Systematic Logic Controller Design as Sequential Function Chart Starting from Informal Requirements

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In processing as well as in manufacturing plants, a large part of the automation software consists of logic control functions which supervise and coordinate local controllers, establish sequential procedures, and enable improved production flexibility. Dependability in the sense of reliability, availability, maintainability and safety of an automation system is a decisive factor for the economic success, operability and product quality of industrial production processes. The design of logic controllers (LC) does in common practice not follow a systematic design process based on precisely defined formats - rather informal requirements are translated manually into commonly used programming languages (IEC 61131-3), The disadvantages of this procedure are that specific design decisions are only insufficiently documented, the design process is inherently error-prone, the correlation between a requirement and the respective piece of logic control code is often not made explicit, the validation of the design is difficult, and subsequent modifications are time consuming and costly. In this work, a methodology for logic controller design as Sequential Function Chan (SFC) is presented starting from natural-language requirements which are often incomplete and ambiguous. The two-part design format is used for a stepwise iterative design process to specify the LC hierarchically. The design decisions are documented in the process preserving a link between the design decision and the respective requirement. The design process is a refinement scheme which develops step-by-step the formal specifications from the informal requirements. The control code as SFC is generated algorithmically from the specifications. In this work, a methodology for logic controller design as Sequential Function Chan (SFC) is presented starting from natural-language requirements which are often incomplete and ambiguous. The two-part design format is used for a stepwise iterative design process to specify the LC hierarchically. The design decisions are documented in the process preserving a link between the design decision and the respective requirement. The design process is a refinement scheme which develops step-by-step the formal specifications from the informal requirements. The control code as SFC is generated algorithmically from the specifications.