Mode switching control design with initial value compensation and its application to head positioning control on magnetic disk drives

To meet an increasing demand for high performance and large-capacity in magnetic hard disk drives, both a fast response and a precise positioning are strongly required for the head positioning control. A mode switching control (MSG) system, which includes a track seeking controller, a track following one, and a switching function, is widely used to meet this requirement. The issue for MSC is to confirm a design method of servo mode switching. This paper proposes the initial value compensation method (IVC). The IVC inputs certain initial values in the controller state variables at mode switching in order to improve the transient response after switching. There are two approaches to determine the values: 1) minimizing a linear-quadratic function of the plant state variables, and 2) cancelling the unfavorable poles of the transfer function between initial values and head position by relocating zeros. Some experimental results are shown to be effective.