Automatic tuning of the PID controller for servo systems based on relay feedback

This paper proposes an automatic tuning method for a PID controller based on relay feedback using single or dual frequency points. The frequency points are selected according to the performance bound of the servo system. The single-point method determines PID control gains based on the ITAE (integral of time and absolute error) optimal equations. The dual-point method utilizes the response information of two neighboring points and determines PID control gains by taking into account the damping ratio of the dominant pole as the main design specification. Both approaches are tested on a hydraulic actuation system of a blow-molding machine for parison control. Experimental results show that both approaches offer a system with satisfactory response characteristics, and the system needs to undergo only a short period of relay excitations