Hierarchical Control of Unmanned Ground Vehicle Formations using Multi-Body Approach

The paper deals with the formation control of Unmanned Ground Vehicles (UGVs) moving in horizontal plane.The control system consists of the high level centralized formation control of the UGVs and the low level decentralized PID type suspension, speed and steering control of the different vehicles.Both problems are discussed in multi-body assumptions.The paper presents the generalization of the multi-body method for underactuated car-like vehicles, developed originally for fully-actuated surface ships.In order to simplify the design and implementation on the formation level, an approximate single track dynamic model was assumed for each vehicle.At low level a more realistic two track dynamic model is used in the form of a multibody system in tree structure.This realistic nonlinear model is obtained by using Appell's method, Pacejka's magic formula for tyre-road connections and kinematic constraints expressing the nullity of vertical accelerations of the contact points.The interface between the higher and lower control levels is presented in the form of acceleration and steering angle prescriptions (output of high level).The decentralized control system of each vehicle converts the specifications in smooth reference signals and performs the desired motion.Simulation results of the high level control of UGV formations are presented for sine-shaped and circular paths.