Experimental study on slider dynamics during touchdown by using thermal flying-height control

Abstract

To investigate the possibility of further lowering the clearance in head–disk interface systems, slider dynamic behavior during a touchdown sequence with a thermal flying-height control (TFC) function was investigated by using a spinstand-level evaluation utilizing an acoustic emission (AE) sensor and a laser Doppler vibrometer (LDV). Experimental results demonstrated that off-track vibration was easier to excite by head–disk contact at the beginning of head–disk contact. We then confirmed that the amplitude of pitch-mode vibration in the flying-height direction increased and sway-mode vibration in the off-track direction decreased when increasing heater power during the touchdown sequence. Moreover, we found that the peak frequency of pitch-mode vibration shifted to a higher frequency under over-push conditions. Time–frequency domain analysis results showed that the peak shift occurred at several locations during a disk rotation. The mechanism of the peak shift is attributed to the increase in stiffness at the head–disk interface (HDI) due to solid–solid contact or mode change occurred in such regions. During the touchdown sequence, the friction force at the HDI continues to increase, even though slider vibration and AE signal decrease when heater power is increased. The friction force at the HDI needs to be decreased to achieve further low-clearance HDI.