Five-dimensional angle measurement device and method based on wavefront interference fringes

Abstract

The invention belongs to the technical field of ultra-precise angle measurement, and discloses a five-dimensional angle measurement device and method based on wavefront interference fringes. The laser wavelength is used as the traceability reference. The homodyne wavefront interference principle is utilized in a single interference measuring head, two paths of detection laser are used for generating two wavefront interference light spots, the spatial frequencies and phases of respective fringe images in the horizontal direction and the vertical direction are calculated respectively, and simultaneous decoupling is carried out to accurately measure the axial displacement, lateral displacement, pitching, deflection and roll angle deviation of the reflector. According to the five-dimensional geometric quantity measurement device, single-principle integrated five-dimensional geometric quantity measurement can be achieved, the measurement resolution is high, the measurement result can be directly traced to the laser wavelength, and the requirement of high-end equipment for ultra-precise five-dimensional geometric quantity measurement is met.

Description

Technical Field

[0001] This invention belongs to the field of ultra-precision angle measurement technology, specifically relating to a five-dimensional angle measuring device and method based on wavefront interference fringes. Background Technology

[0002] In modern industry, ultra-precision CNC machine tools are core equipment in high-end manufacturing. To ensure the machining accuracy of ultra-precision machine tools, 42 geometric errors need to be analyzed and compensated for in five-axis CNC machine tools, while three-axis CNC machine tools and coordinate measuring machines each have 21 geometric errors that need to be measured quickly and accurately. There is an urgent need for integrated five-dimensional high-resolution measuring instruments to significantly improve the efficiency of machine tool error compensation.

[0003] Laser interferometers utilize the interference phenomenon of lasers to measure extremely small displacement and angular changes. They possess advantages such as extremely high measurement resolution, a large measurement range, non-contact measurement capabilities, a simple overall structure, and measurement results traceable to the laser wavelength, making them widely used in ultra-precision geometric measurement. However, currently commercially available multi-degree-of-freedom measurement systems do not utilize a single coordinate reference, i.e., a single measuring instrument simultaneously measuring five-dimensional geometric information. For example, the SIOS SP 15000 C6 NG calibration laser interferometer, based on the principles of laser interferometry and electronic level, achieves five-dimensional measurement. Its axial displacement measurement accuracy reaches 0.2 μm / m, lateral displacement measurement accuracy reaches ±0.1% ±0.25 μm ±0.1•M² (M is axial displacement), yaw or pitch angle measurement accuracy reaches ±0.04% ±0.04 μrad, and roll angle measurement accuracy is ±2.4 μrad ±1.5%. However, this interferometer uses up to six beams for measurement, and pitch and yaw angles cannot be measured simultaneously; the probe must be rotated and measurements performed step by step. Commercial five-dimensional or six-dimensional laser interferometers, represented by this interferometer, generally employ multiple measurement principles and multiple sensors, resulting in problems such as complex measurement principles, complex structures, lack of measurement references between different sensors, and difficult interferometer installation. Consequently, they suffer from low measurement accuracy, low efficiency, and high cost.

[0004] To achieve high-precision five-dimensional measurement using a single instrument and a single measurement principle, several research institutions have proposed their own solutions. For example, in 2012, Professor Liu Jianhong and others from National Chung Hsing University in Taiwan proposed a five-degree-of-freedom measurement device based on a grating. This device utilizes three-dimensional laser tracking technology and inverse kinematics to achieve five-degree-of-freedom measurement of a single probe. Its straightness measurement error is ±0.6 μm, its angle error is ±0.8″, and its linear displacement measurement error is ±1.2 μm.

[0005] For example, in 2017, Yan Liping and colleagues at Zhejiang Sci-Tech University designed a novel combined target-type six-degree-of-freedom measurement device. This method uses a combined target of two right-angle mirrors and one plane mirror, utilizing interference fringes to decouple pitch, yaw, and displacement, and a position-sensitive detector to decouple roll. The system has an axial displacement resolution of 0.01 μm, a lateral displacement resolution of 0.75 μm, a roll angle measurement resolution of 2.94″, and pitch and yaw angle resolutions of 0.069″.

[0006] In summary, currently commercially available multi-degree-of-freedom measurement systems, both domestically and internationally, require the integration of multiple sensors for multi-point measurements in five-dimensional geometric measurements. This presents challenges such as complex measurement principles, numerous measurement beams, and inconsistent measurement benchmarks. Furthermore, five-dimensional angle measurement schemes proposed by research institutions generally suffer from low measurement resolution, large multi-dimensional coupling errors, and complex devices. Therefore, it is urgently needed to research and design an integrated high-resolution five-dimensional measurement device capable of simultaneously measuring axial displacement, lateral displacement, pitch angle, yaw angle, and roll angle using a single measurement principle. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a five-dimensional angle measuring device and method based on wavefront interference fringes, thereby resolving the issues in the prior art. The technical solution adopted by this invention is as follows: A five-dimensional angle measurement method based on wavefront interference fringes includes: Step 1: The laser emitted by the single-frequency laser is split into two beams. The two laser beams are then separated into corresponding transmitted and reflected beams by a composite beam splitter. The reflected beam is used as the measurement beam, and the transmitted beam is used as the reference beam. The measurement beam and the reference beam of one laser beam intersect at one half of the industrial camera's photosensitive element, and the measurement beam and the reference beam of the other laser beam intersect at the other half of the industrial camera's photosensitive element, generating two interference spots with horizontal and vertical fringes. Step 2: Divide the industrial camera image data into two images along the midpoint of the long axis. The two images are the interference spots formed by the two laser beams. Step 3: Convert the two interference fringe images into two-dimensional grayscale matrices respectively, accumulate each row and column of the matrix, and select the row and column with the largest amplitude as the decoupling data source. Step 4: Perform Discrete Fourier Transform on the row and column data with the largest amplitude, and then perform Gaussian peak fitting on the transformed data to obtain the spatial frequency values ​​of the row and column data. Step 5: Using the spatial frequency values ​​of the two interference fringe images, calculate their respective displacement, pitch angle, and yaw angle. Combined with the angle between the two laser beams, calculate the axial displacement Δ using the following formula. z Lateral displacement Δ y yaw angle Δ Pitch angle Δ and roll angle Δ Change data: ; ; ; ; ; in, and These represent the phase changes of the interference fringes for light beams one and two, respectively. and The horizontal and vertical components of the spatial frequency of the interference fringes produced by light beam number one. The vertical component of the spatial frequency of the interference fringes produced by the second beam. Where λ is the laser wavelength and n is the air refractive index. The angle between the two laser beams is denoted by Δ, L is the distance between the reflection points of the two laser beams on the composite measuring mirror, and the rest Δ represents the change of this value relative to the measurement.

[0008] A five-dimensional angle measuring device based on wavefront interference fringes, employing the five-dimensional angle measuring method described in the claims, includes a host computer, a laser beam splitter, an industrial camera, a composite beam splitter group, a composite measuring mirror, and a single-frequency laser; The laser emitted by the single-frequency laser is split into two beams by the laser beam splitter. The two laser beams are then split into corresponding transmitted light and reflected light by the composite beam splitter. The reflected light is used as the measurement light and the transmitted light is used as the reference light. After being reflected by the two reflective surfaces of the composite measuring mirror, the two beams are transmitted through the beam-splitting surface inside the composite beam splitter group to the photosensitive element of the industrial camera and are received. After being reflected by the reflective surface of the composite beam splitter group, the two reference beams are reflected by the beam splitter surface inside the composite beam splitter group and received by the photosensitive element of the industrial camera. The industrial camera is connected to the host computer.

[0009] Furthermore, it also includes single-mode fiber, optical collimator No. 1, and optical collimator No. 2; The output end of the single-frequency laser is connected to the laser beam splitter via the single-mode optical fiber. The output end of the laser beam splitter is connected to the first optical collimator and the second optical collimator via optical cables. The first optical collimator and the second optical collimator emit two laser beams that pass through the composite beam splitter group. The composite measurement mirror is located at the rear end of the composite beam splitter group.

[0010] Furthermore, the composite measuring mirror is V-shaped, comprising two reflecting surfaces that form an angle with each other; There is an angle between the first optical collimator and the second optical collimator, so that the two laser beams emitted by them respectively irradiate the two emitting surfaces of the composite measuring mirror perpendicularly.

[0011] Furthermore, the measuring beam and reference beam of one laser intersect at one half of the industrial camera's image sensor, while the measuring beam and reference beam of the other laser intersect at the other half of the industrial camera's image sensor, generating two interference spots with horizontal and vertical fringes.

[0012] The present invention has the following beneficial effects: (1) The five-dimensional geometric measurement device of the present invention is based entirely on the principle of laser interferometry and can simultaneously measure five-dimensional information such as axial displacement, lateral displacement, pitch, yaw and roll angle. It has high measurement resolution and can be directly traced to the laser wavelength. (2) The device of the present invention can realize point-to-point measurement of five-dimensional information using only a single integrated probe, and there is no problem of inconsistent benchmarks caused by the use of multiple sensors for measurement; (3) The device of the present invention utilizes a composite beam splitter group combined with a composite measuring mirror, making the entire instrument structure simple and easy to adjust; (4) The integrated sensing module of the device of the present invention is easy to disassemble and reinstall, and can be used to ensure the pointing accuracy of the two detection lasers, which is convenient to use and saves costs. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the three-dimensional angle measuring device of the present invention; In the diagram: 1. Host computer, 2. Laser beam splitter, 3. Single-mode fiber, 4. First optical collimator, 5. Second optical collimator, 6. Integrated sensor base, 7. Industrial camera, 8. Composite beam splitter group, 9. Composite measuring mirror, 10. Single-frequency laser. Detailed Implementation

[0014] The following will be based on embodiments of the present invention. Figure 1 The technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0015] A five-dimensional angle measuring device based on wavefront interference fringes includes a host computer 1, a laser beam splitter 2, an industrial camera 7, a composite beam splitter group 8, a composite measuring mirror 9, and a single-frequency laser 10. The laser emitted by the single-frequency laser 10 is split into two beams by the laser beam splitter 2. The two laser beams are then split into corresponding transmitted light and reflected light by the composite beam splitter group 8. The reflected light is used as the measurement light and the transmitted light is used as the reference light. After being reflected by the two reflective surfaces of the composite measuring mirror 9, the two measuring beams are transmitted through the beam-splitting surface inside the composite beam splitter group 8 to the photosensitive element of the industrial camera 7 and are received. The two reference beams are reflected by the reflective surface of the composite beam splitter group 8, and then reflected by the beam splitting surface inside the composite beam splitter group 8 to the photosensitive element of the industrial camera 7 for reception. The industrial camera 7 is connected to the host computer 1.

[0016] Furthermore, it also includes single-mode fiber 3, optical collimator 4 (number one), and optical collimator 5 (number two). The output end of the single-frequency laser 10 is connected to the laser beam splitter 2 through the single-mode optical fiber 3. The output end of the laser beam splitter 2 is connected to the first optical collimator 4 and the second optical collimator 5 through optical cables. The first optical collimator 4 and the second optical collimator 5 emit two laser beams that pass through the composite beam splitter group 8. The composite measurement mirror 9 is located at the rear end of the composite beam splitter group 8.

[0017] Furthermore, the composite measuring mirror 9 is V-shaped, comprising two reflecting surfaces that form an angle with each other; There is an angle between the first optical collimator 4 and the second optical collimator 5. This angle can be positive or negative, corresponding to the two beams of light being emitted along the divergence direction and along the convergence direction. The two laser beams emitted by the two beams are respectively perpendicularly irradiated on the two emitting surfaces of the composite measuring mirror 9.

[0018] Furthermore, there are two camera arrangement schemes. In Scheme 1, the measurement beam and reference beam of one laser intersect at one half of the photosensitive element of the industrial camera 7, and the measurement beam and reference beam of the other laser intersect at the other half of the photosensitive element of the industrial camera 7, generating two interference spots with horizontal and vertical fringes. This scheme has a larger probe volume, but a single industrial camera ensures better consistency and stability of measurement results. In Scheme 2, the single industrial camera is replaced with two industrial cameras, each receiving the interference spot of one laser beam. A trigger signal is used to ensure that the cameras receive images synchronously. This scheme is suitable for scenarios with large measurement distances, and the probe volume is smaller.

[0019] The composite beam splitter group 8 integrates a beam splitter surface and two reference reflector surfaces. The two reflector surfaces are not perpendicular to their respective reference beams, so that the measurement beam and the reference beam are transmitted non-coaxially in the output travel path. It also has two structures, namely, the two reference reflector surfaces are arranged in a "V" shape and a "V" shape, to adapt to different optical paths.

[0020] The two lasers are designated as Laser No. 1 and Laser No. 2. Two fiber collimators are fixed to the integrated sensing base 6 using a special fixture. The special fixture has the ability to adjust forward and backward and fine-tune the three-dimensional attitude angle. Compared with commercially available mounting brackets, it is smaller in size and has a larger adjustable range. The industrial camera 7 and the composite beam splitter group 8 are directly fixed to the integrated sensing base 6. The composite measuring mirror 9 has two reflective surfaces that are angled to each other, which can reflect Laser No. 1 and Laser No. 2 respectively. During measurement, the composite measuring mirror 9 is fixed to the object to be measured.

[0021] like Figure 1 As shown, this is an arrangement mode with a relatively short measurement distance, where the two beams converge in front of the composite beam splitter group. In other arrangement modes, the two beams converge at different locations: behind the composite beam splitter group (where the reference reflector of the composite beam splitter group is in a "V" shape), behind the laser collimator (where the collimators are arranged in mutually divergent directions), and behind the measurement mirror (where the composite measurement mirror is in a "V" shape). These correspond to different mirror group structures and different probe volumes and measurement distances. The working principle of this five-dimensional measurement device is as follows: A 633nm helium-neon single-frequency laser 10 provides a frequency-stabilized laser signal, which is transmitted through a single-mode fiber 3 to a laser beam splitter 2, splitting it into two laser beams with equal frequency and consistent intensity, named Laser No. 1 and Laser No. 2. These are collimated by collimators No. 1 and No. 2, respectively. The laser emission directions of the two fiber collimators have a certain sway angle, which is consistent with the angle between the two reflector surfaces of the composite measurement mirror 9. After passing through the beam-splitting surface in the composite beam splitter assembly 8, the two laser beams are split into their respective measurement beams and reference beams. The two measurement beams are transmitted through the two reflecting surfaces of the composite measuring mirror 9 and return to the composite beam splitter assembly 8. After reflection by the inner beam-splitting surface, they are received by the photosensitive element of the industrial camera 7. The two reference beams are reflected by the reference reflecting surface inside the composite beam splitter assembly 8 and return to the beam-splitting surface. After reflection by the beam-splitting surface, they are received by the photosensitive element of the industrial camera 7. The angle between the two reference reflecting surfaces is almost identical to the angle between the two reflecting surfaces of the composite measuring mirror. By finely adjusting the geometric positions of the first and second collimators and the composite beam splitter assembly, the measurement beam and reference beam of the first laser intersect at the same position on the left half of the photosensitive element of the industrial camera 7, and the measurement beam and reference beam of the second laser intersect at the same position on the right half of the photosensitive element of the industrial camera 7. This produces two interference spots with horizontal and vertical fringes. In a dual-camera mode, these spots are aligned with the center of the photosensitive element of each camera.

[0022] After receiving the dual-spot interference image information, the industrial camera 7 uploads it to the host computer 1 program. The host computer 1 uses an image decoupling algorithm to decouple the three-dimensional angle data.

[0023] A five-dimensional angle measurement method based on wavefront interference fringes includes: Step 1: The laser emitted by the single-frequency laser 10 is split into two beams. The two laser beams are then separated into transmitted and reflected beams by the composite beam splitter group 8. The transmitted beam is used as the measurement beam, and the reflected beam is used as the reference beam. The measurement beam and the reference beam of one laser beam intersect at one half of the photosensitive element of the industrial camera 7, and the measurement beam and the reference beam of the other laser beam intersect at the other half of the photosensitive element of the industrial camera 7. This produces two interference spots with horizontal and vertical fringes. In the dual-camera mode, each spot is aligned with the center of the photosensitive element of the camera. Step 2: Divide the image data from industrial camera 7 into two images along the midpoint of the long axis. The two images are the interference spots formed by the two lasers. This step is not required when using a dual-camera design. Step 3: Convert the two interference fringe images into two-dimensional grayscale matrices respectively, accumulate each row and column of the matrix, and select the row and column with the largest amplitude as the decoupling data source. Step 4: Perform Discrete Fourier Transform on the row and column data with the largest amplitude, and then perform Gaussian peak fitting on the transformed data to obtain the spatial frequency values ​​of the row and column data. Step 5: Using the spatial frequency values ​​of the two interference fringe images, calculate their respective displacement, pitch angle, and yaw angle. Combined with the angle between the two laser beams, calculate the axial displacement Δ using the following formula. z Lateral displacement Δ y yaw angle Δ Pitch angle Δ and roll angle Δ Change data: ; ; ; ; ; in, and These represent the phase changes of the interference fringes for light beams one and two, respectively. and The horizontal and vertical components of the spatial frequency of the interference fringes produced by light beam number one. The vertical component of the spatial frequency of the interference fringes produced by the second beam. Where λ is the laser wavelength and n is the air refractive index. L0 is the angle between the two laser beams, L0 is the distance between the reflection points of the two laser beams on the composite measuring mirror, and the rest Δ represents the change of this value relative to the measurement.

[0024] This invention provides a five-dimensional precision measurement device based on the zero-difference wavefront interferometry principle and dual measurement beams, belonging to the field of precision geometric measurement technology, using laser wavelength as the traceability reference. Utilizing the zero-difference wavefront interferometry principle in a single interferometric probe, two probe lasers generate two wavefront interference spots. The spatial frequency and phase of their respective fringe images in the horizontal and vertical directions are calculated, and the results are decoupled to accurately measure the axial displacement, lateral displacement, pitch, yaw, and roll angle deviations of the measuring mirror. This invention's five-dimensional geometric measurement device enables single-principle integrated five-dimensional geometric measurement with high resolution, and the measurement results can be directly traced back to the laser wavelength, meeting the needs of high-end equipment for ultra-precise five-dimensional geometric measurement.

[0025] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Any modifications, alterations, substitutions, or variations made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention shall fall within the protection scope defined by the claims of the present invention.

Claims

1. A five-dimensional angle measurement method based on wavefront interference fringes, characterized in that, include: Step 1: The laser emitted by the single-frequency laser (10) is split into two beams. The two laser beams are split into corresponding transmitted light and reflected light by the composite beam splitter group (8). The transmitted light is used as the measurement light and the reflected light is used as the reference light. The measurement light and the reference light of one laser beam intersect at one half of the photosensitive element of the industrial camera (7), and the measurement light and the reference light of the other laser beam intersect at the other half of the photosensitive element of the industrial camera (7). Two interference spots with horizontal and vertical stripes are generated. Step 2: Divide the image data of the industrial camera (7) into two images along the midpoint of the long axis. The two images are the interference spots formed by the two lasers. Step 3: Convert the two interference fringe images into two-dimensional grayscale matrices respectively, accumulate each row and column of the matrix, and select the row and column with the largest amplitude as the decoupling data source. Step 4: Perform Discrete Fourier Transform on the row and column data with the largest amplitude, and then perform Gaussian peak fitting on the transformed data to obtain the spatial frequency values ​​of the row and column data. Step 5: Using the spatial frequency values ​​of the two interference fringe images, calculate their respective displacement, pitch angle, and yaw angle. Combined with the angle between the two laser beams, calculate the axial displacement Δ using the following formula. z Lateral displacement Δ y yaw angle Δ Pitch angle Δ and roll angle Δ Change data: ； ； ； ； ； in, and These represent the phase changes of the interference fringes for light beams one and two, respectively. and The horizontal and vertical components of the spatial frequency of the interference fringes produced by light beam number one. The vertical component of the spatial frequency of the interference fringes produced by the second beam. Where λ is the laser wavelength and n is the air refractive index. L0 is the angle between the two laser beams, L0 is the distance between the reflection points of the two laser beams on the composite measuring mirror, and the rest Δ represents the change of this value relative to the measurement.

2. A five-dimensional angle measuring device based on wavefront interference fringes, employing the five-dimensional angle measuring method described in claim 1, characterized in that, It includes a host computer (1), a laser beam splitter (2), an industrial camera (7), a composite beam splitter group (8), a composite measuring mirror (9), and a single-frequency laser (10). The laser emitted by the single-frequency laser (10) is split into two beams by the laser beam splitter (2). The two laser beams are then split into corresponding transmitted light and reflected light by the composite beam splitter group (8). The reflected light is used as the measurement light and the transmitted light is used as the reference light. After being reflected by the two reflective surfaces of the composite measuring mirror (9), the two measuring beams are transmitted through the beam-splitting surface inside the composite beam splitter group (8) to the photosensitive element of the industrial camera (7) and are received. After the two reference beams are reflected by the reflective surface of the composite beam splitter group (8), they are reflected by the beam splitting surface inside the composite beam splitter group (8) and received by the photosensitive element of the industrial camera (7). The industrial camera (7) is connected to the host computer (1).

3. A five-dimensional angle measuring device based on wavefront interference fringes according to claim 2, characterized in that: It also includes single-mode fiber (3), optical collimator No. 1 (4) and optical collimator No. 2 (5); The output end of the single-frequency laser (10) is connected to the laser beam splitter (2) through the single-mode optical fiber (3). The output end of the laser beam splitter (2) is connected to the first optical collimator (4) and the second optical collimator (5) through optical cables. The first optical collimator (4) and the second optical collimator (5) emit two laser beams that pass through the composite beam splitter group (8). The composite measurement mirror (9) is located behind the optical path of the composite beam splitter group (8).

4. A five-dimensional angle measuring device based on wavefront interference fringes according to claim 3, characterized in that: The composite measuring mirror (9) is V-shaped and includes two reflecting surfaces that are at an angle to each other; There is an angle between the first optical collimator (4) and the second optical collimator (5), so that the two laser beams emitted by them are respectively perpendicularly irradiated on the two emitting surfaces of the composite measuring mirror (9).

5. A five-dimensional angle measuring device based on wavefront interference fringes according to claim 2, characterized in that: One laser beam's measuring beam and reference beam intersect at one half of the industrial camera's (7) photosensitive element, while the other laser beam's measuring beam and reference beam intersect at the other half of the industrial camera's (7) photosensitive element, producing two interference spots with horizontal and vertical stripes.

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