Research On Dynamic And Tribological Characteristics Of Hard Disk Drives During Load Unload And Shock Process

As a kind of storage media, hard disk drives are used to store or transfer the information based on the interaction between the slider head and disk. With the increasing requirements of the high capacity and avoiding the accidental shock in the usage, the operational stability and reliability of head/disk interface in hard disk drives are required to be satisfied strictly. The hard disk drives with ramp load/unload technology (U/UL) are beneficial to improve the performance of hard disk drive when the drives are subject to vibration or external shock. Therefore, the study of the dynamics and tribological characteristics of head/disk interface, as well as the prediction of dynamic performance of hard disk drives during loading and unloading process under the external shock and vibration condition, is useful and necessary to increase the lifetime of drives, to strengthen the reliability of head/disk interface, and to realize the optimal design of hard disk drives.In this study, the flying height of slider and related tribological and dynamic characteristics of head and disk were researched. Based on the principles of nano- tribology, the factors to influence the movement stability and reliability of slider head during loading or unloading process were determined. The tribological characteristics between the suspension slider and its supporting were analyzed. Based on the analysis of dynamic response of head/disk interface subject to internal and external excitation, the effects of the contact interface, pressure distribution, air bearing force and its failure, and friction at interface on the dynamics of slider or head were studied theoretically and experimentally.According to the rarefied gas lubrication for the nano- level gap at the head/disk interface, the modified Reynolds equation for rarefied gas film was used in the study to describe the dynamics of gas film, and a new PDE-based method was proposed to get the solution of Reynolds equation for the description of ultra-thin gas film at the head/disk interface with complex profile at the air bearing surface with enough accuracy and efficiency. The pressure distribution at the air bearing surface at head/disk interface in hard disk drives was obtained. In the analysis, the aerodynamics of positive and negative sliders at steady state was compared. The transient characteristics and squeeze effects of these sliders during loading/unloading process were analyzed. Their performance subject to an external shock was also considered in the research. The effects of pressure distribution of air bearing on the performance of hard disk drives were generalized based on this analysis. A dynamic model was proposed to describe the dynamics of suspension assembly during loading and unloading process with consideration of the friction, contact and impact between the disk and slider, lift-tab and ramp, slider and dimple. The performance of hard disk drives with small form factor was simulated numerically. The nano-level contact between lift-tab and ramp was modeled based on Hertzian contact theory. The effects of loading/unloading velocity, ramp angle, ramp slope radius, contact stiffness, and lift-tab surface curvature on the characteristics of contact and friction were studied to optimize the ramp material and structural profile, which are beneficial to improve the dynamic stability and eliminate the possibility of impact between the slider and disk.The performance of hard disk drives with load/unload technology subject to external shock was studied. A dynamic model for the description of the interaction between disk and suspension/slider system under the shock impulse was proposed, in which the air bearing force, obtained by solving the Reynolds equation using MATLAB and COMSOL software, was considered. The effects of amplitude and width of impulse of external shock on the flying height of slider and inner interaction in the system were investigated, from which the limit acceleration of external shock to cause the failure of hard disk drives, i.e., the occurrence of impact between the slider and disk, was determined. A finite element model of hard disk drive was set up to study the effects of impulse width and amplitude of acceleration of external shock on the contact characteristics of components of hard disk drive at non-operational state.Finally, a sensor with two sensing channels to measure the normal load and lateral friction force of suspension/slider during loading and unloading process was designed, fabricated and calibrated. The effects of loading/unloading velocity, ramp angle, and other related parameters on tribological characteristics of suspension assembly during loading/unloading process were tested experimentally. A laser displacement sensor with nano-level resolution and a high speed camera were used to trace the dynamic characteristics of suspension and slider, and the results are used to verify the simulation results. The stiffness matrix and structural damping of suspension assembly were obtained and the dynamic model of the system was rectified.