Adaptive fractional-order control of electrical flexible-joint robots: Theory and experiment

Real-time fractional-order control of electrically driven flexible-joint robots has been addressed in this article. An important contribution of this article is that the control law is designed based on the Fourier series that eliminates the need for computation of regressor matrix. Moreover, the nonlinear effects of actuator saturation are considered in the control law. The lumped uncertainty can be approximated using Fourier series with unknown coefficients. Then, the unknown coefficients are estimated using the adaptation law obtained in the stability analysis. The overall closed-loop system is proven to be robust and bounded-input bounded-output stable. In addition, it has been shown that the joint-position errors are uniformly bounded based on Lyapunov's stability concept. The satisfactory performance of the proposed control scheme is verified by experimental results. To highlight the superiority of the proposed method, experimental results of two voltage-based controllers are also presented.