A modern motion control system, such as a manipulator arm or a positioning system, consists in general of one or several electrical drives operating under the control of a central computer system that coordinates the overall motion. The control problem of such complex systems can be divided into two levels: high-level control and low-level control. High level control involves the coordination of all he actuators to produce the desired motion from one point to another or following a planned trajectory. On the other hand, low-level control deals with the control of each motor drive. In this paper, we will focus our attention on low-level motion control which involves the control of velocity and/or position of an electrical drive.