Machine element or mechanism – Gearing
Utility Patent
1999-07-27
2001-01-02
Marmor, Charles A (Department: 3681)
Machine element or mechanism
Gearing
C074S462000, C074S457000, C074S460000
Utility Patent
active
06167783
ABSTRACT:
TECHNICAL FIELD
This invention relates to a flexible meshing type gear device. More particularly, this invention relates to the tooth profiles of a rigid internal gear and a flexible external gear used in a flexible meshing type gear device.
BACKGROUND OF THE INVENTION
A flexible meshing type gear device typically consists of a rigid circular internal gear, a flexible external gear which has 2g (g being a positive integer) fewer 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, for example, two places, and a wave generator fitted inside the external gear for flexing it into the elliptical shape.
A cup-shaped flexible external gear is known to the art which comprises a cylindrical body, an annular diaphragm formed continuously with one end of the cylindrical body to extend radially inward, a boss formed integrally with the center of the diaphragm, and external teeth formed on the outer periphery of an opening portion of the cylindrical body. Also known to the art is a silk-hat-shaped flexible external gear comprising an annular diaphragm formed to extend radially outward continuously from one end of a cylindrical body and an annular boss formed to continue from the outer edge of the diaphragm.
In a flexible meshing type gear device equipped with such a cup-shaped or silk-hat-shaped flexible external gear, the wave generator flexes a section of the body of the flexible external gear perpendicular to an axis of the body so that the amount of flexing increases from the diaphragm side thereof toward the open end side thereof approximately in proportion to distance from the diaphragm, the external teeth positioned at the extremities of the major axis of the elliptical shape are made to mesh with the internal teeth of the rigid internal gear, and rotation of the wave generator moves the mesh positions of the two gears in the circumferential direction to produce relative rotation between the two gears.
Although the early tooth profiles of gears were linear (see U.S. Pat. No. 2,906,143), the present inventor demonstrated the possibility of using involute gears (see JP-B 45-41171). In addition, for increasing load capacity, the inventor proposed a system using as the addendum profiles of both gears the curve obtained by similarity-transforming the movement locus, at a reduction ratio of ½, over a prescribed range from the meshing limit point on the locus based on the rack approximation of the tooth of the external gear relative to the internal gear (JP-A 63-115943). This is a system for obtaining continuous contact between the addendum profiles of the two gears.
However, these earlier inventions give no consideration to the three-dimensional phenomenon called coning in which the insertion of the elliptical wave generator causes the amount of flexing (half the difference between the major and minor axes of the ellipse) to gradually increase from the diaphragm side toward the end of a cup-shaped or silk-hat-shaped flexible external gear approximately in proportion to the distance from the diaphragm.
In consideration of this coning, the inventor thereafter developed novel tooth profiles enabling provision of flexible meshing type gear devices capable of achieving a wide mesh range, without interference, over the entire tooth trace of the cup-shaped flexible external gear. These profiles are described, for example, in JP-A 4-277354, JP-A 5-172195, JP-A 5-172196 and JP-A 5-209655. Other improved tooth profiles are proposed in, for example, JP-A 62-75153, JP-A 2-62461 and JP-A 7-167228. Among these, JP-A 7-167228 is of particular interest in that it utilizes tooth inclination to eliminate tooth profile interference.
The performance being demanded of flexible meshing type gear devices is becoming increasingly sophisticated. To respond to this demand, it is necessary to further improve device strength, rigidity and wear resistance. Further consideration must be given to the tooth profile to achieve these improvements. The basic tooth profiles derived from the movement locus obtained by rack approximation must also be considered in light of the tooth inclination and change in tooth movement locus that arise in the case of finite teeth.
The invention set out in the aforesaid JP-A 7-167228 ('228) is an improvement that focuses on tooth inclination to eliminate tooth interference. However, the '228 invention does not sufficiently analyze tooth inclination and, moreover, gives no consideration to change in tooth movement locus. Thus, while the '228 invention succeeds in avoiding tooth interference, it fails to maintain the feature to which the basic tooth profiles are directed, namely, the ability to achieve a wide mesh range. Specifically, while it takes into account the angle the tooth center line of the flexible external gear makes with the radial line from the gear center, it does not take into account the angle this tooth center line makes with the tooth space center line of the rigid internal gear (the true tooth inclination angle) and further ignores the point that the tooth movement locus of the flexible external gear differs from the case of a rack. It therefore overestimates the amount of interference. In addition, the '228 invention does not take into account the coning caused by the change in the amount of deflection of the flexible external gear and its tooth profile is therefore valid only in a non-deviated specific section having a standard amount of deflection.
Also with consideration to coning, the inventor developed a rack-approximated tooth profile that effects proper meshing over the entire tooth trace (see JP-A 5-172195). Although this tooth profile is effective when the gear has a large number of teeth (e.g., over 200) and can be viewed as a rack, tooth profile interference arises when the number of teeth is small (e.g., under 100).
DISCLOSURE OF THE INVENTION
The object of this invention is to provide a tooth profile in a flexible meshing type gear device that, by taking into account tooth inclination and change in movement locus of the origin of the tooth profile coordinate system, enables proper wide-range tooth meshing over the entire tooth trace even when the number of teeth is small.
This invention overcomes the problems set out above by fundamentally improving the tooth profiles. Specifically, this invention adopts a convex curve simulating the composite movement locus obtained by rack approximation as the basic addendum profile of both the rigid internal gear and the flexible external gear and corrects the convex curve in consideration of, in the case of a finite number of teeth, (a) the inclination of the tooth center line of the flexible external gear with respect to the tooth space center line of the rigid internal gear in sections perpendicular to the axis and (b) the actual movement locus of the flexible external gear, and further forms the dedendum profile of the rigid internal gear as one enveloped by the addendum profile of the flexible external gear in a section through an opening portion.
More specifically, this invention provides a flexible meshing type gear device including a rigid internal gear, a cup-shaped or silk-hat-shaped flexible external gear and a wave generator, the flexible external gear including a cylindrical body, an annular diaphragm formed continuously with one end of the cylindrical body to extend radially inward or outward, a boss formed at the center or continuously with an outer edge of the diaphragm and external teeth formed on an outer peripheral surface of an opening portion of the body, the external teeth being capable of meshing with internal teeth formed on an internal peripheral surface of the rigid internal gear, the wave generator flexing sections of the body of the flexible external gear perpendicular to the axis of the body into an elliptical shape such that the amount of flexing increases from the diaphragm side thereof toward the opening portion thereof approximately in proportion to distance from
Burns Doane Swecker & Mathis L.L.P.
Harmonic Drive Systems Inc.
Marmor Charles A
Waddell Tisha D.
LandOfFree
Flexible meshing type gearing having three-dimensional,... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Flexible meshing type gearing having three-dimensional,..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Flexible meshing type gearing having three-dimensional,... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2491718