Application of H□ synthesis, sliding mode control and a disturbance observer for robust control of machine axes with linear motors

This paper discusses the application and compares the performance of traditional state feedback and three so-called robust control techniques on a prototype machine tool axis actuated by a linear motor: an H-infinity controller, a sliding mode controller, and a disturbance observer. Robustness with respect to load changes up to 300 % is considered. Experiments show that the sliding mode controller is robustly performant in this load range. Pole placement and the disturbance observer show robust stability, but the performance decreases slightly, although unacceptably with the load. The H-infinity controller is unstable for 300% load change. Based on the sliding mode controller, different pole locations are proposed that allow the pole placement controller to achieve the same robust performance as the sliding mode controller.