| As a common nut,chestnut has a cultivation history of at least two thousand years in China,the planting area and output of chestnut ranks first in the world.At present,chestnut harvesting mainly relies on manual picking,which is inefficient and labor-intensive,and is prone to events falling fruits injure people.The operation method of manual harvesting is negative to the development of the chestnut industry.This research aims to promote the mechanized harvesting of chestnut,a beating harvester was developed to achieve high efficiency in response to the needs in the Dabie Mountain chestnut producing areas in Hubei Province.The main research contents are as follows:(1)The biomechanical properties of chestnut tree was studied.The basic parameters of chestnut tree such as planting scale,terrain slope and tree shape were measured in the chestnut plantation in Dahe Town,Luotian County,Hubei Province.The separation force of chestnut fruit was measured at 0°,45°and 90°tension angles.The main distribution range of separation force and the mechanical law that the average separation force gradually decreased with the increase of tension angle were determined.The relationship between the transverse diameter of chestnut fruit and the separation force was studied.It was concluded that the larger the transverse diameter of chestnut fruit,the greater the separation force between chestnut fruit and branches.The results show that chestnut is easier to pick in the direction perpendicular to the fruit stalk than along the fruit stalk.The separation force in the direction of 0°is the largest,and its value is 65.24 N.In order to ensure the harvest effect,the maximum beating force provided by machine harvesting should not be lower than this.(2)According to the planting terrain and planting scale of the chestnut tree,the beating mechanism was designed as a crank-rocker mechanism with no snapback characteristics,in which the rocker was the beating execution part.The kinematics analysis of the rocker explored the motion law of the rocker’s angular displacement,angular velocity,angular acceleration with crank speed.The results showed that the beating mechanism movement was stability.The dynamic analysis of the beating mechanism was carried out,according to the change curve of the inertial force of the beating bar at different speeds,it was concluded that the inertial force of the beating bar was the largest at the working speed of 600 r/min.At the same time,according to the inertial force,the maximum torque of the crankshaft at this speed was determined to be11.88 N·m,and the power of the motor was preliminarily determined to be 800 W.The positioning structure was designed based on the chestnut tree shape and other parameters.The maximum extension distance of the designed telescopic device was 1800 mm,the angle of the pitching device was±30°,and the rotation angle of the steering device was±30°.Finally,the selection of ejector rod,push rod and steering motor was determined through force analysis.(3)The simulation analysis of the telescopic frame and the T-frame were carried out with ANSYS.The static analysis of the telescopic frame showed that under the working state of the maximum force at the end of the telescopic frame,the maximum equivalent stress of the square pipe was less than the yield strength of 304 stainless steel,and the maximum equivalent stress of the installation groove and pipe were less than the yield strength of 45 steel,indicating that the telescopic frame would not cause structural damage during the working process and met the strength requirements.The modal analysis of the first 6-order modes of the T-frame were analyzed.In this study,the first 6-order resonance frequencies of the T-frame in the actual picking operation were obtained,in order to further explore the resonance frequency of the T-frame in the actual operation,the harmonic response of the T-frame was analyzed,and the frequency range was selected from 0 Hz to 1000 Hz.It was concluded that the amplitude of the T-frame in the Y direction under the external load was very weak,and the X and Z directions have obvious amplitude responses at frequencies of 220 Hz,490 Hz and 820 Hz,indicating that the T-frame is prone to these three frequencies.The machine should avoid the external excitation frequency in the above resonance range during working.(4)At the end of this study,the performance test of the prototype was carried out,the results of the orthogonal test showed that the best beating bar material was low density polyethylene(LDPE).When the motor speed was 600 r/min,the length of the beating bar was 450 mm,and the beating angle was+20°,the beating force was 70.71 N.The beating force provided by the polyurethane(PU)material can’t reach the maximum separation force required for chestnut picking.Although the two materials of iron sheet and glass fiber had sufficient beating force,their bending abilities were lower than that of density polyethylene,which were easy to damage the branches and had a greater impact on the mechanical device.Therefore,the best beating material was low density polyethylene.The vibration measurement test showed that the vibration in the Z direction was the largest under the two working conditions.It could be judged that the vibration at measuring point 1 had the greatest impact on the machine and the operator;through data analysis of the acceleration results,it was concluded that the total acceleration of measuring point 1 without the screw rod fixed was 17.85 m/s~2,when the screw rod was fixed,the total acceleration was 12.19 m/s~2.Compared with the fixed vibration amplitude without screw rod,the vibration amplitude decreased by 31.71%.The total acceleration when the measuring point 2 was not fixed by the screw rod was 4.98 m/s~2,and the total acceleration when the screw rod was fixed was 4.16 m/s~2.Compared with fixing without screw rod,the vibration amplitude decreased by 16.47%.The results showed that fixing the screw rod during work was more conducive to the stability of the fuselage.The field test showed that most chestnut fruit picking could be completed within 10 s of picking time control,and the damage to chestnut branches was very small.During the picking time,the average fruit drop rate of the fruit drop device was 90.1%,which met the design requirement of 80%fruit drop rate and met the chestnut harvesting requirements. |
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