Six-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 six-dimensional angle measurement device and method based on wavefront interference fringes. Three paths of detection laser are used for generating three wavefront interference light spots, spatial frequencies and phases of the light spots in the horizontal direction and the vertical direction are calculated respectively, and simultaneous decoupling is carried out to accurately measure six-degree-of-freedom information of axial displacement, longitudinal displacement, lateral displacement, pitching, deflection and rolling angles of the reflector. According to the six-degree-of-freedom measuring device, single-principle integrated six-degree-of-freedom 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 six-degree-of-freedom 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 six-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 require rapid and accurate measurement of 21 geometric errors. Six-degree-of-freedom measuring devices can accurately describe the spatial attitude changes of all six degrees of freedom of the measured object, significantly improving the efficiency of machine tool error compensation. They are widely used in fields such as lithography, aerospace control, and robot calibration.

[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 simultaneously and accurately measure all six degrees of freedom using a single measurement principle. For example, the RENISHAW XM-60 laser interferometer calibrator, based on both laser interferometry and position-sensitive sensors, achieves six-degree-of-freedom measurement. Its axial displacement measurement accuracy reaches ±0.5 μm / m, lateral displacement measurement accuracy is ±0.01A±1 μm, yaw and pitch angle measurements can achieve a measurement accuracy of ±0.004A±(0.5+0.11M) μrad within a ±500 μrad range, and roll angle measurement accuracy is ±0.01A±6.3 μrad (A is the measured value, M is the axial displacement). Commercial six-degree-of-freedom measurement systems, represented by this interferometer, generally employ multiple measurement principles and multiple sensors. They suffer from problems such as complex measurement principles, complex structures, lack of measurement references between different sensors, and difficulty in installing the interferometer, resulting in low measurement accuracy, low efficiency, and high cost.

[0004] To achieve high-precision six-degree-of-freedom measurement using a single instrument and a single measurement principle, several research institutions have proposed their own solutions. For example, Yan Liping and others from 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 and longitudinal displacement resolution of 0.75 μm, a roll angle measurement resolution of 2.94″, and a pitch and yaw angle resolution of 0.069″.

[0005] In summary, currently commercially available six-degree-of-freedom ultra-precision measurement systems generally require the integration of multiple sensors for multi-point measurements, resulting in complex measurement principles and inconsistent measurement standards. Furthermore, six-degree-of-freedom measurement schemes proposed by research institutions typically 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 measurement device capable of simultaneously measuring six degrees of freedom (axial displacement, longitudinal displacement, lateral displacement, pitch angle, yaw angle, and roll angle) using a single measurement principle. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a six-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 six-dimensional angle measuring device based on wavefront interference fringes includes a host computer, a 1-to-3 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 three beams by the laser beam splitter. The three laser beams are then split into corresponding transmitted and reflected beams by the composite beam splitter. The transmitted beam is used as the measurement beam and the reflected beam is used as the reference beam. The three measurement beams are reflected by the three reflective surfaces of the composite measurement mirror, and then reflected or transmitted through the beam-splitting surface inside the composite beam-splitting mirror group to the photosensitive element of the industrial camera for reception. The three reference beams are reflected by the reflective surface of the composite beam splitter group, and then transmitted or reflected by the beam splitter surface inside the composite beam splitter group to the photosensitive element of the industrial camera for reception. The industrial camera is connected to the host computer.

[0007] Furthermore, it also includes single-mode fiber, optical collimator No. 1, optical collimator No. 2, and optical collimator No. 3; The output of the single-frequency laser is connected to the three-way laser beam splitter via the single-mode optical fiber. The output of the three-way laser beam splitter is connected to the first optical collimator, the second optical collimator, and the third optical collimator via optical cables. The lasers emitted from the first, second, and third optical collimators pass through the composite beam splitter group. The composite measurement mirror is located at the rear end of the composite beam splitter group.

[0008] Furthermore, the composite measuring mirror includes three reflecting surfaces that are angled together; each of the three reflecting surfaces reflects the laser emitted by collimators No. 1, No. 2, and No. 3. There is an angle between optical collimators No. 1, No. 2 and No. 3.

[0009] Furthermore, the measurement and reference beams of the three lasers converge at different positions on the sensor of the industrial camera, generating three interference spots with horizontal and vertical fringes.

[0010] A six-dimensional angle measurement method based on wavefront interference fringes includes: Step 1: Based on the positions of the three interference spots in the industrial camera's photosensitive element, the industrial camera image data is divided into three images, and the three images respectively receive interference spots formed by three laser beams; Step 2: Convert each of the three interference fringe images into a two-dimensional grayscale matrix, 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 three interference fringe images, calculate the displacement, pitch angle, and yaw angle of each image. Combine this with the angle between the three laser beams, and calculate the axial displacement Δ using the following formula. z Longitudinal displacement Δ x Lateral displacement Δ y yaw angle Δ Pitch angle Δ Roll angle Δ Change data: ; ; ; ; ; ; in, , and These represent the phases of the interference fringes for light beams one, two, and three, 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. The vertical component of the spatial frequency of the interference fringes produced by light beam number three. Where λ is the laser wavelength and n is the air refractive index. The angle between the first and second laser beams. The angle between the first and third laser beams. L 2 represents the distance between the two reflection points of the first and second laser beams on the composite measuring mirror. L3 represents the distance between the two reflection points of the first and third laser beams on the composite measuring mirror, and Δ indicates that this quantity is a relative change.

[0011] The present invention has the following beneficial effects: (1) The six-degree-of-freedom geometric measurement device of the present invention is based entirely on the principle of laser interferometry and can simultaneously measure six degrees of freedom information, including axial displacement, longitudinal 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 six degrees of freedom information using only a single single-principle integrated probe, and there is no problem of inconsistent benchmark caused by the use of multiple sensors and multiple measurement principles; (3) The device of the present invention utilizes three laser beams combined with a specially structured composite measuring reflector and a composite beam splitter group, 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 three detection lasers, making it convenient to use and saving costs. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the three-dimensional angle measuring device of the present invention; Figure 2 This is a schematic diagram of the interference optical path and compound mirror group of the six-degree-of-freedom measurement device of the present invention; In the diagram: 1. Host computer, 2. Optical collimator No. 1, 3. One-to-three laser beam splitter, 4. Single-mode fiber, 5. Optical collimator No. 2, 6. Optical collimator No. 3, 7. Industrial camera, 8. Composite beam splitter group, 9. Integrated sensor base, 10. Composite reflector, 11. Single-frequency laser. Detailed Implementation

[0013] The following will be based on embodiments of the present invention. Figures 1-2 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.

[0014] A six-dimensional angle measuring device based on wavefront interference fringes includes a host computer 1, a one-to-three laser beam splitter 3, an industrial camera 7, a composite beam splitter group 8, a composite measuring mirror 10, and a single-frequency laser 11. The laser emitted by the single-frequency laser 11 is split into three beams by the laser beam splitter 3. The three 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. The three measurement beams are reflected by the three reflective surfaces of the composite measurement mirror 10, and then reflected or transmitted by the beam-splitting surface inside the composite beam splitter group 8 to the photosensitive element of the industrial camera 7 for reception. The three reference beams are reflected by the reflective surface of the composite beam splitter group 8, and then transmitted or reflected by the beam splitter 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.

[0015] Furthermore, it also includes single-mode fiber 4, optical collimator 2 (number one), optical collimator 5 (number two), and optical collimator 6 (number three). The output of the single-frequency laser 11 is connected to the three-way laser beam splitter 3 via the single-mode fiber 4. The output of the three-way laser beam splitter 3 is connected to the first optical collimator 2, the second optical collimator 5, and the third optical collimator 6 via optical cables. The lasers emitted by the first, second, and third optical collimators pass through the composite beam splitter group 8. The composite measurement mirror 10 is located at the rear end of the composite beam splitter group 8.

[0016] Furthermore, the composite measuring mirror 10 includes three reflecting surfaces that are angled together; each of the three reflecting surfaces reflects the laser emitted by the first, second, and third optical collimators. There is an angle between optical collimators No. 1, No. 2 and No. 3.

[0017] Furthermore, the measurement beam and reference beam of the three laser beams converge at different positions of the photosensitive element of the industrial camera 8, generating three interference spots with horizontal and vertical stripes.

[0018] The compound beam splitter assembly 8 integrates a beam-splitting surface and three reflecting surfaces, such as... Figure 2As shown, its appearance resembles a beam-splitting cube, constructed by bonding a right-angle prism to a special prism. The bonded surface is coated with a 50:50 beam-splitting film. The special prism is a further processed right-angle prism. On one of its square faces, angles are cut along the pitch and yaw directions, with the horizontal and vertical midlines of the square as axes, transforming the original plane into a frustum with two trapezoidal faces and one rectangular face. These three faces are coated with reflective films, while the remaining square faces of the composite mirror assembly are coated with anti-reflective films. The beam-splitting surface splits the three probe lasers into measurement and reference beams. The three reference beams are reflected back to the beam-splitting surface at the reflective surface inside the composite beam-splitting mirror assembly 8, and the three measurement beams are reflected back to the beam-splitting surface at the composite measurement reflector 10. The three reference reflective surfaces are not perpendicular to their respective reference beams, ensuring that the measurement and reference beams are non-coaxially transmitted in the output path. The interior of the composite beam-splitting mirror assembly 8 can be considered as a combination of a beam-splitting mirror and three measurement reflectors. The three reference reflecting surfaces are not perfectly perpendicular to the incident reference beam, causing a slight angular deviation in the optical axis pointing between the measuring light and the reference light, forming a striped interference image signal that can be effectively detected by the photosensitive element.

[0019] The composite measuring mirror 10 has three reflecting surfaces. The upper reflecting surface and the central reflecting surface have a pitch angle, and the right reflecting surface and the central reflecting surface have a yaw angle, each reflecting three beams of reference light.

[0020] The first, second, and third optical collimators are arranged orthogonally and fixed to the integrated sensing base 9 using a fixture. This fixture has the ability to adjust forward and backward and fine-tune the attitude angle. The industrial camera 7 and the composite beam splitter group 8 are directly fixed to the integrated sensing base 9. The composite measuring mirror 10 has three reflecting surfaces with a certain angle, which can reflect the first measuring light, the second measuring light, and the third measuring light respectively. During measurement, the composite measuring mirror is fixed to the object to be measured.

[0021] like Figure 2As shown, this is one optical path arrangement mode of the six-degree-of-freedom measurement device. Its working principle is as follows: A 633nm helium-neon single-frequency laser 11 provides a frequency-stabilized laser, which is transmitted through a single-mode fiber 4 to a three-way laser beam splitter 3, splitting it into three laser beams with equal frequency and consistent intensity, named beam 1, beam 2, and beam 3. Collimators of beams 1, 2, and 3 output collimated lasers, respectively. The laser emission directions of the three collimators have a certain angle, which is consistent with the angle between the corresponding reflective surfaces of the composite measurement mirror 10. After passing through the composite beam splitter group 8, the three laser beams are split into their respective measurement beams and reference beams. The three measurement beams are reflected by the three reflective surfaces of the composite measurement mirror 10 and return to the composite beam splitter group 8. After reflection (or transmission) by the beam splitter surface of the mirror, they are received by the photosensitive element of the industrial camera 7. The three reference beams are reflected at the three reference reflective surfaces inside the composite beam splitter group 8. After transmission (or reflection) by the beam splitter surface of the mirror, they are received by the photosensitive element of the industrial camera 7. Whether they are transmitted or reflected at the beam splitter surface depends on the arrangement of the optical path. The angle between the reference reflective surfaces inside the composite beam splitter group 8 is consistent with the angle between the three reflective surfaces of the composite measurement mirror 10. The geometric positions of the three optical collimators and the composite beam splitter group 8 are finely adjusted so that the measurement beams and reference beams of the three probe lasers converge at the lower left, lower right, and upper sides of the photosensitive element of the industrial camera 7, forming three interference fringes.

[0022] After receiving the interference image information of three light spots, the industrial camera 7 uploads it to the host computer program. The host computer uses an image decoupling algorithm to decouple the six degrees of freedom data.

[0023] A six-dimensional angle measurement method based on wavefront interference fringes includes: Step 1: Based on the positions of the three interference spots in the photosensitive element of the industrial camera 7, the image data of the industrial camera 7 is divided into three images, and the three images respectively receive interference spots formed by the three lasers; Step 2: Convert each of the three interference fringe images into a two-dimensional grayscale matrix, 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 three interference fringe images, calculate the displacement, pitch angle, and yaw angle of each image. Combine this with the angle between the three laser beams, and calculate the axial displacement Δ using the following formula. z Longitudinal displacement Δ x Lateral displacement Δ y yaw angle Δ Pitch angle Δ Roll angle Δ Change data: ; ; ; ; ; ; in, , and These represent the phases of the interference fringes for light beams one, two, and three, 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. The vertical component of the spatial frequency of the interference fringes produced by light beam number three. Where λ is the laser wavelength and n is the air refractive index. 2 represents the angle between the first and second laser beams. 3 represents the angle between the first and third laser beams. L 2 represents the distance between the two reflection points of the first and second laser beams on the composite measuring mirror. L 3 represents the distance between the two reflection points of the first and third laser beams on the composite measuring mirror, and Δ indicates that this quantity is a relative change.

[0024] This invention uses laser wavelength as the traceability reference. Utilizing the zero-difference wavefront interferometry principle in a single interferometric probe, three wavefront interference spots are generated using three probe lasers. The spatial frequency and phase of each spot's fringe image in the horizontal and vertical directions are calculated separately. These are then decoupled to accurately measure the six degrees of freedom (6 degrees of freedom) of the measuring mirror: axial displacement, longitudinal displacement, lateral displacement, pitch, yaw, and roll angles. This invention's six-degree-of-freedom measuring device enables single-principle integrated six-degree-of-freedom geometric measurement with high resolution. The measurement results are directly traceable to the laser wavelength, meeting the requirements of high-end equipment for ultra-precise six-degree-of-freedom geometric measurement. 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 six-dimensional angle measuring device based on wavefront interference fringes, characterized in that, It includes a host computer (1), a 1-to-3 laser beam splitter (3), an industrial camera (8), a composite beam splitter group (9), a composite measuring mirror (10), and a single-frequency laser (11). The laser emitted by the single-frequency laser (11) is split into three beams by the laser beam splitter (3), and the three laser beams are split into corresponding transmitted light and reflected light by the composite beam splitter group (9), wherein the transmitted light and reflected light are used as measurement light and reference light, respectively. The three measurement beams are reflected by the three reflective surfaces of the composite measurement mirror (10), and then reflected or transmitted through the beam-splitting surface inside the composite beam splitter group (9) to the photosensitive element of the industrial camera (8) for reception. The three reference beams are reflected by the reflective surface of the composite beam splitter group (9), and then transmitted or reflected by the beam splitter surface inside the composite beam splitter group (9) to the photosensitive element of the industrial camera (8) for reception. The industrial camera (8) is connected to the host computer (1).

2. The six-dimensional angle measuring device based on wavefront interference fringes according to claim 1, characterized in that: It also includes single-mode fiber (4), optical collimator No. 1 (2), optical collimator No. 2 (5) and optical collimator No. 3 (6); The output end of the single-frequency laser (11) is connected to the three-way laser beam splitter (3) through the single-mode optical fiber (4). The output end of the three-way laser beam splitter (3) is connected to the first optical collimator (2), the second optical collimator (5), and the third optical collimator (6) through optical cables. The lasers emitted by the first, second, and third optical collimators pass through the composite beam splitter group (9). The composite measurement mirror (10) is located at the rear end of the composite beam splitter group (9).

3. A six-dimensional angle measuring device based on wavefront interference fringes according to claim 2, characterized in that: The composite measuring mirror (10) includes three reflective surfaces that are angled together; each of the three reflective surfaces reflects the laser emitted by collimators No. 1, No. 2 and No. 3 respectively. There is an angle between optical collimators No. 1, No. 2 and No.

3.

4. A six-dimensional angle measuring device based on wavefront interference fringes according to claim 1, characterized in that: The measurement beam and reference beam of the three laser beams converge at different positions of the photosensitive element of the industrial camera (8); generating three interference spots with horizontal and vertical stripes.

5. A six-dimensional angle measurement method based on wavefront interference fringes, applied to the six-dimensional angle measurement device of claim 4, characterized in that, include: Step 1: Based on the positions of the three interference spots in the photosensitive element of the industrial camera (8), the image data of the industrial camera (8) is divided into three images, and the three images receive interference spots formed by the three lasers respectively; Step 2: Convert each of the three interference fringe images into a two-dimensional grayscale matrix, 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 three interference fringe images, calculate the displacement, pitch angle, and yaw angle of each image. Combine this with the angle between the three laser beams, and calculate the axial displacement Δ using the following formula. z Longitudinal displacement Δ x Lateral displacement Δ y yaw angle Δ Pitch angle Δ Roll angle Δ Change data: ； ； ； ； ； ； in, , and These represent the phases of the interference fringes for light beams one, two, and three, 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. 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. 2 represents the angle between the first and second laser beams. L3 is the angle between the first and third laser beams, L2 is the distance between the two reflection points of the first and second laser beams on the composite measuring mirror, L3 is the distance between the two reflection points of the first and third laser beams on the composite measuring mirror, and Δ indicates that this quantity is a relative change.

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