JPH0266743A - Servo control system for optical disk device - Google Patents

Abstract

PURPOSE:To prevent the over-detection of a servo error to occur due to the change of the emitting light power of an optical head by masking the generation of a servo error signal by a gate signal generated from the light emitting power change of an optical head. CONSTITUTION:A servo control part 3 provides a servo error detecting circuit 34b and a gate preparing circuit 38. The servo detecting circuit 34b compares a track error signal and a focus error signal TES with a prescribed slice level and generates a servo error signal. The gate preparing circuit 38 generates the gate signal from the change of the light emitting power of an optical head 2. The gate signal masks the generation of a servo error signal. Consequently, the over-detection of the servo error due to the offset to occur at the change point of the emitting light power can be simply prevented.

Description

[Detailed description of the invention] [Table of contents] Overview Industrial field of application Prior art (Figure 6) Means for solving the problem to be solved by the invention (Figure 1) Working example (a) 1 Explanation of the configuration of the embodiment (Figures 2 and 3) (
b) Explanation of the operation of one embodiment (Fig. 4) (C) Explanation of another embodiment (Fig. 5) (dl Explanation of another embodiment Effect of the invention The servo error signal can be generated by the gate signal. [Summary] This invention relates to a servo control method for an optical disk device that controls the tracking of the light beam of an optical head on an optical disk such as an optical disk or a magneto-optical disk.

The purpose is to prevent over-detection of servo errors caused by changes in the output light power of the optical head.

An optical head that irradiates an optical disk with a light beam and receives light from the optical disk to obtain a light reception signal.

An error signal of the light beam is determined from the received light signal.

In an optical disk device having a servo control unit that tracks and controls a light beam of the optical head based on the error signal, the servo control unit compares the error signal at a predetermined slice level and generates a servo error signal. A servo error detection circuit and a gate generation circuit that generates a gate signal from a change in light output power of the optical head are provided, and the generation of the servo error signal is masked by the gate signal.

[Industrial application field]

The present invention relates to a servo control method for an optical disk device that controls a light beam of an optical head to follow an optical disk such as an optical disk or a magneto-optical disk.

Optical disk devices are attracting attention as large-capacity storage devices because they can perform serial read/write using a light beam, allowing the track spacing to be several microns.

In this optical disk device, track/focus servo control is used to control the tracking of the light beam to the relevant track or focal point position.

In such an optical disk device, there is a need for a technology that does not cause servo errors even when the output light power of the optical head is changed during a write operation or an erase operation.

[Conventional technology]

FIG. 6 is an explanatory diagram of the prior art.

As shown in Part 6, the optical disk device is configured such that an optical head 2 is moved and positioned in the radial direction of the optical disk 1 by a motor (not shown) with respect to an optical disk 1 which is rotated around a rotation axis by a motor 1a. Reading (reproduction)/writing (recording) to 1 is performed.

On the other hand, the optical head 2 transmits light emitted from a semiconductor laser 24, which is a light source, to a lens 25. The light is guided to the objective lens 20 through the polarizing beam splitter 23, focused into a beam spot (spot light) BS by the objective lens 20, and irradiated onto the optical disc 1. The reflected light from the optical disc 1 is transmitted through the objective lens 20 from the polarizing beam splitter 23 to The light is configured to be incident on the split light receiver 26.

In such an optical disk device, a large number of tracks or bits are formed at intervals of several microns in the radial direction of the optical disk 1, and even slight eccentricity causes large track positional deviations, and undulations of the optical disk 1 cause the beam spot to change. Focus position shifts occur, and it is necessary to make the beam spot of 1 micron or less follow these position shifts.

For this reason, a focus actuator (focus coil) 22 (!:) moves the objective lens 20 of the optical head 2 in the vertical direction of the figure to change the focal position.

A track actuator (track coil) 21 is provided that moves the objective lens 20 in the left-right direction in the figure to change the irradiation position in the track direction.

Correspondingly, the focus servo control section 3b generates a focus error signal FES from the light reception signal of the light receiver 26, drives the focus actuator 22, and generates a track error signal TES from the light reception signal of the light receiver 26. , a track servo control section 3a that drives the track actuator 21 is provided.

The track error signal TE8 and focus error signal FBS are below the 2 normal slice level in the servo-on state, and the light beam follows the track and focus position.

On the other hand, a servo error detection circuit is provided to detect when the light beam deviates from the track or focus range.

Track error signal TBS and focus error signal F
Compare E8 with a predetermined slice level SL.

Track error signal TE8. Focus error signal FE
When the amplitude of S exceeds the slice level SL.

The servo was in an error state where it could not follow up, and a servo error signal was generated.

In this way, if a servo error occurs while the servo is on, the track servo is immediately interrupted.

The write or read operation was canceled.

[Problem to be solved by the invention]

By the way, in an optical disk device, the output light power of a laser diode in an optical head is not constant.

When writing or erasing, it changes more like a dog than when on a lead.

When the output light power of the optical head is changed in this way, the two oscillation modes change, and the output angle and oscillation wavelength change. If this change is gradual, the track and focus servo will follow, but it is sudden.

As shown in FIG. 6(B), an instantaneous transient causes an offset in the track error signal TES and the focus error signal FES at a change point.

This offset tends to be equal to or higher than the slice level SL as shown in TBS' and FB8' in FIG.

In other words, even though the track servo and focus servo are following, -fit and erase.

The problem is that the slice level is exceeded due to a transient caused by a change in the emitted light power when switching the leads, and a servo error signal is generated, resulting in overdetection of wrinkle servo errors.

Accordingly, it is an object of the present invention to provide a servo control system for an optical disk device that can prevent over-detection of servo errors caused by changes in the output light power of an optical head.

[Failure to solve the problem]

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

As shown in FIG. 1, the present invention includes an optical head 2 that irradiates a light beam onto an optical disc 1, receives light from the optical disc 1 to obtain a light reception signal, and an error signal of the light beam from the light reception signal. In an optical disk device having a servo control unit 3 that calculates the error signal and controls the optical beam of the optical head 2 to follow based on the error signal, the servo control unit 3 compares the error signal at a predetermined slice level, and a servo error detection circuit 34b that generates a servo error signal.

A gate generation circuit 38 for generating a gate signal from the change in the light output power of the optical head 2 is provided, and the generation of the servo error signal is masked by the gate signal.

Note that the mask may be placed before or after the servo error detection circuit 34b.

[Effect]

In the present invention, since an offset occurs at a change point in the output light power of the optical head 2, the change point is detected and a gate signal is created, thereby masking the occurrence of a servo error.

Therefore, it is possible to easily prevent over-detection of servo errors due to offsets occurring at changing points of the emitted light power.

〔Example〕

(a) Description of the configuration of one embodiment FIG. 2 is an overall configuration diagram of an embodiment of the present invention.

An example in which the present invention is applied to a track servo control section 3a of a magneto-optical disk device is shown.

In the figures, the same parts as those shown in FIGS. 1 and 6 are indicated by the same symbols.

Reference numeral 5 denotes a control section which is composed of a microprocessor and controls the servo control operations of the track servo control section 3a and the servo control operations of the focus servo control section 3b (see FIG. 6).

60 is an RF generation circuit, and the output a of the 4-division light receiver 26
61 is an amplifier circuit that amplifies the outputs a - d of the 4-split optical receiver 26 and outputs the servo output S■aNSVd.

66 is a write pulse generation circuit that converts upper write data into a write pulse having a width according to the inner/outer signal of the MPU 5.

67 is a write/erase circuit that drives the semiconductor laser 24 with write pulses and erase pulses to perform write/erase operations.
This is to perform an erase operation.

30 is a TES creation circuit, which includes amplifiers 61 (61a to 6
1d) to create a track error signal TBS from the servo output 8V a -8V d.

31 is a total signal generation circuit, and servo output SVa ~ 8V
d to create the total signal DEC which is the total reflection level, 32 is A
in Control) circuit, which divides the track error signal TE8 by the total signal (total reflection level) DO8.

It performs AGC using the total reflection level as a reference value,
This is to compensate for fluctuations in irradiation beam intensity and reflectance.

33 is a phase compensation circuit, which outputs the track error signal TES.
is differentiated and added to the proportional portion of the track error signal TE8,
This advances the phase of the high range.

34a is a zero-crossing detector which detects the zero-crossing point of the track error signal TBS and outputs the track zero-crossing signal TZC to the MPU 5; 34b is the aforementioned servo error detection circuit (off-track detection circuit);
The track error signal TBS is a constant value Vo in the positive direction.
(SL) or above and a constant value in the negative direction -Vo
(-8L) or less, that is, an off-track state is detected, and an off-track (servo error) signal TO8 is output to the MPU 5.

35 is a servo switch 4fi, which closes when the servo-on signal SVS of the MPU 5 turns on, closes the servo loop, opens when it turns off, and opens the servo loop.

36 is an inverting amplifier that inverts the output of the servo switch 35, and 37 is a power amplifier.

The output of the inverting amplifier 36 is amplified to generate a track drive current TD.
V is applied to the track actuator 21.

38 is the aforementioned gate creation circuit, and the semiconductor laser 24
From the total signal DC8 indicating the output light level of.

39 is a gate circuit (mask circuit) that detects a change point in the emitted light level and creates a gate signal, and outputs the track error signal TBS to the servo error detection circuit 34b using the gate signal of the gate creation circuit 38. It is for masking.

FIG. 3 is a diagram showing the main part of an embodiment of the present invention.

The total signal generation circuit 31 includes an addition amplifier 310 that adds each servo output 8Va to SVd via input resistors r5 to r8, and generates a total reflection level signal DC8 (=SV a + S
The O gate creation circuit 38 that outputs V b + S V c + 8 V d ) includes a low pass filter 380 that cuts the high frequency range of the total signal DO8, and a loop (the output of the filter 380 is amplified with a gain G>1). A first amplifier 381 that amplifies the output of the loop filter 380 with a gain G<1, and a first amplifier that compares the output DC81 of the first amplifier 381 and the total signal DC8. Comparator 383, total signal DO8 and second amplifier 3
82 and a second comparator 384 for comparing the output DC 82 with the DC 82 output.

The gate circuit 39 includes an inverter 390 that inverts the gate signal GS, a switch 391 that grounds the addition point with the output of the inverter 390, and an addition resistor r for the track error signal TE8.

The off-track detection circuit 34b compares the track error signal TE8 from the gate circuit 39 with a constant value 0, and determines that T
ES〉■ The first comparator 341 outputs a "low" output when 0, and the track error signal TES and a constant value (-
Vo), and a second comparator 342 that outputs a "low" output when TES
Output as O8.

(b) Description of operation of one embodiment FIG. 4 is an explanatory diagram of operation of one embodiment of the present invention. In the O servo-on state, the output of the four-division light receiver 26 is 8 V a -
8V d, the TBS creation circuit 30 creates a track error signal TE8, the AGC circuit 32 performs AGC control, the two-phase compensation circuit 33 performs phase compensation, and the servo switch 35
The track actuator 21 is driven through a 2-inverting amplifier 36° power amplifier 37 to perform so-called track servo control.

Further, the track error signal TFiS is inputted to the servo error detection circuit 34b via the gate circuit 39.

Servo error detection is performed.

In this state, when the erase operation starts as shown in Figure 4,
The level of light emitted from the semiconductor laser 24 increases.

The level of all signals DC8 becomes high.

The total signal DC8 is input to the gate creation circuit 38, and the rising and falling edges of the total signal DC8 are input to the low pass filter 380.
1st each. input to the second amplifier 381.382.

Since the gain G is G>1, the output of the first amplifier 381 is like DC81, and the output of the second amplifier 382 is like DO82 because the gain G is G<1.

Therefore, at the rising edge of erase, the first comparator 38
3, a low level gate signal G8 is generated.

At the falling edge of erase, the second comparator 384 generates a lawn bell gate signal GS. This gate signal GS is input to the gate circuit 39.

The signal is inverted by an inverter 390 and a switch 391 is operated.

That is, the gate signal GS is at low level.

Through the inverter 390, the switch 391 is turned on and the addition point a is grounded, so the track error signal TE8
is not output to the servo error detection circuit 34b and is masked.

Further, when the gate signal G8 is at a high level, the switch 3
91 is off, the track error signal TBS is output to the servo error detection circuit 34b.

Therefore, due to the erase operation of the semiconductor laser 24, the output of the track error signal TES to the servo error detection circuit 34b with an offset generated at the change point of the emitted light level is masked at the change point, and the servo error is over-detected. can be prevented.

Also, although the write operation is not as good as the erase operation, as shown in FIG.
C8 level is dog.

In this case as well, at the rise and fall of the light,
A low level gate signal GS is generated.

Track error signal TES is masked at the change point 0 In this way, the level of the total signal DC8 changes.

That is, detecting the power change of the light emitted from the semiconductor laser 24,
The gate signal G8 is generated by the gate generation circuit 38, and the track error signal TE81 is masked by the gate circuit 39, thereby masking the generation of the servo error signal.

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

The embodiment shown in FIG. 5(5) shows another example of the gate generation circuit 38, in which the gate signal G
8.

In the figure, 385 is the first shift register.

Something that delays the write gate signal WG by a predetermined amount.

386 is a first FOR (exclusive OR) circuit, which calculates the exclusive OR of the write gate signal WG and the output DWG of the first shift register 385; 387 is a second shift register; , which delays the erase gate signal EG by a predetermined amount.

388 is a second EOR circuit, which performs the exclusive OR of the erase gate signal EG and the output signal DEG of the second shift register 387; 389 is an OR gate; Outputs Gl, G of the second BOR circuit 386°388
2, and outputs the gate signal GS.

FIG. 5G3) is a waveform diagram of gate signal generation in the configuration shown in FIG. 5(5).

In this embodiment, the MPU 5 has a write/erase circuit 6
7, a write gate signal WG is generated as a write instruction, and an erase gate signal EG is generated as an erase instruction.
is used as a signal indicating the level of light emitted from the semiconductor laser 24, and the gate signal G8 is generated at the point of change.

That is, write gate signal WG or erase gate signal E
G is delayed by a certain amount in shift registers 385 and 387,
The EOR circuits 386 and 388 perform the exclusive OR of the rising and falling pulses Gl.

G2 is obtained and this is sent to the gate signal GS by the OR gate 389.
This is what is output as.

In this example, since the gate signal GS is high level, the third
The inverter 390 of the gate circuit 39 shown in the figure is not required.

In this way, the gate signal G8 can be digitally obtained by the logic circuit using the control signal for changing the emitted light without using the actual emitted light level of the semiconductor laser 24.

(d) Description of another embodiment In the embodiment described above, the signal representing the light emission power (output light power) of the optical head is converted into a total signal that is a light reception signal, a write gate signal or an erase gate signal that is a power control signal. For example, the output of the semiconductor laser itself or the light-receiving output of a monitoring light-receiving element (such as a pin diode) of the semiconductor laser may be used.

Further, in the above embodiment, the track error signal TE8 is masked with the gate signal G8 at the stage before the servo error detection circuit 34b, but a gate circuit is provided at the stage after the servo error detection circuit 34b, and the servo error signal is gated. Signal G
8 may be masked by 0 Furthermore, 7 In the above-described embodiment, an example was explained in which it was applied to track servo control, but this is because the slice level margin for servo error is narrower than in focus servo control. Since the focus error signal FES also has an offset, it may be applied to focus servo control as well, or only to focus servo control, if necessary.

Furthermore, although the description has been made using a magneto-optical disk as an example, the present invention can also be applied to a write-once optical disk, in which case erasing is not performed.

Although the present invention has been described above using examples, the present invention can be modified in various ways according to the gist of the present invention.

These are not excluded from the present invention.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to prevent over-detection of servo errors due to offsets caused by changes in the output light level of the optical head, and stable write and erase operations are possible.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the principle of the present invention. FIG. 2 is an overall configuration diagram of an embodiment of the present invention. FIG. 3 is a diagram showing the main part of an embodiment of the present invention. FIG. 4 is an explanatory diagram of the operation of one embodiment of the present invention. FIG. 5 is an explanatory diagram of another embodiment of the present invention. FIG. 6 is an explanatory diagram of the prior art. In the figure, 1... optical disc. 2...Optical head. 3... Servo control section. 34b... Servo error detection circuit. 321...Gate creation circuit.

Claims (1)

[Claims] A light beam is irradiated onto the optical disc (1), and the optical disc (1) is
an optical head (2) that receives light from 1) and obtains a light reception signal;
); and a servo control section (3) that determines an error signal of the light beam from the received light signal and controls the light beam of the optical head (2) to follow based on the error signal. The control unit (3) includes a servo error detection circuit (34b) that compares the error signals at a predetermined slice level and generates a servo error signal.
and a gate creation circuit (38) for creating a gate signal from a change in the light output power of the optical head (2), and the gate signal masks generation of the servo error signal. servo control method.