Harmonic gear device, method for manufacturing harmonic gear device, joint device for robot, and gear member

A harmonic gear arrangement (1) comprises a rigid internal gear (2), a flexible external gear (3) and a wave generator (4). The wave generator (4) has a non-circular cam (41) that is rotationally driven about a rotation axis, and a bearing (42) that is attached to the outside of the cam. A harmonic gear device (1) deforms a flexible external gear (3) in accordance with the rotation of a cam (41), and causes the flexible external gear (3) to rotate relative to a rigid internal gear (2) in accordance with a difference in the number of teeth with the rigid internal gear (2) by causing a part of external teeth (31) to mesh with a part of internal teeth (21). A first region (R1) of the inner peripheral surface (301) of the flexible external gear (3) located on the back side of the external teeth (31) has a smaller surface roughness than a second region (R2) other than the first region (R1). Also disclosed are a method for manufacturing the harmonic gear device, a robot joint device including the harmonic gear device, and a gear member used as a flexible external gear of the harmonic gear device.