A controller for a redundant free-flying space robot with spacecraft attitude/manipulator motion coordination

Abstract

A resolved acceleration type controller for free-flying space robots with a kinematically redundant manipulator arm is presented. The arm is controlled to track a desired end-effector trajectory and at the same time to change the attitude of the system in a desired manner and without activating jet thrusters and/or reaction wheels. The formulation is based on the fixed-attitude restricted (FAR) Jacobian matrix which was introduced for path planning and control at the velocity level. A reformulation in terms of accelerations allows the author to address the issue of end-effector velocity step-change response, caused, for example, by a collision between the end-effector and the target. It is shown that when the FAR Jacobian is applied, the joint acceleration is mainly derived from the null space of the manipulator-link inertia matrix, and hence there is very little disturbance of the spacecraft attitude. As a consequence, there is a loose dependence on spacecraft mass and inertia.