Formation Control Methods Research Articles

Microstructure formation mechanisms and property regulation methods during ceramic additive manufacturing

Anisotropic surface lamellar defects, dimensional shrinkage, and bending strength are important scientific issues that constrain vat photopolymerization additive manufacturing of biological, electronic, and core ceramics with high precision and complex structures. Through the single-factor experiment of photoinitiator concentration, average particle size, volume fraction, and refractive index constant in ceramic-resin slurry, this work studies the photopolymerization characteristics and profile curves, surface lamellar defects, and crosslinking density, verifies the reliability of the photopolymerization profile equations affected by the slurry composition, and acquires the anisotropic property formation mechanisms and control methods. The single-point scanning photopolymerization profile shape is parabolic, resulting in x-, y-, and z-direction lamellar defects before and after sintering (1550 °C), with no obvious weakening. After the quantitative description of the lamellar defects, the average surface roughnesses before and after sintering of the green body are 6.82 and 4.92 μm, respectively. Additionally, the laser energy attenuation along the penetration direction induces a gradient distribution of crosslinking density in the photopolymerization profile region. The crosslinking density gradient distribution of the decay from the slurry surface toward the depth direction is influenced by the slurry component concentration, leading to a gradient of cured powder concentration, which induces anisotropic behaviors. Through the crosslinking density controlling, the average bending strength in x(y) and z directions is increased by 63.19 % (46 %), the difference in anisotropic strength is reduced by 22.55 %, and the dimensional shrinkage difference of x and z directions is reduced by 48.32 %. This provides a theoretical and experimental research basis for ceramic vat photopolymerization with high dimensional accuracy, excellent performance, and morphology control.

Formation Mechanisms and Control Methods of Cyanobacteria Bloom

Formation Mechanisms and Control Methods of Cyanobacteria Bloom

A Guidance Module Based Formation Control Scheme for Multi-Mobile Robot Systems With Collision Avoidance

This paper investigates distributed formation control of multi-mobile robot systems with collision avoidance. A novel guidance module based formation control scheme is established, which consists of two main parts. In the first part, on the communication network of the multi-mobile robot system, a distributed guidance module is constructed from some predesigned virtual dynamics scattered in the robots’ feedback loops. By using some proper distributed formation control methods and distributed observer techniques, some formation references are generated by the guidance module. In the second part, by taking these references as the tracking references, some tracking controllers are designed and assigned to the robots such that the robots’ positions track their respective references asymptotically. A “two-layer constraint mechanism” is presented in the above controller design to limit both the formation references and the robots’ tracking errors such that robots’ collision avoidance is guaranteed. In this way, the multi-mobile robot system completes the desired collision-free formation control task. Compared with existing results, the method proposed in this paper has a better plug-and-play function and wider application scope, especially when the practical robots have tight encapsulations such that their pre-equipped tracking controllers cannot be arbitrarily redesigned. Moreover, under the proposed scheme, the asymptotic formation convergence is achieved by the robots without extra limitations on robots’ initial states and the utilization of global information. Some simulations and an experiment are given to validate the effects of the proposed methods. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Note to Practitioners</i> —This paper is motivated by controller encapsulation characteristics of practical mobile robot products. To complete various formation tasks, most of the related existing formation control methods require robots’ controllers to be continually updated and redesigned. However, this purpose is sometimes unachievable because actual mature robot products may have tight controller packages for trade secrets and intellectual property, or engineers want to retain robots’ well-adjusted default performances. To overcome this practical limitation, this paper provides a novel “guidance module based formation control scheme”. Under this scheme, engineers only need to put most efforts on a guidance module design to generate desired real-time desired tracking references for robots. A new “two-layer constraint mechanism” is proposed and applied here to guarantee collision avoidance among the robots when using the proposed scheme. With this scheme, engineers can establish required formation control strategies without robots’ pre-equipped controllers changed and the original control performances abandoned, as long as the robots have some basic capability of tracking given trajectories. Theoretical analysis and experiments on this scheme are all shown. In future research, based on the proposed scheme, we will continue to develop application-oriented formation control methods to improve the anti-disturbance performance and robustness of the multi-mobile robot systems.

Robust Consensus-based Formation Control of a Group of UAV

Consensus-based formation control (CFC) is one of the most phenomenal formation control methods designed to achieve consensus between any vehicles that using and sharing their position and/or linear velocity with each other in a swarm mission. In this paper, a robust CFC (R-CFC) has been designed and proposed to realize pre-defined formation shapes with a team of unmanned aerial vehicles (UAVs). First, the double integrator dynamics of an UAV is presented. Second, the graph theory is explained briefly to understand any adjacency between UAVs. Then, the proposed R-CFC algorithm has been derived and the stability analysis has been proven via algebraic Riccati stability theory based on Lyapunov stability theorem. After that, the effectiveness of the proposed controller has been tested in real time outdoor tests. The experimental results show that the UAVs have been able to create the desired formation shapes and are less affected by external disturbances such as wind thanks to the proposed control algorithm.

Distributed Adaptive Event-Triggered TVGF for Generic Linear Multi-Agent Systems Under Directed Graph

This paper investigates event-triggered time-varying grouping formation (TVGF) problem for generic linear homogeneous multi-agent systems under directed graphs. A distributed adaptive event-triggered TVGF algorithm is proposed to ensure that the goal of TVGF can be achieved and the communication frequency between agents is reduced. Compared with previous formation control methods, the algorithm presented in this paper can complete the group formation task while saving communication energy. In addition, the algorithm’s dependence on global network information is also eliminated by using adaptive techniques. Finally, the availability of the proposed control law is established by numerical simulation.

Crack Formation Mechanisms and Control Methods of Laser Cladding Coatings: A Review

Laser cladding, a novel surface treatment technology, utilizes a high-energy laser beam to melt diverse alloy compositions and form a specialized alloy-cladding layer on the surface of the substrate to enhance its property. However, it can generate substantial residual stresses during the rapid cooling and heating stages, due to inadequate selection of cladding process parameters and disparities in thermophysical properties between the clad layer and substrate material, leading to the formation of various types of cracks. These cracks can significantly impact the quality and performance of the coating. This paper presents a comprehensive review of crack types and their causes in laser cladding coatings, and identifies that three primary sources of residual stresses, thermal stress, organizational stress, and restraint stress, are the fundamental causes of crack formation. The study proposes several strategies to control coating cracks, including optimizing the coating layer material, refining the coating process parameters, incorporating heat treatment, applying auxiliary fields, and utilizing numerical simulations to predict crack initiation and propagation. Additionally, the paper summarizes crack control methods for emerging structural materials and novel preparation processes. Lastly, the paper analyzes the prospects, technical approaches, and key research directions for effectively controlling cracks in laser cladding coatings.

A Survey of Multi-Agent Systems on Distributed Formation Control

Multi-agent formation control is an important part of distributed perception and cooperation, which is convenient to complete various complex tasks and would be a key research direction in the future. This paper reviews the corresponding problems of formation control and the existing centralized and distributed formation control strategies. In particular, we discuss four types of distributed formation control methods based on position and displacement in the global coordinate system and distance and bearing in the nonglobal coordinate system, respectively. Moreover, this paper analyzes affine formation which does not require the global coordinate system. Combined with the current practical applications of multi-agent systems, the latest research for the formation control of the unmanned aerial vehicle (UAV), unmanned ground vehicle (UGV), unmanned surface vehicle (USV) and autonomous underwater vehicle (AUV) is given. Finally, the challenges and opportunities in this burgeoning field are discussed.

Survey of Robot Formation Control Methods

Robot formation control technology has a certain practical significance and application value. efficient and stable formation control is the theoretical basis and technical key to perform complex tasks. Firstly, the basic idea of formation control is introduced, and then several formation control methods such as following the leader method, behavior based method, virtual structure method and artificial potential field method are introduced; This paper summarizes the research achievements of robot formation control in recent 20 years at home and abroad. Finally, the future research direction of formation control is pointed out.

Review of soil erosion modelling involving water with field applications

The literature associated with the topic of soil erosion processes is so vast that coverage must be restricted in some way. The major restriction adopted includes a focus on physically-based soil erosion modelling and its application in field studies including gully formation and sediment control methods. The choice of topics has also been biased towards those in which the authors have had some involvement, ensuring some emphasis on erosion studies in Australia and Southeast Asia.

Leader-follower formation of light-weight UAVs with novel active disturbance rejection control

Considering that the formation composed of light-weight UAVs is highly susceptible to the interference, which may from the changes in the external environment and the uncertainty of system, a formation control method based on the inner and outer loops is proposed. In the inner loop, the single UAV stable flight can be achieved via controlling the state variables of UAV angles. In the outer loop, we can achieve multi-UAVs cooperative flight through the leader-follower strategy. In this paper, we mainly focus on the stability control of each member UAV, which is the basic composition of formation control. For this purpose, an optimized active disturbance rejection control (ADRC) is proposed which combined an improved prescribed-time extended state observer (PTESO) and weight optimization module based on broad learning. In this way, the single UAV can dynamically adjust the control weights according to different wind degrees, so that the influence of environmental changes on the control system is reduced. Then, the effectiveness and superiority of the proposed formation control methods are verified by simulations. The stability enhancement control method proposed in this paper provides a new and effective theoretical support for the actual control of the light-weight UAV formation, which has a well engineering application prospect.

Review of the Formation Mechanisms and Control Methods of Geometrical Defects in Laser Deposition Manufacturing

Laser deposition manufacturing (LDM) is a revolutionary integrated manufacturing technology that expands numerous possibilities for producing large-scale parts in the aerospace and other industries. However, geometrical defects can severely affect the forming accuracy of parts and restrict the progress of LDM technology to large-scale components. This study summarizes the main types of geometrical defects and classifies them into four categories: flatness defects, melting collapse, distortion, cracking, and delamination. To overcome this challenge, one approach that has received considerable attention is process monitoring accompanied by mitigation strategies to improve the forming accuracy and repeatability. This study outlines the current understanding of the formation mechanism of common geometrical defects and discusses techniques to monitor the process and mitigate defects. Further, it discusses approaches for monitoring and controlling the LDM process while emphasizing the monitored melt pool, surface topography, temperature, and distortion. Next, the study focuses on procedures, including optimizing process parameters, thermal control methods, prediction, and compensation, to mitigate geometrical defects. Finally, the aim of the study is to provide a reference for researchers in this field. However, many future research hotpots for LDM precision control that require further investigation are still present.

Study on USV Cluster Formation Control and Cooperative Obstacle Avoidance

With the deepening of research on unmanned vehicles, research on USV (Unmanned Surface Vehicle) has gradually become extensive. In order to cope with complex Marine operations, the study of USV cluster collaborative operations has been emphasized. Therefore, this paper explores USV cluster formation and collaborative obstacle avoidance. In this paper, a formation control method of USV cluster is proposed based on the leader-follower architecture and the consistency algorithm. To solve the problem of formation cooperative obstacle avoidance, the traditional APF (APF method) is improved to avoid falling into the local optimal, and the cluster cooperative obstacle avoidance method is proposed. Finally, the simulation results show that the USV cluster formation control and obstacle avoidance methods are effective.

Formation and Change of Unmanned Ground Vehicles under Formation Change Influence Factor

Traditional formation control methods are widely used in the field of unmanned ground vehicle formation, but they lack mechanisms with which to effectively cope with complex terrains that occur during movement. In order to better improve the adaptation and coping ability of an unmanned ground vehicles (UGVs) fleet to complex terrains, this paper proposes a formation change influence factor to solve the UGVs formation and formation change problem. First, this paper adopts the leader–follower method with more flexible control to design the formation controller and derives a control law that can make the formation system stable so as to ensure that the fleet maintains the preset formation during movement. After that, this paper combines formation geometry change and dynamic adjustment to build a formation change library. The formation change influence factor is used to drive the fleet to choose the appropriate formation change strategy in the formation change library to ensure the fleet can safely pass the complex terrains. The experimental results show that, compared with the traditional formation method, the UGVs formation and change method using the formation change influence factor can flexibly and efficiently cope with various complex terrains while maintaining stability within the fleet, effectively improving the safety of the UGVs fleet and the possibility of practical application.

Laser powder bed fusion of node-reinforced hybrid lattice structure inspired by crystal microstructure: Structural feature sensitivity and mechanical performance

Strut-based lattice structures (SLSs) have been widely used in modern industries including aerospace, automobile and biological implant, due to their unique properties such as lightweight, good energy absorption capability and high specific strength. However, the obtainable mechanical performance is significantly limited by the monotonous strut-based feature without any reinforcement topology. The inherent strengthening mechanisms and atom-scale models in material science may be crucial and valuable to optimize the complex structures with desired properties. Inspired by the solid solution strengthening mechanisms in crystal microstructure, a series of novel crystal-inspired hybrid structures, i.e., the common face-center cubic with Z-strut (FCCZ) structure, the face-center substitutional lattice (FCSL) structure, the edge-center interstitial lattice (ECIL) structure and the vertex-node substitutional lattice (VNSL) structure were designed and fabricated by laser powder bed fusion (LPBF) additive manufacturing in this work. The effect of node location on the LPBF formability, mechanical performance, stress distribution, deformation modes and failure mechanisms of the crystal-inspired components was systematically investigated. The computational fluid dynamics (CFD) method was used to understand the dynamics of molten pool to reveal the formation mechanism and control methods of the dross defect attached to overhanging surfaces. Finite element model (FEM) was established to show the stress distribution and deformation behavior of these hybrid structures during compression. Results showed that the ECIL structure possessed the highest specific energy absorption (SEA) of 13.7 J/g, which increased by 17% compared with the initial FCCZ structure. The crush force efficiency (CFE) of VNSL structure reached the peak value of 66% with a unique axisymmetric shear band during deformation, which increased by 14% compared to the FCCZ structure. The underlying mechanism analysis revealed that the as-designed spherical node could redistribute the stress and the performance of the lattice structures could be manipulated by tailoring the position of the spherical nodes. The present approach suggested that the hardening principles of crystalline materials could inspire the design of novel lattice structures with desired properties.

Formation control for connected and automated vehicles on multi‐lane roads: Relative motion planning and conflict resolution

Existing research has revealed that multi-vehicle coordinated decision making and control can achieve an improvement in both traffic efficiency and driving safety. In the multi-lane scenarios, a typical coordination method is multi-vehicle formation control. The existing formation control methods predefine the formation switching process and have not considered or explained the collision-free behaviour of vehicles in detail. In this paper, a multi-lane formation control strategy for connected and automated vehicles (CAVs) is proposed. The planning framework is bi-level, which can switch the structure of multi-vehicle formation in different scenarios smoothly and effectively. In the upper-level, the relative coordinate system is built to plan the collision-free relative paths for vehicles. In the lower-level, multi-stage trajectory planning and tracking are modelled as an optimal control problem with path constraints. The case study verifies the function of the formation control method in three lane-number-changing scenarios. Large-scale simulations in the lane-drop bottleneck scenario are conducted under different input traffic volumes, and the numerical results indicate that the proposed formation control method reduces congestion and improves both traffic efficiency and fuel economy at high traffic volumes.

Distributed observer based event‐triggered affine formation maneuver control for underactuated surface vessels with positive minimum inter‐event times

AbstractThis article investigates the distributed event‐triggered affine formation maneuver control problem for multiple underactuated surface vessel (USV) systems with positive minimum inter‐event times (MIET). Unlike common formation control methods that only ensure the formation system to keep a fixed geometric shape, the proposed scheme enables multiple USVs maneuver as a group in translation, shearing, rotation, or combinations of them. The proposed control strategy is composed of two parts. First, a distributed event‐triggered observer (DETO) is proposed to observe the time‐varying target formation under the lack of global leaders' information and govern the inter‐vessel communications among the formation group. Besides, the MIET of the designed communication strategy is proved to be strictly positive and computable from formation configurations and control parameters. With these guarantees, the maximum communication frequency can be known in advance. Then, upon the DETO signals, the adaptive local tracking controller is subsequently synthesized for each vessel to realize the target formation track. Rigorous theoretical analysis and simulation results are finally conducted to verify the validness and effectiveness of the proposed algorithm.

A Distributed Multi-Agent Formation Control Method Based on Deep Q Learning.

Distributed control method plays an important role in the formation of a multi-agent system (MAS), which is the prerequisite for an MAS to complete its missions. However, the lack of considering the collision risk between agents makes many distributed formation control methods lose practicability. In this article, a distributed formation control method that takes collision avoidance into account is proposed. At first, the MAS formation control problem can be divided into pair-wise unit formation problems where each agent moves to the expected position and only needs to avoid one obstacle. Then, a deep Q network (DQN) is applied to model the agent's unit controller for this pair-wise unit formation. The DQN controller is trained by using reshaped reward function and prioritized experience replay. The agents in MAS formation share the same unit DQN controller but get different commands due to various observations. Finally, through the min-max fusion of value functions of the DQN controller, the agent can always respond to the most dangerous avoidance. In this way, we get an easy-to-train multi-agent collision avoidance formation control method. In the end, unit formation simulation and multi-agent formation simulation results are presented to verify our method.

Multi-Robot Leader Grouping Consistent Formation Control Method Research with Low Convergence Time Based on Nonholonomic Constraints

Aiming at the formation and maintenance of the multiple formations of nonholonomic constrained multi-robots, a leader-follower formation control method under the grouping consistency is proposed on the trajectory tracking of a nonholonomic constrained mobile robots with the low convergence time. The distributed control structure in the leader-follower formation is adopted. The multi-robot cooperative formation is realized by using the consistency algorithm of graph theory. According to the graph theory, the communication topology matrixes are designed by the consistency algorithm. The mathematical model of nonholonomic constrained robot is established with the wheeled structure as the mobile structure under the nonholonomic constraints. Then the navigation following model is transformed into the error model of a local coordinate system through the global coordinate transformation. The formation control law of multi-robot cooperative motion is put forward based on the leader-follower model. Its convergence is proved by the Lyapunov function. By setting the reasonable communication protocol parameters, the MATLAB software (Natick, MA, USA, R2016b) is employed on the simulation verification and result comparison. Through the comparison of the two leader formation control methods, the convergence time of the algorithm in this article can be 25% less than that of PFC. The effectiveness and feasibility of the formation control law are verified under the leader-follower method. The proposed control method lays a foundation for reducing the convergence time to improve the multi-robot cooperative motion under nonholonomic constraints.

Review on Defect Formation Mechanisms and Control Methods of Metallic Components During Laser Additive Manufacturing

Review on Defect Formation Mechanisms and Control Methods of Metallic Components During Laser Additive Manufacturing

Performance of different Formation control methods between Multiple Spacecraft with local part communications

With the development of network and distributed computing, many applications of multi vehicle system have become possible, and motion transformation can be realized. In multi vehicle coordination, the interaction between information exchange topology and control plays an important role. Different formation control methods have different performance. Thus, in order to figure out which method is suitable for multiple spacecraft, the author simulated the signal unstable environment in space to test the robustness and consensus speed of the following three methods. The author use Bearing-only Formation Control, A leader–follower Formation Control and Affine Formation Control to test their performance with local part communications. The author use matlab and simulink to analog communication process of multiple spacecraft. Finally, the author find Affine Formation Control’s performance is the best. It has the best robustness and the fast consensus speed but more energy and signal paths to communicate.