Guidance Algorithms for Planar Path-based Motion Control Scenarios

Abstract

The problem of performing accurate path maneuvering tasks in planar space is investigated in thesis. The purpose is to utilize limited knowledge about the vehicle's maneuverability constraints to output feasible reference signals. Acceleration limitations of the vehicle have been used in an algorithm that determines forward speeds in such way that a predefined path can be followed at high speeds. The algorithm ensures that the speed is reduced before acute turns. Furthermore, an existing steering law has been modified to dynamically take the limitations of the vehicle into consideration when determining the desired course. This modified steering law exhibits desirable convergence characteristics toward the desired path. A complete guidance system, which combines the path convergence algorithm with the path speed algorithm, has been proposed. This system is able to rapidly converge to the desired path and follow this path, even for paths where the curvature is large. The modified steering law has been combined with a path-tracking speed controller. The path-tracking speed controller makes sure the vehicle can track a target on a predefined path. The resulting path-tracking system is able to follow a leader vehicle's path by creating accurate paths online from periodically sampled positions. A method for creating feasible U-turns in a lawn-mower pattern has been proposed. For a given vehicle speed, the resulting path obeys angular speed and angular acceleration constraints. Finally, the proposed algorithms are tested in simulations to illustrate their behavior and usefulness.