High-precision target attitude and rotating speed detection method based on elliptical vortex light

Abstract

The invention relates to a high-precision target attitude and rotating speed detection method based on elliptical vortex light. The method comprises the following steps: S1, respectively preparing two groups of elliptical vortex light beams which are different in radius and continuously rotate and two groups of elliptical vortex light beams which are different in ellipticity and different in radius; s2, irradiating to a to-be-detected rotating target under a complete non-alignment condition, receiving a signal by using a detector, and processing to obtain two groups of signal time-frequency spectrums; s3, respectively extracting upper edges of the two groups of time-frequency spectrums, carrying out differential operation to obtain a frequency shift change curve, obtaining a target rotating shaft azimuth angle and a target rotating shaft inclination angle in combination with a rotating Doppler model, and completing target three-dimensional rotating shaft parameter measurement; and S4, selecting any time domain echo signal in the step S2 to carry out frequency domain transformation, and extracting a spectrum peak interval to obtain the rotating speed of the object. According to the method, synchronous measurement of the rotating shaft parameters and the rotating speed can be completed under any irradiation condition, the robustness is high, the measurement precision is high, and the method has great application potential in precision machining and telemetering.

Description

Technical Field

[0001] The present invention relates to a high-precision target attitude and rotation speed detection method based on elliptical vortex light. It belongs to the fields of lidar precision measurement, optical detection, rotational Doppler signal analysis, etc. Technical Background

[0002] Currently, due to its unique orbital angular momentum characteristics, vortex beams have been widely used in the field of rotational motion detection. However, existing methods have many limitations in technical applications, such as the strict requirement for the exact alignment of the optical axis and the rotation axis of the target, insufficient robustness to complex conditions such as lateral offset and oblique incidence, and difficulties in synchronously measuring the three-dimensional parameters (rotation axis azimuth angle, rotation axis inclination angle, rotation speed) of the rotating target.

[0003] These technical bottlenecks limit their applicability in actual scenarios and are difficult to meet the urgent needs for high-precision detection in fields such as modern precision machining, laser remote sensing, and high-end manufacturing. To address this problem, the present invention innovatively proposes a high-precision target attitude and rotation speed detection method based on elliptical vortex light. By combining optical field modulation technology and the rotational Doppler frequency shift model, through spectral difference operation, it not only effectively solves the interference of lateral offset and oblique incidence on detection accuracy but also realizes the synchronous high-precision measurement of the three-dimensional parameters of the rotating target under any irradiation conditions. This method has strong robustness, is easy to operate, and has a wide range of applications. It can be widely used in fields such as precision machining, optical detection, and target remote sensing, filling the gaps in the existing technology and providing important technical support for the development of high-end equipment manufacturing and national defense technology. Summary of the Invention

[0004] Aiming at the problems that the irradiation conditions required for the rotational Doppler detection of vortex beams are harsh and the attitude information of the target to be measured is limited, a high-precision target attitude and rotation speed detection method based on elliptical vortex light is proposed. The purpose is to complete the measurement of the three-dimensional rotation axis parameters and rotation speed of the rotating target under any irradiation conditions of the vortex beam, that is, including the measurement of the rotation axis azimuth angle, inclination angle, and rotation speed. This method has high redundancy and strong robustness, and can meet the requirements of any irradiation scenario; it can achieve high-precision measurement of the rotation axis parameters and rotation speed, and has great application potential in precision machining and remote measurement of rotating targets. The technical solution adopted by the present invention is a high-precision target attitude and rotation speed detection method based on elliptical vortex light, including:

[0005] Step S1: Using optical field modulation technology, combined with the complex amplitude modulation method, generate two holograms of elliptical vortex beams with the same ellipticity, different radii, and continuous rotation; then sequentially load the holograms onto a spatial light modulator, and then irradiate a linearly polarized beam onto the device to obtain two elliptical vortex beams with the same ellipticity, different radii, and continuous rotation.

[0006] Step S2: Under the condition of complete misalignment, irradiate the surface of the rotating target to be measured with two sets of vortex beams respectively. Use a photodetector to receive the scattered light signals from the target, and process the signals to obtain the time-frequency spectra of the two sets of scattered signals;

[0007] Step S3: Extract the upper edges of the time-frequency spectra of the two sets of signals and perform a subtraction operation to obtain the calculated frequency shift change curve. According to the established elliptical rotation Doppler frequency shift theory, combined with the change curve, calculate the azimuth angle of the rotating target shaft;

[0008] Step S4: Prepare two sets of elliptical vortex beam groups with continuously varying ellipticity and different radii;

[0009] Step S5: Repeat Steps S2 and S3. According to the frequency shift change curve after subtraction, calculate the tilt angle of the rotating target shaft to complete the measurement of the complete shaft parameters in three-dimensional space;

[0010] Step S6: Select any set of scattered echo signals obtained in Steps S2 and S5 to perform a Fourier transform to obtain the rotational Doppler spectrum, and calculate the rotational speed of the object according to the peak interval of the spectrum.

[0011] The measurement of the three-dimensional shaft parameters is based on the rotational Doppler frequency shift model of elliptical vortex beams under the established complete misalignment conditions (including lateral offset and tilt), as Figure 3 shown, which clarifies the quantitative relationship between the rotational Doppler frequency shift of the scattered signal and the beam ellipticity, shaft tilt angle, shaft azimuth angle, and lateral offset vector, and derives a quantitative rotational Doppler frequency shift expression: where f represents the rotational Doppler frequency shift of the scattered signal, m represents the ellipticity of the vortex beam, e represents the topological charge number of the vortex beam, Ω represents the rotational speed, β represents the tilt angle of the rotating target, γ represents the azimuth angle of the rotating target shaft, θ represents the azimuth angle of any point within the light spot on the surface of the rotating object, d represents the distance between the center of object rotation and the center of the optical axis, and r represents the beam radius;

[0012] The preparation of the elliptical vortex beam is based on the complex amplitude modulation method. By changing the ellipticity, intensity, and phase distribution of the vortex beam, an elliptical vortex beam with adjustable ellipticity and the direction of the major axis of the beam is prepared and used as the detection light source.

[0013] The high-precision target attitude and rotational speed detection method based on elliptical vortex light has no restrictions on the applicable relative pose conditions, and can complete the measurement of the three-dimensional parameters of the target shaft under any conditions, including the simultaneous presence of lateral offset and tilt incidence between the beam and the target rotation center.

[0014] The described method for measuring the azimuth angle of the rotating shaft based on elliptical vortex light is proposed based on the established rotational Doppler frequency shift model. Two sets of elliptical vortex beam groups with the same ellipticity, different radii, and continuous rotation are used to detect the rotating target. The time-frequency analysis of the scattered signals is performed to obtain the time-frequency spectra of the two sets of signals. By extracting the upper edge of the time-frequency spectrum and performing a subtraction operation, the azimuth angle of the rotating shaft can be calculated.

[0015] The described method for measuring the inclination angle of the rotating shaft based on elliptical vortex light uses elliptical vortex beam groups with continuously changing ellipticity and different radii to detect the rotating target. The scattered signals are processed to obtain the time-frequency spectra of the two sets of signals. The upper edges of the time-frequency spectra are respectively extracted and a subtraction operation is performed to calculate the inclination angle of the rotating shaft.

[0016] The signal processing method for measuring the rotating shaft parameters is based on fitting the upper edge curve of the time-frequency spectrum of the echo signal. According to the rotational Doppler frequency shift model of the elliptical vortex beam, a subtraction operation is performed on the upper edge curves of the two sets of echo signals to eliminate the influence of the lateral offset on the echo signal: △f = r1f1 - r2f2, where f1 and f2 represent the two upper edge frequency shifts, and △f represents the rotational Doppler frequency shift value after subtraction. Furthermore, by analyzing the frequency shift change of △f, the measurement of the rotating shaft parameters can be completed.

[0017] The described method for measuring the target rotation speed is based on the 4 sets of scattered echo time-domain signals obtained by measurement. Arbitrarily select one of them and perform a Fourier transform to obtain the rotational Doppler spectrum. According to the peak interval of the rotational Doppler spectrum, the measurement of the target rotation speed is completed.

[0018] The principle of the present invention is:

[0019] The expression of the elliptical vortex beam can be written as:

[0020]

[0021] where (x, y, z) is the cylindrical coordinate system, m represents the ellipticity, defined as the ratio of the minor axis b to the major axis a of the ellipse, i.e., m = b / a, E0 represents the complex amplitude coefficient, l represents the topological charge number, n represents the radial node order, k is the wave number, represents the Laguerre function, R z is the wavefront curvature radius, w z represents the beam waist radius at the distance z. According to Equation (1), the transverse phase of the elliptical vortex beam is Φ = ltan -1 (my / x) = etan -1 (msinθ / cosθ), and its phase gradient can be calculated as:

[0022]

[0023] When an elliptical vortex beam irradiates a rotating object, due to the modulation of the incident light phase by the object's motion, the frequency of the scattered signal shifts, causing a Doppler frequency shift. The total frequency shift value is:

[0024]

[0025] where f0 is the frequency of the beam and c is the speed of light, is the transverse phase gradient, is the velocity of the scattering particles of the object in the transverse plane. The first term in Equation (3) is the linear Doppler frequency shift, and the second term is the rotational Doppler frequency shift. When a superposition state elliptical vortex beam with opposite topological charge numbers and equal magnitudes is used as the probe light, the induced linear Doppler frequency shifts are the same, and they cancel each other out after interference. Only the rotational Doppler frequency shift exists in the scattered signal, that is

[0026] When detecting a rotating target under any misalignment condition, the geometric relationship between the beam and the rotating object is as shown in Figure 3 The attitude of the object's rotation axis in three-dimensional space is determined by two parameters, namely the axis azimuth angle and the axis tilt angle. Figure 3 In, O o represents the center of the rotating object, and O E represents the center of the projection of the elliptical vortex beam on the surface of the rotating object; point A is any point on the cross-section of the elliptical vortex beam perpendicular to the optical axis; point A' is the projection of A on the surface of the rotating object along the beam propagation direction; β represents the tilt angle, which is the angle between and the optical axis. The completely non-coaxial irradiation includes oblique incidence and transverse offset, and the effects of both are considered here. In Figure 3 , with O E as the origin, the beam propagation direction as the Z-axis, and the long axis direction of the cross-section of the elliptical vortex beam as the X-axis, a reference coordinate system O E -XYZ is established. represents the angular velocity vector perpendicular to the rotating object, and the angle between its projection in the XOY plane and the X-axis is the azimuth angle γ. represents the transverse displacement vector between the rotation center and the beam center in the reference coordinate system; represent the position vectors of A and A' in the reference coordinate system respectively; is the linear velocity at point A'; represents the position vector from the object's rotation center to A'. Then, two other coordinate systems are established to facilitate vector coordinate operations. With the optical axis propagation direction as the Z'-axis, that is, with O E as the origin, the beam propagation direction as the Z-axis, the projection direction of in the XOY plane as the X'-axis, a coordinate system O E -X'Y'Z' is established; rotate the coordinate system O E- The coordinate system O is obtained by rotating -X'Y'Z' counterclockwise by an angle β. E - X"Y"Z". is the angle with the X" axis. In the reference coordinate system, it can be expressed as:

[0027]

[0028] where Ω is the angular velocity of the object. The position vector of point A in the reference coordinate system is:

[0029]

[0030] where r is the beam radius. Through coordinate transformation, in the O E -X'Y'Z' coordinate system, it can be expressed as

[0031]

[0032] where R z (γ) is the rotation matrix about the Z axis. According to the geometric projection transformation, extend the X component of by 1 / cosβ, and then rotate the position vector by an angle β about Y', to obtain the position vector of the projection A' of A on the rotating object surface in O E -X'Y'Z',

[0033]

[0034] and then transform this vector to the coordinate system O E -XYZ,

[0035]

[0036] The vector in the O E -X"Y"Z" coordinate system can be expressed as

[0037]

[0038] d is the distance between O E and O o ; is the angle between the line connecting the center of object rotation and the center of the optical axis and the X' axis in the figure at O E . Through the coordinate transformation between O E -X"Y"Z", O E -X'Y'Z' and O E -XYZ, the position vector of in the reference coordinate system is obtained,

[0039]

[0040] Then, the position vector of the scattering point A' relative to the rotation center can be obtained.

[0041]

[0042] The velocity vector of point A' in O E -XYZ is equal to the angular velocity vector cross-multiplied by the position vector of this point relative to the rotation center.

[0043]

[0044] Under the condition of complete misalignment, the rotational Doppler frequency shift is the dot product of the transverse phase gradient of the vortex beam and the transverse linear velocity.

[0045]

[0046] It can be found from Equation (13) that the influence of the transverse offset d on the rotational Doppler frequency shift is related to the radius of the detection beam and is a separate numerical term, which is in a semi-coupled state with the tilt angle. Under the condition of complete non-rotation, two beams with the same ellipticity and topological charge number but different radii are used to detect the rotating object, and then the beam radius is multiplied by the frequency shift value of the scattering signal and the difference is taken, so that the influence of the transverse shift on the final rotational Doppler frequency shift can be completely eliminated, that is

[0047]

[0048] Equation (14) is the expression of the rotational Doppler frequency shift related to the tilt angle β and azimuth angle γ of the rotating shaft. When two sets of elliptical vortex beams with the same and fixed ellipticity, different radii, and continuous rotation are used as the detection light sources, according to Equation (14), the echo signal beams are subtracted, and the obtained frequency shift value shows a periodic variation law with the azimuth angle γ of the rotating shaft. Starting from the initial rotation angle φ1, rotate the major axis direction of the elliptical vortex beam. When the X-axis is perpendicular to the X'-axis, that is, the difference is π / 2, the frequency shift broadening range is the smallest, and the frequency domain amplitude of the echo signal is the highest. The relationship between the rotation angle φ2 and the azimuth angle γ of the rotating shaft is φ2 - φ1 = π / 2 - γ. According to this law, the measurement of the azimuth angle γ of the rotating shaft can be completed. Similarly, when two sets of elliptical vortex beams with continuously varying ellipticity and different radii are used as the detection light sources, after subtracting the echo signals, the obtained frequency shift value shows a periodic variation law with the tilt angle β of the rotating shaft. According to this law, the measurement of the tilt angle β of the rotating shaft can be completed. According to Equation (13), since the topological charge number, that is, the orbital angular momentum value must be an integer, in the rotational Doppler broadening spectrum, the interval of the frequency shift value is a multiple of the rotational speed. By extracting the frequency shift values of each adjacent interval, the rotational speed Ω can be obtained.

[0049] The main advantages of the present invention are as follows:

[0050] (1) For the first time, the measurement of three-dimensional shaft parameters is completed based on vortex beams, with high precision, broadened the application range of rotational Doppler detection, strong practicability, and provided a new shaft measurement scheme for precision machining industry and remote sensing detection of vortex beams.

[0051] (2) The device required for this method is simple, the optical path construction is convenient, and the operation difficulty is low. Only by switching the vortex beam to perform time-frequency analysis on the echo signal, the measurement of the shaft parameters of the object can be completed. At the same time, the preparation of elliptical vortex light is simple, and only relevant parameters need to be modified to flexibly adjust the beam ellipticity and radius.

[0052] (3) This method has a wide application range, strong versatility, and good robustness. It is not necessary to align the beam with the object shaft, and the measurement of the three-dimensional shaft parameters of the rotating target can be completed under any irradiation conditions, greatly broadening the applicable scenarios of vortex beams. Obtaining the three-dimensional shaft parameters has great practical significance for target tracking and trajectory prediction.

[0053] (4) This method has strong comprehensive measurement ability, high measurement efficiency, and reduces the detection cost. While measuring the three-dimensional shaft parameters, it is not necessary to change the device and measure redundant data, and the measurement of the target rotation speed can be completed under non-alignment conditions, improving the measurement efficiency, reducing the detection cost, and simplifying the detection process. Description of the Drawings

[0054] Figure 1 It is a flowchart for measuring the three-dimensional shaft parameters of a rotating target based on elliptical vortex beams.

[0055] Figure 2 It is a schematic diagram of the optical path for measuring the shaft parameters of an object.

[0056] Figure 3 It is a rotational Doppler frequency shift model of elliptical vortex beams under completely non-aligned conditions.

[0057] Figure 4 It is the measurement result of the shaft azimuth angle of a rotating target based on vortex beams. (a) is the time-frequency spectrum of the scattered signal with a continuously rotating elliptical vortex group with a beam radius of 2 mm as the light source, (b) is the time-frequency spectrum of the scattered signal with a continuously rotating elliptical vortex group with a beam radius of 1.5 mm as the light source, and (c) is the frequency shift curve after extracting and subtracting the upper edges of the two time-frequency spectra.

[0058] Figure 5Measurement results of the tilt angle of the rotating target shaft based on vortex beams. (a) is the spectrum of the scattering signal when an elliptical vortex group with continuously varying ellipticity and a beam radius of 2 mm is used as the light source, (b) is the spectrum of the scattering signal when an elliptical vortex group with continuously varying ellipticity and a beam radius of 1.5 mm is used as the light source, and (c) is the frequency shift curve after edge extraction and subtraction on the two spectra.

[0059] Figure 6 Measurement results of the rotational speed of the rotating target based on vortex beams. The values marked in the figure are the frequency shift intervals between adjacent peaks. Specific implementation

[0060] The following further describes the embodiments of the present application in detail. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than an exhaustive list of all embodiments. It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other.

[0061] Based on elliptical vortex light, the present invention realizes the measurement of the attitude and rotational speed of a rotating target in any illumination pose, that is, the high-precision synchronous detection of the three-dimensional shaft parameters and rotational speed. The implementation objects are optical vortices, three-dimensional shaft parameters of the rotating target, and rotational speed. The specific implementation steps are as follows:

[0062] The high-precision target attitude and rotational speed detection method based on elliptical vortex light adopted by the present invention uses continuously varying elliptical vortex beams as the detection source. Its basic detection device is as Figure 2 shown. Two holograms of elliptical vortex beams with the same ellipticity, different radii, and continuous rotation are respectively loaded on the spatial light modulator. The laser beam first passes through a polarizer to be modulated into a horizontally polarized beam, and then irradiates onto the spatial light modulator. After using a spatial filtering system composed of a lens and a diaphragm, the first-order diffracted beam is selected to generate two groups of elliptical vortex beams respectively. Under the completely misaligned condition, they are respectively irradiated onto the rotating target. A photodetector is used to receive the scattered light, and time-frequency analysis is performed on the two groups of scattered signals. The upper edges of the two spectra are extracted by data fitting, and a subtraction operation is performed to eliminate the influence of lateral offset on the rotational Doppler frequency shift. Finally, the change in the frequency shift spectrum after subtraction is analyzed to obtain the azimuth angle of the rotating target shaft. Then, the hologram is switched to two holograms of elliptical vortex beams with continuously varying ellipticity and different radii, and the above process is repeated to measure the tilt angle of the rotating target shaft, completing the complete measurement of the three-dimensional shaft parameters. Then, a Fourier transform is performed on any of the obtained scattered echo time-domain signals to obtain the rotational Doppler spectrum. According to the frequency shift peak interval in the spectrum, the rotational speed of the target can be obtained simultaneously.

[0063] The expression of the elliptical vortex beam can be written as:

[0064]

[0065] where (x, y, z) is the cylindrical coordinate system, m represents the ellipticity, defined as the ratio of the minor axis b to the major axis a of the ellipse, i.e., m = b / a, E0 represents the complex amplitude coefficient, l represents the topological charge number, n represents the radial nodal order, k is the wave number, represents the Laguerre function, R z is the radius of wavefront curvature, w z represents the beam waist radius at a distance z. According to Equation (1), the transverse phase of the elliptical vortex beam is Φ = ltan -1 (my / x) = ltan -1 (msinθ / cosθ), and its phase gradient can be calculated as:

[0066]

[0067] When the elliptical vortex beam irradiates a rotating object, due to the modulation of the incident light phase by the object motion, the frequency of the scattered signal shifts, causing the Doppler frequency shift. The total frequency shift value is:

[0068]

[0069] where f0 is the frequency of the beam, c is the speed of light, is the transverse phase gradient, is the velocity of the scattering particles of the object in the transverse plane. The first term in Equation (3) is the linear Doppler frequency shift, and the second term is the rotational Doppler frequency shift. When using the superposition state elliptical vortex beams with opposite topological charge numbers and equal magnitudes as the probe light, the induced linear Doppler frequency shifts are the same, and they cancel each other out after interference. Only the rotational Doppler frequency shift exists in the scattered signal, i.e.,

[0070] When detecting a rotating target under any misalignment conditions, the geometric relationship between the beam and the rotating object is as shown in Figure 3 . The attitude of the object rotation axis in three-dimensional space is determined by two parameters, i.e., the rotation azimuth angle and the axis tilt angle. Figure 3 In, O o represents the center of the rotating object; O E represents the center of the projection of the elliptical vortex beam on the surface of the rotating object; point A is any point on the cross-section of the elliptical vortex beam perpendicular to the optical axis; point A' is the projection of point A on the surface of the rotating object along the beam propagation direction. β represents the tilt angle, which is the angle between and the optical axis. The completely non-coaxial irradiation includes oblique incidence and lateral offset, and the effects of both are considered here. In Figure 3 , with O E as the origin, the beam propagation direction as the Z-axis, and the long axis direction of the cross-section of the elliptical vortex beam as the X-axis, a reference coordinate system O E -XYZ is established. It represents the angular velocity vector perpendicular to the rotating object, and the angle between its projection in the XOY plane and the X-axis is the azimuth angle γ. It represents the transverse displacement vector between the rotation center and the beam center in the reference coordinate system; They respectively represent the position vectors of A and A' in the reference coordinate system; It is the linear velocity at point A'; It represents the position vector from the rotation center of the object to A'. After that, two other coordinate systems are established to facilitate vector coordinate operations. Taking the optical axis propagation direction as the Z' axis, that is, taking O E as the origin, the optical beam propagation direction as the Z axis, the projection direction in the XOY plane as the X' axis, establish the coordinate system O E -X'Y'Z'; Rotate the coordinate system O E -X'Y'Z' counterclockwise by an angle β around the Y' axis to obtain the coordinate system O E -X"Y"Z". It is the angle with the X" axis. In the reference coordinate system, can be expressed as:

[0071]

[0072] where Ω is the angular velocity of the object. The position vector of point A in the reference coordinate system is:

[0073]

[0074] where r is the beam radius. The vector in the O E -X"Y"Z" coordinate system can be expressed as,

[0075]

[0076] d is the distance between O E and O o ; is the angle between the line connecting the rotation center of the object and the optical axis center and the O E X' axis in the figure. Through coordinate transformation and coordinate scaling, the position vector of any scattering point A' of the rotating object in the light spot relative to the rotation center can be calculated

[0077]

[0078] The velocity vector of point A' in the O E -XYZ is equal to the angular velocity vector cross-multiplied by the position vector of this point relative to the rotation center

[0079]

[0080] Under the condition of complete misalignment, the rotational Doppler shift is the dot product of the transverse phase gradient of the vortex beam and the transverse linear velocity.

[0081]

[0082] According to Equation (23), it can be found that the influence of the transverse offset d on the rotational Doppler shift is related to the radius of the detection beam and is a separate numerical term, which is in a semi-coupled state with the tilt angle. Under the condition of complete non-rotation, two beams with the same ellipticity and topological charge number but different radii are used to detect the rotating object. By multiplying the beam radius and the frequency shift value respectively and taking the difference, the influence of the transverse shift on the final rotational Doppler shift can be completely eliminated, that is

[0083]

[0084] An expression for the rotational Doppler shift related to the tilt angle β and azimuth angle γ of the rotating shaft is obtained. When two sets of elliptical vortex beams with the same and fixed ellipticity, different radii, and continuous rotation are used as the detection light source, according to Equation (24), the echo signal beams are subtracted. The frequency shift value obtained shows a periodic variation law with the azimuth angle γ of the rotating shaft. Starting from the initial rotation angle φ1, the long axis direction of the elliptical vortex beam is rotated. When the X-axis is perpendicular to the X'-axis, that is, the difference is π / 2, the frequency shift broadening range is the smallest, and the frequency domain amplitude of the echo signal is the highest. The relationship between the rotation angle φ2 and the azimuth angle γ of the rotating shaft at this time is φ2 - φ1 = π / 2 - γ. According to this law, the measurement of the azimuth angle γ of the rotating shaft can be completed. Similarly, when two sets of elliptical vortex beams with continuously varying ellipticity and different radii are used as the detection light source, the echo signals are subtracted. The frequency shift value obtained shows a periodic variation law with the tilt angle β of the rotating shaft. According to this law, the measurement of the tilt angle β of the rotating shaft is completed. According to Equation (23), since the topological charge number, that is, the orbital angular momentum value must be an integer, in the rotational Doppler broadening spectrum, the interval of the frequency shift value is a multiple of the rotational speed. By extracting the frequency shift values of each adjacent interval, the target rotational speed can be obtained.

[0085] In the experiment, taking one of the actual detection conditions as an example, the measurement process is described.

[0086] First, measure the azimuth angle of the rotating shaft of the rotating target. The designed ellipticity of the beam is The rotation range of the elliptical vortex beam is [0, π], the interval is cos(π / 36), the radii of the two sets of vortex beams are 2 mm and 1.5 mm respectively, and each set of elliptical vortex beams contains 36 holograms. Set the offset distance between the rotating shaft and the center of rotation of the object to 2 mm; the transverse shift vector and O in the figure EThe angle between the X'-axis is 45 degrees; the rotational speed of the object is set to 50 Hz; the inclination angle of the object's rotating shaft is 45 degrees; the azimuth angle of the rotating shaft is 30 degrees; the topological charge number of the light beam is ±20. The cycle period of a group of elliptical optical vortices is about 1.8 s, that is, the display time of each hologram is 0.05 s. Due to the delay of the hardware and the playback software, there are slight fluctuations in the cycle period duration. The two groups of vortex beams are respectively used to detect the rotating target under the set conditions. In the experiment, the echo signals from the object within 4 s are collected, and then the time-frequency spectrum of the echo signals is obtained by using the short-time Fourier transform, as shown in Figure 4 (a)(b). Then, the fitting function is used to extract the upper edge contours of the two time-frequency spectra. The upper edge frequency shift values of the two groups are multiplied by the corresponding beam radii and then subtracted to obtain the final frequency shift curve as shown in Figure 4 (c). At this time, the lowest point time is 1.477 s, the initial time is 0.844 s, the corresponding beam rotation angle is 57.67 degrees, and the azimuth angle of the object is calculated as γ = 90° - 57.67° - 0° = 32.33°. Compared with the set value of the azimuth angle of the rotating shaft, the measurement accuracy is 92.3%.

[0087] Figure 5 Next, measure the inclination angle of the rotating target shaft. Replace the beam with two groups of elliptical vortex beam groups with continuously changing ellipticity and different radii. The designed range of the beam ellipticity is [cos(11π / 24), 1], the interval is cos(π / 72), the radii of the two groups of vortex beams are 2 mm and 1.5 mm respectively, and each group of elliptical vortex beams contains 36 holograms. The remaining detection conditions and the signal reception duration remain unchanged. The same processing process is repeated for the two groups of received echo signals to obtain the final frequency shift curve as shown in

[0088] (c). At this time, the lowest point time is 2.552 s, the initial time is 1.634 s, and the inclination angle of the object is calculated as 41 degrees. Compared with the set value of the inclination angle of the rotating shaft, the measurement accuracy is 91.82%. Figure 6 The echo time-domain signal obtained when the detection light source is a continuously rotating vortex beam with a radius of 1.5 mm is subjected to Fourier transform to obtain the rotational Doppler spectrum, as shown in Figure 6 According to the peak interval of the rotational Doppler spectrum, the rotational speed of the target can be measured. At this time, according to the results, the rotational speed of the target is 51.02 Hz. Compared with the set value of the rotational speed of 50 Hz, the measurement accuracy is 97.96%.

[0089]

[0090] It can be seen from the experimental results that the influence of the lateral offset is eliminated through the subtraction operation of the two groups of signals. The frequency shift after subtraction is only related to the azimuth angle and the inclination angle of the rotating shaft. The results show that this method can complete the complete measurement of the three-dimensional parameters of the rotating target shaft and the rotational speed under any illumination pose conditions, and the accuracy is relatively high.The content not described in detail in this invention book belongs to the prior art well-known to those skilled in the art.

Claims

1. A high-precision target attitude and rotation speed detection method based on elliptical vortex light, characterized in that: Step S1: Using the optical field control technology and combining the complex amplitude modulation method, prepare two groups of elliptical vortex beam groups with the same ellipticity, different radii, and continuous rotation; Step S2: Under the condition of complete misalignment, irradiate the surface of the rotating target to be measured with the two groups of vortex beams respectively, use a photodetector to receive the scattered light signals from the target, and process the signals to obtain the time-frequency spectra of the two groups of scattered signals; Step S3: Extract the upper edges of the time-frequency spectra of the two groups of signals and perform a subtraction operation to obtain the calculated frequency shift change curve. According to the established elliptical rotation Doppler frequency shift model and combining with the change curve, calculate the azimuth angle of the rotating target shaft; Step S4: Prepare two groups of elliptical vortex beam groups with continuously changing ellipticity and different radii; Step S5: Repeat Steps S2 and S3 to obtain two groups of scattered signals. According to the frequency shift change curve after subtracting the time-frequency spectra, calculate the tilt angle of the rotating target shaft to complete the measurement of the complete shaft parameters in three-dimensional space; Step S6: Select any group of scattered echo signals obtained in Steps S2 and S5 to perform Fourier transform to obtain the rotational Doppler spectrum, and calculate the rotational speed of the object according to the interval between the spectrum peaks.

2. The high-precision target attitude and rotation speed detection method based on elliptical vortex light according to claim 1, wherein: A rotational Doppler frequency shift model of elliptical vortex beams under completely misaligned conditions (including lateral offset and oblique illumination) is established, the quantitative relationship between the rotational Doppler frequency shift of the scattered signal and the beam ellipticity, the tilt angle of the rotation axis, the azimuth angle of the rotation axis, and the lateral offset vector is clarified, and a specific expression for the rotational Doppler frequency shift is derived: where f represents Table Rotational Doppler frequency shift of scattered signals, m represents the ellipticity of the vortex beam, e represents the topological charge number of the vortex beam, Ω represents the rotational speed, β represents the tilt angle of the rotating target, γ represents the azimuth angle of the rotating target shaft, θ represents the azimuth angle of any point within the light spot on the surface of the rotating object, d represents the distance between the center of object rotation and the center of the optical axis, and r represents the beam radius.

3. A high-precision target attitude and rotation speed detection method based on elliptical vortex light according to claim 1, characterized in that: Using the optical field control method, change the ellipticity, intensity, and phase distribution of the vortex beam to prepare an elliptical vortex beam with adjustable ellipticity and the direction of the major axis of the beam, which is used as a detection light source.

4. A high-precision target attitude and rotation speed detection method based on elliptical vortex light according to claim 1, characterized in that: There is no limit to the relative pose conditions for the beam to detect the rotating target. The three-dimensional parameters of the target shaft can be measured under any conditions, that is, including the simultaneous presence of lateral offset and oblique incidence between the beam and the center of target rotation.

5. A high-precision target attitude and rotation speed detection method based on elliptical vortex light according to claim 1, characterized in that: Based on the established rotational Doppler frequency shift model, a measurement scheme for the azimuth angle of the rotating target shaft under any irradiation conditions is proposed. Prepare two groups of elliptical vortex beam groups with the same ellipticity, different radii, and continuous rotation as the light source to detect the rotating target. Use a photodetector to collect the scattered light signals, perform time-frequency transformation on the signals to obtain the time-frequency spectra of the two groups of signals, then extract the upper edges of the time-frequency spectra respectively and perform a subtraction operation to obtain the calculated frequency shift change curve. Combining with the established rotational Doppler frequency shift theory, the measurement of the azimuth angle of the shaft can be completed.

6. The high-precision target attitude and rotation speed detection method based on elliptical vortex light according to claim 1, characterized in that: Based on the established rotational Doppler frequency shift model, a measurement scheme for the tilt angle of the rotating target shaft under any irradiation conditions is proposed. Prepare two groups of elliptical vortex beam groups with continuously changing ellipticity and different radii as the light source to detect the rotating target, collect the scattered light signals, and process the signals to obtain the time-frequency spectra of the two groups. Extract the upper edges of the time-frequency spectra respectively and perform a subtraction operation to obtain the frequency shift change curve. Combining with the established rotational Doppler frequency shift theory, the measurement of the tilt angle of the shaft can be completed.

7. A high-precision target attitude and rotation speed detection method based on elliptical vortex light according to claim 1, characterized in that: A signal processing method for measuring the parameters of a rotating shaft is proposed. After obtaining the time-frequency spectrum of the echo signal, the upper edge frequency shift curve is obtained by numerically fitting the rotating Doppler time-frequency spectrum; two sets of elliptical vortex beam groups with different radii are used, and the subtraction operation is performed on the upper edge curves of the two sets of echo signals to eliminate the influence of the lateral offset on the echo signal: △f = r1f1 - r2f2, where f1 and f2 represent the two upper edge frequency shifts, and △f represents the rotating Doppler frequency shift value after subtraction. The function of the rotating Doppler frequency shift with respect to the shaft inclination angle and azimuth angle is obtained. By measuring the beam ellipticity m and the rotation angle φ corresponding to the final rotating Doppler frequency shift curve, according to n = 0, 1, 2…, m = cosβ, where γ represents the azimuth angle of the object rotating shaft, β represents the shaft tilt angle, m represents the beam ellipticity, and φ represents the beam rotation angle, and the measurement of the rotating shaft parameters can be completed.

8. A high-precision target attitude and rotation speed detection method based on elliptical vortex light according to claim 1, characterized in that: While measuring the three-dimensional rotation axis parameters of the target, the measurement of the target rotation speed is completed. From the time-domain scattered echo signals obtained by acquisition, any one group is taken and Fourier-transformed to obtain the rotational Doppler spectrum. Based on the peak interval of the rotational Doppler spectrum, the measurement of the target rotation speed can be completed.

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