Ronghao Zheng

Enclosing a target by nonholonomic mobile robots with bearing-only measurements

This paper addresses the problem of steering a single or a group of autonomous nonholonomic mobile robots to enclose a target of interest. We develop control schemes which require only local bearing measurements, and deal with encirclement of two types of targets: point target and disk target. When a single robot is used, circumnavigation schemes are proposed to achieve effective encirclement of the target. It is shown that under the proposed control schemes, the robot can circle the target from a prescribed distance without distance measurement. When multiple robots are deployed, the control schemes developed for single robot are modified by introducing a coordination mechanism, which drives the robots to distribute evenly around the target. We further discuss a control scheme that moves the robots to form a static circular formation around the target based on feedback linearization. All the proposed control schemes are validated in experiments on a group of two-wheeled differential drive mobile robots.

Distributed control for uniform circumnavigation of ring-coupled unicycles

The paper studies the general circumnavigation problem for a team of unicycle-type agents, with the goal of achieving specific circular formations and circling on different orbits centered at a target of interest. A novel distributed solution is proposed, in which the control laws are heterogeneous for the agents such that some agents are repellant from the target while attractive to its unique neighbor and some agents are attractive to the target while repellant from its neighbor. A systematic procedure is developed to design the control parameters according to the specific radii of the orbits and the formations that the agents are desired to converge to. Moreover, this control scheme uses a minimum number of information flow links between the agents and local measurements of relative position only. Based on the block diagonalization of circulant matrices by a Fourier transform, asymptotic convergence properties are analyzed rigorously. The validity of the proposed control algorithm is also demonstrated through numerical simulations.

Formation Control With Size Scaling Via a Complex Laplacian-Based Approach

We consider the control of formations of a leader-follower network, where the objective is to steer a team of multiple mobile agents into a formation of variable size. We assume that the shape description of the formation is known to all the agents, which is captured by a complex-valued Laplacian associated with the sensing graph, but the size scaling of the formation is not known or only known to two agents, called the leaders in the network. A distributed linear control strategy is developed in this paper such that the agents converge to the desired formation shape, for which the size of the formation is determined by the two leaders. Moreover, in order to make all agents in a formation move with a common velocity, the distributed control law also incorporates a velocity consensus component, which is implemented with the help of a communication network that may, in general, be of different topology from the sensing graph. Both the setup of single-integrator kinematics and the one of double-integrator dynamics are addressed in the same framework except that the acceleration control in the double-integrator setup has an extra damping term.

Distributed circumnavigation by unicycles with cyclic repelling strategies

The distributed circumnavigation problem, in which the task is to circumnavigate a target of interest by a network of autonomous agents, has many applications in security and surveillance, orbit maintenance, source seeking, etc. This paper deals with the circumnavigation problem using a team of non-holonomic unicycles. A novel distributed solution is proposed based on cyclic repelling strategies to achieve a circular motion around a target in a circular formation. This new approach considers minimum number of information flow links and local measurements only, yet a uniform distribution of unicycles rotated around the target is accomplished. The asymptotic collective behavior is analyzed based on the block diagonalization of circulant matrices by a Fourier transform. Simulation results also verify the validity of the proposed control algorithm.

A barycentric coordinate based approach to formation control of multi-agent systems under directed and switching topologies

This paper studies the formation control problem for a leader-follower network in 3D. The objective is to control the agents to form a globally rigid formation, for which the sensing graph is directed and switching while the communication graph is undirected and switching. Under such a setup, a barycentric coordinate based approach is proposed for the design of formation control laws ensuring global convergence. A necessary and sufficient graphical condition is obtained to guarantee that the followers converge to form a globally rigid formation together with the leaders. By this approach, the formation of the whole group, namely, the orientation, translation and formation scale, can be reconfigured by the leaders.

Distributed localization with mixed measurements under switching topologies

Abstract This paper investigates the distributed localization problem of sensor networks with mixed measurements. Each node holds a local coordinate system without a common orientation and is capable of measuring only one type of information (either distance, bearing, or relative position) to near-by nodes. Thus, three types of measurements are mixed in the sensor networks. Moreover, the communication topologies in the sensor networks may be time-varying due to unreliable communications. This paper develops a fully distributed algorithm called BCDL (Barycentric Coordinate based Distributed Localization) where each node starts from a random initial guess about its true coordinate and converges to the true coordinate via only local node interactions. The key idea in BCDL is to establish a unified linear equation constraints for the sensor coordinates by using the barycentric coordinates of each node with respect to its neighbors though the sensor nodes may have different types of measurements. Then a distributed iterative algorithm is proposed to solve the linear equations under time-varying communication networks. A necessary and sufficient graphical condition is obtained to ensure global convergence of the distributed algorithm.

A barycentric coordinate based approach to three-dimensional distributed localization for wireless sensor networks

This paper introduces a new range-based distributed localization algorithm for wireless sensor networks in the three-dimensional space. To overcome the difficulty in computing the barycentric coordinates of a node with respect to its neighbors in 3D, a new scheme is developed for this purpose by using the fact that a congruent framework of the subnetwork consisting of the node and its neighbors has the same barycentric coordinates. A multidimensional scaling (MDS) method is used to calculate the coordinates of the congruent framework, which can provide a solution for each subnetwork with not only exact range measurements but also noisy range measurements. Thus, a linear equation related to a signed Laplacian is obtained to describe the geometric constraints of the whole network. We then show a globally convergent and linear iterative algorithm called MDS-DILOC for each node to locate itself in the three-dimensional space by solving the linear equation. Simulation is carried out to demonstrate the validity of MDS-DILOC.

A survey on concurrent network localization for autonomous multi-vehicle systems

Network localization plays the key role in position based operations and services of autonomous multi-vehicle systems such as unmanned aerial vehicles and satellite formation, which aims to determine the Euclidean coordinates of all the vehicles given a collection of inter-vehicle measurements and the Euclidean coordinates of a small number of vehicles. Concurrent network localization approaches allow each vehicle solve its own coordinate in a distributed manner via local information exchange with its neighbors and thus exhibit many desirable advantages in applications. This paper reviews recent development on concurrent network localization algorithms and aims to provide a comprehensive insight for these novel ideas. In terms of the types of inter-vehicle information, distance-based, bearing-based, and relative-position-based concurrent network localization are discussed in a unified framework.

Global stabilization of rigid formations via sliding mode control

This paper studies the rigid formation control problem of multi-agent systems, for which finding a local interaction law ensuring global convergence towards a desired formation is the main challenge. A sliding mode control law is proposed in this paper, which steers all the agents to a desired rigid formation in any dimensional space for arbitrarily initial configuration. The main idea is to firstly make the trajectories of all the agents reach a sliding surface in finite time and secondly govern the agents towards the desired rigid formation while confining the motion in the sliding surface. Thus, the difficulty in achieving global convergence towards a desired formation is reduced to a much lower dimensional state space with much less number of agents being controlled to satisfy inter-agent distance constraints. Simulation results are provided to illustrate the effectiveness of our proposed control schemes.

Formation control of heterogeneous agents over directed graphs

This paper studies the formation control problem of a leader-follower heterogeneous network, for which some agents can freely fly in a 3D space while others are confined in a 2D space. The sensing graph is assumed to be directed and the onboard local coordinate systems associated with the agents may not be coincident with each other. More specifically, the agents may have aligned z-axis but hold inconsistent x and y axes due to the absence of a common sense about north. This paper develops a distributed formation control law that solves the formation control problem for a leader-follower heterogeneous network without relying on a common coordinate system. Moreover, it is shown that the proposed control law guarantees global convergence towards any desired formation shape as long as certain graph connectivity conditions hold. Simulation results are provided to validate our control law.