High speed, dead reckoning, and towed implement control for automatically steered farm tractors using GPS

The ability of GPS to provide accurate position and attitude information has led to many advances in land, marine, and air navigation systems. Recently, research has been done in the area of automated farm tractors using GPS. Driver assisted agricultural vehicles have many benefits such as relieving the driver from the tedious task of steering, increased accuracy, allowing for operation during poor visibility periods such as night, fog, and heavy dust environments, as well as providing the opportunity for new agricultural techniques.; In order for automatically steered farm tractors to become more widespread, they must be able to perform accurate control over the range of farm applications. Therefore, this thesis extends the capabilities of current automatically steered farm tractors using GPS. These extensions include the ability to accurately control towed farm implements (rather than the tractor), accurate control at high speeds for spraying, and continuous control through short GPS outages. New fundamental models and estimation techniques were developed to provide these capabilities and determine the limitation of previous models and techniques.; Experimental results are given which verify the ability to extend the cm-level control accuracy of farm tractors to towed implements, high speeds, and through short GPS outages. Accurate lateral control of 4 cm (1σ) of the tractor is performed up to 16 mph, as opposed to limitations of less than 10 mph for similar accuracies in previous work. This potentially represents a 60% improvement in the efficiency of the tractor allowing it to perform accurate automatic spraying in less time. Lateral control of 4 cm without any GPS attitude measurements and lateral errors of less than a foot for 20–40 second complete GPS outages is also presented. Finally, experiments show 10 cm lateral tracking of a towed implement using direct GPS measurements and the techniques developed in this thesis.