A micro-angle measurement device and method based on local interference fringes

Abstract

A kind of micro angle measurement device and method based on local interference fringe, belong to the field of precision optical assembly and detection technology, including lens to be installed, resonant cavity, clamping assembly, resonant cavity mounting seat, single-mode laser light source, optical fiber, autocollimator, light splitting component, reflective image mirror, imaging assembly and image acquisition component, single-mode laser light source is transmitted to autocollimator by optical fiber, autocollimator exports parallel light, is irradiated to the film gap formed between lens to be installed and resonant cavity mounting surface by light splitting component and reflective image mirror, local interference fringe image is collected by imaging assembly and image acquisition component after being turned over by reflective image mirror, and is transmitted to external data processing component to carry out angle resolution.The present application can realize the non-contact measurement of local interference fringe under the condition of clamping obstruction and narrow space, and complete two-axis micro angle deviation detection, suitable for online detection and attitude adjustment in the process of precision optical element mounting.

Description

Technical Field

[0001] This invention belongs to the field of precision optical assembly and testing technology, and relates to a device and method for measuring small angles based on local interference fringes. Background Technology

[0002] In the assembly of precision optical components, the minute angle between the lens mounting surface and the mounting base directly affects the mounting accuracy and subsequent optical performance. Therefore, it is necessary to accurately measure this minute angle. Especially in high-precision mounting scenarios, even a slight orientation deviation between the lens and the mounting base can easily lead to the accumulation of mounting errors, thereby affecting assembly consistency and device stability. Therefore, it is essential to detect minute angular deviations during the mounting process.

[0003] In the prior art, there are already schemes for angle measurement using interferometry. For example, Chinese invention patent CN113607091A discloses an optical measurement system and method for the angle between the optical axis of an off-axis aspherical mirror and its mounting surface. This scheme uses optical components such as an interferometer, a parallel flat mirror, and a compensator to measure the angle between the optical axis of the off-axis aspherical mirror and its mounting surface. Another example is Chinese invention patent CN103791858A, which discloses a common-path laser interferometer device and measurement method for small-angle measurements. This scheme employs a common-path laser interferometer structure and measures small-angle parameters of the target through a glass plate, a corner prism, and the internal optical path system of the interferometer.

[0004] The aforementioned prior art demonstrates that it is feasible to measure angle-related parameters using interferometric methods, but there are still shortcomings: On the one hand, Chinese invention patent CN113607091A mainly targets the measurement of the angle between the optical axis of an off-axis aspherical mirror and the mounting surface. Its measurement object and application scenario are different from the annular thin film gap formed during the lens mounting process, and it does not measure the local interference fringes between the lens and the base surface in the mounting station; on the other hand, Chinese invention patent CN103791858A mainly targets general small angle measurements. Its solution does not consider the local occlusion of the annular mounting area by the clamping structure during the mounting process, nor does it consider the situation where the space below the area to be measured is narrow and the imaging device is difficult to place directly.

[0005] Therefore, existing technologies still have shortcomings in terms of localized stripe visibility, imaging in confined spaces, and online measurement during the mounting process. It is necessary to provide a new device and method for measuring minute angles to solve the above problems. Summary of the Invention

[0006] To address the problem that existing technologies struggle to perform in-situ, non-contact, and high-precision measurement of minute angular deviations between the lens to be mounted and the resonant cavity during the mounting process of precision optical components, especially under clamping, obstruction, and confined space conditions, this invention provides a device and method for measuring minute angles based on local interference fringes. This invention uses a reflective imaging mirror positioned below the area to be measured to extract the image of the local interference fringes from the confined space. This image is then acquired by an external imaging and image acquisition component, and the fringe features are analyzed by an external data processing component. This achieves biaxial measurement of minute angular deviations of the lens to be mounted relative to the resonant mounting base 17, solving the following technical problems: Firstly, during the actual mounting process, the lens to be mounted is usually held and positioned by a clamping assembly. This clamping assembly obscures a portion of the annular mounting surface around the lens, thus preventing the acquisition of a complete annular interference fringe. Only local interference fringes corresponding to the unobstructed portion can be obtained. Existing measurement schemes that rely on complete fringe images are poorly applicable under these conditions.

[0007] Secondly, the mounting area of ​​the lens to be mounted and the resonant cavity is located inside the mounting station, and the space below it is narrow, making it difficult to place the lens and camera directly below the area to be tested. The conventional method of direct imaging from bottom to top is difficult to achieve. Therefore, an optical structure that can extract the fringe image in a narrow space is needed.

[0008] Third, both the lens to be mounted and the resonant cavity are transparent microcrystalline glass components, and a thin film gap will be formed between the annular mounting surface of the lens to be mounted and the mounting base surface of the resonant cavity. The thickness distribution of this thin film gap is related to the attitude deviation of the lens to be mounted relative to the resonant cavity. Therefore, it is necessary to establish a device that can utilize the local interference fringes formed by this thin film gap to measure the biaxial micro-tilt angle of the lens to be mounted relative to the mounting base surface of the resonant cavity.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A micro-angle measuring device based on local interference fringes, comprising a lens to be mounted, a resonant cavity, a clamping assembly, a resonant cavity mounting base, a single-mode laser source, an optical fiber, an autocollimator, a beam splitter, a reflective image guide, a light source adjustment base, an imaging assembly, an image acquisition assembly, a thin-film gap, a moving platform, and a lens mounting bracket. Specifically: The lens to be mounted is a transparent optical component, comprising a central reflecting surface in the middle and an annular mounting surface surrounding the central reflecting surface. The central reflecting surface is the reflective region in the middle of the lens to be mounted, and the annular mounting surface is the annular surface on the outer periphery of the lens to be mounted for bonding and connection with the resonant cavity. The resonant cavity is a transparent optical component that is mounted and fitted with the lens to be mounted, and the bottom of the resonant cavity has a mounting base surface corresponding to the lens to be mounted.

[0010] Before the lens to be mounted is fully attached to the resonant cavity, a thin-film gap is formed between the annular mounting surface of the lens and the mounting base surface of the resonant cavity. This thin-film gap is the test area where interference fringes are generated in this invention. Because the lens to be mounted may undergo slight rotations relative to the resonant cavity in different directions, the thickness of the thin-film gap between the annular mounting surface of the lens and the mounting base surface of the resonant cavity is not completely uniform at different spatial locations, but rather varies continuously along one or more directions. When parallel detection light illuminates the test area, reflection and interference occur between the annular mounting surface of the lens and the mounting base surface of the resonant cavity, thus forming interference fringes.

[0011] The clamping assembly is mounted on a moving platform to clamp the lens to be mounted and deliver it to the mounting position in the resonant cavity. The reflecting mirror is mounted on a lens mounting bracket, which in turn is mounted on the moving platform. The moving platform is used to adjust the positions of the clamping assembly, the lens to be mounted, the lens mounting bracket, and the reflecting mirror relative to the resonant cavity. The clamping assembly is located on the periphery and underside of the lens to be mounted, providing support and clamping fixation. Because the clamping assembly is located near the detection path of the annular mounting surface, it obstructs a portion of the annular mounting surface when clamping the lens, preventing the formation of effective interference fringes in this area. The interference fringe image from the obstructed area cannot pass through the reflecting mirror and beam splitter to enter the imaging and image acquisition components. Therefore, the image acquisition component cannot acquire a complete annular interference fringe image, but only a local interference fringe image corresponding to the area not obstructed by the clamping assembly. A key technical point of this invention is that it does not require the acquisition of a complete annular interference fringe, but allows the acquisition of only local interference fringes and angle measurement under the obstruction condition of the clamping assembly.

[0012] The resonant cavity mounting base is used to support and fix the resonant cavity. Its bottom is installed on the measurement platform or mounting platform as the mounting base of the resonant cavity, so that the resonant cavity remains in a stable position during the measurement process.

[0013] The single-mode laser source is used to generate the detection laser. The detection laser output from the single-mode laser source is transmitted to an autocollimator via optical fiber. The autocollimator organizes the detection laser transmitted through the optical fiber into parallel detection light and outputs this parallel detection light as the incident light in the subsequent measurement optical path. The light source adjustment mount is used to install the autocollimator and adjust its position and orientation so that the parallel detection light output by the autocollimator can enter the beam splitter in a predetermined direction. The purpose of using a single-mode laser source in this invention is to ensure that the detection light has good coherence; using optical fiber to transmit the detection light is beneficial for separating the light source and the measurement head; and using an autocollimator to output parallel detection light is beneficial for improving the consistency and stability of subsequent interference illumination.

[0014] The beam splitter is positioned between the autocollimator and the imaging component to convert the illumination optical path and the imaging optical path. The imaging component is connected to the image acquisition component, which acquires the local interference fringe image formed by the imaging component. The local interference fringe image is transmitted to an external data processing component for processing to obtain the X-axis tilt angle and Y-axis tilt angle of the lens to be installed relative to the resonant cavity.

[0015] Furthermore, the autocollimator and imaging component are respectively arranged on different optical path sides of the beam splitter. The autocollimator is mounted on the light source adjustment seat and is used to output parallel detection light to the beam splitter. The imaging component and image acquisition component are mounted on the imaging adjustment seat and located on the imaging output side of the beam splitter, used to receive the local interference fringe image refracted and extracted by the reflecting mirror and the beam splitter. Specifically, the beam splitter has a dual function: on the one hand, the beam splitter guides the parallel detection light from the autocollimator to the test area formed by the thin film gap; on the other hand, the beam splitter guides the fringe image returned from the test area to the imaging component. The beam splitter adjustment seat 11 is used to install the beam splitter and adjust the position and orientation of the beam splitter to ensure that the parallel detection light and the returned imaging light path meet the predetermined optical path relationship.

[0016] Furthermore, the reflective imaging mirror is positioned in the space below the area to be tested. Its reflective surface receives interference fringe images from a localized area of ​​the annular mounting surface and refracts these images into the imaging acquisition optical path of the beam splitter and imaging components. A lens mounting bracket supports and fixes the reflective imaging mirror, ensuring it is positioned at a predetermined location below the area to be tested, thus enabling the refracting and extraction of the localized interference fringe images. The primary function of the reflective imaging mirror is to induce an image, not to generate interference. Because the space below the thin-film gap formed between the annular mounting surface of the lens to be mounted and the mounting base surface of the resonant cavity is narrow, making it difficult to directly mount the lens and camera directly below, this invention arranges a reflective imaging mirror within the limited space below the area to be tested. This refracts the parallel detection light and interference fringe images from the thin-film gap region, guiding the interference fringe images to the external space, where they are then acquired by the external imaging and image acquisition components.

[0017] Furthermore, the imaging component is positioned outside the area to be measured. It receives the local interference fringe light, which is refracted by the reflecting mirror and transmitted through the beam splitter, and images the local interference fringe light onto the image acquisition component to form a local interference fringe image. The imaging component can be a conventional lens or a telecentric lens. The imaging component and / or the image acquisition component are mounted using an imaging adjustment mount, and their positions are adjusted to ensure that the local interference fringe image transmitted through the reflecting mirror and beam splitter is accurately imaged onto the image acquisition component.

[0018] Furthermore, the mounting base surface is a reference surface on the resonant cavity that is opposite to the annular mounting surface of the lens to be mounted and is used to form a mounting connection.

[0019] Furthermore, the lens to be mounted is preferably a transparent microcrystalline glass component. The resonant cavity is also preferably a transparent microcrystalline glass component.

[0020] Furthermore, the gripping component is a claw-type gripping mechanism, or other mechanical gripping structures capable of grasping and positioning. The moving platform is the motion platform of a robot end effector or the platform of other motion actuators.

[0021] Furthermore, the beam-splitting component is preferably a beam-splitting cubic module. The image acquisition component is preferably an industrial camera.

[0022] Furthermore, the reflecting mirror is preferably a plane mirror, and is preferably set at a 45° tilt angle.

[0023] A method for measuring minute angles based on local interference fringes, implemented using the aforementioned minute angle measuring device, includes the following steps: The first step involves acquiring local interference fringe images using a micro-angle measuring device, and then optically imaging the thin-film gap between the lens to be mounted and the resonant cavity to obtain the local interference fringe images. Specifically: Step 1.1: A detection light is generated by a single-mode laser source. The detection light is transmitted to an autocollimator via an optical fiber. The autocollimator organizes the detection light into a parallel detection light and outputs the parallel detection light to the beam splitter.

[0024] Step 1.2: The beam splitter guides the parallel detection light to the reflective mirror, which then refracts the parallel detection light to the test area where the thin film gap is located. After the parallel detection light illuminates the test area, it is reflected on the opposite surfaces of the annular mounting surface and the mounting base surface. The two reflected beams interfere with each other, forming local interference fringes.

[0025] Step 1.3: The reflecting mirror receives the local interference fringe light from a local area of ​​the annular mounting surface and refracts the local interference fringe light to the beam splitter; the beam splitter transmits the local interference fringe light to the imaging component, the imaging component images the local interference fringe light onto the image acquisition component, and the image acquisition component acquires the local interference fringe image.

[0026] The second step involves preprocessing the local interference fringe image obtained in the first step and pre-calculating the boundary spectrum to obtain a boundary spectrum amplitude map used to eliminate boundary interference. Specifically: Step 2.1: Convert the local interference fringe image into a grayscale image to obtain a local interference fringe grayscale image; if the local interference fringe image is already a grayscale image, then directly use it as the local interference fringe grayscale image.

[0027] Step 2.2: Obtain a boundary reference image to characterize the boundary texture, occlusion contour, or fixed structure contour generated by non-interference fringe factors in the area to be tested; convert the boundary reference image into a grayscale image and make the size of the boundary reference image consistent with the size of the local interference fringe grayscale image.

[0028] Step 2.3: Perform a two-dimensional Fourier transform on the boundary reference image, and perform spectral centering on the two-dimensional Fourier transform result to obtain the boundary spectral amplitude map of the boundary reference image.

[0029] The third step involves performing frequency domain processing on the local interference fringe image obtained in the first step and the boundary spectrum amplitude map obtained in the second step to obtain the fringe spectrum map after removing boundary interference. Specifically: Step 3.1: Normalize the grayscale image of the local interference fringes, and then smooth the normalized grayscale image of the local interference fringes using a Gaussian smoothing method; where the Gaussian smoothing coefficient is set to... , Used to control the smoothing intensity.

[0030] Step 3.2: Perform a two-dimensional Fourier transform on the smoothed local interference fringe grayscale image, and perform spectral centering on the two-dimensional Fourier transform result to obtain the local interference fringe spectral amplitude map.

[0031] Step 3.3: Perform frequency domain subtraction on the local interference fringe amplitude map and the boundary amplitude map to obtain the boundary-removed spectrum map; where the frequency domain subtraction coefficient is set to... , The weights of the boundary spectral magnitude map in frequency domain subtraction are adjusted, and the frequency domain subtraction process satisfies: in, This represents the horizontal frequency coordinate in the spectrum diagram. This represents the vertical frequency coordinate in the spectrum diagram. Indicates the debounded spectrum in coordinates The amplitude at that point, The amplitude diagram of the local interference fringe spectrum is shown on the coordinate system. The amplitude at that point, The boundary spectral magnitude plot is shown on the coordinate system. The amplitude at that point, This represents the frequency domain subtraction coefficient.

[0032] Step 3.4: Perform high-pass filtering on the de-boundary spectrogram to suppress low-frequency background components, obtaining a striped spectrogram; where the high-pass filter cutoff radius is set to... , Used to control the suppression range of low-frequency components.

[0033] The fourth step involves extracting the dominant frequency from the fringe spectrum obtained in the third step to obtain the dominant frequency parameters of the local interference fringes. Specifically: Step 4.1: Find local maxima in the stripe spectrogram and select local maxima with amplitudes greater than a preset threshold as candidate frequency peaks; wherein the preset threshold is determined based on the maximum amplitude of the stripe spectrogram.

[0034] Step 4.2: Sort the candidate frequency peak points according to their amplitude, and select the candidate frequency peak point with the largest amplitude as the main frequency peak point.

[0035] Step 4.3: Calculate the transverse and longitudinal spatial frequencies of the local interference fringes based on the location of the dominant frequency peak point to obtain the dominant frequency parameters; where the width of the local interference fringe grayscale image is assumed to be... The height is The horizontal coordinate of the peak frequency point is The vertical axis is The horizontal coordinate of the center of the spectrum is The vertical axis is Then the transverse spatial frequency and longitudinal spatial frequency They are respectively: in, This represents the width of the grayscale image of the local interference fringes. This represents the height of the grayscale image of the local interference fringes. The horizontal coordinates of the peak frequency point are represented. Represents the vertical coordinate of the peak frequency point. The horizontal coordinates representing the center of the spectrum. The vertical coordinate representing the center of the spectrum. This represents the spatial frequency of the local interference fringes in the horizontal direction of the image. This represents the spatial frequency of the local interference fringes along the longitudinal direction of the image.

[0036] Fifth, based on the dominant frequency parameters obtained in step four, calculate the fringe spacing and fringe direction of the local interference fringes to obtain the geometric parameters of the local interference fringes. Specifically: Step 5.1, based on the lateral spatial frequency and longitudinal spatial frequency Calculate the total spatial frequency ,satisfy: in, This represents the total spatial frequency of the local interference fringes.

[0037] Step 5.2, based on the total spatial frequency Calculate pixel stripe spacing ,satisfy: in, This represents the pixel spacing of the local interference fringes in the image.

[0038] Step 5.3, based on pixel stripe spacing and the physical pixel size of the image acquisition component Calculate the physical fringe spacing ,satisfy: in, Indicates the physical pixel size of the image acquisition component. This represents the physical fringe spacing corresponding to the local interference fringes.

[0039] Step 5.4, based on the lateral spatial frequency and longitudinal spatial frequency Calculate the frequency direction angle of local interference fringes ,satisfy: in, The frequency direction angle represents the local interference fringes. The frequency direction angle is used to characterize the direction of the thin film gap thickness variation in the image coordinate system.

[0040] Step 6: Based on the local interference fringe geometric parameters obtained in Step 5, calculate the minute tilt angle of the lens to be installed relative to the resonant cavity, obtaining the X-axis tilt angle and the Y-axis tilt angle. Specifically: Step 6.1: Based on the detection light wavelength and the spatial frequency of the local interference fringes, calculate the slope of the film gap thickness change in the horizontal and vertical directions of the image; whereby the detection light wavelength is assumed to be... The refractive index of the medium within the thin film gap is The slope of the horizontal thickness change in the image and the slope of the image's longitudinal thickness change They respectively satisfy: Where e represents the wavelength of the detection light. Indicates the refractive index of the medium within the thin film gap. Indicates the physical pixel size of the image acquisition component. This represents the spatial frequency of the local interference fringes in the horizontal direction of the image. This represents the spatial frequency of the local interference fringes along the vertical axis of the image. represents the slope of the thickness change of the film gap in the horizontal direction of the image, and e represents the slope of the thickness change of the film gap in the vertical direction of the image.

[0041] Step 6.2, based on the slope of the horizontal thickness change in the image and the slope of the image's longitudinal thickness change Calculate the X-axis tilt angle of the lens to be installed relative to the resonant cavity. and Y-axis tilt angle ,satisfy: in, This indicates the X-axis tilt angle of the lens to be installed relative to the resonant cavity; This indicates the Y-axis tilt angle of the lens to be installed relative to the resonant cavity.

[0042] Step 6.3, when the small tilt angle satisfies the small angle approximation condition, the X-direction tilt angle... and Y-axis tilt angle They are approximated as follows: This yields the X-axis tilt angle and Y-axis tilt angle of the lens to be installed relative to the resonant cavity.

[0043] The present invention has the following beneficial effects: (1) This invention addresses the actual working condition where the clamping structure partially obstructs the area to be measured during the mounting process. Instead of relying on complete annular interference fringes, it achieves angle detection by measuring and analyzing locally visible interference fringes. Therefore, it can adapt to the measurement needs in real mounting environments and improve its applicability in mounting scenarios.

[0044] (2) In cases where the space below the area to be measured is limited and it is impossible to directly arrange the camera and lens, the present invention sets up a reflective imaging mirror to guide the interference fringe image formed in the area to be measured to an external imaging system, which solves the problem of difficulty in direct imaging in a narrow space and enables the measurement scheme to be applied to compact mounting stations.

[0045] (3) The present invention uses the interference fringes generated by the thin film gap between the lens to be mounted and the mounting base of the resonant cavity for measurement. It is a non-contact optical measurement method, which avoids the problem that contact measurement may affect the posture, position and surface condition of the part to be measured, and helps to ensure the stability and safety of the precision mounting process.

[0046] (4) By extracting and analyzing the characteristics of local interference fringes such as fringe spacing, direction, curvature or density distribution, this invention can realize the biaxial small angle deviation measurement of the lens to be mounted relative to the mounting base of the resonant cavity, thereby providing a basis for attitude adjustment during the mounting process and improving mounting accuracy and assembly consistency.

[0047] (5) This invention combines optical measurement structure with image processing and analysis, realizing a continuous measurement process from stripe acquisition and image acquisition to angle calculation, which facilitates online detection and digital processing, and also provides a technical basis for subsequent automated mounting and calibration.

[0048] (6) This invention is particularly suitable for detecting minute angular deviations during the mounting process of transparent optical components, especially for measurement tasks under conditions of partial obstruction and limited imaging space, and has good engineering application value. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of the overall structure of the micro-angle measuring device based on local interference fringes according to the present invention.

[0050] Figure 2 This is a magnified schematic diagram of a local structure of the area to be tested in this invention.

[0051] Figure 3 This is a schematic diagram of the partial occlusion and reflection mirror of the present invention.

[0052] In the diagram: 1. Lens to be mounted; 2. Resonant cavity; 3. Clamping assembly; 4. Resonant cavity mounting base; 5. Single-mode laser source; 6. Optical fiber; 7. Autocollimator; 8. Beam splitter assembly; 9. Reflecting image guide; 10. Source adjustment base; 11. Beam splitter assembly adjustment base; 12. Imaging adjustment base; 13. Imaging assembly; 14. Image acquisition assembly; 15. Central reflecting surface; 16. Annular mounting surface; 17. Mounting base surface; 18. Thin film gap; 19. Moving platform; 20. Lens mounting bracket. Detailed Implementation

[0053] The present invention will be further described below with reference to specific implementation examples.

[0054] This embodiment provides a small angle measuring device based on local interference fringes, the overall structure of which is as follows: Figure 1As shown, the system mainly includes a lens to be mounted (1), a resonant cavity (2), a clamping assembly (3), a resonant cavity mounting base (4), a single-mode laser source (5), an optical fiber (6), an autocollimator (7), a beam splitter (8), a reflective imaging mirror (9), a light source adjustment base (10), a beam splitter adjustment base (11), an imaging adjustment base (12), an imaging assembly (13), an image acquisition assembly (14), a central reflecting surface (15), an annular mounting surface (16), a mounting base surface (17), a thin film gap (18), a moving platform (19), and a lens mounting bracket (20). The local interference fringe image acquired by the image acquisition assembly (14) is transmitted to an external data processing assembly, which performs image preprocessing, frequency domain analysis, fringe dominant frequency extraction, and angle calculation.

[0055] In this embodiment, both the lens to be mounted 1 and the resonant cavity 2 are preferably transparent microcrystalline glass components. The lens to be mounted 1 is a lens component to be mounted onto the resonant cavity 2, with a central reflecting surface 15 in its middle and an annular mounting surface 16 on its periphery. The central reflecting surface 15 is the optical reflection area in the middle of the lens to be mounted 1, and the annular mounting surface 16 is the annular surface on the periphery of the lens to be mounted for bonding and connection with the resonant cavity 2. A mounting base surface 17 is correspondingly provided on the resonant cavity 2, which is a reference surface opposite to the annular mounting surface 16 and used to form a mounting connection. When the lens to be mounted 1 is not completely mounted onto the resonant cavity 2, a thin film gap 18 is formed between the annular mounting surface 16 and the mounting base surface 17, and the thin film gap 18 is the area to be measured for interferometric measurement in this invention.

[0056] like Figure 2 As shown, the lens to be mounted 1 is located above the resonant cavity 2, with the annular mounting surface 16 and the mounting base surface 17 facing each other. Because the lens to be mounted 1 may undergo slight rotation relative to the resonant cavity 2 around the X or Y direction, the thickness of the thin film gap 18 is not completely uniform at different spatial locations, but rather varies continuously along one or more directions. When parallel detection light illuminates the area to be tested where the thin film gap 18 is located, it is reflected on the opposing surfaces of the annular mounting surface 16 and the mounting base surface 17. The two reflected beams interfere with each other, thus forming local interference fringes. These local interference fringes carry information about the thickness variation of the thin film gap 18, and therefore can be used to reflect the slight angular deviation of the lens to be mounted 1 relative to the resonant cavity 2.

[0057] In this embodiment, the clamping assembly 3 is used to clamp the lens 1 to be installed and deliver the lens 1 to the mounting position of the resonant cavity 2. The clamping assembly 3 is mounted on the moving platform 19, and the lens 1 to be installed is clamped and fixed by the clamping assembly 3. The lens mounting bracket 20 is mounted on the moving platform 19, and the reflecting mirror 9 is mounted on the lens mounting bracket 20. Therefore, the moving platform 19 can drive the clamping assembly 3, the lens 1 to be installed, the lens mounting bracket 20, and the reflecting mirror 9 to adjust their positions relative to the resonant cavity 2. The clamping assembly 3 is disposed on the periphery and lower side of the lens 1 to be installed, and is used to support and clamp and fix the lens 1 to be installed. Since at least part of the structure of the clamping assembly 3 is located near the detection path of the annular mounting surface 16, the clamping assembly 3 will block part of the annular mounting surface 16 when clamping the lens 1 to be installed, so that the image acquisition assembly 14 cannot acquire a complete annular interference fringe image, but can only acquire the local interference fringe image corresponding to the area not blocked by the clamping assembly 3.

[0058] An important feature of this embodiment is that it does not require the acquisition of a complete circumference of the interference fringes. Instead, when the clamping component 3 forms a partial obstruction, the measurement of a small angle is completed only by using the local interference fringe image corresponding to the unobstructed area.

[0059] The resonant cavity 2 is fixedly mounted on the resonant cavity mounting base 4. The resonant cavity mounting base 4 is used to support and fix the resonant cavity 2, so that the resonant cavity 2 remains in a stable position during the measurement process, and avoids the resonant cavity 2 from changing position and affecting the thickness distribution of the thin film gap 18 and the subsequent angle calculation results. The resonant cavity mounting base 4 can be fixed to the measurement platform, mounting platform or other stable mounting base surface.

[0060] In this embodiment, a single-mode laser source 5 is used to generate detection light. The detection light output from the single-mode laser source 5 is transmitted to an autocollimator 7 via an optical fiber 6. The autocollimator 7 organizes the detection light transmitted via the optical fiber 6 into parallel detection light and outputs the parallel detection light to the beam splitter 8. The light source adjustment mount 10 is used to mount the autocollimator 7 and adjust its position and orientation so that the parallel detection light output by the autocollimator 7 can enter the beam splitter 8 in a predetermined direction. Using a single-mode laser source 5 helps to ensure the coherence of the detection light; using an optical fiber 6 to transmit the detection light helps to separate the light source from the measurement head; and using an autocollimator 7 to output parallel detection light helps to improve the consistency and stability of subsequent interference illumination.

[0061] The beam splitter 8 is preferably a beam-splitting cubic structure, and is mounted on a beam splitter adjustment base 11. The beam splitter adjustment base 11 is used to install and adjust the position and orientation of the beam splitter 8. The beam splitter 8 is positioned between the autocollimator 7 and the imaging component 13 to realize the conversion between the illumination optical path and the imaging optical path. Specifically, the beam splitter 8 guides the parallel detection light from the autocollimator 7 to the reflecting mirror 9, and is deflected by the reflecting mirror 9 to the test area where the thin film gap 18 is located; on the other hand, the beam splitter 8 transmits the local interference fringe light returning from the test area and deflected by the reflecting mirror 9 to the imaging component 13.

[0062] like Figure 3 As shown, the reflective mirror 9 is disposed in the space below the area to be tested. In this embodiment, it is a plane mirror and is set at a 45° tilt angle. The reflective mirror 9 receives local interference fringe light from a local area of ​​the annular mounting surface 16 through its reflective surface and refracts the local interference fringe light into the imaging acquisition optical path where the beam splitter 8 and the imaging assembly 13 are located. The lens mounting bracket 20 is used to support and fix the reflective mirror 9 and ensure that the reflective mirror 9 is located at a predetermined position below the area to be tested, so as to realize the refracting and extraction of the local interference fringe light. Since the thin film gap 18 is located inside the mounting station, the space below it is narrow, making it difficult to directly arrange the imaging assembly 13 and the image acquisition assembly 14. Therefore, in this embodiment, the reflective mirror 9 is used to extract the local interference fringe light from the narrow space to the external imaging acquisition optical path. The main function of the reflective mirror 9 is to induce an image and refract the optical path, rather than to generate interference.

[0063] Imaging component 13 is positioned outside the area to be measured. It receives the local interference fringe light, which is deflected by the reflecting mirror 9 and transmitted through the beam splitter 8, and images the local interference fringe light onto the image acquisition component 14 to form a local interference fringe image. Imaging component 13 can be a conventional lens or a telecentric lens. Image acquisition component 14 is preferably an industrial camera, used to acquire the local interference fringe image formed by imaging component 13 and output a digital image signal. Imaging component 13 and image acquisition component 14 are mounted on imaging adjustment base 12, which is used to adjust the positions of imaging component 13 and image acquisition component 14 so that the local interference fringe light transmitted by the reflecting mirror 9 and beam splitter 8 can be accurately imaged within the effective imaging area of ​​image acquisition component 14.

[0064] In this embodiment, the overall optical path process is as follows: The detection light emitted by the single-mode laser source 5 is transmitted to the autocollimator 7 via the optical fiber 6, and the autocollimator 7 outputs parallel detection light; the parallel detection light is guided by the beam splitter 8 and reaches the reflecting mirror 9; the reflecting mirror 9 reflects the parallel detection light to the test area where the thin film gap 18 between the lens to be mounted 1 and the resonant cavity 2 is located; after local interference fringe light is formed at the thin film gap 18, the local interference fringe light is refracted and extracted by the reflecting mirror 9, and then enters the imaging component 13 through the beam splitter 8; the imaging component 13 images the local interference fringe light onto the image acquisition component 14; the image acquisition component 14 acquires the local interference fringe image and transmits the local interference fringe image to the external data processing component.

[0065] The external data processing component is preferably a computer, host computer, or industrial control computer, and is not separately numbered in the attached drawings. The external data processing component is used to receive the local interference fringe image acquired by the image acquisition component 14, and to perform image preprocessing, frequency domain analysis, fringe dominant frequency extraction, fringe geometric parameter calculation, and micro-angle calculation.

[0066] This embodiment also provides a method for measuring minute angles based on local interference fringes. The method is implemented based on the aforementioned minute angle measuring device and includes the following steps: The first step involves acquiring a local interference fringe image using a micro-angle measuring device, and then optically imaging the thin-film gap 18 between the lens 1 to be mounted and the resonant cavity 2 to obtain the local interference fringe image A. Specifically: Step 1.1: A detection light is generated by a single-mode laser source 5. The detection light is transmitted to an autocollimator 7 via an optical fiber 6. The autocollimator 7 organizes the detection light into a parallel detection light and outputs the parallel detection light to a beam splitter 8.

[0067] Step 1.2: The beam splitter 8 guides the parallel detection light to the reflective mirror 9, which refracts the parallel detection light to the test area where the thin film gap 18 is located. After the parallel detection light irradiates the test area, it is reflected on the opposite surfaces of the annular mounting surface 16 and the mounting base surface 17. The two reflected beams interfere with each other, forming local interference fringes.

[0068] Step 1.3: The reflecting mirror 9 receives the local interference fringe light from a local area of ​​the annular mounting surface 16 and refracts the local interference fringe light to the beam splitter 8; the beam splitter 8 transmits the local interference fringe light to the imaging component 13, and the imaging component 13 images the local interference fringe light onto the image acquisition component 14, and the image acquisition component 14 acquires the local interference fringe image A.

[0069] In this embodiment, the local interference fringe image A acquired by the image acquisition component 14 is the fringe image corresponding to the portion of the area to be tested that is not obscured by the clamping component 3. Since the clamping component 3 obscures a portion of the annular mounting surface 16, the local interference fringe image A is not required to contain a complete annular interference fringe, but only needs to contain local fringe information that can reflect the thickness variation of the thin film gap 18.

[0070] The second step involves preprocessing the local interference fringe image A obtained in the first step and pre-calculating the boundary spectrum to obtain the boundary spectrum amplitude map B used to eliminate boundary interference. Specifically: Step 2.1: Convert the local interference fringe image A into a grayscale image to obtain the local interference fringe grayscale image; if the local interference fringe image A is already a grayscale image, then directly use it as the local interference fringe grayscale image.

[0071] Step 2.2: Obtain a boundary reference image, which is used to characterize the boundary texture, occlusion contour, or fixed structure contour generated by non-interference fringe factors in the area to be tested; convert the boundary reference image into a grayscale image, and make the size of the boundary reference image consistent with the size of the local interference fringe grayscale image.

[0072] Step 2.3: Perform a two-dimensional Fourier transform on the boundary reference image, and perform spectral centering on the two-dimensional Fourier transform result to obtain the boundary spectral amplitude map B of the boundary reference image.

[0073] In this embodiment, an image that is not used for the final angle calculation but can represent the boundary contour or fixed structure contour can be selected as the boundary reference image. After grayscale conversion and size matching, the boundary reference image maintains the same pixel size as the local interference fringe grayscale image. As a specific implementation, the spectrum of the boundary reference image can be pre-calculated, and the calculated boundary spectrum amplitude map B can be stored in an external data processing component and repeatedly called in subsequent multi-frame local interference fringe image processing to reduce redundant calculations and improve processing efficiency.

[0074] The third step involves performing frequency domain processing on the local interference fringe image A obtained in the first step and the boundary spectrum amplitude map B obtained in the second step, to obtain the fringe spectrum map C after removing boundary interference. Specifically: Step 3.1: Normalize the grayscale image of the local interference fringes, and then smooth the normalized grayscale image of the local interference fringes using a Gaussian smoothing method; where the Gaussian smoothing coefficient is set to... , Used to control the smoothing intensity.

[0075] In this embodiment, the grayscale values ​​of the local interference fringe grayscale image can be normalized to the range of 0 to 1. As a specific implementation method, A value of 2.0 is used to suppress local noise and maintain the main structure of the stripes.

[0076] Step 3.2: Perform a two-dimensional Fourier transform on the smoothed local interference fringe grayscale image, and perform spectral centering on the two-dimensional Fourier transform result to obtain the local interference fringe spectral amplitude map.

[0077] Step 3.3: Perform frequency domain subtraction on the local interference fringe spectrum amplitude map and the boundary spectrum amplitude map B to obtain the boundary-removed spectrum map; where the frequency domain subtraction coefficient is set to... , The weight of boundary spectral magnitude map B in frequency domain subtraction is used to adjust the frequency domain subtraction process, which satisfies the following: in, This represents the horizontal frequency coordinate in the spectrum diagram. This represents the vertical frequency coordinate in the spectrum diagram. Indicates the debounded spectrum in coordinates The amplitude at that point, The amplitude diagram of the local interference fringe spectrum is shown on the coordinate system. The amplitude at that point, The boundary spectral magnitude plot is shown on the coordinate system. The amplitude at that point, This represents the frequency domain subtraction coefficient.

[0078] In this embodiment, as a specific implementation method, 2.2. By using frequency domain subtraction, the influence of fixed boundaries, occluded contours, or non-fringe structures in the frequency domain can be weakened, making the subsequent extraction of the dominant frequency peak more focused on the local interference fringes themselves.

[0079] Step 3.4: Perform high-pass filtering on the de-boundary spectrogram to suppress low-frequency background components, obtaining the striped spectrogram C; where the high-pass filter cutoff radius is set to... , Used to control the suppression range of low-frequency components.

[0080] In this embodiment, as a specific implementation method, Set the value to 10. High-pass filtering can further suppress the influence of uneven image brightness, background gradation, and low-frequency structures on the extraction of the dominant frequency, thereby improving the stability of local interference fringe frequency analysis.

[0081] The fourth step involves extracting the dominant frequency from the fringe spectrum C obtained in the third step to obtain the dominant frequency parameter D of the local interference fringes. Specifically: Step 4.1: Find local maxima in the stripe spectrogram C, and select the local maxima with amplitudes greater than a preset threshold as candidate frequency peaks; wherein the preset threshold is determined based on the maximum amplitude of the stripe spectrogram C.

[0082] In this embodiment, as a specific implementation, the preset threshold is set to 10% of the maximum amplitude of the fringe spectrum C. That is, if the maximum amplitude of the fringe spectrum C is... The preset threshold is Spectral points that exceed the preset threshold and satisfy the local maximum condition are considered as candidate frequency peak points.

[0083] Step 4.2: Sort the candidate frequency peak points according to their amplitude, and select the candidate frequency peak point with the largest amplitude as the main frequency peak point.

[0084] In this embodiment, the dominant frequency peak point is used to represent the most prominent fringe periodic feature in the local interference fringe image A. As a specific implementation, the number of dominant frequency peak points extracted can be set to 1, that is, the candidate frequency peak point with the largest amplitude can be selected as the dominant frequency peak point. When there are multiple significant directions or multiple frequency components in the local interference fringes, multiple candidate frequency peak points can also be selected for comprehensive analysis.

[0085] Step 4.3: Calculate the transverse and longitudinal spatial frequencies of the local interference fringes based on the location of the dominant frequency peak point, obtaining the dominant frequency parameter D; where the width of the local interference fringe grayscale image is assumed to be... The height is The horizontal coordinate of the peak frequency point is The vertical axis is The horizontal coordinate of the center of the spectrum is The vertical axis is Then the transverse spatial frequency and longitudinal spatial frequency They are respectively: in, This represents the width of the grayscale image of the local interference fringes. This represents the height of the grayscale image of the local interference fringes. The horizontal coordinates of the peak frequency point are represented. Represents the vertical coordinate of the peak frequency point. The horizontal coordinates representing the center of the spectrum. The vertical coordinate representing the center of the spectrum. This represents the spatial frequency of the local interference fringes in the horizontal direction of the image. This represents the spatial frequency of the local interference fringes along the longitudinal direction of the image.

[0086] In this embodiment, the external data processing component obtains the frequency components of the local interference fringes in the horizontal and vertical directions of the image by offsetting the position of the dominant frequency peak point relative to the center of the spectrum. The farther the dominant frequency peak point deviates from the center of the spectrum, the higher the spatial frequency of the local interference fringes and the smaller the corresponding fringe spacing; if the dominant frequency peak point is close to the center of the spectrum, the lower the spatial frequency of the local interference fringes and the larger the corresponding fringe spacing.

[0087] Fifth, based on the dominant frequency parameter D obtained in step four, calculate the fringe spacing and fringe direction of the local interference fringes to obtain the geometric parameters E of the local interference fringes. Specifically: Step 5.1, based on the lateral spatial frequency and longitudinal spatial frequency Calculate the total spatial frequency ,satisfy: in, This represents the total spatial frequency of the local interference fringes.

[0088] Step 5.2, based on the total spatial frequency Calculate pixel stripe spacing ,satisfy: in, This represents the pixel spacing of the local interference fringes in the image.

[0089] Step 5.3, based on pixel stripe spacing and the physical pixel size of the image acquisition component 14 Calculate the physical fringe spacing ,satisfy: in, This indicates the physical pixel size of the image acquisition component 14. This represents the physical fringe spacing corresponding to the local interference fringes.

[0090] In this embodiment, as a specific implementation, the physical pixel size of the image acquisition component 14 is... The pixel stripe spacing is set to 0.0125mm. The external data processing component calculates the pixel stripe spacing based on the main frequency parameter D. Then, multiply it by the physical pixel size. The physical fringe spacing corresponding to the local interference fringes can then be obtained. Physical stripe spacing The smaller the value, the faster the thickness of the film gap 18 changes; physical stripe spacing The larger the value, the slower the thickness change of the film gap 18.

[0091] Step 5.4, based on the lateral spatial frequency and longitudinal spatial frequency Calculate the frequency direction angle of local interference fringes ,satisfy: in, The frequency direction angle represents the local interference fringes. The frequency direction angle is used to characterize the direction of the thickness variation of the thin film gap 18 in the image coordinate system.

[0092] In this embodiment, the frequency direction angle This reflects the direction of the local interference fringe frequency components in the image coordinate system. Combined with the physical fringe spacing... and frequency direction angle This allows us to determine the main thickness change direction and rate of change of the film gap 18, thus providing a basis for subsequent calculations of the X-axis tilt angle and Y-axis tilt angle.

[0093] Step 6: Based on the local interference fringe geometric parameters E obtained in Step 5, calculate the minute tilt angle of the lens 1 to be installed relative to the resonant cavity 2, obtaining the X-axis tilt angle and the Y-axis tilt angle. Specifically: Step 6.1: Based on the detection light wavelength and the spatial frequency of the local interference fringes, calculate the slope of the thickness change of the thin film gap 18 in the horizontal and vertical directions of the image; whereby the detection light wavelength is assumed to be... The refractive index of the medium within the thin film gap 18 is The slope of the horizontal thickness change in the image and the slope of the image's longitudinal thickness change They respectively satisfy: Where e represents the wavelength of the detection light. This indicates the refractive index of the medium within the thin film gap 18. This indicates the physical pixel size of the image acquisition component 14. This represents the spatial frequency of the local interference fringes in the horizontal direction of the image. This represents the spatial frequency of the local interference fringes along the vertical axis of the image. denoted by , e represents the slope of the thickness change of the thin film gap 18 in the horizontal direction of the image, and e represents the slope of the thickness change of the thin film gap 18 in the vertical direction of the image.

[0094] In this embodiment, when the medium within the thin film gap 18 is air, the refractive index is... One value can be chosen. If there are other media within the thin film gap 18, the value can be determined based on the refractive index of the actual medium. The value of .

[0095] Step 6.2, based on the slope of the horizontal thickness change in the image and the slope of the image's longitudinal thickness change Calculate the X-axis tilt angle of the lens 1 to be installed relative to the resonant cavity 2. and Y-axis tilt angle ,satisfy: in, This indicates the X-axis tilt angle of the lens 1 to be installed relative to the resonant cavity 2; This indicates the Y-axis tilt angle of the lens 1 to be installed relative to the resonant cavity 2.

[0096] Step 6.3, when the small tilt angle satisfies the small angle approximation condition, the X-direction tilt angle... and Y-axis tilt angle They are approximated as follows: This yields the X-axis tilt angle and Y-axis tilt angle of the lens 1 to be installed relative to the resonant cavity 2.

[0097] In this embodiment, if the calculated and If the absolute value is small, a small-angle approximation can be used, directly taking the slope of the thickness change as the approximate angle value in the corresponding direction. For higher precision, the arctangent relationship can be used directly for calculation. and .

[0098] In this embodiment, closed-loop adjustment can also be performed on the lens 1 to be mounted based on the obtained X-axis tilt angle and Y-axis tilt angle. Specifically, the external data processing component outputs the X-axis tilt angle and Y-axis tilt angle as attitude error signals. The moving platform 19 drives the clamping component 3 and the lens 1 to be mounted to perform position or attitude fine adjustments based on the attitude error signals, so that the angular deviation of the lens 1 to be mounted relative to the resonant cavity 2 gradually decreases. When both the X-axis tilt angle and the Y-axis tilt angle meet the preset mounting accuracy requirements, the subsequent mounting operation can be performed.

[0099] In this embodiment, the key points of the present invention are: first, local interference fringes are generated by utilizing the thin film gap 18 formed between the annular mounting surface 16 of the lens to be mounted 1 and the mounting base surface 17 of the resonant cavity 2; second, under the condition of being blocked by the clamping component 3, angle measurement is achieved not by relying on a complete annular interference fringe, but only by utilizing the local interference fringe image corresponding to the unblocked area; third, when the space below the area to be measured is limited, the local interference fringe light is refracted and led out to the external imaging acquisition optical path through the reflective imaging mirror 9 and the lens mounting bracket 20; fourth, the local interference fringe image is subjected to frequency domain analysis, main frequency extraction, fringe spacing calculation and angle calculation by the external data processing component to obtain the X-axis tilt angle and Y-axis tilt angle of the lens to be mounted relative to the resonant cavity 2.

[0100] The above description is merely a preferred embodiment of the present invention. For those skilled in the art, various modifications, equivalent substitutions, and improvements can be made to the present invention without departing from its basic concept, and all such modifications, substitutions, and improvements should be considered to fall within the protection scope of the present invention.

Claims

1. A micro-angle measuring device based on local interference fringes, characterized in that, The micro-angle measuring device includes a lens to be mounted (1), a resonant cavity (2), a clamping assembly (3), a resonant cavity mounting base (4), a single-mode laser source (5), an optical fiber (6), an autocollimator (7), a beam splitter (8), a reflective image guide (9), an imaging assembly (13), an image acquisition assembly (14), a moving platform (19), and a lens mounting bracket (20); specifically: The lens to be mounted (1) is a transparent optical component, including a central reflective surface (15) and an annular mounting surface (16). The central reflective surface (15) is the reflective area in the middle of the lens to be mounted (1), and the annular mounting surface (16) is the annular surface on the periphery of the lens to be mounted (1) for bonding and connecting with the resonant cavity (2). The resonant cavity (2) is a transparent optical component that is mounted and fitted with the lens to be mounted (1). The bottom of the resonant cavity (2) is provided with a mounting base surface (17) corresponding to the lens to be mounted (1). When the lens to be mounted (1) is not completely mounted to the resonant cavity (2), a thin film gap (18) is formed between the annular mounting surface (16) of the lens to be mounted (1) and the mounting base surface (17) of the resonant cavity (2). The thin film gap (18) is the test area where interference fringes are generated. After the parallel detection light is irradiated to the test area, reflection and mutual interference occur between the annular mounting surface (16) and the mounting base surface (17), thereby forming interference fringes. The clamping assembly (3) is mounted on the moving platform (19) and is used to clamp the lens to be installed (1) and send it to the mounting position of the resonant cavity (2); the reflective image guide (9) is mounted on the lens mounting bracket (20), the lens mounting bracket (20) is mounted on the moving platform (19), and the moving platform (19) is used to drive the clamping assembly (3), the lens to be installed (1), the lens mounting bracket (20) and the reflective image guide (9) to adjust their positions relative to the resonant cavity (2); The resonant cavity mounting base (4) is used to support and fix the resonant cavity (2), and its bottom is mounted on the measurement platform or mounting platform; The single-mode laser source (5) is used to generate detection laser. The detection laser is transmitted to the autocollimator (7) through the optical fiber (6). The parallel detection light output by the autocollimator (7) enters the beam splitter (8). The beam splitter (8) is positioned between the autocollimator (7) and the imaging component (13) to realize the conversion between the illumination optical path and the imaging optical path. The imaging component (13) is connected to the image acquisition component (14). The local interference fringe image formed by the imaging component (13) is acquired by the image acquisition component (14). The local interference fringe image is transmitted to the external data processing component for processing to obtain the X-axis tilt angle and Y-axis tilt angle of the lens (1) to be installed relative to the resonant cavity (2).

2. The micro-angle measuring device based on local interference fringes according to claim 1, characterized in that, The clamping component (3) is located on the periphery and underside of the lens to be mounted (1). When clamping the lens to be mounted (1), the clamping component (3) will block part of the annular mounting surface (16), making it impossible for it to directly form effective interference fringes. The interference fringe image from the blocked area cannot enter the imaging component (13) and image acquisition component (14) through the reflecting mirror (9) and beam splitting component (8). Therefore, the image acquisition component (14) cannot acquire a complete annular interference fringe image, but can only acquire the local interference fringe image corresponding to the area not blocked by the clamping component (3). That is, under the condition of being blocked by the clamping component (3), only local interference fringes are acquired and angle measurement is completed.

3. The micro-angle measuring device based on local interference fringes according to claim 2, characterized in that, The autocollimator (7) and the imaging component (13) are respectively arranged on different optical path sides of the beam splitter (8); the autocollimator (7) is mounted on the light source adjustment seat (10), and the light source adjustment seat (10) adjusts the position and orientation of the autocollimator (7) so that the parallel detection light output by the autocollimator (7) enters the beam splitter (8) in a predetermined direction; the imaging component (13) and the image acquisition component (14) are mounted on the imaging adjustment seat (12) and located on the imaging output side of the beam splitter (8), and are used to receive the local interference fringe image refracted and extracted by the reflecting mirror (9) and the beam splitter (8); the beam splitter (8) guides the parallel detection light from the autocollimator (7) to the test area formed by the thin film gap (18), and the beam splitter (8) also guides the fringe image returned from the test area to the imaging component (13); the beam splitter adjustment seat (11) is used to install the beam splitter (8) and adjust the position and orientation of the beam splitter (8).

4. The micro-angle measuring device based on local interference fringes according to claim 3, characterized in that, The reflective imaging mirror (9) is positioned below the area to be measured. It receives the interference fringe image from a local area of ​​the annular mounting surface (16) through its reflective surface and folds the local interference fringe image into the imaging acquisition optical path where the beam splitter (8) and imaging assembly (13) are located.

5. A micro-angle measuring device based on local interference fringes according to claim 4, characterized in that, The imaging component (13) is located outside the area to be tested. It is used to receive the local interference fringe light that is refracted by the reflecting mirror (9) and transmitted by the beam splitter (8), and to image the local interference fringe light onto the image acquisition component (14) to form a local interference fringe image.

6. A small angle measuring device based on local interference fringes according to claim 4, characterized in that, The lens to be installed (1) is a transparent microcrystalline glass component; the resonant cavity (2) is a transparent microcrystalline glass component; the beam splitting component (8) is a beam splitting cube; the image acquisition component (14) is an industrial camera; and the reflective image guide (9) is a plane reflector.

7. A method for measuring minute angles based on local interference fringes, characterized in that, Based on the micro-angle measuring device according to any one of claims 1-6, the method includes the following steps: The first step involves acquiring a local interference fringe image using a micro-angle measuring device, and then optically imaging the thin film gap (18) between the lens to be mounted (1) and the resonant cavity (2) to obtain the local interference fringe image; specifically: Step 1.1: The detection light from the single-mode laser source (5) is transmitted to the autocollimator (7) via the optical fiber (6). The autocollimator (7) organizes the detection light into a parallel detection light and outputs the parallel detection light to the beam splitter (8). Step 1.2, the beam splitter (8) guides the parallel detection light to the reflective mirror (9), and the reflective mirror (9) refracts the parallel detection light to the test area where the thin film gap (18) is located; after the parallel detection light is irradiated to the test area, it is reflected on the opposite surfaces of the annular mounting surface (16) and the mounting base surface (17), and the two reflected beams interfere with each other to form local interference fringes; Step 1.3: The reflective mirror (9) receives the local interference fringe light and refracts it to the beam splitter (8); the beam splitter (8) transmits the local interference fringe light to the imaging component (13), and the imaging component (13) images the local interference fringe light onto the image acquisition component (14), and the image acquisition component (14) acquires the local interference fringe image. The second step involves preprocessing the local interference fringe image obtained in the first step and pre-calculating the boundary spectrum to obtain the boundary spectrum amplitude map; specifically: Step 2.1: Convert the local interference fringe image into a grayscale image to obtain a local interference fringe grayscale image; Step 2.2: Obtain a boundary reference image, convert the boundary reference image into a grayscale image, and make the size of the boundary reference image consistent with the size of the local interference fringe grayscale image; Step 2.3: Perform a two-dimensional Fourier transform on the boundary reference image, and perform spectrum centering on the two-dimensional Fourier transform result to obtain the boundary spectrum amplitude map of the boundary reference image. The third step involves performing frequency domain processing on the local interference fringe image obtained in the first step and the boundary spectrum amplitude map obtained in the second step to obtain the fringe spectrum map after removing boundary interference; specifically: Step 3.1: Normalize the grayscale image of the local interference fringes, and smooth the normalized grayscale image of the local interference fringes using the Gaussian smoothing method. Step 3.2: Perform a two-dimensional Fourier transform on the smoothed local interference fringe grayscale image, and perform spectral centering on the two-dimensional Fourier transform result to obtain the local interference fringe spectral amplitude map. Step 3.3: Perform frequency domain subtraction on the local interference fringe amplitude map and the boundary amplitude map to obtain the boundary-removed spectrum map; where the frequency domain subtraction coefficient is set to... ; in, This represents the horizontal frequency coordinate in the spectrum diagram. This represents the vertical frequency coordinate in the spectrum diagram. Indicates the debounded spectrum in coordinates The amplitude at that point, The amplitude diagram of the local interference fringe spectrum is shown on the coordinate system. The amplitude at that point, The boundary spectral magnitude plot is shown on the coordinate system. The amplitude at that point; Represents the frequency domain subtraction coefficients; Step 3.4: Perform high-pass filtering on the de-boundary spectrogram to obtain the fringe spectrogram; where the high-pass filter cutoff radius is set to... ; The fourth step is to extract the dominant frequency from the fringe spectrum obtained in the third step to obtain the dominant frequency parameters of the local interference fringes; specifically: Step 4.1: Find local maxima in the fringe spectrum and select local maxima with amplitudes greater than a preset threshold as candidate frequency peaks. Step 4.2: Sort the candidate frequency peak points according to their amplitude, and select the candidate frequency peak point with the largest amplitude as the main frequency peak point; Step 4.3: Calculate the transverse and longitudinal spatial frequencies of the local interference fringes based on the location of the dominant frequency peak point to obtain the dominant frequency parameters; where the width of the local interference fringe grayscale image is assumed to be... The height is The horizontal coordinate of the peak frequency point is The vertical axis is The horizontal coordinate of the center of the spectrum is The vertical axis is Then the transverse spatial frequency and longitudinal spatial frequency They are respectively: in, This represents the width of the grayscale image of the local interference fringes. This represents the height of the grayscale image of the local interference fringes. The horizontal coordinates of the peak frequency point are represented. Represents the vertical coordinate of the peak frequency point. The horizontal coordinates representing the center of the spectrum. The vertical coordinate representing the center of the spectrum. This represents the spatial frequency of the local interference fringes in the horizontal direction of the image. This represents the spatial frequency of local interference fringes along the longitudinal direction of the image. Fifth, based on the dominant frequency parameters obtained in step four, calculate the fringe spacing and fringe direction of the local interference fringes to obtain the geometric parameters of the local interference fringes; specifically: Step 5.1, based on the lateral spatial frequency and longitudinal spatial frequency Calculate the total spatial frequency ,satisfy: in, This represents the total spatial frequency of the local interference fringes; Step 5.2, based on the total spatial frequency Calculate pixel stripe spacing ,satisfy: in, This represents the pixel spacing of local interference fringes in the image; Step 5.3, based on pixel stripe spacing and the physical pixel size of the image acquisition component (14) Calculate the physical fringe spacing ,satisfy: in, This indicates the physical pixel size of the image acquisition component (14). This represents the physical fringe spacing corresponding to the local interference fringes; Step 5.4, based on the lateral spatial frequency and longitudinal spatial frequency Calculate the frequency direction angle of local interference fringes ,satisfy: in, The frequency direction angle represents the local interference fringes. The frequency direction angle is used to characterize the direction of the thickness change of the thin film gap (18) in the image coordinate system. Step 6: Based on the local interference fringe geometric parameters obtained in Step 5, calculate the minute tilt angle of the lens to be installed (1) relative to the resonant cavity (2) to obtain the X-axis tilt angle and the Y-axis tilt angle; specifically: Step 6.1: Based on the detection light wavelength and the spatial frequency of the local interference fringes, calculate the slope of the thickness change of the thin film gap (18) in the horizontal and vertical directions of the image; whereby the detection light wavelength is assumed to be... The refractive index of the medium within the thin film gap (18) is The slope of the horizontal thickness change in the image and the slope of the image's longitudinal thickness change They respectively satisfy: Where e represents the wavelength of the detection light. Indicates the refractive index of the medium within the thin film gap (18), This indicates the physical pixel size of the image acquisition component (14). This represents the spatial frequency of the local interference fringes in the horizontal direction of the image. This represents the spatial frequency of the local interference fringes along the vertical axis of the image. The slope of the thickness change of the thin film gap (18) in the horizontal direction of the image is represented by , and e represents the slope of the thickness change of the thin film gap (18) in the vertical direction of the image. Step 6.2, based on the slope of the horizontal thickness change in the image and the slope of the image's longitudinal thickness change Calculate the X-axis tilt angle of the lens (1) to be installed relative to the resonant cavity (2). and Y-axis tilt angle ,satisfy: in, This indicates the X-axis tilt angle of the lens (1) to be installed relative to the resonant cavity (2); This indicates the Y-axis tilt angle of the lens (1) to be installed relative to the resonant cavity (2); Step 6.3, when the small tilt angle satisfies the angular approximation condition, the X-direction tilt angle... and Y-axis tilt angle They are approximated as follows: Thus, the X-axis tilt angle and Y-axis tilt angle of the lens to be installed (1) relative to the resonant cavity (2) are obtained.

8. The method for measuring small angles based on local interference fringes according to claim 7, characterized in that, In step 2.1, if the local interference fringe image is already a grayscale image, then it is directly used as the local interference fringe grayscale image.

9. The method for measuring small angles based on local interference fringes according to claim 7, characterized in that, In step 4.1, the preset threshold is determined based on the maximum amplitude of the stripe spectrum.

Images