Positioning Control of Direct Drive Robot with Two-Degree-of-Freedom Compensator.

Abstract

To achieve high performance control of robot manipulator, one has to overcome disturbances added on each joint and nonlinear forces such as a frictional force, gravity, interacting force. To meet these ends, recently a method based on disturbance observer was proposed which is characteristic of the fact that it does not need inverse dynamics calculation and thus can be implemented with a simple microprocessor. However, this method depends on the intutional approach in determining the disturbance estimation filter, so more systematic approach is desirable. In this paper, we propose a new design approach of a two-degree-of-freedom compensator taking into account the robust stability. First of all, we clarify the internal structure of the generalized two-degree-of-freedom compensator. By using this structure, we can make a bridge between a generalized controller and the disturbance observer based controller. Secondly, based on the clarified structure we derive a robust stability condition, and propose a design algorithm of free parameter taking into account it. The proposed design algorithm is ease to execute and, as the result, we obtain the low order free parameter compared with the conventional design algorithm. Thirdly, we show that the clarified structure can also be regarded as an extended version of the conventional PD compensator by adopting an appropriate coprime factorization. Finally, we apply the proposed algorithm to a three-degree-of freedom direct drive robot, and show some experimental results to verify the effectiveness of the proposed algorithm.