JPH011131A - Tracking servo method in optical disk devices - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical disc recording and reproducing apparatus for reproducing an optical disc or recording information on an optical disc, and in particular, a tracking servo control system that detects a tracking error signal using a beam splitting method. This relates to a tracking servo method that is useful when applying

[Summary of the invention]

The tracking servo method in the optical disk device of the present invention detects the positive and negative peak values of the tracking error signal detected by the two-split detector and calculates the values to detect the skew error contained in the tracking error signal. False tracking error signal (push-pull error signal) based on signal, L/Bell change of tracking error signal, and movement of actuator
This system provides a tracking servo method that eliminates such problems, and allows accurate tracking servo to be applied using a simple optical pickup. This is achieved by absorbing assembly precision.

[Conventional technology]

An optical pickup that can irradiate an optical disk with a laser beam and detect recorded information and servo error signals from the reflected signal generally includes a feeding device that moves the entire optical pickup in the radial direction of the optical disk, and an objective lens. It consists of an actuator to control, and this actuator is a two-axis mechanism that mainly controls the focus state and tracking state.

The reflected light detected through the two-axis mechanism is converted into an electrical signal by the light receiving element, and output as a reproduction RF signal, and a tracking error signal is generated by the light receiving element whose light receiving surface is divided into a plurality of parts. It is also possible to detect focus error signals.

FIG. 7 shows an outline of such an optical pickup device, where 1 is an optical disk, and 2 is an actuator (two-axis mechanism) that controls the objective lens 3. For example, the objective lens 3 is controlled by a focusing coil Lt and a tracking coil Lt. It is equipped with a mechanism that allows it to be moved up, down, and in the water direction.

Reference numeral 4 denotes a feeding device, which has a built-in optical system that injects a laser beam into the actuator 2 and detects recorded information, a servo error signal, etc. from the reflected light from the optical disk 1, For example, 1/4 wavelength plate 5. Collimating lens 6, polarizing beam splitter 7, light emitting diode 8. and a light receiving element 9.

Note that L indicates a thread coil (motor coil) that, together with the feeding device 4, feeds the seven cutuators 2 in the radial direction of the optical disk l.

In such an optical pickup, the tracking error signal is divided into two beams (hereinafter referred to as push-pull method).
For detection, as shown in FIG. 8, a light-receiving element 9 with two divided light-receiving surfaces A and B is used, and the far-field image projected on the light-receiving surfaces A and H is converted into an electric signal Ea. , Eb are subtracted by a subtracter lO to detect a tracking error signal TE, which is then combined with a tracking coil L+ via a predetermined servo amplifier [2].

Also, in the same figure, there is a small-sized truck blowfish error message 5; T
E is input to the low-pass filter 11 to extract the DC component, and the DC component is input to the thread coil L via the servo amplifier 13, thereby moving the optical pickup device in the radial direction of the optical disc L, and creating a spiral shape. The recorded tracks have been made to be able to be tracked.

[The dark problem that the device is trying to solve] As mentioned above, the method of detecting the tracking error signal using the push-pull method simplifies the optical system, so it is possible to reduce the weight and cost of the pickup device. , the reflected light projected onto the light-receiving element 9 is affected by the inclination (skew) of the disk due to lens aberration and the optical axis change due to the movement of the objective lens 3, so even in the on-track state yg,
The light intensity distribution of the split detector changes, and these
There is a problem that a false error signal leaks into the king error signal.

In addition, when an optical disc is a write-once type disc or a disc that can be changed over time, differences in the depth of the grooves of the groups forming the tracks or the reflectance of the mirror surface may cause trouble. - There was a problem in that the level of the king error signal itself changed from disc to disc, and proper trough king servo characteristics were not maintained.

Therefore, in the past, a pickup (swing arm method) that integrated a two-axis mechanism and a feed device, and a tracking servo device using the three-spot method were adopted, which made the tracking servo device stable when compared. The arm method has the drawback of increasing the weight of the pickup and placing a burden on the actuator, while the three-spot method has the drawback of complicating the optical system and increasing costs.

The present invention has been made in view of these problems.
In particular, when a tracking error signal is detected by the push-pull method, an electric circuit compensates for the offset signal due to skew and the level fluctuation of the tracking error signal that leaks into the tracking error signal. This is intended to reduce time variations and the adjustment process of the optical pickup.

[Means for solving problems]

FIG. 1 shows a block diagram for explaining the principle of the tracking method in the optical disc device of the present invention.
Reference numeral 9 denotes a detector consisting of a two-part light-receiving surface having at least two or more light-receiving surfaces, and 20A and 20B subtract the signals E a and E b output from the two-part detector, respectively, to detect the error. The gain of the subtractor 20C, which detects the signal and the adder 20C which detects the amount of reflected light, is controlled by the output of the adder 20B, so that a constant level of output is always obtained regardless of the intensity of the laser beam. uf variable gain amplifier, 21 is an AGC amplifier that makes the level output constant when tracking error signals of different levels are output depending on the group groove of the optical disk or 1 reflectance, and 22 is a subtractor for removing offset components due to skew. By adding a push-pull error signal detection circuit 30 as shown in the circuit and described later, false tracking error signals (push-pull error signals) caused by the deviation of the objective lens can also be removed.

23A and 23B are peak value detection circuits that detect the negative peak value and positive peak value 1 of the tracking error signal;
24A and 24B are adders and subtracters for adding and subtracting the outputs of the peak image 1 detection circuit; 25A is a coefficient circuit;
5B is a comparator circuit, and 26° and 27 are first . and the second storage circuit, and the switches S1 and S2 are controlled to open and close by a control signal output from the control gII (CPU) 28 of the optical disc device when the seek mode is set.

Note that 29 indicates a tracking actuator.

[Effect]

When an optical disc is set on the turntable and put into playback mode, the detection signals E a and E of the two-part detector 9 are detected.
From the subtractor 20A to which b is input.

When the optical spot 7 is on track and the O1 optical spot is off track, a tracking error signal is output that is positive or negative corresponding to the direction in which it is off track.

As shown in waveform CI in Figure 2A, this tracking error signal is normally a sinusoidal signal with equal positive and negative peak levels, but depending on the power of the irradiated laser beam,
When the groove depth of the track group and the reflectance of the detector differ, the peak level varies as shown by the dotted line.

In addition, when skew occurs at the inner circumference and outer station of the optical disk, an offset due to the skew occurs in the two-part detector, so the waveform shown in FIG. 2A (
As shown in II) or (m), the DC level fluctuates in the waveform. Therefore, when the tracks of the disc are traversed in the radial direction, the detected tracking error signal will undulate, as shown in FIG. 2B, for example. PR) is on a different level.

Therefore, first, when the laser power changes (recording, /
By adjusting the gain and input of the variable gain amplifier 20C according to the signal proportional to the received light power output from the adder 20B, the tracking error signal t) whose level is constant as shown in FIG. 2C is reproduced. It is adjusted so that

This signal is then transmitted to the AGC amplifier 21. The tracking error signal is supplied to the tracking actuator 29 via the subtraction circuit 22, but when the group (groove) depth or 1 reflectance of the optical disks differs, the level of the detected tracking error signal differs from disk to disk. Therefore, in the present invention, first, the positive peak value and the negative peak value 1 of the tracking error signal (waveform C) input to the actuator during the seek mode of the optical disc are detected by the peak value detection circuit 23A.
23B, and the peak-to-peak value (hereinafter)'P-P (also referred to as fi) of the tracking error signal is detected by manually inputting it to the subtracter 24B. Then, the comparison circuit 25B compares it with the reference voltage Er, and stores the difference output in the first storage circuit 26 via the switch S2.

The input signal to this storage circuit 26 is averaged and stored using a low-panel filter, etc., so if the gain of the AGC amplifier 21 is controlled by the output, the signal will always remain at a constant level even when the optical disc is replaced. A tracking error signal is now output from the AGC amplifier 21.

Next, by inputting the outputs of the peak value detection circuits 23A and 23B to the adder 24A, the DC level of the tracking error signal during traversal (waveform C in FIG.
Since the change in the DC signal due to the influence of this skew is converted into a predetermined value via the coefficient unit 25A, when the switch S1 is closed (during seek), the second The memory circuit 27 is manually powered. Then, when the playback or recording mode is entered, when this DC offset component is subtracted from the tracking and king error signals in the subtraction circuit 22, as shown in the second diagram, the DC offset component due to the skew is
A tracking error signal without offset will be formed.

In this case, if the time constant of the memory circuit 27 is appropriately selected,
The immediately preceding DCQ when a new track is accessed by track jump is stored via switch S1, and the DC offset component can be removed in response to changes in the skew on the inner or outer circumference of the disk. .

As will be explained in detail in the examples below, when detecting tracking error signals using the push-pull method, false tracking error signals ( However, in this case, by supplying the push-pull error signal obtained by detecting the deviation of the objective lens from the push-pull error detection circuit 30 to the subtraction circuit 22, The boost error signal can be removed, and a more accurate tracking error signal can be formed.

〔Example〕

FIG. 3 shows an example of a circuit according to the tracking servo system of the present invention, and the same reference numerals as in FIG. 1 indicate the same parts.

In this example, the first. and second storage circuit 26.27
is A/D converter 26A, 27A, average value hold circuit (
memory) 26B, 27B, and D/A converter 26C, 2
7G, as described in 1. As described above, the difference signal between the signal that detects the P-P value of the tracking error signal and the reference voltage is input from the switch S2 to the A/D converter 26A at the time of track jump, and after being converted into a digital signal, the average value is held. It is stored in circuit 26B.

Therefore, if the track of the optical disk installed is
The signal corresponding to the P-P value of the tracking error signal manually inputted each time by a seek jump is averaged and held in the hold circuit 25B, D during playback or recording
/A converter 26C outputs it as an analog signal and AG
Since the gain of the C amplifier 21 is controlled, it is possible to reliably prevent variations in the group depth and reflectance of the set optical discs from changing the peak of the tracking error signal.

Since the second storage circuit 27 also has a similar average value holding function, the signal for correcting the influence of skew detected every time the set optical disc performs a track jump is averaged and becomes accurate. Even when a DC offset occurs in the tracking error signal, the tracking error signal from which this DC offset signal has been removed can be supplied to the actuator by the output of the D/A converter 27C.

Incidentally, the degree of skew on an optical disc can be thought of as being caused by the assembly precision of the device or by the deflection of the optical disc, and the inner and outer sides of the optical disc often exhibit different skew values.

FIG. 4 shows an embodiment of the second storage circuit 27 that is useful in removing the effects of skew on such an optical disc.

According to this embodiment, the average value hold circuit includes three average value hold circuits 27Bl, 27 which hold the average (lI'i l) of the skew on the inner circumference side, the outer circumference side, and the intermediate skew.
Bz, 27 B3 are provided, and these toy uniform A1
The hold circuit inputs its power and output to the A/D converter 27A and D/'A conversion''A27 by the demultiplexer 27D+ and the multiplexer 27D2, respectively.
It is configured to selectively connect to C.

Then, the address of the jump destination track is input manually to the multiplexer 27D+ and the demultiplexer 27D2. For example, when jumping to the inner circumference of the disk, the average value hold circuit 27B1 is selected, and when jumping to the outer circumference of the disk, the middle value hold circuit 27B1 is selected. Average value hold circuit 27B is selected.

Therefore, according to this embodiment, each of the average value halt circuits 27 Dl, 27 D2. During recording or playback, the average value hold circuit data specified by the address at that position is output, so the DC offset of the tracking signal due to skew can be adjusted to correspond to the disc position. This makes it possible to remove iE more accurately.

Note that more average value hold circuits may be provided to cope with the skew of a disc (a disc bent like a propeller), for example, where different skews occur in the circumferential direction of the optical disc. .

In this case, in order to select the average value hold circuit, it is necessary to use the PG signal indicating the rotation angle of the disk and the sector-7 address signal.

In FIG. 3, the part surrounded by a dashed line shows an example of the configuration of the push/pull error detection circuit 30, and includes an electrical model circuit for reducing the mechanical transmission and characteristics of the low pass valve, C filter 30A, and actuator. 30B, and coefficient circuit 30
It is composed of C.

This push-pull error detection circuit 30 outputs the applied signal of the actuator coil 29B driven by the (<y-phase compensation circuit 29A) of the tracking actuator 29 via the low-pass filter 3OA.
A false tracking error signal (bu-shupuru error signal) generated due to eccentricity of the optical disk is detected.

Then, the model circuit 30B detects an electric signal indicating how the objective lens is deflected due to this false tracking error of 0, and this detection signal is sent to the coefficient circuit 30B.
The subtraction circuit 22 is manually inputted via C.

This makes it possible to eliminate false tracking error signals caused by the first position of the objective lens, which occurs especially in devices that detect tracking error signals using the push-pull method, and improves tracking servo devices with smaller tracking errors. It is possible to Bu.

In addition, in the circuit for removing this false error signal, Boo and Spur error signals, it is necessary that the converted Tobel coefficient of the coefficient circuit 30C is an appropriate value, and the method proposed earlier by the applicant is used. The conversion level coefficient of the coefficient circuit 30C is manually adjusted.

The embodiment shown in FIG. 5 shows an embodiment for automating the removal of this bush blue error when it is 0, and the same parts as those in FIG. 3 are given the same reference numerals.

In this embodiment, as previously proposed by the applicant, the drive circuit of the truck/guac nayuator 29 includes a general phase compensation circuit 29A and a target compensation circuit (resonant) having a peak gain at the disk eccentric frequency. circuit) 29C is used, and the outputs of both are manually input to the tracking coil 29B via an adder 29D to improve the servo characteristics (reduce residual deviation). Model circuit 3 with the output described above
An electric signal corresponding to the deviation of the I lens is generated manually at 0B, and this signal is input to the above-mentioned subtraction circuit 22 via a variable amplifier 30F with a gain of 11.

The gain control signal of the 11-gain variable amplifier 30F is obtained by averaging the DC offset signal due to the skew superimposed on the tracking error signal by the capacitor C.

Therefore, a deflection peak detection circuit 30D is provided to detect when the deflection signal of the objective lens outputted from the model circuit 30B reaches the maximum value or the minimum value 1. Close switch S3.

Then, the skew value of the optical disc at this time is held in the capacitor C via the switch 5xfc, and the held voltage value is input to the control signal generation circuit 30E which converts it into a gain control signal.

Then, the gain of the variable gain amplifier 30F is set by the output of the control signal generation circuit, so that the pluler error (1''i' j) is removed based on the deviation of the objective lens.

With this configuration, the signal output from the model circuit 30B is output every time the disk rotates.

When removing the spur error signal, if there is an excess or deficiency in the footbanked signal, the trafking error signal will be
C offset signal will be applied, but D at the maximum eccentricity point
By detecting the C offset component with the switch S5 and adjusting the gain of the variable gain amplifier 3OF using the average value, it is possible to automatically supply an appropriate feedback component so that the bush pull error signal is canceled out. become able to.

FIG. 6 shows an example of a circuit showing details of an embodiment of the present invention, in which the numbers 1°J and 1.degree.

In this figure, the AGC amplifier 21 is composed of two amplifiers A
1 and A2, and the operational amplifier A7 is connected to the operational amplifier A1. The gain is changed by supplying the feet/゛・tsuku signal. That is, when the switch circuit So repeats inversion based on the PWM signal (pulse width modulation signal) output from the first storage circuit 26, the feedback amount changes in accordance with the pulse duty of the PWMi signal. The resistor R9 and the capacitor C serve as a two-stage low-pass filter for the PWM signal to prevent harmonic signals from being mixed in.

The subtraction circuit 22 is constituted by an operational amplifier AJ, and the subtraction signal is sent to the first storage circuit 27 via resistors R1 and R2.
and is supplied from the coefficient circuit 30C.

Peak value detection circuit 23 (A, B, II are operational amplifiers A4
The negative peak value is held in the capacitors cl and c2 by the operational amplifier A5 and outputted via the buffer amplifiers A h and A t .

The adder 24A and the subtractor ``JA'' 24B are respectively embodied by an operational amplifier A!3 and an operational amplifier A9.

A signal corresponding to the disk skew value outputted from the adder 24A is supplied to the control signal generation circuit 30E via SW=2fs3.

This controller signal t\ generation circuit is an O cross comparator 1/
- operational amplifier AIG that constitutes the main circuit, and this operational amplifier A
An up/down counter CI+ that is added or subtracted depending on the level (L or H) of IG, and a PWM signal generator P1. ). Then, the pulse duty is modulated in accordance with the skew value averaged by the hold capacitor C, and the signal is supplied as a gain controller to the coefficient circuit 30C.

The model circuit 30B is composed of an operational amplifier AI6 and operational amplifiers AI7 and Al1 forming an integral circuit, and by applying feedback through resistors R1 and R2, the overall transfer characteristic becomes t/ which is the mechanical transfer function of the tracking actuator. A model circuit equivalent to (S2+as+b) is embodied. And output end 1'
Signals S and I corresponding to the deviation r,1 of the objective lens are output from T + , and a signal Sb corresponding to the differential output S/(S2+as+b) by 4 is output from the output terminal T2.

The signal Sh is inputted to the operational amplifier AI9 constituting the deviation peak i1 detection circuit 300 and converted into a rectangular wave that crosses at the θ level, and the capacitor ci generates edge pulses indicating the rising and falling points of =bl. death,
The switch S3 is controlled to close.

In addition, the signal 1+S and I are Ni constituting the coefficient circuit 30C.
It is input to the operational amplifier AI3, and is input to the buffer amplifier AI5.
The signal is sent to the subtraction circuit 22 via the subtraction circuit 22.

The operational amplifier AI4 constitutes a feedback circuit for the operational amplifier AI3, and the feedback amount of this feedback circuit is controlled by the opening/closing duty of the switch circuit So, as described above, similarly to the AGC amplifier 21.

That is, it is controlled by the pulse width of the PWM signal output from the control signal 1) generation circuit 30E.

According to the above embodiment, when a push-pull error signal based on the deviation of the hoe lens of the actuator is mixed during playback or recording, this error signal is sent from the adder 24A in the same way as the one based on skew. Output D
Since it is detected as a C offset component, the gain of the coefficient circuit 30H is controlled by the detection output.
A signal corresponding to the deviation of the objective lens outputted from the model circuit 30 is converted into an appropriate gain by the coefficient circuit 30E, and is input to the subtraction circuit 22 with an opposite phase to remove the push-pull error signal component from the tracking error signal. The signal '+Sa of the model circuit 30B is controlled to be θ.

〔Effect of the invention〕

As explained above, in the tracking servo method for an optical disk of the present invention, the optical disk mounted on the tower performs a track jump, detects the peak value of the tracking error signal from the traverse signal when crossing the trunk, and detects the peak value of the tracking error signal. By controlling the AGO amplifier in the servo circuit during recording, an appropriate tracking error signal is formed, and the DC level of the tracking en-signal is determined by the level of the error signal obtained by calculating the Optical disc recording using the push-pull method detects the skew state of the disc based on the change value of and removes the offset component of the tracking error signal caused by the skew.

Alternatively, in a No. 11 production device, the tracking servo can be stably applied.

Furthermore, the signal detected at the first position of the objective 1/lens of the device leaks into the tracking error No. 4.4.
By removing the Chevreux error signal, there is an advantage that highly accurate tracking servo can be applied.

[Brief explanation of drawings]

Fig. 1 shows a final block diagram of the tracking servo system of the present invention, Fig. 2 shows various waveform diagrams of tracking error signals, and Fig. 3 shows an embodiment according to the tracking servo system of the present invention. Block diagram, 4th E;! J is a block diagram showing an embodiment of the second memory circuit, FIG. 5 is a block diagram showing another embodiment of the present invention, FIG. 6 is a wiring diagram showing a specific circuit example, and FIG. 7 is a push An explanatory diagram of a pull type optical system, FIG. 8 shows a conventional tracking servo circuit diagram. In the figure, 21 is an AG amplifier, 22 is a subtraction circuit, 23A, 2
3B is a peak value detection circuit, 26 is a first storage circuit, 27
28 is a tracking actuator, and 30 is a push-pull error detection circuit.

Claims (3)

[Claims] (1) In an optical disk device in which a tracking error signal is detected by a detector having at least two or more light-receiving surfaces and tracking servo is applied, the positive and negative peak values of the tracking error signal output during traverse are detected. and subtracting the sum signal of the positive and negative peak values from the detected tracking error signal to cancel the offset signal of the detector during reproduction or recording of the optical disc. A tracking servo method for optical disc devices. (2) The optical disc according to claim (1), wherein the loop gain of the tracking servo circuit is controlled by the difference signal between the positive and negative peak values of the tracking error signal detected during traverse. Tracking servo method in equipment. (3) In an optical disc device in which a tracking error signal is detected by a detector having at least two or more light-receiving surfaces and a tracking servo is applied, positive and negative peak values of the tracking error signal are detected, and both peak values are detected. A push-pull error signal based on the deflection of the objective lens is mixed into the tracking error signal by feeding it back to the tracking servo circuit via the amplifier. A tracking servo method in an optical disk device characterized by eliminating push-pull error signals.