The QR modes measurement and modeling in the head actuator assembly

This paper studies the characteristics of quasi-rigid body modes (QR modes), which are most important in understanding dynamic behaviour of the head actuator assembly in HDD. Experiment results are presented in terms of the frequency response functions obtained in lateral direction excitation. Finite element models 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 numerical prediction and measurement. It is shown that there may exist six quasi-rigid body modes, and two of them may lead to residual vibration. The causes are likely due to flexibility of the pivot bearing system and the difference in stiffness of the two ball bearings in the pivot system.