8,444 research outputs found
Distributed Obstacle and Multi-Robot Collision Avoidance in Uncertain Environments
This paper tackles the distributed leader-follower (L-F) control problem for
heterogeneous mobile robots in unknown environments requiring obstacle
avoidance, inter-robot collision avoidance, and reliable robot communications.
To prevent an inter-robot collision, we employ a virtual propulsive force
between robots. For obstacle avoidance, we present a novel distributed
Negative-Imaginary (NI) variant formation tracking control approach and a
dynamic network topology methodology which allows the formation to change its
shape and the robot to switch their roles. In the case of communication or
sensor loss, a UAV, controlled by a Strictly-Negative-Imaginary (SNI)
controller with good wind resistance characteristics, is utilized to track the
position of the UGV formation using its camera. Simulations and indoor
experiments have been conducted to validate the proposed methods
Cooperative decentralized circumnavigation with application to algal bloom tracking
Harmful algal blooms occur frequently and deteriorate water quality. A
reliable method is proposed in this paper to track algal blooms using a set of
autonomous surface robots. A satellite image indicates the existence and
initial location of the algal bloom for the deployment of the robot system. The
algal bloom area is approximated by a circle with time varying location and
size. This circle is estimated and circumnavigated by the robots which are able
to locally sense its boundary. A multi-agent control algorithm is proposed for
the continuous monitoring of the dynamic evolution of the algal bloom. Such
algorithm comprises of a decentralized least squares estimation of the target
and a controller for circumnavigation. We prove the convergence of the robots
to the circle and in equally spaced positions around it. Simulation results
with data provided by the SINMOD ocean model are used to illustrate the
theoretical results
Distributed Particle Filter Implementation with Intermittent/Irregular Consensus Convergence
Motivated by non-linear, non-Gaussian, distributed multi-sensor/agent
navigation and tracking applications, we propose a multi-rate consensus/fusion
based framework for distributed implementation of the particle filter (CF/DPF).
The CF/DPF framework is based on running localized particle filters to estimate
the overall state vector at each observation node. Separate fusion filters are
designed to consistently assimilate the local filtering distributions into the
global posterior by compensating for the common past information between
neighbouring nodes. The CF/DPF offers two distinct advantages over its
counterparts. First, the CF/DPF framework is suitable for scenarios where
network connectivity is intermittent and consensus can not be reached between
two consecutive observations. Second, the CF/DPF is not limited to the Gaussian
approximation for the global posterior density. A third contribution of the
paper is the derivation of the exact expression for computing the posterior
Cramer-Rao lower bound (PCRLB) for the distributed architecture based on a
recursive procedure involving the local Fisher information matrices (FIM) of
the distributed estimators. The performance of the CF/DPF algorithm closely
follows the centralized particle filter approaching the PCRLB at the signal to
noise ratios that we tested.Comment: Revised Version Submitted to IEEE Transaction on Signal Processin
Decentralized Ergodic Control: Distribution-Driven Sensing and Exploration for Multi-Agent Systems
We present a decentralized ergodic control policy for time-varying area
coverage problems for multiple agents with nonlinear dynamics. Ergodic control
allows us to specify distributions as objectives for area coverage problems for
nonlinear robotic systems as a closed-form controller. We derive a variation to
the ergodic control policy that can be used with consensus to enable a fully
decentralized multi-agent control policy. Examples are presented to illustrate
the applicability of our method for multi-agent terrain mapping as well as
target localization. An analysis on ergodic policies as a Nash equilibrium is
provided for game theoretic applications.Comment: 8 pages, Accepted for publication in IEEE Robotics and Automation
Letter
Cooperative Set Aggregation for Multiple Lagrangian Systems
In this paper, we study the cooperative set tracking problem for a group of
Lagrangian systems. Each system observes a convex set as its local target. The
intersection of these local sets is the group aggregation target. We first
propose a control law based on each system's own target sensing and information
exchange with neighbors. With necessary connectivity for both cases of fixed
and switching communication graphs, multiple Lagrangian systems are shown to
achieve rendezvous on the intersection of all the local target sets while the
vectors of generalized coordinate derivatives are driven to zero. Then, we
introduce the collision avoidance control term into set aggregation control to
ensure group dispersion. By defining an ultimate bound on the final generalized
coordinate between each system and the intersection of all the local target
sets, we show that multiple Lagrangian systems approach a bounded region near
the intersection of all the local target sets while the collision avoidance is
guaranteed during the movement. In addition, the vectors of generalized
coordinate derivatives of all the mechanical systems are shown to be driven to
zero. Simulation results are given to validate the theoretical results
Bounded Distributed Flocking Control of Nonholonomic Mobile Robots
There have been numerous studies on the problem of flocking control for
multiagent systems whose simplified models are presented in terms of point-mass
elements. Meanwhile, full dynamic models pose some challenging problems in
addressing the flocking control problem of mobile robots due to their
nonholonomic dynamic properties. Taking practical constraints into
consideration, we propose a novel approach to distributed flocking control of
nonholonomic mobile robots by bounded feedback. The flocking control objectives
consist of velocity consensus, collision avoidance, and cohesion maintenance
among mobile robots. A flocking control protocol which is based on the
information of neighbor mobile robots is constructed. The theoretical analysis
is conducted with the help of a Lyapunov-like function and graph theory.
Simulation results are shown to demonstrate the efficacy of the proposed
distributed flocking control scheme
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Task-space coordinated tracking of multiple heterogeneous manipulators via controller-estimator approaches
This paper studies the task-space coordinated tracking of a time-varying
leader for multiple heterogeneous manipulators (MHMs), containing redundant
manipulators and nonredundant ones. Different from the traditional coordinated
control, distributed controller-estimator algorithms (DCEA), which consist of
local algorithms and networked algorithms, are developed for MHMs with
parametric uncertainties and input disturbances. By invoking differential
inclusions, nonsmooth analysis, and input-to-state stability, some conditions
(including sufficient conditions, necessary and sufficient conditions) on the
asymptotic stability of the task-space tracking errors and the subtask errors
are developed. Simulation results are given to show the effectiveness of the
presented DCEA.Comment: 17 pages, 7 figures, Journal of the Franklin Institut
A unified framework of fully distributed adaptive output time-varying formation control for linear multi-agent systems: an observer viewpoint
This paper presents a unified framework of time-varying formation (TVF)
design for general linear multi-agent systems (MAS) based on an observer
viewpoint from undirected to directed topology, from stabilization to tracking
and from a leader without input to a one with bounded input. The followers can
form a TVF shape which is specified by piecewise continuously differential
vectors. The leader's trajectory, which is available to only a subset of
followers, is also time-varying. For the undirected formation tracking and
directed formation stabilization cases, only the relative output measurements
of neighbors are required to design control protocols; for the directed
formation tracking case, the agents need to be introspective (i.e. agents have
partial knowledge of their own states) and the output measurements are
required. Furthermore, considering the real applications, the leader with
bounded input case is studied. One main contribution of this paper is that
fully distributed adaptive output protocols, which require no global
information of communication topology and do not need the absolute or relative
state information, are proposed to solve the TVF control problem. Numerical
simulations including an application to nonholonomic mobile vehicles are
provided to verify the theoretical results.Comment: 21 page
Multi-Agent Distributed Coordination Control: Developments and Directions
In this paper, the recent developments on distributed coordination control,
especially the consensus and formation control, are summarized with the graph
theory playing a central role, in order to present a cohesive overview of the
multi-agent distributed coordination control, together with brief reviews of
some closely related issues including rendezvous/alignment, swarming/flocking
and containment control.In terms of the consensus problem, the recent results
on consensus for the agents with different dynamics from first-order,
second-order to high-order linear and nonlinear dynamics, under different
communication conditions, such as cases with/without switching communication
topology and varying time-delays, are reviewed, in which the algebraic graph
theory is very useful in the protocol designs, stability proofs and converging
analysis. In terms of the formation control problem, after reviewing the
results of the algebraic graph theory employed in the formation control, we
mainly pay attention to the developments of the rigid and persistent graphs.
With the notions of rigidity and persistence, the formation transformation,
splitting and reconstruction can be completed, and consequently the range-based
formation control laws are designed with the least required information in
order to maintain a formation rigid/persistent. Afterwards, the recent results
on rendezvous/alignment, swarming/flocking and containment control, which are
very closely related to consensus and formation control, are briefly
introduced, in order to present an integrated view of the graph theory used in
the coordination control problem. Finally, towards the practical applications,
some directions possibly deserving investigation in coordination control are
raised as well.Comment: 28 pages, 8 figure
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