Design And Research Of Automatic Packaging Device For Hydroponic Lettuce

The development of plant factories can solve the problems of food shortage,food safety,seasonality and regionality of fruits and vegetables.Due to the high water content of the hydroponic lettuce,the quality is tender and easy to damage,and it is easily affected by microorganisms and rot.Therefore,reasonable packaging can maintain the good surface characteristics of the hydroponic lettuce during transportation,and can reduce the mechanical damage caused by the contact,friction and extrusion of the hydroponic lettuce during the handling process.However,at present,hydroponic lettuce has great problems in packaging.Hydroponic lettuce has the phenomenon of “unpackaging or manual packaging”after harvesting.Therefore,in order to realize the mechanization and automation of hydroponic lettuce packaging,this paper developed hydroponic lettuce automatic packaging device with hydroponic lettuce as the research object.The following are the main research contents and conclusions:(1)Study on extrusion characteristics of lettuce and mechanical properties of fresh-keeping film.Using the single factor test method,the relationship between the compression rate of lettuce and lettuce damage was studied with hydroponic butter lettuce.The data showed that the ultimate compression ratio of hydroponic lettuce was 45 %.The test result is the box.Dimensional design provides a theoretical basis.The preservative film has greater elasticity and has a greater influence on the cold cutting of the film.Therefore,the electronic universal testing instrument is used for the drawing and tensile test of the preservative film.The test results show that the pulling force of the preservative film is fluctuated around 2.199 N.The elastic modulus of the wrap film obtained by linear regression was 56 MPa,the elastic limit was 7.27 MPa,and the tensile strength was 24.86 MPa,which provided the basis for the design of the hydroponic lettuce automatic packaging device.(2)The overall scheme of the automatic packaging device is determined.In order to realize the functions of hydroponic lettuce transportation,fresh-keeping film wrapping,fresh-keeping film cutting and sealing,the platter packaging scheme and packaging box packaging scheme were proposed respectively.In consideration of the non-destructive packaging of hydroponic lettuce,the packaging scheme was finally selected.The package packaging scheme consists of a conveyor belt mechanism,a film pulling mechanism,a filmcutting mechanism and a film laminating mechanism.The film drawing mechanism,the film cutting mechanism and the film laminating mechanism of the package packaging scheme are compared and analyzed,and finally the wedge shape is selected.Roller filming mechanism scheme,separate slitting mechanism scheme,and disc brushing and coating scheme.The overall plan for the automatic packaging of hydroponic lettuce was finalized and the workflow of the overall plan was determined.(3)Key components and control system design.The packaging box is the key to the non-destructive packaging of hydroponic lettuce.Firstly,according to the Hertz contact theory,the cross-sectional shape of the packaging box is determined to be circular;then the packaging box is determined according to the relationship between the lettuce compression ratio and the lettuce damage and the range of lettuce expansion.The round bottom box with an inner diameter of 215 mm,a bottom inner diameter of 190 mm and high to the 220 mm was used to check the strength of the package.The wedge-shaped roller and the laminating roller of the film-drawing mechanism,the longitudinal and transverse cutting mechanism of the film-cutting mechanism,and the laminating mechanism are respectively designed and selected.According to the overall scheme of the automatic packaging device for hydroponic lettuce,the core of the control system is determined to be a single-chip microcomputer.The control system also includes two photoelectric switches,one Hall sensor,two stepping motors and drivers,and three relays.According to the workflow of the packaging device and the composition of the control system,the control system flow chart and circuit schematic are designed,and the control program is written based on C language.(4)Prototype and test of automatic packaging device prototype.According to the overall scheme of the automatic packaging device for hydroponic lettuce and the design of the mechanism and control system,the prototype was tested and debugged.Through orthogonal test and range analysis,it is determined that the longitudinal cutter angle is 30°,the film speed is 300 mm/min,and the transverse film speed is 500 mm/min,which is the optimal combination of film parameters.The success rate of the film under the combination was 98.6 %.The test results showed that the efficiency of the prototype of the packaging device was 18.6 s/row;the weight loss rate after the 15 days of the test sample packaging was 1.8 %;packaging success rate is 92 %;the average damage degree of the hydroponic lettuce after the packaging of the test sample was transported 0.094 %.