Patent ID: 8215205

Claim:
A wave gear device having an annular rigid internally toothed gear, an annular flexible externally toothed gear disposed inside the rigid internally toothed gear, and a wave generator for causing the flexible externally toothed gear to bend into an elliptical shape and partially mesh with the rigid internally toothed gear so that enmeshment position of the gears moves in a circumferential direction; wherein the flexible externally toothed gear is shaped as a cup or a “silk hat” provided with a cylindrical body, a diaphragm contiguous with one end of the body and extending inwardly or outwardly in a radial direction, and external teeth formed on an outer circumferential surface of an opening at the other end of the body; and wherein the flexible externally toothed gear is bent into an elliptical shape by the wave generator so as to create a deflection proportionate to a distance from the diaphragm, which is measured as the distance from the diaphragm to the opening; wherein: a rim thickness t of the flexible externally toothed gear satisfies the following relations: (0.5237 Ln ( R )−1.32) d≦t ≦(0.8728 Ln ( R )−2.2) d if R< 80, and (1.5499 Ln ( R )−5.8099) d≦t ≦(2.5832 Ln ( R )−9.6832) d if R≧ 80, where d is a radial deflection, measured at a position of a major axis of a neutral circle of the rim, in the flexible externally toothed gear bent into an elliptical shape, and R is a reduction ratio of the wave gear device; and wherein a ratio L/PCD is a value within a range from 21% to 30%, where L is an effective face width of the external teeth, and PCD is a pitch circle diameter of the external teeth.