High Speed Ring-based Distributed Networked Control System for Real-time Multivariable Applications

T INT raditional centralized control architectures where a supervisory controller directly interfaces in a point-to-point fashion with all sensors and actuators in the system have been successfully implemented in the past. They are generally feasible when a controller interfaces with small number of sensors and actuators and requires short wiring to them. However, it is often difficult to add, remove or reconfigure components in these systems. Moreover, the recent trend of control systems is dealing with much more complicated systems than before, so these systems require the control system to be easily reconfigurable, expandable and maintainable. Hence, the networked control system (NCS) is utilized as an alternative to the conventional centralized control system because of its advantages in flexibility, volume of wiring and capacity of distribution [1]. RODUCTION 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 types 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, collisionfree 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. Various distributed NCSs have been applied in fields such as industrial automation, building automation, office and home automation, intelligent vehicles, and aircrafts and spacecrafts. [2]-[6]. The type of NCS that is used for an application is determined by the network type and its architecture. NCSs using the Ethernet bus with carrier sense multiple access with collision detection (CSMA/CD), token-passing bus (e.g. ControlNet), and controller area network (CAN) bus (e.g. DeviceNet) were described and compared [1]. Their properties are summarized in the Table 1 in the following section. They are based on the common bus architecture where all components are wired to one common shared bus. This architecture generally includes constraints; for example, transmitting nodes on the bus must not transfer messages simultaneously. Collision of messages will result in data loss, failure of data transfer and penalty for retransmission, which makes the network nondeterministic. And the common bus may