JP3819620B2 - Control device for material testing machine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a material testing machine control device that performs PI (proportional integration) control of a material testing machine or the like.
[0002]
[Prior art]
2. Description of the Related Art A material testing machine control device that feedback-controls a material testing machine is known. In such a control device for a material testing machine, when the rigidity of the test sample (TP: test piece) is high and the piston cross section of the material testing machine is small, such as ceramics and rock, proportional control ( It is known that when the gain Kp of the term P) is increased, the gain margin at the frequency at which the phase angle of the one-round frequency transfer function is 180 degrees decreases, resulting in an unstable state or oscillation.
Therefore, the gain Kp for proportional (P) control cannot be increased. As a result, the ability to make the error in the feedback system zero is small, and the control is performed in a state where the steady deviation is large.
As described above, an example of a problem when the control is performed in a state where the steady deviation is large will be described.
[0003]
FIG. 3 is a block diagram of a conventional material testing machine controller. In the figure, 1 is a test wave generating unit, 2 is a comparison unit, 4 is a repetitive load testing machine as an example of a material testing machine, 5 is a servo valve, 6 is a hydraulic actuator, 6a is a cylinder, 6b is a piston, and 7 is a load cell. , 8 are contacts, 9 is a test piece, 10 is a differential transformer, 11 is a displacement sensor amplifier, 12 is a P (proportional) controller, and 19 is a load sensor amplifier.
[0004]
The test wave generator 1 is a waveform generator that outputs a target value Ei (t) of the displacement Ec (t). The target value Ei (t) is compared with the displacement Ec (t) output from the displacement sensor amplifier 11 in the comparison unit 2, and the difference signal is used as the error Ee (t) to determine the P (proportional) controller 12. Is input. The output of the P controller 12 whose input signal is amplified by the gain kp is input to the servo valve 5 of the repeated load tester 4, and the servo valve 5 drives the hydraulic actuator 6. The hydraulic actuator 6 has a cylinder 6 a and a piston 6 b, and the piston 6 b applies a load to the test piece 9 via the load cell 7 and the contact 8.
[0005]
The differential transformer 10 is connected to the piston 6b and measures the amount of displacement of the piston 6b. In a state where the contact 8 presses the test piece 9, the displacement amount of the piston 6 b is equal to the displacement amount of the test piece 9. The control mode during the repeated load test by the output of the load sensor amplifier 19 is omitted in this figure. At the time of the repeated load test, the vibration waveform of the weighted load is output as a target value from the test wave generator 1, and the output of the load sensor amplifier 19 is compared with the comparator 2 to perform load feedback control. Here, the constant displacement speed control performed between the contact 8 being brought into contact with the test piece 9 and applying a predetermined pressure will be described. The outputs of the displacement sensor amplifier 11 and the load sensor amplifier 19 are converted into digital data by an A / D converter (not shown).
[0006]
FIG. 4 is an explanatory diagram showing the positional relationship between the piston 6b and the test piece 9 in the conventional material testing machine control device shown in FIG. 4A is an explanatory view showing a state where the contact 8 is separated from the test piece 9, and FIG. 4B is an explanatory view showing a state where the contact 8 is in contact with the test piece 9. FIG. In the figure, parts similar to those in FIG.
[0007]
When the test piece 9 is repeatedly attached to the load testing machine 4, the contact 8 is in a state separated from the test piece 9 as shown in FIG. A waveform having a target value Ei (t) with a constant displacement speed is output from the test wave generator 1 and amplified by the P controller 12 to drive the hydraulic actuator 6 and move the piston 6b downward (in FIG. 3). 4), the contact 8 is brought into contact with the test piece 9, and thereafter, the displacement target value Ei (t) until the load Load reaches the initial target value. Is increased at a constant speed to provide displacement feedback, which is the initial state of the repeated load test.
[0008]
FIG. 5 is a diagram for explaining the operation of the conventional material testing machine control device shown in FIG. 5A is a diagram showing the target value Ei (t), FIG. 5B is a diagram showing the displacement Ec (t), and FIG. 5C is a diagram showing the load Load (t). .
[0009]
As described above, conventionally, since the gain Kp of the P control is not large, the control is performed in a state where the steady deviation is large. Therefore, as shown in FIG. 5A, the displacement Ec (t) output from the displacement sensor amplifier 11 is slightly smaller than the target value Ei (t). Before the contact 8 comes into contact with the test piece 9, the steady deviation appearing in the error Ee (t) is not so large. However, when the contact 8 comes into contact with the test piece 9, since the gain Kp for P control is insufficient, the error Ee (t) increases due to the high rigidity of the test piece 9. As a result, there is a problem that the gradient of the displacement Ec (t) output from the displacement sensor amplifier 11 suddenly decreases at the time of contact. Therefore, it was impossible to control at a constant displacement speed.
[0010]
In general, it is known to perform PI control including integral (I) control in order to compensate for such gain Kp of P control. It is also known to perform PID control with differential control added for additional compensation, but this PID control is substantially PI control. In the PI control, the error Ee (t) is zeroed by integrating and feeding back the error Ee (t) by the I control. In other words, the steady deviation is attempted to be eliminated by increasing the gain of the low frequency signal near the direct current, such as the steady deviation, and performing feedback control.
[0011]
However, in the servo by software, such as DDC (Direct Digital Control) in which the computer directly functions as a control device, the integral control element has an infinite gain with respect to the frequency signal near DC or DC, unlike the analog system. It shows the ideal characteristic of becoming large. Therefore, it is easy to focus the steady deviation to zero. On the other hand, in the initial state at the start of operation when the hydraulic servo loop system is not established, there is no target value to converge, so the output of the integral control element changes in the direction of divergence to positive or negative infinity and output Has the problem of becoming saturated. Therefore, in the repeated load test apparatus as described above, the PI control cannot be performed simply, and the influence of the steady deviation as described with reference to FIGS. 5 (a) and 5 (b) can be eliminated. could not.
[0012]
[Problems to be solved by the invention]
The present invention has been made to solve the above-described problems, and provides a control device for a material testing machine that can eliminate a steady-state deviation by inserting an integral control element into a feedback loop system without causing abnormal operation. It is intended to provide.
[0013]
[Means for Solving the Problems]
In the first aspect of the present invention, the material testing machine control in which the control element outputs the operation amount of the actuator of the material testing machine based on the error between the feedback value output from the sensor of the material testing machine and the target value. In the apparatus, the apparatus has function switching means for switching the function of the control element, and the function switching means performs feedback control in a state where the control element is a proportional control element, and after the feedback system is established, the control element At the same time that the integration control element is inserted into the control element, a value obtained by reducing the target value by the error immediately before the integration control element is inserted into the control element is set as a new target value, and immediately before the integration control element is inserted. A value obtained by adding the output value of the control element to the output of the control element is used as a new output of the control element.
Therefore, it is possible to eliminate the steady deviation by inserting the integral control element into the feedback loop system without causing abnormal operation.
[0014]
According to a second aspect of the present invention, in the control apparatus for a material testing machine according to the first aspect, in the state having the first and second storage means and the control element as a proportional control element, The first storage means stores the error value, the second storage means stores the output value of the control element, and when the integral element is inserted into the control element by the function switching means, A value obtained by lowering the target value by the value read from the first storage means is used as a new target value, and the value read from the second storage means is added to the output of the control element. The new output of the control element.
Therefore, when the integration control element is inserted, a compensation value for preventing the output of the control element from changing greatly can be easily obtained.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a block configuration diagram of an embodiment of a control apparatus for a material testing machine according to the present invention. In the figure, parts similar to those in FIG. 3 is a control element, 13 is a switch, 14 is an I (integration) controller, 15 is a switch, 16 is an adder, and 17 and 18 are memories.
[0016]
The error Ee (t) output from the comparison unit 2 is input to the control element 3. In the control element 3, the output of the P (proportional) controller 12 becomes the input of the switch 13. One output of the switcher 13 becomes one input of the switcher 15, and the other output of the switcher 13 becomes an input of the I controller 14. The output of the I controller 14 becomes the other input of the switch 15. The output of the switch 15 is supplied to an adder 16, where it is added to the output of a memory 17 to be described later to become the output of the control element 3 and input to the servo valve 5 of the repeated load tester 4.
[0017]
The memory 17 sequentially writes and stores the output Es (t) of the control element 3 before switching the switching devices 13 and 15, and after switching, reads the last stored value and outputs it to the adder 16. . The output of the displacement sensor amplifier 11 is output to the comparator 2. The memory 18 sequentially writes and stores the error Ee (t), which is the output of the comparator 2, before switching the switching units 13 and 15, and after switching, reads the last stored value to generate a test wave. By outputting to the unit 1, the target value Ei (t) is controlled. Switching between the switches 13 and 15 and switching between writing and reading functions of the memories 17 and 18 are performed in a short time in conjunction with each other.
[0018]
When the hydraulic pressure is applied, in order to perform P control, the switch 13 is directly connected to the switch 15, the output of the P controller 12 is used as the output of the control element 3, and the I controller 14 is removed. The memory 17 performs the operation of writing the output Es (t) of the control element 3, that is, the output of the P controller 12, and the memory 18 performs the operation of writing the output of the comparator 2, that is, the output of the error Ee (t). . The write operation of each of the memories 17 and 18 is performed at predetermined processing timings, and the previous write data is erased each time writing is performed. That is, it is updated to the latest value. Note that nothing is read from each of the memories 17 and 18, or a zero value is read.
[0019]
When the switching devices 13 and 15 are controlled to be switched at time t ₀ , the output of the switching device 13 is output to the I controller 14, and the output of the I controller 14 is output to the adder 16 via the switching device 15. And the output of the control element 3. The memory 17 reads the latest output data Es (t ₀ ) of the control element 3 immediately before switching and outputs it to the adder 16. In addition, the memory 18 reads the error Ee (t ₀ ) of the comparator 2 immediately before switching and outputs it to the test wave generator 1. The read outputs of the memories 17 and 18 are held as they are even after switching.
[0020]
As described above, after the hydraulic pressure is turned on, at time t ₀ after a predetermined time sufficient for configuring the hydraulic servo system has elapsed and the servo system is configured, the switches 13 and 15 are switched to switch I. The controller 14 is inserted. In this way, the output of the control element 3 is prevented from diverging. However, simply inserting the I controller 14 causes a problem that the piston 6b of the actuator 6 moves suddenly at the time of insertion, which causes an undesirable behavior as a material testing machine.
[0021]
FIG. 2 is a diagram for explaining the operation of the embodiment of the control device for a material testing machine of the present invention. 2A is a diagram showing the target value Ei (t), FIG. 2B is a diagram showing the output Es (t) of the control element, and FIG. 2C is a diagram showing the displacement Ec (t). FIG. 2 and FIG. 2D are diagrams showing the load Load (t).
As shown in FIG. 2 (a), after the start of hydraulic pressure application (t = 0), the displacement target value Ei (t) is linearly increased to perform P control with a constant displacement speed. During this time, the current displacement amount Ec (t) output from the displacement sensor amplifier 11 increases ideally at a value slightly below this target value. Since it is P control, the steady-state deviation from the target value Ei (t) is small but cannot be ignored. After the hydraulic pressure is applied, P control with a small gain Kp is performed to form a closed loop. During this time, even if the entire loop is balanced as a proportional control system, there is a non-zero deviation as the error Ee (t).
[0022]
In this state, when the I controller 14 is inserted in the subsequent stage of the P controller 12 by switching the switches 13 and 15 at time t ₀ , the non-zero error Ee (t ₀ ) is integrated. As a result, the output Ec (t) of the displacement sensor amplifier 11 is controlled to increase. Then, when the balance is achieved, the error Ee (t) = 0. This means that when the I controller 14 is inserted, the piston 6b of the actuator 6 moves suddenly in accordance with the error Ee (t ₀ ).
[0023]
For this purpose, the input of the I controller 14 is set to zero when the switches 13 and 15 are switched. If the error Ee (t) = 0, even if the P controller 12 multiplies zero by Kp, the input of the I controller 14 is zero and the output of the I controller 14 does not change. In order to set the error Ee (t) = 0, the output Ec (t) of the displacement sensor amplifier 11 is left as it is, and the target value Ei (t) is controlled. That is, since Ee (t) = Ei (t) −Ec (t), in order to make Ee (t) zero, the test wave generator 1 uses the target value Ei (t) (Ei on the left side of the following equation). (T)) with respect to Ei (t) before switching (Ei (t) on the right side of the following equation)
Ei (t) = Ei (t) −Ee (t ₀ )
And output to the comparator 2. That is, the target value Ei (t) so far may be DC shifted by the DC component Ee (t ₀ ).
In FIG. 1, in order to realize this operation, the memory 18 sequentially writes the value of the error Ee (t) before switching, reads this value at the time of switching, and sets the value of the error Ee (t ₀ ) immediately before switching. Is output to the test wave generator 1, and the target value Ei (t) shifted from the test wave generator 1 is output.
Instead, the test wave generator 1 may leave the test wave generator 1 as it is as the target value Ei (t) through a subtracter (not shown) and output it to the comparator 2. This subtracter outputs the output of the test wave generator 1 as it is before switching, but subtracts and outputs the output Ee (t _o ) of the memory 18 after switching.
[0024]
Problems on the input side of the I controller 14 are solved by the above-described processing. However, as shown in FIG. 2B, when the output Es (t) of the control element is viewed, the initial value of the output of the I controller 14 is zero. Therefore, the I controller 14 is inserted for Es (t ₀ ) = Kp · Ee (t ₀ ) that existed in the output Es (t ₀ ) of the control element 3 immediately before the I controller 14 is inserted. It becomes zero by this.
Since the output Es (t) of the control element is applied to the servo valve 5, the feedback loop system is balanced. Therefore, if this value is not maintained even after the switching units 13 and 15 are switched, the hydraulic actuator The 6 piston 6b suddenly moves greatly.
Therefore, before switching the switching units 13 and 15, the memory 17 sequentially writes the output Es (t) = Kp · Ee (t) of the control element 3, which is also the output of the P controller, and reads this when switching. , Es (t ₀ ) = Kp · Ee (t ₀ ) immediately before switching is output to the adder 16. As a result, the output of the control element 3 can be prevented from changing greatly even at the switching time t ₀ of the switches 13 and 15. As a result, the I controller 14 can be smoothly inserted without a shock.
[0025]
When setting the integral constant term in the I controller 14, the output value of the memory 17 may be controlled to be the integral constant term of the I controller 14 instead of the adder 16. . In the above description, the target value is increased with a constant gradient from the beginning of the hydraulic pressure application. Initially, the target value is set to 0 until the servo system is configured by setting the target value to 0 and supplying the hydraulic pressure. You may leave it.
[0026]
As described above, the I controller 14 can be inserted into the feedback loop system without causing an abnormal operation. As a result, the displacement speed is constant before and after the contact 8 contacts the test piece 9. The piston 6b and the contact 7 can ideally be moved at a constant speed until the initial state of the repeated test is maintained.
In the above description, the case where the displacement speed until the initial state of the repeated test is controlled to be constant has been described. However, since the I controller 14 is inserted also when the load feedback control is performed by outputting a periodic waveform from the test wave generator 1 during the repeated test performed thereafter and performing the load feedback control, the target value Error can be made zero, and the control accuracy is improved.
In general, in a material testing machine control device that controls a material testing machine by configuring a feedback loop system, the steady deviation can be made zero without causing abnormal operation. As a result, various problems can be solved in addition to a decrease in control accuracy resulting from the steady-state deviation not being zero.
[0027]
【The invention's effect】
As is apparent from the above description, the present invention has an effect that a steady deviation can be eliminated by inserting an integral control element into the feedback loop system without causing abnormal operation.
[Brief description of the drawings]
FIG. 1 is a block configuration diagram of an embodiment of a control apparatus for a material testing machine according to the present invention.
FIG. 2 is a diagram for explaining the operation of the embodiment of the control device for a material testing machine of the present invention.
FIG. 3 is a block diagram of a conventional material testing machine controller.
4 is an explanatory diagram showing a positional relationship between a piston 6b and a test piece 9 in the conventional material testing machine control device shown in FIG.
5 is a diagram for explaining the operation of the conventional material testing machine control device shown in FIG. 3; FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Test wave generation part, 2 Comparison part, 3 Control element, 4 Repeat load testing machine, 5 Servo valve, 6 Hydraulic actuator, 7 Load cell, 8 Contact, 9 Test piece, 10 Differential transformer, 11 Displacement sensor amplifier, 12 P controller, 13, 15 selector, 14 I controller, 16 adder, 17, 18 memory, 19 load sensor amplifier

Claims (2)

In the material testing machine control device in which the control element outputs the operation amount of the actuator of the material testing machine based on the error between the feedback value output from the sensor of the material testing machine and the target value
Having function switching means for switching the function of the control element;
The function switching means performs feedback control in a state where the control element is a proportional control element,
After the feedback system is established, the integral control element is inserted into the control element,
While reducing the target value by the value of the error immediately before inserting the integral control element into the control element, a new target value,
A value obtained by adding the output value of the control element immediately before inserting the integral control element to the output of the control element is set as a new output of the control element.
A control device for a material testing machine. Having first and second storage means;
In a state where the control element is a proportional control element, the first storage means stores the error value, the second storage means stores the output value of the control element, and the function switching means When an integral element is inserted into the control element by the above, a value obtained by lowering the target value by a value read from the first storage means is set as a new target value, and from the second storage means 2. The control device for a material testing machine according to claim 1, wherein the read value is added to the output of the control element to obtain a new output of the control element.

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