| Aiming at the problems of low weeding rate,high seedling damage rate and poortrafficability in paddy field weeding machine,a riding weeding-cultivating device for paddy was designed.The mechanism of mechanical weeding in paddy fields was analyzed by studying the growth characteristics of weeds.Then the overall structure and working principle of the weeding device was illustrated.A rotating rake tooth type inter-row weeding component,swing spring tine type intra-row weeding component and self-propelled system weeding machine for paddy field were designed by using the methods of theoretical analysis,structural design,simulation and experimental research.The weeding device designed in this research satisfies the requirements of paddy field weeding,and provides a reference for the subsequent research of paddy field weeding machine.The main research contents and results showed as follows:(1)Mechanistic analysis and design of weeding-cultivating component for paddy The varieties of common weeds in paddy fields in China were summarized,and the peak time of emergence of weeds in paddy fields was analyzed,then the best time for weed control in paddy fields was determined.The growth characteristics of weeds and seedlings were studied.Based on the difference of roots growth between weeds and seedlings,the inter-row weeding mechanism and intra-row weeding mechanism of paddy field weeding machinery were analyzed.The creep characteristics of paddy soil were studied.Based on the rheology and thixotropy of paddy soil,the crushing and remodeling process of paddy soil during weeding component operation was analyzed.The design requirements of weeding component in paddy field were proposed according to the agronomic characteristics of rice planting and weeding operation.The overall structure and working principle of weeding-cultivating component for paddy were described and analyzed,and the structure and principle of auxiliary components of weeding component were introduced.The weeding mechanism analysis and machine structure design provide a theoretical basis and operating platform for the design and research of subsequent weeding components.(2)Design and experimental study on rotating rake tooth type inter-row weeding component for paddyA rotating rake tooth type inter-row weeding component for paddy was designed.The trajectory and force condition of weeding wheel during operation were analyzed,then the key components of inter-row weeding component were designed.Based on the discrete element method software EDEM,the simulation experiment was designed to study the change trend of mechanical properties of contact between weeding wheel and paddy soil during weeding operation.The field experiment of the rotating rake tooth type inter-row weeding component for paddy was carried out to verify the feasibility of the simulation experiment and the working performance of the weeding component.The simulation results show that,the order of influence of various factors on weeding torque is as follows:weeding wheel rotation speed>weeding depth>forward speed;the order of influence of each factor on soil disturbance speed is as follows:weeding wheel rotation speed>weeding depth>forward speed.The inter-row weeding component for paddy has the best working performance under the operating conditions of 50 mm weeding depth,240 r/min weeding wheel rotation speed and 0.6 m/s forward speed.The field experiment results show that,the weeding rate of inter-row weeding component was 85.2%;seedling damage rate was 4.8%;working fuel consumption was 14.3 L/hm~2.The inter-row weeding component designed in this study meets the requirements of paddy field inter-row weeding operation.(3)Design and experimental study on swing spring tine type intra-row weeding component for paddyA swing spring tine type intra-row weeding component for paddy was designed.The trajectory model of spring tine was established,and the mechanism of seedling avoidance and intra-row weeding was analyzed.Then the key components of intra-row weeding component were designed.The discrete element method simulation experiment was carried out to study the force change and soil disturbance during the spring tine weeding.The field weeding experiment was carried out to verify the working performance of the intra-row weeding component.The simulation experiment results show that,with the increase of forward speed,the spring tine resistance torque and soil disturbance increase,and probability of seedling injury increases.The field experiment results show that,when the forward speed was 0.30m/s and weeding depth was 40 mm,the weeding rate was 85.0%and seedling damage rate was 3.4%,and the swing spring tine type intra-row weeding component for paddy has the best working performance.The intra-row weeding component designed in this study meets the requirements of paddy field intra-row weeding operation.(4)Design and experimental study on self-propelled system of paddy field weeding machineA self-propelled system of paddy field weeding machine was designed.The overall structure and working principle of self-propelled system were introduced.Theoretical analysis of the influence factors of self-propelled system trafficability.Then the wheel-soil interaction model and wheel subsidence model were established.The wheel traction and surface roughness were selected as the test evaluation indexes to carry out the single wheel soil bin simulation test.In order to verify the steering performance,stability and ridge crossing ability of the self-propelled system,a prototype field experiment was carried out.The simulation experiment results show that,in the process of wheel-soil interaction,the traction of the wheel is approximately 600 N and the surface roughness is less than 30 mm.The field experiment results show that,the minimum turning radius of the weeding component is 2050 mm,the limit overturning angle is 36°,and the maximum ridge crossing height is 400 mm.The speed range of the weeding component in the driving gear on the road is 0.72～16.20 km/h,and the speed range in the weeding gear is 0.72～5.40km/h. |
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