Shock analysis of a head actuator assembly subjected to half-sine acceleration pulses

Shock robustness is an increasingly important design consideration for hard disk drives (HDD), as we move forwards toward consumer applications. For a head actuator assembly (HAA), which is the most important mechanical component of an HDD and consists of a cantilever arm fixed onto a pivot bearing, the maximun relative deflection between the tip of the arm and the pivot can be used as an index for its response to shock. The influence of pulse width/duration and pulse amplitude on the shock response of the relative displacement of the actuator arm is first investigated by the finite element method (FEM). The actuator arm is then simplified as a low-damping single-degree-of-freedom (SDOF) system. The shock response of the finite element model and that of the SDOF system are presented. It is found that, for both the finite element simulation and the theoretical analysis, when subjected to half-sine acceleration shock, the peak relative displacement occurs at a critical frequency ratio ( i . e . β = ω / ω n ≈ 0.6 ) , where ω and ω n are the characteristic frequency of the pulse loading and the first natural frequency of the system. In other words, a pseudo-resonance phenomenon occurs at this critical frequency ratio.