The influence of disturbances in iterative learning control

For systems that perform repetitive tasks, a high performance feedforward signal can be derived using iterative learning control (ELC). The feedforward signal is updated through successive iterations. Disturbances present in the control scheme, such as load and measurement disturbances, are also present in the learning process and deteriorate the performance of ILC. This paper presents an expression for the tracking error of an arbitrary iteration which shows the influence of measurement and load disturbances of the present and previous iterations. The expression is validated by means of simulations and experiments on a motion system. The disturbances of the last two iterations prove to have the largest influence on the tracking error