Paolo Capretta

A simulation and control design environment for single-stage and dual-stage hard disk drives

We describe an integrated tool for the design and evaluation of the performance of different control algorithms and strategies, applied to hard disk drives (HDDs) with single-stage actuators and dual-stage actuators. The tool is composed of a set of procedures for the computer-aided design of servocontrollers and a HDD simulator. In order to perform realistic simulations, each part of the HDD is described with high level of detail. As for the mechanics, the usual inertia plus resonance model of the voice coil motor (VCM) has been enriched with nonlinear friction modeling and, in case of DSAs, with the dynamic coupling between primary and secondary actuator. The nonlinear friction model has been tuned on experimental data, using an experimental system presented in the paper. As for the electronics, the VCM driver model is included and quantizations in the position error signal measurement and computation are explicitly considered. Also, in order to evaluate the tracking performance of different servocontrollers, repetitive run outs and nonrepetitive run outs are included. Such disturbances have been obtained from commercial HDDs, with a procedure that is detailed in the paper. The simulator is then validated by comparing simulation and experimental results, both in open-loop and closed-loop conditions, thus, confirming the effectiveness of the developed tool.

Loop shaping issues in hard disk drive servo system design

In this paper, the design of hard disk drive (HDD) servo systems based on state-space techniques is considered. In particular, we analyze the performances of discrete-time controllers obtained by means of LQG optimal control theory. The key control design issue we address is related to the need of achieving sufficiently high close-loop bandwidth while granting adequate disturbance rejection in the loop gain crossover frequency region. It turns out that the shaping of the sensitivity function is a critical issue, in particular when run-outs compensation schemes are introduced. The effectiveness of discrete-time loop transfer recovery techniques in achieving a satisfactory loop shaping design starting from an LQG regulator is discussed. The proposed control algorithms are then evaluated on a test platform based on a commercial HDD. The experimental results thus obtained are reported and discussed.

Simulator for single stage and dual stage hard disk drives

We describe a simulator for the evaluation of the performance of different control algorithms and strategies, applied to hard disk drives (HDD) with single stage (SSA) and dual stage actuators (DSA). In order to perform realistic simulations, each part of the HDD must be described with high level of detail. As for the mechanics, the usual inertia plus resonance model of the voice coil motor (VCM) has been enriched with non-linear friction modeling and, in case of DSA, with the dynamic coupling between primary and secondary actuator. The non-linear friction model has been tuned on experimental data, using an experimental system presented in the paper. As for the electronics, the VCM driver model is included and quantizations in position error signal (PES) measurement and computation (i.e. finite wordlength calculations) are explicitly considered. Finally, in order to evaluate the tracking performance of different servo-controllers, repetitive and non-repetitive run outs are included, their values obtained from commercial HDDs, with a procedure that is detailed in the paper.