Structure design and test of end effector for non-destructive strawberry harvest robots

ObjectiveAiming at the problems of inadequate clamping force control, easy fruit damage or unstable grasping of existing strawberry picking end effectors, a non-destructive picking end effector that clamps both fruit and peduncle simultaneously was designed. The maximum clamping force was controlled by a linkage assembly and a torsion spring to avoid fruit damage during picking.MethodsFirstly, a mathematical model of the motion trajectory and output torque of the fruit clamping mechanism was established, and adaptive torsion spring parameters were designed. Adams software was used to simulate the motion trajectory and contact force, and the Ls-Dyna module of WorkBench software was utilized to analyze the stress and deformation of strawberries during clamping. Secondly, a model of the peduncle clamping mechanism was established to solve the forces required for stable clamping and peduncle cutting. Finally, a prototype was fabricated, picking tests were carried out in 3 groups according to peduncle diameter, and the fruit damage degree before and after picking was compared.ResultsThe results demonstrate that the end effector can clamp strawberries with a diameter of 24-60 mm, with a maximum contact force of 0.80 N, a maximum stress of 57 640 Pa and a maximum deformation of 0.677 mm, all within the tolerance range of strawberries; the minimum driving force for peduncle cutting is 13.59 N, and the picking success rate is 95%, which meets the requirements of non-destructive strawberry picking.