Analysis Of The Gas Film Lubrication Dynamic Characteristics With Ultra-Low Flying Height In Head/Disk System

Hard disk drives is the main tool for today’s information storage, it’s developing in the direction of smaller size, lower height, higher density and higher speed with the development of information technology. Ultra-low Flying height and ultra-high speed puts forward higher requirement of the hard disk stability control, and become the key issues affecting the stable of hard disk. Preloading Force is the main force to balance the air bearing force, it affects the slider flying height and stability; Disk rotation speed affects slider read-write capacity, and also affects the slider dynamic flying characteristics; Adding helium to hard disk drives, helium percentage will have an impact on the slider dynamic flying characteristics. In this paper, I built a dynamic mathematical model of the hard disk drive and numerical method to solve the questions, then I studied the effect of Preloading Force, disk speed and gas composition on the slider dynamic flying characteristics, and provide a theoretical foundation of the slider flying control.In order to investigate the slider dynamic flying characteristics accurately, this paper based on Reynolds equation with time and slider balance equation, and used Newton method for solving, and established slider dynamic mathematical model, then used the dynamic model to study the slider movement.Using the slider dynamic mathematical model, I studied the effect of Preloading Force and disk rotation speed on slider dynamic flying characteristics. Preloading Force is a necessary to balance the slider bearing force; With the increase in Preloading Force, slider flying height and pitch angle gradually decreasing but the bearing force increasing; Preloading Force can’t keep increasing because it will affect the slider stability and even touch the plate. Disk rotation speed is an important factor influencing hard disk drive storage capacity; When the disk rotation speed is too low, touch-plate phenomenon can also occur, as the speed increases, slider flying height, pitch angles become smaller, and the trend become smaller, flying height too low or too high the stability of slider are reduced.Seal hard disk drive filled with air and helium mixture will have a lot of advantages. In this paper I studied the effect of helium percentage on slider dynamic flying characteristics under different flying height and pressure. As the helium percentage increases, slider minimum flying height at first increases the decreases, the flying height at pivot point be affected less, pitch angle deceases, roll angle at first increases then decreases, shear moment in x decreases and the shear moment in y changes with different disk rotation speed. In addition, the pressure effect on the various parameters is obvious, compared with latm, slider at 0.5atm, the flying height at pivot point significantly become lower and the pitch angle significantly deceases, the fluctuation of the various parameters increases during the time to reach stable, it shows that in 0.5atm the stability of flying height deceases, and the shear moment decreases too.I analysed the contact between slider and disc during the dynamic simulation. Slider contact is due to lack of pressure force, but under different circumstances different phenomenon occur. When occurs in a low flying height, pitch angle is larger, the end of the slider touches the disc; When occurs in a high flying height and low pressure, the slider stability is poor and the head of the slider touches the disc; When occurs in a big Pre-Tightening force, the touch-plate is more serious, pitch angle sharply decrease into negative territory, and the head of the slider touches the disc.