Journals / International Journal of 3D Printing Technologies and Digital Industry / 2025 / Cilt: 9 Sayı: 3

FORCE ESTIMATION IN SMART INSOLES USING RANDOMLY PLACED OPTICAL FIBER SENSORS AND MACHINE LEARNING

Ahmet Özek(PAMUKKALE ÜNİVERSİTESİ, MÜHENDİSLİK FAKÜLTESİ)0000-0002-0939-3547
Murat Ekici(DOKUZ EYLÜL ÜNİVERSİTESİ, EFES MESLEK YÜKSEKOKULU)0000-0002-8875-0775
Pages
569–578
Publication Date
2025-12-28
🏛️Bibliographic metadata and full text access for this article are provided via DergiPark.
DergiPark Record ↗
✨

AI Summary & Key Takeaways

AI Insight
⚡ TL;DR(Too Long; Didn't Read)

Results show that accurate force estimation is possible without anatomically precise sensor placement, reducing hardware complexity and cost while keeping performance suitable for gait analysis and wearable health applications.

📌 3 Key Takeaways

🎯
Objective & Hypothesis:This paper presents a smart insole that combines flexible TPU optical fiber sensors with force-sensitive resistors (FSRs) on a 3D-printed TPU base to estimate plantar forces during walking.
📊
Key Findings & Data:Signals were sampled and streamed via an ESP32 microcontroller over Bluetooth.
💡
Conclusion & Impact:Results show that accurate force estimation is possible without anatomically precise sensor placement, reducing hardware complexity and cost while keeping performance suitable for gait analysis and wearable health applications.
🔬Design:Modeling & Simulation
📍Scope:20 samples
⚙️Variables:Optical Sensor · TPU Optical Fiber · Machine learning

Abstract

This paper presents a smart insole that combines flexible TPU optical fiber sensors with force-sensitive resistors (FSRs) on a 3D-printed TPU base to estimate plantar forces during walking. Three thermoplastic polyurethane optical fibers, illuminated by red lasers and read by light-dependent resistors, were routed in a non-anatomical, irregular (‘random’) layout and compared against six FSR channels taken as reference targets. Signals were sampled and streamed via an ESP32 microcontroller over Bluetooth. Using a sliding-window approach (20 samples), simple statistical features from the three optical channels were used to train supervised regressors—Gradient Boosting, Adaptive Boosting, and a shallow artificial neural network—to predict each FSR output. Across sensors, models achieved R² between 0.865 and 0.951 and mean absolute error (MAE) between 29.0 and 48.9. Adaptive Boosting gave the lowest average MAE and stable R², while the artificial neural network reached the highest R² for several regions. Results show that accurate force estimation is possible without anatomically precise sensor placement, reducing hardware complexity and cost while keeping performance suitable for gait analysis and wearable health applications.

Özet

This paper presents a smart insole that combines flexible TPU optical fiber sensors with force-sensitive resistors (FSRs) on a 3D-printed TPU base to estimate plantar forces during walking. Three thermoplastic polyurethane optical fibers, illuminated by red lasers and read by light-dependent resistors, were routed in a non-anatomical, irregular (‘random’) layout and compared against six FSR channels taken as reference targets. Signals were sampled and streamed via an ESP32 microcontroller over Bluetooth. Using a sliding-window approach (20 samples), simple statistical features from the three optical channels were used to train supervised regressors—Gradient Boosting, Adaptive Boosting, and a shallow artificial neural network—to predict each FSR output. Across sensors, models achieved R² between 0.865 and 0.951 and mean absolute error (MAE) between 29.0 and 48.9. Adaptive Boosting gave the lowest average MAE and stable R², while the artificial neural network reached the highest R² for several regions. Results show that accurate force estimation is possible without anatomically precise sensor placement, reducing hardware complexity and cost while keeping performance suitable for gait analysis and wearable health applications.

🔖

Cite This Article

Öztürksoy, H., Özek, A., Ekici, M., Seçkin, A. Ç. (2025). FORCE ESTIMATION IN SMART INSOLES USING RANDOMLY PLACED OPTICAL FIBER SENSORS AND MACHINE LEARNING. International Journal of 3D Printing Technologies and Digital Industry, Cilt: 9 Sayı: 3, 569–578. https://doi.org/10.46519/ij3dptdi.1784332

📄 Full Text PDF Viewer

📄

PDF görüntüleyici hazırlanıyor...

References (15)

  1. Seçkin, A.Ç., Ateş, B., and Seçkin, M., ‘Review on Wearable Technology in Sports: Concepts, Challenges and Opportunities’, Applied Sciences, Vol. 13, Issue 18, Pages 10399, 2023.
  2. Dong, T., Wang, J., Chen, Y., Liu, L., You, H., and Li, T., ‘Research Progress on Flexible 3-D Force Sensors: A Review’, IEEE Sensors Journal, Vol. 24, Issue 10, Pages 15706–15726, 2024.
  3. Peng, S., Hassan, H., Rosseel, S., Matricali, G.A., Deschamps, K., Vandeginste, V., and Hallez, H., ‘Recent Advances in 3-D Printed, Wearable Pressure Sensors for Plantar Pressure Monitoring: A Review’, IEEE Sensors Journal, Vol. 24, Issue 21, Pages 33903–33921, 2024.
  4. Gan, J., Yang, A., Guo, Q., and Yang, Z., ‘Flexible Optical Fiber Sensing: Materials, Methodologies, and Applications’, Advanced Devices & Instrumentation, Vol. 5, Pages 0046, 2024.
  5. Leal-Junior, A.G., Diaz, C.A.R., Avellar, L.M., Pontes, M.J., Marques, C., and Frizera, A., ‘Polymer Optical Fiber Sensors in Healthcare Applications: A Comprehensive Review’, Sensors, Vol. 19, Issue 14, Pages 3156, 2019.
  6. Chuter, V.H., Spink, M.J., David, M., Lanting, S., and Searle, A., ‘Clinical foot measurements as a proxy for plantar pressure testing in people with diabetes’, Journal of Foot and Ankle Research, Vol. 14, Issue 1, Pages 56, 2021.
  7. Saha, D., Prabhu, S., Thapliyal, A., and Pai, M.M.M., ‘Analysis of Plantar Pressure to detect Foot Abnormalities among various subjects’, 2023 International Conference on Advances in Intelligent Computing and Applications (AICAPS), 2023 International Conference on Advances in Intelligent Computing and Applications (AICAPS), Pages 1–6, 2023.
  8. Castro-Martins, P., Marques, A., Coelho, L., Vaz, M., and Baptista, J.S., ‘In-shoe plantar pressure measurement technologies for the diabetic foot: A systematic review’, Heliyon, Vol. 10, Issue 9, 2024.
  9. Leal-Junior, A.G., Díaz, C.R., Marques, C., Pontes, M.J., and Frizera, A., ‘3D-printed POF insole: Development and applications of a low-cost, highly customizable device for plantar pressure and ground reaction forces monitoring’, Optics & Laser Technology, Vol. 116, Pages 256–264, 2019.
  10. Jo, J., and Park, H., ‘Fiber Optic-embedded Gait-Tracking Insole for Detection of Toe-Walking in Children with Autism Spectrum Disorder’, International Textile and Apparel Association Annual Conference Proceedings, 2022
  11. Noh, Y., Sareh, S., Würdemann, H., Liu, H., Back, J., Housden, J., Rhode, K., and Althoefer, K., ‘Three-Axis Fiber-Optic Body Force Sensor for Flexible Manipulators’, IEEE Sensors Journal, Vol. 16, Issue 6, Pages 1641–1651, 2016.
  12. Mondal, B., and Mandal, D., ‘Geometry-modulated all organic 3D printed smart PLA fibers for flextension amplified giant mechanical energy harvesting and Machine learning assisted pressure mapping’, Chemical Engineering Journal, Vol. 496, Pages 154281, 2024.
  13. Vilarinho, D., Theodosiou, A., Leitão, C., Leal-Junior, A.G., Domingues, M.D.F., Kalli, K., André, P., Antunes, P., and Marques, C., ‘POFBG-Embedded Cork Insole for Plantar Pressure Monitoring’, Sensors, Vol. 17, Issue 12, Pages 2924, 2017.
  14. Lakho, R.A., Yi-Fan, Z., Jin-Hua, J., Cheng-Yu, H., and Ahmed Abro, Z., ‘A smart insole for monitoring plantar pressure based on the fiber Bragg grating sensing technique’, Textile Research Journal, Vol. 89, Issue 17, Pages 3433–3446, 2019.
  15. Mun, F., and Choi, A., ‘Deep learning approach to estimate foot pressure distribution in walking with application for a cost-effective insole system’, Journal of NeuroEngineering and Rehabilitation, Vol. 19, Issue 1, Pages 4, 2022.