Disturbance observers have been used extensively for decoupling control of robot manipulators. But the conventional disturbance observers are sometimes useless for decoupling control because they are usually constructed under the assumption that the disturbance is constant during the sampling period and the trade-off between decay rate of the estimation error and the sensitivity to sensor noise is an inevitable problem. This paper proposes a variable-structure disturbance observer and a method for decoupling control of robot manipulators by applying the proposed observer. The proposed observer can treat a general class of disturbances and overcome the problems of the conventional disturbance observers, that is, sensitiveness to sensor noise and delay of convergence. The proposed control method is implemented into an experimental 3-degree-of-freedom DD robot. It is shown through experimental results that the proposed method can realize decoupling control for robot manipulators more precisely and robustly.
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