Application of PLC's as front-end pre-processors in factory information systems

Factory information systems (FISs) have grown in acceptance largely because of the successful integration of a variety of data-collection, entry and display devices. The traditional factory computer system by and large ignored the moment-by-moment consequences of production processes, and focused instead on the assistance offered by automated shift-end counting and scheduling procedures. Separate systems handled the various functions (e.g. orders, raw materials, inventory, scheduling, etc.) and the assessment of productivity was left to the findings of endless meetings, negotiations and the interpretation of aged data reports. The data under consideration, however carefully collected, was so much after the event that problems forced the factory into a crisis-management mode in the hope that some restitution could be made. Real-time data is normally available in the process itself but is difficult to condense into a form that is useful for scheduling and FIS functions. Such data contains vital information as to the actual rela-time machine performance on the shop floor, and if processed correctly can be used to indicate and forecast production problems so that calm, yet timely, adjustments to schedules, etc. can be made. This paper describes how a PLC (programmable logic controller) was used to collect, pre-process and pass summary results to a low-cost supermicro computer for production monitoring and FIS purposes. This work was undertaken in response to an industry need for low-cost systems that could be retrofitted to factories with minimal disturbance to their day-to-day operations.