A high-precision three-dimensional measurement method for local features of an aircraft shape

Abstract

The present application belongs to the technical field of digital measurement, and particularly relates to a high-precision three-dimensional measurement method for local features of an aircraft shape. First, the imaging center of a camera is aligned with a region to be measured on the surface of the aircraft, and the longitudinal position of a scanning system is adjusted so that the focal plane of the camera is located at an effective scanning position. Then, the included angle between the measurement light path and the surface to be measured is adjusted so that the number of imaging fringe periods is less than 1. The scanning system is controlled to move in a single direction to achieve longitudinal scanning of the surface to be measured. After scanning is completed, the longitudinal light intensity curve is extracted for each pixel point, and the Fourier transform technique and Gaussian curve fitting algorithm are further combined to obtain the accurate focusing position of the pixel point. Finally, height mapping is performed in combination with the scanning step distance to restore the three-dimensional topography of the region to be measured. The technical solution can improve the measurement accuracy, support three-dimensional measurement of small local features of an aircraft shape, and has the characteristics of high demodulation efficiency and wide adaptability.

Description

Technical Field

[0001] This invention belongs to the technical field of digital measurement, and in particular relates to a high-precision three-dimensional measurement method for local features of an aircraft shape. Background Technology

[0002] Even minute deviations in the local features of an aircraft's shape can severely restrict its performance and even threaten pilot safety. Therefore, accurate perception of these local features is crucial for ensuring aircraft production quality and combat performance. Currently, mainstream 3D measurement methods for aircraft shapes are primarily based on vision. This involves using dual or multiple cameras to photograph the area to be measured on the aircraft surface, and then using binocular vision principles to calculate depth and obtain 3D point cloud data of the aircraft's shape. However, this method has relatively low measurement resolution and accuracy, insufficient to support the geometric dimensional analysis of local features of the aircraft's shape.

[0003] In response, Chinese invention patent application number 2011101296377 discloses a high-precision non-contact measurement method and device for the three-dimensional topography of optical freeform surfaces. This method uses a grating projection device to project sinusoidal grating fringes onto the surface of the object being measured. An image acquisition device acquires the deformed fringe pattern modulated by the surface of the object, which is then sent to a computer to reconstruct the three-dimensional topography of the object's surface. A white light scanning interferometric probe performs nanometer-precision scanning measurements on local features of the object. The white light scanning image acquisition device acquires the interference fringe pattern, which is then sent to a computer to obtain the three-dimensional topography data of the measurement area. The data obtained from the grating projection visual inspection unit and the white light scanning interferometric measurement unit are then processed using a multi-sensor massive data fusion algorithm and corresponding error separation and compensation measures to obtain the final result. This invention is mainly applied to high-precision in-situ inspection of parts. While the prior art employs a three-dimensional reconstruction step based on white light interferometry, the accuracy of white light interferometry measurement is sensitive to the tilt of the object's surface. Current related prior art can overcome this problem. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of the prior art by proposing a high-precision three-dimensional measurement method for local features of an aircraft shape. This method is based on the principle of white light interferometry, has extremely high measurement accuracy, and provides excellent reproduction of minute local features of the aircraft shape.

[0005] The technical solution adopted to achieve the above objectives is as follows:

[0006] A high-precision three-dimensional measurement method for local features of an aircraft's shape includes the following steps:

[0007] S1. Set up a white light illumination measurement system, which includes a broadband light source, Tube lens I, Tube lens II, a CCD imaging device, a beam splitter, an interference lens, and a displacement stage; wherein, the interference lens, beam splitter, Tube lens II, and CCD imaging device are arranged sequentially on the same vertical line above the displacement stage; the broadband light source and the beam splitter are on the same horizontal line, and Tube lens I is arranged between them;

[0008] S2, aim the imaging field of view of the white light illumination measurement system at the area to be measured on the aircraft surface;

[0009] S3, using a white light illumination measurement system to scan and acquire images of the area to be measured on the aircraft surface;

[0010] S4, extract the interference light intensity value of each pixel in each image to form a longitudinal light intensity response curve;

[0011] S5. Based on Fourier transform and Gaussian curve fitting, the light intensity signal is processed to obtain the scanning position corresponding to the maximum interference light intensity value, and this position is used as the accurate focusing position of the pixel.

[0012] S6, based on the accurate focusing position of the pixel, performs height mapping in combination with the scanning step distance to complete the three-dimensional shape restoration of the area under test.

[0013] Preferably, in step S3, acquiring an image of the area to be measured on the aircraft surface includes the following steps:

[0014] S31, Adjust the target surface of the scanning camera in the CCD imaging device so that the target surface is parallel to the focal plane of the interference lens.

[0015] S32, Adjust the longitudinal position of the scanning camera in the CCD imaging device so that interference fringes appear in the image of the scanning camera.

[0016] S33, calculate the number of periods of the interference fringes in the imaging field of view; if the number of periods of the interference fringes is greater than 1, adjust the optical path of the beam splitter to change the angle between its optical path and the plane of the area to be measured on the aircraft surface until the number of periods of the interference fringes in the imaging field of view of the camera is less than or equal to 1.

[0017] S34, move the scanning camera upwards until the interference fringes disappear in the camera's imaging field of view, and record the longitudinal position P1 of the scanning camera at this time;

[0018] S35, move the scanning camera downwards until interference fringes appear in the camera's imaging field of view and then disappear again, and record the longitudinal position P2 of this scanning camera.

[0019] S36, set the scan start position to P1 and the scan end position to P2; start scanning based on the scan start position P1 and the scan end position P2, and the scanning camera records the image and saves it to the computer of the CCD imaging device.

[0020] Preferably, in step S4, the interference light intensity value is expressed as:

[0021]

[0022] Where I(p) represents the interference light intensity; I1 represents the reference light intensity; I2 represents the measurement light intensity; Re[R(τ)] d )] represents the real part of the coherence function of the light source; τ d This indicates the time delay between two interfering beams.

[0023] Preferably, in step S32, when the broadband light source interferes, each wavelength of light will produce an independent set of interference fringes, whose Gaussian function broadband spectral distribution is expressed as:

[0024]

[0025] Where S(v) represents the broadband intensity function; exp[] represents the natural exponential function; v represents the spectral frequency; Δv represents the half-height of the Gaussian spectrum; and v0 represents the center frequency of the spectrum.

[0026] Preferably, in step S4, if the two beams separated by the beam splitter are made to have equal intensity, then the interference intensity value is expressed as:

[0027]

[0028] Where I(p) represents the interference light intensity; I0 represents the background intensity; p represents the measurement length; p0 represents the reference arm length; l c λ represents the coherence length of the light source; λ0 represents the center wavelength of the broadband spectrum.

[0029] Preferably, in step S5, a one-dimensional Fourier transform is performed on the light intensity signal. The formula for the one-dimensional Fourier transform is:

[0030]

[0031] Where F(u) is the Fourier transform result; u represents the frequency variable; I(p) represents the interference light intensity; exp[] represents the natural exponential function; i represents the imaginary unit; and dp represents the integral sign with respect to the measurement length p.

[0032] Preferably, in step S5, Gaussian curve fitting involves filtering out the fundamental frequency information using a rectangular window after obtaining the one-dimensional spectrum of the light intensity information, and obtaining the envelope curve of the light intensity curve, which is a Gaussian curve.

[0033] Preferably, in step S6, the height mapping is represented as follows:

[0034] h = P max ×Δp;

[0035] Where h represents the pixel height value; P max Δp represents the precise focus position of a pixel; Δp represents the scan step distance.

[0036] The beneficial effects of this invention are:

[0037] This technical solution proposes a high-precision three-dimensional measurement method for local features of aircraft shape. It employs white light interferometry combined with leveling technology (step S3), improving measurement accuracy and supporting three-dimensional measurement of minute local features of the aircraft shape. Furthermore, this technical solution utilizes Fourier transform and Gaussian curve fitting algorithms, featuring high demodulation efficiency and wide adaptability.

[0038] This technical solution is a non-contact optical measurement method, which is characterized by being non-destructive and highly efficient. Attached Figure Description

[0039] Figure 1 A schematic diagram of the layout structure of a white light illumination measurement system;

[0040] Figure 2 This is a schematic diagram of the signal processing process of this technical solution.

[0041] In the picture:

[0042] 1. Broadband light source; 2. Tube lens I; 3. CCD imaging device; 4. Tube lens II; 5. Beam splitter; 6. Interference objective lens; 7. Displacement stage. Detailed Implementation

[0043] To make the purpose, technical solution and advantages of the invention clearer, the technical solution of the invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the invention, but not all embodiments.

[0044] Therefore, the following detailed description of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0045] Example 1

[0046] This embodiment discloses a high-precision three-dimensional measurement method for local features of an aircraft shape. As a basic implementation scheme of this technical solution, it includes the following steps:

[0047] S1, Deploy a white light illumination measurement system, such as Figure 1 As shown, the white light illumination measurement system includes a broadband light source, Tube lens I, Tube lens II, a CCD imaging device, a beam splitter, an interference lens, and a displacement stage. The interference lens, beam splitter, Tube lens II, and CCD imaging device are sequentially arranged on the same vertical line above the displacement stage. The broadband light source and beam splitter are on the same horizontal line, with Tube lens I positioned between them. The broadband light source provides the white light source for the implementation of this technical solution.

[0048] S2, aim the imaging field of view of the white light illumination measurement system at the area to be measured on the aircraft surface.

[0049] S3 uses a white light illumination measurement system to scan and acquire images of the area to be measured on the aircraft surface.

[0050] S4, extract the interference light intensity value of each pixel in each image to form a longitudinal light intensity response curve.

[0051] At a certain longitudinal scanning position p, when the two beams from the beam splitter satisfy the coherence condition, beam interference can occur, forming stable interference fringes. Based on this, the interference light intensity value is expressed as:

[0052]

[0053] Where I(p) represents the interference light intensity; I1 represents the reference light intensity; I2 represents the measurement light intensity; Re[R(τ)] d )] represents the real part of the coherence function of the light source; τ d This represents the time delay between two interfering beams, and its magnitude is determined by the distance between the field beam splitter and the reference plate.

[0054] S5 processes the light intensity signal based on Fourier transform and Gaussian curve fitting to obtain the scanning position corresponding to the maximum interference light intensity value, and uses this position as the accurate focusing position of the pixel.

[0055] S6, based on the accurate focusing position of the pixel, performs height mapping in combination with the scanning step distance to complete the three-dimensional shape restoration of the area under test.

[0056] The signal processing flow of this technical solution is as follows: Figure 2 As shown, the light intensity curve of each pixel is first extracted, then Fourier transform is performed on it, the fundamental frequency information is filtered out and inverse Fourier transform is performed, and then the target position is located by combining the Gaussian curve fitting algorithm.

[0057] Example 2

[0058] This embodiment discloses a high-precision three-dimensional measurement method for local features of an aircraft shape. As a preferred implementation of this technical solution, it includes the following steps:

[0059] S1. Set up a white light illumination measurement system, which includes a broadband light source, Tube lens I, Tube lens II, a CCD imaging device, a beam splitter, an interference lens, and a displacement stage. The interference lens, beam splitter, Tube lens II, and CCD imaging device are arranged sequentially on the same vertical line above the displacement stage. The broadband light source and the beam splitter are on the same horizontal line, and Tube lens I is arranged between them.

[0060] S2, aim the imaging field of view of the white light illumination measurement system at the area to be measured on the aircraft surface.

[0061] S3. An image of the area to be measured on the aircraft surface is acquired using a white light illumination measurement system. In this step, to achieve optimal measurement conditions, the measurement optical path should be kept as perpendicular as possible to the surface under test. At the start of the measurement, the number of fringe periods in the scanning camera's imaging field of view should be less than or equal to 1 to level the surface. Furthermore, to ensure an effective interference signal, the interference fringes in the scanning camera's image should exhibit a "disappearance-appearance-disappearance" process during the scan.

[0062] Based on this, acquiring an image of the area to be tested on the aircraft surface includes the following steps:

[0063] S31, Adjust the target surface of the scanning camera in the CCD imaging device so that the target surface is parallel to the focal plane of the interference lens.

[0064] S32, adjust the longitudinal position of the scanning camera in the CCD imaging device so that interference fringes appear in the image of the scanning camera.

[0065] S33, calculate the number of periods of the interference fringes in the imaging field of view; if the number of periods of the interference fringes is greater than 1, adjust the optical path of the beam splitter (measurement optical path) to change the angle between its optical path and the plane of the area to be measured on the aircraft surface until the number of periods of the interference fringes in the camera's imaging field of view is less than or equal to 1. According to the theory of white light coherence, interference fringes include black and white fringes, with the same color representing the same altitude value. Therefore, the more numerous and denser the interference fringes within an imaging field of view, the larger the altitude difference within that field of view, meaning that the plane to be measured has an angle relative to the measurement optical path.

[0066] The specific operation involves the following steps: First, rotate the angle controller counterclockwise and observe the changes in the stripes within the imaging field of view. If the stripes become sparser, continue rotating the angle controller counterclockwise until only one black and one white stripe remain in the imaging field of view. Then, move the scanning system up and down until the stripes are clear. If the stripes become denser, rotate the angle controller clockwise until only one black and one white stripe remain in the imaging field of view. Then, move the scanning system up and down until the stripes are clear.

[0067] S34, move the scanning camera upwards until the interference fringes disappear in the camera's imaging field of view, and record the longitudinal position P1 of the scanning camera at this time.

[0068] S35, move the scanning camera downwards until interference fringes appear in the camera's imaging field of view and then disappear again, and record the longitudinal position P2 of this scanning camera.

[0069] S36, set the scan start position to P1 and the scan end position to P2; start scanning based on the scan start position P1 and the scan end position P2, and the scanning camera records the image and saves it to the computer of the CCD imaging device.

[0070] S4, extract the interference light intensity value of each pixel in each image to form a longitudinal light intensity response curve.

[0071] S5. Based on Fourier transform and Gaussian curve fitting, the light intensity signal is processed to obtain the scanning position corresponding to the maximum interference light intensity value. This position is then used as the accurate focusing position of the pixel. It can be understood that the interference signal obtained by this technical solution can be represented as a cosine wave signal modulated by a Gaussian function. To accurately locate the scanning position corresponding to the maximum light intensity value, a Gaussian curve fitting algorithm is needed to fit the discrete signal into a continuous signal.

[0072] S6, based on the accurate focusing position of the pixel, performs height mapping in combination with the scanning step distance to complete the three-dimensional shape restoration of the area under test.

[0073] In this technical solution, the white light illumination measurement system utilizes the poor coherence of the white light source, resulting in interference signals with the highest sensitivity at the peak position.

[0074] Example 3

[0075] This embodiment discloses a high-precision three-dimensional measurement method for local features of an aircraft shape. As a preferred implementation of this technical solution, it includes the following steps:

[0076] S1. Set up a white light illumination measurement system, which includes a broadband light source, Tube lens I, Tube lens II, a CCD imaging device, a beam splitter, an interference lens, and a displacement stage. The interference lens, beam splitter, Tube lens II, and CCD imaging device are arranged sequentially on the same vertical line above the displacement stage. The broadband light source and the beam splitter are on the same horizontal line, and Tube lens I is arranged between them.

[0077] S2, aim the imaging field of view of the white light illumination measurement system at the area to be measured on the aircraft surface.

[0078] S3 uses a white light illumination measurement system to scan and acquire images of the area to be measured on the aircraft surface.

[0079] Acquiring an image of the area to be tested on the aircraft surface includes the following steps:

[0080] S31, Adjust the target surface of the scanning camera in the CCD imaging device so that the target surface is parallel to the focal plane of the interference lens.

[0081] S32, Adjust the longitudinal position of the scanning camera in the CCD imaging device to produce interference fringes in the image captured by the scanning camera. Since the interference formed by the white light source is broadband interference, when broadband light interferes, each wavelength of light will produce an independent set of interference fringes, whose Gaussian function broadband spectral distribution is expressed as:

[0082]

[0083] Where S(v) represents the broadband intensity function; exp[] represents the natural exponential function; v represents the spectral frequency; Δv represents the half-height of the Gaussian spectrum; and v0 represents the center frequency of the spectrum.

[0084] S33, calculate the number of periods of the interference fringes in the imaging field of view; if the number of periods of the interference fringes is greater than 1, adjust the optical path of the beam splitter to change the angle between its optical path and the plane of the area to be measured on the aircraft surface until the number of periods of the interference fringes in the imaging field of view of the camera is less than or equal to 1.

[0085] S34, move the scanning camera upwards until the interference fringes disappear in the camera's imaging field of view, and record the longitudinal position P1 of the scanning camera at this time.

[0086] S35, move the scanning camera downwards until interference fringes appear in the camera's imaging field of view and then disappear again, and record the longitudinal position P2 of this scanning camera.

[0087] S36, set the scan start position to P1 and the scan end position to P2; start scanning based on the scan start position P1 and the scan end position P2, and the scanning camera records the image and saves it to the computer of the CCD imaging device.

[0088] S4, extract the interference light intensity value of each pixel in each image to form a longitudinal light intensity response curve.

[0089] Based on the broad spectral distribution of the Gaussian function, assuming the two beams separated by the beam splitter have equal intensities, the interference intensity value is expressed as:

[0090]

[0091] Where I(p) represents the interference light intensity; I0 represents the background light; p represents the measurement length; p0 represents the reference arm length; l c λ represents the coherence length of the light source; λ0 represents the center wavelength of the broadband spectrum.

[0092] S5 processes the light intensity signal based on Fourier transform and Gaussian curve fitting to obtain the scanning position corresponding to the maximum interference light intensity value, and uses this position as the accurate focusing position of the pixel.

[0093] S6, based on the accurate focusing position of the pixel, performs height mapping in combination with the scanning step distance to complete the three-dimensional shape restoration of the area under test.

[0094] Example 4

[0095] This embodiment discloses a high-precision three-dimensional measurement method for local features of an aircraft shape. As a basic implementation scheme of this technical solution, it includes the following steps:

[0096] S1. Set up a white light illumination measurement system, which includes a broadband light source, Tube lens I, Tube lens II, a CCD imaging device, a beam splitter, an interference lens, and a displacement stage. The interference lens, beam splitter, Tube lens II, and CCD imaging device are arranged sequentially on the same vertical line above the displacement stage. The broadband light source and the beam splitter are on the same horizontal line, and Tube lens I is arranged between them.

[0097] S2, aim the imaging field of view of the white light illumination measurement system at the area to be measured on the aircraft surface.

[0098] S3 uses a white light illumination measurement system to scan and acquire images of the area to be measured on the aircraft surface.

[0099] S4, extract the interference light intensity value of each pixel in each image to form a longitudinal light intensity response curve.

[0100] S5 processes the light intensity signal based on Fourier transform and Gaussian curve fitting to obtain the scanning position corresponding to the maximum interference light intensity value, and uses this position as the accurate focusing position of the pixel. Specifically:

[0101] The light intensity signal in step S4 is a one-dimensional signal, therefore a one-dimensional Fourier transform is performed on it. The formula for the one-dimensional Fourier transform is:

[0102]

[0103] Where F(u) is the Fourier transform result; u represents the frequency variable; I(p) represents the interference light intensity; exp[ ] represents the natural exponential function; i represents the imaginary unit; and dp represents the integral sign with respect to the measurement length p.

[0104] Gaussian curve fitting involves obtaining the one-dimensional spectrum of light intensity information, filtering out the fundamental frequency information using a rectangular window, and obtaining the envelope curve of the light intensity curve, which is a Gaussian curve. Peak location of this Gaussian curve yields the scanning position P corresponding to the maximum light intensity value. max This position is used as the accurate focus point for the pixel.

[0105] S6, based on the accurate focusing position of each pixel, performs height mapping in conjunction with the scanning step distance to complete the 3D topography reconstruction of the area under test. The height mapping is expressed as:

[0106] h = P max ×Δp;

[0107] Where h represents the pixel height value; P max Δp represents the precise focus position of a pixel; Δp represents the scan step distance.

[0108] Example 5

[0109] This embodiment discloses a high-precision three-dimensional measurement method for local features of an aircraft shape. As a basic implementation scheme of this technical solution, it includes the following steps:

[0110] S1. Set up a white light illumination measurement system, as shown in Figure 1. The white light illumination measurement system includes a broadband light source, Tube lens I, Tube lens II, a CCD imaging device, a beam splitter, an interference objective lens, and a displacement stage. The interference objective lens, beam splitter, Tube lens II, and CCD imaging device are arranged sequentially on the same vertical line above the displacement stage. The broadband light source and the beam splitter are on the same horizontal line, and Tube lens I is arranged between them.

[0111] S2, aim the imaging field of view of the white light illumination measurement system at the area to be measured on the aircraft surface.

[0112] S3 uses a white light illumination measurement system to scan and acquire images of the area to be measured on the aircraft surface.

[0113] Acquiring an image of the area to be tested on the aircraft surface includes the following steps:

[0114] S31, Adjust the target surface of the scanning camera in the CCD imaging device so that the target surface is parallel to the focal plane of the interference lens.

[0115] S32, Adjust the longitudinal position of the scanning camera in the CCD imaging device to produce interference fringes in the image captured by the scanning camera. The interference formed by the white light source is broadband interference. When broadband light sources interfere, each wavelength of light will produce an independent set of interference fringes, whose Gaussian function broadband spectral distribution is expressed as:

[0116]

[0117] Where S(v) represents the broadband intensity function; exp[ ] represents the natural exponential function; v represents the spectral frequency; Δv represents the half-height of the Gaussian spectrum; and v0 represents the center frequency of the spectrum.

[0118] S33, calculate the number of periods of the interference fringes in the imaging field of view; if the number of periods of the interference fringes is greater than 1, adjust the optical path of the beam splitter to change the angle between its optical path and the plane of the area to be measured on the aircraft surface until the number of periods of the interference fringes in the imaging field of view of the camera is less than or equal to 1.

[0119] S34, move the scanning camera upwards until the interference fringes disappear in the camera's imaging field of view, and record the longitudinal position P1 of the scanning camera at this time.

[0120] S35, move the scanning camera downwards until interference fringes appear in the camera's imaging field of view and then disappear again, and record the longitudinal position P2 of this scanning camera.

[0121] S36, set the scan start position to P1 and the scan end position to P2; start scanning based on the scan start position P1 and the scan end position P2, and the scanning camera records the image and saves it to the computer of the CCD imaging device.

[0122] S4, extract the interference light intensity value of each pixel in each image to form a longitudinal light intensity response curve.

[0123] At a certain longitudinal scanning position p, when the two beams from the beam splitter satisfy the coherence condition, beam interference can occur, forming stable interference fringes. Based on this, the interference light intensity value is expressed as:

[0124]

[0125] Where I(p) represents the interference light intensity; I1 represents the reference light intensity; I2 represents the measurement light intensity; Re[R(τ)] d )] represents the real part of the coherence function of the light source; τ d This indicates the time delay between two interfering beams.

[0126] Based on the broad spectral distribution of the Gaussian function of the interference fringes, the interference intensity is the broad spectral interference intensity. Building upon this, assuming the two beams separated by the beam splitter have equal intensities, the broad spectral interference intensity (i.e., the interference light intensity) is expressed as:

[0127]

[0128] Where I(p) represents the interference light intensity; I0 represents the background light; p represents the measurement length; p0 represents the reference arm length; l c λ represents the coherence length of the light source; λ0 represents the center wavelength of the broadband spectrum.

[0129] S5 processes the light intensity signal based on Fourier transform and Gaussian curve fitting to obtain the scanning position corresponding to the maximum interference light intensity value, and uses this position as the accurate focusing position of the pixel. Wherein:

[0130] The light intensity signal in step S4 is a one-dimensional signal. A one-dimensional Fourier transform is performed on the light intensity signal. The formula for the one-dimensional Fourier transform is:

[0131]

[0132] Where F(u) is the Fourier transform result; u represents the frequency variable; I(p) represents the interference light intensity; exp[ ] represents the natural exponential function; i represents the imaginary unit; and dp represents the integral sign with respect to the measurement length p.

[0133] Furthermore, Gaussian curve fitting involves filtering out the fundamental frequency information using a rectangular window after obtaining the one-dimensional spectrum of the light intensity information, resulting in the envelope curve of the light intensity curve, which is a Gaussian curve. Peak location of this curve yields the scanning position P corresponding to the maximum light intensity value. max This position is taken as the accurate focus position P of the pixel. max .

[0134] S6, based on the accurate focusing position of each pixel, combines the scanning step distance to perform height mapping, thereby completing the 3D topography restoration of the area under test, as shown below:

[0135] h = P max ×Δp;

[0136] Where h represents the pixel height value; P max Δp represents the precise focus position of a pixel; Δp represents the scan step distance.

[0137] A standard step with a height of 150 nm was used as the experimental sample, and repeatability experiments were conducted using the above-described technical solution. The experimental results are shown in the table below. The experimental results show that the measurement repeatability of this technical solution is better than 0.1%, and the measurement accuracy is better than 1 nm.

[0138] Number of experiments Experimental results (nm) 1 150.2 2 149.7 3 150.9 4 150.8 average value 150.4 Measurement repeatability <0.1％ Measurement accuracy <1nm

Claims

1. A method for high-precision three-dimensional measurement of local features of an aircraft shape, characterized in that, The method comprises the following steps: S1, a white light illumination measurement system is arranged, the white light illumination measurement system comprising a wide spectrum light source, a Tube lens I, a Tube lens II, a CCD imaging device, a beam splitter, an interference objective and a displacement table; the interference objective, the beam splitter, the Tube lens II and the CCD imaging device are arranged in sequence on the same vertical line above the displacement table; the wide spectrum light source and the beam splitter are on the same horizontal line, and the Tube lens I is arranged between the wide spectrum light source and the beam splitter; S2, the imaging field range of the white light illumination measurement system is aimed at the region to be measured on the surface of the aircraft; S3, the image of the region to be measured on the surface of the aircraft is obtained by scanning using the white light illumination measurement system, comprising the following steps: S31, the target surface of the scanning camera in the CCD imaging device is adjusted so as to be parallel to the lens focal surface of the interference objective; S32, the longitudinal position of the scanning camera in the CCD imaging device is adjusted so that the interference fringes appear in the imaging of the scanning camera; S33, the period number of the interference fringes in the imaging field is calculated; if the period number of the interference fringes is greater than 1, the optical path of the beam splitter is adjusted to change the angle between the optical path of the beam splitter and the plane of the region to be measured on the surface of the aircraft, until the period number of the interference fringes in the imaging field of the camera is less than or equal to 1; S34, move the scanning camera upward until the interference fringes disappear in the imaging field of view of the camera, record the longitudinal position of the scanning camera at this time ; S35, move the scanning camera downward until the interference fringes appear and disappear again in the imaging field of view of the camera, record the longitudinal position of this scanning camera ; S36, set the scanning start position as , and the scanning end position as ; start scanning based on the scanning start position and the scanning end position , and the scanning camera records the imaging and saves it to the computer of the CCD imaging device; S4, the interference light intensity value of the pixel point in each image is extracted to form a longitudinal light intensity response curve; the interference light intensity value is represented as: ; wherein, represents the interference light intensity; represents the reference light intensity; represents the measurement light intensity; represents the real part of the light source coherence function; represents the time delay between the two beams of interference light; S5, based on Fourier transform and Gaussian curve fitting processing light intensity signal, get the corresponding scanning position when the interference light intensity value is maximum, this position as the pixel point accurate focusing position; wherein, the light intensity signal is one-dimensional Fourier transform, one-dimensional Fourier transform formula is: ; is the Fourier transform result; represents the frequency variable; represents the natural exponential function; represents the imaginary unit; represents the integral sign for the measured length ; S6, based on the pixel accurate focusing position, height mapping is performed in combination with the scanning step distance to complete three-dimensional topography recovery of the region to be measured; the height mapping is represented as: ; wherein, represents the pixel height value; represents the pixel accurate focusing position; represents the scanning step distance.

2. The method of claim 1, wherein the method further comprises: In the step S32, when the wide spectrum light source interferes, each wavelength of light wave will generate an independent set of interference fringes, and the Gaussian function wide spectrum distribution is represented as: ； wherein, represents a wide spectrum intensity function; represents a spectral frequency, represents a half-height of a Gaussian spectrum, represents a center frequency of a spectrum.

3. The method of claim 1, wherein the method further comprises: In the step S4, if the light intensity of the two beams split by the beam splitter is equal, the interference light intensity value is represented as: ； wherein, represents the background light intensity; represents the measurement length; represents the reference arm length; represents the light source coherence length; represents the wide spectrum center wavelength.

4. The method of claim 1, wherein, In the step S5, the Gaussian curve fitting is to filter out the fundamental frequency information by using a rectangular window after obtaining the one-dimensional spectrum of the light intensity information, so as to obtain the envelope curve of the light intensity curve, which is a Gaussian curve.

Images