Initial value compensation applied to disturbance observer-based servo control in HDD

The mode switching control (MSC) technique makes use of several controllers, each one designed to optimize a particular control objective. The switching between-controllers is performed at the supervisory level. MSC is often used when the control objective is different in different operational regions as in the HDD servo system where three different operation modes can be identified, i.e. seek, settling and track following. The paper presents a novel solution for a bumpless control transfer from the settling controller to the track following controller when both controllers are based on estimated state feedback and are optimized for their operation mode. The proposed procedure has been successfully implemented on a commercial HDD and experimental results have shown a promising improvement of the transient performance.