| This thesis documents the development of position based impedance control for implementation on an industrial hydraulic manipulator. The implementation is made possible by a novel Nonlinear PI (NPI) controller. The NPI controller is demonstrated to improve position tracking accuracy on an existing industrial hydraulic manipulator by a factor of five relative to an optimized linear PI controller, without sacrificing regulation accuracy or robustness. The position based impedance controlled manipulator, incorporating the NPI controller, is shown to be capable of motion in free space, static and dynamic force control, and controlled environmental collisions in both flexible and stiff environments.;Theoretical analysis shows that the position based formulation of impedance control has different force control behaviour from the torque based formulation. Experimental work confirms a new relationship, derived here, between explicit force control and position based impedance control. Further theoretical work shows that the existence of any steady-state positioning error will lead to recurring oscillatory behaviour if the static component of the target impedance is less than twice the stiffness of the combined environment and force sensor. Experiments demonstrate this limitation, and show that application-specific compensation methods can be used to decrease the apparent manipulator stiffness without compromising stability. |
