Written-In RRO and NRRO Characteristics in Mobile Hard Disk Drives

Abstract

The characteristics of repeatable runout (RRO) and nonrepeatable runout (NRRO) of hard disk drives (HDDs) have to be determined for higher tracks per inch since the static positional accuracy has almost reached its limit. To break this limit, it is necessary to identify precisely these track misregistration characteristics. We experimentally estimated the actual component of disturbances in both servowriting and the actual drive using a mixture of helium and air. In the study described in this paper, windage or flow-induced vibration in servo-writing was the dominant component as a torque disturbance in the drive measurement. We then found that written-in RRO was key to understanding the characteristics of disturbances. As a result, the most dominant component in NRRO and even in written-in RRO is torque disturbance followed by positional disturbance for mobile HDDs.Index Terms-Flow-induced vibration (FIV), helium, nonrepeatable runout (NRRO), position error signal (PES), servo-write, torque disturbance, track misregistration (TMR), tracks per inch, written-in RRO.

Aerodynamic Pressure Fluctuations Associated With Flow-Induced Vibration of the Head Gimbals Assembly Inside a Hard Disk Drive

“…The HGA heads inside the HDD were in the inner, middle and outer track following positions respectively. Since inserting pressure probes into the narrow space inside an HDD could introduce obstructions into the original interior flow field and was therefore impractical, we tried in the present study to detect the aerodynamic pressure fluctuations around the HGA The PES and SSSF were measured following a standard method [4], [18] before the modification of the HDD for pressure measurements. The slider OT-FIV spectra were computed by dividing the non-repeatable run-out error spectra [4], [18] in the PES by the SSSF spectra and were compared with the pressure fluctuation spectra.…”

Methodology on Improving Vibration Characteristics of Servo Write Fixture

“…There also have been efforts via control design to improve resistance to noise disturbance [3] and external vibration [4]. In-depth study on the characteristics of disturbances in a servo write process was reported for mobile drives in [5]. Although [6] refers to design of flexible mounts for HDD testing to improve rotational vibration (RV) about its vertical axis, studies on vibration characteristics of servo write fixtures are rare in literature.…”