Material testing machine

Abstract

This reduces the waiting time until the internal temperature of the load cell stabilizes and measurement can begin. [Solution] One embodiment of the material testing machine according to the present invention comprises: a detection unit (105) that detects a test force using a strain gauge type sensor with a bridge circuit (1051); a voltage application unit (317) that applies an excitation voltage to the bridge circuit; and a voltage control unit (316) that controls the voltage application unit to apply a warm-up excitation voltage to the bridge circuit that is higher than the voltage value used when the detection unit measures the test force and less than or equal to the maximum voltage value allowed by the detection unit, for at least a portion of the period from the start of applying the excitation voltage to the bridge circuit until the test force measurement is performed.

Description

TECHNICAL FIELD

[0001] The present invention relates to a material testing machine, and more particularly to a material testing machine that measures a test force using a strain gauge type sensor. BACKGROUND ART

[0002] As an apparatus for measuring test force in tensile tests, compression tests and the like, a material testing machine using a load cell equipped with a strain gauge type sensor (or strain gauge type force sensor) is known. As described in Patent Document 1, the strain gauge type sensor includes a strain gauge bridge circuit that converts a change in electric resistance of a strain gauge deformed by a test force into a voltage signal. PRIOR ART DOCUMENTS PATENT DOCUMENTS

[0003] PATENT DOCUMENT 1 Japanese Unexamined Patent Publication No. 2017-138172 PATENT DOCUMENT 2 Japanese Unexamined Patent Publication No. 2009-281917 SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0004] Since a DC voltage or an AC voltage is applied to the strain gauge bridge circuit as an excitation voltage, the circuit generates heat due to power loss. Therefore, a certain amount of time is required from the start of application of the excitation voltage to the strain gauge bridge circuit until the internal temperature of the load cell stabilizes, that is, until the change in the internal temperature of the load cell is almost eliminated. In particular, in a material testing machine, the load cell is attached to a metal crosshead and the heat conduction from the load cell to the crosshead is large, so it may take a considerable amount of time for the internal temperature of the load cell to stabilize to an extent that does not affect the test force.

[0005] If test force measurements are performed before the internal temperature of the load cell has stabilized sufficiently, the zero point and sensitivity of the test force may change during the measurement, potentially leading to incorrect measurement results. For this reason, test force measurements are generally performed after an appropriate waiting period has elapsed from the time the material testing machine is powered on until the internal temperature of the load cell has stabilized to a certain extent. Furthermore, load cells have a specified rated load, and when performing test force measurements on a material testing machine, measurements may be repeated while exchanging load cells with different rated loads. When a load cell is changed, a waiting period is required until the internal temperature of the load cell stabilizes, similar to when the power is turned on (see Patent Document 2, etc.). However, long waiting periods when powering on or when changing load cells lead to a decrease in measurement efficiency and reduce the operating rate of the material testing machine.

[0006] This invention has been made in view of the above problems, and its main objective is to provide a material testing machine that can shorten the waiting time required before measuring test force and perform efficient measurements. [Means for solving the problem]

[0007] One aspect of the material testing machine according to the present invention is: A detection unit that detects the test force using a strain gauge type sensor with a bridge circuit, A voltage application unit that applies an excitation voltage to the bridge circuit, A voltage control unit controls the voltage application unit to apply a warm-up excitation voltage to the bridge circuit that is higher than the voltage value used during the test force measurement by the detection unit and less than or equal to the maximum voltage value allowed by the detection unit, for at least a portion of the period from the start of application of the excitation voltage to the bridge circuit until the test force measurement is performed. It is equipped with. [Effects of the Invention]

[0008] In the material testing machine according to the above embodiment of the present invention, a warm-up excitation voltage with a higher voltage value than the excitation voltage at the time of measurement is applied to the bridge circuit from the start of application of the excitation voltage to the bridge circuit until the test force measurement is performed. When this warm-up excitation voltage is applied to the bridge circuit, the heat generated in the bridge circuit is greater than when an excitation voltage with a voltage value suitable for test force measurement is applied. Therefore, with the material testing machine according to the above embodiment of the present invention, the internal temperature of the load cell can be rapidly increased, for example, immediately after power-on or immediately after load cell replacement. As a result, the waiting time required to reach a state where accurate and reliable test force measurement can be performed can be shortened, and efficient measurement can be performed. [Brief explanation of the drawing]

[0009] [Figure 1] An overall diagram of the main components of a material testing machine, which is one embodiment of the present invention. [Figure 2] Electrical system block diagram of the material testing machine according to this embodiment. [Figure 3] A functional block diagram related to the strain gauge bridge circuit drive, centering on the control unit and operating unit in Figure 2. [Figure 4] This figure shows an example of a flowchart for controlling the excitation voltage when the material testing machine of this embodiment is powered on or when a load cell is replaced. [Figure 5] A schematic diagram showing an example of the temporal change in excitation voltage and the temperature change of the load cell in the material testing machine of this embodiment and a conventional material testing machine. [Modes for carrying out the invention]

[0010] [Supplement to the above description] The term "material testing machine" as used here typically includes devices for measuring the mechanical properties of materials, such as strength, hardness, fatigue characteristics, and impact characteristics. It also includes extensometers (or displacement meters) for measuring the deformation and displacement of test specimens, and width meters for measuring the width of test specimens.

[0011] Further, the "bridge circuit" of the strain gauge type sensor is a circuit capable of detecting deformation (strain) occurring in the strain gauge as a change in electric resistance. Various configurations of this bridge circuit are known, such as the 1-gauge method, 2-gauge method, and 4-gauge method, and the circuit configuration is not limited to a specific one.

[0012] Further, the "excitation voltage" applied to the bridge circuit is a voltage that drives the bridge circuit, and may be either a DC voltage or an AC voltage.

[0013] Further, the time point of "starting application of the excitation voltage to the bridge circuit" as referred to herein means the time point at which the excitation voltage is first applied immediately after the power of this material testing machine is turned on, or immediately after the detection unit is attached to the apparatus main body in a configuration where the detection unit is attachable to and detachable from the apparatus main body. Accordingly, for example, in a case where the excitation voltage is intermittently applied to the bridge circuit after the power of the material testing machine is turned on until the measurement is performed, it refers to the first time point in the series of intermittent applications of the excitation voltage.

[0014] Hereinafter, one embodiment of a material testing machine according to the present invention will be described with reference to the attached drawings. [Configuration of Material Testing Machine] Figure 1 is a configuration diagram of main parts in the material testing machine of the present embodiment. Figure 2 is an electric system block diagram of the material testing machine of the present embodiment. In the following description, the up, down, left, and right directions of the material testing machine are defined with the right direction in Figure 1 taken as right and the upper direction taken as up.

[0015] As shown in Figure 1, the material testing machine of the present embodiment includes a testing machine main body 100, a control unit 300, and an operation unit 400.

[0016] The testing machine main body 100 includes a box-shaped base 101 with a table at the top, a pair of screw shafts 102 erected on the left and right of the base 101, and a yoke 103 that holds the upper ends of the pair of screw shafts 102. A servomotor 107 and a gear box 108 are housed inside the base 101, and the rotation of the drive shaft of the servomotor 107 is transmitted to each screw shaft 102 via the gear box 108, a plurality of timing pulleys 109, and a timing belt 110, whereby the pair of screw shafts 102 rotate in synchronization with each other. A nut 106 is screwed onto each of the pair of screw shafts 102. A crosshead 104 is horizontally stretched between these nuts 106, and as the screw shafts 102 rotate, the crosshead 104 moves up and down as indicated by the double-headed arrow in FIG. 1.

[0017] An upper gripper 111 is attached to the crosshead 104 via a load cell 105. On the other hand, a lower gripper 112 is attached to a position on the base 101 that is directly below the upper gripper 111. In this material testing machine, a tensile test is performed on the test piece 500 by raising the crosshead 104 in a state where the upper end and the lower end of the test piece 500 are respectively gripped by the upper gripper 111 and the lower gripper 112. In this tensile test, the test force (tensile force) applied to the test piece 500 as the crosshead 104 rises is detected by the load cell 105.

[0018] The load cell 105 is connected to a calibration (CAL) connector 200 via a cable 113, and the CAL connector 200 is connected to a control unit 300. The control unit 300 is connected to an operation unit 400. The control unit 300 is also responsible for controlling the servomotor 107 that raises and lowers the crosshead 104, but the wiring for that purpose is omitted in FIG. 1.

[0019] The load cell 105 is detachable from the crosshead 104. Multiple load cells 105 with different load ratings are available, and the appropriate load cell 105 with the appropriate load rating is used depending on the test piece 500. Basically, the load cell 105 and the CAL connector 200 are a pair, and when the load cell 105 is replaced with one of a different load rating, the CAL connector 200 is also replaced accordingly. This is because, as will be described later, information about the load cell 105 is stored inside the CAL connector 200. The CAL connector 200 and the cable 113 may be integrated, or the load cell 105, cable 113, and CAL connector 200 may be integrated. Also, the functions of the CAL connector 200 may be incorporated into the load cell 105.

[0020] This material testing machine is configured to allow for the performance of material tests other than tensile tests on the test specimen 500, such as compression tests, bending tests, shear tests, and peel tests, by replacing the upper grips 111 and lower grips 112 with other fixtures, and to perform tests on test specimens of various sizes and shapes.

[0021] The control unit 300 controls the main unit 100 of the test machine and the operation unit 400, and also collects data on the test force. As shown in Figure 2, it includes a microprocessing unit (MPU) 301, a field-programmable gate array (FPGA) 302, a digital-to-analog converter (DAC), a power amplifier 304, an instrumentation amplifier 305, an analog-to-digital converter (ADC) 306, and the like. The MPU 301 performs various arithmetic operations according to a program pre-stored in memory. The FPGA 302 performs hardware-defined logical operations and outputs predetermined numerical data.

[0022] The operation unit 400 is used by the operator to input instructions to the control unit 300 and to visually receive information. It includes a microprocessing unit (MPU) 401, a field-programmable gate array (FPGA) 402, a liquid crystal display 404 that functions as a display unit, and a touchscreen 403 that functions as an input unit. The FPGA 402 and FPGA 302 have the function of communicating with each other, thereby facilitating the exchange of data and control signals between the control unit 300 and the operation unit 400. The input unit of the operation unit 400 does not have to be the touchscreen 403; it may also use a general key switch panel or voice input.

[0023] The CAL connector 200 internally includes a memory 201 that can be read and written from the outside, and an R / W circuit (not shown) for reading and writing data to the memory 201. This memory 201 is accessible from the FPGA 302 of the control unit 300. The memory 201 holds information such as the type of load cell 105 paired with the CAL connector 200 and information indicating the rated load. Information indicating the rated voltage value and maximum voltage value of the excitation voltage, which will be described later, may also be stored in the memory 201. In addition, various data necessary for measurement, such as sensitivity correction information in test force measurement using the corresponding load cell 105, may also be written to and stored in the memory 201.

[0024] The load cell 105 includes a strain gauge that deforms under test force and a strain gauge bridge circuit 1051, which includes the strain gauge and a bridge circuit. The control unit 300 applies an excitation voltage to the strain gauge bridge circuit 1051 via the CAL connector 200 and performs calculation processing to calculate the test force by receiving an electrical signal corresponding to the amount of deformation of the strain gauge in the strain gauge bridge circuit 1051.

[0025] Figure 2 shows the configuration of the control unit 300 and the operation unit 400, mainly from a device perspective, while Figure 3 is a schematic configuration diagram showing the configuration of the control unit 300 and the operation unit 400 as functional blocks centered on driving the strain gauge bridge circuit 1051. As shown in Figure 3, the control and operation unit 310 embodied by the control unit 300 and the operation unit 400 includes, as functional blocks, a power-on unit 311, a warm-up operation interruption instruction unit 312, a sensor information reading unit 313, a warm-up operation time count unit 314, a warm-up operation remaining time display unit 315, an excitation voltage control unit 316, an excitation voltage generation unit 317, a measurement processing unit 318, and the like.

[0026] The power-on unit 311 includes, for example, a power switch (not shown) provided on the operation unit 400, and recognizes the operator's power-on operation of the material testing machine. The warm-up interruption instruction unit 312 is implemented by the MPU 401, FPGA 402, and touchscreen 403 in the operation unit 400, and recognizes an instruction to interrupt the warm-up operation in response to a predetermined input operation by the operator. The sensor information reading unit 313 accesses the memory 201 of the CAL connector 200 and reads information corresponding to the cell (load cell 105 or other sensor) held in the memory 201. The warm-up time count unit 314 performs a countdown from a predetermined warm-up time. In the following example, the default warm-up time is assumed to be 15 minutes, but this is just an example, and the configuration may allow the operator or the manufacturer's service personnel to change this value as appropriate.

[0027] The warm-up time remaining display unit 315 displays the remaining warm-up time, which is counted down by the warm-up time count unit 314, in real time in a predetermined area on the screen of the liquid crystal display 404. The excitation voltage control unit 316 is implemented by the MPU 301 and determines and instructs the voltage value of the excitation voltage to be applied to the strain gauge bridge circuit 1051. The excitation voltage generation unit 317 is implemented by the FPGA 302, DAC 303, and power amplifier 304 and generates an excitation voltage having the voltage value determined by the excitation voltage control unit 316. The excitation voltage may be either a DC voltage or an AC voltage (generally a sinusoidal voltage). The measurement processing unit 318 is implemented by the instrumentation amplifier 305, ADC 306, MPU 301, and FPGA 302 and calculates the test force from the electrical signal corresponding to the deformation amount of the strain gauge in the strain gauge bridge circuit 1051.

[0028] [Operation of the material testing machine in this embodiment] When the material testing machine of this embodiment is powered off, the load cell 105 is at approximately room temperature. When the operator turns on the power and an excitation voltage is applied to the strain gauge bridge circuit 1051, the strain gauge bridge circuit 1051 generates heat due to power loss, and the internal temperature of the load cell 105 begins to rise. It takes a certain amount of time for the internal temperature of the load cell 105 to rise to a level that does not significantly affect the test force measurement and to stabilize to a certain extent. If the measurement is performed before this time has elapsed, the accuracy of the measurement cannot be ensured. On the other hand, if this time is long, the operator's waiting time will increase, leading to a decrease in the efficiency of the measurement.

[0029] Therefore, in the material testing machine of this embodiment, a distinctive control is implemented to ensure that the internal temperature of the load cell 105 rises rapidly and stabilizes. This control will be explained with reference to Figures 1 to 3, as well as Figures 4 and 5. Figure 4 is a diagram showing an example of a flowchart of excitation voltage control when the power is turned on or when the load cell is replaced, and Figure 5 is a schematic diagram showing an example of the temporal change in excitation voltage and the temperature change of the load cell.

[0030] When the operator turns on the power to the material testing machine by operating the power switch, predetermined power is supplied to each part, such as the control unit 300, from a power supply unit (not shown) (Step S1). The sensor information reading unit 313 accesses the memory 201 of the CAL connector 200 and reads data such as load cell type information held in the memory 201. As a result, the control and operation unit 310 recognizes that the sensor connected via the CAL connector 200 is a load cell 105, that is, that the connected sensor is equipped with a strain gauge bridge circuit 1051 (Step S2).

[0031] In addition to when the power is turned on, when the CAL connector 200 is newly connected to the control unit 300 due to the replacement of the load cell 105, the sensor information reading unit 313 detects the installation operation of the CAL connector 200 and reads data such as load cell type information from the memory 201 of the newly installed CAL connector 200. Therefore, in both cases, when the power is turned on and when the load cell 105 is replaced, the sensor information reading unit 313 can recognize that the sensor indirectly connected to the control unit 300 is the load cell 105. Furthermore, even if it is detected that a strain gauge type sensor using a strain gauge bridge circuit, such as an extensometer or width meter using a strain gauge type sensor, is indirectly connected to the control unit 300 instead of the load cell 105, the control described below can also be performed.

[0032] As described above, once the load cell 105 is recognized as being connected, the warm-up time count unit 314 starts counting down from a predetermined warm-up time (15 minutes in this case). The remaining warm-up time display unit 315 displays the remaining warm-up time in real time in a predetermined display area (step S3). This display of remaining time allows the operator to know the remaining warm-up time, that is, the waiting time until measurement is possible.

[0033] The excitation voltage control unit 316 determines whether the elapsed time, with the countdown start time for the warm-up time being zero, is within 5 minutes, that is, whether it is within the first 5 minutes of the predetermined warm-up time (step S4). If it is determined to be YES in step S4, the excitation voltage control unit 316 determines whether there is an instruction from the warm-up interruption instruction unit 312 to interrupt the warm-up operation (step S5).

[0034] The operator can interrupt the warm-up operation at any time during the warm-up by performing a predetermined operation on the touchscreen 403. For example, if the operator wants to know the results of the test force measurement quickly, even if it is not very accurate, because the internal temperature of the load cell 105 has not risen sufficiently, the warm-up operation can be interrupted and the measurement can be started. Also, if the operator recognizes that the internal temperature of the load cell 105 is sufficiently high, such as when the power is turned off and then immediately turned back on, or when the load cell 105 and CAL connector 200 that were used for measurement are temporarily removed and immediately reinstalled, the warm-up operation can be interrupted and the measurement can be started. The warm-up interruption instruction unit 312 recognizes that the operator has instructed the warm-up operation to be interrupted by the operation described above, and transmits this instruction to the excitation voltage control unit 316.

[0035] If the operator has not instructed the system to interrupt the warm-up operation, step S5 is determined to be NO, and the excitation voltage control unit 316 sets the excitation voltage value to the maximum voltage value allowed for the load cell 105 (step S6). This maximum voltage value information may be stored in advance in the MPU 301, or it may be read from the memory 201 of the CAL connector 200. As an example, the maximum voltage value is assumed to be 15V. The excitation voltage generation unit 317 generates a warm-up excitation voltage of 15V, which is the voltage value set by the excitation voltage control unit 316, and applies it to the strain gauge bridge circuit 1051 of the load cell 105 via the CAL connector 200 (step S7).

[0036] Specifically, in the control unit 300, the MPU 301 instructs the FPGA 302 to output a voltage with a maximum voltage value, and in response, the FPGA 302 outputs a digital value of the voltage waveform corresponding to that instruction. When the excitation voltage is a DC voltage, the digital value of the voltage waveform is a constant value. When the excitation voltage is an AC voltage, the digital value of the voltage waveform is a repeating value that changes over time, corresponding to one period of sinusoidal voltage. The DAC 303 converts the digital value of the voltage waveform received from the FPGA 302 into an analog voltage, and the power amplifier 304 amplifies the analog voltage output from the DAC 303 by voltage or current and outputs it. As a result, a warm-up excitation voltage of 15V is applied to the strain gauge bridge circuit 1051, as shown in Figure 5(a), and the temperature of the strain gauge bridge circuit 1051 begins to rise, as shown by the solid line in Figure 5(d). Note that when the excitation voltage is an AC voltage, the effective value of that AC voltage should be used as the maximum voltage value.

[0037] After step S7 described above, the process returns to step S4. Therefore, unless the operator instructs to interrupt the warm-up operation, the process from steps S4 to S7 is repeated, and for the first 5 minutes from the start of the warm-up operation, a warm-up excitation voltage with a voltage value of 15V is continuously applied to the strain gauge bridge circuit 1051, as shown in Figure 5(a). The voltage value at this time is higher than the excitation voltage value (rated voltage value: here, let's assume it is 10V as an example) applied to the strain gauge bridge circuit 1051 during test force measurement. Figure 5(c) shows the temporal change of the excitation voltage in a conventional material testing machine. As shown in this figure, conventionally, an excitation voltage of 10V, which is the rated voltage value, is continuously applied to the strain gauge bridge circuit 1051 from the start of the excitation voltage application. Therefore, in the material testing machine of this embodiment, an excitation voltage 1.5 times higher is applied to the strain gauge bridge circuit 1051 compared to a conventional material testing machine.

[0038] The processes in steps S4 to S7 are repeated, and after 5 minutes have elapsed since the start of warm-up operation, step S4 is determined to be NO and the process proceeds to step S9. The excitation voltage control unit 316 then changes the setting of the excitation voltage value to the excitation voltage at the time of measurement, i.e., the rated voltage value of 10V. The excitation voltage generation unit 317 generates an excitation voltage of the voltage value set by the excitation voltage control unit 316, i.e., the rated voltage value in this case of 10V, and applies it to the strain gauge bridge circuit 1051 of the load cell 105 via the CAL connector 200 (step S10). Specifically, in the control unit 300, the MPU 301 instructs the FPGA 302 to output the rated voltage value instead of the maximum voltage value, and in response, the FPGA 302 outputs a digital value of the voltage waveform corresponding to that instruction. Therefore, as shown in Figure 5(a), after 5 minutes have elapsed since the start of excitation voltage application, the excitation voltage applied to the strain gauge bridge circuit 1051 switches from 15V to 10V.

[0039] Let's return to explaining the repetition of steps S4 to S7. If the operator instructs to interrupt the warm-up operation before 5 minutes have elapsed since the start of the warm-up operation, step S5 is determined to be YES, and the process proceeds to step S8. Then, the warm-up operation time count unit 314 changes the remaining time to zero, regardless of the remaining warm-up time. Consequently, the remaining time displayed on the warm-up operation remaining time display unit 315 also becomes zero. After that, the process proceeds to steps S9 and S10, and as described above, the excitation voltage applied to the strain gauge bridge circuit 1051 switches from 15V to 10V. Figure 5(b) shows an example of the change in excitation voltage when the warm-up operation is interrupted before 5 minutes have elapsed since the start of the warm-up operation.

[0040] After step S10, the excitation voltage control unit 316 determines whether the remaining warm-up time is zero (step S11). If it is not zero, it then determines whether the warm-up interruption instruction unit 312 has instructed the operator to interrupt the warm-up operation, similar to step S5 (step S12). If there is no instruction to interrupt the warm-up operation, the process returns to step S9. Therefore, if the operator does not instruct the operator to interrupt the warm-up operation until the predetermined warm-up time, i.e., 15 minutes, has elapsed, the process from steps S9 to S12 is repeated. That is, the strain gauge bridge circuit 1051 is subjected to an excitation voltage of 10V, which is the rated voltage. As a result, the amount of heat generated by the strain gauge bridge circuit 1051 is smaller than that generated during the period from the start of excitation voltage application until 5 minutes have elapsed, and as shown in Figure 5(d), the rise in the internal temperature of the load cell 105 becomes gradual. As the remaining warm-up time approaches zero, the rate of increase in the internal temperature of the load cell 105 becomes gradual and approaches a stable state.

[0041] Then, when the excitation voltage control unit 316 determines that the remaining warm-up time is zero, the process moves from step S11 to step S14, and the control / operation unit 310 enters a test execution standby state while the strain gauge bridge circuit 1051 remains in a state where the rated voltage of 10V is applied as the excitation voltage. On the other hand, if the operator instructs to interrupt the warm-up operation before 15 minutes have elapsed since the start of the warm-up operation during the repetition of steps S9 to S12, the result is determined to be YES in step S12. In this case, the warm-up time count unit 314 changes the remaining time to zero regardless of the remaining warm-up time (step S13), as in steps S8 and P, and proceeds to step S14. Therefore, in this case, the test execution standby state is entered without waiting for 15 minutes to elapse since the start of the warm-up operation. Note that if the remaining warm-up time becomes zero in step S8, the result is determined to be YES in the next step S11 after steps S9 and S10, and the test execution standby state is entered without waiting for 5 minutes to elapse since the start of the warm-up operation.

[0042] The relationship between the processing flow according to the flowchart above and the state of the excitation voltage applied to the strain gauge bridge circuit 1051 is summarized below. If the process transitions from step S4 to step S9 during the repetition of steps S4 to S7, and then from step S11 to step S14 during the repetition of steps S9 to S12, the temporal change in the excitation voltage will be as shown in Figure 5(a). In this case, more power is supplied to the strain gauge bridge circuit 1051 than in a conventional material testing machine (Figure 5(c)), equivalent to a voltage value 1.5 times higher (the ratio of the maximum voltage value to the rated voltage value) that lasts for 5 minutes. Therefore, the time required for the internal temperature of the load cell 105 to stabilize is considerably shorter compared to a conventional material testing machine, as shown in Figure 5(d).

[0043] Furthermore, even when the process transitions from step S4 to step S9 during the repetition of steps S4 to S7, and then from step S12 to step S13 during the repetition of steps S9 to S12, more power is supplied to the strain gauge bridge circuit 1051 than in conventional material testing machines, equivalent to maintaining a voltage value 1.5 times higher (the ratio of the maximum voltage value to the rated voltage value) for 5 minutes. Consequently, the time required for the internal temperature of the load cell 105 to stabilize is considerably shorter compared to conventional material testing machines.

[0044] On the other hand, when the process from step S5 to step S8 is transitioned during the repetition of steps S4 to S7, the temporal change in the excitation voltage is as shown in Figure 5(b). In this case, although the power supplied to the strain gauge bridge circuit 1051 decreases as the time during which the maximum voltage of 15V is applied to the strain gauge bridge circuit 1051 is shortened, the time required for the internal temperature of the load cell 105 to stabilize is shortened compared to conventional material testing machines.

[0045] When the remaining warm-up time display becomes zero and the system is in a test execution standby state in step S14, if the operator performs a predetermined operation on the touchscreen 403, for example, the crosshead 104 rises, and a tensile test is performed on the test piece 500. During this test, a voltage signal proportional to the test force is output from the strain gauge bridge circuit 1051 and input to the measurement processing unit 318 via the CAL connector 200. The measurement processing unit 318 performs a process to convert the received voltage signal into a test force and displays the result in a predetermined area on the screen of the liquid crystal display 404.

[0046] Specifically, the instrumentation amplifier 305 amplifies the voltage signal received from the strain gauge bridge circuit 1051, and the ADC 306 converts the analog voltage output from the instrumentation amplifier 305 into a digital value. The output of the ADC 306 is input to the FPGA 302, and the FPGA 302 calculates the test force by multiplying the read digital voltage value by a conversion coefficient sent from the MPU 301. Even if the test force values ​​are the same, if the excitation voltage applied to the strain gauge bridge circuit 1051 is different, the voltage signal output from the strain gauge bridge circuit 1051 will be different. Therefore, when the test force values ​​are the same, the conversion coefficient is adjusted so that the converted test force value is the same even if the voltage signal output from the strain gauge bridge circuit 1051 is different due to different excitation voltages applied to the strain gauge bridge circuit 1051. In other words, the MPU301 sends a conversion coefficient corresponding to the excitation voltage value to the FPGA302, and the FPGA302 uses this conversion coefficient for multiplication, thereby enabling the accurate determination of the test force regardless of the excitation voltage value applied to the strain gauge bridge circuit 1051.

[0047] As described above, the material testing machine of this embodiment has the following advantages over conventional material testing machines because, for at least a portion of the warm-up period, a warm-up excitation voltage with a voltage value higher than the excitation voltage during measurement is applied to the strain gauge bridge circuit 1051. (1) When the same warm-up period is performed as with conventional material testing machines, the internal temperature stability of the load cell 105 is increased compared to conventional material testing machines, allowing for more accurate, reproducible, and reliable test force measurements. (2) Even when the warm-up time is shortened compared to conventional material testing machines, or when the warm-up is interrupted midway through the warm-up (i.e., the warm-up time is shorter than that of conventional machines) and test force measurement is performed, test force measurement can be performed with accuracy and reliability equivalent to or close to that of conventional material testing machines when the warm-up is performed sufficiently. This makes it possible to reduce the warm-up time, i.e., the waiting time, and improve the efficiency of test force measurement while ensuring accuracy.

[0048] For example, in a typical load cell (input resistance: 350Ω, rated voltage: 10V), when the rated voltage is applied as the excitation voltage, 10V occurs inside the load cell. 2 / 350 = 286mW of heat is generated. In contrast, if a warm-up excitation voltage of 15V is applied only for the first 5 minutes of warm-up operation, the amount of heat generated inside the load cell is 15 2 / 350 = 643mW, resulting in 2.25 times the amount of heat generated. In other words, since increasing the excitation voltage has a proportional effect on the amount of heat generated by the square of the voltage value, the effect is significant. Thus, in this embodiment of the material testing machine, the amount of heat generated in the strain gauge bridge circuit 1051 can be increased, and the temperature of the load cell 105 can be raised in a shorter time.

[0049] Another possible method to shorten the time it takes for the temperature inside the load cell to stabilize is to lower the excitation voltage applied to the strain gauge bridge circuit during measurement. However, lowering the excitation voltage reduces the signal-to-noise ratio of the voltage signal corresponding to the test force obtained from the strain gauge bridge circuit, making it impossible to accurately determine the test force. Therefore, lowering the excitation voltage during measurement is not appropriate. From this perspective, the excitation voltage control method adopted in the material testing machine of this embodiment is an excellent method because it leads to a reduction in waiting time without impairing the accuracy of test force measurement.

[0050] [Differentiation] In the material testing machine of the above embodiment, immediately after power-on or immediately after connecting the load cell 105 to the control unit 300, an excitation voltage is applied to the strain gauge bridge circuit 1051, and a warm-up excitation voltage of the maximum allowable voltage value for the load cell 105 is applied for only 5 minutes. After that, the excitation voltage applied to the strain gauge bridge circuit 1051 is returned to the rated voltage value. However, this is not limited to this, and the time for applying the warm-up voltage may be made longer or shorter. Also, instead of applying the excitation voltage to the strain gauge bridge circuit 1051 immediately after starting to apply the excitation voltage, the excitation voltage may initially be applied at the rated voltage value, and then the excitation voltage value may be increased after a while. In other words, the warm-up excitation voltage may be applied at any timing during the warm-up period, and the period during which the warm-up excitation voltage is applied may be part of the warm-up period or all of it.

[0051] Furthermore, it is clear that raising the excitation voltage to a voltage value at least higher than the measured voltage value, i.e., the rated voltage value, rather than raising it to the maximum voltage value, is effective in accelerating the rise in the internal temperature of the load cell 105. Also, during the warm-up period, the excitation voltage may be changed continuously or in steps over time. For example, at the beginning of the warm-up period, the excitation voltage could be set to the highest possible voltage value, such as the maximum voltage value, and then gradually changed to approach the rated voltage value as time progresses. Thus, various patterns of excitation voltage change during warm-up are conceivable.

[0052] Furthermore, if the maximum voltage value and rated voltage value differ depending on the type of load cell 105 used with the crosshead 104, as described above, the memory 201 built into the CAL connector 200 can store information on the maximum voltage value and rated voltage value corresponding to the load cell 105, and the FPGA 302 can read this information and instruct the FPGA 302 to output either the maximum voltage value or the rated voltage value. Alternatively, the MPU 301 can hold information on the maximum voltage value and rated voltage value corresponding to the load cell 105, and based on the load cell type information read from the memory 201, select the maximum voltage value and rated voltage value, respectively, and instruct the FPGA 302. Of course, it is also conceivable to have the operator input or select the maximum voltage value and rated voltage value corresponding to the load cell 105 being used.

[0053] Furthermore, while the material testing machine in the above embodiment used a load cell to measure the test force, the sensor connected to the control unit is not limited to a load cell, as long as the test force is measured using a strain gauge type sensor with a strain gauge bridge circuit. Therefore, it is clear that the present invention is not limited to general-purpose material testing machines, but can also be applied to, for example, extensometers (or displacement meters) and width meters that use strain gauge type sensors with strain gauge bridge circuits as elongation detectors, as well as to material testing machines that measure test forces on specific test objects such as springs, plastics, concrete, and rubber.

[0054] Furthermore, the embodiments and modifications described above are merely examples of the present invention, and it is clear that any further changes, additions, or deletions made within the scope of the present invention will still be included in the claims of this patent application.

[0055] [Various forms] Those skilled in the art will understand that the exemplary embodiments described above are specific examples of the following embodiments.

[0056] (Section 1) One embodiment of the material testing machine according to the present invention is: A detection unit that detects the test force using a strain gauge type sensor with a bridge circuit, A voltage application unit that applies an excitation voltage to the bridge circuit, A voltage control unit controls the voltage application unit to apply a warm-up excitation voltage to the bridge circuit that is higher than the voltage value used during the test force measurement by the detection unit and less than or equal to the maximum voltage value allowed by the detection unit, for at least a portion of the period from the start of application of the excitation voltage to the bridge circuit until the test force measurement is performed. It is equipped with.

[0057] In the material testing machine described in paragraph 1, a warm-up excitation voltage, for example, the maximum voltage value permissible by the detection unit, is applied to the bridge circuit from the start of application of the excitation voltage to the bridge circuit until the test force measurement is performed. When such a warm-up excitation voltage is applied to the bridge circuit, the heat generated in the bridge circuit is greater than when an excitation voltage suitable for test force measurement is applied. Therefore, with the material testing machine described in paragraph 1, the internal temperature of the detection unit, such as the load cell, can be rapidly raised and stabilized immediately after power-on or immediately after load cell replacement. This reduces the waiting time required to reach a state where accurate and reliable test force measurement can be performed, and enables efficient measurement.

[0058] (Section 2) In the material testing machine described in Section 1, the voltage control unit may control the voltage application unit to apply an excitation voltage, which is the voltage value used when the detection unit measures the test force, to the bridge circuit, except for at least a portion of the period from the start of application of the excitation voltage to the bridge circuit.

[0059] In the material testing machine described in paragraph 2, an excitation voltage lower than the warm-up excitation voltage is applied to the bridge circuit during periods other than when the warm-up excitation voltage is applied to the bridge circuit. This prevents the internal temperature of the detection unit from rising excessively and allows the internal temperature to stabilize quickly. Furthermore, the test force can be measured immediately once the internal temperature of the detection unit has stabilized.

[0060] (3) In the material testing machine described in paragraph 1 or 2, the voltage control unit may control the voltage application unit to apply a warm-up excitation voltage of the maximum voltage value permitted by the detection unit to the bridge circuit for at least a portion of the period.

[0061] According to the material testing machine described in paragraph 3, it is possible to rapidly raise the internal temperature of the detection unit while avoiding the application of excessive voltage to the bridge circuit of the detection unit.

[0062] (Article 4) In the material testing machine described in any one of paragraphs 1 to 3, the aforementioned partial period may be the period that begins at or immediately after the start of application of the excitation voltage to the bridge circuit.

[0063] In the material testing machine described in Section 4, a warm-up excitation voltage is applied to the bridge circuit from the very beginning of the application of the excitation voltage to the bridge circuit. This allows for an efficient increase in the internal temperature of the detection unit, and further reduces the time it takes for the internal temperature to stabilize.

[0064] (Article 5) In the material testing machine described in any one of paragraphs 1 to 4, the period from the start of application of the excitation voltage to the bridge circuit until a predetermined time has elapsed is defined as the warm-up period, and at least a portion of the said period may be the period from the start of application of the excitation voltage to the bridge circuit or immediately thereafter until before the end of the warm-up period.

[0065] In the material testing machine described in Section 5, a warm-up period is predetermined, and the test force measurement is performed after this period has ended. This allows the test force measurement to be performed after the internal temperature of the detection unit has stabilized, resulting in accurate and highly reproducible results.

[0066] (Section 6) The material testing machine described in Section 5 further comprises an operation reception unit that accepts an operation by the operator to interrupt the warm-up operation, The voltage control unit may, in response to the operation reception unit receiving an operation to interrupt the warm-up operation, control the voltage application unit to terminate the warm-up operation period and apply an excitation voltage, which is the voltage value at the time of test force measurement by the detection unit, to the bridge circuit.

[0067] In the material testing machine described in Section 6, the operator can interrupt the warm-up operation and immediately perform the test force measurement. This allows for immediate measurement without waiting time, for example, when it is desirable to obtain measurement results quickly even if some degree of accuracy is sacrificed, or when it is known that the internal temperature of the detection unit is sufficiently stable.

[0068] (Clause 7) In a material testing machine described in any one of paragraphs 1 to 6, the voltage control unit may start applying an excitation voltage to the bridge circuit immediately after the power of the material testing machine is turned on.

[0069] According to the material testing machine described in paragraph 7, the waiting time from when the operator turns on the power to the material testing machine until appropriate test force measurement becomes possible can be shortened.

[0070] (Clause 8) In a material testing machine described in any one of paragraphs 1 to 7, the detection unit is detachable from the material testing machine and further comprises a mounting detection unit that detects when the detection unit is mounted on the material testing machine. The voltage control unit may start applying an excitation voltage to the bridge circuit immediately after the mounting detection unit detects the mounting of the detection unit.

[0071] According to the material testing machine described in Section 8, the application of excitation voltage to the bridge circuit begins without any special operation after the operator replaces a detection unit such as a load cell, thus improving operability. Furthermore, the waiting time until appropriate test force measurement becomes possible after replacing the detection unit can be shortened.

[0072] (Clause 9) In the material testing machine described in any one of paragraphs 1 to 8, the detection unit may be a load cell, an extensometer, a displacement meter, or a width meter.

[0073] According to the material testing machine described in Section 9, the test force in various tests on a test specimen, such as tensile tests, compression tests, bending tests, shear tests, and peel tests, can accurately and efficiently measure the amount of strain. [Explanation of symbols]

[0074] 100... Test machine body 101... Base 102... Screw shaft 103... York 104...Crosshead 105... Load cell 1051... Strain Gauge Bridge Circuit 106... Nut 107…Servo motor 108... Gearbox 109... Timing pulley 110... Timing belt 111... Upper gripping tool 112...Lower gripping tool 113… Cable 200…CAL connector 201...Memory 300... Control Unit 400...Operation Unit 301, 401…MPU 302, 402…FPGA 303…DAC 304... Power amplifier 305... Instrumentation amplifier 306…ADC 403…Touchscreen 404... LCD display 310...Control and operation unit 311...Power supply section 312... Warm-up operation interruption instruction unit 313...Sensor information reading unit 314... Warm-up time counting unit 315... Warm-up time remaining display section 316...Excitation Voltage Control Unit 317...Excitation voltage generation unit 318...Measurement Processing Unit 500... Test piece

Claims

1. A detection unit that detects the test force using a strain gauge type sensor with a bridge circuit, A voltage application unit that applies an excitation voltage to the bridge circuit, A voltage control unit controls the voltage application unit to apply a warm-up excitation voltage to the bridge circuit, which is higher than the voltage value used during the test force measurement by the detection unit and less than or equal to the maximum voltage value allowed by the detection unit, for at least a portion of the period from the start of application of the excitation voltage to the bridge circuit until the test force measurement is performed. A materials testing machine equipped with the following features.

2. The material testing machine according to claim 1, wherein the voltage control unit controls the voltage application unit to apply an excitation voltage, which is the voltage value used when the detection unit measures the test force, to the bridge circuit, except for at least a portion of the period from the start of application of the excitation voltage to the bridge circuit.

3. The material testing machine according to claim 1, wherein the voltage control unit controls the voltage application unit to apply a warm-up excitation voltage of the maximum voltage value permitted by the detection unit to the bridge circuit for at least a portion of the period.

4. The material testing machine according to claim 1, wherein the aforementioned period of at least a portion of the period begins at or immediately after the start of application of the excitation voltage to the bridge circuit.

5. The material testing machine according to claim 1, wherein the period from the start of application of the excitation voltage to the bridge circuit until a predetermined time has elapsed is defined as the warm-up period, and at least a portion of the period is the period from the start of application of the excitation voltage to the bridge circuit or immediately thereafter until before the warm-up period ends.

6. It is further equipped with an operation reception unit that accepts requests from the operator to interrupt the warm-up process. The material testing machine according to claim 5, wherein the voltage control unit, in response to the operation reception unit receiving an operation to interrupt the warm-up operation, terminates the warm-up operation period and controls the voltage application unit to apply an excitation voltage, which is the voltage value at the time of test force measurement by the detection unit, to the bridge circuit.

7. The material testing machine according to claim 1, wherein the voltage control unit starts applying a warm-up excitation voltage to the bridge circuit immediately after the power is turned on to the material testing machine.

8. The detection unit is detachable from the material testing machine and further comprises an attachment detection unit that detects when the detection unit is attached to the material testing machine. The material testing machine according to claim 1, wherein the voltage control unit starts applying a warm-up excitation voltage to the bridge circuit immediately after the mounting detection unit detects the mounting of the detection unit.

9. The material testing machine according to any one of claims 1 to 8, wherein the detection unit is a load cell, an extensometer, a displacement meter, or a width meter.

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