Single-Motor-Driven (4 + 2)-Fingered Robotic Gripper Capable of Expanding the Workable Space in the Extremely Confined Environment

This letter proposes a novel robotic gripper that can expand workable spaces in a target environment to pick up objects from confined spaces. The proposed gripper is most effective for retrieving objects from deformable environments, such as taking an object out of a drawstring bag, or for extracting target objects located behind surrounding objects. The proposed gripper achieves both work-space expansion and grasping motion by using only a single motor. The gripper is equipped with four outer fingers for expanding the environment and two inner fingers for grasping an object. The inner and outer fingers move in different directions for their respective functions of grasping and spatial expansion. To realize two different movements of the fingers, a novel self-motion switching mechanism that switches between the functions as feed-screw and rack-and-pinion mechanisms is developed. The mechanism switches the motions according to the magnitude of the force applied to the inner fingers. This letter presents the mechanism design of the developed gripper, including the self-motion switching mechanism and the actuation strategy for expanding the workable space. The mechanical analysis is also presented, and the analysis result is validated experimentally. Moreover, an automatic object-picking system using the developed gripper is constructed to evaluate the gripper.