Abstract
The objective of the work is two-fold. A first part is devoted to the problem of constructing an observer to the practical system called overhead crane with the position as output. In a second part, the problem of global output feedback stabilisation is solved for a class of Euler-Lagrange systems when the variables of velocity are the unmeasured part of the state. The equations of these systems are non-linear with respect to the velocities. A new output feedback control scheme is proposed. It relies on the determination of a change of coordinates which gives to the systems a triangular form. To illustrate the approach, it is applied to a two-link manipulator.