Research On Automatic Depth-control Technology Of Semi-feeding Peanut Combine Harvester

Peanut is one of the world's four major oil crops,and also China's most internationally competitive premium oil crop.In 2015,China's peanut planting area reached 4.682 million hectares with a total output of 169.72 million tons,ranking in the forefront of the world.However,the mechanization of peanut production has lagged seriously,especially in harvesting,mainly relying on manual and semi-mechanical.At present,the semi-feeding combined harvesting technology are actively promoted at the main production areas of peanuts,whose integration degree is very high with many operation links.And the technology is also complicated,especially in the excavation operation,the excavation depth of equipment is difficult to be controlled due to the poor flatness of the ground in the field.If the harvesting machinery cannot be adjusted to maintain the excavation depth in time,the rate of fruit leakage and breakage increase,in addition,the power consumption of harvestor also increases.Therefore,the research of automatic technology in excavation depth-control has an important and urgent practical significance for improving the automation level and performance of semi-feeding peanut harvesting machinery.Based on the plant characteristics and planting mode of peanuts at the main producing area,this paper carried out automatic depth-control technology research and equipment development,with4HLB-4 type semi-feeding combined harvestor as a carrier.The main research contents and conclusions:1)Based on study and analysis of peanut planting mode,harvesting mode and typical plant characteristics of the main producing areas in China,the design requirements of the semi-feeding peanut combine harvester automatic depth-control system are proposed.After multiple rounds of program design,demonstration and determination,the entire scheme design of the system is completed,and the overall structure layout and working principle are also determined.The automatic depth-control system mainly consists of a depth-control profile mechanism,a hydraulic adjustment system,an electronic control system and a signal feedback system.2)Design the main structure and critical dimensions of the depth-control profile mechanism,and determine the angle sensor model.A large-diameter spoke-shaped profile wheel?R=340 mm?was designed,which can effectively improve extraction signal accuracy by avoiding to overwhelm peanut vine.The spoke-shaped profile wheel is hinged to the mounting base via a swing lever?L=460 mm?,and the hinge shaft and the angle sensor output shaft are fixedly connected by a coupling and an external flange.The angle sensor adopted the absolute single-turn photoelectric encoder RDE58BS10 of Changchun Rongde Co.,Ltd.In normal working conditions,the initial angle of the photoelectric encoder are?₀=?₀=60°,and the profiling range of the profiling mechanism is-120^-20 mm and+20⁺120 mm.3)Design the working principle of the hydraulic adjustment system and the excavation depth adjustment mechanism,and analysis the stability of the hydraulic control system in theory.After comprehensive analysis,the system supply pressure was selected to be 16 MPa.The main structural dimensions of the hydraulic cylinder were calculated,and the parameters and models of the solenoid valve and the system integration method were determined.Then the open-loop transfer function of the hydraulic system was derived,and the Bode diagram of system transfer function were also drawed by Matlab software.It was analyzed by the Bode diagram that the left hydraulic branch system is a stable system and the right hydraulic branch system is an unstable system.According to the nonlinear characteristic of the hydraulic system,this study decieded to adopt the fuzzy PID control algorithm to correct the hydraulic adjustment system.4)Design electronic control system,including hardware selection,hardware circuit design,control algorithm design,fuzzy PID controller design and software program design.In the Simulink environment,the simulation model of the automatic depth-control dynamic system is created by module combination method,which was used to conduct the electro-hydraulic control system joint simulation test.The simulation results showed that the left hydraulic branch system with the fuzzy PID controller had an overshoot of only 7.1%,the adjustment time was only 0.093s,and there was no steady-state error.Compared with the conventional PID controller,the system overshoot was reduced by 4.9 percentage points,and the adjustment time was shortened by 0.026s,which was about 21.8%lower.The overshoot of the right hydraulic branch system with the fuzzy PID controller was only 6.13%,the adjustment time is only 0.079s,and there is no steady-state error.Compared with the conventional PID controller,the system overshoot was reduced by 12 percentage points,the adjustment time was shortened by 0.031s,which was about 28.2%lower.5)Manufacture the prototype,carry out bench and field trials.After the system was prototyped,the hydraulic system reaction time was used as the test index,and the hydraulic flow rate and the oil supply pressure were used as test factors for the hydraulic system bench test.The test results showed that the reaction time of the hydraulic system decreases first and then increases with the increase of hydraulic flow and oil supply pressure.When the hydraulic flow rate is 20 L/min and the oil supply pressure is 16MPa,the reaction time of the hydraulic system was smallest.Finally,the field test was conducted with the leakage rate,breakage rate and average excavation depth as the main control indicators.The test results showed,after adopting the automatic depth-control system,that the average leakage rate is1.08%,the average damage rate is 0.94%,and the average excavation depth is 123 mm.Compared with the artificial depth-control,the average leak rate is reduced by 2.13 percentage points,the average breakage rate was reduced by 1.4 percentage points,and the average excavation depth deviation was reduced by 11 mm.Furthermore,the excavation depth deviation was small and concentrated,so the automatic depth-control system works well.