Agricultural combine harvesters are machines designed for harvesting and processing crops such as wheat or corn. Crops are cut from the field on a wide area by the header mounted at the front of the combine. By an auger or a belt system mounted in the header, the harvested material is brought to a central area of the header, and from there it is transported by the feeder to a threshing mechanism comprising laterally or longitudinally mounted threshing rotors and further to the cleaning section comprising a number of sieves where grains are separated from any remaining crop residue.
The feeder typically comprises a set of chains or belts guided by sprocket wheels mounted at the front and back of a feeder housing, and with transversal slats attached to the chains or belts. The crops are pressed between the moving slats and the floor of the feeder housing and transported in this way from the inlet of the feeder to the outlet, where the crops are fed to the threshing rotors of the combine.
Improvements in the threshing and cleaning sections of modern combine harvesters have increased the capacity of these sections, which requires also an increased throughput through the feeder. One crucial area that determines this throughput is the transition area between the header and the feeder, where crops tend to accumulate in a so-called ‘dead zone’. Document U.S. Pat. No. 4,271,660 discloses a feeder wherein the front drum is provided with retractable fingers rotating about an eccentrically placed axle, so as to grab a higher amount of crops in the transition area and thereby eliminate or lessen the effect of the ‘dead zone’. The slats are attached to chains rotating on a pair of sprocket wheels. It is a known problem however that chains are liable to shift with respect to the sprockets under the influence of high forces. Such a shift would interfere with the timing of transversal slats relative to the retractable fingers, which may lead to a collision between the fingers and the transversal slats. The shifting of chains or belts in the feeder is a drawback in any feeder design, regardless of the presence of the retractable fingers. In the case of belts, inadequate tensioning of these belts is often at the root of the problem.