Experimental and simulation analysis of optimum picking patterns for robotic apple harvesting

•Tension was the dominant parameter during apple stem detachment process.•Apples with a long stem required larger displacement and angle to detach.•Automatic dynamic analysis of mechanical systems, finite element method and response surface methodology were utilized.•Horizontal pull with bending and twisting motion was the potential optimum combination. Robotic apple harvesting requires the motion planning of a series of movements to perform the efficient picking of fruit without bruises. The investigation of the underlying characteristics of fruit detachment picking patterns is an important basis for robotic harvesters. In this study, four basic picking patterns including horizontal pull, vertical tension, bending and twisting were performed in order to analyze the effects of picking patterns on fruit detachment. The tension parameter, which includes the horizontal pull and vertical tension, was found to be the dominant factor during the detachment process, with the vertical pull possibly leading to the pull-out of the stem. Apples with long stems were observed to require a large displacement and angle to break the branch-stem joint, which subsequently increased the risk of picking failure. Moreover, the detachment caused by the tangential force required a smaller detachment force. A dynamic simulation was performed to identify the optimal picking model, whereby detachment force and detachment time were used as the optimization parameters. The response surface methodology was used to determine the effects of the horizontal and vertical velocity on the detachment force and detachment time. Optimized results indicated the horizontal pull with a bending and twisting motion as the potential optimum combination. These results provide a theoretical basis for future studies on robotic apple harvesting.