Dynamic modeling of leveling system of paddy field laser leveler

Abstract: Modern paddy rice planting requires the field with high smoothness since it is conducive to reducing water consumption and improving the crop yields. A paddy land leveler is a complex mechanical system connected to the tractor by hanging. With both plow leveling and working height adjustment mechanisms, the paddy land leveler can automatically adjust the height and leveling of the land-leveling plow to attain high paddy field flatness. In order to improve the control precision, stability and responsiveness of a laser leveler in varying paddy field environment, a dynamic model of the leveling system is proposed in this paper. Considering that the leveling system of paddy field laser leveler is a typical electro-hydro-mechanical system, the dynamic model takes the proportional valve's solenoid current as the input, and the tilt of the plow as the output. Firstly, based on the electro-hydro-mechanical structure and the working principle of the paddy field leveler, an abstract, simplified dynamic model with the diagrams of force analysis is derived, which is composed of a hydraulic subsystem and a mechanical subsystem connected in series, and the hydraulic part generates hydraulic flow rate due to the proportional valve's solenoid current, followed by the mechanical subsystem mainly consisting of a hydraulic cylinder, an installation platform and a plow. A series of differential algebraic equations (DAE) about the two subsystems are then proposed and analyzed based on the diagrams. A typical paddy field leveler is used to demonstrate how to numerically solve these DAEs, and various parameters of the subsystems like resonant frequency, viscosity coefficient of friction, rotation inertia and damping ratio are experimentally determined. Secondly, to verify the model, with the proportional valve's solenoid current as the input and the tilt of the plow as the output, a sine signal response simulation is conducted, and a sine signal response experiment with the actual physical system is done, in which the input is also the proportional valve's solenoid current and the output is the tilt of the plow. The simulation results are then compared with the experimental results of actual physical system. The actual physical system has time delay in the hydraulic system and a certain gap between the mechanicals, and therefore the simulation curve has a little difference from the empirical curve. Overall the experimental result shows that the model proposed behaves in good agreement with the actual tests though with some imperfections. The model represented by DAEs, the way to derive it and the way to numerically solve it, can be used for both hydro-mechanical design and control algorithm design for the leveler, and the modeling principles may be applied to the design of similar electro-hydro-mechanical agricultural operation machines.