material testing machine

Abstract

Shorten the waiting time until the internal temperature of the load cell stabilizes and measurement can be performed. A material testing machine according to one aspect of the invention is provided with a detection section (105) that detects a test force by using a strain gauge sensor with a bridge circuit (1051), a voltage application section (317) that applies an excitation voltage to the bridge circuit, and a voltage control section (316) that controls the voltage application section so that, during at least a part of the period from when the application of the excitation voltage to the bridge circuit is started until the test force measurement is performed, a preheating excitation voltage is applied to the bridge circuit, the preheating excitation voltage being higher than the voltage value when the test force measurement is performed by the detection section and being below the maximum voltage value allowed by the detection section.

Description

Technical Field

[0001] This invention relates to a material testing machine, and more specifically, to a material testing machine that uses strain gauge sensors to measure test forces. Background Technology

[0002] As a device for measuring test forces in tensile tests, compression tests, etc., a material testing machine using a load sensor equipped with a strain gauge sensor (or strain gauge force sensor) is known. As described in Patent Document 1, the strain gauge sensor includes a strain gauge bridge circuit that converts the resistance change of the strain gauge deformed by the test force into a voltage signal.

[0003] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2017-138172 Patent Document 2: Japanese Patent Application Publication No. 2009-281917 Summary of the Invention The technical problem that the invention aims to solve Because a DC or AC voltage is applied as the excitation voltage to the strain gauge bridge circuit, the circuit generates heat due to power loss. Therefore, it takes a certain amount of time from the initial application of the excitation voltage to the stabilization of the load sensor's internal temperature, i.e., until the internal temperature of the load sensor hardly changes anymore. Especially in material testing machines, where the load sensor is mounted on a metal crosshead, the heat conduction from the load sensor to the crosshead is significant. Therefore, it can sometimes take a considerable amount of time for the internal temperature of the load sensor to stabilize to a level that does not affect the test force.

[0004] If test force measurements are performed before the internal temperature of the load sensor is sufficiently stable, the zero point and sensitivity of the test force may change during the measurement process, potentially leading to inaccurate results. Therefore, test force measurements are typically performed after a suitable standby time has elapsed since the material testing machine was powered on, until the internal temperature of the load sensor has reached a certain level of stability. Furthermore, the load sensor has a specified rated load. During test force measurements on the material testing machine, measurements are sometimes repeated while changing load sensors with different rated loads. However, when changing load sensors, a standby time until the internal temperature of the load sensor stabilizes is required, similar to when the power is on (see Patent Document 2, etc.). However, setting a long standby time when power is on or when changing load sensors reduces measurement efficiency and decreases the operating rate of the material testing machine.

[0005] The present invention was made in view of the above-mentioned technical problems, and its main objective is to provide a material testing machine that can shorten the waiting time required before measuring the test force and can perform efficient measurement.

[0006] Solution to the above technical problems According to one aspect of the present invention, a material testing machine comprises: The testing department uses strain gauge sensors with a bridge circuit to detect the test force. The voltage application section applies an excitation voltage to the bridge circuit; and The voltage control unit controls the voltage application unit to apply a preheating excitation voltage to the bridge circuit for at least a portion of the period between the start of applying an excitation voltage to the bridge circuit and the implementation of the test force measurement. The preheating excitation voltage is higher than the voltage value when the detection unit performs the test force measurement, and lower than the maximum voltage value allowed by the detection unit.

[0007] Invention Effects In the material testing machine of the present invention described above, a preheating excitation voltage higher than the excitation voltage at the time of measurement is applied to the bridge circuit from the time the excitation voltage is applied to the bridge circuit until the test force measurement is performed. When this preheating excitation voltage is applied to the bridge circuit, the bridge circuit generates more heat than when an excitation voltage suitable for the test force measurement is applied. Therefore, in the material testing machine of the present invention according to the above aspects, for example, immediately after power is turned on or immediately after the load sensor is replaced, the internal temperature of the load sensor can rise rapidly. This shortens the standby time required until an accurate and reliable test force measurement can be performed, enabling efficient measurement. Attached Figure Description

【 Figure 1 [A diagram showing the overall structure of the main parts of a material testing machine according to an embodiment of the present invention.]

[0008]

【 Figure 2 [Diagram of the electrical system module configuration in the material testing machine of this embodiment.]

[0009]

Figure 3

[0010] 【 Figure 4 This diagram shows an example of a flowchart illustrating the excitation voltage control process of the material testing machine according to this embodiment when the power is turned on or when the load sensor is replaced.

[0011] 【 Figure 5This diagram illustrates an example of the time variation of the excitation voltage and the temperature variation of the load sensor in the material testing machine of this embodiment compared to conventional material testing machines. Detailed Implementation

[0012] [Supplement to the above] The "material testing machine" mentioned 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 gauges) for measuring the deformation or displacement of the specimen, and width gauges for measuring the width of the specimen.

[0013] Furthermore, the "bridge circuit" of a strain gauge sensor is a circuit that can detect the deformation (strain) produced by the strain gauge as a change in resistance. Various configurations of this bridge circuit are known, such as the 1-strain gauge method, the 2-strain gauge method, and the 4-strain gauge method, but its circuit configuration is not limited to a specific configuration.

[0014] In addition, the "excitation voltage" applied to the bridge circuit is the voltage that drives the bridge circuit, which can be either DC voltage or AC voltage.

[0015] Furthermore, the point in time at which "excitation voltage is first applied to the bridge circuit" refers to the point immediately after the power to the material testing machine is turned on, or immediately after the detection unit is installed if it is configured to be detachable from the main body of the device, at the point when the excitation voltage is first applied. Therefore, for example, when the excitation voltage is intermittently applied to the bridge circuit from the time the power to the material testing machine is turned on until the measurement is performed, this refers to the initial point in time of this series of intermittent applications of excitation voltage.

[0016] Hereinafter, a material testing machine according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[0017] [Composition of a material testing machine] Figure 1 This is a diagram showing the main components of the material testing machine in this embodiment. Figure 2 This is a block diagram of the electrical system in the material testing machine of this embodiment. In the following description, [the following text is incomplete and likely refers to a different topic]. Figure 1 The right side is defined as "right" and the top side as "top," defining the up, down, left, and right sides of the material testing machine.

[0018] like Figure 1 As shown, the material testing machine of this embodiment includes a testing machine body 100, a control unit 300, and an operation unit 400.

[0019] The main body 100 of the testing machine includes a box-shaped base 101 with a worktable on top, a pair of lead screws 102 vertically arranged on the left and right sides of the base 101, and an upper crossbeam 103 holding the upper ends of the pair of lead screws 102. A servo motor 107 and a gearbox 108 are housed inside the base 101. The rotation of the drive shaft of the servo motor 107 is transmitted to each lead screw 102 through the gearbox 108, multiple synchronous pulleys 109, and a synchronous belt 110, thus causing the pair of lead screws 102 to rotate synchronously. A nut 106 is screwed onto each of the pair of lead screws 102. A crosshead 104 is horizontally mounted between these nuts 106. As the lead screw 102 rotates, the crosshead 104... Figure 1 Move up and down as indicated by the double-headed arrow.

[0020] An upper clamp 111 is mounted on the crosshead 104 via a load sensor 105. Conversely, a lower clamp 112 is mounted on the base 101 at a position directly below the upper clamp 111. In this material testing machine, a tensile test is performed on the specimen 500 by raising the crosshead 104 while the upper and lower ends of the specimen 500 are clamped by the upper clamp 111 and the lower clamp 112, respectively. During this tensile test, the test force (tension) applied to the specimen 500 as the crosshead 104 rises is detected by the load sensor 105.

[0021] Load sensor 105 is connected to calibration (CAL) connector 200 via cable 113, and CAL connector 200 is connected to control unit 300. Control unit 300 is connected to operating unit 400. Control unit 300 also controls servo motor 107 that raises and lowers crosshead 104, but... Figure 1 The wiring details for this part have been omitted.

[0022] The load sensor 105 is detachable from the crosshead 104. Multiple load sensors 105 with different rated loads are prepared, and the appropriate rated load load 105 is replaced and used according to the sample piece 500. Basically, the load sensor 105 and CAL connector 200 are a set; when the load sensor 105 is replaced with a sensor of a different rated load, the CAL connector 200 is also replaced. This is because, as described later, the CAL connector 200 internally stores information about the load sensor 105. Furthermore, the CAL connector 200 and cable 113 can be integrated, or the load sensor 105, cable 113, and CAL connector 200 can also be integrated. Additionally, the function of the CAL connector 200 can also be integrated into the load sensor 105.

[0023] In this material testing machine, by replacing the upper clamp 111 and the lower clamp 112 with other clamps, it is possible to perform material tests other than tensile tests on the specimen 500, such as compression tests, bending tests, shear tests, peel tests, etc., or to test specimens of various sizes and shapes.

[0024] The control unit 300 collects data on the test force while controlling the main body 100 of the testing machine and the operating unit 400, such as... Figure 2 As shown, it includes a microprocessor unit (MPU) 301, a field-programmable gate array (FPGA) 302, a digital-to-analog converter (DAC) 303, a power amplifier 304, an instrumentation amplifier 305, and an analog-to-digital converter (ADC) 306. The MPU 301 performs various arithmetic operations according to a program pre-stored in memory. The FPGA 302 performs hardware-determined logical operations or outputs predetermined numerical data.

[0025] The operation unit 400 is used by the operator to input instructions to the control unit 300 or to receive certain information visually. In addition to the microprocessor unit (MPU) 401 and the field-programmable gate array (FPGA) 402, it also includes a liquid crystal display 404 (functioning as a display unit) and a touchscreen 403 (functioning as an input unit). The FPGAs 402 and 302 are capable of communicating with each other, thereby exchanging data or control signals between the control unit 300 and the operation unit 400. Furthermore, the input unit in the operation unit 400 is not limited to the touchscreen 403; it can also be an input unit using a general-purpose keypad or an input unit via voice input.

[0026] The CAL connector 200 internally includes an externally readable and writable memory 201 and an R / W circuit (not shown) for reading and writing data to the memory 201. The memory 201 can be accessed by the FPGA 302 of the control unit 300. The memory 201 stores information indicating the type of the load sensor 105 paired with the CAL connector 200, or information indicating the rated load, etc. It may also store information indicating the rated voltage value or maximum voltage value of the excitation voltage (described later). Furthermore, various data required for measurement, such as sensitivity correction information in test force measurements using the corresponding load sensor 105, can be written to and stored in the memory 201.

[0027] The load sensor 105 includes a strain gauge that deforms under the test force, and a strain gauge bridge circuit 1051 consisting of a bridge circuit including the strain gauge. The control unit 300 applies an excitation voltage to the strain gauge bridge circuit 1051 through the CAL connector 200, and simultaneously receives an electrical signal corresponding to the deformation of the strain gauge in the strain gauge bridge circuit 1051, and performs calculation processing to calculate the test force.

[0028] Figure 2 The main focus is on the composition of the control unit 300 and the operating unit 400 from the perspective of the equipment. Figure 3 This is a schematic diagram showing the configuration of the control unit 300 and the operation unit 400 as functional modules centered on the drive of the strain gauge bridge circuit 1051. (See diagram for reference.) Figure 3 As shown, the control / operation unit 310, which is specifically implemented by the control unit 300 and the operation unit 400, includes a power-on unit 311, a preheating operation interruption indicator unit 312, a sensor information reading unit 313, a preheating operation time counting unit 314, a preheating operation remaining time display unit 315, an excitation voltage control unit 316, an excitation voltage generation unit 317, and a measurement processing unit 318.

[0029] The power-on unit 311 includes, for example, a power switch (not shown) provided on the operation unit 400, which recognizes the power-on operation performed by the operator on the material testing machine. The preheating operation interruption indication unit 312 is specifically implemented by the MPU 401, FPGA 402, and touchscreen 403 in the operation unit 400, and recognizes the interruption indication of preheating operation based on a predetermined input operation performed by the operator. The sensor information reading unit 313 accesses the memory 201 of the CAL connector 200 and reads the information stored in the memory 201 corresponding to the sensor (load sensor 105 or other sensor). The preheating operation time counting unit 314 starts a countdown from a predetermined preheating operation time. Furthermore, in the following example, it is assumed that the predetermined preheating operation time is 15 minutes, but this is only an example and can be appropriately changed by the operator or manufacturer's service personnel.

[0030] The preheating operation remaining time display unit 315 displays the remaining preheating operation time, counted down by the preheating operation time counter unit 314, in real time within a predetermined area on the LCD screen 404. The excitation voltage control unit 316, implemented by the MPU 301, determines and indicates the voltage value of the excitation voltage applied to the strain gauge bridge circuit 1051. The excitation voltage generation unit 317, implemented by the FPGA 302, DAC 303, and power amplifier 304, generates an excitation voltage having the voltage value determined by the excitation voltage control unit 316. Furthermore, the excitation voltage can be either a DC voltage or an AC voltage (typically a sinusoidal voltage). The measurement processing unit 318, implemented by the instrumentation amplifier 305, ADC 306, MPU 301, and FPGA 302, calculates the test force based on the electrical signal corresponding to the deformation of the strain gauges in the strain gauge bridge circuit 1051.

[0031] [Operation of the material testing machine in this embodiment] When the material testing machine of this embodiment is powered off, the load sensor 105 is at almost room temperature. When the operator turns on the power and applies an excitation voltage to the strain gauge bridge circuit 1051, the strain gauge bridge circuit 1051 heats up due to power loss, and the internal temperature of the load sensor 105 begins to rise. It takes a certain amount of time for the internal temperature of the load sensor 105 to rise to a level that does not affect the measurement of the test force and to stabilize substantially. If a measurement is performed before this time has elapsed, the accuracy of the measurement cannot be guaranteed. On the other hand, if this time is long, the operator's waiting time will increase, leading to a decrease in measurement efficiency.

[0032] Therefore, in the material testing machine of this embodiment, characteristic control is performed to rapidly raise and stabilize the internal temperature of the load sensor 105. Regarding this control, besides... Figures 1-3 In addition, refer to Figure 4 and Figure 5 Please provide an explanation. Figure 4 This is an example diagram illustrating the flowchart of excitation voltage control when the power is on or when the load sensor is replaced. Figure 5 This is a schematic diagram illustrating an example of the time-varying excitation voltage and the temperature variation of the load sensor.

[0033] When the operator turns on the power to the material testing machine by operating the power switch, predetermined power is supplied from a predetermined power supply unit (not shown) to various units such as the control unit 300 (step S1). The sensor information reading unit 313 accesses the memory 201 of the CAL connector 200 and reads data such as load sensor type information stored in the memory 201. As a result, the control / operation unit 310 identifies that the sensor connected via the CAL connector 200 is the load sensor 105, that is, it identifies that the connected sensor is a sensor equipped with the strain gauge bridge circuit 1051 (step S2).

[0034] In addition to the case where the power is on, when a new CAL connector 200 is connected to the control unit 300 along with the replacement of the load sensor 105, the sensor information reading unit 313 reads data such as load sensor type information from the memory 201 of the newly installed CAL connector 200 once it detects the installation of the CAL connector 200. Therefore, whether the power is on or the load sensor 105 is replaced, the sensor information reading unit 313 can identify that the sensor indirectly connected to the control unit 300 is the load sensor 105. Furthermore, when it is detected that the sensor indirectly connected to the control unit 300 is not the load sensor 105, but a strain gauge sensor such as an extensometer or width gauge that uses a strain gauge bridge circuit, the following control can also be performed.

[0035] After identifying the connection of the load sensor 105 as described above, the preheating run time counter 314 begins counting down from the predetermined preheating run time (15 minutes in this case). The preheating run remaining time display 315 displays the countdown value of the remaining preheating run time in real time within a predetermined display area (step S3). By displaying this remaining time, the operator can know the remaining time of the preheating run, that is, the waiting time until a measurable state is reached.

[0036] The excitation voltage control unit 316 determines whether the elapsed time from the countdown start time of the preheating operation time to zero is within 5 minutes, that is, whether it is within the first 5 minutes of the predetermined preheating operation time (step S4). If the determination in step S4 is "yes", the excitation voltage control unit 316 determines whether there is a preheating operation interruption indication issued by the preheating operation interruption indication unit 312 (step S5).

[0037] The operator can indicate the interruption of the preheating operation at any time during the preheating process by performing a predetermined operation on the touchscreen 403. For example, if the internal temperature of the load sensor 105 has not risen sufficiently and the operator wants to know the test force measurement result as soon as possible even if the accuracy is poor, the preheating operation can be interrupted and the measurement can be switched to. In addition, if the power is temporarily turned off and then immediately turned back on, or if the load sensor 105 and CAL connector 200 that have been used for measurement are temporarily removed and then immediately reinstalled, the operator can also interrupt the preheating operation and switch to measurement when the operator recognizes that the internal temperature of the load sensor 105 is high enough. The preheating operation interruption indication unit 312 recognizes that the preheating operation has been interrupted through the above-mentioned operator operation and conveys the interruption indication to the excitation voltage control unit 316.

[0038] If no preheating operation interruption instruction is issued by the operator, step S5 determines NO, and the excitation voltage control unit 316 sets the excitation voltage value to the maximum voltage value allowed by the load sensor 105 (step S6). This maximum voltage value information can be pre-stored in the MPU 301 or read from the memory 201 of the CAL connector 200. As an example, it is assumed here that the maximum voltage value is 15V. The excitation voltage generation unit 317 generates the voltage value set by the excitation voltage control unit 316, which in this case is the maximum voltage value of 15V for preheating, and applies it to the strain gauge bridge circuit 1051 of the load sensor 105 through the CAL connector 200 (step S7).

[0039] Specifically, in the control unit 300, the MPU 301 instructs the FPGA 302 to output a voltage with a maximum voltage value. Upon receiving this instruction, the FPGA 302 outputs a digital value corresponding to the voltage waveform indicated by the instruction. When the excitation voltage is DC, the digital value of the voltage waveform is a constant value. When the excitation voltage is AC, the digital value of the voltage waveform is a repetition of the time-varying value of a sinusoidal voltage corresponding to one cycle. 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 either voltage or current and outputs it. This applies a voltage to the strain gauge bridge circuit 1051. Figure 5 The 15V preheating excitation voltage shown in (a) is as follows: Figure 5 As shown by the solid line in (d), the temperature of the strain gauge bridge circuit 1051 begins to rise. Furthermore, when the excitation voltage is an AC voltage, the effective value of this AC voltage can be taken as the maximum voltage value.

[0040] After step S7, return to step S4. Therefore, as long as the operator does not issue an interruption instruction for the preheating operation, repeat steps S4 to S7. During the first 5 minutes of the preheating operation, if... Figure 5 As shown in (a), a preheating excitation voltage of 15V is continuously applied to the strain gauge bridge circuit 1051. This voltage is higher than the excitation voltage applied to the strain gauge bridge circuit 1051 during the test force measurement (rated voltage: assumed to be 10V for example). Figure 5 (c) is a graph showing the time variation of the excitation voltage in a conventional material testing machine. As shown in the graph, conventionally, an excitation voltage of 10V is continuously applied to the strain gauge bridge circuit 1051 from the point when the excitation voltage is first applied. Therefore, in the material testing machine of this embodiment, an excitation voltage that is 1.5 times higher than that of the conventional material testing machine is applied to the strain gauge bridge circuit 1051.

[0041] Repeat steps S4 to S7. When 5 minutes have elapsed since the start of preheating operation, step S4 is determined to be "No" and the process proceeds to step S9. Then, the excitation voltage control unit 316 changes the excitation voltage setting to the excitation voltage at the time of measurement, i.e., the rated voltage value of 10V. The excitation voltage generation unit 317 generates the voltage value set by the excitation voltage control unit 316, i.e., the rated voltage value of 10V in this case, and applies it to the strain gauge bridge circuit 1051 of the load sensor 105 through 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. Upon receiving this instruction, the FPGA 302 outputs a digital value corresponding to the voltage waveform indicated by the instruction. Therefore, as... Figure 5 As shown in (a), after 5 minutes from the start of the application of the excitation voltage, the excitation voltage applied to the strain gauge bridge circuit 1051 switches from 15V to 10V.

[0042] The process described in steps S4 to S7 will be repeated. If the operator instructs to interrupt the preheating operation 5 minutes before the start of the preheating operation, step S5 will be determined as "yes" and the process will proceed to step S8. The preheating operation time counter 314 will then change the remaining time to zero, regardless of the remaining preheating operation time. Consequently, the remaining time displayed on the preheating operation remaining time display 315 will also become zero. Then, steps S9 to S10 will proceed, and as described above, the excitation voltage applied to the strain gauge bridge circuit 1051 will switch from 15V to 10V. Figure 5 (b) shows an example of the excitation voltage change when the preheating run is interrupted 5 minutes before the start of the preheating run.

[0043] After step S10, the excitation voltage control unit 316 determines whether the remaining preheating operation time is zero (step S11). If it is not zero, the next step is the same as step S5, determining whether there is a preheating operation interruption indication issued by the preheating operation interruption indication unit 312 (step S12). If there is no preheating operation interruption indication, the process returns to step S9. Therefore, as long as the operator does not issue a preheating operation interruption indication before the predetermined preheating operation time of 15 minutes has elapsed, the processing of steps S9 to S12 is repeated. That is, a rated voltage of 10V is applied to the strain gauge bridge circuit 1051 as the excitation voltage. As a result, the heat generated by the strain gauge bridge circuit 1051 is reduced compared to the period from the application of the excitation voltage until 5 minutes have elapsed. Figure 5 As shown in (d), the internal temperature of the load sensor 105 rises slowly. Then, as the remaining preheating time approaches zero, the rate of increase in the internal temperature of the load sensor 105 slows down and approaches a steady state.

[0044] Then, when the excitation voltage control unit 316 determines that the remaining preheating operation time is zero, it proceeds from step S11 to step S14. While maintaining the application of the rated voltage of 10V as the excitation voltage to the strain gauge bridge circuit 1051, the control / operation unit 310 enters the test execution standby state. On the other hand, if the operator instructs to interrupt the preheating operation during the repeated processing of steps S9 to S12, and 15 minutes have elapsed since the start of the preheating operation, it is determined to be "yes" in step S12. Then, the preheating operation time counting unit 314, similar to step S8, changes the remaining time to zero (step S13) regardless of how much preheating operation time remains, and proceeds to the aforementioned step S14. Therefore, in this case, it enters the test execution standby state without waiting for 15 minutes to elapse since the start of the preheating operation. Furthermore, if the remaining preheating operation time becomes zero in step S8, it is determined to be "yes" in the next step S11 after steps S9 and S10, so it enters the test execution standby state without waiting for 5 minutes to elapse since the start of the preheating operation.

[0045] Summarize the relationship between the processing flow according to the above flowchart and the state of the excitation voltage applied to the strain gauge bridge circuit 1051.

[0046] In the process of repeatedly executing steps S4 to S7, the process moves from step S4 to step S9, and then in the process of repeatedly executing steps S9 to S12, the process moves from step S11 to step S14. The time variation of the excitation voltage is as follows: Figure 5 As shown in (a). In this case, the power supplied for 5 minutes at a high voltage value equivalent to 1.5 times the ratio of the maximum voltage value to the rated voltage value is higher than that supplied by conventional material testing machines. Figure 5 (c) is more connected to the strain gauge bridge circuit 1051. Therefore, as Figure 5 As shown in (d), the time required for the internal temperature of the load sensor 105 to stabilize is significantly reduced compared to conventional material testing machines.

[0047] Furthermore, when the process of repeating steps S4 to S7 is moved from step S4 to step S9, and then when the process of repeating steps S9 to S12 is moved from step S12 to step S13, the power supply is equivalent to a high voltage value of 1.5 times the ratio of the maximum voltage value to the rated voltage value for 5 minutes, which is connected to the strain gauge bridge circuit 1051 more than in conventional material testing machines. Therefore, the time required for the internal temperature of the load sensor 105 to stabilize is greatly shortened compared to conventional material testing machines.

[0048] On the other hand, when the process of repeating steps S4 to S7 is moved from step S5 to step S8, the time change of the excitation voltage is as follows: Figure 5As shown in (b). In this case, the time for the maximum voltage of 15V to be applied to the strain gauge bridge circuit 1051 is shortened, and the power to turn on the strain gauge bridge circuit 1051 is reduced accordingly, but the time required for the internal temperature of the load sensor 105 to stabilize is still shortened compared with conventional material testing machines.

[0049] When the remaining preheating time display reaches zero and the test execution standby state is reached in step S14, if the operator performs a predetermined operation on the touch screen 403, such as performing a tensile test on the specimen 500 by raising the crosshead 104, 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 through the CAL connector 200. The measurement processing unit 318 performs the processing of converting the received voltage signal into a test force and displays the result in a predetermined area on the LCD screen 404.

[0050] 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, which calculates the test force by multiplying the read digital voltage value by a conversion factor sent from the MPU 301. Even if the test force value is 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 also be different. Therefore, even if the voltage signal output from the strain gauge bridge circuit 1051 is different due to different excitation voltages applied to it when the test force value is the same, the conversion factor will be adjusted to make the converted test force value the same. That is, MPU301 sends a conversion coefficient corresponding to the excitation voltage to FPGA302. FPGA302 uses the conversion coefficient to perform multiplication, so that it can obtain the accurate test force regardless of the excitation voltage applied to strain gauge bridge circuit 1051.

[0051] As described above, in the material testing machine of this embodiment, since a preheating excitation voltage with a voltage value higher than the excitation voltage during measurement is applied to the strain gauge bridge circuit 1051 for at least a portion of the preheating operation, it has the following advantages compared to conventional material testing machines.

[0052] (1) When performing the same preheating operation as conventional material testing machines, the internal temperature stability of the load sensor 105 is higher than that of conventional material testing machines, thus enabling more accurate, reproducible and reliable test force measurement.

[0053] (2) Even when the preheating run time is shortened to a shorter time than that of conventional material testing machines, or when the preheating run is interrupted during the preheating run (i.e., the time is shortened to a shorter time than that of conventional preheating run time) and test force measurement is performed, test force measurement can still be performed with the same or similar accuracy and reliability as that of conventional material testing machines with sufficient preheating run. As a result, the preheating run time, i.e., the standby time, can be reduced, and the efficiency of test force measurement can be improved while ensuring accuracy.

[0054] For example, in a typical load sensor (input resistance: 350Ω, rated voltage: 10V), when the rated voltage is applied as the excitation voltage, a 10V voltage will be generated inside the load sensor. 2 The heat generation is 286mW / 350. Therefore, if a preheating excitation voltage of 15V is applied only during the first 5 minutes of preheating operation, the heat generation inside the load sensor becomes 15mW. 2 / 350=643mW, which can generate 2.25 times the heat output. That is to say, if the excitation voltage is increased, the heat output will increase with the square of the voltage value, so the effect is significant. Thus, in the material testing machine of this embodiment, the heat output of the strain gauge bridge circuit 1051 can be increased, and the temperature of the load sensor 105 can be raised in a shorter time.

[0055] Another method to shorten the time required for the overall temperature inside the load sensor to stabilize is to reduce the excitation voltage applied to the strain gauge bridge circuit during measurement. However, if the excitation voltage is reduced, the signal-to-noise ratio (S / N ratio) of the voltage signal corresponding to the test force obtained in the strain gauge bridge circuit will decrease, making it impossible to accurately determine the test force. Therefore, reducing the excitation voltage during measurement is not suitable. From this perspective, the excitation voltage control method used in the material testing machine of this embodiment can be considered superior because it shortens the standby time without compromising the accuracy of the test force measurement.

[0056] [Variation Example] In the material testing machine of the above embodiment, an excitation voltage is applied to the strain gauge bridge circuit 1051 immediately after the power is turned on or immediately after the load sensor 105 is connected to the control unit 300. Immediately thereafter, a preheating excitation voltage of the maximum allowable voltage value of the load sensor 105 is applied for only 5 minutes, after which the excitation voltage applied to the strain gauge bridge circuit 1051 is restored to its rated voltage value. Not limited to this, the time for applying the preheating voltage can be longer or shorter. Furthermore, instead of applying the excitation voltage immediately after starting to apply it to the strain gauge bridge circuit 1051, the rated voltage value may be applied at the beginning, and the excitation voltage value may be increased after a period of time. That is, the preheating excitation voltage can be applied at any point during the preheating operation, and the period for applying the preheating excitation voltage can be part or all of the preheating operation.

[0057] Furthermore, increasing the excitation voltage to at least a value higher than the measurement voltage (i.e., higher than the rated voltage) instead of the maximum voltage value is clearly effective in accelerating the temperature rise inside the load sensor 105. Additionally, during preheating operation, the excitation voltage can be varied continuously or in a stepped manner over time. For example, at the beginning of preheating operation, the excitation voltage can be set to the highest possible value, such as the maximum voltage value, and then varied over time to approach the rated voltage value. Thus, there are various modes of excitation voltage variation during preheating operation.

[0058] Furthermore, in cases where the maximum voltage value or rated voltage value differs due to different types of load sensors 105 installed on the crosshead 104, as described above, information corresponding to the maximum voltage value and rated voltage value of the load sensor 105 can be stored in the memory 201 built into the CAL connector 200. Based on the information read by the FPGA 302, the MPU 301 instructs the FPGA 302 to output either the maximum voltage value or the rated voltage value. Alternatively, the MPU 301 can pre-store the maximum voltage value and rated voltage value corresponding to the load sensor 105, and based on the load sensor type information read from the memory 201, select the maximum voltage value and rated voltage value respectively and issue an instruction to the FPGA 302. Of course, the operator can also input or select the maximum voltage value and rated voltage value corresponding to the load sensor 105 used.

[0059] Furthermore, in the material testing machine of the above embodiment, a load sensor is used to measure the test force. However, as long as the test force is measured by a strain gauge sensor using a strain gauge bridge circuit, the sensor connected to the control unit is not limited to a load sensor.

[0060] Therefore, the present invention is not limited to general material testing machines, but can obviously also be applied to, for example, to extensometers (or displacement gauges) or width gauges that use strain gauge sensors with strain gauge bridge circuits as elongation detectors, and even to material testing machines that measure the test force of specific test objects such as springs, plastics, concrete, and rubber.

[0061] Furthermore, the above embodiments and variations are merely examples of the present invention. Any further changes, additions, deletions, etc., made without departing from the spirit of the present invention are obviously included within the scope of the claims of this application.

[0062] [Various options] Those skilled in the art should understand that the above exemplary implementations are specific examples of the following solutions.

[0063] (Item 1) One embodiment of the material testing machine according to the present invention comprises: The testing department uses strain gauge sensors with a bridge circuit to detect the test force. The voltage application section applies an excitation voltage to the bridge circuit; and The voltage control unit controls the voltage application unit to apply a preheating excitation voltage to the bridge circuit for at least a portion of the period between the start of applying an excitation voltage to the bridge circuit and the implementation of the test force measurement. The preheating excitation voltage is higher than the voltage value when the detection unit performs the test force measurement, and lower than the maximum voltage value allowed by the detection unit.

[0064] In the material testing machine described in claim 1, a preheating excitation voltage, for example, the maximum voltage allowed by the detection unit, is applied to the bridge circuit from the moment an excitation voltage is applied to the bridge circuit until the test force measurement is performed. When this preheating excitation voltage is applied to the bridge circuit, the bridge circuit generates more heat compared to when an excitation voltage suitable for test force measurement is applied. Therefore, according to the material testing machine described in claim 1, the internal temperature of the detection unit, such as the load sensor, can be rapidly increased and stabilized immediately after power is turned on or immediately after the load sensor is replaced. As a result, the standby time required until an accurate and reliable test force measurement can be performed can be shortened, enabling efficient measurement.

[0065] (Item 2) In the material testing machine described in Item 1, the voltage control unit may be configured to control the voltage application unit such that, from the start of applying an excitation voltage to the bridge circuit, except for the at least a portion of the period, an excitation voltage is applied to the bridge circuit, the excitation voltage being the voltage value when the detection unit performs a test force measurement.

[0066] In the material testing machine described in item 2, during a period other than when a preheating excitation voltage is applied to the bridge circuit, an excitation voltage with a value lower than the preheating excitation voltage is applied to the bridge circuit. This prevents excessive rise in the internal temperature of the detection section and quickly stabilizes it. Furthermore, the test force can be measured immediately when the internal temperature of the detection section is approximately stable.

[0067] (Item 3) In the material testing machine described in Item 1 or Item 2, the voltage control unit may be configured to control the voltage application unit to apply a preheating excitation voltage of the maximum voltage value allowed by the detection unit to the bridge circuit during at least a portion of the period.

[0068] According to the material testing machine described in item 3, the internal temperature of the testing section can be rapidly increased while avoiding applying excessive voltage to the bridge circuit of the testing section.

[0069] (Item 4) In the material testing machine of any one of items 1 to 3, the at least part of the period may be a period that begins at the point at which the excitation voltage is applied to the bridge circuit or immediately thereafter.

[0070] In the material testing machine described in item 4, a preheating excitation voltage is applied to the bridge circuit from the very beginning of the application of the excitation voltage. This efficiently increases the internal temperature of the detection section and further shortens the time it takes for the internal temperature to reach a stable state.

[0071] (Item 5) In any one of items 1 to 4, the material testing machine may be configured such that the period from the start of applying an excitation voltage to the bridge circuit until a predetermined time has elapsed is defined as a preheating operation period, wherein at least a portion of the period is the period from the time point at which the excitation voltage is applied to the bridge circuit or the time point immediately thereafter until the end of the preheating operation period.

[0072] In the material testing machine described in item 5, a preheating period is predetermined, and the test force is measured after this period. This allows for test force measurement to be performed after the internal temperature of the testing section has reached a substantially stable state, resulting in accurate and highly reproducible results.

[0073] (Item 6) The material testing machine described in Item 5 further includes an operation receiving unit for accepting preheating operation interruption operations performed by the operator. The voltage control unit may be configured to: in response to the operation receiving unit's acceptance of the preheating operation interruption operation, terminate the preheating operation period, and control the voltage applying unit to apply an excitation voltage to the bridge circuit, wherein the excitation voltage is the voltage value when the detection unit performs test force measurement.

[0074] In the material testing machine described in item 6, the preheating process can be interrupted and the test force measurement can be performed quickly by the operator's judgment. Thus, for example, if a certain degree of accuracy is sacrificed in order to obtain the measurement result quickly, or if the internal temperature of the detection unit is known to be sufficiently stable, the measurement result can be obtained immediately without setting a waiting time.

[0075] (Item 7) In any one of items 1 to 6, the voltage control unit may be configured to apply an excitation voltage to the bridge circuit immediately after the power supply of the material testing machine is turned on.

[0076] According to the material testing machine described in item 7, the waiting time from when the operator turns on the power to the material testing machine until the appropriate test force measurement can be performed can be shortened.

[0077] (Item 8) In the material testing machine of any one of items 1 to 7, the detection unit is detachable from the material testing machine, and further includes an installation detection unit for detecting whether the detection unit is installed in the material testing machine. The voltage control unit can be configured such that, immediately after the installation detection unit detects the installation of the detection unit, it begins to apply an excitation voltage to the bridge circuit.

[0078] According to the material testing machine described in item 8, operability is improved because the operator can begin applying excitation voltage to the bridge circuit without special operation after replacing the detection unit such as the load sensor. Furthermore, the waiting time until appropriate test force measurement can be performed after replacing the detection unit can be shortened.

[0079] (Item 9) In any one of the material testing machines in items 1 to 8, the detection unit may be a load sensor, an extensometer, a displacement gauge or a width gauge.

[0080] The material testing machine described in item 9 can accurately and efficiently measure the test force or strain in various tests on specimens, such as tensile tests, compression tests, bending tests, shear tests, and peel tests.

[0081] Explanation of reference numerals in the attached figures 100…testing machine body 101…base 102…lead screw 103… Upper crossbeam 104… Crosshead 105…load sensor 1051… Strain gauge bridge circuit 106…nut 107…servo motors 108… gearbox 109…Synchronous Belt Pulley 110…synchronous belt 111… Upper clamp 112… Lower clamp 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 monitor 310…Control / Operation Unit 311…Power Connection Section 312…Preheating Operation Interruption Indication Section 313… Sensor Information Reading Unit 314…Preheating Run Time Counting Section 315… Remaining preheating time display section 316…Excitation Voltage Control Unit 317…Excitation Voltage Generation Section 318… Measurement and Processing Department 500… Sample piece.

Claims

1. A material testing machine, comprising: The testing department uses strain gauge sensors with a bridge circuit to detect the test force. The voltage application section applies an excitation voltage to the bridge circuit; and The voltage control unit controls the voltage application unit to apply a preheating excitation voltage to the bridge circuit for at least a portion of the period between the start of applying an excitation voltage to the bridge circuit and the implementation of the test force measurement. The preheating excitation voltage is higher than the voltage value when the detection unit performs the test force measurement, and lower than the maximum voltage value allowed by the detection unit.

2. The material testing machine according to claim 1, characterized in that, The voltage control unit controls the voltage application unit to apply an excitation voltage to the bridge circuit from the start of applying the excitation voltage to the bridge circuit, except for the at least a portion of the period, where the excitation voltage is the voltage value when the detection unit performs the test force measurement.

3. The material testing machine according to claim 1, characterized in that, During at least a portion of the period, the voltage control unit controls the voltage application unit to apply a preheating excitation voltage, the maximum voltage value allowed by the detection unit, to the bridge circuit.

4. The material testing machine according to claim 1, characterized in that, The at least part of the period is the period that begins at the point in time when the excitation voltage is first applied to the bridge circuit or immediately thereafter.

5. The material testing machine according to claim 1, characterized in that, The period from the start of applying the excitation voltage to the bridge circuit until a predetermined time has elapsed is defined as the preheating operation period, wherein at least a portion of the period is the period from the time point at which the excitation voltage is applied to the bridge circuit or the time point immediately following it until the end of the preheating operation period.

6. The material testing machine according to claim 5, characterized in that, Furthermore, it is equipped with an operation receiving unit that can accept preheating operation interruption operations performed by the operator. In response to the operation receiving unit's acceptance of the preheating operation interruption operation, the voltage control unit ends the preheating operation period and controls the voltage application unit to apply an excitation voltage to the bridge circuit. The excitation voltage is the voltage value when the detection unit performs test force measurement.

7. The material testing machine according to claim 1, characterized in that, Immediately after the power to the material testing machine is turned on, the voltage control unit begins to apply the preheating excitation voltage to the bridge circuit.

8. The material testing machine according to claim 1, characterized in that, The detection unit is detachable from the material testing machine, and further includes an installation detection unit for detecting whether the detection unit is installed on the material testing machine. Immediately after the installation detection unit detects the installation of the detection unit, the voltage control unit begins to apply the preheating excitation voltage to the bridge circuit.

9. The material testing machine according to any one of claims 1 to 8, characterized in that, The detection unit is a load sensor, extensometer, displacement gauge, or width gauge.

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