Method for predicting storage life of ultrasonic motor based on locked-rotor torque simulation

Abstract

The present invention discloses a method for predicting the storage life of an ultrasonic motor based on locked-rotor torque simulation, which includes 7 steps, namely Step 1, establishing a locked-rotor torque simulation model of the ultrasonic motor; Step 2, correcting the locked-rotor torque simulation model according to the measured results; Step 3, monitoring the change data of the piezoelectric constant of the stator assembly and the impedance resonance frequency of the whole machine during storage; Step 4, based on the change test data of the resonance frequency, inversely inferring the change of the pre-tightening force through modal analysis; Step 5, calculating the change of the locked-rotor torque according to the changes of the piezoelectric constant and the pre-tightening force; Step 6, modeling the degradation of the locked-rotor torque; Step 7, giving the prediction result of the storage life in combination with the failure criterion. The present invention uses non-destructive testing means combined with a simulation model to realize the prediction of the change of the locked-rotor torque and the storage life, avoiding the wear of the friction pair between the stator assembly and the rotor assembly and the damage to the storage life of the motor, and correcting the simulation model multiple times to ensure the accuracy of predicting the storage life of the motor.

Description

Technical Field

[0001] The present invention relates to the technical fields of aerospace and ultrasonic motors, and particularly to a method for predicting the storage life of an ultrasonic motor based on stall torque simulation. Background Art

[0002] An ultrasonic motor is a new type of motor, which has the advantages of small size, light weight, large torque / weight ratio, power-off self-locking, and no electromagnetic interference. The core component of an ultrasonic motor is a piezoelectric ceramic, which is pasted on the stator elastomer. Under the drive of an alternating voltage in the ultrasonic frequency band (greater than 20 kHz), through the inverse piezoelectric effect, special vibrations are generated on the tooth surface of the stator, and then the rotor is driven to rotate under the action of friction. Ultrasonic motors do not require coils, magnets, or reducers, which is essentially different from traditional electromagnetic motors. This is the fundamental reason for many advantages of ultrasonic motors and determines that ultrasonic motors have important applications in civil and military fields such as aerospace, precision instruments, and intelligent robots. The ultrasonic motors have been applied to the American Mars rovers "Opportunity" and "Curiosity", and China's Chang'e-5 and Zhangheng-1 detectors.

[0003] With the continuous improvement of the life and reliability requirements of various civil and military products, the scenarios of long-term storage of ultrasonic motors are increasing. For example, an ultrasonic motor used in a certain missile requires a storage life of 18 years, and Chang'e-5 was stored on the ground for 3 years before launch. During the long-term storage process, ultrasonic motors are prone to performance drift and creep, such as the decrease of the piezoelectric constant of the piezoelectric ceramic and the pre-tightening force, which directly affect the working performance after storage. Therefore, it is very important to estimate the performance degradation and storage life of ultrasonic motors during storage for whether the tasks can be successfully completed after the storage period.

[0004] Currently, the storage life of ultrasonic motors is mainly evaluated by the method of storing, testing, and evaluating simultaneously, that is, the performance parameters such as the resonance frequency and stall torque of the ultrasonic motor are intermittently tested during the storage process. Among them, the stall torque is a performance that directly reflects the driving ability of the ultrasonic motor and is also the main parameter determining the storage life. By obtaining the change rules of these parameters, it is possible to predict the storage life of the ultrasonic motor. However, a major drawback of this method is that when the motor is stalled, the stator assembly and the rotor assembly are in a state of severe friction, which has an obvious impact on the life of the ultrasonic motor. Multiple tests of the stall torque during the storage process will lead to the distortion of the predicted storage life results. Imagine that if the change of the stall torque can be accurately obtained through non-destructive testing methods such as impedance frequency response testing and piezoelectric constant testing for ultrasonic motors, and then the storage life can be predicted, it will be a promising technical solution. Summary of the Invention

[0005] The object of the present invention is to propose a method for predicting the storage life of an ultrasonic motor based on locked-rotor torque simulation to solve the above problems. The core of the present invention lies in how to obtain the locked-rotor torque change data based on locked-rotor torque simulation and by integrating data obtained from non-destructive testing methods for ultrasonic motors such as impedance frequency response testing and piezoelectric constant testing, and then obtain the storage life through locked-rotor torque degradation modeling.

[0006] The present invention adopts the following technical solutions, where the simulation analysis is all based on the ANSYS-Workbench commercial finite element software:

[0007] Refer to Figure 1 , and the steps of the method for predicting the storage life of an ultrasonic motor based on locked-rotor torque simulation are as follows in sequence:

[0008] Step 1, establish a locked-rotor torque simulation model of the ultrasonic motor;

[0009] The specific sub-steps of this step are shown in Figure 2 ;

[0010] Sub-step 1A: Establish a finite element model of the stator assembly and rotor assembly of the ultrasonic motor, complete the mesh division, and set the material parameters, piezoelectric ceramic partitions, contact pairs, and constraint boundaries;

[0011] Specifically, refer to Figure 3 and Figure 4 , the stator assembly includes an elastomer and piezoelectric ceramics, the rotor assembly includes a rotor disk and a friction material, and the teeth of the elastomer are in contact with the friction material;

[0012] First, complete the mesh division, and equivalent the stator assembly and rotor assembly with many discrete small elements and their nodes;

[0013] Set the material parameters of the elastomer, piezoelectric ceramics, and friction material, including density, elastic modulus, and Poisson's ratio; set the material parameters of the piezoelectric ceramics, including elastic constants, piezoelectric constants, relative permittivity, and density;

[0014] Set the piezoelectric ceramic partitions, refer to Figure 5 , set the polarization directions of the positive polarization region and negative polarization region of the piezoelectric ceramics to be opposite, and set the non-polarized region and the solitary pole as the non-polarized region, that is, without piezoelectricity;

[0015] Set the contact pairs, set the contact pair between the stator assembly and the rotor assembly as a separable contact, and set other contact pairs as bonded contacts;

[0016] Set the constraint boundaries, refer to Figure 6 , and set the stator mounting hole as a fixed constraint.

[0017] Sub-step 1B: Apply a pre-tightening force, complete the static analysis, and obtain the prestress field of the ultrasonic motor in the non-operating state;

[0018] Specifically, apply a pre-tightening force pointing to the stator assembly on the pre-tightening force application surface, and complete the solution analysis in the static analysis module of the ANSYS-Workbench software to obtain the prestress field of the ultrasonic motor caused by the pre-tightening force.

[0019] Sub-step 1C: Complete the modal analysis based on the prestress field to obtain the working wave number, the vibration mode, and the resonant frequency corresponding to the working wave number;

[0020] Specifically, transfer the solution result of the static analysis module to the modal analysis module in the ANSYS-Workbench software, so that the prestress field obtained in sub-step 1B is automatically loaded in the modal analysis module;

[0021] Complete the solution analysis in the modal analysis module of the ANSYS-Workbench software to obtain the vibration mode and the resonant frequency corresponding to the case where the wave number of the traveling wave of the ultrasonic motor stator is equal to the designed working wave number.

[0022] Sub-step 1D: Based on the modal analysis results, apply a voltage load, complete the harmonic response analysis, and obtain the dynamic response at the resonant frequency;

[0023] Specifically, transfer the solution result of the modal analysis module to the harmonic response analysis module in the ANSYS-Workbench software, and all subsequent work in this sub-step is completed in the harmonic response analysis module;

[0024] Set the upper and lower bounds of the analysis frequency band and the frequency solution interval; here, the analysis frequency band should include the resonant frequency corresponding to the working wave number of the ultrasonic motor, and the frequency solution interval should be small enough to ensure that the error between a certain frequency solution point and the resonant frequency is not greater than 50 Hz;

[0025] In Figure 5 apply voltage loads with a phase difference of 90 degrees to regions A and B of the piezoelectric ceramics respectively;

[0026] Turn on the node force option and the reaction force calculation option in the output control;

[0027] In the damping control, set the damping ratio, and generally set the initial value to 0.01;

[0028] Complete the solution analysis to obtain the dynamic response of each frequency solution point of the ultrasonic motor;

[0029] Regard the dynamic response result at the frequency solution point closest to the resonant frequency as the dynamic response result at the resonant frequency.

[0030] Sub-step 1E: Extract the normal contact force between any tooth and the rotor assembly when the tooth moves to the peak of the stator traveling wave at the resonant frequency;

[0031] Specifically, observe the dynamic response of the ultrasonic motor at the frequency solution point closest to the resonant frequency, and adjust the movement positions of each tooth by modifying the phase angle at this frequency;

[0032] Reference Figure 7 , when any tooth moves to the peak of the stator traveling wave, extract the normal contact force at the position of this tooth from the reaction force results of the contact pair between this tooth and the rotor assembly, and denote it as F 0 ;

[0033] Sub-step 1F: Calculate the total normal contact force and the stall torque between the stator assembly and the rotor assembly;

[0034] Specifically, calculate the total normal contact force F between the stator assembly and the rotor assembly through Equation (1):

[0035] F = kF 0 (1)

[0036] In the formula, k is the working wave number of the ultrasonic motor; calculate the stall torque T between the stator assembly and the rotor assembly through Equation (2):

[0037] T = μF (2)

[0038] In the formula, μ is the friction coefficient of the contact pair material between the stator assembly and the rotor assembly, and the initial value is taken as the value in the manual or the empirical value.

[0039] Step 2: Modify the stall torque simulation model according to the measured results;

[0040] Specifically, compare the measured impedance frequency response and stall torque data of the ultrasonic motor before storage with the resonant frequency and stall torque obtained by simulation respectively; reference Figure 8 , the measured resonant frequency data can be obtained through the measured impedance frequency response curve; further, adjust the damping ratio to correct the simulation result of the resonant frequency until the error between the simulation and the measured results is not greater than 2%; then, adjust the friction coefficient to correct the simulation result of the stall torque until the error between the simulation and the measured results is not greater than 5%; finally, record the corrected damping ratio and friction coefficient.

[0041] Step 3: Monitor the change data of the piezoelectric constant of the stator assembly and the impedance resonant frequency of the whole machine of the ultrasonic motor during storage;

[0042] Specifically, monitor the piezoelectric constant of the piezoelectric ceramic in the stator assembly of the ultrasonic motor and the resonant frequency data of the impedance frequency response of the whole machine during storage; the monitoring time span is not less than 1 / 5 of the storage life requirement value, and the number of monitoring time points is not less than 5.

[0043] Step 4: Based on the test data of the resonant frequency change, inversely deduce the preload force change through modal analysis;

[0044] Specifically, substitute the piezoelectric constant change data of the ultrasonic motor stator assembly measured in Step 3 and the corrected damping ratio data in Step 2 into the ultrasonic motor modal analysis simulation model described in Step 1;

[0045] Adjust the simulation results of the resonant frequency in the preload force corrected modal analysis at each time point until the error between the resonant frequency simulation and the measured results at each time point is no greater than 2%;

[0046] Record the corrected preload force at each time point to obtain the preload force change data at each time point.

[0047] Step 5: Calculate the change in the stall torque according to the changes in the piezoelectric constant and the preload force;

[0048] Specifically, substitute the corrected damping ratio and friction coefficient data obtained in Step 2, the piezoelectric constant data of the piezoelectric ceramics in the stator assembly at each time point obtained in Step 3, and the preload force data at each time point obtained in Step 4 into the ultrasonic motor stall torque simulation model described in Step 1, and calculate the stall torque at each time point, that is, obtain the change in the ultrasonic motor stall torque.

[0049] Step 6: Model the degradation of the stall torque;

[0050] Specifically, refer to Figure 9 , fit the degradation law of the stall torque at each time point monitored during storage obtained in Step 5 to obtain a fitting line with a fitting degree not less than 0.95;

[0051] Step 7: Give the storage life prediction result in combination with the failure criterion.

[0052] Specifically, extrapolate on the time axis according to the fitting line, and draw the failure threshold line according to the failure criterion to obtain the intersection point of the fitting line and the failure threshold line. The time corresponding to this intersection point is the predicted storage life.

[0053] So far, the storage life prediction of the ultrasonic motor based on the stall torque simulation is completed.

[0054] Among them, the rotor assembly described in Step 1A may not include the friction material, that is, the rotor disk is in direct contact with the teeth of the elastic body, and the contact pair is set as a separable contact;

[0055] Among them, the wave number described in Step 1C may be an odd number not less than 15;

[0056] Among them, the frequency solving interval described in Step 1D may be a linear interval or a logarithmic interval;

[0057] Among them, the storage described in step 3 can be natural storage, storage test, or accelerated storage test;

[0058] Among them, the piezoelectric constant and resonance frequency monitoring data described in step 3 can be single values or average values of multiple tests;

[0059] Among them, the fitting method in step 6 can be linear fitting, polynomial fitting, logarithmic fitting, or exponential fitting.

[0060] In summary, due to the adoption of the above technical solutions, the beneficial effects of the present invention are as follows:

[0061] In this application, during the storage process, it is not necessary to test the locked-rotor torque. Only by relying on non-destructive testing means such as impedance frequency response testing and piezoelectric constant testing in combination with a simulation model can the prediction of the change in locked-rotor torque and storage life be realized, avoiding the wear of the friction pair between the stator assembly and the rotor assembly and the damage to the storage life of the ultrasonic motor. Moreover, by relying on multi-link data to correct the simulation model multiple times, it is ensured that the predicted results of the change in locked-rotor torque and storage life are accurate and reliable. Description of the Drawings

[0062] Figure 1 is the implementation flowchart of the present invention;

[0063] Figure 2 is the implementation sub-flowchart of step 1 of the present invention;

[0064] Figure 3 is a schematic diagram of the geometric model of the ultrasonic motor including the stator assembly and the rotor assembly for simulation;

[0065] Figure 4 is a sectional view of the geometric model of the ultrasonic motor including the stator assembly and the rotor assembly for simulation;

[0066] Figure 5 is a schematic diagram of the piezoelectric ceramic partition;

[0067] Figure 6 is a schematic diagram of the stator assembly for simulation;

[0068] Figure 7 is a schematic diagram of the deformation of the ultrasonic motor when any tooth moves to the peak of the stator traveling wave;

[0069] Figure 8 is a schematic diagram of the measured impedance frequency response curve;

[0070] Figure 9 is a schematic diagram of the locked-rotor torque degradation modeling; Detailed Embodiments

[0071] Next, in combination with the accompanying drawings in the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0072] Embodiment 1:

[0073] The following technical solutions are adopted in this embodiment, and all simulation analyses are based on the ANSYS-Workbench commercial finite element software:

[0074] Refer to Figure 1 , and the steps of the ultrasonic motor storage life prediction method based on the locked-rotor torque simulation are as follows in sequence:

[0075] Step 1, establish a locked-rotor torque simulation model of the ultrasonic motor;

[0076] For the specific sub-steps of this step, refer to Figure 2 ;

[0077] Sub-step 1A: Establish a finite element model of the stator assembly and rotor assembly of the ultrasonic motor, complete the mesh division, and set the material parameters, piezoelectric ceramic partitions, contact pairs, and constraint boundaries;

[0078] Specifically, refer to Figure 3 and Figure 4 , the stator assembly includes an elastomer and piezoelectric ceramics, the rotor assembly includes a rotor disk and a friction material, and the teeth of the elastomer are in contact with the friction material;

[0079] First, complete the mesh division, and equivalent the stator assembly and rotor assembly with many discrete small elements and their nodes;

[0080] Refer to Table 1 and Table 2, and set the material parameters of the elastomer, piezoelectric ceramics, and friction material, including density, elastic modulus, and Poisson's ratio; set the material parameters of the piezoelectric ceramics, including elastic constants, piezoelectric constants, relative dielectric constants, and density;

[0081] Table 1 Basic material parameters

[0082] Name Material <![CDATA[Density kg / m 3 > <![CDATA[Elastic modulus N·m -2 > Poisson's ratio Stator QSn6.5 8800 <![CDATA[1.13×10 11 > 0.33 Rotor Titanium alloy 4620 <![CDATA[9.6×10 10 > 0.36 Piezoelectric ceramic PZT-8 7600 / /

[0083] Table 2 Piezoelectric ceramic anisotropic material parameters

[0084]

[0085] Set the piezoelectric ceramic partition, refer to Figure 5, the polarization directions of the positive and negative polarization regions of the piezoelectric ceramic are set to be opposite, and the non-polarized region and the solitary pole are set as non-polarized regions, that is, without piezoelectricity;

[0086] Set the contact pairs. The contact pair between the stator assembly and the rotor assembly is set as a frictionless contact (a type of separable contact), and other contact pairs are set as bonded contacts;

[0087] Set the constraint boundary, refer to Figure 6 , and set the stator mounting hole as a fixed constraint.

[0088] Sub-step 1B: Apply a pre-tightening force, complete the static analysis, and obtain the prestress field of the ultrasonic motor in the non-working state;

[0089] Specifically, apply a pre-tightening force of 120 N pointing to the stator assembly on the pre-tightening force application surface, and complete the solution analysis in the static analysis module of the ANSYS-Workbench software to obtain the prestress field of the ultrasonic motor caused by the pre-tightening force.

[0090] Sub-step 1C: Complete the modal analysis based on the prestress field, and obtain the vibration mode and resonance frequency corresponding to the working wave number;

[0091] Specifically, transfer the solution result of the static analysis module to the modal analysis module in the ANSYS-Workbench software, so that the prestress field obtained in sub-step 1B is automatically loaded in the modal analysis module;

[0092] Complete the solution analysis in the modal analysis module of the ANSYS-Workbench software. When the wave number of the stator traveling wave of the ultrasonic motor is 7, which is equal to the designed working wave number of 7, obtain the corresponding vibration mode and resonance frequency.

[0093] Sub-step 1D: Based on the modal analysis results, apply a voltage load, complete the harmonic response analysis, and obtain the dynamic response at the resonance frequency;

[0094] Specifically, transfer the solution result of the modal analysis module to the harmonic response analysis module in the ANSYS-Workbench software, and all subsequent work in this sub-step is completed in the harmonic response analysis module;

[0095] Set the upper bound of the analysis frequency band to 60 kHz, the lower bound to 20 kHz, and the frequency solution linear interval to 800, which can ensure that the error between a certain frequency solution point and the resonance frequency is not greater than 50 Hz;

[0096] In Figure 5 , apply voltage loads with a phase difference of 90 degrees and an amplitude of 90 V to regions A and B of the piezoelectric ceramic respectively;

[0097] Turn on the node force option and the reaction force calculation option in the output control;

[0098] In the damping control, set the damping ratio, and the initial value is set to 0.01;

[0099] Complete the solution analysis to obtain the dynamic responses of each frequency solution point of the ultrasonic motor;

[0100] Regard the dynamic response result at the frequency solution point of 40 kHz, which is the closest to the resonant frequency, as the dynamic response result at the resonant frequency.

[0101] Sub-step 1E: Extract the normal contact force between any tooth and the rotor assembly when the tooth moves to the peak of the stator traveling wave at the resonant frequency;

[0102] Specifically, observe the dynamic response of the ultrasonic motor at the frequency solution point of 40 kHz, which is the closest to the resonant frequency, and adjust the movement positions of each tooth by modifying the phase angle at this frequency;

[0103] Reference Figure 7 , when any tooth moves to the peak of the stator traveling wave, extract the normal contact force of 0.2 N at the position of this tooth from the reaction force results of the contact pair between this tooth and the rotor assembly, and denote it as F 0 ;

[0104] Sub-step 1F: Calculate the total normal contact force and the stall torque between the stator assembly and the rotor assembly;

[0105] Specifically, calculate the total normal contact force F between the stator assembly and the rotor assembly as 1.4 N through Equation (1):

[0106] F = kF 0 (1)

[0107] In the formula, k is the working wave number 7 of the ultrasonic motor; calculate the stall torque T between the stator assembly and the rotor assembly as 0.21 Nm through Equation (2):

[0108] T = μF (2)

[0109] In the formula, μ is the friction coefficient of the contact pair material between the stator assembly and the rotor assembly, and the initial value is taken as 0.15.

[0110] Step 2, correct the stall torque simulation model according to the measured results;

[0111] Specifically, compare the measured impedance frequency response and stall torque data of the ultrasonic motor before the accelerated storage test with the resonant frequency and stall torque obtained by simulation respectively; Reference Figure 8, the measured resonance frequency data can be obtained from the measured impedance frequency response curve; further, adjust the damping ratio to correct the simulation results of the resonance frequency until the error between the simulation and the measured results is no more than 2%; then, adjust the friction coefficient to correct the simulation results of the stall torque until the error between the simulation and the measured results is no more than 5%; finally, record the corrected damping ratio of 0.042 and the friction coefficient of 0.16.

[0112] Step 3, monitor the change data of the piezoelectric constant of the ultrasonic motor stator assembly and the impedance resonance frequency of the whole machine during storage;

[0113] Specifically, monitor the piezoelectric constant of the piezoelectric ceramic in the ultrasonic motor stator assembly and the resonance frequency data of the impedance frequency response of the whole machine during the accelerated storage test. The monitored data of the piezoelectric constant and the resonance frequency are the average values of 3 tests; the monitoring time span is 1 / 5 of the required value of the accelerated storage life, and the number of monitoring time points is 5.

[0114] Step 4, based on the test data of the resonance frequency change, inversely deduce the preload change through modal analysis;

[0115] Specifically, substitute the change data of the piezoelectric constant of the ultrasonic motor stator assembly measured in Step 3 and the corrected damping ratio data in Step 2 into the ultrasonic motor modal analysis simulation model described in Step 1;

[0116] Adjust the preload at 5 time points to correct the simulation results of the resonance frequency in the modal analysis until the error between the resonance frequency simulation and the measured results at 5 time points is no more than 2%;

[0117] Record the corrected preload at 5 time points to obtain the preload change data at 5 time points.

[0118] Step 5, calculate the change of the stall torque according to the changes of the piezoelectric constant and the preload;

[0119] Specifically, substitute the corrected damping ratio and friction coefficient data obtained in Step 2, the piezoelectric constant data of the piezoelectric ceramic in the stator assembly at 5 time points obtained in Step 3, and the preload data at 5 time points obtained in Step 4 into the ultrasonic motor stall torque simulation model described in Step 1, calculate the stall torque at 5 time points, that is, obtain the change of the ultrasonic motor stall torque.

[0120] Step 6, model the degradation of the stall torque;

[0121] Specifically, refer to Figure 9 , perform a parabola (quadratic polynomial) fitting on the degradation law of the stall torque at 5 time points monitored in the accelerated storage test obtained in Step 5 to obtain a fitting line with a fitting degree of 0.99;

[0122] Step 7, give the storage life prediction result in combination with the failure criterion.

[0123] Specifically, extrapolate along the time axis according to the fitting line, and draw the failure threshold line of 0.15 Nm according to the failure criterion. Obtain the intersection point of the fitting line and the failure threshold line, and the time corresponding to this intersection point is the predicted storage life, which is about 10 years.

[0124] Thus, the prediction of the storage life of the ultrasonic motor based on the locked-rotor torque simulation is completed.

[0125] In summary, for the method for predicting the storage life of the ultrasonic motor based on the locked-rotor torque simulation provided in this embodiment, it is not necessary to test the locked-rotor torque during the storage process. Only relying on non-destructive testing means such as impedance frequency response testing and piezoelectric constant testing in combination with the simulation model can realize the prediction of the change of the locked-rotor torque and the storage life, avoiding the wear of the friction pair between the stator assembly and the rotor assembly and the damage to the storage life of the ultrasonic motor. Moreover, relying on the data of multiple links to correct the simulation model multiple times ensures the accuracy and reliability of the predicted results of the change of the locked-rotor torque and the storage life.

[0126] The above description of the embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. Method for predicting storage life of ultrasonic motor based on locked-rotor torque simulation, characterized in that, it includes the following steps: Step 1, establish a locked-rotor torque simulation model of the ultrasonic motor, specifically including the following sub-steps: Sub-step 1A: Establish a finite element model of the stator assembly and rotor assembly of the ultrasonic motor, complete mesh division, and set material parameters, piezoelectric ceramic partitions, contact pairs, and constraint boundaries; Sub-step 1B: Apply a pre-tightening force, complete a static analysis, and obtain the prestress field of the ultrasonic motor in the non-working state; Sub-step 1C: Complete a modal analysis based on the prestress field, and obtain the vibration mode and resonance frequency corresponding to the working wave number; Sub-step 1D: Based on the modal analysis results, apply a voltage load, complete a harmonic response analysis, and obtain the dynamic response at the resonance frequency; Sub-step 1E: Extract the normal contact force between any tooth and the rotor assembly when it moves to the peak of the stator traveling wave at the resonance frequency; Sub-step 1F: Calculate the total normal contact force and locked-rotor torque between the stator assembly and the rotor assembly; Step 2, correct the locked-rotor torque simulation model according to the measured results; Step 3, monitor the change data of the piezoelectric constant of the stator assembly and the impedance resonance frequency of the whole machine during storage of the ultrasonic motor; Step 4, based on the monitored resonance frequency change data, inversely deduce the change of the pre-tightening force through modal analysis; Step 5, calculate the change of the locked-rotor torque according to the changes of the piezoelectric constant and the pre-tightening force; Step 6, establish a locked-rotor torque degradation model; Step 7, give the storage life prediction result in combination with the failure criterion.

2. The method for predicting storage life of an ultrasonic motor based on locked-rotor torque simulation according to claim 1, characterized in that, the working wave number described in sub-step 1C is an odd number not less than 15.

3. The method for predicting storage life of an ultrasonic motor based on locked-rotor torque simulation according to claim 1, characterized in that, the resonance frequency solution interval in sub-step 1D is a linear interval or a logarithmic interval.

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