Excitation pulse shape effects in drop test simulation of the actuator arm of a hard disk drive

For a head actuator assembly (HAA) of a hard disk drive, the deflection of the tip of the arm relative to the pivot can be used as an indicator of its response to shock. To study the pulse shape effects in a shock analysis, the actuator arm of an HAA subjected to different acceleration pulse shapes, such as half-sine, triangular and dual-quadratic, was simulated by using a dynamic finite element package. It has been found that, for the three acceleration pulses, the peak displacements have opposite behaviors for 0.1- and 1-ms pulse widths. The above phenomena have been explained in terms of a power spectrum analysis. It has been found that the relative magnitude of the peak displacement of the actuator arm is mainly determined by the power magnitude of the acceleration pulse at the resonant frequency. A simple mathematical theory was developed to predict the location of a cross-over interval which divides the power spectrum curve into two major regions where opposite behaviors are observed. The theoretical pulse width is correlated with a pulse width based on a threshold value as normally used in experiments. B.J. Shi: On leave from School of Mechanical and Electronic Engineering, Shandong Institute of Architecture and Engineering, Jinan 250014, China