An analytical grain flow model for a combine harvester, part II: Analysis and application of the model

A dynamic grain flow model describes how the grain flow at the end of the t hreshing process reacts to feedrate variations during harvest. These input flow variations have different origins as there are variations in travel sp eed, cutting width and locally variable grain yield. In this study, an anal ysis of the model is performed and a specific application in the domain of precision farming is illustrated. A closer look at the construction of the analytical grain flow model reveal s some complicated dynamics in the system and an internal return loop with a significant time delay. Especially, the latter property makes it difficul t to simplify the model into a linear transfer function, an interesting for m for further applications. Due to a specific property of grain spreading i n the return flow, it is possible to compensate for the variations in the r eturn flow fraction. The grain smoothing effect of the combine harvester fo r 0% return flow was approximated by a fourth-order linear transfer functio n. Some producers of combine harvesters already possess a commercial product f or online grain yield measurement. These sensors are typically mounted at t he end of the threshing process since this is the only place where a flow o f clean grain is present. Nevertheless, this position has also a drawback. Grain flow signals, measured at the end of the threshing process contain un conditionally the influence of disturbing machine dynamics. In practice, th is means that feedrate variations and subsequently estimated yield variatio ns, are smoothed reducing the economic interest of the resultant yield maps . The inverse simplified linear transfer function makes it possible to redu ce these latter errors and to improve immediately the results of further si te-specific grain yield analysis. (C) 2001 Silsoe Research Institute.