| Compared with other planetary transmission types,3K planetary transmission has a larger ratio range and more compact structure,which has a broad application prospect in modern intelligent equipment.The motor-3K planetary gear system for intelligent equipment has rich excitation parameters and complex dynamic characteristics due to its structural specificity and the machine-electric-magnetic coupling relationship between motor and reducer.Meanwhile,as the 3K planetary transmission with a large speed ratio often runs in low speed and heavy load working conditions,the complex working environment often makes the key components fail and affects the normal operation of mechanical equipment.Therefore,the dynamic research on the motor-3K planetary gear system and the analysis of the electromechanical signal characteristics under the condition of failure have important theoretical significance and engineering application value for improving the stability of the system and reducing the operation risk.Given the shortcomings in the existing research of 3K planetary gear transmission,this thesis takes the motor-3K planetary gear system suitable for AGV hub and robot joint as the research object.Through the analysis of dynamics,the electromechanical coupling dynamic characteristics under the combined action of internal parameters such as timevarying meshing stiffness,manufacturing error,and electromagnetic torsional stiffness,as well as the external working conditions such as the speed change and impact load are analyzed.Based on this,taking the tooth root crack as an example,the electromechanical signal characteristics under gear fault are mainly studied.These results can provide theoretical guidance for the dynamic design,application,and fault diagnosis technology of motor-3K planetary gear system.The main research contents of this thesis are as follows:(1)Considering the time-varying meshing stiffness,backlash,damping,support,manufacturing error,and meshing phase,a translation-torsion lumped parameter dynamic model of gear transmission is established.Then,an electromechanical coupling dynamic model of the 3K planetary gear system is established,by taking care of the electricmagnetic coupling and magnetic-mechanical coupling relationship between the motorreducer system and integrating the dynamic model of the gear transmission part and the equivalent circuit model of the permanent magnet synchronous motor.(2)The actual tooth profile of internal and external gears,including dedendum transition curve,is deduced respectively according to the situation that the outer gear is machined by rack cutter and the inner gear ring is machined by pinion cutter.The analytical models of meshing stiffness for internal and external gear pairs which is normal or with a crack are established considering coupling deformation between adjacent teeth and the effect of crack expansion on fillet foundation and tooth deformation.The proposed model is compared with the finite element method and the effect of different crack parameters on the engagement stiffness is analyzed.The correctness of the proposed model is proved.(3)Based on the established electromechanical coupling dynamic model,the inherent mode and mode shapes of the system are analyzed by solving the free vibration equation of the system numerically.The influence of time-varying meshing stiffness and motor magnetic field on the inherent characteristics of the system is explored.By means of Campbell diagram,frequency sweep,time-frequency analysis and modal energy analysis,the effects of motor speed,load impact and manufacturing error of each component on the dynamic characteristics of the system are studied.The resonance speed region and structural weak links were successfully identified,and the dynamic load sharing performance of the gear system under the different eccentric errors of each transmission component and internal or external operating conditions were revealed.(4)The transverse vibration signal expression of the 3K planetary gearbox is derived by considering the influence of transmission path and force direction projection function on excitation force.By means of variational mode decomposition,cepstrum,and other signal analysis methods,the characteristics of box transverse vibration signal and end torsional signal under different root crack faults are studied.Compared with the model only considering the reducer,the dynamic model considering the coupling between the motor and the reducer can better reflect the actual box transverse vibration characteristics.The torsional vibration signal is less affected by the rotating frequency of the carrier and motor,and its frequency sideband composition is relatively simple.However,due to the large transmission ratio of the 3K planetary reducer and the huge mass and rotational inertia difference between the sun gear and the output gear ring 0),it is difficult to identify the sun gear fault through the torsional vibration signal.The fault feature recognition of the simulation signal under variable speed is realized by using the method of combining equal angle resampling with variational mode decomposition,which verifies the feasibility of the electromechanical coupling model proposed in this thesis to simulate the fault signal under non-stationary conditions.(5)In order to better understand the motor stator current characteristics of under gear fault,the AM-FM mathematical model of stator current is deduced by analyzing the mechanical-electromagnetic-magnetic interaction between motor and reducer.The characteristics of current signals under different crack faults are analyzed by using the time-shift superposition spectrum and envelope spectrum.The analysis results of the current signal obtained by the electromechanical coupling model are consistent with those obtained by the AM-FM mathematical model,which verifies the rationality of the electromechanical coupling model proposed in this thesis.By selecting 14 statistical indexes in time domain and frequency domain,the current signals under different crack propagation degrees are analyzed.The results show that the monitoring performance of frequency domain index is better than that of time domain index.Related research can provide theoretical basis for early crack propagation monitoring and fault diagnosis.(6)An experimental platform of the 3K planetary gear transmission system driven by a permanent magnet synchronous motor is built,and the dynamic response experiments under the conditions of different gear crack faults are carried out.The correctness of electromechanical coupling model and the theoretical results of electromechanical signal characteristics under crack fault is verified by comparison. |
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