Abstract: If the model of the controlled system is poorly known, an approximate one, based on experimental data at specified frequencies, is developed and is defined as a limited frequency response series model. Using this model, an amplitude and phase adjusting controller in frequency domain (APACFD) algorithm is developed to improve the tracking accuracy. The simulation result shows that algorithm is very effective in tracking the contour, which has no sharp corners, even if the exact model of the controlled system is unknown.

Key words: Approximate model, Feedforward control, Tracking control