Fractional-Order Ultra-Local Model-Based Optimal Model-Free Control for 7-DOF iReHave Upper-Limb Exoskeleton

This brief proposes a fractional-order
ultra-local model
-based optimal model-free control (FO-OMFC) for trajectory tracking of 7-DOF iReHave upper-limb exoskeleton. This scheme is composed of fractional-order model-free controller (FO-MFC) and marine predators algorithm (MPA)-based parameter optimizer. Different from the existing model-free control, FO-MFC is designed based on a novel fractional-order
ultra-local model
. Then, the FO-MFC incorporates fractional-order time-delay estimation (FOTDE) as well as fractional-order error convergence controller (FOECC). The referred FOTDE is used to eliminate the lumped disturbance of the controlled exoskeleton. And the FOECC guarantees the convergence of the exoskeleton’s trajectory tracking error. After that, the stability of closed-loop system is demonstrated by using Lyapunov theorem. Moreover, to obtain better control performance, the MPA is employed to search for optimal parameters of the FO-MFC. Finally, the co-simulation of iReHave exoskeleton based on SolidWorks and MATLAB is realized, and the results compared with other controllers and results under measurement noise are given to show the effectiveness and superiority of the proposed strategy.