Large-aperture laser rotating speed measuring method and device

Abstract

The invention discloses a large-aperture laser rotating speed measuring method and device, and belongs to the technical field of photoelectric measurement. The device comprises a laser, a polarizing beam splitter, a lambda / 2 wave plate, an acoustic optical modulator, a first lens, a second lens, a sinusoidal signal source, a photoelectric detector, a data acquisition system, an electronic computer and a rotary measured object. According to the invention, two beams of diffracted laser with frequency difference output by monochromatic laser with the same wavelength passing through an acoustic optical modulator are used for irradiating and rotating a measured object in parallel, and the characteristic that Doppler frequency shift symbols generated by parallel irradiation of the two beams of diffracted laser by a rotating body are opposite is utilized; and extracting Doppler frequency shift from the beat frequency of the two reflected laser beams containing Doppler frequency shift generated by rotation, and finally calculating to obtain the angular velocity value of the rotating measured object. Aiming at the difficulty in rotating speed measurement of a large-aperture measurement object, a double-lens measurement method with an adjustable optical axis distance is used, and the method can be suitable for angular speed measurement of rotating objects with any aperture.

Description

Technical Field

[0001] The invention relates to a large-caliber laser rotation speed measurement method and device, belonging to the technical field of photoelectric measurement. Background Art

[0002] Matter is in perpetual motion, so the measurement of motion parameters is one of the basic needs of human social production and practice activities. Usually, it involves the measurement of three motion parameters: velocity, displacement, and acceleration. All three belong to the representation of motion parameters. There are both differences and connections between them. The displacement is the integral of the velocity, and the acceleration is the differential of the velocity. With one of them, the other two can be obtained through calculation and initial condition limitation.

[0003] The same situation also exists in angular motion, including various forms of motion such as rotation, swing, twisting, precession, angular vibration, etc., and the angular velocity (rotation speed), angular displacement, angular acceleration and other numerical parameters 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 motors, engines and other rotating machinery; including the change of angular velocity and angular acceleration over time when the machinery starts and stops, and the measurement of the pulsation of the rotation when the machinery rotates steadily; (3) Other angular motion test requirements; including the real-time measurement of the angular position of various control surfaces used for aircraft attitude control during flight. Angular acceleration to simulate human motion in ejection rescue; angular acceleration and angular velocity used by robots to sense their motion conditions; astronauts' response to angular acceleration and angular velocity required for aerospace biomedical research, etc.

[0004] There are two main methods for measuring rotational speed by laser interferometry: 1) Dual vibrometer method: two laser vibrometers independently measure the vibration between different points of a rotating object using parallel beams with known distances, and convert the rotational speed of the object to be measured; 2) Grating differential laser goniometer method: a grating is engraved on the rotating object to be measured, and a dual-beam differential measurement method is used with the center of the optical axis accurately passing through the center of the rotating axis to obtain the rotational speed measurement result of the rotating object to be measured.

[0005] Among them, the dual vibrometer method is expensive and only suitable for periodic angular motion measurement, and is not applicable to single angular motion measurement. Although the grating differential laser goniometer can achieve high measurement accuracy, it still has several problems:

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

[0007] (2) Although the rotation axis radius can be accurately measured, it has always been a difficult problem to make the center of the optical axis accurately pass through the center of the rotation axis, which will inevitably lead to measurement errors. For on-site angular vibration measurement, the rotation radius is often impossible to obtain accurately;

[0008] (3) It is necessary to install a grating on the surface of the target to be measured. The grating is a precision component that is not resistant to dirt, is easily corroded, cannot be touched, has poor environmental adaptability, cannot be repaired after being damaged, 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 occasions of the laser interferometer angular motion measurement system.

[0009] In addition, the distance between the measuring lenses of most current angular motion laser measuring instruments is not very large. When measuring large-aperture angular motion, there are problems such as unchanged usage and affected accuracy.

[0010] Therefore, angular motion measurement becomes a difficult problem in motion measurement. Summary of the invention

[0011] In view of the problems existing in the measurement of angular motion speed (i.e., rotation speed, angular velocity), the purpose of the present invention is to provide a large-caliber laser rotation speed measurement method and device, using two diffracted laser beams with different frequencies output by a monochromatic laser of the same wavelength after passing through an acousto-optic modulator to irradiate the rotating measured object in parallel, and utilizing the opposite sign characteristics of the Doppler frequency shifts generated by the rotating body to the two diffracted laser beams, extract the Doppler frequency shift from the beat frequency of the two reflected laser beams containing the Doppler frequency shift generated by the rotation, and finally calculate and obtain the angular velocity value of the rotating measured object. The present invention addresses the difficulty of measuring the rotation speed of a large-caliber measurement object, uses a dual-lens measurement method with adjustable spacing, and can be applied to the angular velocity measurement of rotating objects of any caliber.

[0012] The objective of the present invention is achieved through the following technical solutions:

[0013] The invention discloses a large-aperture laser rotation speed measuring device, comprising a laser, a polarization beam splitter, a λ / 2 wave plate, an acousto-optic modulator, a first lens, a second lens, a sinusoidal signal source, a photoelectric detector, a data acquisition system, an electronic computer, and a rotating object to be measured. The diffracted light A from the acousto-optic modulator passes through the focal length of the first lens, and is converted into a parallel light parallel to the optical axis of the first lens after passing through the first lens, and the parallel light parallel to the optical axis of the first lens is parallel to the measuring light B passing through the second lens; the diffracted light B from the acousto-optic modulator passes through the focal length of the second lens, and is converted into a parallel light parallel to the optical axis of the second lens after passing through the second lens, and the parallel light parallel to the optical axis of the second lens is parallel to the measuring light A passing through the first lens; the distance between the two parallel measuring lights of the measuring light A and the measuring light B is d.

[0014] The invention discloses a large-aperture laser speed measurement method, which is implemented based on the large-aperture laser speed measurement device. The invention discloses a large-aperture laser speed measurement method, which includes the following steps:

[0015] Step 1: The frequencies are f A 、f B The two measuring laser beams A and B are parallel to each other, and the distance between the optical axes of the two beams is d. They are incident on both sides of the rotor shaft respectively. The angular velocity of the rotor is ω, and the rotation axis is O. The wavelength of the measuring light A is λ A , the wavelength of the measured light B is λ B .

[0016] The rotational linear velocity of beam A at point a is v ta , the radius of rotation Oa is R a , the linear velocity component in the direction of beam A is v a ; Linear speed v ta The angle between the beam A and the optical axis is α; the linear velocity v ta The direction is perpendicular to Oa.

[0017] The rotational linear velocity of the beam B at the irradiation point b is v tb , the radius of rotation Ob is R b , the linear velocity component in the direction of beam B is v b ; Linear speed v tb The angle β between the beam B and the optical axis; the linear velocity v tb The direction is perpendicular to Ob.

[0018] Then the measurement light A and the measurement light B satisfy the relationship described in equations (1) and (2):

[0019] v a =v ta cosα=ωR a cosα (1)

[0020] v b =v tb cosβ=ωR b cosβ (2)

[0021] Since the actual laser frequency is above several hundred terahertz, in contrast, the frequency difference f between the two cognate laser beams A and B is A -f B Below a few hundred megahertz, the frequency difference f between two co-source laser beams A and B is A -f B The actual laser frequency is simplified to a negligible small amount, and the wavelength λ of the measured light A is A , measure the wavelength λ of light B B is approximately equal to the wavelength λ generated by the laser:

[0022] λ A ≈λ B≈λ(3)

[0023] Define the linear velocities obtained by measuring two laser beams A and B as v a and v b , and their corresponding Doppler frequency shifts are f DA and f DB According to the Doppler principle,

[0024] f DA =2v a / λ A =2(ωR a cosα) / λ A

[0025] ≈2v a / λ=2(ωR a co sα) / λ (4)

[0026] f DB =2v b / λ B =2(ωR b cosβ) / λ B

[0027] ≈2v b / λ=2(ωR b cosβ) / λ (5) According to the geometric relationship, we can get

[0028] d=R a cosα+R b cosβ (6)

[0029] Laser A contains Doppler-shifted reflected light with frequency f Ad for

[0030] f Ad =f A -f DA (7)

[0031] Laser B contains Doppler-shifted reflected light with frequency f Bd for

[0032] f Bd =f B +f DB (8)

[0033] The reflected light frequency f of laser A Ad and the reflected light frequency f of laser B Ad The beat frequency f is obtained by combining the beam beat frequency p

[0034] f p =f Ad -fBd =(f A -f B )-(f DA +f DB )=(f A -f B )-f D (9)

[0035] Among them, f A -f B is the known frequency difference between incident laser A and incident laser B, f D The Doppler shift measurement resulting from rotation. A negative value indicates clockwise rotation, and a positive value indicates counterclockwise rotation.

[0036] According to formulas (1) to (9), we can get

[0037] f D =(f A -f B )-f p =-(f DA +f DB )=-2dω / λ (10)

[0038] Right now

[0039]

[0040] Step 2: The laser generates a laser with a wavelength of λ and a frequency of f, which passes through a polarization beam splitter and a λ / 2 wave plate and reaches the AOM. The frequency of the laser passing through the AOM is modulated using the frequency Δf of the sinusoidal signal source to generate +2nd order diffraction laser A and -2nd order diffraction laser B. The frequency of the diffraction laser A is f A , the frequency f of the diffracted laser B B They are

[0041] f A =f+2Δf (12)

[0042] f B =f-2Δf (13)

[0043] Here, Δf is the frequency shift produced by each diffraction order.

[0044] The diffracted laser A and the diffracted laser B are respectively transformed into parallel light with an optical axis distance d between the two beams through the first lens and the second lens, and irradiate the rotating object to be measured.

[0045] After the diffracted laser A is reflected by the object being measured, the frequency of the reflected light changes to f Ad , passing through the first lens and the acousto-optic modulator, the light frequency becomes f Ad+2Δf, then passes through the λ / 2 wave plate, is reflected by the polarization beam splitter, and combines with the reflected light of another diffracted laser B to produce beat frequency interference, which is received by the photodetector 8 to output a photoelectric detection beat frequency signal.

[0046] After the diffracted laser B is reflected by the object being measured, the frequency of the reflected light becomes f Bd , through the second lens and the acousto-optic modulator, the light frequency becomes f Bd -2Δf, then passes through the λ / 2 wave plate, is reflected by the polarization beam splitter, and combines with the reflected light of another diffracted laser A to produce beat frequency interference, which is received by the photodetector and outputs the photodetection beat frequency signal with a frequency of f p .

[0047] The frequency of the diffracted laser A at the photodetector is

[0048] f Ad8 =f+4Δf-f DA (14)

[0049] The frequency of the diffracted laser B at the photodetector is

[0050] f Bd8 =f-4Δf+f DB (15)

[0051] f p =f Ad8 -f Bd8 =8Δf-f D (16)

[0052] f D =8Δf-(f Ad8 -f Bd8 )=8Δf-f p (17)

[0053] The photodetector outputs an FM signal with a carrier frequency of 8Δf. After the data acquisition system performs waveform acquisition, an electronic computer is used to perform FM signal demodulation calculations, and the Doppler frequency shift f is obtained according to formula (17). D The measurement result is obtained by assuming that the laser wavelength and the distance between the two diffracted laser optical axes are d, and using formula (11) to calculate the angular velocity ω of the rotating object to be measured, that is, to achieve large-aperture laser rotation speed measurement.

[0054] Preferably, 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 beam differential beat frequency in a return path manner, and finally the laser Doppler frequency containing the rotational angular velocity information is extracted, and the instantaneous value of the angular velocity is obtained by calculation.

[0055] Preferably, the rotation direction is determined by the sign of the obtained angular velocity value. When the angular velocity ω value is negative, it indicates clockwise rotation, and when the angular velocity ω value is positive, it indicates counterclockwise rotation.

[0056] Preferably, a dual-lens measurement method with adjustable spacing is used to meet the measurement requirements of large-diameter rotating objects.

[0057] Beneficial effects:

[0058] 1. The present invention discloses a large-aperture laser rotation speed measurement method and device, which uses a wavelength laser to pass through an acousto-optic modulator to generate two coherent lasers of different frequencies, and obtains the angular velocity measurement result of the rotating body through the frequency difference caused by the laser Doppler effect generated by the irradiation of the two sides of the rotating shaft of the rotating body. Compared with other measurement schemes, the present invention only uses one acousto-optic modulation device and utilizes the principle of optical path reversibility to simultaneously complete the three core functions of frequency shifting, light splitting, and beam combining interference, so that the present invention has the advantages of extremely simple, stable, and reliable optical path, few optical components, low cost, and easy implementation.

[0059] 2. The present invention discloses a large-aperture laser rotation speed measurement method and device, which utilizes the opposite sign characteristics of the Doppler frequency shifts generated by the rotating body to the two diffracted laser beams, and constructs a series of relationship groups for obtaining the angular velocity value of the rotating object to be measured from the beat frequency of the two reflected laser beams containing the Doppler frequency shift generated by the rotation according to the optical path geometry, Doppler frequency shift, etc., which can extract the Doppler frequency shift in real time and finally calculate the angular velocity value of the rotating object to be measured, thereby realizing high-precision measurement of large-aperture laser rotation speed. Compared with other measurement methods, the present invention only requires that the axis of the rotating body to be measured is between the two parallel measurement light beams, and there are no restrictions on whether its position is in the middle of the measurement optical axis, whether the shape of the rotating body is regular, whether the rotation speed is uniform, etc. It is easy and reliable to use, has excellent adaptability, and is easy to promote and apply.

[0060] 3. The present invention discloses a large-aperture laser rotation speed measurement method and device, which use a dual-lens measurement method with adjustable spacing to achieve angular velocity measurement of a rotating object. In principle, it can be adapted to the precise measurement of the angular velocity of any large-aperture rotating object, and is an excellent solution for the rotation speed measurement of large-aperture rotating bodies. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 A schematic diagram of the principle of a large-aperture laser rotation speed measurement method of the present invention;

[0062] Figure 2 A schematic diagram of a large-aperture laser rotation speed measurement device of the present invention;

[0063] Among them: 1—laser, 2—polarization beam splitter, 3—λ / 2 wave plate, 4—acousto-optic modulator, 5—first lens, 6—second lens, 7—sine signal source, 8—photoelectric detector, 9—data acquisition system, 10—electronic computer, 11—rotating object to be measured. DETAILED DESCRIPTION

[0064] In order to better illustrate the purpose and advantages of the present invention, the invention is further described below with reference to the accompanying drawings and examples.

[0065] Example 1 (Using ±2nd order diffraction laser)

[0066] This example discloses a large-aperture laser rotation speed measuring device, including a laser 1, a polarization beam splitter 2, a λ / 2 wave plate 3, an acousto-optic modulator 4, a first lens 5, a second lens 6, a sinusoidal signal source 7, a photodetector 8, a data acquisition system 9, an electronic computer 10, and a rotating object to be measured 11. Among them, the diffracted light A from the acousto-optic modulator 4 passes through the focal length of the first lens 5, and after passing through the first lens 5, it is converted into a parallel light ray parallel to the optical axis of the first lens 5 and is parallel to the measuring light B passing through the second lens 6; the diffracted light B from the acousto-optic modulator 4 passes through the focal length of the second lens 6, and after passing through the second lens 6, it is converted into a parallel light ray parallel to the optical axis of the second lens 6 and is parallel to the measuring light A passing through the first lens 5; the distance between the two parallel measuring light beams A and B is d. Figure 2 shown.

[0067] The laser wavelength λ of the laser 1 is selected to be 632.8 nm, and the second diffraction order frequency 2Δf of the acousto-optic modulator 4 is selected to be 40 MHz; the first lens 5 and the second lens 6 are both selected to be convex lenses of the same specification with a diameter of Φ=20 mm and a focal length of 10 mm; the output frequency Δf of the sinusoidal signal source 7 is selected to be 20 MHz; the distance between the two parallel measurement light beams A and B is d=400 mm.

[0068] The large-aperture laser speed measurement method disclosed in this embodiment is implemented based on the large-aperture laser speed measurement device. The specific implementation steps of the large-aperture laser speed measurement method disclosed in this embodiment are as follows:

[0069] like Figure 2 As shown, the laser 1 generates a laser with a wavelength of λ=632.8nm (frequency f), which passes through a polarization beam splitter 2 and a λ / 2 wave plate 3 and reaches an acousto-optic modulator 4. The frequency of the laser passing through the acousto-optic modulator 4 is modulated by using a sinusoidal signal source 7 with a frequency of Δf=20MHz to generate a +2nd order diffracted laser A and a -2nd order diffracted laser B. The frequency f of the diffracted laser A is A , the frequency f of the diffracted laser B B They are

[0070] f A=f+2Δf (12)

[0071] f B =f-2Δf (13)

[0072] Wherein, Δf=20 MHz is the frequency deviation generated by each diffraction order.

[0073] The diffracted laser A and the diffracted laser B are respectively transformed into parallel light with an optical axis distance of d=400 mm through the first lens 5 and the second lens 6, and irradiate the rotating measured object 11.

[0074] After the diffracted laser A is reflected by the measured object 11, the frequency of the reflected light becomes f Ad , through the first lens 5 and the acousto-optic modulator 4, the light frequency becomes f Ad +2Δf, then passes through the λ / 2 wave plate 3, is reflected by the polarization beam splitter 2, and combines with the reflected light of another diffracted laser B to produce beat frequency interference, and is received by the photodetector 8 to output a photoelectric detection beat frequency signal.

[0075] After the diffracted laser B is reflected by the measured object 11, the frequency of the reflected light becomes f Bd , through the second lens 6 and the acousto-optic modulator 4, the optical frequency becomes f Bd -2Δf, then passes through the λ / 2 wave plate 3, is reflected by the polarization beam splitter 2, and then combines with the reflected light of the other diffracted laser A to produce beat frequency interference, which is received by the photodetector 8 and outputs a photodetection beat frequency signal with a frequency of f p .

[0076] The frequency of the diffracted laser A at the photodetector 8 is

[0077] f Ad8 =f+4Δf-f DA (14)

[0078] The frequency of the diffracted laser B at the photodetector 8 is

[0079] f Bd8 =f-4Δf+f DB (15)

[0080] f p =f Ad8 -f Bd8 =8Δf-f D (16)

[0081] f D =8Δf-(f Ad8 -f Bd8 )=8Δf-f p (17)

[0082] The photodetector 8 outputs an FM signal with a carrier frequency of 8Δf=160MHz. The waveform is collected by the data acquisition system 9, and the FM signal is demodulated by the electronic computer 10. The Doppler frequency shift f is obtained according to formula (17). D The measurement results are obtained by assuming that the laser wavelength of the laser and the distance between the optical axes of the two diffracted laser beams is d, and the angular velocity ω of the rotating object 11 is calculated using formula (11).

[0083] Example 2 (Using ±1st order diffraction laser)

[0084] This example discloses a large-aperture laser rotation speed measuring device, including a laser 1, a polarization beam splitter 2, a λ / 2 wave plate 3, an acousto-optic modulator 4, a first lens 5, a second lens 6, a sinusoidal signal source 7, a photodetector 8, a data acquisition system 9, an electronic computer 10, and a rotating object to be measured 11. Among them, the diffracted light A from the acousto-optic modulator 4 passes through the focal length of the first lens 5, and after passing through the first lens 5, it is converted into a parallel light ray parallel to the optical axis of the first lens 5 and is parallel to the measuring light B passing through the second lens 6; the diffracted light B from the acousto-optic modulator 4 passes through the focal length of the second lens 6, and after passing through the second lens 6, it is converted into a parallel light ray parallel to the optical axis of the second lens 6 and is parallel to the measuring light A passing through the first lens 5; the distance between the two parallel measuring light beams A and B is d. Figure 2 shown.

[0085] The laser wavelength λ of the laser 1 is selected to be 632.8 nm, and the first diffraction order frequency Δf of the acousto-optic modulator 4 is selected to be 20 MHz; the first lens 5 and the second lens 6 are both selected to be convex lenses of the same specification with a diameter of Φ=20 mm and a focal length of 10 mm; the output frequency Δf of the sinusoidal signal source 7 is selected to be 20 MHz; the spacing between the two parallel measuring light beams A and B is d=400 mm.

[0086] like Figure 2 As shown, the laser 1 generates a laser with a wavelength of λ=632.8nm (frequency f), which passes through a polarization beam splitter 2 and a λ / 2 wave plate 3 and reaches an acousto-optic modulator 4. The frequency of the laser passing through the acousto-optic modulator 4 is modulated by using a sinusoidal signal source 7 with a frequency of Δf=20MHz to generate a +1-order diffracted laser A and a -1-order diffracted laser B. The frequency f of the diffracted laser A is A , the frequency f of the diffracted laser B B They are

[0087] f A =f+Δf (18)

[0088] f B =f-Δf (19)

[0089] Wherein, Δf=20 MHz is the frequency deviation generated by each diffraction order.

[0090] The diffracted laser light A and the diffracted laser light B are respectively transformed into parallel light with an optical axis distance of d=400 mm after passing through the first lens 5 and the second lens 6 , and irradiate the rotating measured object 11 .

[0091] After the diffracted laser A is reflected by the measured object 11, the frequency of the reflected light becomes f Ad , through the first lens 5 and the acousto-optic modulator 4, the light frequency becomes f Ad +Δf, then passes through the λ / 2 wave plate 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 to output a photoelectric detection beat frequency signal.

[0092] After the diffracted laser B is reflected by the measured object 11, the frequency of the reflected light becomes f Bd , through the second lens 6 and the acousto-optic modulator 4, the optical frequency becomes f Bd -Δf, then passes through the λ / 2 wave plate 3, is reflected by the polarization beam splitter 2, and then combines with the reflected light of the other diffracted laser A to produce beat frequency interference, which is received by the photodetector 8 and outputs a photodetection beat frequency signal with a frequency of f p .

[0093] The frequency of the diffracted laser A at the photodetector 8 is

[0094] f Ad8 =f+2Δf-f DA (20)

[0095] The frequency of the diffracted laser B at the photodetector 8 is

[0096] f Bd8 =f-2Δf+f DB (twenty one)

[0097] f p =f Ad8 -f Bd8 =4Δf-f D (twenty two)

[0098] f D =4Δf-(f Ad8 -f Bd8 )=4Δf-f p (twenty three)

[0099] The photodetector 8 outputs an FM signal with a carrier frequency of 4Δf=80MHz. The waveform is collected by the data acquisition system 9, and the FM signal is demodulated by the electronic computer 10. The Doppler frequency shift f is obtained according to formula (17). DThe measurement results are as follows: the laser wavelength of the laser and the distance between the optical axes of the two diffracted laser beams is d = 400 mm, and the angular velocity ω of the rotating object 11 is calculated using formula (11).

[0100] The specific description above further illustrates the purpose, technical solutions and beneficial effects of the invention in detail. It should be understood that the above 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 in the scope of protection of the present invention.

Claims

1. A large-aperture laser speed measuring device, characterized in that: The invention comprises a laser, a polarization beam splitter, a λ / 2 wave plate, an acousto-optic modulator, a first lens, a second lens, a sinusoidal signal source, a photoelectric detector, a data acquisition system, an electronic computer, and a rotating object to be measured; the diffracted light A from the acousto-optic modulator passes through the focal length of the first lens, and is converted into parallel light parallel to the optical axis of the first lens after passing through the first lens, and the parallel light parallel to the optical axis of the first lens is parallel to the measuring light B passing through the second lens; the diffracted light B from the acousto-optic modulator passes through the focal length of the second lens, and is converted into parallel light parallel to the optical axis of the second lens after passing through the second lens, and the parallel light parallel to the optical axis of the second lens is parallel to the measuring light A passing through the first lens; the distance between the two parallel measuring light beams of the measuring light A and the measuring light B is d.

2. A large-aperture laser rotation speed measurement method, implemented based on a large-aperture laser rotation speed measurement device as claimed in claim 1, characterized in that: The following steps are included: Step 1: The frequencies are f A 、f B The two measuring laser beams A and B are parallel to each other. The distance between the optical axes of the two beams is d. They are incident on both sides of the rotor shaft respectively. The angular velocity of the rotor is ω, and the rotation axis is O. The wavelength of the measuring light A is λ A , the wavelength of the measuring light B is λ B ; The rotational linear velocity of beam A at point a is v ta , the radius of rotation Oa is R a , the linear velocity component in the direction of beam A is v a ; Linear speed v ta The angle between the beam A and the optical axis is α; the linear velocity v ta The direction is perpendicular to Oa; The rotational linear velocity of the beam B at the irradiation point b is v tb , the radius of rotation Ob is R b , the linear velocity component in the direction of beam B is v b ; Linear speed v tb The angle β between the beam B and the optical axis; the linear velocity v tb The direction is perpendicular to Ob; Then the measurement light A and the measurement light B satisfy the relationship described in equations (1) and (2): v a =v ta cosα=ωR a cosα (1) v b =v tb cosβ=ωR b cosβ (2) Measure the wavelength λ of light A A , measure the wavelength λ of light B B is approximately equal to the wavelength λ generated by the laser: l A ≈λ B ≈λ(3) Define the linear velocities obtained by measuring two laser beams A and B as v a and v b , and their corresponding Doppler 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 the geometric relationship d=R a cosα+R b cosβ (6) Laser A contains Doppler-shifted reflected light with frequency f Ad for f Ad =f A -f DA (7) Laser B contains Doppler-shifted reflected light with frequency f Bd for f Bd =f B +f DB (8) The reflected light frequency f of laser A Ad and the reflected light frequency f of laser B Ad The beat frequency f is obtained by combining the beam beat frequency 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 is the known frequency difference between incident laser A and incident laser B, f D It is the Doppler frequency shift measurement value produced by rotation. When its value is negative, it means clockwise rotation, and when its value is positive, it means counterclockwise rotation. According to formulas (1) to (9), we can get f D =(f A -f B )-f p =-(f DA +f DB )=-2dω / λ (10) Right now Step 2: The laser generates a laser with a wavelength of λ and a frequency of f, which passes through a polarization beam splitter and a λ / 2 wave plate and reaches an acousto-optic modulator. The frequency of the laser passing through the acousto-optic modulator is modulated using a sinusoidal signal source with a frequency of Δf to generate +2nd order diffraction laser A and -2nd order diffraction laser B. The frequency of the diffraction laser A is f. A , the frequency f of the diffracted laser B B They are f A =f+2Δf (12) f B =f-2Δf (13) Where Δf is the frequency shift produced by each diffraction order; The diffracted laser A and the diffracted laser B are respectively transformed into parallel light with an optical axis distance d between the two beams through the first lens and the second lens, and irradiate the rotating object to be measured; After the diffracted laser A is reflected by the object being measured, the frequency of the reflected light changes to f Ad , passing through the first lens and the acousto-optic modulator, the light frequency becomes f Ad +2Δf, then passes through the λ / 2 wave plate, 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 8 and outputs a photoelectric detection beat frequency signal; After the diffracted laser B is reflected by the object being measured, the frequency of the reflected light becomes f Bd , through the second lens and the acousto-optic modulator, the light frequency becomes f Bd -2Δf, then passes through the λ / 2 wave plate, is reflected by the polarization beam splitter, and combines with the reflected light of another diffracted laser A to produce beat frequency interference, which is received by the photodetector and outputs the photodetection 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 the data acquisition system performs waveform acquisition, an electronic computer is used to perform FM signal demodulation calculations, and the Doppler frequency shift f is obtained according to formula (17). D The measurement result is obtained by assuming that the laser wavelength and the distance between the optical axes of the two diffracted laser beams are d. The angular velocity ω of the rotating object is calculated using formula (11), thus realizing large-aperture laser rotation speed measurement.

3. A large-aperture laser rotation speed measurement method as claimed in claim 2, characterized in that: Only one acousto-optic modulator is used, and the principle of optical path reversibility is utilized to simultaneously complete the three core functions of frequency shifting, light splitting, and beam combining interference. The single-wavelength laser is converted into two coherent measurement lasers with different frequencies using an acousto-optic modulator, and the beam combining differential beat frequency is formed by returning to the original path using the acousto-optic modulator. Finally, the laser Doppler frequency containing the rotational angular velocity information is extracted, and the instantaneous value of the angular velocity is obtained by calculation.

4. A large-aperture laser rotation speed measurement method as claimed in claim 2, characterized in that: The direction of rotation is determined by the sign of the angular velocity value. When the angular velocity ω value is negative, it indicates clockwise rotation, and when the angular velocity ω value is positive, it indicates counterclockwise rotation.

5. A large-aperture laser rotation speed measurement method as claimed in claim 2, characterized in that: The dual-lens measurement method with adjustable spacing is used to adapt to and meet the measurement needs of any large-diameter rotating object.

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