Integrating domain knowledge and large language models for automatic generation of function block-based PLC logic in maritime systems

Abstract

The growing complexity of shipboard automation and the expanding scale of IEC 61131-3 control logic have increased the demand for systematic engineering workflows. Traditional practices rely on manual interpretation of Function Design Specifications and expert-driven mapping of field I/O signals to vendor-specific Function Blocks (FBs), resulting in variability in logic quality and significant development effort. While recent advances in large language models (LLMs) have improved general code generation, existing approaches remain insufficient for industrial control systems because they overlook FB semantics, hardware constraints, and ship-specific structural relationships. This study presents a domain-aware framework that integrates LLMs with retrieval-augmented domain knowledge to automatically generate FB-based PLC logic for maritime systems. The framework embeds FB manuals and normalized I/O descriptions into vector stores and incorporates graph-based relational knowledge capturing FB selection rules, cooperation patterns, and symmetry and grouping structures in I/O configurations. Using these structured representations, the pipeline performs FB type selection, instance estimation, parameter assignment, and I/O mapping, after which a rule-based generator produces IEC 61131-3 compliant Structured Text to ensure syntactic and structural correctness. Experiments using control narratives, FB manuals, and I/O datasets from operational ship projects show that relational knowledge significantly improves planning accuracy, enhancing FB identification, instance estimation, and I/O mapping across model scales. The framework produces deployable FB-based logic without model fine-tuning, relying solely on in-context knowledge injection. These results demonstrate that domain-grounded LLM workflows can reduce engineering variability and provide a practical, scalable approach for automating control-logic development in maritime systems.