Miniature parallel manipulator using TiNiCu shape-memory-alloy microactuators

This paper reports a 30 mm × 30 mm × 34 mm mini-scale parallel manipulator using shape-memory-alloy (SMA) microactuators that poses various advantages such as a large actuation force and a high robustness with a simple mechanical structure. The developed parallel manipulator that uses four SMA actuators and four bias springs is able to perform linear z-axis movement and tilting motions. Each actuator is driven by pulse width modulation (PWM) using a microcontroller for its actuation, with a voltage and current source of 5 V and 2 A, respectively. The PWM signal is varied to control the level of actuation in terms of the parallel manipulator z-axis displacement and tilting. The tilting direction depends on the SMA actuator that is activated, while all four SMA actuators are activated to control the linear z-axis movement. Each SMA actuator exerts a maximum force of 0.6 N at PWM duty cycle of 100%. The fabricated miniature parallel manipulator yields a full actuation at 55 °C, and able to tilt a maximum angle of 30° with a temporal response of 4.7 mm/s when the PWM duty cycle is set to 75%. Movement in z-axis has a displacement range of up to 12 mm.