In this paper, an enclosing control problem is investigated for
nonholonomic mobile agents with a moving target of unknown velocity. An
adaptive observer containing two internal variables is first designed
for each agent to compensate for the lack of the target velocity
information. One variable is designed to estimate the unknown target
velocity and further its estimation error is assessed by the other
internal variable to subsequently guarantee the control performance.
Then using the estimated information from the adaptive observer, a
dynamic control law for circular formation of nonholonomic agents around
the moving target is designed by a backstepping process. The global
asymptotical stability of the closed-loop system is achieved under the
proposed dynamic control law with the adaptive observer. Finally, a
simulation is conducted to demonstrate the effectiveness of the proposed
approach.