Fractional order adaptive fuzzy terminal sliding mode controller design for a knee joint orthosis

Rehabilitation and assistive robots have drawn a large amount of interest, related to the increase of the elderly and the increase in diseases such as stroke and spinal cord injuries as well as the high cost of rehabilitation. In this paper, a fractional order adaptive fuzzy terminal sliding mode control is proposed for a knee joint orthosis. A model integrating the human lower-limb and orthosis based on the Lagrange equations is used. To overcome the uncertainties and external disturbances, a fractional order terminal sliding mode control is designed, then in order to remove the undesirable chattering phenomenon in control signal, a fractional order adaptive fuzzy controller is designed. To improve the precision and speed of tracking and to decrease the effect of the uncertainties in muscular torque modeling on the system control, a nonlinear disturbance observer is combined with fractional order terminal sliding mode control. The stability of closed loop system is proved by new fractional order extention of Lyapunov theorem. The PSO algorithm is used to determine the coefficients of the adaptive fuzzy terminal sliding mode control and the fuzzy membership functions. Finally, the performance of the proposed controller is compared with conventional sliding mode control and PID control.