Patent ID: 7328632

Claim:
A wave gear drive having a circular rigid internal gear, inside which a flexible external gear is disposed, inside which a wave generator is inserted, the flexible external gear having a flexible cylindrical body and an annular diaphragm that extends in a radial direction from a back end of the cylindrical body, a tooth portion formed on an opening end side region of the cylindrical body being flexed into an elliptical shape by a deflection amount generated by the wave generator from a back end portion on the diaphragm side to a front end portion on the opening end side thereof that is approximately proportional to distance from the diaphragm; wherein: the rigid internal gear is a spur gear of module m; the flexible external gear is a spur gear of module m or a conical gear of module m at the front end portion thereof; a number of teeth of the flexible external gear is 2n (n being a positive integer) fewer than a number of teeth of the rigid internal gear; the deflection amount of the major axis of the elliptical rim neutral line of the flexible external gear at a cross-section of the flexible external gear perpendicular to the axis at an arbitrarily selected location in the direction of the tooth trace thereof (hereinafter referred to as main cross-section) is set as 2 κmn(κ>1); the meshing of the teeth of the rigid internal gear and flexible external gear in the main cross-section is approximated as rack meshing and the moving path of the teeth of the flexible external gear with respect to the teeth of the rigid internal gear that accompanies rotation of the wave generator obtained; from the main axis to a tooth departing side in the moving path, employing a curved portion from a deepest engaged position of the two gears at which an inclination angle of a radial line to the moving path of the rigid internal gear is 90° to the position at which the inclination angle is α(0°<α<30°); employing as a tooth profile of the flexible external gear a first similar curve obtained by enlarging the curved portion by λ times; and employing as a tooth profile of the rigid internal gear a second similar curve obtained by enlarging the curved portion by (λ+1) times.