An object-based representation method for a manufacturing cell controller

This paper presents an object-based approach to the construction of manufacturing cell controllers. The cell components are represented as objects and communication as messages that are passed among the objects. Messages are acted upon by selected 'methods' (procedures) that are accessable to a cell object either directly or through inheritance from a superclass that the object is a member of. Messages are automatically generated by either (1) reasoning from the process plan and world status, (2) the sequence of actions for building the desired product, (3) events that take place in the cell, or (4) commands from a multi-cell coordinator. We present the approach along with a case study implemented in Smalltalk-80, an object-based programming environment. We also expand the scope of the traditional object-based environment by integrating knowledge-based techniques into the approach. The latter techniques provide the complex reasoning mechanisms that are required in a dynamic decision-making environment such as a manufacturing cell.