A Continuous Rotatory Motor Actuated by Multiple Segments of Shape Memory Alloy Wires

The primary objective for this paper is to present the development of a continuous rotatory motor actuated by shape memory alloy wires (SMA motor). The current electrical motors, which are based on electromagnetic induction principle, are very suitable to drive systems working with high rotation speed. When the general electrical motor is used in the cases for low rotation speed and large torque output, the general solution is to add reducers, which of course increases the volume and weight of the driving sources. In some industries, especially in aerospace, the need for electrical motors with low rotation speed and large torque output, and at same time with light weight become more urgently.

The current actuators driving by SMA wires usually output a linear or bending movement, and the movement is discontinuous since the SMA wires need to be cooled after every motivation. A ratchet-pawl mechanism was employed in this investigation to transform the linear movement into the rotating one, and several mechanisms are installed along a shaft in parallel to output a continuous rotating movement. The parameters of the mechanism including diameter and length of SMA wire, stiffness and geometry size of the bias spring are designed based on Liang’s constitutive model and experimental data. 

After design and analysis, a prototype of SMA motor was fabricated and series of tests were carried out. The results show that the average rotation speed of the SMA motor is 0.28 r/min, and the output torque of the SMA motor is 1008N.mm. Moreover, cycling performance tests for single mechanism were carried out and the results show that the rotating angle firstly decreases and finally keeps stable as the actuation going on. The SMA rotatory motor which possessing the advantages of low rotation speed and large torque will have great potential in industry applications.