Iterative Learning Control for Lower Limb Exoskeleton Robot for Rehabilitation

Abstract:

Lower limb exoskeletons assist individuals with mobility impairments by providing support and aiding rehabilitation. However, precise trajectory tracking remains a challenge due to variations in user movement and nonlinear gait dynamics. Traditional control methods, such as PID controllers, require continuous tuning and struggle with long-term adaptability. This study proposes a PID-based Iterative Learning Control (PID-ILC) approach for a 2-DOF lower limb exoskeleton, which refines control inputs over successive gait cycles to improve tracking accuracy. MATLAB simulations demonstrate that the PID-ILC strategy significantly reduces tracking errors over iterations, leading to smoother and more accurate joint movements. The results confirm that iterative learning enhances exoskeleton performance by improving motion precision and adaptability. This approach minimizes manual tuning efforts and provides a more effective solution for rehabilitation applications.

• Periodical: Applied Mechanics and Materials (Volume 928)
• Pages: 61-69
• DOI: https://doi.org/10.4028/p-HcVj6a
• Online since: November 2025
• Authors: Saud Ahmed Khan*, Muhammad Arsalan, Syed Salman Shah, Abid Imran
• Keywords: Gait Rehabilitation, Iterative Learning Control (ILC), Lower Limb Exoskeleton, PID Control, Trajectory Tracking

References

[1] J. O. Pedro and R. V Smith, "Real-time hybrid PID/ILC control of two-link flexible manipulators," IFAC-PapersOnLine, vol. 50, no. 2, p.145–150, 2017.

DOI: 10.1016/j.ifacol.2017.12.027

[2] R. A. M. O. Emara, "Artificial Intelligence Based Controller for a Temperature Control System," Faculty of Engineering, The British University in Egypt, 2024.

[3] A. H. Radhi Mohamed, H. A. Mohamed Abdulla, A. M. Alkhazzaz, M. Arsalan, and S. G. Khan, "Design and Manufacturing of a Walk Assist Device," in 2024 19th International Conference on Emerging Technologies (ICET), 2024, p.1–6.

DOI: 10.1109/ICET63392.2024.10935241

[4] M. N. Alsheikh, "Intelligent control and Sensing Interfaces for a Complaint Knee Exoskeleton toward Enhanced Human-Robot Interaction Dynamics," Khalifa University of Science, 2024.

[5] P. Rangan R and R. Babu S, "Exo skeleton pertinence and control techniques: A state-of-the-art review," Proc. Inst. Mech. Eng. Part C J. Mech. Eng. Sci., vol. 238, no. 14, p.6751–6782, 2024.

DOI: 10.1177/09544062241226842

[6] D. M. Mahfouz, O. M. Shehata, E. I. Morgan, and F. Arrichiello, "A Comprehensive Review of Control Challenges and Methods in End-Effector Upper-Limb Rehabilitation Robots.," Robotics, vol. 13, no. 12, 2024.

DOI: 10.3390/robotics13120181

[7] Q. Zhang, M. Gong, S. Yu, and H. Sun, "Design and Application of Artificial Intelligence-Based Sports Rehabilitation Robot Auxiliary System," in 2024 5th International Conference on Information Science, Parallel and Distributed Systems (ISPDS), 2024, p.722–728.

DOI: 10.1109/ispds62779.2024.10667545

[8] M. Saad, R. N. Enam, and R. Qureshi, "Optimizing multi-objective task scheduling in fog computing with GA-PSO algorithm for big data application," Front. big Data, vol. 7, p.1358486, 2024.

DOI: 10.3389/fdata.2024.1358486

[9] X. Lu, X. Chen, Y. Bai, and R. Liu, "Explicit model based fuzzy control method for lower limb exoskeleton robot," Expert Syst. Appl., vol. 270, p.126601, 2025.

DOI: 10.1016/j.eswa.2025.126601

[10] S. H. Shah, M. S. Alam, M. Arsalan, I. ul Haq, S. G. Khan, and J. Iqbal, "Design and Adaptive Compliance Control of a Wearable Walk Assist Device," in 2023 International Conference on Robotics and Automation in Industry (ICRAI), 2023, p.1–7.

DOI: 10.1109/icrai57502.2023.10089580

[11] M. Arsalan, M. Tufail, S. G. Khan, and S. H. Shah, "Adaptive Learning Inertia Control of Lower Limb Exoskeleton Robot.," in 2021 International Conference on Robotics and Automation in Industry (ICRAI), 2021, p.1–6.

DOI: 10.1109/icrai54018.2021.9651394

[12] S. H. Shah, M. Arsalan, S. G. Khan, M. T. Khan, and M. S. Alam, "Design and compliance control of a robotic gripper for orange harvesting," Proc. - 22nd Int. Multitopic Conf. INMIC 2019, p.1–5, 2019.

DOI: 10.1109/INMIC48123.2019.9022758

[13] M. Arsalan, S. ur Rehaman, M. Umair, A. Imran, and G. Iqbal, "Feedback Linearization Control of Lower Limb Exoskeleton Robot for Rehabilitation," in MATEC Web of Conferences, 2023, p.1016.

DOI: 10.1051/matecconf/202338101016

[14] S. Masroor, M. Arsalan, S. G. Khan, S. H. Shah, M. S. Alam, and A. Imran, "Design and Control of a Bionic Leg," in 2023 International Multi-disciplinary Conference in Emerging Research Trends (IMCERT), 2023, p.1–6.

DOI: 10.1109/imcert57083.2023.10075334

[15] S. S. Shah, M. Akif, M. Arsalan, S. H. Shah, T. Hassan, and A. Imran, "Modeling and Control of Two Degree of Freedom Bionic Foot," in MATEC Web of Conferences, 2024, p.1006.

DOI: 10.1051/matecconf/202439801006

[16] L. Song, C. Ju, H. Cui, Y. Qu, X. Xu, and C. Chen, "Research on Control Strategy Technology of Upper Limb Exoskeleton Robots: Review," Machines, vol. 13, no. 3, 2025.

DOI: 10.3390/machines13030207