Dynamic Surface Control of Cooperating Hydraulic Manipulators in the Presence of Friction

This paper presents development of a new controller that allows two or more hydraulically-actuated robots to cooperatively move a rigid object along a desired trajectory while sharing the load and maintaining an acceptable internal force on the object. The effects of friction (represented by LuGre model in this paper), as well as parametric uncertainties in the manipulators\´ dynamics, hydraulic functions and the payload, are all accommodated through augmentation of the controller by a set of on-line updating laws. In arriving at this new controller, the concept of dynamic surface control is adopted to prevent the "explosion of terms" that was observed in our previously developed controller [10]. Therefore, the new controller has the benefit of not requiring an acceleration observer or the derivative of terms that could be difficult to numerically achieve. Stability analysis shows that the controller guarantees arbitrarily small bounded tracking error even in the presence of nonlinear model uncertainties. Both simulation and experimental results are shown to illustrate the effectiveness of the developed controller for tracking tasks.