Wave gear device

Abstract

The external gear (3) of the cup-type cycloidal gear device (1) has external teeth (34) whose tooth profile gradually changes along the tooth direction. An external tooth portion (34A) capable of meshing with the internal teeth (24) of the internal gear (2), a first external tooth extension portion (34B), and a second external tooth extension portion (34C) that do not mesh with the internal teeth (24) are formed on the external teeth (34). The second external tooth extension portion (34C) has a pointed and tapered tooth profile so that the second external tooth extension portion (34C) becomes a guide when inserting the external teeth (34) into the internal teeth (24). This facilitates the assembly operation of inserting the external gear (3) into the internal gear (2).

Description

Technical Field

[0001] The present invention relates to a harmonic drive device having a flexible external gear, and more particularly to an external gear having an external tooth shape that can be easily assembled to an internal gear. Background Art

[0002] As harmonic drive devices, a cup-type harmonic drive device having a cup-shaped external gear, a top-hat type harmonic drive device having a top-hat-shaped external gear, and a flat-type harmonic drive device having a cylindrical external gear are known. Generally, an external gear, which is a structural component of such a harmonic drive device, is manufactured by cutting. In addition, a method of manufacturing an external gear using a molding die is also known. Patent Document 1 describes a method of manufacturing an external gear integrally formed with external teeth using a die having a cavity portion corresponding to the external teeth of the external gear (Claim 5 etc. of this document). Patent Document 2 describes a method of making a flexible spline (external gear) a resin molded product.

[0003] On the other hand, regarding the external gear of a harmonic drive device, a tooth shape has been proposed that can avoid interference with the internal teeth of the internal gear and improve tooth surface contact in consideration of the flexure state in the tooth direction of the external gear. For example, Patent Document 3 describes a harmonic drive device having a conical external tooth shape, and Patent Document 4 describes an external tooth shape in which the tooth thickness gradually decreases along the tooth direction from the open end side of a cup-shaped external gear.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Patent Laid-Open No. 63-62935

[0007] Patent Document 2: Japanese Utility Model Laid-Open No. 5-52404

[0008] Patent Document 3: Japanese Patent Laid-Open No. 62-75153

[0009] Patent Document 4: Japanese Patent Laid-Open No. 2017-44287 Summary of the Invention

[0010] When manufacturing the external gear of a harmonic drive device as a molded product using a molding die, steps etc. (parting line marks) are formed on the outer peripheral surface of the external gear at a position corresponding to the parting line of the molding die. Therefore, it is necessary to design the die etc. so that the position of the parting line is deviated from the external tooth forming portion of the external gear. In addition, when inserting the external gear into the internal gear, it is necessary to ensure that the parting line marks do not become an obstacle to the insertion operation.

[0011] Further, in order to demold the molded product from the molding die, a draft angle is imparted to the molded product. For example, in the case of a cup-shaped external gear, an external gear shape is adopted in which the tooth profile dimensions gradually decrease along the tooth direction toward the demolding direction. In the case of a molded product of an external gear having a tooth profile (three-dimensional tooth profile) that changes along the tooth direction in the above-described manner, it is difficult to insert and assemble the external gear into the internal gear from the side where the tooth profile dimensions are larger. The above-described problem also occurs in the case of an external gear manufactured by machining.

[0012] Conventionally, the above-described problems or issues regarding the external gear of the harmonic gear device have not been paid attention to. In addition, a solution for solving such problems or issues has not been proposed.

[0013] In view of the above problems, an object of the present invention is to provide a harmonic gear device that can easily perform the operation of assembling an external gear having a tooth profile (three-dimensional tooth profile) that gradually changes along the tooth direction into an internal gear. Another object of the present invention is to provide a harmonic gear device that can eliminate the problem that it is difficult to assemble the external gear into the internal gear due to the parting line trace of the molded product in the case where the external gear is a molded product.

[0014] To solve the above problems, the harmonic gear device of the present invention includes: 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 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 deviated from the internal teeth in the tooth direction. The tooth profile shape of the external tooth portion is a three-dimensional tooth profile that changes along the tooth direction, and the external tooth extension portion continuously extends along the tooth direction with respect to a first end that is at least one end in the tooth direction of the external tooth portion. The pitch diameter of at least the tip of the external tooth extension portion gradually decreases from the first end of the external tooth portion to the front end of the external tooth extension portion, so that the external tooth extension portion becomes a guide when inserting the external tooth into the internal tooth.

[0015] Regarding the external gear, the external tooth extension portion is a portion that does not mesh with the internal teeth of the internal gear. In addition, a tapered external tooth extension portion having a gradually decreasing pitch diameter is formed at one end of the external teeth of the external gear. The tooth profile of the external teeth of the external gear gradually changes along the tooth direction. For example, the external teeth are tapered tooth profiles in which the tooth thickness, pitch diameter, etc. gradually decrease toward the open end side of the external gear.

[0016] Even if the tooth profile of the external tooth portion is a three-dimensional tooth profile that changes in tooth shape along the tooth direction, the small-diameter external tooth extension portion functions as a guide when inserting the external tooth into the internal teeth of the internal gear. Therefore, the assembly operation of the external gear with respect to the internal gear becomes easy.

[0017] The cup-shaped external gear includes: a cylindrical main body portion that can flex in the radial direction; a diaphragm that extends from one end of the cylindrical main body portion toward the inside in the radial direction; and external teeth that are formed on the outer peripheral surface portion on the open end side that is the other end of the cylindrical main body portion. The top hat-shaped external gear includes: a cylindrical main body portion that can flex in the radial direction; a diaphragm that extends from one end of the cylindrical main body portion toward the outside in the radial direction; and external teeth that are formed on the outer peripheral surface portion on the open end side that is the other end of the cylindrical main body portion.

[0018] In this case, for example, the external tooth extension portion extends from the first end on the open end side of the external tooth portion to the open end. By using the external tooth extension portion as a guide, the assembly operation of inserting the external gear from its open end side into the internal gear and engaging it with the internal teeth becomes easy.

[0019] Sometimes, the cup-shaped external gear is inserted and assembled into the internal gear from its cylindrical main body portion side. In order to be able to easily perform this assembly operation, it is sufficient to form an external tooth extension portion for insertion guidance at the end on the diaphragm side of the external teeth. In addition, it is also possible to form external tooth extension portions for insertion guidance at both end portions in the tooth direction of the external teeth.

[0020] The present invention can also be applied to a flat type harmonic gear device. The flat type harmonic gear device has: a rigid first internal gear and a rigid second internal gear; a flexible external gear that is coaxially arranged inside the first internal gear and the second internal gear; and a wave generator that is embedded inside the above-mentioned external gear. The external gear includes: a cylindrical main body portion that can flex in the radial direction; and external teeth that are formed on the outer peripheral surface of the cylindrical main body portion.

[0021] In this case, the external teeth include: a first external tooth portion that can engage with the first internal teeth of the first internal gear; a second external tooth portion that can engage with the second internal teeth of the second internal gear; an external tooth connecting portion that connects between the first external tooth portion and the second external tooth portion; a first external tooth extension portion that extends from the end of the first external tooth portion along the tooth direction to the first open end on one side of the cylindrical main body portion; and a second external tooth extension portion that extends from the end of the second external tooth portion along the tooth direction to the second open end on the other side of the cylindrical main body portion.

[0022] In addition, the external tooth connection portion is located at a position deviated from the first internal tooth and the second internal tooth in the tooth direction. The first external tooth extension portion is located at a position deviated from the first internal tooth in the tooth direction, and the second external tooth extension portion is located at a position deviated from the second internal tooth in the tooth direction. The tooth profile of the external tooth gradually changes from the first external tooth portion of the external tooth to the end of the first external tooth extension portion, and the tooth profile of the external tooth gradually changes from the second external tooth portion of the external tooth to the end of the second external tooth extension portion.

[0023] Moreover, at least the pitch circle diameter of the first external tooth extension portion gradually decreases toward the first open end, so that the first external tooth extension portion becomes a guide when inserting the first external tooth into the first internal tooth. At least the pitch circle diameter of the second external tooth extension portion gradually decreases toward the second open end, so that the second external tooth extension portion becomes a guide when inserting the second external tooth into the second internal tooth.

[0024] In this way, the first external tooth extension portion is continuously formed relative to the end of the first external tooth portion, and the second external tooth extension portion is continuously formed relative to the end of the second external tooth portion. The first external tooth extension portion and the second external tooth extension portion form a conical profile with a pitch circle diameter gradually decreasing toward the front end. When inserting the first external tooth and the second external tooth of the external tooth gear into the first internal tooth and the second internal tooth, the first external tooth extension portion and the second external tooth extension portion function as guides. Therefore, the operation of assembling the first internal tooth gear and the second internal tooth gear relative to the external tooth gear becomes easy.

[0025] Next, the present invention relates to a cup-type harmonic drive device including a cup-shaped external tooth gear as a molded product integrally formed with external teeth by a molding die. The external teeth of the external tooth gear include: an external tooth portion capable of meshing with the internal teeth of an internal tooth gear; and a first external tooth extension portion and a second external tooth extension portion formed at positions deviated from the internal teeth in the tooth direction. The external tooth portion, the first external tooth extension portion, and the second external tooth extension portion are continuous in the tooth direction in the above order along the tooth direction of the external tooth from the open end side of the cup-shaped external tooth gear. The parting line trace of the molding die is located at the boundary between the first external tooth extension portion and the second external tooth extension portion that do not mesh with the internal teeth.

[0026] In addition, the tooth profile of the external teeth gradually changes from the position of the parting line trace of the external teeth to the end on the open end side of the external tooth portion in such a manner that a prescribed draft angle for demolding is formed along the tooth axial direction of the external teeth. For example, the external teeth have a tapered tooth profile in which the tooth thickness, the pitch diameter, etc. gradually decrease toward the open end side of the external gear. Further, at least the pitch diameter of the second external tooth extension portion gradually decreases from the position of the parting line trace to the end on the diaphragm side of the external gear so that the second external tooth extension portion serves as a guide when the external gear is inserted into the internal gear.

[0027] Regarding the cup-shaped external gear, the first external tooth extension portion and the second external tooth extension portion are portions that do not mesh with the internal teeth of the internal gear. Further, the parting line trace is formed at the boundary position between the first external tooth extension portion and the second external tooth extension portion. Irregularities such as steps of the parting line trace do not adversely affect the meshing state of the external teeth of the external gear with the internal teeth of the internal gear. Further, a second external tooth extension portion having a tapered shape in which the pitch diameter gradually decreases toward the diaphragm side is formed at the end on the diaphragm side of the external teeth of the external gear. Even if the tooth profile of the external tooth portion is a three-dimensional tooth profile that changes along the tooth axial direction, the small-diameter second external tooth extension portion functions as a guide when the external teeth are inserted into the internal teeth of the internal gear. Therefore, the assembly operation of the external gear relative to the internal gear becomes easy.

[0028] Next, regarding a top hat type harmonic drive device having a top hat-shaped external gear as a molded product integrally formed with external teeth using a molding die, the external gear is inserted and assembled into the internal gear from its open end side. Regarding the external gear of the top hat type harmonic drive device to which the present invention is applied, a first external tooth extension portion is continuously formed at the end on the diaphragm side of the external teeth relative to the portion of the external teeth that can mesh with the internal teeth, and a second external tooth extension portion is continuously formed at the end on the open end side of the external tooth portion. A parting line trace of the molding die is formed at the portion where the end of the first external tooth extension portion of the cylindrical main body portion of the external gear is located.

[0029] In addition, it is sufficient that the tooth profile of the external teeth gradually changes along the entire tooth axial direction of the external teeth in such a manner that a draft angle is formed in the demolding direction toward the open end side. Regarding the second external tooth extension portion on the open end side, it has a tapered contour in which the pitch diameter gradually decreases toward the open end. Thereby, even if the tooth profile of the external tooth portion of the external teeth that meshes with the internal teeth is a three-dimensional tooth profile that gradually changes along the tooth axial direction, the second external tooth extension portion functions as a guide, and thus the operation of inserting the external gear into the internal gear becomes easy.

[0030] Next, the present invention can also be applied to a harmonic drive device having a flat-shaped (cylindrical-shaped) external gear as a molded product integrally formed with external teeth using a molding die. In this case, the external teeth formed on the outer peripheral surface of the cylindrical main body portion of the external gear include: a first external tooth portion that can mesh with the first internal teeth of a first internal gear as one internal gear; and a second external tooth portion that can mesh with the second internal teeth of a second internal gear as another internal gear. The portion between the first external tooth portion and the second external tooth portion that is deviated with respect to the tooth direction of both internal teeth is connected by an external tooth connecting portion. The parting line trace of the molding die is located at this external tooth connecting portion.

[0031] In addition, a first external tooth extension portion is continuously formed with respect to the end of the first external tooth portion. Similarly, a second external tooth extension portion is continuously formed with respect to the end of the second external tooth portion. The first external tooth extension portion and the second external tooth extension portion are formed into a conical profile in which the pitch circle diameter gradually decreases toward the front end. When the first external teeth and the second external teeth of the external gear are inserted into the first internal teeth and the second internal teeth, the first external tooth extension portion and the second external tooth extension portion function as guides, and thus, the operation of assembling the first internal gear and the second internal gear with respect to the external gear becomes easy. Description of the Drawings

[0032] Figure 1A is a longitudinal sectional view of a cup-shaped harmonic drive device.

[0033] Figure 1B is a front view of a cup-shaped harmonic drive device.

[0034] Figure 1C is an explanatory view showing a cup-shaped external gear.

[0035] Figure 1D is an explanatory view showing another example of a cup-shaped external gear.

[0036] Figure 2A is a longitudinal sectional view of a top hat-shaped harmonic drive device.

[0037] Figure 2B is an explanatory view showing a top hat-shaped external gear.

[0038] Figure 2C is an explanatory view showing another example of a top hat-shaped external gear.

[0039] Figure 3A is a longitudinal sectional view of a flat-type harmonic drive device.

[0040] Figure 3B is an explanatory view showing a flat-shaped (cylindrical-shaped) external gear.

[0041] Figure 3C It is an explanatory diagram showing other examples of an external gear with a flat shape. Detailed implementation

[0042] Hereinafter, embodiments of the harmonic gear device to which the present invention is applied will be described with reference to the drawings. The embodiments described below show application examples of the present invention, and the intention is not to limit the present invention to these embodiments.

[0043] (Embodiment 1)

[0044] Figure 1A It is a longitudinal sectional view of the cup-shaped harmonic gear device according to Embodiment 1, Figure 1B It is a front view thereof, Figure 1C It is an explanatory diagram showing a cup-shaped external gear. The cup-shaped harmonic gear device 1 includes: an annular rigid internal gear 2; a flexible external gear 3 disposed coaxially inside the internal gear; and an elliptical-profile wave generator 4 embedded inside the external gear. The internal gear 2 and the external gear 3 are spur gears of 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 internal gear 2 has more teeth. The external teeth 34 of the external gear 3 are flexed into an elliptical shape by the elliptical-profile wave generator 4 and mesh with the internal teeth 24 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 gears 2 and 3 move circumferentially, and a relative rotation corresponding to the difference in the number of teeth between the two gears is generated between the two gears 2 and 3.

[0045] The cup-shaped external gear 3 includes: a flexible cylindrical main body portion 31; a diaphragm 32 that continuously extends radially inward from the rear end 31b, which is one end of the main body portion; 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 peripheral surface portion on the opening end 31a side, which is the other end (front end) of the cylindrical main body portion 31. The elliptical-profile wave generator 4 embedded in the inner peripheral surface portion of the external tooth forming portion of the cylindrical main body portion 31 causes the cylindrical main body portion 31 to gradually increase the amount of deflection from its rear end 31b on the diaphragm side toward the opening end 31a and toward the outside or inside in the radial direction.

[0046] The external gear 3 of the cup-shaped harmonic gear device 1 is a molded product in which the external teeth 34 are integrally formed at least on the cylindrical main body portion 31 using a molding die. For example, it is an injection molded product of a thermoplastic resin. The internal gear 2 can also be a molded product.

[0047] The external teeth 34 of the external gear 3 will be described. The external teeth 34 include: an external tooth portion 34a that can mesh with the internal teeth 24 of the internal gear 2; and a first external tooth extension portion 34b and a second external tooth extension portion 34c that are formed at positions deviated from the internal teeth 24 in the tooth direction. The external tooth portion 34a, the first external tooth extension portion 34b, and the second external tooth extension portion 34c continuously extend in the above order along the tooth direction from the end on the opening end 31a side of the external teeth 34. In a state where the external gear 3 is inserted and assembled into the internal gear 2, the external tooth portion 34a of the external teeth 34 faces the internal teeth 24. In contrast, the first and second external tooth extension portions 34b, 34c are at positions deviated from the internal teeth 24 in the tooth direction and do not mesh with the internal teeth 24.

[0048] For example Figure 1C As shown by the virtual line in the figure, the molding die 5 of the external gear 3 is composed of a pair of open-close dies 51, 52. When the open-close dies 51, 52 are closed, a cavity for forming the external gear is formed between them. The parting line 53 of the open-close dies 51, 52 is set at the boundary between the first external tooth extension portion 34b and the second external tooth extension portion 34c of the cavity portion for forming the external teeth. Thus, in the external gear 3 after demolding and flash removal, a parting line trace 34d remains at the boundary portion of the first and second external tooth extension portions 34b, 34c of the external teeth 34.

[0049] The tooth profile of the external teeth 34 is a three-dimensional tooth profile that gradually changes along its tooth direction. In this example, the tooth profile of the external teeth 34 continuously and gradually changes from the position of the parting line trace 34d to the end on the opening end 31a side of the external tooth portion 34a in such a way that a prescribed draft angle for demolding is formed along the tooth direction on the external teeth 34. For example, it is formed into a tapered tooth profile in which the tooth thickness, the pitch diameter of the tooth tip circle, and the pitch diameter of the tooth root circle gradually decrease toward the opening end 31a.

[0050] Moreover, the tooth profile of the second external tooth extension portion 34c also becomes a three-dimensional tooth profile in which the tooth profile continuously and gradually changes from the parting line trace 34d toward the diaphragm 32 side. In this example, it is a tapered tooth profile in which the tooth height is the same but the pitch diameter of the tooth tip circle and the pitch diameter of the tooth root circle gradually decrease from the parting line trace 34d to the end on the diaphragm side. In this way, the external teeth 34 are formed into a tapered shape in opposite directions with the parting line trace 34d as the boundary.

[0051] In addition, the inner peripheral surface shape of the cylindrical main body portion 31 of the external gear 3 is defined, for example, by an inner peripheral surface portion 31c with the same inner diameter starting from the opening end 31a side, and an inner peripheral surface portion 31d that is continuous with the inner peripheral surface portion 31c and has an inner diameter gradually decreasing toward the diaphragm 32.

[0052] An internal gear 2 having internal teeth 24 that mesh with the external tooth portions 34a of the external teeth 34 of this shape can also be produced as a molded product. The internal teeth 24 of the internal gear 2 are, for example, tooth profiles that are the same in the tooth direction. They can also be three-dimensional tooth profiles that are slightly formed with a draft angle for demolding in the tooth direction.

[0053] Regarding the external teeth 34 of the external gear 3 in this example, the first and second external tooth extension portions 34b and 34c are portions that do not mesh with the internal teeth 24 of the internal gear 2. In addition, a parting line mark 34d is formed at the boundary between the first and second external tooth extension portions 34b and 34c. The unevenness such as the steps of the first external tooth extension portion 34b and the parting line mark 34d and the second external tooth extension portion 34c 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. In addition, a second external tooth extension portion 34c having a tapered shape with a gradually decreasing pitch circle diameter toward the diaphragm side is formed on the end side on the diaphragm side of the external teeth 34 of the external gear 3. Therefore, even if the tooth profile of the external tooth portion 34a is a three-dimensional tooth profile that changes along the tooth direction, the small-diameter second external tooth extension portion 34c functions as a guide when inserting the external teeth 34 into the internal teeth 24 of the internal gear 2. Thus, the assembly operation of inserting the external gear 3 into the internal gear 2 from the diaphragm 32 side becomes easy.

[0054] (Other examples of cup-shaped external gears)

[0055] The above cup-shaped external gear 3 is a molded product in which external teeth 34 are integrally formed at least in the cylindrical main body portion 31 using a molding die. Refer to Figure 1D An example of an external gear of a machined product that can be used in place of the external gear 3 will be described.

[0056] The external gear 430 includes: a flexible cylindrical main body portion 431; a diaphragm 432 that extends continuously inward in the radial direction from the rear end 431b, which is one end of the main body portion; a rigid annular boss 433 that is continuous with the inner peripheral edge of the diaphragm 432; and external teeth 434 that are formed on the outer peripheral surface portion on the side of the open end 431a, which is the other end (front end) of the cylindrical main body portion 431.

[0057] The external teeth 434 include: an external tooth portion 434a that can mesh with the internal teeth of the internal tooth gear 2; and an external tooth extension portion 434b that is formed at a position deviated from the internal teeth 24 in the tooth direction. The external tooth portion 434a and the external tooth extension portion 434b are continuously formed in the above order along the tooth direction from the end portion on the opening end 431a side of the external teeth 434. In a state where the external tooth gear 430 is inserted and assembled into the internal tooth gear 2, the external tooth portion 434a of the external teeth 434 faces the internal teeth 24. In contrast, the external tooth extension portion 434b is at a position deviated from the internal teeth 24 in the tooth direction and does not mesh with the internal teeth 24.

[0058] The tooth profile of the external teeth 434 is a three-dimensional tooth profile that gradually changes along its tooth direction. In this example, the tooth profile of the external teeth 434 continuously and gradually changes along the tooth direction from the end portion on the diaphragm 432 side of the external tooth portion 434a to the end portion on the opening end 431a side. For example, it is a tapered tooth profile in which the tooth thickness, the addendum circle diameter, and the dedendum circle diameter gradually decrease toward the opening end 431a.

[0059] The tooth profile of the external tooth extension portion 434b is also a three-dimensional tooth profile in which the tooth profile continuously and gradually changes from the end portion on the external tooth portion 434a side toward the diaphragm 432 side. In this example, it is formed into a tapered tooth profile with the same tooth height but gradually decreasing addendum circle diameter and dedendum circle diameter. Thus, the external teeth 434 form a taper in opposite directions from the boundary position between the external tooth portion 434a and the external tooth extension portion 434b.

[0060] Regarding the external teeth 434 of the external tooth gear 430 in this example, the external tooth extension portion 434b is the portion that does not mesh with the internal teeth 24 of the internal tooth gear 2. In addition, on the end portion side on the diaphragm 432 side of the external teeth 434 of the external tooth gear 430, an external tooth extension portion 434b with a tapered shape in which the addendum circle diameter gradually decreases toward the diaphragm 432 side is formed. Even if the tooth profile of the external tooth portion 434a is a three-dimensional tooth profile that changes along the tooth direction, the small-diameter external tooth extension portion 434b functions as a guide when inserting the external teeth 434 into the internal teeth 24 of the internal tooth gear 2. Therefore, the assembly operation of inserting the external tooth gear 430 into the internal tooth gear 2 from the diaphragm 432 side becomes easy.

[0061] (Embodiment 2)

[0062] Figure 2A It is a longitudinal sectional view of the top hat type harmonic drive device according to Embodiment 2, Figure 2BIt is an explanatory diagram showing a top hat-shaped external gear. The top hat type harmonic drive device 100 has: an annular rigid internal gear 120; a flexible external gear 130 coaxially disposed inside the internal gear; and an elliptical profile wave generator 140 embedded inside the external gear. The internal gear 120 and the external gear 130 are spur gears of 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 internal gear 120 has more teeth. The external teeth 134 of the external gear 130 are flexed into an elliptical shape by the elliptical profile wave generator 140 and mesh with the internal teeth 124 at both end portions in the major axis direction of the elliptical shape. When the wave generator 140 rotates, the meshing positions of the two gears 120 and 130 move circumferentially, and a relative rotation corresponding to the difference in the number of teeth between the two gears is generated between the two gears 120 and 130.

[0063] The top hat-shaped external gear 130 includes: a flexible cylindrical main body portion 131; a diaphragm 132 continuously extending radially outward from the rear end 131b which is one end of the main body portion; a rigid annular boss 133 continuous with the outer peripheral edge of the diaphragm 132; and external teeth 134 formed on the outer peripheral surface portion on the opening end 131a side which is the other end (front end) of the cylindrical main body portion 131. The elliptical profile wave generator 140 embedded in the inner peripheral surface portion of the external tooth forming portion of the cylindrical main body portion 131 causes the cylindrical main body portion 131 to gradually increase the amount of deflection toward the opening end 131a from the rear end 131b on the diaphragm side toward the outside or inside in the radial direction.

[0064] The external gear 130 of the top hat type harmonic drive device 100 is a molded product in which the external teeth 134 are integrally formed at least on the cylindrical main body portion 131 using a molding die. For example, it is an injection molded product of a thermoplastic resin. The internal gear 120 can also be a molded product in the same way.

[0065] The external teeth 134 of the external gear 130 will be described. The external teeth 134 include: an external tooth portion 134a that can mesh with the internal teeth 124 of the internal gear 120; and a first external tooth extension portion 134b and a second external tooth extension portion 134c formed at positions deviated from the internal teeth 124 in the tooth direction. The second external tooth extension portion 134c, the external tooth portion 134a, and the first external tooth extension portion 334b are formed in the above order along the tooth direction from the end portion on the opening end 131a side of the external teeth 134. In a state where the external gear 130 is inserted and assembled into the internal gear 120, the external tooth portion 134a of the external teeth 134 faces the internal teeth 124. In contrast, the first and second external tooth extension portions 134b and 134c are at positions deviated from the internal teeth 124 in the tooth direction and do not mesh with the internal teeth 124.

[0066] For example, a forming die (not shown) for the external gear 130 is composed of a pair of open-close dies. When the open-close dies are closed, a cavity for forming the external gear is formed between them. The parting line of the forming die is set at the end on the diaphragm side of the first external tooth extension 134b of the part corresponding to the cylindrical main body 131 in the cavity part for forming the external teeth. Thus, regarding the external gear 130 after demolding, a parting line mark 134d remains at the end of the first external tooth extension 134b of the external teeth 134.

[0067] The tooth profile of the external teeth 134 is a three-dimensional tooth profile that gradually changes along its tooth direction. In this example, the tooth profile of the external teeth 134 gradually changes continuously from the position of the parting line mark 134d to the end (open end 131a) of the second external tooth extension 134c on the external teeth 134 in such a way that a prescribed draft angle for demolding is formed along the tooth direction on the external teeth 134. For example, it is a tapered tooth profile in which the tooth thickness, the pitch diameter of the tooth tip circle, and the pitch diameter of the tooth root circle gradually decrease toward the open end 131a.

[0068] An internal gear 120 having internal teeth 124 that mesh with the external tooth part 134a of the external teeth 134 of this shape can also be manufactured as a molded product. The internal teeth 124 of the internal gear 120 are, for example, of the same tooth profile in the tooth direction. It can also be a three-dimensional tooth profile with a slightly formed draft angle for demolding in the tooth direction.

[0069] Regarding the external teeth 134 of the external gear 130 in this example, irregularities such as the steps of the first external tooth extension 134b and the parting line mark 134d and the second external tooth extension 134c do not adversely affect the meshing state of the external teeth 134 of the external gear 130 with the internal teeth 124 of the internal gear 120. In addition, a pointed second external tooth extension 134c is formed on the open end 131a side of the external teeth 134 of the external gear 130. Even if the tooth profile of the external tooth part 134a is a three-dimensional tooth profile that changes in tooth shape along the tooth direction, the small-diameter second external tooth extension 134c functions as a guide when inserting the external tooth part 134a into the internal teeth 124 of the internal gear 120. Therefore, the assembly operation of inserting the external gear 130 into the internal gear 120 from its open end 131a side becomes easy.

[0070] (Other examples of external gears)

[0071] The above-described top hat-shaped external gear 130 is a molded product in which the external teeth 134 are integrally formed at least on the cylindrical main body 131 using a forming die. Refer to Figure 2C An example of an external gear of a machined product that can be used instead of the external gear 130 will be described.

[0072] The external gear 530 includes: a flexible cylindrical main body portion 531; a diaphragm 532 that extends radially outward continuously from the rear end 531b which is one end of the main body portion; a rigid annular boss 533 that is continuous with the inner peripheral edge of the diaphragm 532; and external teeth 534 formed on the outer peripheral surface portion on the opening end 531a side which is the other end (front end) of the cylindrical main body portion 531.

[0073] The external teeth 534 include: an external tooth portion 534a that can mesh with the internal teeth 124 of the internal gear 120; and an external tooth extension portion 534c formed at a position deviated from the internal teeth 124 in the tooth direction. The external tooth extension portion 534c and the external tooth portion 534a continuously extend in the above order along the tooth direction from the end on the opening end 531a side of the external teeth 534. In a state where the external gear 530 is inserted and assembled into the internal gear 120, the external tooth portion 534a of the external teeth 534 faces the internal teeth 124. In contrast, the external tooth extension portion 534c is at a position deviated from the internal teeth 124 in the tooth direction and does not mesh with the internal teeth 124.

[0074] The tooth profile of the external teeth 534 is a three-dimensional tooth profile that gradually changes along its tooth direction. In this example, the tooth profile of the external teeth 534 continuously and gradually changes from the end on the diaphragm side to the end of the second external tooth extension portion 534c (opening end 531a) on the external teeth 534. For example, it is a tapered tooth profile in which the tooth thickness, the pitch diameter of the addendum circle, and the pitch diameter of the dedendum circle gradually decrease toward the opening end 531a.

[0075] Regarding the external teeth 534 of the external gear 530 in this example, a pointed external tooth extension portion 534c is formed on the opening end 531a side thereof. Even if the tooth profile of the external tooth portion 534a is a three-dimensional tooth profile that changes along the tooth direction, the small-diameter external tooth extension portion 534c functions as a guide when inserting the external tooth portion 534a into the internal teeth of the internal gear. Therefore, the assembly operation of inserting the external gear 530 into the internal gear 120 from its opening end 531a side becomes easy.

[0076] (Embodiment 3)

[0077] Figure 3A It is a longitudinal sectional view of the flat type harmonic gear device according to Embodiment 3, Figure 3BIt is an explanatory diagram showing an external gear with a flat shape (cylindrical shape). The flat type harmonic gear device 200 has: an annular rigid first internal gear 221 and a second internal gear 222; a flexible external gear 230 coaxially disposed inside the internal gears; and an elliptical profile wave generator 240 embedded inside the external gear. The first and second internal gears 221, 222, and the external gear 230 are spur gears with the same module (m). The difference in the number of teeth between the first internal gear 221 and the external gear 230 is 2n (n is a positive integer), and the first internal gear 221 has more teeth. The second internal gear 222 has the same number of teeth as the external gear 230 and rotates integrally.

[0078] The external teeth 234 of the external gear 230 are flexed into an elliptical shape by the elliptical profile wave generator 240, and the two end portions in the major axis direction of the elliptical shape are engaged with the first internal teeth 223 and the second internal teeth 224 of the first and second internal gears 221, 222. If the wave generator 240 is rotated, the meshing position of the external gear 230 with respect to the first internal gear 221 moves circumferentially, and a relative rotation corresponding to the difference in the number of teeth between the two gears is generated between the two gears 221, 230. The first internal gear 221 is fixed so as not to rotate. In this case, the external gear 230 rotates and outputs a decelerated rotation from the second internal gear 222 that rotates integrally with it.

[0079] The external gear 230 of the flat type harmonic gear device 200 is a molded product in which external teeth 234 are integrally formed on a cylindrical main body portion 231 using a molding die. For example, it is an injection molded product of a thermoplastic resin. The first and second internal gears 221, 222 can also be molded products.

[0080] The external gear 230 includes: a flexible cylindrical main body portion 231; and external teeth 234 formed on the outer peripheral surface of the main body portion. The external teeth 234 include: a first external tooth portion 235 that can be engaged with the first internal teeth 223 of the first internal gear 221; and a second external tooth portion 236 that can be engaged with the second internal teeth 224 of the second internal gear 222 as another internal gear. The first and second external tooth portions 235, 236 that deviate from the tooth direction of both internal teeth are connected by an external tooth connecting portion 237. The external tooth connecting portion 237 is located at a position that deviates from both the first and second internal teeth 223, 224 in the tooth direction. The parting line trace 234d of the molding die is located at this external tooth connecting portion 237.

[0081] In addition, a first outer tooth extension portion 238 is continuously formed at the end of the first outer tooth portion 235. The first outer tooth extension portion 238 is formed at a position offset from the first inner tooth 223 in the tooth direction. Similarly, a second outer tooth extension portion 239 is continuously formed at the end of the second outer tooth portion 236. The second outer tooth extension portion 239 is formed at a position offset from the second inner tooth 224 in the tooth direction.

[0082] A molding die (not shown) for the outer tooth gear 230 is constituted by, for example, a pair of opening and closing dies. The parting line of the molding die is set at the outer tooth connecting portion 237 of the cavity portion for forming the outer teeth. Accordingly, with respect to the molded outer tooth gear 230, a parting line mark 234d remains at the outer tooth connecting portion 237 of the outer teeth 234.

[0083] The tooth profile of the outer teeth 234 is a three-dimensional tooth profile that gradually changes along its tooth direction. In this example, the tooth profile of the outer teeth 234 continuously and gradually changes from the position of the parting line mark 234d to the end of the first outer tooth extension portion 238 on the side of the opening end 31a of the cylindrical main body portion in such a manner that a prescribed draft angle for demolding is formed along the tooth direction on the outer teeth 234. For example, it is a tapered tooth profile in which the tooth thickness, the addendum circle diameter, and the dedendum circle diameter gradually decrease toward the opening end 231a. Similarly, the tooth profile of the outer teeth 234 continuously and gradually changes from the position of the parting line mark 234d to the end of the second outer tooth extension portion 239 on the side of the opening end 231b of the other side of the cylindrical main body portion 231. For example, it is a tapered tooth profile in which the tooth thickness, the addendum circle diameter, and the dedendum circle diameter gradually decrease toward the opening end 231b.

[0084] The first inner tooth gear 221 having the first inner tooth 223 that meshes with the first outer tooth portion 235 of the outer teeth 234 having such a shape can be manufactured as a molded product. In addition, the second inner tooth gear 222 having the second inner tooth 224 that meshes with the second outer tooth portion 236 of the outer teeth 234 can be manufactured as a molded product.

[0085] Regarding the outer teeth 234 of the outer-tooth gear 230 in this example, irregularities such as the steps of the outer-tooth connecting portion 237 and the parting line marks 234d, and the first and second outer-tooth extension portions 238 and 239 do not adversely affect the meshing state of the outer-tooth gear 230 with respect to the first and second inner-tooth gears 221 and 222. Additionally, a first outer-tooth extension portion 238 having a tapered shape is formed on the open-end 231a side of one side of the outer teeth 234 of the outer-tooth gear 230. Even if the tooth profile of the first outer-tooth portion 235 is a three-dimensional tooth profile that varies along the tooth direction, the small-diameter first outer-tooth extension portion 238 functions as a guide when inserting the first outer-tooth portion 235 into the first inner teeth 223 of the first inner-tooth gear 221. Similarly, even if the tooth profile of the second outer-tooth portion 236 is a three-dimensional tooth profile that varies along the tooth direction, the small-diameter second outer-tooth extension portion 239 functions as a guide when inserting the second outer-tooth portion 236 into the second inner teeth 224 of the second inner-tooth gear 222. Therefore, the assembly operation of inserting the outer-tooth gear 230 into the first and second inner-tooth gears 221 and 222 becomes easy.

[0086] (Other examples of outer-tooth gears)

[0087] The above-described outer-tooth gear 230 is a molded product in which the outer teeth 234 are integrally formed on the cylindrical main body portion 231 using a molding die. Refer to Figure 3C An example of an outer-tooth gear of a machined product that can be used in place of the outer-tooth gear 230 will be described.

[0088] The outer-tooth gear 630 includes: a flexible cylindrical main body portion 631; and outer teeth 634 formed on the outer peripheral surface of the main body portion. The outer teeth 634 include: a first outer-tooth portion 635 that can mesh with the first inner teeth 223 of the first inner-tooth gear 221; and a second outer-tooth portion 636 that can mesh with the second inner teeth 224 of the second inner-tooth gear 222, which is another inner-tooth gear. The first and second outer-tooth portions 635 and 636, which deviate from each other in the tooth direction of the inner teeth, are connected by an outer-tooth connecting portion 637. The outer-tooth connecting portion 637 is located at a position that deviates from both the first and second inner teeth 223 and 224 in the tooth direction.

[0089] In addition, a first outer-tooth extension portion 638 is continuously formed with the end of the first outer-tooth portion 635. The first outer-tooth extension portion 638 is formed at a position that deviates from the first inner teeth 223 in the tooth direction. Similarly, a second outer-tooth extension portion 639 is continuously formed with the end of the second outer-tooth portion 636. The second outer-tooth extension portion 639 is formed at a position that deviates from the second inner teeth 224 in the tooth direction.

[0090] The tooth profile of the external teeth 634 is a three-dimensional tooth profile that gradually changes along its tooth direction. In this example, the tooth profile of the external teeth 634 continuously and gradually changes from the position 634d at the center in the tooth direction of the external tooth connection portion 637 to the end of the first external tooth extension portion 638 on the side of the open end 631a of the cylindrical main body portion. For example, it is a tapered tooth profile in which the tooth thickness, the addendum circle diameter, and the dedendum circle diameter gradually decrease towards the open end 631a. Similarly, the tooth profile of the external teeth 634 continuously and gradually changes from the central position in the tooth direction of the external tooth connection portion 637 to the end of the second external tooth extension portion 639 on the side of the open end 631b of the other side of the cylindrical main body portion 631. For example, it is a tapered tooth profile in which the tooth thickness, the addendum circle diameter, and the dedendum circle diameter gradually decrease towards the open end 631b.

[0091] Regarding the external teeth 634 of the external tooth gear 630 in this example, a first external tooth extension portion 638 with a pointed shape is formed on the side of the open end 631a. Even if the tooth profile of the first external tooth portion 635 is a three-dimensional tooth profile that changes along the tooth direction, the small-diameter first external tooth extension portion 638 functions as a guide when inserting the first external tooth portion 635 into the first internal teeth 223 of the first internal tooth gear 221. Similarly, even if the tooth profile of the second external tooth portion 636 is a three-dimensional tooth profile that changes along the tooth direction, the small-diameter second external tooth extension portion 639 functions as a guide when inserting the second external tooth portion 636 into the second internal teeth 224 of the second internal tooth gear 222. Therefore, the assembly operation of inserting the external tooth gear 630 into the first and second internal tooth gears 221 and 222 becomes easy.

Claims

1. A wave gear device having: 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 cylindrical main body portion that can flex in the radial direction; a diaphragm extending radially inward from one end of the cylindrical main body portion; and external teeth formed on the outer peripheral surface portion on the opening end side which is the other end of the cylindrical main body portion. The external gear is a molded product in which the external teeth are integrally formed on the cylindrical main body portion using a molding die having a pair of openable and closable dies. The wave gear device is characterized in that the external teeth of the external gear include: an external tooth portion that can mesh with the internal teeth of the internal gear; and a first external tooth extension portion and a second external tooth extension portion formed at positions offset from the internal teeth in the tooth direction, and the first external tooth extension portion and the second external tooth extension portion are portions that do not mesh with the internal teeth of the internal gear. The first external tooth extension portion continuously extends in the tooth direction from the end portion on the diaphragm side of the external tooth portion. The second external tooth extension portion continuously extends in the tooth direction from the end portion on the diaphragm side of the first external tooth extension portion. The parting line trace of the molding die is located at the boundary position between the first external tooth extension portion and the second external tooth extension portion. The tooth profiles of the first external tooth extension portion and the external tooth portion are tapered tooth profiles that gradually decrease from the position of the parting line trace to the end portion on the opening end side of the external tooth portion in such a manner that a prescribed draft angle for demolding is formed along the tooth direction on the external teeth. The pitch diameter of at least the tip circle of the second external tooth extension portion gradually decreases from the parting line trace to the end portion on the diaphragm side so that the second external tooth extension portion becomes a guide when inserting the external teeth into the internal teeth.

Images