Finding the lowest damage picking mode for tomatoes based on finite element analysis

This paper proposes a pure bending picking mode, and analyzes the superiority of this picking mode from the perspective of mechanics. This is intended for the problems of high pressing force in the common tomato picking modes, viz., the stretching mode, large displacement in bending mode, and low efficiency in twisting mode. To explore the optimal tomato picking mode, the reverse engineering method has been employed to establish a finite element model of the tomato components, henceforth a finite element method that could evaluate the degree of damage of tomato has been proposed. Through the finite element simulation of the three picking modes of pure stretching, pure bending, and bending-tension composite, the time curve of the pressing force of the three fingers on the tomato surface, the stress of each component of the tomato, and the damage level of the tomato have been obtained. Further, the effects of the picking mode and maturity on the mechanical damage of the tomato have been analyzed. The accuracy of the tomato finite element model and the feasibility of the pure bending picking mode have been verified by the manual picking test and robot picking test, respectively. The results show that in the picking simulation of the same maturity, the bending mode caused the lowest damage to tomato, followed by the composite mode. The stretching mode caused the highest damage to the tomato, whereas the bending mode caused less damage to the tomato than the bending mode. Therefore, pure bending is the optimal picking mode for tomato. In the robot picking test, both the picking success rate and the damage coincidence have exceeded 90 percent, which has established that the pure bending picking mode is the optimal picking mode suitable for robotic picking. The results have provided a reference for the design and development of a novel type of tomato picking end effector.