RESUMO
A multi-axis gimbal tracking device is necessary for the micro spacecraft to detect the target. The movement of the tracking device can generate a marked impact on its carrier in the microgravity environment, which should be taken into account when high accuracy is required. The model of the micro spacecraft and the gimbal tracking device can be regarded as a multi-axis open-chain manipulator composed of rigid bodies and joints. Then the dynamics of the model is established by the twist-wrench formulation. A novel dual-loop integral-type fast terminal sliding mode control scheme is proposed to improve the attitude tracking performance of the micro spacecraft. The attitude dynamics of the micro spacecraft is decomposed into two parts, which are used to design controllers to track the angle and the dummy angular velocity signals, respectively. An adaptive disturbance observer is designed to estimate and compensate for the external disturbance. To maintain high positioning accuracy and restrict excessive control torque, a modified nonsingular fast terminal sliding mode controller is proposed for the gimbal tracking device. Accordingly, the proposed schemes have the advantages of nonsingularity, fast convergence, good robustness, and high tracking accuracy. The simulation results demonstrate the feasibility of the modeling method and the effectiveness of the control schemes.