Three-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 three-dimensional angle measurement device and method based on wavefront interference fringes. According to the invention, two wavefront interference light spots are generated by using two paths of detection laser in a single interference measuring head with only a single coordinate reference, the spatial frequencies of respective fringe images in the horizontal and vertical directions are respectively calculated, and simultaneous decoupling is carried out so as to accurately measure the pitching, deflection and rolling angle deviations of the reflector. According to the three-dimensional angle measurement device, point-to-point three-dimensional angle 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 three-dimensional angle measurement is met.

Description

Technical Field

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

[0002] To monitor the installation accuracy and structural deformation of the measuring instruments mounted on a satellite during operation, it is necessary to use a single coordinate reference measuring instrument to simultaneously measure the three-dimensional changes in its pitch, yaw, and roll angles point-to-point. As the measurement resolution of spaceborne measuring instruments approaches the microradian level, the devices for monitoring their deformation also need to achieve microradian-level resolution.

[0003] Laser goniometers utilize the interference and diffraction phenomena of lasers to measure extremely minute angular changes. They possess advantages such as high measurement resolution, a large measurement range, non-contact measurement capabilities, and a simple overall structure, making them widely used in ultra-precision angle measurement. However, none of the commercially available laser goniometers currently available can simultaneously measure three-dimensional angle information using a single measurement principle. For example, the SIOS SP 15000 C6 NG calibration laser interferometer, based on both laser interferometry and electronic level principles, achieves six-dimensional measurement. Its yaw or pitch angle measurement accuracy reaches ±0.04% ±0.04 μrad, and its roll angle measurement accuracy is ±2.4 μrad ±1.5%. However, this angle measurement system cannot measure pitch and yaw angles simultaneously; the probe must be rotated and measured step-by-step. Furthermore, the roll angle measurement principle differs from the other two angles, resulting in measurements of angle information from different points, making it difficult to achieve single-target angle information measurement. Commercial goniometers, 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 difficulty in installing the interferometer. Consequently, they suffer from low measurement accuracy, low efficiency, and high cost.

[0004] To achieve high-precision three-dimensional angle measurement with a single instrument, several research institutions have proposed their own solutions. For example, National Cheng Kung University in Taiwan proposed a six-degree-of-freedom measurement system using a double-plane mirror and a corner pyramid as reflectors. Although the method has a simple structure, due to the limitations of its measurement principle, the angle measurement results are affected not only by beam drift but also by the coupling errors of other geometric quantities, resulting in low repeatability of angle measurement. The repeatability of yaw angle, pitch angle, and rotation angle measurements are 18.5″, 5.86″, and 3.91″, respectively.

[0005] For example, Guo Yan et al. from Beijing Institute of Technology designed a novel combined target autocollimator that can simultaneously measure three-dimensional angles. The measurement accuracy of this method for pitch, yaw, and rotation angles is better than 0.67″, 0.70″, and 0.74″, respectively, within a measurement range of ±200″. This method uses optical magnification to improve the measurement resolution of the rotation angle. However, while magnifying the spot displacement, this method also magnifies the beam drift, increasing the instability of the system. Furthermore, the changes in pitch and rotation angles cause the spot displacement received by the detector to be in the same direction, resulting in mutual limitations on the measurement range of these two dimensions.

[0006] In summary, most commercially available laser goniometers currently available have relatively limited functionality, restricting measurements to only one or two angular dimensions. Furthermore, they suffer from inconsistent reference standards in three-dimensional angle measurements. Single-reference three-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 a highly integrated three-dimensional angle measurement device capable of simultaneously measuring pitch, yaw, and roll angles using a single measurement reference. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a three-dimensional angle measurement 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 three-dimensional angle measuring device based on wavefront interference fringes includes a host computer, a laser beam splitter, an industrial camera, a composite beam splitter assembly, 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 transmitted light is used as the measurement light and the reflected light is used as the reference light. After being reflected by the two reflecting surfaces of the composite measuring mirror, the two measuring beams are reflected by the beam-splitting surface inside the composite beam splitter group and received by the photosensitive element of the industrial camera. After being reflected by the reflective surface of the composite beam splitter group, the two reference 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. The industrial camera is connected to the host computer.

[0008] 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.

[0009] Furthermore, the composite measuring mirror is V-shaped, with both its front and back surfaces coated, each including two reflective surfaces that form an angle with each other, one set folded inwards and the other set folded outwards; 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.

[0010] 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.

[0011] A three-dimensional angle measurement method based on wavefront interference fringes includes: Step 1: 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 2: 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 3: 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 four: Using the spatial frequency values ​​of the two interference fringe images, calculate their respective displacement, elevation, and yaw angles. Combined with the angle between the two laser beams, calculate the yaw angle Δ using the following formula. Pitch angle Δ and roll angle Δ Change data: ; ; ; in, and The horizontal and vertical components of the spatial frequency of the interference fringes generated by laser number one. The vertical component of the spatial frequency of the interference fringes generated by the second laser. The wavelength of the laser. n The refractive index of air, The angle between the two laser beams is Δ, which indicates that the quantity is a relative change.

[0012] The present invention has the following beneficial effects: (1) The three-dimensional angle measuring device of the present invention is based entirely on the principle of laser interferometry. It can simultaneously measure three-dimensional angles of pitch, yaw and roll, with 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 three-dimensional angle information using only a single coordinate reference, and there is no problem of inconsistent reference caused by the use of multiple principles or discrete components for measurement. (3) The device of the present invention utilizes a composite beam splitter group combined with a V-shaped composite measuring mirror with a special structure, which makes the entire instrument structure simple and easy to arrange and 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 Single-frequency laser, 2 First optical collimator, 3 Laser beam splitter, 4 Single-mode fiber, 5 Second optical collimator, 6 Host computer, 7 Integrated sensor base, 8 Composite beam splitter group, 9 Composite measuring mirror, 10 Industrial camera. 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 three-dimensional angle measuring device based on wavefront interference fringes includes a single-frequency laser 1, a laser beam splitter 3, a host computer 6, a composite beam splitter group 8, a composite measuring mirror 9, and an industrial camera 10. The laser emitted by the single-frequency laser 1 is split into two beams by the laser beam splitter 3. The two laser beams are then 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. After being reflected by the two reflective surfaces of the composite measuring mirror 9, the two measuring beams are reflected by the beam-splitting surface inside the composite beam splitter group 8 and received by the photosensitive element of the industrial camera 10. After being reflected by the reflective surface of the composite beam splitter group 8, the two reference beams are transmitted through the beam splitting surface inside the composite beam splitter group 8 to the photosensitive element of the industrial camera 10 and are received. The industrial camera 10 is connected to the host computer 6.

[0016] Furthermore, it also includes optical collimator 2, single-mode fiber 4, and optical collimator 5; The output end of the single-frequency laser 1 is connected to the laser beam splitter 3 through the single-mode optical fiber 4. The output end of the laser beam splitter 3 is connected to the first optical collimator 2 and the second optical collimator 5 through optical cables. The first optical collimator 2 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] The composite beam splitter assembly 8 integrates a beam splitting surface and two reflective surfaces. Its appearance is similar to a beam splitting cube. It is made by bonding a right-angle prism with a special prism. The bonding surface is coated with a 50:50 beam splitting film. The special prism is made by further processing the right-angle prism. A glass wedge is bonded to one of its square faces, turning the original plane into a concave V-shaped surface. This V-shaped surface is coated with a reflective film, and the remaining square faces of the composite beam splitter assembly are coated with an anti-reflective film.

[0018] Furthermore, the composite measuring reflector 9 is V-shaped, with both its front and back surfaces coated. Each surface includes two reflective surfaces at an angle to each other, one set folded inwards and the other folded outwards. The outward-folded reflective surface is suitable for measuring closer distances, while the inward-folded reflective surface is suitable for measuring farther objects. Figure 1 The image shows a case where the outward-facing reflective surface is used and the object being measured is relatively close. There is an angle between the first optical collimator 2 and the second optical collimator 5, so that the two laser beams emitted by them respectively irradiate the two emitting surfaces of the composite measuring mirror 9 perpendicularly.

[0019] Furthermore, the measuring beam and reference beam of one laser intersect at one half of the photosensitive element of the industrial camera 10, and the measuring beam and reference beam of the other laser intersect at the other half of the photosensitive element of the industrial camera 10, thus generating two interference spots with horizontal and vertical fringes.

[0020] The two lasers are designated as Laser No. 1 and Laser No. 2. Two fiber collimators are fixed to the integrated sensing base 7 using a fixture, which has the ability to adjust forward and backward and fine-tune the three-dimensional attitude angle. The industrial camera 10 and the composite beam splitter group 8 are directly fixed to the integrated sensing base 7. 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, the working principle of the five-dimensional measurement device is as follows: A 633nm helium-neon single-frequency laser 1 provides a frequency-stabilized laser signal, which is transmitted through a single-mode fiber 4 to a laser beam splitter 3 and split into two laser beams with equal frequency and consistent intensity, named Laser No. 1 and Laser No. 2. The collimated lasers are output through collimators No. 1 and No. 2, respectively. There is a certain sway angle between the laser output directions of the two fiber collimators, which is consistent with the angle between the two reflecting 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 reflected by the two reflecting surfaces of the composite measurement 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 10. 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 transmission through the beam-splitting surface, they are received by the photosensitive element of the industrial camera 10. The angle between the two reference reflecting surfaces is almost identical to the angle between the two reflecting surfaces of the composite measurement 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 converge at the same position on the left half of the photosensitive element of the industrial camera 10, and the measurement beam and reference beam of the second laser converge at the same position on the right half of the photosensitive element of the industrial camera 10. This produces two interference spots with horizontal and vertical fringes.

[0022] After receiving the dual-spot interference image information, the industrial camera 10 uploads it to the host computer 6 program. The host computer 6 uses an image decoupling algorithm to decouple the three-dimensional angle data.

[0023] A three-dimensional angle measurement method based on wavefront interference fringes includes: Step 1: Divide the image data of the industrial camera 10 into two images along the midpoint of the long axis. The two images are the interference spots formed by the two lasers. Step 2: 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 3: 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 four: Using the spatial frequency values ​​of the two interference fringe images, calculate their respective displacement, elevation, and yaw angles. Combined with the angle between the two laser beams, calculate the yaw angle Δ using the following formula. Pitch angle Δ and roll angle Δ Change data: ; ; ; in, and The horizontal and vertical components of the spatial frequency of the interference fringes generated by laser number one. The vertical component of the spatial frequency of the interference fringes generated by the second laser. The wavelength of the laser. n The refractive index of air, The angle between the two laser beams is Δ, which indicates that the quantity is a relative change.

[0024] This invention utilizes two probe lasers to generate two wavefront interference spots in a single interferometric probe with only a single coordinate reference. The spatial frequencies of their respective fringe images in the horizontal and vertical directions are calculated, and the results are decoupled to accurately measure the pitch, yaw, and roll angle deviations of the measuring mirror. The three-dimensional angle measuring device of this invention can achieve point-to-point three-dimensional angle 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 three-dimensional angle 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 three-dimensional angle measuring device based on wavefront interference fringes, characterized in that, It includes a single-frequency laser (1), a laser beam splitter (3), a host computer (6), a composite beam splitter group (8), a composite measuring mirror (9), and an industrial camera (10). The laser emitted by the single-frequency laser (1) is split into two beams by the laser beam splitter (3). The two laser beams are then 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. After being reflected by the two reflective surfaces of the composite measuring mirror (9), the two measuring beams are reflected by the beam-splitting surface inside the composite beam splitter group (8) and received by the photosensitive element of the industrial camera (10). After being reflected by the reflective surface of the composite beam splitter group (8), the two reference beams are transmitted through the beam splitting surface inside the composite beam splitter group (8) to the photosensitive element of the industrial camera (10) and are received. The industrial camera (10) is connected to the host computer (6).

2. The three-dimensional angle measuring device based on wavefront interference fringes according to claim 1, characterized in that: It also includes optical collimator No. 1 (2), single-mode fiber (4) and optical collimator No. 2 (5); The output end of the single-frequency laser (1) is connected to the laser beam splitter (3) through the single-mode optical fiber (4), and the output end of the laser beam splitter (3) is connected to the first optical collimator (2) and the second optical collimator (5) through optical cables respectively; the first optical collimator (2) 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).

3. A three-dimensional angle measuring device based on wavefront interference fringes according to claim 2, characterized in that: The composite measuring mirror (9) is "V" shaped, with both its front and back surfaces coated, each including two reflective surfaces that form an angle with each other; There is an angle between the first optical collimator (2) 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).

4. A three-dimensional angle measuring device based on wavefront interference fringes according to claim 1, characterized in that: One laser beam's measuring beam and reference beam intersect at one half of the industrial camera (10)'s photosensitive element, while the other laser beam's measuring beam and reference beam intersect at the other half of the industrial camera (10)'s photosensitive element, generating two interference spots with horizontal and vertical stripes.

5. A three-dimensional angle measurement method based on wavefront interference fringes, applied to the three-dimensional angle measurement device of claim 4, characterized in that, include: Step 1: Divide the image data of the industrial camera (10) into two images along the midpoint of the long axis. The two images are the interference spots formed by the two lasers. Step 2: 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 3: 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 four: Using the spatial frequency values ​​of the two interference fringe images, calculate their respective displacement, elevation, and yaw angles. Combined with the angle between the two laser beams, calculate the yaw angle Δ using the following formula. Pitch angle Δ and roll angle Δ Change data: ； ； ； in, and The horizontal and vertical components of the spatial frequency of the interference fringes generated by laser number one. The vertical component of the spatial frequency of the interference fringes generated by the second laser. The wavelength of the laser. n The refractive index of air, The angle between the two laser beams is Δ, which indicates that the quantity is a relative change.

Images