STRAIN WAVE GEARING

Abstract

The tooth profile contours of a rigid internally toothed gear and a flexible externally toothed gear in this strain wave gearing are stipulated by: meshing portions which each mesh with the opposing gear; tooth-crest-side convex surface portions which, respectively, are smoothly connected to the addendum-side ends of the meshing portions and extend from said ends to the apices of the tooth crests; and tooth-bottom-side concave surface portions which, respectively, are smoothly connected to the dedendum-side ends of the meshing portions and extend from said ends to the deepest parts of the tooth bottoms. The meshing portions and tooth-crest-side convex surface portions are machined portions that are simultaneously machined by topping gear cutting, and there are no edges on the teeth of either gear on the tooth-crest side.

Claims

1. A strain wave gearing comprising: a rigid gear; a flexible gear capable of meshing with the rigid gear; and a wave generator that causes the flexible gear to flex in a radial direction and partially mesh with the rigid gear and causes positions where the flexible gear meshes with the rigid gear to move in a circumferential direction of the rigid gear along with rotation, wherein tooth profile contours of the rigid gear and the flexible gear are each provided with: a meshing portion where the gear meshes with the opposing gear; a tooth-crest-side convex surface portion that smoothly connects to an addendum-side end of the meshing portion and extends from the addendum-side end to an apex of a tooth crest; and a tooth-bottom-side concave surface portion that smoothly connects to a dedendum-side end of the meshing portion and extends from the dedendum-side end to a deepest part of a tooth bottom.

2. The strain wave gearing according to claim 1, wherein the rigid gear and the flexible gear are both gears of module m, and the tooth-crest-side convex surface portions and the tooth-bottom-side concave surface portions are set so that a gap, which is at maximum 0.5m in a most deeply meshed state, is formed between the rigid gear and the flexible gear.

3. The strain wave gearing according to claim 2, wherein the rigid gear is an internally toothed gear; the flexible gear is an externally toothed gear that are coaxially arranged inside the rigid gear; and the wave generator is configured to cause the flexible gear to flex into an ellipsoidal shape and form the meshing portion with respect to the rigid gear at two locations.

4. The strain wave gearing according to claim 1, wherein the meshing portion and the tooth-crest-side convex surface portion of each of the rigid gear and the flexible gear are machined portions that are simultaneously machined by topping gear cutting.

5. The strain wave gearing according to claim 2, wherein the meshing portion and the tooth-crest-side convex surface portion of each of the rigid gear and the flexible gear are machined portions that are simultaneously machined by topping gear cutting.

6. The strain wave gearing according to claim 3, wherein the meshing portion and the tooth-crest-side convex surface portion of each of the rigid gear and the flexible gear are machined portions that are simultaneously machined by topping gear cutting.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1(a) is a schematic longitudinal cross-sectional view of a strain wave gearing according to an embodiment of the present invention, and FIG. 1(b) is an explanatory drawing of a meshed state of an externally toothed gear and an internally toothed gear of the strain wave gearing; and

[0017] FIG. 2(a) is an explanatory drawing of tooth profile contours of the externally toothed gear and the internally toothed gear of the strain wave gearing of FIG. 1, and FIG. 2(b) is an explanatory drawing of a meshed state of the teeth created through rack approximation.

MODE FOR CARRYING OUT THE INVENTION

[0018] An embodiment of a strain wave gearing to which the present invention is applied is described below with reference to the drawings. FIG. 1(a) is a schematic longitudinal cross-sectional view of the strain wave gearing, and FIG. 1(b) is an explanatory drawing of a meshed state of an externally toothed gear and an internally toothed gear of the strain wave gearing.

[0019] A strain wave gearing 1 is provided with a rigid internally toothed gear 2 (rigid gear), a flexible externally toothed gear 3 (flexible gear) coaxially disposed on the inner side of the internally toothed gear 2, and a wave generator 4 fitted into the inner side of the externally toothed gear 3. The internally toothed gear 2 is provided with a rigid annular body 21 and internal teeth 24 formed on a circular internal peripheral surface of the annular body 21. The externally toothed gear 3 has a cup shape and is provided with a cylindrical barrel part 31, an annular diaphragm 32 extending radially inward from one end of the cylindrical barrel part 31, and a rigid discoidal boss 33 formed so as to be continuous with the internal peripheral edge of the annular diaphragm 32. External teeth 34 are formed on an external peripheral surface portion of the barrel part 31, on a side nearer to an open end. The internally toothed gear 2 and the externally toothed gear 3 together constitute a spur gear of module m, and the external teeth 34 are able to mesh with the internal teeth 24.

[0020] The wave generator 4 is provided with an ellipsoidally contoured rigid cam 41, and a wave bearing 42 provided with a flexible bearing raceway fitted over the external peripheral surface of the rigid cam 41. The wave generator 4 causes ellipsoidal flexure in a portion of the externally toothed gear 3 on the open-end side of the barrel part 31, as shown in FIG. 1(b). Portions of the external teeth 34 positioned at both ends of the ellipsoid along a long-axis direction L1 mesh with the internal teeth 24 of the internally toothed gear 2.

[0021] For example, the internally toothed gear 2 is secured to a secured-side member (not shown), and the wave generator 4 is rotatably driven by a motor, etc. When the wave generator 4 rotates, the meshing positions of the gears 2, 3 move in a circumferential direction. The difference in the number of teeth between the gears is 2n (n being a positive integer), and relative rotation that is greatly reduced relative to the rotation of the wave generator 4 occurs between the gears due to the difference in the number of teeth. Because the internally toothed gear 2 is secured, the externally toothed gear 3 rotates and reduced rotation is outputted to a load side (not shown) connected to the externally toothed gear 3.

[0022] FIG. 2(a) is an explanatory drawing of tooth profile contours of the internal teeth 24 of the internally toothed gear 2 and the external teeth 34 of the externally toothed gear 3 (contour shapes of tooth profile cross-sections cut along an orthogonal plane orthogonal to a tooth-trace direction). The tooth profile contour (tooth flank shape) of the internal teeth 24 is provided with a meshing portion 26 (meshing tooth flank portion) that meshes with the opposing externally toothed gear 3. The tooth profile shape stipulating the meshing portion 26 is stipulated by an involute curve tooth profile employed in the prior art and another known tooth profile shape. One end of a tooth-crest-side convex surface portion 27 (tooth-crest-side tooth flank portion stipulated by a convex surface) smoothly connects to an addendum-side end 26a of the meshing portion 26. The tooth-crest-side convex surface portion 27 extends from the addendum-side end 26a to a tooth-crest apex 27a of the internal tooth 24. One end of a tooth-bottom-side concave surface portion 28 (tooth-bottom-side tooth flank portion stipulated by a concave surface) smoothly connects to a dedendum-side end 26b of the meshing portion 26. The tooth-bottom-side concave surface portion 28 extends from the dedendum-side end 26b to a tooth-bottom deepest part 28a of the internal tooth 24.

[0023] Similarly, the tooth profile contour (tooth flank shape) of the external teeth 34 is provided with a portion 36 (meshing tooth flank portion) that meshes with the opposing internal teeth 24. The meshing portion 36 is stipulated by an involute curve tooth profile or another tooth profile curve employed in the prior art. One end of a tooth-crest-side convex surface portion 37 (tooth-crest-side tooth flank portion stipulated by a convex surface) smoothly connects to an addendum-side end 36a of the meshing portion 36. The tooth-crest-side convex surface portion 37 extends from the addendum-side end 36a to a tooth-crest apex 37a of the external tooth 34. One end of a tooth-bottom-side concave surface portion 38 (tooth-bottom-side tooth flank portion stipulated by a concave surface) smoothly connects to a dedendum-side end 36b of the meshing portion 36. The tooth-bottom-side concave surface portion 38 extends from the dedendum-side end 36b to a tooth-bottom deepest part 38a of the external tooth 34.

[0024] In the present example, the tooth-crest-side convex surface portions 27, 37 and the tooth-bottom-side concave surface portions 28, 38 of the internal tooth 24 and the external tooth 34 are portions that do not contribute to meshing. Basically, these portions can be any convex surfaces and concave surfaces that do not interfere with the teeth of the opposing gear. In the present example, the convex surfaces stipulating the tooth-crest-side convex surface portions 27, 37 and the concave surfaces stipulating the tooth-bottom-side concave surface portions 28, 38 are set so that in the deepest meshing state, a gap Δ of at most 0.5m is formed between the internal tooth 24 and the external tooth 34.

0<Δ≤0.5m

[0025] In the cup-shaped externally toothed gear 3, the amount of radial flexure differs in individual tooth-trace-direction positions on the external teeth 34. The amount of radial flexure in individual tooth-trace-direction positions on the external teeth 34 is 2xmn (0<x≤1). The symbol x denotes a deflection coefficient, m denotes the module, and n denotes a positive integer. For example, the amount of radial flexure in ends of the external teeth on the open-end side of the externally toothed gear 3 is set to 2mn, which is a reference flexure where x=1. From the open-end-side ends of the external teeth 34 toward the diaphragm-side inner ends of the external teeth 34, the amount of flexure gradually decreases from 2mn.

[0026] In a cross-section at a right angle to the tooth in the open-end-side end of an external tooth 34, when the tooth profile shape of the external tooth 34 is set as described above, shifting corresponding to the amount of flexure is carried out in the tooth profile shape from the open-end-side end of the external tooth toward the diaphragm-side inner end of the external tooth. The internal teeth 24 of the rigid internally toothed gear 2 are given the same tooth profile shape in the tooth-trace direction. Due to the external teeth 34 being given a shifted tooth profile, it is possible to prevent interference between the external teeth and the internal teeth caused by the difference in movement loci of the teeth at individual tooth-trace-direction positions.

[0027] FIG. 2(b) is an explanatory drawing of a meshing state, shown by rack approximation, between an external tooth 34 and an internal tooth 24 provided with the tooth profile contours described above. The tooth profile of an external tooth having edges at both ends of the flat tooth crest surface is also shown as overlapping the external tooth 34. Due to the use of the external teeth 34 and the internal teeth 24 of the present example, which have edgeless tooth flank shapes, a smooth meshing state is formed between the teeth when the teeth go into mesh, reach the deepest state of mesh, and come out of mesh.

Other Embodiments

[0028] The example described above is a case in which the present invention is applied to a cup-shaped strain wave gearing. The present invention can similarly be applied to a top-hat-shaped strain wave gearing and a flat strain wave gearing. The example described above includes an internally toothed gear serving as a rigid gear and an externally toothed gear serving as a flexible gear. Conversely, the present invention can be similarly applied to a strain wave gearing in which an externally toothed gear is provided as a rigid gear, and an internally toothed gear is provided as a flexible gear, the internally toothed gear being caused by a wave generator to flex into a non-circular shape, e.g., an ellipsoidal shape from the external side and mesh with the externally toothed gear at positions on both ends of a short axis of the ellipsoidal shape.