High-precision three-dimensional measurement method for local features of aircraft profile

Abstract

The invention belongs to the technical field of digital measurement, and particularly relates to a high-precision three-dimensional measurement method for aircraft profile local features, which comprises the following steps: firstly, aligning a camera imaging center to an aircraft surface area to be measured, and adjusting the longitudinal position of a scanning system to enable a camera focal plane to be positioned at an effective scanning position; then adjusting the included angle between the measuring light path and the surface to be measured, so that the period number of imaging fringes is within 1; controlling the scanning system to move in a single direction so as to longitudinally scan the surface to be measured; after scanning is completed, a longitudinal light intensity curve is extracted for each pixel point, and an accurate focusing position of the pixel point is obtained by further combining a Fourier transform technology and a Gaussian curve fitting algorithm; and finally performing height mapping by combining the scanning step pitch so as to recover the three-dimensional shape of the to-be-detected area. The technical scheme can improve the measurement precision, supports the three-dimensional measurement of the tiny local features of the aircraft profile, and has the characteristics of high demodulation efficiency and wide adaptability.

Description

Technical Field

[0001] The 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 aircraft shape. Background Art

[0002] Slight deviations in the local features of an aircraft's shape can seriously restrict the performance of the aircraft and even threaten the life of the pilot. Therefore, accurate perception of the local features of an aircraft's shape is of great significance for ensuring the quality of aircraft production and combat performance. The current mainstream three-dimensional measurement method for aircraft shape is mainly based on visual measurement. It uses dual or multi-cameras to photograph the surface area to be measured, and uses the principle of binocular vision to perform depth solution to obtain the three-dimensional point cloud data of the aircraft shape. However, this method has low measurement resolution and accuracy, which is not enough to support the geometric size analysis of local features of the aircraft shape.

[0003] In this regard, the Chinese invention patent with application number 2011101296377 in the prior art discloses a high-precision non-contact measurement method and device for the three-dimensional morphology of an optical free-form surface, which uses a grating projection device to project sinusoidal grating stripes on the surface of the object to be measured, and an image acquisition device obtains a deformed stripe pattern modulated by the surface of the object to be measured, and sends it to a computer to restore the three-dimensional morphology of the surface of the object to be measured; a white light scanning interferometer probe is used to perform nanometer-level precision scanning and measurement of the local features of the object to be measured, and a white light scanning image acquisition device obtains an interference stripe pattern, and sends it to a computer to obtain the three-dimensional morphology data of the measurement area; the data measured by the grating projection visual detection unit and the white light scanning interferometer measurement unit are obtained by a multi-sensor massive data fusion algorithm and corresponding error separation and compensation measures. The present invention is mainly used for high-precision in-situ detection of parts. The prior art adopts a three-dimensional reconstruction step based on white light interferometry technology, but the accuracy of white light interferometry measurement is more sensitive to the inclination of the object surface. The current related prior art can overcome such problems. Summary of the invention

[0004] The purpose of the present invention is to address the deficiencies of the above-mentioned prior art and to propose a high-precision three-dimensional measurement method for local features of aircraft shape. The method is based on the principle of white light interferometry technology, has extremely high measurement accuracy, and has good restoration of tiny local features of aircraft shape.

[0005] The technical solutions adopted to achieve the above purpose are as follows:

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

[0007] S1, lay out the white light illumination measurement system, which includes a wide-spectrum light source, Tube lens I, Tube lens II, CCD imaging device, spectroscope, interference objective lens and translation stage; wherein, the interference objective lens, spectroscope, Tube lens II and CCD imaging device are sequentially arranged on the same vertical straight line above the translation stage; the wide-spectrum light source and the spectroscope are on the same horizontal straight line, and Tube lens I is arranged between them;

[0008] S2, aiming 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 an image of the area to be measured on the aircraft surface;

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

[0011] S5, processing 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 using this position as the accurate focusing position of the pixel point;

[0012] S6, based on the accurate focus position of the pixel point and combined with the scanning step length, height mapping is performed to complete the three-dimensional morphology restoration of the area to be measured.

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

[0014] S31, adjusting 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 objective lens;

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

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

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

[0018] S35, moving the scanning camera downward until interference fringes appear and disappear again in the camera imaging field of view, and recording the longitudinal position P2 of the scanning camera;

[0019] S36, setting the scanning start position to P1 and the scanning end position to P2; starting scanning based on the scanning start position P1 and the scanning end position P2, 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 light source coherence function; τ d Represents the time delay between two interfering light beams.

[0023] Preferably, in step S32, when interference occurs in the broad spectrum light source, each wavelength of light wave will generate an independent set of interference fringes, and its Gaussian function broad spectrum distribution is expressed as:

[0024]

[0025] Where S(v) represents the wide spectrum 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, the intensities of the two beams separated by the beam splitter are equal, and the interference light 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 represents the coherence length of the light source; λ0 represents the central wavelength of the wide spectrum.

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

[0030]

[0031] Wherein, 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; dp represents the integral sign for the measured length p.

[0032] Preferably, in step S5, the Gaussian curve fitting is to obtain the envelope curve of the light intensity curve as a Gaussian curve by filtering out the fundamental frequency information with a rectangular window after obtaining the one-dimensional spectrum of the light intensity information.

[0033] Preferably, in step S6, the height map is expressed as:

[0034] h=P max ×Δp;

[0035] Where h represents the pixel height value; P max Indicates the exact focus position of the pixel; Δp indicates the scanning step.

[0036] Beneficial effects of the present invention:

[0037] This technical solution proposes a high-precision three-dimensional measurement method for local features of aircraft shape, which uses a white light interferometric measurement method and combines the leveling technology (step S3) to improve the measurement accuracy and support the three-dimensional measurement of small local features of aircraft shape. In addition, this technical solution also uses Fourier transform and Gaussian curve fitting algorithms, which have the characteristics of high demodulation efficiency and wide adaptability.

[0038] This technical solution is a non-contact optical measurement method, which has the characteristics of being non-destructive and highly efficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a schematic diagram of the layout structure of the 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 figure:

[0042] 1. Broad spectrum light source; 2. Tube lens I; 3. CCD imaging device; 4. Tube lens II; 5. Beam splitter; 6. Interference objective lens; 7. Translation stage. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical solution and advantages of the invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings in the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments.

[0044] Therefore, the following detailed description of the invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] Example 1

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

[0047] S1, set up the white light illumination measurement system, such as Figure 1 As shown, the white light illumination measurement system includes a wide spectrum light source, Tube lens I, Tube lens II, CCD imaging device, spectroscope, interference objective lens and translation stage; wherein, the interference objective lens, spectroscope, Tube lens II and CCD imaging device are arranged in sequence on the same vertical line above the translation stage; the wide spectrum light source and the spectroscope are on the same horizontal line, and Tube lens I is arranged between them. The wide spectrum light source provides a 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, using a white light illumination measurement system to scan and acquire an image of the area to be measured on the aircraft surface.

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

[0051] Among them, at a certain longitudinal scanning position p, when the two beams of the beam splitter meet the coherence condition, beam interference can occur to form 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 light source coherence function; τ d It represents the time delay between two interfering light beams, and its size is determined by the distance from the on-site beam splitter to the reference board.

[0054] S5, processing 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 using this position as the accurate focusing position of the pixel point.

[0055] S6, based on the accurate focus position of the pixel point and combined with the scanning step length, height mapping is performed to complete the three-dimensional morphology restoration of the area to be measured.

[0056] The signal processing flow of this technical solution is as follows Figure 2 As shown, the pixel light intensity curve is first extracted, then Fourier transform is performed on it, the baseband information is filtered out and inverse Fourier transform is performed, and the target position is further 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, which, as a preferred implementation scheme of the technical solution, includes the following steps:

[0059] S1, arrange the white light illumination measurement system, which includes a wide-spectrum light source, Tube lens I, Tube lens II, CCD imaging device, spectroscope, interference objective lens and translation stage; wherein, the interference objective lens, spectroscope, Tube lens II and CCD imaging device are arranged in sequence on the same vertical line above the translation stage; the wide-spectrum light source and the spectroscope 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, use the white light illumination measurement system to scan and obtain an image of the area to be measured on the aircraft surface. In this step, in order to achieve the best measurement conditions, it is necessary to ensure that the measurement light path is perpendicular to the surface to be measured as much as possible, and at the beginning of the measurement, the number of fringe cycles in the imaging field of the scanning camera is less than or equal to 1 to achieve the purpose of leveling the surface to be measured. In addition, in order to ensure that an effective interference signal is obtained, it is necessary to ensure that the imaging of the interference fringes in the scanning camera during scanning has a "disappearance-appearance-disappearance" process.

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

[0063] S31, adjusting 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 objective lens.

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

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

[0066] The specific operation involved is: first rotate the angle controller counterclockwise to observe the changes in the stripes in the imaging field of view. If the stripes become sparse, continue to rotate 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 dense, 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 upward until the interference fringes disappear in the camera imaging field of view, and record the longitudinal position P1 of the scanning camera at this time.

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

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

[0070] S4, extracting the interference light intensity value of the pixel point 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, and this position is used as the accurate focusing position of the pixel point. It can be understood that the interference signal obtained by this technical solution can be expressed as a cosine wave signal modulated by a Gaussian function. In order to accurately locate the scanning position corresponding to the maximum light intensity value, a Gaussian curve fitting algorithm is required to fit the discrete signal into a continuous signal.

[0072] S6, based on the accurate focus position of the pixel point and combined with the scanning step length, height mapping is performed to complete the three-dimensional morphology restoration of the area to be measured.

[0073] In the technical solution, the technical solution is based on a white light illumination measurement system, which utilizes the poor coherence of the white light source, and the interference signal formed has 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, which, as a preferred implementation scheme of the technical solution, includes the following steps:

[0076] S1, arrange the white light illumination measurement system, which includes a wide-spectrum light source, Tube lens I, Tube lens II, CCD imaging device, spectroscope, interference objective lens and translation stage; wherein, the interference objective lens, spectroscope, Tube lens II and CCD imaging device are arranged in sequence on the same vertical line above the translation stage; the wide-spectrum light source and the spectroscope 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, using a white light illumination measurement system to scan and acquire an image of the area to be measured on the aircraft surface.

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

[0080] S31, adjusting 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 objective lens.

[0081] S32, adjusting the longitudinal position of the scanning camera in the CCD imaging device so that interference fringes appear in the imaging of the scanning camera. Since the interference formed by the white light source belongs to wide spectrum interference, when the wide spectrum light source interferes, each wavelength of light wave will produce an independent set of interference fringes, and its Gaussian function wide spectrum distribution is expressed as:

[0082]

[0083] Where S(v) represents the wide spectrum 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, calculating the period number of the interference fringes in the imaging field of view; if the period number of the interference fringes is greater than 1, adjusting the optical path of the beam splitter to change the angle between the optical path and the plane of the aircraft surface area to be measured until the period number of the interference fringes in the camera imaging field of view is less than or equal to 1.

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

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

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

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

[0089] Based on the wide spectral distribution of the Gaussian function, the intensity of the two beams separated by the beam splitter is equal, and the interference light 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 represents the coherence length of the light source; λ0 represents the central wavelength of the wide spectrum.

[0092] S5, processing 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 using this position as the accurate focusing position of the pixel point.

[0093] S6, based on the accurate focus position of the pixel point and combined with the scanning step length, height mapping is performed to complete the three-dimensional morphology restoration of the area to be measured.

[0094] Example 4

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

[0096] S1, arrange the white light illumination measurement system, which includes a wide-spectrum light source, Tube lens I, Tube lens II, CCD imaging device, spectroscope, interference objective lens and translation stage; wherein, the interference objective lens, spectroscope, Tube lens II and CCD imaging device are arranged in sequence on the same vertical line above the translation stage; the wide-spectrum light source and the spectroscope 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, using a white light illumination measurement system to scan and acquire an image of the area to be measured on the aircraft surface.

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

[0100] 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 point. Specifically:

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

[0102]

[0103] Wherein, 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; dp represents the integral sign for the measured length p.

[0104] Gaussian curve fitting is to obtain the one-dimensional spectrum of the light intensity information, filter out the fundamental frequency information with a rectangular window, and obtain the envelope curve of the light intensity curve, which is a Gaussian curve. The peak position of the Gaussian curve can be obtained to obtain the scanning position P corresponding to the maximum light intensity value. max , and use this position as the accurate focus position of the pixel.

[0105] S6, based on the accurate focus position of the pixel point, combined with the scanning step, height mapping is performed to complete the three-dimensional morphology restoration of the area to be measured. The height mapping is expressed as:

[0106] h=P max ×Δp;

[0107] Where h represents the pixel height value; P max Indicates the exact focus position of the pixel; Δp indicates the scanning step.

[0108] Example 5

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

[0110] S1, arrange the white light illumination measurement system, as shown in 1, the white light illumination measurement system includes a wide-spectrum light source, Tube lens I, Tube lens II, CCD imaging device, spectroscope, interference objective lens and translation stage; wherein, the interference objective lens, spectroscope, Tube lens II and CCD imaging device are arranged in sequence on the same vertical straight line above the translation stage; the wide-spectrum light source and the spectroscope are on the same horizontal straight 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, using a white light illumination measurement system to scan and acquire an image of the area to be measured on the aircraft surface.

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

[0114] S31, adjusting 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 objective lens.

[0115] S32, adjusting the longitudinal position of the scanning camera in the CCD imaging device so that interference fringes appear in the imaging of the scanning camera. The interference formed by the white light source belongs to wide spectrum interference. When the wide spectrum light source interferes, each wavelength of light wave will produce an independent set of interference fringes, and its Gaussian function wide spectrum distribution is expressed as:

[0116]

[0117] Where S(v) represents the wide spectrum 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, calculating the period number of the interference fringes in the imaging field of view; if the period number of the interference fringes is greater than 1, adjusting the optical path of the beam splitter to change the angle between the optical path and the plane of the aircraft surface area to be measured until the period number of the interference fringes in the camera imaging field of view is less than or equal to 1.

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

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

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

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

[0123] At a certain longitudinal scanning position p, when the two beams of the beam splitter meet the coherence condition, beam interference can occur to form 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 light source coherence function; τ d Represents the time delay between two interfering light beams.

[0126] Based on the Gaussian function wide spectrum distribution of interference fringes, the interference light intensity is the wide spectrum interference intensity. On this basis, assuming that the two beams of light separated by the spectroscope have equal intensities, the wide spectrum interference intensity (i.e. 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 represents the coherence length of the light source; λ0 represents the central wavelength of the wide spectrum.

[0129] 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 point. 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 one-dimensional Fourier transform formula is:

[0131]

[0132] Wherein, 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; dp represents the integral sign for the measured length p.

[0133] Furthermore, Gaussian curve fitting is to obtain the one-dimensional spectrum of the light intensity information, filter out the fundamental frequency information with a rectangular window, and obtain the envelope curve of the light intensity curve, which is a Gaussian curve. The peak position of the curve can be obtained to obtain the scanning position P corresponding to the maximum light intensity value. max , take this position as the accurate focus position of the pixel point P max .

[0134] S6, based on the accurate focus position of the pixel point, combined with the scanning step distance, performs height mapping to complete the three-dimensional morphology restoration of the area to be measured, which is expressed as:

[0135] h=P max ×Δp;

[0136] Where h represents the pixel height value; P max Indicates the exact focus position of the pixel; Δp indicates the scanning step.

[0137] The standard step with a height of 150 nm was used as the experimental sample, and the repeatability experiment was carried out using the above technical solution. The experimental results are shown in the following table. 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 high-precision three-dimensional measurement method for local features of aircraft shape, It is characterized in that The following steps are involved: S1, lay out the white light illumination measurement system, which includes a wide-spectrum light source, Tube lens I, Tube lens II, CCD imaging device, spectroscope, interference objective lens and translation stage; wherein, the interference objective lens, spectroscope, Tube lens II and CCD imaging device are sequentially arranged on the same vertical straight line above the translation stage; the wide-spectrum light source and the spectroscope are on the same horizontal straight line, and Tube lens I is arranged between them; S2, aiming the imaging field of view of the white light illumination measurement system at the area to be measured on the aircraft surface; S3, using a white light illumination measurement system to scan and acquire an image of the area to be measured on the aircraft surface; S4, extracting the interference light intensity value of the pixel point in each image to form a longitudinal light intensity response curve; S5, processing 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 using this position as the accurate focusing position of the pixel point; S6, based on the accurate focus position of the pixel point and combined with the scanning step length, height mapping is performed to complete the three-dimensional morphology restoration of the area to be measured.

2. A high-precision three-dimensional measurement method for local features of an aircraft shape as claimed in claim 1, It is characterized in that In step S3, obtaining an image of the area to be measured on the aircraft surface includes the following steps: S31, adjusting 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 objective lens; S32, adjusting the longitudinal position of the scanning camera in the CCD imaging device so that interference fringes appear in the imaging of the scanning camera; S33, calculating the period number of interference fringes in the imaging field of view; if the period number of interference fringes is greater than 1, adjusting the optical path of the beam splitter to change the angle between the optical path and the plane of the aircraft surface area to be measured, until the period number of interference fringes in the camera imaging field of view is less than or equal to 1; S34, move the scanning camera upward until the interference fringes disappear in the camera imaging field of view, and record the longitudinal position P of the scanning camera at this time. 1 ; S35, move the scanning camera downward until interference fringes appear and disappear again in the camera imaging field of view, and record the longitudinal position P of this scanning camera. 2 ; S36, set the scanning start position to P 1 , the scanning end position is P 2 ; Based on the scanning starting position P 1 and scanning end position P 2 Start scanning, the scanning camera records the image and saves it to the computer of the CCD imaging device.

3. A high-precision three-dimensional measurement method for local features of aircraft shape as claimed in claim 1, It is characterized in that In step S4, the interference light intensity value is expressed as: Where, I(p) represents the interference light intensity; I 1 Indicates the reference light intensity; I 2 Represents the measured light intensity; Re[R(τ d )] represents the real part of the light source coherence function; τ d Represents the time delay between two interfering light beams.

4. A high-precision three-dimensional measurement method for local features of an aircraft shape as claimed in claim 2, It is characterized in that In step S32, when the wide spectrum light source interferes, each wavelength of light wave will generate an independent set of interference fringes, and its Gaussian function wide spectrum distribution is expressed as: Where S(v) represents the broad spectrum intensity function; exp[ ] represents the natural exponential function; v represents the spectral frequency, Δv represents the half height of the Gaussian spectrum, and v 0 Represents the center frequency of the spectrum.

5. A high-precision three-dimensional measurement method for local features of an aircraft shape as claimed in claim 4, It is characterized in that In step S4, the light intensities of the two beams separated by the beam splitter are equal, and the interference light intensity value is expressed as: Where, I(p) represents the interference light intensity; I 0 represents the background light intensity; p represents the measured length; p 0 Expressed as the reference arm length; l c represents the coherence length of the light source; λ 0 Indicates the central wavelength of the broad spectrum.

6. A high-precision three-dimensional measurement method for local features of aircraft shape as claimed in claim 1, It is characterized in that In step S5, a one-dimensional Fourier transform is performed on the light intensity signal, and the one-dimensional Fourier transform formula is: Wherein, 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; dp represents the integral sign for the measured length p.

7. A high-precision three-dimensional measurement method for local features of an aircraft shape as claimed in claim 6, It is characterized in that In step S5, Gaussian curve fitting is to obtain the envelope curve of the light intensity curve, which is a Gaussian curve, by filtering out the fundamental frequency information with a rectangular window after obtaining the one-dimensional spectrum of the light intensity information.

8. A high-precision three-dimensional measurement method for local features of an aircraft shape as claimed in claim 1, It is characterized in that In step S6, the height map is expressed as: h=P max ×Ap; Where h represents the pixel height value; P max Indicates the exact focus position of the pixel; Δp indicates the scanning step.

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