A virtual factory teaching system in support of manufacturing education

Journal of Engineering Education, Oct 1998 by Dessouky, Maged M, Bailey, Diane E, Verma, Sushil, Adiga, Sadashiv, Et al

Learning networks can promote collaborative learning and the development of important team skills.2723 Rada et al.79 found that students working in collaborative groups are better able to formulate concrete ideas and avoid misconceptions. Group work may also serve to interest female students in engineering careers, as suggested by Heller and Martin.

III. VFTS PROTOTYPE DEVELOPMENT

The prototype VFTS focuses on factory scheduling, a topic covered in a senior-level course in Industrial and Systems Engineering at the University of Southern California, Production Planning and Control (ISE 410). This is a common industrial engineering course, covering factory topics such as inventory control, production planning, and machine scheduling. Simplification of the models used in such courses has caused them to stray from the realities of complex manufacturing systems.3 This course thus provides an ideal environment in which to evaluate the uses of and potential gains from the VI;TS.

Factory scheduling decisions include release and dispatching rules. Release rules determine when to release a new lot of raw material into the production line; they are either push-based such as a Materials Requirement Planning (MRP) system or pull-based such as a Kanban system. The push systems tend to match factory output to customer demand, while the pull systems tend to minimize workin-process (WIP) inventory. Hence, a trade-off must be made between release rules with no single rule dominating in all situations. Dispatching rules select which product(s) to manufacture next when a machine becomes idle; examples are first-in-first-out, shortest processing time, earliest due date, and least slack. Choice of a dispatching rule depends on performance criteria; for example, the shortest processing time rule tends to minimize WIP while the least slack rule tends to minimize the lateness of the production jobs.

These scheduling rules are interrelated, and in most cases no single rule dominates. Their use depends on many factors including the factory layout, processing times, demand pattern, and machine reliability. VFTS demonstrates these rules on one type of a factory, a hybrid flowshop. In a traditional flowshop, all part types visit the manufacturing workcenters in the same sequence. In a hybrid flowshop, each manufacturing workcenter may have multiple identical machines. This type of configuration is selected because it is common in many industries such as electronics, garment, chemical, etc., and an instructor can show factory behavior as a function of the dispatching and release rules using a hybrid flowshop.

The prototype resides at http://vfts.usc.edu/ and requires Microsoft Internet Explorera Version 3.0 or higher. The prototype architecture is outlined in figure 1. The design is simple and modular, with three layers: AweSim3" Server, VFTS Java Server, and Clients. Clients (students) use a web browser to connect to the VFTS Java Server using its Web Page. Most communication between the clients and the server takes place using Java applets. The Java Server functions as a mediator between the AweSim factory servers and the clients. The AweSim Server is responsible for factory knowledge and simulation. The layers interface using a message protocol set up to minimize bandwidth requirements.