Lounis Adouane

Mobile Robot Navigation in Cluttered Environment using Reactive Elliptic Trajectories

Reactive navigation in very cluttered environment while insuring maximum safety and task efficiency is a challenging subject. This paper proposes online and adaptive elliptic trajectories to perform smooth and safe mobile robot navigation. These trajectories use limit-cycle principle already applied in the literature but with the difference that the applied limit-cycles are now elliptic (not circular) and are more generic and flexible to perform navigation in environments with different kinds of obstacles shape. The set points given to the robot are generated while following reactive obstacle avoidance algorithm embedded in a multi-controller architecture (Obstacle avoidance and Attraction to the target controllers). This algorithm uses specific reference frame which gives accurate indication of robot situation. The robot knows thus if it must avoid the obstacle in clockwise or counterclockwise direction and prevent robot from local minima, dead ends and oscillations. The stability of the proposed bottom-up control architecture is proved according to Lyapunov synthesis. Simulations and experiments in different environments are performed to demonstrate the efficiency and the reliability of the proposed control architecture.

Navigation of multi-robot formation in unstructured environment using dynamical virtual structures

In this paper, the control problem for a group of mobile robots keeping a geometric formation is considered. The proposed architecture of control allows to each robot to avoid obstacles and to rejoin the desired formation. To not complicate the control of such a system, it is proposed to divide the overall complex task into two basic tasks: attraction to a dynamical target, and obstacle avoidance. Thus, a desired geometric shape is defined and each robot has to track one node of this mobile shape. Each robot has to be autonomously able to avoid disturbing obstacles and to rejoin the formation in a reactive manner. Moreover, it chooses the optimal avoidance side thanks to limit-cycle method in order to reach as rapidly as possible its virtual target. The proposed control architecture is implemented in a distributed manner. In addition, this architecture uses the same control law (Lyapunov stable) for the two elementary tasks, and the switching from one task to another occurs only by changing the set-points. Experimental results validate the proposed control architecture.

Hybrid behavioral control architecture for the cooperation of minimalist mobile robots

This paper presents a hybrid control architecture based on subsumption and schemas motors principles in order to achieve complex and cooperative tasks. The control architecture implemented is constituted by a set of independent and elementary behaviors organized in layers of skills. Specific low-level behaviors, called altruistic behaviors and inspired by societies of insects (attractive or repulsive signals), are used to improve the efficiency of the control. Therefore, competitive and cooperative mechanisms are used in a unique hybrid architecture of control to perform a complex box-pushing task by a set of mini-robots. The analysis of an elevated number of simulations allows us to have statistical results (time to complete the task was chosen as performance criteria) which show the existence of an optimal number of robots to achieve the box-pushing task and underline the importance of the use of altruistic behaviors to enhance the cooperative task.

Reactive navigation of a mobile robot using elliptic trajectories and effective online obstacle detection

This paper deals with the problem of mobile robot navigation in cluttered environment. Adaptive elliptic trajectories are exploited for reactive obstacle avoidance using only position information and uncertain range data. The obstacle avoidance strategy used is based on the elliptic limit-cycle principle where each obstacle is surrounded by an ellipse. The ellipse parameters are computed online using a sequence of uncertain range data. An online heuristic method combined with the extended Kalman filter (EKF) is used to compute the ellipse parameters. It is demonstrated that this process ensures that all range data are surrounded by a computed ellipse. Moreover, this paper proposes a single control law to the multicontroller architecture where a reactive obstacle avoidance algorithm is embedded. The proposed control law is based on the Kanayama control law; it is designed to improve the performance of the controllers. The stability of this control architecture is proved according to the Lyapunov synthesis. Simulations and experiments in different environments have been performed to demonstrate the efficiency and reliability of the proposed online navigation in cluttered environment.

Punctual versus continuous auction coordination for multi-robot and multi-task topological navigation

This paper addresses the interest of using punctual versus continuous coordination for mobile multi-robot systems where robots use auction sales to allocate tasks between them and to compute their policies in a distributed way. In continuous coordination, one task at a time is assigned and performed per robot. In punctual coordination, all the tasks are distributed in Rendezvous phases during the mission execution. However, tasks allocation problem grows exponentially with the number of tasks. The proposed approach consists in two aspects: (1) a control architecture based on topological representation of the environment which reduces the planning complexity and (2) a protocol based on sequential simultaneous auctions (SSA) to coordinate Robots’ policies. The policies are individually computed using Markov Decision Processes oriented by several goal-task positions to reach. Experimental results on both real robots and simulation describe an evaluation of the proposed robot architecture coupled wih the SSA protocol. The efficiency of missions’ execution is empirically evaluated regarding continuous planning.

Stable navigation in formation for a multi-robot system based on a constrained virtual structure

This paper deals with the navigation in formation of a group of mobile robots. A set of virtual targets (points) forms a virtual structure of the same shape as the desired formation. Hence, to join and to remain in this formation, each robot has only to track one of these targets. In order to track the chosen target, it has to be attainable by the robot despite its kinematic constraints. This paper studies then the maximum allowed dynamic of the virtual structure according to the kinematic constraints of the robots. Both linear and angular velocities of the targets are constrained. Moreover, depending on these velocities, some relative positions (targets) in the formation become unattainable. These positions are also defined. A stable control law allows us to attain the generated set-points. Simulation and experimental results validate the proposed contributions. Constrained virtual structure approach for multi-robot navigation in formation.Stable multi-controller architecture (Obstacle avoidance and Attraction to Dynamical target) based on Lyapunov synthesis.Attainability demonstration of dynamic targets set-points while respecting the kinematic constraints of the group of mobile robots.

A novel safe and flexible control strategy based on target reaching for the navigation of urban vehicles

This paper presents a complete framework for reactive and flexible autonomous vehicle navigation. A human driver reactively guides a vehicle to the final destination while performing a smooth trajectory and respecting the road boundaries. The objective of this paper is to achieve similar behavior in an unmanned ground vehicle to reach a static or dynamic target location. This is achieved by using a flexible control law based on a novel definition of control variables and Lyapunov synthesis. Furthermore, a target assignment strategy to enable vehicle navigation through successive waypoints in the environment is presented. An elementary waypoint selection method is also presented to perform safe and smooth trajectories. The asymptotic stability of the proposed control strategy is proved. In addition, an accurate estimation of the maximum error boundary, according to the controller parameters, is given. With this indicator, the vehicle navigation will be safe within a certain boundaries. Simulations and experiments are performed in different cases to demonstrate the flexibility, reliability and efficiency of the control strategy. Our proposal is compared with different navigation methods from the literature such as those based on trajectory following. Novel control strategy based on static/dynamic target reaching for autonomous navigation.Control law is synthesized using a Lyapunov function based on a new set of variables.Interesting properties of the control law in terms of stability and flexibility.Sequential target assignment strategy allows performing safe navigation.Experiments using actual vehicles and several simulations show the advantages of the proposal.

An overall control strategy based on target reaching for the navigation of an urban electric vehicle

This paper deals with reactive and flexible humanlike autonomous vehicle navigation. A human driver reactively guides his vehicle, performing a smooth trajectory within the roads limits until reaching the defined goal. To obtain a similar behavior with an unmanned ground vehicle (UGV), this paper proposes a flexible control law to drive a vehicle towards desired static or dynamic targets based on a novel definition of control variables and Lyapunov stability analysis. Moreover, a target assignment strategy, combined with an appropriate sigmoid function, that allow to perform smooth, flexible and safe vehicle navigation through successive waypoints is presented. The stability of the proposed control strategy is proved according to Lyapunov synthesis. Simulations and experiments are performed in different cases to demonstrate the reliability and efficiency of the control strategy.

Map partitioning to approximate an exploration strategy in mobile robotics

In this paper, an approach is presented to automatically allocate a set of exploration tasks between a fleet of mobile robots. The approach combines a Road-Map technique and Markovian Decision Processes MDPs. The addressed problem consists of exploring an area where a set of points of interest characterizes the main positions to be visited by the robots. This problem induces a long term horizon motion planning with a combinatorial explosion. The Road-Map allows the robots to represent their spatial knowledge as a graph of way-points connected by paths. It can be modified during the exploration mission requiring the robots to use on-line computations. By decomposing the Road-Map into regions, an MDP allows the current group leader to evaluate the interest of each robot in every single region. Using those values, the leader can assign the exploration tasks to the robots.

Adaptive Leader-Follower Formation in Cluttered Environment Using Dynamic Target Reconfiguration

This paper presents a control architecture for safe and smooth navigation of a group of Unmanned Ground Vehicles (UGV) while keeping a specific formation. The formation control is based on Leader-follower and Behavioral approaches. The proposed control architecture is designed to allow the use of a single control law for different multi-vehicle contexts (navigation in formation, transition between different formation shapes, obstacle avoidance, etc.). The obstacle avoidance strategy is based on the limit-cycle approach while taking into account the dimension of the formation. A new Strategy for Formation Reconfiguration (SFR) of the group of UGVs based on suitable smooth switching of the set-points (according, for instance, to the encountered obstacles or the new task to achieve) is proposed. The inter-vehicles collisions are avoided during the SFR using a penalty function acting on the vehicle velocities. Different simulations on cluttered environments show the performance and the efficiency of the proposal, to obtain fully reactive and distributed control strategy for the navigation in formation of a group of UGVs.