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Autonomously Detecting Defects in Circular Production Using Multimodal Large Language Models and Retrieval Augmentation

Dominik Koch, Marvin Ohland, Di Wen, Kunyu Peng, Martin Benfer, Rainer Stiefelhagen, Gisela Lanza

Repository KITopen (Karlsruhe Institute of Technology), 2026

Abstract

Automated defect detection is a key enabler for scalable inspection in circular production, where varying component conditions and the scarcity of large-scale annotated datasets challenge conventional supervised vision models. This paper investigates whether multimodal large language models (MLLMs) can serve as a flexible alternative for industrial defect detection without task specific training. To bridge the domain gap of general-purpose models, several retrieval-augmented generation (RAG) architectures are designed to leverage ex pert-defined examples for visual defect detection on used gears in a circular pro duction context. The study compares baseline prompting with text-based, image based, and self-reflective retrieval strategies that dynamically provide context relevant examples and descriptions during inference. The results show that MLLMs already achieve good defect detection accuracy out-of-the-box. Integrat ing RAG increases defect detection accuracy to 95.83% and further improves fine-grained defect classification, with gains of up to 63.94% for specific rare defect types. While the models remain weaker in precise localization and still lack deeper object-level understanding, the results indicate that RAG-enhanced MLLMs are a viable, low-barrier solution for inspection tasks in remanufacturing scenarios with limited expert supervision and diverse object classes. These find ings establish a reproducible benchmark for RAG-augmented VLMs in defect classification…

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