Identification of contributors to HDD servo errors by measuring PES only

In this paper, disturbances, the source of TMR being barrier to high track density of HDD are analyzed quantitatively using PES only without extra sensor. Disturbances are separated into RRO and NRRO, then, NRRO is separated into input torque disturbance, output disturbance, and noise. The effect of each disturbance to PES is compared. Using separated disturbances, PSD of PES RRO and NRRO are predicted for various gain levels in track following servo, and they are compared with PSD of PES measured in experiment. We propose that it can be used to predict servo performance accurately.