Filter, repetitive control system and learning control system both provided with such filter

Repetitive control systems and learning control systems using filters composed of delay circuits and having parameters resulting in a very high loop gain for only specific frequencies. The result of this is a substantial reduction of periodic disturbances with frequencies corresponding to the specific frequencies. The parameters of the filters are selected such that the robustness for frequency-variations in the periodic disturbances is improved. Also published as: WO 9613898 (A1) JP H10508130 (A) EP 0774176 (A1) EP 0774176 (B1) DE 69524768 (T2)