Robust control of mechanical systems: a computational design study

Methods for the design of robust controllers for nonlinear systems, especially manipulators, are investigated with emphasis on robustness for unmodeled dynamics. The system to be controlled is a two-degree-of-freedom manipulator, with a rotational and a prismatic joint. The control task is to follow a circular object with trajectory control along the circumference and force control in the direction perpendicular to the circumference. For the trajectory a fixed computed torque with a PD (proportional plus derivative) controller is used. The force is controlled by the controllers under investigation. These controllers are all based on a linearizing state-feedback with acceleration feedforward, and a controller based on a H₂ or H_∞ design for the resulting linear system. A PD controller is used for reference