In this paper, the previous results that the performance of iterative learn
ing control (ILC) algorithm can be improved by adding a proportional term a
nd/or an integral term of error in D-type ILC algorithm are generalized usi
ng an operator. Then, a sufficient condition for convergence and robustness
of the generalized ILC algorithm are investigated against initial state er
ror. As a special case of the operator, a non-linear ILC algorithm is also
proposed and it is shown that the effect of initial state error can be reac
hed to zero in a given finite time. It is shown that the bound of error red
uction can be effectively controlled by tuning gains of the proposed non-li
near ILC algorithm. In order to confirm validity of the proposed algorithms
, two examples are presented.