JPS6332731A - Automatic tracking device - Google Patents

Abstract

PURPOSE:To attain servo of high accuracy by inputting controlling signals to a means that makes correction equal to frequency characteristic of a light spot shifting means, adding the output and detection signals by an adding means, and removing periodic variation component of detection signals. CONSTITUTION:When the frequency of sine wave signals is larger than the resonance frequency of an actuator 14, the signals of a sine wave generator 22 are applied to an actuator through a driving amplifier 18 and error signals phase lagged by 180 deg. by frequency characteristic are outputted from a pre-amplifier 8. On the other hand, the sine wave signals are inputted to a delay circuit 28, and the phase lag of 360 deg. obtained by adding phase lag for correcting offset component to phase lag of 180 deg. due to the frequency characteristic of the actuator 14, and amplitude is corrected, and inputted to an adder 29 together with output error signals of the amplifier 8, and after addition, the offset component of tracking error signals is removed. Thereby, the periodic variation component included in detection signals is removed, and the highly accurate tracking servo can be attained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an automatic tracking device, and in particular removes periodic fluctuation components of a detection signal indicating a positional error between a track of a rotating body and a light spot, thereby improving accuracy. The present invention relates to an automatic tracking method and apparatus designed to perform highly accurate tracking control.

The automatic tracking device according to the present invention is applied to, for example, an optical information recording/reproducing system using an information recording medium such as an optical disk or a magneto-optical disk.

[Prior Art] In a device that optically records or reproduces information on a disc-shaped information recording medium (hereinafter simply referred to as a "disk"), it is important to ensure that a minute light spot follows an information track. It is.

For this reason, conventionally, the positional deviation of the light spot has been reduced by 3.
A tracking control method was used in which detection was performed using a beam method, push-pull method, etc., and the position of the light spot was corrected by driving a mirror or lens according to the error signal.

[Problem to be solved by the invention] The push-pull method described above has the advantage that the number of optical parts is small and the amount of detected light can be efficiently used for recording and reproducing information. There is a problem in that moving the mirror shifts the optical axis, causing an offset in the detection signal indicating the relative position of the light spot and the information track.

[Intermediate Points to be Solved by the Invention] The above problems are related to a light spot moving means for irradiating a light spot onto a desired track of a rotating body having a plurality of tracks, and the position of the light spot and the track. a first control means for generating a first control signal for controlling the light spot moving means based on the detection signal; A second control signal for detecting a periodic positional variation between the light spot and the track by detecting the detection signal, and generating a second control signal for controlling the light spot moving means based on the positional variation. an automatic tracking device having a second control means, a correction means for performing a signal correction equal to the frequency characteristic of the light spot moving means with respect to the second control signal, and an output signal of the correction means and the detection signal; adding means, inputting the second control signal to the correction means, and adding the corrected second control signal to the addition means to cancel the periodic fluctuation component of the detection signal; This problem is solved by the automatic tracking device of the present invention, characterized in that the detection signal with the periodic fluctuation component canceled is input to the first control means.

[Function] When the second control signal is output based on periodic positional fluctuations between the light spot and the track, the light spot moving means moves in response to this signal, and the luminous flux of the light spot and the light An axis misalignment occurs between the spot moving means and the spot moving means. Corresponding to this axis deviation, periodic fluctuations occur in the detection signal. Further, the phase, amplitude, etc. of the periodic fluctuation at this time vary depending on the frequency characteristics of the optical spot moving means with respect to the second control signal.

In the invention, the second control signal is input to a correction means for correcting a signal equal to the frequency characteristic of the light spot moving means, and the output signal of the correction means and the detection signal are added by an addition means, and the detection signal is The light spot moving means is controlled by canceling the periodic fluctuation component of the signal and inputting the detection signal with the periodic fluctuation component canceled to the first control means.

[Example] Hereinafter, an example of the present invention will be described in detail based on the drawings.

FIG. 1 is a block diagram of one embodiment of an automatic tracking device according to the present invention.

In the figure, light from a semiconductor laser 1 is turned into parallel light by a collimator lens 2, passes through a beam splitter 3, and is focused onto an optical disk 5 by an optical system 4.

The reflected light is turned into parallel light by the optical system 4, reflected by the beam splitter 3, and focused onto the optical sensor 7 by the condenser lens 6. The optical sensor 7 is divided into a plurality of parts, and each output signal is input to a preamplifier 8. The preamplifier 8 generates reproduction information signals 9 . A focus error signal lO and a tracking error signal 11 are each output. In this embodiment, autofocus control is performed by an astigmatism method, knife etching method, etc., and autotracking control is performed by a push-pull method.

For autofocus control, the focus error signal lO output from the preamplifier 8 is sent to the autofocus control circuit 1.
2 (hereinafter referred to as AF circuit 12), and this AF
The circuit 12 drives the actuator 14 via the focus actuator drive amplifier 13 (hereinafter referred to as drive amplifier 13), moves the optical system 4 in the direction of its optical axis, and maintains the light spot in focus. It is done by

On the other hand, for auto-tracking control, the tracking error signal 11 output from the preamplifier 8 is input to an auto-tracking control circuit 15 (hereinafter referred to as AT circuit 15) via an adder 29, and this AT circuit 15 controls the tracking open/close switch. 16 (hereinafter referred to as TR switch 16), adder 17. This is performed by driving the actuator 14 by a tracking actuator drive amplifier 18 (hereinafter referred to as drive amplifier 18), moving the optical system 4 in the radial direction of the optical disc 5, and causing the light spot to follow the track.

The optical disc 5 is rotated by a motor 19, and an encoder 20 outputs one pulse 21 for each rotation of the optical disc 5, which is input to a sine wave generator 22 and a control circuit 24. The sine wave generator 22 generates a sine wave having a phase set by the signal 26 output from the control circuit 24, an amplitude set by the signal 27, and a period equal to the rotation of the optical disk 5, and the sine wave generated by the adder 17 and Delay circuit 28
Output to. The delay circuit 28 corrects the phase delay and amplitude reduction caused by the drive amplifier 18 and the actuator 14 with respect to the sine wave signal output from the sine wave generator 22, and outputs a correction signal to the adder 29.

Frequency-voltage conversion circuit 23 (hereinafter referred to as FV circuit 23).

) inputs the tracking error signal 11 and outputs a voltage output FV corresponding to the frequency to the control circuit 24.

The control circuit 24 inputs the pulse 21 from the encoder 20 and the output FV from the FV circuit 23, and gradually changes the phase and amplitude of the sine wave output from the sine wave generator 22, as described later. By changing this, the phase and amplitude of the sine wave that minimizes the peak of the output FV are detected.

Next, the operation of the control circuit 24 will be explained.

FIG. fjS2 is a flowchart showing the operation of the control circuit 24.

The operation of the control circuit 24 is started when the optical disc 5 is rotating normally and autofocus control is being performed. Normally, the operation starts immediately after the optical disc 5 is newly loaded, but it can also start after a certain period of time has passed since the optical disc 5 has been loaded, when no information is being recorded, reproduced, or erased. The following operations are normally performed using the TR switch 16.
Do this with the door closed.

As shown in FIG. 2, first, a value M corresponding to the FV ratio output upper limit is stored in the register FVix in the control circuit 24, and 0 is stored in the register Nm1n. (Sl) Next, store 0 in the variable n that controls the phase of the sine wave generator 22, and store the value ^i corresponding to the uniform eccentricity amount in the variable A that controls the amplitude of the sine wave generator 22. (S2), and the sine wave from the sine wave generator 22 is n/ by one phase control variable n.
The phase is shifted from the rotation pulse 21 by N x 350''. However, N is a desired positive integer and may be any appropriate value depending on the purpose.

Subsequently, the control circuit 24 outputs the rotation pulse 21 (hereinafter referred to as TA
Let's call it CH21. ) will be in a standby state (S 3 ).
, When TACH21 inputs (YES in S3)
.

The phase control variable n and the amplitude control variable aA are set by a sine wave generator 2.
Output to 2. (S4), thereby causing the sine wave generator 2
2 generates a sine wave having a phase and amplitude corresponding to the variables n and A (in the first case, the amplitude ^i is in synchronization with the TACH 21 and in the same phase), and the optical system 4 uses this sine wave to detect the optical disk 5. ! T! -Start moving radially. As a result, the conditions in which the light spot intersects the information track change,
The FV ratio output waveform output from the FV circuit 23 also begins to change.

At the same time that such a sine wave is output from the sine wave generator 22, the control circuit 24 initializes the register FVmx to an FV output value equal to or less than the FV ratio output digitally converted at a certain clock timing. ) and register FV
The magnitude relationship with the contents of sx is compared (S6). If the FV output value is greater than the contents of FVmx (YES in S6)
Store the FV output value in FV-x and update the contents of FVmx (S7), but if the FV output value is less than the contents of FV@X (No in S6), do not update the contents of FVmx, The FV output value at the next clock timing is compared with the contents of FVmx (SS).

This operation (36 to S8) is performed in the next TACH pulse 2.
Repeat until 1 is input, that is, until the optical disc 5 rotates once (No in S8), L/TACH, TACH
When pulse 21 is input (YES in S8), the maximum value of the FV output value is stored in FVwx.

The maximum value of the FV output is the tracking error signal 1 during one rotation when the optical system 4 is vibrated according to the phase control variable n and amplitude control variable A output in step S4.
1 maximum frequency.

When TACH pulse 21 is input (YES in S8),
The magnitude relationship between the maximum FV output value that is the content of FVmx and the upper limit value M that is the content of FVix is compared (S9). If the maximum FV output value is smaller than the content M of FVix (S
9), store the maximum FV output value in FVix and update the contents of FVix, store the phase control variable n at that time in Nwin and update the contents of Nm1n (St
,.

5ll), and if the maximum FV output value is less than the contents of FVix (No in S9), FVix and Nm1
Do not update n, then change the phase control variable n to l-''
) (S12), and if n has not reached N,
That is, the phase difference between the TAC11 pulse 21 and the sine wave is 360
If @ has not been reached (No in S13), steps 34 to S12 are repeated using the new phase control variable nft.

That is, by sequentially increasing the five phase control variables n, the phase of the sine wave output from the sine wave generator 22 is adjusted to TAC1.
The maximum FV output value when the optical system 4 is vibrated by the sine wave of each phase is gradually shifted from 1 pulse 21, and the maximum FV output value is calculated as the maximum FV output value for the previous phase. By comparing and always storing the smaller value in FVix, the smallest maximum FV output value is finally stored in FVix, and the phase control variable n at that time becomes Ma.
Stored in in.

Next, in order for the light spot to follow the periodic position fluctuation of the information track by the sine wave output from the sine wave generator 22, it is necessary to detect the value of the amplitude control variable A corresponding to the amplitude of the sine wave. There is.

The amplitude control variable A is detected in the following steps 314 to S26, but the method of detection is in steps S1 to S1.
It is basically the same as 3.

First, initialize registers FVix and Azen.51
4), Store the contents of N in in the phase control variable an, and store O in the amplitude control sound @A (S15), then TACI
(When pulse 21 is input (516), step S17
- S26 are repeated until the amplitude control variable A exceeds the allowable value A*X of the optical axis deviation of the optical system 4.

That is, by sequentially increasing the amplitude control variable A by an increment a (S25), the amplitude of the sine wave output from the sine wave generator 22 is gradually increased, and the sine wave of each amplitude causes the optical system 4 to be Sequentially find each maximum FV output value in the case of vibration (318 to 321), and compare the maximum FV output value with the maximum FV output value in the case of the previous amplitude (522),
By always storing the smaller value in FVix, the smallest maximum FV output value is finally stored in FVix (S
24), the amplitude control variable A at that time is stored in As+in.

And when the amplitude control variable A exceeds ^■X (Y of 826
The contents of ES) and ^■in are stored in the amplitude control variable A (527), and are output to the sine wave generation window 22 together with the already detected phase control variable an (328).

The sine wave output from the sine wave generator 3122 according to the phase control variable 'gjtn and the amplitude control variable A detected in this manner is directly input to the drive amplifier 18 through the adder 17 when the TR switch 15 is open. The drive amplifier 18 drives the actuator 1 according to the input sine wave.
4 to vibrate the optical system 4, the light spot can best follow the periodic positional fluctuations of the information track.

Therefore, the TR switch 16 is closed and the AT circuit 15
Even when tracking i'l1111 is performed, the detected sine wave is added to the output of the AT circuit 15 in the adder 17. Regarding positional fluctuations, tracking control is performed without placing any burden on the AT circuit 15.

The sine wave signal shown above becomes the main signal for driving the optical spot in the radial direction of the optical disk in tracking control. The reason why a sine wave signal is used is that track deviation due to eccentricity can be approximated to a sine wave.

If the eccentricity is large, the movement of the optical system 4 by the actuator 14 will cause an axis misalignment between the optical system and the beam of light, and an offset will occur in the tracking error signal. Since the offset occurs in response to the optical axis deviation, it should be proportional to the sinusoidal signal, or the actual offset is proportional to the movement of the optical system 4 driven by the actuator 14. That is, due to the frequency characteristics of the actuator, the offset causes a phase lag with respect to the sine wave signal. Although the phase delay is also caused by the drive amplifier 18, it is small compared to the change due to the frequency characteristics of the actuator 14, so the explanation will be omitted in the following explanation.

The operation of the automatic tracking device of the present invention will be described below with reference to the drawings.

FIG. 3(a) is a waveform diagram of a sine wave signal, FIG. 3(b) is a waveform diagram showing a tracking error signal having an offset,
FIG. 3(c) is a waveform diagram of the output of the delay circuit 28, and FIG.
d) is a waveform diagram of the corrected tracking error signal.

FIG. 4 is a characteristic diagram showing an example of the frequency characteristics of the actuator.

As shown in FIG. 4, when a sine wave signal with a frequency exceeding the natural resonance frequency f0 is applied to the actuator 14, the movement of the actuator becomes unable to follow, the amplitude becomes small, and there is a delay in the transfer of the groove 180'. begins to occur.

In this embodiment, a sine wave signal having the same offset and amplitude and a 180° phase lag with respect to the tracking error signal is added to the tracking error signal having a sine wave offset to correct the offset component. Hereinafter, the case where the frequency of the sine wave signal is higher than the resonance frequency f0 of the actuator will be explained using FIG. 3.

When the sine wave signal generated by the sine wave generator 22 is inputted to the drive amplifier 18 and the sine wave output of the drive amplifier 18 shown in FIG. 3(a) is applied to the actuator 14, as shown in FIG.
As shown in b), a tracking error signal with a 180° phase delay is output from the preamplifier 8 due to the frequency characteristics of the actuator 14. On the other hand, the following sine wave signal is input to the delay circuit 28, and the delay circuit 28 adds a 180° phase delay due to the frequency characteristics of the actuator 14 and a 180° phase delay for correcting the offset component.
A 60° phase delay is generated and the amplitude is corrected, and the sine wave signal shown in FIG. 3(c) is output from the delay circuit 28. The tracking error signal shown in FIG. 3(b) and the sine wave signal shown in FIG.
9, the offset component of the tracking error signal is removed as shown in FIG. 3(d).

In the above embodiment, a delay circuit is provided as a correction means, and the tracking error signal is corrected using a sine wave signal. signal or vIA
g! The actuator drive signal output from the J amplifier 18 may be used, and as a correction means, in addition to a delay circuit, a method may be used in which the signal is stored using a memory and the addresses for accessing the two memories are shifted and output. Good too.

[Effects of the Invention] As explained in detail below, according to the automatic tracking device of the present invention, periodic fluctuation components included in the detection signal can be removed, and highly accurate tracking servo can be performed. .

[Brief explanation of drawings]

FIG. 1 is a diagram of one embodiment of an automatic tracking system according to the present invention. FIG. 2 is a flowchart showing the operation of the control circuit. FIG. 3 is a waveform cutting diagram for explaining the operation of the above embodiment. ff14UA is a characteristic diagram showing an example of frequency characteristics of an actuator. ■... Semiconductor laser, 4...-Optical system, 5... Optical disk 57... Optical sensor, lO... Focus error signal,
11--Tracking error signal, 12--Autofocus control circuit, 14--Actuator, 15-
---Auto tracking control circuit, 16-TR switch, 17.29--Adder, 19--Motor, 20-
... Encoder, 21... Rotation pulse (TACH pulse), 21... Sine wave generator, 23-... Frequency voltage conversion circuit. 24...Control circuit. Agent Patent Attorney Seki Yamashita Diagram 4f. 712 skin huan

Claims (1)

[Scope of Claims] A light spot moving means for irradiating a light spot onto a desired track of a rotating body having a plurality of tracks, and detecting a positional error between the light spot and the track and generating a detection signal. a first control means for generating a first control signal for controlling the light spot moving means based on the detection signal; and a first control means for generating a first control signal for controlling the light spot moving means based on the detection signal; and second control means for detecting periodic positional fluctuations with respect to the track and generating a second control signal for controlling the light spot moving means based on the positional fluctuations. , comprising a correction means for performing a signal correction equal to the frequency characteristic of the optical spot moving means with respect to the second control signal, and an addition means for adding an output signal of the correction means and the detection signal, By inputting the second control signal and adding the corrected second control signal to the adding means, the periodic fluctuation component of the detection signal is canceled out, and a detection signal in which the periodic fluctuation component is canceled is obtained. is input into the first (7) control means.