Development and Control of a 2-DOF Reconfigurable SMA End-effector

In this paper, the next generation of an SMA end-effector prototype is presented. The end-effector design is based on a modular concept. Each module has two degrees of freedom (DOFs) with independent SMA-biasspring configurations. The first DOF, denoted as arm, can be positioned in plane within a 90 deg rotation radius. The second DOF, denoted as finger, can be rotated out of plane within a 30 deg rotation radius for adapting to non-planar workpiece geometries. In contrast to the first DOF, the second DOF additionally uses a pull-and-release principle familiar from ball-point pens, to hold three discrete energy-free positions. A microcontroller-based PCB is designed and manufactured to control all eight SMA-wires independently by separate PWM-voltage-controlled current sources. This circuit is also designed for position control by using the “self-sensing” ability of the SMA-wires. The design of the actuator construction is presented along with a prototype. The prototype’s functionality including the positioning of the arms is evaluated and validated.