A wave gear device comprising a circular rigid internally toothed gear, a flexible externally toothed gear disposed coaxially inside the internally toothed gear, and a wave generator fitted inside the externally toothed gear;
- wherein:
- the flexible externally toothed gear has a flexible cylindrical barrel, a diaphragm extending in a radial direction from a rear end of the cylindrical barrel, and external teeth formed in an external peripheral surface portion close to a front end opening of the cylindrical barrel;
- the flexible externally toothed gear is deflected into an ellipsoidal shape by the wave generator and meshed with the rigid internally toothed gear at both ends of the ellipsoidal shape in a major axis direction;
- the amount of deflection in the external teeth of the flexible externally toothed gear deflected into the ellipsoidal shape increases from a side near the diaphragm toward a front end opening along a tooth trace direction, so that it increases substantially in proportion to a distance from the diaphragm;
- a plane of rotation at a desired position in the tooth trace direction of the flexible externally toothed gear is established as a principal section and both the rigid internally toothed gear and the flexible externally toothed gear in the principal section are spur gears having a module m;
- a number of teeth of the flexible externally toothed gear is set to be fewer than a number of teeth of the rigid internally toothed gear by 2n (n being a positive integer);
- in a major axis position in an ellipsoidal rim neutral line of the flexible externally toothed gear in the principal section, an amount of deflection 2κmn (where κ is the deflection coefficient) relative to a rim neutral circle before deflection is set so as to deflect in a normal-deflection- state of 2 mn=1);
- in a tooth profile of the flexible externally toothed gear, the tooth profile portions to either side of the principal section in the tooth trace direction are shifted;
- the meshing engagement of the flexible externally toothed gear and the rigid internally toothed gear is approximated with a rack meshing engagement, and each of moving loci of the teeth of the flexible externally toothed gear relative to the teeth of the rigid internally toothed gear accompanying rotation of the wave generator is determined in a plane of rotation at each of the positions including the principal section in the tooth trace direction of the flexible externally toothed gear;
- in a normal-deflection moving locus obtained in the principal section, a curve portion running from point A at a peak to a next point B at a bottom is scaled down λ times (λ<1) using point B as a similarity center to obtain a first similar curve BC, and the first similar curve is used as a fundamental shape of an addendum of the rigid internally toothed gear;
- a curve obtained by rotating the first similar curve BC 180 degrees about an endpoint C of the first similar curve BC is scaled down (1−λ)/λ times using the endpoint C as a similarity center to obtain a second similar curve, and the second similar curve is used as a fundamental shape of an addendum of the flexible externally toothed gear;
- and
- a shifted amount in the tooth trace direction in the tooth profile of the flexible externally toothed gear is set so that curves tangent at the bottom of the normal-deflection moving locus in the principal section are inscribed both by each of the negative-deflection side moving loci obtained in each of the planes of rotation to deflect in a negative deflection state (deflection coefficient:
- κ<1) closer to the diaphragm side than the principal section, and each of the positive-deflection side moving loci obtained in each of the planes of rotation to deflect in a positive deflection state (deflection coefficient:
- κ>1) closer to the front end opening side than the principal section.