JP2714208B2 - Optical disk tracking device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

The present invention relates to a tracking system in a write-once and erasable optical disk device, and particularly to an improvement in a composite tracking system using a dual servo loop of a push-pull tracking control system and a wobbling tracking control system.

[Prior art]

The composite tracking method using both the push-pull method and the wobbling method is described in, for example,
As described in Japanese Patent Publication No. 38939, various factors (for example, disk tilt, deformation and optical axis shift, optical / mechanical shift) that are generated by the push-pull tracking system by combining the push-pull tracking system and the wobbling tracking system are required. This is a double feedback control system for the purpose of suppressing track deviation due to electrical and electrical drift. Japanese Patent Application Laid-Open No. Sho 62-62173 discloses a problem with the composite tracking method, that is, a problem that the sampling frequency of the wobbling tracking system is low.
As disclosed in Japanese Patent Publication No. 145538, a system in which a wobbling / feedforward system (prediction correction system) is added to a dual feedback control system has been proposed.

[Problems to be solved by the invention]

In the composite tracking method, a voltage corresponding to an offset component which is inevitably generated in a push-pull tracking system due to an optical axis shift or the like is added to the push-pull tracking error signal, that is, an offset component is obtained by shifting a tracking S-shaped curve in parallel. When an unexpected large offset occurs, there is a problem that the symmetry between the positive polarity side and the negative polarity side of the S-shaped characteristic is broken. In addition, the composite tracking method to which the prediction correction system is added does not take into consideration a transient phenomenon when the prediction correction system is turned off, and there is a problem that the switching causes a track deviation more than expected. . SUMMARY OF THE INVENTION An object of the present invention is to provide a composite tracking method in which a track deviation is always small even if the prediction correction system is repeatedly turned on and off. Another object of the present invention is to provide a composite tracking system capable of performing stable tracking with a small gain fluctuation even after a large track offset occurs in a push-pull tracking system and this offset is suppressed or corrected. It is in.

[Means for Solving the Problems]

The present invention is characterized in that the convergence of the correction signal accompanying the OFF operation of the prediction correction system is made slower than the response speed of the wobbling tracking system. More specifically, track deviation information obtained from the track deviation correction wobbling mark (the principle of accurately detecting the track deviation using the wobbling mark is described in detail in Japanese Patent Application Laid-Open No. 62-229534, etc. Wobbling pit 27- shown in FIG.
Using the fact that when the laser beam passes through the central portion of the relative position between 1 and 27-2, the magnitude of the amount of reflected light from the two pits becomes equal). In the push-pull tracking system, the feedforward system (prediction correction system) using this stored optimum correction value is turned on.
A switch for turning off, a capacitor for charging on the output side of the switch, and a resistor for discharging the charge charged in the capacitor when the switch is turned off are added. In addition, the present invention provides a push-pull tracking error detection system for applying offset suppression by a wobbling tracking system or correction by a prediction correction system to a push-pull tracking system using track deviation information obtained from a track deviation correction wobbling mark. The analog input of a multiplying (multiplying) DA converter is connected to each output of the split detector, and the sum of the digital multiplier inputs (suppression coefficient or correction coefficient) of these two multiplying (multiplying) DA converters is all “1”
Alternatively, it is configured to be all "0" (in this case, a carry occurs).

[Action]

A capacitor and a resistor connected to the output side of a switch for turning on / off a prediction correction coefficient (correction amount) of a feed forward system (prediction correction system) using a stored optimal correction value added to a push-pull tracking system are switched. Only when is off, it acts as a discharge loop with a time constant (set to a time slower than the response speed of the wobbling tracking system), and the correction coefficient of the prediction correction system always converges gradually toward zero. To work. Thus, even when the response speed of the wobbling tracking system is slow, the correction coefficient converges to zero at a relatively slower speed, so that the laser beam can always be guided to the track center. In addition, the multiplying DA converter connected to the output side of the split photodetector for detecting the push-pull signal reduces the gain of the photodetector system whose detection sensitivity has increased, and conversely, the detection sensitivity. Since the operation of raising the gain of the other system of the photodetector having become smaller, that is, operating as a differential multiplier, and keeping the relative detection sensitivity of the two systems of photodetectors constant, push-pull tracking The slope (gain) of the so-called S-shaped characteristic of the error signal becomes constant, and the symmetry between the positive polarity side and the negative polarity side is not lost, so that a stable tracking servo system can be configured.

【Example】

Before describing the embodiments, the structure of the optical disk carrier used in the present embodiment and the overall system configuration will be described with reference to the drawings. FIG. 9 is a diagram showing a format structure of an optical disk. FIG. 5A is a view of the entire disk 6 and shows the circumference of a 3.5-inch disk as a plurality of physical sectors (S
T) is shown. FIG .- (b)
Is a diagram showing a breakdown of the physical sector, and shows that it is divided into a preformatted ID information area (IDA) and a user data area (UDA) used later by the user. FIG. 11C shows the ID information area (ID
It is a figure which shows the head part of A) specifically. A pair of wobbling pits 27-1 and 27-2 are arranged vertically from the center of the track with the center between the tracking guide grooves 7-1 and 7-2, that is, the center of the land, as the track center.
Having. A pre-pit 28 for address information and the like is formed at the center of the track. The tracking guidance group 7 is also formed continuously in the user data area (UDA). FIG. 8 is a conceptual diagram showing the entire configuration of the optical disk device used in the embodiment. The entire optical system (optical head) 73 is placed on the moving stage 70, and the linear motor controller 71 moves the optical disk 6 to the inner and outer circumferences, and its coordinates (radial position) are detected by the scaler 72. You. The radial position detected by the scaler 72 is supplied to a tracking servo circuit 74 and an optical disk control unit (ODU) 76. The optical disc 6 is controlled to rotate at a constant speed by a spindle motor controller 75, and the rotation angle information obtained by the spindle motor controller 75 is supplied to a tracking servo circuit 74. The optical disk control unit (ODU) 76 uses SCS
Via an I (small computer system) bus, it receives commands from the host computer 77, handles the progress of specific sequences, and issues on / off and read / write control commands for various servo systems. Next, an embodiment of the tracking servo system will be described with reference to the drawings. FIG. 1 is a functional block diagram of a tracking servo system according to the present invention. The laser beam 2 output from the semiconductor laser 1 becomes parallel light by the lens 3, is deflected by the polarizing beam splitter 8, passes through the half mirror 4, and is condensed on the recording surface of the optical disc 6 by the objective lens 5.
The laser beam reflected from the disk 6 passes through the objective lens 5 in reverse, is split by the half mirror 4, a part of the light enters a photodetector 14 for push-pull tracking detection, and the remaining beam light is polarized. The laser beam goes straight through the beam splitter 8, passes through the condenser lens 9 and the cylindrical lens 10, and is condensed on the photodetectors 12 and 13 which detect the polarization angle of the laser beam by the action of the analyzer 11. The difference between the respective output signals of the photodetector 12 and the photodetector 13 is subjected to error calculation by the subtraction circuit 25, whereby the magneto-optical signal 61 can be obtained.
On the other hand, the output signal 40 of the split photodetector (detector) 14
41 is added by the adder 19 to become a reflected light / dark signal. This light / dark signal is input to a wobbling track error detection circuit 20 to recognize a wobbling mark,
An original signal 47 of a wobbling track error is obtained by taking the difference between the peak value of the wobbling mark 27 included in the light and dark signal and the peak value of the preceding pit portion. The original signal 47 passes through the amplifier 21 and is connected to the ON side of the switch 22 for controlling ON / OFF of the wobbling system.
The common-side output of the switch 22 becomes an offset suppression coefficient K 'via the low-pass filter 23. The output data of the correction table RAM 29 is converted into an analog signal by the digital-to-analog converter DAC 30 and is input to the switch 13 for controlling ON / OFF of the prediction correction. A capacitor C and a resistor R are connected in parallel between the output of the switch 31 and the ground.
The output of the switch 31 includes a capacitor C, a resistor R, and an amplifier 32.
Then, the offset correction coefficient K ″ becomes the offset correction coefficient K ′. The offset suppression coefficient K ′ and the offset correction coefficient K ″ are combined in the adder 24 and act on the multiplier 15 as the multiplier K. The multiplier 15 is composed of two parts, one of which multiplies one output signal 40 of the two-split detector 14 by K, and the other one of which is the other of the two-split photodetector 14. The output signal 41 is doubled by a factor of 1 minus K, and the operation result thereof is subjected to an error operation by the subtractor 16 to generate a push-pull tracking error signal 42. That is, assuming that the output signals of the two-part split photodetector (detector) 14 are A and B, the push-pull tracking error signal 42 is expressed by the following equation. Error signal = 2 · K · A−2 · (1−K) · B At this time, the push-pull tracking error signal when the suppression or correction coefficient is set to zero, that is, K = 0.5, is as follows. This is the same as the generation of the conventional push-pull signal. The push-pull tracking error signal 42 thus generated is phase-shifted by the phase compensation circuit 17, drives the tracking actuator coil 26 via the amplifier 18, and
A tracking servo system is constituted by finely moving the objective lens 5 in parallel in the track direction. FIG. 2 is a block diagram showing the correction table RAM 29 of FIG.
This is an example of a configuration using P01V07 (manufactured by Hitachi). When a reset signal is input to the RES terminal at the time of power-on or the like, the processor 50 is initialized to a single-chip mode state, and enters a state where it can operate using a 4 MHz crystal oscillator as a clock. Under these conditions, when a data sample command is input from the optical disk control unit (76 in FIG. 8) to the MNI (non-maskable interrupt) terminal of the processor, it causes an unconditional interrupt. D / A converter for signal generation 30
Data output ports P30-P
Set to 37. When the wobbling mark 27 is detected, the difference between the magnitudes of the reflected light amounts of the two wobbling pits, that is, the wobbling track error original signal 47 is digitally coded by the AD converter 48, and the value is internally stored at the input ports P40 to P47. take in. In this manner, the current signal data of the wobbling track error for one round of the track is captured every time the wobbling mark 27 is detected, and the steady track offset information for one rotation of the disk is collected, and the noise removal operation and the data interpolation are performed. An operation and a phase shift operation are performed on the original signal data of the wobbling track error stored in the input memory area, and the result is stored in the output memory area of the internal memory 29 of the processor 50. Then, the data in the output memory area is transferred to the output ports P30 to D / A converter input data.
P37, and output including interpolation data for smoothly continuing within the sampling period of the wobbling track error.The D / A converter 30 outputs the prediction correction signal 60 as continuous analog data. It operates to correct the stationary offset component. FIG. 3 is a flowchart showing an initial setting operation when a disc is mounted. As a premise of entering this flow, the disk 6 is mounted on a drive device (FIG. 8), a spindle motor is rotated at a predetermined rotation speed, a laser beam is focused, and then a push-pull servo system is turned on.
The tracking state is established only by the push-pull tracking. Thereafter, the optical head is moved to the innermost circumference (step 51), the tracking deviation amount for one round of the track is measured using a pair of wobbling marks, and stored in the input memory unit (step 52). Next, the track shift amount stored in the input memory (in the embodiment, since a disk having 17 pairs of wobbling marks in one round was used,
Nozzle removal calculation, data interpolation calculation (smoothing), phase shift calculation, etc. are performed on the track shift amount for 17 samples), and the results are stored in the output memory unit. The data is output to the converter 30 (in the embodiment, 136 pieces of data are recorded per track as a result of the smoothing process), and a correction operation for the track deviation is tried (step 53). While trying to correct the prediction in this way, a pair of wobbling marks
The error component 27 is monitored to determine whether the error value is equal to or less than a certain value (step 54). If the error value is equal to or less than the certain value, the optical head 73 is moved to the next measurement point ( Step 55). At this time, it is determined whether or not the disk 6 has reached the outermost circumference (step 56). If it has not reached the outermost circumference, the process returns to the data collection step 52. If it is determined that the disk 6 is the outermost circumference, the initial setting operation ends. I do. FIG. 4 is a time chart showing an example of a time schedule during a seek operation, which will be described below with reference to FIG. In FIG. 4, the horizontal axis represents time, and the vertical axis represents the amount of track offset, and shows a situation in which the offset indicated by the dash-dot line generated in the push-pull system immediately after the movement of the optical head is corrected or suppressed. First, immediately after reaching the seek target track, the prediction correction system is turned on (the switch 31 in FIG. 1 is turned on), so that the offset correction amount indicated by the two-dot broken line rapidly rises (the capacitor C in FIG. 1). In this case, the prediction correction instruction voltage is rapidly charged), and the track offset (track deviation) indicated by the solid line rapidly decreases, leaving the prediction correction error component as a residual offset (in this embodiment, the residual offset amount is 0.01 μm). It was stable). Thereafter, by turning on the wobbling tracking system (turning the switch 22 of FIG. 1 to the ON side), a so-called composite tracking system is formed, and the residual offset component also gradually moves in the suppression direction. Normally, it may be in this state, that is, in a state in which a prediction correction system is added to the composite tracking system,
The prediction correction system is a feedforward servo system, and has a problem in long-term stability. In order to improve the stability of the entire tracking system, the prediction correction system is turned off at this point (switch 31 in FIG. 1).
Is cut off), the predicted correction voltage converges toward the zero potential in the discharge curve having the time constant of the capacitor C and the resistor R shown in FIG. The convergence speed (the time constant of C and R) is determined by the response speed of the wobbling tracking system (mainly,
If it is set later than that determined by the transfer function of the low-pass filter LPF23 shown in FIG. 1 and a 0.5-hertz low-pass filter is employed in this embodiment, wobbling is performed so as to interpolate the decrease in the predicted correction amount as shown in the figure. In a state where the offset suppression amount of the tracking system increases, and finally, only the gain offset component generated because the loop gain of the wobbling tracking system is not infinite remains (0.02 micron or less in the embodiment). Stabilize. FIG. 5 is a block diagram showing the periphery of the multiplier 15 shown in FIG. The respective output currents of the split photodetectors 14-A and 14-B are converted into detector output voltage signals 40 and 41 by current / voltage conversion amplifiers 43-1 and 43-2, respectively.
Multiplying (multiplication type) DA converter 15-1 and
Connected to 15-2 analog input terminal (A.IN). On the other hand, the output K 'of the low pass filter 23 of the wobbling system and the output K "of the amplifier 32 of the prediction correction system are combined by the adder 24 to become a multiplication coefficient K, which is converted by the AD converter 44 into digital code data 46 with polarity bits. A multiplying (multiplying) DA converter 15- connected to the detector output signal (detection signal) of the two-segment photodetector 14-A.
A digital input terminal (D.IN) receives the digital code data 46 as it is, and is connected to the detector output signal (detection signal) of the split photodetector 14-B. The digital code data 46 is inverted and input to the digital input signal (D.IN) of the DA converter 15-2 by the inverter IC 46 so that the multiplier K = 0.
A differential multiplier having a boundary of 5 (a binary number of 8 bits is “10000000”) is provided. By performing an error operation on each analog output (A.OUT) of the differential multiplier 15 by the subtractor 16, even when the detection sensitivities of the two-split photodetectors 14-A and 14-B change, the gain variation does not occur. And a push-pull track error signal 42 having a very small offset. In the method of inverting the digital code data as in this embodiment, since an error of 1 LSB occurs in the multiplier, obtaining a two's complement using a digital addition IC provides a more accurate configuration. FIG. 6 shows detection signals 40 and 41 of the two-segment photodetector and an error calculation result thereof, that is, a push-pull track error signal 42 in an ideal state where there is no offset factor such as an optical axis shift.
Is a waveform diagram showing the relationship, wherein the horizontal axis represents the amount of track deviation and the vertical axis represents the voltage. When the offset factor is small as shown in FIG. 7A, the respective detection signal outputs 40 and 41 of the two-segment photodetector have left-right symmetric waveforms. As a result, as shown in FIG. The track error signal is also completely rotationally symmetric between the positive polarity side and the negative polarity side. FIG. 7 is a waveform diagram showing the relationship between the detection signals 40 and 41 of the two-segment photodetector and the error calculation result thereof when the optical axis is shifted by about 400 microns, that is, the push-pull track error signal 42. And the amount of rack deviation, and the vertical axis represents voltage. When the optical axis shift of about 400 microns occurs, as shown in FIG.
In this case, an asymmetrical waveform having a different magnitude is obtained.
A push-pull track error signal as shown by
A track offset (track deviation) of 0.3 microns will occur. Therefore, as described above, when a push-pull signal is generated using the result obtained by calculating the output signals 40 and 41 of the two-split photodetector 14 with a differential amplifier (see the description of FIG. 5 described above), It becomes a waveform indicated by 42-a in FIG. 6B, and it can be seen that the signal is restored to the ideal push-pull track error signal shown in FIG. 6B. The waveform shown by 42- (b) in FIG. 7 (b) is an example in which the offset push-pull track error signal is suppressed or corrected by an S-shaped shift by applying a bias voltage in the conventional method, and the positive side It can be seen that the symmetry between the negative polarity side and the negative polarity side is broken, and the gain is changed. According to the present embodiment, even in an optical disc device in which the optical axis has shifted significantly, the occurrence of track deviation can be easily prevented, and the tracking characteristics excellent in frequency characteristics (response characteristics) at the time of seek operation and the like. The system can be realized.

【The invention's effect】

According to the present invention, the track offset generated in the push-pull servo system can be reliably predicted and corrected using the track shift amount obtained from the wobbling mark stored in advance, and the low-pass filter set to a low frequency can be corrected. The smooth transition to the wobbling tracking system with improved stability due to the action, that is, the transition from the feedforward correction system to the feedback suppression system is performed reliably, so that a tracking servo system with excellent response characteristics and track tracking accuracy is configured. Has an effect. Further, even if a large offset factor occurs in the push-pull system, the gain fluctuation of the tracking servo system after suppressing or correcting the component is extremely small, and there is an effect that a stable tracking servo system is always configured. .

[Brief description of the drawings]

FIG. 1 is a block diagram showing a tracking servo system according to an embodiment of the present invention, FIG. 2 is a block diagram showing an example of a configuration of a correction table used in the present invention, FIG. 4 is a time chart at the time of a seek operation, FIG. 5 is a block diagram showing an example of a configuration of a differential multiplier, FIG. 6 is a waveform diagram of a push-pull signal in an ideal state, and FIG. Waveform diagram of the push-pull signal of
FIG. 8 is a conceptual diagram of the overall configuration of the optical disk device, and FIG. 9 is a structural diagram of an optical disk carrier used in the present invention. DESCRIPTION OF SYMBOLS 1 ... semiconductor laser, 2 ... laser beam, 6 ... optical disc, 7 ... groove, 12, 13, 14 ... photodetector, 15
…………………………………………………………………………………………………………………………………………………………………………………………………………………………. 30 ... DA converter, 31 ... Prediction correction system on / off switch.

Claims (2)

(57) [Claims] 1. A tracking device for irradiating a laser beam to a predetermined position of an optical disk having a groove having a groove structure along a track and wobbling marks discretely arranged along the track, wherein A first tracking system that continuously forms a first tracking signal by using the diffracted light of (a) and a second tracking system that forms a second tracking signal from a signal that is discretely obtained by the wobbling mark. The second
And a prediction correction system for forming and storing a correction value by using the tracking signal of (1) and causing the first tracking system to perform prediction correction. The convergence of the correction signal accompanying the OFF operation of the prediction correction system A tracking speed of the optical disk, which is lower than a response speed of the second tracking system. 2. A tracking device for irradiating a laser beam to a predetermined position of an optical disk having a groove having a groove structure along a track and a wobbling mark discretely arranged along the track, wherein the tracking device comprises: A first tracking system that continuously forms a first tracking signal by using the diffracted light of (a) and a second tracking system that forms a second tracking signal from a signal that is discretely obtained by the wobbling mark. The second
And a prediction correction system for forming and storing a correction value by using the tracking signal of (1) and causing the first tracking system to perform the prediction correction. An optical disk tracking device, further comprising an independent multiplier for multiplying two output signals of a photodetector, wherein a sum of multipliers of the two multipliers is always constant.