| As an aquatic cash crop,lotus has high ornamental and economic value.Lotus seeds which are rich in many nutrients such as vitamins and amino acids and have high nutritional value.The market demand for lotus seeds in the milk and wax stages has grown significantly in recent years due to their fresh and energizing taste,and an urgent need for mechanized threshing technology for fresh lotus seeds has emerged.The high antidestructive power of fresh lotus tissue and the delicate and flimsy nature of fresh lotus seeds,however,significantly raise the challenge of automated threshing of fresh lotus seeds,and the mechanical threshing technology of fresh lotus seeds is still undeveloped.Therefore,this work builds a fresh lotus seed thresher suitable for milk ripening and wax ripening and investigates the essential components of the thresher based on the analysis of the features of various mature lotus seedpod tissue materials.The main contents of this work are as follows:(1)The tissue components of lotus seedpod at various stages of maturity were characterized.The fundamental physical parameters,such as tissue moisture content and height of rosettes at different maturity levels,were measured and evaluated.The shear and tensile mechanical properties of lotus seedpod at different maturity levels were explored by devising single-factor and orthogonal experiments.To examine the pierce mechanical characteristics of lotus seedpod tissues at various stages of maturity,a single-factor test was created.The results of the fundamental physical parameters demonstrated that the moisture content of all tissues of lotus puffs decreased as the maturity increased,with the epidermal tissue’s moisture content changing the most,from 77.71%to 53.69%,and the flocculent tissue’s moisture content changing the least,from 78.60%to 64.24%.At the stages of milk ripening,wax ripening,and finish ripening,the mean values of lotus puff diameter were 85.51 mm,88.47 mm,and 98.66 mm,respectively.The mean values of height were 53.33 mm,52.19 mm,and 52.90 mm,respectively.The lotus seedpod epidermis had significant anisotropy in shear and tension,and the external load loading method had a stronger impact on the shear and tensile rupture forces,according to the results of the single-factor test on the mechanical characteristics.With increased maturity,the epidermal longitudinal shear rupture force did not change significantly,while the transverse shear rupture force gradually increased.The epidermal transverse tensile rupture force did not change significantly,while the axial tensile rupture force increased sharply.The epidermal shear and tensile rupture forces were not clearly influenced by the loading rate.Anisotropy had no effect on the epidermal puncture damage in lotus seedpod.As the lotus seedpod grew more mature,lotus seed surface’s puncture rupture force gradually decreased while the epidermal puncture rupture force gradually increased.As the probe’s diameter increased,the puncture rupture force of the canopy and the epidermis of lotus seedpod increased.The results of the epidermal shear and tensile orthogonal tests revealed that the loading method had greatest impact on the epidermal loading rupture force,followed by maturity.What’s more,the least significant impact was caused by the loading rate.The external load loading method had the largest impact on the maximum rupture force(p<0.05).The results also showed that different maturity lotus seedpod skin loaded in longitudinal shear or transverse tension could result in less external load loading damage.Consequently,comparing the loading damage state of lotus seedpod under three different loading methods and combining with the existing research on the mechanical properties of lotus seedpod,the suitable loading method was determined.During threshing process,the puncture load will be applied to damage the lotus seedpod tissues first,after that,the tensile load to tear the lotus seeds will be imposed.(2)The overall structure of a fresh lotus seed threshing machine was designed.A"three-step" threshing scheme was proposed to design the fresh lotus seed threshing machine,which was composed of a vertical cone threshing mechanism,a wind-selecting and separating mechanism,and a cone-shaped kneading mechanism,based on the problems that were likely to arise in the threshing process of lotus seedpod according to their material characteristics.The core device of the design,the vertical cone threshing mechanism,was designed with specific structure and parameters,and the inner cone disc was divided into functional areas.A hybrid threshing element with rigid hook teeth and flexible rod teeth was designed for the characteristics of high resistance strength of fresh lotus seedpod and fragility of fresh lotus seeds.Through the analysis of the forces acting on the lotus seedpod during crushing,it was concluded that the crushing effect of the lotus seedpod was more closely related to the inclination angle of the inner cone disc,the rotational speed of the mechanism,and the arrangement of the threshing elements.The results provide a theoretical basis for clarifying the key parameters of the threshing mechanism.(3)The crushing process of fresh lotus seedpod in the proposed vertical cone threshing mechanism was simulated using Discrete Element Method(DEM).The simulation of the crushing process of lotus seedpod was carried out to analyze the effect of different cone disc inclination angles of the threshing mechanism on the crushing effect of lotus seedpod,so as to determine the optimal cone disc inclination angle.In order to conduct the discrete element simulation,the simulation parameters were calibrated.The intrinsic parameters of the lotus seedpod were determined by the basic test.The contact parameters between the lotus seedpod and the lotus seedpod and the contact parameters between the lotus seedpod and the steel plate were determined by the inclined plate test,the collision test,and the simulation.The bonding parameters of the lotus seedpod skin were determined by the physical test and the simulation.The bonding model of the lotus seedpod was established.The calibrated parameters were used to carry out the crushing simulation of lotus seedpod in the designed threshing mechanism,varying the inclination angle of the cone disc of the threshing mechanism.The number of bond key of the lotus seedpod model was taken as the test index in the simulation.The simulation results showed that the number of bond key fractures was the largest and displayed best crushing effect when the inclination angle of the cone disc of the threshing mechanism was 45°.The most suitable cone angle was determined to be 45°.(4)Performance tests of the threshing mechanism prototype were carried out.The prototype of the proposed vertical cone threshing mechanism was processed and prototyped.In response to the problem of blockage caused by lotus seedpod hanging on the teeth during threshing,rigid hook teeth were optimized and the ball-drum hook teeth were designed.Using the working speed,the arrangement of threshing elements and the continuous single feeding volume as test factors,the unthreshing rate and the damage rate of lotus seeds as test indexes,the single-factor test and the orthogonal test were conducted to determine the optimal combination parameters of the threshing mechanism,as the working speed was 190 r/min,two rows of rigid hook teeth area crossed in the upper and lower rows,and the flexible rod teeth area was fully arranged in the upper row and spaced in the lower row,and two lotus seedpod were put in each time.It was verified that the working efficiency of the threshing mechanism for lotus seeds at wax ripening stage could reach more than 80 kg/h,the unthreshing rate was less than 15.8%and the damage rate was less than 13.5%.The lotus seed damage state and damage causes were analyzed,which was closely related to the collision speed,collision frequency and the material and shape of the collision contact elements with lotus seeds.The damage form of lotus seeds mainly included three forms of knockdown damage,scraping damage and internal damage,and the breakage form of lotus seeds was mainly affected by the working speed. |
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