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Hybrid force and motion control of robots with flexible links

Özgören, Mustafa Kemal
Ider, S. Kemal
Considering robot manipulators with flexible links, a new method is proposed to control their constrained end-effector motions and the associated contact forces and/or moments. The equations of motion are separated into two parts that represent the pseudostatic equilibrium and the deviations from it. The feedforward part of the control input based on the pseudostatic equilibrium is determined algebraically and the feedback part of the control input for the stabilization of the deviations is obtained by means of a state-variable feedback law using measurements of the contact forces and/or moments, the strains in the links, the joint variables, and the end-effector position and velocity. The feedback gain matrix is determined online by a continuously updated pole placement process. The method is demonstrated by means of a planar two-link robot with a flexible forearm which is constrained to move on a cylindrical surface. Furthermore, in order to investigate the effects of the modeling discrepancies caused by using lower order models, a "submodel controller" is designed using a model with only the first mode and it is applied to the same system with the two-mode model.