Automation and navigation of a terrestrial vehicle
Wynand Visser · SUNScholar (Stellenbosch University) · 2012
ENGLISH ABSTRACT: This thesis presents the design and implementation of an autonomous navigational system and the automation of a practical demonstrator vehicle. It validates the proposed navigation architecture using simple functional navigational modules on the said vehicle. The proposed navigation architecture is a hierarchical structure, with a mission planner at the top, followed by the route planner, the path planner and a vehicle controller with the vehicle hardware at the base. A vehicle state estimator and mapping module runs in parallel to provide feedback data. The controls of an all terrain vehicle are electrically actuated and equipped with feedback sensors to form a complete drive-by-wire solution. A steering controller and velocity control state machine are designed and implemented on an existing on-board controller that includes a six degrees-of-freedom kinematic state estimator. A lidar scanner detects obstacles. The lidar data is mapped in real time to a local three-dimensional occupancy grid using a Bayesian update process. Each lidar beam is projected within the occupancy grid and the occupancy state of a ected cells is updated. A lidar simulation environment is created to test the mapping module before practical implementation. For planning purposes, the three-dimensional occupancy grid is converted to a two-dimensional drivability map. The path planner is an adapted rapidly exploring random tree (RRT) planner, that assumes Dubins car kinematics for the vehicle. The path planner optimises a cost function based on path length and a risk factor that is derived from the drivability map. A simple mission planner that accepts user-de ned waypoints as objectives is implemented. Practical tests veri ed the potential of the navigational structure implemented in this thesis.