Design and experiment of electro-hydraulic profiling system with consistent pressure for drilling depth of furrow opener

Abstract: The consistency of sowing depth is one of the most important indicators for the seeder. It will not only affect the germination rate of seeds, but also cause inconsistency in plant height which will reduce the quality of the following mechanized such as plant protection and harvesting. Spring profiling is a passive profiling method that has been widely used in ditching depth control at present, but the ditching depth cannot be consistent, because the pressure on the furrow opener is changed with the spring deformation. Using an active profiling method, a consistent pressure control system for the furrow opener was designed, which was composed of the parallel four-bar mechanical system, the hydraulic system and electronic control system. Based on the programmable logic controller, the system controlled the output pressure of the electro-hydraulic proportional reducing valve according to the deviation between the setting pressure and the value detected by the pressure sensor on the furrow opener, making the output pressure of the cylinder and the vertical earth pressure of opener consistent. The parameters of the control system was determined, including the hydraulic circuit of the system, parameters of hydraulic components, types and parameters of control components, hardware connection and software program. To judge the stability and analysis the unit response of the system by using MATLAB, the closed-loop transfer functions of the system was established based on building the transfer function of each link, such as the electro-hydraulic proportional reducing valve, hydraulic cylinder and parallel four-bar mechanism and so on. The simulation results showed that the system was stable, and the static overshoot was 5.02%, the response time was 0.25 s, and the steady-state error was 0.79%. According to the simulation results, the system was debugged and tested using another hydraulic cylinder to simulate the grand surface fluctuation. When the vertical earth pressure of the opener was set at 20 to 200 N, the profiling depth was set at 10 to 80 mm, the experiment results showed that the average response time of the system was about 0.27-0.36 s and the steady-state error was 1.4-1.8 N with the maximum 2.7 N, and the average standard deviation was 0.78%-6.94%, the output pressure was consistent. It also concluded that the response time decreased with the increasing of the profiling depth and the earth pressure, while the steady-state error were not effect by the above two factors, and the average standard deviation decreased with the increase of the earth pressure, so the greater earth pressure was beneficial for higher accuracy of the system. Compared with the simulated results which the response time was 0.25 s and the steady error was 0.79%, the average response time of the experiment was 4%-44% higher and difference between the minimum standard deviation of the experiment and the steady error was 0.01%, verifying the reliability and accuracy of the system model built. The research reduced the response time and the steady error of the electro-hydraulic profiling system based on the pressure sensor, providing the reference for the parameter setting and theoretical analysis of electro-hydraulic profiling control system.