Experiments in manipulation and assembly by two-arm, free-flying space robots

Abstract

Research in advanced manipulation by robotic systems has led to interest in multi-arm/dynamic base manipulator systems--robots in which two or more manipulators extend from a common macro-manipulator or vehicle. These systems possess characteristics that are inherently beneficial to dexterous manipulation, such as redundancy, multiple arms, and macro-mini dynamic properties. Free-flying space robots are one example where the use of multiple manipulators stemming from a single mobile vehicle offer unprecedented capability. A mobile base enables the robot to work over an unlimited workspace; multiple end-effectors enable either the execution of several tasks simultaneously or the cooperative manipulation of cumbersome objects; and redundant degrees of freedom and macro-mini dynamic properties enable the robot to achieve fast, precise manipulation at the end-effectors even though the robot body may be dominated by slower dynamic behavior. While previous research has been conducted to control multi-arm/dynamic-base systems, an approach has never been pursued in which the redundancy of these systems has been exploited fully to focus on just the manipulative task. Past efforts have attempted to control with equal priority both the manipulative task executed at the robot hands and the control of the redundant degrees of freedom associated with the robot body and posture. This thesis investigation proposes a new, dynamically-partitioned control framework for multi-arm/dynamic-base manipulator systems, in which the performance of a robot at the manipulative task is deemed paramount. Pursuant to this goal, the entire redundant system works in concert to achieve the best possible dynamic performance at the robot end-effectors. Control of the redundant degrees of freedom of the robot are controlled using only dynamically consistent combinations of forces and torques that will not introduce undesired accelerations at the task. The novel control framework has been developed by extending the Operational Space Control Framework for single-arm and cooperating single-arm manipulators to the larger class of multi-arm/dynamic-base manipulators. The new Extended Operational Space Framework has been experimentally validated on two-arm, free-flying space robot proto-types. These robots have been programmed to perform object acquisition, transport, and assembly tasks in a free-floating space environment under the new control framework.