JPH11161972A - Information recording and reproducing device and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the stability and a control performance which are not affected by the periodic fluctuation of the disturbance by irradiating a recording medium with a light for recording or reproducing information and controlling the relative position of the light according to an error signal and after delaying the error signal by a prescribed time while detecting the reflected light from the recording medium and performing the position control while adding the delayed error signal to a not delayed error signal. SOLUTION: When a judgement circuit 45 judges that the magnitude of a tracking error signal and the absolute value of the error signal is larger than a reference value, it judges whether the tracking error signal is more increased than that of a previous time or not. When the circuit judges that the signal is more increased, the circuit judges whether the frequency of a wobbling signal is raised or not to return the frequency to an original state by lowering or raising the frequency while controlling a wobbling signal generator 43. When the signal is judged to be more reduced than that of the previuos time, the circuit 45 controls the frequency by controlling the generator 43.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information recording / reproducing apparatus and method, and more particularly to a method for controlling a servo control by using a repetitive control as a learning control even when a periodic disturbance occurs. The present invention relates to an information recording / reproducing apparatus and method capable of reducing a deviation.

[0002]

2. Description of the Related Art As recording media for recording or reproducing information by using light, compact discs (CD) and CD-ROMs are known.
Optical disks such as ROMs have become widespread. When recording or reproducing information on or from an optical disc, it is necessary to control a tracking servo and a focus servo using a two-axis actuator.

[0003] These servo systems are also called follow-up control systems, and it is important in servo system control to promptly follow a control amount to a target value. Further, the servo system is composed of blocks including feedback control, and is required to have stability, quick response, attenuation, sensitivity characteristics, steady characteristics, and the like.

One of the control methods used for these servo systems is learning control. The learning control has a feature that, although learning takes a long time, once the learning is completed, very high control performance is realized. As a learning control that has been widely known, there is a repetitive control. The details of this repetition control are described in, for example, “Repetition Control” edited by the Society of Instrument and Control Engineers.

FIG. 8 is a block diagram for explaining repetitive control in the servo system. The feedback control of FIG. 8 is based on the operation of comparing a control amount as a result of the control with a target value and correcting the operation amount if there is a deviation.
Here, the actuator 42 that performs the tracking control or the focus control receives the operation amount (signal) from the compensator 41 and converts the operation amount into a control amount with high power. The compensator 41 compensates for the phase deviation of the control deviation. Difference between output (control amount) of actuator 42 and target value (error signal)
Is supplied to the compensator 41 as a control deviation.

[0006] Iterative controller (iterative compensator) 48
Are the analog delay element 60 and the low-pass filter (LP
F) It is composed of an analog circuit consisting of 61, delays the control deviation for a predetermined time, smoothes it, and adds it to the undelayed control deviation.

The repetitive control is resistant to periodic disturbances. For example, if the delay time of the repetitive control is made to coincide with the period of the fundamental wave of the disturbance, the disturbance of the fundamental wave and the harmonic component of the fundamental wave can be removed. The control performance of the servo system is improved.

[0008]

However, in the repetitive control of the above-described conventional configuration, if a difference occurs between the signal delay time by the repetitive controller 48 and the rotation period of the optical disk, even if the difference is several percent, However, there is a problem that the characteristics are greatly deteriorated.

The above problem will be described in detail below. The disturbance that occurs in the optical disc in a steady state is dominantly synchronized with the rotation speed of the optical disc.
The optical disk rotation method is CLV (Constant Linear Velo)
In the case of the (city) method, the number of revolutions changes according to the radial position on the optical disc, and accordingly, the period of the disturbance generated also changes. This causes a difference between the delay time of the repetitive control and the period of the disturbance.

A zone CAV (Constant Angular V)
Also in the case of elocity, the rotation frequency of the optical disk changes between zones, so that the period of the disturbance also changes.
Furthermore, even if the CAV method is used, in practice, rotation irregularities occur due to disturbance, and the rotation speed of the optical disk slightly changes due to the influence, and the period of the disturbance also changes.

FIG. 9 shows the output response of the servo system when the delay time of the repetitive control is constant and the frequency of the disturbance increases. FIG. 10 shows the output response of the servo system when the delay time of the repetitive control is constant and the frequency of the disturbance decreases. From FIGS. 9 and 10, it can be seen that even if the delay time of the repetitive control and the period of the disturbance are shifted by only a few percent, the control performance is greatly deteriorated.

As a measure against the periodic fluctuation of the disturbance, a method of utilizing a signal synchronized with the rotation of the optical disk by using a sensor or the like is disclosed in, for example, Japanese Patent Laid-Open No. 6-3019.
As disclosed in Japanese Patent Application Publication No. 96-96, this control method requires a configuration for generating a signal synchronized with the rotation of the optical disk. As a result, not only is the information recording / reproducing apparatus expensive, but also it is difficult to reduce the size.

The present invention has been made in view of such a situation, and while responding to two demands of the price and miniaturization of an information recording / reproducing apparatus, the stability and control performance of the information recording / reproducing apparatus are controlled by the above-mentioned periodic fluctuation of the disturbance. The purpose is to create a robust control system that is less likely to be affected.

[0014]

An information recording / reproducing apparatus according to claim 1 irradiates a recording medium with light for recording or reproducing information, and a relative position of the light with respect to the recording medium. Position control means for controlling the error signal in accordance with the error signal, detection means for detecting the reflected light from the recording medium, and after delaying the error signal by a predetermined time, adding the error signal to the undelayed error signal, It is characterized by comprising learning control means for supplying to the control means, and changing means for changing the delay time of the learning control means.

According to a sixth aspect of the present invention, there is provided an information recording / reproducing method, comprising: irradiating a recording medium with light for recording or reproducing information; A position control step of controlling the position and a detecting step of detecting reflected light from the recording medium;
A learning control step of delaying the error signal by a predetermined time, adding the error signal to the undelayed error signal, and using the error signal as an error signal to be used in the position control step, and a changing step of changing a delay time in the learning control step. It is characterized by having.

In the information recording / reproducing apparatus according to the first aspect, the learning control means delays the error signal by a predetermined time, adds the error signal to the undelayed error signal, and supplies the error signal to the position control means. The changing means changes the delay time of the learning control means.

In the information recording / reproducing method according to the sixth aspect, the error signal is delayed by a predetermined time in the learning control step, and then added to the undelayed error signal.
This is an error signal used in the position control step. In the changing step, the delay time in the learning control step is changed.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below. In order to clarify the correspondence between each means of the invention described in the claims and the following embodiments, each means is described. When the features of the present invention are described by adding the corresponding embodiment (however, an example) in parentheses after the parentheses, the result is as follows. However, of course, this description does not mean that each means is limited to those described.

An information recording / reproducing apparatus according to a first aspect of the present invention includes: an irradiating unit (for example, an optical pickup unit 1 shown in FIG. 1) for irradiating a recording medium with light for recording or reproducing information; Position control means (for example, a tracking servo actuator 6 or a focus servo actuator 7 shown in FIG. 1) for controlling a relative position with respect to the recording medium in accordance with an error signal, and a detection for detecting reflected light from the recording medium Means (for example, the detection circuit 2 shown in FIG. 1) and a learning control means (for example, FIG. 2) which delays the error signal by a predetermined time, adds the error signal to the undelayed error signal, and supplies the error signal to the position control means. And a changing means for changing the delay time of the learning control means (for example, the wobbling signal generator 4 shown in FIG. 2).
3, an adder 44, a determination circuit 45, and a VCO 46).

Further, in the information recording / reproducing apparatus according to a second aspect, the changing means includes a generating means (for example, a VCO 46 shown in FIG. 2) for generating a control signal of a predetermined frequency for changing the delay time; Frequency control means (for example, a wobbling signal generator 43 shown in FIG. 2) for judging the magnitude of the error signal and controlling the frequency of the control signal generated by the generation means in the direction in which the error signal decreases. And

FIG. 1 is a block diagram showing an example of the overall configuration of an information recording / reproducing apparatus to which the present invention is applied. In this embodiment, the spindle motor 8 is controlled by the control circuit 4 to rotate the optical disk 9 at a predetermined speed. The optical pickup unit 1 condenses laser light from a built-in semiconductor laser (not shown) under the control of the control circuit 4, irradiates the laser light to a target position on the optical disk 9, and incorporates reflected light from the optical disk 9. A photodiode (not shown) receives light and supplies a signal output from the photodiode to the detection circuit 2. The detection circuit 2 generates a data detection signal from the output signal of the photodiode and supplies the data detection signal to the reproduction circuit 3, generates a tracking error signal and a focus error signal, and supplies them to the control circuit 4.

The tracking servo actuator 6 is for causing an objective lens (not shown) of the optical pickup unit 1 to follow the track runout of the optical disk 9. Each of them is a drive mechanism for keeping the relative positional relationship between the target position on the optical disc 9 and the light spot constant at all times. The control circuit 4 controls the tracking servo actuator 6 and the focus servo actuator 7 based on the tracking error signal and the focus error signal, and also controls the optical pickup unit 1 and the spindle motor 8. The reproducing circuit 3 generates and outputs a reproduced signal based on the data detection signal.

Next, the servo by the control circuit 4 will be described in detail with reference to FIG. FIG. 2 is a block diagram showing an embodiment of the servo control in the control circuit 4. Hereinafter, the operation in the case where the tracking servo control is performed will be described. The main part of the tracking servo control is constituted by a feedback control system for promptly following a control amount to a target value. In the feedback control system, the compensator 41 calculates a manipulated variable corresponding to a deviation (tracking error) of the control variable, which is a result of the control, with a target value.
The basic operation is that the actuator 42 (in this case, the tracking servo actuator 6) corrects the position of the light spot relative to the track in accordance with the operation amount.

The repetition controller 47 includes a low-pass filter (LPF) 50 for preventing alias, an A / D (analog / digital) converter 51 for converting an analog signal to a digital signal, a shift register 52, and a digital signal for converting an analog signal to an analog signal. And a D / A (digital / analog) converter 53 for converting the data into a digital signal.

The low-pass filter 50 passes only signals having a frequency up to 1/2 of the sampling frequency according to the sampling theorem when performing A / D conversion. The shift register 52 delays data sampled at regular time intervals by a predetermined time. Thereafter, the D / A converter 53 converts the digital signal into an analog signal and returns the analog signal to the control loop, so that the loop gain of the control system can be made infinite and the disturbance is completely removed at the frequency where periodic disturbance is mixed. Can do it.

The determination circuit 45 determines the magnitude of the tracking error signal. The wobbling signal generator 43
A wobbling signal is generated based on the determination result of the determination circuit 45 and supplied to the adder 44. The adder 44 adds the wobbling signal and the tracking error signal, and supplies the added signal to the VCO 46. The VCO 46 outputs a control signal of a predetermined frequency according to the input signal. The output control signal is supplied to the shift register 52. Depending on the frequency of the control signal, the shift register 52
Can be changed.

Next, the control of the determination circuit 45 will be described with reference to the flowchart shown in FIG. First, when the repetitive control is started, in step S1, the determination circuit 4
5 determines the magnitude of the tracking error signal. If it is determined that the absolute value of the tracking error signal is larger than the predetermined reference value, the determination circuit 45 proceeds to step S2, and determines whether the tracking error signal has increased from the previous time. If it is determined in step S2 that the tracking error signal has increased, step S3
The determination circuit 45 determines the frequency of the wobbling signal,
It is determined whether or not it was increased last time. If it is previously determined that the frequency of the wobbling signal has been increased, the determination circuit 45 controls the wobbling signal generator 43 in step S4 to decrease the frequency of the wobbling signal. Then, the process returns to step S1. If it is determined in step S3 that the frequency of the wobbling signal has been previously reduced, the determination circuit 45 controls the wobbling signal generator 43 in step S6,
Increase the frequency of the wobbling signal from the previous time. Then, the process returns to step 1.

If it is determined in step 2 that the tracking error signal has decreased from the previous time, the determination circuit 4
5 determines in step S5 whether the frequency of the wobbling signal has been increased from the previous time. When it is determined that the frequency of the wobbling signal has been increased from the previous time, the determination circuit 45 controls the wobbling signal generator 43 in step S6 to increase the frequency of the wobbling signal from the previous time, and then returns to step S1. If it is determined in step S5 that the frequency of the wobbling signal has been reduced from the previous time, the determination circuit 45 controls the wobbling signal generator 43 in step S4 to reduce the frequency of the wobbling signal from the previous time. Return to

If it is determined in step 1 that the absolute value of the tracking error signal is equal to or smaller than the predetermined reference value, the determination circuit 45 controls the wobbling signal generator 43 in step S7 to fix the frequency of the wobbling signal. Then (to make the same value as the previous time), and return to step 1.

The reason why the frequency of the wobbling signal is fixed will be described below. When the frequency of the control signal output from the VCO 46 is changed, the cycle of the repetitive controller 47 (the delay time of the shift register 52) is constantly changed. When you look at them, they grow and shrink. As a result, when the period of the disturbance does not change, the noise is increased.

If it is determined in step S1 that the tracking error signal is equal to or smaller than the predetermined reference value, the rotation speed of the optical disk 9 hardly changes, and the delay time of the repetition controller 47 and the period of the disturbance are changed. Is determined to match. Then, by fixing the frequency of the wobbling signal in step S7, the delay time of the repetition controller 47 is set to a constant value.

Here, the relationship between the disturbance and the output response of the tracking servo system when the above-described repetitive control is performed will be described with reference to FIGS. FIG. 4 is a simulation of the output response when the rotation time of the optical disk 9 is increased while the delay time of the repetition control is fixed. FIG. 4A shows an output response waveform of the tracking servo system, and FIG. 4B shows the repetition controller 47 at this time.
Of FIG. The vertical axis of FIG. 4A indicates the rate at which the number of rotations increases, and the rate of increase is shown as a rate when the delay time (fixed) of the repetitive controller 47 is set to 100%. FIG. 4 shows that the control deviation can be reduced by making the period of the disturbance (0.02 seconds) and the delay time (0.02 seconds) of the repetitive controller 47 coincide.

FIG. 5 shows the relationship between the applied disturbance and the repetitive control on / off in the simulation performed in FIG. FIG. 5A shows the waveform of the disturbance applied to the tracking servo system (the period is 0.02 seconds), and FIG. 5B shows the on / off state of the repetitive control at that time. . In this example, the repetitive control is turned on at the timing when 0.02 seconds elapse after the start of the simulation.

FIG. 6 is a simulation of how the output response changes when the amplitude of the disturbance applied to the tracking servo system increases. FIG. 6A shows the output response waveform of the tracking servo system, and FIG. 6B shows the waveform of the applied disturbance. The vertical axis in FIG. 6B indicates the rate of increase in the amplitude of the disturbance, and is shown as a rate when the original amplitude is set to 100%. FIG. 6A shows the effect of the increase in the amplitude of the disturbance, but since the learning is performed in one cycle, the output response is stabilized after one cycle.

FIG. 7 is a simulation of how the output response changes when the amplitude of the disturbance applied to the tracking servo system decreases. FIG. 7A shows the output response waveform of the tracking servo system, and FIG. 7B shows the waveform of the applied disturbance. The vertical axis in FIG. 7B indicates the rate of decrease in the amplitude of the disturbance, and is shown as a rate when the original amplitude is set to 100%. FIG. 7A shows the effect of the decrease in the amplitude of the disturbance. However, since learning is performed in one cycle, the influence of the disturbance is removed after one cycle, and the tracking servo system is stabilized.

The control deviation of the tracking servo system can be further reduced by replacing the analog delay element constituting the repetition controller 48 with a digital delay element.

In the above description, the present invention is applied to a tracking servo system, but the present invention is also applicable to a focus servo, a spindle servo, a thread servo, a tilt servo, and the like. Further, in the present invention, design changes can be made without departing from the scope of the invention.

[0038]

According to the information recording / reproducing apparatus according to the first aspect and the information recording / reproducing method according to the sixth aspect, the error signal is delayed by a predetermined time and then added to the undelayed error signal. In addition, since the delay time is changed, it is possible to further reduce the control deviation regardless of the periodic fluctuation of the disturbance.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an overall configuration of an information recording / reproducing apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration example of a control circuit 4 of the information recording / reproducing apparatus of FIG.

FIG. 3 is a flowchart illustrating an operation of a determination circuit 45 in FIG. 2;

FIG. 4 is a diagram illustrating an output response of the tracking servo system of FIG. 2;

FIG. 5 is a diagram illustrating a disturbance applied to the tracking servo system of FIG. 2;

FIG. 6 is a diagram illustrating an output response when the amplitude of disturbance applied to the tracking servo system of FIG. 2 is increased.

7 is a diagram illustrating an output response when the amplitude of a disturbance applied to the tracking servo system of FIG. 2 is reduced.

FIG. 8 is a block diagram showing a configuration example of a tracking servo system of a conventional information recording / reproducing apparatus.

9 is a diagram illustrating an output response when the frequency of disturbance applied to the tracking servo system of FIG. 8 is increased.

10 is a diagram illustrating an output response when the frequency of disturbance applied to the tracking servo system of FIG. 8 is reduced.

[Explanation of symbols]

Reference Signs List 1 optical pickup unit, 2 detection circuit, 3 reproduction circuit, 4 control circuit, 5 input device, 6 tracking servo actuator, 7 focus servo actuator, 8 motor, 9 optical disk, 41
Compensator, 42 actuator, 43 wobbling signal generator, 44 adder, 45 decision circuit, 46
Voltage controlled oscillator (VCO), 47 repetition controller,
48 repetition controller, 50 low-pass filter (LPF), 51 A / D converter, 52 shift register, 53 D / A converter, 60 analog delay element, 61 low-pass filter (LPF)

Claims (6)

[Claims] An irradiating means for irradiating the recording medium with light for recording or reproducing information; a position control means for controlling a relative position of the light with respect to the recording medium in response to an error signal; Detecting means for detecting reflected light from a medium; learning control means for delaying the error signal by a predetermined time, adding the error signal to the undelayed error signal, and supplying the error signal to the position control means; An information recording / reproducing apparatus, comprising: changing means for changing a delay time of the control means. 2. The method according to claim 1, wherein the changing unit generates a control signal of a predetermined frequency for changing the delay time, and determines a magnitude of the error signal. 2. The information recording / reproducing apparatus according to claim 1, further comprising frequency control means for controlling a frequency of a control signal generated by the generation means. 3. The apparatus according to claim 2, wherein the change unit sets the frequency of the control signal to a constant value when the magnitude of the error signal falls within a range of a predetermined reference value. Information recording and playback device. 4. The information recording / reproducing apparatus according to claim 1, wherein the learning control means delays the error signal by using a digital memory, a shift register, or a linear phase digital filter. 5. The error signal includes a tracking error signal, a focus error signal, a spindle error signal,
The information recording / reproducing apparatus according to claim 1, wherein the information recording / reproducing apparatus is a thread error signal or a tilt error signal. 6. An irradiation step of irradiating a recording medium with light for recording or reproducing information, a position control step of controlling a relative position of the light with respect to the recording medium in response to an error signal, A detecting step of detecting reflected light from a medium; and a learning control in which after delaying the error signal by a predetermined time, the error signal is added to the undelayed error signal to obtain the error signal used in the position control step. And a changing step of changing a delay time in the learning control step.