Abstract
Two novel discrete anti-windup (AW) techniques are applied to a dual-stage actuator of an experimental hard disk drive system. The techniques, one low order, the other full order, employ convex l/sub 2/-performance constraints in combination with linear-matrix-inequality-optimization methods. It is shown that the AW compensators can improve the performance of the nominal dual-stage servo-system when the secondary actuator control signal saturates at its allowable design limits. Also, stability is achieved despite saturation of both the secondary actuator and the voice-coil-motor actuator. Practical results show that the performance of each AW compensator is superior to another well-known ad-hoc AW technique, the internal model control AW scheme. The main contribution of the paper is the application of theoretically rigorous AW methods to an industrially relevant servo system.
Highlights
O NE OF THE most important developments in hard disk drive (HDD)-technology during the last decade was the increase in data storage density
High-bandwidth secondary actuators mounted on the voice-coil motor (VCM)-actuator have been investigated for many years [16] and are regarded as a feasible alternative [13] to singlestage servo systems
Due to this strict constraint, secondary actuator signals usually saturate before the VCM-actuator signal, and the performance of a track following controller may become unacceptable during control-signal saturation or the servo-control system may even be driven unstable
Summary
O NE OF THE most important developments in hard disk drive (HDD)-technology during the last decade was the increase in data storage density. For a dual-stage servo system, during track following and without secondary actuator saturation, the controller has to be able to compensate for the most common disturbances. Controller scheduling necessitates add-on sensing techniques, which allow the secondary actuator to be disabled once a disturbance occurs Different techniques, such as extra force sensors [14], [21] or schemes using servo information from all available disk surfaces [2] for better head positioning on one surface are possible. HERRMANN et al.: PRACTICAL IMPLEMENTATION OF A NOVEL ANTI-WINDUP SCHEME IN A HDD-DUAL-STAGE SERVO-SYSTEM the MR-head voltage [14] or to use a sufficiently fast disturbance observer [33] Using any of these methods, switching conditions are needed to disable the secondary actuator.
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