A Harmonic Movable Teeth Drive System Integrated With Shape Memory Alloys

A harmonic movable teeth drive system integrated with shape memory alloys(SMA)and movable teeth drive is proposed in this study,which uses SMA wires to drive movable teeth drive system and realize torque output.The drive integrates SMA wires with movable teeth drive system,both driving and sensing properties of SMA wires,and reduction function of movable teeth drive system are used.It could realize high torque output with a low speed,and has the advantages of small size and measuring at the same time.It will have a broad application prospect in the aerospace,bio-medical,and micro robot technology,etc.In this paper,structure design of the system was carried out,and its working principles were introduced.According to the theory of movable teeth drive,parameter design of the movable teeth drive system was done,dimensions of the movable teeth rack were determined.According to the SMA wire driving model,performance of the SMA driving part had been designed,stiffness of the bias springs was determined.According to the geometric model of the movable teeth drive system,the formulas of output torque were established.Combining with constitutive equations and heat conduction differential equations of the SMA wire,static forces of the system was analyzed.The forces on wave generator and movable teeth were solved,with output torque formulas,changes of the output torque with time were obtained,and influences of the heating currents amplitude and phase difference,and the cooling mode of SMA wires on output torque were analyzed.Based on Hertz theory,the elastic contact vibration model of movable tooth was established.According to Newton’s second law,motion differential equations of the wave generator were established.The contact resonance frequency caused by the elastic contact deformation of the movable tooth was solved,and the vibration characteristics of movable tooth and wave generator were analyzed.Results show that the movable tooth has a high frequency attenuation vibration in the meshing process,and its vibration noise is small.Due to the self damping of SMA wires and the existence of viscous damping,the phasetrack of wave generator is a spiral approach toward the origin.The friction heat flux between movable tooth and center wheel was calculated,and distributions of the frictional heat flow were obtained.The heat conduction differential equation and thermal boundary conditions of central wheel were given.A finite element model of central wheel thermal analysis was established in ABAQUS,and the heat flux distributions of central wheel’s tooth profile surface were obtained.Studies show that the heat flow is mainly distributed near the inflection point of central wheel’s tooth profile curve.Prototype of the system was produced and assembled,resistance of the heating circuit was measured,and a principle test of the system was completed.According to the measured resistance of heating circuit and the heating current needed,output voltage of the signal generator can be adjusted.