Dynamic Behavior of an Ultra Precision Spindle used in Machining of Optical Components

AbstractTo satisfy the increasing demand for parts in optical quality it is necessary to reduce the processing time, e.g. by ultra precision high performance cutting (UP-HPC). One aspect of UP-HPC is the increase of the spindle speed. High speed spindles require a well balanced spindle rotor to enable the machining of optical surfaces. With conventional speed spindles the unbalance is detected by measuring vibrations at the spindle housing. Thus, the unbalance excited vibrations propagate from the rotor through the air bearings to the spindle housing. In order to calculate the angular position and the magnitude of the unbalance from these measurements the dynamic properties of the air bearings and the housing as well must be known. In this paper the dynamic properties of an ultra precision spindle at different speeds are investigated by means of experimental impact tests. It is shown that the tested air bearing provides a good transfer behavior only in the higher frequency range above 200Hz and that the spindle housing is not the preferable location to measure the rotor unbalance