Self-adaptive grasp process and equilibrium configuration analysis of a 3-DOF UACT robotic finger

Self-adaptation is a typical and widespread characteristic in underactuated finger grasp. This paper presents the self-adaptive grasp process and equilibrium configuration of a 3-DOF underactuated finger comprising cable-truss units, which uses a tendon-pulley transmission and parallel four-linkage mechanism to realise grasps. The structure and the self-adaptation at the grasp closing stage are illustrated. On the basis of a situation where one or two phalanges are in contact with the object, fixed-point grasp models and the joint workspaces are discussed, respectively. The corresponding workspace that is formed when the distal phalange contacts the object at a fixed point is assessed through numerical analysis. The expression of general static contact force is established by using the virtual work principle, and expressions reveal that the phalanges’ static statuses are obtained. According to the middle phalange contacting or not contacting with the object, the distributions of every phalange condition are assessed, and the self-adaptive grasp process in complex distribution regions and four equilibrium grasp configurations are analysed from two grasp situations. Valid and adequate self-adaptive grasp experiments are conducted to verify the accuracy of the self-adaptive grasping analysis.