Influence of speed estimation methods and encoder resolutions on the stiffness of a haptic interface

A haptic system is an articulated mechanical structure with motors, sensors, embedded electronics as well computer software allowing force feedback. It enables the user to interact with virtual reality through the sense of touch and sight. The control of such systems can become unstable at low speed because of mediocre speed estimation quality. This paper describes the influence of diminution of the position encoder resolution on the estimated speed, since the speed is calculated using the position information. Further more, this paper illustrates the implementation of various speed estimation techniques, such as a full order state speed observer, Kalman filter and the synchronous constant elapsed time method (direct digital position derivation) for a single degree of freedom haptic interface driven by a permanent magnet synchronous motor. In addition, their influence on system stiffness is illustrated.