Two-stage sliding mode controller for bending mode suppression of a flexible pointing system

The performance of a flexible pointing system mounted on the top of a vehicle is greatly affected by the bending vibrations as the vehicle runs on a bumpy course. In order to improve the pointing accuracy, the pointing structure´s vibrations should be suppressed. In this paper, a nonlinear controller is designed to control the tip position of the pointing system while actively suppressing the vibrations. To cope with high order dynamics and nonlinearity of the plant and the hydraulic actuating system, a two-stage sliding mode controller is devised. The desired actuating pressure is obtained in the first stage and then the input current to the hydraulic servo system is computed to generate the pressure. The simulation results show the effectiveness of this scheme and improvements in pointing accuracy