As track density increases, the effects of nonlinearity in the pivot bearing of the hard disk drive on the servo performance are becoming more important. Recently, increasing attention is given to more precise experimental observation and modeling of pivot nonlinearity to achieve improved servo control. In this paper, we propose a new model that predicts improved pivot nonlinearity over existing "preload+two slope" models in matching simulation and experimental results in both the time and frequency domains. Experimental measurements are carried out to validate and identify the specific nonlinearities present in the pivot bearing when it is in fine motion.
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