Browse Theses

Industrial local area networks carrying digital information among manufacturing devices which are grouped as a Flexible Manufacturing System (FMS) have received considerable attention recently. Although FMS were initially introduced by grouping factory machines and then simply interconnecting the inputs and outputs of their controllers, it is now assumed that each device can be attached to a network and is able to exchange information reciprocally. The FMS data traffic, which is mostly generated by manufacturing devices, NC machines, industrial robots, sensors, programmable controllers, and supervisor computers, consists of both large files and short data messages. The communication network for FMS should be able to accommodate all the needs of the system. The Token Bus is used as one of the standard protocols in the industrial and manufacturing system environment. However, it does not support message service for different types of data found in the FMS site. Prioritizing various data and control messages in FMS is very important so that the delivery of emergency data and urgent network functions is not delayed by other non-critical message transmission.

This research proposes a Prioritized Token Bus (PTB) protocol suitable for industrial FMS networks. All the stations are connected in a predefined order. With the ordered stations, the token delay between a station and its successor can be minimized which greatly affects the message delay. Also, ordered stations provide an immediate detection of node failure which may occur quite frequently in the FMS harsh environment due to heat, dust, humidity, and electromagnetic interference. By implementing a priority counter in each message class, this protocol provides bounded delay time for high priority messages and guarantees deterministic access to other low priority messages.

Analytical queueing model and simulation are developed to predict the behavior of the PTB protocol. Using these models, we have examined the characteristics of the message delay experienced by different priority classes as a function of traffic load, message length, and the number of stations. We have shown that the access protocol is able to maintain a low message delay for the high priority class while guaranteeing some prespecified service cycles for other priority classes.