Theoretical, numerical and experimental analysis of a planar wobble motor driven by shape memory alloy (SMA)wires

Nowadays wobble motors are widely utilized as actuators with high torque rotary motion producing capability without the need for external gearbox. This study contains theoretical, numerical and experimental analysis of a planar wobble motor with compliant mechanism driven by shape memory alloy (SMA) wires. The cyclic expansion and contraction of SMA wires is converted to the plane curvilinear motion with circular path and then to the continuous unlimited rotary motion by means of a compliant mechanism and a gear system consisting of an internal and an external gear. After gear system designing based on achievable motion range caused by SMA wires length change, the relations between output torque, geometrical properties of motor and stress in SMA wire were derived. Also compliant mechanism parameters consisting of length, height, thickness and number of flexures were analyzed with the aim of mechanism stiffness calculating. Then the frequency analysis with finite element method is performed to investigate structural robustness and operational stability of designed mechanism. The designed motor is fabricated as a prototype to investigate its operational feasibility and working performances. The experimental results demonstrate motor capability in producing unlimited continuous rotary motion and repeatability of maximum output torque. The Maximum output torque was measured as 29.9, 32.7 and 34. 3mN.m for 1.6, 1.8 and 2v applied voltages respectively. With consideration of motor characteristics, it is appropriate for high torque and low speed applications with limited work space.