H∞ control versus disturbance-observer-based control

In the motion-control field, a disturbance-observer-based disturbance canceling control is often used as a robust control methodology, However, this method is nothing more than an alternative design of an integral controller, and the robust stability issue cannot be directly accounted for, In this paper, an extended H-infinity control is proposed as a new robust motion control method which achieves the disturbance cancellation ability and guarantees robust stability automatically.