Development And Test Of Mechanical Picking Device For Pear Fruit

Pear picking is seasonal and labor intensive.With the decrease of rural labor force and the increase of labor cost,machine picking instead of manual operation has become an important trend in the future development of modern agriculture.Most of the existing machines use simple pickers,which have the problems of low picking efficiency and high damage rate.Therefore,considering the cultivation mode of pear tree and the physical characteristics of pear fruit with thin skin,it is of great theoretical and practical significance to carry out the research on mechanical picking and low-loss collection technology and device design of pear fruit.The main research contents are outlined below.(1)Based on the intrinsic parameters of typical pear fruit,the simulation parameters between pear fruit and contact material and between pear fruit and pear fruit were calibrated by free fall collision method,slope sliding method and slope rolling method respectively.The collision recovery coefficient,static friction coefficient and rolling friction coefficient between snow pear and EVA material were 0.652,0.472 and 0.00706 respectively.Through the steepest ascent test and the three-factor and five-level rotary combination design test,the relative error between the measured accumulation angle and the simulated accumulation angle was taken as the optimization goal,and the collision recovery coefficient,static friction coefficient and rolling friction coefficient between the pears were obtained.The values were 0.52,0.27 and0.02,respectively.It can provide a theoretical basis for the design and optimization of pear picking collection device.(2)According to the planting mode of pear tree,a series picking mechanism with 5 degrees of freedom was designed,which was mainly composed of flexible claw,mechanical arm and lifting device.The maximum equivalent stress of pear fruit under the maximum clamping force was 0.1039 MPa by finite element analysis.Based on the D-H parameter method,the kinematics equation of the picking mechanism is established to calculate the pose of the flexible claw reference point.The displacement curve of the reference point under specific joint parameters was simulated by Adams,and the maximum error with the calculated value was only 2.75 %.The target workspace of the picking mechanism was determined according to the canopy diameter of the evacuated layered pear tree.The reachable workspace of the flexible claw reference point was generated by Monte Carlo method,and the maximum difference coefficient with the former was 1.81 %.It indicates that this mechanism can meet the requirements of pear picking operation.(3)In order to reduce the drop damage of pears after picking,the multi-stage buffer collection mechanism was optimized,which was mainly divided into three levels of fruit receiving bag,conveyor belt and rotary separation.The collision process between typical pear varieties and buffer mechanism was simulated by ANSYS Workbench,and the maximum equivalent stress was 0.194 MPa.EDEM was used to analyze the influence of conveyor belt inclination,conveyor belt speed and guide plate speed on the force of pear fruit.The force prediction model of pear fruit was established by Design-Expert software.The minimum force of pear fruit during the collection process was 20.19 N,and the optimal values of the above three parameters were 0.58°,0.14 m/s,and 10 deg/s,respectively.It provides the basis for the parameter optimization of the prototype.(4)The prototype was produced,and the picking workspace test,the parameter optimization test of multi-stage buffering low loss collecting mechanism and the picking collection performance test were carried out.The results showed that the maximum difference coefficient between the actual workspace and the target workspace was 2.54 %.The significance of the influence on the damage rate of pear fruit from large to small was as follows:conveyor belt line speed,conveyor belt inclination angle,guide plate speed.When the conveyor belt inclination angle was 0.55°,the conveyor belt line speed was 0.16 m/s,and the guide plate speed was 12.59 deg/s,the average damage rate of pear fruit was 4.31 %.The picking success rate of the whole machine was 92.30 %,and the harvesting efficiency was 7.40 per minute,which was 76.19 % higher than that of manual picking.