Vibration suppression for rotating space slender flexible structures based on novel deformation description and NNSMC controller with hyperbolic tangent function

Rotating Space Slender Flexible Structures (RSSFS) are extensively utilized in space operations because of their light weight, mobility, and low energy consumption. To realize the accurate space operation of the RSSFS, it is necessary to establish a precise mechanical model and develop a control algorithm with high precision. However, with the application of traditional control strategies, the RSSFS often suffers from the chattering phenomenon, which will aggravate structure vibration. In this paper, novel deformation description is put forward to balance modeling accuracy and computational efficiency of the RSSFS, which is better appropriate for real-time control. Besides, the Neural Network Sliding Mode Control (NNSMC) strategy modified by the hyperbolic tangent (tanh) function is put forward to compensate for modeling errors and reduce the chattering phenomenon, thereby improving the trajectory tracking accuracy of the RSSFS. Firstly, a mathematical model for the RSSFS is developed according to the novel deformation description and the vibration theory of flexible structure. Comparison of the deformation accuracy between different models proves that the novel modeling method proposed has high modeling accuracy. Next, the universal approximation property of the Radial Basis Function (RBF) neural network is put forward to determine and compensate for modeling errors, which consist of higher-order modes and the uncertainties of external disturbances. In addition, the tanh function is proposed as the reaching law in the conventional NNSMC strategy to suppress driving torque oscillation. The control law of modified NNSMC strategy and the adaptive law of weight coefficients are developed according to the Lyapunov theorem to guarantee the RSSFS stability. Finally, the simulation and physical experimental tests of the RSSFS with different control strategies are conducted. Experimental results show that the control law according to the novel deformation description and the modified NNSMC strategy can obtain accurate tracking of the rotation and reduce the vibration of the RSSFS simultaneously.