Robot mechanical arm structure, robot and manufacturing method of flexible external gear

The invention provides a robot arm structure, a robot and a method for manufacturing a flexible external gear, wherein the reliability of the robot arm structure is not easy to decrease. The robot arm structure includes a joint device for a robot, the joint device including: a harmonic gear device that deforms a flexible external gear in accordance with rotation of a cam, causes a part of external teeth to mesh with a part of internal teeth, and causes a part of external teeth to mesh with a part of internal teeth; the flexible external gear rotates relative to the rigid internal gear according to the tooth number difference between the flexible external gear and the rigid internal gear, and the flexible external gear comprises: an elastic deformation part which generates stress by elastically deforming the flexible external gear in a manner of uniformly expanding the diameter of the flexible external gear on the whole circumference in the circumferential direction; and a shot peening section ...