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1 2010

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Formal modelling of IEC 61499 function blocks with integer-valued data types

Gerber C., Ivanova-Vasileva I., Hanisch H. M.

Control and Cybernetics

2010

Vol. 39, no 1

197-231

During the last couple of years a lot of component- or object-oriented approaches have been presented to ease the implementation and reconfiguration of distributed control systems. Using these frameworks, the structure of the control objects follows the configuration of the mechanical components, and each object is instantiated as often as the corresponding device occurs in a plant. Having an object library, a control engineer will glue objects together, which means, in the context of the IEC 61499, connecting function blocks by event and data connections. This rapid way of implementation and reconfiguration makes also high demands on the verification process, which has to be done after each change. This means that the model of the plant has to be updated and the model of the distributed controllers have to be automatically generated to connect both in a closed loop. Both formal models should be modular to manage even large systems. Furthermore, the controller must be able to interact with the plant not only via Boolean data but via integer-valued data as well. Thus, the existing verification approaches have to be extended and an execution and a data processing model defined. The execution model includes the function block interface and the Execution Control Chart as well as their interconnections. For the arithmetical operations of adding and subtracting as well as the comparison of Boolean and integer-valued data it is shown how the data processing inside the function blocks has to be transformed to the formal model. Consequently, rules are defined for the transformation of the execution and data processing of function blocks with Boolean and integer-valued data. Due to the proposed separation, the resulting data processing model is not limited to IEC 61499 Basic Function Blocks. As formal model, Net Condition/Event modules (NCEM) and structures are used. Modelling of the plant and the analysis of the resulting closed-loop behaviour are presented using a small, but realistic manufacturing system.