A two-loop implicit force/position control structure, based on a simple linear model: theory and experiment

This paper deals with force/position control applied to robotic manipulators. It is well-known that force/position control for manipulators is a challenging task, because of strong nonlinearities exhibited by both the manipulator itself and by its environment. Despite the complexity inherent in manipulation processes, the classic single-loop feedback system with its advantages and disadvantages is still preferred in industrial use for force/position control. As interesting alternative we suggest the MFC-p (model-following control) two-loop control structure, which is based on a simple linear 2nd order model. The theoretical as well as the practical properties of this new control scheme are discussed in detail. It is shown that with our approach it is possible to achieve a much better control performance than that provided by a classic PID system. To prove the superiority of the concept, results with industrial manipulators under force control are shown