Disk wear as a result of low frequency HDI resonance

Abstract

Spinstand level testing has demonstrated a failure mechanism that may go undetected using standard strain gage and acoustic emission methods of data capture. Since normally static friction is higher than dynamic friction, dynamic friction measurements are often ignored, filtered, or sampled at a much lower data rate than static friction measurements. In this study, dynamic friction peak values significantly higher than the static friction were recorded during take-off of Pico heads on laser-textured media. Furthermore, data collected using an optical surface analyzer (OSA) showed a greater degree of wear on disks exhibiting high dynamic friction. FFT was employed to analyze the signal modulation of the high dynamic friction event. Resonance at a frequency of approximately 1050 Hz was found to be associated with the high dynamic friction. Experiments were designed to reveal factors that influence this resonance occurrence. The factors identified that contribute to this resonance were natural frequency of the head load arm, disk bump pitch, and lubricant thickness. The head/disk interface system is believed to be excited by an improper bump pitch if the lubricant layer is not thick enough to reduce the friction value.