| Facility agriculture is an important part of modern agriculture and one of the important symbols of the agricultural modernization development level of a country or region.Lettuce is one of the crops grown in facility hydroponic agriculture.The technical process of hydroponic lettuce production in facilities mainly consists of sowing,seedling rearing,transplanting,cultivation and harvesting.In order to reduce labor input and realize mechanization and automation of operation links,a series of research and development on supporting equipment of production links has been carried out at home and abroad.Some production links have realized mechanization operation,but the harvest link is still mainly artificial,and most of the relevant equipment research and development is in the experimental stage.In order to solve the problems of large labor demand and low degree of automation in hydroponic lettuce harvesting,this paper took hydroponic cream lettuce as the research object,designed an automatic harvesting device for facility lettuce in factory production on the basis of studying its planting mode and mechanical properties,and carried out the trial production of prototype and the whole machine performance evaluation test.The main research contents are as follows:(1)The physical parameters and mechanical properties of hydroponic lettuce in facilities were studied.The basic physical parameters of hydroponic butter lettuce,such as total height,plant height and rhizome diameter,were measured firstly.The results showed that the damage area increased with the increase of holding distance,pulling height and pulling pressure.When the clamping distance is 30 mm,the pulling height is 20 mm and the pulling pressure is 0.4MPa,the damage area of lettuce reaches the minimum value of 315mm2.The shear force increased with the moving down of the cutting position,and decreased with the increasing of the cutting pressure and the sliding cutting Angle.When the sliding cutting Angle was 20°,the cutting pressure was0.3MPa,and the cutting position was 4mm from the lettuce bottom leaf,the root shear force was the minimum value of 6.3N.(2)The plan for a hydroponic lettuce harvesting facility was designed and selected.Combining the artificial harvesting method and the hydroponic lettuce planting mode of facilities,considering that continuous harvesting method would cause large damage to lettuce,a harvesting scheme based on intermittent harvesting method was determined,and then the mechanical harvesting process of butter lettuce was analyzed.The design and selection of different schemes of intermittent harvesting conveying mechanism,transplanting cup fixing mechanism and lettuce picking and handling mechanism were carried out respectively,and the overall design scheme of harvesting device was finally determined.(3)The harvesting device structure is designed and the control system is developed.Based on the overall scheme of the harvesting device,combined with the characteristics of the research object,the overall structure of the harvesting device was designed,and the key components of the conveying mechanism,the transplanting cup fixing mechanism and the lettuce picking and handling mechanism were designed and selected.Secondly,the harvest device operation control system is designed,the control system hardware selection and programming are completed,and the software and hardware debugging is carried out according to the work flow of the control system.(4)Trial production and performance test of harvesting device.The trial production of the harvest device prototype was completed,and the harvest performance evaluation test was carried out under normal no-load operation of the harvest device.The test results showed that the success rate of lettuce harvest was 94.87% and the damage rate was 8.67% under the conditions that the conveying efficiency of the conveying parts of the planting tray was 210mm/s and the harvesting efficiency of 330 lettuce plants /h.The prototype can achieve the intended design purpose. |
PDF Full Text Request