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Design and Implementation of a Real-Time Nonlinear Model Predictive Controller for a Lower Limb Exoskeleton with Input Saturation

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Iranian Journal of Science and Technology, Transactions of Electrical Engineering Aims and scope Submit manuscript

Abstract

In this paper, a nonlinear model predictive controller (NMPC) with input saturation is designed and modified for a rehabilitative exoskeleton for paraplegic individuals. An analytical solution for the NMPC optimization problem is obtained for small prediction horizons (\(N < 3\)). Additionally, an iterative solution for longer horizon problems (\(N \ge 3\)) is performed by employing the linear time-varying approach and using the active set method to include the constraints. Real-time guarantee for the implementation of both NMPC solutions is derived, and the robustness and stability of the closed-loop system are discussed. Finally, the proposed controller is successfully simulated and implemented on a real exoskeleton robot with 1 ms sampling time. The results show that the proposed controller is more effective than PID and adaptive fuzzy controllers.

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Acknowledgements

We would like to thank all members of the Ferdowsi University of Mashhad Robotics Lab for their kind participation and cooperation.

Funding

This research is supported by grant #101120 from the Ferdowsi University of Mashhad-Iran as well as grant #962297 from the National Institute for Medical Research Development of Iran. This research is also supported by the National Elites Foundation of Iran.

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Authors and Affiliations

  1. Department of Electrical Engineering, Center of Excellence on Soft Computing and Intelligent Information Processing, Ferdowsi University of Mashhad, Mashhad, 9177948974, Iran

    S. Mohammad Tahamipour Zarandi

  2. Department of Electrical Engineering, Ferdowsi University of Mashhad, Mashhad, 9177948974, Iran

    S. Kamal Hosseini Sani & Mohammad-G Farajzadeh-D

  3. Departments of Electrical Engineering and Computer Engineering, Center of Excellence on Soft Computing and Intelligent Information Processing, Ferdowsi University of Mashhad, Mashhad, 9177948974, Iran

    Mohammad Reza Akbarzadeh Tootoonchi

  4. Departments of Mechanical Engineering and Computer Engineering, Center of Excellence on Soft Computing and Intelligent Information Processing, Ferdowsi University of Mashhad, Mashhad, 9177948974, Iran

    Alireza Akbarzadeh Tootoonchi

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  1. S. Mohammad Tahamipour Zarandi
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  2. S. Kamal Hosseini Sani
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  3. Mohammad Reza Akbarzadeh Tootoonchi
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  5. Mohammad-G Farajzadeh-D
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Correspondence to S. Kamal Hosseini Sani.

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Tahamipour Zarandi, S., Hosseini Sani, S., Akbarzadeh Tootoonchi, M.R. et al. Design and Implementation of a Real-Time Nonlinear Model Predictive Controller for a Lower Limb Exoskeleton with Input Saturation. Iran J Sci Technol Trans Electr Eng 45, 309–320 (2021). https://doi.org/10.1007/s40998-020-00358-w

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  • DOI: https://doi.org/10.1007/s40998-020-00358-w

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