A reactive external force loop approach to control manipulators in the presence of environmental disturbances

Conventional force control of manipulators is drastically degraded in the presence of external dynamic disturbances. Such difficulties may occur during unexpected environment motions or sudden changes in the environment dynamics. The solution the authors have developed provides robustness with respect to these disturbances. It consists of encapsulating a dynamic impedance controller with a reactive external force loop. This paper focuses on the external loop, which takes into account both interaction forces and environment displacements to modify the reference trajectory of the inner impedance controller. It is also capable of rapid self tuning when the environment dynamics are changed. The reactive external loop is implemented using fuzzy logic techniques. Observation of the real behavior of the experimental system is used to design some simple fuzzy rules. Experimental results illustrate the efficiency and the robustness of this control method on dynamically complex tasks involving interactions between two industrial manipulators