Comparison of straight line driving synchronous control methods and validation of 4WD sprayer chassis with hydraulic power

Abstract: To meet the plant protection and spraying requirements in complex agricultural and forestry environments, a flexible and intelligent sprayer chassis with hydraulic power system was developed in this study. Two synchronous control plans of four hydraulic motors were proposed for straight line driving requirements of sprayer chassis. The first plan was a single stage direct control with solenoid proportional directional valve and the second plan was a two stage synchronization control with synchronous valve and solenoid proportional directional valve bypass regulation. The principle diagrams of two plans were designed. The inner and outer double layer control structure was designed for the first plan. The PID controller was used to track the reference signal in the outer layer and fuzzy coordinated controller in the inner layer was used to adjust the rotary speed synchronous error of four motors. The fuzzy control rules were designed and the SIMULINK model of the first plan was established. The synchronous control effect of the first plan was simulated through MATLAB/SIMULINK. In the second plan, the synchronous divider/collector valve was used for the primary synchronous control of four motors and the solenoid proportional directional valve was used for bypass flow regulation in order to reduce the synchronous error caused by unbalanced load. The simulation model of the second plan was established with AMESim. The synchronous control system responses of two plans under step input (the step value was 230) were simulated and compared under the conditions of boot stage, unbalanced load torque disturbance, accidental power off and power recovery. The maximum motor speed synchronous errors of the first plan were about 8.5 r/min within 0-0.1 s, 0 r/min within 0.1-0.5 s,4 r/min within 0.5-1.0 s and 0.2 r/min within 1.1-1.5 s, respectively. The synchronous control accuracy of the first plan can be kept under 3.7%. The motor speed fell obviously at the time of 0.5 s because of the accidental power off of the valve and subversive consequences might bring out for the chassis. Compared with the first plan, the maximum motor speed synchronous errors of the second plan were about 4.4 r/min within 0-0.1 s, 1.0 r/min within 0.1-0.5 s, 1.8 r/min within 0.5-1.0 s and 2 r/min within 1.1-1.5 s, respectively. The synchronous control accuracy of the second plan can be kept between 0.6%- 1.9%. The motor speed showed slightly fall (about 6 r/min) at the time of 0.5 s and subversive consequences might not be caused. The experimental structure diagram was designed for the second plan and the experiment table was established referring to the diagram. SIMENS S7-200 CPU and four rotary encoders were used to collect the motor speed signal. Quantized fuzzy control table was written into the PLC and analog quantity (voltage signal) was outputted in accordance with the speed signal input. The output voltage signal was used to control the proportional valve amplifier, thus the valve core was driven and the rate of flow was regulated. The motor speed was adjusted until the speed synchronous error met the accuracy requirements. The experiment results showed that the motor speed fell (about 15 r/min) more obvious than the simulation results (about 6 r/min) because of the oil leakage. But synchronous precision can be kept within 1.0%-2.0% which can meet straight line driving requirements. The simulation and experiment results showed that maximum motor speed synchronous error of the second plan reduced about 50% on various research stage of motor compared with the first plan. Theoretical guidance was provided for the straight line control of the four wheel independently driving chassis and the theoretical reference was proposed for hydraulic synchronous control system design in agricultural engineering field with the demand of higher accuracy, higher reliability and economy.