NURBS path tracking control of a scanning mirror system based on EtherCAT fieldbus

In this paper, an EtherCAT scanning mirror system with function of NURBS path tracking control was investigated. By using EtherCAT protocol to connect master computer with a scanning mirror system, we did a first attempt to implement position control by the master computer, so that one can apply an advanced control algorithm to the system instead of applying a distributed control algorithm on the proprietary driver of the slave device. The technical issue of this configuration like commutation delay caused by the three-buffer-mode is addressed. A two-staged H-infinity with feed-forward controller is designed for the position control loop. Moreover, considering the widely used of non-uniform rational B-spline (NURBS) in the field of CAD/CAM, we added the function of NURBS path planning in the controller so that the system can deal with complex NURBS curves. The experiment results showed that the proposed method can reduce tracking error and have better performance when comparing with traditional distributed control strategy.