Strain gear device and external gear

Abstract

Outer teeth (34) of an external gear (3) of a wave-motion gear device (1) each have a tooth shape that gradually changes in the tooth trace direction. Each of the outer teeth (34) is provided with an outer tooth part (341) engageable with an inner tooth (24) of an internal gear (2), and an outer tooth extension part (342) not engageable with the inner tooth (24). The tooth shape of the outer tooth extension part (342) is a tapered tooth shape, and serves as a guide for inserting the outer tooth (34) into the inner tooth (24). As compared to the tooth shape (341c) of the first end (341a) of the outer tooth part (341), the tooth shape (342c) of the outer tooth extension part (342) connected to the first end is slightly smaller. Protrusion of the tooth shape (342c) from the tooth shape (341c) in tooth length and thickness directions resulting from misalignment of a molding die will not be caused. Using the outer tooth extension part (342) as a guide facilitates easy assembling work of inserting the external gear (3) into the internal gear (2).

Description

[Technical field]

[0001] The present invention relates to a strain wave gear device equipped with an external gear that is a molded product, and in particular to an external gear equipped with an external tooth shape that can be easily assembled to an internal gear. [Background technology]

[0002] The external gear of a strain wave gear device is generally manufactured by cutting, but it is also known to manufacture it using a molding die. Patent Document 1 describes the manufacture of an external gear with external teeth integrally formed therein using a die equipped with a cavity portion corresponding to the external teeth of the external gear (claim 5 and the like in said document). Patent Document 2 describes the manufacture of a flexspline (external gear) as a resin molded product.

[0003] Meanwhile, for the external gear of a strain wave gearing, proposals have been made to have a tooth profile that takes into account the deflection state of the external gear in the tooth trace direction, avoiding interference with the internal teeth of the internal gear and improving tooth contact. For example, Patent Document 3 describes a strain wave gearing with a tapered external tooth profile, and Patent Document 4 describes an external tooth profile in which the tooth thickness gradually decreases from the open end side of the cup-shaped external gear along the tooth trace.

[0004] When the external gear of a strain wave gear device is manufactured as a molded product using a mold, a parting line trace remains on the outer circumferential surface of the external gear at a location corresponding to the parting line of the mold. It is necessary to design the mold so that the parting line is located at a position outside the external teeth forming portion of the external gear. It is also necessary to ensure that the parting line trace does not hinder the insertion work when inserting the external gear into the internal gear. Furthermore, in order to demold the molded product from the mold, it is necessary to give the molded product a draft angle. In addition, for example, in the case of a cup-shaped external gear, an external tooth shape is adopted in which the tooth profile size gradually decreases along the tooth trace in the demolding direction. In the case of a molded product of an external gear having a tooth profile (three-dimensional tooth profile) in which the tooth profile changes along the tooth trace, it is difficult to insert the external gear into the internal gear from the side with the larger tooth profile size and assemble them.

[0005] In view of this, the present inventor has proposed in Patent Document 5 a strain wave gearing device that can solve the problem that when the external gear is a molded product, it becomes difficult to assemble the external gear to the internal gear due to parting line marks. In this strain wave gearing device, the external teeth of the external gear include an external tooth portion that can mesh with the internal teeth of the internal gear, and an external tooth extension portion formed at a position offset from the internal teeth in the tooth trace direction. The mold is designed so that the parting line of the mold is located at the boundary between the external tooth portion and the external tooth extension portion. In addition, the external tooth portion and the external tooth extension portion are provided with drafts for demolding in opposite directions along the tooth trace direction, with the parting line as the boundary. In addition, the tooth profile of the external tooth extension portion changes along the tooth trace direction so that the external tooth extension portion serves as a guide when inserting the external gear into the internal gear. Even if the tooth profile of the external tooth portion is a three-dimensional tooth profile that changes along the tooth trace direction, the small diameter external tooth extension portion functions as a guide when inserting the external teeth into the internal teeth of the internal gear, making it easier to assemble the external gear to the internal gear. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 63-62935 [Patent Document 2] Japanese Utility Model Application Publication No. 5-52404 [Patent Document 3] Japanese Patent Application Publication No. 62-75153 [Patent Document 4] JP 2017-44287 A [Patent Document 5] International Publication No. 2021 / 140592 Summary of the Invention [Problem to be solved by the invention]

[0007] In the external gear of the strain wave gear device proposed in Patent Document 5, the external tooth portion and the external tooth extension portion have tooth profiles of the same size at the boundary position between the external tooth portion, where the parting line of the mold is located, and the external tooth guide portion, which is the external tooth extension portion. Also, at this position, the size of the tooth profile (height, outer diameter, etc.) is largest.

[0008] If a molding die is misaligned during molding of the external gear, a misalignment occurs between the tooth profiles of the external tooth portion and the external tooth extension portion (external tooth guide portion) in the molded external gear. This misalignment causes the tooth profile at the boundary between the external tooth portion and the external tooth extension portion to be larger than necessary, and when inserting the external tooth into the internal tooth, the boundary between the external tooth and the external tooth guide portion becomes an obstacle, making it difficult to insert the external tooth into the internal tooth. In addition, if a burr occurs as a parting line trace at the boundary where the misalignment occurs, it is not easy to remove the burr.

[0009] The present invention has been made with a focus on these new problems, and its purpose is to provide an external gear in which an external tooth guide portion is appropriately formed so that the external gear, which is a molded product with a three-dimensional tooth profile such as a tapered tooth profile, can be easily assembled into an internal gear, and a wave gear device equipped with such an external gear. [Means for solving the problem]

[0010] In order to solve the above problems, a wave gear device according to the present invention comprises: The gearbox comprises a rigid internal gear, a flexible external gear arranged coaxially inside the internal gear, and a wave generator fitted inside the external gear, the external gear being a molded product, The external teeth of the external gear are An external tooth portion capable of meshing with the internal teeth of the internal gear; and The external teeth are provided with an external tooth extension portion that is formed at a position offset from the internal teeth in a tooth trace direction and does not participate in meshing with the internal teeth, The external tooth portion has at least a tooth tip circle diameter that gradually decreases from a first end on one side to a second end on the other side in the tooth trace direction, and a first draft angle is formed for punching in a first direction along the tooth trace direction, the external tooth extension portion is an external tooth insertion guide for inserting the external tooth from the first end side into the internal tooth along the tooth trace direction, and is continuous with the first end of the external tooth portion and extends in a direction away from the first end along the tooth trace direction, The tip diameter of the external tooth extension portion is smaller than a tip diameter of the external tooth portion at the first end, The die is characterized in that a second draft angle is formed which gradually decreases from a connection end connected to the first end along the tooth trace direction as it moves away from the connection end, for punching in a second direction opposite to the first draft angle.

[0011] Moreover, the external gear of the wave gear device according to the present invention is A molded product comprising a cylindrical body portion flexible in a radial direction and external teeth formed on an outer circumferential surface portion of the cylindrical body portion, the external teeth being integrally formed on the cylindrical body portion using a molding die, The external teeth are An external tooth portion capable of meshing with the internal teeth of the internal gear of the wave gear device; and and an external tooth extension portion that does not engage with the internal tooth, The external tooth portion has at least a tooth tip circle diameter that gradually decreases from a first end on one side to a second end on the other side in the tooth trace direction, and a first draft angle is formed for punching in a first direction along the tooth trace direction, the external tooth extension portion is an external tooth insertion guide for inserting the external tooth from the first end side into the internal tooth along the tooth trace direction, and is continuous with the first end of the external tooth portion and extends in a direction away from the first end along the tooth trace direction, The tip diameter of the external tooth extension portion is smaller than a tip diameter of the external tooth portion at the first end, The die is characterized in that a second draft angle is formed which gradually decreases from a connection end connected to the first end along the tooth trace direction as it moves away from the connection end, for punching in a second direction opposite to the first draft angle. Effect of the Invention

[0012] In the present invention, the tooth height (tooth tip circle diameter) of the external tooth extension portion that functions as an external tooth insertion guide when inserting the external gear into the internal tooth gear is set lower than the tooth height (tooth tip circle diameter) at the first end of the external tooth portion. It is sufficient to set the extent to which the tooth height of the external tooth extension portion is lower than the tooth height at the first end of the external tooth portion, taking into account the deviation of the forming mold. As a result, even if the forming mold is deviated, the tooth profile of the external tooth extension portion connected to the first end does not protrude from the tooth profile end face at the first end of the external tooth portion. Therefore, the maximum height of the external teeth is always the height of the tooth profile at the first end of the external tooth portion that meshes with the internal teeth, so that the problem of difficulty in inserting the external teeth into the internal teeth due to deviation of the forming mold can be solved. In addition, burrs generated at the boundary between the external tooth portion and the external tooth extension portion can be easily removed. [Brief description of the drawings]

[0013] [Figure 1] 1A is a longitudinal sectional view of a strain wave gear device, and FIG. 1B is an explanatory diagram showing the meshing state of the external teeth and internal teeth. [Diagram 2]FIG. 2 is an explanatory diagram showing an external gear together with a molding die. [Diagram 3] FIG. 1A is an explanatory diagram showing the portion where the external teeth of an external gear are formed, FIG. 1B is an explanatory diagram showing a state where there is no misalignment between the tooth profiles at the junction between the external tooth portion and the external tooth extension portion, and FIG. 1C is an explanatory diagram showing a state where there is a misalignment between the tooth profiles at the junction. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of a wave gear device to which the present invention is applied will be described with reference to the drawings. The embodiment described below shows an application example of the present invention, and is not intended to limit the present invention to the embodiment.

[0015] (Embodiment 1) FIG. 1(A) is a vertical cross-sectional view of a cup-type wave gear device according to an embodiment, and FIG. 1(B) is an explanatory diagram showing the meshing state of the external teeth and internal teeth. The wave gear device 1 has an annular rigid internal gear 2, a flexible external gear 3 arranged coaxially inside the internal gear 2, and a wave generator 4 with an elliptical contour fitted inside the internal gear 2. The internal gear 2 and the external gear 3 are spur gears of the same module (m). The difference in the number of teeth between the two gears is 2n (n is a positive integer), with the internal gear 2 having more teeth. The external teeth 34 of the external gear 3 are bent into an elliptical shape by the wave generator 4 with an elliptical contour, and mesh with the internal teeth 24 of the internal gear 2 at both ends in the direction of the major axis L1 of the ellipse. When the wave generator 4 is rotated, the meshing positions of the gears 2 and 3 move in the circumferential direction, and a relative rotation according to the difference in the number of teeth between the gears 2 and 3 occurs between the gears 2 and 3.

[0016] The cup-shaped external gear 3 comprises a flexible cylindrical body 31, a diaphragm 32 that extends radially inwardly from one end, that is, a rear end 31b, a rigid annular boss 33 that is continuous with the inner peripheral edge of the diaphragm 32, and external teeth 34 formed on the outer circumferential surface portion on the side of an opening end 31a that is the other end (front end) of the cylindrical body 31. A wave generator 4 with an elliptical contour is fitted into the inner circumferential surface portion of the portion of the cylindrical body 31 where the external teeth are formed, so that the cylindrical body 31 gradually increases in the amount of bending radially outward or inward from the rear end 31b on the diaphragm side toward the opening end 31a.

[0017] Fig. 2 is an explanatory diagram showing the external gear 3 of the strain wave gear device 1, and Fig. 3 is an explanatory diagram showing the external teeth 34 of the external gear 3. The external gear 3 is a molded product in which the external teeth 34 are integrally formed with a cylindrical body portion 31 using a molding die 5 shown by imaginary lines in Fig. 2. For example, it is an injection molded product of a thermoplastic resin. The internal gear 2 can also be a molded product in the same manner.

[0018] The external teeth 34 of the external gear 3 will be described. The external teeth 34 are composed of an external tooth portion 341 having a predetermined effective tooth width capable of meshing with the internal teeth 24 of the internal gear 2, and an external tooth extension portion 342 formed at a position offset in the tooth trace direction from the internal teeth 24. The external tooth portion 341 and the external tooth extension portion 342 are formed in this order from the end of the external teeth 34 on the side of the opening end 31a toward the diaphragm side along the tooth trace direction W (see FIG. 3). As can be seen from FIG. 1(A), in a state in which the external gear 3 is inserted into the internal gear 2 and assembled, the external tooth portion 341 of the external teeth 34 faces the internal teeth 24. In contrast, the external tooth extension portion 342 is offset in the tooth trace direction from the internal teeth 24 and is not involved in meshing with the internal teeth 24.

[0019] The molding die 5 for the external gear 3 is composed of a pair of openable and closable dies 51, 52, as shown in Fig. 2, for example. When the openable and closable dies 51, 52 are closed, a cavity for molding the external gear is formed between them. A parting line 53 of the openable and closable dies 51, 52 is set so as to be located at the boundary between the external tooth portion 341 and the external tooth extension portion 342 in the cavity. As a result, in the external gear 3 after being demolded and deburred, the boundary between the external tooth portion 341 and the external tooth extension portion 342 of the external teeth 34 is the location where the parting line 53 was located.

[0020] The tooth profile of the external tooth portion 341 of the external teeth 34 gradually changes along the tooth trace direction. Referring to FIG. 3(A), the external tooth portion 341 has a tapered three-dimensional tooth profile in which the tooth height is constant and the tooth tip diameter, tooth bottom diameter, and tooth thickness gradually decrease from the first end 341a, which is the end on the diaphragm side in the tooth trace direction, to the second end 341b, which is the end on the open end 31a side. As a result, the external tooth portion 341 has a first draft angle for removing the molded external gear 3 from the opening and closing die 52 of the molding die 5 in the first direction W1 from the second end 341b to the first end 341a in the tooth trace direction W. The tooth profile of the external tooth portion 341 can be such that at least the tooth tip diameter gradually decreases from the first end 341a to the second end 341b. In addition, the tooth profile of the external tooth portion 341 may be such that at least one of the tip diameter, tooth height, bottom diameter, and tooth thickness gradually decreases from the first end 341a to the second end 341b.

[0021] The external teeth extension portion 342 is a portion used as an external teeth insertion guide for inserting the external teeth 34 from the first end 341a side into the internal teeth 24 along the tooth trace direction, and is continuous with the first end 341a of the external teeth portion 341 and extends toward the diaphragm side (direction away from the first end 341a) along the tooth trace direction. As shown in FIG. 3B, the tooth profile of the connection end 342a of the external teeth extension portion 342 connected to the first end 341a is slightly smaller than the tooth profile at the first end 341a of the external teeth portion 341. Therefore, the size of the tooth profile of the external teeth 34 is maximum at the first end 341a of the external teeth portion 341, and the connection end 342a of the small-sized external teeth extension portion 342 is connected to this first end 341a in a stepped state.

[0022] In this example, the tooth height, tip circle diameter, root circle diameter and tooth thickness of the tooth profile at the connection end 342a of the external tooth extension portion 342 are slightly smaller than the tooth height, tip circle diameter, root circle diameter and tooth thickness at the first end 341a of the external tooth portion 341. The tooth profile at the connection end 342a of the external tooth extension portion 342 can be one whose tip circle diameter is at least smaller than the tip circle diameter of the tooth profile at the first end 341a of the external tooth portion 341.

[0023] The external tooth extension portion 342 has a tapered three-dimensional tooth profile in which the tooth height, tooth tip diameter, tooth bottom diameter, and tooth thickness gradually decrease from a connection end 342a connected to the first end 341a toward a tip end 342b on the diaphragm side along the tooth trace direction W. As a result, the external tooth extension portion 342 has a second draft for removing the molded external gear 3 from the opening and closing die 51 of the molding die 5 in a second direction W2 from the first end 341a toward the second end 341b in the tooth trace direction. The external tooth extension portion 342 also functions as an external tooth insertion guide for inserting the external teeth 34 into the internal teeth 24 from the side of the first end 341a along the tooth trace direction.

[0024] The tooth profile of the external tooth extension portion 342 may be such that at least the tip diameter gradually decreases along the tooth trace direction from the connecting end 342a to the tip 342b on the diaphragm side. The tooth profile of the external tooth extension portion 342 may be such that at least one of the tip diameter, tooth height, bottom diameter, and tooth thickness gradually decreases from the connecting end 342a to the tip 342b on the diaphragm side.

[0025] On the other hand, the inner circumferential surface shape of the cylindrical body 31 of the external gear 3 is defined, for example, by an inner circumferential surface portion 31c having the same inner diameter from the opening end 31a side, and an inner circumferential surface portion 31d continuing from this inner circumferential surface portion 31c and having an inner diameter gradually decreasing toward the diaphragm 32.

[0026] The internal gear 2 having the internal teeth 24 that mesh with the external teeth portion 341 of the external teeth 34 of this shape can also be manufactured as a molded product. The internal teeth 24 of the internal gear 2 have, for example, the same tooth profile in the tooth trace direction. They can also have a three-dimensional tooth profile with a slight draft angle for mold removal in the tooth trace direction.

[0027] In the external teeth 34 of the external gear 3 configured in this manner, the external teeth extension portion 342 is a portion that does not mesh with the internal teeth 24 of the internal gear 2. Furthermore, when the external gear 3 is molded using the molding die 5, the joint between the external teeth portion 341 and the external teeth extension portion 342 is located outside the effective tooth width of the external teeth portion 341 that meshes with the internal teeth 24, and a parting line 53 of the molding die 5 is located at this position when the external gear 3 is molded. Therefore, the external teeth extension portion 342, the irregularities left by the parting line 53, and the like do not adversely affect the meshing state of the external teeth 34 of the external gear 3 with the internal teeth 24 of the internal gear 2.

[0028] Furthermore, the external tooth extension portion 342 has a tapered shape in which the tooth profile gradually decreases toward the diaphragm 32 side. Even if the tooth profile of the external tooth portion 341 is a three-dimensional tooth profile in which the tooth profile changes along the tooth trace direction, the small-diameter external tooth extension portion 342 functions as a guide when inserting the external teeth 34 into the internal teeth 24 of the internal gear 2. This facilitates the assembly work of inserting the external gear 3 into the internal gear 2 from the diaphragm 32 side.

[0029] Furthermore, the size of the tooth profile of the external tooth extension portion 342, which functions as an external tooth insertion guide when inserting the external gear 3 into the internal gear 2, is made slightly smaller than the size of the tooth profile at the first end 341a of the external tooth portion 341. The extent to which the size of the tooth profile of the external tooth extension portion 342 should be made smaller than the size of the tooth profile at the first end 341a of the external tooth portion 341 can be determined in consideration of the misalignment between the open and closed dies 51, 52 of the molding die 5 in the mold clamped state.

[0030] As a result, even if the molding die 5 is misaligned, the tooth profile of the external tooth extension portion 342 connected to the first end 341a does not protrude from the end face of the first end 341a of the external tooth portion 341. For example, as shown in FIG. 3B, the tooth profile 342c of the connection end 342a of the external tooth extension portion 342 connected thereto is made slightly smaller than the tooth profile 341c of the first end 341a of the external tooth portion 341. If a misalignment occurs between the opening and closing dies 51 and 52 of the molding die 5 in the mold clamped state, for example, as shown in FIG. 3C, the tooth profile 342c of the connection end 342a of the external tooth extension portion 342 on the opening and closing die 51 side is misaligned in the tooth height direction and tooth thickness direction with respect to the tooth profile 341c of the external tooth portion 341 on the opening and closing die 52 side. By appropriately setting the sizes of both tooth profiles 341c, 342c, it is possible to prevent the tooth profile 342c of the external tooth extension portion 342 from protruding from the tooth profile 341c of the external tooth portion 341 in the tooth height direction or tooth thickness direction.

[0031] As a result, the maximum tooth profile of the external teeth 34 is always the tooth profile 341c at the first end 341a of the external teeth portion 341, and it is possible to avoid a problem in which a protruding portion in the tooth height or tooth thickness direction from the tooth profile 341c occurs at the joint between the external teeth portion 341 and the external teeth extension portion 342 due to misalignment of the molding die 5, making it difficult to insert the external teeth 34 into the internal teeth 24. In addition, since no such protruding portion occurs, burrs that occur at the boundary between the external teeth portion 341 and the external teeth extension portion 342 due to the parting line can be easily removed.

Claims

1. A wave gear device (1) comprising a rigid internal gear (2), a flexible external gear (3) coaxially arranged inside the internal gear (2), and a wave generator (4) fitted inside the external gear (3), the external gear (3) being a molded product, The external teeth (34) of the external gear (3) are An external tooth portion (341) capable of meshing with the internal teeth (24) of the internal gear (2); and The external tooth extension portion (342) is formed at a position offset from the internal teeth (24) in the tooth trace direction (W) and is not involved in meshing with the internal teeth (24), The external tooth portion (341) has at least a tooth tip circle diameter that gradually decreases from a first end (341a) on one side in the tooth trace direction (W) to a second end (341b) on the other side, and a first draft angle is formed for punching in a first direction (W1) along the tooth trace direction (W); The external tooth extension portion (342) is an external tooth insertion guide for inserting the external tooth (34) from the side of the first end (341 a) along the tooth trace direction (W) into the internal tooth (24), and is continuous with the first end (341 a) of the external tooth portion (341) and extends in a direction away from the first end (341 a) along the tooth trace direction (W), The tip diameter of the external tooth extension portion (342) is smaller than the tip diameter of the external tooth portion (341) at the first end (341a) of the external tooth portion (341); A wave gear device (1) characterized in that a second draft gradient is formed from a connection end (342a) connected to the first end (341a) along the tooth trace direction (W), gradually decreasing as it moves away from the connection end (342a), for punching in a second direction (W2) opposite to the first draft gradient.

2. The external tooth portion (341) has a three-dimensional tooth profile in which at least one of a tip circle diameter of the external tooth portion (341) and a tooth height, a tooth thickness, and a bottom circle diameter of the external tooth portion (341) gradually decreases from the first end (341a) to the second end (341b), The external tooth extension portion (342) has a three-dimensional tooth profile in which at least one of the tip circle diameter of the external tooth extension portion (342) and the tooth height, tooth thickness, and bottom circle diameter of the external tooth extension portion (342) gradually decreases as the external tooth extension portion (342) moves away from the connection end (342a) along the tooth trace direction (W). A strain wave gear device (1) according to claim 1.

3. The external gear (3) comprises a cylindrical body portion (31) flexible in the radial direction, a diaphragm (32) extending radially inward from one end (31b) of the cylindrical body portion (31), and an annular or disk-shaped boss (33) formed continuously with the inner peripheral edge of the diaphragm (32), The external teeth (34) are formed on the outer circumferential surface portion on the side of the opening end (31a), which is the other end of the cylindrical body portion (31), and the first end (341a) of the external teeth portion (341) is located on the side of the diaphragm (32), and the second end (341b) is located on the side of the opening end (31a). A strain wave gear device (1) according to claim 1.

4. An external gear (3) for a wave gear device (1) comprising a cylindrical body portion (31) flexible in the radial direction, a diaphragm (32) extending radially inward from one end (31b) of the cylindrical body portion (31), and external teeth (34) formed on an outer circumferential surface portion on the side of an opening end (31a) which is the other end of the cylindrical body portion (31), the external teeth (34) being a molded product formed integrally with the cylindrical body portion (31) using a molding die, The external teeth (34) are an external tooth portion (341) capable of meshing with the internal teeth (24) of the internal gear (2) of the wave gear device (1); and and an external tooth extension portion (342) that does not engage with the internal teeth (24); The external tooth portion (341) has at least a tooth tip circle diameter that gradually decreases from a first end (341a) on one side in the tooth trace direction (W) to a second end (341b) on the other side, and a first draft angle is formed for punching in a first direction (W1) along the tooth trace direction (W); The external tooth extension portion (342) is an external tooth insertion guide for inserting the external tooth (34) from the side of the first end (341 a) along the tooth trace direction (W) into the internal tooth (24), and is continuous with the first end (341 a) of the external tooth portion (341) and extends in a direction away from the first end (341 a) along the tooth trace direction (W), The tip diameter of the external tooth extension portion (342) is smaller than the tip circle diameter of the external tooth portion (341) at the first end (341a) of the external tooth portion (341); The external gear (3) of the wave gear device (1) is characterized in that a second draft gradient is formed which gradually decreases from a connection end (342a) connected to the first end (341a) along the tooth trace direction (W) as it moves away from the connection end (342a), for punching in a second direction (W2) opposite to the first draft gradient.

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