Distributed attitude synchronization control of multi-agent systems with switching topologies

This paper addresses the attitude synchronization problem in multi-agent systems with directed and switching interconnection topologies. Two cases for the synchronization problem are discussed under different assumptions about the measurable information. In the first case the agents can measure their rotations relative to a global reference coordinate frame, whilst in the second case they can only measure the relative rotations between each other. Two intuitive distributed control laws based on the axis–angle representations of the rotations are proposed for the two cases, respectively. The invariance of convex balls in SO(3)$SO\left(3\right)$ is guaranteed. Moreover, attitude synchronization is ensured under the well-known mild switching assumptions, the joint strong connection for the first case and joint quasi-strong connection for the second case. To show the effectiveness of the proposed control schemes, illustrative examples are provided.     

Event-based broadcasting for multi-agent average consensus

A novel control strategy for multi-agent coordination with event-based broadcasting is presented. In particular, each agent decides itself when to transmit its current state to its neighbors and the local control laws are based on these sampled state measurements. Three scenarios are analyzed: Networks of single-integrator agents with and without communication delays, and networks of double-integrator agents. The novel event-based scheduling strategy bounds each agent’s measurement error by a time-dependent threshold. For each scenario it is shown that the proposed control strategy guarantees either asymptotic convergence to average consensus or convergence to a ball centered at the average consensus. Moreover, it is shown that the inter-event intervals are lower-bounded by a positive constant. Numerical simulations show the effectiveness of the novel event-based control strategy and how it compares to time-scheduled control.     

Multimedia teleorchestra with independent sources: Part 2 — synchronization algorithms

Based on the time-flow graph models proposed for the multimedia presentation scenarios, a scheduling algorithm and control scheme are presented for the synchronization control which involves multiple sources in a teleorchestra system. In the scheduling, a synchronization dialogue among the independent sources will be conducted to evaluate the presentation scenario. Then the real-time data objects from the different sources can be synchronized in the remote presentation according to the required scenario. The algorithm can be performed in a distributed manner.     

Cooperative Control of Multiple Nonholonomic Mobile Agents

This paper considers two cooperative control problems for nonholonomic mobile agents. In the first problem, we discuss the design of cooperative control laws such that a group of nonholonomic mobile agents cooperatively converges to some stationary point under various communication scenarios. Dynamic control laws for each agent are proposed with the aid of $sigma $-processes and results from graph theory. In the second problem, we discuss the design of cooperative control laws such that a group of mobile agents converges to and tracks a target point which moves along a desired trajectory under various communication scenarios. By introducing suitable variable transformations, cooperative control laws are proposed. Since communication delay is inevitable in cooperative control, in each of the above cooperative control problems, we analyze the effect of delayed communication on the proposed controllers. As applications of the proposed results, formation control of wheeled mobile robots is discussed. It is shown that our results can be successfully used to solve formation control problem. To show effectiveness of the proposed approach, simulation results are included.      

Fast Algorithms for Computing the Smallest k-Enclosing Circle

For a set $P$ of $n$ points in the plane and an integer $k \leq n$, consider the problem of finding the smallest circle enclosing at least $k$ points of $P$. We present a randomized algorithm that computes in $O( n k )$ expected time such a circle, improving over previously known algorithms. Further, we present a linear time $\delta$-approximation algorithm that outputs a circle that contains at least $k$ points of $P$ and has radius less than $(1+\delta)r_{opt}(P,k)$, where $r_{opt}(P,k)$ is the radius of the minimum circle containing at least $k$ points of $P$. The expected running time of this approximation algorithm is $O(n + n \cdot\min((1/k\delta^3) \log^2 (1/\delta), k))$.     

A unified optimal planner for autonomous parking vehicle

In order to reduce the controlling difficulty caused by trajectory meandering and improve the adaptability to parking into regular lots, a versatile optimal planner (OP) is proposed. Taking advantage of the low speed specificity of parking vehicle, the OP algorithm was modeled the planning problem as a convex optimization problem. Collision-free constraints were formalized into the shortest distance between convex sets by describing obstacles and autonomous vehicle as affine set. Since employing Lagrange dual function and combining KKT conditions, the collision-free constraints translated into convex functions. Taking the national standard into account, 5 kinds of regular parking scenario, which contain $0^\circ$, $30^\circ$, $45^\circ$, $60^\circ$ and $90^\circ$ parking lots, were designed to verify the OP algorithm. The results illustrate that it is benefit from the continuous and smooth trajectory generated by the OP method to track, keep vehicle''s stability and improve ride comfort, compared with A* and hybrid A* algorithms. Moreover, the OP method has strong generality since it can ensure the success rate no less than 82% when parking planning is carried out at the start node of 369 different locations. Both of evaluation criteria, as the pear error and RMSE in x direction, y axis and Euclidean distance d, and heading deviation $\theta$, are stable and feasible in real tests, which illustrates that the OP planner can satisfy the requirements of regular parking scenarios.     

Cooperative Target-centric Formation Control without Relative Velocity Measurements under Heterogeneous Networks

This paper proposes distributed control laws for a group of unmanned aerial vehicles (UAVs) to make and maintain a circular formation around a maneuvering target. The work considers usage of heterogeneous communication networks to achieve the desired formation. Two different scenarios are considered on velocity information. In both scenarios, it is assumed that each UAV has its own position and velocity measurements available to itself. However, the team is unable to exchange velocity information among themselves. In the first scenario, each agent uses its own position and velocity information in the consensus algorithm. In the second scenario, agents need only position information for the consensus algorithm. For both the approaches, each agent calculates a virtual estimate of target’s velocity from the received information and exchanges the estimate with its neighbors. The control algorithms are developed using heterogeneous communication networks to satisfy a communication bandwidth constraint. Three different communication networks are used to circulate position information, virtual estimates, and its time derivatives. The graphs representing communication networks are undirected and connected. Further, it is considered that there is at least one UAV (agent) receiving position, velocity, and acceleration information of the target. The agent receiving target’s position need not be the same agent which receives velocity and/or acceleration information of the maneuvering target. However, the target does not receive any information from any agent. Using Barbalat’s lemma, the stability of the target-centric formation of a group of UAVs is analyzed. The performance of the proposed laws are illustrated through numerical simulations.     

Using the agent-based model to simulate and evaluate the interaction effects of agent behaviors on groundwater resources,a case study of a sub-basin in the Zayandehroud River basin

The present study aims to identify and assess the parameters affecting agent behaviors and to simulate their effects on groundwater resources under the existing water regulations and policies. For this purpose, agent-based models are exploited to simulate the different groups of agents including Regional Water Authority, Public Prosecutor's Office, and the stakeholders as well as their interactions. The systems dynamic model is employed to investigate the effects of changes in agent behaviors on groundwater resources. The Any Logic software package is also used as a powerful tool for simulating both models and identifying the relationships between human behavior and water resources. Two efficient and inefficient scenarios are defined for assessing the effects of such parameters as ‘meetings of regional water agencies held with other public organizations”. Results revealed that changes in the behavior and interactions of Regional Water Authority with other public organizations under the first (inefficient) scenario led to increased renewable storage by 11.6 MCM while elimination of this parameter in the second (efficient) scenario led to a decrease of 52.6 MCM in renewable storage. Results of both scenarios showed that proper interactions of the Regional Water Authority with other stakeholders led to the control of illegal water abstractions and the rise of water table in the aquifers from the scenario one 1777.4 m–1778.1 m under the second scenario.     

The Random Members of a Π 1 0 ${\Pi }_{1}^{0}$ Class

Theory of Computing Systems - We examine several notions of randomness for elements in a given ${\Pi }_{1}^{0}$ class $\mathcal {P}$ . Such an effectively closed subset $\mathcal {P}$ of 2 ω...     

Adaptive robust consensus tracking for nonlinear second‐order multi‐agent systems with heterogeneous uncertainties

This paper addresses the consensus tracking problem for a class of heterogeneous nonlinear second‐order multi‐agent systems with parametric uncertainties, unmodeled dynamics, and bounded external disturbances. By linearly parameterizing the control input of the leader, two distributed adaptive robust consensus tracking control protocols with dynamic and fixed coupling gains are constructed based on the relative information from neighboring agents. The global tracking errors are shown to be guaranteed to exponentially converge to a ball with a constant radius at a prescribed rate of convergence under external disturbances. Finally, a numerical example is provided to verify the theoretical results. Copyright © 2017 John Wiley & Sons, Ltd.     

交互式多模型算法性能分析

广泛应用于目标跟踪和故障诊断的动态多模型估计（SMME）假设模式的切换服从马尔可夫过程,对马尔可夫切换概率（MTP）的非MonteCarlo分析有助于深入了解SMME的机理,发现参数寻优的法则,设计或发展新的自适应多模型估计器,然而由于SMME的复杂性,非Monte Carlo分析很难给出,本文针对SMM中著名的交互式多模型（IMM）估计器,通过将IMM看作是输入交互和子滤波器串联,分析了具有m个参数的MTP矩阵,给出了六条不依赖主动应用环境及子滤波器设计的结论,部分结果也适用于一阶广义伪贝叶斯算法（GPBI）。     

Relative blending

Solid models may be blended through filleting or rounding operations that typically replace the vicinity of concave or convex edges by blends that smoothly connect to the rest of the solid’s boundary. Circular blends, which are popular in manufacturing, are each the subset of a canal surface that bounds the region swept by a ball of constant or varying radius as it rolls on the solid while maintaining two tangential contacts. We propose to use a second solid to control the radius variation. This new formulation supports global blending (simultaneous rounding and filleting) operations and yields a simple set-theoretic formulation of the relative blending R_B(A) of a solid A given a control solid B. We propose user-interface options, describe practical implementations, and show results in 2 and 3 dimensions.     

Cooperative Constrained Control of Distributed Agents With Nonlinear Dynamics and Delayed Information Exchange: A Stabilizing Receding-Horizon Approach

This paper addresses the problem of cooperative control of a team of distributed agents with decoupled nonlinear discrete-time dynamics, which operate in a common environment and exchange-delayed information between them. Each agent is assumed to evolve in discrete-time, based on locally computed control laws, which are computed by exchanging delayed state information with a subset of neighboring agents. The cooperative control problem is formulated in a receding-horizon framework, where the control laws depend on the local state variables (feedback action) and on delayed information gathered from cooperating neighboring agents (feedforward action). A rigorous stability analysis exploiting the input-to-state stability properties of the receding-horizon local control laws is carried out. The stability of the team of agents is then proved by utilizing small-gain theorem results.      

Approximation Algorithms for Quickest Spanning Tree Problems

Let $G=(V,E)$ be an undirected multigraph with a special vertex ${\it root} \in V$, and where each edge $e \in E$ is endowed with a length $l(e) \geq 0$ and a capacity $c(e) > 0$. For a path $P$ that connects $u$ and $v$, the {\it transmission time} of $P$ is defined as $t(P)=\mbox{\large$\Sigma$}_{e \in P} l(e) + \max_{e \in P}\!{(1 / c(e))}$. For a spanning tree $T$, let $P_{u,v}^T$ be the unique $u$--$v$ path in $T$. The {\sc quickest radius spanning tree problem} is to find a spanning tree $T$ of $G$ such that $\max _{v \in V} t(P^T_{root,v})$ is minimized. In this paper we present a 2-approximation algorithm for this problem, and show that unless $P =NP$, there is no approximation algorithm with a performance guarantee of $2 - \epsilon$ for any $\epsilon >0$. The {\sc quickest diameter spanning tree problem} is to find a spanning tree $T$ of $G$ such that $\max_{u,v \in V} t(P^T_{u,v})$ is minimized. We present a ${3 \over 2}$-approximation to this problem, and prove that unless $P=NP$ there is no approximation algorithm with a performance guarantee of ${3 \over 2}-\epsilon$ for any $\epsilon >0$.     

Approximation Algorithms for Quickest Spanning Tree Problems

Let $G=(V,E)$ be an undirected multigraph with a special vertex ${\it root} \in V$, and where each edge $e \in E$ is endowed with a length $l(e) \geq 0$ and a capacity $c(e) > 0$. For a path $P$ that connects $u$ and $v$, the {\it transmission time} of $P$ is defined as $t(P)=\mbox{\large$\Sigma$}_{e \in P} l(e) + \max_{e \in P}\!{(1 / c(e))}$. For a spanning tree $T$, let $P_{u,v}^T$ be the unique $u$--$v$ path in $T$. The {\sc quickest radius spanning tree problem} is to find a spanning tree $T$ of $G$ such that $\max _{v \in V} t(P^T_{root,v})$ is minimized. In this paper we present a 2-approximation algorithm for this problem, and show that unless $P =NP$, there is no approximation algorithm with a performance guarantee of $2 - \epsilon$ for any $\epsilon >0$. The {\sc quickest diameter spanning tree problem} is to find a spanning tree $T$ of $G$ such that $\max_{u,v \in V} t(P^T_{u,v})$ is minimized. We present a ${3 \over 2}$-approximation to this problem, and prove that unless $P=NP$ there is no approximation algorithm with a performance guarantee of ${3 \over 2}-\epsilon$ for any $\epsilon >0$.     

一种改进ε约束飞蛾火焰优化算法及其在约束优化问题中的应用

提出一种改进ε约束法的飞蛾火焰优化算法(ε improved moth-flame optimization algorithm, εIMFO)求解约束优化问题.该算法采用ε约束法对约束进行处理,考虑种群整体的约束违反度变化,提出一种基于火焰种群约束违反度的阈值ε计算公式;改进火焰种群的更新方法,首先,根据种群中个体的约束违反度与ε的关系将其分为两类:一类是约束违反度小于等于ε的个体,按照目标函数值排序,另一类是约束违反度大于ε的个体,按约束违反度排序;然后,先选择第1类中的个体,若数量没有达到种群数量的要求,继续从第2类中选取个体形成新一代火焰种群;最后,提出一种改进的飞蛾变异策略,在原始飞蛾变异策略的基础上引入2个随机火焰个体影响飞蛾变异,并增加优秀火焰个体对飞蛾变异的指导作用.通过25个测试函数以及2个实际的工程优化问题分别与其他13种算法进行的算法性能测试对比表明, εIMFO算法在求解精度和稳定性等方面具有优势.     

Synchronization of ball and beam systems with neural compensation

Ball and beam system is one of the most popular and important laboratory models for teaching control system. It is a big challenge to synchronize ball and beam systems. There are two problems for ball and beam synchronized control: 1) many laboratories use simple controllers such as PD control, and theory analysis is based on linear models, 2) nonlinear controllers for ball and beam system have good theory results, but they are seldom used in real applications. In this paper we first use PD control with nonlinear exact compensation for the cross-coupling synchronization. Then a RBF neural network is applied to approximate the nonlinear compensator. The synchronization control can be in parallel and serial forms. The stability of the synchronization is discussed. Real experiments are applied to test our theory results.     

Water film washers and mixers: their rotational modes and electro-hydrodynamical flows induced by square-wave electric fields

Our study indicates suspended water films, driven by crossed square-wave electric fields, may act as “washers”, “centrifuges” and “mixers”. Based on our recent model successfully describing experimentally observed electro-hydrodynamical flows in water films, we derive conditions for generating specific rotational flows. Our main findings, which are advantageous for microfluidic devices and basic research, are as follows: (1) the film’s rotational patterns depend on the phase difference $\Updelta\varphi$ and frequencies f of the applied fields. (2) For $\Updelta\varphi=\pi/2$ and $f\sim10^{-1}-10^{0}$  Hz, the film exhibits symmetrical reciprocating rotations, i.e. it constitutes a washer. (3) For $\Updelta\varphi=0$ and any f, it exhibits an ordinary anticlockwise (or clockwise) rotation, i.e. it constitutes a centrifuge or motor. (4) For $\Updelta\varphi$ with other values and f below 1 Hz, it exhibits asymmetrical reciprocating rotations, it constitutes an asymmetrical mixer.