Adaptive Fractional-Order Fast-Terminal-Type Sliding Mode Control For Nonlinear Robotic Manipulators

Abstract

An adaptive fractional-order fast-terminal-type sliding mode control (AFO-FTSMC) method is presented to improve the response characteristics of robotic manipulators and reduce uncertainty. This method employs a fractional-order sliding mode (FO-SM) manifold and a fast-terminal-type reaching law to achieve precise tracking, fast response speed, and chatterfree control inputs. The FO-SM manifold contains fractionalorder differential and fractional-order integral terms, which avoids deterioration in tracking accuracy when the system state reaches the sliding manifold. The fast-terminal-type reaching law ensures fast reaching speed and effective chatter suppression. The designed adaptive law realizes an immediate response to tracking error, avoids excessive high or low switching gain, and effectively enhances the robustness against lumped uncertainties by adjusting the switching gain of the SMC online. Therefore, the AFO-FTSMC control method, which combines the respective advantages of adaptive law and FOSMC, can significantly improve the control performance of conventional SMC and has strong robustness to uncertain disturbances. The AFO-FTSMC is also proved to be stable using the Lyapunov method. Finally, both simulation and experiments verify the effectiveness and superiorities of the AFO-FTSMC control scheme.