Experimental Study On Harvesting Mechanical Properties Of Greenhouse Leafy Vegetables

In this paper,the lettuce leaf and celery leafy vegetables in the greenhouse were taken as research objects.Considering the specific production and harvesting methods,the experimental study and mechanism analysis of the mechanical properties of greenhouse leafy vegetables were carried out to provide basic research for the optimization of leafy harvest mechanized equipment design.Data support has important academic significance and practical value.The mechanical properties of leaf extract from soil,tensile force and cutting force of the roots were analyzed by experiments,and the effects of related factors on the mechanical properties of leafy vegetables were analyzed.Based on the shear test of the physical property tester,the root-stem cutting mechanics simulation model of lettuce was constructed based on LS-DYNA,and the cutting simulation analysis and experimental research were combined to further analyze the cutting force and stress distribution during root cutting of lettuce.The main research contents and results of this paper are as follows:(1)Combining the harvesting methods of leafy vegetables,the extraction force of extracting leafy vegetables from soil was studied.The effects of extraction angle,soil compaction and soil moisture content on the extraction force of greenhouse leafy vegetables were analyzed.The test results show that the greater the soil compaction,the greater the extraction force of the leaf rhizome.In the test,the soil compaction reached 468.7 KPa,and the lettuce and celery extracting power reached a minimum of 8.63 N and 7.45 N.When the soil compaction reached 740 KPa,the extraction force of lettuce and celery reached the maximum,which was 16.85 N and 15.08 N,respectively.When the soil moisture content is 9.7% and the extraction angle is 30°,the extraction force is the smallest,lettuce is 8.63 N,and celery is 7.45 N.(2)In order to prevent the stems and leaves of leaf vegetables from being broken during the harvesting process of leafy vegetables,the tensile mechanical properties of greenhouse lettuce and celery stems were studied.The effects of leaf leaf stretching rate,stretching position and stem moisture content on the tensile strength and tensile load of leaf stalk were analyzed.The results showed that with the increase of stalkmoisture content,leaf stalk The maximum tensile load will gradually decrease and the maximum tensile stress will also decrease.Under the same stretching position and water content of leaf stalk,the tensile speed had no significant effect on the tensile strength of stalks of butter lettuce and celery.When the same tensile speed and sap moisture content,the maximum tensile load and tensile strength of lettuce and celery stem parts were smaller than that of roots and stems.Through comparative experiments,the tensile load and tensile strength limit of each part of celery are much larger than that of lettuce stalk.(3)The shear mechanical properties of lettuce roots were studied.The effects of shearing speed,sliding angle,shearing position and shearing tool type on the cutting of lettuce rhizomes were analyzed by single factor and multi-factor shear test.The multi-factor orthogonal test and variance analysis of shear force show that the influence of each factor is shearing speed>shearing position>slip angle,and the shearing speed and shearing position have significant influence on shearing force.The single-factor design shear force test was carried out on the tool type.The test shows that the shearing effect of the serrated knife is better than that of the optical knife.Under the conditions of the same cutting angle and shearing speed,the maximum shearing force of the serrated knife is higher than that.The light knife was1.97 N small.One-way analysis of variance showed that the type of tool had a significant effect on the shearing force of lettuce roots.(4)According to the requirements of field harvesting cutting speed,the simulation model of lettuce root and stem cutting dynamics was established based on LS-DYNA software,and the simulation test analysis of lettuce root and stem cutting under multi-case conditions was carried out.The cutting test of lettuce roots and stems was carried out on the pendulum cutting test bench.The test model of the cutting dynamics of lettuce was verified by the test bench test data.The error of the maximum cutting force measured value and simulated simulation value were between 4.9% and 9.8%,respectively.The validity of the simulation model was verified.As the cutting speed increases,the breaking stress also increases.At thesame time,the power consumption under the cutting speed of 0.2m/s,0.5m/s and1m/s is 650 mJ,0.96 J,1.18 J,and the cutting power is 0.6W.Using validated simulation models of the actual work is further given feed rate of the knife for cutting lettuce roots simulation results show that implement forward speed 0.5m/s under no force and power were less than the forward speed simulation of working conditions,respectively 9.8N,540 mJ.The cutting force and power consumption were reduced by34.4% and 16.9%,respectively.