JPH05334818A - Control loop and optical information recording and reproducing device - Google Patents

Abstract

PURPOSE:To perform a stable position control even to a control object which includes a mechanical resonance by inserting a resonance suppression means in a control loop. CONSTITUTION:A position control detection means 3 (G0) compares a position 9 of a control object and a target position 8 outputs a signal corresponding to the deviation. A gain block 4 gives a DC gain required by a control loop. A characteristic compensation means 5 (G1) is designed so as to obtain a sufficient phase margin for a gain zero cross frequency of the loop at the vicinity of 4kHz to 5kHz and compensates for a phase characteristic. G1 is defined to be the transfer function. A resonance suppression means 6 (G2) consists of a second order low pass filter which has the same resonance frequency of a control object 7 and makes the second order mechanical resonance as an apparent fourth order resonance to stablilize the control loop. G2 is defined to be the transfer function. The control object 7 (G3) controls the position of the object 7 so that it coincides with a target position. G3 is defined to be the transfer function.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of stability of a control loop used in an optical information recording / reproducing device, FA equipment and the like.

[0002]

2. Description of the Related Art A block diagram of a conventional control loop is shown in FIG.
Shown in. When the controlled object 7 has a large mechanical resonance,
The open loop characteristic shown in FIG. 11 is obtained, and the step response waveform becomes a waveform oscillating at the resonance frequency as shown in FIG. Therefore, a method of reducing the gain at the resonance frequency by using a low pass filter, a notch filter or the like has been adopted.

[0003]

However, in this conventional method, the phase margin is reduced due to the insertion of the low-pass filter, and the control loop may become unstable. In addition, the cutoff frequency of the notch filter is deviated, which may adversely affect the stability.

[0004]

The present invention is intended to solve such problems. (1) An error between the position of a controlled object and a target position is fed back to the controlled object to perform precise position control. In the control loop, a position error detecting unit that detects a deviation amount between the control target and the target position, a characteristic compensating unit that compensates a phase characteristic of an output of the position error detecting unit, and a frequency that is the same as the natural vibration of the control target. It is characterized by having a resonance suppressing means that resonates at.

(2) In an optical information recording / reproducing apparatus for condensing laser light on an optical disk to record / reproduce information, a light source for emitting the laser light, and the laser light emitted from the light source for the optical disk An objective lens for concentrating light on the top, spot position control means for controlling the position of the focus of the light generated by the objective lens on the optical disc, and the focus and target position of the light controlled by the spot position control means. A spot position error detecting means for detecting a deviation amount between the spot position error detecting means, a lead compensation for compensating a frequency characteristic of an output signal of the spot position error detecting means, and a driver for generating a current for driving a movable part of the spot position controlling means. A second-order low-pass filter having a peak at the same frequency as the mechanical resonance frequency generated in the spot position control means It is characterized by

[0006]

The position error detecting means detects the amount of deviation between the position of the controlled object and the target position, and the phase compensation is compensated for by the characteristic compensating means to stabilize the signal corresponding to the amount of deviation before being controlled. By feeding back, the controlled object can be accurately moved to the target position. When the controlled object has a large mechanical resonance, the control loop becomes very unstable, but a resonance suppressing means composed of a second-order low-pass filter having a peak at the same frequency as the resonance frequency is inserted. As a result, the second-order mechanical resonance can be apparently set to the fourth-order resonance, and the control loop can be stabilized. If the above configuration is performed by spot position control of the optical information recording / reproducing apparatus, it is possible to provide an optical information recording / reproducing apparatus with extremely stable operation.

[0007]

【Example】

(Embodiment 1) FIG. 1 shows open loop characteristics for position control of a controlled object having a mechanical resonance of 30 kHz. The curve 1 shows the gain curve, and the curve 2 shows the phase curve. In the Bode plots showing open loop characteristics used herein, all 1 curves show gain curves and 2 curves show phase curves. The alternate long and short dash line shows the gain of 0 dB, and the broken line shows the phase of -180 °. The meanings of the alternate long and short dash line and the broken line are also common to all Bode diagrams. Since the controlled object has a mechanical resonance of 30 kHz, the gain is 0 dB at 30 kHz where the phase is delayed by 180 ° or more due to the influence. In such a state, the control loop may become unstable and oscillate.

FIG. 2 shows a step response waveform in the control loop shown in FIG. FIG. 2 shows a time response when a step input of size 1 is performed. 30 when rising
Although a vibration waveform of kHz is generated, the waveform disappears in about 300 μsec and converges to the target value. When the control loop is unstable and oscillates, the step response waveform does not converge to the target value as shown in FIG. 12, and the sine wave of the oscillation frequency gradually increases and diverges. In addition, even if it does not diverge, it vibrates for a long time at a frequency where the gain is 0 dB. That is, FIG.
It shows that the control loop shown by is stable.

The reason why it is stable will be described. Focusing on the phase curve 2 in FIG. 1, it can be seen that the phase starts to be rapidly delayed in the vicinity of 30 kHz and is delayed by 360 ° in the high frequency region. That is, it is shown that the resonance of 30 kHz is the fourth-order resonance. If this is secondary resonance, it becomes unstable like the control loops shown in FIGS. 11 and 12. That is, it diverges like the step response waveform shown in FIG. 12 at the frequency of 30 kHz where the gain becomes 0 dB. However, the control loop shown in FIGS. 1 and 2 is not unstable because the resonance is the fourth resonance.

From the above viewpoint, FIG. 3 is a block diagram for stably controlling a controlled object having a secondary mechanical resonance.
Shown in. Reference numeral 3 is a position error detecting means, which compares the position 9 of the controlled object with the target position 8 and outputs a signal corresponding to the amount of deviation. (Hereinafter, the amount of deviation between the position of the controlled object and the target position is called the residual.) 4 is a gain block, which gives the DC gain required in the control loop. If the gain given to the loop in the gain block 4 is large, the residual is small. However, if it is made larger than necessary, it becomes an unstable element of the control loop. Therefore, it is necessary to set the target residual and set the gain to the extent that the target can be achieved. 5
Is a characteristic compensating means for compensating the phase characteristic so that a sufficient phase margin can be obtained at the gain 0 cross frequency of the control loop shown in FIG. Characteristic compensation means 5 used in this embodiment
In consideration of the fact that the gain 0 cross frequency is changed from 4 kHz to 5 kHz, was designed so that a sufficient phase margin can be secured in the vicinity of 4 kHz to 5 kHz. The transfer function of the characteristic compensation means 5 is shown in Equation 1.

[0011]

[Equation 1]

Reference numeral 7 is a control target. The control loop shown in FIG. 3 controls so that the position of the controlled object 7 coincides with the target position. The transfer function of the controlled object 7 is expressed by Equation 2.

[0013]

[Equation 2]

The transfer function expressed by the equation (2) has a resonance at 30 kHz, and if a control loop is formed only by the above-mentioned elements without taking any measures in the usual way, the result shown in FIG.
1 becomes the control loop shown in FIG. 12, and becomes very unstable.

Therefore, in the present invention, the resonance suppressing means 6 is inserted in the control loop. The resonance suppressing means 6 is composed of the transfer function shown in Equation 3.

[0016]

[Equation 3]

Equation 3 shows a second-order low-pass filter having a peak of 3 dB at 30 kHz. Resonance suppressing means 6
Is inserted, the mechanical resonance of the controlled object 7 has the same characteristic as the fourth-order resonance. The open loop characteristic of the control loop shown in FIG. 3 is shown in FIG. 4, and the step response waveform is shown in FIG. Comparing FIG. 4 and FIG. 11,
It can be seen that the phase is abruptly delayed in the vicinity of 30 kHz and is 180 ° in the high frequency range, but is 360 ° in the high frequency range. This indicates that the resonance at 30 kHz is the fourth resonance. Although the gain at the resonance frequency exceeds 0 dB, it can be regarded as a fourth-order resonance, and can be ignored in practical use according to the above description. When FIG. 5 and FIG. 12 are compared, FIG. 5 does not have a step response waveform indicating oscillation as in FIG. 12, but a waveform that converges to a target value is obtained. This result also shows that the control loop in FIG. 3 is stable. These results show that the resonance suppressing means 6 has a great effect on the stabilization of the control loop.

Generally, when there is mechanical resonance in the high frequency range and the gain margin is small, a low-pass filter having a cutoff frequency at a frequency lower than the resonance frequency is inserted in the control loop to obtain the gain at the resonance frequency. Is taken to increase the gain margin. However, if such a measure is taken, the phase will start to be delayed from the low frequency region, and this will have an adverse effect of reducing the phase margin of the control loop. According to the present invention, since the resonance suppressing means 6 is constituted by the second-order low-pass filter having a peak at the same frequency as the resonance point of the controlled object 7, the frequency at which the phase delay starts is moved to a higher frequency range. Therefore, the phase delay at the frequency at which the gain becomes zero crossing point could be set to a level with no problem in practical use. As a result, the phase margin of the entire control loop can be sufficiently secured.

The transfer functions of the resonance suppressing means 6 and the characteristic compensating means 5 are examples for carrying out the present invention. When performing on another control target, it is necessary to use an element represented by an optimum transfer function according to the characteristics of the control loop and the characteristics of the control target.

(Embodiment 2) When a control loop is configured, no oscillation occurs, but the gain margin is reduced due to the mechanical resonance of the control target, and the control target is at the frequency of the mechanical resonance due to slight disturbance. May vibrate. This is shown in FIGS. 13 and 14. 13 and 14
FIG. 11 is a characteristic diagram when the transfer function of the controlled object 7 in the block diagram shown in FIG.

[0021]

[Equation 4]

As can be seen from FIG. 13, the control loop has two
A resonance of 0 kHz is included. In this case, since the gain margin is about 7 dB, no oscillation occurs. But,
If some disturbance is applied to the control loop, the controlled object will vibrate. This is shown in FIG. It can be seen that when a step waveform of size 1 is added, the vibration occurs for about 300 μsec. Depending on the purpose of the control loop, it may be necessary to settle the controlled object within a time of about 200 μsec. For such things, this control loop cannot be used. As a remedy for this, the present invention can be implemented.

As the resonance suppressing means 6 shown in FIG. 3, an element whose transfer function is expressed by Equation 5 may be used.

[0024]

[Equation 5]

Resonance suppressing means 6 whose transfer function is expressed by the equation 5
By using, the Bode diagram shown in FIG. 6 is obtained. Gain margin is 5 dB at the resonance frequency of 20 kHz
Although it is reduced to some extent, the phase delay in the high frequency range is 360
You can see that it is becoming °. As a result, the step response waveform changes to the waveform shown in FIG. The vibration of 20 kHz remains at the time of rising, but the vibration waveform disappears at about 150 μsec. 6 and 7 show that the present invention has a great effect not only for preventing oscillation but also for suppressing vibration.

The mechanical resonance frequency is 2 as in this embodiment.
When the resonance suppression method is adopted in which the gain margin is increased with a low-pass filter when the frequency is lowered to 0 kHz, the cutoff frequency must be 10 kHz or less in order to obtain a sufficient effect. Then, it can be implemented only in the control loop in which the gain 0 cross frequency is about 1 kHz. However, the present invention can be implemented in a control loop having a gain 0 cross frequency of about 4 kHz to 5 kHz even if there is mechanical resonance near 20 kHz.

(Embodiment 3) A method of applying the present invention to an optical information recording / reproducing apparatus will be described. The block diagram is shown in FIG.
An optical information recording / reproducing apparatus generally has a focus of light condensed on an optical disc (hereinafter, the focus of light is referred to as a spot).
Tracking and focusing for position control of
Directional position control is performed. FIG. 8 shows a configuration diagram for performing position control in the tracking direction.

Reference numeral 10 denotes a light source, which emits a laser beam which serves as information recording / reproducing means of the optical information recording / reproducing apparatus. In the figure, the broken line indicates the path of the emitted light. 1
Reference numeral 1 denotes a spot position control means, which causes the laser light emitted from the light source 10 to enter the objective lens 17. The laser light that has passed through the objective lens 17 is an information recording guide groove on the optical disc 12 (hereinafter, the information recording guide groove is referred to as a track).
A focused spot is formed on the top. This spot must be located exactly on the track. The spot position control means 11 has a mirror inside, and the incident angle of the laser light to the objective lens 17 can be changed by changing the inclination of the mirror. Reference numeral 16 denotes a driver, which generates a drive current necessary to change the tilt of the mirror of the spot position control means 11.

The reflected light from the optical disk 12 passes through the objective lens 17 and the spot position control means 11 and enters the spot position error detection means 13. The spot position error detecting means 13 has a plurality of optical sensors, each of which independently outputs an electric signal according to the amount of light. The electric signal output from the optical sensor is calculated in the spot position error detection means 13 and an error signal indicating the amount of deviation between the spot position and the track position which is the target position is output. By feeding back the error signal output from the spot position error detection means 13 to the spot position control means 11 through the driver 16, accurate spot position control becomes possible. Reference numeral 14 is lead compensation, which compensates the phase characteristic of the error signal. The lead compensation 14 corresponds to the characteristic compensating means 3 in FIG. 3, but the characteristic compensating means includes not only lead compensation but also delay compensation used for increasing the low-frequency gain. In this embodiment, since the low frequency gain was sufficient, only the lead compensation 14 was used as the characteristic compensation means.
When the low frequency gain is insufficient, delay compensation can improve the characteristics. A spot position control loop is configured by the above elements.

The spot position control means 11 of the optical information recording / reproducing apparatus is extremely small and lightweight, and mechanical resonance is likely to occur. It is easy to make a structure that is large in shape and can be configured with blocks so that mechanical resonance does not occur, but the spot position control means of the optical information recording / reproducing apparatus, which is required to be small and lightweight, has a mechanical resonance. It is difficult to create a structure that does not cause Generally, when mechanical resonance is analyzed, it is often secondary resonance.

In the present invention, in order to reduce the adverse effects of such mechanical resonance, the secondary low-pass filter 1 is used.
5 was inserted in the spot position control loop. The secondary low-pass filter 15 has a peak at the same frequency as the mechanical resonance frequency of the spot position control means 11. As a result, the mechanical resonance of the spot position control means 11 apparently lags the phase in the high frequency region by 360 ° similarly to the fourth-order resonance, showing a great effect as an oscillation preventing measure.

When the optical information recording / reproducing apparatus has mechanical resonance and the resonance frequency is low, a method of reducing the gain in a narrow frequency band near the resonance frequency by using a notch filter has been adopted. However, it was very difficult to match the cutoff frequency of the notch filter with the mechanical resonance frequency. Further, in the case of the notch filter, even a slight deviation between the mechanical resonance frequency and the cutoff frequency has an adverse effect. FIG. 9 shows a step response waveform when the peak frequency of the second-order low-pass filter 15 inserted to prevent oscillation due to mechanical resonance of 30 kHz becomes 25 kHz for some reason. From FIG. 9, it can be seen that even if the peak frequency of the second-order low-pass filter 15 deviates by 10% or more, there is a great effect in preventing oscillation.

The notch filter serves to reduce the gain to prevent oscillation, and the second-order low-pass filter 15 of the present invention delays the phase to increase the apparent phase margin, thereby improving stability. Is improving. In the case of a notch filter, if the cutoff frequency shifts, the gain at the resonance frequency does not become small, so that not only the effect is not exerted, but it is rather adversely affected. However, in the second-order low-pass filter 15 of the present invention, the phase delay at the resonance frequency is a sufficient delay amount for preventing oscillation even if the phases are slightly shifted, so the apparent phase margin becomes large, Improves stability.

In the conventional optical information recording / reproducing apparatus in which oscillation is prevented by a notch filter or the like, the frequency of mechanical resonance may change and become unstable due to environmental changes such as temperature changes. However, the present invention was very effective as a quality stabilizing measure for such an optical information recording / reproducing apparatus.

The spot position control in the tracking direction is
Not only the spot position control means 11 using the mirror shown in this embodiment, but also the spot position control using the method of moving the objective lens in the tracking direction is performed. This embodiment can be applied to that case as well. When the position control loop in the focusing direction and the position control in the tracking direction are performed by a combination of the coarse position control and the fine position control, both position control loops can be implemented.

[0036]

According to the present invention, in order to control the controlled object including mechanical resonance, the resonance suppressing means is inserted into the control loop, so that the control loop is very stable. Moreover, since it is possible to cope with changes in mechanical characteristics due to changes in conditions such as temperature changes, a wide operating range can be set and a high quality control loop can be constructed.

By applying it to the optical information recording / reproducing apparatus, the data quality of recording / reproducing was significantly improved. In addition, the design and manufacture of parts for optical information recording / reproducing devices, where attention has been focused on preventing resonance, can now be focused on durability and cost reduction, increasing the durability of parts and greatly reducing costs. Was realized. Since it was possible to stabilize it against changes in the environment, it was possible to relax the environmental conditions under which the device was used.

[Brief description of drawings]

FIG. 1 is a Bode diagram of a control loop according to the configuration of the present invention.

FIG. 2 is a step response wave diagram of a control loop according to the configuration of the present invention.

FIG. 3 is a block diagram of a control loop according to the configuration of the present invention.

FIG. 4 is a Bode diagram when a control loop according to the present invention is implemented to prevent oscillation.

FIG. 5 is a step response waveform diagram when a control loop according to the configuration of the present invention is implemented to prevent oscillation.

FIG. 6 is a Bode diagram when a control loop according to the configuration of the present invention is implemented for suppressing vibration.

FIG. 7 is a step response waveform diagram when a control loop according to the configuration of the present invention is implemented for vibration suppression.

FIG. 8 is a block diagram of an optical information recording / reproducing apparatus according to the configuration of the present invention.

FIG. 9 is a step response waveform diagram when the peak frequency of the second-order low-pass filter of the present invention is shifted.

FIG. 10 is a block diagram of a conventional control loop.

FIG. 11 is a Bode diagram in the case where there is a resonance point where the gain exceeds 0 dB in the conventional control loop.

FIG. 12 is a step response waveform diagram in the case where there is a resonance point where the gain exceeds 0 dB in the conventional control loop.

FIG. 13 is a Bode diagram of a conventional control loop having a small gain margin due to mechanical resonance.

FIG. 14 is a step response waveform diagram of a conventional control loop having a small gain margin due to mechanical resonance.

[Explanation of symbols]

 1 gain curve 2 phase curve 3 position error detection means 4 gain block 5 characteristic compensation means 6 resonance suppression means 7 control target 10 light source 11 spot position control means 12 optical disk 13 spot position error detection means 14 advance compensation 15 second low pass type Filter 16 Driver 17 Objective lens

Claims (2)

[Claims] 1. A position error detecting means for detecting a deviation amount between the control target and the target position in a control loop for feeding back an error between the position of the control target and the target position to the control target for precise position control. And a characteristic compensation means for compensating the phase characteristic of the output of the position error detection means, and a resonance suppression means for resonating at the same frequency as the natural vibration of the controlled object. 2. An optical information recording / reproducing apparatus for condensing laser light on an optical disk to record / reproduce information, wherein a light source for emitting the laser light and the laser light emitted from the light source are on the optical disk. An objective lens for converging light, a spot position control means for controlling the position of the focal point of the light generated by the objective lens on the optical disc, and a focal point and a target position of the light controlled by the spot position controlling means. A spot position error detecting means for detecting a shift amount of the spot position, a lead compensation for compensating a frequency characteristic of an output signal of the spot position error detecting means, and a driver for generating a current for driving a movable part of the spot position controlling means. A second-order low-pass filter having a peak at the same frequency as the mechanical resonance frequency generated in the spot position control means; A characteristic optical information recording / reproducing device.