Design and optimisation of end effector for loose substrate grasping based on discrete element method

Abstract

The transplantation of seedlings represents a pivotal stage in plug tray seedling cultivation. Conventional end effectors used in transplanters are primarily tailored for seedlings with well-established root systems and tightly bound substrates. However, when the substrate lacks sufficient root wrapping and remains loose, independent seedling removal devices utilising blowing or suction methods are often employed. This results in structural complexity and increased costs for the transplanter. To address the challenge of grasping loose substrate, this study advocates for a novel approach utilising a diagonal oblique-insertion type end effector. Through repose angle trials, discrete element simulation parameters were calibrated. Subsequently, leveraging these calibrated simulation parameters, the end effector was optimisation through orthogonal experiments. Findings reveal that the relative error between simulated and actual repose angles is minimised under specific conditions, with the shear modulus at 8.2 × 106 Pa, the particle-particle rolling friction coefficient at 0.234, the particle-steel static friction coefficient at 0.36, and the JKR surface energy at 0.347 J m−2. Employing these simulation parameters for end effector optimisation, it was determined that the average substrate integrity rate reaches 79.26% with an end effector featuring 5 tines, a gripper positioned 2.5 mm from the edge of the hole, and a gripper ascent speed of 0.056 m s−1. The average relative error between actual grasping experimental and simulation results was observed at 10.21%, indicating the suitability of these discrete element parameters for optimising simulations of end effectors for transplanters. Furthermore, the end effector devised in this study demonstrated efficacy in transplanting loose substrates.