Robust adaptive control for robot manipulators using a combined method

The authors present a control scheme which combines a direct adaptive control (DAC) law with a variable structure adaptive control (VSAC) law for a nonlinear robot manipulator system. The DAC law assures asymptotical stability, while the VSAC law improves the transient behavior of the robot system. The combined method improves the transient behavior and robustness to external input disturbances and unmodeled dynamics and also overcomes the chattering problem which is the main drawback of the variable-structure method. The fact that a skew-symmetric matrix is not used in the control scheme increases its flexibility. Fast tracking convergence and robustness are confirmed by extensive computer simulations