Analysis Of Air Bearing Dynamic Characteristics Involved The Gas Rarefaction Effect

Hard disk drives have become a dominant electronic information storage media, inwhich the data storage and exchange have been conducted at a head/disk interface. Withthe decrease of working distance, i.e., the flying height of read/write head, theinstability of the magnetic head/disk interface in hard disk drives may increasesignificantly. Furthermore, the gas rarefaction effect on air bearing dynamiccharacteristics shows when the slider flying height is in nano levels. The study ofdynamic characteristics and stability of head/disk interface of hard disk drives showsgreat importance to prolong the service life of the hard disk drive and optimize therelated components, especially for the design of slider surface morphology and thestructure of the magnetic head.The present study is focused on pressure distribution on slider surface and thedynamic characteristic of the head components when the flying height is in nanoscale.Firstly, the research status for air bearing working principle and stability influencefactor was generalized and analyzed. A method for calculation of air bearing dynamiccharacteristics and stability was proposed with consideration of gas rarefaction effectand Van der Waals force. A simplified model was proposed and expression of Van derWaals force at head/disk interface was derived. Based on the modified Reynoldsequation and Van der Waals force, the pressure distribution on the slider surface withdifferent mrphology was calculated and the influence of surface morphonogy on thestress distribution was analyzed. The dynamic characteristic of head sliders wasanalyzed by solving the dynamic equation for this system. The effects of surfacetopography, contact mechnanism at interface, pressure distribution, air bearing formingmechnism on head silder dynamic characteristics were studied by theoretical analysisand simulation, respectively.A calculation method for solving modified Reynolds equation for the description ofultra-thin gas film lubrication and Van de Waals force was proposed based on the thinfilm module in COMSOL software. The pressure distribution and air bearing force atthe head/disk interface of hard disk drive were analyzed, and the effect of slidermonography, including palnar and dual-track type air bearing surfaces, as well as theeffect of complicated motion states, on the gas film pressure distribution were studied.With consideration of the contact and impact between slider and disk, slider andsuspension, a three degree of freedom model was proposed and a differential equationof motion for suspension slider disk system was built, in which the parameters,including equivalent stiffness, mass, damping, and moment of inertia were claculated, repectively. The MATLAB program was used to solve the quaiton and dynamiccharacteristics and equilibrium restoring time of sliders with different working surfaceand working conditions wre obtained, indicating that the slider surface monogrpahy andworking condition affect the hard disk drive working performance, and theconsideration of van de Waals force existing at the head/disk interface is more realisticto the study of air bearing force for a slider with a nanoscale flying height.