Research On An Electromechanical Integrated Harmonic Piezodrive System

Electromechanical integrated harmonic piezodrive system(EIHPS)is a novel drive which integrates piezoelectric(PZT)driving,harmonic drive and movable tooth drive.The EIHPS overcomes shortcomings such as quick-wearing,short-life(for friction-type PZT motor)and small ouput torque(for non-contact PZT motor),has merits of fast response,long lifetime,low speed large torque,no electromagnetic interference,etc.So,the EIHPS has wide application prospect in fields of aerospace,biomedicine,precision positioning,micro-robot,etc.This dissertation analyzes the working principle of the EIHPS.And then,the electromechanical coupling statics equations are set up,the working process and the force changed with rotation angle of the movable tooth system are analyzed.Besides,the law of output torque changes with voltage and other parameters are also investigated.The study found that the output torque generates cyclical fluctuations with period of specific angle.On the basis of piezoelectricity,continuous body vibration theory and discrete body vibration theory,the electromechanical coupling dynamic model of EIHPS is built,the electromechanical coupling free vibration equations are deduced.The natural frequencies and modal shapes are solved,and the impact of parameters on coupling frequencies is analyzed.In addition,the influence of system coupling on frequencies under different modes is investigated.The research found that the close modes frequencies of driving part and total vibration mode frequencies of transmission part are changed with system coupling.For the three conditions(driving part,drive part and system coupling),the forced vibration dynamic equations of EIHPS under PZT incentive are established,respectively.In addition,the interaction effect law of driving and drive parameters on coupling forced vibration of the coupling system is discussed.The result show that the impact of parameters of driving part and drive part on forced vibration mainly in altering the amplitude.Considering non-linear PZT effect from PZT stack and non-linear effect caused by the changing of meshing movable teeth,non-linear dynamic models and dynamic equations of driving part and drive part are established.Using Linz Ted-Poincaré method,non-linear approximate solutions of weak non-linear free vibration and forced vibration near to resonance are deduced.Applying perturbation method,non-linear approximate solutions of forced vibration far from resonance are deduced.Besides,amplitudefrequency characteristic,displacement response and their parameters influence are given.The research found that the influence of non-linear PZT effect from PZT stack and non-linear effect caused by the changing of meshing movable teeth on the system is prominent,and the impact of the number of meshing movable teeth on non-linear is large.The effect of system parameters on chaotic vibration of EIHPS is studied,and the system chaotic vibration bifurcation diagram when parameters altering is given.When the bifurcation parameter are constant,the status of chaotic motion is determined through time-domain diagram,phase diagram,Poincaré diagram and power spectrum diagram,in addition,the generation conditions of chaotic vibration are indicated.The prototype of EIHPS is designed and fabricated.Utilizing test system,the maximum ouput torque of the prototype is 0.383 Nm when the peak-to-peak voltage is 150 V.Using hammer vibration test system to test the natural frequencies of the prototype,result show that the maximum error between the experimental result and theoretical analysis is 12.47%.And the experiments show the validity of the theoretical analysis.