Petri Nets is an emerging tool in Industrial Automation technology. They provide an uniform environment for the modelling, analysis and design of event systems. The model which is used for analysis of behavioral properties of the system can be used for the construction of simulators and controllers.
a. Finite State Machines
These are the forms in which Petri nets could be represented. One example is that of a Vending machine (figure shown below) which sells candy bars when the 5 or 10 cents are inputs at the inlet. The circular representations are called places and rectangular boxes are transitions. In this figure, each transition has only one incoming and one out-going arc. There are several ways a 20 cent bar can be released from the vending machine. One of the paths could be as follows: Input 5 cents – 5 cents – 5 cents – 5 cents. In this path, each transition is fired with a 5 cents coin and takes 4 firing transitions before candy bar is released from the machine.
Fig 18: Vending machine state diagram representation of Petri net
b. Producer – Consumer Problem:
A Petri net representation of the Producer – Consumer problem has been described below with reference to the diagram. In this system, producer puts information into the buffer and consumer collects and deletes information from the buffer. If the buffer is full, Producer will be in “sleep” mode until consumer receives and deletes the information from the buffer. Similarly, consumer will be in “sleep” mode when the buffer is empty until producer puts some information into the buffer. A wake-up signal algorithm is set up in either case to ensure none of them goes into “sleep” mode permanently.
Fig 19: Petri net model of Producer and Consumer problem
c. Graphical T...
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...een made in the analysis of software systems using colored Petri nets. According to G.Rozenberg[10], Colored Petri net is a useful language for the specification, design, simulation, analysis and verification of large software systems. V. Pinci and M. Shapiro[10] describe an integrated software development procedure based on hierarchical colored Petri nets, where analysis is done through automatic translation from SADT diagrams into colored Petri nets for formal analysis and then into an executable code.
g. Communication Systems:
In communication networks, research was performed on Fiber Optics Local Area Networks such as Fastnet, Expressnet, D-Net, U-Net and Token Ring as they are key networks for factory automation. This leads to interest in modelling and testing of High Speed Networks, which is paramount for the successful development of multimedia systems.
The project that will be examined is an upgrade to our main Human-Machine Interface (HMI) software: Cimplicity, to SQL Server and to the Windows OS. Cimplicity is a product of the GEFanuc group of General Electric. This group develops a full suite of applications used in the manufacturing environment. By way of introduction, the manufacturing floor environment uses a variety of types of equipment. To control these machines, a specialized computer is used. For the purposes of simplicity (not the program), this paper will refer to them all as PLC's or Programmable Logic Controllers. Most of these PLC's are accessible via the ethernet and communicate to our Protocol Data Units (PDU) in the computer room. These PDU's have Cimplicity installed on them in the form of projects that are named for the various areas or functions of our plant such as GA or General Assembly. The project we are undertaking will be a fundamental change to these PDU's in our computer room. The servers currently run Windows NT and will be upgraded to Windows Server 2003 or Windows 2000 and SQL Server will will be upgraded from version 7 to SQL 2000.
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This paper focuses on the use of Petri nets to model traffic signals at intersections. An
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