Patent ID: 8028603

Claim:
A method for setting a tooth profile in a flat wave gear device that has a D-side and an S-side rigid internally toothed gears disposed in parallel in a coaxial state with each other, an annular flexible externally toothed gear disposed in a coaxial state within the D-side and the S-side rigid internally toothed gears, and a wave generator for causing a cross-section of the flexible externally toothed gear given perpendicularly with respect to an axis thereof to flex elliptically and the resulting shape to rotate, the number of teeth on the D-side rigid internally toothed gear being the same as the number of teeth on the flexible externally toothed gear, and the number of teeth on the S-side rigid internally toothed gear having 2n more teeth (n being a positive integer) than the number of teeth on the flexible externally toothed gear, wherein the method is comprising: using both the flexible externally toothed gear and the D-side rigid internally toothed gear as spur gears of module m; using κmn (κ: flexing coefficient as the degree of radial flexing on a major axis of a rim neutral line passing through a center along a thickness direction of a tooth root rim when the cross-section of the flexible externally toothed gear given perpendicularly with respect to the axis is caused to deform into an elliptical shape; giving a main part of a tooth profile of the flexible externally toothed gear a convex arcuate tooth profile composed of a convex arc having a radius r and point A as a center; determining a momentary center S of relative motion of the flexible externally toothed gear and the D-side rigid internally toothed gear generated accompanying rotation of the wave generator; establishing a point at which a line segment that connects the arc center of the convex arc and the momentary center intersects the convex arc as a contact point C between the convex arcuate tooth profile of the flexible externally toothed gear and a tooth profile of the D-side rigid internally toothed gear; and using a movement locus of the contact point on the convex arcuate tooth profile of the flexible externally toothed gear accompanying rotation of the wave generator as a tooth profile of a main part of the D-side rigid internally toothed gear.