He Xiaoxia

Gao Zhongyu

Wang Yongliang

Department of Precision Instruments

and Machinery,

Tsinghua University,

Beijing 100084, China

ICAL ROTOR WITH CONTACTLESS

Abstract: Based on the motion equations of an unbalanced spherical rotor with contactless suspension, three methods of MUM (mass unbalance measurement) are put forward to measure the total mass unbalance, radical mass unbalance and radical mass unbalance of the rotor. Total mass unbalance is obtained when the unbalanced rotor plays as a simple pendulum in static situation. The pendulant period and pendulant midpoint indicate magnitude and direction of total mass unbalance of the rotor respectively. Analysis of the motion equations by using the averaging method yields that the rotor will do a special side oscillation when an auxiliary system makes the rotor spin about its pole axis which is orientating toward the local vertical. The radical mass unbalance can be obtained by building a proper displacement sensor to sense the amplitude of the side oscillation. Necessary analysis of the motion equations also shows that when the rotor spins at a small angular velocity and the rotary axis is perpendicular to the vertical, the pole axis of the rotor will precess slowly about the vertical by virtue of the axial mass unbalance. The axial mass unbalance can be estimated from the time history of the spin vector of the rotor. Finally, measurement precision of the three methods is compared and how the external torque affects the measurement precision for the three methods are examined.

Key words: Mass unbalance measurement  Radical mass unbalance  Axial mass unbalance  Static balancing  Averaging method