Strain wave gearing and robotic arm

A strain wave gearing, comprising:

• an electric motor;
• an outer ring member for rotation output having a tubular outer ring portion, and an internal gear which is provided so as to protrude into an inner side of the outer ring portion and has internal teeth formed along an inner periphery of the internal gear;
• a flexible gear having an external gear which has external teeth formed along an outer periphery of the external gear and is arranged on an inner side of the internal gear, the flexible gear formed of a tubular flexible member which has a pair of flange portions arranged on both end sides of the external gear, a number of the external teeth of the external gear differing from a number of the internal teeth of the internal gear;
• a tubular cam member configured to distort the flexible gear in a radial direction so as to partially engage the external gear with the internal gear, the tubular cam member rotated by a rotational force transmitted from the electric motor so as to move engagement positions in a circumferential direction so that a relative rotation between the internal gear and the external gear is generated;
• a pair of fixing plates, to each of which a corresponding flange portion of the pair of flange portions is fixed;
• and
• a coupling member penetrating the tubular cam member and coupling the pair of fixing plates to each other,
• wherein the flexible gear has a pair of deformable portions and each of the deformable portions has at least one spiral slit which is formed in a plate-like portion connecting the external gear to the corresponding flange portion which swirls in the circumferential direction of the flexible gear and extends in an axial direction
• wherein each deformable portion of which is formed between the external gear and each of the pair of flange portions, and to be deformed by being pressed by the tubular cam member so that the external gear protrudes in the radial direction.