Object-oriented modeling and implementation of control software for a robotic flexible manufacturing cell

This paper discusses the development of an object-oriented software for the control of a robotic flexible manufacturing cell (FMC). The control software is based on a formal modeling of the entities involved in a cell and their interactions. An entity-relationship model, message flow diagrams, and state transition models are used to specify the software objects needed to model the operation of an FMC. In an object-oriented approach, the cell controller takes care of coordination and synchronization issues while the individual objects are responsible for their own activities. This approach has numerous advantages over the conventional state transition method where the number of state grows exponentially with the increase in cell components and complexity of control tasks. Implemented in Turbo C++ on an IBM PS/2 computer, the software can accommodate cell configuration changes, such as the number of machines, without reprogramming. Robot dispatching rules that are independent of the cell configuration were developed for handling the simultaneous setups, prevention of order sequence interference and batch break-up situations that are often encountered in FMC control.