Shape memory alloy rotary actuator for CubeSat deployable structures

Abstract

Small satellites have lowered the barrier to entry for space-bound science and technology demonstrations. However, the small form factor requires extremely low size, weight, and power for any on-board hardware. Precision actuation of deployable structures has previously been achievable only through low SWaP single-use actuators or motor-driven, high SWaP multiple-use actuators. The Folded Lightweight Actuated Positioning System has the potential to provide an ultra-lightweight multiple-use actuator by using a Joule-heated shape memory alloy-based hinge. The hinge uses two shape memory alloy strips which are trained in opposite directions and mounted into a rotary actuator. Two different shape memory alloy geometries are explored: a rectangular cross-section and a circular cross-section. The rectangular hinge actuates over a range of ±20° with an average power of 0.14 W. The circular hinge actuates over a range of ±23° with an average power of 0.073 W. A closed-loop controller uses pulse width modulation and encoder measurements to actuate the rectangular hinge to within 2' of the desired angle.