JP4123099B2 - Material testing machine - Google Patents

Description

  The present invention relates to a material testing machine using an electromagnetic force actuator, and more particularly to a material testing machine that performs PID feedback control of an electromagnetic force actuator.

  In material testing machines that perform fatigue strength tests by applying an arbitrary waveform load (test force) to the test piece, electrohydraulic actuators are generally used as load actuators, but control of the load (test force) In recent years, material testing machines using electromagnetic force actuators have become widespread in order to further improve accuracy.

  In this electromagnetic force actuator, a magnetic circuit is formed by a core, a permanent magnet, and a yoke, a coil is wound around a bobbin that is movable with respect to the core, and a driving current is supplied to the coil. Is generated.

  For the control when the electromagnetic force actuator is used in the material testing machine, PID feedback control is usually used as in the case of the electrohydraulic actuator.

  PID feedback control is one of feedback control methods for controlling a deviation (control deviation) between a target signal and a response signal to be zero by feeding back a response signal (displacement signal or load signal) to the target signal. The feedback gain is determined by combining the proportional component (P), the integral component (I), and the differential component (D) with respect to the deviation at appropriate ratios, and a signal obtained by multiplying the deviation by the feedback gain is fed back as a control signal. Therefore, optimal control is performed. (For example, refer to Patent Document 1).

  In PID feedback control used for controlling the actuator of the material testing machine, the PID ratio is set so that overshoot does not occur in order to prevent the specimen from being destroyed by the overshoot phenomenon.

  FIG. 2 is a block diagram illustrating a schematic configuration of a control system of a conventional material testing machine using an electromagnetic force actuator that performs PID feedback control.

  This material testing machine includes an electromagnetic force actuator 61 that applies a load (test force) to a test piece, a load sensor 62 that detects a load applied to the test piece, and a test machine main body 60 that includes a displacement sensor that detects the displacement of the test piece. And a target signal generating unit 70 that generates a target signal of a load applied to the test piece, and a feedback control unit 80 that generates and outputs a drive signal of the electromagnetic force actuator 61 of the tester main body 60.

  The feedback control unit 80 adds a point 81 for obtaining a deviation (control deviation) between the target signal from the target signal generation unit 70 and the detection signal from either the load sensor 62 or the displacement sensor 63, and PID control based on the deviation. A PID control signal output unit 82 that generates and outputs a signal, and a power amplifier 83 that amplifies the PID control signal and applies it to the electromagnetic actuator 61 to drive the electromagnetic actuator 61.

The PID control signal output unit 82 outputs a PID control signal so that the deviation at the addition point 81 approaches zero, and the electromagnetic current actuator 61 is supplied with a coil current from the power amplifier 83 that has received the PID control signal. Drive.
JP 2000-180328 A

  In the case of electromagnetic force type actuators, when the actuator position is controlled in a no-load stationary state, almost no current is required to flow through the coil (only current that supports the weight of the actuator is sufficient). The same control as that of the electrohydraulic actuator can be performed only by performing normal PID feedback control.

  However, when a test piece is actually attached and a load is applied thereto, it is necessary to continue supplying a coil current for continuously applying a load to the test piece even in a stationary state.

  However, the normal PID feedback control outputs a control signal so that the deviation between the target signal and the response signal approaches zero as described above. If the deviation becomes zero, the control signal also becomes zero. The drive current to the coil of the actuator is also zero, that is, the load (test force) becomes zero, and no load is applied.

  In order to solve this contradiction, an integral component (I) is provided when control by PID feedback control is performed with an electromagnetic force actuator. That is, among the proportional component (P), the integral component (I), and the differential component (D), the proportional component (P) and the differential component (D) have a great influence on the instantaneous correction when there is a sudden change in the deviation. However, the integral component (I), on the contrary, has a property of affecting a gentle correction for a steady deviation. For this reason, the gain (time constant) of the integral component (I) is increased to gradually reduce the deviation to zero. In other words, the balance between the slow correction of the integral component (I) and the correction of the steep proportional component (P) and the differential component (D) can be used to hold the position of the actuator so that the feedback gain does not become zero. The test is conducted by driving the actuator at a low speed.

  However, when the frequency of the target signal is increased, that is, when the test speed is increased, the slow correction by the integral component (I) cannot be followed, so that the waveform response is deteriorated, and the target value can be reached by PID feedback control. In some cases, it will disappear.

  If the gains of proportional component (P) and differential component (D) are increased relative to the gain of integral component (I) in order to reach the target value, problems such as overshoot and hunting will occur and the test piece will be mistakenly There is also a risk of damage.

  Therefore, the present invention improves the conventional PID feedback control in a material test using an electromagnetic force actuator, and thereby performs a feedback control in which the waveform response is good even when the test speed is increased. The purpose is to provide a machine.

The material testing machine of the present invention made to solve the above problems includes an electromagnetic force actuator that applies a load to a test piece, a target signal generator that provides a target signal that is a control target of the electromagnetic force actuator, and a test piece A load sensor that detects a load applied to the load signal and outputs a load signal; a PID control signal output unit that outputs a PID control signal based on a deviation between the target signal and the load signal; and a constant added signal based on the load signal And an addition signal output unit that outputs the PID control signal multiplied by the ratio K (0 <K <1), and drives the electromagnetic actuator based on the sum signal of the PID control signal and the addition signal. I am doing so.

  According to this material testing machine, a target signal having a desired waveform, amplitude, and frequency such as a rectangular wave, a sine wave, and a triangular wave is output from the target signal generator according to the test purpose, and a load applied to the test piece from the load sensor. Is detected and a load signal is output. The PID control signal output unit outputs a PID control signal based on the deviation between the target signal and the load signal. On the other hand, the addition signal output unit outputs an addition signal based on the load signal. This addition signal is a signal obtained by reducing the load signal. For example, a signal obtained by multiplying the load signal by a certain ratio K (0 <K <1) is used.

  Then, the electromagnetic force actuator is driven based on the sum signal obtained by adding the addition signal to the PID control signal. That is, apart from the PID control signal, a part of the load signal is positively fed back so as not to hunt, so that a part of the deviation compensated only by the PID control signal is compensated by the addition signal.

  Therefore, the deviation that must be compensated by the PID control signal is reduced, the rise of the response waveform is improved, and the burden of correction by the integral (I) component is reduced, so that the response waveform can be improved.

  The material testing machine further includes a displacement sensor and a switch for selecting either the displacement signal or the load signal, and is based on a deviation between the target signal and either the load signal or the displacement signal selected by the switch. Then, a PID control signal may be output, and an addition signal may be added to the PID control signal to obtain a sum signal.

  According to this, not only the load feedback control based on the load signal but also the control similar to the case where a load load is applied in the displacement feedback control based on the displacement signal can be performed by selecting the switch.

  According to the material testing machine of the present invention, by adding the addition signal from the addition signal output unit to the PID control signal, even in the case of a material test with a high test speed, the control followability is improved and the response waveform is good. A test can be performed.

  In addition, since the response waveform is improved by feeding back the actual load (test force), the runaway phenomenon may occur even when there is no load or the test piece breaks during the test and the load becomes zero. It does not easily occur and does not adversely affect the control.

  Hereinafter, the material testing machine of this invention is demonstrated using drawing.

  FIG. 1 is a diagram showing a configuration of a material testing machine using an electromagnetic force actuator according to an embodiment of the present invention. This material testing machine includes a testing machine main body 10 that applies a load to a test piece and a control system that controls the testing machine. The control system includes a target signal generating unit 30 that generates a target signal of a load to be applied to the test piece, and a feedback control unit 50 that generates a drive signal for the electromagnetic force actuator 12 of the testing machine main body unit 10.

  The testing machine main body 10 has an electromagnetic force actuator 12 supported by a frame 11. The electromagnetic force actuator 12 can drive the piston rod 13 in the vertical direction. That is, in the electromagnetic force actuator 12, a cylindrical bobbin (not shown), a coil wound around the bobbin, and a magnetic circuit for forming a magnetic field (B) at the coil position are formed, and the bobbin follows the central axis of the bobbin. The piston rod 13 is fixed in the vertical direction.

  By causing a drive current (A) to flow through this coil, a thrust (F) is generated in the bobbin, and the vertical thrust is transmitted to the piston rod 13 fixed to the bobbin.

  When the length of the coil is L, the thrust F is expressed by the following equation.

F = A ・ B ・ L
That is, a thrust (F) proportional to the coil current (A) is transmitted to the piston rod 13.

  Further, a displacement sensor 14 is attached to the frame 11, and the displacement sensor 14 detects the displacement of the piston rod 13 (displacement of the upper end of the rod) and outputs it to the feedback control unit 50.

  Below the piston rod 13 is a test piece TP placed on the test jig 15, and comes into contact with the test piece TP when the piston rod 13 is lowered. When the piston rod 13 and the test piece TP are in contact, the displacement of the piston rod 13 and the displacement of the test piece TP coincide with each other. Therefore, the output signal of the displacement sensor 14 in the contact state represents the displacement of the test piece TP. It will be. Needless to say, the shape of the test piece is various, and the test jig 15 can have various shapes and structures depending on the shape of the test piece.

  A load sensor 16 (for example, a load cell) is provided in the vicinity of the lower end of the piston rod 13, and the load sensor 16 detects the load load and outputs it to the feedback control unit 50.

  The target signal generating unit 30 has a known setting unit (not shown) and a signal forming circuit for setting a target, and needs a waveform, amplitude, frequency, displacement, average value of load, etc. according to the purpose of the material test. By setting various information, a target signal corresponding to the setting information can be output.

  The feedback control unit 50 amplifies and outputs the load signal detected by the load sensor 16, the displacement amplifier 52 that amplifies and outputs the displacement signal detected by the displacement sensor 14, and the load from the load amplifier 51. The deviation (control deviation) between the load signal or the displacement signal and the switch 53 for selectively extracting either the signal or the load signal from the displacement amplifier 52 and the target signal supplied from the target signal generator 30 is calculated. A PID control signal output unit that calculates the gain of each of P, I, and D based on the added point 51 and the calculated deviation, and outputs a PID control signal by calculating a feedback gain by combining them at a predetermined ratio set in advance 55, an add signal that multiplies the load signal from the load amplifier 51 by a coefficient K (0 <K <1) as a gain. The signal output unit 58 positively feeds back the addition signal to the PID control signal, a second addition point 56 for calculating the sum signal of the PID control signal and the addition signal, and the sum signal calculated at the second addition point 56 is amplified. The power amplifier 57 outputs a coil current of the electromagnetic force actuator 12.

  Next, the control operation by the feedback control unit 50 will be described. When the load feedback control or the displacement feedback control is selected, the switch 53 is manually or automatically switched by the control system, and either the load signal from the load amplifier 51 or the displacement signal from the displacement amplifier 52 is selected. It is sent to the addition point 54.

  At the addition point 54, a deviation (control deviation) is calculated by negatively feeding back a load signal or a displacement signal with respect to the target signal from the target signal generator 30.

The PID control signal output unit 55 has gain coefficients set in advance for each of the P, I, and D components, and calculates a feedback gain by calculating each of these coefficients and the deviation calculated at the addition point 54 to perform PID control. A signal is output to the second addition point 56 as a signal.
To do.

  The addition signal output unit 58 calculates an addition signal obtained by multiplying the load coefficient by a preset coefficient K, and outputs this to the second addition point 56. By setting the value of K to an appropriate value of 1 or less, the added signal is positively fed back as a signal obtained by attenuating the load signal. If the value of K is set to 1 or more and positive feedback is made to the second addition point 56, the feedback control signal to the electromagnetic actuator will not converge to the target value and will be hunted. is there. The value of K is preferably about 0.1 to 0.9.

  In addition, although the value which multiplied the coefficient K to the load signal is used for the addition signal in this embodiment, it is not restricted to this, When calculating an addition signal based on a load signal, the frequency of a waveform or a target signal The addition signal may be calculated in consideration of the influence of the above.

  At the second addition point 56, a sum signal is calculated by positively feeding back the addition signal to the PID control signal, and this is sent to the power amplifier 57. The power amplifier 57 amplifies the sum signal and outputs it as a coil current of the electromagnetic actuator.

  In this manner, by adding the addition signal obtained by attenuating the load applied to the electromagnetic force actuator to the feedback control loop, the control output signal is compensated according to the load of the electromagnetic actuator. As a result, the correction by the PID control signal is reduced, especially the burden of the response of the integral (I) component is reduced, and the waveform response is improved.

  Next, the response characteristics of the load and the coil current will be described based on waveform data obtained when the test piece is measured under various conditions using an actual material testing machine.

  3 and 4 are diagrams showing a response waveform and a coil current signal when a square wave is given as a target signal, and FIG. 3 shows load feedback control (test force control) when a load is applied. FIG. 4 is a diagram showing displacement feedback control without load.

  In the case of load feedback control, the response waveform and the current signal waveform have the same waveform shape. This is because in an electromagnetic actuator, the load (test force) and the coil current are in a proportional relationship, and the coil current must be maintained as long as the load is maintained.

  On the other hand, in the displacement feedback control with no load, a waveform obtained by differentiating the response waveform is a current signal waveform. With no load, the load (test force) applied to the electromagnetic actuator is zero, and the coil current is zero. However, since the position of the electromagnetic actuator is displaced corresponding to the rising and falling of the square wave, the coil current necessary for the displacement flows in a pulsed manner.

  In the case of normal PID feedback control (used in an electrohydraulic actuator), it is assumed that the current (control) signal is a waveform-shaped response in the no-load state of FIG. ) When the signal is a response of the current (control) signal as in the case where the load in FIG. 3 is applied, the response characteristic is deteriorated.

  That is, when a square wave as shown in FIG. 3 is given, the load (test force) rises steeply up to a certain value and then gradually converges from there to the target value. Here, the first steep rise is a change in which the steep correction by the proportional component (P) and the differential component (D) is performed in the PID feedback control, and the waveform portion that converges gently is the integral component (I). This is a change with a gentle correction by.

  Next, the influence on the response waveform due to the test speed of the material test and the addition signal of the present invention will be described using actual measurement data.

  5, 6, and 7 are diagrams illustrating the relationship between the response waveform by the load feedback control and the coefficient K of the addition signal output unit when a 1 Hz rectangular wave target signal is given, and FIG. FIG. 6 shows response waveforms when 0 (addition signal is zero), FIG. 6 shows K = 0.25, and FIG. 7 shows K = 0.5.

  Here, the frequency of the rectangular wave target signal corresponds to the test speed, and the higher the frequency, the higher the test speed.

  Further, as the coefficient K is increased, feedback control is performed in which the influence of the addition signal on the PID control signal is increased.

  Comparing the test force (load) waveforms of FIGS. 5, 6, and 7, as the coefficient K increases, the steepness at the time of rising increases, and the gentle portion that converges to the target value thereafter becomes smaller. Yes. In particular, when K = 0.5 (see FIG. 7), the waveform is improved to a substantially square wave.

  The increase in the steepness of the rise is due to the addition of compensation due to positive feedback of the addition signal in addition to compensation by the proportional component (P) and differential component (D) of PID control. Since the burden of compensation by the integration component (I) of the subsequent PID control has been reduced, the followability of the response waveform is improved, and the effect of waveform improvement is obtained.

  8 and 9 show response waveforms by load feedback control when a 10 Hz rectangular wave target signal is given. FIG. 8 shows K = 0 (addition signal is zero), and FIG. 5 is a response waveform when 5. The conditions other than the frequency are the same as in FIG.

  In the case of FIG. 8, the addition signal is zero and the response waveform is obtained when the load feedback control is performed using only the PID control signal. However, the slow response due to the integral component (I) can follow the frequency change of the target signal. The response waveform does not reach the target value.

  On the other hand, in FIG. 9, the waveform is improved by positively feeding back the added signal, and the waveform itself reaches the target value although it is slightly distorted. This also reduces the burden of the integral component (I) of the PID control by adding the addition signal, and improves the followability of the response waveform.

  The waveform data shown in FIGS. 5 to 9 are data comparing the effects of adding the addition signal in the load feedback control. However, the waveform improvement using the same addition signal can also be obtained in the displacement feedback control.

  That is, in the case of displacement feedback control, the PID control signal is calculated based on the deviation between the target signal and the displacement signal from the displacement sensor, while the addition signal is calculated based on the load signal from the load sensor, A sum signal of the PID control signal and the addition signal is obtained. As a result, even in the displacement feedback control, compensation of the control output signal according to the load of the electromagnetic force actuator can be used to reduce the correction by the PID control signal, especially the response of the integral (I) component. it can.

  In the material testing machine of the above embodiment, the load feedback control and the displacement feedback control can be selected by switching the switch of the feedback control unit. However, when only the load feedback control is performed, the displacement sensor or the switch There is no need to provide. In this case, a load sensor that detects a load applied to the test piece and outputs a load signal, a PID control signal output unit that outputs a PID control signal based on a deviation between the target signal and the load signal, and a load signal And an addition signal output unit that calculates the addition signal and outputs it so as to be added to the PID control signal.

  According to the present invention, in a material testing machine using an electromagnetic force actuator, the waveform response when a load is applied can be improved, so that it can be applied to a material test measurement with a high test speed and can be measured. A material testing machine with a higher maximum test speed can be provided.

The figure which shows the structure of the material testing machine which is one Embodiment of this invention. The figure explaining PID feedback control of the conventional material testing machine. The figure which shows the relationship between a response waveform when giving the target signal of a rectangular wave (1 Hz), and a coil current (load feedback control). The figure which shows the relationship between the response waveform when giving the target signal of a rectangular wave (1 Hz), and a coil current (non-load displacement feedback control). The figure which shows the response waveform when the target signal of a rectangular wave (1 Hz) is given (coefficient K = 0 of an addition signal output part). The figure which shows the response waveform when the target signal of a rectangular wave (1 Hz) is given (coefficient K = 0.25 of an addition signal output part). The figure which shows the response waveform when the target signal of a rectangular wave (1 Hz) is given (coefficient K = 0.5 of an addition signal output part). The figure which shows the response waveform when the target signal of a rectangular wave (10 Hz) is given (coefficient K = 0 of an addition signal output part). The figure which shows the response waveform when the target signal of a rectangular wave (10Hz) is given (coefficient K = 0.5 of an addition signal output part).

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Test machine main part 12 Electromagnetic force type actuator 13 Piston rod 14 Displacement sensor 16 Load sensor 30 Target signal generation part 50 Feedback control part 53 Switch 54 Addition point 55 PID control signal output part 56 2nd addition point 57 Power amplifier 58 Addition signal Output section

Claims (2)

An electromagnetic actuator that applies a load to the specimen;
A target signal generating unit that provides a target signal that is a control target of the electromagnetic force actuator;
A load sensor that detects a load applied to the test piece and outputs a load signal;
A PID control signal output unit that outputs a PID control signal based on a deviation between the target signal and the load signal;
An addition signal output unit that outputs an addition signal obtained by multiplying the load signal by a constant ratio K (0 <K <1) to the PID control signal;
A material testing machine that drives an electromagnetic force actuator based on a sum signal of a PID control signal and an addition signal. An electromagnetic actuator that applies a load to the specimen;
A target signal generating unit that provides a target signal that is a control target of the electromagnetic force actuator;
A displacement sensor that detects the displacement of the test piece and outputs a displacement signal;
A load sensor that detects a load applied to the test piece and outputs a load signal;
A switch for selecting either a displacement signal or a load signal;
A PID control signal output unit that outputs a PID control signal based on a deviation between either the load signal or the displacement signal selected by the switch and the target signal;
An addition signal output unit that outputs an addition signal obtained by multiplying the load signal by a constant ratio K (0 <K <1) to the PID control signal;
A material testing machine for driving an electromagnetic force actuator based on a sum signal of a PID control signal and an addition signal.

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