Model Predictive Control System For 4WID High-clearance Sprayer

High-clearance sprayer plays an important role in plant protection equipments because of high spray efficiency and wide applicability.The four-wheel independent electric drive high-clearance sprayer adopted a special steering structure with front and rear axles.Because of the strong coupling and nonlinear characteristics,an effective controller can greatly improve the adaptability and stability of the sprayer.Aiming at the problems of coordination control,this paper proposed a steering control system of the Four Wheel Independent Drive(4WID)high-clearance sprayer.The dynamic steering model of the sprayer was established by using Newtonian rigid body mechanics and Direct Yaw Control(DYC),the Model Predictive Control(MPC)was used for MIMO control,then,the coordination control of 4WID sprayer is realized.The main research as follows:(1)A 4WID wheel speed steering model was established.The rotation angle of front and rear axles were controlled to be same by four-wheel speed.So,the indentations of front and rear wheels overlap to reduce the damage to crops.The influence of wheels’ speed on the sprayer’s speed,rotation angles and position was analyzed.The trajectory tracking simulation was carried out based on the kinematics model of the sprayer in MATLAB,and the motion parameters of sprayers under different steering radii were obtained.(2)According to the strong coupling and nonlinear characteristics of traditional sprayer kinematics models,a sprayer dynamical model based on DYC and Newtonian rigid body mechanics was established.By analyzing the relationship between rotation angles and the torque from wheels,the differential equations between motor voltage and rotation angles were set.The yaw moment coordination control equation between rotation angles was obtained from DYC analysis on simplified two-degree-of-freedom model.The mechanical model of sprayer was optimized by combining these equations.(3)The MPC system was established according to the mechanical model,and the simulation and experimental verification were designed.The dynamic and anti-disturbance performance of MPC system were simulated in MATLAB.Results showed that the system owns good stability and robustness.In field test,the working steering radius was 9.1m,the speed was 1m/s and the deflection of rotation axles was5°.Results showed that rotation angles were 4.79° and the deviation of steering radius was less than 0.05 m.The minimum steering radius was 1.5m,the speed was 0.5m/s and the rotation axles were 30°.Results showed that rotation angle of the front axle was 29.37° and 29.3° of the rear,the deviation of steering radius was less than 0.1m.The experimental results show that MPC system is effective for sprayer and can meet requirements of practical application.