Analysis of servo system realized by disturbance observer

It is desirable to realize a nominal system which can control acceleration in order to realize a fast and precise servo system, even if the servo system has parameter variation and suffers from disturbance. In this paper, first, we transform the disturbance observer system to a filter-type two-degrees-of-freedom control system, which indicates that the disturbance observer system includes series compensators such as D, PD, and PID depending on the order of the disturbance observer. By clarifying the feature of the series compensator, we describe the bandwidth and stability of the realized system