Analysis and implementation of a 6 DOF Stewart Platform-based robotic wrist

Abstract

In this paper, we present the kinematic analysis and implementation of a 6 DOF robotic wrist which is mounted to a general open-kinematic chain manipulator to serve as a testbed for studying precision robotic assembly in space. The wrist design is based on the Stewart-Platform mechanism and consists mainly of two platforms and six linear actuators driven by d.c. motors. Position feedback is achieved by linear displacement transducers mounted along the actuators and force feedback is obtained by a 6 DOF force sensor mounted between the gripper and the payload platform. The robot wrist inverse kinematics which computes the required actuator lengths corresponding to Cartesian variables has a closed-form solution. The forward kinematics is solved iteratively using the Newton-Raphson method which simultaneously provides a modified Jacobian matrix which relates length velocities to Cartesian translational velocities and time rates of change of roll-pitch-yaw angles. Results of computer simulation conducted to evaluate the efficiency of the forward kinematics and modified Jacobian matrix are presented and discussed.