On Formal Methods in Development of Control Logic Using IEC 61499

Doktorsavhandling, 2009

In the present global economy the manufacturing industry is faced with the challenges that need to be overcome in order to remain competitive and avoid outsourcing. One of the challenges is the efficient development of the control logic for the distributed control systems that are often used to control the manufacturing equipment in the industry. Formal methods are mathematical frameworks that might be useful for overcoming that challenge. The control logic is often developed using the IEC 61131 standard that is focused on programming languages for non-distributed control systems. However, the new IEC 61499 standard provides the communication support as well as the programming units, i.e. function blocks, that are aimed at the control logic development for the distributed control systems. In the thesis, it is shown that the unclear specification of the function block scheduling order in the IEC 61499 might result in the control logic not being portable across IEC 61499 implementations. Therefore, the block scheduling order has to be considered during the control logic development. As a consequence, the developers might lose the focus on the high-level control logic that may result in the time-consuming development. The thesis presents contributions that may help the automatic formal model generation of the IEC 61499 control logic, assuming different block scheduling orders. The generated formal models may be used for verification of the control logic behavior using the algorithms of the framework called supervisory control theory (SCT). A synthesis algorithm from the SCT is used in the thesis for calculation of all deadlock free block scheduling orders from the automatically generated formal models. The contributions may help developers to concentrate on the high-level control logic since they may be able to use the formal methods to reduce the possible impact that the block scheduling orders, used in different IEC 61499 implementations, might have on the correctness of their control logic. Therefore, the developers may receive some benefits of the formal methods for the efficient development of the IEC 61499 control logic for the distributed control systems.