Two Simple Deadlock Prevention Policies for S3PR Based on Key- Resource/Operation-Place Pairs

This paper proposes the concept of Key-resource/operation-place Pairs (KP) of (SPR)-P-3 (systems of simple sequential processes with resources). Based on KP, two policies are presented to prevent deadlocks in flexible manufacturing systems (FMS) that can be modeled by (SPR)-P-3. The idea is to control some key resource places only to guarantee that all strict minimal siphons (SMS) never become empty, thereby making the controlled system live. It enables one to design two easy-to-implement control policies. The first one can guarantee that the controlled system is live, and the second one can also make the controlled system live if there is no SMS containing any control place in the controlled system. At last, a well-known FMS example is used to illustrate the proposed concept and policies. Note to Practitioners-This work is motivated by the problem of deadlock prevention in flexible manufacturing systems (FMSs). Petri-net-based deadlock prevention policies are popular. We propose a new concept of Petri nets, KP. Based on it, we develop two easy-to-implement deadlock prevention policies for FMS. The idea behind them is simple, i.e., deadlocks can be prevented by controlling some key resources such as machines and robots. Compared with such policies as iterative control policy and elementary-siphon-based policy, the proposed ones can make the supervisor simpler. They also enjoy higher adaptability to the change of the resource quantities. In other words, when some new resources are put in service or some resources have to quit, the corresponding supervisor requires trivial adjustment. This is certainly important in achieving the goal of agile manufacturing and automation. However, the computational complexity of the proposed policies is still high despite their low control implementation cost since all strict minimal siphons have to be computed in order to generate the KP-based supervisors.