Adaptive Robust Controller Designs Applied to Free-Floating Space Manipulators in Task Space

Space robots are featured by a dynamic coupling which causes the rotation of the main body with the coordinated motions of the arm. A number of dynamic and control problems are unique to this area due to the distinctive and complex dynamics found in many applications. In-space operations such as assembly, inspection and maintenance of satellites or space stations have been receiving considerable research efforts. Considering the hostile environment where a space robot operates, which can deteriorate its structure and physical characteristics, and also considering the difficulty of taking the system back to reformulate its dynamic model due to these uncertainties, the proposal of intelligent adaptive robust controllers to this kind of system becomes very interesting. One of the representative types of space robotic systems identified by [Dubowsky & Papadopoulos (1993)], free-floating space manipulators are systems that allows the spacecraft to move freely in response to the manipulator motions in order to conserve fuel and electrical power, [Papadopoulos & Dubowsky (1991)]. Trajectory planning algorithms have been developed in order to minimize the reaction motion of the free-floating base while executing the manipulator task, [Huang & Xu (2006); Liu et al. (2009); Papadopoulos et al. (2005); Torres & Dubowsky (1992); Tortopidis & Papadopoulos (2006)]. In case of redundant manipulators, coordinated spacecraft/manipulator motion control has been addressed in [Caccavale & Siciliano (2001); Dubowsky & Torres (1991)]. Solving control problems in joint space is an inconvenient task for a space robot with a freefloating base. When the base is free-floating, the kinematic mapping from task space to joint space, where the control is executed, becomes non-unique because of non-integrable angular momentum conservation. This may cause non-existence of the reference trajectory in joint space. Also, parametric uncertainties appear not only in the dynamic equation, but also in kinematic mapping from the joint space to the task space due to the absence of a fixed base. The model inaccuracies lead to the deviation of operational space trajectory provided by the kinematic mapping. [Parlaktuna & Ozkan (2004)] and [Abiko & Hirzinger (2009)] applied on-line adaptive techniques to deal with parametric uncertainties in controlling free-floating 1