Drop and impact dynamics analysis of hard disk drive (HDD) systems
Date of Issue2017-03-27
School of Mechanical and Aerospace Engineering
Nowadays, hard disk drives (HDDs) are widely used in portable consumer appliances and gadgets. These HODs are more susceptible to shock and vibration during using. Their shock performance under operation and non-operation is becoming an increasingly important issue. One important damage mode of the HOD is the "head slap" behaviour, which is triggered by a shock load that exceeds the suspension preload, causing the head to fly off from the disk and then slap on the di sk. Thus, the particles generated on the disk medium may cause contamination problem. The head slap should be strictly avoided. One approach for dealing with the shock problems is to design a robust mechanical system and slider/disk interface. It is very clear that the trend of the HOD development is higher areal density and higher speed. The size of the HOD and its components become smaller and smaller. The improved performance of the mechanical parts has been of great significance in this progress. A better understanding of dynamic characteristics of the mechanical parts is essential. To investigate the drop and impact dynamic characteristics of hard disk drives, both experiments and numerical simulations are conducted here. Firstly, the boundary condition of disk of an HOD was investigated by finite element analysis and experimental tests. Modal analysis is conducted with simplified FE model and the results are compared with experimental results. The rea l boundary condition of disk is simulated with FE model considering the contact between clamp and disk and the contact between disk and hub. Based on the contact model, design parametric studies are conducted. It is found it help to decrease the shock response of the disk with higher clamping force and higher contact stiffness between disk and hub. The effect of clamping force on the shock response of the disk is further verified experimentally. The experimental results were agreeable with the numerical results. Secondly, both linear drop tests and rotary drop tests simulation were conducted. The HOD shows more sensitivity to the shorter duration shock. And the magnitude of the slider lift-up height grows significantly with the greater amplitude of shocks. Comparison between linear drop tests and rotary drop tests shows that the slap behavior in linear drop tests is more significant than in rotary drop tests. The fragility test on head slap was conducted experimentally. The results confirmed the numerical result that drives under linear drop test with greater amplitude and shorter du ration shock was more vulnerable in consideration of the head slap behavior. Moreover, the effect of inclination angle on the head slap behavior was investigated experimentally. Thirdly, an FEM model of operational HOD is developed. The air bearing between the disk and the slider is modeled by nonlinear springs. The nonlinearity of the vertical stiffness of the air bearing is considered. The contact between the disk and the slider is also considered. The disk clamping condition and the shock pulse amplitude and width effects are investigated. This numeri ca l model can be applied to predict the shock tolerance during the design stage. Fourthly, strain gauge was for the first time used to measure the dynamic strain of the HAA of an HOD in drop tests. It shows that the mounting of the stain gauge causes the increase of the natural frequency of the HAA and the first mode shape dominates the shock response of the HAA. The max1mum strain and the damping increases with the amplitude of the shock pulse. The maximum strain increases with the pulse width of the shock pulse. The effect of the pulse width on the damping is more complicated and can be further investigated in future studies. This work suggests the measurement of the dynamic strain of the HAA is conductible. A new way of measuring the shock response of small form factor HOD is proposed. Finally, dynamic contact forces and impact-induced vibration of an HAA are measured and simulated by using LMM method and FEA. LMM method utilizes the first principles of Second Newtonian Law and the Doppler frequency shift and minimizes the uncertainties of using many sensors. A good agreement between the FEA results and experimental data is observed. The limitation of the current experimental setup in oblique impact test and in inelastic impact test is verified by the FEA. This initial attempt demonstrates the feasibility of applying FEA and LMM method to minute dynamic forces measurement involved in HODs.