This paper reviews recent advances (mostly after year 2000) in shock and vibration analysis of hard disk drives (HDD) considering the presence of nonlinearities and discontinuities. Components and dynamic phenomena in HDD where effects of mechanical nonlinearity and discontinuities are significant are discussed, e.g., head actuator suspension, dimple and slider, head-disk interface, fluid dynamic bearing, spinning disks, and load/unload dynamics. Ways to model these nonlinearities and discontinuities are reviewed in detail. Our research on modeling an entire HDD in operating mode subject to shock and vibration using a flexible multibody dynamics formulation is also presented. The numerical simulation of the shock response of a 1-in. form factor HDD is presented. A halfsinusoidal acceleration shock is applied at the base of the HDD. Response of the flying height for different shock amplitudes and duration times is simulated.
Recent development of the shock analysis on the HDD is briefly reviewed. A flexible multi-body dynamics formulation is developed to simulate the shock response of the HDD. If one component in the HDD is changed, only mode shapes and frequencies of that component should be re-calculated and then used to obtain the system's response. Steady state Reynolds equation is solved to obtain the air pressure on the slider and disk for various slider positions. An air pressure table is formed and used to model the nonlinear air bearing during the simulation. Responses of flying height for different direction and shock duration time are analyzed. Results show that the flying state of the slider is more sensitive to the shock with shorter duration time.
This paper emphasizes the importance of a fast and reliable tool for design parametric studies. Three methods that have been used in studying the shock phenomena in hard disk drives (HDD) are discussed briefly. A more efficient (i.e. faster and reasonably accurate) method is proposed. This new method uses state-space formulation to model the structural components of the HDD and quasi-static concept to model the non-linearity of the air bearing. The structural and the air bearing response, and their coupled interaction are evaluated simultaneously. The computation time and the accuracy of the proposed method are compared against two existing methods: the full finite element model and CML's HDD dynamics event simulator. The proposed method is found to be much faster with reasonably good accuracy. Experimental shock tests also show that the method is reliable in predicting the shock tolerance of the HDD. A procedure on how to do parametric study with this method is proposed and the effect of overmold and voice coil stiffness on the shock tolerance is studied.
Abstract. An effective vibration isolation system is important for hard disk drives (HDD) used in a harsh mechanical environment. This paper describes how to design, simulate, test and evaluate vibration isolation systems for operating HDD subjected to severe shock and random vibrations based on military specifications MIL-STD-810E. The well-defined evaluation criteria proposed in this paper can be used to effectively assess the performance of HDD vibration isolation system. Design concepts on how to achieve satisfactory shock and vibration isolation for HDD are described. The concepts are tested and further enhanced by the two design case studies presented here. It is shown that an effective vibration isolation system, that will allow a HDD to operate well when subjected to severe shock and random vibration, is feasible.
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