Development And Performance Study Of The Lifting Platform For Hilly Orchards

In recent years,the orchard industry has gradually become the main source of income for the fruit farmers.With the continuous expansion of the planting area of fruit trees,the orchard operation mechanization has also been rapidly developed.Hilly orchard has a low degree of mechanization limited by the topography,most farmers still use ladders,stools and other climbing ways especially in picking and pruning operations,which not only has low efficiency and high labor intensive,but also a high security risk when working on the rugged slope.The orchard lifting platform is a kind of semi-automation implement that assists the farmers to complete the orchard operation.Although some simple lifting platforms were developed,there were still some problems in terms of structure and function,such as single operating form,small operating range,and they were basically used for flat terrain such as plain areas.However,there were lack of models which could work and apply to the hilly orchard complex terrain and fruit planting environment.Therefore,it is of practical significance to design an orchard lifting machine suitable for hilly terrain operations.Therefore,the development and performance study of the hilly orchard lifting platform are carried out in this paper.The main contents are as follows:(1)Planting patterns of standardized orchard was researched and geometric parameters of fruit trees were measured in hilly orchards,which provided reference for the design of structural parameters of the lifting platform.Compared with the structure and function of the existing models,the folding arm mechanism was chosen as the lifting form.Then the design value of the main operating parameters was determined based on the geometric parameters of fruit trees,operating range and the operation stability on slopes:the maximum lifting height was 1.2 m and the maximum operating radius was 1.4 m.The main components of the lifting device were designed,including the lifting arm,rotary support,manned worktable,leveling mechanism,and hydraulic components.According to the relationship between the lifting arm and the design values of the operating parameters,the length of the lower arm was set as 590 mm,the length of the upper arm was set as 900 mm,then the installation position of the lifting cylinders was designed.The manned worktable with a door on one side was designed,and it was connected with the lifting arm through the leveling device.The leveling device realized front and back leveling of worktable by hydraulic cylinder and left and right leveling by rotary drive to reduce the effect of leveling operation on the stability of the whole machine.The strength of the lifting arm was checked and the structure parameters of link arm were designed.Hydraulic components were designed and type selected,among which,rotary drive used worm gear structure.Besides,hydraulic circuit was integrated and the oil connection was completed according to the location of the components.Then,the control device with 10 buttons of lifting,rotating and leveling was installed on the front of the manned worktable.(2)The relationship between the installation position parameters of the lifting device on the crawler chassis,the center of gravity,the obstacle performance and the running performance of the whole machine was studied.According to the design objectives,the installation position of the lifting device was determined through the theoretical analysis and dynamic simulation of Recurdyn,and it was 90 mm to the left of the longitudinal center line of the chassis table and 670 mm to the trailing edge.At this time,the center of gravity of the lifting platform was 59.3 mm away from the center of the chassis,37.7 mm to the right,and the height to the ground was 645.7 mm.The operation stability on slopes was verified,and the tilting angle of two extreme operating positions with the maximum lifting height and maximum extension radius were 24°and 23.6°,23°and 22.4°,respectively,which showed that the lifting platform had good operation stability on slopes.The influence of leveling operation on the center of gravity and the stability of slope operation was studied,and the results showed that it had relatively little performance impact.The trajectory of the worktable during the lifting and rotating operations was analyzed,and the trajectory boundary equations in the space coordinate system were obtained to calculate the longitudinal operating range,which was 1.9 m2.Combined with the horizontal operation range of 3.6 m2,this lifting platform had certain advantages in operating range compared with other existing scissor lifting machinery orchard machines..(3)After processing the components of the lifting device,the prototype of the lifting platform for hilly orchard was assembled.A preliminary test of the prototype was carried out to examine hydraulic system,the operation performance of lifting,rotating,leveling,tilting and traveling.The AMESIM simulation showed that the designed hydraulic system was reasonable.The results of performance test showed that the maximum lifting height of the manned worktable was 1.22 m and the maximum height to the ground was 2.12 m;when the lifting height was greater than 0.62 m,it could be rotated 360°,and at this time,the lower arm lifted 0.44 m,the upper arm lifted 0.18 m,and the maximum operating radius of 3600 rotation was 1.42 m.Besides,leveling device could be completed front and back,left and right leveling operation within 25°,and the error was smaller than 0.4°.Lifting,rotating and leveling operation were stable and slow,parameters of them met the design requirements.The whole machine had good traveling performance on flat ground and slope under different road conditions.The linear deviation of 35 m without load and full load were 1.1 m and 0.97 m,respectively,which were smaller than the limit value of 1.2 m.What’s more,the tilting stability of lifting platform was studied based on a mathematical model of tilting critical angle when it was operating at different parking positions on the slope,and the main influencing factors were the parking position parameterβ1,the rotating position parameter β2,the lifting height h and the load m.This model was universal for different types of crawler orchard lifting platforms and could provide a theoretical reference for the study of the tilting stability of such lifting machinery.The test and simulation of the tilting stability were carried out,and the the minimum tilting critical angle in different working conditions was 21°,which indicated that this lifting platform had a better tilting stability.The influence of various factors on tipping stability was analyzed through the establishment of response surface,then the relationship between the slope angle and operating radius was studied,which indicated that this lifting platform could rotate at the maximum operating radius under the condition of hilly slope within 20°.And it had a maximum operating range of 3.7 m2 to fruit trees.The prototype performance basically met the design requirements,but there were some problems in the operating stability of the lifting arms need to be improved.(4)Problems in insufficient stiffness of the lifting arms were analyzed,and the statics finite element analysis of the lifting arms under eight typical conditions was carried out by using ANSYS software.The results quantified the existing problems,and the improvement scheme was determined through further calculation,then a verification analysis was conducted to show the strength and stiffness of lifting arms meet the requirements.In order to improve the operating stability of the whole machine in the loose and muddy soil slope,the frog leg was designed to improve the operating stability and safety.In addition,the circuit and parts of the hydraulic system were improved to ensure that all the hydraulic components can operate normally on the slope condition and do not interfere with each other.It not only improved the performance of the whole machine,but also created the precondition for the smooth operation of the hilly orchard by improving the components.(5)Field experiments on hilly orchards were carried out.The results showed that the improved lifting arms had good operating stability under different terrains and operating conditions and achieved the anticipated improvement effect.The platform had ability to travel normally under the uneven road conditions and cross the channel with a width of 511 mm and the step with a height of 128 mm,which indicated obstacle performance met the requirements of the orchard operation.After standardized pruning the fruit trees,the machine could smoothly walk and turn between lines.The necessity of the frog leg for the operation in the hilly terrain of the platform was also verified through the experiments of static operation and dynamic operation.The operation efficiency index of hilly orchard was put forward,and the range and efficiency test of picking and pruning were carried out according to the different growth period and different operation of the fruit trees.When the distance between the whole machine and the fruit tree was 1.5 m,the fruit removal rate of the picking operation could reach 79.1%,at same time,the platform had a better cutting ability to the middle crown layer of the fruit tree.the efficiency of pruning and picking operations by lifting platform was increased by 42%,45%and 47.2%respectively compared with the pure manual work;in the actual harvesting,the equipment could improve the operation efficiency of 45.8%,which reached the design goal.The operating efficiency of the folding arm lifting platform was 148.5 kg/h and the oil consumption was about 2 kg/h.Overall,the actual operation showed that the designed lifting platform had good hilly orchard operation effect after some components were improved and could pass smoothly in the standardized orchard,as well as the auxiliary legs to improve the stability and safety of the operation on the slope.Compared with the existing lifting machinery,this lifting platform has a larger operating range,and a better slope operating stability;according to the results of the simulation operation and the actual operation,the lifting platform could effectively assist the farmers in picking,pruning and other operations to save costs,reduce labor intensity and improve the efficiency of the orchard.