Design, structural analysis, and ROS-based kinematic simulation of a robotic arm for capsicum harvesting in greenhouse environments

This study presents an integrated mechanical design, structural validation, and kinematic simulation framework for a 6-DOF robotic manipulator tailored to precision capsicum harvesting in greenhouse environments. The robot was designed using a lightweight, modular architecture based on a hybrid-material approach: Polylactic Acid Plus (PLA+) structural links, Thermoplastic polyurethane (TPU) gripper fingers, and stainless-steel scissor cutters. The serial-link configuration was optimized for maneuvering within a canopy width and plant height range, with a total manipulator reach of approximately 700 mm and a payload capacity of 200 g. Structural safety was verified via Finite Element Analysis (FEA) using SolidWorks Simulation, considering direction-specific harvesting loads. Maximum von Mises stress occurred in the shoulder joint (Link 2), while the forearm link (Link 5) showed the highest displacement, both remaining within allowable PLA+ limits. All links exhibited high Factors of Safety, with the minimum being 88.58, confirming mechanical integrity under worst-case loading. Kinematic modeling and motion planning were implemented using a URDF-based robotic model within ROS 2 (Humble), RViz2, and MoveIt2. Forward kinematics showed a mean end-effector pose error of 2.3 mm across sampled target positions, validating model accuracy. The manipulator executed a full harvesting cycle in 6 seconds with sequential joint actuation, including base rotation, arm extension, wrist alignment, and gripping. Reachability and 3D workspace analysis confirmed full coverage of the capsicum canopy (0.40 m radius) within a maximum reach of 0.70 m. The results demonstrate a biologically compatible, structurally safe, and kinematically feasible solution for greenhouse fruit harvesting.