The Motion Message Estimator in Real-Time Network Control Systems

In network systems, the time-delay effect is unavoidable and it usually degrades system performance. Furthermore, in the real-time network control system (NCS), messages are required to be transmitted on time to meet specifications of the deadline. Otherwise, it leads to data dropout which occurs randomly in real-time NCS control. The data dropout not only degrades performance of the NCS but also causes the NCS to be unstable. In this paper, a second-order motion message estimator is proposed to compensate for the missing messages containing motion commands and measurements, since most motion systems can be described suitably by second-order Newtonian motion law. The dropout rate of the controller area network (CAN) bus has been evaluated in different transmission rate in this paper. The proposed NCS with the message estimator has been successfully implemented on a CNC machine to achieve significantly improved motion accuracy.