Patent ID: 7836786

Claim:
A flat type wave gear device comprising: an annular rigid internal gear, an annular flexible external gear disposed inside the rigid internal gear, and a wave generator for flexing the flexible external gear into an elliptical shape to cause it to partially mesh with the rigid internal gear and for circumferentially moving positions at which the gears mesh, wherein: when d is an amount of radial flexing at a major axis location of a rim neutral circle of the flexible external gear flexed into an elliptical shape and t is rim thickness of the flexible external gear, then (0.5237 Ln( R )−1.32) d≦t ≦(0.8728 Ln( R )−2.2) d when reduction ratio R of the wave gear device is less than 80, and (1.5499 Ln( R )−5.8099) d≦t ≦(2.5832 Ln( R )−9.6832) d when reduction ratio R of the wave gear device is 80 or more; wherein Ln is a natural logarithm whose base is Napier's constant e.