Analysis of Fingertip Force Vector for Pinch-Lifting Gripper With Robust Adaptation to Environments

This article presents an underactuated gripper with a single actuator to perform a robust pinch capability under various environmental constraints. Its fingertips have the ability not only to slide on sloped surfaces of the tabletop on which the objects to be grasped are located, but also to lift lightweight objects for subsequent tasks, such as vertical in-hand manipulation and simple peg-in-hole tasks. The finger mechanism is constructed with a well-known four-bar linkage, including two phalanges, and then its fingertip is modeled as a slider to realize the fingertip sliding, which is a four-bar driven slider-crank. Kinematic and static analyses are conducted to determine the operation principle of the slider through the input-output relationship on the Plücker coordinates. Especially, the vector of the force, which the fingertip exerts, is analyzed, and then its direction is designed through the dimensional synthesis of the linkage according to several criteria for sliding and lifting. Simulations and experiments are conducted to verify the designed directions and performances of the synthesized linkage. Finally, the gripper equipped on a manipulator is demonstrated under contacts and collisions with various environmental constraints to confirm the feasibility and effectiveness of the gripper design.