SIX-DEGREE-OF-FREEDOM

Abstract

This is a semiannual report presenting the research results obtained from the research grantentitled Control of Robot Manipulator Compliance, funded by the Goddard Space Flight Center(NASA) under a research grant with Grant Number NAG 5-780, for the period between Augusti, 1990 and January 1, 1991.In this report we present the kinematic analysis and implementation of a 6 DOF roboticwrist which is mounted to a general open-kinematic chain manipulator to serve as a testbed forstudying precision robotic assembly in space. The wrist design is based on the Stewart Platformmechanism and consists mainly of two platforms and six linear actuators driven by dc motors.Position feedback is achieved by linear displacement transducers mounted along the actuatorsand force feedback is obtained by a 6 DOF force sensor mounted between the gripper and thepayload platform. The robot wrist inverse kinematics which computes the required actuatorlengths corresponding to Cartesian variables has a closed-form solution. The forward kinematicsis solved iteratively using the Newton-Raphson method which simultaneously provides a ModifiedJacobian Matrix which relates length velocities to Cartesian translational velocities and time ratesof change of Roll-Pitch- )Paw angles. Results of computer simulation conducted to evaluate theefficiency of the forward kinematics and Modified Jacobian Matrix are presented and discussed.