Evaluation of Branch Cutting Torque Requirements Intended for Robotic Apple Tree Pruning

Robotic pruning is a potential solution to address the issue of labor shortages, but it has certain design challenges. The torque required for cutting branches is an important parameter for designing a pruning end-effector. In this study, branch cutting torque and angle were investigated with envisioning the development of robotic end-effector. The experimental system comprised of a manual shear pruner with a force measurement sensor, capable of detecting the forces exerted by the hand. Besides, an Inertial Measurement Unit (IMU) was also used to record the orientation of the shear blade. A series of field tests were conducted on four apple cultivars (Fuji, Gala, Honeycrisp, and Golden Delicious), and the cutting torque was calculated for different diameter branches. The Statistical analysis suggested that the torque required for pruning Honeycrisp is significantly lower than that for Gala, Fuji, and Golden Delicious. The paired comparison between Golden Delicious with Gala and Fuji suggested that the cutting torque variations were non-significant. The Gala has the highest torque requirements while the lowest torque requirements was observed for Honeycrisp. The results also indicated that no significant difference in required cutting torque was found among the different cutting angles for Fuji apple trees. While, the branch-blade contact point significantly affects the torque required for cutting branches of Fuji apple trees. The required cutting torque was higher for branches placed at cutter center compared to cutter pivot. The outcomes of the study are vital to select appropriate cutting mechanism for the future development of automated pruning system.