Flat type wave gear device
A flat type wave gear device is realized having a much improved load capacity. When d is an amount of radial flexing at a major axis location of a rim neutral circle of the flexible external gear of a flat type wave gear device flexed into an elliptical shape and t is the rim thickness of the flexible external gear, then (0.5237 Ln( R )−1.32) d≦t ≦(0.8728 Ln( R )−2.2) d when the 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 the reduction ratio R of the wave gear device is 80 or more. Using this setting makes it possible to increase the tooth root fatigue limit strength of the flexible external gear, thereby making it possible to improve the load capacity of the flexible external gear.
1. 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.
2. The flat type wave gear device according to claim 1 , characterized in the flexible external gear having a material hardness HRC value within a range of 40 to 50.