Mechanical design of a 3-DOF humanoid soft arm based on modularized series elastic actuator

Aiming at the safety issues in the human-robot interfacing environment, this paper presents a modularized series elastic actuator to improve the compliance of the robotic arm, analyzes the mechanism and how it works, designs and fabricates a prototype of 3-DOF humanoid soft arm. A task-oriented method to determine the joint stiffness is proposed, first of all we choose N typical postures of the robotic arm within its work space, directly give the desired stiffness of the end-effector, use the Jacobian matrix to get the joint stiffness of the chosen posture, thus we have N groups of joint stiffness of the N different postures respectively, then give a weighing factor to each group of joint stiffness based on the importance of each posture, sum up the stiffness multiplied by its own factor to get the reference value. A simulation is implemented to verify the validity of this method, in ADAMS we imply a given force on end-effector, compare the simulation displacement with the given one, the results show that the method is effective and feasible.