Two stress-separation strain wave gearing
AssigneeHarmonic Drive Systems Inc.
InventorShoichi Ishikawa
Life of this patent
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Abstract
In a strain wave gearing, the addendum tooth profile of an inner gear is defined by a formula and that of an outer gear is by another formula at a principal cross-section located at a tooth-trace-direction center of the outer gear, on the basis of a movement locus (Mc) of κ=1 by the teeth of the outer gear with respect to those of the inner gear. The tooth profiles of the dedenda of each of the inner gear and the outer gear are set to any shape that does not interfere with the tooth profile of the addendum of the other gear. It is possible to avoid superimposed flexion-induced bending stresses and tensile stresses caused by load torque arising at the long-axis locations of the outer gear, and the transmission torque capacity of a strain wave gearing can be improved.
Claims6
A strain wave gearing comprising:
- a rigid internally toothed gear, a flexible externally toothed gear arranged coaxially to an inside of the rigid internally toothed inner gear, and a wave generator fitted inside the flexible externally toothed gear;
- the externally toothed gear being flexed into an ellipsoidal shape by the wave generator, outer teeth of the ellipsoidally flexed externally toothed gear meshing with inner teeth of the internally toothed gear in proximity to sections at opposite ends of the ellipsoidally flexed externally toothed gear in a long axis direction thereof;
- the internally toothed gear, and the externally toothed gear, are both spur gears of module m;
- a number of teeth of the externally toothed gear being fewer by 2n than a number of teeth of the internally toothed gear, where n is a positive integer;
- at a location along the long axis on an ellipsoidal rim neutral curve of the externally toothed gear in an axis-perpendicular cross-section at a predetermined location along a tooth trace direction of the externally toothed gear, radial flexion with respect to a rim neutral circle prior to flexion being 2κmn, where κ is a deflection coefficient, and where an axis-perpendicular cross-section established at a predetermined location along the tooth trace direction of the externally toothed gear is a principal cross-section, the principal cross-section being a non-deflection cross-section in which the deflection coefficient κ=1;
- a movement locus where the deflection coefficient κ=1 by the teeth of the externally toothed gear with respect to the internally toothed gear, and where meshing of the externally toothed gear with respect to the internally toothed gear in the principal cross-section, comprises rack meshing;
- a tooth profile of an addendum of the internally toothed gear being specified by the following formula a,
- xCa=0.25 mn (π+θ−sin θ)
- yCa=0.5 mn (−1+cos θ) (formula a)
- where 0≤θ≤π;
- a tooth profile of an addendum of the externally toothed gear being specified by the following formula b,
- xFa=0.25 mn (π−θ+sin θ−ε cos(θ/2))
- yFa=0.5 mn (1−cos θ) (formula b)
- where 0≤ε≤0.1 and 0≤θ≤π;
- and
- the tooth profiles of dedenda of each of the gear and the externally toothed gear being set to any shape that does not interfere with the tooth profile of the addendum of the other gear.
Dependencies are inferred from the claim text.