Kinetostatic modeling of clamping force in a tendon-driven soft robotic gripper for tea shoot plucking

The mechanized plucking of tea shoots presents several challenges due to their delicate nature, small size, and dense growth, all of which pose significant difficulties in the design of the end-effector. This study proposes a soft robotic gripper specifically designed for tea shoot plucking, featuring two identical tendon-actuated fingers. To accurately determine the clamping force of the gripper, a kinetostatic model was established based on the Chain-Beam Constraint Model (CBCM), which characterizes the relationship among tendon tension, tendon displacement, and the clamping force. The accuracy of the model was validated through finite element analysis (FEA) and experimental testing, with maximum discrepancies in clamping force of 0.35 N under tendon tension and 0.28 N under tendon displacement. Using this model, the required tendon tension and tendon displacement for plucking tea shoots were determined, and a prototype of the gripper was subsequently developed. A field experiments demonstrated an overall plucking success rate of 94.33 %, with a 78.33 % probability that the breakpoint of the tea stem corresponded to the clamping position of the gripper. These results confirm that the clamping force predicted by the model is suitable for tea shoot plucking. In conclusion, the findings demonstrate that the proposed soft robotic gripper is a promising solution for tea shoot plucking.