| Water chestnut,also called alias horsetail,water chestnut,ocotillo,etc.,is the bulb of the monocotyledonous perennial herb water chestnut,which is loved by the nation for its crunchy and sweet taste and rich nutrition.Water chestnut grows in the 9～20cm soil layer,and manual harvesting requires plucking the soil layer and collecting the corm.Water chestnut harvesting is difficult and operationally intensive,which seriously restricts the development of water chestnut industry,therefore,there is an urgent need for a machine that can effectively harvest water chestnut.The mechanized harvesting of water chestnut is mainly divided into four parts:digging,conveying,soil-corm separation,and corm collection.The soil where water chestnut is grown belongs to the southern clayey soil,which is sticky and strongly bonded,easily forming lumps and not easily separating from the corm,therefore,soil-corm separation is a difficult part of water chestnut mechanized harvesting.In response to this problem,this paper designs a spring roller water chestnut harvester soil-corm separation device,which combines soil block crushing and soil screening to improve the efficiency of soil-corm separation.The main research contents of the whole paper are as follows:(1)Water chestnut and its field soil material characteristics test was carried out.The basic physical parameters such as triaxial size,density and compressive mechanical properties of water chestnut and density,moisture content and particle size distribution of water chestnut field soil as well as the contact parameters between water chestnut,soil and machine were measured to provide a parameter basis for subsequent machine structure design and simulation optimization tests.(2)The structure design of spring-roller type soil-corm separation device was completed.In view of the technical requirements of soil-corm separation for dryland water chestnut harvesting,three soil-corm separation schemes were proposed,and the spring-roller type soil-corm separation scheme was determined after analysis and demonstration.Subsequently,the design of the spring roller structure size,installation method and transmission system were carried out,and the spring roller soil-corm separation principle and the relative motion process of water chestnut-spring were analyzed.(3)The simulation and optimization test of spring roller structure parameters were completed.Combined with the preliminary material characteristics tests,a discrete element model of water chestnut and soil mixture was established.The EDEM simulation software was used to simulate the sieving process of soil-corm mixture on the spring roller,and single-factor tests on spring outer diameter,pitch,rotational speed,spacing,high and low interval arrangement,and feeding speed were conducted to determine the influence of each factor on soil-corm separation.The quadratic regression orthogonal test was conducted with water chestnut sieving rate and soil sieving rate as the test index,and the regression equations of water chestnut sieving rate and soil sieving rate were obtained,and the optimal combination of parameters was obtained by using Design-Expert software:100 mm outer diameter,30 mm pitch,9 mm spacing and 420 r/min rotational speed.The water chestnut sieving rate was 80%and soil sieving rate was 80.69%,and the accuracy of model prediction was verified by simulation test.(4)The analysis of spring roller rotational vibration characteristics was carried out.The radial vibration of the spring is simplified to a single-degree-of-freedom vibration system,and the vibration differential equation is established and the factors affecting the vibration characteristics of the spring are analyzed.The inherent frequency of the spring was determined by modal analysis to avoid resonance during spring operation.A spring vibration test platform was built to measure the amplitude and frequency of the spring by means of a high-speed camera to determine the spring wire diameter and speed suitable for the operation of the machine.The collision process between the water chestnut and the spring was analyzed to determine the effect of different factors on water chestnut damage and to provide reference for subsequent machine structure improvement and operation parameter adjustment.(5)The field performance test of water chestnut harvester was carried out.The simulated harvesting test was carried out to consider the soil-corm separation effect of different wire diameter spring operation and the stability of machine operation,and it was determined that 12 mm wire diameter spring was selected to assemble the soil-corm separation device of water chestnut harvester.The actual harvesting performance test was conducted,and a total of nine sets of experiments were conducted on three factors:spring speed,soil moisture content,and whether the cutter disc was installed.The average values of the performance indexes of the water chestnut harvester were measured as follows:operating speed 0.21m/s,operating efficiency 0.19m~2/s,soil crushing rate 75.61%,bright caper rate 82.42%,wounding rate 14.73%,and skin breaking rate 7.01%.Comparing the operating effect before and after the installation of the cutter disc,it was found that the cutter disc would significantly increase the damage rate of water chestnut and the front cutter disc should be removed.Comparing the operating effect of different spring speed,it was found that the water chestnut injury rate increased when the speed was too high,and the speed should not exceed 369 r/min.Comparing the operating effect of different soil moisture content,it was found that the lower moisture content soil was beneficial to water chestnut harvesting operation,but too low moisture content soil was easy to cause water chestnut collision damage. |
PDF Full Text Request