Study on walnut dynamic response to different excitations

Abstract

To address the limitations of a single excitation mode and the unclear dynamic response of fruit in walnut vibration harvesting, this study develops an excitation device based on an eccentric block structure, capable of generating three excitation modes: linear, circumferential, and combined. By establishing dynamic models of the picker-branch and fruit-stalk systems and integrating rigid-flexible coupling simulation technology with a custom-built vibratory picking experimental platform incorporating an electronic fruit testing system, this study systematically analyzes the fruit’s dynamic responses, including acceleration, velocity, and trajectory, under different excitation modes. The results indicate that circumferential excitation yields the highest peak acceleration and shedding rate, though with an uneven acceleration distribution, making it suitable for side-branch picking. Combined excitation provides a more uniform acceleration distribution with the smallest coefficient of variation and a slightly lower shedding rate than circumferential excitation, making it more appropriate for whole-tree harvesting. Linear excitation results in lower acceleration and shedding rates but offers easier control. The fruit’s instantaneous velocity exhibited quasi-sinusoidal fluctuations under all three excitation modes, progressing through three stages: initiation, energy conversion, and separation. Circumferential excitation resulted in the shortest separation time. Regarding fruit trajectory, linear excitation primarily induced movement along the Y-axis, whereas circumferential excitation exhibited greater motion amplitude in both the X- and Y-axes. Combined excitation involved motion in all three directions, though with a lower synthesized amplitude compared to circumferential excitation. The fruit trajectories under circumferential and combined excitations were denser and exhibited more cycles, increasing the likelihood of dislodgement. Dislodged fruits followed a parabolic trajectory under all excitation modes. This study elucidates the mechanism by which different excitation modes influence fruit shedding efficiency, providing a theoretical foundation for the design and optimization of vibratory walnut harvesting equipment.