A Path Following Control for Unicycle Robots

In this work we present a new path following control for unicycle robots that is applicable for almost all the possible desired paths and whose analysis is very straightforward. First we select the path following method that consists of two steps: choosing a ‘‘projection’’ that relates the actual posture to the desired path and imposing a ‘‘motion exigency’’ to ensure that the robot advances. A ‘‘projection’’ that considers all the error coordinates is selected and closed equations are obtained for it. The uniqueness projection is carefully analyzed and a necessary and sufficient condition is also presented. This condition shows that a slight bound on the curvature derivative of desired paths must be imposed to preserve uniqueness. It is remarkable that the selected path following is applicable for paths containing zero-radius turns, a problem that has never been resolved as far as we know. In addition, an asymptotically stable control law is found using the closed form equation of the proposed path following and the second Lyapunov method. Finally, we show the behavior of the path following and the control law through several simulated and experimental results, using a computerized wheelchair built at our research facility.Comisión Interministerial de Ciencia y Tecnología TER96-2056-C02-0

Using virtual potential fields for electric wheelchair guidance

TetraNauta is an electric wheelchair guidance system intended for people with heavy motion impairments (such as persons with tetraplegia). It is specially useful when impairments also affect wheelchair steering as it is able to automatically guide wheelchairs between different points in a known environment (a hospital, a school, etc), conditioned with track marks painted on the floor. It also provides a semiautomatic navigation mode, where control is shared between user and navigation system. It is intended for learning wheelchair manipulation and as an aid in places where navigation is difficult or dangerous (i.e. for crossing narrow corridors)

Improving tracking of trajectories through tracking rate regulation: application to UAVs

The tracking problem (that is, how to follow a previously memorized path) is one of the most important problems in mobile robots. Several methods can be formulated depending on the way the robot state is related to the path. “Trajectory tracking” is the most common method, with the controller aiming to move the robot toward a moving target point, like in a real-time servosystem. In the case of complex systems or systems under perturbations or unmodeled effects, such as UAVs (Unmanned Aerial Vehicles), other tracking methods can offer additional benefits. In this paper, methods that consider the dynamics of the path’s descriptor parameter (which can be called “error adaptive tracking”) are contrasted with trajectory tracking. A formal description of tracking methods is first presented, showing that two types of error adaptive tracking can be used with the same controller in any system. Then, it is shown that the selection of an appropriate tracking rate improves error convergence and robustness for a UAV system, which is illustrated by simulation experiments. It is concluded that error adaptive tracking methods outperform trajectory tracking ones, producing a faster and more robust convergence tracking, while preserving, if required, the same tracking rate when convergence is achieved