He Bai

Rigid body attitude coordination without inertial frame information

We study a motion coordination problem where the objective is to achieve identical orientation and synchronous rotation for a group of rigid bodies. Unlike existing designs which assume that the inertial frame is available to each agent, we develop a passivity-based design which relies only on relative attitude information with respect to neighboring agents. The desired equilibria, where all the rigid bodies possess the same attitude and rotate at a desired angular velocity, are shown to be locally asymptotically stable and a manifold of undesired equilibria may exist. We then consider the situation where the reference angular velocity is available only to the leader, and propose a distributed adaptive controller with which the other agents reconstruct this reference angular velocity.

Adaptive design for reference velocity recovery in motion coordination

We study a coordination problem where the objective is to steer a group of agents to a formation that translates with a prescribed reference velocity. Unlike existing designs which assume that the reference velocity information is available to each agent, we consider the situation where this information is available only to a leader. We then develop an adaptive design with which the other agents reconstruct the reference velocity and recover the desired formation. This design relies only on relative distance information with respect to neighbouring agents and, thus, can be implemented in a decentralized fashion.

Robust dynamic average consensus of time-varying inputs

We consider the dynamic average consensus problem in which each agent in a network has access to its own local input signal, but it must compute and track the average of all such inputs. Each agent communicates only with neighbors in the network, and local communication, computation and memory requirements should be independent of the number of the agents in the network. The Proportional-Integral (PI) estimator in [1] guarantees zero steady-state error under constant inputs for constant, connected, and balanced networks, even in the presence of estimator initialization errors. In this work, we employ the internal model principle to generalize the PI estimator so that it achieves zero steady-state error for classes of time-varying inputs, including polynomial inputs of known order and sinusoidal inputs with known frequencies. Like the PI estimator, our new estimator is robust to initialization errors.

Brief paper: Adaptive motion coordination: Using relative velocity feedback to track a reference velocity

We study a coordination problem where the objective is to steer a group of agents to a formation that translates with a prescribed reference velocity. In Bai et al. [Bai, H., Arcak, M., & Wen, J. (2008). Adaptive design for reference velocity recovery in motion coordination. Systems and Control Letters, 57(8), 602-610.] we considered the situation where the reference velocity information is available only to a leader, and developed a decentralized adaptive design that uses relative position feedback. Although Bai et al. (please see above reference) guaranteed the desired formation, it did not ensure tracking of the reference velocity with the exception of special cases. We now propose a new adaptive redesign that guarantees tracking of the reference velocity by incorporating relative velocity feedback in addition to relative position feedback.

Cooperative Control Design

1 Introduction.- 2 Passivity As a Design Tool for Cooperative Control.- 3 Adaptive Design for Reference Velocity Recovery: Internal Model Approach.- 4 Adaptive Design for Reference Velocity Recovery: Parameterization Approach.- 5 Attitude CoordinationWithout Inertial Frame Information.- 6 The Agreement of Euler-Lagrange Systems.- 7 Synchronized Path Following.- 8 Cooperative Load Transport.- 9 Caveats for Robustness.

Cooperative Load Transport: A Formation-Control Perspective

We consider a group of agents collaboratively transporting a flexible payload. The contact forces between the agents and the payload are modeled as gradients of nonlinear potentials that describe the deformations of the payload. The load-transport problem is then treated in a similar fashion to the formation-control problem. Decentralized control laws are developed such that without explicit communication, the agents and the payload converge to the same constant velocity; meanwhile, the contact forces are regulated. Experimental results illustrate the effectiveness of our designs.

DIstributed Kalman Filtering Using The Internal Model Average Consensus Estimator

We apply the internal model average consensus estimator in [1] to distributed Kalman filtering. The resulting distributed Kalman filter and the embedded average consensus estimator update at the same frequency. We show that if the internal model average consensus estimator is stable, the estimation error of the distributed Kalman filter is zero mean in steady state and has bounded covariance even when the dynamical system to be estimated is neutrally stable or unstable.

Passivity As a Design Tool for Cooperative Control

In this chapter, we formulate a coordination problem that is applicable to formation stabilization and group agreement as special cases, and present a class of feedback laws that solve this problem with local information. A key observation is that bidirectional communication gives rise to Structure 4 in Section 1.5, which guarantees that the resulting feedback loop will inherit the passivity properties of its components. By exploiting this structure, we develop a design method which results in a broad class of feedback laws that achieve passivity and, thus, stability of the interconnected system. The passivity approach also leads to a systematic construction of a Lyapunov function in the form of a sum of storage functions for the subsystems. As detailed in this chapter, several existing feedback rules for formation stability and group agreement become special cases in the passivity framework.

Instability mechanisms in cooperative control

We consider a motion coordination problem with second order agent dynamics and examine the closed-loop robustness with respect to switching topology, variation of link gain, and unmodeled dynamics. In each case, we illustrate with examples possible instability mechanisms and discuss under what conditions stability is maintained.

A decentralized design for group alignment and synchronous rotation without inertial frame information

We study a motion coordination problem where the objective is to achieve identical orientation and synchronous rotation for a group of rigid bodies. Unlike existing designs which assume that the the inertial frame is available to each agent, we develop a passivity-based design which relies only on relative attitude information with respect to neighboring agents. The desired equilibria, where all the rigid bodies possess the same attitude and rotate at a desired angular velocity, are shown to be locally asymptotically stable and a manifold of undesired equilibria may exist. We then consider the situation where the reference angular velocity is available only to the leader, and propose a distributed adaptive controller with which the other agents reconstruct this reference angular velocity.