Attitude observer and trajectory tracking for a group of unicycle-type robots

This paper presents three trajectory tracking control strategies for groups unicycle-type robots based on the leader-followers scheme using an observer to estimate the orientation angle of each robot. The leader robot converges asymptotically to a smooth trajectory while the follower robots are formed in an undirected open-chain configuration at the same time. The control laws are based on a dynamical extension of the kinematic model of each robot. The output functions to be controlled are the midpoint of the wheels axis of each robot. This choice leads to an ill defined control law when the robot is at rest. To avoid such singularities, a complementary control law is enabled momentarily when the linear velocity of the unicycles is close to zero. Numerical simulations complete the paper.