Effects of different picking patterns and sequences on the vibration of apples on the same branch

Robots picking apples cause vibration of other fruit on the same branch and fruit may even fall off. This not only affects subsequent picking, but also causes fruit loss. In this research, the branch-fruit system was taken as the research object, and a mixed-mode cohesive contact model was used to simulate the tangential and directional mechanical behaviour of fruit detachment. The branch with apples was simplified as a cantilever beam model, and a multi-body finite element model of a branch with apples was established. The average error of the simulation results was 6.81%. The simulation results demonstrate that the type I picking sequence (picking fruit beginning farther from the trunk) shortened the settling time of the branch with apples than the type II picking sequence (picking fruit beginning closer to the trunk). Field experiments showed that the maximum accelerations of fruit detachment were respectively 3.826 +/- 1.859g, 2.971 +/- 1.374g, 2.246 +/- 0.757g (g = 9.8 m s-2) under three picking patterns (pulling, pull-twisting, and pull-bending). Linear correlations were found between the vibration displacement and settling time of fruit under different picking patterns and sequences. The response index (RI) is defined to comprehensively evaluate the degree of disturbance to other fruits on the same branch during the fruit-picking process. The test results reveal that the use of the type I sequence and pull-bending pattern is better for reducing the overall disturbance to other apples on the same branch. This study provides a technical and theoretical reference for designing the picking pattern and planning the picking sequence of robotic arms.