A Compact Ratchet Clutch Mechanism for Fine Tendon Termination and Adjustment

Adaptive, underactuated and compliant robot systems have received an increased interest over the last decade. Possible applications of these systems range from the development of adaptive robot hands to tendon-driven, soft exosuits. Despite the significant progress in the field, some basic design issues such as the tendon termination and adjustment have not yet been addressed properly. In this paper, we focus on tendon-driven, underactuated systems and we propose a compact ratchet clutch mechanism that facilitates a fine tendon termination and adjustment. The proposed mechanism is experimentally compared with six common tendon termination solutions, using two different tests: i) an accuracy test to verify how precisely each mechanism can adjust the tendon length and ii) a tensile test to derive the strength limit of each mechanism. The experiments validate that the ratchet clutch system is a precise and robust mechanism that outperforms all the solutions compared. A cable driven finger was designed and built to accommodate the proposed mechanism and test its efficiency and applicability to devices that require compactness (e.g., adaptive robot hands). The design of the mechanism is disseminated in an open-source manner.