  Based on recent advances in contraction methods in systems and control, in
this paper we present the virtual differential passivity based control (v-dPBC)
technique. This is a constructive design method that combines the concept of
virtual systems and of differential passivity. We apply the method to the
tracking control problem of flexible joints robots (FJRs) which are formulated
in the port-Hamiltonian (pH) framework. Simulations on a single flexible joint
link are presented for showing the performance of a controller obtained with
this approach.
