Improving the performance of Higher Order Disturbance Observers: A position approach

The disturbance observer (DOB) is a tool for the robust motion control and it is used to compensate the disturbances. In the design of the DOB, it is assumed that, the system disturbance is observed and compensated by the DOB in the range of its bandwidth. However, the whole bandwidth cannot be compensated by the DOB due to the dynamical characteristics of the disturbance observer's low pass filter (LPF). Higher Order Disturbance Observer (HODOB) is one of the fundamental tools to increase the performance of the DOB, even though it has some disadvantages. However, the performance analysis of HODOB has not been clearly reported yet. In this paper, analysis and design methods of the HODOB are presented by using a more general disturbance model. This general model gives more freedoms to design HODOB. Also the superiors of the position measurement based HODOB design are shown. Simulation and experimental results are given to show the validity of the proposed methods.