The Study On Contact Mechanical Behavior Between Soil And Wheel And Walking Drive Of Blueberry Harvester

Blueberry has always enjoyed the reputation of "the king of berries" in recent years,its nutritional value has been favored by the public,and the blueberry industry has shown a booming trend.Mechanical harvesting has become an inevitable trend of blueberry harvesting.Although European and American developed countries have developed a high degree of modernization of the blueberry harvesting machine,but its operation mode is not matching the domestic blueberry farming agronomy;the domestic developed blueberry picking machine,because the pooring field surface environment and narrow collecting space,the wheel transmissibility and stability of havesting locomotive are not guaranteed,the damage of fruit tree and fruit has easily happened when harvesting,so study the change about contact behavior between soil and wheel when harvesting machine field operation,promote field transmissibility and stability of domestic blueberry picking machine,achieve the blueberry harvesting mechanization popularization become a difficult problem to be solved.In view of the above problems,this paper uses the combination of theoretical analysis,computer simulation and experimental research to study the contact mechanical behavior between soil and wheel and walking drive system of blueberry.The contact mechanical behavior between wheel and soil and wheel transmissibility when blueberry harvester field operation were studied theoretically.Firstly,the working principle of the self-propelled blueberry harvester and the contact compaction phenomenon of wheel-soil were analyzed,establishing contact stressing model about wheel and soil,obtain the stress expression of different contact area between wheel and soil.Secondly,the mechanical behaviors during contact process between wheel and soil were analyzed,include wheel driving moment,wheel load,wheel subsidence and drawbar pull,and the influencing factors of wheel transmissibility were obtained.Discrete element analysis and simulation were carried out for the contact process between wheel and soil during field walking.Hertz-JKR contact model considering soil particle viscosity was established by discrete element method.The Hertz-JKR model parameters were calibrated by soil accumulation Angle test,and it applied to the Discrete element simulation of wheel-soil contact process.The variation of contact mechanical behavior of wheel-soil under the influence factors of wheel transmissibility was obtained,including contact pressure of wheel-soil,the wheel torque of wheel-soil contact,soil fluctuation rate.Theoretical design,virtual modeling,prototype construction and field performance test were carried out for the walking drive system of blueberry harvester.Firstly,closed hydrostatic drive system is designed,and the components selection of the drive system is assured.Secondly,establishing the AMESim model of walking drive system,wheel multi-working adaptability of walking drive system is analyzed on the basis of variation of wheel-soil contact mechanical behavior,including the wheel synchronous stability,single wheel fall,wheel fell on the same side and the double rear wheels fall.The field test of the prototype verifies the consistency of the four wheels output of the walking driving system,and the maximum deviation of the center line of the tire is 180 mm.The time of crossing the subsidence is 3.3 s,and the whole machine has no purposeful steering deviation.The driving system and the harvesting system are well matched,with the harvesting efficiency of 7.01 kg/min,fruit collected of the tree rate of 92%,and the tree damage rate of 11.5%,the walking drive system and collection system matching fully meet,the working performance of the walking drive system is suitable for field operation.