Design and experiment of slide-combing roller finger for Polygonum cuspidatum root-soil separation

Root-soil separation is a critical link in Polygonum cuspidatum harvesting. It has been shown that combing machines are very useful for separating soil from root. However, it is a common occurrence during this process for Polygonum cuspidatum to be entangled by the machine, which leads to excessive energy consumption. In order to overcome the imperfections and defects of this kind of machine, a new roller finger for root-soil separation was designed. By applying the slide-cutting theory, the critical slide-cutting angle of the roller finger was calculated. Considering the friction coefficient between between Polygonum cuspidatum and roller finger, the slide-cutting angle was found to be more than 30°. By solving the differential equation and the logarithmic spiral equation, the curve equation of the roller finger was established in polar coordinates. With a mechanical model between Polygonum cuspidatum and roller finger set up, a function involving energy consumption, rotational speed of roller, length of roller finger and slide-cutting angle of the roller finger was obtained. It was found that the optimal slide-cutting angle varied in energy consumption with the difference of the coefficient of friction between Polygonum cuspidatum and roller finger. A pseudo-color energy figure about the relationship among consumption, angle of friction and angle of slide-cutting was shown with the MATLAB (Matrix Laboratory) software by the function derivation of the slide-cutting angle. It turned out that the optimal slide-cutting angle increased slowly as the coefficient of friction grew. Utilizing the curve, the maximal slide-cutting angle was obtained. The rotational speed of roller (Factor A), the slide-cutting angle (Factor B) and the length of roller finger (factor C) were selected as 3 factors of the orthogonal simulation experiment in order to explore their impact on the rate of soil-detachment and energy consumption. The priority order of the factors for the rate of soil-detachment was A > C > B > A×B > A×C > B×C, and that for the energy consumption was C > A > B > A×B > A×C > B×C. The rotational speed of roller and the length of roller finger had an extremely profound effect on the rate of soil-detachment while the slide-cutting angle had a profound effect on it. Meanwhile, those 3 factors also had an extremely profound effect on the energy consumption. Although the 3 factors performed differently on the rate of soil-detachment and energy consumption, by utilizing a fuzzy comprehensive evaluation method, a comprehensive evaluation on the results of the rate of soil-detachment and energy consumption was carried out by the multi-objective optimization design method. Results reflected the important differences between the rate of soil-detachment and energy consumption, and a weight matrix was set for fuzzy calculation. According to the comprehensive evaluation, the sequence of the influence of the factors on the comprehensive result was A > C > B×C > A×C > A×B > B, and the rotational speed of roller had an extremely profound effect on the comprehensive result while both the length of roller finger and the slide-cutting angle × length of roller finger had a profound effect on it. The results of fuzzy calculation showed that the optimal parameters were as follows: the rotational speed of roller of 350 r/min, the slide-cutting angle of 67°, and the length of roller finger of 30 mm, and under these conditions the rate of soil-detachment was 93.03% and the energy consumption was 76.73 W. © 2017, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.