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Unambiguous Interpretation of IEC 60848 GRAFCET based on a Literature Review

Robin Mroß, Aron Schnakenbeck, Marcus Völker, Alexander Fay, Stefan Kowalewski

TL;DR

The paper tackles the problem of unambiguous interpretation of IEC 60848 GRAFCET, which is hampered by its semiformal nature and divergent literature.It conducts a comprehensive literature review to identify ambiguities across evolution rules, events, structuring, macro-steps, forcing orders, enclosures, and time/determinism, and synthesizes these into a consolidated interpretation framework.A concrete interpretation algorithm is then proposed, leveraging initial activation, variable copying for simultaneous updates, hierarchical processing, and preemptive handling of forcing and enclosures to resolve conflicts and ensure deterministic behavior.The study provides a practical pathway for consistent model-driven development and verification of Grafcet-based control, while acknowledging residual ambiguities and the need for careful tool support, funded in part by the Deutsche Forschungsgemeinschaft.Overall, the work bridges literature-based insights with a implementable algorithm to align Grafcet interpretations with the latest standard.

Abstract

IEC 60848 GRAFCET is a standardized, graphical specification language for control functions. Because of the semiformal nature of IEC 60848, the details of specifications created with GRAFCET can be interpreted in different ways, possibly leading to faulty implementations. These ambiguities have been partially addressed in existing literature, but solved in different manners. Based on a literature review, this work aims at providing an overview of existing interpretations and, based on that, proposes a comprehensive interpretation algorithm for IEC 60848, which takes all relevant ambiguities from the literature review into account.

Unambiguous Interpretation of IEC 60848 GRAFCET based on a Literature Review

TL;DR

The paper tackles the problem of unambiguous interpretation of IEC 60848 GRAFCET, which is hampered by its semiformal nature and divergent literature.It conducts a comprehensive literature review to identify ambiguities across evolution rules, events, structuring, macro-steps, forcing orders, enclosures, and time/determinism, and synthesizes these into a consolidated interpretation framework.A concrete interpretation algorithm is then proposed, leveraging initial activation, variable copying for simultaneous updates, hierarchical processing, and preemptive handling of forcing and enclosures to resolve conflicts and ensure deterministic behavior.The study provides a practical pathway for consistent model-driven development and verification of Grafcet-based control, while acknowledging residual ambiguities and the need for careful tool support, funded in part by the Deutsche Forschungsgemeinschaft.Overall, the work bridges literature-based insights with a implementable algorithm to align Grafcet interpretations with the latest standard.

Abstract

IEC 60848 GRAFCET is a standardized, graphical specification language for control functions. Because of the semiformal nature of IEC 60848, the details of specifications created with GRAFCET can be interpreted in different ways, possibly leading to faulty implementations. These ambiguities have been partially addressed in existing literature, but solved in different manners. Based on a literature review, this work aims at providing an overview of existing interpretations and, based on that, proposes a comprehensive interpretation algorithm for IEC 60848, which takes all relevant ambiguities from the literature review into account.
Paper Structure (12 sections, 11 figures, 2 algorithms)

This paper contains 12 sections, 11 figures, 2 algorithms.

Table of Contents

  1. Introduction
  2. Methodical approach
  3. Results of the literature review and discussion of ambiguities
  4. Evolution rules and actions
  5. Events
  6. Structuring of GRAFCET
  7. Macro-steps
  8. Forcing orders
  9. Enclosing steps
  10. Remarks regarding synchronicity, determinism and algebraic notations
  11. Interpretation of ambiguities
  12. Conclusion

Figures (11)

  • Figure 1: Methodical approach of the literature review.
  • Figure 2: Example of a read-write conflict in the context of evolution rule four.
  • Figure 3: Example Grafcet with a transition condition depending on an input event $\mathbin{\uparrow}a$ and on an internal event $\mathbin{\uparrow}y$, where the former triggers the latter.
  • Figure 4: A Grafcet containing an action on event and a transition, both having possibly contradicting conditions depending on rising/falling edges of the step activity variable $X2$.
  • Figure 5: A partial Grafcets $G1$, $G2$, with ambiguous behavior regarding $G1$ forcing $G2$ into its current situation (adapted from Azevedo.99).
  • ...and 6 more figures