Thermal shape memory alloy (SMA) actuators are known for their superior energy density (force-volume ratio) compared to other actuation principles, allowing the construction of lightweight and compact systems. Furthermore, SMA actuators can be used as sensors, as their electrical resistance changes during activation. Using this multifunctionality, this work aims at presenting the development, fabrication, and validation of an SMA-driven robotic end-effector. The end-effector prototype is designed in a modular concept and consists of four independent arms with two degrees of freedom (DOF). Each arm can rotate in-plane and also tilt out-of-plane to allow gripping of various workpiece geometries. Both DOF actuator components consist of an SMA wire working against a tension spring. The tilting joint has an additional mechanism that creates two energy-free rest positions to improve energy efficiency. The end-effector is designed to carry a maximum load of 10 kg. In a test bench for the validation of the SMA-driven end-effector joints, hall sensors are used to measure the gripping arm displacement. In addition, the resistance of the SMA wires is monitored during activation. The dynamic system performance is analyzed using different activation current levels. Finally, a proportional integral (PI) control with Hall sensor feedback is implemented to position the first DOF at arbitrary angles within its 90° rotation radius.
1Universität des Saarlandes (Germany)