In recent years, an increasing number of portable electronic devices, such as portable computers and MP3 digital audio players, have been equipped with hard disk drives (HDDs) to store digital data. In these portable devices, HDDs are exposed to external vibrations and shocks. These external disturbances increase the position error, consequently reducing the performance of the HDDs. We propose adaptive feed forward (FF) control with a single shock sensor to improve the head positioning accuracy in magnetic hard disk drives. Since the transfer function relating the acceleration measured by a shock sensor and the position error signal (PES) depend on the characteristics of the applied force, such as the direction or the frequency, an on-line identification of the relating system is needed. Our proposed scheme applies an adaptive control technique to indirectly identify this relationship, i.e., the coefficients of the finite impulse response (FIR) controller are updated by a gradient algorithm so that the magnitude of the PES is minimized. Our numerical simulations and experiments illustrate the effectiveness of our proposed method.
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.