Optimized design and experiment of the picking mechanism for brush-roller castor harvesters

Abstract: Castor is one of the top ten oil crops in the world, which has a extremely high economic value. For a long time, the harvesting of castor bean has relied on manual operations, so the development of the castor industry have been greatly restricted by the high labor intensity and low efficiency. At present, there are few studies on harvesting machinery of castor, and the mechanization of castor harvesting is still in the initial stage. The existing castor harvesting equipments are not suitable for the growth features of castor, which has the problems of high loss rate and high damage rate. In order to solve these problems, a brush-roller harvesting method was proposed in this paper. The harvesting principle of brush-roller castor harvester is that the castor capsules are separated from the plant by the brushing force caused from the brush wire. According to the physical characteristics and planting mode of castor, the picking mechanism of brush-roller castor harvester was designed. Firstly, the structure of the picking mechanism was introduced, the picking mechanism is mainly composed of crop divider, brush roller, screw conveyor, transfer case, et. Then, the kinematic and mechanical analysis of the working process of the mechanism was carried out, so as to determine the structural parameters and working parameters of each part of the picking mechanism. In order to improve the harvesting quality of castor, we conducted a field experiment in October 2020 in Hohhot, Inner Mongolia. In the field experiment, Box-benhnken response surface design theory was used on the basis of single fator experiment to optimize the working parameters of the picking mechanism. The picking rate, the breakage rate and the impurity rate were used as the evaluation indexes of working quality. And the moving speed, the brush roller speed and the length of brush wire were taken as three factors influencing the working quality. The quadratic polynomial response surface regression model was established, and the influence of various factors on the response value was analyzed. From the regression model and variance analysis of regression equation, it could be seen that: lower moving speed, moderate brush roller speed, and shorter brush wire led to higher picking rate; Lower moving speed, lower brush roller speed, and longer brush wire led to lower breakage rate; Higher moving speed, lower brush roller speed, and longer brush wire led to lower impurity rate. The experiment results also showed that the significant effects of moving speed, length of brush wire and brush roller speed on increasing the picking rate were in a decreasing order. The significant effects of brush roller speed, length of brush wire and moving speed on reducing the breakage rate and the impurity rate were in a decreasing order. At the same time, the factors were multi-objective optimized comprehensively, and the optimization results were verified by experiments. The results showed that the optimum parameters were: 0.72 m/s for the moving speed, 372 r/min for the brush roller speed and 57 mm for the length of brush wire. Under these conditions, the picking rate was 91.36%, the breakage rate was 0.18%, and the impurity rate was 11.67%. The measured values of each index were in good agreement with the theoretical optimization values, which meant that the model established was reliable and could be used for optimization. The results can provide a reference for further improving the structure design and working parameters optimization of the brush-roller castor harvester.