A calibration device and calibration method for strain gauges

Abstract

The present application relates to a kind of calibration device for strain extensometer calibration, including device support, lower clamping structure for clamping the lower end of strain extensometer and upper clamping structure for clamping the upper end of strain extensometer are provided on device support, device support also includes cross slide that the action output end can be left and right movement adjustment and front and back movement adjustment, lower clamping structure is fixed on the action output end of cross slide, upper clamping structure, lower clamping structure all include a pair of clamping block that can be moved along the radial opposite of strain extensometer and opposite movement, upper clamping structure, lower clamping structure also include the clamping block drive mechanism of driving corresponding pair of clamping block synchronous opposite movement and synchronous opposite movement.The purpose of the present application is to provide a kind of calibration device and the calibration method using the calibration device, which can realize the calibration of strain extensometer.

Description

Technical Field

[0001] This invention relates to the field of metrological calibration, and more particularly to a calibration device and calibration method for a strain gauge extensometer. Background Technology

[0002] An extensometer, also known as an electronic alignment measuring device, is used to measure the angle and axis deviation of the actual test load chain from the axis of the load chain in the test system. It can be applied to static material testing machines and dynamic testing machines.

[0003] For example, a tensile testing machine includes a frame with an upper clamping structure and a lower clamping structure. During use, the two ends of the specimen to be stretched are connected to the upper and lower clamping structures respectively. The upper clamping structure then moves upward under the corresponding driving action, applying an axial tensile force to the specimen. To accurately measure the tensile strength of the specimen, it is necessary to ensure that the upward movement direction of the upper clamping structure is completely consistent with the length direction of the specimen itself. In other words, the upper and lower clamping structures need to be coaxial. Whether the upper and lower clamping structures are coaxial needs to be measured using an extensometer.

[0004] Existing strain gauges 1 such as Figure 1 As shown, the main body 3 includes a rod-shaped structure, with a hollow structure in the middle. Multiple sets of strain gauge groups 2 are attached to the inner wall of the main body, arranged at intervals along the length of the main body. Each strain gauge group includes four strain gauges arranged at intervals along the circumference. Two strain gauges arranged opposite each other are a pair. That is, at a certain height position in the inner cavity of the main body, there are two pairs of strain gauges. Two strain gauges in one pair are arranged front and back, and two strain gauges in the other pair are arranged left and right. In this patent document, one pair of strain gauges is defined as the first pair of strain gauges 4, and the other pair of strain gauges is defined as the second pair of strain gauges 5.

[0005] When it is necessary to measure whether the upper and lower clamping structures of a tensile testing machine are coaxial, the upper clamping structure clamps the upper end of the extensometer, and the lower clamping structure clamps the lower end of the extensometer. If the upper and lower clamping structures are coaxial, then the body of the extensometer should be vertical, and the deformation readings of a pair of strain gauges should be the same. If the upper and lower clamping structures are not coaxial, the extensometer will deform. Taking the extensometer bending to the left from bottom to top as an example, the readings of the strain gauge on the left and the strain gauge on the right in a pair of strain gauges will be different. By the corresponding reading difference, the skewness of the upper and lower clamping structures can be known.

[0006] The problem with existing technology is that, as a measuring device, strain gauges need to be calibrated and traced over a certain period of time to ensure their accuracy. However, there is currently a lack of equipment for calibrating strain gauges that have strain gauges attached to the inner wall of a cavity. Summary of the Invention

[0007] The purpose of this invention is to provide a calibration device capable of calibrating strain gauges; another purpose of this invention is to provide a calibration method using the calibration device.

[0008] To solve the above-mentioned technical problems, the technical solution of the calibration device for strain gauges in this invention is as follows: A calibration device for calibrating a strain gauge includes a device support, on which are provided a lower clamping structure for clamping the lower end of the strain gauge and an upper clamping structure for clamping the upper end of the strain gauge. The device support also includes a cross slide with an action output end that can be adjusted to move left and right and back and forth. The upper or lower clamping structure is fixed to the action output end of the cross slide. Both the upper and lower clamping structures include a pair of clamping blocks that can move relative to each other and back to back along the radial direction of the strain gauge. The upper and lower clamping structures also include a clamping block driving mechanism that drives the corresponding pair of clamping blocks to move synchronously relative to each other and synchronously back to back.

[0009] Furthermore, the opposite sides of the pair of clamping blocks have V-shaped clamping surfaces for clamping strain gauges.

[0010] Furthermore, the clamping block drive mechanism includes a horizontally arranged clamping block drive screw, which is threadedly connected to a corresponding pair of clamping blocks. The clamping block drive mechanism also includes a screw drive motor that is driven by the clamping block drive screw.

[0011] Furthermore, the device support includes a device base and a device crossbeam located on the upper side of the device base. The upper clamping structure is fixed to the lower end of the device crossbeam, the cross slide is fixed to the upper end of the device base, and the lower clamping structure is located on the upper end of the cross slide.

[0012] Furthermore, a device column is fixed on the device base, and a device beam is guided and mounted on the device column in the vertical direction. A top beam is fixed on the top of the device column, and a beam drive mechanism is provided on the top beam to drive the device beam to move up and down.

[0013] Furthermore, the beam drive mechanism includes a vertically arranged drive cylinder, the piston rod of which is connected to the beam of the device.

[0014] The technical solution of the calibration method in this invention is as follows: A calibration method includes the following steps: When calibrating a strain gauge extensometer, firstly, the upper end of a standard strain gauge is clamped and fixed to an upper clamping structure, and the lower end of the standard strain gauge is clamped and fixed to a lower clamping structure. The horizontal position of the lower clamping structure is adjusted by the corresponding cross slide to make the readings of each strain gauge in the first pair and the second pair of strain gauges at each position of the standard strain gauge extensometer the same. Secondly, the upper and lower clamping structures are released, and the upper and lower ends of the strain gauge to be calibrated are clamped to the upper and lower clamping structures respectively, and the strain gauge to be calibrated is calibrated once.

[0015] Furthermore, in the third step, the upper end of the standard strain gauge is clamped and fixed to the upper clamping structure, and the lower end of the standard strain gauge is clamped and fixed to the lower clamping structure. The horizontal position of the lower clamping structure is adjusted by the corresponding cross slide, so that the readings of the two strain gauges of the first pair of strain gauges at each position of the standard strain gauge are the same, and the readings of the two strain gauges of the second pair of strain gauges are different, and the strain gauge readings are recorded; or, the readings of the two strain gauges of the first pair of strain gauges at each position are different, and the readings of the two strain gauges of the second pair of strain gauges are the same, and the strain gauge readings are recorded; or, the readings of the two strain gauges of the first pair of strain gauges at each position are different, and the readings of the two strain gauges of the second pair of strain gauges are also different, and the strain gauge readings are recorded. In the fourth step, the upper and lower clamping structures are released, and the upper and lower ends of the strain gauge to be calibrated are clamped to the upper and lower clamping structures respectively, and the strain gauge to be calibrated is calibrated a second time.

[0016] The beneficial effects of this invention are as follows: There are two key points to this invention: the use of a cross slide and the synchronous relative and opposite movements of the clamping blocks of the upper and lower clamping structures. When calibrating the strain gauge to be calibrated, a standard strain gauge is first used. This standard strain gauge is a strain gauge stored in the metrology unit that does not require calibration. The upper clamping structure clamps the upper end of the standard strain gauge. The horizontal position of the lower clamping structure is adjusted by the cross slide. Because a standard strain gauge is used, when the readings of the first pair and the second pair of strain gauges at each position of the standard strain gauge are the same, it indicates that the upper and lower clamping structures are coaxial. This is used to locate the position of the lower clamping structure relative to the upper clamping structure. At this point, release the upper and lower clamping structures and clamp and fix the upper and lower ends of the strain gauge to be calibrated onto the upper and lower clamping structures. Since the corresponding pair of clamping blocks of the upper and lower clamping structures move synchronously relative to each other and in opposite directions, after the upper and lower clamping structures re-clamp and fix the ends of the strain gauge to be calibrated, the upper and lower clamping structures are still in a coaxial state. At this time, the readings of the first pair of strain gauges and the second pair of strain gauges at the corresponding positions of the strain gauge to be calibrated should also be the same as the readings of the first pair of strain gauges and the second pair of strain gauges at the corresponding positions of the standard strain gauge. Therefore, the strain gauge to be calibrated can be calibrated by comparing the readings of the standard strain gauge with the readings of the strain gauge to be calibrated. Attached Figure Description

[0017] The above and other objects, features, and advantages of this disclosure will become readily apparent from the following detailed description of exemplary embodiments with reference to the accompanying drawings. In the drawings, several embodiments of this disclosure are illustrated by way of example and not limitation, and like or corresponding reference numerals denote like or corresponding portions, wherein: Figure 1 This is a schematic diagram of the strain gauge extensometer in the background art of this invention; Figure 2 This is a usage state diagram of an embodiment of the present invention; Figure 3 yes Figure 2 A schematic diagram showing the fit between the strain gauge to be calibrated and the upper clamping structure. Explanation of reference numerals in the attached drawings: 1. Strain gauge extensometer; 2. Strain gauge assembly; 3. Main body; 4. First pair of strain gauges; 5. Second pair of strain gauges; 6. Drive cylinder; 7. Piston rod; 8. Top crossbeam; 9. Device crossbeam; 10. Column; 11. Upper clamping structure; 12. Lower clamping structure; 13. Clamping block drive screw; 14. Screw drive motor; 15. Clamping block; 16. Cross slide; 17. Longitudinal moving block; 18. Lateral moving block; 19. Device base; 20. V-shaped clamping surface. Detailed Implementation

[0018] To facilitate understanding of the present invention, a more detailed description is provided below with reference to the accompanying drawings and specific embodiments. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0019] It should be noted that, unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention.

[0020] An embodiment of a calibration device for a strain gauge in this invention is as follows: Figures 1-3 As shown: The device includes a support frame, which includes a base 19. Four support columns 10 are fixed on the base 19. A top crossbeam 8 is fixed on the top of the four support columns 10. A crossbeam 9 is mounted on the support columns in a vertical direction between the base and the top crossbeam. A crossbeam drive mechanism is provided on the top crossbeam to drive the crossbeam to move up and down. In this embodiment, the crossbeam drive mechanism includes a vertically arranged drive cylinder 6. The piston rod 7 of the drive cylinder 6 is fixedly connected to the crossbeam.

[0021] The lower end of the device beam is provided with an upper clamping structure 11 for clamping the upper end of the strain gauge, and the upper end of the device base is provided with a cross slide 16. The cross slide includes an action output end that can be adjusted left and right and forward and backward. The action output end is provided with a lower clamping structure 12 for clamping the lower end of the strain gauge.

[0022] like Figure 2 As shown: Item 18 represents the transverse moving block of the cross slide, and Item 17 represents the longitudinal moving block of the cross slide. The transverse moving block can move left and right under the drive of the corresponding transverse drive mechanism. The longitudinal moving block is assembled on the transverse moving block and can move back and forth under the drive of the corresponding longitudinal drive mechanism. Both the transverse drive mechanism and the longitudinal drive mechanism include a motor and a lead screw connected to the motor. The lead screw is threadedly connected to the corresponding moving block, and the lead screw and the corresponding moving block form a lead screw and nut mechanism. The cross slide is prior art and will not be described in detail here.

[0023] The longitudinal moving block forms the action output end of the cross slide, and the lower clamping structure 12 is set on the longitudinal moving block.

[0024] Both the upper clamping structure and the lower clamping structure include a pair of clamping blocks 15 that can move relative to each other and move away from each other in the radial direction of the strain gauge extensometer. In this embodiment, the two clamping blocks in the pair can move relative to each other and move away from each other in the left and right directions. The upper clamping structure and the lower clamping structure also include a clamping block driving mechanism that drives the corresponding pair of clamping blocks to move synchronously relative to each other and synchronously move away from each other.

[0025] Specifically, the clamping block drive mechanism includes a horizontally arranged clamping block drive screw 13, which is threadedly connected to a corresponding pair of clamping blocks. The threads on the two clamping blocks of the corresponding pair of clamping blocks rotate in opposite directions. The clamping block drive structure also includes a screw drive motor 14 that is connected to the clamping block drive screw. The clamping block drive screw and the corresponding clamping blocks also constitute a screw and nut mechanism. When the clamping block drive screw rotates forward, the two clamping blocks can move synchronously relative to each other. When the clamping block drive screw rotates in reverse, the two clamping blocks can move synchronously in opposite directions.

[0026] The opposite sides of a pair of clamping blocks have V-shaped clamping surfaces 20 for clamping strain gauges.

[0027] The calibration equipment also includes standard strain gauges, which are strain gauges stored by metrology units that do not require calibration. A strain gauge is an extensometer with strain plates attached internally.

[0028] When calibrating a strain gauge extensometer, first clamp and fix the upper and lower ends of the standard strain gauge extensometer to the upper and lower clamping structures. Adjust the horizontal position of the lower clamping structure using the cross slide. When the lower clamping structure is coaxial with the standard strain gauge extensometer, the readings of the first pair of strain gauges and the second pair of strain gauges at the corresponding positions should be the same. In other words, when the readings of the first pair of strain gauges and the second pair of strain gauges corresponding to a strain gauge group are the same, it indicates that the upper clamping structure and the lower clamping structure are set to be coaxial. Then, release the clamps on the standard strain gauge extensometer.

[0029] The specific loosening process can be as follows: the pair of clamping blocks of the upper and lower clamping structures only need to move 5mm away from each other to slightly loosen the clamping of the standard strain gauge extensometer. Then, the device beam moves upward to remove the standard strain gauge extensometer. Next, the lower end of the strain gauge extensometer to be calibrated is placed between the two clamping blocks of the lower clamping structure. Then, the device beam moves downward, and the upper and lower clamping structures clamp the upper and lower ends of the strain gauge extensometer to be calibrated. The relative movement of the two clamping blocks of the upper and lower clamping structures is very small to complete the clamping of the strain gauge extensometer to be calibrated. This setting has two effects: one is that the movement distance of the clamping blocks is very short, which helps to improve calibration efficiency; more importantly, it can minimize the error caused by the fit clearance between the clamping block drive screw and the clamping blocks. The impact of calibration is due to the threaded fit between the clamping block drive screw and the clamping block, which has a clearance. Ideally, after synchronous opposite movement and synchronous relative movement adjustment, the clamping center, i.e., the axis position, of the two clamping blocks should remain unchanged. However, due to the existence of the clearance, after the two clamping blocks move a long distance relative to each other, there will be a certain deviation when they return to their original position. For example, after the two clamping blocks move 10cm away from each other and then move 10cm relative to each other to return to their original position, there will be a certain error between this position and the initial position. This error is due to the cumulative error caused by the large number of rotations of the clamping block drive screw. However, if the two clamping blocks move 5mm away from each other (the clamping block drive screw rotates one revolution or less) and then move 5mm relative to each other, they can accurately return to their original position.

[0030] In other embodiments of the present invention, when the calibration accuracy requirement is not so high, the device beam can also be fixed. In this case, it is necessary to loosen the clamping mechanism of the strain gauge and move the two clamping blocks of the clamping structure back to back to the strain gauge so that it can be moved radially away.

[0031] An implementation of a calibration method for a strain gauge, for example Figures 1-3 As shown: The method includes the following steps. When calibrating a strain gauge extensometer, the first step is to clamp and fix the upper end of the standard strain gauge extensometer to the upper clamping structure of the calibration device, and clamp and fix the lower end of the standard strain gauge extensometer to the lower clamping structure. The horizontal position of the lower clamping structure is adjusted by the corresponding cross slide so that the readings of each strain gauge in the first pair and the second pair of strain gauges at each position of the standard strain gauge extensometer are the same. The second step is to loosen the upper and lower clamping structures, clamp the upper and lower ends of the strain gauge to be calibrated to the upper and lower clamping structures respectively, and perform a calibration on the strain gauge to be calibrated.

[0032] The specific structure of the calibration device is the same as that described in the above embodiments of the calibration devices for strain gauges, and will not be detailed here. The release and clamping of the standard strain gauge and the strain gauge to be calibrated are also performed in the above manner. That is, the pair of clamping blocks of the upper and lower clamping structures only need to move 5mm away from each other to slightly loosen the clamping of the standard strain gauge. Then, the device beam moves upward to remove the standard strain gauge. Next, the lower end of the strain gauge to be calibrated is placed between the two clamping blocks of the lower clamping structure. Then, the device beam moves downward, and the upper and lower clamping structures clamp the upper and lower ends of the strain gauge to be calibrated.

[0033] The third step involves clamping and fixing the upper end of the standard strain gauge to the upper clamping structure and the lower end to the lower clamping structure. The horizontal position of the lower clamping structure is adjusted using the corresponding cross slides so that the readings of the two strain gauges in the first pair at each position of the standard strain gauge are the same, while the readings of the two strain gauges in the second pair are different. The strain gauge readings are then recorded. Alternatively, the readings of the two strain gauges in the first pair at each position are different, while the readings of the two strain gauges in the second pair are the same. The strain gauge readings are also recorded. Finally, the fourth step involves loosening the upper and lower clamping structures and clamping the upper and lower ends of the strain gauge to be calibrated onto the upper and lower clamping structures respectively, performing a second calibration of the strain gauge.

[0034] Through steps three and four, multi-directional, full-angle calibration of each strain gauge in the strain gauge extensometer to be calibrated can be achieved. Specifically, the bending direction and amplitude of the lower end of the standard strain gauge extensometer can be adjusted using the cross slide, thereby calibrating the first pair and second pair of strain gauges in each strain gauge group separately.

[0035] In the foregoing description of this specification, unless otherwise expressly specified and limited, the terms "fixed," "installed," "connected," or "linked" should be interpreted broadly. For example, the term "linked" can refer to a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; or it can refer to the internal communication of two components or the interaction between two components. Therefore, unless otherwise expressly limited in this specification, those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0036] Based on the above description in this specification, those skilled in the art will also understand that terms used, such as "upper," "lower," "front," "rear," "left," "right," "length," "width," "thickness," "vertical," "horizontal," "top," "bottom," "inner," "outer," "axial," "radial," "circumferential," "center," "longitudinal," "transverse," "clockwise," or "counterclockwise," are terms indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings of this specification. They are only for the purpose of facilitating the explanation of the present invention and simplifying the description, and do not imply that the devices or elements involved must have the specific orientation, or be constructed and operated in a specific orientation. Therefore, the above-mentioned orientation or positional relationship terms should not be understood or interpreted as limitations on the present invention.

[0037] Furthermore, the terms "first" or "second," etc., used in this specification to refer to numbers or ordinal numbers are for descriptive purposes only and should not be construed as indicating, explicitly or implicitly, relative importance or specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this specification, "a plurality of" means at least two, such as two, three, or more, unless otherwise explicitly specified.

[0038] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

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