Journal
IRANIAN JOURNAL OF SCIENCE AND TECHNOLOGY-TRANSACTIONS OF ELECTRICAL ENGINEERING
Volume 45, Issue 1, Pages 309-320Publisher
SPRINGER INT PUBL AG
DOI: 10.1007/s40998-020-00358-w
Keywords
Exoskeleton robot; Nonlinear model predictive control (NMPC); Linear time-varying (LTV) MPC; Real-time controller; Input saturation
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Funding
- Ferdowsi University of Mashhad-Iran [101120]
- National Institute for Medical Research Development of Iran [962297]
- National Elites Foundation of Iran
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A nonlinear model predictive controller (NMPC) with input saturation was designed and modified for a rehabilitative exoskeleton, with analytical solutions for small prediction horizons and an iterative solution for longer horizons. Real-time guarantees and successful implementation on a real exoskeleton robot demonstrated the effectiveness of the proposed controller over traditional controllers.
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 >= 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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