Development of a Bendable and Extendable Soft Gripper Driven by Differential Worm Gear Mechanism

A gripper mechanism using flexible double-rack finger actuated using differential worm gear mechanism that can change its finger length according to the object being grasped was developed. Thermoplastic polyurethane (TPU) based fingers were soft, impact resistant, highly compliant, and were able to conform to the contour of the objects when grasping. The fingers can extend, contract and bend in 2D space when driven by the differential worm gear mechanism. A normal worm and an inner worm gear was used to actuate the flexible double-rack fingers. The relative motions between the two worm gears resulted in different motions of the finger. Multiple fingered configuration of the gripper can be driven from the same mechanism actuated using two actuators. A mathematical model was developed to describe the kinematics of the finger for positioning experiments. Experiments were also conducted to measure the fingertip force for different lengths of the finger. Grasping experiments of two and three-finger gripper were performed to test the grasping performance of the gripper for objects of different size, shape and weight. The gripper successfully grasped objects of different sizes by adjusting the finger length and conforming to the shape of the objects.