Automatic control of header height has been employed in combine harvesters as a means to reduce harvest losses, operator fatigue and the risks of equipment damage. State-of-the-art combine harvesters usually incorporate on-off controllers to keep the header at the desired height. The fixed control signals and the relatively broad dead-bands required for stabilization of this type of controller impose serious limitations on the performance of such systems. This paper describes an alternative control system aiming to improve the performance of combine harvesters in following the soil profile. The linear quadratic Gaussian with loop transfer recovery (LQG/LTR) method has been used to design a robust and optimal header height controller. The results obtained indicate that the use of the LQG/LTR controller can significantly improve the disturbance rejection capacity of the system, while keeping its energy expenditure levels unchanged with respect to the conventional on-off system.
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