JPS60191303A - Servo circuit - Google Patents

Abstract

PURPOSE:To reduce the effect of disturbance high in magnitude of signal amplitude and to minimize a following error regardless of the level of the disturbance amplitude, by giving nonlinear control to a loop gain in response to the output given from a means which detects an abnormal disturbance. CONSTITUTION:An output signal given from a control subject is detected by a detector 10 and applied to an adder 12 after amplification 11. The output signal received by the adder 12 undergoes addition/subtraction with the prescribed target value. Thus an error signal is detected and then divided into two parts. One of these two divided error signals is supplied to an amplification degree controllable amplifier 13; while the other error signal is supplied to a filter 14 which transmits an abnormal disturbance. The amplitude of the abnormal disturbance signal passed through the filter 14 is detected by an amplitude detector 15 and supplied to a nonlinear amplifier 16. The amplifier 16 gives the linear amplitude to the disturbance signal when it has a level higher than the threshold value. Then the voltage of a fixed level is delivered when the disturbance signal has a level less than the threshold value. Both the amplifier 13 and a central frequency controllable phase compensator 17 are controlled by the output of the amplifier 16. Then the loop gain is controlled according to the output of the amplifier 16. Thus it is possible to reduce the effect of the disturbance which is high in signal amplitude.

Description

[Detailed description of the invention]

(Technical Field) The present invention relates to a servo circuit, and particularly to a servo circuit that can accurately follow a disturbance with a small signal amplitude or a disturbance with a large signal amplitude υ. (Prior Art) Actuators and the like used in optical disc playback devices are designed to be able to accurately follow and drive the optical beam information track using a servo mechanism even if a disturbance occurs. The types of disturbances that occur during operation include disturbances that normally occur with small signal amplitudes due to disk eccentricity and surface play, and disturbances that occur normally when the signal amplitude is small due to disk eccentricity and surface play, and disturbances that occur when the JJ is running, such as when mounted on a car.
[] There are abnormal disturbances with large signal amplitudes due to speed fluctuations and finger movements of the vehicle body. FIG. 1 is a block diagram showing the configuration of a conventional servo circuit. As for the deviation of the actuator l, the amount of deviation due to ordinary disturbance and the deviation due to abnormal disturbance are detected by a detector 2, and are inputted to an adder/subtractor 4 via an amplifier 3. A preset target value is input manually to the adder/subtractor 4 and an error signal is detected. After this error signal is phase compensated by the phase compensator 5, it is input to the actuator l via the drive amplifier 62. And the operation of actuator l? The signal representing i: is fed back to the detector 2 through the feedback loop, and is configured so that accurate tracking operation can be performed even if a disturbance occurs. With this configuration, normal disturbances with small signal amplitudes can be dealt with as is, while abnormal disturbances with large signal amplitudes can be dealt with by selecting a sufficiently large gain of the open-loop transfer function in advance. will be dealt with. However, if the gain of the open-loop transfer function is set large to deal with abnormal disturbances, noise in the circuit and detection system will also be amplified.
The disadvantage 1) is that the ratio deteriorates and the tracking error increases. On the other hand, if the loop gain is set to be optimal for a small signal amplitude (A curvature σ), the loop gain will be insufficient for abnormal disturbances with large amplitudes, resulting in a tracking error. This results in the inconvenience of not being able to keep it small. In other words, in a conventional servo circuit

[However, it has the drawback that it cannot satisfactorily deal with both small-amplitude normal disturbances and large-amplitude abnormal disturbances. (Object of the invention) The object of the invention is to eliminate the above-mentioned drawbacks, to further reduce the influence of abnormal disturbances with large signal amplitudes, and to operate well even with normal disturbances with small signal amplitudes. Our goal is to provide a servo circuit that can. (Summary of the invention) f: The servo circuit according to the invention is characterized in that it comprises means for detecting an abnormal disturbance, and means for nonlinearly controlling a loop gain according to the output from the abnormal disturbance detection means. It is. The inventive servo circuit is an amplification controllable type that processes an error signal, which is the difference between the actual value representing the operation of the controlled object, and a target value, and outputs a drive signal for the controlled object. a servo loop having an amplifier, a center frequency controllable phase compensator, and a drive amplifier; a filter for detecting a spectrum component due to an abnormal disturbance in the error signal; and an amplitude detector for detecting the amplitude of an output signal of the filter. , this amplitude detector σ) a nonlinear amplifier that amplifies the output signal, and the amplification degree of the amplification controllable amplifier in the servo loop and the center frequency of the center frequency controllable phase compensator according to the output signal of the nonlinear amplifier. (Example) FIG. 2 is a block diagram showing the configuration of an example of a servo circuit according to the invention. (4) The output signal from the detector 10 is input to the adder/subtractor 12 via the amplifier 11. A preset target value is input to this 7JO subtracter 12, and an error signal that is the difference between the target value and the actual value is detected. The detected error signal is divided into two routes, one of which is input to the amplification controllable amplifier 3, and Ikekata manually inputs it to the abnormal disturbance passing filter 14. This abnormal disturbance pass filter 14 detects abnormal disturbances that occur during operation, and analyzes the frequency of abnormal disturbance signals that occur under a pre-assumed usage environment, and passes the spectrum components as abnormal disturbances. Characteristics that make it? have. The amplitude detector 15 detects the amplitude of the abnormal disturbance signal that has passed through the abnormal disturbance pass filter J4.As the amplitude detector 5, it is preferable to use an effective value-to-DC voltage converter, an absolute circuit, or the like. Amplitude detector] The signal amplitude of the abnormal disturbance detected by the amplitude detector 5 is input to a nonlinear amplifier 16. As shown in FIG. 8, this nonlinear amplifier 16 has nonlinear input/output characteristics, and the input amplitude signal has the same predetermined value V. If it exceeds V, it is amplified or attenuated by a predetermined amplification degree or attenuation degree, and the darkness value V. In the following cases, a constant voltage is always output. In exceptional cases, the abnormal disturbance signal has a dark value of V. If it is larger, it is amplified linearly and the darkness value is V. If it is smaller, the amplification degree of the amplification controllable amplifier 18 is set to 1, and the amplification degree is changed depending on the magnitude of the signal amplitude of the abnormal disturbance. The output of this non-linear amplifier 16 is then inputted to an amplifier 13 of an 18 degree controllable type amplifier 13 into which the error signal detected by the adder/subtractor 3 is input, and the center frequency of the amplifier 13 connected to this amplifier 13 is It is input to the controllable phase compensator 17. If intercepted in this way, the error signal input to the amplification controllable amplifier 18 will be nonlinearly amplified according to the output of the nonlinear amplifier 16, and the loop gain will be controlled according to the magnitude of the signal amplitude of the abnormal disturbance. will be done. In other words, when the amplitude of the abnormal disturbance is the same as or less than the normal disturbance, a constant loop gain is set, and when the signal amplitude of the abnormal disturbance is larger than the normal disturbance, the loop gain is set according to the signal amplitude of the abnormal disturbance. Since the gain is set at a high processing speed, accurate tracking operation can be performed even if the error □ signal increases dramatically. It is preferable to use an analog multiplier or an automatic gain control amplifier as the amplification controllable amplifier 18. The error signal amplified by the amplification controllable amplifier 18 is also supplied to the center frequency controllable phase compensator 17 to control the center frequency. This center frequency controllable phase compensator 17 has the disadvantage that if the center frequency of the phase compensation circuit is fixed when controlling the loop gain, the phase margin of the open-loop transfer function will be lost and an oscillation phenomenon will occur. The center frequency of phase compensation is controlled according to the underlying loop gain. The output of the center frequency controllable phase compensator 17 is transmitted to the actuator 9 via the drive amplifier 18 to control the following operation of the actuator 19. Figure @4 is an equivalent circuit diagram of the center frequency controllable phase compensator 17. The input voltage signal supplied to the input terminal 20 is supplied to the first and second adders 21 and (7) 22 and the output terminal 28. 1st JJO Calculator 2
A resistor 25 and a capacitor 26 are connected in series between the connection @24 that connects the adder 22 and the reference potential point (earth), and the connection point 27 between the resistor 25 and the capacitor 26 is connected to the amplification degree. It is fed back to the first adder 2] via the first amplifier 28 of 5 and is fed forward to the second adder 22 via the second amplifier 29 with the amplification factor α. Roughly, connection point 27'? The i-connections @80 and 31 connect directly to the first and second adders 21 and 22. Now, input signal Th Ein(81, output signal E.ut(
S), the output signal of the first adder 21 is E□(S), and the signal at the connection point 27 is E, (8), then the following equation holds true. K, (Sl=EIJ1(Sl+E, (8)・To(8)
・Tl-1) -A2) Eout(S)=E, (sl+
E. (8) Each represents the transfer function of the branch voltage signal in the 26 series circuits. From equation (3), the transfer function T(S) between the input and output terminals is given by the following equation: Eout(S) ) Frequency characteristic 'f given by equation (4) is shown in Fig. 5. Fig. 5 A shows the +1 amplitude frequency characteristic 2, and Fig. 5 B shows the phase 'frequency characteristic. In the figure, the resonance frequency ω.G:j represents OB.As can be understood from FIGS. 5A and 5B, if at least one of the resistance value R of the resistor 25 or the capacitance C of the capacitor 26 is changed, the phase compensation characteristic can be changed on the frequency axis. By using the center frequency controllable phase compensator 17 as a phase compensation circuit, it is possible to directly control the center frequency value and the phase value at the center frequency. By changing the center frequency of the phase compensation circuit accordingly, the servo system can be kept stable even if the loop gain changes drastically, and problems caused by oscillation etc. can be avoided. - Figure 6 shows center frequency control. 2 is a block diagram showing the configuration of an embodiment of a phase compensator. In this example, a resistor 25
Instead, a field effect transistor (FET) is used as a voltage controlled resistance element. In other words, the NET becomes GS −■D as shown in Figure 7.
Since it has the S characteristic, the FET can be used as a voltage-controlled resistance element. The output of the nonlinear amplifier 16 is input to the adder 32, and the output of the adder 32 is input to the FET 8.
Input to gate 8. The drain of FET 88 is connected to input terminal 20 and output terminal 28, and the source is connected via capacitor 26 to a reference potential. Then, the connection point between the source and the capacitor 26 is fed back to the adder 82 via the connection line 84. In addition, in order to correct the linearity of FET 88 as a voltage-controlled resistance element,
It is sufficient to connect a nonlinear amplifier having characteristics opposite to those of 88. In the configuration example shown in FIG. 4, the phase compensator is not provided with a delayed phase compensation circuit, but as shown in FIG. 8, delayed phase compensation circuits may be connected in cascade to ensure gain in the low frequency region. That is, in FIG. 8 (11) A-0, the horizontal axis represents the frequency of the signal amplitude, and the vertical axis represents the gain. Figure 8A shows the frequency characteristics of the gain of the actuator alone, and Figure 8B shows the frequency characteristics of the gain when a leading phase compensation circuit is connected.
Figure C shows the frequency characteristics of the gain when a delayed phase compensation circuit is connected. That is, if a leading phase compensation circuit is provided, gain in a high frequency region can be secured, and if a delayed phase compensation circuit is provided, a gain in a low frequency region can be secured. Therefore, if a lead phase compensation circuit or a lag phase compensation circuit is provided depending on the frequency and wave frequency characteristics of the abnormal disturbance/disturbance,
A wide dynamic range can be secured. FIG. 9 is a block diagram showing the configuration of a modified example of the servo circuit according to the present invention. Components that are the same as those shown in FIG. 2 will be described with the same reference numerals. In this example, a linear amplifier, a switch, and an analog comparator are used instead of a nonlinear amplifier to control the loop gain according to the signal amplitude of the abnormal disturbance. With this configuration, when the signal amplitude of the abnormal disturbance is larger than a predetermined threshold, the switch 41 is switched from L to H by the analog comparator 42, and the amplitude of the abnormal disturbance is linearly amplified by the linear amplifier 40, thereby controlling the amplification degree. The signal is input to the variable layer width converter 18 and set to a loop gain according to the signal amplitude of the abnormal disturbance, and the center frequency controllable phase compensator 17 is also switched from a fixed characteristic to a variable characteristic. Further, if the signal amplitude of the abnormal disturbance is smaller than a predetermined threshold, the analog comparator 42 &
This causes the switch 41 to switch from H to L, and the error signal is input to the center frequency controllable phase compensator 17 whose characteristics have been switched to a fixed characteristic without being amplified. FIG. 1θ is a block diagram showing the configuration of another modified example of the servo circuit according to the present invention. In this example, a configuration is adopted in which nonlinear amplification is performed by digital control. An A/D converter 60 is connected to the amplitude detector 16 , and the signal amplitude of the abnormal disturbance is digitally converted by the A/D converter 50 and input to a digital comparator 61 . When the signal amplitude of the abnormal disturbance is smaller than a predetermined threshold, the switch 62 is switched from H to L to directly input the error signal to the center frequency control type phase compensator 17, and when it is larger than the predetermined threshold, the switch 62 is switched from H to L. Switch from L to H and convert the error signal to D/A
The signal is input to the center frequency controllable phase compensator 17 via the converter 5B, the linear amplifier 54, and the switch 52 to ensure a loop gain corresponding to the signal amplitude of the abnormal disturbance. In the above-mentioned embodiment, an abnormal disturbance passing filter is used as an abnormal disturbance detection means, and the abnormal disturbance is detected based on the vibration spectrum of the abnormal disturbance. You can also do that. In this case, the error signal does not pass through the abnormal disturbance pass filter.
It is sufficient to input it directly to the amplitude detector. Furthermore, if the loop gain is set to a small value close to zero when the signal amplitude of the disturbance is small, there is a risk that a tracking error will occur and servo misalignment will occur if the error signal suddenly increases. Therefore, the output characteristics of the nonlinear amplifier are set so that a predetermined loop gain can be secured even when the signal amplitude of the disturbance is small, and when the signal amplitude of the disturbance is larger than a predetermined threshold, the output characteristics of the nonlinear amplifier are set so that the loop gain is set according to the signal amplitude of the abnormal disturbance. It should be set so that the gain can be secured. Therefore, the output characteristics of the nonlinear amplifier can be changed stepwise according to the signal amplitude of the abnormal disturbance. (Effects of the Invention) As explained above, the servo circuit according to the present invention is set to a loop gain that minimizes the error signal for normal disturbances with small amplitude, and is set to a loop gain that minimizes the error signal for normal disturbances with large amplitude. This is possible because the loop gain can be controlled according to the magnitude of the abnormal disturbance amplitude, and the frequency characteristics of the phase compensation circuit are automatically set so that the round transfer function is always stable according to the magnitude of the disturbance amplitude. This makes it possible to always minimize the tracking scissor difference regardless of the magnitude of the disturbance amplitude.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the configuration of a conventional servo circuit, (15) Figure 2 is a diagram showing the configuration of an example of the servo circuit according to the present invention, Figure 8 is a graph showing the amplification characteristics of a nonlinear amplifier, Figure 4 is a block diagram showing an equivalent circuit of a center frequency controllable phase compensator, Figure 6 A and B are graphs showing amplitude frequency characteristics and phase frequency characteristics of a center frequency controllable phase compensator. A block diagram showing the configuration of an example of a center frequency controllable phase compensator, Fig. 7 is a graph showing the characteristics of FIT, and Fig. 8 A-0 shows a phase compensator with a compensation circuit and a delayed phase compensation circuit. FIG. 9 is a block diagram showing the configuration of a modified example of the servo circuit according to the present invention, and FIG. 10 is a block diagram showing the configuration of another modified example of the servo circuit according to the present invention. 10...Detector 11...Amplifiers 12, 21
, 22182...Adder (16) 18...Amplification controllable amplifier 14...Abnormal disturbance passing filter 16...Amplitude detector 16...Nonlinear amplifier 17.
... Center frequency controllable phase compensator 18... Drive amplifier 19... Actuator 20... Input terminal 28...
Output terminals g4, 80, 81, 84... Connection line 25... Resistor 26... Capacitor 27... Connection point 28, l... Amplifier 88°.
・Field effect transistor 40 I 54...Linear amplifier 41, 51!・・・
- Switch 42 - Analog/4G comparator 50... A/D converter 61... Digital comparator 58... D/A converter. Figure 6 2θ 3 76D 23 Medium 14s -+ G 10, 26 Figure 8 A and B) A (dB)

Claims (1)

[Scope of Claims] 1. A servo circuit comprising: means for detecting abnormal disturbance; and means for nonlinearly controlling a loop gain in accordance with an output from the abnormal disturbance detecting means. 2 A controllable amplification type amplifier that processes a control object and an error signal that is the difference between an actual value representing the operation of this control object and a target value and outputs a drive signal for the control object, and a center frequency control pJ function type amplifier. a servo loop having a phase compensator and a drive amplifier; a filter for detecting a spectrum component due to an abnormal disturbance in a verbal error signal; an amplitude detector for detecting the amplitude of an output signal of the filter; a nonlinear amplifier for amplifying an output signal of the servo loop; A servo circuit characterized by comprising: