“…A minimal-order disturbance observer (DOB) (Fortmann and Williamson, 1972;Gopinath, 1971;Iwai et al, 1998) is also constructed to attenuate the speed disturbance of the rolling motor. While the DOB applied to the looper system did not include the dynamics of the actuators such as the main/looper motor (Kimura et al, 1996), the proposed DOB includes the actuator dynamics and it is easy to apply the works because of the simple algorithms.…”