Nonlinear PID control of electrical flexible joint robots-Theory and experimental verification

Almost, any back-stepping based control strategy proposed for position control of flexible joint electrically driven robots (FJEDR) require convergence of internal signals to its desired value called as fictitious control signal. This problem is complicated and time consuming, whereas each joint of the robot is described by a 5th-order differential equation. The best idea is that we focus on the convergence of main signal, while the other signals remain bounded, which in turns reduce the control law dimension and its implementation costs. Robust tracking control of electrically flexible joint robots has been addressed in this paper. The proposed approach is related to the key role of electrical subsystem of the actuators. Thus, it is free from mechanical subsystem of the motor dynamics, considered here as unmodeled dynamics. It is proved that the actuator/link position errors are Uniformly-Ultimately Bounded (UUB) stable in agreement with Lyapunov's direct method in any finite region of the state space while other signals remain bounded. The analytical studies as well as experimental results produced using MATLAB/SIMULINK external mode control on a flexible-joint electrically driven robot demonstrate high performance of the proposed control scheme.