JP7172802B2 - MATERIAL TESTING MACHINE AND CONTROL METHOD FOR MATERIAL TESTING MACHINE - Google Patents

Description

The present invention relates to a material testing machine and a control method for the material testing machine.

Conventionally, in a material test of a material testing machine, feedback control is performed in which an instruction is given to a drive target of a load mechanism that applies a load to a test target and a measured value to be controlled is fed back (for example, Patent Document 1 reference). Patent Literature 1 discloses a material testing machine that performs feedback control of a load mechanism that moves a crosshead and applies a test force as a load to a test piece.

JP 2005-337812 A

In the material test as described in Patent Document 1, in feedback control, the ratio of the change in the physical quantity of the feedback object that occurs in the test object or the load mechanism and the change in the physical quantity that is highly correlated with the instruction value given to the load mechanism is used as a control parameter. It may be seasoned. In this case, since the material testing machine can add how much physical quantity change occurs in the test object or the load mechanism with respect to how much response change, the accuracy of the feedback control of the load mechanism is improved.

By the way, some material tests involve switching the moving direction of a moving member for applying a load to a test object. In this type of material test, depending on the state of the test object when switching the moving direction of the moving member, the ratio may be inappropriate as a value to be added to the control parameter, and the accuracy of the feedback control of the load mechanism is reduced. can. Therefore, in this type of test, the ratio is often set as a fixed value. However, in a material test in which the ratio is set as a fixed value, it is necessary to reset the fixed value each time the type or size of the test object is changed, which is troublesome for the user.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to enable feedback control of a load mechanism with high accuracy without requiring a user's time and effort in a material test involving switching of the moving direction of a moving member.

A first aspect of the present invention includes a load mechanism that moves a moving member to apply a load to a test piece , and a first measuring unit that measures a first physical quantity generated in the test piece or the load mechanism according to the load. a second measuring unit that measures a second physical quantity that is a response in feedback control of the load mechanism; a first change amount that indicates a change in the first physical quantity measured by the first measuring unit; and the second measurement a calculation unit that calculates a change amount ratio that is a ratio to a second change amount that indicates a change in the second physical quantity measured by the unit; and based on the change amount ratio calculated by the calculation unit, the actual second a feedback control unit that feedback-controls the load mechanism so as to reduce a deviation between a physical quantity and a target second physical quantity that is a target value of the second physical quantity; a storage unit that stores the change amount ratio calculated by the calculation unit before switching and the change amount ratio before switching when the test piece is in an elastic state , wherein the feedback control unit is and a material testing machine that feedback-controls the load mechanism so as to reduce the deviation based on the pre-switching variation ratio stored in the storage unit for a predetermined period when the moving direction of the moving member is switched.

A second aspect of the present invention includes a load mechanism that moves a moving member to apply a load to a test piece , and a first measuring unit that measures a first physical quantity generated in the test piece or the load mechanism according to the load. , a second measuring unit that measures a second physical quantity that is a response in feedback control of the load mechanism, a first change amount that indicates a change in the first physical quantity measured by the first measuring unit, and the second measuring unit that a calculation unit for calculating a change amount ratio, which is a ratio to a second change amount indicating a change in the measured second physical quantity; and an actual second physical quantity based on the change amount ratio calculated by the calculation unit. and a feedback control unit that feedback-controls the load mechanism so as to reduce the deviation of the second physical quantity from the target second physical quantity, which is the target value of the second physical quantity. is the change amount ratio calculated by the calculating unit from when the control device starts the material test to before the moving member switches the moving direction , and when the test piece is in an elastic state storing a pre- switching variation ratio, and feedback-controlling the load mechanism so as to reduce the deviation based on the stored pre-switching variation ratio for a predetermined period when the moving direction of the moving member is switched; The present invention relates to a method of controlling a material testing machine.

According to the first aspect of the present invention, when the moving direction of the moving member is switched, the load mechanism is feedback-controlled based on the change amount ratio calculated from the start of the material test to before the switching for a predetermined period of time. The change amount ratio calculated when the change in the amount ratio is stabilized can be taken into account in the feedback control of the load mechanism, and the load mechanism can be feedback-controlled with high accuracy. In addition, since the change amount ratio when switching the movement direction of the moving member is automatically stored, the user does not need to set the change amount ratio value in advance, which saves the user time and effort. As described above, in a material test involving switching of the moving direction of the moving member, feedback control of the load mechanism can be performed with high accuracy without requiring the user's trouble.

According to the second aspect of the present invention, the same effects as those of the first aspect of the present invention can be obtained.

It is a figure which shows the structure of a material testing machine typically. 4 is a block diagram of the control system of the load mechanism; FIG. It is a figure which shows an example of the time change of measured stress, measured strain, and control compliance. It is a flow chart which shows operation of a control device. It is the measurement data which shows the time change of the test force and the movement displacement of a crosshead. It is the measurement data which shows the time change of the test force and the movement displacement of a crosshead. It is measurement data of a fracture toughness test.

[1. Configuration of material testing machine]
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram schematically showing the configuration of a material testing machine 1 according to this embodiment.
The material testing machine 1 is a testing machine that performs material tests such as a tensile test, a compression test, and a bending test, and tests the mechanical properties of a test piece TP to be tested. The test objects are various materials, industrial products, parts or members of these industrial products, etc., and the test piece TP is prepared based on a predetermined standard for material testing.

The material testing machine 1 of this embodiment performs a material test involving switching of the moving direction of the crosshead 10 . In this embodiment, a case of performing a fracture toughness test as the material test will be exemplified. The crosshead 10 corresponds to an example of the "moving member" of the present invention. The fracture toughness test is a test for determining the fracture resistance of a material against fracture.

In the fracture toughness test, the material testing machine 1 of the present embodiment applies a tensile force that is a test force F as a load to the test piece TP by strain control, and unloads the tensile force applied to the test piece TP by stress control. A series of actions such as doing is repeated several times. Strain control indicates feedback control of the load mechanism 12 so that the strain SA of the test piece TP generated in the material test matches a target value set for the strain SA. Further, stress control indicates feedback control of the load mechanism 12 so that the stress SE generated in the material test matches a target value set for the stress SE.

As shown in FIG. 1, a material testing machine 1 includes a testing machine main body 2 that applies a test force F to a test piece TP to perform a fracture toughness test, and a control unit that controls the operation of the fracture toughness test by the testing machine main body 2. 4 and .

The test piece TP of this embodiment is called a notched CT test piece, and has a pair of through holes. The test piece TP is connected to the jig 21 provided on the crosshead 10 and the jig 22 provided on the table 6 via pins inserted into the respective through-holes, thereby attaching the test piece TP to the tester main body 2. mounted against.

As shown in FIG. 1, the material testing machine 1 includes a clip gauge 90 that detects the amount of displacement of the notch formed in the test piece TP (hereinafter referred to as "opening displacement amount"). The clip gauge 90 is a sensor that measures the amount of opening displacement and outputs an opening displacement amount measurement signal A2 to the control device 30 .

[2. Configuration of tester main body]

The testing machine main body 2 includes a table 6, a pair of screw rods 8, 9 rotatably erected on the table 6 in a vertical direction, and movable along the screw rods 8, 9. A crosshead 10, a load mechanism 12 for vertically moving the crosshead 10 to apply a test force F to the test piece TP, and a load cell 14 are provided. The load cell 14 is a sensor that measures a test force F, which is a load applied to the test piece TP, and outputs a test force measurement signal A1. The vertical direction in which the crosshead 10 moves corresponds to an example of the "moving direction" of the present invention. Note that the testing machine main body 2 may be configured to have a single screw neck.

The pair of screw threads 8 and 9 are ball screws, and the crosshead 10 is connected to each of the screw threads 8 and 9 via nuts (not shown). The load mechanism 12 includes worm reduction gears 16 and 17 connected to the lower ends of the screw rods 8 and 9 , a servo motor 18 connected to the worm reduction gears 16 and 17 , and a rotary encoder 20 . The rotary encoder 20 is a sensor that measures the rotation amount Tr of the servomotor 18 and outputs a rotation measurement signal A3 having a number of pulses corresponding to the rotation amount Tr to the signal input/output unit 40 .
The load mechanism 12 transmits the rotation of the servomotor 18 to the pair of screw necks 8 and 9 via the worm reduction gears 16 and 17, and the screw necks 8 and 9 rotate synchronously, whereby the crosshead 10 is rotated. moves up and down along the screw rods 8 and 9.

The crosshead 10 is provided with a jig 21 for supporting the upper end of the test piece TP, and the table 6 is provided with a jig 22 for supporting the lower end of the test piece TP. When the test piece TP is pulled in the fracture toughness test, the testing machine body 2 supports the upper end of the test piece TP with the jig 21 and supports the lower end of the test piece TP with the jig 22. The crosshead 10 is moved upward by control. As a result, the testing machine main body 2 applies tensile force as the test force F to the test piece TP. The upward direction UP is the direction in which the crosshead 10 moves away from the table 6 along the screw threads 8 and 9, and corresponds to an example of the "first direction" of the present invention. The testing machine main body 2 moves the crosshead 10 downward DW under the control of the control device 30 when unloading the tensile force applied to the test piece TP in the fracture toughness test. As a result, the tensile force applied to the test piece TP is released from the testing machine main body 2 . The downward direction DW is the direction in which the crosshead 10 approaches the table 6 along the screw threads 8 and 9, and corresponds to an example of the "second direction" of the present invention.

[3. Configuration of control unit]
The control unit 4 includes a control device 30 , a display device 32 and a test program execution device 34 .

The control device 30 is a device that centrally controls the tester main body 2 and is connected to the tester main body 2 so that signals can be transmitted and received. Signals received from the testing machine main body 2 include a test force measurement signal A1 output by the load cell 14, an opening displacement amount measurement signal A2 output from the clip gauge 90, a rotation measurement signal A3 output by the rotary encoder 20, and signals for control and testing. appropriate signals required.

The display device 32 is a device that displays various types of information based on signals input from the control device 30. For example, the control device 30 displays information based on the test force measurement signal A1 during a material test including a fracture toughness test. The display device 32 displays the measured value of the test force F applied to the test piece TP.

The test program execution device 34 accepts user operations such as setting operations of various setting parameters such as test conditions for material tests including fracture toughness tests and execution instruction operations, and functions to output to the control device 30 and the measured value of the test force F It is a device equipped with a function to analyze the data of The test program execution device 34 comprises a computer, which includes processors such as CPU and MPU, memory devices such as ROM and RAM, storage devices such as HDD and SSD, control device 30 and various peripheral devices. and an interface circuit for connecting. The various functions described above are realized by the processor executing a material test program, which is a computer program stored in the memory device or storage device.

Next, the control device 30 will be described in detail.
As shown in FIG. 1 , the control device 30 includes a signal input/output unit 40 and a control circuit unit 50 .

The signal input/output unit 40 constitutes an input/output interface circuit that transmits and receives signals to and from the testing machine body 2. In this embodiment, the first sensor amplifier 41, the second sensor amplifier 42, the counter circuit 43, and a servo amplifier 44 .

The first sensor amplifier 41 is an amplifier that amplifies the test force measurement signal A1 output from the load cell 14 and inputs it to the control circuit unit 50 .

The second sensor amplifier 42 is an amplifier that amplifies the opening displacement amount measurement signal A<b>2 output from the clip gauge 90 and inputs it to the control circuit unit 50 .

The counter circuit 43 counts the number of pulses of the rotation measurement signal A3 output by the rotary encoder 20, and calculates the rotation amount Tr of the servomotor 18, that is, the movement amount (also called stroke value) of the crosshead 10 moved by the rotation of the servomotor 18. ) to the control circuit unit 50 as a digital signal.

The material testing machine 1 may be configured to include an encoder attached to at least one of the screw necks 8 and 9 instead of the rotary encoder 20 . In this configuration, the encoder generates a signal that outputs one pulse each time at least one of the mounted screw heads 8 and 9 rotates by a predetermined angle, and outputs the signal to the counter circuit 43 . The counter circuit 43 counts the number of pulses of the signal output by the encoder, and outputs a rotation measurement signal A3 indicating the amount of rotation of the screw neck, that is, the amount of movement of the crosshead 10 caused by the rotation of the screw neck. 50 as a digital signal.

The servo amplifier 44 is a device that controls the servo motor 18 under the control of the control circuit unit 50 .

The control circuit unit 50 includes a communication section 52 , a control section 54 and a storage section 56 .
The control circuit unit 50 communicates with a processor such as a CPU or MPU, a memory device such as a ROM or RAM, a storage device such as an HDD or SSD, an interface circuit for the signal input/output unit 40, and the test program execution device 34. A computer including a communication device that controls the display device 32, a display control circuit that controls the display device 32, and various electronic circuits. 54 functional units are realized. An interface circuit of the signal input/output unit 40 is provided with an A/D converter, and the analog test force measurement signal A1 is converted into a digital signal by the A/D converter.
Note that the control circuit unit 50 is not limited to a computer, and may be configured by one or a plurality of appropriate circuits such as integrated circuits such as IC chips and LSIs.

The communication unit 52 communicates with the test program execution device 34 to set material test conditions including fracture toughness tests, set values of various setting parameters, execute instructions and interruption instructions for material tests including fracture toughness tests, and the like. It is received from the test program execution device 34 . The communication unit 52 also transmits various measured values such as the test force F based on the test force measurement signal A1 to the test program execution device 34 at appropriate timings.

The storage unit 56 is configured by a memory device and stores pre-switching control compliance 561 and target data 562 . Since the pre-switching control compliance 561 is stored in the storage unit 56 during the fracture toughness test, it is not stored in the storage unit 56 except during the fracture toughness test. The pre-switching control compliance 561 corresponds to an example of the "pre-switching deformation amount ratio" of the present invention.

The pre-switching control compliance 561 will be described later.
The target data 562 is time-series data indicating temporal fluctuations of target values of various physical quantities in the material test. The target data 562 of the present embodiment is time-series data of target values of strain SA and stress SE in the fracture toughness test. This target data is changed and stored by the control circuit unit 50 according to the user's setting operation on the test program execution device 34 .

The control unit 54 is a functional unit that feedback-controls the servomotor 18 as the load mechanism 12 of the testing machine main body 2 to execute processing related to material testing including fracture toughness testing. Here, before describing each functional unit provided in the control unit 54, a control system for feedback control of the servo motor 18, which is one mode of feedback control of the load mechanism 12, will be described.

[3-1. Control system configuration]
The configuration of a control system that feedback-controls the servomotor 18 will be described with reference to FIG. The control system described with reference to FIG. 2 is a control system for feedback control of the servomotor 18 in stress control.
FIG. 2 is a block diagram showing a control system for feedback control of the servomotor 18. As shown in FIG. In FIG. 2, "t" indicates the execution timing of the control cycle.

In the feedback control of the servo motor 18, PID control is performed as shown in FIG. 2 to determine the amount of rotation Tr(t) of the servo motor 18. FIG. In the feedback control of the servomotor 18, the rotation amount Tr(t) of the servomotor 18 is updated every preset control cycle.

The block diagram of the feedback control as shown in FIG. 2 includes a subtractor 70, a converter 71 and a controller 78. The controller 78 includes a proportionalor 72 , an integrator 73 , a first differentiator 74 , a first adder 75 , a second adder 76 and a second differentiator 77 .

The subtractor 70 calculates a deviation e(t) by subtracting the measured stress SEs(t) from the target stress SEc(t) in each control cycle, and outputs the calculated deviation e(t) to the converter 71 . The target stress SEc indicates the target stress SE. The stress SE corresponds to an example of the "second physical quantity" of the present invention. Also, the target stress SEc corresponds to an example of the "target second physical quantity" of the present invention. Also, the measured stress SEs is the stress SE measured based on the test force F measured by the load cell 14, and corresponds to an example of the "actual second physical quantity" of the present invention.

The converter 71 multiplies the deviation e(t) output by the subtractor 70 by the control compliance Comp calculated by the control compliance calculator 543 (to be described later) or the pre-switching control compliance 561, and converts the deviation e(t) to the test piece It is converted into a deviation e'(t) corresponding to the amount of change in the strain SA of the TP. The converter 71 inputs the converted deviation e′(t) to the proportional device 72 , the integrator 73 and the first differentiator 74 .

The first adder 75 adds the outputs of the proportionalor 72 , the integrator 73 and the first differentiator 74 and outputs a first addition value K1(t) to the second adder 76 . Further, the second adder 76 adds the movement amount initial value U0 to the first addition value K1(t) output from the first adder 75, and outputs the second addition value K2(t) to the second differentiator 77. do.

The second differentiator 77 differentiates the second addition value K2(t) output from the second adder 76, so that the strain SA of the test piece TP indicated by the second addition value K2(t) is , the rotation amount Tr(t) of the servomotor 18 is calculated. Then, in the feedback control shown in FIG. 2, a command signal B1 indicating the amount of rotation Tr(t) of the servo motor 18 is output to the servo amplifier 44. FIG.

[3-2. Configuration of control circuit unit]
The functional blocks of the control unit 54 will be described with reference to FIG.
The control unit 54 includes a stress measurement unit 541 , a strain measurement unit 542 , a control compliance calculation unit 543 and a feedback control unit 544 . The stress measuring section 541 corresponds to an example of the "second measuring section" of the present invention. Also, the strain measuring section 542 corresponds to an example of the "first measuring section" of the present invention. Also, the control compliance calculator 543 corresponds to an example of the "calculator" of the present invention.

The stress measuring unit 541 measures the stress SE by dividing the test force F indicated by the test force measurement signal A1 input from the load cell 14 via the first sensor amplifier 41 by the cross-sectional area of the predetermined test piece TP. . Regarding the cross-sectional area of the test piece TP, the data of the test piece TP to be tested is stored in advance as data in the storage unit 56 before the fracture toughness test is started.

The strain measurement unit 542 divides the opening displacement amount indicated by the opening displacement amount measurement signal A2 input from the clip gauge 90 via the second sensor amplifier 42 by the width of the notch before the fracture toughness test, thereby Measure the strain SE of the piece TP. The width of the notch before the fracture toughness test is stored in advance in the storage unit 56 as data.

The control compliance calculator 543 calculates the control compliance Comp. The control compliance Comp is a physical quantity change that occurs in the test piece TP or the load mechanism 12, and a physical quantity change that correlates with an instruction value given to the object to be driven by the load mechanism 12 (in this embodiment, the rotation amount Tr of the servo motor 18). is the ratio of In this embodiment, the control compliance calculation unit 543 calculates the amount of change in the measured stress SEs measured by the stress measurement unit 541 (hereinafter referred to as “stress change amount” and denoted by “SEd”), and the strain measurement unit 542 A control compliance Comp, which is a ratio to the amount of change in the measured strain SAs of the test piece TP (hereinafter referred to as "strain change amount" and denoted by "SAd"), is calculated. Control compliance Comp corresponds to an example of the variation ratio of the present invention. Also, the stress change amount SEd corresponds to an example of the "second change amount" of the present invention. Also, the strain change amount SAd corresponds to an example of the "first change amount" of the present invention.

The control compliance calculator 543 calculates the control compliance Comp based on, for example, the following formula (1).
Comp(t)=SAd(t)/SEd(t) (1)
In Equation (1), t is the execution timing of the control cycle. Comp(t) indicates the control compliance in each control period. Also, SAd(t) represents the amount of strain change SAd in each control cycle, for example, the amount of change in strain SA of the test piece TP based on the measured value in the previous control cycle and the measured value in the current control cycle. Further, SEd(t) indicates the amount of stress change SEd in each control cycle, for example, the amount of change in stress SE generated in the test piece TP based on the measured value in the previous control cycle and the measured value in the current control cycle.

In addition, the control compliance calculation unit 543 causes the storage unit 56 to store a pre-switching control compliance 561 that is a control compliance Comp calculated from the start of the fracture toughness test to before the movement direction of the crosshead 10 is first switched. . The control compliance calculation unit 543 causes the storage unit 56 to store the initially calculated control compliance Comp as the pre-switching control compliance 561 after a predetermined period has elapsed since the start of the fracture toughness test. This predetermined period is appropriately determined by prior tests, simulations, or the like so that the stored pre-switching control compliance 561 is, for example, the control compliance Comp when the test piece TP is in an elastic state. .

A feedback control unit 544 performs feedback control of the servo motor 18 .
Here, the feedback control section 544 will be described separately for strain control and stress control. The feedback control unit 544 switches the feedback control of the servomotor 18 between strain control and stress control based on the target data 562, the test conditions received from the test program execution device 34, and the like.

First, the feedback control section 544 for strain control will be described.
The feedback control unit 544 is a servo motor that reduces the deviation between the target value of the strain SA(t) and the strain SA(t) of the test piece TP measured by the strain measuring unit 542 in each control cycle of the strain control. 18, and outputs a command signal B1 indicating the rotation amount Tr(t) to the servo amplifier 44 .

Next, the feedback control section 544 for stress control will be described.
The feedback control unit 544 calculates the deviation e(t) between the target stress SEc(t) and the measured stress SEs(t) measured by the stress measurement unit 541 by the control compliance calculation unit 543 in each control cycle in the stress control. The deviation e′(t) is calculated by multiplying the obtained control compliance Comp or the pre-switching control compliance 561 stored in the storage unit 56 . Then, based on the calculated deviation e'(t), the feedback control unit 544 reduces the deviation e(t) between the measured stress SEs(t) and the target stress SEc(t). (t) and outputs a command signal B1 indicating the amount of rotation Tr(t) to the servo amplifier 44 .

Further, in the fracture toughness test, when the moving direction of the crosshead 10 is switched from the upward direction UP to the downward direction DW, the feedback control unit 544 controls the pre-switching stored in the storage unit 56 for a predetermined period from the switching timing. Feedback control of the servo motor 18 is performed based on the control compliance 561 . In the following description, a predetermined period from the timing of switching is referred to as a "post-switching stiffness control period". The post-switching stiffness control period corresponds to an example of the "predetermined period" of the present invention. The post-switching stiffness control period is a period from when the movement direction is switched until the change in the control compliance Comp stabilizes, and is appropriately determined by prior tests, simulations, or the like.

When the movement direction of the crosshead 10 is switched to the downward direction DW, the feedback control unit 544 compares the latest control compliance Comp calculated by the control compliance calculation unit 543 at the time of switching (hereinafter referred to as "latest control compliance at switching time"). , and the pre-switching control compliance 561 stored in the storage unit 56 . Then, when the latest control compliance at switching time is equal to or less than the control compliance before switching 561, the feedback control unit 544 multiplies the deviation e(t) by the latest control compliance at switching time during the post-switching stiffness control period to obtain a deviation e'(t). Calculate On the other hand, when the latest control compliance at switching is greater than the pre-switching control compliance 561, the feedback control unit 544 multiplies the deviation e(t) by the pre-switching control compliance 561 stored in the storage unit 56 during the post-switching stiffness control period. Calculate e'(t).

FIG. 3 is a diagram showing an example of temporal changes in the measured stress SEs, the measured strain SAc, and the stiffness Comp calculated by the control compliance calculator 543. In FIG. The example of FIG. 3 is the change over time of the measured stress SEs, the measured strain SAs, and the control compliance Comp when the test piece TP is pulled to the plastic region and then the applied tensile force is unloaded.

In FIG. 3, the left vertical axis is set to stress SE and strain SA, the right vertical axis is set to control compliance Comp, and the horizontal axis is set to time (sec). In the case of stress SE, 40000000 indicates 400 (MPa), and in the case of strain SA, 40000000 indicates 4% on the left vertical axis. In FIG. 3, the characteristic graph Tg-1 shows the time change of the measured stress SEs. A characteristic graph Tg-2 shows the time change of the measured strain SAc. A characteristic graph Tg-3 shows the change over time of the control compliance Comp.

As shown in the characteristic graph Tg-3 before timing TA1 in FIG. 3, the control compliance Comp sharply increases in value when the test piece TP is pulled beyond the yield point to the plastic region by strain control. This is because the stress SE does not increase even though the strain SA increases. In FIG. 3, the moving direction of the crosshead 10 switches to the downward direction DW at timing TA1, and the unloading of the tensile force starts. Then, as shown by the characteristic graph Tg-3 in FIG. 3, the control compliance Comp tends to stabilize after the timing TA1, while the amplitude of change is large between the timing TA1 and the timing TA2. In particular, the control compliance Comp immediately after timing TA1 is a very large value compared to the control compliance Comp in the elastic region. Therefore, if the control compliance Comp that changes unstably between the timing TA1 and the timing TA2 is used, the feedback control of the servomotor 18 becomes unstable. Further, if a large control compliance Comp is added to the feedback control of the servomotor 18, the response becomes excessive.

Therefore, in the case of FIG. 3, the feedback control unit 544 compares the pre-switching control compliance 561 indicating the value of "Comp-1" with the latest switching-time control compliance at timing TA1. Then, the feedback control unit 544 converts the pre-switching control compliance 561, which indicates the smaller value of "Comp-1", into the deviation e(t) during the period from the timing TA1 to the timing TA3, which is the post-switching stiffness control period. to feedback-control the servomotor 18 by multiplying by . From timing TA1 to timing TA2, the control compliance Comp calculated by the control compliance calculator 543 has a large value and a large change. The servomotor 18 can be feedback-controlled using the stable pre-switching control compliance 561 that has almost the same value as the control compliance Comp and does not change over time.

[4. Operation of material testing machine]
Next, the operation of the control device 30 of the material testing machine 1 will be described.
FIG. 3 is a flowchart showing the operation of the control device 30, and particularly shows the operation related to stress control in the feedback control of the servomotor 18. As shown in FIG.

In the flowchart shown in FIG. 3, it is assumed that the control compliance calculator 543 calculates the control compliance Comp each time a control cycle arrives during strain control and stress control.

The feedback control section 544 of the control section 54 of the control device 30 determines whether or not to start the fracture toughness test (step SA1). For example, when the feedback control unit 544 receives a fracture toughness test execution instruction from the test program execution device 34 via the communication unit 52, it makes an affirmative determination in step SA1.

When the feedback control unit 544 determines to start the fracture toughness test (step SA1: YES), the feedback control unit 544 feedback-controls the servomotor 18 by strain control to start tensioning the test piece TP (step SA2).

Next, the feedback control section 544 determines whether or not a predetermined period has elapsed since the fracture toughness test was started (step SA3).

When the feedback control section 544 determines that the predetermined period has not passed (step SA3: NO), it returns the process to step SA3 and continues the tensioning of the test piece TP by strain control.

On the other hand, when the feedback control unit 544 determines that the predetermined period has elapsed (step SA3: YES), the control compliance calculation unit 543, after the affirmative determination in step SA3, calculates the first calculated control compliance Comp as It is stored in the storage unit 56 as the pre-switching control compliance 561 (step SA4).

Next, the feedback control unit 544 determines whether to switch the movement direction of the crosshead 10 to the downward direction DW, that is, whether to switch from strain control to stress control and start unloading the tensile force (step SA5). For example, the feedback control section 544 performs the determination of step SA5 based on the target data 562 and the test conditions received from the test program execution device 34. FIG.

If a negative determination is made in step SA5, the feedback control section 544 returns the process to step SA3 and continues tensioning of the test piece TP by strain control.

On the other hand, when the feedback control unit 544 makes an affirmative determination in step SA5, it determines whether or not the pre-switching control compliance 561 stored in the storage unit 56 is smaller than the latest control compliance at switching (step SA6). In this embodiment, the feedback control unit 544 switches the moving direction of the crosshead 10 when the feedback control unit 544 makes an affirmative determination in step SA5.

When the feedback control unit 544 determines that the pre-switching control compliance 561 stored in the storage unit 56 is smaller than the latest control compliance at the time of switching (step SA6: YES), the control compliance Comp by which the deviation e(t) is multiplied. is determined as the pre-switching control compliance 561 (step SA7).

Then, the feedback control section 544 feedback-controls the servomotor 18 by stress control based on the pre-switching control compliance 561 to start unloading the tensile force applied to the test piece TP (step SA8).

Returning to the description of step SA6, when the feedback control unit 544 determines that the pre-switching control compliance 561 stored in the storage unit 56 is greater than the latest switching control compliance (step SA6: NO), the deviation e(t ) is determined as the latest control compliance at switching (step SA9).

Then, the feedback control unit 544 feedback-controls the servomotor 18 by stress control based on the latest control compliance at the time of switching, and starts unloading the tensile force applied to the test piece TP (step SA10).

The feedback control unit 544 determines whether or not the post-switching stiffness control period has elapsed (step SA11). When the feedback control unit 544 determines that the post-switching stiffness control period has not elapsed (step SA11: NO), the feedback control unit 544 returns the process to step SA11, and adjusts the tension based on the control compliance Comp determined in step SA7 or step SA9. Continue force unloading.

On the other hand, when the feedback control unit 544 determines that the post-switching stiffness control period has elapsed (step SA11: YES), the feedback control unit 544 reduces the tensile force based on the control compliance Comp calculated by the control compliance calculation unit 543 in the control cycle. Continue loading (step SA12).

Next, the feedback control unit 544 determines whether or not to switch the movement direction of the crosshead 10 to the upward direction UP, that is, whether or not to switch from stress control to strain control and start applying tensile force (step SA13 ).

If a negative determination is made in step SA13, the feedback control unit 544 determines whether or not to end the fracture toughness test (step SA14). When the feedback control unit 544 determines to end the fracture toughness test (step SA14: YES), it ends this process. On the other hand, when the feedback control unit 544 determines not to end the fracture toughness test (step SA14: NO), it executes the process of step SA13 again.

Returning to the description of step SA13, when the positive determination is made in step SA5, the feedback control unit 544 feedback-controls the servomotor 18 by strain control to start applying the tensile force applied to the test piece TP (step SA15). . After executing the process of step SA15, the feedback control unit 544 shifts the process to step SA5.

[5. Verification by measurement data]
5 and 6 are measurement data showing changes over time in the test force F and the movement displacement of the crosshead 10. FIG. The time change of the test force F corresponds to the time change of the stress SE generated in the test piece TP. Also, the time change of the movement displacement of the crosshead 10 corresponds to the time change of the strain SA of the test piece TP. Therefore, the measurement data of FIGS. 5 and 6 correspond to the measurement data of the time change of the stress SE occurring in the test piece TP and the time change of the strain SA of the test piece TP.

5 and 6, the left vertical axis is set to the test force F (N: Newton), the right vertical axis is set to the movement displacement (mm) of the crosshead 10, and the horizontal axis is set to time (sec). be done.

The measurement data shown in FIGS. 5 and 6 show that the crosshead 10 is moved upward by the displacement control of the crosshead 10 corresponding to the strain control, the test piece TP is pulled to the plastic region, and then the crosshead is pulled for a predetermined period. 10 is stopped, and then the crosshead 10 is moved downward DW by test force control corresponding to stress control to unload the tensile force applied to the test piece TP. In the displacement control of the crosshead 10 in the measurement data shown in FIGS. 5 and 6, the movement displacement of the crosshead 10 is controlled so that the movement displacement per unit time is constant. Further, in the test force control in the measurement data shown in FIGS. 5 and 6, control is performed such that the amount of change in the test force per unit time is constant.

6 shows measurement data during a period in which the movement of the crosshead 10 is stopped, while FIG. 5 omits measurement data during this period.

FIG. 5 shows measurement data obtained by the conventional material testing machine 1. FIG. That is, FIG. 5 shows measurement data when feedback control of the servomotor 18 is executed using the control compliance Comp sequentially calculated by the control compliance calculator 543 .

In FIG. 5, the characteristic graph Tg-1 shows the measured data of the test force F, the characteristic graph Tg-2 shows the measured data of the displacement of the crosshead 10, and the characteristic graph Tg-3 shows the target value of the test force F. It is the data which shows a time change.

As shown in FIG. 5, when the unloading of the tensile force applied to the test piece TP is started at the timing TB1, the test force F is measured as a value greatly separated from the target test force F. Further, when the unloading of the tensile force applied to the test piece TP is started at the timing TB1, the movement displacement of the crosshead 10 changes greatly as indicated by the dot frame E1. This indicates that, as shown in FIG. 3, when feedback control of the servomotor 18 was performed using a control compliance Comp having a large value, the response was excessive and the tensile force was suddenly unloaded. there is

FIG. 6 shows measurement data by the material testing machine 1 of the present invention. That is, FIG. 6 shows measurement data when feedback control of the servomotor 18 is executed by executing the operation shown in FIG.

In FIG. 6, the characteristic graph Tg-4 shows the measured data of the test force F, the characteristic graph Tg-5 shows the measured data of the displacement of the crosshead 10, and the characteristic graph Tg-6 shows the target value of the test force F. It is data showing the time change of .

As shown in FIG. 6, when the unloading of the tensile force applied to the test piece TP is started at timing TB2, the test force F becomes a value along the target test force F and is measured. Further, when the unloading of the tensile force applied to the test piece TP is started at the timing TB2, the movement displacement of the crosshead 10 does not decrease significantly, as is clear from comparison with the dotted frame E1 in FIG. This indicates that the tensile force is being unloaded appropriately at a constant speed, and that the feedback control of the servo motor 18 is accurately performed when the moving direction of the crosshead 10 is switched. is shown.

FIG. 7 shows measurement data of a fracture toughness test by the material testing machine 1 of the present invention.
The measurement data shown in FIG. 7 is obtained by pulling the test piece TP to the plastic region under strain control so that the change in strain SA per unit time is constant, and then switching the moving direction of the crosshead 10 to the downward direction DW. It is measurement data of a test in which the tensile force was repeatedly removed from the test piece TP by stress control so that the change in stress SE per unit time was constant.

The characteristic graph TG-7 in FIG. 7 indicates that the interval at which unloading is started is divided into equal intervals with high accuracy, indicating that the fracture toughness test is performed with high accuracy.

[6. Effect of this embodiment]
As described above, the material testing machine 1 includes the load mechanism 12 that moves the crosshead 10 to apply the test force F to the test piece TP, and the strain measurement unit 542 that measures the strain SA occurring in the test piece TP. , a stress measurement unit 541 that measures the stress SE generated in the test piece TP, a control compliance calculation unit 543 that calculates the control compliance Comp that is the ratio of the stress change amount SEd and the strain change amount SAd, and the control compliance calculation unit 543 a feedback control unit 544 that feedback-controls the servo motor 18 so as to reduce the deviation e between the measured stress SEs and the target stress SEc based on the calculated control compliance Comp; and a storage unit 56 that stores the pre-switching control compliance Comp. , provided. Then, when the crosshead 10 switches the movement direction, the feedback control unit 544 operates the servomotor 18 so as to reduce the deviation e based on the pre-switching control compliance Comp stored in the storage unit 56 during the post-switching stiffness control period. feedback control.

According to this configuration, when the moving direction of the crosshead 10 is switched, the servo motor 18 is feedback-controlled based on the control compliance Comp calculated from the start of the fracture toughness test to before the switching during the post-switching stiffness control period. The control compliance Comp calculated when the change in the control compliance Comp stabilizes can be taken into consideration in the feedback control, and the precision of the feedback control of the servomotor 18 can be improved. In addition, since the control compliance Comp when the movement direction of the crosshead 10 is switched is automatically stored, the user does not need to set the value of the control compliance Comp in the fracture toughness test in advance, saving the user time and effort. As described above, in the fracture toughness test, which is a material test involving switching of the moving direction of the crosshead 10, the servomotor 18 can be feedback-controlled with high accuracy without requiring the user's trouble.

Further, when the crosshead 10 switches the movement direction, the feedback control unit 544 selects the value between the latest control compliance Comp calculated by the control compliance calculation unit 543 and the pre-switching control compliance 561 stored in the storage unit 56. During the post-switching stiffness control period, the servo motor 18 is feedback-controlled by multiplying the deviation e(t) by the small control compliance Comp.

According to this configuration, the servomotor 18 can be feedback-controlled based on the stable control compliance Comp during the post-switching stiffness control period. Even so, the servomotor 18 can be feedback-controlled with high accuracy. In addition, since the smaller value is adopted, it is possible to prevent the response from becoming excessive, and feedback control of the servomotor 18 can be performed with higher accuracy.

The load mechanism 12 moves the crosshead 10 upward to apply a tensile force to the test piece TP, and moves the crosshead downward DW to release the tensile force applied to the test piece TP. The feedback control unit 544 reduces the deviation e based on the pre-switching control compliance 561 stored in the storage unit 56 during the post-switching stiffness control period when the moving direction of the crosshead 10 is switched from the upward direction UP to the downward direction DW. The servo motor 18 is feedback-controlled as follows.

According to this configuration, feedback control of the servomotor 18 when unloading the tensile force in the fracture toughness test can be accurately performed, so the accuracy of the fracture toughness test can be improved.

[7. Other embodiments]
Note that the above-described embodiment is merely an example of one aspect of the present invention, and can be arbitrarily modified and applied without departing from the gist of the present invention.

Although the fracture toughness test was exemplified as the material test in the above-described embodiment, the material test executed by the material testing machine 1 is not limited to this. The present invention can be applied to the material test executed by the material testing machine 1 as long as the test involves switching the movement direction of the crosshead 10 . For example, the material test may be a test in which the test piece TP is pulled and then the tensile force is removed, a test in which the test piece TP is compressed and then the compressive force is removed, or a tensile compression test. In the case of compression, the "first direction" of the present invention corresponds to the downward direction DW, and the "second direction" of the present invention corresponds to the upward direction UP. As the jig for attaching the test piece TP to the testing machine main body 2, an appropriate jig is adopted according to the type of material test.

For example, in the above-described embodiment, the strain measuring unit 542 of the control unit 54 is used as the "first measuring unit" of the present invention. 90 is the "first measuring section" of the present invention.

For example, in the above embodiment, as shown in the block diagram of FIG. 2, feedback control of the servo motor 18 is performed by PID control. As another configuration, feedback control of the servomotor 18 may be performed by general PD control.

For example, in the above embodiment, the strain SA of the test piece TP is the first physical quantity of the present invention, the strain change amount SAd is the first change amount of the present invention, and the stress SE generated in the test piece TP is the second physical quantity of the present invention. , the feedback control of the servo motor 18 when the stress change amount SEd is the second change amount of the present invention is exemplified. The first amount of change, the first physical quantity, the second amount of change, and the second physical quantity are not limited to these. For example, the first amount of change may be the amount of movement of the crosshead 10 or the amount of elongation of the test piece TP. Also, the second physical quantity may be the test force F, torque, pressure, displacement, or the like.

For example, in the above embodiment, the servomotor 18 is used as the drive source for the load mechanism 12, but other drive source such as a hydraulic power source may be used. In this case, the output to the controlled object in the block diagram of FIG. 2 is set to a physical quantity according to the drive source.

For example, in the above-described embodiment, the functional blocks shown in FIG. 1 are schematic diagrams showing constituent elements classified according to main processing contents for easy understanding of the present invention. , which can also be classified into more components. Also, one component can be grouped to perform more processing.

For example, the step unit of the operation shown in FIG. does not limit the invention. It may be divided into more steps depending on the processing contents. Also, one step unit may be divided to include more processes. Also, the order of the steps may be changed as appropriate within the scope of the present invention.

[8. mode]
It will be understood by those skilled in the art that the above-described embodiments and modifications are specific examples of the following aspects.

(Section 1)
A material testing machine according to one aspect includes a load mechanism that moves a moving member to apply a load to a test object, and a first measurement unit that measures a first physical quantity generated in the test object or the load mechanism according to the load. a second measuring unit that measures a second physical quantity that is a response in feedback control of the load mechanism; a first change amount that indicates a change in the first physical quantity measured by the first measuring unit; and the second measurement a calculation unit that calculates a change amount ratio that is a ratio to a second change amount that indicates a change in the second physical quantity measured by the unit; and based on the change amount ratio calculated by the calculation unit, the actual second a feedback control unit that feedback-controls the load mechanism so as to reduce a deviation between a physical quantity and a target second physical quantity that is a target value of the second physical quantity; a storage unit that stores the pre-switching change amount ratio that is the change amount ratio calculated by the calculation unit before switching, and the feedback control unit controls the change amount ratio before switching for a predetermined period when the moving direction of the moving member is switched. and feedback-controlling the load mechanism so as to reduce the deviation based on the change amount ratio before switching stored in the storage unit.

According to the material testing machine according to item 1, when switching the moving direction of the moving member, the load mechanism is feedback-controlled based on the change amount ratio calculated from the start of the material test to before the switching for a predetermined period. , the change amount ratio calculated when the change in the change amount ratio is stabilized can be added to the feedback control of the load mechanism, and the load mechanism can be feedback-controlled with high accuracy. In addition, since the change amount ratio when switching the movement direction of the moving member is automatically stored, the user does not need to set the change amount ratio value in advance, which saves the user time and effort. As described above, in a material test involving switching of the moving direction of the moving member, feedback control of the load mechanism can be performed with high accuracy without requiring the user's trouble.

(Section 2)
2. In the material testing machine according to claim 1, when the moving direction of the moving member is switched, the feedback control unit controls the latest change amount ratio calculated by the calculation unit and the pre-switching ratio stored in the storage unit. The load mechanism is feedback-controlled by multiplying the deviation by the change amount ratio having a smaller value among the change amount ratios for the predetermined period.

According to the material testing machine described in item 2, since the load mechanism can be feedback-controlled based on the change amount ratio whose change is stable for a predetermined period, when the moving direction of the moving member is switched, the actual change amount ratio Even if the change is unstable, the load mechanism can be feedback-controlled with high accuracy. Moreover, since a change amount ratio with a small value is adopted, it is possible to prevent the response from becoming excessive. As described above, when the moving direction of the moving member is switched, the load mechanism can be accurately feedback-controlled while preventing the response from becoming excessive.

(Section 3)
The load mechanism according to item 1 or 2 moves the moving member in a first direction to apply a test force to the test object, and moves the moving member in a second direction to apply the test force to the test object. and the feedback control unit controls the switching stored in the storage unit for a predetermined period when the moving direction of the moving member is switched from the first direction to the second direction. feedback control of the load mechanism to reduce the deviation based on the previous variation ratio;

According to the material testing machine described in paragraph 3, since the feedback control of the load mechanism when unloading the test force can be performed with high accuracy, the application of the test force and the material test for unloading the applied test force Can improve accuracy.

(Section 4)
The method for controlling a material testing machine according to item 4 includes a load mechanism that moves a moving member to apply a load to a test object, and measures a first physical quantity that occurs in the test object or the load mechanism according to the load. a first measurement unit that measures a second physical quantity that serves as a response in feedback control of the load mechanism; a first change amount that indicates a change in the first physical quantity measured by the first measurement unit; a calculation unit that calculates a change amount ratio that is a ratio to a second change amount indicating a change in the second physical quantity measured by the second measurement unit; and based on the change amount ratio calculated by the calculation unit, an actual and a feedback control unit that feedback-controls the load mechanism so as to reduce the deviation between the second physical quantity and a target second physical quantity that is a target value of the second physical quantity. wherein the control device stores the pre-switching change ratio, which is the change ratio calculated by the calculating unit from the start of the material test to before the movement direction of the moving member is switched. and feedback-controlling the load mechanism so as to reduce the deviation based on the stored pre-switching variation ratio for a predetermined period when the moving direction of the moving member is switched.

According to the control method of the material testing machine described in item 4, the same effects as those of the material testing machine described in item 1 can be obtained.

1 material testing machine 2 testing machine body 10 crosshead (moving member)
12 load mechanism 30 control device 56 storage unit 541 stress measurement unit (second measurement unit)
542 Strain measurement unit (first measurement unit)
543 control compliance calculator (calculator)
544 Feedback control unit 561 Pre-switching control compliance (pre-switching variation ratio)
561 target data 562 target data DW downward direction (second direction)
F Test force (load)
SA strain (first physical quantity)
SAd Strain change amount (first change amount)
SE stress (second physical quantity)
SEc target stress (target second physical quantity)
SEd stress change amount (second change amount)
SEs Measured stress (actual second physical quantity)
Comp Control compliance (variation ratio)
TP test piece (test object)
e Deviation

Claims (4)

a load mechanism that moves the moving member to apply a load to the test piece ;
a first measuring unit that measures a first physical quantity generated in the test piece or the load mechanism according to the load;
a second measuring unit that measures a second physical quantity that is a response in feedback control of the load mechanism;
A change ratio that is a ratio between a first change amount indicating a change in the first physical quantity measured by the first measuring unit and a second change amount indicating a change in the second physical quantity measured by the second measuring unit a calculation unit that calculates
feedback-controlling the load mechanism so as to reduce a deviation between the actual second physical quantity and a target second physical quantity, which is a target value of the second physical quantity, based on the change amount ratio calculated by the calculator; a feedback controller;
It is the change amount ratio calculated by the calculation unit from the start of the material test to before the moving member switches the moving direction , and the change amount ratio before switching when the test piece is in an elastic state and a storage unit for storing,
The feedback control unit feedback-controls the load mechanism so as to reduce the deviation based on the pre-switching variation ratio stored in the storage unit for a predetermined period when the moving direction of the moving member is switched.
material testing machine. The feedback control unit is
When the movement direction of the moving member is switched, the change in which the instruction value given to the load mechanism is smaller than the latest change amount ratio calculated by the calculation unit and the change amount ratio before switching stored by the storage unit. feedback-controlling the load mechanism by multiplying the deviation by the quantity ratio for the predetermined period;
The material testing machine according to claim 1. The load mechanism moves the moving member in a first direction to apply a test force to the test piece , and moves the moving member in a second direction to remove the test force applied to the test piece . death,
The feedback control unit reduces the deviation based on the pre-switching change amount ratio stored in the storage unit for a predetermined period when the moving direction of the moving member is switched from the first direction to the second direction. feedback-controlling the load mechanism to
The material testing machine according to claim 1 or 2. a load mechanism that moves the moving member to apply a load to the test piece ;
A first measurement unit that measures a first physical quantity generated in the test piece or the load mechanism according to the load, a second measurement unit that measures a second physical quantity that becomes a response in feedback control of the load mechanism, and the first measurement A calculation for calculating a change amount ratio, which is a ratio of a first change amount indicating a change in the first physical quantity measured by the second measurement unit and a second change amount indicating a change in the second physical quantity measured by the second measurement unit and the load mechanism so as to reduce a deviation between the actual second physical quantity and a target second physical quantity, which is a target value of the second physical quantity, based on the variation ratio calculated by the calculating section. A control method for a material testing machine comprising a control device having a feedback control unit that feedback-controls the
The control device
It is the change amount ratio calculated by the calculation unit from the start of the material test to before the moving member switches the moving direction , and the change amount ratio before switching when the test piece is in an elastic state remember,
feedback-controlling the load mechanism so as to reduce the deviation based on the stored pre-switching variation ratio for a predetermined period when the moving direction of the moving member is switched;
Control method of material testing machine.

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