High Speed Ring-Based Distributed Networked Control System for Real-Time Multivariable Applications

A networked control system (NCS) is a control architecture where sensors, actuators and controllers are distributed and interconnected. It is advantageous in terms of interoperability, expandability, installation, volume of wiring, maintenance, and cost-effectiveness. Many distributed network systems of various topologies and network type have been developed, but NCS systems tend to suffer from such issues as nondeterminism, long network delays, large overheads and unfairness. This paper presents the ring-based protocol, called the ExoNet, and its network architecture which are built to achieve better performance as a distributed networked system. A Cypress transceiver CY7C924ADX is applied to the network as a communication unit. The protocol is based on the transceiver and developed to achieve fast communication and allowable latency for controls with high control loop frequency. Compared with other standard network types such as Ethernet, ControlNet or DeviceNet, the network is characterized by its ring-based architecture, simple message and packet formats, one-shot distribution of control data and collection of sensor data, multi-node transmission, echo of a message, and other features. The network also guarantees determinism, collision-free transmission, relatively small overhead, fairness between nodes and flexibility in configuration. Its analysis and comparison with these network types are also provided and its application on the Berkeley Lower-Extremity Exoskeleton (BLEEX) is described.