| Rice,as China's major food crops,which cultivation area domains the largest amoung the three major food crops,shows its great influence in ensuring national food security.Weeds in paddy fields seriously affect the yield and quality of rice,and effective weed control during the mid-tillage period is a vital part during the rice growing process.Mechanical weeding has been widely used as an effective technical measure with the advantages of avoiding chemical pollution,which improve the physical environment of the soil and promoting crop growth and development.The mechanical weeding device is the core of the implementation of mechanical weeding technology and its performance directly affects the quality and efficiency of weeding operations.Therefore,it is important to develop efficient mechanical weeding devices to realise the whole process of mechanisation of rice production.Existing mechanical weeding devices are difficult to complete the full width of the weeding operation between rows and plants at one time,and due to the complex environment of paddy fields,the weeding rate of the devices is low and the seedling injury rate is high,which makes it difficult to ensure the quality of operation.To address these p roblems,this paper adopted a series of theoretical analysis,mechanical structure design,automatic control technology,virtual simulation analysis,and experimental research to carry out the research on automatic control weeding devices in paddy fields,with considering the actual field conditions.We focused on breakthrough design and research of core devices such as jet type inter-plant weeding device and bionic flexible inter-row weeding device,and finally completed the integration and trial production of bionic weeding device for paddy field based on water jet weeding device.This research provides theoretical support and reference for the innovative design of mechanical weeding devices for paddy fields.The main research contents and methods are as f ollows.(1)Testing of physical and mechanical properties of plants and soil in paddy fieldsThe geometrical dimensions of rice plants and barnyard grasses,as well as the tensile ultimate strength of single rice roots and barnyard grasses were obtained.T he theoretical basis and boundary conditions were provided for the structural design and simulation analysis of the weeding device.(2)Mechanistic analysis and design of inter-plant weed control devicesBased on the water jet weeding method and the mechanical structure design,a jet type inter-plant weeding device was developed.The mechanism of jet weeding operation was explained according to the agronomic requirements of rice weeding period and the growth characteristics of rice and weeds.The critical breaking pressure model of the nozzle was established by applying the momentum conservation theorem,viscous hydrodynamics and soil mechanics principles;through the results of the theoretical analysis,the selection of the power system of the inter-plant weeding device was completed.(3)Design and analysis of bionic flexible inter-row weeding deviceThrough the study of the weeding operation characteristics of the inter-row weeding device for rice,the paws of the sparrow-feathered duck were used as the bionic prototype,and the kinematic characteristics of the duck's paws were observed and analysed by high-speed camera technology,and the macroscopic morphological data and structural parameters of the key parts of the duck's paws were obtained.Through theoretical analysis,the main structural parameters affecting the bionic flexible weeding wheel performance were determined by combining theoretical analysis with mechanical design;the axial inclination of the bionic duck paw flexible webbing on the webbing mounting wheel plate was set at 170°,and the lateral deflection angle between the bionic duck paw flexible webbing and the webbing mounting plate was set at 15°.In order to improve the operational stability of the bionic flexible inter-row weeding device,the single hinge structure bionic mechanism was designed and the main structural parameters of the mechanism were determined through theoretical analysis.(4)LS-DYNA-based weeding component-water-soil fluid-solid coupling simulation testIn order to analyse the main factors affecting the operational performance of the jet inter-plant weeding device,the influence of jet inclination angle and nozzle opening diameter on soil digging depth and soil disturbance rate was investigated,and the optimal combination of structural parameters was sought.A nozzle-water-soil model of the inter-plant weeding device was developed based on the LS-DYNA simulation technique,a single-factor virtual simulation test was carried out to analyse the results of the bionic flexible inter-plant weeding device using Design-Expert8.0.6 software.The optimum digging performance of the jet type inter-row weed control device was determined.(5)Weed control device performance bench test and device field testThe rice root system impact test was conducted to obtain the ultimate impact pressure of1.5MPa for the rice root system,which provided a reference basis for the selection of factors for the bench test of the jet interstitial weeding device.The weeding performance of the weeding device was evaluated by single-factor tests to determine the influence of each factor on the weeding performance of the plant and row weeding devices;multiple factors with significant influence on the weeding performance of the devices were selected for multi-factor optimisation tests,while the weeding rate and injury rate were used as the indicators of the device to study the influence of the working parameters of the weeding device on the weeding performance;a mathematical model was established for the regression between the weeding performance indicators and the test parameters.The results showed that when the forward speed was 0.3m/s and the nozzle pressure was 1.50 MPa,the weeding performance of the jet inter-plant weeding device showed an optimal result,with a weeding rate of 92.78%;when the forward speed as 0.67m/s and the depth of entry was 47.07 mm,the weeding rate and seedling injury rate of the bionic flexible inter-row weeding device were optimal,with a weeding rate of 92.79% and a seedling injury rate of 1.53%.(6)Field test of weeding deviceBased on the agronomic requirements of live rice planting,the overall configuration design of the bionic weeding device for paddy field based on water jet was carried out.When the forward speed was 0.4m/s,the maximum weeding rate was 92.88% and the injury rate was 1.89%,which can complete the weeding between rows and plants at one time,and the weeding rate was high,the seedling injury rate was low,and the operation quality could meet the agronomic requirements of paddy field mid-tillage weeding. |
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