Device for FTP calibration and FTP calibration method

Abstract

The invention discloses a device for FTP (File Transfer Protocol) calibration and an FTP calibration method, relates to the field of aero-engine testing, and is used for accurately calibrating FTP of an inlet rotor blade of an aero-engine in a limited space. The device comprises a grating projection device, a reflector, a calibration plate and an imaging module, stripe light projected to a rotor blade by the grating projection device is reflected and projected to the calibration plate through the reflector, the imaging module collects an image of the calibration plate in the reflector, and FTP calibration is carried out by using multiple groups of collected stripe images and calibration plate images. According to the invention, the precision limitation that only light path parameters during rotor blade morphology measurement can be approximately calibrated due to the fact that a calibration plate cannot be arranged at the rotor blade in the engine is broken through.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of aero-engine testing, and particularly relates to a device for FTP (Fourier transform profilometry) calibration and a FTP calibration method. BACKGROUND

[0002] It is of great significance to measure the surface profile of a fan blade on line and evaluate the damage degree of the fan blade for fine evaluation of aerodynamic and strength changes. However, there is no effective means for measuring the damage degree of the surface profile of the fan blade on line at present.

[0003] In the process of three-dimensional measurement of high-speed changing dynamic scenes, even if the shooting speed is fast, theoretically, the patterns photographed by the front and rear frames are changed in position, so that the three-dimensional reconstruction algorithm based on a single frame pattern is most suitable for the three-dimensional measurement scheme of dynamic scenes in principle. In order to meet the requirements of three-dimensional measurement of dynamic scenes, scholars have designed a series of three-dimensional reconstruction algorithms based on a single frame pattern. These algorithms are roughly divided into two categories: 1) single-frame reconstruction method based on binary pattern projection; and 2) single-frame reconstruction method based on stripe pattern projection.

[0004] The single-frame reconstruction method based on binary pattern projection uniquely marks each sampling point in the plane by projecting a designed code pattern, but this method needs to use the pixels in the surrounding area of the current point to assist in coding, and the spatial resolution is not high, and the recovery ability for detailed information of the object is weak.

[0005] The single-frame method based on stripe pattern projection projects gray continuous change stripe information, and then extracts phase information containing object height information in the transform domain, and completes three-dimensional reconstruction by using point-by-point phase information dense coding to mark the surface to be measured. Among them, FTP has the characteristics of high calculation efficiency and easy parameter selection, and has been most widely applied in high-speed three-dimensional topography measurement of transient processes.

[0006] Before three-dimensional reconstruction by FTP, the grating projection device for emitting stripe light and the imaging module for receiving stripe light need to be calibrated (internal and external parameters). In the known three-dimensional topography calibration method of an imaging object, a calibration plate can be placed at the position of the imaging object, stripe light is emitted to the calibration plate, and then the imaging module is used for acquisition, and the parameters are calibrated according to the image pairs acquired when there is / without stripe light. However, this method is only suitable for regular imaging objects, and for irregular objects such as rotor blades (there are flow tubes, fairing support plates and other components in the inlet), the calibration plate cannot be placed at the position of the imaging object, and only the calibration plate can be placed close to the rotor blade for approximate FTP calibration, and there is a certain error between the calibration value and the actual parameter. SUMMARY

[0007] The application aims at providing a device and method for FTP calibration to accurately calibrate the FTP of an aero-engine inlet rotor blade in a limited space.

[0008] The technical scheme adopted by the application is as follows: A device for FTP calibration is used for online measurement of the surface morphology of an aero-engine inlet rotor blade, and the device comprises: A grating projection device emits fringe light to the rotor blade in an open state; A mirror is arranged between the rotor blade and the grating projection device to reflect the fringe light to a calibration plate; An imaging module is used to respectively collect images of the calibration plate in the mirror with and without the fringe light.

[0009] Further, the mirror is parallel to the aero-engine inlet interface.

[0010] Further, the distance from the mirror to the calibration plate is equal to the distance from the mirror to the rotor blade or the difference is within a set range.

[0011] Further, the calibration plate is a chessboard pattern calibration plate, and the number of chessboards contained in the rows and columns of the chessboard pattern is not equal.

[0012] The application also provides an FTP calibration method based on the device for FTP calibration, and the method comprises: S1, the grating projection device and the imaging module are respectively arranged according to the device for FTP calibration and are debugged; S2, the device for FTP calibration is built; S3, the grating projection device is alternately opened and closed for multiple rounds, and the imaging module is used to alternately collect multiple groups of fringe images of the calibration plate with fringe light and calibration plate images without fringe light; S4, FTP calibration is performed by using the collected multiple groups of fringe images and calibration plate images.

[0013] Further, step S3 comprises: S31, the grating projection device is closed, and the imaging module is used to collect the image of the calibration plate in the mirror as a calibration plate image; S32, the grating projection device is opened to reflect the fringe light to the calibration plate through the mirror, and the imaging module is used to collect the image of the calibration plate in the mirror as a fringe image; S33, repeating step S31 and step S32 for multiple rounds, each round adjusting the pose of the calibration board relative to the mirror, and each round obtaining a set of calibration board images and fringe images.

[0014] Further, step S4 comprises: S41, calibrating the intrinsic and extrinsic parameters of the imaging module using the acquired calibration board images; S42, calculating the phase of the fringe image based on Fourier transform according to the fringe image; S43, constructing a parameter model matrix based on the phase calculated in step S42 according to the calibration board image, and solving the calibration coefficient; S44, evaluating the calibration error of the calibration coefficient, and if the calibration error does not meet the set standard, jumping to step S3 until the calibration error of the calibration coefficient meets the set standard.

[0015] Further, step S42 comprises: reading the fringe image; windowing the fringe image; performing Fourier transform on the windowed fringe image, and extracting the center position of the fundamental frequency and bandwidth estimation from the amplitude-frequency image obtained by Fourier transform; designing a Gaussian band-pass filter based on the center of the fundamental frequency and the bandwidth, performing frequency domain filtering on the windowed fringe image using the Gaussian band-pass filter, and performing inverse Fourier transform on the filtered image; calculating the original phase of the image after inverse Fourier transform; unwrapping the original phase to obtain the phase of the fringe image.

[0016] Further, step S43 comprises: reading the calibration board image; detecting the two-dimensional coordinates of the calibration board corner points from the calibration board image, and converting the two-dimensional coordinates of the calibration board corner points [u i , v i ] to three-dimensional coordinates [X Ci , Y Ci , Z Ci ] in the camera coordinate system according to the intrinsic and extrinsic parameters of the imaging module, i denotes the i-th calibration board corner point, u i , v i represent the horizontal and vertical coordinates of the i-th calibration board corner point in the calibration board image, and X Ci , Y Ci , Z Ci represent the horizontal, vertical and actual height coordinates of the i-th calibration board corner point in the camera coordinate system; reading the phase of the fringe image, and obtaining the position [X Ci , YCi Z Ci Phase data θ i ; Based on the two-dimensional coordinates of the calibration board corner points and the phase data [ui, vi, θi], a parameter model matrix A is constructed. i ; Based on the parameter model matrix A corresponding to each calibration plate corner point i The actual height Z of the calibration plate corner point Ci The calibration coefficient 'a' is fitted.

[0017] Further, the calibration error of the calibration coefficients is evaluated, including: Based on the calibration coefficient a, the two-dimensional coordinates of each calibration plate corner point, and the phase data [u] i v i θ i Estimate the height Zc of the corner point of the calibration plate. i '; With each estimated height Zc i 'Actual height Z of the corner point of the calibration plate Ci The mean of the differences between them is used as the calibration error.

[0018] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: This application innovatively proposes an FTP calibration method and device suitable for measuring the surface morphology of rotor blades at the inlet of an aero-engine. By placing a reflector between the engine inlet and the imaging module, the reflection of the stripe light is achieved. The rotor blade is illuminated by the reversal of the light path. FTP calibration of rotor blade morphology measurement can be achieved outside the engine, overcoming the accuracy limitation of the optical path parameters when measuring rotor blade morphology, which can only be approximately calibrated because a calibration plate cannot be set at the rotor blade inside the engine. Attached Figure Description

[0019] The present invention will be described by way of example and with reference to the accompanying drawings, wherein: Figure 1 This is a structural diagram of an aero-engine inlet rotor blade surface morphology measurement system based on FTP.

[0020] Figure 2 This is a structural diagram of an apparatus for FTP calibration designed in one embodiment of this application.

[0021] Figure 3 This is a flowchart of an FTP calibration method designed in one embodiment of this application.

[0022] In the diagram, 1 is the engine inlet component, 2 is the rotor blade, 3 is the speed sensor, 4 is the speed synchronization control device, 5 is the imaging module, 6 is the grating projection device, 7 is the reflector, and 8 is the calibration plate. Detailed Implementation

[0023] All features disclosed in this specification, or all steps in all disclosed methods or processes, may be combined in any way, except for mutually exclusive features and / or steps.

[0024] Any feature disclosed in this specification (including any appended claims and abstract) may be replaced by other equivalent or similar features, unless specifically stated otherwise. That is, unless specifically stated otherwise, each feature is merely one example of a series of equivalent or similar features.

[0025] To address the issue that known FTP calibration methods are not applicable to irregular objects such as aero-engine inlet rotor blades 2, this application provides an apparatus and method for FTP calibration, aiming to achieve accurate calibration of the surface morphology of aero-engine inlet rotor blades 2 based on FTP.

[0026] The principle of the FTP calibration method used in this application is as follows: Using a single-frame fringe analysis method based on FTP (Focus on the Frame of Truth), the continuous phase carrying object height information can be calculated. However, to convert this continuous phase into coordinates in real 3D space and complete the reconstruction of the dynamic 3D shape, a camera calibration model is necessary. The core of this process lies in establishing two types of mapping relationships: one is the relationship between phase and object height Z... C The mapping relationship is twofold: firstly, the mapping relationship between two-dimensional image coordinates [u, v] and world coordinates [X]. C Y C The correspondence between ] .

[0027] System calibration is crucial in fringe projection systems, as its accuracy directly determines the precision of the 3D reconstruction results. During calibration, it is necessary to accurately acquire the system's geometric parameters (such as the intrinsic and extrinsic parameters of imaging module 5, and the relative position of the grating projection device 6 and imaging module 5) and optical parameters (such as optical path deviation and lens distortion). Only by accurately constructing a phase-height mapping model through system calibration can the authenticity and accuracy of the measured 3D data be guaranteed, thereby meeting the stringent requirements for high-speed, high-precision topography reconstruction in dynamic measurement scenarios.

[0028] like Figure 1As shown, the system for measuring the surface morphology of the aero-engine inlet rotor blade 2 based on the FTP method comprises a grating projection device 6, an imaging module 5, a rotating speed synchronous control device 4 and necessary cables. The grating projection device 6 projects the fringe light to the rotor blade 2, the imaging module 5 is responsible for collecting the image of the rotor blade 2 under the irradiation of the fringe light, the rotating speed synchronous control device 4 is responsible for synchronously controlling the collection speed of the imaging module 5 according to the rotating speed of the rotor blade 2, and the rotating speed of the rotor blade 2 can be collected by using the rotating speed sensor 3. Finally, the three-dimensional morphology of the rotor blade 2 is calculated according to the image collected by the imaging module 5 and the parameters of the system calibration.

[0029] The device for FTP calibration proposed in the embodiments of the present application is used for online measurement of the surface morphology of the aero-engine inlet rotor blade 2, as shown in the figure. Figure 2 The device comprises: The grating projection device 6 emits the fringe light to the rotor blade 2 in the open state. It needs to be explained that this refers to the direction of emitting the fringe light to the rotor blade 2, rather than needing to irradiate the fringe light to the rotor blade 2.

[0030] The mirror 7 is arranged between the rotor blade 2 and the grating projection device 6, and reflects the fringe light to the calibration plate 8. Therefore, it can be known that the calibration plate 8 is located on the other side of the mirror 7 relative to the rotor blade 2.

[0031] The imaging module 5 is used to collect the images of the calibration plate 8 in the mirror 7 under the conditions of having the fringe light and not having the fringe light, respectively. In the present application, the collected image under the condition of having the fringe light is called the fringe image, and the collected image under the condition of not having the fringe light is called the calibration plate image.

[0032] Through the above-mentioned device, the mirror 7 is arranged between the engine inlet assembly 1 and the imaging module 5, the turning of the light path is realized, the equivalent light path of the FTP-based aero-engine inlet rotor blade 2 surface morphology measurement light path is obtained, the FTP calibration of the imaging module 5 and the grating projection device 6 is realized outside the aero-engine by performing FTP calibration on the equivalent light path, and the problem that the light path cannot be accurately calibrated due to the fact that the calibration plate 8 cannot be arranged at the aero-engine inlet rotor blade 2 is solved.

[0033] As an optional implementation manner, the above-mentioned mirror 7 is parallel to the aero-engine inlet interface. The mutually parallel engine inlet interface and mirror 7 can maximize the difficulty of setting the equivalent light path and maximize the measurement error introduced by the complexity of the device structure. The calibration plate 8 is parallel to the mirror 7 when initially installed, so as to facilitate the observation of whether it is located in the center of the imaging picture.

[0034] As a preferred embodiment, the distance between the mirror 7 and the calibration plate 8 is designed to be as equal as possible to the distance between the mirror 7 and the rotor blade 2. Specifically, the distance between the mirror 7 and the calibration plate 8 and the distance between the mirror 7 and the rotor blade 2 are designed to be equal or within a set range, which is obviously a small error range. The above device can be constructed by first measuring the distance between the mirror 7 and the rotor blade 2, and then setting the calibration plate 8 at an equal distance on the other side of the mirror 7 relative to the rotor blade 2.

[0035] The calibration plate 8 has an easily identifiable feature as a tool for calibrating parameters. In some alternative embodiments, the calibration plate 8 is a checkerboard pattern calibration plate. In addition, the number of checkerboards contained in the rows and columns of the checkerboard pattern is not equal, for example, one of the two contains an odd number of checkerboard patterns, and the other contains an even number of checkerboard patterns, i.e. the calibration plate 8 is a calibration plate 8 containing an odd (row / column) x even (column / row) number of checkerboards. In this way, the length and width directions of the calibration plate 8 can be quickly identified, and the angle of the calibration plate 8 can be quickly identified.

[0036] Based on the device for FTP calibration designed in the above embodiments, the present application also provides an FTP calibration method for FTP-based measurement of the surface topography of the inlet rotor blade 2 of an aero-engine. As shown in Figure 3 the method includes the following processes: S1, set up the grating projection device 6 and the imaging module 5 according to the device for FTP calibration and debug.

[0037] In this step S1, the device designed according to the above embodiments is set up with the grating projection device 6 and the imaging module 5. Specifically, as shown in Figure 1 the grating projection device 6 and the imaging module 5 are set up opposite to the rotor blade 2 respectively to build an FTP imaging light path.

[0038] After setting up the grating projection device 6 and the imaging module 5, the grating projection device 6 is adjusted until the fringe light projected onto the rotor blade 2 is clearly visible; the focal length of the imaging module 5 is adjusted, etc., until the captured fringe image is clear. In this way, the grating projection device 6 and the imaging module 5 are debugged.

[0039] S2, build the device for FTP calibration.

[0040] According to Figure 2The configuration of the device for FTP calibration is shown, and the device is built. That is, on the basis of setting and debugging the grating projection device 6 and the imaging module 5, the mirror 7 is placed at a position about halfway between the imaging module 5 and the engine inlet interface. The mirror 7 is adjusted to ensure that the plane of the mirror 7 is parallel to the engine inlet interface. The distance between the mirror 7 and the rotor blade 2 is measured by a range finder, and the calibration plate 8 is placed at a position of the same distance on the other side of the mirror 7. The calibration plate 8 is adjusted to ensure that its plane is parallel to the mirror 7, and at the same time, it is clearly imaged in the imaging module 5, and preferably, the image is located at the center of the field of view.

[0041] S3, the grating projection device 6 is alternately turned on and off for multiple rounds, and multiple groups of images of the calibration plate 8 under the striped light and the calibration plate under the non-striped light are alternately collected by the imaging module 5.

[0042] After the device is built, the collection of the images of the calibration plate and the images of the calibration plate 8 projected by the grating projection device 6 can be started.

[0043] In some optional embodiments, the step S3 comprises: S31, the grating projection device 6 is turned off, and the image of the calibration plate 8 in the mirror 7 is collected by the imaging module 5 as the image of the calibration plate. For the calibration plate 8 at one angle, one image of the calibration plate can be collected.

[0044] S32, the grating projection device 6 is turned on to reflect the striped light to the calibration plate 8 through the mirror 7, and the image of the calibration plate 8 in the mirror 7 is collected by the imaging module 5 as the image of the calibration plate. Similarly, for the calibration plate 8 at one angle, one image of the calibration plate can be collected.

[0045] S33, steps S31 and S32 are repeated for multiple rounds, and the pose of the calibration plate 8 relative to the mirror 7 (including the pitch angle, the rotation angle, and the displacement) is adjusted each round, and each round obtains a group of images of the calibration plate and the images of the calibration plate. In some optional embodiments, the angle of the calibration plate 8 is adjusted repeatedly, and at least 2 groups of images of the calibration plate and the images of the calibration plate are collected, and preferably, more than 8 groups of images of the calibration plate and the images of the calibration plate are collected. When the images of the calibration plate and the images of the calibration plate are collected, the pose of the calibration plate 8 is ensured to be fixed.

[0046] Through the above steps, the images for FTP calibration can be obtained.

[0047] S4, FTP calibration is performed by using the collected multiple groups of images of the calibration plate and the images of the calibration plate.

[0048] As mentioned above, for the calibration of the optical path, the internal and external parameter calibration of the grating projection device 6 and the imaging module 5 is involved. In some optional embodiments, the step S4 comprises the following process: S41, calibrate the intrinsic and extrinsic parameters of the imaging module 5 using the collected calibration board images.

[0049] The calibration of the intrinsic parameters of the imaging module 5 can refer to the calibration method of a camera in the prior art, and in addition, the calibration of the intrinsic parameters of the imaging module 5 can also be realized by means of ready-made tools. For example, the intrinsic and extrinsic parameters of the imaging module 5 are calculated based on a plurality of sets of calibration board images by using a single camera calibration program provided by a tool such as matlab, and K represents the intrinsic and extrinsic parameters of the imaging module 5.

[0050] S42, calculate the phase of the fringe image based on the Fourier transform according to the fringe image.

[0051] In some optional embodiments, the step S42 comprises: 1) reading the fringe image.

[0052] 2) windowing the fringe image.

[0053] The windowing operation is applicable to each fringe image, and the parameters of the windowing function are adjusted according to the size of the fringe image. The so-called windowing is to perform windowing processing on the fringe image by using a window function of the same size as the fringe image.

[0054] 3) performing Fourier transform on the windowed fringe image, and extracting the center position of the fundamental frequency (i.e. the fundamental frequency position) [u0, v0] and the bandwidth estimation (effective bandwidth) of the amplitude-frequency image obtained by the Fourier transform.

[0055] 4) designing a Gaussian band-pass filter based on the center position of the fundamental frequency [u0, v0] and the bandwidth σ, the Gaussian band-pass filter filters information outside the corresponding frequency band, and the windowed fringe image is filtered in the frequency domain by using the Gaussian band-pass filter, and the filtered image is inverse Fourier transformed.

[0056] 5) calculating the original phase of the image after the inverse Fourier transform.

[0057] 6) unwrapping the original phase to obtain the phase of the fringe image.

[0058] S43, constructing a parameter model matrix based on the phase calculated in step S42 according to the calibration board image, and solving the calibration coefficient.

[0059] In some optional embodiments, the step S43 comprises the following process: 1) reading the calibration board image.

[0060] 2) detecting the two-dimensional coordinates [u i , v i] (i represents the i-th calibration plate corner point), and the two-dimensional coordinates of the calibration plate corner point [u] are calculated based on the intrinsic and extrinsic parameters K of the imaging module 5. i v i Transform to 3D coordinates in the camera coordinate system [X] Ci Y Ci Z Ci ], u i v i Let X and Y represent the x and y coordinates of the i-th calibration plate corner point in the calibration plate image, respectively. Ci Y Ci Z Ci These represent the x and y coordinates and the actual height of the i-th calibration plate corner point in the camera coordinate system, respectively.

[0061] 3) Read the phase of the stripe image to obtain the location of the calibration plate corner points [X]. Ci Y Ci Z Ci Phase data θ i .

[0062] 4) Based on the two-dimensional coordinates and phase data of the calibration board corner points [u i v i θ i Construct the parameter model matrix A i Parametric model matrix A i The structure is as follows: A i =[1, θ i u i v i θ i u i θ i v i u i v i θ i u i v i ].

[0063] 5) Based on the parameter model matrix A corresponding to each calibration plate corner point i The actual height Z of the calibration plate corner point Ci The calibration coefficient 'a' is calculated. Specifically, based on Z... C =A×a, calculated from multiple sets of Z Ci and A i The calibration coefficient 'a' is obtained using the least squares method. a = [a0, a1, a2, a3, a4, a5, a6, a7]. This represents the j-th element in the calibration coefficient a.

[0064] S44, evaluate the calibration error of the calibration coefficient, if the calibration error does not meet the set standard, jump to step S3 to re-collect the image group until the calibration error of the calibration coefficient meets the set standard.

[0065] In some optional embodiments, the process of step S44 evaluating the calibration error of the calibration coefficient includes: Based on the calibration coefficient a, the two-dimensional coordinates of each corner point of the calibration board and the phase data [u i , v i , θ i ], the height Z Ci ’ of each corner point of the calibration board is estimated according to Z i =A Ci ×a.

[0066] The mean of the difference between each estimated height Z Ci ' and the actual height Z Ci of the corner point of the calibration board is taken as the calibration error.

[0067] The invention is not limited to the foregoing specific embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification, and to any novel method or process disclosed, or any novel combination of steps of the disclosed methods or processes.

Claims

1. A device for FTP calibration for online measurement of surface topography of an aeroengine inlet rotor blade, characterized in that, The device comprises: A grating projection device emits a stripe light to the rotor blade in an open state; A mirror is arranged between the rotor blade and the grating projection device, and reflects the stripe light to a calibration board; An imaging module is used to respectively collect images of the calibration board in the mirror with and without the stripe light.

2. The apparatus for FTP calibration of claim 1, wherein, The mirror is parallel to the inlet interface of the aero-engine.

3. The apparatus for FTP calibration of claim 2, wherein, The distance from the mirror to the calibration board is equal to the distance from the mirror to the rotor blade or the difference is within a set range.

4. The apparatus for FTP calibration according to any one of claims 1 to 3, characterized in that, The calibration board is a chessboard pattern calibration board, and the number of chessboards contained in the rows and columns of the chessboard pattern is not equal.

5. A FTP calibration method based on the apparatus for FTP calibration according to any one of claims 1-4, characterized in that, Comprise: S1, set up a grating projection device and an imaging module according to the device for FTP calibration and debug; S2, build the device for FTP calibration; S3, open and close the grating projection device alternately for multiple rounds, and use the imaging module to alternately collect multiple groups of stripe images of the calibration board with stripe light and calibration board images without stripe light; S4, use the collected multiple groups of stripe images and calibration board images to perform FTP calibration.

6. The FTP calibration method of claim 5, wherein, Step S3 comprises: S31, close the grating projection device, and use the imaging module to collect the image of the calibration board in the mirror as a calibration board image; S32, open the grating projection device to reflect the stripe light on the calibration board through the mirror, and use the imaging module to collect the image of the calibration board in the mirror as a stripe image; S33, repeat steps S31 and S32 for multiple rounds, adjust the pose of the calibration board relative to the mirror in each round, and obtain a group of calibration board images and stripe images in each round.

7. The FTP calibration method of claim 5, wherein, Step S4 comprises: S41, use the collected calibration board images to calibrate the intrinsic and extrinsic parameters of the imaging module; S42, calculate the phase of the stripe image based on Fourier transform according to the stripe image; S43, construct a parameter model matrix based on the phase calculated in step S42 according to the calibration board image, and solve the calibration coefficient; S44, evaluate the calibration error of the calibration coefficient, and if the calibration error does not meet the set standard, jump to step S3 until the calibration error of the calibration coefficient meets the set standard.

8. The FTP calibration method of claim 7, wherein, Step S42 comprises: Read the stripe image; Window the stripe image; Perform Fourier transform on the windowed stripe image, and extract the center position of the fundamental frequency and bandwidth estimation from the amplitude-frequency image obtained by Fourier transform; Design a Gaussian band-pass filter based on the fundamental frequency center and bandwidth, perform frequency domain filtering on the windowed stripe image using the Gaussian band-pass filter, and perform inverse Fourier transform on the filtered image; Calculate the original phase of the image after inverse Fourier transform; Unwrap the original phase to obtain the phase of the stripe image.

9. The FTP mapping method of claim 7, wherein, Step S43 comprises: Read the calibration board image; The two-dimensional coordinates of the calibration board corner points are detected from the calibration board image, and the two-dimensional coordinates of the calibration board corner points are [u] based on the intrinsic and extrinsic parameters of the imaging module. i v i Transform to 3D coordinates in the camera coordinate system [X] Ci Y Ci Z Ci ], i refers to the i-th calibration plate corner point, u i v i Let X and Y represent the x and y coordinates of the i-th calibration plate corner point in the calibration plate image, respectively. Ci Y Ci Z Ci These represent the x and y coordinates and the actual height of the i-th calibration plate corner point in the camera coordinate system, respectively. reading the phase of the stripe image, obtaining phase data θ i of the position [X Ci , Y Ci , Z Ci ] where the corner point of the calibration plate is located; Based on the two-dimensional coordinates and phase data [u i , v i , θ i ] of the corner points of the calibration board, a parameter model matrix A i is constructed; Based on the parameter model matrix A corresponding to each corner point of the calibration plate i and the actual height Z of the corner point of the calibration plate Ci , the calibration coefficient a is fitted.

10. The FTP mapping method of claim 7, wherein, Evaluate the calibration error of the calibration coefficient, including: Based on the calibration coefficient a, the two-dimensional coordinates of each corner point of the calibration plate, and phase data [u i , v i , θ i ], the height Zc i of the corner point of the calibration plate is estimated. The mean of the difference between each estimated height Zc i and the actual height Z of the corner point of the calibration plate is taken as the calibration error. Ci and the actual height Z of the corner point of the calibration plate is taken as the calibration error.

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