JPS58170901A - Electro-hydraulic servo system - Google Patents

Abstract

PURPOSE:To provide for stable and immediately responsive operation without influence of load, external disturbance and so on by incorporating static, compressibility and dynamic compensating elements at the preceeding steps of a servo amplifier of a closed loop system, and integrating a stabilization compensating element in a feedback loop. CONSTITUTION:A compressibility compensating element 9, a static compensating element 10 and a dynamic compensating element 11 are provided at the preceeding steps of a servo amplifier 8 of an electro-hydraulic servo system in a closed loop system and a stabilization compensating element 14 is integrated in a feedback loop. Influence of the compressibility of working oil, load pressure, a delay of transfer characteristic and oscillation of an electro-hydraulic servo valve are compensated by the compressibility compensating element 9, the static compensating element 10, the dynamic compensating element 11 and the stabilization compensating element 14, respectively so that the system may be controlled to closely follow a target value without influence of load fluctuation, the effect of any external disturbance, delay characteristic of the servo valve and so on.

Description

DETAILED DESCRIPTION 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 video testing machines, various testing machines for material testing, various simulators, rolling mills, and robots. Depending on the purpose of use, the load to be controlled varies, such as when it is only mass, when it is an elastic body, or when it combines the characteristics of both, and the quantity to be controlled also includes displacement, velocity charging, strain, etc.

In this type of closed-loop electro-hydraulic servo system, the system characteristics are not affected by loads, disturbances, and friction of shearing parts.
However, it is extremely important that the system operates stably and with high response.

However, in reality, the transmission characteristics of an electro-hydraulic servo system are affected by changes or fluctuations in load, the effect of external disturbances, friction in shearing parts, delay characteristics of servo valves, etc. The reality is that it is not possible to stably control the

In other words, when the characteristics of the load change, for example, when the mass of the load is MO, the transmission characteristics of the warm-up hydraulic servo system are set to be optimal, but when the mass of the load changes significantly, the mass of the load changes. The displacement becomes vibratory. Further, when a disturbance acts on the electro-hydraulic servo system, the position of the load changes. As a result, the electro-hydraulic servo system cannot faithfully realize the followability of the control amount to the target one shift.

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 performance. The purpose of this invention is to provide a load/disturbance-free electro-hydraulic servo system that operates in response.

A feature of the present invention is that the servo amplifier of the closed-loop electro-hydraulic servo system is equipped with a servo amplifier that is designed to handle changes or fluctuations in the load to be controlled, disturbances, and the characteristics of the servo valve that depend on the friction of the shearing parts. A compensating element is provided to remove the influence, and a stabilizing compensating element is further provided to stably operate the electro-hydraulic servomechanism including these compensating elements.

Embodiment 13-IJ 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 indicates a load to be controlled, 2
is a hydraulic actuator that drives the load 1; 3 is a servo valve that controls the flow rate and direction of pressure oil to the actuator 2; 4 is a hydraulic pressure source; 5 is a signal generator that generates the displacement target (iiV) of the load 1; is a feedback circuit (in this embodiment, the control amount is the displacement of the load), and this feedback circuit 6 consists of a displacement meter 68 that detects the displacement of the load 1 and a displacement detection circuit 6b. 7 is a signal An adder for calculating the deviation e between the target direct voltage from the generator 5 and the feedback signal from the feedback circuit 6; 8 is the servo valve 3;
This is a servo amplifier that amplifies the power of the input signal to the servo amplifier. At the front stage of this servo amplifier 8, a signal generator 5i! From lO, a hydraulic fluid compressibility compensation element 9 of the servo valve 3, a pressure flow characteristic compensation element of the servo valve 3, a so-called static compensation element 10, and a transmission delay characteristic compensation element of the servo valve 3, a so-called dynamic compensation element 11 are provided. I'm running away. The static compensation element 10 receives a signal of the load pressure P acting on the actuator 3. This load pressure P is detected by the load pressure detector 12. A differential value signal of the load pressure P obtained by a differentiator 13 is applied to the compressibility compensation element 9. 14 is a stabilizing compensation element for stably operating the electro-hydraulic servomechanism including the compressible compensation element 9, the static compensation element 10 and the dynamic compensation element 11.

Next, the operation of the electro-hydraulic servo system which is an embodiment of the present invention described above will be explained.

Before explaining the operation, the characteristics and operating principle of each component of the electro-hydraulic servo system will be explained.The characteristics of the servo amplifier 8 are generally expressed by the characteristics of the first-order delay element, but the corner frequency is different from that of the electro-hydraulic servo system. Since it can be designed with sufficient precision for the operating frequency, it can be expressed by the characteristics of the proportional element as follows. In other words, the deviation voltage e is E(S) = K, V(8) -at(a)y(s)
・・・・・・・・・・・・(1) However, E
(S), V(8) and Y(S) are the Laplace transforms of the deviation voltage e1 target value ■ and the displacement y of the load 1, respectively, and G1(S) represents the transfer function of the stabilization compensation element 14. The stabilization compensation element 14 is a so-called feedback compensation element. Next, the servo valve 30 input current l is 1=l(-e...
(2) However, K: is given by the gain of the servo amplifier 8.

The pressure flow characteristics and the frequency characteristics of the servo valve 3 are often expressed by the following equation. That is, servo valve 3
The output flow rate of is QII, and the output flow rate of servo valve 3 at no load is ql. , the load pressure is P, and the hydraulic oil supply pressure is P
, then the output flow rate q of the servo valve 3 is given by, and its frequency characteristic at no load is Q,. (
S) = G, (S)・I (8) ・・・・・・
It is given by (5). In this equation (5), Q. (飄) and I (8) are the output flow iQ of the servo valve 3 at no load, respectively. and servo valve 3
is the Laplace transform of the input current ■. Also, G in equation (5), (8) is a transfer function that represents the delay of the servo valve 3, and in many cases, kI: flow rate gain ω of the servo valve 3,: natural frequency ζ of the servo valve 3: servo valve 3 It is approximated by the characteristic of the second-order lag element, which is the reduction ratio of .

Considering the kingship 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 as follows: Ap: Cross-sectional area of the piston of the actuator 2 C: Drive system It is expressed as a constant y that affects the Oka 11 property: displacement of negative load t: time.

The equation of motion of the load 1 is as follows: Ft is the frictional force acting on the piston sliding surface of the load 1 and the actuator 2, F% is the disturbance acting on the load 1 from the outside, and m is the mass of the load 1.

As mentioned above, in the case where the characteristics of the main components of the hydration hydraulic servo system are expressed by formulas (1) to (8),
The operating principle of the compressible compensation element 9 and the static compensation element 10 is as follows:
The deviation voltage of the static compensation element 10 is e.

Then, the following formula is obtained.

Alternatively, since there is a relationship between the current i and the deviation voltage e as shown in equation (2), it is also possible to correct the output current i as shown in the following equation.

The two clusters of nests in the parentheses of equation (9) or equation αO are compression compensation □
One is about compensation, and the other is about static compensation.

Next, the transfer function of the dynamic compensation element 11 of the servo valve 3 is defined as G −
As (8), we get Q, (s)==k.G (8)...
・・・・・・・・・・・・・・・αυ and Nashi, formula (9
), or the signal 1, represented by 2○O. A correction of the transfer function expressed by the equation α is added to the equation. 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 as・Mark... Old and old... (6) ω1! becomes. By the way, since equation (6) includes a differential operation, it is quite difficult to ideally realize this with the current technology. Therefore, in practice, it is effective to use an i-function that can be expressed within the intended frequency range. The numerator of this equation (to) is a quadratic advance element for canceling the delay of the servo valve 3. It is necessary to carefully select the value of α, for example 3 or more, to such an extent that the influence of the second-order lag element in the denominator of equation (to) can be ignored.

As the stabilization compensation element 14, for example, its transfer function a
t(S) directly to GM(8)=+KW60Kall'...
......Select α→, where K-: Displacement feedback gain, : Velocity feedback gain, : Acceleration feedback gain. That is, in addition to the feedback of the displacement of the load, which is the control amount of the electro-hydraulic servo system shown in FIG. is added. of course,
Instead of the one-time differential value and the one-time differential value of displacement, the velocity and acceleration signals may be detected directly by a detector to calculate the feet. Note that the same effect can be obtained by adding a series compensation element next to the adder 7 in FIG. 1 instead of the feed compensation shown in the embodiment in FIG. can be obtained.

Next, the operation of the electro-hydraulic servo system of the present invention will be explained based on the operating principle of each compensation element described above.

In the embodiment of the apparatus of the present invention shown in FIG. 1, in consideration of practical feasibility, a case will be described in which compensation is performed at the stage of negative pressure as shown in equation (9).

Depending on the target value ■ from the signal generator 5 and the output signal of the stabilizing compensation element 14, the adder 7 applies its deviation signal e to the compressible compensation element 9. As shown in FIG. 2, the compressible compensation element 9 applies the time differential value of the load pressure P from the differentiator 13 to the static compensation element 10 as an output signal e' through its coefficient multiplier 9a. This output signal e' is expressed by the following equation (9) as described above.
This corresponds to the term in parentheses on the right side of , and the deviation signal e has been corrected to a signal that compensates for the compressibility of the hydraulic fluid.

As shown in FIG. 2, the static compensation element 10 uses its square root function function unit 10a to divide the output signal e' from 9b based on the load pressure signal P from the load pressure detector 12 by a division 110b. Then, this divided signal [signal e corresponding to equation (10)] is applied to the dynamic compensation element 11. Note that the square root function unit 10a described above performs a positive calculation of i[75E of the output signal e.

Determination of whether the output signal e is positive or negative can be performed using a normal comparator.

The dynamic compensation element 11 is constituted by a phase lead/lag circuit, and with respect to the output signal e from the static compensation element 1o,
A signal e corrected to cancel the delay of the servo valve 3 is applied to the servo valve 3 through the servo amplifier 8. Therefore, a signal corrected to compensate for the compressibility, static compensation, and dynamic compensation of the servo valve 3 is applied to the deviation signal e to the servo valve 3. As a result, servo valve 3
It is possible to remove the influence of apparent changes or fluctuations in the load 1 from the characteristics of the friction force FM of the actuator 2 and the disturbance F acting on the load 1.

In addition, it is possible to eliminate the delay in the transmission characteristics of the servo valve 3, and it is possible to improve the control accuracy of a machine equipped with an electro-hydraulic servo system.

Next, the role of the stabilization compensation element 14 will be explained. If the stabilizing compensation element 14 is not present in the blood-hydraulic servo system of FIG. 1, which shows an embodiment of the present invention, the electro-hydraulic servo system is unstable and often oscillates. Such a situation is a common problem in general industrial machines including vibration testing machines, material testing walls, simulators, rolling mills, and robots to which the present invention is applied. The stabilizing compensation element 14 is added to solve this problem. By adding the stabilization compensation element 14, the electro-hydraulic servo system of the present invention can eliminate the effects of load changes or fluctuations, external disturbances, and friction of sliding parts, and can operate stably and with high response. It becomes possible.

The response results of one embodiment of the device according to the present invention described above and a conventional device not provided with the compensation element according to the present invention are shown in FIGS. 3 to 6.

Figures 3 and 4 show the response results showing the effect of changing the mass of load 1, and Figure 3 shows the conventional response results.
FIG. 4 shows the response results of the present invention.

When the quality of load 1 is t”o, the target value and the corresponding load displacement response when the transmission characteristics of the electro-hydraulic servo system are set to be optimal are shown in Figure 3 (a). Figure 4 (a
). In this state, when the mass of the load 1 is tripled, the displacement of the load 1 becomes extremely vibratory in the conventional device as shown in FIG. 3(b). On the other hand, in the present invention, as shown in FIG. 4(b), it is experimentally clear that the effect of changing the load 1 does not appear.

Figures 5 and 6 show the influence of disturbance, that is, Figure 3 (a
), which shows the response results when a disturbance acts on the electro-hydraulic servo system set to the state shown in FIG. 4(a), FIG. 5 shows the conventional response results, and FIG. This is the response result. In the conventional type, the displacement of the load 1 fluctuates due to the action of disturbances, as shown in FIG. On the other hand, in the present invention, it is experimentally clear that the influence of disturbance does not appear on the displacement of the load 1, as shown in FIG.

In addition, in the above embodiment, the compressive compensation element 9 and the static compensation element 1 are connected from the signal generator 59111 to the stage before the servo amplifier 8.
0 and the dynamic compensation element 11 are sequentially provided, but if the oil chamber volume of the actuator is small, compressibility can be ignored, so the compressibility compensation element 9 can be omitted in this case. Alternatively, in the region where the output flow rate of the servo valve 3 given by equations (3) and (4) can be approximated by qmu '' qm 6 , the silent complementary fX element 10 can be omitted.Also, the delay of the servo valve 3 can be ignored. Of course, if it is possible, the dynamic compensation element 11 can be omitted.

Furthermore, although the above-mentioned embodiment has been described in the case where the characteristic of the load 1 is an inertial mass, completely similar control is possible when the characteristic of the load is an elastic body.

As described in detail above, according to the present invention, the transmission characteristics of the electro-hydraulic servo system are not affected by load changes or fluctuations, disturbance effects, delay characteristics of the servo valve, etc., and the control amount relative to the target value is It is possible to faithfully realize the following performance.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 shows the configuration of an embodiment of the electro-hydraulic servo system of the present invention, and FIG. 2 shows the detailed configuration of the main parts of the electro-hydraulic servo system shown in FIG. 1. Figure 3 is a diagram showing the response results of the influence of load fluctuation in a conventional electro-hydraulic servo system.
FIG. 4 is a diagram showing the response results of the influence of load fluctuation in the device of the present invention, FIG. 5 is a diagram showing the response results of the influence of disturbance in the conventional electro-hydraulic servo system, and FIG. FIG. 3 is a diagram showing a response result of the influence of disturbance in the device. DESCRIPTION OF SYMBOLS 1... Load, 2... Actuator, 3... Servo valve, 5... IM 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, 14.
...Stabilization compensation element.

Claims (1)

[Claims] 1. Operating the servo valve by adding the deviation between the input signal, which is a target value, and the control amount, which is the output signal of the controlled object or an actuator that drives the controlled object, to the servo valve through a servo amplifier; Adjust the actuator so that the deviation is small.
An electro-hydraulic servo mechanism for controlling the flow rate and direction of oil supplied to the actuator includes a static compensation element for compensating the output flow rate of the servo valve so that it does not apparently depend on the load pressure, and a static compensation element for compensating the apparent dependence of the output flow rate of the servo valve on the load pressure, and a compressible compensation element that compensates for the associated influence, and a dynamic compensation element that compensates for the delay in the transmission characteristics of the servo valve, including at least one of a static compensation element and a compressibility compensation element, or as necessary. A dynamic compensation element added to these is provided at the front stage of the servo amplifier, and further a stabilization compensation element is provided to stably operate the electro-hydraulic servo mechanism including these compensation elements, thereby changing the load to be controlled. Alternatively, an electro-hydraulic servo system is characterized in that it eliminates the effects of fluctuations, disturbances, and friction of shearing parts, and that the closed-loop system operates stably and with high response. 2. In the electrohydraulic servo system according to claim 1, when a static compensation element is included, the static compensation element is used to convert the load pressure acting on the actuator into a signal,
The input signal to the servo valve is calculated based on this load pressure signal and the deviation signal of the servo mechanism so that the output flow rate of the servo valve does not apparently depend on the load pressure, and this signal is applied to the servo valve. An electro-hydraulic servo system featuring: 3. In the electro-hydraulic servo system according to claim 1, when a compressibility compensation element is included, the compressibility compensation element is differentiated from the load pressure signal acting on the actuator and is proportional to this differential value. An electro-hydraulic servo system characterized by being configured to add a signal to a deviation signal. 4. In the electrohydraulic servo system according to claim 1, the dynamic compensation element compensates the output signal of the static compensation element so as to practically cancel out the delay in transmission of the servo system. An electro-hydraulic servo system characterized in that it is configured to convert the signal into a number and apply it to a servo valve. 5. The electrohydraulic servo system according to claim 1, wherein the stabilization compensation element is constituted by a feedback compensation element. 6. An electrohydraulic servo system according to claim 1, characterized in that the stabilizing compensation element is constituted by a series compensation element. 7. The electrohydraulic servo system according to claim 1, wherein the stabilization compensation element is comprised of a feedback compensation element and a series compensation element.