` Intelligent and Mobile Robotics

Control and Localization for Swarms of low-cost helicopters (COLOS)

Project partners:

Intelligent and Mobile Robotics group (IMR)GRASP laboratory
CTU in PragueUniversity of Pennsylvania
Ing. Libor Přeučil, CSc.Prof. Vijay Kumar
http://imr.felk.cvut.cz/http://grasp.upenn.edu/

People involved: Martin Saska, Justin Thomas, Matthew Turpin, Jan Chudoba, Tom Krajnik, Jan Faigl, Giuseppe Loianno, Tomas Baca, Zdenek Kasl, Vojtech Vonasek

Project topic:

The aim of the proposed project is to develop a control framework that enables to settle boundness of cooperative localization of particles in robotic swarms. The motivation of such an effort is to improve standard cooperative navigation and localization approaches based on swapping obtained information between robots via communication. Utilization of these methods is limited in scenarios, where a large robotic teams needs to be utilized. Extensive deployment of robots in a small area decreases communication bandwidth or even disenable transmission of messages between the robots at all. Here, we can find an inspiration in nature: individuals in big school of fish, clusters of insect or flocks of birds cannot directly communicate with neighbors due to surrounding noise and their relative localization is realized through observation of neighbors. Our idea is to transfer similar concepts to localization in robotics, mainly in applications of autonomous low-cost helicopters (small quad-rotor helicopters equipped with simple panoramatic cameras). The challenging problem in such a task is, how to keep localization precision above a given threshold which is a key property. This requirement leads to necessity of particles movement stability analysis. Such a theoretical framework should provide control boundness that results from limits of movement given by requirements of localization (e.g. each particle should perceive a minimal amount of neighbors), environment (e.g. helicopters should keep suficient distance from obstacles and neighbors) and application (the complete swarm should follow a mission plan).

The proposed project COLOS aims to integrate principles and theoretical background of helicopters control and swarm behavior with methodology and theory describing existing approaches for cooperative localization of heterogenous teams of mobile robots and a single helicopter. The Czech (IMR - Intelligent Mobile Robotics group at the Gerstner Laboratory, CTU in Prague) partner is continuously developing a framework that is focused on main principles how to increase the localization precision leading to reliable navigational techniques. Within the project, their approach and developed theory will be used as a core of arising system for localization of swarms. The US partner (Department of Mechanical Engineering and Applied Mechanics, University of Pennsylvania) is one of leading bodies in area of control of cooperating quad-rotor helicopters. Within the project, their experience with control of cooperating UAVs and knowledge of stability analysis will be utilized to develop a robust system applicable in scenarios of swarm robotics that cannot be realized with existing methods.

Demos:

Leader follower formation based on relative visual localization - triangular formation

UAV group flying in a compact formation. The method relies on a top-view visual relative localization provided by the micro aerial vehicle flying above the rest of the group. It provides a robust solution applicable in complex environments with static and dynamic obstacles. The core of the leader-follower based formation driving method consists in a representation of the entire 3D formation as a convex hull projected along the trajectory of the group. Such an approach provides non-collision solution and respects requirements of the direct visibility between the team members. The obstacle avoidance ability of the method is demonstrated by the two no-fly zones considered during the planning. Distance between UAVs is kept constant during the experiment and it is measured by the relative localization module. The two UAVs flying in the same altitude are equipped with cameras oriented to the side to observe each other. The UAV flying above may observe both UAVs flying lower.




Swarm coverage with relative visual localization

Deployment of the system in surveillance tasks, where locations of interest with different priorities are covered by a self stabilized swarm of UAVs. The planning approach suited for the swarm particles mutually localized by the on-board camera modules and identification patterns. In the planning, the target shape of the spread swarm is found together with trajectories from initial configurations to this target shape. The method does not guarantee that the found distribution of the swarm and the obtained trajectories from initial positions into the found locations are optimal, but feasibility of the solution is guaranteed. The plan of swarm distribution in the environment satisfies constraints given by range of the relative localization, viewing angle of the on-board cameras and it respects mutual UAVs heading and movement constraints. The feasibility of the plan, obtained based on known sets of areas of interest, no-fly zones and initial positions of UAVs, is verified in the experiment.




Tangible PSO for odor source localization

PSO searching process modified for an odor source localization with swarms of unmanned helicopters. The entire UAV group is represented by the PSO swarm with fitness function corresponding to a virtual concentration of a simulated smoke plume. Each PSO rule is decomposed to independent motion primitives of separate helicopters. UAVs are subsequently moved into new positions required by the PSO process. In each subsequent movement, a quadrocopter approaches into the new location, while the remaining robots keep constant pose and only their Yaw angle is changed to track the moving UAV and to realize the required relative localization. The advantage of such an approach is the possibility to keep the global position of the swarm during the mission.




Leader follower formation based on relative visual localization - line formation

UAV group flying in a compact formation. The method relies on a visual relative localization between UAVs. It provides a robust solution applicable in complex environments with static and dynamic obstacles. The core of the leader-follower based formation driving method consists in a representation of the entire 3D formation as a convex hull projected along the trajectory of the group. Such an approach provides non-collision solution and respects requirements of the direct visibility between the team members. The obstacle avoidance ability of the method is demonstrated by the two no-fly zones considered during the planning. Distance between UAVs is kept constant during the experiment and it is measured by the relative localization module. The three UAVs are steered in the same altitude in a line formation. The relative positions between robots are measured by cameras oriented to the side. The cameras are placed onboard of each robot. In the experiment, the formation was repeatedly navigated through the environment to show robustness of the method.




Tangible Fish School Search

Utilization of Fish School Search (FSS) based method for searching in 3D environment. The FSS based algorithm is modified for control a swarm of quadrocopters and it respects motion constraints and limits of the visual relative localization (each UAV must see at least one neighbouring UAV all the time). The adjustment of the FSS algorithm, originally developed for dimensionless particles, is given by deployment of physical swarm particles (UAVs) and mainly includes restrictions that are caused by movement in real search space (collisions during flight, collisions in the target locations given by the FSS rules, dynamic model of UAVs etc.). In the experiments, UAVs cooperatively search for locations with lowest intensity of a signal transmitted from four transmitters distributed in the environment in different altitude. The intensity of the signal is simulated in the experiment based on known locations and transmission power of virtual transmitters.




3D simulation of swarm movement using the escape behavior method

This movie presents an investigation of swarm control dealing with an escape behavior, which is important functionality in application with human-swarm coexistence. The escape behavior algorithm was extended for the swarm purposes. The movement strategies originally developed for holonomic point particles were replaced with dynamic models of UAVs. Examples of the swarm movement under the rules of the escape behavior using the dynamic models of UAVs are shown in the movie.




Navigation, localization and stabilization of formations of unmanned aerial and ground vehicles

A leader-follower formation driving algorithm is employed for control of heterogeneous groups of unmanned micro aerial and ground vehicles stabilized under a top-view relative localization in this video. The core of the method lies in an avoidance function, in which the entire 3D formation is represented by a convex hull projected along a desired path to be followed by the group. Such a representation of the formation provides non-collision trajectories of the robots and respects requirements of the direct visibility between the team members in environment with static as well as dynamic obstacles, which is crucial for the top-view localization. The algorithm is suited for utilization of a simple yet stable visual based navigation of the group (referred to as GeNav), which together with the on-board relative localization enables deployment of large teams of micro-scale robots in environments without any available global localization system.




See IMR demos page for more records of experiments of the SWARM stream and Intelligent and Mobile Robotics Group in general.


Journal publications:

  • Saska, M. - Vonásek, V. - Krajník, T. - Přeučil, L. Coordination and navigation of heterogeneous MAV–UGV formations localized by a ‘hawk-eye’-like approach under a model predictive control scheme. International Journal of Robotics Research. OnlineFirst 2014; DOI: 10.1177/0123456789123456.
  • Krajník, T - Nitsche, M - Faigl, J. - Vaněk, P. - Saska, M. - Duckett, T. - Přeučil, L. - Mejail, M.: A practical multirobot localization system. Journal of Intelligent & Robotic Systems, OnlineFirst, 2014.
  • Saska, M. - Krajník, T. - Vonásek, V. - Kasl, Z. - Spurný, V. - Přeučil, L.: Fault-tolerant formation driving mechanism designed for heterogeneous MAVs-UGVs groups, Journal of Intelligent & Robotic Systems, 73 (1-4), 603-622, 2014.
  • Saska, M. - Mejía, J. S. - Stipanović, D. M. - Vonásek, V. - Schilling, K. - Přeučil, L.: Control and navigation in manoeuvres of formations of unmanned mobile vehicles, European Journal of Control, 19(2), 157-171, 2013.
  • Saska, M. - Vonásek, V. - Přeučil, L.: Trajectory Planning and Control for Airport Snow Sweeping by Autonomous Formations of Ploughs, Journal of Intelligent & Robotic Systems, 72(2), 239-261, April, 2013. [pdf]