Development of an integrated 3R end-effector with a cartesian manipulator for pruning apple trees

Abstract

Robotic pruning is a potential solution to address the issues of labor shortages and high associated costs, but it has challenges due to the unstructured working environment. For successful robotic pruning, target branches have to be reached with fewer spatial requirements for the end-effector cutter and the manipulator. A three-rotational (3R) degrees of freedom (DoF) end-effector was designed considering maneuvering, spatial, mechanical, and horticultural requirements. Simulations were conducted with the end-effector to investigate the reachable workspace, the cutter frame orientation, and the manipulability index. The simulation results suggested that the proposed design has a spherical reachable workspace with a void due to the presence of a physical constraint of the linear arm. The manipulability index was determined to be independent of the rotation of the first and last joint of the end-effector. The prototype of the proposed end-effector was integrated with a cartesian manipulator. An Arduino-based control system was developed along utilizing a Matlab graphical user interface (GUI). A series of field tests were conducted on ‘Fuji’/Bud. 9 apple trees with trellis-trained architecture. The field tests validated the simulation results, and the end-effector successfully cut branches up to ~25 mm diameter at wide range of orientations. This study provides the foundation for future investigations of branch accessibility for pruning with an integrated 3R end-effector and a cartesian manipulator system following a collision free trajectory.