Header loss sensing and computer modelling of the grain stripping process

Abstract

Investigation of the header loss in relation to the grain distribution within the hood enclosure, was carried out using the laboratory grain stripping rig. The main variable that was used, was the vertical hood height in relation to the crop height. It is known from previous work that header losses can be mainly affected by the relationship of the hood inlet edge relative to the crop height. The header loss measurements in the laboratory conditions, were found to be approximately 0.5 to 1.0 higher than those measured in field conditions. The distribution of the number of grains impacting per unit area on the underside of the hood, has been shown to have a positive correlation with the grain loss level. This means that if the distribution of grain impacts on the hood can be continuously recorded, then this can be used to give the operator an indication of the amount of grain that is being lost on the ground. In particular, the header losses increased as the number of grains impacting on the area of the hood nearest to the inlet section, also increased. Thus an impact sensor at the hood inlet could indicate the level of grain loss. In order to determine optimum position of the hood, however, it is necessary not only to measure the grain impacts at the hood inlet region, but to determine the distribution of the grain over the whole hood area. This means that a number of grain impact sensors need to be distributed over the hood area. The information from these sensors may be fed into a microprocessor which will indicate to the operator information which will allow him to select the best position for the stripper header settings.

Conventional loss sensors, as used to determine straw walker and sieve losses, can be used, provided that a suitable filtering and damping system is included in the circuitry. However, benefits will be obtained by developing a purpose-built impact sensor that is not sensitive to the velocity at which grains impact.

The basic construction of a computer model of the grain stripping process has been achieved. It is now able to describe the distribution of grain around the hood, at a given setting of the parameters and crop height. If losses, as measured on the laboratory rig are added to the program, it will be possible to estimate the loss levels that may be expected from different settings. In the future, the model can be used in two ways; firstly to answer questions on the effect of rotor diameter, hood configuration, number of stripping elements on the rotor in respect to performance, and secondly, the model can be programmed into an on-board microprocessor and with the information fed to it from the grain impact sensors, will be able to take over automatic control of the stripping header.