Modified AFC runout cancellation and its influence on track following

This paper investigates the design and implementation of an adaptive feedforward cancellation (AFC) technique to cancel runout in a hard disk drive. An extension to the AFC, the modified AFC, is proposed to overcome some of the limitations of the AFC scheme. When designed to compensate for one runout frequency, the modified AFC can eliminate the intended harmonic without amplifying the adjacent harmonics. This eases the design of a controller to cancel multiple harmonics. Also, the modified AFC is more robust than the AFC since it improves the phase and gain margins. Simulation and laboratory implementation results are presented to show the performance improvements of the proposed modified AFC.