Identification of contributors to HDD servo errors by measuring PES only

In this paper, disturbances, the source of TMR being the barrier to high track density of HDD are analyzed quantitatively using PES only without extra sensors. Disturbances are separated into RRO and NRRO, then, NRRO is separated into input torque disturbance, output disturbance, and noise. The effect of each disturbance on PES is compared. It is shown that PES NRRO measured in open-loop and in closed-loop can be used to calculate sensitivity transfer function. 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 experiments. We propose that this can be used to predict servo performance accurately. Also addressed are some discussions on the differences between this work and the former contributing work.