Spacecraft formation reconfiguration with multi-obstacle avoidance under navigation and control uncertainties using adaptive artificial potential function method

In this paper,an adaptive artificial potential function(AAPF)method is developed for spacecraft formation reconfiguration with multi-obstacle avoidance under navigation and control uncertainties.Furthermore,an improved Linear Quadratic Regular(ILQR)is proposed to track the reference trajectory and a Lyapunov-based method is employed to demonstrate the stability of the overall closed-loop system.Compared with the traditional APF method and the equal-collision-probability surface(ECPS)method,the AAPF method not only retains the advantages of APF method and ECPS method,such as low computational complexity,simple analytical control law and easy analytical validation progress,but also proposes a new APF to solve multi-obstacle avoidance problem considering the influence of the uncertainties.Moreover,the ILQR controller obtains high control accuracy to enhance the safe performance of the spacecraft formation reconfiguration.Finally,the effectiveness of the proposed AAPF method and the ILQR controller are verified by numerical simulations.

Path-Following Control With Obstacle Avoidance of Autonomous Surface Vehicles Subject to Actuator Faults

This paper investigates the path-following control problem with obstacle avoidance of autonomous surface vehicles in the presence of actuator faults,uncertainty and external disturbances.Autonomous surface vehicles inevitably suffer from actuator faults in complex sea environments,which may cause existing obstacle avoidance strategies to fail.To reduce the influence of actuator faults,an improved artificial potential function is constructed by introducing the lower bound of actuator efficiency factors.The nonlinear state observer,which only depends on measurable position information of the autonomous surface vehicle,is used to address uncertainties and external disturbances.By using a backstepping technique and adaptive mechanism,a path-following control strategy with obstacle avoidance and fault tolerance is designed which can ensure that the tracking errors converge to a small neighborhood of zero.Compared with existing results,the proposed control strategy has the capability of obstacle avoidance and fault tolerance simultaneously.Finally,the comparison results through simulations are given to verify the effectiveness of the proposed method.

Polygon formation of multiple nonholonomic mobile robots with double-level-control collision avoidance scheme

This paper considers a polygon formation control of multiple robots with nonholonomic constraintsenclosing a goal target and double-level-control collision avoidance scheme. Doublelevel-control scheme consisted of upper-level and lower-level controls are proposed for trajectorygeneration and tracking control of multi-robot systems. Both upper-level and lower-levelcontrols operate collision avoidance mechanisms based on potential functions. The proposedcontrol scheme guarantees that the group of robots are kept in the polygon formation and drivento a goal, while avoiding collisions during the travel. Moreover, the designed interaction betweenthe upper- and lower-level controls guarantees that the mobile robots are not trapped in localminima or deadlock case. Experiments of the formation of three-robots are conducted to showthe performance of the mobile robots in accomplishing a polygon formation while achieving thegoal without any collision and no local minima.