JPH0118281B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an electrohydraulic servo system that operates stably without being affected by the characteristics of a load to be controlled. Electro-hydraulic servo systems are used in the drive parts of general industrial machinery, including vibration testing machines, various testing machines such as material testing machines, various simulators, rolling mills, and robots. [Prior Art] The following types of conventional electro-hydraulic servo systems are known. In other words, an adder calculates the deviation between the target value for the amount of load to be controlled (for example, the displacement of a shaking table) and the amount of feedback from the actual controlled object, and this deviation is sent to the servo amplifier as a control deviation, and the servo Amplify the current with an amplifier,
Drive the servo valve. In the servo valve, the direction and flow rate of pressure oil supplied to the hydraulic cylinder are controlled by this input current, and the actuator (for example, a vibration table) is moved in a direction that reduces the control deviation. Thus, if the response of the servo system is sufficiently fast and this deviation can be kept small at all times, the actuator will be moved as instructed. This type of technology is disclosed on pages 135 to 145 of Proceedings of the Japan Society of Mechanical Engineers, Vol. 42, No. 353 (January 1976). [Problem to be solved by the invention] However, in reality, the transmission characteristics of the electro-hydraulic servo system are affected by changes or fluctuations in the load, making it difficult to stably control a machine equipped with the electro-hydraulic servo system. The reality is that it is not possible. That is,
If the characteristics of the load change, e.g. the mass of the load changes.
If the mass of the load is changed significantly while the transmission characteristics of the electro-hydraulic servo system are set to be optimal at Mo, the displacement of the load will become extremely oscillatory. As a result, the electrohydraulic servo system is unable to faithfully follow the control amount to the target value. The present invention has been made based on the above-mentioned problems, and an object of the present invention is to provide a load-unresponsive electro-hydraulic servo system that is unaffected by changes or fluctuations in the load to be controlled. [Means for solving the problem] The first configuration for achieving the above object is an electro-hydraulic servo system with a closed loop configuration that controls a servo valve so that a feedback signal from a controlled object or an actuator matches a target value. In,
A load pressure detector outputs a load pressure signal acting on the actuator, and a calculation process is performed to indicate the inverse function characteristic of the load pressure flow rate characteristic of the servo valve based on the load pressure signal with respect to the deviation between the target value and the feedback signal. A static compensation element is provided, the output of the static compensation element is input to a servo amplifier, and the output of the servo amplifier drives a servo valve. In addition, a second configuration for achieving the above object is an electro-hydraulic servo system with a closed loop configuration that controls a servo valve so that a feedback signal from a controlled object or an actuator matches a target value. A load pressure detector that outputs a pressure signal, a compressibility compensation element that outputs a value obtained by adding a signal proportional to the differential value of the load pressure signal to the deviation between the target value and the feedback signal, and an output of this compressibility compensation element. In addition, a static compensation element is provided which performs arithmetic processing that indicates the inverse function characteristic of the load pressure flow rate characteristic of the servo valve based on the load pressure signal, and the output of this static compensation element is input to the servo amplifier. The output of the servo amplifier drives the servo valve. [Operation] In the first configuration in the section of means for solving the above problems, the load pressure acting on the actuator is detected by the load pressure detector, and this detection signal is used to adjust the servo control to the input deviation. The static compensation element performs arithmetic processing that indicates the inverse function characteristic of the load pressure flow rate characteristic of the valve. That is, the flow rate characteristics vary greatly depending on the load pressure of the servo valve. Therefore, in the static compensation element, while looking at the load state, a function characteristic for canceling the influence on the flow rate due to load fluctuations, that is, a calculation process that indicates the inverse function characteristic of the load pressure flow characteristic, is input to the deviation. going against This makes it possible to obtain extremely stable control operations that are not dependent on large fluctuations or changes in load. In addition, in the second configuration in the section of means for solving the above problems, in addition to the load pressure detector and static compensation element similar to the first configuration, a load pressure A compressible compensation element is provided that outputs a value obtained by subtracting a signal proportional to the differential value of the signal. As a result, as in the case of the first configuration, the influence on the flow rate due to fluctuations or changes in the load pressure of the servo valve can be reduced, and stable control operations can be performed. Furthermore, considering the compressibility of the oil in the oil chamber of the actuator, the amount of compression is influenced by the temporal change (differential value) of fluctuations in the load pressure, but in the second configuration, this influence is suppressed by the compressibility compensation element. As a result, the characteristics of the system are made independent of the load. That is, in the second configuration, by determining the differential value of the load pressure and adding a signal proportional to this differential value to the deviation,
The effects of oil compression are removed. For this reason,
It is possible to realize a load-unresponsive electro-hydraulic servo system that is not affected by load fluctuations or changes. [Examples] Examples of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of an embodiment of the electro-hydraulic servo system of the present invention. In the figure, 1 is a load to be controlled, 2 is a hydraulic actuator that drives the load 1, and 3 is a pressure applied to the actuator 2. a servo valve that controls the flow rate and direction of oil; 4 is a hydraulic pressure source; 5 is a signal generator that generates a target value v of displacement of load 1;
6 is a feedback circuit, and this feedback circuit 6 is composed of a displacement meter 6a for detecting displacement of the load 1 and a displacement detection circuit 6b. 7 is an adder for calculating the deviation e between the target value v from the signal generator 5 and the displacement signal from the feedback circuit 6; and 8 is a servo amplifier for amplifying the power of the input signal to the servo valve 3. In the preceding stage of the servo amplifier 8, a compressible compensation element 9, a static compensation element 10, and a dynamic compensation element 11 are provided in order from the adder 7 side. The compressibility compensation element 9 is supplied with a value obtained by differentiating a signal of the load pressure Pm acting on the actuator 3 with a differentiator 13 together with a deviation e. The static compensation element 10 is supplied with the load pressure Pm and the output e' of the compressible compensation element 9. This load pressure Pm is detected by the load pressure detector 12. Next, the operation of the electro-hydraulic servo system which is an embodiment of the present invention described above will be explained. First, before explaining the specific operation, the characteristics and operating principle of each component of the electrohydraulic servo system will be explained. The characteristics of the servo amplifier 8 are generally expressed by the characteristics of a first-order delay element, but since its corner frequency can be designed to be sufficiently higher than the operating frequency of the electro-hydraulic servo system, it is expressed by the characteristics of a proportional element as follows. . In other words, the deviation voltage e is as follows: e=K _r・v−K _y・y (1) where v: Target value y: Displacement of load 1 K _r : Input conversion coefficient K _y : Displacement feedback gain, Further, the input current i of the servo valve 3 is given by i=K·e (2) where K=the gain of the servo amplifier 8. In many cases, the pressure flow characteristics and frequency characteristics of the servo valve 3 are approximately expressed by the following equation. In other words, if the output flow rate of the servo valve 3 is qm, the output flow rate of the servo valve 3 at no load is qmo, the load pressure is Pm, and the hydraulic oil supply pressure is Ps, then the servo valve 3
The output flow rate qm is The frequency characteristic at no load is given by Qmo(s)= _Gs (s)・I(s)...(5). In this equation (5), Qmo(s) and I
(s) is the Laplace transform of the output flow rate qmo of the servo valve 3 and the input current i of the servo valve 3 at no load, respectively. Furthermore, G _s (s) in equation (5) is a transfer function that represents the delay of the servo valve 3, and in most cases, G _s (s) = ki・ωn ² /s ² +2ζωns+ωn ² ...(6) However, ki: Flow rate gain ωn of the servo valve 3: Natural frequency ζ of the servo valve 3: Approximate by the characteristic of a second-order lag element, which is the damping ratio of the servo valve 3. Considering the compressibility of the oil in the actuator 2 and the piping, and the expansion of the actuator 2 and the piping in response to changes in internal pressure, the equation of continuity regarding the oil flowing into the actuator 2 is: qm=Ap・dy/dt+C・dPm/dt...(7 ) However, Ap: Cross-sectional area of the piston of actuator 2 C: Constant representing the rigidity of the drive system y: Displacement of load 1 t: Expressed as time. The equation of motion for load 1 is the frictional force acting on load 1 and the piston sliding surface of actuator 2.
If Ff is the disturbance acting from outside of load 1, and Fn is the mass of load 1, then m・d ² y/dt ² +Ff=Ap・Pm+Fn ……(8). As described above, when the characteristics of the main components of the electrohydraulic servo system are expressed by equations (1) to (8), the operating principles of the compressible compensation element 9 and the static compensation element 10 are static Letting the deviation voltage of the compensation element 10 be e _c , the following equation is obtained. Alternatively, between the current i and the deviation voltage e, the formula
Since the relationship (2) exists, it is also possible to correct the output current i as shown in the following equation. The second term in parentheses in equation (9) or equation (10) relates to compressive compensation, and the other elements relate to static compensation. Next, when the transfer function of the drive compensation element 11 of the servo valve 3 is expressed as G _c (s), it becomes G _c (s) = ki・G _s ^-1 (s) ...(11), which is expressed by equation (9). The correction of the transfer function expressed by Expression (11) is added to the signal e _c expressed by Expression (10) or the signal i _C expressed by Expression (10). That is, when the transmission delay of the servo valve 3 is expressed by equation (5), the transfer function of the dynamic compensation element 11 of the servo valve 3 is expressed by the following equation from equation (11). G _c (s)=S ² +2・ζ・ωn・S+ωn ² /ωn ² ...(12) By the way, since equation (12) includes a differential operation, it is impossible to ideally realize this with the current technology. It is quite difficult. Therefore, in practice, G _c (s) = α ²・s ² +2・ζ・ωn・s
+ωn ² /s ² +2・ζ・α・ωn・s+(α・ωn) ² ……
(13) It is effective to use a transfer function that can be realized within the intended frequency range of use. The numerator of this equation (13) is a secondary advance element for canceling the delay of the servo valve 3. It is necessary to select the value of α large, for example, 3 or more, to the extent that the influence of the second-order lag element in the denominator of equation (13) can be ignored. Next, the operation of the electro-hydraulic servo system in the embodiment of the present invention will be explained based on the operation principle of each compensation element described above. In the embodiment of the device of the present invention shown in FIG. 1, a case will be described in which compensation is performed at the voltage stage as shown in equation (9), taking into consideration practical feasibility. The adder 7 calculates the deviation signal e using the target value v from the signal generator 5 and the displacement signal of the load 1 from the feedback circuit 6, and supplies the calculation result e to the compressible compensation element 9. Compressibility compensation element 9
As shown in FIG. 2, the coefficient multiplier 9a multiplies the time differential value (dPm/dt) signal of the load pressure Pm from the differentiator 13 by the coefficient (C/K・ki), and The output signal from 9a (C/K・ki・dPm/dt) and the deviation signal e from adder 7 are added by adder 9b, and this added signal (e+C/K・Ki・dPm/dt) is obtained. is applied to the static compensation element 10 as an output signal e'. This output signal e' corresponds to the term in parentheses on the right side of the above-mentioned equation (9), and has been corrected to a signal that compensates for the compressibility of the hydraulic oil with respect to the deviation signal e. The static compensation element 10, as shown in FIG.
Based on the load pressure signal Pm from 2

[Formula] Performs the calculation, and this calculation signal

[Equation] and the output signal e' from the adder 9b of the compressibility compensation element 9 are divided by the divider 10b, and this divided signal [signal e _c corresponding to equation (10)] is activated. The target compensation element 11 is added to the target compensation element 11. Note that the square root function unit 10a described above operates when the value of the output signal e _c is positive and zero.

Perform the calculation in [Formula], and when the value of the output signal e _c is negative,

〔Effect of the invention〕

As detailed above, according to the present invention, the transmission characteristics of the electrohydraulic servo valve are not affected by changes or fluctuations in the load, and the followability of the control amount to the target value can be faithfully realized. It is something that can be done.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of an embodiment of the electro-hydraulic servo valve of the present invention, FIG. 2 is a diagram showing the detailed configuration of the main parts of the electro-hydraulic servo valve shown in FIG. 1, and FIG.
The figure is a line diagram showing the response results of the influence of load fluctuations in a conventional electro-hydraulic servo system, Figure 4 is a line diagram showing the response results of the influence of load fluctuations in the device of the present invention, and Figure 5 is a diagram showing the response results of the influence of load fluctuations in the conventional electro-hydraulic servo system. FIG. 6 is a diagram showing a response result to the influence of disturbance in the servo system. FIG. 6 is a diagram showing a response result to the influence of disturbance in the apparatus of the present invention. DESCRIPTION OF SYMBOLS 1... Load, 2... Actuator, 3... Servo valve, 5... Signal generator, 6... Feedback circuit, 8... Servo amplifier, 9... Compressible compensation element, 10... Static compensation element , 11...dynamic compensation element, 12...load pressure detector, 13...differentiator.

Claims (1)

[Claims] 1. An adder that calculates the deviation between an input signal that is a target value and a feedback signal from a controlled object or an actuator that drives the controlled object, and a servo amplifier that inputs the deviation and amplifies the signal. an electro-hydraulic servo system comprising: a servo valve that controls the flow rate and direction of pressure oil according to the output of the servo amplifier; and an actuator that drives a load with the pressure oil supplied from the servo valve. a load pressure detector that outputs a load pressure signal acting on the actuator; and a static detector that performs arithmetic processing on the deviation to indicate an inverse function characteristic of the load pressure flow rate characteristic of the servo valve based on the load pressure signal. An electro-hydraulic servo system, comprising: a compensation element, and an output of the static compensation element is input to the servo amplifier. 2. An adder that calculates the deviation between an input signal that is a target value and a feedback signal from a controlled object or an actuator that drives the controlled object, a servo amplifier that inputs the deviation and amplifies the signal, and a servo amplifier that amplifies the signal by inputting the deviation. In an electro-hydraulic servo system having a servo valve that controls the flow rate and direction of pressure oil by output, and an actuator that drives a load using the pressure oil supplied from the servo valve, the load acting on the actuator a load pressure detector that outputs a pressure signal, a compressibility compensation element configured to add a signal proportional to the differential value of the load pressure signal to the deviation and output it, and an output signal of the compressibility compensation element; On the other hand, a static compensation element is provided which performs calculation processing indicating an inverse function characteristic of the load pressure flow rate characteristic of the servo valve based on the load pressure signal, and the output of the static compensation element is inputted to the servo amplifier. An electro-hydraulic servo system characterized by: