Non-repeatable runout of ball-bearing spindle-motor for 2.5" HDD

Quantitative estimation of non-repeatable runout (NRRO) in head tracking mode on the hard disk drive was performed by an experimental investigation of ball-bearing spindle motor NRRO. The characteristic difference between the spindle motor NRRO and the head tracking error is discussed. This head tracking error is caused by the NRRO in tracking mode and NRRO in servo track writing, taking head tracking control into account. The amplitude of spindle motor NRRO is 130 nm peak-to-peak in this experiment. While the low frequency components of NRRO caused by bearing geometry are compressed, rotor resonance frequency vibrations are predominantly enhanced by the characteristics of the sensitivity function of the head positioning system. The amplitude of the error caused by the motor NRRO is twice as large as that of the motor NRRO itself. Neither of the probability density functions, namely motor NRRO and tracking error caused by NRRO, is Gaussian distribution.