Analysis of non-repeatable radial vibration of magnetic disk spindles.

This paper describes the theoretical and experimental investigation on strict comparison of non-repeatable radial vibrations (NRRV) between time and frequency domains. The statistical characteristics of NRRV are revealed by analyzing amplitude distributions of both asynchronous and synchronous vibration components in frequency domain. As a result of this study, it is found that the main part of NRRV is composed of asynchronous components in almost all spindles. The amplitudes of some asynchronous components are varying randomly and can be approximately expressed by Rayleigh distribution function. It is also found that the synchronous vibrations include also non-repeatable components. The variance of NRRV in time domain is shown theoretically and experimentally to be equal to the total power of asynchronous components and varying components of synchronous ones. From this relation, the cause of tracking error can be analyzed quantitatively in frequency domain.