Research On Key Technologies Of Agricultural UAV Gimbal

Recently,the combination of unmanned aerial vehicle(UAV)low-altitude remote sensing technology and traditional monitoring techniques has promoted the development of China’s agricultural production towards better aviation,informazation and precision.The research on UAV-related techniques is booming,which has become the engine of high-speed and high-quality development of agriculture and accelerated the transition from traditional agriculture to modern agriculture in China.The UAV gimbal used for installing sensors directly affects the measurement accuracy,but the current UAV gimbal has poor versatility and can not meet the needs of carrying multiple sensor devices simultaneously in agricultural remote sensing operations.This article develops a UAV gimbal system for RGB camera and multi-spectral camera to ensure the stability of camera equipment during operation and thus improve the imaging quality.The main research contents of this article include the following four aspects:(1)The parameters and mechanical structure design of agricultural UAV gimbal system are completed.According to the working mode of UAV gimbal and the characteristics of equipment installed,the main performance parameters of the UAV gimbal and the selection of main components are determined,and the frame structure,shock absorption system and overall control system of UAV gimbal are also designed.According to the structural characteristics and performance requirements of the UAV gimbal,the processing materials of UAV gimbal are selected and the design of key components(like the pitch axis,roll axis and gimbal connection plate)are completed.The three-dimensional modeling of all components and interference inspection are also completed by Solid Works software.(2)The static analysis,topology optimization and modal analysis of the UAV gimbal are conducted based on the finite element method.A static analysis on the pitch axis,roll axis and platform connection plate of the UAV gimbal is carried out using the ANSYS Workbench finite element analysis software.The results show that the maximum equivalent stress of each component is less than the allowable stress of the material and the maximum deformation meets the strength and rigidity requirements of the UAV gimbal design.The topology optimization analysis of the gimbal connection plate is completed and the optimized scheme of gimbal connection structure is given.The results show that the weight of the UAV gimbal is reduced by51.8 % while the strength and rigidity requirements are met.In addition,the modal analysis of the gimbal system has been carried out,and the results show that the 1-6th natural frequencies are all above 60 Hz,which is higher than the UAV vibration frequency.Thus,the gimbal will not resonate with the UAV,verifying the rationality and reliability of the design of the gimbal structure.Finally,the mechanical processing and assembly of the gimbal prototype are complete.(3)The design of the control algorithm of UAV gimbal is completed.Based on the structure of the two-axis,a mathematical model of the UAV gimbal control system is established to obtain the transfer function models of the pitch channel and roll channel.Based on the classic PID control algorithm,the variable structure PID control algorithm is introduced to resist various interferences,which can change the structure and parameters of the PID controller in real time according to the changing errors.The algorithm is verified by Simulink,which shows that the system with variable structure PID control has a faster response speed,a smaller speed overshoot than that with the classic PID control algorithm.During operation,the steady-state error of the UAV gimbal is less than 0.2%,which can meet the experimental requirement.(4)The design and performance verification test of the UAV gimbal control system is completed.For hardware,the STM32 microcontroller,MPU6050 and steering gear are respectively employed as the UAV gimbal controller,the attitude acquisition module and the driving motor.For software,the UAV gimbal system software based on the Free RTOS real-time operating system is designed.The main program of the system and the subprogram flow of serial port sending,attitude reading,and variable structure PID algorithm are designed.After completing the construction of the experimental prototype,the static and dynamic control accuracy of the UAV gimbal is tested through the ground simulation test.The results show that the maximum static of the pitch angle and roll angle does not exceed 0.05o and the maximum dynamic error does not exceed 1.5o,which indicate that the UAV gimbal system has a good stability enhancement performance.