Shock response and power spectrum analysis of a head actuator assembly

摘要

Shock performance of hard disk drives is becoming an increasingly important issue, and disk drive manufacturers have been steadily increasing the threshold of shock level that the drive can withstand. A half-sine acceleration pulse is usually adopted as input loading to simulate the shock. The pulse width, the pulse amplitude, and the pulse shape play an important role during the simulation. For a head actuator assembly, the maximum relative displacement between the tip of the actuator arm and the pivot can be used as an indicator for assessing the extent of damage on the disk and head slider during shock. In the previous work by the authors, the maximum relative displacement of an actuator arm subjected to a single half-sine acceleration pulse was analyzed by finite element simulation. The maximum relative displacement experiences a peak value as the pulse width increases, i.e., a pseudo resonance phenomenon of the maximum relative displacement was observed when the acceleration pulse width is equal to a critical value and an explanation was given by a single degree of freedom system. To further investigate this phenomenon, three types of acceleration shocks different in pulse shape (half-sine, triangular and dual-quadratic acceleration pulses) are selected as input acceleration shock loadings. Dynamic analyses of the actuator arm subjected to these acceleration shocks are carried out. Numerical results show that pseudo resonance phenomena occur again for the maximum relative displacement but at different pulse widths for these different acceleration shocks. Power spectrum analyses are implemented for these different acceleration shocks. An explanation is given in terms of the acceleration power at the natural frequency of the actuator arm. Moreover, a characteristic frequency is defined for the acceleration pulse shock. A corollary is derived from a theorem developed previously by the authors. A prediction is made by the corollary that when the characteristic frequencies of a group of acceleration shocks with different pulse shapes are very close to the natural frequency of the dynamic system, these acceleration shocks will have equal acceleration powers at the natural frequency and will, consequently, produce equal shock responses. This prediction is confirmed by numerical results.