Jiaming Fang, Nianzu Dai, Zhenbo Xin, Jin Yuan, Xuemei Liu

Abstract

Tomatoes grow in clusters, shading each other and ripening non-uniformly even within the same cluster. This variability poses a challenge in designing an end-effector to efficiently pick fruits individually with minimal damage. A novel hybrid bending-twisting-pulling end-effector for robotic single-fruit tomato picking is designed, and the interaction dynamics between the tomato and the fruit-stem are analyzed. First, a bionic robotic tomato-picking model based on the force levels in manual operations is proposed by analyzing fruit-stem characteristics during manual picking. Next, a compact rigid-flexible hybrid end-effector, utilizing a compliant deformed belt for wrap-around clamping, is designed to apply hybrid bending-twisting-pulling forces on the stem’s abscission layer to detach the fruit. Then, a multi-body dynamics model involving the stem, tomato, and end-effector is established to analyze the interaction dynamics during picking. Finally, performance criteria are presented to evaluate the end-effector’s harvesting efficiency. Simulation results showed that clamping only 1/3 of the tomato’s surface can still roll the target tomato from the cluster into the end-effector. Successful picking of tomatoes in various postures was achieved through the application of hybrid forces at the abscission layer, with peak bending torque ranging from 71.6 to 262.68 N·mm, peak twisting torque from 18.46 to 32.36 N·mm, and peak pulling force from 25.18 to 31.64 N. Field tests showed a tomato clamping success rate of 93.3 %, and the picking success rates for tomatoes in four different postures were 93.3 % (vertical), 90.0 % (front), 76.7 % (left-front), and 83.3 % (right-front). The average single picking time of the end-effector was 1.8 s when the flexible belt ran at 282.7 mm/s, and the fruit damage rate was 1.9 %, demonstrating the effectiveness and feasibility of this end-effector in addressing the aggregated growth characteristics and picking requirements of tomatoes.

Paper Linkage:https://doi.org/10.1016/j.compag.2025.110011