Machine element or mechanism – Gearing
Patent
1994-09-14
1996-01-23
Wright, Dirk
Machine element or mechanism
Gearing
F16H 132
Patent
active
054857660
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
The present invention relates to a flexing-contact-type gear drive, and particularly to tooth profiles of a rigid internal gear and a flexible external gear employed in this type of gear drive.
2. Background Art
A flexing-contact-type gear drive typically consists of a rigid circular internal gear, a flexible external gear which has 2n (n being a positive integer) less teeth than the internal gear and which is disposed inside the internal gear and flexed into an elliptical shape so as to mesh with the internal gear at two places, and wave generator fitted inside the external gear for flexing it. The basic tooth profile for the gears of a flexing contact gear drive is linear (see U.S. Pat. No. 2,906,143). On the other hand, an involute tooth profile has also been proposed (see Japanese Patent Publication No. SHO 45-41171). However, where the linear or the involute tooth profile is adopted as that of each of the internal and external gears, the addendum faces of the gears cannot be continuously meshed with each other.
For increasing load capacity the inventor of the present invention proposed in Japanese Patent Laid Open No. SHO 63-115943 a system using as the basis for the tooth face profile the curve obtained by similarity transforming the locus of motion at a reduction ratio of 1/2 over a prescribe range from the meshing limit point on the locus of motion based on the rack approximation of the tooth of the external gear relative to the internal gear determined by the shape of the wave generator. With the tooth profile disclosed in this publication, the addendum faces of the internal and external gears can be continuously meshed with each other.
In the meantime, as a flexing-contact-type gear drive, one having a cup-shaped flexible external gear has been known. If the internal and external gears of this type gear drive are designed to have the same tooth profiles as disclosed in the above Japanese Patent Laid Open No. SHO 63-115943, it cannot be realized to form a continuous meshing between the teeth of the gears all along the tooth trace direction.
More specifically, in a cup-shaped, flexing-contact-type gear drive, the cup-shaped flexible external gear is subjected to deflection called coning, in which the deflection value of the external gear increases gradually in the direction from its diaphragm side to its opening side and in proportional to a distance from the diaphragm (the deflection being a difference in the length between the major axis and the minor axis of the elliptical shape of the external gear). The change in the deflection along the axis of the external gear due to the coning is not considered in determination of the tooth profiles disclosed in Japanese Patent Laid Open No. SHO 63-115943.
Accordingly, where a cup-shaped, flexing-contact-type gear drive is provided with the internal and external gears of the tooth profiles as disclosed in the above publication, both gears can be meshed continuously with each other only at a specific sectional portion along the tooth trace direction (for example, at such a sectional portion of non-deviation where a normal deflection occurs), while they may be improperly meshed to cause tooth interference or the like at the other sectional portions.
Measures to avoid the defect are disclosed, for example, in Japanese Patent Laid Open Nos. SHO 62-75153 and HEI 2-62461. In these measures, however, it is required to apply special additional processings such as crowning, relieving and the like to the teeth of gears.
In order to achieve a wider range of meshing of the external and internal gears along the tooth trace direction of the cup-shaped flexible external gear without tooth interference between the external and internal gears, the inventor of the present invention proposes a tooth profile disclosed in Japanese Patent Application No. HEI-3-357036.
The invention disclosed in this patent application was made based on the recognition that, in a flexing contact type gear drive, moving loci of teeth of the cup-shaped flexible exte
REFERENCES:
patent: 2906143 (1959-09-01), Musser
patent: 4823638 (1989-04-01), Ishikawa
patent: 4974470 (1990-12-01), Ishikawa et al.
Harmonic Drive Systems Inc.
Wright Dirk
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