Extending Petri net to reduce control strategies of railway interlocking system

摘要

In our previous articles we gave step by step refinement process towards the development of safety properties of moving block interlocking system (MBRIS). The refinement process started from abstraction to fuzzy based safety properties using Z and then fuzzy multi agent specification language. However, one dimensional control of train passing through a switch and level crossing were not discussed. This paper reduces the existing two dimensional controls along the switch and level crossing to one dimensional for shifting it to a train only. For example, in the existing model the train movement along components switches and level crossings depends on both the train and components control. Whereas, in one dimensional control train is the only authority to control a switch and level crossing required for its desired operation. For this reduction, concurrent and mobile agent concepts are required. Therefore, we integrate mobile agent concepts with Petri nets to develop the mobile Petri net (MPN) a new class of PNs. This supports both mobility and concurrency. Further, we prove that the collection of different MPNs in a connected network is a PN. This proof allowed us to use the properties of PN to verify the system. Finally, we use MPN to model the safety properties of MBRIS along the switch and level crossing. This provides one dimensional control to a train along a switch and level crossing which increases the safety of the railway interlocking system. Moreover, we use reachability graph (RG) to verify the switch and level crossing models.