MICRO-DYNAMIC STICTION MODEL AND CONTROL OF A HUB-APPENDAGE SYSTEM

摘要

A hub-beam system driven by a DC torque motor is studied. The motor is mounted on two ordinary ball bearings. Therefore, static friction is significant in this system. Traditionally, in modeling a flexible structure system, people treat static diction as a force equal but opposite to the applied force. Furthermore, there is no displacement once the system is stuck by the static friction. With this dead zone type static friction concept, it is theoretically very hard to control the line of sight (L. O. S) of the flexible beam with very high precision due to the residue deviation of hub angle and small vibration that remain when the system is stuck by static friction. However, based on a large amount of experimental results, more detail of static friction behavior has been revealed. It turns out that the static friction behavior can be summarized in several simple rules. A new static friction model that is described elsewhere is hence developed according to these rules. In this paper, this new friction model is applied to the hub beam system to describe the motion of the system during stiction phase. This micro dynamic stiction model is experimentally proved. It is shown that, after linearization, the stiction force is equivalent to a spring force with high stiffness together with a damping force. With the help of this new model, we successfully point the L. O. S. of the beam to the target with arc-second level precision.