JP2003149109A - Electrohydraulic servo-type material testing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrohydraulic servo-type material testing apparatus, which can always obtain an optimum response as long as the tuning is conducted in a certain amplitude, even when a test is conducted in an arbitrary amplitude. SOLUTION: Detection means (pressure sensor 6a, 6b) for detecting a pressure difference in a hydraulic actuator 14 that is a driving source for load mechanism are provided so as to calculate an optimum proportional gain KP( N) , based on a proportional gain KP( T) set by tuning, using detection result of pressure difference between tuning and actual operation and a hydraulic fluid supply pressure to the hydraulic actuator 14, the gain KP( N) enabling a constant loop gain of a system at times of tuning and operating to conduct a test in an arbitrary amplitude. The setting is automatically changed to the calculated proportional gain KP( N) , thereby always obtaining an optimum response when conducting a test in an arbitrary amplitude.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called electro-hydraulic servo type material testing machine for feedback controlling a hydraulic actuator for applying a load to a test piece.

[0002]

2. Description of the Related Art In an electro-hydraulic servo type material testing machine, generally, a load mechanism for applying a load to a test piece is driven by a hydraulic actuator, and a physical quantity selected as a control quantity, for example, a load mechanism. By supplying the target value related to the displacement and the load acting on the test piece with the displacement, from the waveform generator, etc., at the same time, by feeding back the detected value of the controlled variable to the target value,
Load the test piece according to the target value.

In the electro-hydraulic servo type material testing machine provided with such a feedback loop, the deviation obtained by feeding back the detected value to the target value is usually used as the PID.
(Proportional / integral / derivative) control method to obtain manipulated variable,
That is, PID control is adopted.

In feedback control including PID control, tuning of the control system,
That is, in the PID control system, it is necessary to optimally set the so-called PID constants of the proportional gain, the integral time and the derivative time in order to properly apply the load according to the target value to the test piece.

As a typical example of the method of adjusting each constant of PID control, there is known a method of adjusting the tine based on the response waveform of the system to a rectangular wave input having a certain amplitude. .

[0006]

By the way, after the feedback loop is tuned by the above method, when the load is repeatedly applied to the test piece in the actual test, the amplitude corresponding to the input signal used at the time of tuning, More specifically, when the target value is a repetitive waveform with an amplitude equal to the maximum amplitude of the input waveform used during tuning, the optimum response is obtained and accurate load control can be performed, but the amplitude during testing If the setting is different from the amplitude at the time of tuning, the optimum response cannot be obtained, and in such a case, it is necessary to tune again.

The present invention has been made in view of such a situation, and if tuning is performed once with a certain amplitude, even if a test is performed with an arbitrary amplitude different from that amplitude, an optimum response is always obtained. It is an object of the present invention to provide an electro-hydraulic servo type material testing machine capable of obtaining the above-mentioned characteristics.

[0008]

[Means for Solving the Problems]
Therefore, the electro-hydraulic servo type material testing machine of the present invention is
It is equipped with a load mechanism that uses the actuator as the drive source, and
Feedback for controlling hydraulic actuators in
An electro-hydraulic servo type material testing machine equipped with a control system
Differential pressure detection to detect the differential pressure in the hydraulic actuator.
Output means and the feedback system during actual driving
Proportional gain K of your system_{P (N)}Is set by tuning
Proportional gain K_{P (T)}Based on the
Detection result P _TAnd the differential pressure detection result P during operation_TWhen,
Supply pressure P of hydraulic oil to hydraulic actuator_SWith and
Proportion calculated by the following formula and automatically changed.
It is characterized by having a gain optimization setting means.
(Claim 1).

K _{P (N)} = K _{P (T).} (P _S −P _T ) ^1/2 /
(P _S -P _N) ^1/2

Here, in the present invention, in place of the differential pressure detecting means according to claim 1, there is provided a calculating means for converting a detected value of the load acting on the test piece into a differential pressure (claim 2). ), The same purpose can be achieved.

According to the present invention, in the electro-hydraulic servo type material testing machine, the flow rate of the hydraulic oil to the hydraulic actuator is proportional to the loop gain of the system, and the flow rate to the hydraulic actuator is the supply pressure of the hydraulic oil to the hydraulic actuator. Also, by utilizing the point that can be calculated from the internal differential pressure, the loop gain of the system is always changed by automatically changing the proportional gain of the feedback control system according to the detection result of the differential pressure in the hydraulic actuator during the test. It is intended to keep it constant and achieve the intended purpose.

That is, as shown in the model in FIG. 1, it is assumed that a load is applied to the test piece TP by driving the hydraulic actuator H in the direction indicated by the arrow F, and the hydraulic actuator H is supplied to the test piece TP via a servo valve SV. Hydraulic unit H
Hydraulic fluid shall be supplied from U. In addition, the amount of hydraulic oil in each of the two oil chambers RA and RB partitioned by the piston HP in the hydraulic actuator H at a certain time point is x.
Let _A0 and _xB0 be the pressure receiving areas of the pistons HP in these oil chambers RA and RB, respectively.

Assuming that the test piece TP is deformed by d in the load direction F by driving the hydraulic actuator H, the hydraulic oil amounts x _A and x _{B in} the respective oil chambers RA and RB of the hydraulic actuator 1 after the deformation d. Becomes x _A = x _A0 + Sd ··· (1) x _B = x _B0 −Sd ··· (2).

Considering the balance of forces due to the deformation d, if the spring constant of the test piece W is k and the pressures in the oil chambers RA and RB of the hydraulic actuator 1 are P _A and P _B , respectively, S ( P _A −P _B ) = kd (3) Oil chamber RA, the differential pressure between _{RB P (= P A -P B} )
Then, the equation (3) can be expressed as SP = kd ... (4).

On the other hand, the supply pressure of the hydraulic oil to the hydraulic actuator H is P _S , the density of the hydraulic oil is ρ, and the oil chambers RA, R
Let v _A and v _B be the flow rates of hydraulic oil into _B , respectively.
From Bernoulli's theorem, a ^{_{P S -P A = ρv A 2}} /2 ···· (5) P B = ρv B 2/2 ···· (6), since generally put a v _A = v _B , V _A = v _B =
If v, then P _S − (P _A −P _B ) = ρv ² ··· (7), so P _S −P = ρv ² ··· (8) Therefore v = (P _S −P ) ^1/2 / ρ ^1/2 ... (9)

Let P _{T be the} differential pressure during tuning (the differential pressure when the waveform input signal used for tuning exhibits its maximum amplitude, in other words, the maximum differential pressure during tuning). The flow rate v _{T at this} time can be expressed as v _T = (P _S −P _T ) ^1/2 / ρ ^1/2 ... (10).

On the other hand, when the differential pressure at the maximum amplitude during actual operation (test) is P _N , the flow rate v _{N at} that time is v _N = (P _S -P _N ) ^1/2 / ρ ^1/2 ... (11)

As described above, since the loop gain of the system is proportional to the hydraulic oil flow rate for the hydraulic actuator, the loop gain at the time of tuning was G _T , and the actual test was carried out while maintaining the tuning state. the loop gain when the G _N, can be expressed as _{G N / G T = (P} S -P N) 1/2 / (P S -P T) 1/2 ···· (12) of the time.

Therefore, among the constants of the feedback control system, when the value set by the tuning D for the proportional gain K _P is K _{P (T)} , the hydraulic oil flow rate is v
_When it becomes _N , in other words, when the differential pressure becomes P _N , the proportional gain K _{p (N)} is K _{P (N)} = K _{p (T)} · (P _S −P _T ) ^1/2 / (P By changing to _{S- PN} ) ^1/2 ... (13), the loop gain during operation can be made equal to that during tuning,
It is possible to always keep the loop gain constant.
Therefore, if tuning is performed once with a constant amplitude, the response of the system can always be kept constant even if a test is performed with an arbitrary amplitude different from that.

Here, the differential pressure P in the hydraulic actuator used in the above calculation can be obtained by detecting the pressure in each oil chamber, and can also be calculated from the detection result of the load acting on the test piece.

That is, the differential pressure P in the hydraulic actuator
Have the relationship shown in the above formula (4). The right side kd in the equation (4) is the load F acting on the test piece.
Therefore, using the detected value F of the load by the load cell for detecting the test load provided in the ordinary material testing machine and the pressure receiving area S of the oil chamber, P = F / S. 14), the differential pressure in the hydraulic actuator can be calculated.

The invention according to claim 2 utilizes this point, and the differential pressure P _T during tuning and the differential pressure P _N during actual operation are not detected but the differential pressure inside the hydraulic actuator is detected. , The load detection value F is calculated by the equation (14), and the result is applied to the equation (13).

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. 2 is a device configuration diagram of an embodiment of the present invention, and FIG. 3 is a block diagram showing a configuration of a feedback control system thereof.

The tester main body 1 is provided with two columns 12a and 12b on a table 11, and the columns 12a and 12b are provided.
It has a structure in which both ends of the cross yoke 13 are supported by b.

On the lower surface side of the table 11, a hydraulic actuator 1 operated by hydraulic oil of a constant pressure P _S supplied from a hydraulic unit (not shown) via a servo valve 2.
4 is provided, a lower grip 15a is mounted on the upper end of the piston of the hydraulic actuator 14, and an upper grip 15b is mounted on the cross yoke 13 via the load cell 3. The test piece TP is used for the test in a state where both ends thereof are held by the upper and lower grippers 15a and 15b.

That is, the test piece TP whose both ends are held by the upper and lower grippers 15a and 15b is loaded by the drive of the hydraulic actuator 14, and the load acting on the test piece TP at the time of the test is the load cell 3. The displacement of the load mechanism 14 is detected by the displacement gauge 4
Detected by.

The load and displacement detection signals from the load cell 3 and the displacement meter 4 are taken into the control device 5 every moment. The controller 5 stores the momentary outputs of the load cell 3 and the displacement meter 4 as test data, and includes a waveform generator 51 that outputs a target value r in FIG. 3 and a PID adjuster 52, and selects it as a controlled variable z. Physical quantity,
For example, the detection signal of the load by the load cell 3 is introduced as the observed amount y to construct a feedback loop, and the manipulated variable u to be supplied to the controlled object 53 is generated. In addition, this FIG.
The block shown as the control target 53 in FIG. 2 means a system including the servo valve 2, the load mechanism of the tester main body 1 driven by the hydraulic actuator 14, and the test piece TP. This is a control signal for the valve opening of the servo valve 2.

The pressures in the hydraulic chambers on both sides of the piston in the hydraulic actuator 14 are detected by the pressure sensors 6a and 6b communicating with the respective hydraulic chambers, and the detection results are also taken into the control device 5. Be done.

The proportional gain K _P , the integration time T _I, and the derivative time T _D of the PID adjusting unit 52 are set by a known tuning method, for example, a rectangle having a certain amplitude, as in the above-mentioned Zine's method. The optimum value is set based on the response when a wave is input. The control device 5 reads the pressure detection data by the pressure sensors 6a and 6b at the time of this tuning, calculates the difference between the two values, that is, the differential pressure P _T in the hydraulic actuator 14 and stores it in the memory 5a. The supply pressure P _S from the hydraulic unit to the hydraulic actuator 14 is also stored in the memory 5a in advance.

In actual operation, the waveform generator 51
Outputs a desired waveform signal from the target value r from the control unit 52 set at the time of tuning at the beginning of operation.
Feedback control is performed using each constant of. And
The outputs of the pressure sensors 6a and 6b during the operation are taken into the control device 5, and the differential pressure P in the hydraulic actuator 14 is taken.
_N is calculated, and the differential pressure P _N during this operation and the memory 5
The differential pressure P _T at the time of tuning stored in a and the hydraulic oil supply pressure P _S to the hydraulic actuator 14
Using the above equation (13), the proportional gain K
Automatically setting change to K _{P (N)} values of _P from K _{p (T)} at the time of tuning.

The value of the proportional gain K _{P (N)} is the same as in (1) above.
~ As shown in equation (13), the target value r during operation
Is a proportional gain that can make the loop gain G _N of the feedback loop during operation equal to the loop gain G _T during tuning, even if the amplitude of is different from the amplitude of the waveform used during tuning. According to the mode, when tuning is performed using a waveform having an arbitrary amplitude, and when a load is applied to the test piece TP by supplying a target value having an arbitrary amplitude different from the amplitude, the value of the proportional gain K _P is automatically calculated. The load having the amplitude according to the target value can be correctly applied to the test piece TP.

In the above-described embodiment, the differential pressure P in the hydraulic actuator 14 during tuning and operation is set.
_T and the differential pressure P _N during operation are set to the hydraulic actuator 14
Although an example obtained from the outputs of the pressure sensors 6a and 6b provided in the above is shown, the load detection value by the load cell 3 is described above (1
Even if the differential pressure at the time of tuning and at the time of operation is calculated by substituting it into the equation (4),
It is possible to achieve the same effect as the above.

Further, in the above embodiment, an example in which the present invention is applied to the electro-hydraulic servo type material testing machine of the type in which the load mechanism is PID controlled is shown, but the control rule of the feedback control is limited to the PID control. It is needless to say that the present invention can be equally applied to other control laws, and the point is that any control law includes a proportional gain as a constant of the feedback control system.

[0034]

As described above, according to the present invention, the differential pressure in the hydraulic actuator, which is the drive source of the load mechanism, is detected at the time of tuning and at the time of operation, or is calculated from the detected load value. Using the respective differential pressures and the hydraulic oil supply pressure to the hydraulic actuator, the optimum value of the proportional gain during operation is calculated based on the proportional gain set by tuning, and the proportional gain is automatically calculated based on the result. Since the setting is changed, it is possible to always keep the loop gain of the system constant regardless of the magnitude of the amplitude of the target value during operation. As a result, you only need to tune once using a signal with a certain amplitude,
Eliminates the need for retuning when testing arbitrary amplitudes.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the principle of the present invention using a model.

FIG. 2 is a device configuration diagram of an embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration of a feedback control system of the embodiment shown in FIG.

[Explanation of symbols]

1 Testing machine body 11 table 12a, 12b columns 13 Cross York 14 Hydraulic actuator 15a, 15b grasping tool 2 Servo valve 3 load cell 4 displacement meter 5 control device 51 Waveform generator 52 PID controller 53 control target 6a, 6b Pressure sensor TP test piece

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tokuaki Komine             1st Nishinokyo Kuwabara-cho, Nakagyo-ku, Kyoto City Stock Association             Inside the Shimadzu factory (72) Inventor Mitsuhiko Araki             80-2 Kamigamokachimachi, Kita-ku, Kyoto-shi (72) Inventor Hidefumi Taguchi             4-8-13-303 Shibahara-cho, Toyonaka-shi, Osaka F term (reference) 2G061 DA03 EA01 EA02 EA05 EB05

Claims (2)

[Claims] 1. An electro-hydraulic servo type material testing machine, comprising: a load mechanism using a hydraulic actuator as a drive source; and a feedback control system for controlling the hydraulic actuator. a differential pressure detecting means for detecting a, the actual the feedback control system during operation the proportional gain K _{P (N),} based on the set proportional gain K _P to _(T) by tuning, the pressure difference during tuning Detection result P
_T , a differential pressure detection result P _N during operation, and a hydraulic oil supply pressure P _S to the hydraulic actuator, and a proportional gain optimization setting means for calculating and automatically changing the setting by the following formula. An electro-hydraulic servo type material testing machine characterized by comprising: K _{P (N)} = K _{P (T)}・ (P _S −P _T ) ^1/2 / (P _S −P _N )
^1/2 2. An electro-hydraulic servo system characterized in that, in place of the differential pressure detecting means according to claim 1, there is provided arithmetic means for converting a detected value of a load acting on the test piece into a differential pressure. Material testing machine.