Control of Space Free-Flying Robots Using Regulated Sliding Mode Controller

In this paper, considering space free-flyer robots as highly nonlinear coupled systems, a chattering avoidance sliding mode controller is developed with confined computational burden for online implementations. A regulating routine is proposed to determine proper positive values for the coefficient of sliding condition. In addition, to reduce the computational cost for online applications, an explicit direct relationship between the SFFR´s actuators (force/torque) demands and measurement of distances from the corresponding sliding surfaces is proposed. Then this model is optimally parameterized using prediction error method (PEM). Also, to achieve an acceptable performance, the parameters are estimated recursively using Kalman filter as a parameter estimator. To this end, first an explicit dynamics model of a 14-DOF SFFR is derived via SPACEMAPLE where recursive PEM method is used for parameterization of the SFFR model. Then, based on the estimated dynamics, a multi input sliding mode control law is applied to the given SFFR to catch a moving target. 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 are available, which can just generate a constant positive or negative force/torque. The obtained results show that the proposed regulated sliding mode controller can significantly alleviate the chattering trend, and consequently energy consumption is substantially decreased as well as reduced computational burden with reasonable running time duration for online implementations