Machine element or mechanism – Gearing
Reexamination Certificate
1999-06-15
2001-02-06
Marmor, Charles A. (Department: 3681)
Machine element or mechanism
Gearing
Reexamination Certificate
active
06182532
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a cup-type wave gear device having a flexible external gear of a cup shape. More specifically, this inventions pertains to a fastening structure of a flexible external gear and an output member of a cup-type wave gear device.
PRIOR ART DESCRIPTION
There has been known a wave gear device referred to as the cup-type which is provided with a cup-shaped flexible external gear. This type of wave gear device has a circular rigid internal gear, a cup-shaped flexible external gear disposed inside the rigid internal gear, and a wave generator for flexing the flexible external gear into a non-circular shape to mesh it partially with the rigid internal gear and for shifting meshing portions of these gears in a circumferential direction.
The cup-shaped flexible external gear is generally constituted by an annular body formed with external teeth, a circular diaphragm plate extending radially and inwardly from one end of the body, and a thick boss formed integrally on the inner peripheral edge of the diaphragm plate.
The number of teeth of the flexible external gear is different from that of the rigid internal gear by 2n (n: positive Integer), and generally is two less than that of the rigid internal gear. In this case, the flexible external gear is flexed into an elliptical shape by the wave generator so that it meshes with the rigid internal gear at both ends along the major axis of the elliptical shape.
The wave generator is driven to rotate at a high speed by a high-speed rotational source such as a motor so that the meshing portions of both gears move circumferentially, which causes to generate relative rotation between the gears in accordance with the difference In number of teeth between them. Typically, the rigid internal gear is fixed not to rotate, and a rotational output of a greatly reduced speed is derived from the flexible external gear and is transferred to the side of an output shaft.
The flexible external gear is fixedly connected at its boss to an output shaft In a coaxial state by means of fastening bolts which are inserted into the boss and arranged concentrically.
In the flexible external gear, the boss thereof fixedly connected to the output shaft has an outer diameter which is smaller than that of the annular body formed with the external teeth. More specifically, the annular body is flexed elliptically at Its opening end by the wave generator, which may cause to occur stress concentration where the annular body is connected to the diaphragm plate supported by the boss. In order to avoid this stress concentration, the diaphragm plate connected between the boss and body must have a prescribed radial length. This inevitably reduces the outer diameter of the boss connected on the inner circumferential edge of the diaphragm plate.
As a result, the fastening bolts for fixedly connecting the boss with the output shaft must be arranged concentrically on the boss having a small diameter, which cannot assure a large fastening torque.
There has been known a method of assuring a large fastening torque even if the diameter of the boss is small, wherein the boss is constituted to have a small-diameter part continued to an inner peripheral edge of the diaphragm plate and a large-diameter part which is Integrally formed with and arranged axially adjacent to the small-diameter part, and the large-diameter part is connected with the output shaft by fastening bolts. When the flexible external gear having the boss of the above shape, which is so called as the wineglass-shaped flexible external gear, is used, the fastening torque between the flexible gear and the output shaft can be increased, but the axial length of the flexible external gear is also increased by an amount that the large-diameter part is formed. This is an obstacle to making the device small and compact.
An object of this invention is to realize a cup-type wave gear device which is able to increase a fastening torque between a flexible external gear and an output shaft without increasing the side of the device.
SUMMARY OF THE INVENTION
In order to achieve the above and other objects, according to this invention, a cup-type wave gear device having a circular rigid internal gear, a cup-shaped flexible external gear disposed inside the rigid internal gear, and a wave generator inserted into the flexible external gear for flexing the flexible external gear into a non-circular shape to mesh it partially with the rigid internal gear and for shifting meshing portions circumferentially to produce relative rotation between the gears, characterized in that it has an output member and a fastening means for fastening the output member to the flexible external gear, wherein the flexible external gear has an annular boss formed with external teeth, a circular diaphragm plate extending radially and inwardly from one end of the body, and a boss integrally connected to an inner peripheral edge of the diaphragm plate and projecting from the diaphragm plate in a device axial direction, and wherein the fastening means includes a screw fastening mechanism constituted between the boss and the output member.
The screw fastening mechanism may comprise an external thread formed on an outer circumferential surface of the boss and an internal thread formed on an inner circumferential surface of the output member, whereby the boss is screwed into the output member.
With the screw fastening means to screw the boss into the output shaft, it is possible to increase the fastening torque in comparison with the case where fastening bolts are used to fasten it to the output member.
In order to increase the fastening torque further more, driving pins are preferably used to fasten the boss and the output member, together with the screw fastening mechanism. It is also preferable that adhesive is used to connect the boss to the output member as well as the screw fastening mechanism. It is, of course, more preferable that the driving pins and adhesive are both used, together with the screw fastening mechanism.
On the other hand, it is possible to form through holes in the boss and wave generator, whereby a hollow-type wave gear device can be realized which has a hollow portion extending along a device axial direction.
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Burns Doane Swecker & Mathis L.L.P.
Harmonic Drive Systems Inc.
Marmor Charles A.
Pang Roger
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