15th Triennial World Congress of the International Federation of Automatic Control
  Barcelona, 21–26 July 2002 
PRECISION-LIMIT POSITIONING OF DIRECT DRIVE SYSTEMS WITH THE EXISTENCE OF FRICTION
T.-Y. Lin, Y.-C. Pan and C. Hsieh
Institute of Aeronautics and Astronautics
National Cheng Kung University,
Tainan, Taiwan, 701, R. O. C.

This paper discusses the issue of precision-limit positioning of a direct drive system with the existence of friction. By precision-limit positioning we mean that, in addition to the common sense of high precision requirement, the precision error equals to the resolution of the position sensor used in the feedback loop. This means a zero-count precision error when a digital type position sensor is used. Precision-limit positioning also enforces 100 % repeatability as precision is concerned. Of course, this is the limit of the precision that a real control system can achieve. Traditionally, this kind of performance was not considered possible mainly for lacking accurate and enough information about friction, especially the static friction. However, as more and more knowledge of the pre-sliding motion has been revealed, it is shown in this research that such kind of performance can be achieved.
Keywords: Positioning systems, Position accuracy, Position control, Friction
Session slot T-Fr-A19: Robot Control/Area code 1d : Robotics