Abstract: We propose a new,one-degree-of-freedom,mechanical,rotational,robot end-effector for grippingcylindrical workpieces.The end-effector is simple in structure,easy to manufacture,and convenient to use.It has the capability to grip a wide range of part sizes and has high accuracy.Each side of the gripper includesa rocker-slide mechanism and a parallelogram four-bar linkage.This concentric robot gripper is based on thegeometric relationship that chords of concentric circles at a central angle are parallel and the motion charac-teristic of a parallelogram four-bar linkage.