Improving Force Control using Zero Coupling Impedance Criterion in Series Manipulator Systems

Using industrial manipulators for force control normally suffers from large impedance due to their large inertia, friction and stiffness. Series macro-mini system has been proposed as a solution to lower the robot impedance. However, the force control performance of a series macro-mini manipulator system may be compromised due to the low frequency resonance modes of the macro manipulator. Although changing the dynamics of the macro manipulator has been proved to be useful to improve the force control performance, it cannot be easily done due to closed control architecture. In this paper, we propose a Zero Coupling Impedance criterion to address the aforementioned problem. Since modifying the dynamic of the macro is not feasible, the coupling between the macro and mini is changed instead. Experiments are used to validate the proposed criterion. The results suggest that by satisfying the Zero Coupling Impedance criterion, force control performance of the series manipulator system will not be limited by macro manipulator. This research provides a general guideline of designing and controlling an end effector that is carried by a manipulator for force control tasks.