Comprehensive review on controller for leader-follower robotic system

985-1007This paper presents a comprehensive review of the leader-follower robotics system. The aim of this paper is to find and elaborate on the current trends in the swarm robotic system, leader-follower, and multi-agent system. Another part of this review will focus on finding the trend of controller utilized by previous researchers in the leader-follower system. The controller that is commonly applied by the researchers is mostly adaptive and non-linear controllers. The paper also explores the subject of study or system used during the research which normally employs multi-robot, multi-agent, space flying, reconfigurable system, multi-legs system or unmanned system. Another aspect of this paper concentrates on the topology employed by the researchers when they conducted simulation or experimental studies

Constrained Consensus in Continuous-Time Multi-Agent Systems

Since the consensus problem is getting popular in recent researches and the applications based on it are expanding in current years! the consensus problem under the condition that constraints exist on agents’ state in continuous-time in a multi-agent system has been studied here. This work combines the projection operator method in a general consensus algorithm to avoid the violation of state on its individual constraint set. When the projection operator works in the general consensus algorithm, the constraint region is divided into the projection-operator working region and the non-projection region. The boundary between these two regions is a circular line. Once the state of the correspond agent cross this line, the projection operator starts to work when the state is going out from the non-projection region and moves towards to its constraint boundary. The boundary of the starting circle for projection opera- tor has the same shape with the constraint set boundary. The difference is it has a smaller area with a certain ratio. With a one dimensional projection-based consensus algorithm, we analyzed the projection-based consensus algorithm on the expected-to- arrival (ETA) requirement which is always the problem at the simultaneous arrival task on multiple unmanned aerial vehicles (UAVs) system. The stability and con- vergence rate of the proposed algorithm has been analyzed. Based on the stability and convergence rate, the conditions to guarantee the feasibility of the simultaneous arrival task has also been presented. Then the analysis for projection-based consensus algorithm has been extended in a high dimensions, in this case, the agents can only exchange their state information in continuous time in a connected and undirected communication network topology. The result is proven that since the intersection set of every state constraint is non-empty, the global consensus will eventually be achieved. At last, the projection-based algorithm has been applied on a UAV module, with the UAV dynamics, the algorithm makes a multi-UAV system with different ability in flying reach the global spatial consensus achievement for simultaneous arrival task

Robust and Cooperative Formation Control of Nonlinear Multi-Agent Systems

Compared with the conventional approach of controlling autonomous systems individually, building up a cooperative multi-agent structure is more robust and efficient for both research and industrial purposes. Among the many subbranches of multiagent systems, formation control has been a popular research direction due to its close connection with complex missions such as spacecraft clustering and intelligent transportation. Hence, this thesis focuses on providing new robust formation control algorithms for first-order, second-order and mixed-order nonlinear multi-agent systems to construct and maintain stable system structure in practical scenarios. System uncertainties and external disturbances are commonly seen factors that could negatively affect the formation tracking precision. Among the many popular tools of uncertainty estimation, the implementation of approaches including neural network adaptive estimation and observer-based approximation are discussed in this thesis. Regarding the neural-based approximation process, different neural network structures including Chebyshev neural network, radial basis function neural network, twolayer artificial neural network and three-layer artificial neural network are tested and implemented. The merits and drawbacks of each network design in the field of control is then analysed. Apart from that, this thesis also offers detailed comparison between the cooperative tuning approach and the observer-based tuning approach regarding the neural network structure to find their corresponding applicable scenarios. To ensure the safety of the formation control algorithms, the issues of obstacle avoidance and inter-agent collision avoidance are both considered. Although the method of constructing artificial potential fields is a popular approach in both the field of path planning and motion control, few have discussed the effect of the inter-agent communication on the collision avoidance scheme. For the obstacle avoiding scenarios, the passive correcting behaviour of individual agent is defined and investigated. A new algorithm is then introduced to modify the reference of individual agents to act as the mitigation. The issue of insufficient information accessibility is then discussed for multi-agent systems with a static and uncompleted communication topology. A distance-based communication topology is proposed to create necessary information exchange channel for unconnected agent pairs that are close enough. The actuator saturation issue is also considered for both first-order multi-agent systems and second-order multi-agent systems to increase the practicality of the formation control schemes. Apart from restricting the amplitudes of the control input, the effect of the input coupling phenomenon is investigated. The oscillation of states brought by the coupled and saturated control input is then summarised as the reverse effect. To attenuate the state oscillation, the methods of developing control input regulation algorithms and employing auxiliary compensator are discussed and validated. The last technical problem to discuss is the hierarchical control scheme. The issue of how to decouple the inter-agent communication and the motion dynamics is discussed for both unified-order and mixed-order multi-agent systems. By using a hierarchical formation control structure, the inter-agent communication process is considered based on a group of virtual agents with ideal characteristics, which can significantly reduce the complexity of the system design. Adaptive hierarchical control schemes are then proposed and validated for both unified-order and mixed-order multi-agent systems through the examples of a multi-drone system and a multiple omni-directional robot system, respectively.Thesis (Ph.D.) -- University of Adelaide, School of Electrical and Electronic Engineering, 202

Heterogeneous robots: Model Predictive Control for bearing-only formation and tracking

openMulti-agent systems are systems composed by more than one autonomous robots which usually work under the assumption that they can communicate sending and receiving positions of other robots that operate in the network. The introduction of this kind of systems is due to the fact that in many situations it is preferable to use more than one robot in order to reach more complex goal without the help of the humans, especially in dangerous situations. In this thesis, the focus is on the heterogeneous robots which are robots whose components are heterogeneous in terms of actuation capabilities, even if it is assumed they can receive bearing information with respect to the other agents in the network. Hence, it is developed an heterogeneous MAS composed by 2 UGVs and 2 UAVs. The goals of the thesis is that the formation has to be maintained and the four agents has also to track a desired trajectory through a leader follower approach based on bearing-only implemented using MPC controllers. The role of the leader is to track the desired trajectory while the followers have to form and maintain the formation also during the tracking. The followers do not know the trajectory to be tracked, nor the distance to the other agents and the leader. The approach is based on decentralized leader follower control with bearing-only. The controllers used are the Model Predictive ones since this type of control allow to prevent the critical situations, solving an online optimization problem at each time instant to select the best control action that drives the predicted output to the reference. The proposed approach is implemented in Matlab and Simulink and the results obtained by the simulations will be discussed.Multi-agent systems are systems composed by more than one autonomous robots which usually work under the assumption that they can communicate sending and receiving positions of other robots that operate in the network. The introduction of this kind of systems is due to the fact that in many situations it is preferable to use more than one robot in order to reach more complex goal without the help of the humans, especially in dangerous situations. In this thesis, the focus is on the heterogeneous robots which are robots whose components are heterogeneous in terms of actuation capabilities, even if it is assumed they can receive bearing information with respect to the other agents in the network. Hence, it is developed an heterogeneous MAS composed by 2 UGVs and 2 UAVs. The goals of the thesis is that the formation has to be maintained and the four agents has also to track a desired trajectory through a leader follower approach based on bearing-only implemented using MPC controllers. The role of the leader is to track the desired trajectory while the followers have to form and maintain the formation also during the tracking. The followers do not know the trajectory to be tracked, nor the distance to the other agents and the leader. The approach is based on decentralized leader follower control with bearing-only. The controllers used are the Model Predictive ones since this type of control allow to prevent the critical situations, solving an online optimization problem at each time instant to select the best control action that drives the predicted output to the reference. The proposed approach is implemented in Matlab and Simulink and the results obtained by the simulations will be discussed

Perpetual flight in flow fields

Tese de Doutoramento. Engenharia Electrotécnica e de Computadores. Faculdade de Engenharia. Universidade do Porto. 201

Intelligent Autonomous Decision-Making and Cooperative Control Technology of High-Speed Vehicle Swarms

This book is a reprint of the Special Issue “Intelligent Autonomous Decision-Making and Cooperative Control Technology of High-Speed Vehicle Swarms”,which was published in Applied Sciences

Advancements in Adversarially-Resilient Consensus and Safety-Critical Control for Multi-Agent Networks

The capabilities of and demand for complex autonomous multi-agent systems, including networks of unmanned aerial vehicles and mobile robots, are rapidly increasing in both research and industry settings. As the size and complexity of these systems increase, dealing with faults and failures becomes a crucial element that must be accounted for when performing control design. In addition, the last decade has witnessed an ever-accelerating proliferation of adversarial attacks on cyber-physical systems across the globe. In response to these challenges, recent years have seen an increased focus on resilience of multi-agent systems to faults and adversarial attacks. Broadly speaking, resilience refers to the ability of a system to accomplish control or performance objectives despite the presence of faults or attacks. Ensuring the resilience of cyber-physical systems is an interdisciplinary endeavor that can be tackled using a variety of methodologies. This dissertation approaches the resilience of such systems from a control-theoretic viewpoint and presents several novel advancements in resilient control methodologies. First, advancements in resilient consensus techniques are presented that allow normally-behaving agents to achieve state agreement in the presence of adversarial misinformation. Second, graph theoretic tools for constructing and analyzing the resilience of multi-agent networks are derived. Third, a method for resilient broadcasting vector-valued information from a set of leaders to a set of followers in the presence of adversarial misinformation is presented, and these results are applied to the problem of propagating entire knowledge of time-varying Bezier-curve-based trajectories from leaders to followers. Finally, novel results are presented for guaranteeing safety preservation of heterogeneous control-affine multi-agent systems with sampled-data dynamics in the presence of adversarial agents.PHDAerospace EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/168102/1/usevitch_1.pd

New decentralized algorithms for spacecraft formation control based on a cyclic approach

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 223-231).When considering the formation control problem for large number of spacecraft, the advantages of implementing control approaches with a centralized coordination mechanism can be outpaced by the risks associated with having a primary vital control unit. Additionally, in formations with a large number of spacecraft, a centralized approach implies an inherent difficulty in gathering and broadcasting information from/to the overall system. Therefore, there is a need to explore efficient decentralized control approaches. In this thesis a new approach to spacecraft formation control is formulated by exploring and enhancing the recent results on the theory of convergence to geometric patterns and exploring the analysis of this approach using the tools of contracting theory. First, an extensive analysis of the cyclic pursuit dynamics leads to developing control laws useful for spacecraft formation flight which, as opposed to the most common approaches in the literature, do not track fixed relative trajectories and therefore, reduce the global coordination requirements. The proposed approach leads to local control laws that verify global emergent behaviors specified as convergence to a particular manifold. A generalized analysis of such control approach by using tools of partial contraction theory is performed, producing important convergence results. By applying and extending results from the theory of partially contracting systems, an approach to deriving sufficient conditions for convergence is formulated. Its use is demonstrated by analyzing several examples and obtaining global convergence results for nonlinear, time varying and more complex interconnected distributed controllers. Experimental results of the implementation of these algorithms were obtained using the SPHERES testbed on board the International Space Station, validating many of the important properties of this decentralized control approach. They are believed to be the first implementation of decentralized formation flight in space. To complement the results we also consider a short analysis of the advantages of decentralized versus centralized approach by comparing the optimal performance and the effects of complexity and robustness for different architectures and address the issues of implementing decentralized algorithms in a inherently coupled system like the Electromagnetic Formation Flight.by Jaime Luís Ramírez Riberos.Ph.D

Computational intelligence approaches to robotics, automation, and control [Volume guest editors]

No abstract available