Design and Development of an Auto-Steering System Control for Off-Road Vehicles

ABSTRACT: In this thesis, a control method is developed to enhance the path tracking accuracy of an agricultural vehicle steering system. Therefore, in order to boost the mean error value, the lateral error of a farm tractor at the curvature transitions is minimized by introducing a second look-ahead reference point (LARP) to the conventional lateral deviation controller. Since automation and precision have been significant objectives in the recent studies of land vehicle guidance controllers, a reasonable trade-off has been sought to come up with a steering control system approach with respect to the modern farming operation needs, recent industrial developments, sophistication degree of the approach, reliability, manoeuvrability, accuracy, computational cost, implementation feasibility and sensitivity to variation of system parameters. Present study develops a simple automatic path tracking system to satisfy the typical requirements of an unmanned agricultural tractor application based on properties of two look-ahead reference points (LARPs) on the desired path. The main objective of the proposed control system is to track the desired path within reasonable tolerances of a typical farming process including considerable slippage. Since the path shape of the farm field depends strongly on the terrain and surrounding environment such as crop rows pattern, the curvature of the reference path is subject to change. Thus, the employed look-ahead reference points provide compensation for centrifugal forces and reduction of the peak lateral deviation due to curvature transition, using only simple arithmetic operations. Extensive numerical tests were carried out on the computer simulation of the system dynamics driven by the proposed control method. Simulation results indicate enhancements in vehicle manoeuvrability and reduction of peak lateral displacement error at the curvature transitions to one fifth of single LARP error. The proposed 2-LARP control strategy performs exactly same as the conventional lateral deviation controller on the linear and circular paths but it outperforms the conventional controller at the curvature transitions where the second LARP behaves independent to the first LARP. Keywords: look-ahead reference point (LARP) control, path tracking, automatic steering agricultural vehicle, curvature transition. ……………………………………………………………………………………………………………………………………………………………………………………………………………………