Advanced Application of Centralized Control for a Scanning Mirror System Based on EtherCAT Fieldbus

Distributed control is the most popular control strategy for controlling numerous slave devices. However, the performance of slave devices is hard to improve because the control algorithm is handled by the commercial slave devices. Therefore, this paper proposes a hybrid control structure that follows the concept of centralized control strategy and handles part of the control loop on the master computer in a distributed control system through EtherCAT fieldbus. In this study, different advanced control methods such as robust control and learning control were applied to handle the position control loop of a scanning mirror system in a selective laser melting (SLM) system with stringent demand of position error around 40 µm based on EtherCAT fieldbus. By designing a proper controller, the experiment results showed that the tracking performance was significantly improved. The tracking error dropped by about 80% after the proposed hybrid control structure was applied. By applying the proposed hybrid control structure, one can improve the high-performance-requirement devices, while reducing the calculation burden of the master computer for other low-performance-requirement devices by retaining the benefit of distributed control.