Wearable Multifunctional Additive Hand System for Enhancing the Workspace and Grasping Capability of the Human Hand

In this study, a wearable multifunctional additive hand (MAH) system is proposed for enhancing the workspace and grasping capability of the human hand. The MAH system consists of a main body and three fingers, and each finger has two joints. To optimize the performance, the following five parameters are considered: finger length, number of fingers, number of joints, base frame size, and joint angle range. The MAH system is designed to assist the human hand in the inward and outward modes. In the inward mode, the finger joints of the proposed system rotate in the same direction as the finger flexion of the human hand, whereas in the outward mode, the robotic fingers of the MAH system rotate in opposite directions. The proposed system provides assistive torque and expands the workspace of the human hand in the inward mode. When the additive finger joints rotate outward, they grasp an object as a third hand. The validity of the proposed system is verified analytically by changing the design parameters, considering the workspace expansion and joint torque reduction. An alpha shape is introduced to calculate the expanded workspace volume using the proposed system. The joint torque was estimated by utilizing kinematics and the force equilibrium equation, assuming that the human hand with the MAH system holds a postulated object.