  In this work, we present solutions to the flocking and target interception
problems of multiple nonholonomic unicycle-type robots using the distance-based
framework. The control laws are designed at the kinematic level and are based
on the rigidity properties of the graph modeling the sensing/communication
interactions among the robots. An input transformation is used to facilitate
the control design by converting the nonholonomic model into the single
integrator-like equation. We assume only a subset of the robots know the
desired, time-varying flocking velocity or the target's motion. The resulting
control schemes include distributed, variable structure observers to estimate
the unknown signals. Our stability analyses prove convergence to the desired
formation while tracking the flocking velocity or the target motion. The
results are supported by experiments.
