Development of a compact wrist with multiple working modes

This paper presents the design, modeling and control of a compact wrist, which can work in active mode with position or torque control, or passive mode with interactive force compensation. This characteristic makes it suitable for dexterous manipulation in unstructured environments, such as door opening. Mechanism design is presented briefly, and forward, inverse as well as differential kinematics are derived to map the motions and velocities between the task space and joint space. A distributed robust adaptive controller is developed for tracking control of the wrist in active mode; and a new interactive force compensation technique is proposed on the basis of force sensor measurement, which enables passive working mode of the compact wrist. A DSP based control system is developed to test the developed control methods. A prototype has been fabricated and some preliminary experiments have been conducted to validate the proposed design and to verify the developed algorithms.