Regulated Sliding Mode Control of Robotic Manipulators

Chattering elimination of control actuators is an important issue in robotic systems, due to the damages caused by this phenomenon. Although the sliding mode controller usually results in an acceptable performance especially in the presence of modeling uncertainties and system’s nonlinearities, but it may lead to chattering phenomenon which in turn causes damages besides significant energy dissipation. In this paper, in order to fulfill stability requirements, robustness properties and chattering elimination, a regulating routine is proposed to determine proper positive values for the coefficient of sliding condition. The main idea of developing this new method is to keep the state of the system close to the nominal (desired) value near the sliding surface. So the coefficient of sliding condition is tuned by a function of distance from sliding surface. To this end, first a multi input sliding mode control law is applied to a given manipulator in order to control its end-effector position. Next, focusing on the chattering phenomenon that is of main concern in implementation of Sliding Mode Control (SMC), the aforementioned new approach is proposed to alleviate (ideally eliminate) the chattering trend. The developed control law is applied on a SCARA manipulator during a planar motion. To consider practical aspects, the system dynamics is modeled in the presence of parametric uncertainties. The simulation results show that the amplitude of chattering motion is significantly reduced, also energy consumption substantially decreases which reveals the merits of the developed control law.