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Design and analysis of sequential function charts using sensor-based stage Petri Nets
Abstract
Sequential function chart (SFC) is currently one of the design diagrams for automated control systems to capture the sequence of operations executed by the system's control software. This method grows so complex that locating the cause when a problem is detected becomes extremely difficult. Researchers are constantly pursuing to develop tools that eliminate the limitations and increase the design performance using SFCs. Petri nets are among the most widely used tools to model and evaluate the behaviour of automated control systems. Petri net control of real-worlds systems is achieved by mapping sensor signals and actuator commands to Petri net transitions. Being a well-defined and well-developed tool based on a mathematical formulation, PN models are used to analyze and implement real-time control for discrete industrial systems. This paper discusses a methodology to convert the SFC of an automated control system for design and analysis using the sensor-based stage Petri nets (SBSPN). Appropriate rules are suggested to convert all the I/O sensors of SFC into stages Petri net picture. A pneumatic control system is illustrated as an example to demonstrate the practical use of this technique.
... There is no unified approach to the formal analysis of their properties and their operation depends on implementation. They can be converted to the finite machine [72][73][74], timed automata [72,[75][76][77][78], or formal PNs [79][80][81][82][83]. ...
Petri nets (PNs) have many advantages such as graphical representation, formal description , and the possibility of sequential and concurrent control. An important aspect of using PNs is hierarchical modeling, which may be provided in different ways. In this paper, a new concept and definition of the hierarchical structure for Fuzzy Interpreted Petri Net (FIPN) are proposed. The concept of macroplace with several input, output, and input-output places is introduced to the net. The functionality of the macroplace instances and the hierarchy graph are also proposed. They are implemented in a computer simulator called HFIPN-SML. In this study, FIPN is employed since it allows the use of analogue sensors directly for process control. Better visualization and more precise control are among advantages of the introduced approach.
... Other authors define methods for translating SFCs into Petri nets [6,14]. Those methods do not account for time. ...
Sequential function charts (SFCs) are among the standard languages for programmable logic controllers (PLCs) ubiquitous in automated manufacturing and production systems. While SFCs are quite user friendly to developers, it is not easy to guarantee the correctness of safety-critical SFC programs. Thus, methods and tools for verifying the correctness of SFC programs are highly desirable. Here we introduce a transformation technique that converts a significant subset of an SFC to a time Petri net (TPN). Thanks to a large body of literature and mature tools that can analyze TPNs, our technique will bridge the gap between a user-friendly manufacturing control programming tool, the SFC, and powerful analysis tools for TPNs.
This paper solves the problem of converting Sequential Function Charts to Function Block Diagrams in Programmable Logic Controllers. The algorithm presented here works for systems where the order of flip-flop evaluation is performed in a series of independently evaluated networks. This approach can be used when SFC programming is not available on a given platform but FBD support is provided instead.
This paper presents a method and a tool for converting Sequential Function Charts into Function Block Diagrams in a manner that models states with the use of flip-flops. Order of evaluation is enforced through the use of explicit delays. Presented approach can be used when SFC programming is not directly available but the developer wants to use advantages of SFC modeling.
Due to its low cost and increased reliability, the programmable logical controller (PLC) plays an important role in industry automation. However, as systems become larger and more complex, efficient and systematic analysis and design of PLCs become a more important issue. In this research, an integrated IDEF0-3/CTPN/SFC (IPS) for developing discrete event control systems (DECSs) is presented. The proposed integrated methodology provides a complete and systematic development process for the DECSs. The development process is divided into four stages: functional analysis, system behaviour analysis, system design, and system implementation. The IDEF0-3, coloured timed Petri net (CTPN) and sequential function chart (SFC) are integrated into the corresponding stages based on their characteristics. In addition, the transformation rules between the IDEF0-3 and CTPN and between CTPN and SFC are also conducted for developing DECSs. The transformation rules provide a straightforward mapping from the IDEF0-3 to CTPN and from the CTPN to SFC. The result of the integrated IPS systematically leads to SFC for PLC implementation. Finally, a ball assorting system is given to illustrate how the integrated IPS approach is implemented for developing the DECSs.
The application of control theory into the domains of manufacturing, robotics, computer and communication networks, and so on, has led to the creation of a new discipline, known as discrete event systems (DES) [1,2].
Petri nets have been extensively applied for specification, design, verification, performance evaluation, and simulation of discrete event control systems (DECS). The usual way to verify the dynamic behaviour of DECS design is to employ a process-based model, which proves to be impractical in application because the process-based model does not usually fully correspond to the control programming behaviour. This paper proposes a sensor-based stage Petri net (SBSPN) to represent a programmable logic controller (PLC) stage logic diagram (LD) for discrete-event control design. The new technique is able to simplify the modelling process of the complex PLC program without considering the interlocking problem within the ladder diagram. An illustrated example is used to explore the new methodology. The proposed method contains the power and flexibility of the Petri net analysis prior to the PLC implementation. It is believed that this technique is significant for industry practice.
Petri nets have been extensively applied for specification, design, verification, performance evaluation, and simulation of discrete event control systems (DECS). This paper proposes a real-time stage Petri net (RTSPN), to represent the stage programming of a programmable logic controller (PLC) for DECS. The new technique is able to simplify the design process of the complex PLC program without considering the interlocking problem within the ladder diagram. An illustrated example is used to explore the new methodology. The proposed method contains the power and flexibility of the Petri net analysis. It is believed that this technique is significant for the industry practice.
Petri nets have been extensively applied for specification, design, verification, performance evaluation, and simulation of the DECS. A real-time Petri net is a further improvement over timed Petri net. It is aimed for both control and simulation of the system under study. This paper proposes to use a real-time Petri net to represent the stage programming of a programmable logic controller for a discrete-event control system. An illustrated example is used to explore the Petri net-based PLC stage programming methodology.
Modern manufacturing systems have challenged the use of LDs for
PLCs to design their discrete-event controllers. Researchers are
constantly pursuing integrated tools that eliminate the limitations of
LDs. These tools are aimed not only for control but also for system
analysis, evaluation, and simulation. For the past decades, Petri nets
(PNs) have emerged as an important tool to provide an integrated
solution for modeling, analysis, simulation, and control of industrial
automated systems Different types of PN-based controllers in academia
are intended for application in industry. There is a need for more
benchmark studies of PN and LD methods in order to form a structured and
integrated framework for logic control software development. The paper
surveys work on these methods with focus on the conversion methods
between PNs and LDs
For the past few decades, programmable logic controllers (PLCs)
using relay ladder logic (RLL) programming have been the workhorse for
controlling event-driven industrial automated systems. RLL proved to be
flexible compared to the hardwired RLL control implementation, due to
its feature of software implementation. As automated systems become more
complex, they also become more difficult to understand and maintain. It
takes tremendous effort to accommodate specification changes (which are
becoming frequent) to meet today's flexible automation needs. Several
methods are emerging to overcome the shortcomings of RLL. Petri nets
(PNs), initially proposed as a modeling tool, have been developed as
such a method. This paper adopts an industrial-scale system to compare
RLL and PN design methods so that the advantages of PN-like approaches
are fully recognized. The criteria are: (i) the understandability that
relates to the ability to evaluate the programmed logic, to verify its
correctness and to maintain the control system, and (ii) the flexibility
that relates to the easy modification of logic when the specification
changes. This network takes an existing industrial system, conducts
discrete event control designs by using both RLL programming and PN
methods, and performs a comparative study on them. Together with
previous comparison results using small-scale systems, the results of
this study support that PN-like advanced discrete event control design
methods are better than RLL in terms of the understandability and
flexibility of the resulting control design
Petri Nets and Grafcet
- david
David, R, and H. Alla, Petri Nets and Grajicef, Prentice Hall, New York, 1992.
GRAFCET and Petri Nets in Manufachuing Systems Intelligent Manufomring: Progrmnming Environments for Modeling, Simulation, and Control of Flexible Manufacturing Systems -A Petri Net Approach
- A Giua
- F Dicesare
Giua, A. and F. DiCesare, "GRAFCET and Petri Nets in Manufachuing Systems," Intelligent Manufomring: Progrmnming Environments for CIM, W.A. Gruver and J. Boudreaux (Eds.), Springer-Verlag, London, 1993, pp. 153-176. 3. 731011, M. C., and Venkatesh, IC, Modeling, Simulation, and Control of Flexible Manufacturing Systems -A Petri Net Approach. World Scientific Publishers, Singapore, 1998. Peng, S. S., and Zhou, M. C., "Sensor-Based Stage Petri Net Modeling of PLC Logic 4.
GRAFCET and Petri Nets in Manufacturing Systems
- A Giua
- F Icesare
- W A Gruver
- J Boudreaux