A laser measurement method and device for large-diameter torsional vibration

Abstract

This invention discloses a laser measurement method and apparatus for large-diameter torsional vibration, belonging to the field of photoelectric measurement technology. The apparatus includes a laser, a polarizing beam splitter, a λ / 2 waveplate, an acousto-optic modulator, a plane mirror, a sinusoidal signal source, a photodetector, a data acquisition system, a computer, and a rotating object under test. The laser generates a laser beam with wavelength λ and frequency f. A sinusoidal signal source modulates and splits the laser beam after it passes through the acousto-optic modulator, outputting diffracted laser A and diffracted laser B, which are then converted into parallel beams with an optical axis distance d by the plane mirror. These beams illuminate the rotating object under test. Utilizing the characteristic that the rotating body produces opposite signs of Doppler frequency shifts in the two diffracted laser beams, the two laser beams reflected from the rotating object, containing the Doppler frequency shifts generated by rotation, are again subjected to frequency shifting, beam combining, and beat interference by the acousto-optic modulator. The Doppler frequency shifts are extracted, and the angular velocity of the rotating object is calculated.

Description

Technical Field

[0001] This invention relates to a laser measurement method and device for large-diameter torsional vibration, belonging to the field of photoelectric measurement technology. Background Technology

[0002] Matter is in perpetual motion; therefore, the measurement of motion parameters is one of the fundamental needs in human social production practices. Typically, this involves measuring three motion parameters: velocity, displacement, and acceleration. All three are methods of representing motion parameters. They are distinct yet interconnected: displacement is the integral of velocity, while acceleration is the differential of velocity. Having one of these parameters allows one to obtain the other two through calculation and initial condition constraints.

[0003] The same situation exists in angular motion, including various forms of motion such as rotation, oscillation, twisting, precession, and angular vibration. Quantitative parameters such as angular velocity (rotational speed), angular displacement, and angular acceleration are abstracted and widely exist in various practical systems. For example: (1) inertial navigation systems of missiles, aircraft, and submarines; (2) transient rotation measurement of various rotating machinery such as motors and engines; including the changes in angular velocity and angular acceleration over time during mechanical start-up and shutdown, and the measurement of rotational pulsation during stable mechanical rotation; (3) other angular motion testing needs; including real-time measurement of the angular position of various control surfaces used for aircraft attitude control during flight. Angular acceleration is tested to simulate human motion during ejection rescue; angular acceleration and angular velocity are used by robots to sense their motion; and the reaction of astronauts to angular acceleration and angular velocity is required for aerospace biomedical research.

[0004] There are currently two main methods for measuring rotational speed using laser interferometry: 1) Dual vibrometer method: Two laser vibrometers independently measure the vibration between different points of the rotating object using parallel beams at a known distance, and calculate the rotational speed of the object under test; 2) Grating differential laser goniometer method: By engraving a grating on the object under test, the rotational speed of the object under test is obtained by a dual-beam differential measurement method with the center of the optical axis precisely passing through the center of the rotation axis.

[0005] Among these methods, the dual-vibration meter method is expensive and only suitable for measuring periodic angular motion, making it unsuitable for measuring single angular motion. While the grating differential laser goniometer can achieve high measurement accuracy, it still has several drawbacks:

[0006] (1) The angular vibration amplitude that can be measured is very small, usually not exceeding ±5°;

[0007] (2) Although the radius of rotation can be accurately measured, it has always been a difficult problem to make the center of the optical axis pass through the center of the rotation precisely, which will inevitably lead to measurement error. For on-site angular vibration measurement, the radius of rotation is often not accurately obtained.

[0008] (3) A grating needs to be installed on the surface of the target to be measured. The grating is a precision component, which is not resistant to dirt, is easily corroded, cannot be touched, has poor environmental adaptability, cannot be repaired after damage, and brings additional mass and damages the surface to be measured. Therefore, the use of the grating not only brings additional measurement uncertainty and limits the measurement angle range, but also greatly limits the application of the laser interferometric angle motion measurement system.

[0009] In addition, the distance between the measuring lenses of most laser motion measuring instruments is not very large at present. When measuring large-diameter angular motion, there are problems such as inconsistency in use and impact on accuracy.

[0010] Therefore, angular motion measurement has become a challenging problem in motion measurement. Summary of the Invention

[0011] To address the problems in measuring angular velocity (i.e., rotational speed and angular velocity) during torsional vibration, this invention aims to provide a laser measurement method and apparatus for large-diameter torsional vibration. It utilizes a monochromatic laser of the same wavelength, which, after passing through an acousto-optic modulator, outputs two diffracted laser beams with a frequency difference. These two beams are then parallelized by a plane mirror and used to illuminate the torsional object under test. Taking advantage of the opposite signs of the Doppler frequency shifts generated by the torsional body on the two parallel diffracted laser beams, the two laser beams reflected from the torsional object, containing the Doppler frequency shifts caused by torsion, are again subjected to frequency shifting, beam combining, and beat interference by the acousto-optic modulator. The Doppler frequency shifts are extracted, and the angular velocity of the torsional object is finally calculated, thus achieving laser measurement of large-diameter torsional vibration. This invention eliminates the need for a focusing lens and has the advantage of simple structure.

[0012] The present invention is achieved through the following technical solution.

[0013] This invention discloses a large-diameter torsional vibration laser measurement device, comprising a laser, a polarizing beam splitter, a λ / 2 waveplate, an acousto-optic modulator, a plane mirror, a sinusoidal signal source, a photodetector, a data acquisition system, a computer, and a torsional test object. The laser generates a laser beam with wavelength λ and frequency f, which passes through the polarizing beam splitter and the λ / 2 waveplate before reaching the acousto-optic modulator. A sinusoidal signal source modulates the frequency of the laser beam after passing through the acousto-optic modulator, generating diffracted laser A and diffracted laser B. Diffracted laser A and diffracted laser B are respectively converted into parallel beams with an optical axis distance d by the plane mirror, illuminating the torsional test object. Utilizing the characteristic that the torsional body produces two diffracted laser beams with opposite signs, the two laser beams reflected from the torsional test object, containing the torsional Doppler frequency shift, are again subjected to frequency shifting, beam combining, and beat frequency interference by the acousto-optic modulator. The Doppler frequency shift is extracted, and the angular velocity value of the torsional test object is finally calculated, realizing large-diameter torsional vibration laser measurement.

[0014] Preferably, the beams are converted into parallel beams with an optical axis distance of d by a plane mirror, and then irradiate the torsion test object in parallel through the plane mirror. Utilizing the characteristic that the torsion body produces two beams of diffracted laser with opposite signs of Doppler frequency shifts, the beat frequency of the two laser beams reflected from the torsion test object, containing the Doppler frequency shifts caused by the torsion, can be achieved in two ways:

[0015] Method 1: Dual-diffraction laser method; Diffraction laser A and Diffraction laser B are converted into parallel beams with an axial distance of d by the first and second plane mirrors, respectively, and then illuminate the torsion test object. After being reflected back by the test object, the frequency of the reflected light becomes f. Ad After passing through the first planar mirror and the acousto-optic modulator again, the light frequency becomes f. Ad The light beam is +2Δf, then passes through a λ / 2 waveplate, is reflected by a polarizing beam splitter, and then combines with the reflected light from another diffracted laser B to produce beat frequency interference. This interference is received by a photodetector, which outputs a photodetector beat frequency signal. After being reflected back from the object being measured, the frequency of the reflected light from the diffracted laser B becomes f. Bd After passing through the second plane mirror and the acousto-optic modulator again, the light frequency becomes f. Bd -2Δf, then passes through the λ / 2 waveplate, is reflected by the polarizing beam splitter, and then combines with the reflected light of another diffracted laser A to produce beat frequency interference. This interference is received by the photodetector, outputting a photodetector beat frequency signal with a frequency of f. p .

[0016] Method 2: Single diffraction laser method; Diffraction laser A passes through the first plane mirror and is transformed into parallel light parallel to the 0th order diffracted (direct light, no diffraction) laser B, with the distance between the optical axes of the two beams being d. This parallel light then illuminates the torsional object under test. After being reflected back by the object under test, the frequency of the reflected light becomes f.Ad After passing through the first planar mirror and the acousto-optic modulator again, the light frequency becomes f. Ad The light beam is +2Δf, then passes through a λ / 2 waveplate, is reflected by a polarizing beam splitter, and then combines with the reflected light from another 0th-order diffracted laser B to produce beat frequency interference. This interference is received by a photodetector, which outputs a photodetector beat frequency signal. After the 0th-order diffracted laser B is reflected back from the object under test, the frequency of the reflected light becomes f. Bd After passing through the acousto-optic modulator again, the optical frequency remains f. Bd Then, passing through the λ / 2 waveplate, it is reflected by the polarizing beam splitter and combines with the reflected light of another diffracted laser A, producing beat frequency interference. This interference is received by the photodetector, outputting a photodetector beat frequency signal with a frequency of f. p .

[0017] This invention also discloses a method for measuring large-diameter torsional vibration using laser technology, implemented based on the aforementioned large-diameter torsional vibration laser measuring device. The method for measuring large-diameter torsional vibration using laser technology disclosed in this invention includes the following steps:

[0018] Step 1: The frequencies are f A f B Two parallel measuring laser beams, measuring beam A and measuring beam B, are incident on opposite sides of a rotor shaft. The distance between their optical axes is d. The rotor rotates at an angular velocity of ω, with its axis of torsion at point O. The wavelength of measuring beam A is λ. A The wavelength of light B is measured to be λ. B .

[0019] The torsional linear velocity at point a of beam A is v ta The radius of torsion Oa is R a The linear velocity component in the direction of beam A is v a Linear velocity v ta The angle between the beam and the optical axis A is α; the linear velocity v ta The direction is perpendicular to Oa.

[0020] The torsional linear velocity at point b where beam B illuminates is v tb The radius of torsion Ob is R b The linear velocity component in the direction of beam B is v b Linear velocity v tb The angle β between the beam and the optical axis B; the linear velocity v tb The direction is perpendicular to Ob.

[0021] Then, measuring light A and measuring light B satisfy the relationships described in equations (1) and (2):

[0022] v a =v ta cosα=ωR a cosα (1)

[0023] v b =v tb cosβ=ωR b cosβ (2)

[0024] Since the actual laser frequency is above several hundred terahertz, while in comparison, the frequency difference f between two lasers from the same source, A and B, is... A -f B Below several hundred megahertz, the frequency difference f between two laser beams A and B originating from the same source is... A -f B If the actual laser frequency is simplified to a negligible value, then the wavelength λ of the measured light A is... A Measuring the wavelength λ of light B B The wavelength λ produced by the laser is approximately equal to that of the laser:

[0025] λ A ≈λ B ≈λ(3)

[0026] Define the linear velocities obtained by measuring two laser beams A and B as v, respectively. a and v b The corresponding Doppler frequency shifts are f DA and f DB According to the Doppler principle,

[0027] f DA =2v a / λ A =2(ωR) a cosα) / λ A

[0028] ≈2v a / λ=2(ωR a co sα) / λ (4)

[0029] f DB =2v b / λ B =2(ωR) b cosβ) / λ B

[0030] ≈2v b / λ=2(ωR b cosβ) / λ (5) According to geometric relations, we get

[0031] d = R a cosα+R b cosβ (6)

[0032] Laser A contains the reflected light frequency f with a Doppler shift. Adfor

[0033] f Ad =f A -f DA (7)

[0034] Laser B contains the reflected light frequency f of the Doppler shift Bd for

[0035] f Bd =f B +f DB (8)

[0036] The reflected light frequency f of laser A Ad The reflected light frequency f of laser B Ad The beat frequency f is obtained by combining the beat frequencies. p

[0037] f p =f Ad -f Bd =(f A -f B )-(f DA +f DB )=(f A -f B )-f D (9)

[0038] Among them, f A -f B Given the known frequency difference between incident laser A and incident laser B, f D The value is the Doppler frequency shift measurement caused by torsion. A negative value indicates clockwise torsion, and a positive value indicates counterclockwise torsion.

[0039] Based on equations (1) to (9), we can obtain...

[0040] f D =(f A -f B )-f p =-(f DA +f DB )=-2dω / λ (10)

[0041] Right now

[0042]

[0043] For method one, step two: A laser with wavelength λ and frequency f is generated by a laser source, passes through a polarizing beam splitter and a λ / 2 waveplate, and reaches an acousto-optic modulator. The frequency Δf of a sinusoidal signal source is used to modulate the laser frequency after passing through the acousto-optic modulator, generating a +2nd order diffracted laser A and a -2nd order diffracted laser B. The frequency f of diffracted laser A is...A The frequency f of the diffracted laser B B They are respectively

[0044] f A =f + 2Δf (12)

[0045] f B =f-2Δf (13)

[0046] Here, Δf represents the frequency shift generated for each diffraction level.

[0047] Diffracted laser A and diffracted laser B are transformed into parallel beams with an optical axis distance of d after passing through the first and second plane mirrors, respectively, and then irradiate the torsion test object.

[0048] After the diffracted laser A is reflected back from the object being measured, the frequency of the reflected light becomes f. Ad After passing through the first planar mirror and the acousto-optic modulator again, the light frequency becomes f. Ad +2Δf, then passes through the λ / 2 waveplate, is reflected by the polarization beam splitter, and then combines with the reflected light of another diffracted laser B to produce beat frequency interference, which is received by the photodetector and outputs a photodetector beat frequency signal.

[0049] After the diffracted laser B is reflected back from the object being measured, the frequency of the reflected light becomes f. Bd After passing through the second plane mirror and the acousto-optic modulator again, the light frequency becomes f. Bd -2Δf, then passes through the λ / 2 waveplate, is reflected by the polarizing beam splitter, and then combines with the reflected light of another diffracted laser A to produce beat frequency interference. This interference is received by the photodetector, outputting a photodetector beat frequency signal with a frequency of f. p .

[0050] The frequency of the diffracted laser A at the photodetector is

[0051] f Ad8 =f + 4Δf - f DA (14)

[0052] The frequency of the diffracted laser B at the photodetector is

[0053] f Bd8 =f - 4Δf + f DB (15)

[0054] f p =f Ad8 -f Bd8 =8Δf-f D (16)

[0055] f D =8Δf-(f Ad8 -fBd8 )=8Δf-f p (17)

[0056] The photodetector outputs an FM signal with a carrier frequency of 8Δf. After waveform acquisition by the data acquisition system, the FM signal is demodulated by a computer, and the Doppler frequency shift f is obtained according to equation (17). D The measurement results are obtained by using the laser wavelength of the laser and the distance between the optical axes of the two diffracted lasers as d, and the angular velocity ω of the torsional test object is calculated using Equation (11), thus realizing large-diameter torsional vibration laser measurement.

[0057] For method two, step two: A laser with wavelength λ (frequency f) is generated by a laser source, passes through polarizing beam splitter 2 and λ / 2 waveplate, and reaches the acousto-optic modulator. The frequency Δf of a sinusoidal signal source is used to modulate the laser frequency after passing through the acousto-optic modulator, generating a +2nd order diffracted laser A and a 0th order diffracted laser B, where the frequency f of diffracted laser A is... A The frequency f of the diffracted laser B B They are respectively

[0058] f A =f + 2Δf (18)

[0059] f B =f (19)

[0060] Here, Δf represents the frequency shift generated for each diffraction level.

[0061] The diffracted laser A passes through the first plane mirror and is transformed into parallel light parallel to the diffracted laser B, with a distance d between the optical axes of the two beams, which then illuminates the torsion test object.

[0062] After the diffracted laser A is reflected back from the object being measured, the frequency of the reflected light becomes f. Ad Through the first plane mirror and the acousto-optic modulator, the light frequency becomes f. Ad +2Δf, then passes through the λ / 2 waveplate, is reflected by the polarization beam splitter, and then combines with the reflected light of another diffracted laser B to produce beat frequency interference, which is received by the photodetector and outputs a photodetector beat frequency signal.

[0063] After the diffracted laser B is reflected back from the object being measured, the frequency of the reflected light becomes f. Bd After passing through the acousto-optic modulator again, the optical frequency remains f. Bd Then, passing through the λ / 2 waveplate, it is reflected by the polarizing beam splitter and combines with the reflected light of another diffracted laser A, producing beat frequency interference. This interference is received by the photodetector, outputting a photodetector beat frequency signal with a frequency of f. p .

[0064] The frequency of the diffracted laser A at the photodetector is

[0065] f Ad8 =f + 4Δf - f DA (20)

[0066] The frequency of the diffracted laser B at the photodetector is

[0067] f Bd8 =f +f DB (twenty one)

[0068] f p =f Ad8 -f Bd8 =4Δf-f D (twenty two)

[0069] f D =4Δf-(f Ad8 -f Bd8 )=4Δf-f p (twenty three)

[0070] The photodetector outputs an FM signal with a carrier frequency of 4Δf. After waveform acquisition by the data acquisition system, the FM signal is demodulated by a computer, and the Doppler frequency shift f is obtained according to equation (23). D The measurement results are obtained by using the laser wavelength of the laser and the distance between the optical axes of the two diffracted lasers as d, and the angular velocity ω of the torsional test object is calculated using Equation (11), thus realizing large-diameter torsional vibration laser measurement.

[0071] As a preferred method, an acousto-optic modulator is used to convert a single-wavelength laser into two coherent measurement lasers of different frequencies, and the acousto-optic modulator is used to form a combined differential beat frequency in the original path return mode. Finally, the laser Doppler frequency containing rotational angular velocity information is extracted, and the instantaneous value of angular velocity is obtained by calculation.

[0072] Preferably, the direction of torsion is determined by the sign of the obtained angular velocity value. When the angular velocity ω is negative, it indicates clockwise torsion, and when the angular velocity ω is positive, it indicates counterclockwise torsion.

[0073] As a preferred method, a dual-lens measurement method with adjustable spacing is used to meet the measurement needs of large-diameter torsional objects.

[0074] Beneficial effects:

[0075] 1. This invention discloses a method and apparatus for measuring large-diameter torsional vibration using laser technology. It employs a monochromatic laser of the same wavelength, which, after passing through an acousto-optic modulator, outputs two diffracted laser beams with a frequency difference. These two beams are reflected by a plane mirror and then irradiate the torsional test object in parallel. Utilizing the characteristic that the torsional body produces opposite signs of the Doppler frequency shifts of the two parallel diffracted laser beams, the Doppler frequency shift is extracted from the beat frequencies of the two laser beams reflected back from the torsional test object, and the angular velocity of the torsional test object is ultimately calculated, thus achieving large-diameter torsional vibration laser measurement. Compared with other measurement schemes, this invention uses only one acousto-optic modulator and utilizes the principle of optical path reversibility to simultaneously complete three core functions: frequency shifting, beam splitting, and beam combining interference. This makes the invention extremely simple, stable, and reliable in its optical path, requiring fewer optical components, and being low-cost and easy to implement. Furthermore, this invention does not require focusing with a focusing lens, grating installation, or alignment of the measuring optical axis with the axis of the torsion body. It has no limitation on the range of angular motion and can be used to measure both periodic motion and single motion.

[0076] 2. This invention discloses a laser measurement method and apparatus for large-diameter torsional vibration. It uses an acousto-optic modulator to convert a single-wavelength laser into two coherent measurement laser beams of different frequencies. These beams are then combined using the acousto-optic modulator in a return-to-origin manner to form a differential beat frequency. Based on optical path geometry and Doppler frequency shift, a series of relational formulas are constructed to obtain the angular velocity of the torsional object under test. This allows for real-time extraction of the laser Doppler frequency containing rotational angular velocity information, and the instantaneous value of the transient angular velocity is calculated, thus achieving laser measurement of diameter torsional vibration. Compared to other measurement methods, this invention only requires the axis of the torsional body to be between the two parallel measurement beams. It does not restrict the object's position (whether it is in the center of the measurement optical axis), the shape of the torsional body (whether it is regular), or the rotational speed (whether it is uniform). It is convenient, reliable, highly adaptable, and easy to promote and apply.

[0077] 3. The present invention discloses a laser measurement method and device for large-diameter torsional vibration, which uses a dual-beam measurement method with adjustable spacing to realize the measurement of the angular velocity of a rotating object. In principle, it can be adapted to the accurate measurement of the angular velocity of any large-diameter torsional object, and is an excellent solution for measuring the rotational speed of a large-diameter torsional body. Attached Figure Description

[0078] Figure 1 A schematic diagram of a laser measurement method for large-diameter torsional vibration according to the present invention;

[0079] Figure 2 A schematic diagram of a large-diameter torsional vibration laser measurement device according to the present invention (corresponding to method one);

[0080] Figure 3A schematic diagram of a large-diameter torsional vibration laser measurement device according to the present invention (corresponding to method two);

[0081] Wherein: 1—laser, 2—polarizing beam splitter, 3—λ / 2 waveplate, 4—acousto-optic modulator, 5—first plane mirror, 6—second plane mirror, 7—sine wave source, 8—photodetector, 9—data acquisition system, 10—computer, 11—torsional object under test. Detailed Implementation

[0082] To better illustrate the purpose and advantages of the present invention, the invention will be further described below in conjunction with the accompanying drawings and examples.

[0083] Example 1 (using ±2nd order diffraction laser)

[0084] This embodiment discloses a large-diameter torsional vibration laser measurement device, including a laser 1, a polarizing beam splitter 2, a λ / 2 waveplate 3, an acousto-optic modulator 4, a first plane mirror 5, a second plane mirror 6, a sinusoidal signal source 7, a photodetector 8, a data acquisition system 9, a computer 10, and a torsional object under test 11. Figure 2 As shown.

[0085] The laser wavelength of laser 1 is selected as λ = 632.8 nm, the second-order diffraction frequency of acousto-optic modulator 4 is 2Δf = 40 MHz, the output frequency of sinusoidal signal source 7 is Δf = 20 MHz, and the distance between the two parallel measurement beams A and B is d = 400 mm.

[0086] This embodiment discloses a laser measurement method for large-diameter torsional vibration, which is implemented based on the aforementioned laser measurement device for large-diameter torsional vibration. The specific implementation method of this embodiment is as follows:

[0087] like Figure 2 As shown, a laser with a wavelength of λ = 632.8 nm (frequency f) is generated by laser 1, passes through polarizing beam splitter 2 and λ / 2 waveplate 3, and reaches acousto-optic modulator 4. A sinusoidal signal source 7 with a frequency Δf = 20 MHz modulates the frequency of the laser passing through acousto-optic modulator 4, generating a +2nd order diffracted laser A and a -2nd order diffracted laser B. The frequency f of diffracted laser A is... A The frequency f of the diffracted laser B B They are respectively

[0088] f A =f + 2Δf (12)

[0089] f B =f-2Δf (13)

[0090] Here, Δf represents the frequency shift generated for each diffraction level.

[0091] Diffracted laser A and diffracted laser B pass through the first plane mirror 5 and the second plane mirror 6, respectively, and are converted into parallel light with a distance d between their optical axes, which then illuminate the torsion test object 11.

[0092] After the diffracted laser A is reflected back by the object under test 11, the frequency of the reflected light becomes f. Ad After passing through the first planar reflector 5 and the acousto-optic modulator 4 again, the light frequency becomes f. Ad +2Δf, then passes through the λ / 2 waveplate 3, is reflected by the polarization beam splitter 2, and then combines with the reflected light of another diffracted laser B to produce beat frequency interference, which is received by the photodetector 8 and output as a photodetector beat frequency signal.

[0093] After the diffracted laser B is reflected back by the object under test 11, the frequency of the reflected light becomes f. Bd The light frequency changes to f after passing through the second plane mirror 6 and the acousto-optic modulator 4 again. Bd -2Δf, then passes through the λ / 2 waveplate 3, is reflected by the polarizing beam splitter 2, and then combines with the reflected light of another diffracted laser A to produce beat frequency interference. This interference is received by the photodetector 8, which outputs a photodetector beat frequency signal with a frequency of f. p .

[0094] The frequency of the diffracted laser A at photodetector 8 is

[0095] f Ad8 =f + 4Δf - f DA (14)

[0096] The frequency of the diffracted laser B at photodetector 8 is

[0097] f Bd8 =f - 4Δf + f DB (15)

[0098] f p =f Ad8 -f Bd8 =8Δf-f D (16)

[0099] f D =8Δf-(f Ad8 -f Bd8 )=8Δf-f p (17)

[0100] The photodetector 8 outputs an FM signal with a carrier frequency of 8Δf. After waveform acquisition by the data acquisition system 9, the FM signal is demodulated by the computer 10, and the Doppler frequency shift f is obtained according to equation (17). DThe measurement results are obtained by using equation (11) to calculate the angular velocity ω of the object under test 11, with the laser wavelength of the laser and the distance between the optical axes of the two diffracted lasers being d.

[0101] Example 2 (using ±1st order diffraction laser)

[0102] This embodiment discloses a large-diameter torsional vibration laser measurement device, including a laser 1, a polarizing beam splitter 2, a λ / 2 waveplate 3, an acousto-optic modulator 4, a first plane mirror 5, a second plane mirror 6, a sinusoidal signal source 7, a photodetector 8, a data acquisition system 9, a computer 10, and a torsional object under test 11. Figure 2 As shown.

[0103] The laser wavelength of laser 1 is selected as λ = 632.8 nm, the first-order diffraction frequency of acousto-optic modulator 4 is Δf = 20 MHz, the output frequency of sinusoidal signal source 7 is Δf = 20 MHz, and the distance between the two parallel measurement beams A and B is d = 400 mm.

[0104] This embodiment discloses a laser measurement method for large-diameter torsional vibration, which is implemented based on the aforementioned laser measurement device for large-diameter torsional vibration. The specific implementation method of this embodiment is as follows:

[0105] like Figure 2 As shown, a laser with a wavelength of λ = 632.8 nm (frequency f) is generated by laser 1, passes through polarizing beam splitter 2 and λ / 2 waveplate 3, and reaches acousto-optic modulator 4. A sinusoidal signal source 7 with a frequency Δf = 20 MHz modulates the frequency of the laser passing through acousto-optic modulator 4, generating a +1st order diffracted laser A and a -1st order diffracted laser B. The frequency f of diffracted laser A is... A The frequency f of the diffracted laser B B They are respectively

[0106] f A =f + Δf (18)

[0107] f B =f-Δf (19)

[0108] Here, Δf represents the frequency shift generated for each diffraction level.

[0109] Diffracted laser A and diffracted laser B pass through the first plane mirror 5 and the second plane mirror 6, respectively, and are converted into parallel light with a distance d between their optical axes, which then illuminate the torsion test object 11.

[0110] After the diffracted laser A is reflected back by the object under test 11, the frequency of the reflected light becomes f. Ad After passing through the first planar reflector 5 and the acousto-optic modulator 4 again, the light frequency becomes f.Ad +Δf, then passes through the λ / 2 waveplate 3, is reflected by the polarization beam splitter 2, and then combines with the reflected light of another diffracted laser B to produce beat frequency interference, which is received by the photodetector 8 and output as a photodetector beat frequency signal.

[0111] After the diffracted laser B is reflected back by the object under test 11, the frequency of the reflected light becomes f. Bd The light frequency changes to f after passing through the second plane mirror 6 and the acousto-optic modulator 4 again. Bd -Δf, then passes through the λ / 2 waveplate 3, is reflected by the polarizing beam splitter 2, and then combines with the reflected light of another diffracted laser A to produce beat frequency interference. This interference is received by the photodetector 8, which outputs a photodetector beat frequency signal with a frequency of f. p .

[0112] The frequency of the diffracted laser A at photodetector 8 is

[0113] f Ad8 =f + 2Δf - f DA (20)

[0114] The frequency of the diffracted laser B at photodetector 8 is

[0115] f Bd8 =f - 2Δf + f DB (twenty one)

[0116] f p =f Ad8 -f Bd8 =4Δf-f D (twenty two)

[0117] f D =4Δf-(f Ad8 -f Bd8 )=4Δf-f p (twenty three)

[0118] The photodetector 8 outputs an FM signal with a carrier frequency of 4Δf. After waveform acquisition by the data acquisition system 9, the FM signal is demodulated by the computer 10, and the Doppler frequency shift f is obtained according to equation (17). D The measurement results are obtained by using equation (11) to calculate the angular velocity ω of the object under test 11, with the laser wavelength of the laser and the distance between the optical axes of the two diffracted lasers being d.

[0119] Example 3 (using +2nd order and 0th order diffractive lasers)

[0120] This embodiment discloses a large-diameter torsional vibration laser measurement device, including a laser 1, a polarizing beam splitter 2, a λ / 2 waveplate 3, an acousto-optic modulator 4, a first plane mirror 5, a sinusoidal signal source 7, a photodetector 8, a data acquisition system 9, a computer 10, and a torsional test object 11. Figure 3 As shown.

[0121] The laser wavelength of laser 1 is selected as λ = 632.8 nm, the second-order diffraction frequency of acousto-optic modulator 4 is 2Δf = 40 MHz, the output frequency of sinusoidal signal source 7 is Δf = 20 MHz, and the distance between the two parallel measurement beams A and B is d = 400 mm.

[0122] This embodiment discloses a laser measurement method for large-diameter torsional vibration, which is implemented based on the aforementioned laser measurement device for large-diameter torsional vibration. The specific implementation method of this embodiment is as follows:

[0123] like Figure 3 As shown, a laser with a wavelength of λ = 632.8 nm (frequency f) is generated by laser 1, passes through polarizing beam splitter 2 and λ / 2 waveplate 3, and reaches acousto-optic modulator 4. A sinusoidal signal source 7 with a frequency Δf = 20 MHz is used to modulate the frequency of the laser passing through acousto-optic modulator 4, generating a +2nd order diffracted laser A and a 0th order diffracted laser B. The frequency f of diffracted laser A is... A The frequency f of the diffracted laser B B They are respectively

[0124] f A =f + 2Δf (24)

[0125] f B =f (25)

[0126] Here, Δf represents the frequency shift generated for each diffraction level.

[0127] The diffracted laser A passes through the first plane mirror 5 and is transformed into parallel light parallel to the diffracted laser B with a distance d between the optical axes of the two beams, which then illuminates the torsion test object 11.

[0128] After the diffracted laser A is reflected back by the object under test 11, the frequency of the reflected light becomes f. Ad After passing through the first planar reflector 5 and the acousto-optic modulator 4 again, the light frequency becomes f. Ad +2Δf, then passes through the λ / 2 waveplate 3, is reflected by the polarization beam splitter 2, and then combines with the reflected light of another diffracted laser B to produce beat frequency interference, which is received by the photodetector 8 and output as a photodetector beat frequency signal.

[0129] After the diffracted laser B is reflected back by the object under test 11, the frequency of the reflected light becomes f. BdAfter passing through the acousto-optic modulator 4 again, the optical frequency remains f. Bd Then, passing through the λ / 2 waveplate 3, it is reflected by the polarizing beam splitter 2 and combined with the reflected light from another diffracted laser A to produce beat frequency interference. This interference is received by the photodetector 8, which outputs a photodetector beat frequency signal with a frequency of f. p .

[0130] The frequency of the diffracted laser A at photodetector 8 is

[0131] f Ad8 =f + 4Δf - f DA (26)

[0132] The frequency of the diffracted laser B at photodetector 8 is

[0133] f Bd8 =f+f DB (27)

[0134] f p =f Ad8 -f Bd8 =4Δf-f D (28)

[0135] f D =4Δf-(f Ad8 -f Bd8 )=4Δf-f p (29)

[0136] The photodetector 8 outputs an FM signal with a carrier frequency of 4Δf. After waveform acquisition by the data acquisition system 9, the FM signal is demodulated by the computer 10, and the Doppler frequency shift f is obtained according to equation (29). D The measurement results are obtained by using equation (11) to calculate the angular velocity ω of the object under test 11, with the laser wavelength of the laser and the distance between the optical axes of the two diffracted lasers being d.

[0137] The above detailed description further illustrates the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A laser measuring device for large-diameter torsional vibration, characterized in that: The system includes a laser, a polarizing beam splitter, a λ / 2 waveplate, an acousto-optic modulator, a plane mirror, a sinusoidal signal source, a photodetector, a data acquisition system, a computer, and a torsional test object. The laser generates a laser beam with wavelength λ and frequency f, which passes through the polarizing beam splitter and the λ / 2 waveplate before reaching the acousto-optic modulator. A sinusoidal signal source modulates and splits the laser frequency after passing through the acousto-optic modulator, generating diffracted laser A and diffracted laser B. Diffracted laser A and diffracted laser B are converted into parallel beams with an optical axis distance d by the plane mirror and illuminate the torsional test object. Utilizing the characteristic that the torsional body produces two parallel diffracted laser beams with opposite signs of Doppler frequency shifts, the two laser beams reflected from the torsional test object, containing the Doppler frequency shifts generated by the torsion, are again subjected to frequency shifting, beam combining, and beat frequency interference by the acousto-optic modulator. The Doppler frequency shifts are extracted, and the angular velocity of the torsional test object is finally calculated, realizing large-diameter torsional vibration laser measurement.

2. The large-diameter torsional vibration laser measuring device as described in claim 1, characterized in that: Diffracted laser A and diffracted laser B are transformed into parallel beams with an axial distance of d after passing through the first and second plane mirrors, respectively, and then illuminate the torsion test object. After being reflected back from the test object, the frequency of the reflected light becomes f. Ad After passing through the first planar mirror and the acousto-optic modulator again, the light frequency becomes f. Ad +2Δf, then passes through the λ / 2 waveplate, is reflected by the polarizing beam splitter, and then combines with the reflected light of another diffracted laser B to produce beat frequency interference. This interference is received by the photodetector, which outputs a photodetector beat frequency signal. After the diffracted laser B is reflected back from the object under test, the frequency of the reflected light becomes f. Bd After passing through the second plane mirror and the acousto-optic modulator again, the light frequency becomes f. Bd -2Δf, then passes through the λ / 2 waveplate, is reflected by the polarizing beam splitter, and then combines with the reflected light of another diffracted laser A to produce beat frequency interference. This interference is received by the photodetector, outputting a photodetector beat frequency signal with a frequency of f. p .

3. The large-diameter torsional vibration laser measuring device as described in claim 1, characterized in that: The diffracted laser A passes through the first plane mirror and is transformed into parallel light parallel to the diffracted laser B, with a distance d between the optical axes of the two beams. This parallel light then illuminates the torsion test object. After being reflected back from the test object, the frequency of the reflected light changes to f. Ad Through the first plane mirror and the acousto-optic modulator, the light frequency becomes f. Ad +2Δf, then passes through the λ / 2 waveplate, is reflected by the polarizing beam splitter, and then combines with the reflected light of another 0th-order diffracted laser B to produce beat frequency interference. This interference is received by the photodetector, which outputs a photodetector beat frequency signal. After the 0th-order diffracted laser B is reflected back from the object under test, the frequency of the reflected light becomes f. Bd Through the acousto-optic modulator, the optical frequency remains f. Bd Then, passing through the λ / 2 waveplate, it is reflected by the polarizing beam splitter and combines with the reflected light of another diffracted laser A, producing beat frequency interference. This interference is received by the photodetector, outputting a photodetector beat frequency signal with a frequency of f. p .

4. A laser measurement method for large-diameter torsional vibration, implemented based on the laser measurement device for large-diameter torsional vibration as described in claim 2, characterized in that: Includes the following steps, Step 1: The frequencies are f A f B Two measuring laser beams, measuring beam A and measuring beam B, are parallel to each other, with a distance d between their optical axes. They are incident on opposite sides of the rotor shaft, where the rotor's angular velocity is ω and the axis of rotation is O. The wavelength of measuring beam A is λ. A The wavelength of light B is measured to be λ. B ; The torsional linear velocity at point a of beam A is v ta The radius of torsion Oa is R a The linear velocity component in the direction of beam A is v a Linear velocity v ta The angle between the beam and the optical axis A is α; the linear velocity v ta The direction is perpendicular to Oa; The torsional linear velocity at point b where beam B illuminates is v tb The radius of torsion Ob is R b The linear velocity component in the direction of beam B is v b Linear velocity v tb The angle β between the beam and the optical axis B; the linear velocity v tb The direction is perpendicular to Ob; Then, measuring light A and measuring light B satisfy the relationships described in equations (1) and (2): v a =v ta cosα=ωR a cosα (1) v b =v tb cosβ=ωR b cosβ (2) Measuring the wavelength λ of light A A Measuring the wavelength λ of light B B The wavelength λ produced by the laser is approximately equal to that of the laser: l A ≈λ B ≈λ(3) Define the linear velocities obtained by measuring two laser beams A and B as v, respectively. a and v b The corresponding Doppler frequency shifts are f DA and f DB According to the Doppler principle, f DA =2v a / l A =2(ωR a cosα) / l A ≈2v a / λ=2(ωR a co sα) / λ (4) f DB =2v b / l B =2(ωR b cosβ) / λ B ≈2v b / λ=2(ωR b cosβ) / λ (5) According to geometric relations, we get d=R a cosα+R b cosβ (6) Laser A contains the reflected light frequency f with a Doppler shift. Ad for f Ad =f A -f DA (7) Laser B contains the reflected light frequency f of the Doppler shift Bd for f Bd =f B +f DB (8) The reflected light frequency f of laser A Ad The reflected light frequency f of laser B Ad The beat frequency f is obtained by combining the beat frequencies. p f p =f Ad -f Bd =(f A -f B )-(f DA +f DB )=(f A -f B )-f D (9) Among them, f A -f B Given the known frequency difference between incident laser A and incident laser B, f D The value is the Doppler frequency shift measurement caused by torsion. A negative value indicates clockwise torsion, and a positive value indicates counterclockwise torsion. Based on equations (1) to (9), we can obtain... f D =(f A -f B )-f p =-(f DA +f DB )=-2dω / λ (10) Right now Step 2: A laser with wavelength λ and frequency f is generated by a laser source. The laser passes through a polarizing beam splitter and a λ / 2 waveplate, reaching an acousto-optic modulator. The frequency Δf of a sinusoidal signal source is used to modulate the laser frequency after passing through the acousto-optic modulator, generating a +2nd order diffracted laser A and a -2nd order diffracted laser B. The frequency f of diffracted laser A is... A The frequency f of the diffracted laser B B They are respectively f A =f+2Δf (12) f B =f-2Δf (13) Where Δf is the frequency shift generated for each diffraction order; Diffracted laser A and diffracted laser B are converted into parallel beams with an optical axis distance of d after passing through the first and second plane mirrors, respectively, and then irradiate the torsion test object. After the diffracted laser A is reflected back from the object being measured, the frequency of the reflected light becomes f. Ad After passing through the first planar mirror and the acousto-optic modulator again, the light frequency becomes f. Ad +2Δf, then passes through the λ / 2 waveplate, is reflected by the polarization beam splitter, and then combines with the reflected light of another diffracted laser B to produce beat frequency interference, which is received by the photodetector and outputs the photodetector beat frequency signal; After the diffracted laser B is reflected back from the object being measured, the frequency of the reflected light becomes f. Bd After passing through the second plane mirror and the acousto-optic modulator again, the light frequency becomes f. Bd -2Δf, then passes through the λ / 2 waveplate, is reflected by the polarizing beam splitter, and then combines with the reflected light of another diffracted laser A to produce beat frequency interference. This interference is received by the photodetector, outputting a photodetector beat frequency signal with a frequency of f. p ; The frequency of the diffracted laser A at the photodetector is f Ad8 =f+4Δf-f DA (14) The frequency of the diffracted laser B at the photodetector is f Bd8 =f-4Δf+f DB (15) f p =f Ad8 -f Bd8 =8Δf-f D (16) f D =8Δf-(f Ad8 -f Bd8 )=8Δf-f p (17) The photodetector outputs an FM signal with a carrier frequency of 8Δf. After waveform acquisition by the data acquisition system, the FM signal is demodulated by a computer, and the Doppler frequency shift f is obtained according to equation (17). D The measurement results are obtained by using the laser wavelength of the laser and the distance between the optical axes of the two diffracted lasers as d, and the angular velocity ω of the torsional test object is calculated using Equation (11), thus realizing large-diameter torsional vibration laser measurement.

5. A laser measurement method for large-diameter torsional vibration, implemented based on the laser measurement device for large-diameter torsional vibration as described in claim 3, characterized in that: Includes the following steps, Step 1: The frequencies are f A f B Two measuring laser beams, measuring beam A and measuring beam B, are parallel to each other, with a distance d between their optical axes. They are incident on opposite sides of the rotor shaft, where the rotor's angular velocity is ω and the axis of rotation is O. The wavelength of measuring beam A is λ. A The wavelength of light B is measured to be λ. B ; The torsional linear velocity at point a of beam A is v ta The radius of torsion Oa is R a The linear velocity component in the direction of beam A is v a Linear velocity v ta The angle between the beam and the optical axis A is α; the linear velocity v ta The direction is perpendicular to Oa; The torsional linear velocity at point b where beam B illuminates is v tb The radius of torsion Ob is R b The linear velocity component in the direction of beam B is v b Linear velocity v tb The angle β between the beam and the optical axis B; the linear velocity v tb The direction is perpendicular to Ob; Then, measuring light A and measuring light B satisfy the relationships described in equations (1) and (2): v a =v ta cosα=ωR a cosα (1) v b =v tb cosβ=ωR b cosβ (2) Measuring the wavelength λ of light A A Measuring the wavelength λ of light B B The wavelength λ produced by the laser is approximately equal to that of the laser: l A ≈λ B ≈λ(3) Define the linear velocities obtained by measuring two laser beams A and B as v, respectively. a and v b The corresponding Doppler frequency shifts are f DA and f DB According to the Doppler principle, f DA =2v a / l A =2(ωR a cosα) / l A ≈2v a / λ=2(ωR a co sα) / λ (4) f DB =2v b / l B =2(ωR b cosβ) / λ B ≈2v b / λ=2(ωR b cosβ) / λ (5) According to geometric relations, we get d=R a cosα+R b cosβ (6) Laser A contains the reflected light frequency f with a Doppler shift. Ad for f Ad =f A -f DA (7) Laser B contains the reflected light frequency f of the Doppler shift Bd for f Bd =f B +f DB (8) The reflected light frequency f of laser A Ad The reflected light frequency f of laser B Ad The beat frequency f is obtained by combining the beat frequencies. p f p =f Ad -f Bd =(f A -f B )-(f DA +f DB )=(f A -f B )-f D (9) Among them, f A -f B Given the known frequency difference between incident laser A and incident laser B, f D The value is the Doppler frequency shift measurement caused by torsion. A negative value indicates clockwise torsion, and a positive value indicates counterclockwise torsion. Based on equations (1) to (9), we can obtain... f D =(f A -f B )-f p =-(f DA +f DB )=-2dω / λ (10) Right now Step 2: A laser with wavelength λ and frequency f is generated by the laser source. This laser passes through polarizing beam splitter 2 and a λ / 2 waveplate, reaching the acousto-optic modulator. The frequency Δf of the sinusoidal signal source 7 is used to modulate the laser frequency passing through the acousto-optic modulator 4, generating a +2nd order diffracted laser A and a 0th order diffracted laser B. The frequency f of diffracted laser A is... A The frequency f of the diffracted laser B B They are respectively f A =f+2Δf (12) f B =f (13) Where Δf is the frequency shift generated for each diffraction order; The diffracted laser A passes through the first plane mirror and is transformed into parallel light parallel to the diffracted laser B with a distance d between the optical axes of the two beams, which then illuminates the torsion test object. After the diffracted laser A is reflected back from the object being measured, the frequency of the reflected light becomes f. Ad After passing through the first planar mirror and the acousto-optic modulator again, the light frequency becomes f. Ad +2Δf, then passes through the λ / 2 waveplate, is reflected by the polarization beam splitter, and then combines with the reflected light of another diffracted laser B to produce beat frequency interference, which is received by the photodetector and outputs the photodetector beat frequency signal; After the diffracted laser B is reflected back from the object being measured, the frequency of the reflected light becomes f. Bd Through the acousto-optic modulator, the optical frequency remains f. Bd Then, passing through the λ / 2 waveplate, it is reflected by the polarizing beam splitter and combines with the reflected light of another diffracted laser A, producing beat frequency interference. This interference is received by the photodetector, outputting a photodetector beat frequency signal with a frequency of f. p ; The frequency of the diffracted laser A at the photodetector is f Ad8 =f+4Δf-f DA (14) The frequency of the diffracted laser B at the photodetector is f Bd8 =f +f DB (15) f p =f Ad8 -f Bd8 =4Δf-f D (16) f D =4Δf-(f Ad8 -f Bd8 )=4Δf-f p (17) The photodetector outputs an FM signal with a carrier frequency of 4Δf. After waveform acquisition by the data acquisition system, the FM signal is demodulated by a computer, and the Doppler frequency shift f is obtained according to equation (17). D The measurement results are obtained by using the laser wavelength of the laser and the distance between the optical axes of the two diffracted lasers as d, and the angular velocity ω of the torsional test object is calculated using Equation (11), thus realizing large-diameter torsional vibration laser measurement.

6. A laser measurement method for large-diameter torsional vibration as described in claim 4 or 5, characterized in that: Using an acousto-optic modulator, the three core functions of frequency shifting, beam splitting, and beam combining interference are simultaneously achieved by utilizing the principle of optical path reversibility. The acousto-optic modulator converts a single-wavelength laser into two coherent measurement lasers of different frequencies, and then uses the acousto-optic modulator to form a beam combining differential beat frequency in the original path return manner. Finally, the laser Doppler frequency containing rotational angular velocity information is extracted, and the instantaneous value of angular velocity is obtained by calculation.

7. A laser measurement method for large-diameter torsional vibration as described in claim 4 or 5, characterized in that: The direction of torsion is determined by the sign of the obtained angular velocity value. When the angular velocity ω is negative, it indicates clockwise torsion, and when the angular velocity ω is positive, it indicates counterclockwise torsion.

8. A laser measurement method for large-diameter torsional vibration as described in claim 4 or 5, characterized in that: The adjustable-spacing dual-beam measurement method meets the measurement needs of large-diameter torsional objects and can be adapted to the accurate measurement of the angular velocity of any large-diameter torsional object.

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