Helicopter rotor blade deformation measuring device and method

Abstract

This invention relates to a device and method for measuring helicopter rotor blade deformation, comprising: two semiconductor lasers, two sinusoidal gratings, two linear CCD arrays, and a data receiving and processing unit. The semiconductor lasers emit light beams as optical cutters. The sinusoidal gratings receive the light beams, which then fall onto the spanwise plane of the rotor blade, forming stripes. The linear CCD arrays collect all the stripes on the blade surface. The data receiving and processing unit receives the stripe information collected by the linear CCD arrays and applies Fourier transform profilometry to obtain the three-dimensional surface profile of the rotor blade under test. Furthermore, by comparing the three-dimensional surface profiles of the rotor blade under test at different rotor speeds, the amount of blade deformation is obtained. Determining the blade deformation at two different rotor speeds using the three-dimensional surface profile of the blade improves the accuracy of blade deformation measurement.

Description

Technical Field

[0001] This invention relates to the field of rotor blade deformation measurement, and in particular to a device and method for measuring helicopter rotor blade deformation based on linear CCD and Fourier transform profilometry. Background Technology

[0002] Helicopter rotors integrate thrust, pull, and control force, enabling vertical takeoff and landing as well as hovering. Their excellent flight performance and handling characteristics make them widely used in both civilian and military fields.

[0003] Under the high-speed rotation of a helicopter rotor, blade deformation is inevitable, and the degree of blade deformation reflects the operating performance of the rotor system. Therefore, measuring blade deformation is crucial. Existing methods for measuring rotor blade deformation mainly include contact and non-contact methods.

[0004] Contact measurement methods mainly involve two approaches: attaching sensors to the blade surface or embedding sensors. The most common are strain gauges and fiber Bragg grating (FBG) sensors. Strain gauges have a large measurement area, require additional wiring, and are susceptible to environmental factors such as humidity and temperature, severely affecting the accuracy of blade deformation measurements. FBG sensors are widely used due to their small size, light weight, and strong resistance to electromagnetic interference; however, attaching them to the rotor blade surface can cause them to detach and affect the aerodynamic shape, while embedding sensors can easily damage the internal structure of the rotor blade, reducing its strength.

[0005] Non-contact measurement methods mainly rely on optical measurement methods, using devices such as multi-view cameras and lidar to acquire images of the blades. The image from one camera is used as a reference image, while the other cameras are used as search images. The three-dimensional spatial information of the blade surface is obtained through stereo vision methods, thereby deriving the blade deformation parameters.

[0006] like Figure 1 As shown, a helicopter rotor blade deformation measurement device based on speckle light is available, comprising: an excitation light source 01, a beam expander lens 02, a speckle generator 03, a reflector 04, camera assemblies 06 and 07, a synchronization controller 08, and a computer 09. A point light source is generated by the 532nm excitation light source. After being expanded by the lens, the light signal is received by the speckle generator and then reflected by the reflector onto the rotor blade plane. Image information is acquired by the camera assemblies, and the three-dimensional spatial information of the blade surface is obtained using a binocular vision method. Based on this, the blade deformation parameters are calculated. However, this method's measurement range is limited to the area covered by the speckle light source on the blade, resulting in a small measurement range. Furthermore, it can only measure the three-dimensional information of the upper surface of the blade; if the blade profile is deformed, the measurement results will be inaccurate. Summary of the Invention

[0007] The purpose of this invention is to provide a helicopter rotor blade deformation measurement device and method that determines the blade deformation at two different rotor speeds by using the three-dimensional surface profile of the blade, thereby improving the accuracy of blade deformation measurement.

[0008] To achieve the above objectives, the present invention provides the following solution:

[0009] A helicopter rotor blade deformation measuring device includes: a first semiconductor laser, a first sinusoidal grating and a first linear CCD disposed above the rotor blade to be measured; a second semiconductor laser, a second sinusoidal grating and a second linear CCD disposed below the rotor blade to be measured; and a data receiving and processing unit.

[0010] The light blade emitted by the first semiconductor laser passes through the first sinusoidal grating and irradiates the upper spanwise surface of the rotor blade under test, forming stripes on the spanwise surface of the rotor blade under test.

[0011] The beam emitted by the second semiconductor laser passes through the second sinusoidal grating and illuminates the lower spanwise surface of the rotor blade under test, forming stripes on the lower spanwise surface of the rotor blade under test.

[0012] The first linear CCD is used to capture the first stripe image on the spanwise surface of the rotor blade under test.

[0013] The second linear CCD is used to capture a second stripe image of the spanwise surface of the rotor blade under test;

[0014] The data receiving and processing unit is used to receive the first stripe image captured by the first linear array CCD and the second stripe image captured by the second linear array CCD, and to obtain the three-dimensional surface profile of the rotor blade under test by applying Fourier transform profilometry based on all the first stripe images and the second stripe images, and to obtain the blade deformation by comparing the three-dimensional surface profile of the rotor blade under test at different rotor speeds.

[0015] Optionally, the first semiconductor laser, the second semiconductor laser, the first sinusoidal grating, the second sinusoidal grating, the first linear CCD array, and the second linear CCD array are all symmetrically distributed along the rotor blade under test.

[0016] Optionally, the length of the stripes formed on the spanwise surface of the rotor blade under test is greater than or equal to the length of the rotor blade under test.

[0017] Optionally, the emission beam of the first semiconductor laser, the optical axis of the first linear CCD, and the rotation axis of the rotor blade under test are on the same plane.

[0018] Optionally, there is an angle between the output optical axis of the first semiconductor laser and the optical axis of the first linear CCD.

[0019] The present invention also provides a method for measuring the deformation of helicopter rotor blades, comprising:

[0020] The first linear array CCD and the second linear array CCD are controlled to capture the stripes on the upper surface and the lower surface of the rotor blade under test at a set interval, respectively, to obtain 2n real stripe images; the 2n real stripe images include n first stripe images and n second stripe images.

[0021] For each of the real-shot stripe images, the Fourier transform profilometry method is applied to obtain 2n local profile images of the surface of the rotor blade to be tested.

[0022] By stitching together 2n partial contour images of the rotor blade surface to be tested, a three-dimensional surface contour image of the rotor blade to be tested is obtained.

[0023] By comparing the three-dimensional surface profile diagrams of the rotor blade under test at two different rotor speeds, the blade deformation is obtained.

[0024] Optionally, before stitching together the 2n partial contour images of the rotor blade surface to be tested, the method further includes:

[0025] Each of the aforementioned local contour maps is trimmed to retain the contour map of the area containing the stripes on the surface of the rotor blade under test.

[0026] Optionally, the step of applying Fourier transform profilometry to each of the actual fringe images to obtain 2n local contour maps of the rotor blade surface under test specifically includes:

[0027] Perform Fourier transforms on the k-th real-shot stripe image and the corresponding k-th reference stripe image respectively;

[0028] Frequency domain filtering is performed on the k-th transformed real-shot stripe image and the k-th transformed reference stripe image respectively to extract the first fundamental frequency component corresponding to the k-th transformed real-shot stripe image and the second fundamental frequency component corresponding to the k-th transformed reference stripe image;

[0029] Perform inverse Fourier transform on the first fundamental frequency component corresponding to the kth transformed real-shot stripe image and the second fundamental frequency component corresponding to the kth transformed reference stripe image respectively.

[0030] The phase distribution of the k-th real-shot stripe image is obtained by subtracting the inverse transform result corresponding to the k-th reference stripe image from the inverse transform result of the k-th real-shot stripe image.

[0031] The phase distribution of the k-th real-shot stripe image is expanded to obtain the height distribution of the surface of the rotor blade to be tested corresponding to the k-th real-shot stripe image.

[0032] Determine if k is 2n. If not, let k = k + 1 and return to the step "perform Fourier transform on the k-th real stripe image and the corresponding k-th reference stripe image respectively", until k = 2n. If yes, then obtain 2n local contour images of the surface of the rotor blade to be tested.

[0033] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0034] This invention relates to a device and method for measuring helicopter rotor blade deformation, comprising: two semiconductor lasers, two sinusoidal gratings, two linear CCD arrays, and a data receiving and processing unit. The semiconductor lasers emit light beams as light cutters. The sinusoidal gratings receive the light cutters and, after falling onto the spanwise plane of the rotor blade, form stripes. The linear CCD arrays collect all the stripes on the blade surface. The data receiving and processing unit receives the stripe information collected by the linear CCD arrays and applies Fourier transform profilometry to obtain the three-dimensional surface profile of the rotor blade under test. It also compares the three-dimensional surface profiles of the rotor blade under test at different rotor speeds to obtain the blade deformation. Using linear CCDs for non-contact measurement results in lower costs than area CCD arrays of the same area and resolution, faster data processing, higher measurement accuracy, and higher resolution. Furthermore, by determining the blade deformation at two different rotor speeds through the three-dimensional surface profile of the blade, the accuracy of blade deformation measurement is improved. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 A structural diagram of an existing helicopter rotor blade deformation measurement device based on speckle light provided for this invention;

[0037] Figure 2 This is a structural diagram of the helicopter rotor blade deformation measuring device provided in Embodiment 1 of the present invention;

[0038] Figure 3 This is a schematic diagram of the angle that the propeller blade rotates from the moment the foremost tip of the blade contacts the light cutter to the moment the foremost tip leaves the light cutter blade, provided in Embodiment 1 of the present invention.

[0039] Figure 4This is a flowchart of the helicopter rotor blade deformation measurement method provided in Embodiment 2 of the present invention;

[0040] Figure 5 This is a schematic diagram of the helicopter rotor blade deformation measurement method provided in Embodiment 2 of the present invention;

[0041] Figure 6 This is a diagram showing the relative positions of the virtual cylinder, the rotor blade under test, and the reference plane provided in Embodiment 2 of the present invention.

[0042] Figure label:

[0043] 1-1: First semiconductor laser; 1-2: First sinusoidal grating; 1-3: First linear CCD; 2-1: Second semiconductor laser; 2-2: Second sinusoidal grating; 2-3: Second linear CCD; 3: Data receiving unit; 4: Computer; 5: Rotor blade under test. Detailed Implementation

[0044] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] Existing helicopter rotor blade deformation measurement devices measure blade deformation using laser speckle and binocular vision. The measurement range is limited to the speckle area and its vicinity, making it too restrictive and only suitable for measurements based on the rigid periphery assumption—that the reference profile maintains its airfoil shape before and after deformation. Therefore, this invention proposes a device to reproduce the three-dimensional profile of helicopter rotor blades. Using a linear charge-coupled device (CCD) and Fourier transform profilometry (FTP), it achieves 360° measurement of helicopter rotor blades, expanding the measurement range, eliminating the rigid periphery assumption, and thus more closely approximating the actual blade deformation.

[0046] The purpose of this invention is to provide a helicopter rotor blade deformation measurement device and method. By determining the blade deformation at two different rotor speeds using the three-dimensional surface profile of the blade, the accuracy of blade deformation measurement is improved. Furthermore, because the deformation is determined based on the three-dimensional surface profile of the blade, the deformation of the cross-section can be accurately measured.

[0047] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0048] Example 1

[0049] like Figure 2 As shown, this embodiment provides a helicopter rotor blade deformation measuring device, including:

[0050] The system comprises two semiconductor lasers, two one-dimensional sinusoidal gratings, two linear CCD arrays, a data receiving unit 3, and a high-performance computer 4. The output beam from the semiconductor lasers is a beam cutter formed by a combination of cylindrical mirrors and lenses (the laser's own structure). The one-dimensional sinusoidal gratings receive the beam cutter and it falls onto the spanwise plane of the rotor blade 5, forming stripes. The linear CCD array collects all the stripes on the blade surface. The data receiving unit 3 receives the stripe information collected by the linear CCD array and transmits the stripe image to the high-performance computer 4. In other words, this embodiment of the system includes:

[0051] The system includes a first semiconductor laser 1-1, a first sinusoidal grating 1-2, and a first linear CCD 1-3 located above the rotor blade 5 under test; a second semiconductor laser 2-1, a second sinusoidal grating 2-2, and a second linear CCD 2-3 located below the rotor blade 5 under test; and a data receiving and processing unit.

[0052] The light beam emitted by the first semiconductor laser 1-1 passes through the first sinusoidal grating 1-2 and irradiates the upper spanwise surface of the rotor blade 5 under test, forming stripes on the spanwise surface of the rotor blade 5 under test.

[0053] The beam emitted by the second semiconductor laser 2-1 passes through the second sinusoidal grating 2-2 and then illuminates the lower spanwise surface of the rotor blade 5 under test, forming stripes on the lower spanwise surface of the rotor blade 5 under test.

[0054] The first linear array CCD1-3 is used to capture the first stripe image on the spanwise surface of the rotor blade 5 under test.

[0055] The second linear array CCD2-3 is used to capture the second stripe image of the spanwise surface of the rotor blade 5 under test.

[0056] The data receiving and processing unit is used to receive the first stripe image captured by the first linear CCD 1-3 and the second stripe image captured by the second linear CCD 2-3, and to obtain the three-dimensional surface profile of the rotor blade 5 under test by applying Fourier transform profilometry based on all the first and second stripe images. It also compares the three-dimensional surface profile of the rotor blade 5 under test at different rotor speeds to obtain the blade deformation. The calculation of the blade deformation can be implemented by the high-performance computer 4. The function implemented by the data receiving and processing unit here is the same as the function jointly implemented by the data receiving unit 3 and the computer 4 in the first paragraph mentioned above.

[0057] As an optional implementation, the first semiconductor laser 1-1, the second semiconductor laser 2-1, the first sinusoidal grating 1-2, the second sinusoidal grating 2-2, the first linear CCD array 1-3, and the second linear CCD array 2-3 are all symmetrically distributed along the rotor blade 5 to be tested.

[0058] The length of the stripes formed by the one-dimensional sinusoidal grating and the semiconductor laser is determined by the rotor blade dimensions. The one-dimensional sinusoidal grating and the semiconductor laser adjust their relative positions according to the rotor blade dimensions, thereby ensuring that the length of the stripes formed by the optical grating is greater than or equal to the rotor blade radius (spanwise length). Therefore, to ensure that the stripes can more comprehensively cover the blade surface, the length of the stripes formed on the spanwise surface of the rotor blade 5 under test can be required to be greater than or equal to the length of the rotor blade 5 under test.

[0059] As another optional implementation, the emission beam of the first semiconductor laser 1-1, the optical axis of the first linear CCD 1-3, and the rotation axis of the rotor blade 5 under test are on the same plane. That is, the forward direction of the laser emission beam, the rotation axis of the rotor blade, and the optical axis of the linear CCD are in the same plane, forming a coaxial optical system.

[0060] There is an angle between the output optical axis of the first semiconductor laser 1-1 and the optical axis of the first linear CCD 1-3.

[0061] For semiconductor lasers, AlGaAs double heterojunction lasers can be selected. The wavelength of semiconductor lasers is 750-890nm.

[0062] The linear CCD can be selected as a typical dual-channel parallel output two-phase CCD-TDC1703C to capture the fringe pattern falling on high-speed rotating propeller blades. CCD (Charge Coupled Device) is a new type of semiconductor integrated optoelectronic device developed in the early 1970s.

[0063] The specific process for acquiring a stripe image using the measurement system of this embodiment is as follows:

[0064] (1) Set up a measuring device including a semiconductor laser, a one-dimensional sinusoidal grating, a linear CCD, a data receiving unit 3 and a high-performance computer 4 (data receiving and processing unit).

[0065] (2) Arrange two semiconductor lasers, two one-dimensional sinusoidal gratings, and two linear CCD arrays symmetrically above and below the blade under test. The two linear CCD arrays can be symmetrically arranged directly above and below the blade under test to facilitate accurate capture of stripe images.

[0066] (3) Adjust the angle between the semiconductor laser light path and the sinusoidal grating and the blade surface so that the stripes formed after the light path passes through the grating fall exactly on the spanwise direction of the upper and lower surfaces of the rotor blade 5 to be tested, the stripe length is greater than or equal to the rotor blade radius, and the semiconductor laser light path, the rotor blade rotation axis, and the optical axis of the linear CCD are in the same plane to form a coaxial optical system.

[0067] (4) Starting from the moment the blade comes into contact with the light path stripe, the linear CCD camera is triggered by the data receiving unit 3 to capture the stripe falling on the blade surface, and the stripe information is transmitted to the high-performance computer 4.

[0068] (5) Based on the rotor speed fed back by the data receiving unit 3 (this speed is output to the data receiving unit 3 by the computer 4, and the speed is a predetermined value), the rotor blade rotates a total angle (θ1+θ2) from the moment it contacts the light knife at the very tip (i.e., the leading edge of the blade root) to the moment it leaves the light knife at the very end (i.e., the last edge of the blade root). At each time interval Δt, the linear CCD cameras on the upper and lower surfaces of the blade are simultaneously triggered until the upper and lower surfaces of the blade are completely scanned, and all stripe information is sent to the computer 4. The specific expression of Δt is as follows:

[0069] θ1=arctan(a / e) (4.1)

[0070] θ2=arctan(b / e) (4.2)

[0071] Δt=(θ1+θ2) / (ω·n) (4.3)

[0072] In the formula, a is the distance from the junction of the rotor root and rotor hub to the leading edge of the rotor blade, b is the distance from the junction of the rotor root and rotor hub to the trailing edge of the rotor blade, e is the distance from the rotor root to the center of the rotor hub, ω is the rotor speed, and n is the number of times the linear CCD is scanned. The specific geometric relationship is as follows: Figure 3 As shown, Figure 3 In the diagram, the dashed line indicates the position where the light cutter lands on the propeller blade, which is in the same plane as the rotor's axis of rotation.

[0073] In this embodiment, (1) a linear CCD is used for non-contact measurement, which is cheaper than a surface CCD with the same area and resolution. Data processing is faster, measurement accuracy is higher, and resolution is higher. (2) The Fourier transform profile method is used to realize the true 360° three-dimensional surface profile of the rotor blade during rotation, expanding the range of blade deformation measurement. (3) The problem of difficult non-contact measurement of blade deformation is solved. By eliminating the assumption of rigid periphery of the blade, the true 360° three-dimensional surface profile measurement can be realized. It has the advantages of simple equipment, wide measurement range, non-contact, high accuracy, and low cost. (4) The helicopter rotor blade deformation measurement device does not require processing of the blade surface or excessive processing of the excitation light source, such as the commonly used speckle pattern processing. Therefore, the device is simple and quick to operate, and the subsequent processing is not so complicated. (5) Compared with the existing fiber optic grating sensing technology, strain gauges on the blade surface or internally embedded strain gauges for deformation measurement, the helicopter rotor blade deformation measurement device will not affect the aerodynamic shape of the blade or damage the blade structure.

[0074] Example 2

[0075] like Figure 4 and 5 As shown, this embodiment provides a method for measuring the deformation of helicopter rotor blades, including:

[0076] S1: Control the first linear array CCD1-3 and the second linear array CCD2-3 to take pictures of the stripes on the upper surface and the lower surface of the rotor blade 5 under test at a set interval, respectively, to obtain 2n real stripe images; the 2n real stripe images include n first stripe images and n second stripe images.

[0077] S2: Apply Fourier transform profilometry to each of the real-shot stripe images to obtain 2n local profile images of the surface of the rotor blade 5 to be tested.

[0078] Fourier transform profilometry (FTP) is a technique that uses deformable grating images to achieve non-contact three-dimensional shape measurement. This technique projects a grating onto the surface of a three-dimensional object, uses a CCD to receive the deformable grating image modulated by the object's surface, and then performs a Fourier transform on the acquired image in the computer. The phase information of the modulated image is then extracted in the frequency domain, and the three-dimensional information is extracted using the two-dimensional image, ultimately achieving a stereoscopic reconstruction of the three-dimensional object.

[0079] Specifically, step S2 includes:

[0080] S21: Perform Fourier transform on the k-th real-shot stripe image and the corresponding k-th reference stripe image respectively.

[0081] That is, each fringe pattern on the upper and lower surfaces of the blade corresponds to a reference fringe pattern. The k-th fringe pattern of the actual photograph of the blade and the corresponding k-th reference fringe pattern are both subjected to Fourier transform.

[0082] S22: Perform frequency domain filtering on the k-th transformed real-shot fringe image and the k-th transformed reference fringe image respectively, and extract the first fundamental frequency component corresponding to the k-th transformed real-shot fringe image and the second fundamental frequency component corresponding to the k-th transformed reference fringe image.

[0083] That is, after performing Fourier transform on the k-th real fringe pattern of the propeller and the corresponding k-th reference fringe pattern, frequency domain filtering is performed on each of them, and one of the fundamental frequency components is taken.

[0084] S23: Perform inverse Fourier transform on the first fundamental frequency component corresponding to the k-th transformed real-shot stripe image and the second fundamental frequency component corresponding to the k-th transformed reference stripe image, respectively.

[0085] That is, perform inverse Fourier transform on the fundamental frequency components of the k-th fringe pattern captured by the propeller and the corresponding k-th reference fringe.

[0086] S24: The phase distribution of the k-th real-shot stripe image is obtained by subtracting the inverse transform result corresponding to the k-th reference stripe image.

[0087] That is, by subtracting the inverse Fourier transform results of the k-th real-shot fringe pattern of the propeller blade from the corresponding k-th reference fringe pattern, the phase distribution of the k-th real-shot fringe pattern of the propeller blade and the corresponding k-th reference fringe pattern is obtained.

[0088] S25: Expand the phase distribution of the k-th real-shot stripe image to obtain the height distribution of the surface of the rotor blade 5 to be tested corresponding to the k-th real-shot stripe image.

[0089] S26: Determine if k is 2n. If not, let k = k + 1 and return to the step "perform Fourier transform on the k-th real stripe image and the corresponding k-th reference stripe image respectively" until k = 2n. If yes, then obtain 2n local contour images of the surface of the rotor blade 5 to be tested.

[0090] The height distribution on the blade surface is obtained by phase unwrapping, thus obtaining a three-dimensional image of the blade, i.e., the local contour.

[0091] S3: The local contour images of the surface of the rotor blade 5 to be tested are stitched together to obtain the three-dimensional surface contour image of the rotor blade 5 to be tested.

[0092] Prior to step S3, the procedure also includes:

[0093] Each of the aforementioned local contour images is trimmed to retain the contour image of the area where the stripes are located on the surface of the rotor blade 5 to be tested (retaining the stripes when they are in the common plane of the rotor rotation axis, linear CCD, and laser).

[0094] After trimming, it is necessary to further rotate and transform the local contours of the upper and lower surfaces of the trimmed blade at corresponding angles to obtain a unified three-dimensional coordinate space. That is, each stripe corresponds to a different angle on the blade, and in order to better stitch them together, the images of each stripe are aligned according to their respective angular positions.

[0095] By stitching together the partial outlines of the upper and lower blade surfaces after trimming and rotation transformation, the true 360° three-dimensional surface outline of the blade can be completely restored.

[0096] S4: By comparing the three-dimensional surface profile diagrams of the rotor blade 5 under two different rotor speeds, the blade deformation is obtained.

[0097] In this embodiment, the true 360° three-dimensional surface profile of the rotor blade during rotation is restored by using Fourier transform contouring, which expands the measurement range of blade deformation and solves the problem of difficult non-contact measurement of blade deformation.

[0098] The following section introduces the calculation of the blade surface height distribution using the Fourier transform profilometry method. This describes the specific process of phase solving in calibration from the perspective of mathematical formula calculation. Through this process, the three-dimensional coordinates of any point on the blade can be obtained, i.e., the blade surface height distribution.

[0099] Assuming the existence of a virtual cylinder with a fixed radius R, and using reference fringes on a reference plane tangent to it as a reference, n fringe images of each of the upper and lower surfaces of the blade are processed separately to obtain partial contour maps of 2n blade surfaces. This process is called calibration, and is detailed below:

[0100] like Figure 6 The image shows a left view of the measuring device. It is assumed that a fixed virtual cylinder (the midpoint of the blade section chord coincides with the center of the cylinder, and the entire blade section is enclosed within the circle) serves as a reference, and the reference plane of the projection grating (sine grating) (i.e.,...) Figure 5 Points A and B are tangent to the virtual reference cylinder. When the blade rotates around the hub, the distance from any point P on the blade surface to the reference plane is denoted as h. That is, the distance r from point P to the surface of the virtual reference cylinder uniquely corresponds to the phase distribution of the deformation fringes projected onto the object at that point. The specific value of the distance h from point p to the reference plane varies at different locations, but the same letter is used. The three-dimensional coordinates of any point P obtained by the blade rotation are uniquely represented by the following transformation relationship, as follows: Figure 3The geometric relationships shown indicate that:

[0101] x=Rsin(β)(1-r / R) (4.4)

[0102] y=Rcos(β)(1-r / R) (4.5)

[0103] The coordinates of point p in the real three-dimensional Cartesian coordinate system are (x, y), and β is the angle between the line containing the center of the circle and the blade measurement point and the plane containing the upper and lower light cutters of the blade, that is, the angle between the line containing the center of the circle and the blade measurement point and the y-axis.

[0104] Knowing the phase distribution on the blade surface reveals the blade's surface profile. In the FTP measurement method, the height h (i.e., r) of any point on the blade from the reference plane and the phase value at that point have the following relationship:

[0105]

[0106] In the formula, f0 is the fundamental frequency of the projection grating. The phase modulation is caused by the height distribution h(x,y) of the object, d refers to the horizontal distance between the beam emission point and the imaging system receiving point, and L0 is the vertical distance from the laser to the reference plane. Substituting equation (4.6) into equations (4.4) and (4.5) above, we can obtain:

[0107]

[0108]

[0109] The phase distribution of the blades can be obtained from the above formula, which is the partial profile of the surface of 2n blades.

[0110] In this embodiment, the reference stripe refers to the stripe that falls on the reference plane. Whether the blade deforms or not, the stripe on the reference plane will not change, serving as a baseline stripe. For each stripe pattern measured on the blade, there is a corresponding reference stripe pattern on the reference plane.

[0111] Alternatively, replacing the Fourier transform profilometry method in this embodiment with the Spatial Phase Detection (SPD) method can also achieve the same objective. However, the SPD method has lower accuracy in phase calculation and is not the best choice for measuring blade deformation.

[0112] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0113] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A device for measuring the deformation of a helicopter rotor blade, characterized in that The application relates to a method for measuring the three-dimensional surface profile of a rotor blade. The first semiconductor laser, the first sinusoidal grating and the first linear array CCD are arranged above the rotor blade to be measured; the second semiconductor laser, the second sinusoidal grating and the second linear array CCD are arranged below the rotor blade to be measured; and a data receiving and processing unit is arranged. The light beam emitted by the first semiconductor laser is irradiated on the upper span surface of the rotor blade to be measured after passing through the first sinusoidal grating, and a stripe is formed on the upper span surface of the rotor blade to be measured. The light beam emitted by the second semiconductor laser is irradiated on the lower span surface of the rotor blade to be measured after passing through the second sinusoidal grating, and a stripe is formed on the lower span surface of the rotor blade to be measured. The first linear array CCD is used for shooting the first stripe image of the upper span surface of the rotor blade to be measured. The second linear array CCD is used for shooting the second stripe image of the lower span surface of the rotor blade to be measured. The data receiving and processing unit is used for receiving the first stripe image shot by the first linear array CCD, receiving the second stripe image shot by the second linear array CCD, and obtaining the three-dimensional surface profile of the rotor blade to be measured by applying the Fourier transform profilometry method based on all the first stripe images and the second stripe images, and the deformation of the rotor blade is obtained by comparing the three-dimensional surface profiles of the rotor blade to be measured under different rotor rotating speeds.

2. The apparatus of claim 1, wherein, The first semiconductor laser, the second semiconductor laser, the first sinusoidal grating and the second sinusoidal grating, and the first linear array CCD and the second linear array CCD are symmetrically distributed along the rotor blade to be measured.

3. The apparatus of claim 2, wherein, The length of the stripe formed on the upper span surface of the rotor blade to be measured is greater than or equal to the length of the rotor blade to be measured.

4. The apparatus of claim 2, wherein, The emitting light beam of the first semiconductor laser, the optical axis of the first linear array CCD and the rotating shaft of the rotor blade to be measured are located on the same plane.

5. The apparatus of claim 2, wherein, An included angle exists between the emitting optical axis of the first semiconductor laser and the optical axis of the first linear array CCD.

6. A method of measuring the deformation of a helicopter rotor blade based on the apparatus according to any one of claims 1 to 5, characterized in that, The application relates to a method for measuring the three-dimensional surface profile of a rotor blade. The first linear array CCD and the second linear array CCD are controlled to shoot the stripes on the upper surface and the lower surface of the rotor blade to be measured at a set interval time, and 2n real shot stripe images are obtained; the 2n real shot stripe images include n first stripe images and n second stripe images. The Fourier transform profilometry method is applied to each real shot stripe image to obtain 2n local profile images of the surface of the rotor blade to be measured. The 2n local profile images of the surface of the rotor blade to be measured are spliced to obtain a three-dimensional surface profile image of the rotor blade to be measured. The deformation of the rotor blade is obtained by comparing the three-dimensional surface profile images of the rotor blade to be measured under two different rotor rotating speeds.

7. The method of claim 6, wherein, Before the 2n local profile images of the surface of the rotor blade to be measured are spliced, the following steps are further included. Each local profile image is trimmed to retain the profile image of the area where the stripe on the surface of the rotor blade to be measured is located.

8. The method of claim 6, wherein, The Fourier transform profilometry method is applied to each real shot stripe image to obtain 2n local profile images of the surface of the rotor blade to be measured. performing Fourier transform on the kth real shot fringe image and the corresponding kth reference fringe image respectively; performing frequency domain filtering on the kth transformed real shot fringe image and the kth transformed reference fringe image respectively, extracting the first fundamental frequency component corresponding to the kth transformed real shot fringe image and the second fundamental frequency component corresponding to the kth transformed reference fringe image; performing inverse Fourier transform on the first fundamental frequency component corresponding to the kth transformed real shot fringe image and the second fundamental frequency component corresponding to the kth transformed reference fringe image respectively; subtracting the inverse transform result corresponding to the kth real shot fringe image from the inverse transform result corresponding to the kth reference fringe image, obtaining the phase distribution of the kth real shot fringe image; performing unwrapping on the phase distribution of the kth real shot fringe image, obtaining the height distribution of the surface of the to-be-measured rotor blade corresponding to the kth real shot fringe image; judging whether k is 2n, if not, setting k=k+1 and returning to the step of performing Fourier transform on the kth real shot fringe image and the corresponding kth reference fringe image, until k=2n; if yes, obtaining the local profile map of the surface of the to-be-measured rotor blade with 2n.

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