Kinematic GPS for Closed Loop Control
of Farm and Construction Vehicles

Michael L. O'Connor, Gabriel H. Elkaim, and Bradford W. Parkinson


Department of Aeronautics and Astronautics
Stanford University

ABSTRACT

Operating heavy equipment can be a difficult and very tedious task; control of an agricultural tractor requires the continuos attention of the driver, and farmers often work long hours during the critical times of planting and harvesting. Loaders and other ground vehicles are frequently used in situations which are unpleasant or even hazardous for the human operator. In the past, some efforts have been made to automate agricultural vehicles, but they have been largely unsuccessful due to sensor limitations.

This paper explores the use of kinematic GPS as the primary sensor in closed loop control of farm and construction vehicles. A single, low-cost GPS receiver can measure position to within a few centimeters and attitude to within 0.1 degrees, and does not drift with time. The ability to provide accurate information about multiple vehicle states makes GPS ideal for system identification and control of dynamic systems. In this work, a ground vehicle control system was designed and simulated using realistic plant, sensor, and disturbance models. Optimal control methods were examined to deal with non-linear and time-varying vehicle dynamics. To validate this simulation, experimental data was taken at Stanford using a GPS-equipped electric golf cart.

This research builds upon previous work in developing GPS-based aircraft autopilots. It is significant because it is the first step towards a safe, low-cost system for adaptive, highly accurate control of a ground vehicle. It is anticipated that the implementation of these ideas will take place in three steps: (1) driver-in-the-loop control using a graphical display; (2) driver assisted automatic control, with an on-board operator making only high-level decisions; and (3) vehicle autonomous guidance and control with on-line parameter identification and adaptive control that will operate for several hours without human intervention.

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