A hybrid navigation strategy for multiple mobile robots

This paper investigates finite-time tracking control problem of multiple non-holonomic mobile robots via visual servoing. It is assumed that the pinhole camera is fixed to the ceiling, and camera parameters are unknown. The desired reference trajectory is represented by a virtual leader whose states are available to only a subset of the followers, and the followers have only interaction. First, the camera-objective visual kinematic model is introduced by utilising the pinhole camera model for each mobile robot. Second, a unified tracking error system between camera-objective visual servoing model and desired reference trajectory is introduced. Third, based on the neighbour rule and by using finite-time control method, continuous distributed cooperative finite-time tracking control laws are designed for each mobile robot with unknown camera parameters, where the communication topology among the multiple mobile robots is assumed to be a directed graph. Rigorous proof shows that the group of mobile robots converges to the desired reference trajectory in finite time. Simulation example illustrates the effectiveness of our method.

A new hybrid navigation algorithm for mobile robots in environments with incomplete knowledge

This article, concerned with a part of the research on distributed coordination work by multiple robots, discusses an algorithm for creating maps of unknown environments which are searched for and observed by multiple mobile robots, and on the results of a simulation experiment using this algorithm. This algorithm comprises a moving method, an observation method, and a task planning method which are intended to help the multiple mobile robots carry out an efficient search of unknown environments.

Consensus problems of multiple nonholonomic mobile robots are considered in this paper. These problems are simplified into consensus problems of two subsystems based on structure of nonholonomic mobile robots. Linear distributed controllers are constructed respectively for these two subsystems thanks to the theory of nonautonomous cascaded systems. Consensus of multiple nonholonomic mobile robots has been realized using the methodology proposed in this paper no matter whether the group reference signal is persistent excitation or not. Different from previous research on cooperative control of nonholonomic mobile robots where the consensus problem under persistent exciting reference has received a lot of attention, this paper reports the first consensus result for multiple nonholonomic mobile robots whose group reference converges to zero. Simulation results using Matlab illustrate the effectiveness of the proposed controllers in this paper.

This paper deals with a framework of decentralized approach to division of labor by multiple mobile robots. An iterative-transportation task by multiple robots with multiple sets of starts (pick-up place of the object) and goals (put down place) is considered as the task. On each route between a start and a goal, the efficiency of transportation improves when the number of robots increases. Due to jams, however, excessive number of robots on the same route causes inefficiency. We propose a control law of each robot to choose an appropriate route so as to optimize the total efficiency of the transportation, where each robot utilizes information which can be obtained only by local observation (without any explicit communication among robots). The proposed control is based on the estimation of the number of robots on the routes in the future. In simulation, it was verified that the proposed control law realized 96% efficiency of the fully centralized control by appropriately choosing the route, compared with the case where global information can be utilized.

This paper investigates the distributed fixed-time consensus-based formation tracking problems for multiple nonholonomic wheeled mobile robots under a directed interaction topology. The distributed fixed-time consensus-based controllers under the directed interaction topology are proposed for the multiple wheeled mobile robots with nonholonomic constraints, which can guarantee the group of robots converge to a predefined formation pattern with its centroid moving along the predefined reference trajectory in a fixed time. The fixed-time formation tracking can be achieved within a fixed settling time, which is independent of the initial states of the whole system. Moreover, the conditions of formation stability control are analysed by utilising graph and Lyapunov stability theories. Finally, the feasibility of the proposed distributed controllers is verified by numerical simulation.

Formation tracking control problem of multiple nonholonomic mobile robots is considered in this paper. Previous tracking control results of single nonholonomic mobile robots are extended to solve the formation tracking control of multiple nonholonomic mobile robots. By using the theory of cascaded systems and cooperative control of linear agents, formation tracking control problem is converted into multi-linear time-varying systems' stabilization problem. Under some persistent excitation condition on the virtual leader, linear cooperative controllers are constructed for the formation tracking control problem. Simulation results using Matlab validates the theoretic results.

This paper deals with multi-objective behavior coordination and sensory networks based on fuzzy control for multiple mobile robots. In multi-objective behavior coordination, weights are assigned to basic behaviors and updated gradually according to the time series of sensory inputs. A robot with our behavior coordination can take a smooth action. The sensory network is the self-update mechanism of a sensory range in order to realize flexible control with a small number of control rules. Both methods have been successfully applied to a single mobile robot. In this paper, we focus on an environment including multiple mobile robots. We examine the effects of the values for updating behavior weights and sensory ranges on the performance of multiple mobile robots. From the experimental results, we show the effectiveness of the multi-objective behavior coordination and sensory networks in the environment including multiple mobile robots.

This paper proposes an approach to the motion coordination of multiple industrial mobile robots (AGVs). The task of the robots is to cooperatively transport a common object. An ordinary mobile robot has uncertain dynamics, and its motion is constrained by a non-holonomic constraint. Furthermore, multiple robots with a common object form a closed-chain structure which would cause the severe dynamical interactions. The authors' approach overcomes the inherent problems by introducing a robot-mounted coupler with mechanical compliance which provides compliance between each robot and the object. The hierarchical coordinative control scheme is presented to perform accurate object-transportation based on the synchronous motions of the robots. Simulation and fundamental experiment by using a commercially available AGV demonstrate the effectiveness of the authors' approach.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Symmetric caging formation for convex polygonal object transportation by multiple mobile robots based on fuzzy sliding mode control

Multiple mobile robots are a practical platform for realizing the concept of distributed manipulation. New approach for manipulating large number of objects using distributive actuators or agent has been suggested. Multiple mobile robots provide the ability to conduct actions simultaneously from various locations and directions. Using two mobile robots and flexible tool such as a piece of string or rope, a large number of objects that are placed at sparse locations can be sorted and grouped by single action. The Voronoi separation algorithm is proposed as a path generation method for preplanning cooperative actions of multiple robots. The sorting task is conducted on-line using fuzzy logic controller with preplanned subgoals. The proposed control framework was verified by an experiment using two autonomous mobile robots with a flexible tool attachment of fixed length.

This paper presents a way of collecting indoor RF propagation loss data utilizing multiple mobile robots collaborating through double-layered networks. The collected data are used to place wireless access points to maximize coverage with a minimum number of access points. A novel approach is used to navigate multiple robots using grid based maps which is a key issue in mobile robot utilization. Using grid based maps and range-finders to acquire surrounding information and match with a pre-populated information, robot locations are correctly identified. This resolved the problem of weak or no GPS signal in an indoor environment for position determination. The data acquisition strategy is studied without requiring a central source of timing and synchronization f or multiple robots. This is done using script-based robot command execution with exchange of request and response control messages. Lastly, numerical analysis of effects of navigation and data errors and their tolerances for proper interpretation of the collected data is presented.

Cooperative path following control of multiple nonholonomic mobile robots

An autonomous and decentralized robot system, ACTRESS, is being developed as an intelligent robot system which is composed of multiple robotic agents. In this paper, the basic concept of ACTRESS and a strategy for organizing multiple mobile robots including a communication framework in ACTRESS are introduced. The negotiation for distributed problem solving and cooperative actions is discussed. Especially, in order to manage and share the changing environment information, negotiation between multiple mobile robots and an environment manager is required. Finally, a wireless communication system for negotiation between multiple robotic agents is developed. Its performance is analyzed by experimental evaluation on searching for an environment manager by mobile robots, and some examples of communication including negotiation are shown. >

In this paper, we propose a motion planning method for cooperative transportation of a large object by multiple mobile robots in a complicated environment. We must plan the motions of the object and mobile robots to avoid obstacles in a three-dimensional environment. A computation time to solve this problem is exploded, since we need search a solution in a high dimensional configuration space (C-space). Accordingly, we reduce the dimensions of C-space using the feature of the transportation by multiple mobile robots. In our method, all things (the object, the robots and the obstacles) are represented by an octree that is the approximate cell decomposition method for a three-dimensional environment. We can find a solution with A* search algorithm in this smaller dimensional C-space using the potential field. We verify the effectiveness of our proposed motion planning method through simulations.