Method for setting non-positive deflection, maximum meshable tooth profile in flat wave gear device

A flat wave gear device, having a tooth profile of the flat wave gear device set using a method for setting the tooth profile in the 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 S-side rigid internally toothed gear as spur gears of module m;
• setting κmn, wherein κ≦1, and −κmn as a degree of radial flexing on, respectively, a major and minor axis of an elliptically shaped rim neutral line of the flexible externally toothed gear, a line passing through the center part along a thickness direction of a tooth root rim when the flexible externally toothed gear is deformed into an elliptical shape, in the cross-section of the flexible externally toothed gear given perpendicularly with respect to the axis;
• determining a rack-approximated movement locus of the flexible externally toothed gear with respect to the S-side rigid internally toothed gear accompanying rotation of the wave generator;
• taking ρOPT as a minimum value of a radius of curvature of the movement locus;
• and
• using a convex arc having a radius ρ, wherein ρ≦ρOPT, on a main part of a tooth profile of the flexible externally toothed gear.