In this study one considers the tracking control problem of a class of nonsmooth Lagrangian systems with flexible joints and subject to frictionless unilateral constraints. The task under consideration consists of a succession of free-motion and constrained-motion phases. Particular attention is paid to impacting and detachment phases. A passivity-based switching controller that allows one to extend the stability analysis described in our previous works to the case of systems with lumped flexibilities, is proposed. Numerical tests show the effectiveness of the controller. (C) 2009 Elsevier Ltd. All rights reserved.