JP4390077B2 - Fluid pressure servo type material testing machine - Google Patents

Description

  The present invention relates to a material testing machine, and more particularly to a servo type material testing machine using a hydraulic or pneumatic cylinder as an actuator of a load mechanism.

  In a material testing machine, in general, a load corresponding to a preset target value signal is applied to a test piece by driving a load mechanism. Conventionally, a hydraulic cylinder is used as an actuator for the load mechanism ( For example, a device using an electromagnetic actuator (see, for example, Patent Document 2) is known.

  In general, an actuator with a hydraulic cylinder as a load mechanism actuator is suitable for applying a high load of about 500N to several hundreds kN to a test piece, and an electromagnetic actuator is used to test a small load of about 100 to 500N. It is said that it is suitable for giving to a piece.

  By the way, a hydraulic unit is required to drive the hydraulic cylinder, and piping for reciprocating hydraulic fluid is required for the hydraulic unit, which causes a problem of complicated piping. In view of this, the present inventors have focused on a pneumatic cylinder as an actuator for the load mechanism of a material test machine having a medium load range of about 1000N to 5000N in order to make the load mechanism in the material test machine compact. Various researches are repeated.

  When a fluid pressure cylinder such as a hydraulic or pneumatic cylinder is used as an actuator for a load mechanism, a direct acting servo valve is often used for supply control of working fluid to the actuator. A direct-acting servo valve is a type of servo valve that displaces a spool that determines the opening of the valve by an electromagnetic force generated by passing a current through the coil, and an electromagnetic coil for displacing the spool inside the valve And a displacement sensor for detecting the displacement of the spool. The current passed through the electromagnetic coil is a current corresponding to a deviation obtained by feeding back a spool displacement detection signal from the displacement sensor to an operation target value signal supplied from the outside (see, for example, Patent Document 3).

  Specifically, a deviation obtained by feeding back a spool displacement detection signal by a displacement sensor to an operation target value signal supplied from the outside is generated by converting the deviation into a current signal by a servo amplifier (power amplifier). That is, the spool is moved in accordance with the magnitude of the operation target value signal from the outside to change the valve opening, thereby controlling the flow rate of the hydraulic oil.

Here, when used for supply control of the working fluid to the fluid pressure cylinder of the load mechanism of the material testing machine, the servo valve operation target value signal is a test for the test piece detected by the load cell of the material testing machine. A signal corresponding to a deviation signal obtained by feeding back a detection value selected as a control amount among a force detection value, a stroke detection value of a fluid pressure cylinder, and the like to a target value signal of a load is used.
Japanese Patent Laid-Open No. 10-38780 Japanese Patent Laid-Open No. 11-40413 JP-A-5-164109

  By the way, in the fluid servo type material testing machine that controls the supply of the working fluid to the hydraulic cylinder or pneumatic cylinder as the actuator of the load mechanism by the servo valve, the spool of the servo valve is controlled based on the position as described above. In the control method that follows the target operation value, that is, the control method that uses the flow characteristics of the servo valve, if the resonance point of the actuator is within the response range of the servo system, the control gain of the system cannot be increased and the control rigidity is increased. There is a problem that can not be. As a result, the control becomes unstable, and it becomes easy to hunting. This problem is particularly problematic when an air servo type material testing machine used in a medium load range is operated at a relatively high frequency as described above.

  The present invention has been made in view of such a situation, and even if the resonance point of the fluid pressure cylinder is within the response range of the servo system, the resonance can be suppressed and the control gain can be increased. An object of the present invention is to provide a fluid pressure servo type material testing machine capable of performing stable load control in a frequency range near the resonance frequency of the cylinder.

In order to solve the above-described problems, the fluid pressure servo type material testing machine of the present invention uses a fluid pressure cylinder as an actuator of a load mechanism that applies a dynamic load to a test piece, and uses a working fluid of the fluid pressure cylinder. Fluid pressure is supplied via the servo valve, and the spool of the servo valve is driven and controlled based on a deviation signal obtained by feeding back the detected value of the control amount to the load target value waveform signal. In the servo type material testing machine, both the speed detection signal and the displacement detection signal of the spool of the servo valve are fed back to the deviation signal, the respective differences are calculated, and each difference is weighted and added to each other. while being subjected to the driving of the spool, the weight of the difference between the deviation signal and the speed detection signal, the deviation signal and the displacement detection It characterized by greater than the weight of the difference between capital No. of (claim 1).

  Here, in the present invention, there is provided a displacement sensor for detecting the displacement of the spool and a differentiation circuit for differentiating the displacement detection signal from the displacement sensor, and the output of the differentiation circuit is used as the spool speed detection signal ( Claim 2) can be preferably employed.

  The present invention is intended to solve the problem by controlling the spool of the servo valve substantially at a speed in a high frequency range.

  That is, in the present invention, a signal for driving the spool of the servo valve, specifically, a current to be passed through the electromagnetic coil for displacing the spool, is applied to an external operation target value signal, that is, a load target value signal. With respect to the deviation signal obtained by feeding back the control value detection value, both the spool displacement detection signal and the speed detection signal are fed back to calculate each difference, and each difference is weighted. In this case, the weight of the difference in the speed detection signal of the spool with respect to the operation target value signal from the outside is made larger than the weight of the difference in the displacement detection signal. ing. Thereby, in a state where the speed of the spool is high, that is, in a high frequency range, the speed control of the spool becomes dominant, the control of the fluid pressure cylinder based on the pressure control characteristic of the system is performed, and the resonance can be suppressed. Further, in a state where the speed of the spool is low, that is, in a low frequency range, the displacement control of the spool becomes dominant, and the control of the fluid pressure cylinder based on the flow rate control characteristic of the system is performed as in the conventional case.

  As in the invention according to claim 2, the spool speed detection signal is obtained by differentiating the spool displacement detection signal, so that the sensor may be only a displacement sensor for detecting the spool displacement, and the servo valve itself is the conventional one. The above-described effects can be achieved using the product as it is.

  According to the present invention, when a fluid pressure cylinder is used as an actuator of the load mechanism and the hydraulic fluid supply to the fluid pressure cylinder is controlled by a servo valve, the load mechanism is operated near its resonance point. However, since the resonance can be suppressed, the control gain can be increased and the rigidity of control can be increased. As a result, it is possible to apply a load according to the waveform set under stable control up to a higher frequency range than in the past.

  Further, when the servo valve spool speed detection signal is obtained by differentiating the displacement detection signal as in the invention according to claim 2, the sensor incorporated in the servo valve may be only a displacement sensor. There is an advantage that a servo valve having exactly the same structure can be used.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is an overall configuration diagram of an embodiment in which the present invention is applied to a pneumatic servo type material testing machine.

  The testing machine main body 1 has a structure in which a cross head 13 is supported on a table 11 via a plurality of support columns 12. A pneumatic cylinder 14 for loading is fixed to the table 11, and a piston of the pneumatic cylinder 14 is fixed. A lower gripping tool 15 a is attached to the upper end of the rod 14 a, and an upper gripping tool 15 b is attached to the lower surface of the crosshead 13 via the load cell 16.

  Accordingly, a tensile or compressive load is applied to the test piece W by driving the pneumatic cylinder 14, and the test force acting on the test piece W at that time is detected by the load cell 16 every moment. Further, the displacement of the piston 14 a of the pneumatic cylinder 14 is detected by the stroke sensor 17 every moment.

  High pressure air from an air supply source is supplied to the pneumatic cylinder 14 via a servo valve 18. The valve opening degree of the servo valve 18 is driven and controlled by the control device 2. That is, the control device 2 is introduced with a test force detection value by the load cell 16 and a displacement detection value of the piston 14a of the pneumatic cylinder 14 by the stroke sensor 17, and as shown below, the control amount is set as a control amount. The selected detection value is fed back to the load target value waveform signal generated by the control device 2, and a signal corresponding to the deviation is supplied to the servo valve 18 as an operation target value signal.

FIG. 2 is a block diagram showing the configuration of the control device 2 and the relationship with other members.
As schematically shown in FIG. 2, the servo valve 18 includes a casing 18a, a spool 18b that is movably provided in the axial direction therein, an electromagnetic coil 18c that displaces the spool 18b, and a spool 18b. A displacement sensor 18d that detects displacement is mainly used.

  The control device 2 includes a target value waveform generator 21 that generates a load target value waveform signal, a load amplifier 22 and a stroke amplifier 23 that amplify the output of the load cell 16 and the output of the stroke sensor 17, respectively, and the load cell 16. A switch 24 that selects one of the test force detection value and the displacement detection value of the piston 14 a by the stroke sensor 17 as a control amount, and a signal selected by the switch 24 is a target value waveform signal from the target value waveform generator 21. A feedback circuit 25 that feeds back the signal, and an amplifier 26 that amplifies the deviation obtained by the feedback circuit 25, and a valve control circuit 3 that drives and controls the spool 18b of the servo valve 18 using the output of the amplifier 26 as an operation target value signal. It has.

  The valve control circuit 3 amplifies the output of the displacement sensor 18d that detects the displacement of the spool 18b of the servo valve 18 and outputs it as a displacement detection value of the spool 18b, and the output of the spool displacement amplifier 31. Is differentiated into a speed detection value of the spool 18b and output, and the displacement detection value and the speed detection value are respectively output to the operation target value signal of the servo valve 18 which is the output of the amplifier 26. Feedback loops 33 and 34 for feedback, amplifiers 35 and 36 for individually amplifying the deviations obtained by the feedback loops 33 and 34, and an adder circuit 37 for adding the outputs of the amplifiers 35 and 36, And a power amplifier 38 that converts the addition result into current. There.

  In the configuration of the valve control circuit 3 described above, both the displacement detection value and the speed detection value of the spool 18b are fed back to the operation target value signal of the servo valve 18 supplied through the amplifier 26, and the respective deviations are obtained. These deviations are added after being amplified by the respective amplifiers 35 and 36, and the added value determines the magnitude of the current flowing through the electromagnetic coil 18c that displaces the spool 18b. The gains K1 and K2 are K2 >> K1. That is, the weight of the deviation of the speed detection signal with respect to the motion target value signal is extremely heavier than the weight of the deviation of the displacement detection signal, for example, several tens of times.

  According to the above-described embodiment of the present invention, the spool 18b has a speed control dominant when the speed is high, and a displacement control when the speed is low. This means that when the frequency of the target value waveform signal of the load is low, the servo valve 18 operates based on the flow rate control characteristics as in the prior art, but when the frequency is high, the servo valve 18 is pressure controlled. It will operate under the characteristics. As a result, resonance of the load mechanism including the pneumatic cylinder 14 can be suppressed.

  FIG. 3 is a graph showing the frequency response characteristics of the load mechanism according to the above-described embodiment of the present invention. FIG. 4 shows a case where the spool 18b is displaced as in the conventional case, that is, in the configuration of FIG. It is a graph which shows the frequency response characteristic of the load mechanism at the time of doing. As is apparent from these graphs, in the configuration equivalent to the conventional configuration in which the spool 18b is displacement controlled, the resonance occurs in the vicinity of 90 Hz, whereas in the embodiment of the present invention, the resonance is suppressed.

  Therefore, according to the embodiment of the present invention, the resonance of the load mechanism can be suppressed. As a result, the control gain (the gain of the amplifier 26 in FIG. 2) can be increased even when a test is performed near the resonance point. The control rigidity can be increased and the test according to the waveform of the target value can be performed stably.

  In the above embodiment, the example in which the present invention is applied to an air servo type material testing machine has been shown. However, the present invention can be applied to a hydraulic servo type material testing machine equally. .

1 is an overall configuration diagram of an embodiment in which the present invention is applied to an air servo type material testing machine. It is a block diagram which shows the relationship between the structure of the control apparatus 2 in embodiment of FIG. 1, and another member. It is a graph which shows the frequency response characteristic of the load mechanism by embodiment of this invention. It is a graph which shows the frequency response characteristic when driving the same load mechanism as what was used in FIG. 3 under the control similar to the past.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Test machine main body 11 Table 12 Support | pillar 13 Cross head 14 Pneumatic cylinder 15a, 15b Grasp 16 Load cell 17 Stroke sensor 18 Servo valve 18a Casing 18b Spool 18c Electromagnetic coil 18d Displacement sensor 2 Controller 21 Target value waveform generation part 25 Feedback circuit 26 Amplifier 3 Valve control circuit 31 Spool displacement amplifier 32 Differentiation circuit 33, 34 Feedback loop 35, 36 Amplifier 37 Addition circuit 38 Power amplifier W Test piece

Claims (2)

A fluid pressure cylinder is used as an actuator of a load mechanism that applies a dynamic load to the test piece, and the working fluid of the fluid pressure cylinder is supplied via a servo valve. The spool of the servo valve is a target load value. In a fluid pressure servo type material testing machine configured to be driven and controlled based on a deviation signal obtained by feeding back a detected value of a control amount to a waveform signal,
Both the speed detection signal and the displacement detection signal of the spool of the servo valve are fed back to the deviation signal, the respective differences are calculated, and a signal obtained by weighting and adding each difference is provided for driving the spool. Rutotomoni, the deviation signal and the weighting of the difference between the speed detection signal, the fluid pressure servo type testing machine, which comprises greater than the weight of the difference between the deviation signal and the displacement detection signal.   2. A displacement sensor for detecting the displacement of the spool and a differentiation circuit for differentiating a displacement detection signal from the displacement sensor, and an output of the differentiation circuit is used as a speed detection signal of the spool. The fluid pressure servo type material testing machine described.

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