Two degree of freedom control synthesis with applications to agricultural systems

This paper presents a two degree of freedom (DOF) controller for combine harvester header height control (HHC). Fundamental limitations to the tracking and disturbance rejection bandwidth for feedback control designs exist in the HHC system due to the considerable actuator delay and underactuated and noncollocated mechanical design. In this work, we utilize H1 optimal control design to ensure closed-loop stability and robust performance, and augment the feedback loop with a feedforward control structure based on readily available global positioning system (GPS) information. The GPS provides anticipatory information of the field map elevation; albeit with noise, resolution limits, and latency. The elevation changes result in disturbances to the header height control problem and the feedforward controller uses the knowledge of the field to increase the overall disturbance rejection bandwidth. Simulation and experimental results illustrate the performance improvements resulting from the 2-DOF design over the stand alone feedback controller, which removes a long standing obstacle in increasing the harvesting productivity. Additionally, an error analysis examines the effect of uncertainties from system modeling and field map measurements on the system performance.