JPH02166633A - Method for correcting tracking servo offset of optical disk device - Google Patents

Abstract

PURPOSE:To remove the offset of a tracking error signal by attaching an offset correction signal on the tracking error signal, and adjusting the offset correction signal so as to set the zero cross duty of the tracking error signal on which the offset correction signal is attached at a duty of 50%. CONSTITUTION:In an optical disk device having a tracking servo control part 3 which generates the tracking error signal from the light receiving signal of an optical head 2, and performs the track follow-up control of the light beam of the optical head 2 based on the tracking error signal, the offset correction signal is attached on the tracking error signal TES of the tracking servo control part 3. And the zero cross duty of the tracking error signal TES on which the offset correction signal is attached is measured, and the offset correction signal is adjusted so as to set a measured result at the duty of 50%. In other words, the tracking error signal TES goes to a signal symmetric in upper and lower directions when the zero cross duty of the tracking error signal TES is set at the duty of 50%, and the offset can be removed. In such a way, it is possible to remove the offset of the tracking error signal.

Description

[Detailed description of the invention] [Next] Overview Industrial field of application Prior art (Fig. 6) Means for solving the problem to be solved by the invention (Fig. 1) Working example (a) ) Description of one embodiment (Figs. 2, 3, and 4) (b) Description of another embodiment (Fig. 5) (C) Description of another embodiment Effects of the invention [Summary] Optical disc Regarding a method of correcting track servo offset in a track servo control unit that controls the tracking of a light beam on a track, this paper aims to eliminate the offset of a track error signal caused by the characteristics of an optical disc or an optical head. , an optical head that receives light from the optical disk, and a track servo control unit that creates a track error signal from the light reception signal of the optical head and controls the optical beam of the optical head to follow the track based on the track error signal. In an optical disk device having the following steps, the steps include: adding an offset correction signal to the track error signal of the track servo control unit; measuring a zero-cross duty of the track error signal to which the offset correction signal is added; and changing the offset correction signal so that the duty becomes 50%.

[Industrial application field]

The present invention relates to a track servo offset correction method for a track servo control unit that controls a light beam to follow a track on an optical disc.

Optical disk devices using optical disks and magneto-optical disks are capable of reading/writing with a light beam, allowing track spacing to be several microns, and are attracting attention as large-capacity storage devices.

In this optical disc device, track servo control is used to control the tracking of a light beam to the relevant track.

Track servo control uses diffraction of a guide groove (pre-group) of an optical disk medium to obtain a track error signal, and applies servo to cause a light beam to follow a track (guide groove).

In such track servo control, there is a demand for stable track servo control by removing offsets of track error signals that occur due to various causes.

[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 l.
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 the optical disk 1 rotating around the rotation axis by a, and the optical head 2 reads (plays)/writes (records) the optical disk 1. will be held.

On the other hand, the optical head 2 guides the light emitted from the semiconductor laser 24, which is a light source, to the objective lens 20 via the lens 25 and the polarizing beam splitter 23. It is configured such that the reflected light from the polarizing beam splitter 23 enters a four-split light receiver 26 via an objective lens 20.

In such an optical disk device, a large number of tracks or pits 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 waviness of the optical disk 1 causes 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 purpose, a focus actuator (focus coil) 22 moves the objective lens 20 of the optical helid 2 in the vertical direction in the figure to change the focal position, and a focus actuator (focus coil) 22 moves the objective lens 20 in the left and right directions in the figure to track the irradiation position. A track actuator (track coil) 21 for changing the direction is provided.

Correspondingly, the focus servo control section 4 generates a focus error signal FES from the light reception signal of the light receiver 26, drives the focus actuator 22, and generates a tracking error signal TBS from the light reception signal of the light receiver 26. , a track servo control section 3 for driving a track actuator 21 is provided.

Incidentally, the track error signal TBS of the track servo control section 3 is desirably free of offset and is symmetrical about 0■ as shown in FIG. 6(B).

However, due to the circuit-specific offset, the inclination of the optical disk, and the positional deviation of the head optical system, an offset occurs in the track error signal TES as shown in FIG. 6(C), and the track error signal TES becomes asymmetrical with respect to 0.

When an offset occurs in the track error signal TES,
TES that detected the zero cross of the track error signal TBS
Access means such as track jumping based on speed detection based on the zero-crossing signal become inaccurate.

In addition, the detection of servo errors is performed using the track error signal TES.
Since an off-track signal is generated by slicing at slice levels vertically symmetrical with respect to Ov, servo error detection becomes uncertain.

Furthermore, when the track servo is on, as shown in FIG. 6(D), there is a kickback at a position of 0.0 mm which is shifted due to the offset, and it is not possible to on-track to an accurate position.

Therefore, when writing/reading is performed at this position, the position is shifted from the center of the track, so if used with a device having a different offset, track cross-tock will occur, making reading impossible, and compatibility of the device will be lost.

For this reason, conventionally, the state where no servo signal is output, fftJ
First, turn off the semiconductor laser 24 in the optical head 2, move the optical head 2 to a place where there is no optical disk, and apply an offset correction voltage to the track servo loop so that the track error signal TES becomes zero to correct the circuit offset. Attempts were made to make adjustments.

[Problem to be solved by the invention]

However, the offset of the track error signal is also caused by the inclination of the optical disk, especially the bending, the positional shift of the optical system of the optical disc 2, the drift of the emitted light due to temperature change, and the change in light receiving characteristics.

Conventional techniques have a problem in that even though circuit offsets can be removed, offsets caused by optical disks and optical heads cannot be removed.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a track servo offset correction method for an optical disc device that can also eliminate offsets in a track error signal caused by the characteristics of an optical disc or an optical head.

[Means to solve the problem]

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

As shown in FIG. 1, the present invention irradiates an optical disc 1 with a light beam, and creates a track error signal from an optical disc 2 that receives light from the optical disc 1 and a light reception signal of the optical head 2. , and a track servo control unit 3 that controls the optical beam of the optical disc 2 to follow the track based on a track error signal, in which an offset correction signal is added to the track error signal of the track servo control unit 3. measuring the zero-cross duty of the track error signal to which the offset correction signal has been added; and changing the offset correction signal so that the measurement result has a duty of 50%. .

[Effect]

In the present invention, when the zero cross duty of the track error signal TBS is 50%, the track error signal TB
Since S is vertically symmetrical and the offset has been removed, an offset correction signal is applied, the zero cross duty of the track error signal TBS is measured, and the zero cross duty becomes 50% by the applied offset correction signal. The purpose of this adjustment is to remove the offset on the track error signal.

〔Example〕

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

In the figure, the same parts as those explained in Figures 1 and 6 are:
Indicated by the same symbol.

5 is a main control unit, which is composed of a microprocessor;
The servo control operation of the track servo control unit 3 is controlled using the track zero cross signal TZC, the off-track signal TO3, and the servo-on signal SVS, and the track servo offset is removed by the adjustment process shown in FIG. 3, which will be described later, and the focus servo Control unit 4 (see Figure 6)
This controls the sabot operation of the

6 is a head circuit section, and the output a of the 4-division light receiver 26 is
It has an RF generation circuit 60 that generates an RF signal RFS from -d, and an amplifier 61 that amplifies the outputs a - d of the four-division light receiver 26 and outputs servo outputs S Va - S V d.

30 is a TBS creation circuit, and the servo output S of the amplifier 61
Track error signal TBS from V a - S V d
31 is a total signal creation circuit which adds the servo outputs 5Va-3Vd to create a total signal DC3 which is the total reflection level, 32 is A G C (Aut
This is a matic Galn Control) circuit that divides the track error signal TBS by the total signal (total reflection level) DC3 and performs AGC using the total reflection level as a reference value, and compensates for fluctuations in the irradiation beam intensity and reflectance. It is something.

33 is an offset applying circuit, which applies an offset correction level (voltage) from the main control unit (hereinafter referred to as MPU) 5 to the track error signal TBS;
It has an addition amplifier AMP that adds the output of the circuit 32 and an offset correction voltage TSO from a D/A converter, which will be described later.

34a is a zero-crossing detector which detects the zero-crossing point of the 1-track error signal TBS and outputs the MPU5 track zero-crossing signal TZC; 34b is an off-track detection circuit which detects the zero-crossing point of the 1-track error signal TBS and outputs the track error signal TBS in the positive direction; The off-track signal TO3 is set to MP upon detecting that the value has fallen below -3L or below a constant value of -3L in the negative direction, that is, that an off-track state has occurred.
What is output to U5 is a phase compensation circuit 35, which differentiates the track error signal TBS and outputs the track error signal T.
In addition to the proportional portion of ES, it advances the phase of the high frequency range.

36 is a servo switch, which closes when the servo-on signal SVS of the MPU 5 is turned on, closes the servo loop, and opens when it turns off, opening the servo loop; 37 is a digital/analog converter (referred to as a D/A converter);
The offset correction value TSO of No. 5 is converted into an analog offset correction voltage and outputted to the offset applying circuit 33.

39a is an inverting amplifier, which inverts the output of the servo switch 36; 39 is a power amplifier, which amplifies the output of the inverting amplifier 3'9a to generate a track drive current TDV.
is given to the track actuator 21.

FIG. 3 is a flowchart of an offset correction process according to an embodiment of the present invention, and FIG. 4 is an explanatory diagram of the operation of an embodiment of the present invention.

(2) 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 process shown in FIG. 3(B), which will be described later.

Then, the time PTZC when the amplitude of the track error signal TES is greater than zero and the time NTZC when it is less than zero are determined.

Next, the MPU 5 calculates the sum of PTZC and NTZC.

Furthermore, the MPU calculates the duty ratio B by (PTZC÷A). This may be (NTZC÷A).

■ Next, the MPU 5 sets a to the allowable range value and calculates B>
Determine whether it is 0.5 +a.

If B > 0.5 +a, there is an offset in the e direction, so add rl to the TBS offset correction value and convert this to D
/A converter 37, the offset correction voltage is increased, and the process returns to step (2).

(2) Conversely, if the MPU 5 determines that B > 0.5 + a, it determines whether B < 0.5 - a.

If B<0.5-a, there is an offset in the ■ direction, so
Subtract “1” from the TBS offset correction value and convert this to D/
The voltage is output to the A converter 37, the offset correction voltage is decreased, and the process returns to step (2).

On the other hand, if B<0.5-a, then 0.5-a≦B≦
0.5 + a, and the duty ratio is approximately 50%, so it is assumed that the offset has been removed.

Next, the duty measurement process shown in FIG. 3(B) will be explained.

- The MPU5 sets a timer interrupt time t in the built-in timer 5b.

This time is a duty measurement time, and is preferably longer than the time required for half a revolution of the optical disc, and in this example, it is the time required for one revolution.

In addition, the MPU 5 uses the PTZC and NTZC of the built-in memory 5a.
Initialize to "0".

Then, the timer 5b is started.

■ The MPU 5 detects that the track zero cross signal TZC is “I”.
” (high).

As shown in FIG. 4, the track zero cross signal TZC is obtained by slicing the track error signal TES by O.

Therefore, if TZC−“1′, TBS≧0, TZC=“O
If n, TES<0.

When MPU 5 determines that TZC="l", TB
Since S≧O, the PTZC of the memory 5a is (P T
7. Update to C-1).

Conversely, when it is determined that TZC≠“1”, since TBS<0, NTZC in the memory 5a is updated to (NTZC+-1).

■ Then, the MPU 5 checks whether there is a count-up interrupt of the timer 5b, and if there is not, returns to step ■.
If so, stop timer 5b to end the measurement time.
finish.

In this way, as shown in FIG. 4, in FIG. 3(B), the time PTZC of TES≧01TZC−“B” and the time N of TES<01TZC−“0” in the measurement time
Measure TZC.

As shown in Figure 3 (A), the duty is approximately 5.
It is determined whether it has become 0% or not, and the offset correction ITsO is changed until it becomes 50%.

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

This offset correction may be performed when the power is turned on or when the optical disk medium is replaced.If the change over time due to temperature is large, an internal timer is provided and the offset correction is performed when a seek command arrives after a certain period of time has elapsed. You can do it like this.

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

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

In the figure, the same parts as those shown in Fig. 2 are shown with the same symbols, and 70.71 is an ant gate,
5 Sample (Measurement) #J] A circuit that is opened by a high-level sample enable signal in the middle and outputs the track zero cross signal TZC or its inverted signal *TZC, 72 is an inverting circuit, and the track zero cross signal TZ
73 which inverts C and outputs it to AND gate 71;
．． 7/I is each counter, which counts the clock when the outputs of the AND gates 70 and 71 are at a "high" level.

In this embodiment, the duty measurement is performed by hardware instead of the firmware shown in FIG. 3(B) in the embodiment shown in FIG. 2.

That is, the AND gates 70 and 71 are opened only during the measurement period,
If TZC is "1", counter 73 counts clocks and calculates time PTZC, and if TZC is "0", counter 74 counts clocks and calculates time NTZC.

In FIG. 3(A), when M P tJ 5 requires measurement, it first clears the counters 73 and 74 with a clear signal, and issues a sample enable signal for a certain period of time, totaling 7! j
After Q and measurement, both counters 73 and 74 are read to obtain PTZC and NTZC.

The subsequent processing is as shown in FIG. 3(A).

(C) Description of another embodiment In the embodiment described above, the main controller 5 performs the correction.
This may be performed by a separate dedicated device or circuit, and although the explanation has been made using an optical disk, it may also be applied to a magneto-optical disk.

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, and these are not excluded from the present invention.

〔Effect of the invention〕

As explained above, according to the present invention, the zero-cross duty of the track error signal TBS is measured while applying the offset correction signal, and the correction signal is changed so that the zero-cross duty becomes approximately 50%. Therefore, not only the circuit offset but also the offset due to the characteristics of the optical disk and the optical head can be corrected and removed, and stable track servo can be realized using an offset-free track error signal.

[Brief explanation of the drawing]

FIG. 1 is a principle diagram of the present invention, FIG. 2 is a block diagram of an embodiment of the present invention, FIG. 3 is an adjustment processing flow of an embodiment of the present invention, and FIG. 4 is an explanatory diagram of the operation of an embodiment of the present invention. FIG. 5 is an explanatory diagram of another embodiment of the present invention, and FIG. 6 is an explanatory diagram of the prior art. In the figure, 1-optical disk, 2-optical head, 3-) rack servo control section.

Claims (1)

[Claims] (1) An optical head (2) that irradiates the optical disc (1) with a light beam and receives the light from the optical disc (1), creates a track error signal from the light reception signal of the optical head (2), and tracks the optical disc (1). In an optical disk device comprising a track servo control section (3) that controls track following of a light beam of the optical head (2) based on an error signal, an offset correction signal is added to the track error signal of the track servo control section (3). measuring the zero-cross duty of the track error signal to which the offset correction signal has been added; and changing the offset correction signal so that the measurement result has a duty of 50%. A track servo offset correction method for an optical disc device, characterized in that: