Robotic Manipulation with Flexible Link Fingers

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Sudipto Sur
PhD Dissertation, Caltech, January 1997

Robots with structural flexibility provide an attractive alternative to rigid robots for many of the new and evolving applications in robotics. In certain applications their use is unavoidable. The increased complexity in modeling and control of such robots is offset by desirable performance enhancements in some respects. In this thesis we present a singular perturbation approach for modeling, analysis and control of robots with flexibility. As our singular perturbation approach does not treat the flexible manipulator as a perturbation of the rigid manipulator, it can treat significant flexibility, beyond the linear range. Analysis based on this approach leads to some provably stable control laws for the hybrid position and force control of flexible-link manipulators. The analysis is done in the framework of a single robot manipulator in a constrained motion task. Simulations and experimental results are presented for this case. To show applicability of the results to more general and complex systems with flexibilities we also present experimental data from a planar, two-fingered, reconfigurable grasping setup which allows rigid and flexible configurations. The aim of the experimentation is to show the applicability of the control laws and analysis developed, and to determine the performance enhancements resulting from the introduction of flexibility. Experimental data is analysed to show the tradeoffs between controller complexity and performance enhancement as we deal with greater flexibility. Various performance criteria are set up and experimental results are discussed within their framework. We conclude that large flexibility can be controlled without too much additional effort, has performance comparable to that of rigid robots, and possesses enhancing properties which make it appealing for use in certain types of applications.