In this paper, a controller that solves the problem of position synchronization of two (or more) robot systems, under a cooperative scheme, in the case when only position measurements are available, is presented. The synchronization controller consists of a feedback control law and a set of nonlinear observers. Coupling errors are introduced to create interconnections that render mutual synchronization of the robots. It is shown that the controller yields semiglobal exponential convergence of the synchronization closed-loop errors. Experimental results show, despite obvious model uncertainties, a good agreement with the predicted convergence.