Machine element or mechanism – Gearing
Reexamination Certificate
1999-07-30
2001-03-20
Bucci, David A. (Department: 3682)
Machine element or mechanism
Gearing
C074S411000
Reexamination Certificate
active
06202508
ABSTRACT:
TECHNICAL FIELD
This invention relates to a silk-hat type flexible engagement gear device having a silk-hat shaped flexible external gear. More specifically, this invention relates to a silk-hat type flexible engagement gear device which is capable of relieving stress concentration occurred respective portions of a silk-hat shaped external gear to thereby reduce the outer diameter thereof.
BACKGROUND ART
As the flexible engagement gear device, there has been known one that has a flexible external gear of a silk hat shape. In this specification, this type of device is referred to as a silk-hat type flexible engagement gear device.
FIG. 8
is a longitudinal sectional view of a flexible external gear of a silk-hat type flexible engagement gear device, cutting along a plane including its device axial line. As shown in this FIGURE, the flexible external gear
1
has a annular body part
2
, a circular diaphragm
3
having an inner decumferential end connected to a proximal-side opening end, and a circular thick boss
5
connected to an outer circumferential end of the diaphragm
3
. External teeth
4
are formed integrally on an outer circumferential portion of a distal-side opening end of the body part
2
in a circumferential direction.
The device of this type has an advantage in that a rotational member, various wires and the like can be arranged passing through the device. Namely, since the flexible external gear has the diaphragm
3
extending radially and outwardly from the end of the body part
2
, an inner space of the body part
2
can be utilized effectively.
Recently, robots and other machinery have been required to construct compact in size, and therefore miniaturization of reduction device and other mechanisms assembled in robots et al. has also been strongly demanded more than ever. In order to meet this demand, the silk-hat type flexible engagement gear device may be reduced in axial length. For this end, the silk-hat shaped flexible external gear must be reduced in axial length. The conventionally used external gear has a ratio of about 1:1 between the axial length thereof and the pitch circular diameter of the external teeth thereof. If the axial length is made shorter, the coning angle of the external gear is also increased according to the shortening of the axial length.
FIG. 9
illustrates the increase of the coning angle &THgr; of the flexible external gear
1
according to the axial length thereof. As shown in this FIGURE, the increase of the coning angle causes to increase an amount of deformation occurred on portions of the diaphragm
3
. As a result, there is a high possibility that an excess stress concentration occurs on the respective portions of the diaphragm
3
, especially on the inner end portion
3
a
and the outer end portion
3
b
thereof (see FIG.
8
).
On the other hand, shearing stress due to transfer torque is also occurred on these inner and outer end portions
3
a
,
3
b
of the diaphragm
3
, and stress due to misalignment of the component parts is also occurred.
Thus, shortening of the axial length of the flexible external gear tends to cause the excess stress concentration on the portions of the diaphragm
3
. For relieving the stress concentration, it is necessary to increase the outer diameter of the diaphragm. It is, however, in the silk-hat type flexible engagement gear device that the size of the outer diameter thereof depends on that of the outer diameter of the flexible external gear. Thus, increase the size of the outer diameter of the flexible external gear causes to increase in size of the device outer diameter. This may be an obstacle to downsizing and compacting of the device.
DISCLOSURE OF INVENTION
An object of this invention is, in consideration of aforementioned points, to realize a structure that is able to relieve the stress occurred on the diaphragm of the flexible external gear without increasing the outer diameter of the flexible external gear.
In order to achieve the above object, according to this invention, novel sectional shapes are employed for the respective portions of the silk-hat shaped flexible external gear of the silk-hat type flexible engagement gear device.
A silk-hat type flexible engagement gear device to which this invention can be applied comprises a circular rigid internal gear, a flexible external gear inside the rigid internal gear, and a wave generator arranged inside the flexible external gear for flexing the external gear radially to engage partially with the internal gear and for moving engagement portions of these gears along a circumferential direction. Further, the flexible external gear has a silk-hat shape having an annular body part formed on an outer circumferential surface at a side of one opening end thereof with external teeth, a circular diaphragm integrally connected at its inner circumferential end with the other opening end of the body part, and a circular boss integrally formed on an outer circumferential end portion of the diaphragm. Furthermore, the diaphragm has a root part connected to the boss, a plate-shaped part extending radially and inwardly from the root part, and a curved part for connecting the plate-shaped part to the body art smoothly. In addition, the body part has a tooth part where external teeth are formed, and a body main part extending from the tooth part to the curved part and connected to the curved part smoothly.
In the above constituted silk-hat type flexible engagement gear device according to this invention, the flexible external gear has the diaphragm having a shape of a cross section including a device axis, the shape being defined as follows. Namely, one side of the shape of the cross section including the device axis of the plate-shaped part of the diaphragm is defined by a first profile line which includes a straight line extending perpendicular to the device axial line. The other side of the shape of the cross section including the device axis of the plate-shaped part is defined by a second profile line which includes a first convex circular arc smoothly connected to the root part, a concave circular arc smoothly connected to the first convex circular arc, and a second convex circular arc smoothly connected to the concave circular arc which is connected smoothly to the curved part. Further, a portion defined by the straight line and the concave circular arc is set to be the minimum thickness portion of the diaphragm.
Among the first convex circular arc, the second convex circular arc and the concave circular arc defining the second profile line, the first convex circular arc is set to have the smallest curvature and the concave circular arc is set to have the maximum curvature, which is preferable.
It is also preferable to locate the minimum thickness portion at the middle of the plate-shaped part of the diaphragm.
With the thickness of the diaphragm being set as aforementioned, it is possible to reduce the stress occurred on the flexible external gear (bending stress by the wave generator, shearing stress accompanied by torque transfer and stress due to misalignment).
Next, a silk-hat type flexible engagement gear device according to this invention is characterized by setting the curved part of the diaphragm of the flexible external gear thicker than the body part. In an preferred embodiment, the curved part of the diaphragm is set thicker than the plate-shaped part thereof, wherein the curved part of the diaphragm is preferably thickest at the middle portion thereof. It is also preferable that the thickness of the curved part is set to reduce gradually from the middle portion thereof toward the side of the body and toward the plate-shaped part
By setting the thickness of the curved part as mentioned above, the stress occurred on the flexible external gear can be reduced. In particular, fatigue strength and buckling strength of the flexible external gear can be enhanced.
On the other hand, a silk-hat type flexible engagement gear device according to this invention is characterized by setting a portion of the body main part of the body part of th
Bucci David A.
Burns Doane Swecker & Mathis L.L.P.
Hansen Colby
Harmonic Drive Systems Inc.
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