Effects of environmental temperature and humidity on thermal flying height adjustment

Abstract

Thermal actuated sliders are being widely used in today's hard disk drive industry for its advantages of easier control of flying height (FH) and less risk of contacts with the disk. This article uses a coupled-field analysis method, which includes an air bearing model, a heat transfer model and a thermal-structural finite element model to investigate the FH changes of thermal actuated sliders at various environmental conditions. The mechanism of water vapour's contribution to air bearing pressure loss is explained and a new humidity model is proposed to calculate this pressure loss. The temperature effects are also considered in the simulation models. It is observed that the environmental temperature and humidity have significant effects on slider's FH changes, but their effects on the thermal protrusion height are limited. A humidity sensitivity study is also made and the results are discussed. It is found that the slider with thermal protrusion on its trailing pad will be more sensitive to the humidity. Besides air bearing stiffness, some other factors such as peak pressure, protrusion shape and air bearing surface (ABS) design will also contribute to the slider's humidity sensitivity.

Servo signal processing for flying height control in hard disk drives

“…The relationship seems nearly linear, although the slope of the curve (which corresponds to the static gain) is slowly decreasing as P in increases. This could be due to the air bearing cooling effect (increased thermal conductivity between head and disk as local air bearing pressure increases and flying height decreases) (Chen and Bogy ) and/or the so-called push-back effect (due to higher air bearing pressure at lower flying heights) (Zhou et al 2010). Another explanation would be an increasing heater resistance with increasing heater voltage yielding an actual lower heater power compared to the computed heater power assuming a constant resistance.…”