QSMC based on reaching law using saturation sliding surface for 6R industrial robots

Quasi Sliding Mode Control (QSMC) based on reaching law has the advantages of simplicity and robustness. The chattering is also reduced by using a saturation function. But this control strategy only guarantees an asymptotic convergence. In order to increase the tracking speed for robotic joints when tracking error is small, a sliding surface with saturation function of the error is proposed in this paper. By applying this sliding surface, a fast finite time convergence is achieved. 6R industrial robots have highly coupled inertia coefficients in the inertia matrix. When modeling error exists, system precision and stability would be affected greatly. To improve the system robustness property, separate sliding surface feedback compensation torques mainly for the last three joints are applied in this paper. The compensation torques also help increase the tracking speed. The proposed controller is tested through ADAMS-MATLAB co-simulations on a 6R serial industrial robot prototype to prove its effectiveness.