System identification and two DOF PID controller for an industrial sewing machine

The purpose of this paper is to obtain an accurate nonlinear system model to test various control schemes for a motion control system that requires high speed, robustness and accuracy. An industrial sewing machine equipped with a brushless DC motor is considered. It is modeled by a neural network that is configured as an output-error dynamical system. The identified model is essentially a one step ahead prediction structure in which past inputs and outputs are used to predict the current output. Using the model, a 2 degree-of-freedom PID controller to compensate the effects of disturbance without degrading tracking performance has been designed. In this experiment, it is not preferable for safety reasons to tune the controller online on the actual machinery. Experimental results show that the model is a good approximation of the sewing machine dynamics and that the proposed control methodology is effective.