Localization and follow -the -leader control of a heterogeneous group of mobile robots

Most investigations of multi-robot cooperative control involve groups of robots with similar capabilities. It is often desirable to have a heterogeneous group of mobile robots with dramatically different onboard sensing, control and computation. This work investigates the control and localization of a heterogeneous (e.g. different sensing, mechanical, computational capabilities) group of mobile robots in which several inexpensive sensor-limited and computationally-limited robots follow a leader with a desired geometric formation. Specifically, the robots in this work are designed for highway safety applications where they automatically deploy and maneuver safety barrels commonly used to control traffic in highway work zones. Complex sensing and computation are performed by the leader, while the followers only perform simple operations under the leader\u27s guidance. The main challenge is that the followers are sensor-limited and do not have the capabilities of localization and navigation. This work presents two approaches to address the localization and follow-the-leader control for this heterogeneous robot team. One method uses the global localization and Bézier trajectory based following control. The global localization uses a least squares tracking method to approximate a cubic function of the follower\u27s recent Bézier trajectory, and obtains its global orientation by differentiating the approximated function. Statistical simulations are conducted to choose the appropriate distance between two tracking positions, and analyze the lower bound of the arc radii such that the least squares estimation can work efficiently. A simple Bézier trajectory based following mechanism is also developed to enable a group of follower robots to follow the leader. The global localization and following control method is mathematically simple and easy to implement, and is well suited for long distance navigation. A second method is the use of an Extended Kalman Filter to estimate the relative orientation between the leader and the follower. This relative localization method is able to achieve efficient localization in arbitrary motions including short turn motions. Relative localization eliminates the need for expensive global localization systems in all robots, and prevents the localization errors from accumulating over time as they would in traditional dead reckoning. A nonlinear feedback controller is also implemented to control the desired separation and bearing angle between the leader and the follower such that the desired group formation can be maintained. Stability of the formation controller is analyzed. Extensive experiments under indoor and outdoor environments demonstrate the validity of the relative localization and formation control method. This work also presents a static fixed-priority real-time model for the leader robot system. Given the number of followers to be controlled, the system schedulability is analyzed with time demand analysis to choose a proper localization period such that all tasks in the leader system can meet their individual deadlines. Furthermore, this work considers actual localization requirement to address the real-time scalability problem, i.e. the maximum number of followers to be controlled given a real-time model with specific temporal parameters. Real-time analysis allows the designer to make better decisions in choosing the number of followers to be controlled by a single leader in large scale robotic applications