Innovative Fin Ray gripper with integrated SMA actuator wires

Abstract:
In the growing field of Shape Memory Alloys (SMA), there is a wide scope for innovative actuator designs, modelling approaches as well as control algorithms using the self-sensing capability of SMAs. Lightweight and compact gripping systems based on SMAs have been of increased interest over the past years, pursuing the optimization of the gripper design while supporting or even improving the functionality. Mostly, current research work is not investigating the enhancement of the overall system, but rather deploying well-known traditional rigid-link gripper designs. In contrast, this work focuses on the system optimization by combining SMAs with an optimized gripper geometry exploiting the Fin Ray(r) Effect (FRE). FRE-based grippers feature a soft structure, a low weight and a high adaptability to different shapes and sizes of objects. There is a considerable amount of research work done on using FRE-based grippers in modelling, simulations, and experimental results but there is still room for work specifically in building a smart FRE gripper actuated by self-sensing SMA wires, resulting in a highly integrated and smart actuator-sensor system. SMA actuators provide the advantage of not needing a bulky pneumatic periphery or motor drive or an external sensor for adapting to fragile objects. This motivation directs investigating the placement, sensitivity, and calibration of SMA wires on the FRE structure in such a gripper system. A major part of the work focuses on optimizing the SMA-FRE integration and a first investigation is done on exploring self-sensing behavior to detect the contact with an object gripped by the gripper system. The study's key finding demonstrates that it is possible to detect object contact with the proposed gripper system. This discovery opens avenues for enhancing FRE-based grippers by utilizing the self-sensing property of SMA further for also accurately measuring applied force on gripped objects, enabling fragile object manipulation without needing additional weight or installation space.