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Operating agricultural equipment accurately can be difficult, tedious, or even hazardous. Automatic control offers many potential advantages over human control; however, previous efforts to automate agricultural vehicles have been unsuccessful due to sensor limitations. With the recent development of Carrier Phase Differential GPS (CDGPS) technology, a single inexpensive GPS receiver can measure a vehicle's position to within a few centimeters and heading to within 0.1˚. The ability to provide accurate real-time information about multiple vehicle states makes CDGPS ideal for automatic control of vehicles. In this work, a CDGPS-based steering control system was designed, simulated, and tested on a large farm tractor. A highly simplified vehicle model proved sufficient for accurate controller design. After various calibration tests, closed-loop heading control was demonstrated to a one-σ accuracy of better than 1˚, and closed-loop line tracking to a standard deviation of better than 2.5 cm. Future plans for research include the use of a pseudo-satellite to eliminate any position bias and extending the current control system to control a towed implement.

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No abstract

High-precision ‘autofarming’ makes possible farming techniques previously impractical using metre-level Differential GPS-based control systems: techniques such as tape irrigation, the elimination of guess rows, and precise contour farming. A Carrier-Phase Differential gps positioning and attitude system with centimetre-level and 0·1° accuracy was installed in a large farm tractor. Four types of trajectories (lines, arcs, spirals, and curves) were identified as basic building blocks necessary to generate a ‘global’ trajectory for a realistic autofarming path. Information about each trajectory type was translated into reference state specifications that a linear controller used to control the tractor over velocities between 0·7 and 2·8 m/s to within approximately 6 cm (1 σ) without implement and 10 cm (1 σ) with implement on sloped terrain using a previously developed tractor model. These results are a significant step towards a realistic autofarming system because they not only demonstrate accurate control over various realistic operating speeds but over different types of trajectories necessary for a commercial system.