In real applications, a remote control system is generally an integration of different networks consisting of a commercial network for message transmission and an industrial network to control the remote hardware through a communication gateway. Since the induced time-delay in network control system (NCS) may cause system instability, this paper proposes a remote NCS structure by implementing the adaptive Smith predictor with an online time-delay estimator. As the delay in a commercial network Ethernet is significantly time-varying depending on the number of end-users, the delay is estimated in this paper by processing the online measurement of the round-trip time (RTT) between the application layers of the server and the client. The adaptive Smith predictor control scheme is developed by directly applying the estimated time-delay. To prove the feasibility of the proposed remote control system, the developed design has been applied to an AC 400 W servo motor tested from a 15 km distance. The experimental results indicate that the significantly improved stability and motion accuracy can be reliably achieved by applying the proposed approach.
- Adaptive Smith predictor; controller area network (CAN); Ethernet; networked control system (NCS); remote control; time-delay