Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Agricultural and Biosystems Engineering

First Advisor

Donald C. Erbach


A global position-sensing system using navigational technology has been researched and applied to control a farm tractor in field conditions. Besides guiding a tractor in conservation tillage systems, navigational positioning systems can be used to generate field maps which can help in the application of chemicals and in visualizing variation of soil and crop conditions;A tractor dynamic simulator was developed by using a semi-recursive formulation which uses the variational vector approach and relative coordinates in Cartesian space. Typical joints were formulated for automatic assembly of equations of motion, and cut-joint Jacobians were used to handle with a closed-loop mechanism;A self-tuning steering controller, which can be used for all non-contact types of the positioning systems, was designed for tractor guidance systems. A simple two degrees-of-freedom model of a tractor was chosen to develop a prediction model used in recursive least-squares parameter estimation. A variable forgetting factor was implemented, and its algorithm was modified to cope with time-varying nonlinear systems. The self-tuning steering controller based upon minimum variance control was tested and verified by using the tractor dynamic simulator. Test paths used were a circular path with a radius of 36 m and a composite path which consisted of two lane-change and continuous sinusoidal maneuvers. The test speeds considered were in the range of 0-18 km/h;The study found: (1) an accurate position-sensing system is the most important factor to control the tractor path within ±5 cm of the desired path; (2) a fast sampling can be achieved in practical applications because the execution time of the controller program was about 5 msec; (3) the self-tuning controller that can be used to guide a tractor with any non-contact types of positioning system can measure the position or the position error with respect to the desired path; (4) with the sampling interval 0.1 and 0.2 seconds, the controller could control the tractor position within ±5 cm of the desired path at all test speeds. (Abstract shortened with permission of author.)



Digital Repository @ Iowa State University,

Copyright Owner

Kwang-Mo Noh



Proquest ID


File Format


File Size

187 pages