Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Agricultural and Biosystems Engineering

First Advisor

Donald C. Erbach


Use of the conservation tillage system known as ridge-till has steadily increased for corn and soybean production. It is important to plant rows at the same location and to rebuild the ridges in the same location every year. Without a system to guide along the previous ridge, "guess" rows become wide in places and narrow in others. This causes plants to be damaged during cultivation and yield to be lost during harvest;An automatic guidance system based upon two position-sensing systems was designed to follow a desired path. The position sensing system generates and transmits radio signals to a pair of repeaters through a main antenna. Returned signals from repeaters are used to determine the tractor position in the field. A microcomputer calculated the lateral position error, determined the proper steering angle, and controlled a stepping motor to steer the tractor. The lateral position error was determined by comparing the present measured position with the desired tractor position. A control algorithm was developed based upon the kinematic behavior of the tractor. The control algorithm determined the steering angle which would reduce the lateral position error. The position error of the front wheel at the "looking-ahead" next measurement position, the current front wheel angle, and the angle difference between the tractor yaw and the slope of curvature of the desired path were used to determine the steering angle;The steering control algorithm was evaluated for different front wheel turning ratios and sampling distance intervals through use of computer simulation. Experiments were conducted to verify the algorithm under field conditions. A John Deere 4430 tractor was equipped with the automatic guidance system. Paths considered for the field experiments were a 70-m straight line path, a sinusoidal path with a 5-m amplitude and 50-m period, and a 5-m step path. Position error at the tractor front wheel and at a three-point-hitch mounted implement was analyzed. Maximum absolute error, RMS (Root Mean Squared) error, and percentage of measured points where the absolute error was greater than 50 cm were calculated. Results showed that acceptable precision for field operations requires a guidance system with a position-measurement error of less than 5 cm. More accurate position and tractor yaw angle measurement, and faster error processing are required to improve the field performance of the guidance system.



Digital Repository @ Iowa State University,

Copyright Owner

Chang Hyun Choi



Proquest ID


File Format


File Size

140 pages