Study On Key Technologies Of Mechanical Weeding For Rice Seedling Avoidance

In rice paddy ecosystems,weeds and rice compete for growth space,fertilizer nutrients,light,heat and other resources,which is one of the important reasons that affect rice yield decline and quality decline.Effective control of weed growth is an important part of rice growth.The application of chemical herbicides is a widely used method for weed control.Long-term,large-scale,high-frequency application can cause negative problems such as weed resistance,herbicide injury and environmental pollution.Therefore,vigorous development of mechanical weeding is the key to ensure the sustainable development of agriculture.However,in actual operation,the change of seedling belt bend causes seedling injury of weeding executive parts,which seriously restricts the development of mechanical weeding technology.Therefore,it is very necessary and urgent to carry out research on rice plant identification and positioning technology,to implement differential control on the operation path of weeding executive parts,and to realize mechanical weeding of seedling avoidance.According to the physiological characteristics of rice and weeds during weeding period,a tactile method was proposed to identify and locate rice plants,and then to obtain the control quantity of seedling avoidance.On this basis,the hydraulic control system of four-bar mechanism was constructed to complete the automatic seedling avoidance control system based on tactile perception.A rigid-flexible compound weeding wheel suitable for lateral control operation was designed.The key technologies such as perception,control and execution are integrated to realize automatic seedling avoidance and mechanical weeding,and the working performance is tested in soil tank,which verifies the feasibility of the seedling avoidance technology.The main research contents and conclusions are as follows:(1)The perception system of seedling avoidance regulation was studied,and the differences of physiological characteristics between rice plants and weeds during weeding period were analyzed.The conditions for identifying and locating rice plants by using bending sensors as sensing beams were proposed.The bending resistance of rice base stems during weeding period was tested,and the basic data for identifying rice plants were obtained.The mechanical analysis of rice plants and sensing sensors was carried out.The structure parameters of the measuring device for seedling avoidance control are determined,and the calibration platform of the measuring device is built.According to the calibration data,the functional relationship between the bending and transverse deviation of the front and rear bending sensors of the measuring device is fitted,which provides basic data for the seedling avoidance control system.(2)The control system of seedling avoidance was studied.According to the principle of weeding and seedling avoidance of paddy field machinery,a set of four-bar hydraulic control system was designed.Through the modeling and analysis of the control mechanism,the length of the tie rod was L=200 mm,the distance of the tie rod was a=1000mm,the maximum transverse adjustment angle was about 30 degrees,and the maximum transverse regulation amount was h=100 mm,and the expansion amount of the hydraulic rod and the regulation amount of transverse seedling avoidance were The numerical model.It provides decision-making for the operation path control of weeding executing components.(3)The design of rigid-flexible compound weeding wheel was carried out.According to the principle and actual situation of mechanical weeding,the arc of the back section of rigid weeding wheel was chosen as Archimedes spiral,and the optimum proportion constant K=31 was determined.The optimum slip angle of cutting edge was solved by MATLAB software.The kinematics simulation analysis of rigid weeding wheel was carried out by ADAMS View kinematics simulation software,and the single weeding blade was obtained.The weeding width is 62 mm,and the optimal number of blades is N=11.On this basis,according to the operation characteristics of rigid weeding components,an active flexible weeding component was designed and its related parameters were determined.(4)According to the automatic seedling avoidance system,soil trough performance test was carried out,weeding rate and seedling injury rate were selected as test indexes,and three factors and three levels of orthogonal test were carried out with weeding depth,speed and traveling speed of flexible weeding wheel as test factors.The results showed that when the depth of weeding was 60 mm,the speed of flexible weeding wheel was 2 r/s and the speed of traveling was 0.6 m/s,the weeding rate reached 82.5% and the seedling injury rate was 3.5%,which met the agronomic requirements of rice weeding.