Abstract
This paper presents a navigation strategy for a platoon of n non-holonomic mobile robots with a time-varying spacing policy between each pair of successive robots at the platoon, such that a safe trailing distance is maintained at any speed, avoiding the robots getting too close to each other. It is intended that all the vehicles in the formation follow the trajectory described by the leader robot, which is generated by bounded input velocities. To establish a chain formation among the vehicles, it is required that, for each pair of successive vehicles, the ()-th one follows the trajectory executed by the former i-th one, with a delay of units of time. An observer is proposed to estimate the trajectory, velocities, and positions of the i-th vehicle, delayed units of time, consequently generating the desired path for the ()-th vehicle, avoiding numerical approximations of the velocities, rendering robustness against noise and corrupted or missing data as well as to external disturbances. Besides the time-varying gap, a constant-time gap is used to get a secure trailing distance between each two successive robots. The presented platoon formation strategy is analyzed and proven by using Lyapunov theory, concluding asymptotic convergence for the posture tracking between the ()-th robot and the virtual reference provided by the observer that corresponds to the i-th robot. The strategy is evaluated by numerical simulations and real-time experiments.
Highlights
There are several mobile robot applications that take advantage of platooning strategies to improve performance or because of safety issues
When comparing the simulated (NE) results, Section 5.1, and real-time experiments for the Lemniscate path (RTE-a), Section 5.3.1, we note that convergence of the observation errors is rather faster than the tracking errors, as established from the stability analysis, since the observations errors present exponential convergence, Lemma 1, while the tracking errors converge asymptotically, Lemma 2
As to show robustness, when sudden perturbations at positions and orientation are introduced, simulating lost or failure of sensors measurements, or communication channel problems, it can be seen that the observers filtered the peak changes on measurements values, and smoothness of the signals is propagated through the mobile robots chain
Summary
There are several mobile robot applications that take advantage of platooning strategies to improve performance or because of safety issues. The present paper proposes an extension of the work developed in [23,24] where a fixed time-delay spacing policy is proposed, broadening the work to a time-varying spacing policy inspired by artificial potential fields, which ensures a safe distance between the members of the string, avoiding robots from getting too close to each other Under these conditions, the work considers a squad of non-holonomic mobile robots, where each robot is intended to follow the position and orientation of its precedent vehicle in the formation, while maintaining a time-varying gap that avoids collisions when the robots approach each other.
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