Numerical Investigation of Operational Shocks and Vibrations in Mobile Hard Disk Drives
Over the last decade, there has been a continuous increase in the demand of hard disk drives (HDDs) for the mobile applications. In such devices, HDDs are often subjected to mechanical shocks and vibrations. Such external disturbances can degrade the read/write (R/W) performance of mobile drives and in extreme cases it can even cause the loss of stored magnetic information. Hence the ability of the head-disk interface (HDI) to withstand such excitation becomes critical in determining the reliability of a mobile disk drive. This dissertation presents a simulation method to accurately model the response of a mobile HDD to external disturbances which can aid the design process.
A numerical investigation was conducted on a 2.5 inch form factor laptop drive to understand the dynamics of the HDI during dynamic events such as operational shocks. A detailed model for the mobile disk drive was developed which includes a spinning disk, a fluid dynamic bearing (FDB) based spindle motor, a base plate and an actuator. The behavior of the HDI subjected to various disturbances was determined by solving a fluid-structure interaction problem in which a spinning disk and a head (slider) were coupled through an air bearing. Case studies were conducted to determine the effect of parameters like shock pulse width, HDD orientation, parking ramp contact and FDB dynamic coefficients on the performance of a HDD during the excitation.
It was observed that the proximity of the pulse to the HDD component's natural frequencies has an adverse effect on the shock resistance of the HDI. Furthermore, the orientation of the HDD during the shock can also affect the stability of the HDI. In the case of planar excitations, the FDB dynamics becomes critical in determining the slider's vibration amplitude. This knowledge about the HDI failure mechanism and its vibration characteristics can be helpful in designing a mobile HDD with a better shock performance.