H_∞ controller design for a robotic research and educational mining loader

A robotic platform consisting of a skid-steer compact loader is employed as a setup to design and study strategies for reducing material spillage by robotic mining mobile manipulators. The present work describes the design methodology for a controller approach to reduce disturbances on the end-effector induced by the terrain and propagated through the wheels and arm links of the machine. The proposed approach H_∞ control strategy that includes a feedforward action, computed using the pitch rate of the mobile base, and considers the hydraulic arm dynamics, as well as the reaction forces in the contact points of the mobile base. Alternative control schemes based on the classic proportional-derivative (PD) H_∞ strategy without feedforward action, were also implemented and evaluated on simulations and experiments using a semi-Autonomous Cat^® 262C compact skid-steer loader equipped with inclination and inertial sensors. The best results were obtained using the proposed approach. The control scheme proposed reduces ground disturbances around 89% and 68% when traversing a 4 m long ramp at 12.5% and 25% of maximum vehicle speed, respectively.