Research And Design Of The Robotic End-effectors For Tomato Holding

Picking and sorting are the most time-consuming and labor-intensive processes in traditional fruit and vegetable production.The aging of the population and the continuous transfer of labor have resulted in the reduction of agricultural labor and the development of mechanized production.Due to the differences in working requirements and working environments for fruit picking and fruit sorting,it is difficult for a single holding end-effector to be suitable for both fruit picking and fruit sorting.In the existing mechanized production of fruits,picking robots separate the fruits from the crops,and then sorting robots sort the fruits.At present,the main problems of tomato picking and tomato sorting include:(1)The Challenge in separating the target tomatoes from the fruit clusters when picking tomatoes;(2)The lack of low-cost and specific end-effector design scheme when sorting tomatoes.Based on the physical characteristics of tomatoes,this paper designed a tomato picking end-effector and a tomato sorting end-effector for the existing problems to complete the full coverage of tomato picking and sorting scenarios.By conducting this study,a tomato picking end-effector and a tomato sorting end-effector were proposed to provide valuable references for future studies in the agriculture field.The main research contents are as follows:(1)Research on the physical characteristics of tomatoes.The geometry,weight and friction properties of tomatoes,the mechanical properties of tomato pulp and the mechanical properties of tomato stalk were tested as theoretical basis for the design of tomato holding end-effectors.The test showed that the bottom of the tomatoes had the strongest compressive ability,and other test points,transverse diameter and mass had no significant relationship with the rupture force of the tomatoes.The non-destructive clamping force of tomatoes was 15.95 N,and the maximum stalk rupture force was 8.62 N.(2)The design scheme of the tomato holding end-effectors.Aiming at the problem that the current tomato picking end-effector would be interfered by the non-target fruits in the tomato cluster,a design scheme of the underactuated tomato picking end-effector with the wrap picking strategy was proposed.The end-effector could adaptively wrap the target tomato and separate the non-target tomato on the outside.Aiming at the delicate and vulnerable characteristics of tomatoes,a design scheme of adaptive fluid elastic driven end-effector for tomato sorting was proposed.(3)The detailed design,simulation and manufacture of the tomato holding end-effectors.Based on the proposed design of the picking end-effector,the sizes of the key components of the picking end-effector were solved through kinematic analysis and mechanical analysis,and the performance of the picking end-effector was verified.The control system was built and the prototype was manufactured.Based on the proposed design of the sorting end-effector,Ansys Workbench was used to carry out finite element simulation to analyze the bending performance and clamping performance of the flexible fingers in the sorting end-effector from the radial and axial directions.According to the radial and axial simulation results of the flexible fingers,a lowcost and specifical sorting end-effector was designed with driving cost and manufacturing cost as the optimization objectives.The control system was built and the prototype was manufactured.(4)Performance test of the tomato holding end-effectors.The picking test of the picking endeffector shows that the total picking success rate and the total non-destructive picking success rate of the end-effector were 92.5% and 85% respectively,and the picking process was not interfered by non-target fruits.The bending test,the static clamping test and the dynamic sorting test were carried out on the sorting end-effector,the results show that the error of the finite element simulation of the flexible fingers was less than 3%.The tomato sorting end-effector,consisting of three four-chamber fingers,was able to hold tomatoes non-destructively at the inflation pressure lower than the optimal pressure of 31.645 k Pa in a static environment,and could sort tomatoes non-destructively at 32 k Pa.The picking success rate was 100%.