Scalable motion control system using EtherCAT-based shared variables

This paper presents the design of a scalable multi-axis control system that incorporates efficient data sharing using EtherCAT multicast over a set of homogeneous motion controllers. By associating each shared variable with a global clock-based timestamp and a dirty flag and by ensuring total order of distributed writes, the proposed system enables a cluster-architecture motion control environment for increased flexibility and scalability. Two types of data update schemes, i.e., synchronous update using clock events and asynchronous update using frame events, are described. The results from a preliminary experiment indicate that the design of an efficient frame relay is required in the EtherCAT master for the minimized cycle time and data inconsistency period.