Modeling, Optimization, and Experimentation of the ParaGripper for In-Hand Manipulation without Parasitic Rotation

Recently, underactuated robotic hands have been exploited for dexterous in-hand manipulation, after having been proven efficient in performing versatile adaptive grasps. However, the reported in-hand manipulation skills are usually associated with parasitic motion, which may complicate control and application of the hand. This paper presents the modeling, optimization and experimentation of the ParaGripper, an underactuated gripper capable of performing in-hand manipulation without parasitic rotation. The underactuated finger uses two serially connected parallelograms to ensure pure translation of the fingertips. If the object remains stationary within the fingertips, the gripper can translate the object without parasitic rotation. The kinematics and kinetostatics of the hand-object system are derived and the manipulation workspace is optimized. The ParaGripper is designed and fabricated according to suitable optimal parameters. Experiments show that the ParaGripper could perform non-parasitic in-hand manipulation and versatile adaptive grasps.