Two-stage design method of robust deadlock control for automated manufacturing systems with a type of unreliable resources

This paper proposes robust deadlock prevention controllers for automated manufacturing systems (AMSs) with a type of unreliable resources, and the aim is to ensure that the parts of all types can be processed continuously through any of their processing routes, even if one of unreliable resources fails. These AMSs under consideration can be modeled by Petri nets, where deadlocks are characterized by strict minimal siphons (SMSs). The design of our robust controller consists of two stages. The first stage, called SMS-based control, adds a control place to the original net for each SMS so as to prevent it from being emptied even if one of unreliable resources fails. This controller is maximal permissive for preventing all SMSs from being emptied during one resource failure period. Since some so-called augmented-siphon is created after the first stage, the second stage, called augmented-siphon-based control, is required. This stage adds a control place to each minimal augmented-siphon with its output arcs pointing to the source transitions of the system such that no new siphon is created. In addition, an algorithm based on mix integer programming (MIP) is used to find all minimal augmented-siphons. Finally, some examples are used to illustrate the proposed method. (C) 2019 Elsevier Inc. All rights reserved.