Underactuated Robotic Gripper With Fiber-Optic Force Sensing Tendons

We present a novel design for a multi-fingered robotic gripper, featuring underactuation and fiber-optically sensorized tendons for force sensing, inspired by the Golgi tendon organs found in biological muscles. Our robotic gripper comprises three rigid fingers, each with three joints: the metacarpophalangeal (MCP), proximal interphalangeal (PIP), and distal interphalangeal (DIP). To enable flexion and extension, each is actuated using a combination of two types of tendons: an active tendon and three passive tendons. The active tendon is a single-mode optical fiber with an embedded fiber Bragg grating (FBG) that detects the tension of the fiber during the gripper's grasping motions. Meanwhile, three elastic passive tendons, made of soft elastomer and located on the dorsal side of the finger, retract the finger to its initial extended position upon the release of the active tendon. Through the measurement of the wavelength shift of the FBG, induced by the strain applied to the fiber-optic tendon, we can convert this data into force values, facilitating grasping force control. Our proposed gripper is tested with objects of varying stiffness and demonstrates the force-sensing capability of the sensorized tendons.