| Hilly and mountainous area accounts for more than 2/3 of the total cultivated land area in China,and its land parcel is narrow and scattered.This situation makes its cultivation not suitable for large and medium-sized agricultural machinery,but only compatible with small or tiny machinery.The mini-tiller is widely used in hilly and mountainous areas because of its simple structure,light weight,easy operation and convenient transfer in field.Moreover,with the promotion of the urban and rural development in recent years,a large number of rural labors have transferred to non-agricultural industries,which causes a lack of rural labor force.To release the shortage of labor,solve land abandonment issues,and improve agricultural mechanization level in hilly areas,mini-tiller has become an indispensable agricultural machinery.However,the mini-tiller taking the internal combustion engine as the power generally results in high vibration and noise and causes environmental pollution.Therefore,the research of the electric mini-tiller is an urgent demand at the present stage.So far there are few researches on the electric mini-tiller,this thesis took a developed electric mini-tiller prototype as the research object,tested its basic performance through field test,and analyzed its parameters and structure to provide a theoretical basis for its further optimization and researches on related electric mini-tiller.The main contents of this paper are as follows:The field tests for electric mini-tiller prototype were conducted to test the basic performance parameters,which showed a tillage depth of 117.9mm,an actual tillage width of 801.9mm,a normal working rotary blade speed of 143.13r/min,a normal working power consumption of1727.86W,a productivity of 786.67m~2/h,and a life time of 0.883h,and provided a theoretical basis for the subsequent performance improvement for the electric mini-tiller prototype.The performance parameters of prototype were regarded as the design parameters of electric mini-tiller,and its structure was a basis for the whole structure design.After a theoretical calculation and a performance comparison and analysis of the power transmission system components,the permanent magnet brush-less DC motor with a power consumption of 2kW was selected as drive motor.6020 lithium battery in 541 groups was chosen as working battery.Straight bevel gears acted as the main drive manner with a transmission ratio of 3.22.Through analyzing the structure of the prototype,the parts such as knife roller,handrail,body frame,controller and other parts of the electric mini-tiller have been confirmed,and the theoretical design of the whole structure has been completed.In order to improve the prototype structure and improve the performance of the whole machine,a criterion of optimization and discrimination for prototype with small handrail force and small vibration was proposed.Based on this criterion,the gravity center was determined,and the structure of the whole machine was optimized by adjusting the layout.A three-dimensional model calculation was adopted to test gravity center of this prototype,and a 3D model prototype was established on the basis of the physical size and the parts of this machine were endowed with relevant material properties.The feasibility of gravity center calculation though 3D model was evaluated through the comparative analysis of the quality of the actual prototype and parts of 3D model,and the gravity center of prototype was located by this calculation method.The relationship between gravity position and handrail force was determined through the stress analysis of electric mini-tiller.Based on the basis structure and operating principle working,the vibration theory was used to study the excitation force and the key dynamic process in“electric mini-tiller-soil”system and a dynamical model of this system was established through the simplification and parameter identification in the dynamic process of whole structure and components.Based on the characteristics of the dynamic model,the Newton method was used to establish a systematic mathematical model to obtain differential equations of the vibration system.The combination of the equation group and the gravity center calculation method confirmed the relation between gravity center and vibration.MATLAB/Simulink software was employed to establish the simulation model of the“electric mini-tiller-soil”system.The vibration characteristics of the system were simulated by setting the model parameters and simulation parameters.The time domain change curves of the vibration acceleration signals at the handrail frame,the body frame and the motor were obtained with root mean square values of 5.724 m/s2,2.884m/s2 and 2.953m/s2,respectively.Field vibration tests were carried out to test the vibration acceleration signals of the handrail frame,body frame and motor and the signal time domain curve was obtained through filtering and time domain analysis with the RMS values of 5.840 m/s2,3.163 m/s2 and 3.102m/s2,respectively.The comparison of the test results with the simulation results found that the relative errors were 1.99%,7.03%and6.64%,respectively,which were less than 10%,and met the accuracy requirements of mechanical vibration characteristic model.This further verified that the dynamics model of“electric mini-tiller-soil”system is correct.The layout of electric mini-tiller was optimized on the strength of the structure optimization principle and the position of gravity center was located based on the minimum handrail force.It was found that the optimal gravity position could be obtained when the machine center in the forward direction get a distance of 10.24 cm from the drive shaft center between handrail and the drive shaft,where the normal working arm force was 101.1N with a 25.9%reduction.The layout of the electric mini-tiller was adjusted by adjusting the location of the battery.The optimized layout was that in the forward direction the battery located between the handrail and driving shaft and with a distance of 6.99 cm from the driving shaft center.The optimized vibration system model was established and simulated to acquire vibration acceleration signal of the handrail frame,body frame,and motor with the RMS values of 5.347m/s2,2.693m/s2 and 2.807m/s2,respectively,which got decrease of 6.59%,6.62%and 4.94%,respectively,compared the non-optimized simulation results of mini-tiller vibration. |
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