Abstract
In real-world automated manufacturing systems (AMSs), a breakdown of unreliable resources in operation often makes most existing deadlock control policies inapplicable. This work focuses on robust deadlock control problem in AMSs with multi-type and multi-unit unreliable resources. The unreliable resource's failure and repair activities are modeled by Petri nets. We introduce a concept of strong controllable siphon basis, which can be seen as an extension of the controllable siphon basis proposed in our previous work. Then by adding a control place with proper depth variable to each strict minimal siphon (SMS) and R-type SMS in a strong controllable siphon basis, we successfully develop a small-scaled robust deadlock controller for AMSs under consideration. Such a robust controller can guarantee that, as long as at least one unit of each unreliable resource type is available, all types of parts can be processed smoothly through any one of their routes even during downtime. Moreover, the number of control places of the proposed controller is no more than that of the activity places in the Petri net model and its size grows polynomially with Petri net model.
Highlights
Deadlock-free resource allocation problem in automated manufacturing systems (AMSs) has been an active research area and received increasingly attentions in both industry and academia during the last decades [1]–[4]
(2) By adding a control place with a proper depth control variable and suitable related arcs to each strict minimal siphon (SMS) in a strong controllable siphon basis, we develop a robust controller with small size
This work deals with the deadlock control problem in AMSs with multi-unit and multi-type unreliable resources and synthesizes their deadlock prevention controllers with small structure
Summary
Deadlock-free resource allocation problem in automated manufacturing systems (AMSs) has been an active research area and received increasingly attentions in both industry and academia during the last decades [1]–[4]. Based on the concept of strong transition covers, Feng et al [39] developed a 1-robust deadlock controller for the same AMSs. Later, Wu et al extended these results to general cases with multi-unit resource failures [41]. This paper concentrates on a robust deadlock prevention policy for AMSs with multi-type and multi-unit unreliable resources. The failed resources can return to the system to continue processing parts after their repair Those AMSs can be modeled by a class of Petri nets, namely, systems of simple sequential processes with resources (S3PRs) in the absence of resource failures. (3) Compared with existing works [34], [36]–[41], we believe that the robustness level of our proposed controller is improved largely because it allows that multi-type and multi-unit unreliable resources fail simultaneously.
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