A work-in-process tracking system for experimental manufacturing

A work-in-process (WIP) tracking system directs and monitors the flow of product in a factory. The author describes a WIP tracking system that supports the management of complex process plans, ensures that products receive their intended processing, and can be used to determine the actual processing received by finished products. The two major features of the tracker are the representation of process plans as ordered trees of parameterized subprocess plans, and the logging of process data at each process step. The tree representation encourages modular process plans, which makes the plans easier to create and document, and is flexible enough to allow specific items to follow nonstandard subplans or to change plans after processing has begun. The log makes it possible to reconstruct the entire processing sequence of an item and permits measurement values obtained earlier in an item´s processing to be used as the value of a later step´s parameter, creating a form of feed-forward process control