Parameter Calibration and Experimentation of a Discrete Element Model for Tomato Stems

Abstract

Tomato pruning robots are limited by the absence of accurate shear simulation models for tomato stems. Conventional homogeneous discrete element models are incapable of characterizing the multi-layer heterogeneous structure of tomato stems, which gives rise to significant simulation deviations. With Zheza No. 8 tomato stems as research objects, this study measured intrinsic and contact parameters through physical tests and constructed a three-layer bonded discrete element model to simulate the epidermis, xylem and pith with particles of different sizes. Bonding parameters were calibrated using a two-level factorial design, steepest ascent test and Box–Behnken design with shear force as the evaluation index. The optimal parameters reduced simulation errors by 75.8% and 43.7% relative to traditional and pre-optimized models, and accurately reproduced the double-peak shear behavior. The model accuracy improves with xylem maturation, providing a dependable simulation method for the optimization of tomato pruning robots.