I. Introduction
Controlling robot manipulators using only link position measurements has received considerable attention due to the fact that nearly all commercially available robot manipulators do not have link velocity sensors and the ones that have velocity sensors the sensor outputs are, most of the time, contaminated with noise. The existing solutions to the forementioned problem can be categorized as observer based [1], [2] and filter based [3], [4], [5], [6], [7] methods. In most observer based methods, a model based observer [2], [8] is used to estimate the velocity signal, where in filtered based approaches surrogate filters are used to overcome the need of velocity measurements. However, when the robot parameters are not precisely known, the observer based methods fail as most of them require the exact knowledge of system parameters.