Analysis of the interaction between end-effectors, soil and asparagus during a harvesting process based on discrete element method

To meet the high-efficiency and low-damage harvesting requirements for white asparagus, two novel types of end-effectors were designed to selectively harvest white asparagus. One is the transverse-cut end-effector (TCEE), while the other is the clip-cut end-effector (CCEE). To select the best harvesting scheme and achieve a suitable range in driving forces, we propose a discrete element method (DEM)-based model of the end-effectors, soil and white asparagus for the comparative analysis of a harvesting process using two end-effectors. The biomechanical properties of white asparagus were measured to determine the constraints of non-damaging harvesting, after which we derived the theoretical driving forces of the two end-effectors. Combined with an analysis of DEM simulation, the driving forces of end-effectors are quantitatively described in this paper. A test bench was built to carry out field harvesting tests. Finally, after considering the comprehensive results of the simulations and field tests, we determined TCEE to be the final harvesting component. The validated experiment showed that the relative errors between the field test and the simulation, given the driving forces of penetration, shearing and clamping, were 6%, 11.9% and 18.2%, respectively. This proves that the DEM model is capable of simulating the biomechanical properties of white asparagus, and can be used to simulate the harvesting process. The optimum combination of driving force parameters for TCEE is penetration force 200N, shearing force 4.2N and clamping force 11N. Under this scheme, the harvesting process met the requirements for high efficiency and low damage, which demonstrates the effectiveness of the white asparagus robotic harvester. (C) 2020 IAgrE. Published by Elsevier Ltd. All rights reserved.