Development of a planetary gear mechanism-based end-effector with a toggle force amplification mechanism for a weed-removal robot

In this study, we propose an end-effector gripper for a weed-removal robot used in mulch sheet agriculture. Unlike conventional open-field agriculture, weeds in mulch sheet agriculture are often located close to crops. Therefore, the proposed gripper adopts a planetary gear structure and uses only a single actuator to realize two different motions, namely, gripping the weed and pulling it out in the vertical direction. The proposed gripper also incorporates a toggle mechanism that provides force amplification, enabling a large grasping force to be generated from a small input torque. Through parameter design of the planetary gear structure, the proposed gripper first completes the grasping of the weed via the rotation of the carrier under continuous torque applied to the sun gear, and then sequentially drives the weed and the entire mechanism to move vertically through the rotation of the outer ring gear to perform the pulling-out motion. A prototype of the gripper was fabricated using 3D printing to verify the effectiveness of the proposed mechanism. The prototype has a total weight of only 538 g. The total time from the start of motion to weed removal is only 0.195 s, and the maximum grasping force can reach 87 N. Field experiments show that the proposed device can quickly remove weeds while maintaining soil integrity, thereby protecting the seeds and roots of crops from damage.