| The development of agricultural mechanization is greatly restricted by the sloping farmland of 6°~15°and 15°~25°in Hilly and mountainous areas of China,which are small and fragmentary,and lack of necessary field infrastructure such as machine-ploughing road.It is difficult for large and medium-sized machinery to complete the operation link.Because of its light structure and easy operation,the electric micro-cultivator has better overcome the problem of large and medium-sized machinery“difficult to go to the field”,and has the advantage of zero emission of cultivation links.It has good application prospects in Hilly and mountainous areas of China.Actual tillage of electric micro-tiller is accompanied by vibration.The deeper the actual tillage depth is,the more violent the vibration of the whole machine is,and the worse the operational comfort.At present,the tillage depth of electric micro-tiller in the agricultural machinery market is mostly less than 10 cm,but the electric micro-tiller with tillage depth greater than 10 cm plays an irreplaceable role in the specific crop planting process.Therefore,this paper takes a trial-produced electric micro-tiller whose tillage depth is more than 10cm as the research object,analyses its vibration performance,and puts forward vibration reduction measures,which provides theoretical basis and reference for the follow-up optimization of the electric micro-tiller and the development of related agricultural prototype.The main research contents and conclusions of the thesis are as follows:Establish dynamics vibration model of the whole machine.The simplified principle of vibration analysis of the whole machine is described,and the force analysis of the whole machine is carried out.The exciting force of the whole machine is calculated,including the electromagnetic excitation force of the motor,the force of the knife roll and the impact force of the soil.The interaction model between the battery box,the motor,the armrest and the support frame is simplified into a single-degree-of-freedom undamped forced vibration model.According to the vibration theory and the foundation,the armrest frame and the support frame are obtained without considering the frame disturbance and deformation,motor first-order constant coefficient differential equation and its matrix equation.At the same time,the vibration mechanics model of the two-dimensional vibration of the whole machine is established,and the differential equation of the second-order vibration and its stiffness matrix,damping matrix and excitation force matrix are obtained.The vibration mathematical model and simulation model of the whole machine are established,and the root mean square values of vibration acceleration at the armrest,motor shell and support plate are obtained.According to the one-dimensional vibration differential equation of the whole machine vibration,the simulation model is built based on Matlab/Simulink,the relevant parameters are input in the simulation model,and the initial value of the integral is set,and the vertical direction of the armrest frame,the support frame plate and the motor casing is obtained.The time-domain variation curve of vibration acceleration and its root mean square value are 10.06 m/s~2,39.51 m/s~2,35.61m/s~2 under fast-speed conditions,and the simulation error is relatively small compared with the vibration test,indicating that it can be used within a certain accuracy range.The improved machine model was simulated and analyzed,and its vibration acceleration was analyzed.Through the field tillage test,the performance parameters of the electric micro-cultivator are measured:the working depth is about 115mm,the width is 80mm,the speed of the knife roll is 140r/min.The productivity of the work is 786.67 m~2/h,and the power consumption of the whole machine is 1.82kW,which provides parameter support for the subsequent performance improvement of the whole machine.Through the field tillage experiment,the tillage performance parameters were measured:the actual tillage depth was about 115 mm;the width was 80 mm;the cutter roll speed was 140 r/min;the battery life was 0.8 h;and the working productivity was about 786.67 m~2/h.The overall power consumption is about 1.82kW.The whole planting performance basically meets the requirements of project establishment and actual farming.Considering the endurance of the whole machine,the quality of the whole machine can be appropriately reduced and the power consumption of the whole machine can be reduced.In the reverse gear,slow gear,mid-range and fast gear,the left and right armrests of the electric micro-cultivator,the support frame plate,the armrest frame crossbar,the motor casing and the cutter shaft connection are tested based on the LMS Test lab platform.The three-way vibration acceleration and the root mean square value of the time domain vibration acceleration curve indicate that the root mean square value of the vibration acceleration in the vertical upward direction is the largest,and the root mean square value of the vibration acceleration in the axial direction of the knife roll is second.The root value is the smallest;the frequency domain acceleration curve indicates that the first-order resonance of the armrest frame and the support frame in the axial direction of the knife roll under the slow working condition has an amplitude of 2.8m/s~2.When the whole machine is in the fast working condition,the root mean square value of the vibration acceleration in the vertical upward direction of the armrest frame,the support frame and the motor casing is 9.45m/s~2,49.08 m/s~2,44.1 m/s~2,which lays a foundation for the establishment and simulation of the subsequent vibration model.Topology optimization of support plate and structural improvement of armrest are carried out.Vibration acceleration of support plate and armrest is simulated based on Simulation model.Considering the optimization of the structure of the whole machine and the vibration reduction requirements of the armrest frame,the continuous topology optimization theory is used to support the support.The topology of the rack is optimized,and the simulation and parameter setting are based on the Ansys/workbench platform.Under the condition of ensuring the mechanical performance,the support frame is reduced by 1.43 kg before optimization.Using the continuous impedance medium theory and the one-dimensional acoustic black hole theory to optimize the armrest frame,three kinds of vibration reduction schemes are obtained.When the mass of the armrest frame is increased by 1.8kg,the root mean square value of the vibration acceleration at the armrest frame is weakened to 8.762m/s~2.Considering the vibration damping effect(increased damping)caused by the structural change of the armrest frame,the root mean square value of the acceleration at the armrest frame It will be smaller. |
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