Set Of Mobile Robots Research Articles

Multirobot Transport of Deformable Objects With Collision Avoidance

In the problem of autonomous transport of deformable objects, we propose a multirobot approach for steering a large object to a target configuration (object dimensions, orientation, and position). Firstly, we present a deformation model based on the evolution over time of the dimensions and rotation of the object's bounding box (BB). We consider the object is grasped by a set of mobile robots with double-integrator dynamics. Then, we propose a set of nominal controllers that allows reaching a desired configuration of the BB that models the deformable object. In order to prevent collisions of the object with static or dynamic obstacles, we formulate a control barrier function (CBF) that exploits our deformation model. Finally, we integrate the nominal controllers and the CBF into a quadratic-programming controller, which includes overstretching avoidance and velocity constraints. We report simulation results to show the performance of this approach in different test scenarios.

Optimal patrolling of high priority segments while visiting the unit interval with a set of mobile robots

Consider a region that requires to be protected from unauthorized penetrations. The border of the region, modeled as a unit line segment, consists of high priority segments that require the highest level of protection separated by low priority segments that require to be visited infinitely often. We study the problem of patrolling the border with a set of k robots. The goal is to obtain strategies that minimize the maximum idle time (the time that a point is left unattended) of each point of the high priority segments while visiting each point of the low priority segments infinitely often. We use the concept of single lid cover (segments of fixed length) where each high priority point is covered with at least one lid, and then we extend it to strong double-lid cover where each high priority point is covered with at least two lids, and the unit line segment is fully covered. Let λk−1 be the minimum lid length that accepts a single λk−1-lid cover with k−1 lids and Λ2k be the minimum lid length that accepts a strong double Λ2k-lid cover with 2k lids. We show that 2min⁡(Λ2k,λk−1) is the lower bound of the idle time when the max speed of the robots is one. To compute Λ2k and λk−1, we present an algorithm with time complexity O(max⁡(k,n)log⁡n) where n is the number of high priority segments. Our algorithm improves by a factor of min⁡(n,k) the previous O(knlog⁡n) running time algorithm. For the upper bound, first we present a strategy with idle time λk−1 where robot k patrols the unit line segment, and robot i patrols the i-lid of a single λk−1-lid cover with k−1 lids. Then, we present a simple strategy with idle time 3Λ2k that splits the unit line into not-disjoint k segments of equal length that robots synchronously cover, i.e., reaching the leftmost and rightmost point simultaneously. Then, we present a complex strategy that splits the unit line into k non-disjoint segments that robots asynchronously cover. We show that the combination of strategies one and two attains an approximation of 1.5 the optimal idle time and combining strategies one and third attains an optimal idle time.

Optimal rendezvous on a line by location-aware robots in the presence of spies*

A set of mobile robots is placed at arbitrary points of an infinite line. The robots are equipped with GPS devices and they may communicate their positions on the line to a central authority. The collection contains an unknown subset of “spies”, i.e., byzantine robots, which are indistinguishable from the non-faulty ones. The set of the non-faulty robots needs to rendezvous in the shortest possible time in order to perform some task, while the byzantine robots may try to delay their rendezvous for as long as possible. The problem facing a central authority is to determine trajectories for all robots so as to minimize the time until all the non-faulty robots have met. The trajectories must be determined without knowledge of which robots are faulty. Our goal is to minimize the competitive ratio between the time required to achieve the first rendezvous of the non-faulty robots and the time required for such a rendezvous to occur under the assumption that the faulty robots are known at the start. In this paper, we give rendezvous algorithms with bounded competitive ratio, where the central authority is informed only of the set of initial robot positions, without knowing which ones or how many of them are faulty. In general, regardless of the number of faults [Formula: see text] it can be shown that there is an algorithm with bounded competitive ratio. Further, we are able to give a rendezvous algorithm with optimal competitive ratio provided that the number [Formula: see text] of faults is strictly less than [Formula: see text]. Note, however, that in general this algorithm does not give an estimate on the actual value of the competitive ratio. However, when an upper bound on the number of byzantine robots is known to the central authority, we can provide algorithms with constant competitive ratios and in some instances we are able to show that these algorithms are optimal. Moreover, in the cases where the number of faults is either [Formula: see text] or [Formula: see text] we are able to compute the competitive ratio of an optimal rendezvous algorithm, for a small number of robots.

Herding by caging: a formation-based motion planning framework for guiding mobile agents

We propose a solution to the problem of herding by caging: given a set of mobile robots (called herders) and a group of moving agents (called sheep), we guide the sheep to a target location without letting them escape from the herders along the way. We model the interaction between the herders and the sheep by defining virtual “repulsive forces” pushing the sheep away from the herders. This enables the herders to partially control the motion of the sheep. We formalize this behavior topologically by applying the notion of caging, a concept used in robotic manipulation. We demonstrate that our approach is provably correct in the sense that the sheep cannot escape from the robots under our assumed motion model. We propose an RRT-based path planning algorithm for herding by caging, demonstrate its probabilistic completeness, and evaluate it in simulations as well as on a group of real mobile robots.

Gathering in the plane of location-aware robots in the presence of spies

A set of mobile robots (represented as points) is distributed in the Cartesian plane. The collection contains an unknown subset of byzantine robots which are indistinguishable from the reliable ones. The reliable robots need to gather, i.e., arrive to a configuration in which at the same time, all of them occupy the same point on the plane. The robots are equipped with GPS devices and at the beginning of the gathering process they communicate the Cartesian coordinates of their respective positions to a central authority. On the basis of this information, and without the knowledge of which robots are faulty, the central authority designs a trajectory for every robot. The central authority aims to provide the trajectories which result in the shortest possible gathering time of the reliable robots. The efficiency of a gathering strategy is measured by its competitive ratio, i.e., the maximal ratio between the time required for gathering achieved by the given trajectories and the optimal time required for gathering in the offline case, i.e., when the faulty robots are known to the central authority in advance. The role of the byzantine robots, controlled by the adversary, is to act so that the gathering is delayed and the resulting competitive ratio is maximized.The objective of our paper is to propose efficient algorithms when the central authority is aware of an upper bound on the number of byzantine robots. We give optimal algorithms for collections of robots known to contain at most one faulty robot. When the proportion of byzantine robots is known to be less than one half or one third, we provide algorithms with small constant competitive ratios. We also propose algorithms with bounded competitive ratio in the case where the proportion of faulty robots is arbitrary.

Programmable mobile robots as hands-on platform for basic programming

Nowadays, mobile robots platforms are being used in different education contexts. The state of the art shows that 197 papers have been published in this area knowledge over ten years. Latin America faces a problem regarding the enrolled students in engineering programs. The SPADIES program (Colombia) affirms that the lack of motivation and interaction with real artifacts relating theory and practice is an important aspect for dropout. In this work, a platform composed by a set of programmable mobile robots, and a WEB-responsive software tool for programming at different levels of knowledge were implemented. The set of mobile robots were implemented with proximity, trajectory, light, inertial, and vision sensors; also, tools such as Bluetooth and LEDs-ring are included; and, a mechanical support for an erasable marker. The WEB-responsive tool supports graphical programming for novice, Python programming for middle, and ANSI-C for advanced level learners.

Energy constrained collection of multiple robots in 3D space

This reported work addresses a collaborative approach to path planning in continuous space for the energy constrained robot collection problem. The objective is to minimise the overall duration the mobile robots return from where the given tasks are completed. For time- and energy-efficient collection, the authors use a large-scale ground vehicle that can load and transport relatively small mobile robots. However, determining time-optimal collection locations requires too much computation in this problem setting. Therefore, a heuristic algorithm for a set of mobile robots is proposed and verified through simulations.

A unified approach for gathering and exclusive searching on rings under weak assumptions

Consider a set of mobile robots placed on distinct nodes of a discrete, anonymous, and bidirectional ring. Asynchronously, each robot takes a snapshot of the ring, determining the size of the ring and which nodes are either occupied by robots or empty. Based on the observed configuration, it decides whether to move to one of its adjacent nodes or not. In the first case, it performs the computed move, eventually. This model of computation is known as Look-Compute-Move. The computation depends on the required task. In this paper, we solve both the well-known Gathering and Exclusive Searching tasks. In the former problem, all robots must simultaneously occupy the same node, eventually. In the latter problem, the aim is to clear all edges of the graph. An edge is cleared if it is traversed by a robot or if both its endpoints are occupied. We consider the exclusive searching where it must be ensured that two robots never occupy the same node. Moreover, since the robots are oblivious, the clearing is perpetual, i.e., the ring is cleared infinitely often. In the literature, most contributions are restricted to a subset of initial configurations. Here, we design two different algorithms and provide a characterization of the initial configurations that permit the resolution of the problems under very weak assumptions. More precisely, we provide a full characterization (except for few pathological cases) of the initial configurations for which gathering can be solved. The algorithm relies on the necessary assumption of the local-weak multiplicity detection. This means that during the Look phase a robot detects also whether the node it occupies is occupied by other robots, without acquiring the exact number. For the exclusive searching, we characterize all (except for few pathological cases) aperiodic configurations from which the problem is feasible. We also provide some impossibility results for the case of periodic configurations.

A Comparison of the Manufacturing Resilience between Fixed Automation Systems and Mobile Robots in Large Structure Assembly

The modern manufacturing industry is undergoing major transformations due to global competition and rapidly changing market demands. Traditional systems with rigid structures are very difficult to reconfigure every time a change in production is required. A promising alternative to these is seen in mobile, self-organising manufacturing systems, where self-deploying and independent entities such as mobile robots are used to facilitate a more reconfigurable assembly process. In addition, an integral part of manufacturing is the transportation of components within the manufacturing environment. Conveyor systems are often unsuitable for moving components that are large, heavy or awkward, making them difficult to use in large structure assembly. Currently, such components are commonly transported by cranes to dedicated automation systems which are seen as expensive and unadaptable. In this paper we investigate the differences in resilience to variations between a set of mobile robots and the widely accepted fixed automation systems under different conditions. Therefore, instead of transporting components or parts to manufacturing equipment we analyse the potential benefits of transporting the equipment to the large parts. By means of simulations, the two systems are compared to one-another in scenarios of identical part arrival times and part processing capacities. Assuming equal production rates, we assess their ability to respond to (1) rush orders, (2) fluctuating arrival times and (3) production mix variations. Currently, there are no specific algorithms for process control of such mobile systems. For this reason we apply the First-In-First-Out task-selection rule. We present a comparison of resilience measures between the systems.

Optimal swarm formation for odor plume finding.

This paper presents an analytical approach to the problem of odor plume finding by a network of swarm robotic gas sensors, and finds an optimal configuration for them, given a set of assumptions. Considering cross-wind movement for the swarm, we found that the best spatial formation of robots in finding odor plumes is diagonal line configuration with equal distance between each pair of neighboring robots. We show that the distance between neighboring pairs in the line topology depends mainly on the wind speed and the environmental conditions, whereas, the number of robots and the swarm's crosswind movement distance do not show significant impact on optimal configurations. These solutions were analyzed and verified by simulations and experimentally validated in a reduced scale realistic environment using a set of mobile robots.

A Mobile Robots Experimental Environment with Event-Based Wireless Communication

An experimental platform to communicate between a set of mobile robots through a wireless network has been developed. The mobile robots get their position through a camera which performs as sensor. The video images are processed in a PC and a Waspmote card sends the corresponding position to each robot using the ZigBee standard. A distributed control algorithm based on event-triggered communications has been designed and implemented to bring the robots into the desired formation. Each robot communicates to its neighbors only at event times. Furthermore, a simulation tool has been developed to design and perform experiments with the system. An example of usage is presented.

Gossip algorithms for heterogeneous multi-vehicle routing problems

In this paper we address a class of heterogeneous multi-vehicle task assignment and routing problems. We propose two distributed algorithms based on gossip communication: the first algorithm is based on a local exact optimization and the second is based on a local approximate greedy heuristic. We consider the case where a set of heterogeneous tasks arbitrarily distributed in a plane has to be serviced by a set of mobile robots, each with a given movement speed and task execution speed. Our goal is to minimize the maximum execution time of robots.

A Gossip Algorithm for Heterogeneous Multi-Vehicle Routing Problems

In this paper we address the heterogeneous multi-vehicle routing problem by proposing a distributed algorithm based on gossip. We consider the case where a set of tasks arbitrarily distributed in a plane, each with a service cost, have to be served by a set of mobile robots, each with a given movement speed and task execution speed. Our goal is to minimize the maximum execution time of robots.

Self-stabilizing robot formations over unreliable networks

We describe how a set of mobile robots can arrange themselves on any specified curve on the plane in the presence of dynamic changes both in the underlying ad hoc network and in the set of participating robots. Our strategy is for the mobile robots to implement a self-stabilizing virtual layer consisting of mobile client nodes, stationary Virtual Nodes (VNs), and local broadcast communication. The VNs are associated with predetermined regions in the plane and coordinate among themselves to distribute the client nodes relatively uniformly among the VNs' regions. Each VN directs its local client nodes to align themselves on the local portion of the target curve. The resulting motion coordination protocol is self-stabilizing, in that each robot can begin the execution in any arbitrary state and at any arbitrary location in the plane. In addition, self-stabilization ensures that the robots can adapt to changes in the desired target formation.

Using eventually consistent compasses to gather memory-less mobile robots with limited visibility

Reaching agreement among a set of mobile robots is one of the most fundamental issues in distributed robotic systems. This problem is often illustrated by the gathering problem, where the robots must self-organize and meet at some location not determined in advance, and without the help of some global coordinate system. While very simple to express, this problem has the advantage of retaining the inherent difficulty of agreement, namely the question of breaking symmetry between robots. In previous works, it has been proved that the gathering problem is solvable in asynchronous model with oblivious (i.e., memory-less) robots and limited visibility, as long as the robots share the knowledge of some direction, as provided by a compass. However, the problem has no solution in the semi-synchronous model when robots do not share a compass, or when they cannot detect multiplicity. In this article, we define a model in which compasses may be unreliable, and study the solvability of gathering oblivious mobile robots with limited visibility in the semi-synchronous model. In particular, we give an algorithm that solves the problem in finite time in a system where compasses are unstable for some arbitrary long periods, provided that they stabilize eventually. In addition, we show that our algorithm solves the gathering problem for at most three robots in the asynchronous model. Our algorithm is intrinsically self-stabilizing.

Using Mobile Robots in Intelligent Assembly or Disassembly Process

The intelligent assembly or disassembly concept integrates the control and the planning of an automated material handling system based on a set of mobile robots. This work presents and analyses some results in path tracking control on complex plane trajectories for a differential wheeled mobile robot with memorized trajectories. For the same model of the robot, the control uses alternatively two different algorithms. The first one is a bang-bang algorithm and the second is a classical solution in path tracking control.

Analyzing the Multiple-target-multiple-agent Scenario Using Optimal Assignment Algorithms

This work considers the problem of maximum utilization of a set of mobile robots with limited sensor-range capabilities and limited travel distances. The robots are initially in random positions. A...

Nonlinear control for a convoy-like vehicle

This paper presents a nonlinear control law for a set of unconnected carts which are expected to move as a convoy-like vehicle. Applications of such control scheme can be found in highways where cars are desired to move at the same speed while controlling the distance between them, in automated flexible factories where set of mobile robots are required to follow a leader mobile robot and also in public transports programs where personalized vehicles are assumed to move in a convoy-like configuration. The control law presented in this paper is based on a previous work on feedback design for a train-like vehicle consisting of connected carts (see Canudas-de-Wit, NDoudi-Likoho & Micaelli, Conference on robotics and automation vol. 1 (pp. 14–19). New York: IEEE Press).

Nonlinear control for a convoy-like vehicle

This paper presents a nonlinear control law for a set of unconnected carts which are expected to move as a convoy-like vehicle. Applications of such control scheme can be found in highways where cars are desired to move at the same speed and to control the distance between them. Also in automated flexible factories where set of mobile robots are required to follow a leader mobile robot and also in public transports programs where personalized vehicles are assumed to move in a convoy-like configurations. The control law presented in this paper is based on a previous work on feedback design for a train-like vehicle (Canudas et al., 1994) consisting of connected carts.