In this paper, a new sliding mode output feedback algorithm is developed to
control the vibration of mechanical systems subjected to disturbance force
s. It has been assumed that the number of states is greater than the number
of sensors, The sliding mode control law is designed to be robust to exter
nal disturbances provided their upper bounds are known. A boundary layer ha
s been introduced around each sliding hyperplane to eliminate the chatterin
g phenomenon. The results from numerical simulations are presented to corro
borate the validity of the proposed controller.