Wave gear device with three-dimensional tooth profile

Abstract

Regarding the three-dimensional tooth profile of the internal teeth (20) of the harmonic gear device (1), at the outer end (20a) of the internal teeth, it is the basic internal tooth profile (20(0)), and at other positions in the tooth trace direction, it is a reduced tooth profile obtained by reducing the basic internal tooth profile (20(0)) proportionally only in the lateral direction at a ratio proportional to the distance from the outer end (20a) of the internal teeth. Regarding the three-dimensional tooth profile of the external teeth (3), at the position of the outer end (30a) of the external teeth, it is the basic external tooth profile (30(0)), and at other positions in the tooth trace direction, it is an enlarged tooth profile obtained by enlarging the basic external tooth profile (30(0)) proportionally only in the lateral direction at a ratio proportional to the distance from the outer end (30a) of the external teeth. Compared with the case where only the external teeth (30) are formed into a three-dimensional tooth profile, the gear cutting process becomes easier. In addition, since the tooth profile is obtained by reducing and enlarging proportionally only in the lateral direction in the tooth trace direction, the gear cutting process becomes even easier.

Description

Technical Field

[0001] The present invention relates to a cup-shaped or top-hat-shaped harmonic gear device. More specifically, it relates to a harmonic gear device having a three-dimensional tooth profile capable of forming a three-dimensional meshing state in which an internal gear and an external gear mesh at each position in the tooth line direction. Background Art

[0002] A cup-shaped or top-hat-shaped harmonic gear device includes: a rigid internal gear; a flexible external gear in a cup shape or a top-hat shape, which is coaxially arranged inside the internal gear; and a wave generator, which is embedded inside the external gear. The external gear includes: a flexible cylindrical main body portion; a diaphragm that extends radially from the rear end of the cylindrical main body portion; and external teeth that are formed on the outer peripheral surface portion of the open end side of the cylindrical main body portion. The external gear is flexed into an elliptical shape by the wave generator and meshes with the internal gear at both ends in the major axis direction of the ellipse.

[0003] As a basic tooth profile of a harmonic gear device, a reference rack tooth profile (involute curve tooth profile) that is easy to perform gear cutting is widely adopted. The application of the involute curve tooth profile is proposed in Patent Document 1 (Japanese Patent Publication No. Sho 45-41171).

[0004] A commonly used harmonic gear device includes: a rigid internal gear; a flexible external gear; and a wave generator that flexes the external gear into an elliptical shape and meshes it with the internal gear. Each tooth of the external gear is repeatedly flexed in the radial direction with a constant amplitude by the wave generator, and thus the meshing state and the meshing disengagement state with respect to the internal gear repeatedly occur. The movement locus of the meshing of the external gear with respect to the internal gear can be represented by a rack fitting. For example, FIG. 7 of Patent Document 2 (International Publication No. WO 2016 / 006102) shows the movement state of the external gear with respect to the internal gear from the meshing disengagement state to the deepest meshing state (the movement state from the deepest meshing state to the meshing disengagement state).

[0005] The flexure state of the external teeth of the external gear flexed into an elliptical shape is different at each position in the tooth line direction. Therefore, the meshing state of the external teeth of the external gear flexed into an elliptical shape with the internal teeth of the internal gear is also different at each position in the tooth line direction. Even if an external tooth tooth profile capable of forming a state of continuous meshing with the internal teeth is set in a cross section perpendicular to the axis at one position in the tooth line direction of the external teeth, an appropriate meshing state cannot be formed at other positions in the tooth line direction.

[0006] In Patent Document 3 (Japanese Patent Application Laid-Open No. 2017-44287), the tooth profile of the internal gear is formed into the same tooth profile at each position in the tooth line direction, the external tooth profile is formed into a straight tooth profile, and the tooth surfaces on both sides thereof are formed into inclined surfaces that are inclined in such a manner that the tooth thickness gradually increases from the end on the diaphragm side toward the end on the opening end side of the external gear along the tooth line direction. Accordingly, in the meshing operation between the external teeth and the internal teeth, interference between the tooth tips on the diaphragm side of the external teeth and the tooth tips of the internal teeth can be prevented.

[0007] In Patent Document 4 (International Publication No. 2013 / 046274), regarding a cup-type or top-hat type harmonic gear device, the basic tooth profiles of the internal teeth and the external teeth are set based on the movement locus of the teeth of the flexible external gear relative to the teeth of the rigid internal gear. The tooth profile of the internal gear adopts the same internal tooth basic tooth profile at each position in the tooth line direction. In addition, as the tooth profile of the external teeth, the following conical tooth profile is adopted: the tooth tip circle diameter gradually decreases from the opening end side toward the diaphragm side in the tooth line direction by displacing both side portions in the tooth line direction of the external tooth basic tooth profile. By adopting a three-dimensional tooth profile in which the tooth profile changes along the tooth line, not only can a two-dimensional meshing state in which meshing is formed in a cross section perpendicular to the axis in the tooth line direction be achieved, but also a three-dimensional meshing state in which the external teeth and the internal teeth mesh in a relatively large range along the tooth line direction can be achieved.

[0008] In Patent Document 5 (International Publication No. 2019 / 077719), regarding a cup-type or top-hat type harmonic gear device, the tooth profile of the internal teeth of the rigid internal gear is the same at each position in its tooth line direction. In addition, the tooth profile of the external teeth of the flexible external gear is set in the following manner. The tooth tip thickness of the external teeth gradually decreases from the outer end of the external teeth on the opening end side of the external gear toward the inner end of the external teeth on the diaphragm side of the external gear along the tooth line direction. In addition, the pressure angle at the pitch point of the external teeth gradually increases from the outer end of the external teeth toward the inner end of the external teeth along the tooth line direction. By forming the tooth profile of the external teeth into a three-dimensional tooth profile that changes along the tooth line direction, not only can a two-dimensional meshing state in which meshing is formed in a cross section perpendicular to the axis in the tooth line direction be formed, but also a three-dimensional meshing state in which the external teeth and the internal teeth mesh in a relatively large range along the tooth line direction can be formed.

[0009] Prior Art Documents

[0010] Patent Documents

[0011] Patent Document 1: Japanese Patent Publication No. 45-41171

[0012] Patent Document 2: International Publication No. 2016 / 006102

[0013] Patent Document 3: Japanese Patent Application Laid-Open No. 2017-44287

[0014] Patent Document 4: International Publication No. 2013 / 046274

[0015] Patent Document 5: International Publication No. 2019 / 077719 Summary of the invention

[0016] Generally, in order to form a three-dimensional meshing state, the tooth profile of the internal gear is formed to be the same along its tooth line, and the external teeth of the external gear are formed to have a three-dimensional tooth profile whose shape changes along the tooth line.

[0017] When designing an external gear with a three-dimensional meshing tooth profile, there are the following problems: Due to the restrictions of gear cutting using a gear cutting machine, it is sometimes difficult to cut a tooth profile in which the tooth thickness, pressure angle, tooth height, etc. change along the tooth line direction as designed.

[0018] In view of this, an object of the present invention is to provide a wave gear device that can easily achieve three-dimensional meshing in the entire tooth trace direction and adopt a three-dimensional tooth shape that is easy to cut as the tooth shape of external teeth and internal teeth.

[0019] In order to solve the above-mentioned problems, the present invention provides a cup-shaped or top-hat-shaped wave gear device, which includes a rigid internal gear, a flexible external gear formed in a cup-shaped or top-hat shape, and a wave generator, wherein when a cross section is cut at a predetermined position in the tooth line direction of the external teeth of the external gear by an orthogonal plane orthogonal to the tooth line direction, the end of the internal teeth of the internal gear corresponding to the external teeth outer end in the tooth line direction is the internal teeth outer end, and the other end is the internal teeth inner end, both the external teeth and the internal teeth are set to a three-dimensional tooth profile. The tooth profile profile of the external teeth on the reference cross section is formed as a basic external tooth profile, and the tooth profile profile of the internal teeth at the cross-sectional position of the internal teeth corresponding to the reference cross section is formed as a basic internal tooth profile that is set to mesh with the basic external tooth profile. In addition, the tooth profile profile of the internal teeth at each position in the tooth line direction of the internal teeth is a tooth profile obtained by proportionally reducing the basic internal tooth profile only in the tooth thickness direction by a factor corresponding to the deflection amount of the external teeth at each position. When observed along the tooth line direction, the external teeth are formed as: a conical tooth shape in which the tooth bottom circle gradually increases from the outer end of the external tooth to the inner end of the external tooth and the tooth height is constant, and the tooth profile at each position in the tooth line direction of the external tooth is: a proportionally enlarged tooth shape obtained by proportionally enlarging the basic external tooth shape only in the tooth thickness direction at a ratio corresponding to the deflection amount of the external tooth at each position.

[0020] In order to achieve three-dimensional meshing between two gears, compared with the case where only the tooth profile of the external teeth is formed into a three-dimensional tooth profile, by forming the tooth profiles of both sides into three-dimensional tooth profiles, the amount of change (the amount of change in tooth thickness, pressure angle, tooth height, tip circle diameter, etc.) in the tooth trace direction in each three-dimensional tooth profile can be reduced. Therefore, compared with the case where only the external tooth profile is formed into a three-dimensional tooth profile, the restrictions on gear cutting are alleviated, and the gear cutting of the external teeth and internal teeth that can achieve three-dimensional meshing becomes easier.

[0021] In addition, regarding the three-dimensional tooth profile of the internal teeth, the basic internal tooth profile is at the outer end of the internal teeth, and at other positions in the tooth trace direction, it is a reduced tooth profile obtained by proportionally reducing the basic internal tooth profile only in the lateral direction. Regarding the three-dimensional tooth profile of the external teeth, the basic external tooth profile is at the outer end of the external teeth, and at other positions in the tooth trace direction, it is an enlarged tooth profile obtained by proportionally enlarging the basic external tooth profile only in the lateral direction. It is possible to easily achieve three-dimensional meshing between the external teeth and the internal teeth in the entire tooth trace direction, and it is possible to obtain three-dimensional tooth profiles of the external teeth and internal teeth that are easy to perform gear cutting. Brief Description of the Drawings

[0022] Figure 1 are a longitudinal sectional view and an end view of a cup-shaped harmonic gear device.

[0023] Figure 2 are explanatory diagrams showing the flexure states of cup-shaped and top-hat-shaped external tooth gears, where Figure 2 (a) shows the state before deformation, Figure 2 (b) shows the state of a cross-section including the major axis of the external tooth gear deformed into an elliptical shape, Figure 2 (c) shows the state of a cross-section including the minor axis of the external tooth gear deformed into an elliptical shape.

[0024] Figure 3 are explanatory diagrams showing three examples of the movement locus of the external teeth relative to the internal teeth in an arbitrary cross-section perpendicular to the axis in the tooth trace direction of the tooth profile.

[0025] Figure 4 (a) is an explanatory diagram showing the tooth profile shapes in the tooth trace direction of the internal teeth and the external teeth, Figure 4 (b) is an explanatory diagram showing the tooth profile shapes in each cross-section in the tooth trace direction of the internal teeth, Figure 4 (c) is an explanatory diagram showing the tooth profile shapes in each cross-section in the tooth trace direction of the external teeth.

[0026] Figure 5 (a) to Figure 5 (f) are explanatory diagrams showing the meshing states of the internal teeth and the external teeth at each cross-section position in the tooth trace direction. Detailed Description of the Preferred Embodiments

[0027] Hereinafter, a harmonic gear device to which the present invention is applied will be described with reference to the accompanying drawings. Figure 1 (a) is a longitudinal sectional view showing an example of a cup-shaped harmonic gear device to which the present invention is applied, Figure 1 (b) is an end view thereof.

[0028] The harmonic gear device 1 includes: an annular rigid internal gear 2; a flexible external gear 3 coaxially disposed inside the internal gear 2; and an elliptical-profile wave generator 4 embedded inside the external gear 3. The internal gear 2 and the external gear 3 are spur gears with the same module (m). In addition, the difference in the number of teeth between the two gears is 2n (n is a positive integer), and the number of teeth of the internal teeth 20 of the internal gear 2 is larger. The external teeth 30 of the external gear 3 are deflected into an elliptical shape by the elliptical-profile wave generator 4 and mesh with the internal teeth 20 of the internal gear 2 at both end portions in the direction of the major axis L1 of the ellipse. When the wave generator 4 rotates, the meshing positions of the two teeth 20 and 30 move in the circumferential direction, and a relative rotation corresponding to the difference in the number of teeth between the two teeth 20 and 30 is generated between the two gears 2 and 3.

[0029] The external gear 3 includes: a flexible cylindrical main body portion 31; a diaphragm 32 that is continuous with one end, i.e., the rear end 31b, of the cylindrical main body portion 31 and extends in the radial direction; and a rigid annular boss 33 that is continuous with the diaphragm 32. External teeth 30 are formed on the outer peripheral surface portion on the other end (front end), i.e., the open end 31a side, of the cylindrical main body portion 31. The wave generator 4 is embedded in the inner peripheral surface portion of the external tooth forming portion of the cylindrical main body portion 31 of the external gear 3. Due to the elliptical-profile wave generator 4, the amount of deflection of the cylindrical main body portion 31 of the external gear 3 toward the outside or inside in the radial direction gradually increases from the rear end 31b on the diaphragm side toward the open end 31a.

[0030] Figure 2 The state in which the cup-shaped external gear 3 is deflected into an elliptical shape is shown, where, Figure 2 (a) is a sectional view showing the state before deformation, Figure 2 (b) is a sectional view at the position of the major axis of the deformed elliptical curve, Figure 2 (c) is a sectional view at the position of the minor axis of the deformed elliptical curve. In addition, Figure 2 (a) to Figure 2 (c) The dashed lines in show a top-hat-shaped external gear 3A. Regarding the top-hat-shaped external gear 3A, the diaphragm 32A extends outward in the radial direction from the rear end 31b of the cylindrical main body portion 31, and an annular boss 33A is formed at the outer peripheral end of the diaphragm 32A. The deflection state of the external tooth forming portion of the external gear 3A is the same as that of the cup-shaped external gear 3.

[0031] As Figure 2(b), in the cross section including the major axis L1 of the elliptical curve, the amount of deflection toward the outside gradually increases in proportion to the distance from the rear end 31b toward the open end 31a, as Figure 2 (c), in the cross section including the minor axis L2 of the elliptical curve, the amount of deflection toward the inside gradually increases in proportion to the distance from the rear end 31b toward the open end 31a. The amount of deflection of the external teeth 30 formed on the outer peripheral surface portion on the open end 31a side changes in each cross section perpendicular to the axis in the tooth line direction thereof. That is, the amount of deflection in the radial direction gradually increases in proportion to the distance from the inner end 30b of the external teeth on the diaphragm side in the tooth line direction of the external teeth 30 toward the outer end 30a of the external teeth on the open end 31a side.

[0032] Figure 3 is a diagram showing three examples of the movement locus of the external teeth 30 of the external tooth gear 3 of the harmonic gear device 1 relative to the internal teeth 20 of the internal tooth gear 2. In any cross section perpendicular to the axis at an arbitrary position in the tooth line direction of the external teeth 30 of the external tooth gear 3, at the position of the major axis L1 on the neutral line of the elliptical rim of the external teeth 30, the amount of deflection relative to the neutral circle of the rim before the external teeth 30 are deflected into an elliptical shape is 2κmn, where κ is the deflection coefficient.

[0033] Figure 3 The origin of the y-axis in [] is the average position of the amplitude of the movement locus. The non-deviating movement locus M1 in the movement locus is obtained in the case where the deflection coefficient κ = 1, that is, in the standard deflection state without deviation, and the positive deviation movement locus M o is obtained in the case where the deflection coefficient κ > 1, that is, in the deflection state of positive deviation, and the negative deviation movement locus M i is obtained in the case where the deflection coefficient κ < 1, that is, in the deflection state of negative deviation. A cross section perpendicular to the axis at an arbitrary position in the tooth line direction, for example, the position of the diameter line C passing through the center of the ball 4a of the harmonic bearing or the position of the outer end 30a of the external teeth on the open end 31a side (refer to Figure 2 ) is set as the reference cross section. In the reference cross section, the amount of deflection is set so as to obtain a non-deviating movement locus with a deflection coefficient κ = 1.

[0034] (Example of three-dimensional tooth profile)

[0035] In this example, based on the amount of deflection in the radial direction of the external teeth 30 at each position in the tooth line direction of the external teeth 30, the tooth profiles of both the external teeth 30 and the internal teeth 20 are formed into three-dimensional tooth profiles in which the tooth profile shapes gradually change along their tooth line directions. Hereinafter, examples of the tooth profile shapes of the internal teeth 20 and the external teeth 30 will be described.

[0036] Figure 4(a) is an explanatory diagram showing the contour shapes of the internal teeth 20 of the internal gear 2 and the external teeth 30 of the external gear 3 in the tooth trace direction. Figure 4 (b) is an explanatory diagram showing the tooth profile shape at the position of each cross section in the tooth trace direction (a cross section when cut along an orthogonal cross section orthogonal to the tooth trace direction) of the internal teeth 20. Figure 4 (c) is an explanatory diagram showing the tooth profile shape at each cross section (a cross section when cut at an orthogonal cross section orthogonal to the tooth trace direction) in the tooth trace direction of the external tooth 30. In these figures, the tooth thickness direction is set to X, the tooth height direction is set to Y, the tooth trace direction is set to Z, the internal tooth outer end 20a is set to the cross section position of Z=0, and the internal tooth inner end 20b is set to the cross section position of Z=10.

[0037] The tooth profile of the internal teeth 20 is a three-dimensional tooth profile in which the tooth profile gradually changes along the tooth line. For example, at the cross-sectional position (Z=0) of the internal tooth outer end 20a in the tooth line direction Z of the internal teeth 20, the tooth profile profile of the internal teeth 20 is set to the basic internal tooth profile 20(0). The tooth profiles at other cross-sectional positions in the tooth line direction of the internal teeth 20 are proportionally reduced tooth profiles obtained by proportionally reducing the basic internal tooth profile 20(0) only in the lateral direction at a reduction ratio set in accordance with the deflection amount at the position of the corresponding external teeth 30.

[0038] Figure 4 (b) shows the basic internal tooth profile 20(0) at the cross-sectional position (internal tooth outer end 20a) where the Z value is "0", and the scaled-down tooth profiles 20(2.6), 20(4.6), 20(7), 20(8.5), and 20(10) at five cross-sectional positions where the Z values ​​are "2.6", "4.6", "7", "8.5", and "10" (internal tooth inner end 20b). For example, the position where Z=0 is the position where the flexure coefficient κ=1.

[0039] The reduction ratio of the proportionally reduced tooth profile in the transverse direction, i.e., the tooth thickness direction X, at each cross-sectional position in the tooth trace direction Z of the internal tooth 20 decreases substantially in proportion to the distance from the internal tooth outer end 20a to each cross-sectional position in the tooth trace direction Z. The tooth height of the internal tooth 20 in the tooth trace direction is constant. In addition, the tooth thickness decreases in accordance with the distance in the tooth trace direction relative to the internal tooth outer end 20a, and the pressure angle at the node increases in accordance with the distance in the tooth trace direction relative to the internal tooth outer end 20a. For example, if the ratio of the basic internal tooth profile 20(0) at the cross-sectional position of the internal tooth outer end 20a is set to "1", the proportionally reduced tooth profile 20(10) at the cross-sectional position (Z=10) of the internal tooth inner end 20b is a shape obtained by proportionally reducing the tooth profile in the transverse direction at a ratio of 1.3.

[0040] The tooth profile of the external teeth 30 is also a three-dimensional tooth profile in which the tooth profile gradually changes along the tooth line. In this example, at the cross-sectional position (Z = 0) of the outer end 30a of the external teeth 30 in the tooth line direction Z, the tooth profile shape of the external teeth 30 is set to: a basic external tooth profile 30(0) that can mesh with the basic internal tooth profile 20(0) of the outer end 20a of the internal teeth 20. For example, the external teeth 30 are conical tooth profiles with a constant tooth height, and the pitch circle gradually increases from the outer end 30a of the external teeth towards the inner end 30b of the external teeth. The amount of deflection at each position in the tooth line direction of the pitch circle increases accordingly (increases correspondingly with the distance from the outer end 30a of the external teeth).

[0041] The outer end 30a of the external teeth is the cross-sectional position at Z = 0, and the inner end 30b of the external teeth is the cross-sectional position slightly closer to the inside than Z = 10. The tooth profiles at other cross-sectional positions in the tooth line direction Z of the external teeth 30 are: proportionally enlarged tooth profiles obtained by proportionally enlarging the basic external tooth profile 30(0) only in the lateral direction. Figure 4 (c) shows the basic external tooth profile 30(0) at the cross-sectional position (outer end 30a of the external teeth) where the value of Z is "0", and the proportionally enlarged tooth profiles 30(2.6), 30(4.6), 30(7), 30(8.5), and 30(10) at 5 cross-sectional positions where the value of Z is "2.6", "4.6", "7", "8.5", and "10". In addition, the cross-sectional position of the external teeth 30 at Z = 10 is a position deviating from the inner end 30b of the external teeth (a position deviating from the effective tooth width), and the tooth height decreases. The proportionally enlarged tooth profile 30(10) represented by the imaginary line becomes the shape represented by the solid line 30(10a).

[0042] The magnification ratio in the lateral direction, that is, the tooth thickness direction X, of the proportionally enlarged tooth profiles at each cross-sectional position in the tooth line direction Z of the external teeth 30 increases substantially in proportion to the distance in the tooth line direction Z from the outer end 30a of the external teeth to each cross-sectional position. Therefore, the tooth thickness increases correspondingly with the distance in the tooth line direction from the outer end 30a of the external teeth, and the pressure angle at the pitch point increases correspondingly with the distance in the tooth line direction from the outer end 30a of the external teeth. For example, the proportionally enlarged tooth profile 30(10) at the cross-sectional position of the inner end 30b of the external teeth is a shape obtained by proportionally enlarging the basic external tooth profile 30(0) at the cross-sectional position of the outer end 30a of the external teeth in the lateral direction at a magnification ratio of "1.3".

[0043] Here, the basic internal tooth profile 20(0) at the cross-sectional position (the position of the reference cross-section) of the outer end 20a of the internal teeth, and the basic external tooth profile 30(0) at the cross-sectional position (the position of the reference cross-section) of the outer end 30a of the external teeth can be set according to well-known tooth profile setting methods.

[0044] The tooth profile (tooth surface shape) of the basic internal tooth profile 20(0) of the internal teeth 20 has a meshing tooth surface portion 201 that meshes with the external teeth 30 of the mating external gear. One end of the tooth tip side tooth surface portion 202 defined by a convex curve and a straight line is smoothly connected to the tip side end of the meshing portion 201. The tooth tip side tooth surface portion 202 extends from the tooth tip side end of the meshing tooth surface portion 201 to the tooth tip top 203 of the internal teeth 20. On the other hand, one end of the tooth root side tooth surface portion 204 defined by a concave curve is smoothly connected to the root side end of the meshing tooth surface portion 201. The tooth root side tooth surface portion 204 extends from the root side end of the meshing tooth surface portion 201 to the deepest part 205 (tooth groove center position) of the tooth root of the internal teeth 20.

[0045] Similarly, the basic external tooth profile 30(0) of the external teeth 30 has a meshing tooth surface portion 301 that meshes with the mating internal teeth 20. One end of the tooth tip side tooth surface portion 302 defined by a convex curve is smoothly connected to the tip side end of the meshing portion 301. The tooth tip side tooth surface portion 302 extends from the tooth tip side end to the tooth tip top 303 of the external teeth 30. On the other hand, one end of the tooth root side tooth surface portion 304 defined by a concave curve and a straight line is smoothly connected to the root side end of the meshing tooth surface portion 301. The tooth root side tooth surface portion 304 extends from the root side end of the meshing tooth surface portion 301 to the deepest part 305 (tooth groove center position) of the tooth root of the external teeth 30.

[0046] The tooth profile shape that defines the meshing tooth surface portions 201 and 301 of the internal teeth 20 and the external teeth 30 is defined by a tooth profile curve such as an involute curve used in the past. In addition, the movement locus of the external teeth 30 relative to the internal teeth 20 can be obtained, and a part of the curve representing the movement locus is used to set the tooth profile of the meshing tooth surface portions of the internal teeth and the external teeth. For example, the tooth profile curve can be defined as described in Japanese Patent Laid-Open No. 63-115943 and Japanese Patent Laid-Open No. 64-79448. In these publications, a curve portion within a specified range is selected from the meshing boundary points on the movement locus of the external teeth 30 obtained when the meshing fit of the external teeth 30 relative to the internal teeth 20 is a rack meshing, and the tooth profile curve of the meshing tooth surface portions of the internal teeth and the external teeth is set based on the fitting curve of this curve portion.

[0047] On the other hand, the tooth tip side tooth surface portions 202 and 302 and the tooth root side tooth surface portions 204 and 304 of the basic internal tooth profile 20(0) and the basic external tooth profile 30(0) are portions that do not participate in meshing. Basically, they can be defined by any convex curve, concave curve, and straight line that do not interfere with the mating teeth.

[0048] Figure 5 (a)~ Figure 5(f) is an explanatory diagram showing a meshing state when the meshing of the external teeth 30 with respect to the internal teeth 20 is regarded as a rack meshing. In these figures, in order to easily understand and show the meshing state of the external teeth 30 with respect to the internal teeth 20, two curves are shown: a curve showing the tooth profile of the internal teeth 20 with a meshing backlash of zero with the external teeth 30, and a curve obtained by slightly shifting the tooth profile in the radial direction, and these are used as the tooth profile curves showing the internal teeth 20.

[0049] In addition, the tooth profile of the internal teeth 20 is modified so that the tooth tip circle is enlarged at the portion (Z=8.5-10) on the side of the inner end 20b of the internal teeth in the tooth line direction, thereby avoiding interference with the external teeth 30. In addition, as described above, the position of the inner end 20b of the internal teeth (Z=10) is a position deviated from the effective tooth width of the external teeth 30 (a position closer to the diaphragm side than the inner end 30b of the external teeth), and is a position where the tooth tip of the external teeth 3 is lowered, as shown in FIG. Figure 5 As shown in (f), they are not formed as teeth and therefore do not interfere with the external teeth 30.

[0050] As described above, the wave gear device 1 adopts a three-dimensional tooth profile in which the tooth profile gradually changes along the tooth line as the tooth profile of the internal teeth 20 and the external teeth 30. Compared with the case where only the external teeth 30 are formed into a three-dimensional meshing tooth profile, the restrictions on the gear cutting process performed by the gear cutting machine are relaxed. Therefore, it is easy to manufacture a three-dimensional meshing wave gear device that meshes in a wide range along the tooth line direction.

[0051] In addition, in this example, the tooth profile at each position in the tooth trace direction of the internal tooth 20 is a tooth profile obtained by scaling down the basic internal tooth profile of the internal tooth outer end 20a only in the horizontal direction. For example, when the internal tooth 20 is cut by turning, the tool tooth profile is made so that the workpiece can be processed at a predetermined intersection angle for the basic internal tooth profile at Z=0. In the tooth trace direction, the gear cutting process in which the basic internal tooth profile 20(0) is gradually scaled down in the horizontal direction to obtain a scaled-down tooth profile only requires that the intersection angle of the tool tooth profile be gradually reduced along the tooth trace direction, so the gear cutting process is relatively easy.

[0052] Similarly, the tooth profile at each position of the external tooth 30 in the tooth line direction is a tooth profile obtained by proportionally enlarging the basic external tooth profile of the external tooth outer end 30a only in the horizontal direction. For example, in the case of gear cutting using a hob, the thickness variation of the external tooth 30 of Z=0 to 10 is continuously formed into a tool tooth profile. During gear cutting, if the hob is moved in coordination with the processing in the Z direction, it is easy to achieve a tooth profile obtained by proportionally enlarging the basic external tooth profile in the horizontal direction. Moreover, by gradually changing the distance between the workpiece and the hob along the Z direction, a tapered tooth profile in which the tooth tip circle gradually increases along the tooth line direction can be achieved.

[0053] (Other embodiments)

[0054] In addition, the example in the case where the present invention is applied to a cup-shaped harmonic gear device has been described above. The present invention can also be similarly applied to a top hat-shaped harmonic gear device.

Claims

1. A wave gear device, characterized in that: the wave gear device has: a rigid internal gear; a flexible external gear coaxially disposed inside the internal gear; and a wave generator embedded inside the external gear, the external gear includes: a flexible cylindrical main body portion; a diaphragm extending radially from the rear end of the cylindrical main body portion; and external teeth formed on the outer peripheral surface portion of the front end, i.e., the open end side, of the cylindrical main body portion, the cylindrical main body portion of the external gear is flexed into an elliptical shape by the wave generator, and at both ends in the major axis direction of the elliptical shape, the external teeth mesh with the internal teeth of the internal gear, when sectioned in a plane including the central axis and the major axis of the elliptical shape, the deflection amount of the external teeth of the external gear in the flexed elliptical shape toward the outside in the radial direction increases in proportion to the distance from the diaphragm side inner end of the external teeth to the outer end of the external teeth on the open end side along the tooth line direction, when taking the section obtained by sectioning in an orthogonal plane orthogonal to the tooth line direction at a specified position in the tooth line direction of the external teeth as the reference section, taking the end on the side corresponding to the outer end of the external teeth in the tooth line direction of the internal teeth as the internal tooth outer end, and taking the other end as the internal tooth inner end, the tooth profile shape of the external teeth on the reference section is the basic external tooth profile, the tooth profile shape of the internal teeth at the cross-sectional position of the internal teeth corresponding to the reference section is: a basic internal tooth profile capable of meshing with the basic external tooth profile, the tooth profile shape at each position in the tooth line direction of the internal teeth is: a tooth shape obtained by proportionally reducing the basic internal tooth profile only in the tooth thickness direction by a magnification set corresponding to the deflection amount of the external teeth at each position, when observing along the tooth line direction, the external teeth are formed into: a conical tooth shape with the pitch circle diameter gradually increasing from the outer end of the external teeth to the inner end of the external teeth and a constant tooth height, the tooth profile shape at each position in the tooth line direction of the external teeth is: a tooth shape obtained by proportionally enlarging the basic external tooth profile only in the tooth thickness direction by a magnification set corresponding to the deflection amount at each position.

2. The wave gear device according to claim 1, characterized in that: the basic internal tooth profile and the basic external tooth profile each have: a meshing tooth surface portion that meshes with the tooth surface of a mating gear; a tooth tip side tooth surface portion that extends from the end on the tooth tip side of the meshing tooth surface portion to the tooth tip top and does not participate in meshing; and a tooth bottom side tooth surface portion that extends from the end on the tooth root side of the meshing tooth surface portion to the deepest part of the tooth bottom and does not participate in meshing, the tooth profile curve that defines the meshing tooth surface portion is defined by an involute curve or a fitting curve, and the fitting curve is obtained by performing a fitting transformation on a part of the movement curve obtained by fitting the meshing of the external teeth and the internal teeth at the position of the reference section as a rack meshing.

3. The wave gear device according to claim 2, wherein: the tooth tip side tooth surface portion and the tooth root side tooth surface portion are defined by a curve or a straight line set so as not to interfere with the tooth surface of a mating gear.

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