Gripper with Thumb Adduction/Abduction Joint for Enhanced In-Hand Orientation Manipulation

A new gripper with a Thumb Adduction/Abduction joint (TAA joint) is presented in this study. The purpose of the proposed gripper is to enable the orientation control of an object along all axes using in-hand manipulation and the last wrist joint. Using TAA joint motion, it was possible to achieve not only stable grasping but also in-hand orientation control. The gripper can produce 13 out of 16 human grasp motions according to hand taxonomy, including four of the most used hand postures [1] [2]. The grasping performance was evaluated using various objects. Some of them were tools for specific tasks such as electric drill, screwdriver, and hammer. The others were objects in daily life such as ball, CD, pen, cup, wallet, and card. To evaluate the capability of in-hand orientation control, the maximum ranges of rotations were also estimated using circular cross-sectional objects. The gripper can consecutively rotate the object along the roll and yaw directions, and this was demonstrated using a spherical object.