Balanced differential laser rotating speed measuring method and device

Abstract

The invention discloses a balanced differential 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 lens, a rotary measured object, a sinusoidal signal source, a photoelectric detector, a data acquisition system and an electronic computer. The intersection point of the optical axes of the diffracted light A and the diffracted light B output by the acousto-optic modulator is located at the focal length position of the subsequent lens, the diffracted light A and the diffracted light B pass through the lens and then are converted into two parallel diffracted lasers which are parallel to the optical axes of the lens and have frequency difference, and the distance between the diffracted lasers is d. The method comprises the following steps of: irradiating a rotary measured object in parallel by using two beams of balanced differential diffraction laser, extracting Doppler frequency shift of the balanced differential laser from beat frequencies of two beams of laser containing Doppler frequency shift generated by rotation and reflected by the rotary measured object by utilizing the characteristic that Doppler frequency shift symbols generated by the rotary body on the two beams of diffraction laser are opposite, and calculating the Doppler frequency shift of the balanced differential laser according to the Doppler frequency shift. And finally, the angular velocity value of the rotating measured object is calculated and obtained.

Description

Technical Field

[0001] The invention relates to a balanced differential 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] Therefore, angular motion measurement becomes a difficult problem in motion measurement. Summary of the invention

[0010] 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 balanced differential laser rotation speed measurement method and device, using a monochromatic laser of the same wavelength to output two diffracted laser beams with frequency differences after passing through an acousto-optic modulator, the two balanced differential diffracted laser beams are parallelly irradiated on a rotating object to be measured, and the Doppler frequency shift of the balanced differential laser beams is extracted from the beat frequency of the two reflected laser beams containing the Doppler frequency shift generated by the rotation, and finally the angular velocity value of the rotating object to be measured is calculated, thereby realizing balanced differential laser rotation speed measurement.

[0011] The objective of the present invention is achieved through the following technical solutions:

[0012] The invention discloses a balanced differential laser speed measurement device, comprising a laser, a polarization beam splitter, a λ / 2 wave plate, an acousto-optic modulator, a lens, a rotating object to be measured, a sinusoidal signal source, a photoelectric detector, a data acquisition system, and an electronic computer. The intersection of the optical axes of the two diffracted light beams A and B of the acousto-optic modulator is located at the focal length position of the lens, and after passing through the lens, they are converted into two parallel diffracted laser beams with frequency differences parallel to the optical axis of the lens, and the spacing between them is d. The two balanced differential diffracted laser beams are parallel to the rotating object to be measured, and the Doppler frequency shift generated by the rotating body to the two diffracted laser beams is opposite in sign. The Doppler frequency shift of the balanced differential laser is extracted from the beat frequency of the two reflected laser beams containing the Doppler frequency shift generated by the rotation, and the angular velocity value of the rotating object to be measured is finally calculated to achieve balanced differential laser speed measurement.

[0013] The present invention also discloses a balanced differential laser rotation speed measurement method, which is implemented based on the balanced differential laser rotation speed measurement device. The present invention discloses a balanced differential laser rotation speed measurement method, which includes the following steps:

[0014] Step 1: The frequencies are f A 、f BThe 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 .

[0015] 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.

[0016] The rotational linear velocity of beam B at 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.

[0017] Then the measurement light A and the measurement light B satisfy the relationship described in equations (1) and (2):

[0018] v a =v ta cosα=ωR a cosα (1)

[0019] v b =v tb cosβ=ωR b cosβ (2)

[0020] 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:

[0021] λ A ≈λ B ≈λ(3)

[0022] Define the linear velocities obtained by measuring two laser beams A and B as va and v b , and their corresponding Doppler frequency shifts are f DA and f DB According to the Doppler principle,

[0023] f DA =2v a / λ A =2(ωR a cosα) / λ A

[0024] ≈2v a / λ=2(ωR a co sα) / λ (4)

[0025] f DB =2v b / λ B =2(ωR b cosβ) / λ B

[0026] ≈2v b / λ=2(ωR b cosβ) / λ (5) According to the geometric relationship, we can get

[0027] d=R a cosα+R b cosβ (6)

[0028] Laser A contains Doppler-shifted reflected light with frequency f Ad for

[0029] f Ad =f A -f DA (7)

[0030] Laser B contains Doppler-shifted reflected light with frequency f Bd for

[0031] f Bd =f B +f DB (8)

[0032] 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

[0033] f p =f Ad -f Bd =(f A -f B )-(f DA+f DB )=(f A -f B )-f D (9)

[0034] 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.

[0035] According to formulas (1) to (9), we can get

[0036] f D =(f A -f B )-f p =-(f DA +f DB )=-2dω / λ (10)

[0037] Right now

[0038]

[0039] 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

[0040] f A =f+2Δf (12)

[0041] f B =f-2Δf (13)

[0042] Here, Δf is the frequency shift produced by each diffraction order.

[0043] Diffracted laser A and diffracted laser B are transformed into two parallel light beams with an optical axis distance d through a lens, and irradiate the rotating object to be measured.

[0044] After the diffracted laser A is reflected by the object being measured, the frequency of the reflected light changes to f Ad , and then pass through the lens and the acousto-optic modulator again, 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 and outputs a photoelectric detection beat frequency signal.

[0045] After the diffracted laser B is reflected by the object being measured, the frequency of the reflected light becomes f Bd , and then pass through the lens and the acousto-optic modulator again, 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 .

[0046] The frequency of the diffracted laser A at the photodetector is

[0047] f Ad8 =f+4Δf-f DA (14)

[0048] The frequency of the diffracted laser B at the photodetector is

[0049] f Bd8 =f-4Δf+f DB (15)

[0050] f p =f Ad8 -f Bd8 =8Δf-f D (16)

[0051] f D =8Δf-(f Ad8 -f Bd8 )=8Δf-f p (17)

[0052] 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 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 is calculated using formula (11).

[0053] 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.

[0054] 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.

[0055] Beneficial effects:

[0056] 1. The present invention discloses a balanced differential laser speed measurement method and device, which uses two diffracted laser beams with different frequencies outputted by a monochromatic laser of the same wavelength after passing through an acousto-optic modulator. The two balanced differential diffracted laser beams are parallelly irradiated on the rotating object to be measured, and the Doppler frequency shift of the two diffracted laser beams produced by the rotating body is opposite in sign. The Doppler frequency shift of the balanced differential laser beam is extracted from the beat frequency of the two reflected laser beams containing the Doppler frequency shift produced by the rotation, and the angular velocity value of the rotating object to be measured is finally calculated to achieve balanced differential laser speed measurement. Compared with other measurement schemes, the present invention uses only one acousto-optic modulation device and utilizes the principle of optical path reversibility to simultaneously complete the three core functions of frequency shift, light splitting, and beam combining interference, and has the advantages of simple optical path, stable system, few optical components used, low cost, and easy implementation. In addition, the present invention does not require grating installation, nor does it require the measurement optical axis to be aligned with the axis of the rotating body. There is no limit on the range of angular motion amplitude, and it can be used for the measurement of periodic motion as well as the measurement of single motion.

[0057] 2. The present invention discloses a balanced differential 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 constructs a series of relationship groups for obtaining laser rotation speed measurement of a rotating object according to the optical path geometry, Doppler frequency shift, etc., and can obtain the angular velocity measurement result of the rotating body in real time based on the frequency difference caused by the laser Doppler effect generated by irradiation on both sides of the rotating body's shaft, and can obtain the instantaneous value of the transient angular velocity. Compared with other measurement methods, the present invention only requires that the axis of the rotating body to be measured is between two parallel measurement light beams, and there is no restriction 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 to use and reliable, has excellent adaptability, and is easy to promote and apply.

[0058] 3. The present invention discloses a balanced differential laser rotation speed measurement method and device, which uses a measuring lens to realize dual-beam angular velocity measurement, and the beam spacing is a fixed constant with excellent stability and reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 A schematic diagram of a balanced differential laser rotation speed measurement method of the present invention;

[0060] Figure 2 A schematic diagram of a balanced differential laser rotation speed measurement of the present invention;

[0061] Among them: 1—laser, 2—polarization beam splitter, 3—λ / 2 wave plate, 4—acousto-optic modulator, 5—lens, 6—rotating object to be measured, 7—sinusoidal signal source, 8—photodetector, 9—data acquisition system, 10—electronic computer. DETAILED DESCRIPTION

[0062] 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.

[0063] Example 1 (Using ±2nd order diffraction laser)

[0064] The present embodiment discloses a balanced differential laser speed measurement device, comprising a laser 1, a polarization beam splitter 2, a λ / 2 wave plate 3, an acousto-optic modulator 4, a lens 5, a rotating object to be measured 6, a sinusoidal signal source 7, a photodetector 8, a data acquisition system 9, and an electronic computer 10, wherein the intersection of the optical axes of the two diffracted light beams A and B output by the acousto-optic modulator 4 is located at the focal length position of the lens 5, and after passing through the lens 5, they are converted into two parallel light beams parallel to the optical axis of the lens 5, and the distance between them is d. Figure 2 shown.

[0065] The laser wavelength λ of the laser 1 is selected to be 632.8 nm, the second diffraction order frequency 2Δf of the acousto-optic modulator 4 is selected to be 40 MHz; the diameter Φ of the lens 5 is selected to be 60 mm, and the focal length is selected to be 50 mm; the output frequency Δf of the sinusoidal signal source 7 is selected to be 20 MHz; and the spacing between the two parallel measuring light beams A and B is selected to be d=40 mm.

[0066] This embodiment discloses a balanced differential laser speed measurement method, which is implemented based on the balanced differential laser speed measurement device. This embodiment discloses a balanced differential laser speed measurement method, and the specific implementation method is as follows:

[0067] 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

[0068] f A =f+2Δf (12)

[0069] f B =f-2Δf (13)

[0070] Wherein, Δf=20 MHz is the frequency deviation generated by each diffraction order.

[0071] The diffracted laser A and the diffracted laser B are transformed into parallel light with an optical axis distance of d=40 mm by lens 5, and irradiate the rotating object 6 to be measured.

[0072] After the diffracted laser A is reflected by the measured object 6, the frequency of the reflected light changes to f Ad , and then passes through lens 5 and acousto-optic modulator 4, the optical 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.

[0073] After the diffracted laser B is reflected by the measured object 6, the frequency of the reflected light becomes f Bd , and then passes through lens 5 and 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 .

[0074] The frequency of the diffracted laser A at the photodetector 8 is

[0075] f Ad8 =f+4Δf-f DA (14)

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

[0077] f Bd8 =f-4Δf+f DB (15)

[0078] f p =f Ad8 -f Bd8 =8Δf-f D (16)

[0079] f D =8Δf-(f Ad8 -f Bd8 )=8Δf-f p (17)

[0080] 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 as follows: the laser wavelength of the laser and the distance between the optical axes of the two diffracted laser beams is d = 40 mm, and the angular velocity ω of the rotating object 6 is calculated using formula (11).

[0081] Example 2 (Using ±1st order diffraction laser)

[0082] The present embodiment discloses a balanced differential laser speed measurement method and device, comprising a laser 1, a polarization beam splitter 2, a λ / 2 wave plate 3, an acousto-optic modulator 4, a lens 5, a rotating object to be measured 6, a sinusoidal signal source 7, a photodetector 8, a data acquisition system 9, and an electronic computer 10, wherein the intersection of the optical axes of the two diffracted light beams A and B of the acousto-optic modulator 4 is located at the focal length position of the lens 5, and after passing through the lens 5, they are converted into two parallel light beams parallel to the optical axis of the lens 5, and the distance between them is d. Figure 2 shown.

[0083] The laser wavelength λ of the laser 1 is selected to be 632.8 nm, the first-order diffraction frequency Δf of the acousto-optic modulator 4 is selected to be 20 MHz; the diameter Φ of the lens 5 is selected to be 60 mm, and the focal length is selected to be 50 mm; the output frequency Δf of the sinusoidal signal source 7 is selected to be 20 MHz; and the spacing between the two parallel measuring light beams A and B is selected to be d=40 mm.

[0084] This embodiment discloses a balanced differential laser speed measurement method, which is implemented based on the balanced differential laser speed measurement device. This embodiment discloses a balanced differential laser speed measurement method, and the specific implementation method is as follows:

[0085] 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

[0086] f A =f+Δf (18)

[0087] f B =f-Δf (19)

[0088] Wherein, Δf=20 MHz is the frequency deviation generated by each diffraction order.

[0089] The diffracted laser A and the diffracted laser B are transformed into parallel light with an optical axis distance of d=40 mm by lens 5, and irradiate the rotating object 6 to be measured.

[0090] After the diffracted laser A is reflected by the measured object 6, the frequency of the reflected light changes to f Ad , and then passes through lens 5 and acousto-optic modulator 4, the optical 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.

[0091] After the diffracted laser B is reflected by the measured object 6, the frequency of the reflected light becomes f Bd , and then passes through lens 5 and 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 .

[0092] The frequency of the diffracted laser A at the photodetector 8 is

[0093] f Ad8 =f+2Δf-f DA (20)

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

[0095] f Bd8 =f-2Δf+f DB (twenty one)

[0096] f p =f Ad8 -f Bd8 =4Δf-f D (twenty two)

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

[0098] 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 (23). D The 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 = 40 mm, and the angular velocity ω of the rotating object 6 is calculated using formula (11).

[0099] 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 balanced differential laser speed measurement device, characterized in that: The invention comprises a laser, a polarization beam splitter, a λ / 2 wave plate, an acousto-optic modulator, a lens, a rotating object to be measured, a sinusoidal signal source, a photoelectric detector, a data acquisition system and an electronic computer, wherein the intersection of the optical axes of two diffracted light beams A and B output by the acousto-optic modulator is located at the focal length position of the lens, and after passing through the lens, they are converted into two parallel diffracted laser beams with frequency difference and parallel to the optical axis of the lens, and the spacing between them is d; two balanced differential diffracted laser beams are parallelly irradiated on the rotating object to be measured, and the Doppler frequency shift of the balanced differential laser beam is extracted from the beat frequency of the two laser beams containing the Doppler frequency shift generated by the rotation reflected from the rotating object by utilizing the opposite sign characteristics of the Doppler frequency shift generated by the rotating body to the two diffracted laser beams, and finally the angular velocity value of the rotating object to be measured is calculated, so as to realize the balanced differential laser rotation speed measurement.

2. A balanced differential laser rotation speed measurement method, implemented based on a balanced differential 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 measured 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 beam B at 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; Diffracted laser A and diffracted laser B are transformed into parallel light with an optical axis distance d between the two beams through a 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 , and then pass through the lens and the acousto-optic modulator again, 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 and outputs a photodetection beat frequency signal; After the diffracted laser B is reflected by the object being measured, the frequency of the reflected light becomes f Bd , and then pass through the lens and the acousto-optic modulator again, 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 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 is calculated using formula (11).

3. A balanced differential laser rotation speed measurement method as claimed in claim 2, characterized in that: Only one acousto-optic modulation device 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. 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 beam combining differential beat frequency in a return path. 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 balanced differential 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 balanced differential laser rotation speed measurement method as claimed in claim 2, characterized in that: A dual-beam angular velocity measurement is achieved using a measuring lens, with the beam spacing being a fixed constant.

Images