Measurements for the PES Pareto Method of Identifying Contributors to Disk Drive Servo System Errors

This is the second in a series of three papers describing a method of allocating the uncertainty in the Position Error Signal (PES) of a magnetic disk drive servo system among its constitutive components (“noises”). Once identified and ranked, the most critical noises can be attacked first, either by finding ways of reducing them or by altering system components to be less sensitive to them. The method requires the measurement of frequency response functions and output power spectra of each servo system element. Each input noise spectrum can then be inferred and applied to the closed loop model to determine its effect on the PES uncertainty. The current paper describes the techniques and measurements that were obtained as part of the PES Pareto Method. 1. Measurements for the PES Pareto Method In a companion paper [1], a method is presented for separating the contributions of various sources of uncertainty (“noises”) in the Position Error Signal (PES) of the track–follow servo in a disk drive. This method requires the construction, from measurements or design models, of component filters and output power spectra; these filters and spectra are then used to compute input noise spectra. The noise spectra are then fed individually through the closed loop model to determine their individual contribution to PES uncertainty [2]. Disk ? RT NRROf? PSN Dem. } {{ } D(s) PES AD? ADC Noise } {{ } C(s) -Comp. -DA ? DAC Noise -Xin Xout f 6 ?-PA }{{} A(s) ? PA Noise 6 Kis Isense -Ktf? Windage 1 J s Res. To LDV Velocity Kv @ @I 1sRes. To LDV Pos. Kp B B BM −