JP2698635B2 - Optical disk apparatus and track servo offset correction method therefor - Google Patents

Description

Detailed Description of the Invention [Table of Contents] Overview Industrial field of application Conventional technology (Fig. 6) Problems to be solved by the invention Means for solving the problem (Fig. 1) Action Embodiment (a) One Description of Embodiment (FIGS. 2, 3 and 4) (b) Description of Another Embodiment (FIG. 5) (c) Description of Another Embodiment Effect of the Invention [Overview] A method of correcting a track servo offset of a track servo control unit that controls a tracking of a light beam, which is intended to remove an offset of a track error signal caused by characteristics of an optical disk or an optical head, and irradiates the optical disk with a light beam. An optical head for receiving light from an optical disk; a track error signal generated from a light reception signal of the optical head; and a track following control of a light beam of the optical head based on the track error signal. Providing an offset correction signal to the track error signal of the track servo control unit, and measuring a zero cross duty of the track error signal provided with the offset correction signal in the optical disk device having the track servo control unit. And changing the offset correction signal so that the measurement result has a duty of 50%.

[Industrial applications]

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

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. 6 is an explanatory diagram of the prior art.

As shown in FIG. 6 (A), the optical disc device has a motor.
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. Will be

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 control unit 3 has essentially no offset and is symmetric about 0 V as shown in FIG. 6 (B).

However, due to the circuit-specific offset, the tilt of the optical disk, and the displacement of the head optical system, FIG.
As described above, an offset occurs in the track error signal TES, and the track error signal TES becomes asymmetric around 0V.

When an offset occurs in the track error signal TES,
The speed is detected by the TES zero-cross signal in which the track error signal TES is zero-cross detected, and the access means such as a track jump becomes inaccurate.

The servo error is detected by the track error signal TES
Is sliced at a slice level that is vertically symmetric with respect to 0 V to generate an off-track signal, so that servo error detection becomes uncertain.

Further, when the track servo is on, FIG.
Kickback at 0V offset by the offset as shown above, and it is not possible to track on the exact position.

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]

However, the offset of the track error signal is
It is also caused by the tilt of the optical disk, particularly the bending, the displacement of the optical system of the optical head 2, the drift of the emitted light due to the temperature change, and the change of the light receiving characteristic.

In the related art, there is a problem that even if the circuit offset can be removed, the offset due to the optical disk or the optical head cannot be removed.

Accordingly, an object of the present invention is to provide an optical disc apparatus capable of removing an offset of a track error signal caused by the characteristics of an optical disc and an optical head, and a track servo offset correction method therefor.

[Means for solving the problem]

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

According to the present invention, as shown in FIG. 1, 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 error signal from a light receiving signal of the optical head 2 are created. A step of providing an offset correction signal to the track error signal of the track servo control section in an optical disc apparatus having a track servo control section 3 for controlling the track following of the light beam of the optical head 2 based on the track error signal; Measuring the zero-cross duty of the track error signal to which the offset correction signal has been applied for a time required for a half turn of the optical disc 1 and changing the offset correction signal so that the measurement result has a duty of 50%. The above steps are performed when the power is turned on or when the optical disk is replaced.

[Action]

According to the present invention, when the zero-cross duty of the track error signal TES is 50%, the track error signal TES is vertically symmetric and the offset has been removed. The zero cross duty is measured and the zero cross duty is 50% by the offset correction signal to be applied.
Is adjusted so as to eliminate the offset on the track error signal.

〔Example〕

 (A) Description of one embodiment FIG. 2 is a block diagram of one embodiment of the present invention.

In the figure, the same components as those described in FIGS. 1 and 6 are denoted by the same symbols.

Reference numeral 5 denotes a main control unit which is composed of a microprocessor and controls the servo control operation of the track servo control unit 3 using a track zero cross signal TZC, an off-track signal TOS, and a servo-on signal SVS, and a third adjustment described later. The processing removes the track servo offset and controls the servo operation of the focus servo controller 4 (see FIG. 6).

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 31 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 DCS 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.

33 is an offset adding circuit, which is a track error signal
An addition amplifier for adding an offset correction level (voltage) from a main control unit (hereinafter referred to as an MPU) 5 to TES, and adding an output of the AGC circuit 32 and an offset correction voltage TSO from a D / A converter described later. Has AMP.

34a is a zero cross detector, which has a 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 a servo-on signal SV of MPU5.
37 is a digital / analog converter (referred to as D / A converter) that closes when S turns on, closes the servo loop, opens when off, and opens the servo loop, and converts the offset correction value TSO of MPU5 to the analog offset correction voltage. It is converted and output to the offset applying circuit 33.

39a is an inverting amplifier that inverts the output of the servo switch 36, 39 is a power amplifier, and the inverting amplifier 39
The output of a is amplified and the track drive current TDV is supplied to the track actuator 21.

FIG. 3 is a flowchart of the offset correction processing in one embodiment of the present invention, and FIG. 4 is an explanatory diagram of the operation of one embodiment of the present invention.

The MPU 5 turns off the track servo switch 36, and measures the duty of the track zero cross signal TZC of the zero cross detection circuit 34a by the processing of FIG.

Then, the time PTZC when the amplitude of the track error signal TES is larger than zero and the time NTZC when it is smaller than zero are obtained.

 Next, the MPU 5 obtains the sum A of PTZC and NTZC.

Further, the MPU obtains the duty ratio B by (PTZC ÷ A). This may be (NTZC @ A).

Next, the MPU 5 sets B> 0.5 + a with a being an allowable range value.
Is determined.

If B> 0.5 + a, there is a direction offset, so T
"1" is added to the ES offset correction value, which is output to the D / A converter 37, the offset correction voltage is increased, and the process returns to the step measurement.

Conversely, if the MPU 5 determines that B> 0.5 + a is not satisfied,
<0.5-a is determined.

If B <0.5-a, there is a direction offset, so T
Subtract “1” from the ES offset correction value, output this to the D / A converter 37, reduce the offset correction voltage,
Return to step measurement.

On the other hand, unless B <0.5−a, 0.5−a ≦ B ≦ 0.5 +
a, and the duty ratio is about 50%, so that the processing ends assuming that the offset has been removed.

Next, the duty measurement processing of FIG. 3B will be described.

The MPU 5 sets the timer interrupt time t in the built-in timer 5b.

This time t is a duty measurement time, and is preferably equal to or longer than the time required for a half turn of the optical disc, and in this example, is set as the time required for one turn.

Further, the MPU 5 initially sets PTZC and NTZC of the internal memory 5a to “0”.

 Then, the timer 5b is started.

For MPU5, the track zero cross signal TZC is "1" (high)
Find out what.

The track zero cross signal TZC is obtained by slicing the track error signal TES at 0 V as shown in FIG.
If ES ≧ 0, it indicates “1”, and if TES <0, it indicates “0”.

Therefore, if TZC = "1", TES≥0, if TZC = "0", TES <
0.

When determining that TZC = "1", the MPU 5 updates PTZC in the memory 5a to (PTZC + 1) because TES ≧ 0.

Conversely, when TZC ≠ “1” is determined, TES <0,
Update NTZC in memory 5a to (NTZC + 1).

Then, the MPU 5 checks whether there is a count-up interrupt of the timer 5b. If not, the MPU 5 returns to the step.

In this way, as shown in FIG. 4, FIG.
Then, at the measurement time t, the time of TES ≧ 0 and TZC = “1”
The PTZC and the time NTZC when TES <0 and TZC = "0" are measured.

Then, as shown in FIG.
It is determined whether it has reached 50%, and the offset correction amount TSO is changed until it reaches 50%.

Thereby, in addition to the circuit offset, a total offset including the characteristics of the optical disk and the optical head can be corrected.

This offset correction may be performed when the power is turned on or when the optical disk medium is replaced. When the temporal change due to the temperature is large, the timer has an internal timer and is performed when a seek command arrives after a predetermined time has elapsed. You may do so.

Further, in this embodiment, no special hardware is required since the firmware is realized by the firmware of the MPU 5.

(B) Description of another embodiment FIG. 5 is an explanatory diagram of another embodiment of the present invention.

In the drawing, the same components as those shown in FIG. 2 are denoted by the same symbols, and 70 and 71 are AND gates, which are supplied by a "high" level sample enable signal during a sample (measurement) period t of the MPU 5. Open, track zero cross signal TZC
Or, an output of the inverted signal * TZC, 72 is an inverting circuit, which inverts the track zero cross signal TZC and outputs it to the AND gate 71, 73 and 74 are counters, and AND gates 70 and 71, respectively. When the output is at a "high" level, the clock is counted.

In this embodiment, the measurement of the duty in the embodiment of FIG. 2 is performed by the firmware of FIG. 3B, but is performed by hardware.

That is, the AND gates 70 and 71 open for the measurement period t, and TZ
If C is “1”, the counter 73 counts the clock and the time PTZ
C is calculated, and if TZC is “0”, the counter 74 counts the clock and calculates the time NTZC.

In FIG. 3 (A), when measurement is necessary, the MPU 5 first clears the counters 73 and 74 with a clear signal, issues a sample enable signal for a certain period of time, causes the measurement, and reads both counters 73 and 74 after the measurement. To get PTZC and NTZC.

 The subsequent processing is as shown in FIG.

(C) Description of Another Embodiment In the above-described embodiment, the main control unit 5 performs the correction. However, the correction may be performed by a dedicated device or circuit. May be.

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 zero cross duty of the track error signal TES is measured while applying the offset correction signal, and the correction signal is changed so that the zero cross duty becomes approximately 50%. In addition to the circuit offset, there is an effect that the offset due to the characteristics of the optical disk and the optical head can be corrected and removed,
Stable track servo can be realized by a track error signal without offset.

[Brief description of the drawings]

FIG. 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 flowchart of an adjusting process of one embodiment of the present invention, and FIG. FIG. 5, FIG. 5 is an explanatory view of another embodiment of the present invention, and FIG. 6 is an explanatory view of a conventional technique. In the figure, 1 ... optical disk, 2 ... optical head, 3 ... track servo control unit.

Claims (2)

(57) [Claims] An optical head (2) for irradiating an optical disk (1) with a light beam and receiving light from the optical disk (1).
An optical disc having a track servo control unit (3) for generating a track error signal from the light receiving signal of the optical head (2) and controlling the track following of the light beam of the optical head (2) based on the track error signal; In the apparatus, an offset correction means for applying an offset correction signal to the track error signal of the track servo control unit (3), and a zero-cross duty of the track error signal to which the offset correction signal has been added is set to a half cycle of the optical disc (1). And a zero-cross duty measuring means for measuring the time required for the offset correction signal, so that when the power is turned on or the optical disk is replaced, the offset correcting signal is output by the offset correcting means so that the measurement result of the zero-cross duty measuring means has a duty of 50%. An optical disk device characterized by being changed. 2. An optical head (2) for irradiating an optical disk (1) with a light beam and receiving light from the optical disk (1).
An optical disc having a track servo control unit (3) for generating a track error signal from the light receiving signal of the optical head (2) and controlling the track following of the light beam of the optical head (2) based on the track error signal; In the apparatus, a step of applying an offset correction signal to the track error signal of the track servo control unit (3), and a half cross duty of the track error signal to which the offset correction signal is added is required for a half turn of the optical disc (1). An optical disc device, comprising: a step of measuring for a time longer than a given time; and a step of changing the offset correction signal so that the measurement result has a duty of 50%. Track servo offset correction method.