| Mechanization with high work efficiency and low labor costs is the prospective of cassava harvesting.As an important part of the cassava harvester,separation mechanism now still has lots of problems such as poor equipment adaptability and serious harvest loss,which cannot satisfy farmers'utilize requirements.On the basis of existing research results a new type of separation mechanism of cassava harvester was designed by using theoretical analysis,simulation and experimental study,which can improve equipment adaptability and reduce cassava harvest loss.Besides,the relationships between structural and working parameters of separation mechanism and cassava obvious rate and broken rate were discussed.The main conclusions are as follows:1.Soil compaction,soil water content,soil density,growth depth,tuber number,growth width,tuber length,tuber diameter and tuber weight from typical soil sites were measured and studied to give a reference to entire scheme,structural composition and function design of cassava harvester.And main working parameters were designed as following:maximum excavation depth was 40cm,harvesting width 140cm and mating power 66.18kW.2.On the basis of analyzing the kinematics and dynamic of the separation sieve,occurrence conditions of three motion states with forward sliding,backward sliding and jumping movement were summarized.By analyzing the clod crushing process,collision times required for clod crushing were obtained.The whole deformation process of the cassava tubers and sieve surface were recorded by using a high-speed camera.The results showed that cassava damages were caused by transverse bending of inertia force,and the collision force from sieve surface to cassavas calculated from the impact bruise tests of cassavas should be less than 460N.Combined with theoretical analysis and the impact bruise tests of cassavas,the parameters of the separation mechanism,such as crank radius,crank speed and sieve surface inclination,were preliminarily determined.3.In allusion to motion law of separation sieve,a virtual prototype model of the separation mechanism was built by using dynamic simulation software-ADAMS.The simulation analysis results showed that crank radius,crank speed and slop angle of sieve surface were significant factors during the working process of separation sieve.4.Single-factor experiments,with crank radius,crank speed,slop angle of sieve surface and forward speed as dependent factors and cassava obvious rate and broken rate as independent factors,were made to determine the optimal parameters range.On the basis of the single factor experiment results,Box-Benhnken design(BBD)response surface method was used to design the field experiments.An orthogonal rotary combination experiment was conducted with the crank speed,slop angle of sieve surface and forward speed of cassava harvester as three independent factors,as well as cassava obvious rate and broken rate dependent indices,while using NanZhi 199 cassava as the test materials.Design-Expert software was employed to analyze the test results,mathematical equations between in dependent and dependent factors were gained.At the 447.76 rpm of crank speed,12.44° of sieve inclination angle,and 2.05 km/h of forward speed,the separation mechanism parameters of 4UM-140 showed optimal performance with cassava obvious rate of 99.003%and broken rate of 5.022%.Field verification test was carried out after the combination of the optimal parameters,and the results showed that the regression model had good reliability to predict the cassava obvious rate and broken rate.According to comparison of transplanting performance before and after parameter optimization,the cassava obvious rate was increased by 0.52 percentage points and broken rate was reduced by 1.32 percentage points.which was superior to the technique indexes of national and industry standards as well. |
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