| As a special aquatic vegetable,lotus seed has a long history of planting and eating in China.Lotus seeds at milk and wax stages are considered as fresh lotus seeds.With thin,tender and crisp shell,fresh lotus seeds show poor compressive strength and low shear strength.The particular physical properties lead to the problems of crushing and high loss rate in the process of shelling and core opening,which restricts the development of fresh lotus seed processing industry.In order to solve the above problems,based on the study of mechanical properties of lotus seeds with different maturity,a small-scale fresh lotus seed shelling-core opening integrated machine was developed,and the key technologies of shelling were studied.The main research contents of the paper are as follows:（1）Characteristics research of lotus seeds with different maturity.In this study,the lotus seeds from Honghu Lake in Hubei Province with variety of space lotus No.36 were chosen as research object.Firstly,the shape dimensions and water content were measured.Secondly,the mechanical properties of the testing lotus seeds were investigated.The compression test at directions of long-axis and short axis,the whole lotus seed crush test,the shear test during under different speeds and depths and the triaxial compression test were conducted.According to these experiments,the long axis and short axis elastic modulus were analyzed and calculated.After that,the ultimate failure load,and the relationship between shear stress and depth,speed and maturity were obtained.The results show that the average longitudinal and transverse ratios of the lotus seeds with milk maturity,wax maturity and maturity are 1.35,1.28,1.19,respectively,and the water content is 79.84%,70.28%,57.72%,respectively.In addition,the long axis elastic modulus of lotus seeds with milk maturity,wax maturity and maturity are 1.09MPa,1.22 MPa,and 1.85 MPa,respectively,and the short axis elastic modulus are 1.33 MPa,1.42 MPa,and 2.16 MPa,respectively.The ultimate damage loads of three maturity lotus seeds are 81.995N,117.107N,and 167.640N,respectively.Under the same maturity and shear depth,shear force does not change with shear speed.On the other hand,under the same maturity and shear speed,shear force is linearly correlated with shear depth.The compression shelling force of lotus seed in the X,Y and Z directions increases with maturity.Under the same maturity,the triaxial compression forces show the relation that is X<Y<Z,and the elastic modulus of the lotus shell increases with maturity.In addition,with same maturity,the elastic modulus in the vertical direction is smaller than that in the horizontal direction.（2）The overall structure scheme of a small-scale shelling-core opening integrated machine for fresh lotus seeds According to the special mechanical properties of fresh lotus seeds,combined with the problem of high loss rate of fresh lotus seeds processed by the existing lotus seed shelling machine,the overall structure scheme of a small-scale shelling-core opening integrated machine for fresh lotus seeds was analyzed and determined.The proposed machine was composed of hopper,frame,shelling mechanism,core opening mechanism,hydraulic flushing system and power system.Chain drive and synchronous belt drive were employed to transfer power in this machine,and three stepping motors controlled by PLC were chosen as power source of the machine..The overall dimensions of the proposed machine is 1211mm×330 mm×855 mm,and the weight of the whole machine is 54.5kg.working efficiency of the whole machine is 39.2kg/h,shell rate 97%,damage rate 3%.（3）The shelling mechanism design and theoretical analysis of shelling process.According to the special biological characteristics of fresh lotus seed,such as thin lotus shell,tender lotus kernel and crisp whole lotus,a multi-channel integrated low damage shelling mechanism was analyzed and determined.The mechanism is composed of groove wheel group,inner cutter head,outer baffle,shaft,hopper,etc.According to the mechanical parameters of lotus seeds,the structural and working parameters of each key part of the mechanism were comprehensively calculated and analyzed.According to the analysis results,the structural parameters were determined.The diameters of groove wheel and groove base circle were is 240mm and 20mm,respectively.Furthermore,the thickness of groove wheel is 30mm,and the number of grooves is 6.The working parameter was also determined.The limit rotational speed of shelling mechanism is less than 21.3 r/min.According to the force analysis of lotus seed posture adjustment and shell cutting process,the torque of lotus seed in the groove can meet the design requirements under the action of gravity,blade friction and centripetal force.（4）Simulation analysis of shelling process.Whether the lotus seed can be peeled in the shelling mechanism depends on the posture adjustment and the motion state of the lotus seeds in the shelling mechanism.In order to analyze the movement of lotus seeds in the shelling mechanism and to explore the influence of different structural factors on the posture adjustment,the simulation analysis of the shelling process of the shelling mechanism were carried out based on the software EDEM and ADAMS.The results show that the mechanism shows highest posture adjustment rate when the groove wheel speed is 20 r/min,centripetal teeth is used,the tooth pitch is 5mm,and the blade tooth pitch is 1.5c（c=54.7mm is the average circumference of short axis of fresh lotus seeds）.ADAMS software was employed to simulate and analyze the trajectory of any point on the short axis of lotus seed in the mechanism.Through Matlab,the trajectory of lotus seed in the shelling mechanism was plotted.The results show that the motion of lotus seed in the mechanism is the combination of rotation around its own axis and uniform circular motion.（5）Performance test and analysis of shelling mechanism.Taking the tooth shape distance,tooth shape and blade tooth distance as test factors,the shelling rate of lotus seeds at milk ripening and wax ripening stages as test indicators,orthogonal experiments were carried out on three different structures of outer baffles that affect the shelling performance.What’s more,the single factor test was carried out for different level of blade pitch.The best level combination of each factor was determined by analyzing the test results,which was centripetal tooth,tooth spacing of 5mm and blade tooth spacing of 1.5c（C3A3B3）.Under this condition,the shelling rate of fresh lotus seeds can reach 97%,and the damage rate is less than 3%.The results of the single factor test are fitted by quadratic curve,and the theoretical calculation and simulation analysis are further verified. |
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