Machine element or mechanism – Gearing – Teeth
Patent
1987-08-17
1989-07-25
Diehl, Dwight G.
Machine element or mechanism
Gearing
Teeth
74640, F16H 5508
Patent
active
048502375
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to the tooth profiles of externally- and internally-toothed gears in a planetary gear mechanism or the tooth profiles of a rack and a pinion rack in a rack meshing mechanism, and, more particularly, to tooth profiles for use in meshing mechanisms in which the load on each tooth is reduced and play and clearances are minimized.
BACKGROUND ART
Planetary gear mechanisms are employed in various kinds of reduction mechanism since they have a large reduction gear ratio and can bear a large transmission load. Of these planetary gear mechanisms, a known mechanism called a harmonic reduction gear is provided with two internally-toothed gears having mutually different numbers of teeth, a phase difference due to the difference in the number of teeth of the two internally-toothed gears is created for each rotation of an input shaft, by deflecting an annular externally-toothed gear which meshes with the internally toothed gears, and rotational speed is reduced by transmitting this phase difference to an output shaft. Such gear mechanisms are shown in Examined Publication Nos. 36137/75 and 46115/75, and Japanese Patent Examined Publication Nos. 32883/71 and 41172/70.
A more detailed description of this harmonic reduction gear will be given below.
Referring to FIGS. 1 and 2, an oval eccentric member 2 is fixed to an input shaft 1, and an annular externally-toothed gear 3 is slidably supported by the outer periphery of the eccentric member 2. The annular externally-toothed gear 3 is deflectable and meshes with internally-toothed gears (discribed below) at two portions on the long-diameter sides of the oval eccentric member 2, but does not mesh with the internally-toothed gear on the short-diameter sides thereof. Two internally-toothed gears 4, 5 are provided around the external periphery of the exterally-toothed gear 3, the internally-toothed gear 4 being secured to a casing 6 and the internally-toothed gear 5 being connected to an output shaft 7. In this embodiment, the number of teeth of the internally-toothed gear 4 is identical to that of the externally-toothed gear 3, and there is a small difference in the number of teeth between the internally-toothed gears 4 and 5.
In operation, when the eccentric member 2 eccentrically rotates once, the externally-toothed gear 3 meshes with the internally-toothed gears 4 and 5. Since the internally-toothed gear 4 is fixed, the internally-toothed gear 5 is displaced by a relative amount given by the difference in the number of teeth, the output shaft 7 rotates through an angle given by the difference in the number of teeth, and thus rotation of the input shaft 1 is transmitted to the output shaft 7 to cause the same to rotate at a reduced speed.
However, the meshing mechanism of the above-described conventional harmomic reduction gear has the drawbacks described below.
In the first place, the gear transmission mechanism provides faulty transmission based on play and backlash, so that rotation of the input shaft 1 is sometimes not transmitted directly as rotation of the output shaft 7. Such relative faulty transmission between the input shaft 1 and the output shaft 7 is hereafter called angular backlash.
Position-controlling reduction gears used in precision machinery such as industrial robots and machine tools are required to have a high reduction gear ratio and high efficiency, high rigidity, and low angular backlash characteristics.
Referring to FIG. 3, a tooth profile 8 of the externally-toothed gear 3 is a triangular or involute tooth profile, and the envelope of the locus of the tooth profile when the externally-toothed gear 3, which has the tooth profile 8, meshes with the internally-toothed gear 5, which has a different number of teeth, is determined by the locus of an angular portion 9 of the tooth profile 8. In other words, a tooth profile 10 of the internally-toothed gear 5 which provides low angular backlash is determined on the basis of the envelope drawn by the angular portion 9 of the tooth profile 8 of the externally-
REFERENCES:
patent: 2209201 (1940-07-01), Hill
patent: 2960884 (1960-11-01), Hill
patent: 3709055 (1973-01-01), Grove
patent: 3856440 (1974-12-01), Wildhaber
patent: 4348918 (1982-09-01), Fakni
patent: 4673342 (1987-06-01), Saegusa
Hatayama Takayoshi
Kawamoto Kunio
Diehl Dwight G.
Sumitomo Heavy Industrie's, Ltd.
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