| The problem of"no machine available"for mechanized water chestnut harvesting seriously restricts the development of water chestnut industry,and the development of efficient and low-loss water chestnut harvesting machine is an urgent need for practical production.The paper developed a vibratory extrusion type water chestnut harvester to address the problems of low productivity,high labor intensity and high damage rate in manual water chestnut harvesting and difficulties in digging and soil separation in mechanized harvesting.The main research contents are as follows:（1）The overall design of the water chestnut harvester was carried out according to the current status of research on water chestnut harvesters and rootstock harvesters such as potatoes at home and abroad,combined with the experience summarized in the preliminary research.The main structure of the water chestnut harvester was clarified to include key components such as:frame,vibrating digging shovel,primary vibrating screen,vibrating extrusion separation device and secondary conveying screen.Through the layout of the overall structure and transmission system,the position of each component and the form of transmission were determined.（2）The selection,design and theoretical analysis of the key components of the water chestnut harvester were carried out.Through the kinematic analysis of the digging shovel tip,the equations of displacement,velocity and acceleration of the shovel tip were obtained to determine the trajectory of the shovel tip movement.The kinetic analysis of the excavating shovel reveals the force on the shovel body and the mechanism of breaking the soil during the process of entering and leaving the soil.According to the design requirements of the vibrating shovel,it is determined that the shovel body is a flat shovel body,the width is 900 mm,the shovel length is 105 m,the shovel surface inclination is 25°,the eccentric bearing eccentricity of the vibrating mechanism is 9 mm,the vibration frequency changes with the tractor rear power output shaft speed,which is 9-12 Hz,and the shovel amplitude is calculated as 50.1 mm according to the geometric relationship.The screen body is driven by the rear drive rubber wheel.The vibrator of the conveyor screen is an active double roller type vibrator,which can make the upper screen surface to be simple harmonic vibration.Through the motion analysis of the upper screen surface of the conveying sieve,the equation of motion at the vibration point is obtained,and the force and motion process of the fruit and soil mixture in the process of throwing are analyzed,and it is determined that the conveying line speed of the conveying sieve should be greater than1.39 m·s-1,and the reasonable range of vibrator vibration frequency is 2.33～9.12 Hz,and the vibration frequency of the vibrator is selected to be 8 Hz in combination with the characteristics of the soil in the water chestnut field which is difficult to be broken.The separation device includes vibrating plate,eccentric vibration mechanism,extrusion roller and other components.The motion trajectory of the vibrating plate was simulated by RecurDyn,and the motion of the vibrating plate at the squeezing point was analyzed,and the motion of the vibrating plate was determined as an inclined sine oscillation around the vibration center.The clods entering the separation device are classified and the form of clod crushing is analyzed.Analysis of the motion of the squeeze rollers and the impact force of the nail teeth.The comprehensive force and crushing mechanism of medium and large soil blocks at the vibrating squeezing and separating device are studied,and it is found that the soil block crushing is mainly related to the amplitude of vibrating plate,vibrating frequency of vibrating plate and the speed of squeezing roller,which provides theoretical support for the simulation test.（3）Simulation test and analysis of excavation shovel based on DEM-MBD coupling simulation.Excavation shovel digging performance experiment.With the shovel vibration frequency,digging depth and forward speed of the machine as the test factors and the digging resistance as the evaluation index,a three-factor,three-level Box-Behnken center combination test was conducted on the shovel to investigate the influence of different working parameters of the shovel on the digging performance.The test results show that the main order of influence on the digging resistance is:forward speed>digging depth>digging shovel frequency,and the regression equation is established and the parameters are optimized.（4）Simulation experiments and analysis of separation device based on coupled DEM-MBD simulation.The single-factor simulation test was conducted to investigate the influence of the vibration frequency of the vibrating plate,the speed of the squeezing roller and the distance between the vibrating plate and the squeezing roller on the anti-clogging performance of the separation device,taking the time required for complete separation of the soil layer and the average force on the water chestnut model as the evaluation indexes.The test results of the effect of excavation shovel vibration frequency on the anti-clogging performance show that:with the increase of vibration frequency of the vibrating plate,the time required for separation tends to decrease,and after the vibration frequency of the vibrating plate is greater than 5.2 Hz,the time required for separation is less than 1.0 s,and the shortest time is 0.832 s,which is not easy to produce congestion.The average force on water chestnut tends to increase,and the maximum force is 46.9 N,which is less than the maximum shear force that water chestnut can withstand,67.2 N.It is not easy to damage water chestnut.The test results of the effect of the speed of the extrusion roller on the anti-clogging performance showed that the time required for separation tended to decrease as the speed of the extrusion roller increased,and when the speed of the extrusion roller was greater than 260 r/min,the separation time was less than 1.0 s,and the shortest time was0.790 s,which was not easy to produce congestion.The average force on water chestnut was increasing,and the maximum force was 60.7 N.After the speed reached 300 r/min,the trend of increasing the speed of the squeeze roller on the separation time decreased,but it would cause a sharp increase in the average force on water chestnut.Therefore,the squeeze roller speed should be selected near 300 r/min.The experimental results of the effect of the minimum distance between plate rollers on the anti-clogging performance show that:as the minimum distance between the vibrating plate and the squeeze roller decreases,the time required for separation decreases,and when the minimum distance between plate rollers reaches 8 cm,the separation time is less than 1.0 s,and the shortest time is 0.796 s,which is not easy to produce congestion.The average force on water chestnut rose slightly with the minimum distance between plate rollers and then decreased,and the maximum force was 43.7 N,which was not easy to damage water chestnut.The single-factor experiment showed that the separation device had better anti-clogging performance and was less likely to damage water chestnut when the vibration frequency of vibration plate was about 6.5 Hz,the speed of extrusion roller was about 300 r/min,and the distance between vibration plate and extrusion roller was about 8 cm.The soil crushing performance of the separation device was tested with the vibration plate amplitude,vibration plate frequency and squeeze roller speed as the test factors,and the soil crushing rate as the evaluation index.The CCD central combination test was designed using Design-Expert 10.0.7 software,and significance analysis,ANOVA and response surface analysis were performed.The test showed that the main order of influencing soil crushing rate was:vibrating plate frequency>vibrating plate amplitude>squeezing roller speed,and the interaction of vibrating plate frequency and squeezing roller speed had a significant effect on soil crushing rate.After parameter optimization,the optimal working parameters are 33.05 mm vibrating plate amplitude,6.63 Hz vibrating plate frequency and 336.72 r/min squeezing roller speed,and the optimal soil crushing rate is 93.58%.In summary,the actual selection of vibrating plate frequency 6.5 Hz,squeeze roller speed 330 r/min,the distance between vibrating plate and squeeze plate is 8 mm,and the eccentric bearing with eccentric distance 15 mm is selected during processing,and the amplitude of vibrating plate is 32.41 mm calculated according to the geometric relationship.（5）Field performance test and analysis of the prototype machine.The performance test of the prototype machine was conducted in the water chestnut field of Tuanfeng County,Hubei Province,China,and the average soil breaking rate was measured as 93.55%,the rate of bright water chestnut was 80.33%,and the damage rate was 28.09%.The test showed that the machine operated well and had strong soil crushing ability,However,the damage rate is relatively high,and the rate of Mingluo needs to be improved. |
PDF Full Text Request