Height stability control of a large sprayer body based on air suspension using the sliding mode approach

Abstract

When a high clearance self-propelled sprayer sprays, the sprung mass varies with the amount of liquid in the tank, which causes a change in the height of the sprayer body. This change not only is harmful to the sprayer ride comfort, but also has a greater impact on the sprayer application quality. In this paper, a large-scale high clearance self-propelled sprayer with air suspension was taken as the research object. Based on vehicle dynamics and air thermodynamics theory, a mathematical model of air spring inflation/deflation was established, then a 3 degree of freedom (3-dof) vertical dynamics model of sprayer air suspension was built. On this basis, the height control strategy of the sprayer body was formulated. Due to the nonlinear characteristics of air suspension, two control algorithms, namely sliding mode control and the on-off control, were used to design the suspension height stability controller, respectively. A simulation experiment was carried out by using the sprayer spraying crops as an example. The simulation experiment results showed that sliding mode control and on-off control could track and stabilize the height of the sprayer body when it changed under no excitation and D-grade road random excitation. However, due to strong nonlinearity and hysteresis of the pneumatic system, on-off control precision was poor. With the on-off control method, further reduction of the sprung mass would change the internal parameters of the pneumatic system, cause the air spring over deflation, even worse, the over deflation phenomenon presented a serious trend and cause system instability under random road excitation. Compared with on-off control method, sliding mode control approach had good control ability and precision due to its robustness to change in model parameters. The research will provide a reference for the height stability adjustment of large high clearance self-propelled sprayers during spraying and dosing operations.