Self-adaptive grasp analysis of a novel under-actuated cable-truss robotic finger

This paper presents the self-adaptive grasp of a novel cable-driven finger, which is an underactuated finger comprising cable-truss units. The underactuated cable-truss finger uses tendon-pulley transmission and parallel four-linkage mechanism to realize grasps. The working principle of the underactuated cable-truss finger and the self-adaptation at the grasp-closing stage are introduced. A self-adaptive grasping model is constructed to analyze the self-adaptation, and a new analysis method that considers the position and posture of grasping point in distal phalange is proposed. A new generalized coordinate, which directly shows the contacting position and the relative angular displacement in the distal phalange, is established. The expression of general static grasping force is established by using the virtual work principle, which reveals the relationship among the driving force, the equivalent torques on joints and the grasping forces. The workspace of the underactuated cable-truss finger and distributions of grasping force in new generalized coordinate are assessed through numerical analysis. The balance conditions of the self-adaptive grasp and the corresponding statuses are theoretically illustrated. Valid and adequate self-adaptive grasping experiments are conducted to verify the accuracy of self-adaptive grasping analysis.