-c2-c4 = Z2 (measured value) From these two simultaneous equations, b1 + b3-b2-b4 = (Z1-Z2) / (AB) c1 + c3-c2-c4 = (AZ2-BZ1) / (A-
B) becomes, and according to this formula, A + C−B−D = (b1 + b3-b2-b4) x + c1
+ C3-c2-c4 = (Z1-Z2) x / (AB) + (AZ2-BZ1)
/ (AB)

It can be Therefore, when the laser power x is changed, the above values Z1 and Z2
The focus offset can be calculated by measuring When adjusting this offset, the ROM 11 is preset so that the offset value becomes the reference value.
The offset value of the table written in d is output.

Next, a ninth embodiment of the present invention will be described. First, when the tracking offset is adjusted, the state where no current is passed through the focus coil is set as the initial position, the laser power is turned off (x = 0), and the tracking offset Z1 is measured and stored in this state.

[0065]

[Equation 10] EF = c1-c2 = Z1 (measured value)

Next, when reproducing the data area which is the MO area, the laser power x is set to 0.5 mW (= B), and the tracking offset Z2 is measured and stored in this state.

[0067]

[Equation 11] EF = (b1-b2) B + c1-c2 = Z2 (measured value) From these two simultaneous equations b1-b2 = (Z2-Z1) / B c1-c2 = Z1 And this formula gives EF = (b1-b2) x + c1-c2 = (Z2-Z1) x / B + Z1

It can be Therefore, when the laser power x is changed, the above values Z1 and Z2
The tracking offset can be calculated by measuring Next, the operation of adjusting the focus offset in the ninth embodiment will be described. The state where no current is applied to the focus coil is set as the initial position, and the laser power is turned off (x = 0).
Measure 1 and store.

[0069]

## EQU12 ## A + C-B-D = c1 + c3-c2-c4 = Z1 (measured value)

Next, when reproducing the data area which is the MO area, the laser power x is set to 0.5 mW (= B), and the focus offset Z2 is measured and stored in this state.

[0071]

## EQU13 ## A + C-B-D = (b1 + b3-b2-b
4) B + c1 + c3-c2-c4 = Z2 (measured value) From these two simultaneous equations, b1 + b3-b2-b4 = (Z1-Z2) / Bc1 + c3-c2-c4 = Z1, and from this formula, A + C-B-D = (B1 + b3-b2-b4) x + c1
+ C3-c2-c4 = (Z1-Z2) x / B + Z1

It can be Therefore, when the laser power x is changed, the above values Z1 and Z2
The focus offset can be calculated by measuring When adjusting the offset,
The ROM 11d is preset so that the offset value becomes the reference value.
The offset value of the table written in is output.

In the first to ninth embodiments, the focus offset and the tracking offset are adjusted by detecting the focus error signal FE (= A + C-B-D) and the tracking error signal TE (= E-F). The case where the eight signals A to F, TE, and
Any of FE may be used, and a combined signal such as a sum signal of A + C and B + D may be used. Also,
The offset adjustment may be performed by the follow-up adjustment instead of using the table written in the ROM 11d in advance, and the PWM adjustment may be performed instead of the D / A converter 35.
The signal may be converted into a DC voltage and applied to the adders 32F and 32T.

In the eighth and ninth embodiments, the laser power x is set to 0 mW (off), 0.25 mW (when reproducing the TOC area), and 0.5 mW (when reproducing the data area). The offset can be adjusted without setting it to 5 mW when recording in the MO area, and the measurement is completed in a short time without the risk of erasing the necessary data with the method that normally outputs 5 mW and adjusts the offset. There are also merits. Further, the above-mentioned arithmetic expression is an example, and may be simplified, or the tables may be switched and used instead of the arithmetic operation.

[0075]

As described above, according to the present invention, the offset is adjusted at the focus positions different from the first and second focus positions respectively corresponding to the surface of the optical disk and the data recording surface in the optical disk. It is possible to adjust the offset due to the circuit or optical system in "the state where there is no original unnecessary signal", so it is possible to obtain accurate tracking error signal and focus error signal, and as a result, during playback and writing. The best data signal can be obtained.

In the present invention, the laser diode
Since the offset is adjusted based on the maximum value or the minimum value of the signal detected when the amount of light that exits and returns to the optical pickup is the minimum, the offset by the circuit or the optical system is adjusted in the "no signal" state. Therefore, an accurate tracking error signal or focus error signal can be obtained, and as a result, the best data signal can be obtained at the time of reproduction or writing.

Further, in the present invention, the offset is adjusted by the constant term of the signal detected by the laser power of at least two levels and the variable term by the power change. Therefore, the offset is adjusted even when the laser power is different. Therefore, it is possible to obtain an accurate tracking error signal or focus error signal,
As a result, the best data signal can be obtained during reproduction or writing.

[Brief description of drawings]

FIG. 1 is a MD to which an offset adjusting device of the present invention is applied.
It is a block diagram showing a recording device.

FIG. 2 is a block diagram showing the preamplifier of FIG.

FIG. 3 is an explanatory diagram showing a relationship between a focus current and an amount of reflected light.

FIG. 4 is an explanatory diagram showing a relationship between laser power and various detection signal levels.

FIG. 5 is an explanatory diagram showing a constant term in a detection signal and a variable term due to a power change.

[Explanation of symbols]

1 disc 2 optical pickup 9 preamplifier (detection / adjustment means) 11 Microcomputer (control means) 31A to 31F, 33F, 33T adder 32F, 32T calculator

─────────────────────────────────────────────────── --- Continuation of the front page (56) Reference JP-A-3-141038 (JP, A) JP-A-4-186532 (JP, A) JP-A-63-155425 (JP, A) JP-A-63- 306540 (JP, A) JP-A-4-177621 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G11B ^7/ 09-7/10

Claims (3)

(57) [Claims] 1. A detection means for detecting a signal reproduced from an optical disc by an optical pickup, a tracking error signal generation means, and a focus error signal generation means,
An offset measuring unit that measures an offset of one or both of a tracking error signal and a focus error signal, an offset correcting unit that corrects an offset of one or both of the tracking error signal and the focus error signal, and the optical pickup to the optical disc. With respect to the focus direction, means for sequentially measuring the offset by the offset measuring means during this movement, means for storing the measurement result of the measured offset in relation to the focus position, the measurement result Means for comparing with a predetermined threshold value, means for detecting first and second focus positions respectively corresponding to the surface of the optical disc and the data recording surface in the optical disc from the comparison result, the first and second Focus position different from the focus position Move the serial optical pickup, and control means for correcting an offset by the offset correction means, the offset adjustment device of an optical disk apparatus having. 2. A detection means for detecting a signal reproduced from an optical disc by an optical pickup, a tracking error signal generation means, a focus error signal generation means,
Offset measuring means for measuring an offset of one or both of a tracking error signal and a focus error signal, an offset correcting means for correcting an offset of one or both of the tracking error signal and the focus error signal, and laser power of the optical pickup. To at least two values for emitting light, means for measuring the offset in the respective laser power values by the offset measuring means, and the measurement result of the measured offset is the respective laser power values. And a means for storing a constant offset component not related to the laser power value at the offset and an offset component due to a stray light component that changes due to laser power change, and each laser power based on the calculated value. And control means for correcting an offset by the offset correcting means by a value, the offset adjustment device of an optical disk apparatus having. 3. The offset adjusting device for an optical disk device according to claim 2 , wherein one of two values for changing the laser power of the optical pickup is laser power off.