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Automatic tractor guidance system based on global positioning system
Abstract
An automatic tractor guidance system using the global positioning system (GPS) was developed to steer a tractor along a predetermined path. The guidance path was the Nebraska Tractor Test track. The length of a complete loop of the track is 586 m. The guidance path was defined by a series of 586 positions represented by easting and northing coordinates. The GPS was operated using real time differential correction (DGPS). The DGPS provided positions (easting, northing) with circular error probable (CEP) of 5.5 m, and distance root mean square (DRMS) of 6.82 m. The maximum easting and northing errors were 12.7 m and 21.4 m, respectively. The DGPS positions of the moving tractor were not affected by the moving error. The average deviation of the DGPS positions of the moving tractor from the true locations was 6.2 m, and the standard deviation was 2.2 m. Due to the fluctuation of the DGPS positions, a dead reckoning (DR) positioning method was coupled with the DGPS positioning to provide the guidance system with smoothed positions. A guidance control algorithm was developed to determine the proper steering angle to correct front wheel angle to follow the guidance path. The angular velocity to steer front wheels varied with the amount of required steering and the time to reach the look-ahead position on the guidance path. The automatic guidance system was simulated through computer simulation and field test. Using a computer simulation, the system was evaluated at three travel speeds (1, 2, and 3 m/s). The simulated guidance paths were a step function and a sine wave function. The simulation test suggested that the average position error does not depend on travel speed at a probability of 0.05. In the field test, the automatic guidance system was tested at the low speed (1 m/s). The field test was to evaluate the system ability to complete one loop (586 m) of the Nebraska Tractor Test track which provided straight and turning patterns. The automatic guidance system controlled the tractor with a mean deviation of 18.65 cm from the guidance path, and a standard deviation of 2.3 m. Sixty eight percent of the actual position errors were less than the standard deviation for the DGPS positions of a moving tractor. The computed errors were compared with the measured errors of the guidance system. It was found that the computed errors by the program can be used to represent those errors measured with a measuring tape at a probability of 0.05.
Subject Area
Agricultural engineering
Recommended Citation
Al-Hamed, Saad A. I, "Automatic tractor guidance system based on global positioning system" (1996). ETD collection for University of Nebraska-Lincoln. AAI9700072.
https://digitalcommons.unl.edu/dissertations/AAI9700072