JPH0231243B2 - DENKYUATSUSAABOKEI - Google Patents

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention relates to an electro-hydraulic servo system that is not affected by the characteristics of a load to be controlled or disturbances, and operates stably and with high response. 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). In this type of closed-loop electro-hydraulic servo system,
It is extremely important that the characteristics of the system are not easily affected by loads, disturbances, and friction of shearing parts, and that it operates stably and with high response. As a solution to such problems, we published the Proceedings of the Society of Instrument and Control Engineers, Volume 16, No. 3 (June 1982).
The technique disclosed on pages 391 to 397 of the publication (Japanese) is known. This technology improves the fact that the characteristics of a closed-loop system are affected by the load.
Static and dynamic compensation elements are installed upstream of the servo valve. [Problems to be Solved by the Invention] Incidentally, the electrohydraulic servo system having the static compensation element and the dynamic compensation element described above operates well when the compensation element is ideally set.
However, in reality, it is difficult to ideally set the compensation element, and due to characteristic fluctuations of each component of the control system, even if the compensation element is set ideally at a certain point, it will deviate from the ideal state after that. is common. In that case, the electro-hydraulic servo system becomes unstable. In particular, the installation of the static compensation element and the dynamic compensation element has created a new problem in that when the system deviates from the ideal state, the instability becomes greater than when no compensation element is provided. In this case, the compensation element cannot be fully utilized, and the meaning of installing the compensation element is diminished. The present invention has been made based on the above-mentioned matters, and is not affected by changes or fluctuations in the load to be controlled, the effect of external disturbances, friction of sliding parts, delay characteristics of servo valves, etc., and is stable and has high response. The purpose of this invention is to provide an electro-hydraulic servo system that operates without any load or disturbance response. [Means for Solving the Problems] In order to solve the above problems, the present invention includes the following:
In a closed-loop electro-hydraulic servo system, a compressibility compensation element configured to add a signal proportional to the differential value of a load pressure signal acting on an actuator to a deviation signal and output it, and an output signal of the compressibility compensation element In contrast, a static compensation element that 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 is installed in the front stage of the servo amplifier, and the compressibility compensation element and the static A stabilizing compensation element is installed in the feedback loop to stabilize the electro-hydraulic servo system including the compensation element. [Operation] In the means for solving the above-mentioned problems, in the front stage of the servo amplifier of the electro-hydraulic servo system,
A compressible compensation element and a static compensation element are installed in series. Therefore, it basically has the ability to compensate for the influence on the characteristics of the servo valve that depends on fluctuations in the load to be controlled, disturbances, and friction of the sliding part. Furthermore, in order to stabilize the entire electro-hydraulic servo system caused by installing these compensation elements, a stabilization compensation element is installed in the feedback loop, so it compensates for the effects of load fluctuations, disturbances, etc. It is possible to fully demonstrate its capabilities and achieve stable and highly responsive operation. [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;
Reference numeral 6 denotes a feedback circuit (in this embodiment, the controlled variable is the displacement of the load), and the feedback circuit 6 is composed of a displacement meter 6a for detecting the 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 feedback 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 this servo amplifier 8, from the signal generator 5 side, there is a compressibility compensation element 9 for the hydraulic oil of the servo valve 3, a so-called static compensation element 10, a pressure flow characteristic compensation element 10 for the servo valve 3, and a transmission of the servo valve 3. Delay characteristic compensation element, so-called dynamic compensation element 1
1 is provided. A signal of the load pressure P _n acting on the actuator 3 is applied to the static compensation element 10 . This load pressure P _n is the load pressure detector 1
Detected by 2. A differential value signal of the load pressure P _n obtained by a differentiator 13 is applied to the compressibility compensation element 9 . 14 is a stabilizing compensation element for stably operating the electrohydraulic servomechanism including the compressible compensation element 9, the static compensation element 10, and the dynamic compensation element 11. Next, before explaining the operation of the electro-hydraulic servo system which is an embodiment of the present invention, the characteristics and operating principle of each component of the electro-hydraulic servo system will be explained. First, the characteristics of the servo amplifier 8 are generally expressed by the characteristics of the 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, the characteristics of the proportional element can be expressed as follows. expressed. That is, the deviation voltage e is E(s)=K _r V(s)-G _f (s)Y(s) (1). However, E(s), V(s) and Y(s)
are the deviation voltage e, target value v and load 1, respectively.
is the Laplace transform of the displacement y, and G _f (s) represents the transfer function of the stabilization compensation element 14. The stabilization compensation element 14 is a so-called feedback compensation element. Next, input current i of servo valve 3
is i=K・e...(2) where K: is given by 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 q _n , the output flow rate of the servo valve 3 at no load is q _n0 , the load pressure is P _n , and the supply pressure of hydraulic oil is P _s , then the output flow rate of the servo valve 3 is q _n is The frequency characteristic at no load is given by Q _n0 (s)=G _s (s)·I(s) (5). In this equation (5), Q _n0 (s) and I
(s) are the Laplace transforms of the output flow rate q _n0 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 many cases G _s (s) = k _i ·ω _o ² /s ² +2ζω _o s + ω _o ² ...( 6) However, k _i :flow gain of servo valve 3 ω _o : natural frequency of servo valve 3 ζ : damping ratio of servo valve 3, which is approximated by the characteristics of a second-order lag element. 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 q _n =A _p・dy/dt+C・dP _n /dt... ...(7) However, A _P : 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 the external disturbance F _o acts on F _f load 1 and the mass of load 1 is m, then m・d ² y/dt ² +F _f =A _P・P _n +F _o ……(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 flow rate 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, if the transfer function of the dynamic compensation element 11 of the servo valve 3 is expressed as G _c (s), then G _c (s) = K _i · G (s) ... (11), which is expressed by equation (9). This is to add the correction of the transfer function expressed by Equation (11) to the signal e _c or the signal i _c expressed by Equation (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 calculated from equation (11) as G _c (S)=s ² +2ζω _o s+ω _o ² /ω _o ² ...(12). By the way, since equation (12) includes a differential operation, it is quite difficult to ideally realize this with the current technology. Therefore, in practice, G _c (s) = α ² · s ² + 2ζω _o s + ω _o ² /s ² + 2ζαω _o
It is effective to use a transfer function that can be realized within the intended frequency range of use, such as s+(αω _o ) ² (13). 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. For the stabilization compensation element 14, for example, its transfer function G _f (s) is selected as G _f (s) = K _d + K _v s + K _a s ² (14). Here, K _d : Displacement feedback gain K _v : Velocity feedback gain _Ka : Acceleration feedback gain. That is, the first example showing one embodiment of the present invention
In addition to the feedback of the displacement of the load, which is the control variable of the electro-hydraulic servo system shown in the figure, feedback of signals corresponding to the first and second differential values is added. Of course, instead of the first and second differential values of displacement, velocity and acceleration signals may be detected directly by a detector and fed back. Next, the operation of the embodiment of the present invention shown in FIG. 1 will be explained based on the operating principle of each compensation element described above. In the embodiment shown in FIG. 1, a case will be described in which compensation is performed at the voltage stage as shown in equation (9) in consideration of practical feasibility. The target value v from the signal generator 5 and the signal obtained by stabilizing and compensating the feedback signal from the feedback circuit 6 by the stabilizing compensation element 14 are supplied to the adder 7. The adder 7 calculates these deviations e and applies the deviations e to the compressible compensation element 9. As is clear from equation (7), the compressibility compensation element 9 is an element that compensates for the dependence of the load movement on the time differential term of the load pressure P _n , and the apparent load Compensate so that the movement becomes dy/dt=1/A _P q _n . In the calculations of equations (9) and (10), the action is shown in parentheses on the right side. As shown in FIG.
Multiply the time differential value (dP _n /dt) signal of P _n by the coefficient (C/K・k ₁ ) and add it to the output signal (C/K・k ₁・dP _n /dt) from the coefficient multiplier 9a. The adder 9b adds the deviation voltage e from the device 7 to the static compensation _element 10, and the added signal (e+C/ _{K.k.sub.1.dP.sub.n} /dt) 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 voltage e. The static compensation element 10, as shown in FIG.
Based on the load pressure signal P _n from 2

[Formula] Performs the calculation, and this calculation signal

[Equation] and the output signal e' from the adder 9b of the compressible compensation element 9 are divided by the divider 10b, and this divided signal [signal e _e corresponding to equation (10)]
is added to the dynamic 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 system are not affected by changes or fluctuations in load, the action of disturbances, the delay characteristics of the servo valve, etc., and are stable. This allows faithful tracking of the control amount to the target value.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of an embodiment of the electro-hydraulic servo system of the present invention, FIG. 2 is a diagram showing the detailed configuration of the main parts of the electro-hydraulic servo system 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. 1... Load, 2... Actuator, 3... Servo valve, 5... Signal generator, 6... Feedback circuit, 7... Adder, 8... Servo amplifier, 9
...Compressible compensation element, 10...Static compensation element, 1
1...Dynamic compensation element, 12...Load pressure detector,
13...Differentiator, 14...Stabilization compensation element.

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 compressibility compensation element configured to add a signal proportional to a differential value of a load pressure signal acting on the actuator to the deviation signal and output the resultant signal; A static compensation element that performs arithmetic processing indicating an inverse function characteristic of the load pressure flow rate characteristic of the servo valve based on a signal is installed upstream of the servo amplifier, and the compressibility compensation element and the static compensation element An electro-hydraulic servo system characterized in that a stabilizing compensation element is installed in a feedback loop to stabilize the electro-hydraulic servo system.