Guidance control of agricultural vehicles at high field speeds

The main objective of this study was to develop an automated agricultural vehicle guidance system capable of controlling the vehicle during high-speed agricultural field operations. The posture sensor used in the study was a kinematic differential Global Positioning System (GPS) receiver. Experimental frequency response tests were used to develop models of steering equipment and vehicle dynamics. Classical feedback control was developed based on these models. Guidance controller effectiveness was evaluated with experimental step response tests. Frequency response tests of vehicle dynamics showed that the transfer function relating vehicle lateral deviation to steering angle was a double integrator. The dynamics of the automatic steering were within the same frequency range as desired vehicle dynamics. Guidance controller design had to compensate for both vehicle and steering equipment dynamics. When the GPS sensor was mounted above the front axle of the vehicle, guidance control to within 16 cm of the desired path was demonstrated at speeds up to 6.8 m/s. Moving the sensor rearward to a more practical location added phase lag to the system, and guidance control was less effective.