Measurement and modeling of quasi-rigid-body modes in the head actuator assembly

As the track density increases and the seeking time reduces, residual vibra tion problems become increasingly critical in the design and performance of hard disk drives. It is essential to further understand the dynamics of th e head actuator assembly, such as the effect of pivot bearing. This paper s tudies the characteristics of quasi-rigid-body modes, which are most import ant in understanding the dynamic behavior of the head actuator assembly. Ex perimental results are presented in terms of the frequency response functio ns obtained in lateral and vertical direction excitation. Finite-element mo dels are used to predict the quasi-rigid-body modes and their dependence on the stiffness of pivot bearing. A good agreement is obtained between the n umerical prediction and measurement. It is shown that six quasi-rigid-body modes may exist, and two of these may lead to residual vibration and track misregistration in the frequency range of interest. The causes are likely t he flexibility of the pivot-bearing system and the difference in the stiffn ess of the two bearings in the pivot-bearing system.