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Automated assembly quality inspection by deep learning with 2D and 3D synthetic CAD data
KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Robotics, Perception and Learning, RPL. Scania CV AB (publ), 151 87, Södertälje, Sweden; KTH Royal Institute of Technology, 100 44, Stockholm, Sweden.ORCID iD: 0000-0002-4180-3809
Scania CV AB (publ), 151 87, Södertälje, Sweden.
University of Skövde, 541 28, Skövde, Sweden.
KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Robotics, Perception and Learning, RPL.ORCID iD: 0000-0003-0579-3372
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2025 (English)In: Journal of Intelligent Manufacturing, ISSN 0956-5515, E-ISSN 1572-8145, Vol. 36, no 4, p. 2567-2582, article id e222Article in journal (Refereed) Published
Abstract [en]

In the manufacturing industry, automatic quality inspections can lead to improved product quality and productivity. Deep learning-based computer vision technologies, with their superior performance in many applications, can be a possible solution for automatic quality inspections. However, collecting a large amount of annotated training data for deep learning is expensive and time-consuming, especially for processes involving various products and human activities such as assembly. To address this challenge, we propose a method for automated assembly quality inspection using synthetic data generated from computer-aided design (CAD) models. The method involves two steps: automatic data generation and model implementation. In the first step, we generate synthetic data in two formats: two-dimensional (2D) images and three-dimensional (3D) point clouds. In the second step, we apply different state-of-the-art deep learning approaches to the data for quality inspection, including unsupervised domain adaptation, i.e., a method of adapting models across different data distributions, and transfer learning, which transfers knowledge between related tasks. We evaluate the methods in a case study of pedal car front-wheel assembly quality inspection to identify the possible optimal approach for assembly quality inspection. Our results show that the method using Transfer Learning on 2D synthetic images achieves superior performance compared with others. Specifically, it attained 95% accuracy through fine-tuning with only five annotated real images per class. With promising results, our method may be suggested for other similar quality inspection use cases. By utilizing synthetic CAD data, our method reduces the need for manual data collection and annotation. Furthermore, our method performs well on test data with different backgrounds, making it suitable for different manufacturing environments.

Place, publisher, year, edition, pages
Springer Nature , 2025. Vol. 36, no 4, p. 2567-2582, article id e222
Keywords [en]
Assembly quality inspection, Computer vision, Point cloud, Synthetic data, Transfer learning, Unsupervised domain adaptation
National Category
Computer Sciences Production Engineering, Human Work Science and Ergonomics
Identifiers
URN: urn:nbn:se:kth:diva-363099DOI: 10.1007/s10845-024-02375-6ISI: 001205028300001Scopus ID: 2-s2.0-105002924620OAI: oai:DiVA.org:kth-363099DiVA, id: diva2:1956348
Note

QC 20250506

Available from: 2025-05-06 Created: 2025-05-06 Last updated: 2025-11-12Bibliographically approved
In thesis
1. Towards Automated Parts Recognition in Manufacturing with Synthetic Data
Open this publication in new window or tab >>Towards Automated Parts Recognition in Manufacturing with Synthetic Data
2025 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis advances the understanding and application of synthetic data for manufacturing parts recognition. Vision-based inspection systems in manufacturing rely heavily on real image data, which are costly to collect, annotate, and adapt across products and environments. To address these challenges, this work presents a systematic investigation of how synthetic data can be effectively generated, evaluated, and applied for robust and scalable performance. The research introduces a series of new industrial benchmark datasets covering multiple manufacturing use cases and factory environments: SIP-17, SIP15-OD, and SIP2A-OD, to enable unified evaluation of sim-to-real transfer in classification and detection tasks. Building on these datasets, a domain randomization pipeline is developed to systematically explore the effects of rendering parameters, material variability, and illumination on model generalization. To further automate data generation, the thesis proposes Synthetic Active Learning (SAL), a closed-loop framework that identifies model weaknesses and adaptively refines synthetic data generation without requiring real samples or manual tuning. Experiments across the benchmark datasets show that the proposed method improves model robustness compared to existing approaches while reducing manual labeling requirements. Collectively, these contributions provide new insights into how synthetic data can be systematically leveraged to build data-efficient, automated, and reliable vision systems for manufacturing, aiming to support future development of intelligent and flexible production systems.

Abstract [sv]

 Denna avhandling bidrar till förståelsen och tillämpningen av syntetisk data för igenkänning av tillverkningskomponenter. Visionsbaserade inspektionssystem inom industrin är starkt beroende av verkliga bilddata, vilka är kostsamma att samla in, annotera och anpassa mellan olika produkter och miljöer. För att hantera dessa utmaningar presenterar arbetet en systematisk undersökning av hur syntetisk data effektivt kan genereras, utvärderas och tillämpas för robust och skalbar prestanda. Forskningen introducerar en serie nya industriella benchmark-datamängder som täcker flera användningsfall och fabriksmiljöer: SIP-17, SIP15-OD ochSIP2A-OD, för att möjliggöra en enhetlig utvärdering av sim-to-real-överföring inom klassificerings- och detektionsuppgifter. Med utgångspunkt i dessa datamängder utvecklas en domain randomizationpipeline som systematiskt undersöker effekterna av renderingsparametrar, materialvariation och belysning på modellens generaliseringsförmåga. För att ytterligare automatisera datagenereringen föreslås Synthetic Active Learning (SAL), ett slutet ramverk som identifierar modellens svagheter och adaptivt förfinar den syntetiska datagenereringen utan att kräva verkliga prover eller manuell justering. Experiment över benchmark-datamängderna visar att de föreslagna metoderna förbättrar modellens robusthet jämfört med befintliga tillvägagångssätt, samtidigt som behovet av manuell annotering minskar. Sammantaget ger dessa bidrag nya insikter i hur syntetisk data systematiskt kan utnyttjas för att bygga dataeffektiva, automatiserade och tillförlitliga visionssystem för tillverkningsindustrin, med målet att stödja utvecklingen av framtida intelligenta och flexibla produktionssystem.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2025. p. xix, 75
Series
TRITA-EECS-AVL ; 2025:105
Keywords
Synthetic Data, Sim-to-real Transfer, Object Detection, Domain Randomization, Ac tive Learning, Dataset Generation, Automation, Computer Vision, Industrial Inspec tion, Syntetisk Data, Sim-to-real-överföring, Objektigenkänning, Domain Randomization, Aktivt Lärande, Datagenerering, Automation, Datorseende, Industriell Inspektion
National Category
Computer Sciences
Identifiers
urn:nbn:se:kth:diva-372644 (URN)978-91-8106-466-7 (ISBN)
Public defence
2025-12-09, https://kth-se.zoom.us/j/62913476523, Kollegiesalen, Brinellvägen 8, Stockholm, 13:00 (English)
Opponent
Supervisors
Funder
Wallenberg AI, Autonomous Systems and Software Program (WASP)
Note

QC 20251112

Available from: 2025-11-12 Created: 2025-11-11 Last updated: 2025-11-24Bibliographically approved

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Zhu, XiaomengBjörkman, MårtenMaki, Atsuto

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