Acknowledgment SKLB1002 The research presented was undertaken within the scope of the Swedish Hydropower
With the world population increasing over the next several decades, agriculture will be called upon to provide greater yields in food production with relatively little increase in land usage. Therefore, it is imperative that efficiencies associated with automation become part of the overall solution. A key aspect is the machinery used to perform the agricultural tasks; one example of this, the Inhibitors,Modulators,Libraries combine harvester system, is discussed in this article. The combine harvester is used to extract the crops from the field and during this harvesting process seed loss is a critical problem [1]. It has been estimated that approximately 75% of the crop losses occur at the header [2] and a significant portion of the header loss is caused by improper setting of the header height.

Therefore, the header height control problem under study is motivated by the interest in improving the efficiency and productivity of the harvesting process, specifically to increase the harvest yield and decrease the total harvest time. Figure Figure11 shows a schematic of a combine harvester Inhibitors,Modulators,Libraries system operating in the vertical plane. The header height is defined as the distance between the header tip and ground. By raising or lowering the header with an actuator, usually hydraulic, the header height can be adjusted. If the header height is too large, there is a reduction in harvest yield since much of the viable crop will be left unharvested. Conversely, Inhibitors,Modulators,Libraries if the header height is maintained at too low a level, equipment damage or operator fatigue will result.

Fig. 1 Combine system The primary solution approach Inhibitors,Modulators,Libraries taken to date is the feedback system depicted in Fig. Fig.2.2. Some look-ahead feedforward approaches have been attempted in industry using laser, ultrasonic, and radar sensors. However, each has been sufficiently challenging as to preclude introduction in practice. The accepted feedback sensor is usually a ��feeler�� that drags along the ground. Rotation of the feeler relative to the header mount is measured and translated into header height Inhibitors,Modulators,Libraries as shown in Fig. Fig.1.1. The goal is to design the controller C(s) in Fig. Fig.22 so as to regulate the header height to a prescribed setpoint in the face of unknown ground disturbances.

Physically, the ground disturbances are induced by the interaction between the ground and the flexible tires; when the combine is driving over irregular terrain, the changing ground height works as disturbance signal to excite the vibration of the combine body. Therefore, the header height control can be seen as the ability to have Carfilzomib the header track the changing profile of the terrain at the header tip, and at the same time reject the disturbances under the tires.