Disturbance-observer design for magnetic hard-disk drive serve systems

This paper presents a disturbance-observer design for the magnetic hard-dis k-drive servo systems. To facilitate the disturbance-observer design for th e disk-drive servo, a variation on the general form of these compensators i s proposed. Compared to the highly generalized disturbance observer of the prior art, the proposed structure provides more intuition about the design process compared with the general form and various realizations appearing i n the literature. The velocity type of disturbance observer appearing in th e prior art is shown to be a special case of the proposed disturbance-obser ver architecture. Although a standard factorization approach can be used in the design of the proposed observer structure, the proposed structure also enables classical feedback design methods to be employed. Disturbance obse rvers with an improved noise attenuation and faster disturbance rejection a re derived naturally fi om the proposed disturbance-observer structure. Bot h simulation and experimental results from a test stand with a 3.5-in. (sim ilar to 8.9 cm) disk-drive actuator demonstrate a 40% reduction in settle t ime and a 10-dB improvement in measurement noise attenuation between distur bance-observer designs, using a first-order filter and a constant feedback.