| Tiger nut is an oil crop with high comprehensive utilization value.The key problem that plagues the development of tiger nut industry is how to realize mechanized harvesting of it.At present,China’s tiger nut harvester is still in the experimental research stage,and the separation and screening of tiger nut is one of the core aspects of its harvesting process.In the process of separation and screening,there are problems such as difficulty in separation,high content and low efficiency,which seriously restrict the quality and level of mechanized harvesting operation of tiger nuts in China.To promote the healthy development of the tiger nut industrial system,it is necessary to solve the problem of efficient and low-loss mechanized harvesting of tiger nuts,propose an tiger nut harvesting operation mode suitable for China’s national conditions,research and elucidate the mechanism of tiger nut screening,and develop the matching tiger nut harvesting machinery.To this end,this paper addresses the problems of difficult manual harvesting and low mechanized harvesting efficiency of tiger nuts,takes sieving device as the research object,carries out the design of sieving device structure by means of structural design,theoretical analysis,simulation and field test,etc.,applies the discrete element technology to simulate the motion process of detritus particles on the sieve surface,reveals the motion characteristics of oilseed bean on the sieve surface and The theoretical basis was laid for the research and development of mechanized harvesting equipment and the improvement of operational performance of tiger nuts.In this paper,research was conducted in the following aspects.（1）Taking the integration of agricultural machinery and agronomy as the starting point,the design of the screening device of the crawler self-propelled tiger nut harvester is designed.In view of the incomplete separation of beans and grasses and the large amount of soil particles in the process of harvesting and screening of tiger nut,a mechanized harvesting mode of "threshing first and then separation" was proposed.The grass roots are separated,and then the sieving of the mixture of beans,soil and grass is completed,and a screening device for tiger nut is designed,which is compatible with the mechanized harvesting mode of "threshing first and then separation".It is composed of core components such as layer anisotropic reciprocating vibrating screen and crushing soil guide roller.The kinematic characteristics of the sieving mechanism of the tiger nut harvester were elucidated.By using the matrix method to analyze the motion of the upper sieve of the sieving device,the equations of motion characteristics at any point of the sieve surface were obtained,and the factors affecting the motion characteristics of the sieve surface（frequency,amplitude,and inclination of the sieve surface）were found.Through ADAMS simulation analysis,the motion characteristics of the screen surface were studied,and the results show that the trend of velocity and acceleration changes at each moment of each marker point on the screen surface is the same,and the maximum horizontal velocity and horizontal maximum velocity at each point along the screen surface direction gradually increases,promoting the material to move to the back end of the screen surface;the vertical velocity and acceleration at each point gradually decreases,and the material obtains a larger force in the vertical direction at the front end of the screen,improving the material Looseness,increase the probability of material particles through the screen,verify the reasonableness of the movement of the screening mechanism,and provide a basis for the analysis of the movement characteristics of the particles on the screen surface.（2）The transport pattern and motion characteristics of the detrital particle population in the sieving process were clarified.The sieving process of detritus particles was simulated based on EDEM software with bean and soil particles in the sieving process as the research object.Combined with the image processing technology,the transport law of the population of detritus particles was analyzed from different perspectives,such as the sieve surface distribution characteristics of the particles,the average motion speed,the particle distribution rate,the screening efficiency and the loss rate.The effects of factors such as screen amplitude（SA）,vibration frequency（VF）and inclination angle（IA）on the screening performance of the threshing and screening device were investigated.The effects of screen amplitude and screening frequency on screening efficiency and loss rate were consistent,and the screening efficiency and loss gradually increased as the values of the test factors increased,because the increase of amplitude and frequency promoted the movement of particles in horizontal and vertical directions The reason is that the increase in amplitude and frequency promotes the movement of particles in horizontal and vertical directions,separation and dispersion,improves the probability of particle penetration and promotes the screening efficiency,at the same time,the violent movement of particles leads to the increase in loss rate; the increase in the inclination of the screen surface improves the movement of particles on the screen surface,and the dispersion of particles is enhanced,which is conducive to improving the screening efficiency;too large an inclination will cause the particles to move too fast and reduce the number of collision contacts with the screen surface,reducing the screening efficiency.（3）Optimization of the operating parameters of the sieving device based on RSM and NSGA-Ⅱ algorithm.Based on Box-Behnken,the influence of each working parameter of the threshing sieving device on the sieving performance is studied.The vibration frequency（X1）,screen amplitude（X2）and inclination angle（X3）are selected as the test factors,and the screening efficiency（Y1）and loss rate（Y2）are the test indexes,and the regression mathematical model of each working parameter with the screening efficiency and loss rate is obtained through the ANOVA of the experimental results.Based on the NSGA-Ⅱ algorithm,the regression mathematical model of screening efficiency and loss rate was optimized under the constraints,and the best optimization solution（vibration frequency of 14 Hz,sieve amplitude of 12 mm,and inclination angle of 2°）was selected in the Pareto non-dominated optimal solution set according to the actual mechanized harvesting operation of tiger nuts and requirements,and verified by field tests.The results show that the average sieving efficiency of the threshing and sieving device of the crawler self-propelled tiger nut harvester is 92.87% and the loss rate is 1.83% under these parameters;compared with the simulation test results,the error of the screening efficiency in the simulation test results is 1.93% and the error of the loss rate is 3.83%,both of which are less than 4%,and the results prove that the sieving device based on EDEM and NSGA-Ⅱ algorithm The results prove the effectiveness of the simulation test and working parameter optimization method based on EDEM and NSGA-Ⅱ algorithm. |
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