JPH03303A - Method and apparatus for compensating pressure fluid characteristic of servo valve in electrohydraulic servo device - Google Patents

Abstract

PURPOSE:To enhance the control ability of an electrohydraulic servo device by adjusting a loop gain to the maximum value (maximum permissible value) less than hunting limit in each load pressure corresponding to load pressure alteration. CONSTITUTION:A loop gain is made to be a total gain of loop running through an adder 8, a multiplier 101, an amplifier 5, a servo valve 3, a hydraulic cylinder 2, a pressure detector 11, and an amplifier 10, and becomes variable by the output (y) of a function generator 102 to the multiplier 101. In the vicinity of load pressure PL=0, the gain of the amplifier 5 is determined so as not to generate hunting in a servo system. In this case, the output (y) of the function generator 102 to the multiplier 101 is determined one (1). When the load pressure becomes PL=PS (the gradient between the pressure of the valve 3 and fluid amount becomes the maximum), the output (y) is determined to form the loop gain being limit not to generate hunching in a servo system.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to the pressure control of a servo valve in an electro-hydraulic servo mechanism used in presses, brakes, material destruction testing machines, etc.
The present invention relates to a method and device for compensating flow characteristics.

[Conventional technology]

FIG. 3 is a system diagram of a conventional electrohydraulic servo mechanism known from Japanese Patent Publication No. 53-43061. In this figure, a load 1 is driven by a hydraulic cylinder 2. The hydraulic cylinder 2 is connected to a hydraulic power source 4 via a servo valve 3. The amount of displacement of the hydraulic cylinder 2 is detected by a displacement detector 6.

It is fed back via amplifier 7. Then, an adder 8 adds the voltage signal (displacement command) corresponding to the control displacement from the input signal supply section 9 and the feedback signal from the amplifier 7, and the resulting value is sent to the servo amplifier 5 constituting the servo amplifier section. The signal is amplified and sent to the servo valve 3, which is then controlled. As a result, the load 1 is driven according to the displacement command from the input signal supply section 9.

From the input current i of the servo valve 3 in this Fig. 3, the load 1
A control block diagram up to displacement Y is shown in FIG. The meanings of the symbols in FIG. 4 are as follows.

i: Input current of servo valve 3 (mA) Ki: Gain constant of servo valve 3 ((a&/s)/m
A) Ti: Time constant (S) of servo valve 3 S Niraplus variable Q: Discharge flow rate of servo valve 3 (, ff1) Q'Inflow flow rate of Niji cylinder 2 (cj) CI = Pressure-flow rate gradient of servo valve 3 [alls /kg-
8] and is expressed as .

C2: Leakage rate of servo valve 3 and cylinder 2 [works/kg
-9], and when the leakage flow rate of the servo valve 3 and cylinder 2 is QQ.

It is expressed as

Pm Niji cylinder 2 pressure difference at the entrance and exit (kg/aJ) k
: Volumetric expansion of pipe line and cylinder 2 ke (am”/k
gl, the volume of oil in cylinder 2 and one side of the pipe is V Cc
d), when the bulk elastic modulus of oil is K Ckg/aJ), C3: viscous drag coefficient of moving parts [-・s/an)A
: Pressure-receiving area of the piston of the movable cylinder 2 [d] N: Speed of the movable part (tyrr/s) C2. Since the value of C3 is extremely small compared to the values of other elements, an equivalent block diagram in which this is omitted is shown in FIG. In this FIG. 5, the natural frequency ωm in the block (b).

The damping rate (damping coefficient) ζ is.

It is expressed as

M: Total mass of movable parts (Load 1. Refers to movable parts on the load side such as hydraulic cylinder 2, the same applies hereinafter) [Taft/S'/am)
It is indicated by.

It is well known that in such an equivalent block, the frequency response is a quadratic system, and the resonance peak is determined by ζ. As can be seen from equation (2) above, ζ is M, A,
k and C1, and in an electro-hydraulic servomechanism, M, A and k have constant values for the mechanism. However, C1 is the pressure-flow gradient of the servo valve 3, which, as before, is denoted by .

Furthermore, the relationship between Q and Pl is nonlinear as shown in (4): Q=Ki-1Blue.

This relationship is illustrated in Figure 6, where ps is the hydraulic power source 4.
The supply pressure of , iR is ix at the rated value, and the others are the same as above. As shown in FIG. 6, C+ (=ix) is
Due to the relationship expressed by equation (3) above, it changes significantly depending on Pl at that time. Also, Pm (pressure difference at the entrance and exit of cylinder 2) is
Proportional to load pressure PL. Therefore, Figure 3 (Figure 4, Figure 5)
In the conventional technology shown in Figure), C+
(pressure-flow rate gradient of servo valve 3) changes, and as a result ζ
There was a problem in that the frequency characteristics changed as a result of the change in the frequency characteristics.

[Problem to be solved by the invention]

Even in the prior art, the above-mentioned problem does not occur when the load pressure, that is, the load 1 is constant.

However, when the purpose of controlling the load 1 is wide*S pressure control by pushing displacement of the hydraulic cylinder 2, such as press pressure, brake oil pressure, pressure control of a material destructive testing machine, etc.

The load pressure pL is controlled in the range from 0 to the rated value. Therefore, in this case, the frequency characteristics of the servo system change as described above, and the resonance point ωm shown in the Bode diagram shown in Figure 7
However, as shown in a, there is a problem in that the OdB is exceeded, resulting in control hunting.

In order to avoid this problem, in the prior art, as shown in FIG. 8, regardless of the magnitude of C+(PL), a negative measure had to be taken to lower the loop gain of the entire servo system using the servo amplifier 5.

This means that the loop gain of the entire electro-hydraulic servo control system (electro-hydraulic servo mechanism) is determined by the minimum value C.

However, the change in C1 is PL:O(C+minimum), pL2P
The control performance (accuracy) of the entire electro-hydraulic servo mechanism is 20 to 50 times higher between s (C+maximum).

response).

The purpose of the present invention is to always obtain the maximum loop gain for the load pressure even when performing pressure control over a wide range.
An object of the present invention is to provide a method and device for compensating the pressure-flow characteristics of a servo valve in a servo mechanism in an electrohydraulic servomechanism, which can improve control performance (accuracy, response).

[Means to solve the problem]

The above object is achieved by adjusting the loop gain in the electro-hydraulic servomechanism to the maximum value (maximum allowable value) within a range that does not exceed the hunting limit at each load pressure, in response to changes in load pressure.

When the output of the input signal supply section is a pressure command and constitutes a load pressure feedback system, the output of the input signal supply section may be used to detect the load pressure. Furthermore, when the output of the input signal supply section is a displacement command, the differential pressure of the hydraulic cylinders may be used to detect the load power.

As for the device, since C changes depending on the load pressure PL, the change in the load pressure PL is obtained, and 5 is calculated depending on the magnitude of the change.
The above object can be achieved by providing a loop gain adjustment means for adjusting the loop gain so as not to exceed the hunting limit.

[For production]

If the loop gain is adjusted according to changes in load pressure to the maximum value (maximum allowable value) within the range that does not exceed the hunting limit at each load pressure, the loop gain will always be automatically adjusted to the optimal value due to the servo mechanism. As a result, control performance (accuracy, response) is always maintained at a high level regardless of the load pressure.

【Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is according to the invention. This is a control system diagram showing one embodiment of a method and device for compensating the pressure-flow characteristics of a servo valve in an electro-hydraulic servomechanism, and FIG. 1 is an example in which the present invention is applied to the conventional technology shown in FIG. 3. (However, the output of the input signal supply section 9 is not the displacement command EY but the pressure command EP.) Parts with the same reference numerals as in FIG. 3 indicate the same or equivalent parts.

Here, as described above, the output of the input signal supply section 9 is the pressure command EP, and the load pressure PL at the load 1 is detected by the pressure detector 11.
This is an example of a case in which the signal is detected by the amplifier 10 and fed back via the amplifier 10, and this will be explained below.

That is, the load pressure PL of the load 1 is detected by the pressure detector 11, amplified by the amplifier 10, and fed back as an output (feedback signal) Fp. These E and FP are added by an adder 8 and output, and feedback control is performed, so that the load pressure PL becomes equal to the output EP of the input signal supply section 9.

This is not particularly different from the prior art described above, and in the present invention, each load pressure PL
A loop gain adjustment means is added to adjust the loop gain to follow the maximum value (maximum allowable value) within the range that does not exceed the hunting limit. In the illustrated example, the loop gain adjusting means determines the maximum loop gain allowable at each load pressure pL, changes the amplification factor of the servo amplifier based on the value, and adjusts the loop gain to the maximum allowable at each load pressure. The servo amplification unit is composed of amplification factor adjustment means that sets the value to a value. More specifically, in the illustrated example, the servo amplification section includes a multiplier 101 and a servo amplifier 5, and the servo amplification section amplification factor adjustment means is configured to adjust the amplification factor of each load pressure PL.
The function generator 102 has a hunting limit gain function set in advance, and the multiplier 101 multiplies the signal from the function generator 102 by the signal from the input signal supply section 9. The apparatus of the present invention illustrated in FIG. 1 will now be described. Input of the function generator 102 (output of the input signal supply section 9) E
The relationship between p and output y is set to simulate the change in CI in equation (3) above, that is, the relationship between C3 and Pm (-PL) shown in FIG. Also multiplier 10
The calculation formula for 1 is Z=xy (5). Here, y is the output of the function generator 102, X is the output of the adder 8, and Z is the input of the servo amplifier 5.

Therefore, the loop gain is calculated from the output of adder 8 to the output of multiplier 1.
01, servo amplifier 5, servo valve 3, hydraulic cylinder 2,
This is the total gain that goes around the pressure detector 11 and the amplifier 10, and is variable depending on the value of the function generator 102 output y to the multiplier 101.

On the other hand, the gain of the servo amplifier 5 is set so that the servo system does not hunt when C1 is at its minimum, that is, near the 22nd side of the load pressure PL.

At this time, the value of the function generator 102 output y to the multiplier 101 is set to 1 (therefore, the input X of the multiplier 101 is output as is). Next, when CI is maximum, that is, when the load pressure pL=ps, , the value of the function generator 1028 force y to the multiplier 101 is determined so as to have a loop gain that is the limit at which the servo system does not cause hunting.

This y is generated by the function generator 102 when EP corresponds to pL=ps.

As described above, the function generator 102 is set and adjusted to obtain y such that the servo system has a loop gain that does not cause hunting at each load pressure pL.

As mentioned above, since the relationship is E P o CP L, if EP is input to the function generator 102, y will change according to the load pressure PL at that time, and the loop gain will change on the hunting limit line. .

FIG. 2 is a control system diagram showing another embodiment of the method and apparatus of the present invention. Here, the output EY of the input signal supply section 9 is a displacement command, which will be explained below. In FIG. 2, a load displacement Y of the load 1 is detected by a displacement detector 6, amplified by an amplifier 7, and fed back as an output (feedback signal) FY. These EY and FY are added by the adder 8 and output, and feedback control is performed, and as a result, the load displacement Y becomes equal to the output EY of the input signal supply section 9, as described in the prior art. However, here, a multiplier 101 is added between the adder 8 and the servo amplifier 5, and a function generator 102 for inputting the pressure difference PI1 of the hydraulic cylinder 2 is added.

In this case, in order to obtain the pressure difference Pm of the hydraulic cylinder 2,
It has the following means: That is, pressure detectors 105 and 106 that detect the pressure PI+P2 of the hydraulic cylinder 2;
It includes amplifiers 103 and 104 that amplify these outputs, and a subtracter 107 that outputs 1 of the output P1 of the amplifier 103 and P2 of the amplifier 104, that is, the pressure difference P+a at the entrance and exit of the hydraulic cylinder 2.

In the example of FIG. 2, the output EY of the input signal supply section 9 is not directly proportional to the load pressure PL. Therefore, the above-mentioned means is provided to detect the pressure difference Pm at the entrance and exit of the hydraulic cylinder 2,
This is replaced by load pressure P. Note that the load pressure PL is pL=P, -p2...
...(6), and it is well known that it takes the same value as P+w.

Further, the multiplier 101 and the function generator 102 are set and adjusted in the same manner as in the case illustrated in FIG.

As described above, when Pm is input to the function generator 102, the value of y to the multiplier 101 changes according to the load pressure PL at that time, and the loop gain takes the maximum value and changes on the hunting limit line. become.

Here, as described above, when the load pressure PL is near O and near the rated value, the change in the pressure characteristic C1 of the servo valve reaches 20 to 50 times. In addition, the resonance peak Mp of the servo system
is determined by ζ, which is proportional to CI, as described above, and its value is expressed by .

Now, if this change is calculated by multiplying it by 20 times, for example, the resonance peak Mp will be a difference of about 24 dB from equation (7) (when ζ = 0.6 near the load pressure rating). This means that the gain needs to be lowered by 25 dB near the load pressure O.

As mentioned above, in the conventional technology, the loop gain had to be set under the minimum CI condition near 0 load pressure, which resulted in a decrease in loop gain over the entire range from 0 load pressure to the rated value. .

According to the present invention described above, the loop gain can be automatically shifted on the hunting limit line (on the level along the maximum value (maximum allowable value) within a range that does not exceed the hunting limit) according to the load pressure.

It is well known that the accuracy and response, which are the basic performance of servo control, are proportional to the loop gain, and the higher the loop gain, the better the performance. Therefore, as mentioned above, if the loop gain can be adjusted to the highest possible value over the entire load pressure range, control performance (accuracy, response) can be significantly improved.

Control performance (accuracy, response) is greatly improved.

In particular, near the load pressure drop, which is the most frequently used area,
In the trial calculation example, the gain was increased by 24 dB or more, making it possible to significantly improve control performance (accuracy, response).

〔Effect of the invention〕

As described above, according to the present invention, even when performing pressure control over a wide range, the maximum loop gain can always be obtained for the load pressure, and control performance (accuracy) can be improved.

This has the effect of improving response (response).

[Brief explanation of drawings]

1 and 2 are control system diagrams showing an example of the method and apparatus of the present invention, FIG. 3 is a control system diagram according to the conventional method, FIG. 4 is a control block diagram of FIG. 3, and FIG. 5 is a control system diagram of the conventional method. The equivalent control block diagrams shown in FIGS. 6 to 8 are diagrams for explaining problems in the prior art. DESCRIPTION OF SYMBOLS 1...Load, 2...Hydraulic cylinder, 3...Servo valve, 4...Hydraulic pressure source, 5...Servo amplifier, 6...Displacement detector. 7.10... Amplifier, 8... Adder, 9... Input signal supply section, 11... Pressure detector, 101... Multiplier, 102... Function generator, 103...・Amplifier, 1
04...Amplifier, 105...Pressure detector, 106.
...Pressure detector, 107...Adder, pL...Load pressure, FYeFP...Output of amplifiers 7 and 10 (feedback signal) -EPy Ey...Input signal supply unit 9
output (pressure, displacement command), Pa...Pressure difference at the entrance and exit of the hydraulic cylinder.

Claims (1)

[Claims] 1. An input signal supply section that supplies a signal for driving and controlling a load, a servo amplifier section that amplifies the signal from the input signal supply section, and a device that is controlled by the signal from the servo amplifier. a servo valve, a hydraulic cylinder which is driven by controlling the supply direction and flow rate of hydraulic pressure from a hydraulic source by controlling the servo valve, and drives and controls the load, and at least the pressure or displacement of the load as a feedback element. In an electro-hydraulic servo mechanism equipped with a feedback system and an adder that adds a signal from the feedback system and a signal from the input signal supply section and supplies the sum to the servo amplification section, each load is adjusted according to changes in load pressure. Maximum value within the range that does not exceed the hunting limit for pressure (maximum allowable value)
A method for compensating pressure-flow characteristics of a servo valve in an electro-hydraulic servomechanism, characterized by adjusting a loop gain accordingly. 2. An input signal supply section that supplies a signal for driving and controlling the load, a servo amplifier section that amplifies the signal from the input signal supply section, and a servo valve that is controlled by the signal from the servo amplifier; A hydraulic cylinder is driven by controlling the supply direction and flow rate of hydraulic pressure from a hydraulic source by controlling the servo valve, and drives and controls the load, a pressure feedback system having the pressure of the load as a feedback element, and this pressure feedback system. In a hydraulic servomechanism equipped with an adder that adds a signal from a system and a signal from the input signal supply section and supplies the sum to the servo amplifier section, a change in load pressure is detected by a signal from the input signal supply section. A method for compensating pressure-flow characteristics of a servo valve in an electro-hydraulic servomechanism according to claim 1. 3. An input signal supply section that supplies a signal for driving and controlling the load, a servo amplifier section that amplifies the signal from the input signal supply section, and a servo valve that is controlled by the signal from the servo amplifier; A hydraulic cylinder that is driven by controlling the supply direction and flow rate of hydraulic pressure from a hydraulic source through the control of this servo valve and drives and controls the load, a displacement feedback system that has displacement of the load as a feedback element, and a displacement feedback system that controls the load. In an electro-hydraulic servomechanism equipped with an adder that adds a signal from the system and a signal from the input signal supply section and supplies the sum to the servo amplification section, changes in load pressure are detected by differential pressure at the entrance and exit of the hydraulic cylinder. A method for compensating pressure-flow characteristics of a servo valve in an electro-hydraulic servomechanism according to claim 1. 4. An input signal supply section that supplies a signal for driving and controlling the load, a servo amplifier section that amplifies the signal from the input signal supply section, and a servo valve that is controlled by the signal from the servo amplifier; A hydraulic cylinder that is driven by controlling the supply direction and flow rate of hydraulic pressure from a hydraulic source through the control of the servo valve to drive and control the load; a feedback system that has at least the hydraulic pressure or displacement of the load as a feedback element; In an electro-hydraulic servo mechanism equipped with an adder that adds a signal from a feedback system and a signal from the input signal supply section and supplies the sum to the servo amplification section, the hunting limit at each load pressure is determined according to changes in load pressure. A compensating device for pressure-flow characteristics of a servo valve in an electro-hydraulic servomechanism, comprising loop gain adjusting means for following and adjusting the loop gain to a maximum value (maximum allowable value) within a range that does not exceed the range. 5. The loop gain adjusting means determines the maximum loop gain allowable for each load pressure, changes the amplification factor of the servo amplification section based on the value, and adjusts the loop gain to the maximum value allowable for each load pressure. 5. The compensating device for pressure-flow characteristics of a servo valve in an electro-hydraulic servomechanism according to claim 4, which is a servo amplifying section amplification factor adjusting means for setting. 6. The servo amplification unit includes a multiplier and a servo amplifier, and the servo amplification unit amplification factor adjustment means includes a function generator in which a hunting limit gain function at each load pressure is set in advance, and this function generator. 6. The servo valve in the electrohydraulic servomechanism according to claim 5, further comprising the multiplier for multiplying the signal from the input signal supply section by the signal from the input signal supply section, and applying the signal from the multiplier to the servo amplifier. Compensation device for pressure-flow characteristics.