JP5605910B2 - Material testing machine - Google Patents

Description

  The present invention relates to a material testing machine that executes a material test by applying a test force to a test piece.

  Such a material testing machine has, for example, a configuration in which a pair of screw rods are rotatably supported on a table in synchronization with each other, and both end portions of the crosshead are supported on these screw rods via nuts. Then, the crosshead is moved along the pair of screw rods by rotating the pair of screw rods in synchronization with each other by the rotation of the motor. A jig such as a gripping tool is connected to the crosshead and the table. And it is comprised so that a test force may be applied with respect to a test piece by moving a crosshead in the state which hold | gripped both ends of the test piece with jigs, such as these pair of grips.

  In such a material testing machine, the test force acting on the test piece is detected by a load cell or the like. In addition, as a method for measuring the displacement of the test piece, a strain gauge is attached inside the measuring instrument for measuring elongation, and the measuring instrument is directly attached to the test piece to measure the strain amount of the test piece. The measurement by a type extensometer and the measurement by a non-contact type extensometer are known. In the non-contact extensometer, the distance between the gauge points is obtained by performing image processing on the data obtained by photographing the mark marks and the like attached to the predetermined vertical position of the test piece with an optical video camera. The displacement amount of the piece is calculated (see Patent Document 1).

Japanese Patent Laid-Open No. 2005-3579

  The frame rate when a specimen is photographed with a normal optical video camera is, for example, about 30 FPS (Frame Per Second). For this reason, it is not possible to collect images that capture the destruction phenomenon at the time of the specimen breakage with a normal optical video camera. Therefore, when trying to collect an image that captures the destruction phenomenon at the time of specimen breakage, for example, a high-speed video camera capable of high-speed shooting with a frame rate of about 1 million FPS is used for an existing material testing machine. It will be connected separately to the configuration.

  FIG. 4 is a block diagram illustrating a main electrical configuration when a high-speed video camera 15 is added to the configuration of the material testing machine by a conventional method. FIG. 4A shows a configuration before the high-speed video camera 15 is added, and FIG. 4B shows a configuration after the high-speed video camera 15 is added.

  As shown in FIG. 4A, before adding the high-speed video camera 15, the electric signal detected by the load cell 14 is a load measurement arranged in the control unit 123 that controls the entire material testing machine. The signal is directly input to the amplification unit 141 of the unit 140. The input signal is converted into a digital signal by the A / D converter 142 and transmitted to the data processing unit 145. When the high-speed video camera 15 is additionally connected to such a configuration, as shown in FIG. 4B, the timing of loading the test force on the test piece and the test piece by the high-speed video camera In order to obtain a signal that synchronizes the shooting timing, a dynamic strain amplifier 18 is interposed between the load cell 14 and the control unit 123.

  The load cell 14 of this type of material testing machine is a strain gauge type load cell, and the test force data output from the load cell 14 is an electric signal on the order of μV to mV. For this reason, the dynamic strain amplifier 18 amplifies the electric signal from the load cell 14 and outputs the amplified signal to the A / D converter 142 of the load measuring unit 140. On the other hand, the dynamic strain amplifier 18 generates a high-magnification analog signal obtained by further amplifying the electrical signal from the load cell 14 than the signal output to the load measuring unit 140, and this signal is output to the high-speed video camera. 15 to send. A digital signal (H or L) is derived from a high-magnification analog signal transmitted to the high-speed video camera 15 by a digital logic circuit such as TTL (Transistor Transistor Logic) or CMOS (Complementary Metal Oxide Semiconductor). A trigger signal will be generated.

  The trigger signal is a signal that triggers the end of shooting with the high-speed video camera 15, that is, the operation to stop saving the image data of each frame obtained by shooting. For this reason, the high-speed video camera 15 performs shooting after the start of shooting until the trigger signal for the end of shooting is input.

  By the way, this type of high-speed video camera 15 is usually provided with a storage memory for storing image data. However, the capacity of this storage memory is limited. For this reason, when the capacity of the storage memory becomes insufficient during the execution of the test, new image data is stored by sequentially overwriting the area in which image data having a short storage time is stored. This overwriting is continued until a trigger signal for ending photographing is input.

  Next, generation of a trigger signal will be described by taking a material test as an example when it is assumed that the test piece is broken when the test force is 800 N. The trigger signal for the end of imaging is set to be generated when the test force detected by the load cell 14 falls below a certain value when the test piece is broken and the load is released.

  It is assumed that the dynamic strain amplifier 18 is set and used for analog output with 1500N as 5V. In the case of TTL, approximately 0.8V or less is determined to be L, and 2V or more is determined to be H. Therefore, when the test force once exceeds 600N, it drops to 240N or less, and the signal is determined to be L. As a result, a trigger signal for the end of shooting is generated. In the case of CMOS, since 1.5V or less is judged as L and 2.5V or more is judged as H, in this case, the test force drops to 450N or less once it exceeds 750N. When the signal is determined to be L, a test end trigger signal is generated. However, there are variations in the test, and even if the output of the dynamic strain amplifier 18 is set assuming that the test piece breaks when the test force is 800 N, all the test pieces break when the test force is 800 N. Not always. For example, in the case of CMOS, when the test piece breaks before the test force exceeds 750 N, the voltage determined to be H is never given to the logic circuit. Then, when the test piece breaks, the test force drops, and even if a voltage that should be determined as L is applied to the logic circuit, a state where H and L cannot be determined occurs, and a test end trigger signal is also generated. do not do. That is, the result cannot cope with the variation in the test.

  In order to cope with such variations in the test, the dynamic strain amplifier 18 is set to 5 V for analog output so that a trigger signal for completion of photographing can be generated even when the test piece is broken with a test force lower than 800 N. Suppose that it is set and used. In the case of TTL, a shooting end trigger signal is generated when the test force drops to 160 N and the signal is determined to be L. Further, in the case of CMOS, it drops to 300 N or less, and when the signal is determined to be L, a shooting end trigger signal is generated. However, in an actual test, if the test piece breaks at 800 N as assumed when the dynamic strain amplifier 18 is set, a longer time than expected is required from the breakage to the generation of the trigger signal for completion of shooting, which is unnecessary. Overwriting of correct image data will continue. In this case, an image capturing the destruction phenomenon of the test piece is lost due to overwriting of unnecessary image data.

  As described above, in the conventional technique, the analog output of the dynamic strain amplifier 18 is set in anticipation of the test force at which the test piece breaks, that is, the maximum test force in the material test. However, it is difficult to accurately grasp the information on the maximum test force in advance, and there are some test objects that cannot predict the maximum test force. In addition, since the test force at the time of breakage varies from one test piece to another, the time from the breakage of the test piece to the generation of a trigger signal for the end of shooting by the high-speed video camera 15 is also the same as the variation for each material test. It will be different.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a material testing machine capable of stably generating a shooting end trigger signal for a high-speed video camera.

  The invention according to claim 1 is a material testing machine for applying a test force to a test piece and detecting the test force at that time by a load cell, and a high-speed video camera for photographing the test piece, and the load cell. A load measuring unit that measures a signal detected by the amplifying unit, the load measuring unit amplifying the detection signal from the load cell, and a conversion unit digitizing the detection signal amplified by the amplifying unit And updating and holding the maximum value of the test force that changes during the test execution, and calculating and holding a reference value for generating a shooting end trigger signal for the high-speed video camera from the maximum value, A comparison operation unit that generates a shooting end trigger signal for the high-speed video camera when the value of the test force is smaller than the reference value. The features.

  According to a second aspect of the present invention, in the first aspect of the invention, the comparison operation unit calculates the reference value by performing a bit shift process on the maximum value by a predetermined number of bits. .

  According to a third aspect of the present invention, in the material testing machine according to the first aspect, the comparison operation unit includes a 1-bit shift unit that performs a 1-bit right bit shift process on the maximum value, and the maximum value. A 2-bit shift unit that performs 2-bit right bit shift processing, and a 3-bit shift unit that performs 3-bit right bit shift processing on the maximum value, the 1-bit shift unit, the 2-bit shift unit, By calculating the reference value by any one of the 3-bit shift units, any one of 1/2, 1/4, and 1/8 of the maximum value is updated and held as a reference value.

  According to the first aspect of the present invention, the load measurement unit includes the comparison calculation unit, and thus the maximum value and the reference value of the test force are updated and held, thereby being based on the individual maximum test force that is different for each material test. Thus, a trigger signal for the end of shooting can be generated. For this reason, the input to the high-speed digital camera can be a digital signal instead of an analog signal, and the time variation between the breakage of a different test piece and the generation of a trigger signal for each material test can be reduced. be able to.

  According to the second aspect of the present invention, the comparison operation unit performs the bit shift process for the predetermined number of bits with respect to the maximum value of the test force, so that the photographing to the high-speed video camera can be completed in a short time. A reference value for generating a trigger signal can be calculated.

  According to the third aspect of the present invention, a 1-bit shift unit that performs 1-bit right bit shift processing on the maximum value of the test force, a 2-bit shift unit that performs 2-bit right bit shift processing, and 3-bit right And a 3-bit shift unit that performs bit shift processing, so that a trigger signal for the end of shooting to a high-speed video camera can be generated in one clock by one of the 1-bit shift unit, 2-bit shift unit, and 3-bit shift unit. A reference value for generation can be calculated. For this reason, it is possible to reduce a trigger signal generation delay at the end of photographing due to a long calculation time of the reference value.

1 is a schematic diagram of a material testing machine according to the present invention. It is a block diagram explaining the main electric structures of the material testing machine which concerns on this invention. 5 is a flowchart illustrating a processing procedure in a comparison calculation unit 43. It is a block diagram explaining the main electric structures at the time of adding the high-speed video camera 15 to the structure of a material testing machine with the conventional method.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram of a material testing machine according to the present invention.

  This material testing machine is movable along a table 16, a pair of screw rods 11, 12 that are erected on the table 16 so as to be vertically oriented, and these screw rods 11, 12. A crosshead 13 and a load mechanism 30 for moving the crosshead 13 to apply a test force to the test piece 10 are provided.

  The cross head 13 is connected to the pair of screw rods 11 and 12 via nuts (not shown). Worm speed reducers 32 and 33 in the load mechanism 30 are connected to lower ends of the screw rods 11 and 12. The worm speed reducers 32 and 33 are connected to a servo motor 31 that is a drive source of the load mechanism 30, and the rotation of the servo motor 31 is transferred to the pair of screw rods 11 and 12 via the worm speed reducers 32 and 33. It is configured to be transmitted. As the pair of screw rods 11 and 12 rotate in synchronization with the rotation of the servo motor 31, the crosshead 13 moves up and down along these screw rods 11 and 12.

  The crosshead 13 is provided with an upper gripping tool 21 for gripping the upper end portion of the test piece 10. On the other hand, the table 16 is provided with a lower gripping tool 22 for gripping the lower end portion of the test piece 10. When performing a tensile test, the test force (tensile load) is applied to the test piece 10 by raising the cross head 13 in a state where both ends of the test piece 10 are held by the upper gripping tool 21 and the lower gripping tool 22. ).

  At this time, the test force acting on the test piece 10 is detected by the load cell 14 and input to the control unit 23. The test piece 10 is illuminated by the lighting device 17, and the deformation and breakage phenomenon of the test piece 10 due to the application of the test force is photographed by the high-speed video camera 15.

  The control unit 23 includes a computer, a sequencer, and peripheral devices thereof, and includes a load measurement unit 40, a data processing unit 45, and the like, which will be described later. The control unit 23 controls the start and end of shooting in the high-speed video camera 15 and feedback-controls the servo motor 31.

  FIG. 2 is a block diagram showing the main electrical configuration of the material testing machine according to the present invention.

  The control unit 23 includes a load measurement unit 40 and a data processing unit 45, and the load measurement unit 40 includes an amplification unit 41, an A / D conversion unit 42, and a comparison calculation unit 43. Test force data from the load cell 14 is taken into the load measuring unit 40 and further amplified by the amplifying unit 41 in the load measuring unit 40. The amplified test force data is converted into a digital signal by the A / D converter 42 and transmitted to the data processing unit 45 and the comparison calculation unit 43. In the data processing unit 45, various data processing is executed. On the other hand, the comparison calculation unit 43 executes calculation processing for generating a shooting end trigger signal for transmission to the high-speed video camera 15.

  The comparison calculation unit 43 is configured by a programmable calculation device such as a field programmable gate array (FPGA) or a digital signal processor (DSP). For this reason, the comparison operation unit 43 programs each process to be executed in an arithmetic device, thereby performing a 1-bit shift unit 51 that performs right 1-bit shift processing in 1 clock and a right 2-bit shift process in 1 clock. A 2-bit shift unit 52 to perform and a 3-bit shift unit 53 to perform right 3-bit shift processing with one clock are mounted. In addition, the comparison calculation unit 43 includes a memory that holds a current value of a test force, which will be described later, a memory that holds a maximum value of the test force, and a reference value that is calculated from the maximum value of the test force and serves as a reference for generating a trigger signal It has a memory to hold.

  FIG. 3 is a flowchart for explaining a processing procedure in the comparison operation unit 43. In FIG. 3, A is a current value indicating a current test force during execution of a material test, B is a maximum value of the test force during execution of the material test, and C is a reference value serving as a reference for generating a trigger signal for completion of imaging. is there.

  When the material test is started, first, 0 which is the lowest value is assigned to B and C (step S1). When the digitization of data in the A / D converter 42 is completed and a new value of A is acquired (step S2), the values of A and C are compared (step S3). If no new A value is acquired, the process does not proceed to the next step.

  Since C is 0 immediately after the start of the material test, when A and C are compared, A, which is the current value, becomes a larger value, and the process proceeds to step S4 where A and B are compared. Also here, B, which is the maximum value, is 0 immediately after the start of the material test, so B is smaller than A. The comparison calculation unit 43 substitutes the value of A for B in order to update and hold the maximum value of the test force during execution of the material test (step S5). When the value of B is larger than A, there is no need to update the maximum value, and the process returns to step S2.

  Next, B that has been replaced with the value of A is shifted by 1 bit to the right, and a value that is ½ of B is substituted into C as a reference value (step S6). The right 1-bit shift process in step S6 is executed by the 1-bit shift unit. When the bit shift process in step S6 is executed by the 2-bit shift unit or the 3-bit shift unit, the value assigned to C as the reference value is a value of 1/4 or 1/8 of B, respectively. It becomes.

In this embodiment, the comparison operation unit 43 includes the 1-bit shift unit 51, the 2-bit shift unit 52, and the 3-bit shift unit 53. However, the present invention is not limited to this. In the comparison operation unit 43 constituted by an arithmetic device such as an FPGA or DSP, a value of ½ ⁿ of the maximum value is obtained by rewriting the program so as to perform the right bit shift processing for a predetermined number of bits (n bits). Can be executed in one clock. Furthermore, if the program is rewritten so that not only the right bit shift process but also the bit shift process is performed for a predetermined number of bits, the reference value can be calculated with a small number of clocks.

  During the execution of the material test, the test force detected by the load cell 14 increases as the test time elapses. Then, until the test piece 10 breaks and the test force decreases, the above-described steps S2 to S6 are repeated, and the comparison operation unit 43 is a new one having a value larger than the reference value and larger than the maximum value up to that time. Each time the value A is acquired, the maximum value of the test force and the reference value are updated and held in the comparison calculation unit 43.

  When the test piece 10 breaks, the test force detected by the load cell 14 decreases. At this time, the value of C in step S3 is the largest test force from the start of the material test until the test piece 10 breaks, that is, half the maximum test force at the time of the test piece break in the test. It is a value. When the value of A, which is the current value of the test force acquired after the test piece 10 is broken, becomes a value smaller than the reference value C, a shooting end trigger signal is output to the high-speed video camera 15 (step S7). ), The photographing of the test piece 10 by the high-speed video camera 15 is completed.

As described above, in the material testing machine according to the present invention, by performing the bit shift process on the maximum value of the test force, the value of ½ ⁿ of the maximum value of the test force, etc. A value decreased by a predetermined rate from the maximum test force can be held as a reference value for generating a trigger signal. Therefore, the reference value can be calculated by a programmable calculation device such as FPGA or DSP without using TTL or CMOS as in the prior art, and the trigger signal can be generated accurately and at high speed. It becomes possible.

DESCRIPTION OF SYMBOLS 10 Test piece 11 Screw rod 12 Screw rod 13 Crosshead 14 Load cell 15 High-speed video camera 16 Table 17 Illumination device 18 Dynamic strain amplifier 21 Upper gripper 22 Lower gripper 23 Control part 30 Load mechanism 31 Servo motor 40 Load measurement part 41 Amplifying section 42 A / D conversion section 43 Comparison operation section 45 Data processing section 51 1-bit shift section 52 2-bit shift section 53 3-bit shift section

Claims (3)

In a material testing machine that applies a test force to a test piece and detects the test force at that time by a load cell,
A high-speed video camera for photographing the specimen;
A load measuring unit for measuring a signal detected by the load cell,
The load measuring unit is
An amplifying unit for amplifying a detection signal from the load cell;
A converter for digitizing the detection signal amplified by the amplifier;
The maximum value of the test force that changes during the test execution is updated and held, and the reference value for generating the shooting end trigger signal for the high-speed video camera is calculated from the maximum value and is updated and held. A comparison operation unit for generating a shooting end trigger signal for the high-speed video camera when the force value is smaller than the reference value;
A material testing machine comprising: The material testing machine according to claim 1,
The comparison operation unit is a material testing machine that calculates the reference value by performing bit shift processing for a predetermined number of bits with respect to the maximum value. The material testing machine according to claim 1,
The comparison operation unit
A 1-bit shift unit that performs 1-bit right bit shift processing on the maximum value;
A 2-bit shift unit that performs 2-bit right bit shift processing on the maximum value;
A 3-bit shift unit that performs a 3-bit right bit shift process on the maximum value;
With
By calculating the reference value by any one of the 1-bit shift unit, 2-bit shift unit, and 3-bit shift unit, one of the values of 1/2, 1/4, and 1/8 of the maximum value is used as a reference. Material testing machine that keeps updated as value.

Images