A Finite -Time Robust Control for a Manipulator with Output Constraints and Unknown Control Directions

This paper presents a finite time robust control for a robotic manipulator regardless of the time-varying output constraints and unknown control direction. First, a transformation technique is investigated to handle the output constraints by converting a constrained system into a free constrained system. When the stability of the free constrained system is guaranteed, the constrained system will overcome the violation of system output. Next, the backstepping control is developed on the unconstrained system with fractional order term to improve the accuracy and transient time of the output responses. Furthermore, a Nussbaum gain function is integrated into the control algorithm to address the problem of unknown control direction. A numerical simulation is provided to confirm the superiorities of the proposed control.