Study On Dynamic Characteristics And Reliability Of Permanent Magnet Cutting Transmission System In Shearer

Drum shearer is the core equipment of mechanized"three machines matching"in fully mechanized coal face.With the continuous improvement of coal mine safety production and high-yield and high-efficiency requirements,higher requirements are put forward for the working efficiency,working condition adaptability and reliability of drum shearer.Cutting transmission system is the key part for coal crushing of shearer.The traditional shearer cutting transmission system mainly adopts the transmission mode of"asynchronous motor+three-stage spur gear reduction+planetary gear deceleration+cutting drum".However,under the action of heavy load and strong impact load caused by hard inclusions or stone layers in coal seam,the planetary deceleration mechanism inside the cutting drum is prone to various faults.Adopting low-speed and high-torque permanent magnet synchronous motor(PMSM)combined with three-stage gear reduction mechanism to drive the cutting drum can remove the planetary gear reduction transmission link,shorten the transmission chain,reduce the failure rate and improve the transmission efficiency of the system,which meets the performance requirements of high power,high efficiency and few failures of the drum shearer.However,with the reduction of the gear mechanism transmission ratio,the dynamic load inside and outside of the system has a great incentive effect on the gear reduction mechanism and PMSM,which influences the dynamic performance and reliability of the system.In addition,the multi-energy domain and multi-parameter coupling relationship between the low-speed high-torque PMSM and the gear transmission system easily leads to the instability of the system under the action of load impact and internal parameter excitation,which restricts the improvement of the transmission performance and reliability.Therefore,in order to achieve the reliable,stable and efficient cutting work of shearer under complex working conditions,this dissertation funded by the National Natural Science Foundation of China,combined with the performance characteristics of PMSM and the end drum load characteristics,made an in-depth study on the dynamic characteristics and reliability of permanent magnet cutting transmission system in shearer.The research work mainly includes:(1)The working principle and structure of permanent magnet cutting transmission system in shearer are expounded.Based on lumped parameter method and Kelvin-Vogit model,a translation-rotation dynamic model of three-stage gear reduction system with variable speed and load is established.According to the variation law of permanent magnet flux linkage under the action of space harmonic and cogging effect,the equivalent circuit mathematical model of PMSM is established by the equivalent circuit method and the control strategy of_di(28)0.The coal breaking mechanism of the cutting drum pick is analyzed,and the load model of the cutting drum is constructed accordingly.On this basis,according to the coupling relationship of PMSM,gear reduction system and cutting drum,the electromechanical coupling global dynamics model of permanent magnet cutting transmission system is established.Finally,according to the principle of similarity and magnetic powder dynamometer,an experimental platform of small-scale permanent magnet cutting transmission system is built,and the loading characteristics and speed stability of the experimental system under various working conditions are tested and analyzed.(2)The natural frequencies and modal shapes of the permanent magnet cutting transmission system are studied.The variation law of natural frequency under the influence of transmission shaft torsional stiffness,gear meshing stiffness and bearing supporting stiffness is analyzed.The expressions of torsional electromagnetic stiffness and torsional electromagnetic damping of PMSM are derived by frequency response function method,and the influence law of PMSM electromagnetic effect on the modal characteristics of the system is revealed.The potential resonant speed and excitation source of the system in the variable speed range is identified using Campbell diagram.Combined with modal energy method and sweep frequency analysis method,the resonant speed is discriminated.Furthermore,the dynamic response characteristics of gear system and PMSM under the coupling effect of gear wear and resonant speed are explored.Finally,the correctness of the proposed system coupling dynamic model and dynamic characteristic simulation analysis is verified by the small-scale permanent magnet cutting transmission system experimental platform.(3)Considering the coupling effect of the internal electromagnetic vibration and the external shaft torsional vibration,the PMSM rotor shaft electromechanical coupling torsional dynamic model of the permanent magnet cutting transmission system is established from the angle of energy.The accurate analytical solution of PMSM rotor torsional vibration is deduced by multi-scale method,and the influence of electromechanical parameters on nonlinear response characteristics is revealed.The motor rotor stable region under the influence of cutting load is determined by numerical method,and the suppression effect of the time-delay feedback controller parameters on the motor rotor torsional vibration is discussed.Aiming at the electromechanical coupling vibration of PMSM stator system,based on conformal transformation method,the electromagnetic force and magnetostrictive force acting on the motor stator core teeth are analyzed.The coupling vibration mechanism of stator silicon steel core and amorphous alloy core under electromechanical parameters and sudden load is proved,and the resonance speed of stator silicon steel core and amorphous alloy core in the system speed change range is identified.Finally,based on the small-scale permanent magnet cutting transmission system experimental platform,the correctness of the electromechanical coupling relationship and the amplitude-frequency response characteristics analysis is verified.(4)Combining the probability statistics theory with the dynamic model of the permanent magnet cutting transmission system,the random dynamic load of each gear pair under the influence of external random drum load,electromechanical coupling and other factors are obtained.The action process of gear pair random stress is described by rain flow counting method and stationary binomial random process.Based on the nonlinear cumulative damage criterion and the modified P-S-N curve,the dynamic reliability model of permanent magnet cutting transmission system is established,which takes into account the random load number and nonlinear strength degradation.The developmental rule of transmission system reliability under the influence of rated working condition,different rotational speeds and gear wear is discussed.On this basis,according to Copula theory,the failure modes of gears and the correlation among different gears are described.The edge distribution of gear life is determined by kernel density estimation.Copula function is determined by binary frequency histogram and maximum likelihood function,and unknown parameters are estimated.On this basis,from the failure mode of single gear to the gradual analysis of gear transmission system,the influence of failure correlation and failure independence on system reliability is discussed.This dissertation has 132 figures,19 tables and 193 references.