Discrete-time implementation of disturbance observer based on robust internal-loop compensator framework: Easy-to-implement approach

The disturbance observer (DOB) has been widely used in the field of robust motion control. There have been numerous studies investigating them, together with design guidelines for Q-filter; however, a digital implementation is not always straightforward. In this paper, we propose a simplified implementation based on a robust internal-loop compensator framework. The digital implementation is only required for single function block that is reduced in size, and the causality of the inverse model of the nominal plant is guaranteed by separated integral elements. A minimum-size Q-filter is also derived. A force control problem using the DOB is discussed briefly. The performance of the proposed method is compared with conventional DOB implementation experimentally using a linear-motion system. We show that the two methods provide equivalent results; however, our method allows for a considerably simplified implementation.