Auto-tuning PID/PI control and its application to paper basis weight control

After the brief production process of ordinary fourdrinier is introduced, the difficulty of paper basis weight control is analyzed. A PID/PI control algorithm which is capable of controlling large time-delay processes is presented. PID/PI parameter tuning can be finished only by obtaining the oscillation amplitude and frequency at the point where the Nyquist curve of the process intersects the negative imaginary axis in S plane via modified relay feedback identification method in frequent domain. Such a simple tuning method is little dependent on the process model and easy to implement on line. On the other hand, the PID/PI parameters are tuned based on the specified robust specifications of amplitude margin and phase margin, which is strongly robust and is very suitable for controlling such industrial processes with large time-delay as paper basis weight.