Optimal track-following design for the highest tracks per inch in hard disk drives

This paper presents an optimal track-following control design procedure tha t can find the theoretical highest tracks per inch (TPI) achievable in hard disk drives. By formulation of the hard disk drive servo system into an H- 2 optimal control problem, achieving the highest achievable TPI is equivale nt to minimizing the corresponding H-2 norm from the disturbances and noise to the true PES. Thus, the standard output feedback H-2 optimization proce dure can be used. The design method is applied to a single-stage actuator s ystem and dual-stage actuator system, and the corresponding output feedback controllers have been found. Compared with other design approaches, a high er TPI rate can be achieved by the proposed method. The resultant TPI rate can be a criterion of evaluation of any other linear design work toward TPI budget improvement.