JP2019219336A - Displacement gauge - Google Patents

Abstract

To provide a displacement gauge capable of measuring a distance between a plurality of gauge marks in a tensile test.SOLUTION: A displacement gauge 40 comprises: three pairs of arms 41a, 41b and 41c with respective edges brought into contact with a test piece 100; and distortion gauge bridge circuits SG1, SG2 and SG3 which are installed at base sections 42a, 42b and 42c on a base end side of the respective arms opposite to the edges as detection sections measuring changes in distances between gauge marks. A control section 30 has sensor amplifier units 36a, 36b and 36c which receive input from the distortion gauge bridge circuits SG1, SG2 and SG3 as built-in units. Displacement values of distances between the gauge marks GL1, GL2 and GL3 input through the sensor amplifier units 36a, 36b and 36c are input into a main unit 31 and displayed on a display section 18 through operation of a display control section 33.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a contact type displacement meter that measures a distance between gauge points in a tensile test.

  In the tensile test, a tensile load is applied to a test piece having both ends held by upper and lower grips. The elongation of the test piece at this time is measured by a displacement meter. As a displacement meter, a contact type displacement meter that detects a displacement of a distance between gauge points by contacting an arm that moves with the elongation of a test piece (see Patent Document 1), and an image captured by a camera is subjected to image processing. There is a non-contact type displacement meter that calculates a displacement of a distance between gauge points by using a method (see Patent Document 2).

Japanese Patent Application No. 2002-195805 Japanese Patent Application No. 2011-169727

  The contact type displacement meter as described in Patent Literature 1 is assumed to measure elongation of a homogeneous material. Therefore, there are two gauge points on the test piece in the tensile test, and the gauge distance at which elongation can be measured is one. On the other hand, in recent years, carbon fiber and resin composite materials such as CFRP (Carbon Fiber Reinforced Plastics) in which a thermosetting resin and carbon fibers are composited, and CFRTP (Carbon Fiber Reinforced Thermo Plastics) in which a thermoplastic resin and carbon fibers are composited. There is a demand for a material test to evaluate the material properties of the material. These composite materials are heterogeneous materials in which the direction of carbon fibers is random with respect to the resin serving as the base material. When a small test piece stipulated by the conventional plastic tensile test standard is made of such a material, a difference in elongation of the material occurs due to a difference in the direction of the carbon fiber in each test piece. In particular, in a carbon fiber chopped tape reinforced thermoplastic resin composite material in which a unidirectional carbon fiber tape is cut and spread over the cut CFRTP, when measuring the distance between one gauge with a conventional contact type displacement meter, The variation of the elastic modulus calculated using the displacement data of the test piece becomes large, and it is difficult to evaluate the material properties.

  As image processing in a non-contact displacement meter, a digital image correlation method (DIC: Digital Image Correlation) using a digital image obtained by photographing with a camera is known. In this digital image correlation method, a random pattern is arranged on the surface of a test object to be tested using paint or the like, and the amount of deformation of the random pattern before and after a load such as tension is applied is observed. It is possible to measure elongation. Since the displacement data can be acquired by setting an arbitrary distance between the reference points on the image from the random pattern, the method is attracting attention as a method for analyzing the deformation behavior of the composite material.

  On the other hand, measurement accuracy realized by a conventional strain gauge type contact displacement meter for measuring the distance between two gauge points (for example, required by the international standard ISO527-1 for plastic tensile test). At present, it is difficult to obtain (± 1 μm absolute accuracy) for a non-contact type displacement meter. In other words, in the tensile test, the relative distance between the camera and the test piece tends to fluctuate, and there are restrictions due to the resolution of the camera that acquires the image. Therefore, the digital image correlation method is used to analyze the digital image acquired by the non-contact displacement meter. Even if is adopted, anxiety remains from the viewpoint of obtaining highly reliable data. In addition, there is an individual difference in a user's installation of a random pattern applied to the surface of a test object to be tested, and there is also a problem that the reproducibility of the marking is reduced depending on the skill of the user.

  The present invention has been made to solve the above-described problem, and has as its object to provide a displacement meter capable of measuring a plurality of gauge lengths in a tensile test.

  The invention according to claim 1 is a displacement meter, wherein in the displacement meter, a plurality of arms each having an edge at an end thereof that comes into contact with a plurality of test points of the test piece, and the distance between the test points according to relative movement between the arms. And a detector for measuring a change in

  According to a second aspect of the present invention, in the displacement gauge according to the first aspect, the arm is a pair of two arms, and the detecting unit is provided on a side opposite to an edge of the arm forming the pair. And strain gauge bridge circuits respectively disposed on the base end side.

  According to a third aspect of the present invention, in the displacement meter according to the first aspect, the detection unit includes an optical fiber strain sensor provided with an FBG having a different Bragg wavelength between arms adjacent to the arm.

  According to the first to third aspects of the present invention, since the displacement meter includes a plurality of pairs of arms that abut on the test piece at the edges, it is possible to measure the displacement of a plurality of gauge lengths. . Since one test piece can be divided and measured in a heterogeneous material, it is possible to evaluate the average value and statistical processing of the elastic modulus calculated based on a plurality of displacement data. Thereby, the displacement characteristics can be more quantitatively evaluated. In addition, by accurately defining the distance between the reference points as the distance between the arms, it is possible to repeatedly execute a reliable test from the viewpoint of test reproducibility.

  According to the third aspect of the invention, by adopting the optical fiber strain sensor for the displacement measurement system of the gauge length, it is possible to easily perform multi-point measurement.

It is a schematic diagram of a material testing machine to which the displacement meter 40 of the present invention is applied. FIG. 2 is a schematic diagram showing a displacement meter 40 according to the first embodiment together with a block diagram showing a main control system related to measurement of elongation of a test piece 100 of a material testing machine. FIG. 3 is a plan view illustrating a holding mechanism 60. It is a top view explaining other pinching mechanisms 60. It is a schematic diagram showing a displacement meter 50 according to a second embodiment together with a block diagram showing a main control system related to measurement of elongation of a test piece 100 of a material testing machine.

  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 to which a displacement meter 40 of the present invention is applied.

  The material testing machine includes a base 14, a cross yoke 12, a pair of screw rods 11 erected rotatably from the base 14 to the cross yoke 12, and a cross movable along the pair of screw rods 11. It includes a head 13 and a load mechanism 26 for rotating the pair of screw rods 11. The crosshead 13 is connected to the pair of screw rods 11 via nuts not shown. The lower ends of the pair of screw rods 11 are connected to a load mechanism 26 disposed in the base 14, and power from a power source in the load mechanism 26 is transmitted to the pair of screw rods 11. ing. When the pair of screw rods 11 rotate in synchronization, the crosshead 13 moves up and down along the pair of screw rods 11.

  An upper grip 21 for gripping the upper end of the test piece 100 is provided on the crosshead 13 via a load cell 23. On the other hand, the base 14 is provided with a lower grip 22 for gripping a lower end of the test piece 100. When a tensile test is performed, the crosshead 13 is raised in a state where both ends of the test piece 100 are gripped by the upper grip 21 and the lower grip 22, so that the test force ( (Tensile load).

  At this time, the test force acting on the test piece 100 is detected by the load cell 23. On the other hand, the displacement generated in the test piece 100 is detected by the displacement meter 40. The detection signals of the load cell 23 and the displacement meter 40 are input to the control unit 30. The control unit 30 controls the operation of the load mechanism 26. The control unit 30 is connected to a display unit 18 including a liquid crystal panel having a touch panel that receives input from the user, and an operation unit 19 operated by the user to start and stop the movement of the crosshead 13. I have.

  FIG. 2 is a schematic diagram showing the displacement meter 40 according to the first embodiment together with a block diagram showing a main control system related to the measurement of the elongation of the test piece 100 of the material testing machine. In FIG. 2, a partial front view of the test piece 100 is also shown for explanation of the distance between gauge points. FIG. 3 is a plan view illustrating the holding mechanism 60.

  The displacement gauge 40 is attached to a flat test piece 100 gripped by the upper grip 21 and the lower grip 22. The displacement meter 40 includes three pairs of arms 41a, 41b, and 41c that come into contact with the test piece 100 at the tip knife edge NA (see FIG. 3), and bases 42a and 42b that are opposite to the edges of each pair. 42c is provided with strain gauge bridge circuits SG1, SG2, SG3 as a detecting unit for measuring a change in the distance between gauge points. The strain gauge bridge circuits SG1, SG2, SG3 are attached to leaf springs mounted between base arms of the pair of arms 41a, 41b, 41c. The bases 42a, 42b, 42c in which the base ends of the arms and the strain gauge bridge circuits SG1, SG2, SG3 are accommodated are supported by a support plate 46 whose lower end is fixed to the base 14. The height positions of the bases 42a, 42b, 42c with respect to the support plate 46 are movable. The point where the knife edge NA of the arms 41a, 41b, 41c of the displacement meter 40 is in contact with the test piece 100 becomes the reference point of the test piece 100. The displacement of the arm 41b is a displacement of the distance GL2, and the displacement of the arm 41c is a displacement of the distance GL3.

  As shown in FIG. 3, a clamping mechanism 60 for preventing the contact position of the knife edge NA on the test piece 100 from being shifted is provided on the knife edge NA side of the three pairs of arms 41a, 41b, 41c. . The holding mechanism 60 shown in FIG. 3 includes an edge supporting portion 61 fixed to the arm side and a pressing portion 62 for arranging an opposing member 63 such as a punch at a position opposing the knife edge NA with the test piece 100 interposed therebetween. A screw 64 for connecting the pressing portion 62 to the edge supporting portion 61 and for moving the pressing portion 62 toward and away from the edge supporting portion 61. The screw portion of the screw 64 passes through the holding portion 62 and is screwed into a screw hole of the guide 71 connected to the edge support portion 61. A guide 72 is connected to a position facing the guide 71 on the holding portion 62 side, and a cylindrical spring 65 is inserted between the holding portion 62 and the head of the screw 64. In the clamping mechanism 60, the test piece 100 is clamped between the opposing member 63 and the knife edge NA using a reaction force when the spring 65 is compressed by fastening the screw 64.

  Referring to FIG. 2 again, a sensor amplifier unit that inputs an excitation signal to each of strain gauge bridge circuits SG1, SG2, and SG3 and receives an input from strain gauge bridge circuits SG1, SG2, and SG3 is provided to control unit 30. 36a, 36b and 36c are arranged as built-in units. Each of the sensor amplifier units 36a, 36b, and 36c extracts an expanded signal from an amplifier that amplifies a signal, a filter for removing noise from the signal, an A / D converter, a D / A converter, and an input signal. It is composed of a digital circuit using an FPGA or the like that outputs a displacement value.

  The control unit 30 includes a memory 32 in which an operation program necessary for controlling the apparatus is stored, an MPU 35 which is an arithmetic unit for performing a logical operation, a main unit 31 in which a storage element for storing data is arranged, A plurality of built-in units connected to the unit 31 are provided. The memory 32 executes display control for displaying the displacement values of the reference points GL1, GL2, and GL3 to the display unit 18 and the built-in unit communication unit 34 for communicating with the sensor amplifier units 36a, 36b, and 36c. The display control unit 33 is provided as a program. The displacement values of the gauge lengths GL1, GL2, GL3 input from the sensor amplifier units 36a, 36b, 36c are input to the main unit 31 and displayed on the display unit 18 by the operation of the display control unit 33.

  When the crosshead 13 is raised by the operation of the load mechanism 26 and a tensile test force is applied to the test piece 100, the displacement of the pair of arms 41a is detected by the strain gauge bridge circuit SG1 and input to the control unit 30. You. In the control unit 30, the distortion signal is input to the main unit 31 via the sensor amplifier unit 36a, and the displacement value of the distance GL1 between the gauges is obtained. The displacement of the pair of arms 41b is detected by the strain gauge bridge circuit SG2 and input to the control unit 30. In the control unit 30, the distortion signal is input to the main unit 31 via the sensor amplifier unit 36b, and the displacement value of the gauge length GL2 is obtained. Further, the displacement of the pair of arms 41c is detected by the strain gauge bridge circuit SG3 and input to the control unit 30. In the control unit 30, the distortion signal is input to the main unit 31 via the sensor amplifier unit 36c, and the displacement value of the gauge length GL3 is obtained. That is, the displacement of the gauge lengths GL1, GL2, GL3 is measured as the elongation of the test piece 100 by the three pairs of arms 41a, 41b, 41c. In this embodiment, the sensor amplifier units 36a, 36b, and 36c are provided as built-in units in the control unit 30. However, the sensor amplifier is configured as an external device, and connection to an external device provided in the control unit 30 is performed. A signal may be input via an input / output unit having a terminal.

  FIG. 4 is a plan view illustrating another holding mechanism 60. In addition, about the structure similar to FIG. 3, the same code | symbol is attached | subjected and detailed description is abbreviate | omitted.

  In the holding mechanism 60 shown in FIG. 4, a permanent magnet 67 is disposed on the holding section 62, and an electromagnet 66 including an iron core and a coil is disposed on the edge support section 61. A slide bearing 68 is provided between the pressing portion 62 and the edge support portion 61 to penetrate and support a shaft 69 connected to the electromagnet 66. In the holding mechanism 60, the energization of the electromagnet 66 causes the pressing portion 62 and the edge supporting portion 61 to approach each other, and the test piece 100 is held between the knife edge NA and the facing member 63. In this case, a digital circuit for controlling the energization of the electromagnet 66 may be provided in the main unit 31 of the control unit 30, and the controller of the clamping mechanism 60 is connected to the displacement meter 40 separately from the control unit 30. You may.

  In the holding mechanism 60 shown in FIG. 3, the user manually tightens the screw 64. On the other hand, in the holding mechanism 60 shown in FIG. You can do it.

  FIG. 5 is a schematic diagram showing a displacement meter 50 according to the second embodiment together with a block diagram showing a main control system related to the measurement of the elongation of the test piece 100 of the material testing machine. In FIG. 5, similarly to FIG. 2, a partial front view of the test piece 100 is also shown for explanation of the distance between gauge points.

  The displacement meter 50 is attached to the flat test piece 100 gripped by the upper grip 21 and the lower grip 22 as in the first embodiment. The displacement meter 50 includes a plurality of arms 51 that come into contact with the test piece 100 at the tip of the knife edge NA. Note that FIG. 5 shows the pair of arms 51a, 51b, and 51c, but these are collectively referred to as the arm 51. On the knife edge NA side of each arm 51, a clamping mechanism 60 for preventing the contact position of the knife edge NA on the test piece 100 described above with reference to FIGS. 3 and 4 is provided. I have. The base ends of the arms 51 opposite to the knife edge NA are connected to an optical fiber 57 provided with FBGs (Fiber Bragg Gratings) 1, FBG 2, and FBG 3 as a detection unit for measuring a change in the distance between gauge points. , FBG1, FBG2, and FBG3 form a pair for measuring a change in the distance between gauge points. The FBG is a sensor unit of an optical fiber sensor in which a diffraction grating is formed in the core of an optical fiber and has a function as an optical filter. FBG1, FBG2, and FBG3 are manufactured by performing processing for forming gratings (diffraction gratings) having different pitches in one optical fiber.

  The optical fiber 57 is fixed to a comb-shaped support plate 56 having slits formed at intervals of 1 mm. The permanent magnets 54 are attached to the tips of the comb teeth of the support plate 56. Each arm 51 is disposed movably along a guide 53 having both ends fixed to a support plate 56, and an electromagnet 55 is attached to the base end side of each arm 51. After each arm 51 is moved to a position where the knife edge NA contacts the reference point, a magnetic force is generated by energizing the electromagnet 55, and each arm 51 is fixed at a predetermined position by the attractive force with the permanent magnet 54. ing. The position of each arm 51 can be independently changed, and can correspond to a plurality of distances between gauge points having different lengths. Further, the positions of the arms 51 can be collectively performed by energizing the electromagnet 55, and the user can quickly fix the arms 51 even when there are a number of reference points. When the optical fiber 57 is deformed due to the relative movement between the arms 51 during the test, the distortion is detected by utilizing the fact that the grading pitch of the FBG1, FBG2, and FBG3 changes and the Bragg wavelength changes.

  The displacement meter 50 is connected to the control unit 30 via a measuring device 59 for FBG. The measuring device 59 includes a light source that supplies incident light to the optical fiber 57 including the Bragg wavelength of the FBG, and simultaneously transmits a plurality of wavelengths (optical signals) to one optical fiber 57 using a wavelength division multiplexing filter. , Has a function as a wavelength measuring device for measuring the wavelength of the reflected light from each of the FBG1, FBG2, and FBG3. The measuring device 59 includes a photoelectric element that converts an optical signal into an electric signal and an A / D converter that converts an analog signal into a digital signal. The measurement result of the measuring device 59 is input to the control unit 30. The memory 32 of the control unit 30 recognizes how much the center-of-gravity wavelength of the spectrum of the Bragg wavelength has moved during the test as compared with before the start of the test due to the displacement of each arm 51, and shifts the center-of-gravity wavelength. A conversion unit 39 for converting the amount into an increase in the distance between the gauges in the test piece 100 is provided as a program.

  In FIG. 5, the extension of the distance GL1 between the gauges is detected by detecting the displacement of the pair of arms 51a based on the shift amount of the Bragg wavelength of the FBG1 on the base end side. The extension of the reference point distance GL2 is detected by the amount of shift of the FBG2 Bragg wavelength at the base end of the two arms 51b forming a pair. The extension of the reference point distance GL3 is detected by the amount of shift of the Bragg wavelength of the FBG 3 on the base end side of the pair of arms 51c. Although FIG. 5 illustrates an example in which two arms 51 are arranged as one set of a plurality of pairs, the arms 51 need not necessarily be pairs. By arranging the FBG between the adjacent arms 51, it is possible to measure the variation in the distance between the arms.

  The main unit 31 of the control unit 30 obtains displacement values of the distances GL1, GL2, and GL3 based on the input from the measuring device 59, and displays the displacement values on the display unit 18. In this embodiment, unlike the first embodiment, there is no need to arrange the number of sensor amplifier units corresponding to the strain gauge bridge circuit, and one measuring instrument 59 can detect a plurality of strains. it can. Further, in this embodiment, three diffraction gratings having different Bragg wavelengths are formed in the optical fiber 57, but the present invention is not limited to this. The required number of FBGs may be arranged on one optical fiber at an appropriate interval between measurement points. Further, since the displacement meter 50 of the second embodiment uses optical communication by the optical fiber 57, it is affected by magnetism like the strain gauge type displacement meter 40 using the electric circuit of the first embodiment. This allows stable measurement with less noise.

  As described above, by applying the displacement gauges 40 and 50 having a plurality of pairs of arms of the present invention to a material test, displacement of a plurality of gauge lengths for one test piece can be measured in one test. can do. For this reason, one test piece can be divided and measured in a heterogeneous material, and the average value and statistical processing evaluation of the elastic modulus calculated based on a plurality of displacement data can be performed. Thereby, the displacement characteristics can be more quantitatively evaluated. In addition, by accurately defining the distance between the reference points as the distance between the paired arms, it is possible to depend on the skill of the user in setting the reference point, such as setting a random pattern of a non-contact type displacement meter. Absent. Therefore, it is possible to repeatedly execute a reliable test from the viewpoint of test reproducibility.

DESCRIPTION OF SYMBOLS 11 Screw rod 12 Cross yoke 13 Cross head 14 Base 18 Display part 19 Operation part 21 Upper grip 22 Lower grip 23 Load cell 26 Load mechanism 30 Control part 31 Main unit 32 Memory 33 Display control part 34 Built-in unit communication part 35 MPU
36 Sensor amplifier unit 37 Input / output unit 40 Displacement meter 41a, 41b, 41c Arm 42 Base 50 Displacement meter 51a, 51b, 51c Arm 53 Guide 54 Permanent magnet 55 Electromagnet 56 Support plate 57 Optical fiber 59 Measuring device 60 Clamping mechanism 61 Edge support Part 62 Holding part 63 Opposing member 64 Screw 65 Spring 66 Electromagnet 67 Permanent magnet 68 Slide bearing 69 Shaft 71 Guide 72 Guide 100 Test piece GL Distance between gauge points SG Strain gauge bridge circuit NA Knife edge

Claims (3)

A plurality of arms having at their ends an edge abutting on a plurality of gauge points of the test piece,
A detection unit that measures a change in the distance between the gauges according to the relative movement between the arms,
Displacement meter equipped with. The displacement meter according to claim 1,
The arm is a pair of two,
A displacement meter comprising: a strain gauge bridge circuit disposed on a base end side opposite to an edge of the pair of arms, the detection section being opposite to an edge of the pair of arms. The displacement meter according to claim 1,
The displacement meter, wherein the detection unit includes an optical fiber strain sensor provided with an FBG having a different Bragg wavelength between arms adjacent to the arm.

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