Design of a Petiole Tensile-Separation End-Effector with Central Growing Region Protection for Low-Damage Perilla Leaf Harvesting

Abstract

Abstract

Selective harvesting of perilla (Perilla frutescens) leaves requires the repeated removal of mature outer leaves while preserving the central growing region, including the apical meristem and immature inner leaves, on the same plant. Conventional harvesting end-effectors developed for fruits or whole-head leafy vegetables are not directly applicable to this task because of the dense leaf arrangement, thin and flexible leaf blades, and the need to protect the central growing region. This study proposes and evaluates a dual-module end-effector that integrates a central growing region protection and stem-support (CPS) module with a petiole grasping (PG) module using pneumatic soft pads and a scissor-lift mechanism for petiole tensile separation. FSR-based pneumatic-pressure calibration and photoelectric-sensor-based position-adaptive stopping control were implemented to reduce grasping damage and accommodate plant-to-plant variation in petiole height. The developed end-effector was evaluated using mock perilla plants under aligned, rotated, and overlapped leaf conditions and cultivated perilla plants over two harvesting sessions separated by two weeks. In the mock-plant experiment, the system achieved an attempt success rate of 96.7% and a leaf harvest rate of 98.3%. In the real perilla experiment, it achieved an attempt success rate of 88.5% and a leaf harvest rate of 90.4%. The target-leaf damage rate was 2.1%, and no damage was observed on the main stem. In the second harvesting session, the system maintained an attempt success rate of 91.7% for newly developed leaves on the same plants. These results indicate that the developed end-effector can selectively harvest mature perilla leaves with low damage while preserving plant structures required for continued growth.