Online laser measurement system and method for six-degree-of-freedom kinematic error of linear workbench

Abstract

The invention relates to the technical field of precision optical measurement, in particular to an online laser measurement system and method for six-degree-of-freedom motion errors of a linear workbench, and the measurement system comprises a laser emission unit, a laser beam splitting error compensation unit, a fixing module and a motion module which are sequentially arranged. According to the online laser measurement system for the six-degree-of-freedom kinematic error of the linear workbench, full modular design is carried out, and the online laser measurement system is suitable for being systematically integrated with a to-be-measured target so as to adapt to application in various industrial environments; through multi-beam path design and sensitivity analysis, effective compensation can be carried out for beam drift and installation errors, and the accuracy and reliability of measurement are improved; a mapping model between a detection result image and a light beam target image is constructed by utilizing machine learning, so that the beam splitting precision of a laser beam can be fully improved, the measurement deviation caused by an optical path and an equipment error can be reduced, and the aim of fully improving the motion error measurement effect of the linear workbench is fulfilled.

Description

Technical Field

[0001] This application belongs to the field of precision optical measurement technology. More specifically, it relates to an on-line laser measurement system and method for six-degree-of-freedom motion errors of a linear stage. Background Art

[0002] In modern mechanical manufacturing, the extremely high precision requirements for manufactured workpieces and automated large-scale production are significant, and the demand for high-efficiency and precise multi-axis machine tools is increasing day by day. The linear stage is an essential key component of multi-axis machine tools. Therefore, the precision measurement technology of the geometric errors of the moving axes plays an important role in improving the machining accuracy of multi-axis machine tools. Generally speaking, there are a total of 21 geometric errors in a three-axis machine tool, and the motion errors of the linear stage mainly lie in position errors, horizontal straightness errors, vertical straightness errors, roll errors, pitch errors, and yaw errors.

[0003] Combined with the current degree-of-freedom error measurement methods, such as the laser interferometry method, although it has high precision in length measurement, it cannot achieve high-precision control of the tiny errors during the beam splitting process, which limits its application in multi-degree-of-freedom measurement; while the laser collimation and autocollimation measurement technologies are suitable for the detection of tiny linear and angular quantities, but they are still insufficient in high-precision multi-axis error compensation capabilities. These methods usually cannot provide comprehensive measurement parameters and are difficult to compensate for beam drift and installation errors in real time, resulting in a reduction in measurement accuracy and efficiency. Summary of the Invention

[0004] The purpose of the embodiments of this application is to provide an on-line laser measurement system and method for six-degree-of-freedom motion errors of a linear stage to solve the technical problem of poor measurement effect of the motion errors of the linear stage in the prior art.

[0005] To achieve the above purpose, in the first aspect, this application provides an on-line laser measurement system for six-degree-of-freedom motion errors of a linear stage, including a laser emission unit, a laser beam splitting error compensation unit, a fixed module, and a motion module arranged in sequence, where:

[0006] The motion module is arranged on the mounting surface of the linear stage to be measured;

[0007] The fixed module is fixedly arranged corresponding to the motion module and is far away from the linear stage to be measured;

[0008] The laser emission unit emits a laser beam, which is reflected and split by the laser beam splitting error compensation unit to form a first beam and a second beam entering the fixed module. The laser beam splitting error compensation unit acquires the detection result image of the laser beam splitting and establishes a mapping model between the detection result image and the beam target image to improve the beam splitting accuracy;

[0009] The fixed module cooperates with the motion module to combine the incident first light beam and second light beam for beam drift monitoring and measurement of the six-degree-of-freedom motion error of the to-be-measured linear workbench.

[0010] According to some embodiments of the present application, the laser beam splitting error compensation unit includes a CCD camera, an image mapping compensation device, a spatial light modulator, and a first plane mirror. The spatial light modulator is arranged corresponding to the laser emitted by the laser emission unit. The first plane mirror cooperates with the spatial light modulator to split the laser beam into the first light beam and the second light beam. The image mapping compensation device is connected to the CCD camera and the spatial light modulator. The CCD camera is used to detect the output light field image of the spatial light modulator and input it into the image mapping compensation device as the detection result image.

[0011] According to some embodiments of the present application, the mapping model is established by a CNN algorithm and is:

[0012] f CNN (im out ) = im in

[0013] wherein, im out is the detection result image, and im in is the light beam target image.

[0014] According to some embodiments of the present application, the laser emission unit includes a laser emitter, a single-mode optical fiber, a beam collimating mirror, and an expansion lens arranged in sequence.

[0015] According to some embodiments of the present application, the fixed module includes a first quadrant photodetector, a first plano-convex lens, a first polarization beam splitter prism, a second quadrant photodetector, a half-wave plate, a first beam splitter prism, a first quarter-wave plate, and a second plane mirror arranged corresponding to the first light beam; and a third plane mirror, a second beam splitter prism, a first corner cube prism, a second polarization beam splitter prism, a third beam splitter prism, a second quarter-wave plate, a first polarizer, a second polarizer, a position sensor, a second plano-convex lens, a fourth beam splitter prism, a first photodetector, a second photodetector, and a third quadrant photodetector arranged corresponding to the second light beam.

[0016] According to some embodiments of the present application, the motion module includes a semi-transmissive semi-reflective film and a second corner cube prism arranged corresponding to the first light beam, and a third corner cube prism arranged corresponding to the second light beam.

[0017] According to some embodiments of the present application, the semi-transmissive semi-reflective film is attached to the incident part of the second corner cube prism.

[0018] According to some embodiments of the present application, the beam drift compensation formula adopted based on the reading change of the position sensor is:

[0019]

[0020] wherein, δlx and δly represent the translational drift amounts of the laser beam in the X direction and the Y direction; ∈lx and ∈ly represent the angular drifts of the laser beam in the X direction and the Y direction; C and S are the cosine function and the sine function respectively.

[0021] In a second aspect, the present application further provides an on-line laser measurement method for the six-degree-of-freedom motion error of a linear workbench, including:

[0022] The laser emission unit, the laser beam splitting error compensation unit, the fixed module, and the motion module are sequentially arranged correspondingly, and the motion module is arranged on the installation surface of the linear workbench to be measured;

[0023] The laser emission unit is used to emit a laser beam, and the laser beam is reflected and split by the laser beam splitting error compensation unit to form a first beam and a second beam that enter the fixed module;

[0024] The laser beam splitting error compensation unit is used to obtain a detection result image of the laser beam splitting, and establish a mapping model between the detection result image and the beam target image;

[0025] The fixed module is used in cooperation with the motion module to monitor the beam drift and measure the six-degree-of-freedom motion error of the linear workbench to be measured by combining the incident first beam and the second beam.

[0026] According to some embodiments of the present application, the motion module is coaxially arranged with the linear workbench to be measured.

[0027] The beneficial effects of the on-line laser measurement system and method for the six-degree-of-freedom motion error of the linear workbench provided by the present application are as follows:

[0028] Compared with the prior art, the on-line laser measurement system for the six-degree-of-freedom motion error of the linear workbench provided by the present application has a fully modular design with a laser emission unit, a laser beam splitting error compensation unit, a fixed module, and a motion module, and is suitable for system integration with the target to be measured, so it is applicable to various industrial environments. On this basis, through the multi-beam path design and sensitivity analysis, the system can effectively compensate for beam drift and installation errors, improving the accuracy and reliability of measurement; at the same time, by using machine learning to construct a mapping model between the detection result image and the beam target image, the beam splitting accuracy of the laser beam can be fully improved, which is conducive to reducing the measurement deviation caused by optical path and equipment errors, and can fully achieve the purpose of improving the measurement effect of the motion error of the linear workbench. Description of the Drawings

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0030] Figure 1 Optical path schematic diagram of the on-line laser measurement system for the six-degree-of-freedom motion error of the linear workbench provided by the embodiment of the present application;

[0031] Figure 2 For Figure 1 Monitoring schematic diagram of the beam drift shown in;

[0032] Figure 3 For Figure 1 Measurement schematic diagram of the pitch angle error and yaw angle error shown in;

[0033] Figure 4 For Figure 1 Measurement schematic diagram of the horizontal straightness error, vertical straightness error, and roll angle error shown in;

[0034] Figure 5 For Figure 1 Measurement schematic diagram of the position error shown in;

[0035] Figure 6 Flowchart of IFTA (Iterative Fourier Transform algorithm) based on CNN (Convolutional Neural Network) for the on-line laser measurement system for the six-degree-of-freedom motion error of the linear workbench provided by the embodiment of the present application;

[0036] Figure 7 It is a structural diagram of the reverse CNN (Convolutional Neural Network) of the on-line laser measurement system for the six-degree-of-freedom motion error of the linear workbench provided by the embodiment of the present application;

[0037] Figure 8 It is a schematic diagram of the structural composition of the image mapping compensation device provided by the embodiment of the present application;

[0038] Figure 9 It is a schematic diagram of the structure of the hardware operating environment involved in the on-line laser measurement system for the six-degree-of-freedom motion error of the linear workbench provided by the embodiment of the present application. Specific embodiments

[0039] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application clearer, the present application will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0040] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element.

[0041] It should be understood that the orientation or positional relationship indicated by the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present application.

[0042] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present application, "a plurality" means two or more unless otherwise specifically defined.

[0043] Please refer to Figure 1 , the on-line laser measurement system for the six-degree-of-freedom motion error of the linear workbench provided by the embodiment of the present application includes a laser emission unit 34, a laser beam splitting error compensation unit 35, a fixed module 36, and a motion module 37 arranged in sequence, where:

[0044] The motion module 37 is arranged on the mounting surface of the linear workbench to be measured;

[0045] The fixing module 36 is fixedly arranged corresponding to the motion module 37 and is away from the linear workbench to be measured;

[0046] The laser emitting unit 34 emits a laser beam, and the laser beam is reflected and split by the laser beam splitting error compensation unit 35 to form a first light beam 38 and a second light beam 39 entering the fixing module 36. The laser beam splitting error compensation unit 35 obtains a detection result image of the laser beam splitting and establishes a mapping model between the detection result image and the light beam target image to improve the splitting accuracy;

[0047] The fixing module 36 cooperates with the motion module 37 to monitor the light beam drift and measure the six-degree-of-freedom motion error of the linear workbench to be measured by combining the incident first light beam 38 and second light beam 39.

[0048] It can be understood that the laser beam splitting error compensation unit 35 here needs to be combined with a control device (such as a controller) preset in the system or connected to an external computing terminal (such as a PC, tablet or smart phone, etc.) for machine learning to construct and iteratively optimize the mapping model between the detection result image and the light beam target image. At the same time, the on-line measurement of this measurement system can also be reflected by the system's on-line collection and processing of measurement data.

[0049] The on-line laser measurement system for the six-degree-of-freedom motion error of the linear workbench provided by the embodiments of the present application. The proposed laser emitting unit 34, laser beam splitting error compensation unit 35, fixing module 36 and motion module 37 can be flexibly assembled according to actual measurement requirements, thereby providing a flexible modular design, being suitable for system integration with the target to be measured, and thus adapting to the application in a variety of industrial environments. On this basis, by splitting the laser beam through the laser beam splitting error compensation unit 35, it can effectively provide a multi-light beam path design and sensitivity analysis, and then effectively compensate for the light beam drift and installation error, improving the accuracy and reliability of the measurement; at the same time, the laser beam splitting error compensation unit 35 is combined with machine learning to construct a mapping model between the detection result image and the light beam target image, which can fully improve the splitting accuracy of the laser beam, and then is beneficial to reducing the measurement deviation caused by the optical path and equipment error, and can fully achieve the purpose of improving the measurement effect of the linear workbench motion error.

[0050] Please refer to again Figure 1, in a further embodiment of the present application, the laser beam splitting error compensation unit 35 includes a CCD camera 5, an image mapping compensation device 6, a spatial light modulator 7, and a first planar mirror 8. Among them, the spatial light modulator 7 is arranged corresponding to the laser emitted by the laser emitting unit 34; the first planar mirror 8 cooperates with the spatial light modulator 7 to split the incident laser beam into a first beam 38 and a second beam 39; the image mapping compensation device 6 is connected to the CCD camera 5 and the spatial light modulator 7, and the CCD camera 5 is used to detect the output light field image of the spatial light modulator 7 and input it into the image mapping compensation device 6 as a detection result image.

[0051] It can be understood that the image mapping compensation device 6 here, as a computing terminal of machine learning, has the functions of data acquisition, data analysis, and data output. It can construct a model algorithm using two types of data sets, namely the detection result image and the beam target image, and determine the mapping relationship between the input and output images through training. In this way, in actual application, by combining the establishment of the mapping model between the detection result image and the beam target image, the error generated by laser beam splitting can be compensated and calculated to form a compensation signal to adjust the spatial light modulator 7, so as to achieve the purpose of overcoming or eliminating the laser beam splitting error.

[0052] Obviously, the laser beam splitting error compensation unit 35 provided by the embodiment of the present application can, while performing on-line laser beam splitting, fully compensate the laser beam splitting error by using the method of establishing a mapping model between the detection result image and the beam target image through machine learning. This is conducive to improving the actual measurement accuracy of motion error and ensuring the accuracy and reliability of the measurement result.

[0053] Please refer to Figure 1 and Figure 8 , in some embodiments of the present application, the image mapping compensation device 6 includes a data acquisition module 100, an analysis module 200, and an output module 300. Among them, the data acquisition module 100 can collect the detection result image detected by the CCD camera in real time and the pre-screened input beam target image, and then the analysis module 200 combines the two types of data, namely the detection result image and the beam target image, to construct a model and analyze the model to obtain a prediction image capable of compensating the laser beam splitting error, which is output as the output result of the output module 300.

[0054] Please further refer to Figure 6 and Figure 7, in a further embodiment of the present application, the above mapping model is established by the CNN algorithm. Specifically, both the detection result image and the beam target image are processed into 10×10 images of the same size, and a dataset is collected and generated; a CNN algorithm is constructed using the two datasets of the detection result image and the beam target image, and the mapping relationship between the input image and the output image is determined through training, thereby achieving the purpose of establishing a mapping model between the input detection result image and the output beam target image. In terms of its mapping relationship, it can be approximately represented by the inverse CNN function, and its input and output relationship is as follows:

[0055] f CNN (im out )=im in

[0056] where im out is the detection result image, and im in is the beam target image.

[0057] The CNN model uses the mean absolute error (MAE) and the robust regression loss function (HuberRegression Loss, Huber) as the loss function. The definition of MAE is as follows:

[0058]

[0059] In the formula, n represents the total number of data in the dataset, y pred.i and y true.i are the predicted value and the true value of the i-th sample, respectively.

[0060] The Huber loss function L(a) is defined as shown in the formula:

[0061]

[0062] where δ is the threshold (hyperparameter) of the loss function, used to distinguish the range of square penalty and linear penalty; y pred and y true are the predicted value and the true value, respectively.

[0063] Global average pooling (GlobalAveragePooling, GAP) in the model is used to extract global features. The GAP layer outputs a single value to represent the information of each channel, and its mathematical expression is:

[0064]

[0065] X i,j,c represents the pixel value at position (i, j) in the c-th channel, and Y c is the global average pooling result of the c-th channel, used to extract the overall features of this channel.

[0066] Please refer to again Figure 1 In a further embodiment of the present application, the laser emission unit 34 includes a laser emitter 1, a single-mode optical fiber 2, a beam collimator 3, and an expansion lens 4 arranged in sequence.

[0067] After the laser emitter 1 emits laser light, it is sequentially transmitted through the single-mode optical fiber 2 to the beam collimator 3 and the expansion lens 4, and then enters the laser beam splitting error compensation unit 35 in the form of a laser beam.

[0068] Optionally, the laser emitter 1 is a semiconductor laser emitter. Compared with the traditional helium-neon laser, it has lower cost, higher power, and better industrial adaptability, thus significantly reducing the system construction cost and improving the application flexibility of the system.

[0069] Please refer to again Figure 1 In a further embodiment of the present application, the fixing module 36 includes a first quadrant photodetector 9, a first plano-convex lens 10, a first polarization beam splitter prism 11, a second quadrant photodetector 12, a half-wave plate 13, a first beam splitter prism 14, a first quarter-wave plate 15, and a second plane mirror 16 corresponding to the first light beam 38; and a third plane mirror 17, a second beam splitter prism 18, a first corner cube prism 19, a second polarization beam splitter prism 20, a third beam splitter prism 21, a second quarter-wave plate 22, a first polarizer 23, a second polarizer 24, a position sensor 25, a second plano-convex lens 26, a fourth beam splitter prism 27, a first photodetector 28, a second photodetector 29, and a third quadrant photodetector 30 corresponding to the second light beam 39.

[0070] Please refer to again Figure 1 In a further embodiment of the present application, the motion module 37 includes a beam splitter 31 and a second corner cube prism 32 corresponding to the first light beam 38, and a third corner cube prism 33 corresponding to the second light beam 39.

[0071] Please refer to again Figure 1 In a further embodiment of the present application, the beam splitter 31 is attached to the incident part of the second corner cube prism 32.

[0072] Combined with the specific content of the above embodiments, in the on-line laser measurement system for the six-degree-of-freedom motion error of a linear workbench, the six-degree-of-freedom error mainly includes roll angle error, horizontal straightness error, vertical straightness error, pitch angle error, yaw angle error, and position error. The specific measurement process includes:

[0073] The laser emitter 1 emits a laser beam, which is transmitted through a single-mode optical fiber 2 and passes through a beam collimating mirror 3 and an expanding lens 4 in sequence before entering the spatial light modulator 7. The CCD camera 5 collects beam data. The CCD camera 5 is connected to the image mapping compensation device 6. The image mapping compensation device 6 has performed model training on the aforementioned mapping model before working. The image mapping compensation device 6 controls the spatial light modulator 7 to load a phase hologram to achieve precise modulation and beam splitting of the laser beam. The first beam 38 and the second beam 39 emitted by the spatial light modulator 7 are sequentially split and interferometrically measured through different optical components.

[0074] On this basis, the first beam 38 is reflected by the first plane mirror 8 and adjusted by the half-wave plate 13, and then enters the motion module 37 through the first beam splitter prism 14 and the first quarter-wave plate 15. At the same time, a part of the first beam 38 is reflected by the semi-transparent and semi-reflective film 31, passes through the first quarter-wave plate 15, the first beam splitter prism 14 and the first polarization beam splitter prism 11, and is then focused on the first quadrant photodetector 9 by the first plano-convex lens 10, thereby realizing the measurement of the pitch angle error and the yaw angle error.

[0075] Furthermore, the first beam 38 passing through the semi-transparent and semi-reflective film 31 is reflected by the second corner cube prism 32 and the second plane mirror 16 to the second quadrant photodetector 12, thereby realizing the measurement of the horizontal straightness error and the vertical straightness error.

[0076] Furthermore, after the second beam 39 is split by the second polarization beam splitter prism 20, one of the second beams 39 is reflected by the first corner cube prism 19 and returns to the second polarization beam splitter prism 20, and the other second beam 39 passes through the second polarization beam splitter prism 20 and is reflected by the third corner cube prism 33 and the third beam splitter prism 21, and finally forms interference light in space. The interference light is split by the second beam splitter prism 18, and the reflected beam is received by the second photodetector 29 after passing through the polarizer 24; the transmitted beam is received by the first photodetector 28 after passing through the third plane mirror 17, the second quarter-wave plate 22 and the polarizer 23. Since the interference phases of the first photodetector 28 and the second photodetector 29 differ by 90 degrees, the phase change of the interference light forms a position measurement signal, so that high-precision measurement of the position error can be realized.

[0077] Furthermore, the second beam 39 passing through the fourth beam splitter prism 27 is received by the third quadrant photodetector 30, thereby realizing the measurement of the roll angle error.

[0078] At the same time, the second beam 39 reflected by the third beam splitter prism 21 is reflected by the third beam splitter prism 27 and focused on the position sensor 25 by the second plano-convex lens 26, and the real-time monitoring of the beam drift can also be realized.

[0079] To facilitate the understanding of the working principle of the system solution by those skilled in the art, the following description is further provided in combination with the measurement principle of the system:

[0080] The six-degree-of-freedom error measurement mentioned in this application includes horizontal straightness error, vertical straightness error, position error, pitch angle error, roll angle error, and yaw angle error. Its measurement model is as follows:

[0081]

[0082] Among them, (V1, V2, V3, V4) are the voltage values of the four quadrants of the second quadrant photodetector 12 in the second and fourth quadrants, k x and k y are the sensitivities of the detector in the horizontal direction (i.e., the X direction of the coordinate system shown in all the drawings) and the vertical direction (the Y direction of the coordinate system shown in all the drawings), respectively; θ is the pitch angle error, φ is the yaw angle error, V 9_x is the output signal of the first quadrant photodetector 9 in the horizontal direction, V 9_y is the output signal of the first quadrant photodetector 9 in the vertical direction, f is the focal length of the plano-convex lens 10, k θ and k φ are the system calibration coefficients; ΔZ is the linear straightness error (position error), N is the number of quarter-waves, δ fist is the starting phase angle of the signal, δ last is the ending phase angle, mod is the modulo operation, L r is the nominal displacement of the measured linear workbench, λ is the laser wavelength; ψ is the roll angle error, V 12_x is the output signal of the second quadrant photodetector 12, V 30_x is the output signal of the third quadrant photodetector 30, k ψ is the system calibration coefficient.

[0083] Please refer to Figure 1 and Figure 4 . When there are errors in the horizontal and vertical directions of the measured linear workbench, the light spot of the second quadrant photodetector 12 will be displaced, resulting in changes in the voltage values (V1, V2, V3, V4) of its four quadrants. The calculation formulas for the horizontal straightness error ΔX and the vertical straightness error ΔY can be expressed as:

[0084]

[0085] Among them, (V1, V2, V3, V4) are the voltage values of the four quadrants of the second quadrant photodetector 12, k x and k y are the sensitivities of the detector in the horizontal and vertical directions, respectively.

[0086] Please refer to Figure 1 and Figure 3 . When there are pitch angle error θ and yaw angle error φ in the linear workbench to be measured, the first quadrant and fourth quadrant photodetector 9 calculates the angular deviation of the light beam by detecting the displacement of the light spot. The calculation formulas for the pitch angle error θ and the yaw angle error φ can be expressed as:

[0087]

[0088]

[0089] where, V 9_x and V 9_y respectively represent the output signals of the first quadrant and fourth quadrant photodetector 9 in the horizontal and vertical directions, f represents the focal length of the plano-convex lens 10, k θ and k φ represent the system calibration coefficients.

[0090] Please refer to Figure 1 and Figure 5 . When the linear workbench to be measured has a displacement, the interference phases of the first photodetector 28 and the second photodetector 29 differ by 90 degrees. The calculation formula for the linear straightness error ΔZ can be expressed as:

[0091]

[0092] In the formula, N is the number of quarter-waves, δ fist is the phase angle at the start of the signal, δ last is the phase angle at the end of the signal, mod is the modulo operation, L r is the nominal displacement of the measured linear platform, and λ represents the laser wavelength.

[0093] Please refer to Figure 1 and Figure 4 . The roll error ψ is measured by the second quadrant and fourth quadrant photodetector 12 and the third quadrant and fourth quadrant photodetector 30. The roll angle error ψ is caused by the rotation of the light spot and is calculated through the signal difference of the second quadrant and fourth quadrant photodetector 12 and the third quadrant and fourth quadrant photodetector 30. Its calculation formula can be expressed as:

[0094] ψ = k ψ × (V 12_x - V 30_x )

[0095] In the formula, V 12_x and V 30_x respectively represent the output signals of the second quadrant and fourth quadrant photodetector 12 and the third quadrant and fourth quadrant photodetector 30. k ψ is the system calibration coefficient, which is used to correct errors and improve the measurement accuracy.

[0096] Please refer to Figure 1 and Figure 2 , since each laser source has an inherent 4DOF (degrees of freedom) beam drift, which is mainly due to the deformation of the laser resonator caused by temperature changes and the displacement of the mechanical structure supporting the laser source. According to the principles of geometric optics, all 4DOF beam drifts will affect the sensor, resulting in changes in the readings of the position sensor 25. Through the 4DOF laser beam drift compensation formula, the translation of the laser beam in the X and Y directions (δlx and δly) and the angular drift in the X and Y directions (∈lx and ∈ly) can be corrected, and the calculation formula of its compensation matrix can be expressed as:

[0097]

[0098] where δlx and δly represent the translational drift amounts of the laser beam, and ∈lx and ∈ly represent the angular drifts of the laser beam; C and S are the cosine and sine functions respectively, used to describe the angular offsets.

[0099] Please refer to Figure 1 and Figure 4 , since it is difficult to avoid installation errors during the assembly process, it is necessary to analyze the sensitivity of the installation errors to determine the installation error terms to be compensated. The installation error compensation model is based on the X and Y offset data read by the second and fourth quadrant photodetector 12 and the third and fourth quadrant photodetector 30, and its model expression can be expressed as:

[0100] X Yi = k(δ ins , δ li )

[0101] where δ ins represents the vector of 22 installation errors, and δ li represents the 4DOF laser beam drift vector.

[0102] By linearizing this model, the installation error problem can be solved. Assuming that the installation error is small, this equation can be approximated as a function of the Jacobian matrix J, that is:

[0103] ΔX Yi = J ins (0)δ ins + J l (0)δ li

[0104] After collecting data at multiple measurement points, the installation error is solved by the least squares method, and the calculation formula is:

[0105] δ = (J T J) -1 JT ΔX Yi

[0106] Substitute the solution into the model for iterative update until the error value converges within the tolerance range, so as to obtain a stable installation error compensation value.

[0107] In summary, the online laser measurement system for the six-degree-of-freedom motion error of the linear workbench provided by the embodiments of the present application has the following advantages compared with the prior art:

[0108] 1. The provided online measurement system for the six-degree-of-freedom error of the linear workbench with high-precision laser beam splitting adopts a modular design, which is convenient for integration with the system to be measured, adapts to various industrial environments, can meet the requirements of high measurement accuracy, and is particularly suitable for error detection and fine calibration of precision equipment.

[0109] 2. A high-precision laser beam splitting online measurement method based on interferometric measurement and geometric optics is provided. Through multi-beam path design and sensitivity analysis, it can effectively compensate for beam drift and installation error, and significantly improve the accuracy and reliability of measurement.

[0110] 3. A laser beam splitting error compensation method is provided, which can construct a mapping relationship between the target image and the detection image through machine learning, so as to effectively reduce the deviation caused by optical path and equipment errors and improve the beam splitting accuracy of the laser beam.

[0111] 4. A beam drift compensation method is provided, which can measure and compensate for beam drift in real time, reduce the computational amount and quantity of optical elements, and effectively overcome the problem of low measurement accuracy.

[0112] 5. An installation error compensation method is provided, which can optimize and iterate the installation error model by the least squares method, comprehensively consider the influence of installation error on measurement, and thus effectively improve the accuracy of laser multi-degree-of-freedom measurement.

[0113] Based on the above embodiments, the present application further provides a measurement method implemented based on the above online laser measurement system for the six-degree-of-freedom motion error of the linear workbench, including:

[0114] Arrange the laser emission unit 34, the laser beam splitting error compensation unit 35, the fixed module 36, and the motion module 37 in sequence, and set the motion module 37 on the installation surface of the linear workbench to be measured;

[0115] Use the laser emission unit 34 to emit a laser beam, which is reflected and split by the laser beam splitting error compensation unit 35 to form a first beam 38 and a second beam 39 entering the fixed module 36;

[0116] The laser beam splitting error compensation unit 35 is used to obtain the detection result image of the laser beam splitting, and a mapping model between the detection result image and the beam target image is established;

[0117] The fixed module 36 and the motion module 37 are used to cooperate to monitor the beam drift and measure the six-degree-of-freedom motion error of the to-be-measured linear workbench by combining the incident first beam 38 and second beam 39.

[0118] Obviously, the measurement method provided here benefits from the advantages of the measurement system and can achieve high-precision measurement of the to-be-measured linear workbench.

[0119] In some embodiments of the present application, the motion module 37 is coaxially arranged with the to-be-measured linear workbench to further improve the measurement accuracy.

[0120] Please further refer to Figure 9 , the memory 1005 provided in the embodiments of the present application can be used to store computer programs. For example, application programs and modules of application software, such as the computer program corresponding to the measurement method of the online laser measurement system for the six-degree-of-freedom motion error of the linear workbench in the embodiments of the present application, so as to execute various functional applications and data processing, that is, to implement the above method. The memory 1005 may further include a remote memory remotely set relative to the processor 1001, and these remote memories can be connected to the computer through a network. On this basis, examples of this network include but are not limited to the Internet, enterprise intranets, local area networks, mobile communication networks, and combinations thereof.

[0121] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An online laser measurement system for six-degree-of-freedom motion error of a linear worktable, characterized in that: It includes a laser emitting unit, a laser beam splitting error compensation unit, a fixing module and a moving module which are arranged in sequence, wherein: The motion module is arranged on the mounting surface of the linear workbench to be tested; The fixed module is fixedly arranged corresponding to the motion module and is far away from the linear workbench to be tested; The laser emitting unit emits a laser beam, which is reflected and split by the laser beam splitting error compensation unit to form a first beam and a second beam entering the fixed module. The laser beam splitting error compensation unit obtains a detection result image of the laser beam splitting, and establishes a mapping model between the detection result image and the beam target image to improve the beam splitting accuracy. The fixing module cooperates with the motion module to perform beam drift monitoring and six-degree-of-freedom motion error measurement of the linear workbench to be tested in combination with the incident first light beam and the second light beam.

2. The online laser measurement system for six-degree-of-freedom motion error of a linear table according to claim 1, characterized in that: The laser beam splitting error compensation unit includes a CCD camera, an image mapping compensation device, a spatial light modulator and a first plane reflector. The spatial light modulator is set corresponding to the laser emitted by the laser emitting unit. The first plane reflector cooperates with the spatial light modulator to split the laser beam into the first light beam and the second light beam. The image mapping compensation device is connected to the CCD camera and the spatial light modulator. The CCD camera is used to detect the output light field image of the spatial light modulator to input the image mapping compensation device as the detection result image.

3. The online laser measurement system for six-degree-of-freedom motion error of a linear table according to claim 2, characterized in that: The mapping model is established by the CNN algorithm, which is: f CNN (in the out )=in in Among them, out is the detection result image, and imin is the beam target image.

4. The online laser measurement system for six-degree-of-freedom motion error of a linear table according to any one of claims 1 to 3, characterized in that: The laser emitting unit comprises a laser emitter, a single-mode optical fiber, a beam collimator and an expansion lens which are arranged in sequence.

5. The online laser measurement system for six-degree-of-freedom motion error of a linear table according to claim 4, characterized in that: The fixed module includes a first four-quadrant photodetector, a first plano-convex lens, a first polarization beam splitter, a second four-quadrant photodetector, a half-wave plate, a first beam splitter, a first quarter-wave plate and a second plane reflector arranged corresponding to the first light beam; and a third plane reflector, a second beam splitter, a first corner cube prism, a second polarization beam splitter, a third beam splitter, a second quarter-wave plate, a first polarizer, a second polarizer, a position sensor, a second plano-convex lens, a fourth beam splitter, a first photodetector, a second photodetector and a third four-quadrant photodetector arranged corresponding to the second light beam.

6. The online laser measurement system for six-degree-of-freedom motion error of a linear table according to claim 5, characterized in that: The motion module includes a semi-transmissive and semi-reflective film and a second corner cube prism arranged corresponding to the first light beam, and a third corner cube prism arranged corresponding to the second light beam.

7. The online laser measurement system for six-degree-of-freedom motion error of a linear table according to claim 6, characterized in that: The semi-transparent and semi-reflective film is bonded to the incident part of the second corner cube prism.

8. The online laser measurement system for six-degree-of-freedom motion error of a linear table according to claim 5, characterized in that: The beam drift compensation formula used based on the reading change of the position sensor is: Wherein, δlx and δly represent the translation drift of the laser beam in the X direction and the Y direction; ∈lx and ∈ly represent the angular drift of the laser beam in the X direction and the Y direction; C and S are the cosine function and the positive selection function respectively.

9. An online laser measurement method for six-degree-of-freedom motion error of a linear worktable, comprising: The laser emission unit, the laser beam splitting error compensation unit, the fixed module and the motion module are arranged in sequence and correspondingly, and the motion module is arranged on the installation surface of the linear workbench to be measured; The laser emitting unit is used to emit a laser beam, and the laser beam is reflected and split by the laser beam splitting error compensation unit to form a first light beam and a second light beam entering the fixing module; Acquire the detection result image of the laser beam splitting by using the laser beam splitting error compensation unit, and establish a mapping model between the detection result image and the beam target image; The fixing module is used in cooperation with the motion module to perform beam drift monitoring and six-degree-of-freedom motion error measurement of the linear workbench to be tested in combination with the incident first light beam and the second light beam.

10. The online laser measurement method for six-degree-of-freedom motion error of a linear table according to claim 9, characterized in that: The motion module is coaxially arranged with the linear workbench to be tested.

Images