| Construction and maintenance of on-orbit crew-operated hardware is currently done mostly by extra-vehicular astronauts. Use of robotics for some of these tasks provides the opportunity for both increased safety for the astronauts and major cost savings.; An effective space robotic manipulator must be lightweight, have a large workspace, and be capable of fine dexterous control. A large lightweight manipulator will necessarily be quite flexible, limiting the achievable end-point bandwidth. One way to achieve all of the objectives is via advanced control of a macro/mini manipulator: a large lightweight manipulator carrying a small dexterous manipulator, such as is planned for the International Space Station.; The goal of this work is to control a flexible-joint macro carrying a two-arm mini manipulator. For ease of use, a low-level controller should be designed such that the user or automated planner need only command the desired end-point motions and forces. Designing an end-point controller for a macro/mini manipulator presents many challenges. Such a manipulator system is non-linear, has low frequency flexibility, and has dynamic coupling between the macro and mini.; A smart method for controlling manipulators is impedance control, which specifies a desired force-velocity relationship at the end-point of the manipulator, enabling smooth contact with the environment. Using operational space control, the dynamics of the manipulator are transformed into operational coordinates for implementation of the impedance law. The operational space method also enables a secondary control of the redundant degrees of freedom, without degrading the end-point impedance task. This thesis presents new theoretical advances that enable extending the concepts of operational space and impedance control to redundant joint-flexible robots. Important advances include a new method for choosing the end-point impedance and a null-space controller that performs much better.; The new control concepts are verified on an experimental macro/mini manipulator. The experimental system is a two-link flexible macro carrying a two-arm mini. The control law is used to semi-autonomously perform a variety of tasks including manipulating objects and interacting with the environment. |
