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On the dynamics and control of manipulators with slewing and deployable links Chen, Yuan

Abstract

Space manipulators present several features uncommon to ground-based robots: they are highly flexible, often mobile, and have a degree of redundancy. As space robots become more complex, effective formulation procedures and efficient algorithms are required to evaluate their performance. The present study aims at development of some basic tools and their application to assess dynamics and control of a novel, flexible, multi-module manipulator with slewing and deployable links. To begin with, a rather general three-dimensional, order N, Lagrangian formulation for the system is developed which accounts for interactions between orbital, librational, slew, deployment and elastic degrees of freedom. The versatile character of the formulation makes it applicable to a large class of manipulator systems of contemporary interest. Validity of the formulation and associated computer code is established through conservation of energy in the absence of dissipation. A planar parametric study follows which provides better appreciation as to the influence of several important system variables, initial disturbances and maneuver profiles. Behaviour of a two-unit gross and fine manipulator is also discussed. Results suggest that the system flexibility could significantly affect the manipulator's performance, which may not be acceptable. This suggests a need for control. A nonlinear controller based on the Feedback Linearization Technique (FLT) is developed to regulate rigid degrees of freedom which proves to be quite effective. Flexible generalized coordinates, though not actively controlled, are regulated through coupling. Optimal trajectory design for the gross-fine manipulator system with redundant degrees of freedom is also investigated. Finally, the general formulation is reduced to represent the ground-based two-unit prototype manipulator thus demonstrating its wide scope of application. Simulation results for the ground-based system are obtained with the FLT control and compared with those given by the prototype. Considering the friction and backlash effects for the prototype, the correlation may be considered satisfactory. Such a comprehensive investigation involving a novel configuration of the space-based manipulator, three-dimensional formulation, dynamics and controlled performance, as well as ground-based experiments on a prototype system is indeed rare. It should prove useful in the design of this new class of manipulators.

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