Further advances in automating base cutter height control

Dirt levels in the cane supply are affected by the height of the harvester's base cutters relative to the ground. It is essential that the base cutters be operated at ground level to capture the crop and minimise the dirt sent to the factory. At present, operators rely on a gauge relative to the harvester frame, but this does not allow for variations in the ground surface, consequently the ground level setting is not maintained. Operators also use base cutter speed and hydraulic pressure as indicators of cutting depth, but base cutter speed and pressure are dependent on soil type and condition (wet, dry, hard, loose), as well as forward speed and crop density. This makes base cutter speed and pressure unreliable height indicators. This paper describes work during the 1999 harvest season which has used ultrasonic sensors to measure the height of the base cutters above the ground. The sensors were attached to the harvester frame slightly ahead of the base cutters. The sensors' outputs of the height measurements were relayed to a commercial PI (proportional, integral) controller. The controller compared the average height recorded by the sensors with the desired height (set point), and adjusted the harvester's height position so as to maintain the set point. This base cutter height control system has advanced the use of line of sight sensors (such as the ultrasonic sensors) by allowing the sensors to be used in burnt and green cane conditions, while a previous ultrasonic-based control system was restricted to burnt cane conditions. The limitations of the system described in this paper were that it was unable to automatically detect the top of the stool, and it maintained incorrect base cutter heights whenever significant changes in stool profile were experienced in the paddock. Given reasonably consistent stool profiles the control system was shown to be stable and reliable.