Performance of automatic ball balancers on optical disc drives

Abstract

The balancing performance of an automatic ball balancer fitted on the spindle motor of optical disc drives, for instance CD-ROM or DVD drives, is analysed. It is well known that the operating speed of an optical disc drive with an automatic ball balancer should be higher than the translational natural frequency of the system to be balanced. However, the influence of the rotational natural frequency on the performance of automatic ball balancers has not yet been investigated. In this study, considering not only the translational but also the rotational motion of the system, the non-linear equations of motion are derived using Lagrange's equation. Applying a perturbation method to the non-linear equations, the linearized equations in the neighbourhood of a balanced equilibrium position are obtained. These equations have time-dependent periodic coefficients, which require application of the Floquet theory for stability analysis. From the stability analysis the effects of the stiffness and damping of rubber suspensions on the automatic ball balancer's performance are evaluated for the variation of operating speed. To verify the results, time responses are also computed from the non-linear equations. It is finally found that the natural frequency of not only the translational but also the rotational motion has an influence on the balancing performance of automatic ball balancers.