Regulated sliding mode control of Space Free-Flying Robots

Energy consumption of control actuators is an important issue in space systems, due to considerable cost of transferring supplies to orbit. In this paper, a chattering avoidance sliding mode controller is developed for space free-flyer robots (SFFR) as highly nonlinear coupled systems. Chattering phenomenon results in significant energy dissipation and causes practical difficulties for actuators. 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. To this end, first a multi input sliding mode control law is applied to the given SFFR in order to control its orientation and position to catch a moving target. Next, focusing on the chattering phenomenon, the new approach is employed to alleviate the chattering trend. Then, the explicit dynamics of a 14-DOF SFFR is derived via SPACEMAPLE. To consider practical aspects, the system dynamics is modeled in the presence of parametric uncertainties, also deviations (noises) in measurements are considered. Besides, to evaluate the new proposed algorithm in a more complicated condition, it is assumed that for controlling the base of SFFR only on-off actuators, which can just generate a constant positive or negative force/moment, are available as it is the case in real systems. Therefore, the exact demanded force/moment can not be supplied on the base, which will affect control of the whole system. The obtained results show that the proposed regulated sliding mode controller can significantly alleviate the chattering trend, and consequently energy consumption will be substantially decreased