| Screening of agricultural materials is an important link of mechanical harvesting process. Clogging problem in this section leads to a low efficiency and a high cleaning loss. In China, rape materials are easily adhered on cleaning screen owing to their high water content and viscosity. This restricted the popularity of rape combine harvester. On the other hand, along with the increasing mechanical harvesting level of main food coops and the upgrade of harvesting technology, the clogging problem caused by threshing structure or by high feeding quantity become a new focus. That means the traditional screening model should be improved.Bionic research is a hot issue in recent years and has provided many useful technology or inspiration for solving some problems in many areas. In order to solve these clogging problems in screening section, friction and particles’motion in bionic anti-clogging screening process of agricultural materials have been deeply studied in this paper by theoretical analysis and simulation software and experiments respectively from surface bionics and motion bionics. The main research work is summarized as follows.(1) In order to reveal the drag reduction mechanism of bionic nonsmooth surface for rape materials, reciprocating friction between rape stalk and nonsmooth surface was studied both from experimental and theoritical aspect. In experimental aspect, the stick length L was defined and used in the analysis of reciprocating friction force in phase diagram from the angle of stick-slip friction. The result shows that the reciprocating friction between a rape stalk and nonsmooth metal surface contains slip friction and stick friction, and the friction force both on convex surface and concave surface all decrease by about 200N with the increase of reciprocating frequency. It is also showed that the stick length L on concave surface is equal to the one on somooth surface but smaller than the one on convex surface, which partly explains the better drag reduction effect of convex surface than the concave surface in field experiment. In theoritical aspect, a physical contact model and mathematical model between a rape stalk and nonsmooth metal surface in reciprocating condition were builded, and a theoretical calculation example was provided later to interpret the micro-vibration mechanism in vertical direction. Comparative analysis between theoretical value and test value indicates that every impulse response caused by convex contains forced vibration response and free vibration response when the scale factor η≠1, and the free vibration response decaied by damping coefficient c. It is also showed that the theoretical displacement in vertical direction when ζ=0.2 and η=2 probably fit with the test value, and the chang regulation of theoretical amplitude fit the test value well when frequency is 5 Hz but smaller than the test value when frequency is 1.67 Hz and higher when frequency is 8.33 Hz or 11.67 Hz.(2) Based on high-speed camera technology and target image tracking technology, the waving process of winnowing pan using by human was studied from the angle of motion bionics and the trajectories both of the front and back marker points on the bottom of winnowing pan were obtained. Analysis of the trajectory showed that it could be decomposed as 2 translations and 1 rotation and be synthesized as rising stage, dropping stage and pushing stage. The rising stage and pushing stage are all in favor of the dispersion and back-moving of particles materials. Inspired by the motion bionic research, a new variable-amplitude screening mechanism was developed based on traditional derrick-like reciprocating screening mechanism. Displacements of 11 marker points on the variable-amplitude screen and the turning angle ys of the screen were obtained using Adams software. Then the amplitude |ri|, vibration direction angle β1 and the local throwing strength Dp of every marker points on the screen were decucted and calculated. Effects of the dip angle of the front derrick ad on these parameters were analyzed.(3) In order to facilitate the particles simulation in EDEM software, motion of the variable-amplitude screen was decomposed as 3 DOF (2T-1R) from the angle of one-way coupling. Then the simulations of particles’motion were carried out in EDEM software. Frequency f and dip angle of the front derrick ad were selected as control factors in the simulation, and the particles is a misture of rice grain and rice stalk. Based on the principle of statistics, expansion coefficient δx(t) and δz(t), deformation coefficient φb(t), layring coefficient λf and back-moving coefficient γq(j) were defined and analyzed in this paper. The results showed that ad influenced δx(t) obviously (especially when αd is 15°), and f influenced γq(j) obviously but is unstable. It is also showed that the back moving efficiency in the whole range of the screen could be enhanced when αd increased.(4) Both kinetic energy (E谷' and E茎杆) and potential energy (W谷' and W茎杆) of these moving particles on the variable-amplitude screen were investigated with the analysis of their absorptivity (XE and XW) in this paper. The effect of αd and f on these energy indicators were also analyzed, and the motion characteristics of these particles were depicted from the angle of energy. The results showed that the activity of rice grain and rice stalk on the front of the screen is similar to each other, the kinetic energy of particles increased and the absorptivity decreased when αd is 45° It is also showed that the kinetic energy of particles increased when frequency increased, and the potential energy of particles increased when αd increased. The absorptivity of potential energy of particles is much higher when αd is 15° or 30(5) Based on high-speed camera technology, rice particles were choosed as representative materials in the experiments on variable-amplitude screening test-bed when αd was adjusted by 5° between 0 ° and 45 °. Indicators of Scx (displacement in x direction of the particles’ center),S1 (former distance of particles), S2 (length of particles) and S3 (thickness of particles) were defined and measured based on image measurement technology. Comparison between the experiment and the simulation both in 1 cycle and 8 cycles under same conditions showed that the decomposition of variable-amplitude screen motin is feasible, and the result of the simulation is correct. Analysis of these indicators showed that the back-moving efficiency could be enhanced quicly when ad increased (especially after 15°).Friction and particles’ motion in the anti-clogging screening process of agricultural materials were studied from the angle of bionic in this paper. These investigations deepened the original drag reduction researching works of bionic nonsmooth surface and expaned the researching area of bionic technology in agriculture area. So it is useful for resolving the clogging problems in cleaning section and meaningful for promoting bionic researching in agriculture area. |
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