Distributed supervisor synthesis for automated manufacturing systems with flexible routes and assembly operations using Petri nets

Abstract

Automated manufacturing systems (AMSs) are developing rapidly with increasingly sophisticated operations and complex topologies. In this paper, we propose a new kind of AMS structure, namely, AESMs, with processes expressed by flexible routes and embedded by marked graph blocks. Flexible routes and assembly operations are combined organically in this model, making it structurally complex and applicably adaptable. Deadlock resolution in AMSs is a fundamental and prerequisite issue. Conventional approach is based on monolithic methodologies by means of siphons, i.e., a special structural object closely related to deadlocks. Analysis shows that siphon-based mechanism is of limited applicability to control AESMs. On the contrary, we utilize a distributed approach in accordance with the philosophy of model predictive control techniques, which can create a trajectory dynamically leading the entire system to its desired destination. In our strategy, whether or not concerned tokens can reach critical places or critical place unities determines the feasibility of each step's execution. Control strategy is applied to processes locally such that they can concurrently proceed at the same pace. Global goals become attainable through the local observation, control, and execution upon local processes without knowing external and extra information.