Study On Design,Optimization And Soil-cutting Performance Of A Handheld Tiller’s Rotary Blade

Handheld tillers are indispensable agricultural machines that are broadly used in regions of hills,mountains and plateaus.The handheld tillers are easy to transfer from one land to another,and to make turns in any land of different scales in the mentioned regions.The rotavator is the tilling part of a handheld tiller,and it consists of many rotary blades.The functions of tilling and moving are both achieved by interaction between rotavator and soil,and the tilling function includes soil-cutting,pulverization,soil-turning,soil-throwing,and soil-levelling.The shapes and parameters of the rotary blades directly affect the performance of a rotavator and the corresponding handheld tiller.In this study,taking the handheld tiller’s rotary blade as a case study,the mathematical model of a handheld tiller’s rotary blade was established according to the geometric relations between each parameters,and the CAD system of rotary blade was obtained by means of the secondary development of AutoCAD based on Visual Basic,then characteristics of partical parameters were studied.Soil-cutting simulation was performed by means of Smoothed Particle Hydrodynamics（SPH）modelling in this study,then the movement of soil particals,effective stress distribution of soil,soil resistance,energy consumption and power consumption in process of soil-cutting were studied.Taking cornerite of bending point（X₁）,alpha angle（X₂）and bending angle（X₃）as control factors and power consumption（Y）as evaluation index,soil-cutting experiments by simulation were conducted according to Taguchi method.The simulation results were analyzed by the variance and regression analysis,and the optimized parameters of the blade were obtainer by response surfaces of control factors.Finally,correctness of the simulation was validated by soil bin test.The main conclusions from the study are as follows:（1）The mathematical model of the rotary blade was built,and the CAD system of the rotary blade was obtained.Three rotary blades with different maximum rotation radius and different edge curves were designed through the CAD system,the relative error of system output and calculated values（Excel）of parameters were studied,and the variation between different geometric parameters were analysed as well.The results showed that:the average relative error of the system output and calculated values are 0.41%;the grass removing angle and scoop angle of edge curve edge are in the preferred value range;with increase of the cornerite,the grass removing angle and scoop angle linearly increase at large;on conditions of other parameters being constant,the tilling width decreases with increase of alpha angle and bending angle.（2）Three rotary blades with different parameters were studied,comined with the characteristics of rotary blade operation,the soil-cutting model of rotary blades were established based on SPH method;then the movement of soil particals,effective stress distribution of soil,soil resistance,energy consumption and power consumption in process of soil-cutting were effectively simulated,based on the actual working conditions of the cutting soil,the rationality of soil cutting model based on SPH method was verified.With orders of cutting resistance and power consumption of three rotary tillage blades as rotary blade 1,rotary blade 2 and rotary blade 3,which is consistence with theoretical analysis based CAD system.（3）According to response surfaces to power consumption of soil-cutting as functions of X₁,X₂,and X₁,X₃,and considering practical use and roundness of parameters of a rotary blade,the optimized parameters of the blade are X₁ 30°,X₂ 52°,and X₃ 120°.The power consumption of the optimized rotary blade is 0.161kW by SPH modelling,with a relative error of 4.30%compared with 0.154kW（by means of regression）.By statistical analysis of four representative rotary blades of soil bin test,the mean relative error of power consumption between soil bin test and simulation is 11.57%,which shows good feasibility of parameter optimization of rotary blade by SPH modelling and Taguchi method.