Discrete control for a computer hard disk by using a fractional order hold device

It is well known that the type of hold circuit used in a digital control scheme critically influences the position of the discrete-time zeros. Most digital control systems use a zero-order hold (ZOH). Nevertheless, there are more convenient alternatives to the use of a ZOH signal reconstruction device in certain digital control problems. A fractional order hold (FROH) circuit is proposed in the paper in order to manage a computer hard disk read-write head described as a second order system. Significant improvements in the transient performance of the closed-loop system are obtained with respect to the use of a ZOH when using a properly adjusted FROH device