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This paper considers a class of distributed aggregative games for first-order and second-order integrator-type multi-cluster systems, respectively. Two Nash equilibrium seeking algorithms are designed based on a distributed aggregation observer which is used to estimate the aggregations of the clusters. The convergence is proved by the input-to-state stable method. Moreover, the algorithms are applied to a class of location control problems, that is, distributed nonlinear placement problems for multi-cluster systems. Finally, some simulations are presented to illustrate the effectiveness of the designed algorithms. [ABSTRACT FROM AUTHOR]

Automated tobacco curing systems have been widely deployed to meet the demand of large-scale production of high-quality tobacco. Existing tobacco curing systems control the process based on a fixed standard curing curve to increase the production of high-quality tobacco and reduce the cost. However, it is difficult to adapt the standard curing curve to the various qualities of tobacco leaves and different experience of operators. In this paper, we propose an end-cloud collaborative intelligent curing technique which can continuously extract and integrate curing experience by using clustering and regression analysis method. At the terminal, we use a microcontroller to receive sensor data collected and exchange the information with servers through a 4G communication module. On the server side, we use a clustering-based method to separate the data of high-quality tobacco, and use regression analysis and kalman filtering for data fusion. Compared with the existing automatic curing method, our proposed method can continuously extract curing experience and optimize curing curves. [ABSTRACT FROM AUTHOR]

Existing tobacco curing process assumes a uniform distribution of temperature and humidity in a barn without considering surface, texture, and biochemical properties of leaves, leading to low quality or even inferior end products. This paper proposes a novel curing process by combining image recognition and data analysis techniques that aims to intelligently improve curing quality of tobacco leaves. Specifically, an image recognition technique is first proposed to classify tobacco leaves and determine their placement in a curing barn. Then, data analysis of the biochemical spectrum of the tobacco leaves are conducted to correlate the temperature and humidity with biochemical data features. Extensive experimental results show that proposed curing process achieves 98.68% accuracy in image recognition for tobacco position control and provides an accurate mapping between tobacco state and biochemical spectrum signals. [ABSTRACT FROM AUTHOR]

Accurate, robust and drift-free global pose estimation is a fundamental problem for autonomous vehicles. In this work, we propose a global drift-free map-based localization method for estimating the global poses of autonomous vehicles that integrates visual–inertial odometry and global localization with respect to a pre-built map. In contrast to previous work on visual–inertial localization, the global pre-built map provides global information to eliminate drift and assists in obtaining the global pose. Additionally, in order to ensure the local odometry frame and the global map frame can be aligned accurately, we augment the transformation between these two frames into the state vector and use a global pose-graph optimization for online estimation. Extensive evaluations on public datasets and real-world experiments demonstrate the effectiveness of the proposed method. The proposed method can provide accurate global pose-estimation results in different scenarios. The experimental results are compared against the mainstream map-based localization method, revealing that the proposed approach is more accurate and consistent than other methods. [ABSTRACT FROM AUTHOR]

Sun-oriented attitude control is one of the most important attitude control modes for most micro/nano satellites, which directly affects the on-orbit energy acquisition. Therefore, it is of great importance to use the simplest sensors and actuators and the most reliable algorithm to achieve sun-oriented attitude control. A sun-oriented spin-stabilized attitude control method for micro/nano satellites using only magnetic control is proposed in this paper, in which the control progress is divided into four phases: initial damping phase, sun-aligned phase, spin-up phase, and spin-stabilized phase. The influence of the shadow zone of the orbit, offset installation of sun sensor and solar panel, limitation of the field of view of the sun sensor, and environmental disturbance torques are all considered in the proposed method. The control performance is evaluated by numerical simulations, and the simulation results show that the proposed method is applicable to the satellite equipped with a sun sensor and a 3-axis magnetometer as attitude sensors and three magnetic torquers installed orthogonally as attitude actuators. The proposed method is applicable to most Earth-orbit satellites for which the geomagnetic field can provide sufficient attitude control torque. [ABSTRACT FROM AUTHOR]

In this article, the leader‐following attitude tracking problem is considered for a group of rigid bodies, and a distributed control algorithm is proposed with global exponential stability on the rotational orthogonal group SO(3). In particular, we consider that only a subset of followers has access to the leader's trajectory, and a semi‐global exponential distributed observer is first proposed for each follower to estimate the leader's trajectory. Then, we introduce the shifted reference attitude of the leader to circumvent the topological obstruction on SO(3), and a combined distributed observer algorithm is developed by synthesizing different reference attitude trajectories. By constructing two Lyapunov functions, it is demonstrated that the leader's trajectory can be accurately estimated by the proposed distributed observer with exponential convergence. Next, an observer‐based attitude tracking control algorithm is synthesized, which is continuous in time but is discontinuous with respect to initial conditions. It is shown that the trajectory of the leader can be tracked by all followers with global exponential stability on SO(3). Finally, numerical simulation examples are provided to illustrate the effectiveness of the proposed control algorithms. [ABSTRACT FROM AUTHOR]

In this article, the distributed nonlinear placement problem for a class of multicluster Euler–Lagrange systems is considered. The problem is first converted into a time-varying noncooperative game. A distributed Nash equilibrium seeking algorithm composed of an auxiliary double-integrator system and a coordinated-tracking observer is designed to solve the problem. The convergence results are established by an iterative approach and the small gain theorem. The effectiveness of the algorithm is demonstrated via simulations. [ABSTRACT FROM AUTHOR]

This article studies a fully distributed optimal coordinated control problem with the global cost function for networked Euler–Lagrange (EL) systems subject to unknown model parameters. In particular, the global cost function is the sum of all the local cost functions assigned to each agent and only available to itself. The objective is to minimize the global cost function in a distributed manner while achieving a consensus on its optimal solution. Since the model parameters of the considered EL systems are not available, a new auxiliary system is introduced as a reference model, and its outputs exponentially converge the optimal solution of the global cost function. A fully distributed optimal control algorithm without requiring global information is first proposed. Then, an alternative distributed optimal algorithm via the event-triggered mechanism is proposed to reduce the communication cost. In particular, by combining an edge-based adaptive gain method, the proposed event-triggered optimal algorithm is also fully distributed. Finally, numerical simulation is carried out to validate the theoretical results. [ABSTRACT FROM AUTHOR]

Addressing the problems of insurmountable unknown frictional disturbance and balancing the trade-off between high maneuverability and stability during attitude maneuver are important in low-cost miniaturized single control moment gyro clusters (SGCMGs) for hyper-agile satellite. This paper proposes a new concept of reconfigurable octagonal cone-type SGCMGs by considering practical engineering requirements of hyper-agile satellites. Firstly, the momentum characteristics of typical configurations are quantitatively explained, and the evaluation metrics for SGCMGs based on norm L ∞ and norm L 2 are defined, respectively. Secondly, a reconfiguration design of SGCMGs from octagonal cone-type into pyramid-type is proposed by analyzing the unknown disturbance mechanism based on SGCMGs. When the hyper-agile satellite is supported to perform fast attitude maneuvers, all units of SGCMGs can work together to output rough and large torque. On the other hand, when the maneuvering ends with stable pointing control, gimbles of one pyramid-type SGCMGs are locked down and fine torque is outputted using another pyramid-type SGCMGs. This will greatly reduce the difficulty of controller design and improve the satellite attitude performance indices. The superiority of the control strategy and selection of the proposed actuator is verified by experiments. [ABSTRACT FROM AUTHOR]

In this article, we propose a simultaneous localization and mapping (SLAM) framework that combines the methods of the unscented particle filter (UPF) and particle smoothers (PS). The UPF is used to estimate the position and orientation of the mobile robot and PS are used to update the locations of landmarks. We show that UPF is capable of estimating the pose of the robot more consistently and accurately than generic particle filter and unscented Kalman filter (UKF) do, especially when the dynamic models of the robot are highly nonlinear or noises are nonGaussian. Then, the proposed SLAM framework is applied to high-frequency (HF) band radio-frequency identification (RFID) system. Since detection model of the HF band RFID system is highly nonGaussian, the traditional SLAM frameworks with the Gaussian assumption are not suitable and the proposed UPF-PS framework presents the superior performance. The proposed SLAM framework is evaluated through simulated experiments with an HF band RFID system and a range and bearing sensor. The comparisons between the proposed SLAM framework and four other SLAM frameworks, i.e., FastSLAM, UFastSLAM, and P-SLAM 1.0 and 2.0 are also given. Finally, the proposed SLAM framework is verified in a real experimental environment. The experimental results validate the effectiveness and superiority of the proposed SLAM framework. [ABSTRACT FROM AUTHOR]

This article investigates the targeted bipartite consensus problem of opinion dynamics in cooperative–antagonistic networks. Each agent in the network is assigned with a convergence set to represent a credibility interval, in which its opinion is trustworthy. The network topology is characterized by a signed switching digraph. The objective is to achieve the bipartite consensus targeted within these credibility intervals. A gradient term is introduced in the opinion dynamics besides the consensus term. Under the assumption that the underlying graph is uniformly jointly strongly connected and structurally balanced, it is first shown that the considered opinion dynamics reaches the targeted bipartite consensus within the intersections of the convergence sets associated with two antagonistic groups. Next, by relaxing the connectivity condition to uniform joint quasistrong connectivity, the targeted bipartite consensus result is also proven with an additional convergence set assumption. Numerical examples are provided to validate the proposed theoretical results. [ABSTRACT FROM AUTHOR]

In this article, a class of distributed quadratic games is considered over an undirected graph. The issue on the communication topology restriction is introduced and the players’ dynamics are with nonlinear dynamics and unknown time-varying perturbation. A distributed Nash equilibrium seeking algorithm is proposed based on a high-gain observer method, and the convergence is analyzed by the Lyapunov stability theory. It is shown that each player estimates the rival players’ states, and the errors between the players’ states and the Nash equilibrium are ultimately bounded by a small bound. Moreover, the presented algorithm is free of chattering phenomena because it is designed using the hyperbolic tangent function instead of the signum function to dominant the perturbation. The effectiveness of the proposed algorithm is validated via a simulation of the oligopoly game in which five firms produce the same products in a duopoly market structure. [ABSTRACT FROM AUTHOR]

This article investigates the distributed localization and circumnavigation problem for a group of agents using bearing measurements. In particular, there is one agent appointed as a pathfinder in the group that is responsible for measuring the relative bearing with respect to an uncertain target. We consider both persistent and intermittent measurement cases. The objective is to drive all the agents such that they first localize the given target and then circumnavigate it isometrically. First, for the persistent measurement case, a distributed control algorithm is developed by introducing a distributed observer. In terms of Lyapunov theorem, it is shown that the proposed control algorithm guarantees the achievement of the localization and circumnavigation objective. Next, we focus on the case of the intermittent bearing measurement. In particular, another feasible distributed control algorithm is designed. Based on the nonlinear contraction theory, it is demonstrated that the localization and circumnavigation objective can also be achieved. Simulation and experiment results verify the effectiveness of the proposed distributed control algorithms. [ABSTRACT FROM AUTHOR]

In signed networks, the cooperation and antagonism cause great difficulties for their behavior analysis, especially, when they are subject to time-varying topologies. This is different from unsigned networks involving only cooperations, of which behavior analysis can be feasibly achieved based on the nonnegative matrix theory. With these facts, this article first bridges a relation between signed and unsigned networks and then takes advantage of the relation for the behavior analysis of signed networks under directed switching topologies. In particular, a solution is provided for the connection of signed and unsigned networks via solving a class of linear dynamic systems, which is obtained by separating antagonisms from cooperations. The solution makes it possible to employ the convergence results for unsigned networks to address the convergence issues for signed networks. If the joint spanning tree condition is met, then switching signed networks can achieve the quasi-interval bipartite consensus. Moreover, the established results can be applied to signed networks with both continuous-time and discrete-time dynamics. [ABSTRACT FROM AUTHOR]

The range-only simultaneous localization and mapping (RO-SLAM) problem is considered in this article. This is a difficult problem since bearing measurements are not available. Also, the frequent outliers induced by the sensor nature (typically sonar or radio pulses) render the RO-SLAM problem more challenging. The non-Gaussian distribution found in the RO-SLAM problem makes that the landmarks cannot be directly updated using the approach based on the Gaussian assumption. We propose a region-based particle filter and a proper likelihood model to realize the reduction of particle numbers and allow the introduction of new landmarks without delayed processing. A transition mode is designed from the loosely coupled way to the tightly coupled way and used to estimate the pose of the robot and locations of landmarks. Furthermore, two detection methods are, respectively, used to remove the outliers generated by the range-only sensors according to the distribution status of the landmark estimation. The proposed algorithm is evaluated through simulations and experiments with a range-only sensor, i.e., Ultrawideband (UWB). Furthermore, the obtained results are compared with the classical algorithm. The simulation and experiment results verify the validity and superiority of the proposed RO-SLAM algorithm. [ABSTRACT FROM AUTHOR]

In this article, we consider a convex optimization problem which minimizes the sum of local agents’ cost functions subject to certain local constraints. Besides, both the local cost function and local constraints are only known by the local agent itself. To solve this problem, a new accelerated distributed gradient-based algorithm is proposed, which is inspired by the “momentum” phenomena in nature and aims to accelerate the convergence speed of conventional distributed gradient algorithms. Sufficient conditions for the stepsizes and the acceleration gains are derived to ensure the convergence of the proposed algorithm. Furthermore, based on this proposed fast distributed algorithm, a new decentralized approach is proposed to solve economic dispatch problem, especially for a large-scale power system. Based on the idea of virtual agent, it is proved that this decentralized algorithm is equivalent to the original fast distributed gradient method. Several case studies implemented on IEEE 30-bus, IEEE 118-bus power systems, and a large-scale power system consisting of 1000 generators are conducted to validate the proposed method. [ABSTRACT FROM AUTHOR]

The distributed time‐varying constrained convex optimization problem over a connected undirected network topology is studied in this article. The proposed distributed optimization algorithm is composed of a projection map term, a consensus term, and a gradient term, and is feasible for any initial condition. We first show that the states of the optimization algorithm uniformly converge to a neighborhood of the constraint set while an approximate global consensus is achieved. Then the states are proven to uniformly converge to a neighborhood of the time‐varying optimal trajectory. The theoretical results are validated by some simulations. [ABSTRACT FROM AUTHOR]

Summary: This article addresses a surveillance problem where the goal is to achieve a circular motion around a target by a non‐holonomic differentially driven mobile robot. The available information for the mobile robot includes its own position, velocity with respect to the inertial frame, and the bearing angle of the target in its body frame. Since the target position is unavailable, an estimator is first proposed to localize it. Then a two‐step controller is given to drive the mobile robot to move onto a circular trajectory with a desired radius around it. It is shown that the proposed algorithm guarantees the convergence of the estimation error to a small neighborhood of zero and the motion of the robot to a small neighborhood of a designed radius. The performance of the proposed algorithm is first verified by simulations. Then, several experiments on a differentially driven mobile robot, Pioneer 3‐DX, are presented to further validate the proposed algorithm. [ABSTRACT FROM AUTHOR]

This article studies the leader–follower formation tracking problem of multiple quadrotors. In particular, the quadrotors are steered to track a reference trajectory while maintaining a desired configuration. The reference trajectory is partially available to a subset of quadrotors, and each quadrotor just interacts locally with its neighbors. A distributed control algorithm is proposed under a hierarchical framework. First, by introducing a distributed saturation control strategy, a command force is synthesized for the position to track the reference trajectory with a desired displacement. Second, a bounded applied force and a nonsingular command attitude are extracted from the synthesized command force based on a proper choice criterion of control parameters. Last but not the least, an applied torque is designed for the attitude to track the command one. In terms of Lyapunov theory, it is shown that the overall closed-loop error system is asymptotically stable. This indicates the accomplishment of the concerned leader–follower formation tracking control objective of multiple quadrotors. Finally, the effectiveness of the proposed distributed control algorithm is verified through both simulations and experiments. [ABSTRACT FROM AUTHOR]

The distributed economic dispatch problem for power generation in electricity grids is studies. A simple centralised algorithm is designed to obtain the solution of the dispatch problem without the external disturbances. Inspired by the centralised algorithm, a distributed algorithm is presented using the distributed average tracking algorithm. As far as we know, the proposed algorithm is the first one that is capable of time‐varying loads and external disturbances while the tracking errors are asymptotic convergent. Simulations on the IEEE 14‐BUS system are provided to validate the theoretical results. [ABSTRACT FROM AUTHOR]

Due to the sensors’ latency, unsynchronized clocks, triggering, and data jams, there usually exists an inevitable time offset between image streams and inertial measurement unit (IMU) data sequences in visual-inertial systems. Such a time offset has a significant effect on the robustness and accuracy of the system. In this article, an online temporal calibration algorithm is proposed based on a modified projection model. In particular, we introduce the time offset as an estimated state variable in an extended Kalman filter (EKF)-based visual-inertial odometry (VIO). In addition, in order to align camera and IMU measurements in the time domain, the projection model is sophisticatedly given, and we propose a systematic method to obtain features’ virtual observations with respect to the time offset. Our approach is general and can be easily applied to different EKF-based VIO frameworks. Experimental results demonstrate that the time offset is calibrated quickly and accurately even compared with other existing offline tools, and the proposed online temporal calibration method significantly improves the performance of VIO. [ABSTRACT FROM AUTHOR]

This paper investigates the coordinated attitude synchronization and tracking problems of multiple rigid-body spacecraft subject to inaccurate inertial parameters. Two adaptive distributed control algorithms are developed based on communications among spacecraft connected through a switching communication network, which allow each switching subgraph to be disconnected. In the first place, by introducing an adaptive strategy for the inertial parameters, a distributed attitude synchronization control algorithm is designed. In particular, a gain selection criteria is specified for the asymptotic attitude synchronization under uniform joint connectivity. In the second place, for the coordinated attitude tracking problem, we first develop a distributed observer for each spacecraft to estimate the reference information associated with a leader over a switching network with uniform joint quasi-strong connectivity. Then, we propose an adaptive tracking scheme such that each spacecraft tracks the estimated information. Finally, numerical examples are given to validate the effectiveness of two proposed adaptive distributed control algorithms. [ABSTRACT FROM AUTHOR]

This paper studies the cooperative set aggregation problem for second-order multiagent systems by utilizing the approximate projection algorithm. First, an aggregation law that uses the approximate projection is proposed, where the feasible set of the approximate projection points is established based on an Euclidean distance with respect to the targeted set and a deviated angle with respect to the exact projection point. Under the proposed law, the position vectors of all the agents are shown to reach an agreement in the intersection of their individual targeted sets and the velocity vector of each agent is shown to converge to zero. Then, a time-dependent performance bound is set for the norm of the weighted error of the relative positions among neighboring agents and the absolute velocity of the agent, and a performance-guaranteed aggregation controller is designed to guarantee the prescribed transient performance. During the process of aggregation, the norm of the weighted error is shown to not exceed the performance bound. The convergence conditions of the proposed algorithms with respect to the control strength and the terms induced by the approximate projection are obtained by using the techniques of convex analysis and Lyapunov stability. Simulations are provided to validate the theoretical results. [ABSTRACT FROM AUTHOR]

This study investigates the coordinated attitude synchronisation and tracking problems of multiple spacecraft without angular velocity measurements. The spacecraft attitudes are represented by modified Rodrigues parameters. First, for the attitude synchronisation problem, a distributed control algorithm with local information interaction is developed by introducing two auxiliary systems to address the velocity‐free problem. Next, for the attitude tracking problem, the authors first design a non‐linear distributed observer for each follower spacecraft such that the leader reference information can be estimated accurately. By treating this estimation information as a reference, a tracking control with the help of an auxiliary system is then developed for the attitude tracking without using angular velocity measurements. For both cases, the asymptotic stability of the overall closed‐loop systems is proven in terms of Lyapunov theory. Finally, numerical examples are given to validate the effectiveness of the proposed distributed control algorithms. [ABSTRACT FROM AUTHOR]

This paper studies the distributed formation control problem of second-order multi-agent systems (MASs) with limited communication ranges and collision avoidance constraints. A novel connectivity preservation and collision-free distributed control algorithm is proposed by combining prescribed performance control (PPC) and exponential zeroing control barrier Lyapunov functions (EZCBFs). In particular, we impose the time-varying performance constraints on the relative position and velocity errors between the neighboring agents, and then a PPC-based formation control algorithm is developed such that the connectivity of the communication graph can be preserved at all times, and the prescribed transient and steady performance on the relative position and velocity error can be achieved. Subsequently, by introducing the EZCBFs method, an inequality constraint condition on the control input is derived to guarantee the collision-free formation motion. By regarding the PPC-based formation controller as a nominal input, an actual formation control input is given by solving the quadratic programming (QP) problem such that each agent achieves collision-free formation motion while guaranteeing the connectivity and prescribed performance as much as possible. Finally, numerical simulation is carried out to validate the effectiveness of the proposed algorithm. [ABSTRACT FROM AUTHOR]

A distributed control algorithm is proposed in this paper to achieve the leader–follower cooperative attitude tracking of multiple rigid bodies without using absolute and relative angular velocity information. The nonlinear manifold SO(3) is applied to represent the attitude of each rigid body. By considering the case of limited information exchange, i.e., not all the rigid bodies have access to the leader’s information, a novel continuous nonlinear distributed estimator satisfying the rotation matrix dynamics is first introduced for each rigid body to estimate the leader’s information asymptotically. Then, two auxiliary systems driven by proper inputs are designed such that the issues due to the angular velocity unavailability are effectively solved. Next, a feasible distributed protocol is designed by implementing the outputs from the distributed estimator and the auxiliary systems. It is demonstrated in terms of Lyapunov theory that, the developed distributed control algorithm ensures the asymptotically stable cooperative attitude tracking of multiple rigid bodies under the weak tree connectivity assumption. Finally, illustrative examples are provided to validate and highlight the proposed results. [ABSTRACT FROM AUTHOR]

This paper develops a novel immersion and invariance (I&I)-based adaptive controller for nonlinear under-actuated quadrotor systems subject to uncertain inertial parameters. The objective is to drive the quadrotor to accurately track a reference trajectory. The controller synthesis is based on a hierarchical framework. First, the solution to the trajectory tracking problem is transformed to stabilizing its corresponding error system asymptotically. Second, to avoid singularity in the command attitude extraction, a saturated backstepping control strategy with smooth hyperbolic tangent functions is developed to synthesize a command force in the position loop, where an I&I adaptive methodology is introduced to update the mass estimation. The I&I adaption guarantees the asymptotic convergence of the mass estimation to its actual value. Third, in the attitude loop, the projection algorithm is used to update the inertial tensor estimations, which enables the estimations to be maintained within a prescribed range. Then, a rotation matrix-based applied torque with an initial condition constraint is synthesized. It is proven that, with appropriate control parameters, the proposed controller guarantees the asymptotic stability of the error system and then the trajectory tracking of the quadrotor is achieved. Finally, numerical simulations are given to verify and highlight the performance of the proposed controller. [ABSTRACT FROM AUTHOR]

In this study, the distributed optimisation problem for linear multi‐agent systems with disturbance rejection is considered. The topology graph is assumed to be uniformly jointly strongly connected and the disturbance is not limited to satisfy the matching condition. Each agent is assigned with a local quadratic cost function and the objective is to minimise the sum of local cost functions based on information exchange. The authors propose a distributed observer for each agent such that other agents' cost functions are obtained. Then, the state feedback and output feedback optimal algorithms are designed based on the output of the distributed observer. The theoretical results are validated by simulations. [ABSTRACT FROM AUTHOR]

Summary: A distributed formation control algorithm is proposed for multiple vertical takeoff and landing (VTOL) unmanned aerial vehicles (UAVs) in this paper. The neighboring information is obtained by active measurements rather than by nonactive communications as done in the current literatures. By properly expanding the distance‐based network topology structure between each pair of UAVs, a distributed algorithm is proposed such that the switching topology remains connected along the time. Since a VTOL UAV system is typically underactuated, a hierarchical idea is introduced to derive the control design procedure. More specifically, the studied formation control problem of multiple VTOL UAVs is first transformed into the consensus problem of their corresponding error systems. Then, a command force and an applied torque are synthesized for each VTOL UAV such that the error systems reach a consensus. It is demonstrated in terms of Lyapunov theory that the proposed distributed hierarchical control algorithm guarantees the formation realization of multiple VTOL UAVs while maintaining the network connectivity. Finally, simulations are performed to validate the theoretical results. [ABSTRACT FROM AUTHOR]