Stability of Robust Lyapunov Based Control of Flexible-Joint Robots Using Voltage Control Strategy Revisited

Many advanced robot applications such as assembly and manufacturing require mechanical interaction of the robot manipulator with the environment. Any back-stepping based control strategy proposed for position control of electrical flexible joint robots requires a convergence of internal signals to its desired value called a fictitious control signal. This problem is complicated and time-consuming, whereas a 5th-order nonlinear differential equation describes each joint of the robot. The best idea is to focus on the convergence of main signals while the other signals in the system remain bounded. With this in mind, this paper present a robust Lyapunov-based controller for the flexible joint electrically driven robot (FJER) considering input nonlinearities associated with actuator constraints. It also finds uncertainties associated with robot dynamics. The proposed approach is based on a third-order model instead of a fifth-order model of the robotic system. The stability is guaranteed in the presence of both structured and unstructured uncertainties. The actuator/link position errors asymptotically converge to zero while the other signals are bounded. Simulation results on a 2-DOF electrical robot manipulator effectively verify the efficiency of the proposed strategy.