Friction Effect on Loading Process and Multiple Stable Flying States of Air Bearing Sliders

Load∕unload (L∕UL) technology has been widely applied in hard disk drives for a long period of time. One main promise of this technology compared with the contact start-stop (CSS) technology was no damage from the friction and stiction between sliders and disks during power on and off that exists in CSS. However, the friction between sliders and disks can still occur and has a strong effect on the L∕UL process because sliders may contact disks during loading. When friction is large and the pitch static attitude (PSA) is not in the preferred range, the loading process might fail. In this paper, a new simplified friction model was proposed based on experimental observations. The model was implemented into a L∕UL simulation code. Two cases were studied: a $10,000rpm∕84mm$ server drive and a $3600rpm∕25.4mm$ microdrive. The PSA and friction force effects on the loading process were simulated. A large PSA results in slider loaded onto a second stable state with a very large flying pitch angle. In this paper, a third stable state, which results from a small or negative PSA and a sufficiently large friction force, was discovered and investigated. It was found that the friction effect was smaller in the server drive case, while it was dramatic in the microdrive case. In the third stable state, the slider had a negative pitch angle, and its leading edge continuously dragged on the disk. In this state, reading∕writing operation was not possible, and disks and sliders could be damaged.