Signal optimization method of laser Doppler vibrometer for transmission shaft torsional vibration measurement

Abstract

The present invention provides a laser Doppler vibrometer signal optimization method for measuring torsional vibration of a transmission shaft system. The method comprises: estimating the maximum rotational speed of a measured shaft in the transmission shaft system and setting the laser Doppler vibrometer range; adjusting the laser Doppler vibrometer and determining offset points to be traversed based on the measured shaft; acquiring the vibration signal of the measured shaft based on the offset points to be traversed and calculating an improved signal-to-noise ratio index; determining an optimal incident offset based on the improved signal-to-noise ratio index by interpolation; and measuring the vibration signal based on the optimal incident offset to obtain a smoothed torsional vibration signal for measuring torsional vibration of the transmission shaft system. Based on the Vold-Kalman filtering algorithm, the EEMD algorithm, and the median filtering algorithm, the method has a fast computational speed and high accuracy, and can assist in the real-time and rapid measurement of shaft system torsional vibration.

Description

Technical Field

[0001] The invention belongs to the technical field of non-contact torsional vibration measurement, in particular to a laser Doppler vibrometer signal optimization method for transmission shaft system torsional vibration measurement. Background Art

[0002] The transmission shaft system is generally composed of rotating components such as shafts, bearings, and gears, and is a core component of the power unit. Due to errors in the manufacturing and assembly of transmission components, the input and output torques of the shaft system also vary within a certain range. Under the influence of internal and external excitation sources, the shaft system produces normal torsional vibrations, also commonly known as torsional vibrations, which manifest as periodic fluctuations in the rotational speed of each rotating component in the system around the nominal value. When subjected to abnormal excitation such as component degradation, the system's torsional vibration response undergoes significant changes, such as the appearance of periodic pulses and a significant increase in the amplitude of specific cycles. Measuring and identifying abnormal torsional vibration responses can predict transmission shaft system failures and ensure reliable system operation. This is of great significance for large-scale equipment with long-term service, such as wind power main drive chains and nuclear power cooling water circulation pump reducers.

[0003] Currently, the most widely used torsional vibration measurement technology uses tachometer gears and electromagnetic / optical displacement sensors. However, due to the limitations of the number of teeth, manufacturing and assembly precision, and the sensor's frequency response, the resolution of transient pulse events at low and medium speeds is insufficient, making it difficult to accurately identify abnormal conditions. Heterodyne laser Doppler vibrometers (LDVs) offer the advantages of high resolution and wide-band response and have been applied in scenarios such as structural health monitoring and modal analysis. However, LDVs are still relatively unused in measuring rotating shaft torsional vibrations, primarily due to the low signal-to-noise ratio when measuring the rotating shaft surface. The reason for this is that a single-channel LDV measures vibration velocity collinear with the laser. Therefore, for torsional vibration measurement, the laser light must be incident on the curved shaft surface, offset from the center of rotation, to obtain the linear velocity component of the shaft surface. This component is proportional to the distance the incident light deviates from the axis. Theoretically, it reaches its maximum value when the laser light is incident tangentially to the shaft surface. However, the curved shaft surface severely affects the focusing of the laser spot and the collection of scattered light. Furthermore, the translation, pitch, yaw, and rotation of the shaft cause the laser speckle pattern to constantly change. These combined factors cause sudden changes in optical signal intensity, which can cause impulsive noise in the demodulated signal, known as speckle noise. Some researchers have designed rotational speed measurement systems based on laser Doppler velocimetry, but they have not addressed the evaluation and control of speckle noise. Other researchers have proposed post-processing methods to suppress colored and random noise, but spectral methods struggle to effectively reduce impulsive noise. Current LDVs generally rely solely on optical signal intensity for adjustment, which also fails to meet practical monitoring needs.

[0004] Therefore, in order to control the intensity of speckle noise, it is urgent and necessary to seek a signal optimization method for laser Doppler vibrometer used for transmission shaft torsional vibration measurement to achieve real-time and rapid measurement of shaft torsional vibration. Summary of the Invention

[0005] In response to the above-mentioned deficiencies in the prior art, the present invention proposes a method for optimizing laser Doppler vibrometer signals for measuring torsional vibrations in transmission shaft systems. The method comprises estimating the maximum rotational speed of the measured shaft and setting the range of the laser Doppler vibrometer based on the measured shaft in the transmission shaft system; adjusting the laser Doppler vibrometer and determining the offset points to be traversed based on the measured shaft; collecting the vibration signal of the measured shaft based on the offset points to be traversed, and calculating an improved signal-to-noise ratio index; determining the optimal incident offset based on the improved signal-to-noise ratio index by means of interpolation; and measuring the vibration signal based on the optimal incident offset to obtain a smoothed torsional vibration signal for measuring torsional vibrations in transmission shaft systems. The present invention is based on the Vold-Kalman filtering algorithm, the EEMD algorithm, and the median filtering algorithm, and has a fast computing speed and high accuracy. It can assist in the real-time and rapid measurement of shaft system torsional vibrations, reduce dependence on operator experience, and is reliable in operation and highly practical.

[0006] The present invention provides a laser Doppler vibrometer signal optimization method for measuring torsional vibration of a transmission shaft system, which comprises the following steps:

[0007] S1. Based on the transmission shaft system, determine the maximum speed of the shaft system to be measured and set the measuring range of the laser Doppler vibrometer;

[0008] S2. Based on the measured axis system, adjust the laser Doppler vibrometer and determine the offset point to be traversed:

[0009] S3. Based on the offset point to be traversed, collect the vibration signal of the measured shaft system and calculate the improved signal-to-noise ratio index;

[0010] S31. Based on the offset point to be traversed, collect the vibration signal u of the measured shaft system t ,

[0011] S32. Calculate the instantaneous speed ω of the nth offset point of the measured shaft system based on the relationship between linear velocity and angular velocity. t :

[0012] ω t =-u t / (nΔy) (1)

[0013] Where Δy represents the feed step size of the offset adjustment;

[0014] S33, instantaneous phase function c of the vibration harmonics of the measured shaft system t for:

[0015] c t=2cos(ω t f r Δt) (2)

[0016] Wherein, Δt represents the vibration signal u t The sampling rate F s The reciprocal of f r Indicates the first-order torsional vibration frequency of the measured shaft system;

[0017] S34, based on the instantaneous phase function c t , solve the vibration signal u t The harmonic components x of each order to be monitored t ;

[0018] S35, subtracting each order harmonic component x from the vibration signal t The sum of the residual signal res t , and for each order harmonic component x t sum and the residual signal res t Calculate the corresponding L2 / L1 norms respectively:

[0019]

[0020] Where k represents the order;

[0021] S36, normalizing the light intensity signal output by the laser Doppler vibrometer to obtain a basic signal-to-noise ratio SNR, and based on the harmonic components x of each order t sum The L2 / L1 norm and residual signal res t The L2 / L1 norm of is used to obtain the improved signal-to-noise ratio indicator ISNR:

[0022]

[0023] S4. Determine the optimal incident bias based on the improved signal-to-noise ratio index by interpolation: establish a rectangular coordinate system with the cross-sectional view of the rotating shaft, use the height y of the bracket as the independent variable, and use the improved signal-to-noise ratio index ISNR under each bias as the dependent variable, perform interpolation densification, and take the Mth position y corresponding to the maximum value of the improved signal-to-noise ratio index ISNR m is the optimal incident bias;

[0024] S5. Measure the vibration signal based on the optimal incident bias to obtain a smooth torsional vibration signal for the transmission shaft torsional vibration measurement: Measure the vibration signal u to be analyzed under the optimal incident bias condition. m (t), design a median filter with adaptive window width to suppress speckle noise and obtain a smooth torsional vibration signal The smoothed torsional vibration signal Used for torsional vibration measurement of transmission shafting.

[0025] Preferably, step S5 specifically includes the following steps:

[0026] S51. Measure the vibration signal u to be analyzed under the optimal incident bias condition m (t), and based on step S34, obtain the torsional vibration signal u to be analyzed m The residual component res of (t) m (t);

[0027] S52, decomposing the residual component res based on an integrated empirical mode decomposition algorithm m (t), obtain the intrinsic mode components IMF of each order i (t):

[0028]

[0029] Among them, AM i (t) and FM i (t) represent the amplitude modulation component and frequency modulation component of the eigenmode component respectively;

[0030] S53, determine the time when the impulse noise event occurs: for the first-order intrinsic mode component IMF1, use Hilbert transform to calculate the envelope signal AM1(t) of the first-order intrinsic mode component IMF1, and refer to the preset pulse amplitude detection threshold A min , determine the moment when the impulse noise event occurs;

[0031] S54, estimate the noise impact interval: for the retrieved T impulse noise events, take the actual width W of each impulse noise event t a times of the noise impact interval length, where a represents the impact interval length coefficient;

[0032] S55. For each noise impact interval, use the length The median filter is used to filter the residual component to obtain a smoothed residual component, which is added to the harmonic component to obtain a smoothed torsional vibration signal. The smoothed torsional vibration signal Used for torsional vibration measurement of transmission shafting; where b represents the filter length coefficient.

[0033] Preferably, step S2 specifically includes the following steps:

[0034] S21. Adjusting the indicator light spot of the laser Doppler vibrometer: placing the indicator light spot of the laser Doppler vibrometer at a point on the surface of the measured shafting, so that the measurement plane of the laser Doppler vibrometer's light beam is coplanar with the cross section of the measured shafting and avoids a low signal quality area of ​​the laser Doppler vibrometer;

[0035] S22. Determine the upper limit of the offset adjustment: Adjust the height of the bracket of the laser Doppler vibrometer through the servo control system. The indicator light spot of the laser Doppler vibrometer is close to the upper edge of the measured shaft system and focused. If the return light intensity RSSI read by the laser Doppler vibrometer is greater than or equal to 80%, record the first offset distance Y. u Used as a bias to adjust the upper bound;

[0036] S23, determining the lower limit of the offset adjustment: starting the continuous measurement mode of the laser Doppler vibrometer, collecting the initial vibration signal x of the measured shaft system t , input the vibration signal into the control system of the bracket, aiming at keeping the mean value of the vibration signal within a small interval [-Δε, Δε] close to 0, adjust the height of the bracket through feedback control, and record the stable second offset distance Y d Used as a bias to adjust the lower bound;

[0037] S24, determine the offset points to be traversed: set the feed step length Δy of the offset adjustment on the host computer so that the set of offset points to be traversed is {Y u ,Y u -Δy,…,Y u -NΔy}, and satisfy Y u -NΔy≈Y d , where N represents the number of bias points to be traversed.

[0038] Preferably, the vibration signal u in step S34 t The harmonic components x of each order to be monitored t The solution equation is:

[0039]

[0040] Where m represents the sequence length; ε t Indicates the error in the filtering process; η t Indicates measurement error.

[0041] Preferably, the step S1 specifically includes the following steps:

[0042] S11. Calculate the limit speed V of the shaft system under test: Based on the transmission shaft system, determine the limit value of the surface linear velocity of the shaft system under test, i.e., the limit speed V;

[0043] S12. Based on the limit rotational speed V of the measured shaft system, set a measuring range of the laser Doppler vibrometer, wherein the measuring range of the laser Doppler vibrometer is greater than or equal to the limit rotational speed V of the measured shaft system.

[0044] Preferably, the filtering bandwidth of the filter set in step S34 is the instantaneous speed ω of the measured shaft system.t The filter order is set to 2, and the number of extracted harmonic orders is 10.

[0045] Preferably, the sampling rate F of the initial vibration signal in step S23 is s0 Greater than or equal to 25.6kHz; the sampling rate F of the vibration signal in step S31 s Greater than or equal to the first-order torsional vibration frequency f of the measured shaft system r The acquisition length of the vibration signal covers 15 to 30 cycles of the first-order torsional vibration harmonic of the measured shaft system.

[0046] Preferably, the interpolation function used in the interpolation in step S4 is a spline function and the interpolation step size is 0.2Δy.

[0047] Preferably, the number of decomposition modes of the integrated empirical mode decomposition algorithm in step S52 is 10, the number of integrations is 20, and the added noise amplitude index is 0.4σ, where σ represents the residual component res m (t) standard deviation; the pulse amplitude detection threshold A in step S53 min Take the 85% to 95% quantile of the envelope signal AM1(t); the influence interval length coefficient a in step S54 is 3 to 5; the filter length coefficient b in step S55 is an even number between 6 and 12

[0048] Compared with the prior art, the technical effects of the present invention are:

[0049] 1. The present invention proposes a signal optimization method for a laser Doppler vibrometer for measuring torsional vibrations in a transmission shaft system. This method is a non-contact vibration measurement method designed based on the LDV vibration measurement system. It facilitates on-site inspection or monitoring of rotating shafting equipment and is simple to operate and highly practical.

[0050] 2. The present invention proposes a signal optimization method for a laser Doppler vibrometer for measuring torsional vibration of a transmission shaft system. The method is based on the Vold-Kalman filtering algorithm, the EEMD algorithm, and the median filtering algorithm. It has a fast operation rate, is simple and efficient, and can assist in the real-time and rapid measurement of torsional vibration of the shaft system. The method innovatively constructs an improved signal-to-noise ratio of the laser vibrometer. The proposed method avoids the limitations of manually setting the laser incident bias parameters and smoothing filter parameters, can improve the vibration measurement signal-to-noise ratio in different engineering application scenarios, reduce dependence on operator experience, provide strong support for monitoring and diagnosis, and realize the automated measurement of torsional vibration of rotating shaft systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Other features, objects and advantages of the present application will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings.

[0052] Figure 1 This is a flow chart of a laser Doppler vibrometer signal optimization method for measuring torsional vibration of a transmission shaft system according to the present invention;

[0053] Figure 2 It is a schematic diagram of a measurement method of a specific embodiment of the present invention;

[0054] Figure 3 is a graph of harmonic components of various orders according to a specific embodiment of the present invention;

[0055] Figure 4 is a residual signal curve diagram of a specific embodiment of the present invention;

[0056] Figure 5 FIG. 1 is a bias-signal-to-noise ratio curve obtained by interpolation and densification of each measuring point in a specific embodiment of the present invention;

[0057] Figure 6 This is a diagram showing the smoothing and denoising results of a torsional vibration signal according to a specific embodiment of the present invention;

[0058] Figure 7 is a torsional vibration signal curve diagram of a specific embodiment of the present invention;

[0059] Figure 8 It is a curve diagram of the encoder torsional vibration signal processing result of a specific embodiment of the present invention. DETAILED DESCRIPTION

[0060] The present application will be further described in detail below with reference to the accompanying drawings and examples. It will be understood that the specific embodiments described herein are intended only to explain the relevant inventions and are not intended to limit the inventions. It should also be noted that, for ease of description, only portions relevant to the relevant inventions are shown in the accompanying drawings. It should be noted that, unless there is a conflict, the embodiments and features in the embodiments of the present application may be combined with one another. The present application will be described in detail below with reference to the accompanying drawings and in conjunction with the examples.

[0061] Figure 1 The present invention shows a laser Doppler vibrometer signal optimization method for measuring torsional vibration of a transmission shaft system, which includes the following steps:

[0062] S1. Based on the transmission shaft system, determine the maximum speed of the shaft system to be measured and set the measuring range of the laser Doppler vibrometer.

[0063] S11. Calculate the limit rotational speed V of the measured shaft system: Based on the transmission shaft system, determine the limit value of the surface linear velocity of the measured shaft system, and calculate the limit rotational speed V of the measured shaft system.

[0064] S12. Based on the limit rotational speed V of the measured shaft system, set the range of the laser Doppler vibrometer, wherein the range of the laser Doppler vibrometer is greater than or equal to the limit rotational speed V of the measured shaft system.

[0065] S2. Based on the measured axis system, adjust the laser Doppler vibrometer and determine the offset point to be traversed.

[0066] S21. Adjust the indicator light spot of the laser Doppler vibrometer: Place the indicator light spot of the laser Doppler vibrometer at a point on the surface of the measured shaft system. The measurement plane of the laser Doppler vibrometer's light beam should be coplanar with the cross section of the measured shaft system and avoid the low signal quality area of ​​the laser Doppler vibrometer.

[0067] S22. Determine the upper limit of the offset adjustment: Adjust the height of the laser Doppler vibrometer bracket through the servo control system. The indicator light spot of the laser Doppler vibrometer is close to the upper edge of the measured shaft system and focused. If the return light intensity RSSI read by the laser Doppler vibrometer is greater than or equal to 80%, the first offset distance Y is recorded. u Acts as a bias to adjust the upper bound.

[0068] S23. Determine the lower limit of the offset adjustment: Start the continuous measurement mode of the laser Doppler vibrometer and collect the initial vibration signal x of the measured shaft system. t , input the vibration signal into the control system of the bracket, aiming at keeping the mean value of the vibration signal within a small interval [-Δε, Δε] close to 0, adjust the height of the bracket through feedback control, and record the stable second offset distance Y d As a bias to adjust the lower boundary. The sampling rate F of the initial vibration signal s0 Greater than or equal to 25.6kHz.

[0069] S24, determine the offset points to be traversed: set the feed step length Δy of the offset adjustment on the host computer so that the set of offset points to be traversed is {Y u ,Y u -Δy,…,Y u -NΔy}, and satisfy Y u -NΔy≈Y d , where N represents the number of bias points to be traversed.

[0070] S3. Based on the offset points to be traversed, collect the vibration signal of the measured shaft system and calculate the improved signal-to-noise ratio index: At each offset point, collect the vibration signal u of the measured shaft system t , the sampling rate of the vibration signal F s Greater than or equal to the first-order torsional vibration frequency f of the measured shaft system r10k times, it is empirically set that the k-order frequency multiplication needs to be retained. According to the application convention of the sampling theorem in engineering, Fs≥10×kf r The vibration signal acquisition length must cover at least 15 to 30 cycles of the first-order torsional vibration harmonic of the measured shaft system to ensure filtering quality. For the vibration signal at each offset point, an improved signal-to-noise ratio index is calculated based on Vold-Kalman filtering and the L2 / L1 norm.

[0071] S31. Based on the offset point to be traversed, collect the vibration signal u of the measured shaft t .

[0072] S32. Calculate the instantaneous speed ω of the nth offset point of the measured shaft system based on the relationship between linear velocity and angular velocity. t :

[0073] ω t =-u t / (nΔy) (1)

[0074] S33, instantaneous phase function c of the vibration harmonics of the measured shaft t for:

[0075] c t =2cos(ω t f r Δt) (2)

[0076] Where Δt represents the vibration signal u t The sampling rate F s The reciprocal of f r Indicates the first-order torsional vibration frequency of the measured shaft system.

[0077] S34, based on the instantaneous phase function c t , according to the Vold-Kalman filtering principle, solve the vibration signal u t The harmonic components x of each order to be monitored t :

[0078]

[0079] Where m represents the sequence length; ε t Indicates the error in the filtering process; η t Indicates measurement error.

[0080] In a specific embodiment, the filter bandwidth of the Vold-Kalman filter is set to the instantaneous speed ω of the measured shaft. t The Vold-Kalman filter order is set to 2, and the number of extracted harmonic orders is 10.

[0081] S35. Subtract each order harmonic component x from the vibration signal t The sum of the residual signal res t , and each order harmonic component x t sum and the residual signal res t Calculate the corresponding L2 / L1 norms respectively:

[0082]

[0083] Where k represents the order. Impulsive speckle noise is mainly retained in the residual signal.

[0084] S36, normalize the 0~5V light intensity signal output by the laser Doppler vibrometer to obtain the basic signal-to-noise ratio SNR, and based on the harmonic components x t sum The L2 / L1 norm and residual signal res t The L2 / L1 norm of is used to obtain the improved signal-to-noise ratio indicator ISNR:

[0085]

[0086] S4. Based on the improved signal-to-noise ratio index, the optimal incident bias is determined by interpolation: a rectangular coordinate system is established with the cross-sectional view of the rotating shaft, the height y of the bracket is used as the independent variable (vertical direction), and the improved signal-to-noise ratio index ISNR under each bias is used as the dependent variable. Interpolation densification is performed, and the interpolation function used is a spline function. The preferred interpolation step is 0.2Δy. The Mth position y corresponding to the maximum value of the improved signal-to-noise ratio index ISNR is taken. m is the optimal incident bias.

[0087] S5. Measure the vibration signal based on the optimal incident bias to obtain a smooth torsional vibration signal for the transmission shaft torsional vibration measurement: Measure the vibration signal u to be analyzed under the optimal incident bias condition. m (t), design a median filter with adaptive window width to suppress speckle noise and obtain a smooth torsional vibration signal Smooth torsional vibration signal Used for torsional vibration measurement of transmission shafting.

[0088] S51. Measure the vibration signal u to be analyzed under the optimal incident bias condition m (t), and based on the Vold-Kalman filtering principle in step S34, the torsional vibration signal u to be analyzed is obtained m The residual component res of (t) m (t).

[0089] S52, based on the ensemble empirical mode decomposition (EEMD) algorithm, further decompose the residual component res m (t), obtain the intrinsic mode components IMF of each order i (t)(Intrinsic modefunction, IMF):

[0090]

[0091] Among them, AM i (t) and FM i (t) represent the amplitude modulation component and frequency modulation component of the eigenmode component respectively.

[0092] The integrated empirical mode decomposition adds a certain amplitude of white noise to the decomposed signal, and takes the average of multiple empirical mode EMD decomposition results to improve the decomposition effect. The number of decomposition modes of the integrated empirical mode decomposition algorithm is 10, the number of integrations is 20, and the added noise amplitude index is 0.4σ, where σ represents the residual component res m The standard deviation of (t).

[0093] S53, determine the time when the impulse noise event occurs: for the first-order intrinsic mode component IMF1, use Hilbert transform to calculate the envelope signal AM1(t) of the first-order intrinsic mode component IMF1, and refer to the preset pulse amplitude detection threshold A min , determine the moment when the impulse noise event occurs. Pulse amplitude detection threshold A min Take the 85% to 95% quantiles of the envelope signal AM1(t).

[0094] S54, estimate the noise impact interval: for the retrieved T impulse noise events, take the actual width W of each impulse noise event t a times of the noise impact interval length is taken as the corresponding noise impact interval length, where a represents the impact interval length coefficient and is 3 to 5.

[0095] S55. For each noise impact interval, use the length The median filter is used to filter the residual component to obtain a smoothed residual component, which is then added to the harmonic component to obtain a smoothed torsional vibration signal. Smooth torsional vibration signal Used for torsional vibration measurement of transmission shaft systems; where b represents the filter length coefficient and is an even number between 6 and 12.

[0096] In a specific embodiment, taking the industrial planetary gear transmission shaft test platform test as an example, a planetary single tooth wear gearbox with a reduction ratio of 5:1 is used in this embodiment, and a high-precision rotary encoder installed on the output shaft is used to obtain a torsional vibration reference signal.

[0097] The whole system includes laser Doppler vibrometer 1, bracket 2, host computer and acquisition system 3, drive motor 4, planetary gearbox under test 5, output shaft section under test 6, simulated load 7, etc. Figure 1 Among them, 1 to 3 are the vibration test and processing equipment used, and 4 to 7 are the test benches.

[0098] In a specific embodiment, the radius of the output shaft to be measured is 25 mm, and the maximum average rotational speed of the output shaft is about 2.513 Hz, then the average linear velocity of the surface is about 395 mm / s, and the range of the heterodyne laser Doppler vibrometer LDV is set to 500 mm / s to meet the requirements. The distance from the light-emitting point to the surface is set to ΔX≈450 mm. The height of the bracket is adjusted by a servo control system such as an electric drive or hydraulic system. According to engineering experience, traversing 20 measuring points can meet the optimal requirements, that is, Δy is set to 25 / 20=1.25 mm. In this example, the torsional vibration of the shaft system is mainly caused by gear meshing, so the gear meshing frequency is obtained by theoretical calculation as the first-order torsional vibration frequency f of the shaft system. r At a certain measuring point, the sum of the harmonic components of each order is obtained as follows: Figure 3 As shown, the residual signal is Figure 4 As shown. A rectangular coordinate system is established with the cross-sectional view of the shaft, the height y of the bracket is used as the independent variable (vertical direction), and the improved signal-to-noise ratio index ISNR under each bias is used as the dependent variable. For all bias measurement point data, a smooth y-ISNR curve is obtained using the interpolation function, and the interpolation step is set to 0.25mm. The curve is plotted as shown below. Figure 5 The offset-SNR curve shown in the figure takes the offset corresponding to the maximum ISNR as the optimal incident offset. The actual offset is set to 6.8mm as shown in the figure, and the smoothing noise reduction effect of the median filter with adaptive window width is as follows Figure 6 As shown in the figure, the results of the shaft torsional vibration analysis obtained by the laser Doppler vibrometer are as follows: Figure 7 As shown, Figure 8 The impact torsional vibration characteristics measured by the rotary encoders shown are basically consistent.

[0099] The present invention proposes a laser Doppler vibrometer signal optimization method for measuring torsional vibration of a transmission shaft system. The proposed method is a non-contact vibration measurement method designed based on the LDV vibrometer system, which facilitates on-site inspection or monitoring of rotating shaft equipment and is simple to operate and highly practical. The proposed method is based on the Vold-Kalman filtering algorithm, the EEMD algorithm, and the median filtering algorithm, and has a fast computing speed, simplicity, and high efficiency, which can assist in the real-time and rapid measurement of torsional vibration of the shaft system. The proposed method innovatively constructs an improved laser vibrometer signal-to-noise ratio, avoiding the limitations of manually setting laser incident bias parameters and smoothing filter parameters. The proposed method can improve the vibration measurement signal-to-noise ratio in different engineering application scenarios, reduce dependence on operator experience, provide strong support for monitoring and diagnosis, and realize the automated measurement of torsional vibration of rotating shaft systems.

[0100] Finally, it should be noted that the above embodiments are only intended to illustrate rather than limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for optimizing laser Doppler vibrometer signals for measuring torsional vibration of a transmission shaft system, characterized in that: It includes the following steps: S1. Based on the transmission shaft system, determine the maximum speed of the shaft system to be measured and set the measuring range of the laser Doppler vibrometer; S2. Based on the measured axis system, adjust the laser Doppler vibrometer and determine the offset point to be traversed: S3. Based on the offset point to be traversed, collect the vibration signal of the measured shaft system and calculate the improved signal-to-noise ratio index; S31. Based on the offset point to be traversed, collect the vibration signal u of the measured shaft system t , S32. Calculate the instantaneous speed ω of the nth offset point of the measured shaft system based on the relationship between linear velocity and angular velocity. t : ωt=-ut / (nΔy) (1) Where Δy represents the feed step size of the offset adjustment; S33, instantaneous phase function c of the vibration harmonics of the measured shaft system t for: c t =2cos(ω t f r Δt) (2) Wherein, Δt represents the vibration signal u t The sampling rate F s The reciprocal of f r Indicates the first-order torsional vibration frequency of the measured shaft system; S34, based on the instantaneous phase function c t , solve the vibration signal u t The harmonic components x of each order to be monitored t ; S35, subtracting each order harmonic component x from the vibration signal t The sum of the residual signal res t , and for each order harmonic component x t sum and the residual signal res t Calculate the corresponding L2 / L1 norms respectively: Where k represents the order; S36, normalizing the light intensity signal output by the laser Doppler vibrometer to obtain a basic signal-to-noise ratio SNR, and based on the harmonic components x of each order t sum The L2 / L1 norm and residual signal res t The L2 / L1 norm of is used to obtain the improved signal-to-noise ratio indicator ISNR: S4. Determine the optimal incident bias based on the improved signal-to-noise ratio index by interpolation: establish a rectangular coordinate system with the cross-sectional view of the rotating shaft, use the height y of the bracket as the independent variable, and use the improved signal-to-noise ratio index ISNR under each bias as the dependent variable, perform interpolation densification, and take the Mth position y corresponding to the maximum value of the improved signal-to-noise ratio index ISNR m is the optimal incident bias; S5. Measure the vibration signal based on the optimal incident bias to obtain a smooth torsional vibration signal for the transmission shaft torsional vibration measurement: Measure the vibration signal u to be analyzed under the optimal incident bias condition. m (t), design a median filter with adaptive window width to suppress speckle noise and obtain a smooth torsional vibration signal The smoothed torsional vibration signal Used for torsional vibration measurement of transmission shafting.

2. The laser Doppler vibrometer signal optimization method for transmission shaft torsional vibration measurement according to claim 1, characterized in that: The step S5 specifically includes the following steps: S51. Measure the vibration signal u to be analyzed under the optimal incident bias condition m (t), and based on step S34, obtain the torsional vibration signal u to be analyzed m The residual component res of (t) m (t); S52, decomposing the residual component res based on an integrated empirical mode decomposition algorithm m (t), obtain the intrinsic mode components IMF of each order i (t): Among them, AM i (t) and FM i (t) represent the amplitude modulation component and frequency modulation component of the eigenmode component respectively; S53, determine the time when the impulse noise event occurs: for the first-order intrinsic mode component IMF1, use Hilbert transform to calculate the envelope signal AM1(t) of the first-order intrinsic mode component IMF1, and refer to the preset pulse amplitude detection threshold A min , determine the moment when the impulse noise event occurs; S54, estimate the noise impact interval: for the retrieved T impulse noise events, take the actual width W of each impulse noise event t a times of the noise impact interval length, where a represents the impact interval length coefficient; S55. For each noise impact interval, use the length The median filter is used to filter the residual component to obtain a smoothed residual component, which is added to the harmonic component to obtain a smoothed torsional vibration signal. The smoothed torsional vibration signal Used for torsional vibration measurement of transmission shafting; where b represents the filter length coefficient.

3. The laser Doppler vibrometer signal optimization method for transmission shaft torsional vibration measurement according to claim 1, characterized in that: The step S2 specifically includes the following steps: S21. Adjusting the indicator light spot of the laser Doppler vibrometer: placing the indicator light spot of the laser Doppler vibrometer at a point on the surface of the measured shafting, so that the measurement plane of the laser Doppler vibrometer's light beam is coplanar with the cross section of the measured shafting and avoids a low signal quality area of ​​the laser Doppler vibrometer; S22. Determine the upper limit of the offset adjustment: Adjust the height of the bracket of the laser Doppler vibrometer through the servo control system. The indicator light spot of the laser Doppler vibrometer is close to the upper edge of the measured shaft system and focused. If the return light intensity RSSI read by the laser Doppler vibrometer is greater than or equal to 80%, record the first offset distance Y. u Used as a bias to adjust the upper bound; S23, determining the lower limit of the offset adjustment: starting the continuous measurement mode of the laser Doppler vibrometer, collecting the initial vibration signal x of the measured shaft system t , input the vibration signal into the control system of the bracket, aiming at keeping the mean value of the vibration signal within a small interval [-Δε, Δε] close to 0, adjust the height of the bracket through feedback control, and record the stable second offset distance Y d Used as a bias to adjust the lower bound; S24, determine the offset points to be traversed: set the feed step length Δy of the offset adjustment on the host computer so that the set of offset points to be traversed is {Y u ,Y u -Δy,…,Y u -NΔy}, and satisfy Y u -NΔy≈Y d , where N represents the number of bias points to be traversed.

4. The laser Doppler vibrometer signal optimization method for transmission shaft torsional vibration measurement according to claim 1, characterized in that: The vibration signal u in step S34 t The harmonic components x of each order to be monitored t The solution equation is: Where m represents the sequence length; ε t Indicates the error in the filtering process; η t Indicates measurement error.

5. The laser Doppler vibrometer signal optimization method for transmission shaft torsional vibration measurement according to claim 1, characterized in that: The step S1 specifically includes the following steps: S11. Calculate the limit speed V of the shaft system under test: Based on the transmission shaft system, determine the limit value of the surface linear velocity of the shaft system under test, i.e., the limit speed V; S12. Based on the limit rotational speed V of the measured shaft system, set a measuring range of the laser Doppler vibrometer, wherein the measuring range of the laser Doppler vibrometer is greater than or equal to the limit rotational speed V of the measured shaft system.

6. The laser Doppler vibrometer signal optimization method for transmission shaft torsional vibration measurement according to claim 1, characterized in that: The filtering bandwidth of the filter in step S34 is set to the instantaneous speed ω of the measured shaft system. t The filter order is set to 2, and the number of harmonic orders extracted is 10.

7. The laser Doppler vibrometer signal optimization method for transmission shaft torsional vibration measurement according to claim 3, characterized in that: The sampling rate F of the initial vibration signal in step S23 is s0 Greater than or equal to 25.6kHz; the sampling rate F of the vibration signal in step S31 s Greater than or equal to the first-order torsional vibration frequency f of the measured shaft system r The acquisition length of the vibration signal covers 15 to 30 cycles of the first-order torsional vibration harmonic of the measured shaft system.

8. The laser Doppler vibrometer signal optimization method for transmission shaft torsional vibration measurement according to claim 1, characterized in that: The interpolation function used in the interpolation in step S4 is a spline function and the interpolation step size is 0.2Δy.

9. The laser Doppler vibrometer signal optimization method for transmission shaft torsional vibration measurement according to claim 2, characterized in that: The number of decomposition modes of the integrated empirical mode decomposition algorithm in step S52 is 10, the number of integrations is 20, and the added noise amplitude index is 0.4σ, where σ represents the residual component res m (t) standard deviation; the pulse amplitude detection threshold A in step S53 min The 85% to 95% quantiles of the envelope signal AM1(t) are taken; the influence interval length coefficient a in step S54 is taken to be 3 to 5; and the filter length coefficient b in step S55 is taken to be an even number between 6 and 12.

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