Research On Control System Of Two-axis Airborne Stabilized Platform For Multi-rotor UAV

To obtain high quality low-level remote sensing images,the airborne aerial photography equipment should be fixed on the high-precision stabilized platform.The stabilizing control technique is used to stabilize the attitude of the stabilized platform in inertial space to maintain the stability of the visual axis of the aerial photography equipment,and then to obtain stable and clear video images.To obtain stable,clear and low jitter images,designing an airborne stabilized platform with higher accuracy of stability,faster response,smaller overshoot has important theoretical and practical value.This paper is in three parts: 1)the developments of airborne stabilized platform and stability control techniques of stabilized platforms are reviewed;2)the mechanical structure,physical model and the disturbance source of the stabilized platform are introduced,and the mechanism of the stabilized platform is analyzed;3)focusing on the control of the stabilized platform,the attitude detection and the position servo control of the motor are studied.In this paper,MEMS inertial sensors are used to detect the attitude of the stabilized platform.To improve the accuracy of attitude calculation,the discrete Kalman algorithm is applied to the multi-sensor attitude fusion solution.Compared to the complementary filtering algorithm,the detection accuracy of the attitude detection module using the discrete Kalman filtering algorithm is improved.Brushless direct current motor(BLDCM)is chosen as the actuator for the stabilized platform in this paper.Firstly,applying field oriented control in the BLDCM position servo control system is to reduce the torque ripple.Secondly,the three closed-loop control structure of stabilized platform control system is analyzed,and the simulation model of the BLDCM position servo control system is built by using the SIMULINK toolbox in MATLAB software.Finally,the Logic Rule+PI control method for the three closed-loop control system is proposed to improve the dynamic performance of the system.The simulation results show that the system has the characteristics of small overshoot,high stability accuracy,and strong anti-disturbance when logic Rule+PI control is applied on the position loop of BLDCM position servo control system.Especially,the rise time of Logic Rule+PI control is only 53.8% of the conventional PID control,and its dynamic performance was better.To verify the above control methods,a two-axis stabilized platform experimental prototype is built.In the static experiments of stabilized platform attitude control,the overshoots of the two control methods are small,and the steady-state errors of the attitude angles of all axes are less than 0.15°.However,for the PID control method,the rise time of the pitch axis and roll axis of the stabilized platform using the Logic Rule+PI control are reduced by 13.4% and 11.5%,respectively.In the dynamic experiment,when the stabilized platform is controlled by PID,the maximum absolute errors of the attitude angles of the pitch and roll axes are less than 0.48°and 0.52°,respectively.When the Logic Rule+PI control method is applied,the maximum absolute errors of the attitude angles of the pitch axis and the roll axis are less than 0.40° and 0.43°,respectively.Therefore,the Logic Rule+PI control method improves the attitude control accuracy of the pitch and roll axes of the stabilized platform by 16.7% and 17.3%,respectively.The simulation experiments on the ground and the actual flying experiments show that the two-axis stabilized platform based on Logic Rules+PI control has a significant effect on enhancing stability.