JP2661294B2 - Tracking control device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tracking control device of an optical recording / reproducing device used for data files, image files, and the like.

2. Description of the Related Art Hereinafter, an example of a conventional tracking control device will be described with reference to the drawings.

FIG. 7 is a block diagram of a tracking control device in a conventional example, FIG. 8 is a tracking error signal waveform diagram, and FIG.
The figure is a distribution diagram of reflected light on a tracking error signal detection photodiode when tracking error detection is performed by the far field method. In FIG. 7, 1 is an optical disk, 2 is a light beam, 3 is an objective lens, 4 is an optical head, and a light beam 2 emitted from the optical head 4 is focused on a minute spot by the objective lens 3 and is incident on the optical disk 1. Records and reproduces information. Reference numeral 5 denotes a focus servo circuit that performs focus servo so that the light beam 2 is focused on the medium surface of the optical disk 1. Reference numeral 6 denotes a tracking error signal detector, and reference numeral 7 denotes a phase compensation circuit for performing position compensation and the like on the tracking error signal obtained by the tracking error signal detector 6. Reference numeral 8 denotes an actuator drive circuit, and reference numeral 9 denotes a tracking actuator which performs tracking servo for moving the objective lens 3 in a direction substantially perpendicular to the information recording track on the medium surface of the optical disk 1 so that the light beam 2 follows the information recording track.
Reference numeral 10 denotes a transfer unit for moving the optical head 4 and the tracking actuator 9 in a direction substantially perpendicular to the information recording track. 12 is an offset generator, and 11 is a subtractor for subtracting the output of the offset generator 12 from the tracking servo error signal.

The operation of the tracking control device configured as described above will be described below. In the conventional tracking control device, first, after the focus servo is started to perform a stable focus servo operation by applying the focus servo, a tracking error signal generated when the light beam 2 crosses the information recording track due to the eccentricity of the rotation of the optical disk 1 is obtained. The tracking servo is performed by giving an offset so that the average of the local maximum value and the local minimum value becomes the tracking position and adjusting the position of the tracking servo.

Problems to be Solved by the Invention In the conventional tracking control device, the average value of the maximum value and the minimum value of the tracking error signal is set as the tracking position. However, in the tracking error signal detection by the far field method, an offset occurs in the tracking error signal when the optical axis of the reflected light from the optical disc is shifted. This will be described with reference to FIG.

In FIG. 9, 92 is a photodiode for detecting a tracking error signal, 910 is a 0-order reflected light of the light beam, 911 is a primary reflected light of the light beam, 912 is a −1st-order reflected light of the light beam, 9
01 is a dividing line of the photodiode when the optical axis of the 0-order reflected light coincides with the dividing line, and 902 is a dividing line of the photodiode when the optical axis of the 0-order reflected light does not coincide with the dividing line. As shown in FIG. 9, the light beam 2 from the optical disk 1 is placed on the tracking photodetector.
There are a secondary reflected light 910, a primary reflected light 911, and a primary reflected light 912, and the difference between the light amount on the right side and the light amount on the left side of the photodetector dividing line 901 or 902 is detected as a tracking error signal. Here the photodetector dividing line 90
1 and the tracking position of the tracking error signal TE shown in Figure 8 when you have the center of the 0-order light 910 becomes the position of the center P _ave maximum points P ₁ and the minimum point P ₂ of the TE. However photodetector dividing line is at the position of the dividing line 902, the tracking position P ₀ of the tracking error signal TE shown in Figure 8 when the deviates the center of the zero-order reflected light 910 is the local maximum point P ₁ and the minimum point of the TE It should not be in the position of the center P _ave of P _2. Therefore, the conventional tracking control apparatus has a problem that a correct tracking position cannot be detected, for example, when an optical axis shift occurs.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem, and has as its object to provide a tracking control device capable of reliably and automatically detecting a tracking position.

Means for Solving the Problems In order to achieve the above object, in the tracking control device of the present invention, a means for detecting a shift between a light spot focused on an optical recording medium and an information recording track,
A means for detecting the sum of the reflected light amounts of the light spots focused on the optical recording medium, a means for detecting an extreme point of the sum of the reflected light amounts, and a means for changing a target value of tracking servo; The target value of the tracking servo is changed by an amount corresponding to the shift amount between the light spot focused on the optical recording medium and the information recording track when the pole of the sum is detected. .

In the tracking control device of the optical recording / reproducing device configured as described above, the value of the tracking error signal at the extreme point of the sum of the reflected light amounts is used as the tracking position. FIG. 2 is a signal waveform diagram showing the relationship between the tracking position, the tracking error signal, and the sum of the reflected light amounts. In FIG. 2, TE is a tracking error signal of a light spot focused on a minute spot with respect to an information recording track, and TS is a reflected light sum signal. When the optical axis deviates from the photodetector of the tracking error signal detector, TE at the track center or groove center becomes P0 instead of 0 at the track center. However, at the center of the land, the TS has a maximum value, and at the center of the groove, the TS has a minimum value. At the center of the information recording track, the sum of the reflected light amounts is an extreme point, that is, a maximum point in the case of groove recording and a minimum point in the case of groove recording, so that the tracking position can be reliably detected.

Embodiment A tracking control device according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a tracking control device according to an embodiment of the present invention, and FIG. 3 is a signal waveform showing a relationship between a tracking error signal, the sum of reflected light amounts, and the output of a phase shifter that receives the sum of reflected light amounts. FIG. In FIG. 1, 3 is an objective lens, 4 is an optical head, 5 is a focus servo circuit,
Light beam 2 narrowed down to a minute spot by objective lens 3
Is moved in a direction substantially perpendicular to the medium surface of the optical disk 1 to focus on the medium surface of the optical disk 1. Reference numeral 6 denotes a tracking error signal detector for detecting a shift between the light beam 2 and an information recording track on the medium surface of the optical disk 1 from the light beam 2 reflected from the optical disk 1. Reference numeral 21 denotes a reflected light amount sum detector for calculating the sum of the reflected light amounts of the light beam 2 from the optical disk 1. twenty two
Is a pole detector for detecting the maximum point or the minimum point of the reflected light sum output signal of the reflected light sum detector 21. 23 is a tracking position detector and 11 is a subtractor for subtracting the output signal of the tracking position detector 23 from the output signal of the tracking error signal detector 6. Reference numeral 7 denotes a phase compensation circuit that performs phase compensation and the like on the corrected tracking error signal obtained by the subtractor 11.
Reference numeral 8 denotes an actuator drive circuit, and reference numeral 9 denotes a tracking actuator, which performs tracking servo of the light beam 2 by moving the objective lens 3 in a direction substantially perpendicular to an information recording track on the medium surface of the optical disk 1. Reference numeral 10 denotes a phase shifter for moving the optical head 4 and the tracking actuator 9 in a direction substantially perpendicular to the information recording track. 24 is a movement signal generator which is a tracking actuator 9 or a transfer device.
Outputs a control signal to move or vibrate 10. 1 optical disk, 2 light beam, 3 objective lens, 4 optical head, 5 focus servo circuit, 6 tracking error signal detector,
The 7 phase compensation circuit, 8 actuator drive circuit, 9 tracking actuator, and 10 phase shifter are the same as those of the conventional tracking control device.

The operation of the tracking control device according to the embodiment of the present invention constituted by the above elements will be described with reference to FIG. FIG. 3 is a waveform diagram of the reflected light sum signal TS output from the reflected light sum detector, the output signal TSD of the pole detector, and the tracking error signal TE signal. The pole detector 22 obtains a maximum point and a minimum point of the reflected light amount sum signal TS by phase-shifting, differentiating or function approximating the TS. In FIG. 3, the maximum point of TS is detected as a rising edge of TSD from 0 to 1, and the minimum point is detected as a falling edge of TSD from 1 to 0. In the case of land recording, the TE at the rising edge of the TSD is sampled by the tracking position detector 23, and at the time of groove recording, the TE at the falling edge of the TSD is sampled and detected as the tracking position signals TESL and TESG. You. Required TESL, TESG
Is the tracking error signal for the true tracking position
Since the offset is TE, TESL and TESG can be subtracted from the tracking error signal TE by the subtractor 11 to obtain a true tracking error signal.

Note that the accuracy of the detected value can be increased by obtaining TESL and TESG twice or more and taking the average.

In the above embodiment, the position adjustment is performed using the track crossing signal generated by the track crossing caused by the eccentricity of the optical disk 1 as in the conventional example. By moving or vibrating the transfer 9 or the transfer device 10, a stable track crossing signal can be created.

Next, an embodiment of a pole detector according to the present invention will be described with reference to the drawings.

FIG. 4 is a block diagram of an extreme point detector according to one embodiment of the present invention, FIG. 5 is a discrete value signal waveform diagram of each part of the extreme point detector according to one embodiment of the present invention, and FIG. FIG. 6 is a discrete value signal waveform diagram showing a tracking error signal of a pole detector and a sum of reflected light amounts in one embodiment of the present invention. 401 to 408 delay unit of the delay time ts in FIG. 4, 411-417 performs multiplication of the coefficients of the a- _n ~a _n in a multiplier. 42 is an adder, 43
Reference numeral 44 denotes a low-pass filter having substantially equal frequency characteristics. An arithmetic unit 45 calculates the value of X when the signal U becomes 0.

The operation of the pole detector and the tracking position detector in the embodiment of the present invention constituted by the above elements will be described. The digital circuit including the delay units 403 to 406, the multipliers 411 to 417, and the adder 42 is generally called an FIR filter. The transfer function H of this FIR filter
(Z) is given by the following equation.

In this case, the number of multipliers is 2n + 1. The number of delay units is
2n.

At this time, the coefficient a _i In this case, a phase shifter having a phase delay of 90 ° in a frequency band from 0 to 1 / (2 · ts) can be constructed. If a _i = −1 / i when i ≠ 0, a phase shifter whose phase advances by 90 ° can be constructed. In the above equation, the coefficient a _i when i is an even number
Is set to 0, the gain characteristic can be made flat.

When the number of coefficients is small, a flatter gain characteristic can be obtained by multiplying by a window function such as Hanning or Blackman. The operation of the pole detector using this phase shifter will be described with reference to FIGS.

In FIG. 5, TSq is a digitized reflected light sum signal, TShq is an output of the adder 42, TEq is a digitized tracking error signal, and TESLq and TESGq are output signals of the calculator 45. TSq is phase-shifted by -90 ° by a phase shifter composed of delay units 403 to 406, multipliers 411 to 417 having the coefficient of Equation 2, and an adder 42, to become TSShq. Since the phases of TSq and TShq are shifted by 90 °, the zero crossing point of TShq becomes the pole of TSq. Thereby, the pole of TSq can be easily detected. TShq is input to the low-pass filter 43 to remove high-frequency noise. The output of the low pass filter 43 becomes U _n-1 to enter only ts in U _n a delay unit 407 for input to the arithmetic unit 45 delays to the arithmetic unit 45. TEq is n · t by n delay units 401 to 402
The signal is delayed by s, and the low-pass filter 44 removes noise in the high frequency region. The output of the low-pass filter 44 is a computing unit 45
In X _n and delay 408 to input delayed by ts becomes X _n-1 to be input to the calculator 45. FIG. 6 shows U and X input to the arithmetic unit 45. U intersect 0 and between U _n-1 and U _n. Arithmetic unit 45
In this case, y = ( _Un * _Xn-1 + _Un-1 * _Xn ) / ( _Un-1 + _Un ) is calculated and output. In the case of land recording, the tracking position signal TESLq is used when U changes from negative to positive. In the case of groove recording, the tracking position signal TEL is used when U changes from positive to negative.
SGq can be detected.

In the case of an analog signal, a phase shifter is configured using an analog delay unit, an analog multiplier, and an analog adder, and a tracking position detector that detects a zero crossing point by a comparator and a sample hold is provided. Can be configured.

Effect of the Invention Since the present invention is configured as described above,
Reliable track position detection can be automatically achieved.

[Brief description of the drawings]

FIG. 1 is a block diagram of a tracking control device in one embodiment of the present invention, FIG. 2 is a signal waveform diagram of a tracking position, a tracking error signal, and a reflected light amount sum, and FIG. 3 is a tracking error signal and a reflected light amount sum. FIG. 4 is a block diagram of a pole detector in one embodiment of the present invention, and FIG. 5 is a block diagram of a pole detector in one embodiment of the present invention. FIG. 6 is a waveform diagram of a discrete value signal of each part of the pole detector in FIG. 6, FIG. 6 is a waveform diagram of a discrete value signal showing a tracking error signal of the pole detector and a sum of reflected light amounts in the embodiment of the present invention, FIG. FIG. 8 is a block diagram of a tracking control device in a conventional example, FIG. 8 is a waveform diagram of a tracking error signal, and FIG. 9 is a reflection on a photodiode for detecting a tracking error signal when the tracking error signal is performed by the far field method. light It is a distribution diagram. DESCRIPTION OF SYMBOLS 1 ... Optical disk, 2 ... Light beam, 3 ... Objective lens, 4 ... Optical head, 5 ... Focus servo circuit, 6
…… Tracking error detection circuit, 7 …… Phase compensation circuit,
8 Actuator drive circuit, 9 Tracking actuator, 10 Transfer device, 11 Subtractor, 12 Offset generator, 21 Reflected light sum detector, 22 Pole detector, 23 ... Tracking position detector, 24 ... Moving signal generator, 401-408 ... Delay device, 411-417 ... Multiplier,
42 ... Adder, 43 ... Low-pass filter, 44 ... Low-pass filter, 45 ... Calculator.

Claims (4)

(57) [Claims] A tracking error signal detecting means for detecting a tracking error signal which is a deviation between an information recording / reproducing track formed in a convex or concave state on an optical disk and a light spot focused on the optical disk; Tracking control means for performing a tracking servo based on a tracking error signal; reflected light sum signal detection means for detecting a sum signal of the reflected light of the light spot from the optical disc surface; Pole detection means for detecting a pole of the reflected light sum signal which changes when a spot crosses the information recording / reproducing track and outputting a timing signal, and calculating a value of a tracking error signal when the timing signal is output. Tracking position detecting means for setting a target value of the tracking servo. Tracking control apparatus according to claim and. 2. The method according to claim 1, wherein the tracking error signal is obtained a plurality of times by a tracking position detecting means in accordance with the timing signal, and an average value of the plurality of tracking error signals is set as a target value of a tracking service. Item 2. The tracking control device according to Item 1. 3. A light spot driving means for moving or oscillating the light spot in the tracking direction, and the pole detection means detects a pole of a reflected light sum signal when the light spot is moved or oscillated by the light spot driving means. The tracking control device according to claim 1, wherein the control is performed. 4. The tracking control device according to claim 3, wherein the pole detection means shifts the phase of the input signal by approximately 90 degrees and outputs a timing signal at a timing when this signal crosses zero.