On Path Planning and Path Following for Wheeled Mobile Robots
Doctoral thesis, 1995
The aim of the research documented and discussed in this thesis is to develop navigation methods including Path Planning, Location Measurement, and Path Following for supporting the navigation of wheeled mobile robots (WMR). The concept provides
methods for path planning, i.e. the generation of reference trajectories that the vehicle is able to follow as long as its speed does not exceed the value for which the trajectory is generated, and methods to ascertain that the resulting path is collision-free. The reference trajectories are generated while taking the dynamic and kinematic constraints of the steering mechanisms into account.
odometric methods to calculate location estimates that can be calibrated by absolute-measuring locating devices. Described in this thesis are inductive antennas sensing the lateral deviation from wires embedded in the floor, and a laser radar perceiving the geometry of the environment.
methods that allow the robot vehicle to follow a reference trajectory with a minimum of tracking error.
When analyzing the different types of locating systems and vehicle configurations, we can see that each individual solution or design has certain advantages in performance, cost, etc. The emphasis is on finding methods that allow the use of different kinds of locating systems and are applicable to mobile robots independently of how the steered and driven wheels of the vehicle are configured. Striving for that goal, a method of path planning and path following using virtual wheels is introduced to simplify trajectory tracking, especially for curved trajectories. This method is applied to different vehicle configurations such as tricycle-type vehicles, differential vehicles, and vehicles with multiwheel steering.
To support planning and verification of the resulting paths for these configurations, a concept of reference path and corresponding resulting path generation is proposed. Based on this concept, an interactive CAD-Simulator software package was developed providing tools for visualization and storage of path elements such as reference trajectory and resulting trajectory, sweep surface, and wheel tracks.
In order to improve mobility during certain maneuvers for vehicles transporting heavy loads, a locomotion and steering concept utilizing a conical wheel is described.
The concepts described have been implemented in actual applications and the architecture of both hardware and software is documented in Papers A, B, C, and D.