Control and Evaluation Methods for Multi-Mode Steering

A self-propelled agricultural sprayer was modified to enable both front and rear wheel steering through electrohydraulic control valves. These modifications, in conjunction with a digital controller, enabled the vehicle to be four-wheel steered in multiple modes. The research focused on modeling and evaluating the effect of multi-mode four-wheel steering on vehicle handling characteristics and vehicle performance of the sprayer. The multi-mode steering system was evaluated by driving the sprayer through specified paths in the different steering modes. The position and heading of the vehicle were measured for each mode using two dual frequency DGPS receivers. From the measure of vehicle posture, sprayer performance measures such as over/underspray and crop damage were assessed for each steering mode. Preliminary results show that drivers were able to take advantage of added maneuverability in headland turning procedures. Crab steering reduced the amount of area sprayed in error during lateral course adjustments. The steering and vehicle models yielded similar responses to steering inputs as experimental responses.