JPH07128207A - Material testing machine - Google Patents

Abstract

(57) [Abstract] [Purpose] To improve the frequency response characteristics of a material testing machine by a simple and inexpensive method. [Structure] Normally, the command value is set momentarily along the waveform of the command value of the physical quantity to be loaded on the test piece, and the set command value (command signal) of the set physical quantity and the detected value are detected from the loaded test piece. Feedback control is performed so that the detected value always matches the command value based on the detected value (control amount) of the physical quantity. The command value of the physical quantity is increased at time t2 when the waveform of the command value of the physical quantity reaches the maximum portion, and the command value of the physical quantity is decreased at time t3 when the waveform becomes the minimum portion, and the increased or decreased command value and the load. Feedback control is performed on the basis of the detected value of the physical quantity detected from the tested sample.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a material testing machine, and more particularly to a material testing machine which improves frequency response characteristics of the testing machine employing digital feedback control.

[0002]

2. Description of the Related Art Conventionally, an electrohydraulic servo type material testing machine to which a feedback control system as shown in FIG. 4 is applied is known. The feedback control system shown in FIG. 4 is a servo system that causes the control amount to follow a command value that changes with time of the physical amount that is loaded on the sample, and also performs operational amplification processing by a microcomputer (hereinafter referred to as CPU). This is a digital control system. Here, the physical quantity applied to the specimen includes load and displacement. A digital command signal of a command value waveform (hereinafter referred to as a test waveform) such as load or displacement is converted into an analog command signal by the D / A converter 3 and output to the servo valve 4a of the actuator 4. The servo valve 4a opens and closes the valve in accordance with the analog command signal, controls the flow rate of the pressure oil to the actuator 4, and loads the test piece 5.

On the other hand, the load and displacement applied to the specimen 5 are detected by a detector 6 such as a load cell or a displacement gauge, amplified by an amplifier 7, and then converted into a digital signal by an A / D converter 8. . This digital signal is compared with the digital command signal in the adder 1 as a digital feedback signal to obtain the control deviation. The operational amplifier 2 performs operational amplification processing on this control deviation, and the test object 5 to be controlled
The operation amount of the actuator 4 that loads is calculated. Here, the operational amplification processing means processing such as well-known PID control for adjusting the response and control accuracy of the feedback control system. The calculated operation amount is converted into an analog signal by the D / A converter 3 and output to the servo valve 4a. The servo valve 4a opens and closes the valve in accordance with the operation amount, and changes the flow rate of the pressure oil to the actuator 4. The specimen 5 is controlled and loaded. That is, the control amounts such as the load and the displacement applied to the sample 5 by the feedback control are made to follow those target values.

Here, the CPU executes the control program shown in FIG. 5 at predetermined time intervals, and the D / A converter 3 and A / D
The converter 8 and the adder 1 are controlled to perform the operational amplification process. First, in step S1, the control amounts such as load and displacement detected by the detector 6 and amplified by the amplifier 7 are A / D converted by the A / D converter 8, and in the subsequent step S2, a test waveform command is issued from the memory. Read the signal. In step S3, the adder 1 calculates the control deviation between the command signal and the detection signal of the control amount, and further performs the operation amplification process on this control deviation to calculate the operation amount. D in step S4
The / A converter 3 converts the manipulated variable into an analog signal and outputs it to the servo valve 4a of the actuator 4.

[0005]

However, in the conventional material testing machine, when the frequency of the test waveform becomes high, the controlled variable cannot follow the test waveform.
In the case of the triangular wave as shown in (a), the control amount corresponding to the maximum and minimum parts of the waveform (here, the apex of the triangular wave) becomes dull as shown in FIG. The problem is that

In order to solve such a problem, it is considered to improve the frequency response characteristic of the control system by using an actuator having a high frequency response performance, but such an actuator is expensive and a material testing machine is used. This is not preferable because it increases the cost.

An object of the present invention is to provide a material testing machine having improved frequency response characteristics by a simple and inexpensive method.

[0008]

The present invention will be described with reference to FIG. 1 showing an embodiment. In the present invention, a load means 20e for loading a physical quantity on a specimen 21 and a load means 20e.
The physical quantity detection means 22 and 23 for detecting the physical quantity of the test piece 21 loaded by e, the storage means 30m for storing the waveform of the command value of the physical quantity loaded on the test piece 21, and the storage means 30m. A maximum / minimum calculating means 30 for calculating the maximum and minimum parts of the waveform of the command value of the physical quantity;
The waveform of the command value of the physical quantity is read from the storage means 30m, and the command value of the physical quantity is set every moment along the waveform of the command value, and the waveform of the command value of the physical quantity is the maximum calculated by the maximum / minimum calculating means 30. Command value setting means 30 that increases the command value of the set physical quantity when it becomes a part and decreases the command value of the set physical quantity when it becomes a minimum part, and the command value of the physical quantity set by this command value setting means 30 and the detection of the physical quantity. Control means 3 for performing feedback control based on the detected value of the physical quantity detected by the means 22 and 23.
And 0, thereby achieving the above object.

[0009]

In general, the command value is set every moment along the waveform of the command value of the physical quantity to be loaded on the test piece 21, and the command value of the set physical quantity and the physical quantity detected from the loaded test piece 21 are detected. Feedback control is performed so that the detected value always matches the command value based on the value and. Then, when the waveform of the command value of the physical quantity reaches the maximum portion, the command value of the physical quantity is increased, and when it becomes the minimum portion, the command value of the physical quantity is decreased, and the increased or decreased command value and the detected specimen 21 are detected. Feedback control is performed based on the detected value of the physical quantity. As a result, even if the frequency of the waveform of the command value becomes high, the physical quantity of the specimen loaded at the maximum and minimum portions of the waveform does not become blunt, and the frequency of the material testing machine is simple and inexpensive. The response characteristics can be improved.

Incidentally, in the section of means and action for solving the above problems for explaining the constitution of the present invention, the drawings of the embodiments are used for the purpose of making the present invention easy to understand. It is not limited to.

[0011]

FIG. 1 is a functional block diagram showing the structure of an embodiment. In the figure, 20 is a main body of the tester, and a column 20g
A crosshead 20b attached to the crosshead 20b so as to be vertically movable, an upper jig 20c attached to the crosshead 20b via a load cell 22, an actuator 20e for load loading installed in a base 20d, and the actuator 2
The lower jig 20f attached to the movable part of 0e is provided, and the test piece 21 is interposed between the lower jig 20f and the upper jig 20c. Reference numeral 23 is an operation transformer for detecting the stroke of the actuator 20e, that is, the displacement under load.

Reference numeral 30 denotes a CPU having peripheral components such as a memory 30m, which executes a control program described later to perform feedback control. The load cell 22 is connected to the CPU 30 via an amplifier 31 and an A / D converter 32, and the operating transformer 23 is connected to the CPU 30 via an amplifier 33 and an A / D converter 34. The CPU 30 also
The servo valve 20e1 of the actuator 20e is connected via the D / A converter 35 and the amplifier 36. The memory 30m of the CPU 30 stores test waveforms such as a sine wave, a triangular wave, a rectangular wave, and a ramp wave as digital values for each unit time, and reads them for each unit time according to the test conditions of the test piece 21. And output as a command signal.

Next, the overall operation of the material testing machine of this embodiment will be described. Prior to the test, the physical quantity to be loaded on the test piece 21 according to the test condition of the test piece 21 and the waveform of the command value of the physical quantity such as a sine wave, a triangular wave, a rectangular wave, a ramp wave (hereinafter referred to as a test waveform) The type, amplitude, frequency, etc. are set by an input device (not shown). In this embodiment, load and displacement will be described as an example of physical quantities to be loaded on the test piece 21. When the test starts, the CPU 30
The load / displacement digital command signal of the set test waveform is output to the D / A converter 35. This digital command signal is converted into an analog signal by the D / A converter 35, amplified by the amplifier 36, and supplied to the servo valve 20el of the actuator 20e. Servo valve 20e
1 controls the amount of oil pressure-fed to the actuator 20e from a hydraulic power source (not shown) according to this analog command signal, whereby the actuator 20e loads the sample 21 via the lower jig 20f.

The CPU 30 applies the load and displacement applied to the test piece 21 to the load cell 22 and the operating transformer 23.
Respectively, and A / D converters 32 and 34 perform A / D conversion to input digital feedback signals of load and displacement. Then, the set load or displacement command signal is compared with each feedback signal, the control deviation is calculated, the feedback amplification calculation amplification processing is performed, and the operation amount of the actuator 20e, which is the operation unit, is calculated. The calculated manipulated variable is converted into an analog signal by the D / A converter 35, amplified by the amplifier 36, and output to the servo valve 20e1 of the actuator 20e. The servo valve 20e1 controls the amount of oil pressure-fed to the actuator 20e from a hydraulic source (not shown) according to the operation amount signal, and the actuator 20e loads the test piece 21 via the lower jig 20f. Hereinafter, such an operation is repeated, the test piece 21 is loaded according to the set test waveform, and the test is performed.

FIG. 2 shows a program for detecting the time when the test waveform reaches the maximum and minimum portions, and FIG. 3 shows a feedback control program. The operation of the embodiment will be described with reference to these flowcharts. In this embodiment, a test waveform of a triangular wave as shown in FIG. 6A will be described as an example, and the maximum and minimum of the triangular wave will be referred to as apexes. C
The PU 30 executes the vertex arrival time detection program shown in FIG. 2 at predetermined time intervals. First, in step S11, the test waveform selected by the input device from the memory 30m is prefetched for a predetermined time from the current time. For example,
As shown in FIG. 6A, assuming that the current time is t1, the test waveform data from the current time t1 to time t4 after a predetermined time T is read. The pre-read test waveform is differentiated in step S12, and it is determined in step S13 whether the differential value is 0 or not. If the value obtained by differentiating the test waveform is 0,
It is assumed that the point is the maximum or minimum, that is, the apex of the triangular wave, and the process proceeds to step S14 to calculate the apex part arrival time,
It is stored in the memory 30m. In the example shown in FIG. 6A, time t2 and time t3 are times at which the triangular test waveform reaches its apex. If the differential value of the test waveform is not 0 in step S13, it is determined that there is no large peak in the test waveform, and the process ends.

Here, the predetermined value K, which is the criterion for determining the apex of the test waveform, is changed according to the set frequency of the test waveform. That is, the higher the set frequency of the test waveform, the more difficult the control system is to follow the test waveform. Therefore, the higher the set frequency of the test waveform, the smaller the predetermined value K and the lower the criterion for determining the apex. The arrival time of the apex may be a time earlier than the apex of the actual test waveform by a predetermined time, and the predetermined time may be changed according to the set frequency of the test waveform. Further, the execution time interval of the vertex arrival time detection program shown in FIG. 2 and the pre-reading time T of the test waveform data may be determined as an optimum time depending on the type, amplitude, frequency, etc. of the set test waveform.

The CPU 30 executes the feedback control program shown in FIG. 3 at predetermined time intervals. In step S21, the load of the sample 21 detected by the load cell 22 is converted into a digital signal by the A / D converter 32 and input, and the displacement of the sample 21 detected by the operating transformer 23 is A / D converted. The signal is converted into a digital signal by the device 33 and input. In a succeeding step S22, the command value of the present time of the set test waveform is read from the memory 30m. In step S23, it is determined whether or not the vertex arrival time stored in the memory 30m is reached. If the vertex arrival time is reached, the process proceeds to step S24, and if not, the process proceeds to step S26.

When the current time is the peak arrival time stored in the memory 30m, the peak value of the load waveform of the load and the displacement detected in step S21 and the area per unit time are detected in step S24. Continued Step S25
In, the peak value of the detected load waveform and the area per unit time are compared with the peak value of the test waveform and the area per unit time respectively, and the amplitude of the entire test waveform is determined based on the comparison result, The amplitude of the peak portion is increased at a constant rate as compared with the other portions. At this time, for example, if the area of the load waveform per unit time is smaller than the area of the test waveform, it is determined that the control system is distorted, the amplitude of the entire test waveform is increased, and the amplitude of the apex is decreased to reduce distortion. To eliminate. The rate of increase in the amplitude of the apex of the test waveform may be changed depending on the type, amplitude, frequency, etc. of the test waveform, or may be changed between the true apex and its periphery.

In step S26, a control deviation between the amplitude of the determined load or displacement test waveform, ie, the command value, and the detected value of the load or displacement, ie, the feedback value, detected in step S21 is calculated, and this control deviation is calculated. The operation amount of the actuator is calculated by performing the operational amplification process on the. In a succeeding step S27, the digital signal of the calculated manipulated variable is converted into an analog signal by the D / A converter 35, and is amplified by the amplifier 36 to be servo valve 20el.
Output to.

The actuator 20e is shown in FIG.
As shown by the broken line in (a), it is driven by the command signal whose amplitude is increased at the apex portion of the test waveform, and conventionally, as shown in FIG.
As shown in FIG. 6C, the load waveform of the test piece 21, which is blunt at the apex as shown in FIG.
The original test waveform shown by the solid line in (a) is approximated, and the frequency response of the control system is improved.

In the above-mentioned embodiment, the load and the displacement are taken as an example of the physical quantity to be applied to the sample, but the physical quantity to be applied to the sample is not limited to the example.

In the structure of the above embodiment, the actuator 20e serves as a load means, the load cell 22 and the operating transformer 23 serve as a physical quantity detection means, the memory 30m serves as a storage means, and the CPU 30 serves as a maximum / minimum calculation means, a command value setting means and a control. Each means is configured.

[0023]

As described above, according to the present invention, the command value of the physical quantity is increased when the waveform of the command value of the physical quantity becomes the maximum portion, and the command value of the physical quantity is decreased when it becomes the minimum portion,
Since the feedback control is performed based on the increased or decreased command value and the detected value of the physical quantity detected from the loaded specimen, even if the frequency of the command value waveform becomes high, the maximum part of the waveform Further, the physical quantity of the specimen loaded in the minimum portion does not become dull, and the frequency response characteristics of the material testing machine can be improved by a simple and inexpensive method.

[Brief description of drawings]

FIG. 1 is a functional block diagram showing the configuration of an embodiment.

FIG. 2 is a flowchart showing a vertex arrival time detection program.

FIG. 3 is a flowchart showing a feedback control program.

FIG. 4 is a control block diagram showing a configuration of a conventional material testing machine.

FIG. 5 is a flowchart showing a calculation process of a conventional material testing machine.

FIG. 6 is a time chart showing the command signal of the test waveform and the control amount applied to the test piece.

[Explanation of symbols]

 20 Testing machine main body 20e Actuator 20el Servo valve 20b Crosshead 20c Upper jig 20d Base 20g Support 22 Load cell 23 Working transformer 30 Microcomputer 30m Memory 31, 33, 36 Amplifier 32, 34 A / D converter 35 D / A conversion vessel

Claims (1)

[Claims] 1. A load means for loading a physical quantity on a specimen, a physical quantity detecting means for detecting a physical quantity of the specimen loaded by the loading means, and a waveform of a command value of a physical quantity to be loaded on the specimen. Storage means, a maximum / minimum calculating means for calculating the maximum and minimum portions of the waveform of the command value of the physical quantity stored in this storage means, and the waveform of the command value of the physical quantity read from the storage means While setting the command value of the physical quantity every moment along the waveform of, the command value of the set physical quantity is increased when the waveform of the command value of the physical quantity becomes the maximum value calculated by the maximum / minimum calculation means, and the minimum value is increased. Command value setting means for decreasing the set command value of the physical quantity, and the command value of the physical quantity set by the command value setting means and the physical quantity detected by the physical quantity detecting means. Material testing machine, characterized in that it comprises a control means for performing feedback control on the basis of the detected value