Mechanical Design and Kinematic Analysis of an Autonomous Wrist with DC Motor Actuators for Space Assembly

This paper deals with the mechanical design and kinematic analysis of an autonomous wrist for space assembly (AWSA) whose actuators are activated by DC motors and ball screw drives. This robotic wrist was developed and built as a prototype to investigate in-space robotic operations including maintaining and repairing spacecraft of the US National Aeronautics and Space Administration (NASA) such as the International Space Station (ISS) or satellites. Parallel structure instead of serial structure was selected for the design of the AWSA due to several advantages it has over a serial robot manipulator (SRM), including higher payload, greater stiffness and better stability. The present paper also introduces a hybrid concept for robotic space operations, which combines a SRM performing gross motion and a parallel robot manipulator (PRM) performing fine motion. It then discusses the design and construction of the DC motor actuators and ball screw drives and presents the kinematic equations developed for the AWSA. The paper provides a closed-form solution to the inverse kinematics of the AWSA and a numerical solution using Newton-Raphson Method to its forward kinematics.