高地隙四轮独立驱动喷雾机路径跟踪模型预测控制

针对传统燃油驱动、前轮转向的高地隙喷雾机传动效率低、碳排放高、环境污染、智能化水平低、灵活性差等问题，本研究提出了一种适用于无人驾驶的高地隙四轮独立驱动（Four Wheel Independent Drive，4WID）喷雾机。其采用混合动力、前后双转向桥的4WID，转向半径小，前后轮的运行轨迹高度一致，能够减少田间植保作业时的压苗现象。考虑水田极端作业环境下驱动轮的滑移、陷坑等问题，基于喷雾机线性时变的运动学模型（LTV），构建了考虑驱动轮滑移的分层路径跟踪控制。上层模型预测控制（Model Predictive Control，MPC）器根据预期路径、车辆当前位置，获得喷雾机的转向角和运动速度，实现路径跟踪。下层以模糊控制和积分分离PID控制构建驱动轮滑移控制器，从而实现路径跟踪、运动速度、驱动轮滑移的有效控制，提高了喷雾机在复杂作业环境中的稳定性和路径跟踪精度。采用Adams/Matlab的联合仿真结果表明，在复杂的工况条件下，喷雾机驱动轮的滑移率依然控制在±20%之内，防止驱动轮发生过度滑移对车速和转向角产生不良影响，有利于喷雾机稳定性的提升。本喷雾机能够快速准确地跟踪期望路径，与未考虑驱动轮滑移的控制相比，能够适应更加复杂的工作环境，跟踪精度有明显提升。

Path Following Model Predictive Control of Four Wheel Independent Drive High Ground Clearance Sprayer

In order to solve the problems of low transmission efficiency, high carbon emissions, environmental pollution, low intelligence, and poor flexibility in traditional fuel-driven and front-wheel steering high ground clearance sprayers, a new type of high ground clearance four-wheel independent drive (4WID) sprayer which was suitable for the unmanned driving was proposed in this research. The sprayer adopted the hybrid power of fuel and battery and was steered by the 4WID driving mode of the front and rear double steering axles. For this reason, the turning radius of the proposed 4WID sprayer was small, and the running track of the front and rear wheels were uniform in height, which reduced the phenomenon of seedling crushing during field plant protection operations. Considering the slippage and sinking of the driving wheel in the extremely complex operating environment of the paddy field, based on the linear time-varying kinematics model (LTV) of the sprayer, a layered path tracking control considering the slippage of the driving wheel was constructed. The upper model predictive controller (MPC) obtained the steering angle and movement speed of the sprayer according to the expected path and the current position of the vehicle to realize path tracking. The lower layer used fuzzy control and integral separation PID control to construct a driving wheel slip controller, so as to achieve effective control of path tracking, speed, and driving wheel slip, which improved the stability and path tracking accuracy of the sprayer in a complex operating environment. The co-simulation results of Adams and Matlab showed that under complex working conditions, the slip rate of the driving wheel of the sprayer was controlled within ±20%, so as to prevent excessive slip of the driving wheel from having adverse effects on the speed and steering angle, which was conducive to the improvement of the stability of the sprayer. The sprayer could be tracked quickly and accurately the desired path, the path tracking in road conditions outside attached coefficients were 0.3 and 0.7 of the lateral deviation could be controlled within ±0.018 m. In stage C roughness 3D road conditions, the sprayer could adjust the steering angle of the front wheels in time to stabilize the body posture and the lateral deviation could be controlled within ±0.054 m. Compared with the controller that didn't consider the slip of the driving wheel, the stability and path tracking accuracy of the sprayer had been significantly improved.