Positioning control of direct drive robot with two-degree-of-freedom compensator

Recently, a disturbance observer based controller has been widely used in the industrial world because of its simplicity. However, this method depends on the intuitive approach in determining the disturbance estimation filter, and therefore, more systematic approach is desired. In this paper, we first combine the generalized compensator and the disturbance observer based controller by clarifying the internal structure of the generalized 2-degree-of-freedom (DOF) compensator. Secondly, based on the clarified structure, we derive a robust stability condition, and propose the design algorithm of a free parameter taking into account the condition. The proposed design algorithm is easy to implement and, as a result, we obtain a lower order free parameter than that of the conventional design algorithm. Thirdly, we show by adopting an appropriate coprime factorization that the clarified structure can also be regarded as an extended version of the conventional PD compensator. Finally, we apply the proposed algorithm to a positioning control of a 3-DOF direct drive robot, and show some experimental results to verify the effectiveness of the proposed algorithm