Fundamental limits in combine harvester header height control

This paper investigates fundamental performance limitations in the control of a combine harvester´s header height control system. Utilizing standard frequency domain analysis tools, we are able to demonstrate closed-loop bandwidth limitations that stem from specific system design configurations. There are two primary sub-system characteristics that influence the available bandwidth by affecting the open loop transfer function. The first sub-system is the mechanical configuration of the combine and header while the second sub-system is the electro-hydraulic actuation for the header. The mechanical combine + header sub-system results in an input-output representation that is both under-actuated and has a non-collocated sensor/actuator pair. The electro-hydraulic sub-system introduces a significant time delay. In combination they each reinforce the effect of the other thereby exacerbating the overall system limitation. Simulation and experimental results are provided to validate the existence of these performance limiting sub-systems. Additionally, the overall effect of the system limitations is presented.