The Design For Precision Seed-metering Devices And Simulation Analysis Of Working Process Based On The DEM

The research and design of seed-metering mechanism mainly have two kindsof methods. One is the design method and theory based on the continuummechanics method, but it considers granular particles as a continuous whole, as aresult it can not analyze the movement process of every particle and interactionsbetween particles, so it can not solve problems existing during designingseed-metering device well. Another method is according to the experience and trial,whereas usually it is not only time-consuming but also strenuous without idealresults.The discrete element method (DEM) proposed by Cundall in seventies of the20th century is popular method to research particles dynamics problems. Theinteractions between granular materials (such as soybean seeds) and seed-meteringand the flow process of seeds are studied by the DEM, which can be used toestimate the working performance of seed-metering, such as the single index, missindex and the rate of destroyed seeds etc., and also to simulate and evaluate thedynamic working process of seed-metering machine. Thus the seed-meteringmechanism of new theory can be found, however, it can not be realized by theexisting design methods and technologies.Based on studying the present conditions and existing problems concerningthe DEM that the domestic and external literatures have been reported, this papersets up the basic theory of DEM of the 2-dimension round and oval to simulate thesoybean seed, including the establishment of coordinate system (reference frame),building of granular particles, foundation of boundary analytical model, the methodof contacting detection and searching algorithm, and the methodology and theoryof DEM computing.According to the require of the DEM to analyze and calculation, in this papersome properties of two kinds of soybean (Ping'An-1008 and JiDou-2) aremeasured or tested. and the analysis results of the soybean's normal stiffness testshow: â‘ When the deformation rate of soybean is 0.3mm/s, the loading speed with5N/s to 30N/s has little influence on the stiffness and the fracture resistance; â‘¡When the loading speed is 10N/s,the stiffness descreases and the fracture resistancefluctuates within the certain range with the increasing deformation rate from0.05mm/s to 0.8mm/s; â‘¢The stiffness and the fracture resistance with theperpendicular load on the center of the cotyledon plane are bigger than those withthe load along the cotyledon plane; â‘£The stiffness is little dependence on the...