A mode-switching controller with initial value compensation for hard disk drive servo control

In various kinds of servo positioning systems, both fast movement and precise positioning are required. To meet these demands, a mode-switching control (MSC) method, which has several controllers for each requirement and switches from one to the other, has been proposed. The issue raised by the use of this technique is the transient response after switching. This paper proposes the use of the initial value compensation (IVC) method to handle this problem. Under the IVC, initial values are placed in the controller state variables, or an additional input is added at switching. From experiments using hard disk drives, it is proved that the IVC improves transient responses after switching.