A Lightweight Linear Actuating System for Finger Articulation: A Proof-of-Concept Study

This paper provides a proof of concept for an actuating system comprised of a linear actuator and a spring steel strip that enables bidirectional articulation of a finger by transmitting the force directly to the finger tip. This proposed design can be distinguished from other orthosis designs, which use rigid linkages or cables with DC motors or fluidic systems for force generation and transmission. We designed an experimental setup with a 3D-printed model finger to mimic a passive human finger on which the actuation system was mounted and tested. The finger was positioned such that it would curl upward to lift various masses when articulated by the actuating system to demonstrate the system’s force generation capability. We tested two linear actuators and two steel strips, using a wide range of masses to determine which would be the most suitable components for our design. We analyzed motion profiles, joint angles, force generation, and actuator stroke velocities during various experimental trials. Our results demonstrate that our actuating system is capable of generating sufficient forces and motions with an adequate response time to be used in the design of a hand orthosis for grasping/releasing assistance. From our tests, a prototype was designed with three linear actuators positioned on the dorsal side of the hand and actuated the thumb, index, and middle fingers. Future work will include sensor integration and performance evaluation of the orthosis.