High-precision displacement measurement method and system for micro-deformation of large structure

Abstract

The application belongs to the technical field of precision measurement and structure health monitoring, and discloses a high-precision displacement measurement system and method for small deformation of a large structure, wherein the system comprises an integrated structure comprising a laser light source, two fixed mirrors with an included angle of 146°, two imaging light screens, two observation cameras and a Raspberry Pi data processing unit; the application reduces mutual interference between modules by optimizing optical path design and structure layout; a laser light lever optically amplifies small deformation; a camera measurement captures the movement of the amplified laser spot; a data processing unit realizes real-time calculation; the three are organically integrated, and together realize high-precision, non-contact laser measurement of small deformation and small displacement of a large structure. Compared with existing dispersed laser measurement equipment, the instrument has high integration degree, small volume and light weight, is convenient to deploy and use on site, and overcomes the limitations of traditional single technology or dispersed equipment.

Description

Technical Field

[0001] This invention belongs to the field of precision measurement and structural health monitoring technology, specifically relating to a high-precision displacement measurement method and system for small deformations of large structures. Background Technology

[0002] Precise measurement of minute distances is crucial in numerous engineering and scientific research fields. In aerospace, the manufacturing and assembly precision of aircraft components directly impacts flight performance and safety; accurate measurement of minute distances is key to ensuring component fit. In electronic chip manufacturing, the spacing between internal circuit lines is extremely small; high-precision measurement of these minute distances is fundamental to ensuring normal chip function. Therefore, there is a need for an economical, efficient, adaptable, and highly accurate method for measuring minute deformations in large structures, providing data support for safety monitoring, mechanical analysis, and risk assessment of large structures.

[0003] Existing measurement methods include contact measurement, which allows direct contact with the object and provides intuitive results, but this method is inefficient, costly, has limited applicability, and may damage the object being measured; laser rangefinders, which are non-contact devices with millimeter-level accuracy, but cannot measure small deformations in large structures or detect angular deformation; digital image correlation methods, which are easy to operate and have high accuracy, but require printing speckle or other features, altering the surface morphology of the structure; and video measurement, which has diverse applications, is susceptible to vibration affecting external parameter stability, is inconvenient to install, and requires further accuracy improvement.

[0004] Therefore, in order to address the functional limitations and scenario adaptability deficiencies of existing laser measuring instruments, developing a high-precision displacement measurement method and system suitable for small deformations in large structures has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] Therefore, the purpose of this invention is to provide a high-precision displacement measurement method and system for small deformations of large structures, so as to overcome the shortcomings of laser PSD-based angle measurement methods that cannot measure spacing deformation, and meet the needs of engineering sites for multi-dimensional measurement data.

[0006] The technical solution provided by this invention is as follows: Firstly, this invention provides a high-precision displacement measurement system for minute deformations of large structures, comprising:

[0007] Two reflectors, with an included angle of 146º;

[0008] A laser source is used to emit a collimated laser beam, which is directed perpendicularly towards the center of the two reflectors, with a beam divergence angle ≤0.1mrad;

[0009] Two observation cameras are positioned opposite two imaging screens to continuously capture images of the laser spots on the screens; the optical axes of the observation cameras are perpendicular to the reference side of the measurement system.

[0010] Two imaging screens are used to receive the laser spot formed by the reflection of the mirror. They are located in front of two observation cameras respectively. The distance between the imaging screens and the observation cameras is adjustable, with an adjustment range of 50-200mm. The plane of the imaging screens is perpendicular to the optical axis of each camera.

[0011] The data processing unit is used to control the observation camera to acquire laser spot images;

[0012] The display, connected to the data unit signal, is used to display the measurement results in real time;

[0013] The laser source, two reflectors, two imaging screens, two observation cameras, and data processing unit are integrated into a single structure.

[0014] Preferably, the reflector is a quartz reflector, which is fixed on the XYR three-axis fine-tuning platform; the XYR three-axis fine-tuning platform is used to adjust the displacement and rotation of the quartz reflector on the X and Y axes to simulate the displacement and rotation deformation of the deformed edge, wherein the displacement adjustment range is ±10mm and the rotation adjustment angle is ±5°.

[0015] Preferably, the laser source is generated by a laser, wherein the laser is fixedly installed in a slot directly opposite the reference positioning edge of the measurement system, and the slot is equipped with an angle fine-tuning rotary component for adjusting the laser emission angle ±5° to calibrate the laser emission direction and adapt to the alignment requirements of different measurement scenarios.

[0016] The laser source operates at 5V and is powered by the data processing unit. The laser source is equipped with a dustproof shell and a heat dissipation structure, and the operating temperature is controlled below 60℃.

[0017] Preferably, the imaging screen is a diffuse reflective screen with a diffuse reflectivity of ≥90%, and is mounted in front of the two cameras via sliding guide rails.

[0018] Preferably, the observation camera is an industrial camera with a USB interface, a resolution of 1920×1080 pixels, a frame rate of ≥30fps, a lens focal length of 8mm, and an adjustable height range of 100~300mm; the observation camera is connected to the data processing unit to realize real-time data transmission.

[0019] Preferably, the data processing unit uses a Raspberry Pi 4B motherboard with the following parameters: quad-core Cortex-A72 processor, 4GB memory, equipped with a 16GB MicroSD card as storage medium, running a Linux operating system, and a built-in power management module.

[0020] Preferably, the system further includes: a support and fixing structure for carrying and positioning all functional modules, including a fixing bracket, a PVC board base and stainless steel connectors; the PVC board base serves as the basic support platform of the system, and the fixing bracket is installed on the base in a modular manner, which can be used to fix the laser light source, two reflectors, two observation cameras and the Raspberry Pi data processing unit respectively; each optical and electronic module is tightly integrated with the base through the fixing bracket.

[0021] Secondly, the present invention also provides a high-precision displacement measurement method for minute deformations of large structures, comprising:

[0022] The measurement parameters are calibrated, including: the equivalent focal length (f1, f2) of the observation camera, the principal point position, and the distortion coefficient; the vertical distance S from the laser source to the center of the reflector, and the vertical distance B from the laser source to the screen; and the initial reflection angles θ1 and θ2 between the reflected laser and the laser source emitted beam.

[0023] Extract the laser spot position and determine the coordinates of the laser spot center:

[0024] Calculate the deformation, wherein the deformation includes the spacing change t and the rotation angle change α.

[0025] Preferably, the extraction of the laser spot position and the determination of the laser spot center coordinates include:

[0026] The acquired images are preprocessed by the data processing unit:

[0027] The image is then processed to remove distortion using the calibrated distortion coefficients, and then the image is converted to grayscale to obtain a grayscale image.

[0028] A sub-pixel-level laser spot center extraction algorithm is used to process grayscale images, specifically employing a Gaussian surface fitting method.

[0029] As shown in equation (1), it is assumed that the pixel grayscale distribution of the laser spot approximately follows a two-dimensional Gaussian distribution:

[0030] (1)

[0031] Taking the logarithm of both sides of equation (1), as shown in equation (2), the problem is transformed into a problem of fitting a two-variable quadratic polynomial:

[0032] (2)

[0033] The least squares method is used to solve the problem, and the image coordinates corresponding to the extreme points of the fitted curve are used as the sub-pixel level coordinates of the laser spot center.

[0034] Preferably, the calculation of deformation includes:

[0035] Based on the laser spot movement, the final spacing change t and rotation angle change α are solved using a nonlinear iterative algorithm:

[0036] Calculate the pixel movement of the laser spot: As shown in equations (3)-(4), based on the initial coordinates and deformed coordinates of the laser spot center, the pixel changes ΔX1, ΔX2, ΔY1, ΔY2 of the laser spot on the image are obtained;

[0037] (3)

[0038] (4)

[0039] Calculate the actual movement distance of the laser spot: As shown in Equation (5-7), based on the similar triangle relationship of the perspective projection of the camera center, combined with the known equivalent focal length of the camera (f1, f2), the screen pixel size P and the screen physical size L, the actual movement distance ΔX' and ΔY' of the laser spot on the imaging screen are calculated.

[0040] (5)

[0041] (6)

[0042] (7)

[0043] Construct and solve the system of nonlinear equations:

[0044] As shown in equation (8-9), ΔX' and ΔY' are taken as the observed quantities, and the spacing deformation t and the rotation deformation α are taken as the measured quantities, and substituted into the equation set established by the geometric relationship of the laser lever;

[0045] (8)

[0046] (9)

[0047] As shown in equation (10-11), error functions F1 and F2 are defined;

[0048] (10)

[0049] (11)

[0050] A nonlinear iterative solution algorithm is used:

[0051] As shown in equations (12-13), calculate the partial derivatives of the error function with respect to t and α respectively, and construct the Jacobian matrix J;

[0052] (12)

[0053] (13)

[0054] b. Using the inverse of the Jacobian matrix and the error vector, as shown in Equation (14), the values ​​of the deformation parameters t and α are iteratively updated;

[0055] (14)

[0056] c. Set the initial value of the iteration to 0.

[0057] This invention presents a high-precision displacement measurement system based on optical lever and camera measurement technology. It enables high-precision, non-contact measurement of minute distances, filling the gaps in traditional measurement methods and providing more accurate and reliable measurement data for related fields, thus contributing to technological innovation and development. Furthermore, by measuring the spacing and angular deformation of the structure, it overcomes the limitation of laser PSD-based angular measurement methods in measuring spacing deformation, meeting the needs of engineering sites for multi-dimensional measurement data.

[0058] This invention achieves sub-millimeter-level high measurement accuracy, overcoming the shortcomings of distributed optical fiber-based track deformation measurement methods in spacing measurement, and highlighting the high-precision advantages of laser measuring instruments.

[0059] Based on the aforementioned measurement system, this invention also provides a non-contact measurement method based on laser technology, which avoids potential damage to the measured object caused by contact measurement and improves efficiency and applicability. This method optimizes the operation process of the laser measuring instrument, allowing measurement without the need for speckle printing, and overcomes the insufficient accuracy in spacing measurement of track deformation measuring equipment based on distributed optical fibers.

[0060] This invention improves the overall measurement accuracy and stability of laser measuring instruments by deeply integrating the laser lever principle with algorithm optimization, overcoming the problems of insufficient accuracy and susceptibility to vibration in ordinary camera measurement methods, and enhancing the environmental adaptability of the instruments. Attached Figure Description

[0061] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0062] Figure 1 A schematic diagram of the laser source mounting bracket structure provided by the present invention;

[0063] Figure 2 This is a schematic diagram of the laser source structure provided by the present invention;

[0064] Figure 3 This is a schematic diagram of the reflector structure provided by the present invention;

[0065] Figure 4 This is a schematic diagram of the XYR three-axis fine-tuning platform structure provided by the present invention;

[0066] Figure 5 This is a schematic diagram of the imaging screen structure provided by the present invention;

[0067] Figure 6 This is a schematic diagram of the observation camera support structure provided by the present invention;

[0068] Figure 7 This is a schematic diagram of the data processing unit structure provided by the present invention;

[0069] Figure 8 This is a schematic diagram of the high-precision displacement measurement system provided by the present invention;

[0070] Figure 9 This is a schematic diagram of the high-precision displacement measurement system provided by the present invention;

[0071] Figure 10 This is a schematic diagram of the high-precision displacement measurement method provided by the present invention. Detailed Implementation

[0072] The present invention will be further explained below with reference to specific implementation schemes, but this explanation does not limit the scope of the invention.

[0073] Traditional laser rangefinders, while offering the advantage of non-contact measurement, can only measure distance and cannot simultaneously monitor angle and displacement; dedicated angle measurement laser instruments lack the ability to measure spacing deformation.

[0074] Therefore, in view of the problems of existing products in the field of laser measuring instruments, such as single function, low integration and poor environmental adaptability, this invention provides a laser measuring instrument with multi-parameter synchronous measurement function, which can simultaneously measure the spacing deformation and angular deformation of the structure, so as to overcome the defect that the angular measurement method based on laser PSD cannot measure the spacing deformation, and meet the needs of engineering site for multi-dimensional measurement data.

[0075] Specifically, the system of the present invention includes the following:

[0076] Laser source 1, as the core emitting unit of the laser measuring instrument, adopts a semiconductor laser module with a wavelength of 650nm and a power controlled at 5mW (Class IIIa, safe and radiation-free). It is fixedly installed in a dedicated slot directly opposite the system reference edge. Figures 1-2 As shown, the card slot is equipped with a fine-tuning knob that allows for ±5° angle adjustment.

[0077] The laser source is used to emit a collimated laser beam, which is directed perpendicularly to the center of the two reflectors 2. The beam divergence angle is ≤0.1mrad, ensuring that the laser spot diameter does not exceed 1mm within a 10m range, thus providing a stable light source foundation for high-precision measurement.

[0078] The laser source uses a low-cost, low-power semiconductor laser module with a working voltage of 5V (which can be powered by the data processing unit). It has a continuous working time of ≥8 hours, meeting the needs of long-term on-site measurements. At the same time, the module is equipped with a dustproof shell and a heat dissipation structure. The heat sink adopts an aluminum fin design with dimensions of 30mm×20mm×5mm. It is mounted on the back of the laser module, with a heat dissipation area of ​​≥15cm² and a thermal conductivity of ≥200W / (m·K). This can keep the working temperature of the laser module below 60℃, effectively avoiding laser power attenuation or wavelength drift caused by excessive temperature during long-term operation, and improving the service life of the instrument in complex environments.

[0079] Two reflectors: such as Figures 3-4 As shown, the core optical amplification element of the laser measuring instrument uses a high-reflectivity (≥99.5%) quartz mirror with a surface size of 20mm × 20mm and a thickness of 3mm. It is fixed to an XYR three-axis fine-tuning platform at an angle of approximately 146º using a dedicated fixture. This fine-tuning platform serves as the instrument's measurement reference adapter unit, enabling ±10mm displacement adjustment and ±5° rotation adjustment along the X and Y axes. It is used to simulate the displacement and angular deformation of deformed edges and adapts to the installation requirements of structures of different sizes.

[0080] The fixture for the reflector assembly is 3D printed in one piece and made of ABS engineering plastic, which is lightweight and rigid, effectively reducing the impact of vibration on optical components; the reflector surface is coated with an anti-reflection film, optimized for 650nm laser wavelength, reducing light energy loss and ensuring the intensity stability of the reflected beam, providing a clear signal for subsequent spot detection;

[0081] Two imaging screens, such as Figure 5As shown, a diffuse reflection screen is used, made of milky white acrylic sheet, measuring 100mm × 100mm with a thickness of 5mm and a diffuse reflectivity of ≥90%. It can be mounted in front of two cameras via sliding rails, the distance between the screen and the cameras being adjustable (adjustment range 50–200mm), to receive the laser spot formed by the reflection from the mirror. The screen surface is frosted to ensure uniform light spot imaging without obvious bright spots, facilitating the camera to capture clear light spot images.

[0082] Preferably, the imaging screen can be equipped with a light shield, which can effectively reduce the interference of ambient light on the light spot imaging and improve the measurement stability of the instrument in outdoor or strong light environments; the above-mentioned guide rail adopts a locking design, and can be fixed by the knob after adjustment, avoiding errors caused by screen position shift during measurement.

[0083] Two observation cameras serve as the image acquisition unit for the laser measurement instrument. These are industrial cameras with USB interfaces, a resolution of 1920×1080 pixels, a frame rate of ≥30fps, and a lens focal length of 8mm. The fixed focal length design avoids errors caused by focal length adjustment. The cameras are mounted perpendicular to the reference edge of the measurement system on a dedicated instrument bracket, with their optical axes perpendicular to this reference edge, and are aligned with two imaging screens respectively. The bracket height is adjustable (adjustment range 100~300mm) to continuously capture images of the laser spot on the screens.

[0084] The camera module supports automatic exposure adjustment, adjusting exposure parameters in real time according to ambient light intensity to ensure the clarity of the spot image. At the same time, the camera incorporates existing noise reduction algorithms, which can effectively reduce the impact of image noise on spot center extraction, providing high-quality image data for high-precision measurement. The camera and data processing unit are connected via a USB 3.0 interface, with a data transfer rate of ≥5Gbps, ensuring real-time transmission of image data.

[0085] The data processing unit, as the core control and computing unit of the laser measuring instrument, uses a Raspberry Pi 4B motherboard (quad-core Cortex-A72 processor, 4GB RAM), equipped with a 16GB MicroSD card as storage media, and runs a Linux operating system. It integrates functions such as camera control, image acquisition, data processing, and result output. This unit is responsible for controlling the camera to acquire laser spot images, calibrating the camera using a planar checkerboard calibration board, and running subsequent image processing and data processing algorithms. It can also connect to a monitor via an HDMI interface to display measurement results in real time, or transmit data to a computer terminal via a WiFi module.

[0086] The data processing unit has a built-in power management module that supports 12V DC power supply (can be connected to an external power bank or AC adapter), with a power consumption of ≤10W, meeting the needs of portable use in the field; the motherboard has reserved expansion interfaces, which can add a GPS module (for outdoor measurement and positioning) or a 4G module (for remote data transmission) according to actual needs, improving the instrument's expandability; the algorithm program is written in C++, with high running efficiency, and can realize real-time calculation of measurement data (single calculation time ≤0.1 seconds).

[0087] Support and Fixing Structure: This structure consists of a PVC board base, a 3D-printed mounting bracket, and stainless steel connectors. The PVC board base serves as the system's foundation platform, with anti-slip rubber pads on the bottom and multiple positioning holes on the top. The 3D-printed bracket is an independent module, fixed to the base via stainless steel connectors.

[0088] (1) The upper part of the light source bracket is provided with a slot, and the bottom of the bracket is installed on the front side of the base by adjusting screws; the laser light source is fixed in the slot of the light source bracket;

[0089] (2) The reflector platform is fixed to the special reflector bracket by screws, which is located in the middle of the base;

[0090] (3) The two observation cameras are fixed on the camera bracket respectively. The camera bracket is an adjustable pole structure and is connected to the base through clamps;

[0091] (4) The Raspberry Pi data processing unit is fixed on a dedicated bracket, which is fixed to the base by a snap-fit ​​structure.

[0092] The mounting positions of each bracket can be finely adjusted using adjusting screws, and the total weight of the entire system is ≤5kg. Pre-drilled mounting holes in the base allow for expansion bolt fixing, making it suitable for long-term monitoring deployments.

[0093] The design of the support structure fully considers the portability and stability of the instrument. The modular components can be quickly disassembled and assembled. After disassembly, it can be placed in a storage box with dimensions of 50cm×40cm×30cm for easy transportation. At the same time, the surface of the structure is treated with rust prevention, which can adapt to complex outdoor environments such as humidity and dust, and improve the service life of the instrument.

[0094] This invention combines the principle of laser levers with camera measurement technology into a single laser measuring instrument system, achieving a high degree of integration of functional modules. The laser measuring instrument comprises an integrated structure including a laser source, two reflectors fixed at a 146º angle, two imaging screens, two observation cameras, and a Raspberry Pi data processing unit. Each module is integrated with a dedicated bracket and base, forming a compact and fully functional dedicated measuring instrument. The instrument adopts a modular design, allowing each functional module to be independently disassembled and maintained. Furthermore, optimized optical path design and structural layout reduce mutual interference between modules.

[0095] The laser lever optically magnifies minute deformations, while the camera captures the movement of the magnified laser spot. The data processing unit performs real-time calculations. These three components are organically integrated to achieve high-precision, non-contact laser measurement of minute deformations and displacements in large structures. Compared to existing distributed laser measurement equipment, this instrument is highly integrated, small in size, and lightweight, facilitating on-site deployment and use, and overcoming the limitations of traditional single-technology or distributed equipment.

[0096] In view of the above system composition, the present invention also provides a laser measuring instrument with a simple operation process, which can be deployed and measured without the need for professional technicians. The specific steps are as follows:

[0097] Step 1: Installation and debugging of laser measuring instruments

[0098] according to Figure 6 The installation and positioning of the laser optics are shown. Ensure that the optical axes of the two observation cameras are perpendicular to the reference edge, the planes of the two imaging screens are perpendicular to the optical axes of their respective cameras, and the laser beams are simultaneously directed perpendicularly towards the centers of the two reflectors.

[0099] Step 2: Laser measurement parameter calibration

[0100] Camera calibration: Using a planar checkerboard calibration tool, the intrinsic parameters of the two cameras are calibrated using a Python camera calibration tool to accurately obtain their equivalent focal lengths (f1, f2), principal point positions, and distortion coefficients.

[0101] Reference measurement: Using tools such as a rangefinder, determine the vertical distance S from the laser source to the center of the reflector, and the vertical distance B from the laser source to the screen.

[0102] Initial angle measurement: Start the laser source and use tools such as a goniometer to measure the initial reflection angles θ1 and θ2 between the two reflected laser beams and the laser source emitted beam.

[0103] Step 3: Laser spot position monitoring and center extraction

[0104] After the system is running, the two cameras capture images of the laser spot on the imaging screen.

[0105] The acquired images are preprocessed as follows: First, the distortion parameters obtained from the calibration are used to perform distortion correction on the images, and then the distortion-corrected images are converted to grayscale.

[0106] A sub-pixel-level laser spot center extraction algorithm is used to process grayscale images. Specifically, a Gaussian surface fitting method is employed.

[0107] As shown in equation (1), it is assumed that the pixel grayscale distribution of the laser spot approximately follows a two-dimensional Gaussian distribution.

[0108] (1)

[0109] Taking the logarithm of both sides of equation (1), as shown in equation (2), the problem is transformed into a problem of fitting a two-variable quadratic polynomial.

[0110] (2)

[0111] By using the least squares method, the image coordinates corresponding to the extreme points of the fitted curve are used as the sub-pixel level coordinates of the laser spot center, and the positioning accuracy can reach 0.01 pixels.

[0112] Step 4: Deformation calculation:

[0113] The core of this step is to use a nonlinear iterative algorithm to solve for the final spacing change t and rotation angle change α based on the laser spot movement.

[0114] Calculate the pixel movement of the laser spot: As shown in equation (3-4), based on the initial coordinates and deformed coordinates of the laser spot center, the pixel changes ΔX1, ΔX2, ΔY1, ΔY2 of the laser spot on the image are obtained.

[0115] Equation (3)

[0116] Equation (4)

[0117] Calculate the actual movement distance of the laser spot: As shown in Equation (5-7), based on the similar triangle relationship of the perspective projection of the camera center, combined with the known equivalent focal length of the camera (f1, f2), the pixel size of the screen P and the physical size of the screen L, the actual movement distances ΔX' and ΔY' of the laser spot on the imaging screen are calculated.

[0118] (5)

[0119] (6)

[0120] (7)

[0121] Construct and solve the system of nonlinear equations:

[0122] As shown in equation (8-9), ΔX' and ΔY' are taken as the observed quantities, and the spacing deformation t and the rotation deformation α are taken as the measured quantities, and substituted into the equation system established by the geometric relationship of the laser lever.

[0123] (8)

[0124] (9)

[0125] As shown in equation (10-11), error functions F1 and F2 are defined.

[0126] (10)

[0127] (11)

[0128] A nonlinear iterative solution algorithm is used:

[0129] a. As shown in equations (12-13), calculate the partial derivatives of the error function with respect to t and α respectively, and construct the Jacobian matrix J.

[0130] (12)

[0131] (13)

[0132] b. Using the inverse of the Jacobian matrix and the error vector, as shown in Equation (14), the values ​​of the deformation parameters t and α are iteratively updated.

[0133] (14)

[0134] c. The initial value for iteration can be set to 0. Experiments show that the results tend to stabilize after 10 iterations (displacement change within 5 × 10⁻⁶). -9 Level, corner at 5×10 -12 Therefore, it is possible to stop after 10 iterations to balance computational efficiency and accuracy.

[0135] This invention integrates a sub-pixel laser spot extraction algorithm and a nonlinear iterative solution algorithm into a laser measuring instrument, forming a high-precision data processing link. The instrument's data processing unit incorporates a Gaussian surface fitting method for laser spot center localization. For the distortion-free and grayscale-converted laser spot image, it uses the spot's grayscale information to fit a two-dimensional Gaussian distribution using the least squares method, determining the laser spot center coordinates based on the curve's extreme points. Simultaneously, a nonlinear iterative solution algorithm is integrated to establish a geometric model between laser spot movement and structural deformation, synchronously inverting displacement and rotation. The algorithm program has been optimized for efficient operation on a Raspberry Pi motherboard, enabling real-time calculation of measurement data.

[0136] The sub-pixel algorithm improves the positioning accuracy of the laser spot center to 0.01 pixels, while the nonlinear iterative algorithm ensures the accuracy of deformation calculation. The combination of these two technologies provides core support for the instrument's sub-millimeter measurement accuracy. Compared with existing laser measuring instruments, this instrument's algorithm has high integration and fast operation efficiency, enabling real-time output of measurement data and meeting dynamic monitoring requirements.

[0137] This invention, as a laser measuring instrument, achieves sub-millimeter (<0.1mm) displacement measurement accuracy. In a comparative experiment with a track deformation measuring device based on distributed optical fibers, under the same track spacing measurement conditions, the laser measuring instrument of this invention has a spacing measurement error ≤0.05mm, while the optical fiber measuring device has a measurement error ≥0.5mm, representing a 10-fold improvement in accuracy. In a comparative experiment with a traditional laser rangefinder, the traditional laser rangefinder cannot measure angular deformation, and its displacement measurement accuracy is only ±1mm, while the displacement measurement accuracy of this instrument reaches ±0.05mm, representing a 20-fold improvement in accuracy.

[0138] In the simulated track deformation measurement experiment, the XYR three-axis fine-tuning platform was used to set the actual displacement to 0.5 mm and the rotation angle to 0.5°. The measurement results of this system were 0.503 mm displacement and 0.498° rotation angle, with a displacement error of 0.003 mm and a rotation angle error of 0.002°. When the actual displacement was set to 1.0 mm and the rotation angle to 1.0°, the measurement results were 0.997 mm displacement and 1.002° rotation angle, with a displacement error of 0.003 mm and a rotation angle error of 0.002°, which fully verified its sub-millimeter level laser measurement capability.

[0139] This invention, as a dedicated laser measuring instrument, can simultaneously measure the spacing deformation (displacement) and angular deformation of a structure.

[0140] Comparative Explanation: Compared to angle measuring instruments based on laser position sensitive detectors (PSD), this instrument maintains comparable angle measurement accuracy (≤0.01°) while adding laser measurement functionality for spacing deformation, enabling simultaneous measurement of multiple parameters. Compared to track deformation measuring equipment based on distributed optical fibers, this instrument adds laser measurement functionality for angle deformation while measuring spacing, with higher measurement accuracy and easier deployment. Compared to ordinary laser rangefinders, this instrument not only has higher measurement accuracy but also adds angle measurement functionality, making it applicable to a wider range of scenarios.

[0141] Application scenarios expanded: The instrument can be widely used in multiple fields such as track deformation monitoring (synchronous measurement of track spacing and rotation angle), bridge health monitoring (measurement of displacement and rotation deformation of bridge structure), building structure monitoring (monitoring of minor settlement and tilt of buildings), and precision equipment installation calibration (measurement of installation displacement and angular deviation of equipment). Its comprehensive functionality is significantly better than existing laser measuring instruments.

[0142] The laser measuring instrument of this invention performs non-contact measurement based on the principle of laser optics, requiring no contact with the structure being measured. Unlike laser measuring equipment that uses digital image correlation methods, it does not require speckle printing. The operation process is simple and has no impact on the object being measured.

[0143] Advantages: ① It avoids potential damage to the measured object caused by contact measuring instruments, making it especially suitable for measuring precision or fragile structures; ② It eliminates the extra work required for pre-treatment (spraying, drying, etc.), shortening the measurement preparation time (single measurement preparation time ≤ 30 minutes); ③ It does not require altering the surface morphology of the structure, making it suitable for structures with unsuitable surface treatment (such as bridge coatings, historical buildings, etc.), thus expanding the instrument's applicability; ④ The non-contact measurement method allows the instrument to perform measurements at long distances (measurement distance range 0.5-10m), making it suitable for measuring structures in high-risk areas or those that are difficult to access.

[0144] The core solution algorithm of the laser measuring instrument provided by this invention has fast convergence and good stability, and can realize real-time output of measurement data and long-term continuous monitoring, meeting the measurement needs of different scenarios.

[0145] In the deformation calculation, after 10 iterations, the nonlinear iterative solution algorithm reduced the changes in displacement and rotation to 5 × 10⁻⁶. -9 and 5×10 -12 The order of magnitude indicates that the algorithm has rapidly stabilized; the single measurement cycle is ≤0.1 seconds (including image acquisition, processing and calculation), which can meet the needs of dynamic deformation monitoring (such as structural vibration deformation monitoring); the instrument supports continuous 24-hour uninterrupted monitoring and can store ≥1 million measurement data, which can meet the needs of long-term deformation monitoring (such as long-term track settlement monitoring).

[0146] Real-time monitoring capabilities enable the instrument to capture dynamic deformation processes, while long-term monitoring capabilities enable it to analyze structural deformation trends. Compared to the limitations of some existing laser measuring instruments that only support static or short-term measurements, the applicable scenarios are further expanded.

[0147] The complete laser measurement instrument system constructed in this invention has a low manufacturing cost. Specifically, the total estimated cost of the main components of the system (including the laser source, reflector, screen, camera, Raspberry Pi, etc.) is approximately RMB 1145. Compared to many expensive high-precision measurement devices, this instrument achieves high-precision laser measurement functions at an extremely low cost, demonstrating outstanding economic efficiency and making it more suitable for large-scale application and promotion in engineering practice.

[0148] Through a multi-dimensional error optimization system and anti-interference design, this laser measuring instrument exhibits significantly superior anti-interference capabilities and environmental adaptability compared to existing similar instruments, resulting in high reliability of measurement data. Experimental verification shows that in outdoor strong light environments (light intensity ≥10000 lux), the instrument's displacement measurement error is ≤0.08mm, and its rotation angle measurement error is ≤0.015°, with a measurement accuracy difference of ≤0.03mm compared to indoor environments. In environments with slight vibration (vibration frequency 5-10Hz, amplitude 0.1mm), the instrument's measurement error is ≤0.07mm, far superior to ordinary laser measuring instruments (error ≥0.5mm under vibration conditions). In low-temperature environments of -10℃ and high-temperature environments of 60℃, the instrument's measurement accuracy fluctuation is ≤0.05mm, meeting the usage requirements under different climatic conditions.

[0149] This invention integrates statistical analysis (Z-score filtering for outliers), physical constraints (laser optical path geometric modeling), and hardware anti-interference design. Through multi-model integrated fitting and error weighted fusion, it effectively reduces random and systematic errors in laser measurement. This enables the laser measurement instrument to maintain high-precision measurement results even in complex environments, solving the problems of poor environmental adaptability and insufficient data reliability in existing laser measurement instruments.

[0150] The laser measuring instrument of this invention is small in size (length × width × height = 40cm × 30cm × 25cm), lightweight (≤ 5kg), highly portable, easy to deploy and operate, and can be used without professional technicians, thus lowering the threshold for using laser measuring instruments.

[0151] Comparative advantages: Existing high-precision laser measuring instruments of the same type are usually bulky (such as laser interferometers, with a volume of ≥1m×0.5m×0.5m) and heavy (≥20kg), requiring professional technicians for installation, debugging and operation; while this instrument can be carried by a single person, the entire installation and debugging process takes ≤30 minutes, and the operation process only requires three steps: "installation-calibration-start measurement". The measurement results are intuitive and easy to understand, and ordinary engineering technicians can use it proficiently after simple training.

[0152] Application value: The portability and ease of operation make the instrument widely applicable to scenarios such as rapid on-site measurement and emergency monitoring (e.g., emergency monitoring of building structures after earthquakes and real-time quality inspection during construction). Compared with existing complex laser measurement equipment, it can better meet the actual needs of engineering sites.

[0153] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0154] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A high-precision displacement measurement method for minute deformations in large structures, characterized in that, The measurement system used in this method includes: Two reflectors (1), the included angle between the two reflectors is 146º; The laser source (2) is used to emit a collimated laser beam that is directed perpendicularly toward the center of the two mirrors, with a beam divergence angle ≤0.1mrad; Two observation cameras (3) are respectively aligned with two imaging screens (4) to continuously capture images of laser spots on the screens; the optical axis of the observation camera (3) is perpendicular to the reference side of the measurement system; Two imaging screens (4) are used to receive the laser spot formed by the reflection of the mirror. They are located in front of two observation cameras (3). The distance between the imaging screens (4) and the observation cameras (3) is adjustable, with an adjustment range of 50 to 200 mm. The plane of the imaging screens (4) is perpendicular to the optical axis of each camera. The data processing unit (5) is used to control the observation camera to acquire laser spot images; The display is connected to the data processing unit and is used to display the measurement results in real time. The laser source (2), two reflectors (1), two imaging screens (4), two observation cameras (3) and data processing unit (5) are integrated into a single structure; The measurement method includes: The measurement parameters are calibrated, including: the equivalent focal length (f1, f2) of the observation camera, the principal point position, and the distortion coefficient; the vertical distance S from the laser source to the center of the reflector, and the vertical distance B from the laser source to the screen; and the initial reflection angles θ1 and θ2 between the reflected laser and the laser source emitted beam. Extract the laser spot position and determine the coordinates of the laser spot center: Calculate the deformation, wherein the deformation includes the spacing change t and the rotation angle change α; The extraction of the laser spot position and the determination of the laser spot center coordinates include: The acquired images are preprocessed by the data processing unit: The image is then processed to remove distortion using the calibrated distortion coefficients, and then the image is converted to grayscale to obtain a grayscale image. A sub-pixel-level laser spot center extraction algorithm is used to process grayscale images, specifically employing a Gaussian surface fitting method. As shown in equation (1), it is assumed that the pixel grayscale distribution of the laser spot approximately follows a two-dimensional Gaussian distribution: Equation (1) Taking the logarithm of both sides of equation (1), as shown in equation (2), the problem is transformed into a problem of fitting a two-variable quadratic polynomial: Equation (2) The least squares method is used to solve the problem, and the image coordinates corresponding to the extreme points of the fitted curve are used as the sub-pixel level coordinates of the laser spot center. The calculation of deformation includes: Based on the laser spot movement, the final spacing change t and rotation angle change α are solved using a nonlinear iterative algorithm: Calculate the pixel movement of the laser spot: As shown in equations (3)-(4), based on the initial coordinates and deformed coordinates of the laser spot center, the pixel changes ΔX1, ΔX2, ΔY1, ΔY2 of the laser spot on the image are obtained; （3） （4） Calculate the actual movement distance of the laser spot: As shown in Equation (5-7), based on the similar triangle relationship of the perspective projection of the camera center, combined with the known equivalent focal length of the camera (f1, f2), the screen pixel size P and the screen physical size L, the actual movement distance ΔX' and ΔY' of the laser spot on the imaging screen are calculated. （5） （6） （7） Construct and solve the system of nonlinear equations: As shown in equation (8-9), ΔX' and ΔY' are taken as the observed quantities, and the spacing deformation t and the rotation deformation α are taken as the measured quantities, and substituted into the equation set established by the geometric relationship of the laser lever; （8） （9） As shown in equation (10-11), error functions F1 and F2 are defined; （10） （11） A nonlinear iterative solution algorithm is used: As shown in equations (12-13), calculate the partial derivatives of the error function with respect to t and α respectively, and construct the Jacobian matrix J; （12） （13） b. Using the inverse of the Jacobian matrix and the error vector, as shown in Equation (14), the values ​​of the deformation parameters t and α are iteratively updated; （14） c. Set the initial value of the iteration to 0.

2. The high-precision displacement measurement method for minute deformations of large structures according to claim 1, characterized in that, The reflector (1) is a quartz reflector, which is fixed on the XYR three-axis fine adjustment platform. The XYR three-axis fine adjustment platform is used to adjust the displacement and rotation of the quartz reflector on the X and Y axes to simulate the displacement and rotation deformation of the deformed edge. The displacement adjustment range is ±10mm and the rotation adjustment angle is ±5°.

3. The high-precision displacement measurement method for minute deformations of large structures according to claim 1, characterized in that, The laser source (2) is generated by a laser, wherein the laser is fixedly installed in a slot directly opposite the reference positioning edge of the measurement system. The slot is equipped with an angle fine-tuning rotary component to adjust the laser emission angle ±5° to calibrate the laser emission direction and adapt to the alignment requirements of different measurement scenarios. The laser source operates at 5V and is powered by the data processing unit. The laser source is equipped with a dustproof shell and a heat dissipation structure, and the operating temperature is controlled below 60℃.

4. The high-precision displacement measurement method for minute deformations of large structures according to claim 1, characterized in that, The imaging screen (4) is a diffuse reflective screen with a diffuse reflectivity of ≥90%, and is installed in front of the two cameras via sliding guide rails.

5. The high-precision displacement measurement method for minute deformations of large structures according to claim 1, characterized in that, The observation camera (3) is an industrial camera with a USB interface, a resolution of 1920×1080 pixels, a frame rate of ≥30fps, a lens focal length of 8mm, and an adjustable height range of 100~300mm; the observation camera (3) is connected to the data processing unit (5) to realize real-time data transmission.

6. The high-precision displacement measurement method for minute deformations of large structures according to claim 1, characterized in that, The data processing unit (5) uses a Raspberry Pi 4B motherboard with the following parameters: quad-core Cortex-A72 processor, 4GB memory, equipped with a 16GB MicroSD card as storage medium, running a Linux operating system, and a built-in power management module.

7. The high-precision displacement measurement method for minute deformations of large structures according to claim 1, characterized in that, Also includes: The supporting and fixing structure used to carry and position all functional modules includes a fixing bracket, a PVC board base and stainless steel connectors; the PVC board base (6) serves as the basic support platform of the system, and the fixing bracket is installed on the base in a modular manner, which can be used to fix the laser source, two reflectors, two observation cameras and Raspberry Pi data processing unit respectively; each optical and electronic module is tightly integrated with the base through the fixing bracket.

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