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

Abstract

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.

Keywords

• front and rear double steering axles
• four-wheel independent drive
• model predictive control
• fuzzy control
• slip
• path tracking