A device and method for measuring a small displacement based on a michelson interferometer and a wedge

Abstract

This invention discloses a micro-displacement measurement device and method based on a Michelson interferometer and a wedge. The device includes a wedge assembly, a loading test platform, and a vertical Michelson interferometer. The vertical interferometer guides the measurement beam vertically downward through a beam splitter. The wedge assembly is located in this optical path and can move laterally with the deformation of the sample under test, thereby changing the thickness of the medium through which the beam passes, causing changes in the interference fringes. The method automatically identifies the number of fringe changes through image acquisition and processing, calculates the micro-displacement by combining it with the wedge parameters, and then solves for material parameters such as Young's modulus and coefficient of linear expansion. This invention solves the problem of spatial integration with large loading equipment by using a vertical optical path, avoids frictional interference from the traditional moving mirror method by using a laterally moving wedge, and improves measurement accuracy and efficiency through automated image processing.

Description

Technical Field

[0001] This invention belongs to the field of micro-displacement measurement technology, specifically relating to a micro-displacement measurement device and method based on a Michelson interferometer and a wedge. Background Technology

[0002] When determining material parameters such as Young's modulus and coefficient of linear expansion of metallic materials, calculations are generally performed by measuring the minute deformations produced by the material under physical excitation. These deformations and displacements are typically in the micrometer or even nanometer range and are often accompanied by dynamic changes in the physical state, which places extremely high demands on the sensitivity, linearity, and anti-interference capabilities of the measurement system.

[0003] Currently, the mainstream methods for measuring minute displacements include mechanical contact measurement, optical lever amplification, and optical interferometry. Among these, measurement devices based on the Michelson interferometry principle, which utilize laser wavelength as the measurement standard, possess extremely high sensitivity and are often the preferred solution for high-precision physical quantity detection. For example... Figure 1 The diagram shows the structure of a commonly used Michelson interferometer. It uses a beam splitter to divide the light emitted from the light source into a reference beam and a measurement beam. The optical path difference is changed by moving a mirror in the measurement optical path (i.e., the "moving mirror method"), and the displacement is then inferred from the changes in the interference fringes. Chinese patent CN218036101U discloses a Young's modulus measurement system based on a Michelson interferometer, which employs a similar principle. It connects the metal wire to be measured to a moving mirror, and the elongation of the metal wire directly drives the movement of the moving mirror, thereby measuring the minute deformation of the metal wire through interference fringes.

[0004] However, existing micro-displacement measurement technologies still have significant shortcomings in practical applications. The aforementioned traditional devices and disclosed patented technologies typically employ a conventional horizontal planar layout, where all optical elements are mounted on a low horizontal base, with the optical path propagating parallel to the tabletop. This structure is problematic when performing multi-physics coupling tests requiring integration with large tensile drive mechanisms or tubular furnaces. The testing equipment is difficult to place within the low optical path space, hindering effective spatial coupling between the optical path and the sample, making system integration extremely difficult. Furthermore, existing technologies rely on the "moving mirror method," where sample deformation drives a mirror to move along the optical axis. However, the inherent static and dynamic friction forces of the moving mirror guide rail easily lead to lag or nonlinear distortion in displacement transmission, failing to accurately and in real-time reflect the sample's deformation process. Moreover, the manual observation of fringes is prone to introducing subjective errors. Therefore, there is an urgent need to improve existing technologies to address the technical problems of low spatial integration, significant mechanical friction interference, and limited measurement accuracy in current micro-displacement measurements. Summary of the Invention

[0005] To achieve the above objectives, the present invention provides a micro-displacement measurement device and method based on a Michelson interferometer and a wedge, in order to solve the problems of difficult spatial integration of interferometers, large frictional interference, and high manual reading errors in the prior art.

[0006] In a first aspect, the present invention provides a micro-displacement measurement device based on a Michelson interferometer and a wedge, comprising: A wedge assembly includes an optical wedge and a mounting housing, wherein the mounting housing is provided with a mounting groove, the optical wedge is detachably mounted in the mounting groove, and the mounting housing is fixedly connected to the free end of the sample to be tested. A loading test platform is connected to the fixed end of the sample under test and configured to apply physical excitation to the sample under test to cause deformation; and A vertical Michelson interferometer includes a base, a column support vertically mounted on the base, and an interference optical path assembly mounted on the column support; The interference optical path assembly is used to form an interference optical path and includes a laser source, a beam splitter, a first reflector, a second reflector, and a screen. The laser source is configured to emit a horizontal beam. The beam splitter is located in front of the optical path of the laser source. The first reflector is located directly below the beam splitter, and the second reflector is located behind the reflected optical path of the beam splitter. The beam splitter is set at a 45-degree angle relative to the horizontal plane, such that the horizontally incident laser beam is split at the beam splitter into a horizontal beam that is transmitted to the second reflector and a vertically downward beam that is reflected to the first reflector. The wedge assembly is located in the beam path between the beam splitter and the first reflector, and is configured to move slightly in a direction perpendicular to the vertically downward beam as the sample under test deforms, thereby changing the medium thickness through which the vertically downward beam passes through the wedge assembly.

[0007] Furthermore, the loading test platform is configured to install the following functional components: The mechanical loading assembly includes a force sensor and a tensile drive mechanism connected in series with the wedge assembly and the sample to be tested, for applying tensile force to the sample to be tested to cause deformation; A thermal loading assembly includes a heating device arranged along the axial direction of the sample to be tested. The fixed end of the sample to be tested passes through the heating device, and its free end passes through the heating device and connects to the wedge assembly. The assembly is used to change the temperature of the sample to be tested so that it undergoes thermal expansion deformation.

[0008] Furthermore, the device also includes an image acquisition device and a data processing device; The image acquisition device is aligned with the screen or located on the output optical path of the interference beam to acquire interference fringe images; The data processing device is connected to the image acquisition device and is equipped with an algorithm program for identifying changes in interference fringes and calculating minute displacements.

[0009] Secondly, the present invention provides a method for measuring minute displacements based on any of the above-described devices, comprising the following steps: S100: Construct an interference optical path using the vertical Michelson interferometer, adjust the height of the optical path, and make the vertically downward measurement beam pass through the optical wedge; S200: The sample to be tested is mounted on the loading test platform and its free end is fixedly connected to the wedge assembly; physical excitation is applied to the sample to cause it to deform, driving the optical wedge to follow the deformation of the sample to produce a small displacement relative to the interference optical path, thereby changing the interference optical path. S300: Acquires dynamic images of interference fringes caused by changes in optical path, and uses computer image processing algorithms to automatically identify and count the dynamic images to obtain the number of changing interference fringes. S400: Based on the number of changes in the interference fringes, and using a preset mathematical model, the minute displacement of the sample under test is calculated in combination with the geometric and optical parameters of the optical wedge.

[0010] Preferably, step S100 specifically includes: Select the optical wedge tip with a predetermined wedge angle and install it in the mounting slot of the mounting housing; Adjust the tilt angle of the first or second reflector until clear concentric ring-shaped interference fringes appear on the screen.

[0011] Preferably, in step S200, applying the physical excitation includes: When measuring Young's modulus, a tensile force is applied to the sample under test through the mechanical loading component. The tensile force causes the sample under test to undergo tensile deformation, thereby driving the optical wedge to move. When measuring the coefficient of linear expansion, the temperature of the sample under test is changed by the thermal loading component, and the sample under test is axially deformed by the thermal expansion and contraction effect, which in turn drives the optical wedge to move.

[0012] Preferably, step S300 specifically includes: The image acquisition device acquires a video stream of interference fringe changes; The acquired video stream is decomposed into frame images, and grayscale processing, filtering and sharpening processing, and edge enhancement processing are performed sequentially. The center-positioning algorithm is used to identify the center coordinates of the concentric rings of the interference fringes, and the number of extreme points of gray value change over time at or in the neighborhood of these coordinates is counted to determine the number of different interference fringes.

[0013] Furthermore, step S300 also includes a step of determining the direction of stripe change: By comparing the expansion or contraction trend of the concentric ring radius in consecutive frame images, it can be determined whether the interference fringes are emerging or sinking, thereby determining the moving direction of the optical wedge and the deformation direction of the sample under test.

[0014] Furthermore, after step S400, a material parameter calculation step is also included, specifically including: When measuring Young's modulus, the original length, cross-sectional area, and applied tensile force of the sample to be tested are obtained. Based on the tensile force, original length, cross-sectional area, and the small displacement calculated in step S400, the Young's modulus of the sample to be tested is calculated according to the stress-strain ratio. When measuring the coefficient of linear expansion, the original length and temperature change of the sample under test are obtained. Based on the small displacement, original length, and temperature change, the relative rate of change of length under unit temperature change is calculated, thereby obtaining the coefficient of linear expansion of the sample under test.

[0015] Furthermore, the calculation steps for the material parameters also include a tilt correction step for the optical wedge, used to eliminate additional optical path errors caused by the refraction and deflection of the laser beam within the optical wedge, specifically including: Based on the law of refraction in optics, the refraction path of the laser beam at the optical wedge interface is analyzed to determine the actual propagation direction of the laser beam inside the optical wedge. Based on the actual propagation direction, a mapping relationship is established between the lateral displacement of the optical wedge and the actual optical path difference change of the interference optical path. A geometric correction factor determined by the refractive index and wedge angle of the optical wedge is introduced into the mapping relationship. The calculation model for the minute displacement or the material parameters is corrected using the geometric correction factor to compensate for the optical path calculation deviation caused by the non-perpendicular incident laser beam on the optical wedge surface.

[0016] This invention discloses a method and system for measuring minute displacements based on a Michelson interferometer and a wedge. Its core lies in the innovative combination of a vertical optical path and a laterally moving wedge. Compared to existing technologies, this invention offers significant advantages: First, it innovatively employs a vertical Michelson interferometer architecture, using a beam splitter to project the measurement beam vertically downwards, thus freeing up ample "test operation space" below the optical path. This design allows for the convenient placement of large horizontal loading test platforms (such as horizontal tensile testing machines or tubular furnaces) below the interferometer, perfectly resolving the spatial conflict between traditional horizontal interferometers and large mechanical / thermal testing equipment, and achieving efficient integration of multi-physics systems. Second, this invention abandons the traditional "moving mirror method," instead utilizing the sample under test to drive the optical wedge for lateral movement. Because the wedge is lightweight and experiences minimal resistance during lateral movement, it effectively avoids the problem of small sample deformations struggling to overcome the static friction of the moving mirror guide rail in traditional methods, eliminating hysteresis and nonlinear distortion in displacement transmission, and ensuring the accuracy and high linearity of the measurement results. Furthermore, by combining automated image processing technology, the automatic identification, counting, and direction determination of interference fringes are realized, eliminating the subjective error of manual observation and significantly improving the measurement accuracy and efficiency. This provides a reliable means for achieving high-precision automated measurement of parameters such as Young's modulus and coefficient of linear expansion of materials. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the structure of a Michelson interferometer, which is commonly used in existing technologies. Figure 2 A schematic diagram of the overall structure of the micro-displacement measuring device based on a Michelson interferometer and a wedge provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the structure of the wedge assembly and the sample to be tested provided by the present invention; Figure 4 This is a physical image of the vertical Michelson interferometer in an embodiment of the present invention; Figure 5 A physical diagram of the overall structure of the micro-displacement measuring device and loading test platform for measuring Young's modulus provided in an embodiment of the present invention; Figure 6 A physical diagram of the overall structure of the micro-displacement measuring device and loading test platform for measuring the linear elastic coefficient provided in an embodiment of the present invention; Figure 7 A schematic diagram of the process for measuring minute displacements based on a Michelson interferometer and a wedge, provided in an embodiment of the present invention; Figure 8 This is a schematic diagram of the interference fringe image processing process in an embodiment of the present invention; Figure 9 This is a schematic diagram of the curve showing the change of gray value at the center of the interference fringes over time in an embodiment of the present invention; Figure 10 This is a schematic diagram of the refraction path of the laser beam inside the optical wedge in an embodiment of the present invention.

[0019] The following are the markings in the attached diagram: 1. Base; 2. Column support; 3. Laser source; 4. Beam splitter; 5. First reflector; 6. Second reflector; 7. Screen; 8. Wedge assembly; 81. Optical wedge; 82. Mounting housing; 83. Mounting slot; 9. Loading test platform; 91. Mechanical loading assembly; 92. Thermal loading assembly; 10. Image acquisition device; 11. Data processing equipment; 12. Sample to be tested. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0021] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0022] Traditional micro-displacement measurement techniques, when combined with large loading equipment for multi-physics coupling testing, often employ a horizontal planar layout, leading to difficulties in system integration and hindering effective coupling of the optical path with the sample. Furthermore, reliance on the "moving mirror method" is susceptible to mechanical friction interference, resulting in lag or nonlinear distortion in displacement transmission, and manual observation of fringes is prone to subjective errors, limiting measurement accuracy.

[0023] Based on this, and to improve the problems in related technologies, embodiments of this application provide a micro-displacement measurement device based on a Michelson interferometer and a wedge, such as... Figure 2 , Figure 3and Figure 4 As shown, the device includes a wedge assembly 8, a loading test platform 9, and a vertical Michelson interferometer. The wedge assembly 8 includes an optical wedge 81 and a mounting housing 82. The mounting housing 82 has a mounting groove 83, and the optical wedge 81 is detachably mounted within the mounting groove 83. The mounting housing 82 is fixedly connected to the free end of the sample 12 under test. The loading test platform 9 is connected to the fixed end of the sample 12 under test and is configured to apply physical excitation to the sample 12 to cause deformation. The vertical Michelson interferometer includes a base 1, a column support 2 vertically mounted on the base 1, and an interference optical path assembly mounted on the column support 2. The interference optical path assembly is used to form an interference optical path and includes a laser source 3, a beam splitter 4, a first reflector 5, a second reflector 6, and a screen 7. The laser source 3 is configured to emit a horizontal beam. The beam splitter 4 is positioned in front of the optical path of the laser source 3, the first reflector 5 is positioned directly below the beam splitter 4, and the second reflector 6 is positioned behind the reflected optical path of the beam splitter 4. Beam splitter 4 is positioned at a 45-degree angle relative to the horizontal plane, splitting a horizontally incident laser beam at beam splitter 4 into a horizontal beam that transmits to the second reflector 6 and a vertically downward beam that reflects to the first reflector 5. Wedge assembly 8 is located in the beam path between beam splitter 4 and the first reflector 5, and is configured to move slightly in a direction perpendicular to the vertically downward beam as the sample 12 under test deforms, thereby changing the dielectric thickness through which the vertically downward beam passes.

[0024] For ease of understanding, the following explains some key terms in this embodiment: The wedge assembly 8 is an optical structure used to introduce variable optical path difference, with its core component being the optical wedge 81. The optical wedge 81 can be made of transparent glass, quartz, or polymer material and has a small wedge angle, allowing the light beam to experience different medium thicknesses as it passes through different positions. The optical wedge 81 can be machined into rectangular, circular, or other geometric shapes to accommodate different beam sizes and measurement requirements. A mounting housing 82 houses and protects the optical wedge 81 and has an internal mounting groove 83. The shape and size of the mounting groove 83 can match the profile of the optical wedge 81. The optical wedge 81 can be detachably mounted in the mounting groove 83 in various ways, such as by clamping screws, spring clips, or magnetic adsorption, to facilitate replacement of optical wedges 81 with different wedge angles or materials. The mounting housing 82 is fixedly connected to the free end of the sample 12 under test. This connection can be achieved through gluing, welding, threaded connection, or mechanical clamping, ensuring that the deformation of the sample 12 under test is effectively transmitted to the wedge assembly 8.

[0025] The loading test platform 9 is configured as a device to apply external physical excitation to the sample 12 under test. This platform can be connected to the fixed end of the sample 12 under test, and by applying force, heat, or other forms of energy, it causes controlled deformation of the sample 12 under test, such as tension, compression, or thermal expansion. The loading test platform 9 is configured to apply physical excitation to the sample 12 under test, causing it to deform. For example, a clamp with a screw and a handwheel can be used, and the sample 12 under test can be stretched or compressed by rotating the handwheel. Alternatively, the platform can be a heating device, such as an electric furnace or a water bath, which causes the sample 12 under test to thermally expand or contract by changing the temperature.

[0026] The vertical Michelson interferometer is designed to provide ample vertical space. The base 1 can be made of materials such as cast iron, granite, or aluminum alloy to provide stable support. The support column 2 is vertically mounted on the base 1 and can be one or more metal rods, such as stainless steel rods or aluminum alloy profiles; its height can be adjusted according to actual needs. The interferometric optical path components are mounted on the support column 2 and fixed using an optical adjustment bracket or a custom-made bracket to ensure the stability and adjustability of the optical path elements.

[0027] The interference optical path assembly is used to form the interference optical path. Its components include a laser source 3, a beam splitter 4, a first reflector 5, a second reflector 6, and a screen 7. The laser source 3 can be a wavelength-stable, highly coherent laser, such as a helium-neon laser or a semiconductor laser, whose output beam is collimated and expanded. The beam splitter 4 can be a semi-transparent, semi-reflective plane glass plate or prism, used to split the incident beam into two paths. The first reflector 5 and the second reflector 6 can be highly reflective plane mirrors used to reflect the beam. The screen 7 can be a frosted glass screen, a CCD camera sensor, or a CMOS camera sensor, used to observe or record interference fringes.

[0028] Laser source 3 is configured to emit a horizontally oriented beam. Beam splitter 4 is positioned in front of the optical path of laser source 3 at a 45-degree angle relative to the horizontal plane. This configuration splits the horizontally incident laser beam into two paths at beam splitter 4: one path is transmitted to the second reflector 6, forming a horizontal beam; the other path is reflected to the first reflector 5, forming a vertically downward beam. The first reflector 5 is positioned directly below beam splitter 4 to reflect the vertically downward beam. The second reflector 6 is positioned behind the reflected optical path of beam splitter 4 to reflect the horizontal beam. This optical path arrangement enables the implementation of the reference arm and measuring arm of a Michelson interferometer.

[0029] The wedge assembly 8 is located in the beam path between the beam splitter 4 and the first reflecting mirror 5, specifically in the path of the vertically downward beam. The wedge assembly 8 is configured to move in a direction perpendicular to the vertically downward beam as the sample 12 under test deforms. For example, when the sample 12 under test undergoes tensile deformation, its free end causes the wedge assembly 8 to move horizontally. This lateral movement allows the vertically downward beam to pass through different regions of the optical wedge 81, thereby changing the thickness of the medium through which the beam propagates within the optical wedge 81. This change in medium thickness directly alters the optical path length of the measurement optical path, resulting in a shift or change in the interference fringes.

[0030] Specifically, the design of the wedge assembly 8 utilizes the wedge-angle characteristics of the optical wedge 81 to convert the lateral mechanical displacement of the sample 12 under test into a change in optical path difference. Specifically, when the sample 12 under test elongates or shortens under physical excitation, it drives the mounting housing 82 and the optical wedge 81 to perform a lateral "cut-in" or "cut-out" movement within the vertical beam. Due to the wedge-angle structure of the optical wedge 81, the propagation distance of light within it changes linearly and regularly with the lateral movement of the optical wedge 81, thus causing a corresponding change in the optical path difference. This design utilizes the "optical path amplification" effect of the optical wedge 81, meaning that a small lateral displacement leads to a significant change in optical path, which is then captured by the interferometer. The core advantage of this structural design lies in the combination of "vertical layout" and "tangential motion": the vertical column support 2 raises the optical path and turns it downward, freeing up a huge operating space below the beam splitter 4. This space is large enough to accommodate loading equipment such as horizontal tensile testing frames or tubular heating furnaces, solving the problem that traditional interferometers cannot be integrated with large mechanical / thermal equipment; at the same time, the lightweight wedge component 8 is used to replace the heavy reflector for movement, and the direction of movement is perpendicular to the beam, effectively avoiding the interference of static and dynamic friction forces of the guide rails encountered when pushing the reflector along the optical axis in the traditional "moving mirror method", ensuring high fidelity of displacement transmission.

[0031] This device, employing a vertical Michelson interferometer structure, effectively solves the spatial integration difficulties of traditional horizontal layouts when combined with large loading equipment, thus improving system compatibility. Simultaneously, by utilizing the lateral movement of the wedge component 8 to alter the optical path difference, it avoids the frictional interference of mechanical guide rails in the traditional "moving mirror method," ensuring the authenticity and real-time nature of displacement transmission. Therefore, this device can achieve precise and stable measurement of minute deformations, and is particularly suitable for solving material parameters such as Young's modulus and coefficient of linear expansion, improving measurement accuracy and reliability.

[0032] In some embodiments described above in this application, a loading test platform 9 is proposed for applying physical excitation. Further, this application proposes that the loading test platform 9 is configured to install the following functional components: a mechanical loading component 91, including a force sensor and a tensile drive mechanism connected in series with the wedge component 8 and the sample 12 to be tested, for applying tensile force to the sample 12 to cause deformation; and a thermal loading component 92, including a heating device arranged along the axial direction of the sample 12 to be tested, wherein the fixed end of the sample 12 to be tested passes through the heating device, and its free end passes through the heating device and connects to the wedge component 8, for changing the temperature of the sample 12 to cause thermal expansion deformation.

[0033] The mechanical loading component 91 is used to apply a precise and controllable mechanical force, typically tensile force, to the sample 12 to induce deformation. Its core function is to provide stable force output and accurate force measurement. A force sensor, connected in series with the wedge component 8 and the sample 12, is used to measure the force applied to the sample 12 in real time and with precision. Connecting it in series with the wedge component 8 and the sample 12 ensures that the force sensor directly senses the actual load acting on the sample, thus avoiding measurement errors caused by internal friction or transmission losses in the loading mechanism. Various types of force sensors can be used, such as resistance strain gauge force sensors or piezoelectric force sensors. Furthermore, the force sensor can be integrated at the connection between the loading mechanism and the sample, or directly as part of the sample clamp, to ensure the directness of the force transmission path. The tension drive mechanism is responsible for generating and precisely controlling the tensile force applied to the sample 12. The implementation methods are diverse. For example, a ball screw mechanism driven by a precision stepper motor or servo motor can be used to convert rotational motion into precise linear displacement, thereby achieving slow and stable stretching of the sample. Alternatively, a piezoelectric ceramic actuator can be used to generate precise displacement at the micron or even nanometer level using the piezoelectric effect, which is suitable for ultra-high precision micro-deformation loading. Or a hydraulic or pneumatic drive system can be used to apply and adjust the tensile force by controlling the fluid pressure, which is suitable for testing larger loads.

[0034] The thermal loading component 92 is used to apply precise and controllable temperature changes to the sample 12 under test to induce thermal expansion or contraction deformation. Its main function is to provide a uniform and stable heating or cooling environment. The heating device, arranged along the axial direction of the sample 12, is designed to ensure that the sample is heated uniformly along its length, avoiding uneven deformation caused by local overheating or excessive temperature gradients. This arrangement helps to obtain more accurate linear expansion coefficient measurement results. The heating device can take various forms, such as a tubular resistance furnace, where the furnace chamber is heated by an electric heating wire and the sample is placed in the center of the furnace chamber; or an induction heating coil, which generates eddy currents inside the conductive sample through electromagnetic induction. The fixed end of the sample 12 under test passes through the heating device, and its free end passes through the heating device and connects to the wedge component 8. This connection method is designed to ensure that the free end of the sample 12 under test can move axially without constraint when it expands under heat or contracts under cooling, thereby accurately transferring the deformation to the wedge component 8. At the same time, the fixed end is stably supported inside the heating device, ensuring the positional stability of the sample during the heating process. For example, the fixed end can be securely fixed to the support structure inside the heating device via clamps or threaded connections, while the free end extends out of the heating device through a low-friction guide mechanism and is reliably connected to the mounting housing 82 of the wedge assembly 8, ensuring the linearity and accuracy of deformation transfer. This function aims to induce predictable thermal expansion or contraction of the sample 12 under test by precisely controlling the temperature of the heating device, thereby producing minute displacements. This allows the device to be used to measure the thermophysical properties of materials, such as the coefficient of linear expansion.

[0035] As one specific implementation, when measuring Young's modulus, a mechanical loading component 91 is installed, a tension drive mechanism (such as a precision lead screw) provides a stable tensile force, and a force sensor provides real-time feedback of the force value. Figure 6 As shown, the mechanical loading component 91 in this embodiment is constructed based on a horizontal test frame, which has an effective measurement length of up to 70cm, meeting the testing requirements of metal wires of different lengths. To solve the problem of unstable clamping in traditional experiments, the clamping device was optimized by disassembling the original flat clamp component and performing precision tapping on the screw to ensure that the metal wire is firmly clamped and subjected to uniform force. The tension drive mechanism adopts a metal wire rotation elongation device, which causes the metal wire to produce micron-level lateral elongation by rotating the screw. The force sensor, which is connected in series with the wedge component 8 and the sample to be tested 12, is a high-precision digital display force gauge with a range of 1000N and an accuracy of 0.1N. This force gauge records the force value change during the tensioning process in real time, thereby overcoming the defects of the traditional optical lever method, such as discontinuous tension, scale image wobbling, and poor operation safety caused by the reliance on weight loading, and realizing synchronous, continuous, and accurate measurement of stress and strain.

[0036] When measuring the coefficient of linear expansion, a thermal loading assembly 92 (such as a tubular resistance furnace) is installed to provide a uniform temperature field for the sample 12 to be tested, and the wedge assembly 8 is moved by thermal expansion. Figure 7 As shown, this embodiment is an improvement on the online coefficient of thermal expansion measuring instrument. The original dial indicator is disassembled, and the probe position of the dial indicator is replaced by a wedge assembly 8. The sample 12 to be tested (such as a metal rod) is placed inside a tubular heating device, which provides a uniform temperature field and is equipped with a temperature sensor (such as a thermocouple) to monitor the sample temperature in real time. When the metal rod expands due to heat, its free end directly pushes the wedge assembly 8, which is rigidly connected to it, to move laterally. This design completely avoids the mechanical resistance and hysteresis error caused by the contact between the probe and the sample in the traditional dial indicator method. Utilizing the non-contact characteristics of optical interference, it can capture minute thermal expansion displacements that cannot be detected by a dial indicator, significantly improving the measurement sensitivity for materials with low coefficient of thermal expansion or under small temperature difference conditions.

[0037] Through the above technical solution, the design of the loading test platform 9 is intended to provide a high degree of modularity and flexibility to adapt to different physical stimulus requirements. This design allows users to flexibly select and replace the required loading modules according to specific experimental purposes, thereby avoiding the complexity and cost of customizing independent equipment for each test scenario.

[0038] In some of the embodiments described above in this application, a micro-displacement measuring device based on a Michelson interferometer and a wedge is proposed for measuring micro-displacements. However, in its implementation, it relies on manual observation of the changes in interference fringes, which can easily introduce subjective errors and affect the measurement accuracy.

[0039] In this regard, this application further proposes that the above-mentioned device also includes an image acquisition device 10 and a data processing device 11. The image acquisition device 10 is aligned with the screen 7 or located on the output optical path of the interference beam to acquire interference fringe images. The data processing device 11 is connected to the image acquisition device 10 and is equipped with an algorithm program for identifying changes in the interference fringes and calculating minute displacements.

[0040] The image acquisition device 10 typically uses a high-frame-rate, high-resolution industrial camera to capture rapidly changing interference fringes. The data processing device 11 (such as a computer) performs real-time analysis of the image using a preset algorithm. Specifically, the image acquisition device 10 uses a high-frame-rate industrial camera or CCD sensor to capture a video stream of the dynamic changes in the interference fringes in real time, aligned with the screen 7. The data processing device 11 processes the video stream using a self-developed MATLAB program. This algorithm first converts the acquired RGB color image to a grayscale image and then uses a weighted average method (Gray = 0.2989R + 0.5870G + 0.1140). B) Brightness information is preserved; subsequently, median filtering is performed to remove speckle noise, and high-pass filters such as the Laplacian filter are used for image sharpening to enhance the contrast between fringe edges and the background; finally, the coordinates of the center of the interference rings are automatically identified using the Hough Transform or the bidirectional probe circle ergonomic method, and the number of interference fringes is automatically counted by monitoring the change curve of the gray value of the center region over time (peak and trough statistics). This system can improve the counting accuracy to 0.1 fringe periods, completely eliminating visual fatigue and subjective estimation errors caused by manual reading. This photoelectric combined automated measurement method not only eliminates visual fatigue and manual reading errors caused by long-term observation, but also further improves the measurement resolution through sub-pixel algorithms, ensuring the objectivity and accuracy of the data.

[0041] This application further proposes a method for measuring minute displacements based on a Michelson interferometer and a wedge, such as... Figure 7 As shown, it includes the following steps: S100: Construct an interference optical path using the vertical Michelson interferometer, adjust the height of the optical path, and make the vertically downward measurement beam pass through the optical wedge 81; S200: The sample to be tested 12 is mounted on the loading test platform 9 and its free end is fixedly connected to the wedge assembly 8; physical excitation is applied to the sample to be tested 12 to cause it to deform, and the optical wedge 81 is driven to follow the deformation of the sample to be tested 12 to produce a small displacement relative to the interference optical path, thereby changing the interference optical path. S300: Acquires dynamic images of interference fringes caused by changes in optical path, and uses computer image processing algorithms to automatically identify and count the dynamic images to obtain the number of changing interference fringes. S400: Based on the number of changes in the interference fringes, and using a preset mathematical model, the minute displacement generated by the sample 12 under test is calculated in combination with the geometric and optical parameters of the optical wedge 81.

[0042] Step S100 involves constructing an interference optical path using a vertical Michelson interferometer and adjusting the optical path height to ensure that the vertically downward measurement beam can accurately pass through the optical wedge 81. Specifically, the optical path height can be adjusted by a mechanical adjustment mechanism, for example, by adjusting the height of the base 1 of the entire vertical Michelson interferometer using a lifting platform or a precision displacement stage, or by adjusting the installation position of the interference optical path components on the column support 2 to change the vertical height of components such as the laser source 3 and the beam splitter 4.

[0043] Step S200 describes mounting the sample 12 to be tested on the loading test platform 9 and fixing its free end to the wedge assembly 8. A physical excitation is then applied to cause deformation, thereby driving a minute displacement of the optical wedge 81. This step aims to effectively convert the minute deformation of the sample 12 into a lateral displacement of the optical wedge 81. For example, the sample 12 can be securely fixed to the loading test platform 9 by means of clamps, bolts, or adhesives, and its free end can be connected to the mounting housing 82 of the wedge assembly 8 using a similar connection method. The physical excitation can include, but is not limited to, mechanical tension, compression, or torsion, applied by the mechanical loading assembly 91; it can also be a temperature change, where the sample is heated or cooled by the thermal loading assembly 92 to cause thermal expansion or contraction. These excitation methods can all cause deformation of the sample 12, driving the connected optical wedge 81 to move in a direction perpendicular to the vertically downward beam, thereby changing the thickness of the medium through which the beam passes through the optical wedge 81.

[0044] Step S300 involves acquiring a dynamic image of the interference fringes caused by changes in optical path length, and using a computer image processing algorithm to automatically identify and count the dynamic image to obtain the number of changing interference fringes. The image acquisition device 10 can employ a high-speed CCD camera or a CMOS camera to continuously capture the real-time changes of the interference fringes on the screen 7 at a sufficiently high frame rate. The computer image processing algorithm can include various techniques. For example, in addition to frame decomposition, grayscale conversion, filtering, sharpening, and edge enhancement of the video stream, it can also employ fringe analysis methods based on Fourier transform to extract the phase information of the fringes, or use pattern recognition technology to track the center or specific feature points of the interference fringes. Furthermore, sub-pixel-level positioning algorithms can be used to improve the accuracy of identifying the fringe center or extreme points, thereby more accurately counting the number of changing interference fringes.

[0045] Step S400 involves calculating the minute displacement of the sample 12 under test based on the number of changes in the interference fringes, using a preset mathematical model and considering the geometric and optical parameters of the optical wedge 81. This step converts the optical measurement results into an actual physical displacement. The preset mathematical model is typically based on the principles of optical interference and the geometric characteristics of the optical wedge 81. For example, when the optical wedge 81 undergoes lateral displacement, the effective thickness of the vertically downward beam passing through the wedge changes, leading to a change in the optical path difference and consequently causing the interference fringes to shift. This model considers geometric and optical parameters such as the laser wavelength, the wedge angle of the optical wedge 81, and the refractive index. For instance, the displacement can be expressed as a function of the number of changes in the interference fringes and the laser wavelength, the wedge angle of the optical wedge 81, and the refractive index. By substituting these parameters into the model, the lateral displacement of the optical wedge 81 can be accurately calculated, which represents the minute deformation of the sample 12 under test.

[0046] As a specific implementation method, the preset mathematical model is constructed based on the principle of equal inclination interference. The wavelength of the laser light source used is set to... The refractive index of optical wedge 81 is n The wedge angle of the wedge is Initially, the measurement beam passes perpendicularly through the wedge. When the sample 12 under test deforms, it causes the wedge assembly to move a distance horizontally. When the light beam passes through the wedge, the thickness of the medium changes, and the amount of geometric thickness change is: Because the measuring beam passes through the wedge twice within the measuring arm of the Michelson interferometer, and the wedge medium (such as glass) replaces the original air medium, the resulting change in optical path difference Δδ is 2(n−1)Δd. According to the principle of interference, for every wavelength change in optical path difference... λ When the interference fringes change in brightness (i.e., shift by one fringe), a change in brightness occurs. Therefore, the relationship between the change in optical path difference and the number of fringe changes, N, can be expressed as Δδ = Nλ. Combining these relationships, the minute displacement Δ of the sample 12 under test can be derived. x The calculation model is as follows: Using this mathematical model, the data processing device only needs to obtain the number of stripes N identified in real time, and combine it with the pre-calibrated wedge parameter n and This allows us to infer the real-time deformation and displacement of the sample.

[0047] This application further proposes that step S100 specifically includes: selecting the optical wedge 81 with a predetermined wedge angle and installing it in the mounting groove 83 of the mounting housing 82; adjusting the tilt angle of the first reflector 5 or the second reflector 6 until clear concentric ring-shaped interference fringes appear on the light screen 7.

[0048] Specifically, the choice of wedge angle directly determines the measurement range and sensitivity of the system. Specifically, based on actual experimental research and reading accuracy requirements, optical wedges 81 with different wedge angles provide different magnifications for displacement. For example, for Young's modulus measurement, since the tensile deformation of the metal wire is relatively large (accumulated at the millimeter level), a small-angle optical wedge 81 of approximately 5° is preferred to prevent the fringe movement speed from exceeding the camera sampling frequency. For linear expansion coefficient measurement, since the thermal expansion under micro-temperature differences is extremely small (at the micrometer level), a large-angle optical wedge 81 of approximately 20° is preferred to obtain a greater optical path change rate, thereby improving measurement sensitivity. By changing the optical wedge 81 with different angles, this device can be flexibly adapted to 10⁻³m to 10⁻ 8Different displacement measurement needs on the order of meters. Adjusting the tilt angle of the reflector is to obtain equal-tilt interference fringes. Concentric ring-shaped fringes have good central symmetry, which facilitates the image algorithm for center location and counting. Concentric ring-shaped interference fringes are formed by the Michelson interferometer under ideal conditions when the two interference beams have good parallelism and a moderate optical path difference. Clear concentric ring fringes are the basis for accurate fringe counting and displacement measurement. By adjusting the tilt angle of the first reflector 5 or the second reflector 6, the relative angle and optical path difference of the two interference beams can be changed, thereby optimizing the shape and clarity of the interference fringes. For example, the tilt adjustment screw of the reflector can be manually fine-tuned while observing the interference fringes on the screen 7 until clear and stable concentric rings are obtained.

[0049] This application further proposes that in the above method, step S200, the application of physical excitation includes: when measuring Young's modulus, applying a tensile force to the sample 12 to be tested through the mechanical loading component 91, using the tensile force to cause the sample 12 to undergo tensile deformation, thereby driving the optical wedge 81 to move; when measuring the coefficient of linear expansion, changing the temperature of the sample 12 to be tested through the thermal loading component 92, using the thermal expansion and contraction effect to cause the sample 12 to undergo axial deformation, thereby driving the optical wedge 81 to move.

[0050] Different excitation methods correspond to different physical models, but ultimately all translate into the lateral displacement of the wedge. Specifically, in this embodiment, when measuring Young's modulus, the force sensor reading is slowly increased from 0N to a predetermined value (e.g., 30N) by rotating the handwheel of the test frame. Under tension, the metal wire elastically elongates, causing the 5° optical wedge 81 to move laterally. At this time, the fringe count N is linearly related to the tension F, and the modulus can be calculated by recording the FN data pairs. In another embodiment, when measuring the coefficient of linear expansion, a heating device is activated to slowly raise the temperature of the metal rod from an initial temperature t0 to a final temperature tᵢ (e.g., increasing the temperature by 2-3°C per minute). The heated metal rod expands, pushing the 20° optical wedge 81 to move. At this time, the fringe count N is linearly related to the temperature change ΔT, and the expansion coefficient can be calculated by recording the TN data pairs. This decoupling design of excitation and measurement gives the measurement system strong versatility and scalability.

[0051] This application further proposes that the above-mentioned step S300 specifically includes: acquiring a video stream of the interference fringe changes through the image acquisition device 10; decomposing the acquired video stream into frame images, and sequentially performing grayscale processing, filtering and sharpening processing, and edge enhancement processing; applying a center positioning algorithm to identify the center coordinates of the concentric rings of the interference fringes, and counting the number of extreme points of grayscale value changes over time at or in the neighborhood of these coordinates, so as to determine the number of changing interference fringes.

[0052] Specifically, acquiring a video stream of interference fringe changes aims to continuously record an image sequence of interference fringes changing over time. By continuously capturing interference fringe images at a preset frame rate (e.g., 30 frames per second, 60 frames per second, or higher), a video stream can be formed, thus completely capturing the entire dynamic process of interference fringes from their formation to their disappearance or from one state to another. This continuous recording method provides sufficient data for subsequent automated analysis, avoiding information loss or discontinuity that may occur with single-frame images.

[0053] Decomposing the acquired video stream into frame images refers to splitting the continuous video stream data into a series of independent static image frames in chronological order. For example, a video stream of 30 frames per second will be decomposed into 30 independent images per second. This step is fundamental to subsequent image processing, enabling the computer to independently analyze and process the interference fringe state at each moment. Subsequently, these frame images are sequentially converted to grayscale, a process that converts color images to grayscale images. Grayscale conversion can be implemented using various algorithms, such as weighted averaging (e.g., 0.299R + 0.587G + 0.114B), maximum value methods, or average value methods. The aim is to simplify the image data, reduce the complexity of subsequent calculations, and preserve the brightness information of the interference fringes, which is crucial for recognizing changes in fringe brightness. Next, filtering and sharpening processing is performed to eliminate noise in the image and enhance image details. Filtering can employ methods such as Gaussian filtering and median filtering to smooth the image, remove random noise, and prevent noise from interfering with fringe recognition. Sharpening can be achieved using edge detection operators such as the Laplacian, Sobel, or Prewitt operators to enhance the edge contrast of interference fringes, making the fringe outlines clearer and facilitating subsequent identification. Further edge enhancement, building upon this, further emphasizes the boundaries of the interference fringes in the image. Edge enhancement can employ more complex algorithms such as the Canny or LoG (Laplacian of Gaussian) operators, or be achieved by adjusting the image's contrast and brightness. The aim is to make the boundaries of the interference fringes more distinct, providing more accurate input for center location and fringe counting.

[0054] After image preprocessing, a center-localization algorithm is applied to identify the coordinates of the centers of the concentric rings of the interference fringes. This algorithm is an image processing technique used to accurately determine the center position of concentric ring-shaped interference fringes. Common implementations include Hough Transform for circle detection, center detection based on gray-level gradient symmetry, or determining a common center by fitting multiple ring edge points. This algorithm can overcome slight distortions or noise interference that may exist in the interference fringes, accurately finding the geometric center of the interference pattern and providing a stable reference point for subsequent fringe counting. Subsequently, the number of extreme points of gray-level value changes over time at or near the center coordinates is counted. This refers to monitoring the change of pixel gray-level values ​​over time (i.e., the playback order of video frames) within a small area at or near the center after determining the center coordinates. As the interference fringes move, the brightness at the center periodically changes from bright to dark or from dark to bright. One complete cycle of brightness change corresponds to the movement of one interference fringe. By detecting the frequency of local maxima (bright fringes) and local minima (dark fringes) in grayscale values, the number of changing interference fringes can be accurately counted. For example, a grayscale threshold can be set, and a counter is incremented when a grayscale value crosses this threshold and reaches an extreme value. Finally, based on the results of the extreme point statistics, the total number of moving interference fringes during the entire measurement process can be obtained, thus determining the number of changing interference fringes. This number is a key parameter for calculating minute displacements.

[0055] As a specific implementation, the above-mentioned automated identification and counting processing is achieved through a self-written MATLAB algorithm program. The program first reads in the acquired video of the interference fringe changes and decomposes it into consecutive frame images. For each frame image, the following operations are performed sequentially: grayscale conversion is performed using a weighted average method; speckle noise is removed using a median filter; overall contrast is enhanced using adaptive histogram equalization (adaptthisteq function); and finally, sharpening is performed using an unsharpened mask (imsharpen function) to make the fringe edges clearer. For center location, the program uses a circle detection method based on Hough transform (imfindcircles function) to automatically identify the innermost or clearest interference ring and obtain its center coordinates (x, y, y). c , y c To achieve accurate counting, the program doesn't simply count the number of stripes throughout the entire image; instead, it focuses on the grayscale changes at the center position of the circle. Specifically, it iterates through all video frames, extracting the grayscale changes at the center (x) of each frame. c , y cThe average gray value I(t) within a very small neighborhood (e.g., 3×3 pixels) at a given location is used to generate a curve It showing the gray value changing with time t (i.e., the frame sequence). When interference fringes "emerge" or "fall in," the light intensity at the center undergoes a periodic change of alternating brightness and darkness, which is represented by a series of peaks and troughs on the It curve. The program identifies each complete cycle of brightness and darkness by finding the local extrema of the curve (using the findpeaks function to find peaks and troughs respectively). Each pair of adjacent peaks and troughs (or troughs and peaks) is counted as a change in fringe. This method based on time-domain signal analysis has strong anti-interference capabilities and can effectively distinguish between fringe movement caused by sample deformation and gray value fluctuations caused by small fluctuations in ambient light, thus achieving high-precision automated fringe counting.

[0056] like Figure 8 As shown in (a)-(d), this process demonstrates the complete image processing flow from the original interferometric image (a), through grayscale conversion, filtering and edge enhancement preprocessing (b), to center location and radial line drawing (c), and finally to the identification of the feature ring position on a single radial grayscale curve (d).

[0057] Through the above technical solution, this application proposes an automated and high-precision processing flow for dynamic change images of interference fringes. This method avoids the subjective error of traditional manual observation and significantly improves the accuracy and efficiency of micro-displacement measurement, enabling accurate and reliable acquisition of interference fringe change information when the sample 12 under test undergoes micro-deformation.

[0058] This application further proposes that step S300 include a step for determining the direction of fringe change. This determination step aims to address the problem that simply counting the number of fringes does not reveal the displacement direction, providing complete directional information for minute displacement measurements. Its function is to correlate the dynamic changes of interference fringes with the directionality of physical displacement. Specifically, this determination step can be implemented by analyzing the evolution of interference fringes over time, such as observing the positions where fringes form or disappear; alternatively, it can be implemented by combining the initial settings of the interferometer and the fringe change pattern to pre-determine the correspondence between fringe emergence / disappearance and the displacement direction.

[0059] This discrimination step is specifically achieved by comparing the expansion or contraction trend of the concentric ring radii in consecutive frame images. This technical feature is one of the specific methods for discerning the direction of fringe change. By processing continuously acquired frame images, the radius information of the concentric ring-shaped interference fringes can be extracted, and the trend of these radii changing over time can be analyzed. For example, in each frame image, image processing algorithms such as Hough transform, edge detection combined with least squares fitting, etc., can be used to accurately identify and measure the radius of the concentric rings. Then, the radius data of adjacent frames or multiple frames are compared to determine whether they are gradually increasing (expanding) or gradually decreasing (contracting). Alternatively, specific interference fringes in the central region of the image can be selected, and their position or size changes in consecutive frames can be tracked. For example, by calculating the distance from the fringe center to the edge and comparing the change of this distance at different time points, the expansion or contraction trend of the radius can be determined.

[0060] Based on the above comparison results, it is further determined whether the interference fringes are "emerging" or "trailing." This technical feature is to provide a physical explanation of the interference phenomenon based on the trend of radius change. "Emerging" usually refers to the interference fringes spreading outward from the center, or new fringes being generated at the center and moving outward, which corresponds to an increase in optical path difference; while "trailing" usually refers to the interference fringes contracting from the outside towards the center, or the fringes disappearing at the center, which corresponds to a decrease in optical path difference. Specifically, if the radius of the concentric rings shows an expanding trend, it is judged as interference fringes "emerging"; if it shows a shrinking trend, it is judged as interference fringes "trailing." Alternatively, it can also be determined by monitoring the gray value changes in the central region of the image. When the central gray value changes from bright to dark or from dark to bright, combined with the overall movement direction of the fringes, it is determined whether it is an emergence or a trailing.

[0061] Finally, the direction of movement of the optical wedge 81 and the deformation direction of the sample 12 under test are determined based on the judgment result. This technical feature is the ultimate goal of the discrimination step, which transforms optical phenomena into actual physical displacement directions. According to the working principle of the Michelson interferometer, interference fringes emerge when the optical path difference increases and fall into place when the optical path difference decreases. Combining the geometry and optical path setting of the optical wedge 81, a correspondence between the change in optical path difference and the direction of movement of the optical wedge 81 can be established in advance. For example, if the optical wedge 81 moves in the direction of increasing thickness, the optical path difference increases and fringes emerge; conversely, the fringes fall into place. Once the direction of movement of the optical wedge 81 is determined, the deformation direction of the sample 12 under test can be determined simultaneously since the optical wedge 81 is fixedly connected to the free end of the sample 12 under test. In addition, a clear mapping relationship can also be established by applying a small displacement of the optical wedge 81 in a known direction during the system calibration stage and recording the emergence or fall of the interference fringes at this time. In actual measurement, the direction of movement of the optical wedge 81 and the direction of deformation of the sample 12 under test are deduced in reverse based on the observed stripe change state.

[0062] As a specific implementation, this discrimination step is also integrated into the aforementioned MATLAB algorithm program. The program determines the direction of fringe change based on the analysis of the geometric features of specific interference rings in consecutive frame images. After completing the center location and image preprocessing, the program selects a specific interference ring with a high signal-to-noise ratio and easy tracking (e.g., the third bright or dark ring counting outwards from the center) as the feature ring. To determine the radius of this ring, the program starts from the center (x... c , y c Starting from the center, grayscale values ​​are sampled along multiple radial lines at equal angular intervals (e.g., one every 45 degrees, for a total of 8 lines), resulting in a grayscale distribution curve from the center to the image edge. By detecting the extreme points of the grayscale curve on each radial line, the radius of the feature ring in that direction can be determined. Finally, the average value is taken to obtain the average radius R(t) of the feature ring in that frame. The program compares the changing trend of R(t) values ​​in multiple consecutive frames: if R(t) continuously increases with time, it is determined that the interference fringes are "emerging" from the center; if R(t) continuously decreases, it is determined that the fringes are "falling" towards the center.

[0063] The present invention further proposes that, after step S400, a material parameter calculation step is also included, specifically including: when measuring Young's modulus, obtaining the original length, cross-sectional area, and applied tensile force of the sample 12 to be tested; based on the tensile force, original length, cross-sectional area, and the minute displacement calculated in step S400, calculating the Young's modulus of the sample 12 to be tested according to the stress-strain ratio; when measuring the coefficient of linear expansion, obtaining the original length and temperature change of the sample 12 to be tested; based on the minute displacement, original length, and temperature change, calculating the relative change rate of length under unit temperature change, thereby obtaining the coefficient of linear expansion of the sample 12 to be tested.

[0064] As a specific implementation method, in the embodiment for measuring Young's modulus, the sample to be tested 12 is a metal wire, and its original length is denoted as . L The cross-sectional area is denoted as S During the experiment, the force sensor recorded the tensile force value. F According to Hooke's Law, Young's modulus Y Defined as the ratio of normal stress to linear strain, i.e. Where ΔL is the elongation of the metal wire. In this device, the elongation ΔL of the metal wire is equal to the lateral displacement Δ of the wedge tip. x Substituting the displacement formula derived in step S400 above, we obtain the formula for calculating Young's modulus as follows: In this embodiment for measuring the coefficient of linear expansion, the sample 12 is a metal rod with an original length of L. During the experiment, the initial and final temperature changes Δ of the sample are recorded using a temperature sensor. TThe coefficient of linear expansion β is defined as the relative rate of change of an object's length with temperature, i.e., β = 1 / 2. Similarly, the wedge displacement Δ... x Substituting the thermal expansion ΔL into the equation, we obtain the formula for calculating the coefficient of linear expansion: This step is implemented through programming in the data processing equipment, which can dynamically calculate and display the physical parameters of the material based on the real-time collected N, F, and ΔT data.

[0065] This application further proposes that the calculation steps for material parameters also include a tilt correction step for the optical wedge 81, used to eliminate additional optical path errors caused by the refraction and deflection of the laser beam inside the optical wedge 81. Specifically, this correction step includes: analyzing the refraction path of the laser beam at the interface of the optical wedge 81 based on the law of refraction of optics, and determining the actual propagation direction of the laser beam inside the optical wedge 81; establishing a mapping relationship between the lateral displacement of the optical wedge 81 and the actual optical path difference change of the interference optical path according to the actual propagation direction, wherein a geometric correction factor determined by the refractive index and wedge angle of the optical wedge 81 is introduced into the mapping relationship; and using the geometric correction factor to correct the calculation model of the minute displacement or the material parameters to compensate for the optical path calculation deviation caused by the non-perpendicular incident of the laser beam on the surface of the optical wedge 81.

[0066] The tilt correction step for the optical wedge 81 aims to address the optical path error caused by the refraction and deflection of the laser beam within the optical wedge 81, thereby ensuring the accuracy of the measurement results, especially in high-precision micro-displacement measurements. This correction can be achieved by pre-calibrating the geometric parameters (e.g., wedge angle) and optical parameters (e.g., refractive index) of the optical wedge 81 in the data processing device 11 and establishing a theoretical model based on Snell's law; alternatively, it can be achieved experimentally by measuring the change in interference fringes with a known displacement, deriving the correction factor, and then applying it to subsequent measurements.

[0067] Furthermore, the analysis of the refraction path of the laser beam at the interface of the optical wedge 81, based on the optical refraction law, and the determination of the actual propagation direction of the laser beam inside the optical wedge 81, forms the basis for tilt angle correction. By applying Snell's law, the refraction angle and path of the laser beam as it enters the optical wedge 81 medium from air and as it enters air from the medium can be accurately calculated. This is crucial for understanding the actual propagation path of the beam inside the optical wedge 81, because only by knowing the actual path can the optical path be accurately calculated. In practice, an optical model can be established in the data processing device 11, inputting the refractive index of the optical wedge 81, the wedge angle, and the incident angle of the laser beam. The propagation direction of the beam inside the optical wedge 81 can then be calculated using geometric optics principles. Alternatively, ray tracing software can be used to simulate the propagation of the beam inside the optical wedge 81, thereby visualizing and determining its propagation direction.

[0068] Based on this, a mapping relationship is established between the lateral displacement of the optical wedge 81 and the actual optical path difference change in the interference path. This mapping relationship incorporates a geometric correction factor determined by the refractive index and wedge angle of the optical wedge 81. This is a core step in constructing the mathematical model. Traditional interferometry typically assumes perpendicular incident light, with the optical path difference directly linearly related to the displacement. However, when the light beam is not perpendicularly incident on the optical wedge 81, the lateral displacement not only changes the thickness of the medium through which the beam passes but also causes a nonlinear change in the optical path difference due to refraction. This mapping relationship, by introducing a geometric correction factor, takes into account the geometric characteristics (wedge angle) and optical characteristics (refractive index) of the optical wedge 81, thus accurately linking the lateral displacement of the optical wedge 81 with the actual optical path difference change. This mapping relationship can be described by deriving a mathematical formula containing the refractive index and wedge angle based on geometric optics and interferometry principles to describe the nonlinear relationship between the lateral displacement and the optical path difference change; alternatively, it can be calculated using numerical simulation or finite element analysis methods under different lateral displacements, and an empirical mapping function containing the geometric correction factor can be fitted.

[0069] Finally, the calculation model for the minute displacement or the material parameters is corrected using the geometric correction factor to compensate for the optical path calculation deviation caused by the non-perpendicular incident laser beam on the surface of the optical wedge 81. This is the final application of the correction step. By substituting the previously established mapping relationship containing the geometric correction factor into the calculation formula for the minute displacement or material parameters, the optical path calculation error caused by non-perpendicular incident can be eliminated. This directly improves the accuracy and reliability of the final measurement results. Specifically, in the data processing device 11, the preliminary displacement calculated based on the number of changing interference fringes can be corrected using the geometric correction factor to obtain a more accurate minute displacement value; alternatively, the corrected optical path difference change can be directly substituted into the calculation formula for Young's modulus or the coefficient of linear expansion to directly obtain the corrected material parameters.

[0070] As a specific implementation method, considering that in actual optical paths, after light rays are incident perpendicularly on the wedge's right-angled surface, refraction occurs upon exiting the wedge's inclined surface, resulting in the optical path change not having a simple tangential relationship with the wedge displacement. Based on Snell's law of refraction... (Where θ1 is the incident angle inside the wedge, i.e., the wedge angle α, the geometric correction factor after refraction correction is derived. After introducing this correction factor, the precise relationship between the change in optical path difference Δδ and the wedge displacement Δx is corrected to...) = Correspondingly, the calculation model for Young's modulus is updated. The corrected calculation model for the coefficient of linear expansion has been updated to... By introducing the inclusion term (tan 2 The correction factor (α+n) effectively compensates for the refraction error caused by the large-angle wedge, making the calculation model closer to the physical reality. Through the above technical solution, the problem of additional optical path error caused by the refraction and deflection of the laser beam inside the optical wedge 81 is solved, resulting in more accurate calculations of minute displacements and material parameters.

[0071] To verify the measurement accuracy and reliability of the device and correction method of this invention, this embodiment designed a systematic verification experiment. Metal wires of different materials (steel wire, copper wire, and aluminum wire) were selected as test samples 12 for Young's modulus measurement, and a steel rod was selected for linear expansion coefficient measurement. The experimental data were plotted into charts to visually display the measurement results (e.g., Figure 9 (As shown). Experimental environment settings: laser source wavelength. The optical wedge 81 is made of K9 glass, and its refractive index is... .

[0072] In the Young's modulus measurement experiment, a small-angle wedge was selected to accommodate the large tensile deformation of the metal wire. Its geometric measurement shows the wedge angle... Taking a steel wire sample as an example, its original length was measured. ,diameter The experiment employed a stepwise loading method, controlling the tension F starting at 0 N and gradually increasing to 30.00 N in increments of 5.00 N using a mechanical loading component 91. At each loading node, the corresponding cumulative interference fringe variation number $N$ was automatically recorded using an image processing algorithm. Experimental data showed that the number of interference fringes exhibited a strictly linear increasing trend with the linear increase of tension. Specifically, when the tension was 5 N, 10 N, 15 N, 20 N, 25 N, and 30 N, the measured cumulative fringe variation numbers were approximately 18, 36, 55, 73, 91, and 110 fringes, respectively. A linear fit was performed between the experimentally measured tension F and the fringe number N, and the correlation coefficient was... The result reached 0.999, verifying the system's extremely high linear response characteristics. Substituting the fitted slope into the Young's modulus calculation formula after tilt angle correction, the Young's modulus of the steel wire was calculated as follows: Compared to the standard value of Young's modulus for steel Its relative error is only 1.2%. Using the same experimental procedure, the Young's modulus of the copper wire samples was measured to be... (Standard value approximately) (with an error of 0.6%), the Young's modulus of the aluminum wire sample is (Standard value approximately) (with an error of 0.8%). The experimental data of the above multiple sets of materials show that this device can maintain extremely high measurement accuracy and stability in the testing of materials with different elastic moduli.

[0073] In the online thermal expansion coefficient measurement experiment, a large-angle wedge with higher sensitivity was selected to capture minute thermal expansion displacements. Sample 12 to be tested is a steel bar, with an original length of... The sample temperature was slowly increased from an initial 30.0℃ to 80.0℃ using a thermal loading assembly 92, with the heating rate controlled at 2℃ / min to ensure uniform heating. The cumulative fringe count was recorded every 5.0℃ during the experiment. Experimental data showed that within a temperature difference range of 50℃, the number of interference fringes exhibited a good linear relationship with temperature change. The recorded temperature changes were then recorded. With the corresponding number of stripes Substituting into the modified linear expansion coefficient calculation model, the calculated linear expansion coefficient of the steel bar is: With standard physical constants ( Compared to the previous method, the relative measurement error is approximately 2.0%. This result is significantly better than the 5% to 10% error range typically found in the traditional dial indicator method, fully demonstrating the superiority of this device in the field of measuring minute thermal deformation by combining large-angle wedges and tilt correction algorithms.

[0074] The above description is merely an embodiment of this application and is not intended to limit the scope of protection of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A micro-displacement measurement device based on a Michelson interferometer and a wedge, characterized in that, The device includes: A wedge assembly includes an optical wedge and a mounting housing, wherein the mounting housing is provided with a mounting groove, the optical wedge is detachably mounted in the mounting groove, and the mounting housing is fixedly connected to the free end of the sample to be tested. A loading test platform is connected to the fixed end of the sample under test and configured to apply physical excitation to the sample under test to cause deformation; and A vertical Michelson interferometer includes a base, a column support vertically mounted on the base, and an interference optical path assembly mounted on the column support; The interference optical path assembly is used to form an interference optical path and includes a laser source, a beam splitter, a first reflector, a second reflector, and a screen. The laser source is configured to emit a horizontal beam. The beam splitter is located in front of the optical path of the laser source. The first reflector is located directly below the beam splitter, and the second reflector is located behind the reflected optical path of the beam splitter. The beam splitter is set at a 45-degree angle relative to the horizontal plane, such that the horizontally incident laser beam is split at the beam splitter into a horizontal beam that is transmitted to the second reflector and a vertically downward beam that is reflected to the first reflector. The wedge assembly is located in the beam path between the beam splitter and the first reflector, and is configured to move slightly in a direction perpendicular to the vertically downward beam as the sample under test deforms, thereby changing the medium thickness through which the vertically downward beam passes through the wedge assembly.

2. The micro-displacement measuring device based on a Michelson interferometer and a wedge according to claim 1, characterized in that, The loading test platform is configured to install the following functional components: The mechanical loading assembly includes a force sensor and a tensile drive mechanism connected in series with the wedge assembly and the sample to be tested, for applying tensile force to the sample to be tested to cause deformation; A thermal loading assembly includes a heating device arranged along the axial direction of the sample to be tested. The fixed end of the sample to be tested passes through the heating device, and its free end passes through the heating device and connects to the wedge assembly. The assembly is used to change the temperature of the sample to be tested so that it undergoes thermal expansion deformation.

3. The micro-displacement measuring device based on a Michelson interferometer and a wedge according to claim 1, characterized in that, The device also includes an image acquisition device and a data processing device; The image acquisition device is aligned with the screen or located on the output optical path of the interference beam to acquire interference fringe images; The data processing device is connected to the image acquisition device and is equipped with an algorithm program for identifying changes in interference fringes and calculating minute displacements.

4. A method for measuring minute displacement based on the device according to any one of claims 1 to 3, characterized in that, Includes the following steps: S100: Construct an interference optical path using the vertical Michelson interferometer, adjust the height of the optical path, and make the vertically downward measurement beam pass through the optical wedge; S200: The sample to be tested is mounted on the loading test platform and its free end is fixedly connected to the wedge assembly; physical excitation is applied to the sample to cause it to deform, driving the optical wedge to follow the deformation of the sample to produce a small displacement relative to the interference optical path, thereby changing the interference optical path. S300: Acquires dynamic images of interference fringes caused by changes in optical path, and uses computer image processing algorithms to automatically identify and count the dynamic images to obtain the number of changing interference fringes. S400: Based on the number of changes in the interference fringes, and using a preset mathematical model, the minute displacement of the sample under test is calculated in combination with the geometric and optical parameters of the optical wedge.

5. The method for measuring minute displacements based on a Michelson interferometer and a wedge according to claim 4, characterized in that, Step S100 specifically includes: Select the optical wedge tip with a predetermined wedge angle and install it in the mounting slot of the mounting housing; Adjust the tilt angle of the first or second reflector until clear concentric ring-shaped interference fringes appear on the screen.

6. The method for measuring minute displacements based on a Michelson interferometer and a wedge according to claim 4, characterized in that, In step S200, applying the physical excitation includes: When measuring Young's modulus, a tensile force is applied to the sample under test through the mechanical loading component. The tensile force causes the sample under test to undergo tensile deformation, thereby driving the optical wedge to move. When measuring the coefficient of linear expansion, the temperature of the sample under test is changed by the thermal loading component, and the sample under test is axially deformed by the thermal expansion and contraction effect, which in turn drives the optical wedge to move.

7. The method for measuring minute displacements based on a Michelson interferometer and a wedge according to claim 4, characterized in that, Step S300 specifically includes: The image acquisition device acquires a video stream of interference fringe changes; The acquired video stream is decomposed into frame images, and grayscale processing, filtering and sharpening processing, and edge enhancement processing are performed sequentially. The center-positioning algorithm is used to identify the center coordinates of the concentric rings of the interference fringes, and the number of extreme points of gray value change over time at or in the neighborhood of these coordinates is counted to determine the number of different interference fringes.

8. The method for measuring minute displacements based on a Michelson interferometer and a wedge according to claim 7, characterized in that, Step S300 further includes a step of determining the direction of stripe change: By comparing the expansion or contraction trend of the concentric ring radius in consecutive frame images, it can be determined whether the interference fringes are emerging or sinking, thereby determining the moving direction of the optical wedge and the deformation direction of the sample under test.

9. The method for measuring minute displacements based on a Michelson interferometer and a wedge according to claim 4, characterized in that, Following step S400, a material parameter calculation step is also included, specifically: When measuring Young's modulus, the original length, cross-sectional area, and applied tensile force of the sample to be tested are obtained. Based on the tensile force, original length, cross-sectional area, and the small displacement calculated in step S400, the Young's modulus of the sample to be tested is calculated according to the stress-strain ratio. When measuring the coefficient of linear expansion, the original length and temperature change of the sample under test are obtained. Based on the small displacement, original length, and temperature change, the relative rate of change of length under unit temperature change is calculated, thereby obtaining the coefficient of linear expansion of the sample under test.

10. The method for measuring minute displacements based on a Michelson interferometer and a wedge according to claim 9, characterized in that, The calculation steps for the material parameters also include a tilt correction step for the optical wedge, used to eliminate additional optical path errors caused by the refraction and deflection of the laser beam inside the optical wedge, specifically including: Based on the law of refraction in optics, the refraction path of the laser beam at the optical wedge interface is analyzed to determine the actual propagation direction of the laser beam inside the optical wedge. Based on the actual propagation direction, a mapping relationship is established between the lateral displacement of the optical wedge and the actual optical path difference change of the interference optical path. A geometric correction factor determined by the refractive index and wedge angle of the optical wedge is introduced into the mapping relationship. The calculation model for the minute displacement or the material parameters is corrected using the geometric correction factor to compensate for the optical path calculation deviation caused by the non-perpendicular incident laser beam on the optical wedge surface.

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