Multilevel hierarchical control applied to a demonstration flexible assembly cell

The authors review a flexible assembly cell comprising five robots, two direct vision systems, and a ring transport system connected to the control system by a local communication network. The demonstration relates to assembling car oil pumps from bulk parts. The description of this cell is dealt with. The principles are presented that govern the control system. It is a multilevel hierarchical control designed to address two major issues, the breaking down of control into levels of expertise and the integration of the information exchanged between the decision levels. To provide a consistent form of exchange and to facilitate the description, the set of real time control levels of the flexible assembly cell is modeled by using a single formal model, i.e., either weighted Petri nets allowing the control levels of the process itself to be modeled or object Petri nets enabling the control levels designed to coordinate the previous levels to be modeled, while still complying with the rules defined by scheduling