speed reduction device

Abstract

To provide a speed reduction device that can reduce the influence of creep of resin members.SOLUTION: A speed reduction device 10 according to an embodiment comprises output members 26 and 27 to which a driven member 50 is connected. The output members 26 and 27 are made of resin, and comprise a plurality of bottomed first screw holes H1 into which fine thread screws B1 for connecting the driven member 50 are screwed. The output members 26 and 27 are provided with a lightening part between the plurality of first screw holes H1 in a circumferential direction.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a speed reducer. Background Art

[0002] Conventionally, attempts have been made to apply resin materials to speed reducer components for the purpose of weight reduction. For example, Patent Document 1 describes a second internal gear that is a member mounted on a gear device and formed of a resin material. The second internal gear is provided with a connection hole for connecting to an external member to be driven and a connection hole for connecting to a second cover. These connection holes are formed with female threads for fastening connection bolts. Prior Art Documents Patent Documents

[0003] Patent Document 1 Japanese Unexamined Patent Publication No. 2021-181126 (Fig. 2(A)) Summary of the Invention Problem to be Solved by the Invention

[0004] Resin materials have self-lubricating properties, and also cause unique phenomena such as creep, so it is important to give sufficient consideration to the fastening structure. In particular, in screw fastening using resin female threads, excessive tightening torque may cause shear fracture or creep fracture of the female thread. In order to reduce the influence of creep and the like, insert molding of metal female threads can be considered, but this is disadvantageous in terms of manufacturing cost and may be a factor of reduced accuracy. Patent Document 1 cannot be said to provide sufficient disclosure from the viewpoint of reducing the influence of creep and the like on resin members.

[0005] One object of the present invention is to provide a speed reducer capable of reducing the influence of creep on a resin member. Means for Solving the Problem

[0006] To solve the above problems, a reduction gear according to one aspect of the present invention is a reduction gear having an output member to which a driven member is connected, wherein the output member is made of resin and has a first screw hole into which a fine-thread screw for connecting the driven member is screwed, the first screw hole is bottomed, and a weight-reducing portion is provided between the first screw holes in the circumferential direction.

[0007] Furthermore, any combination of the above components, or in which the components or expressions of the present invention are mutually substituted among methods, systems, etc., are also valid embodiments of the present invention. [Effects of the Invention]

[0008] According to the present invention, a speed reducer capable of reducing the effects of creep in resin components can be provided. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic side view showing the reduction gear of the embodiment. [Figure 2] Figure 1 shows the output component of the reduction gear as viewed from the input side. [Figure 3] Figure 2 shows a cross-section of the output member along lines AA and BB.

[0010] The present invention will be described below with reference to the drawings, based on preferred embodiments. In embodiments and modifications, the same or equivalent components and members will be denoted by the same reference numerals, and redundant explanations will be omitted as appropriate. In addition, the dimensions of the members in each drawing will be enlarged or reduced as appropriate for ease of understanding. Furthermore, some members that are not important for explaining the embodiments will be omitted from the drawings.

[0011] Furthermore, separate components that share common characteristics are distinguished by adding ordinal numbers such as "1st" and "2nd" to the beginning of their component names, and these are omitted when referring to them collectively. In addition, terms including ordinal numbers such as "1st" and "2nd" are used to describe various components, but these terms are used solely for the purpose of distinguishing one component from others, and the components are not limited by these terms.

[0012] [Embodiment] The overall configuration of the reduction gear of an embodiment of the present invention will be described below with reference to Figure 1. Figure 1 is a schematic side view showing the reduction gear of the embodiment. As an example, the reduction gear 10 is a flexible mesh type gear device. The reduction gear 10 of the embodiment comprises an input shaft 11, vibrators 12 and 13, external gears 14 and 15, a main bearing 24, input shaft bearings 30 and 31, vibrator bearings 34 and 35, internal gears 16 and 17, casings 21, 22 and 23, output members 26 and 27, and receiving plate members 36 and 37.

[0013] Hereinafter, the direction along the central axis La of the internal gears 16 and 17 will be referred to as the "axial direction," and the circumferential and radial directions of the circle centered on that central axis La will be referred to as the "circumferential direction" and "radial direction," respectively. Also, for convenience, one side of the axial direction (right side in the figure, the side where the drive source is located) will be referred to as the input side, and the other side (left side in the figure, the side where the driven member is located) will be referred to as the non-input side. This notation of directions does not restrict the operating position of the reduction gear 10, and the reduction gear 10 can be used in any position.

[0014] Of the vibrators 12 and 13, the first vibrator 12 is positioned on the opposite side of the second vibrator 13. Of the external gears 14 and 15, the first external gear 14 is positioned on the opposite side of the second external gear 15. Of the internal gears 16 and 17, the first internal gear 16 is positioned on the opposite side of the second internal gear 17. Of the input shaft bearings 30 and 31, the first input shaft bearing 30 is positioned on the opposite side of the second input shaft bearing 31. Of the vibrator bearings 34 and 35, the first vibrator bearing 34 is positioned on the opposite side of the second vibrator bearing 35. Of the receiving plate members 36 and 37, the first receiving plate member 36 is positioned on the opposite side of the second receiving plate member 37.

[0015] The reduction gear 10 is a deflection meshing type gear device that rotates the external gears 14 and 15, which mesh with the internal gears 16 and 17, while causing them to bend and deform, thereby causing the external gears 14 and 15 to rotate on their own axis and outputting the component of that rotation.

[0016] The input shaft 11 is a hollow shaft member, and the motor of the drive unit is connected to the input side of the input shaft 11, and rotational power from the motor is input. The input shaft 11 has vibrators 12 and 13 and also functions as a vibrator shaft. The vibrators 12 and 13 are integrally formed on the outer circumference of the input shaft 11. The outer circumference shape of the cross-section of the vibrators 12 and 13, perpendicular to the direction along the central axis La, is elliptical. In this specification, "ellipse" is not limited to a geometrically strict ellipse, but also includes an approximate ellipse.

[0017] The external gears 14 and 15 are flexible cylindrical members. The external gears 14 and 15 are provided axially separated on the outer circumference of the cylindrical part that functions as the external gear base. The first external gear 14 and the second external gear 15 are integrally formed axially on the outer circumference of the cylindrical base, and both have the same number of teeth. The first external gear 14 meshes with the first internal gear 16, which functions as an output internal gear, and the second external gear 15 meshes with the second internal gear 17, which functions as a reduction internal gear.

[0018] The external gears 14 and 15 follow the rotation of the vibrators 12 and 13 and are deflected and deformed in an elliptical shape by the vibrators 12 and 13 via the vibrator bearings 34 and 35. At this time, the external gears 14 and 15 are deflected and deformed to match the shape of the vibrators 12 and 13 while changing the meshing position with the internal gears 16 and 17 in the circumferential direction. The vibrator bearings 34 and 35 are positioned between the vibrators 12 and 13 and the external gears 14 and 15. In this embodiment, the vibrator bearings 34 and 35 have retainers 32 and 33.

[0019] The number of teeth of the first internal gear 16 is equal to the number of teeth of the first external gear 14, and the number of teeth of the second internal gear 17 is greater than the number of teeth of the second external gear 15 by 2i, where i is a natural number of 1 or greater. Accordingly, when the exciters 12 and 13 rotate, rotation having the same magnitude as the rotation components of the external gears 14 and 15 on their own axes is output to the first internal gear 16.

[0020] Casings 21, 22 and 23 include a first casing 21 that rotatably supports the first internal gear 16 via a main bearing 24, a second casing 22 disposed on the input side of the first casing 21, and a third casing 23 disposed on the input side of the second casing 22. The second internal gear 17 is integrated with the second casing 22. The first casing 21 and the second casing 22 are connected to each other by a bolt B3. The second casing 22 and the third casing 23 are connected to each other by a bolt B4.

[0021] Output members 26 and 27 take out the rotation components of the external gear 14 on its own axis and transmit the same to a driven member 50. The output members 26 and 27 include a first output member 26 and a second output member 27 disposed on the opposite input side of the first external gear 14. The first output member 26 is integrated with the first internal gear 16. The first output member 26 and the second output member 27 are connected to each other by a connection bolt B2.

[0022] A first input shaft bearing 30 is disposed between the second output member 27 and the input shaft 11. A second input shaft bearing 31 is disposed between the third casing 23 and the input shaft 11. The input shaft bearings 30 and 31 rotatably support the input shaft 11 having the exciters 12 and 13 relative to the second output member 27 and the third casing 23. There is no limitation on the configuration of the input shaft bearings 30 and 31, and in this example, the input shaft bearings 30 and 31 are ball bearings.

[0023] The main bearing 24 is disposed between the first casing 21 and the first output member 26. The main bearing 24 rotatably supports the output members 26 and 27 relative to the first casing 21. There is no limitation on the configuration of the main bearing 24, and in this example, the main bearing 24 is a ball bearing.

[0024] A first receiving plate member 36 is positioned on the non-input side of the first external gear 14. A second receiving plate member 37 is positioned on the input side of the second external gear 15. The receiving plate members 36 and 37 are annular plate members that surround the input shaft 11. The receiving plate members 36 and 37 extend to the non-input and input sides of the external gears 14 and 15 and the vibrator bearings 34 and 35, respectively, restricting the axial movement of the external gears 14 and 15 and the retainers 32 and 33 toward the non-input and input sides, respectively.

[0025] The operation of the reduction gear 10 will now be explained. When the input shaft 11 rotates due to the rotation of the motor (not shown), the vibrators 12 and 13 rotate together with the input shaft 11. As the vibrators 12 and 13 rotate, the external gears 14 and 15 are continuously deflected and deformed to match the shape of the vibrators 12 and 13, while changing the meshing position with the internal gears 16 and 17 in the circumferential direction. For each rotation of the vibrators 12 and 13, the external gears 14 and 15 rotate relative to the second internal gear 17 by an amount equivalent to the difference in the number of teeth between the second internal gear 17 and the second external gear 15.

[0026] At this time, the rotation of the vibrators 12 and 13 is reduced by a reduction ratio corresponding to the difference in the number of teeth, causing the external gears 14 and 15 to rotate. The first internal gear 16 has the same number of teeth as the first external gear 14. Therefore, the first internal gear 16 rotates synchronously with the external gears 14 and 15 with the same rotational component as the external gears 14 and 15, without changing its relative meshing position with the external gears 14 and 15 before and after one rotation of the vibrators 12 and 13. The first output member 26 is integrally formed with the first internal gear 16, and the rotation of the first internal gear 16 is transmitted to the driven member 50 via the first output member 26 and the second output member 27. As a result, the rotation input to the input shaft 11 is reduced and transmitted as the rotation of the driven member 50.

[0027] The materials of each component constituting the reduction gear 10 will now be described. The materials of each component other than the gears are not particularly limited, but in this embodiment they are configured as follows. The casings 21, 22, 23, output members 26, 27, and receiving plate members 36, 37 are made of resin material. The resin material can be a resin alone or a resin containing reinforcing fibers, and various resin materials such as PEEK (Poly Ether Ether Ketone) or POM (Polyacetal or Polyoxymethylene, etc.) can be used. As resins containing reinforcing fibers, composite materials such as CFRP (Carbon Fiber Reinforced Plastics), composite materials of resin and other materials, and bakelite (paper bakelite, cloth bakelite, etc.) can be used. By making these components out of resin, the reduction gear 10 can be made lower cost and lighter.

[0028] The input shaft 11, vibrators 12 and 13, and external gears 14 and 15 are made of steel materials (metallic materials) such as nickel-chromium-molybdenum steel. On the other hand, the internal gears 16 and 17 are made of carbon fiber reinforced resin material, in which carbon fibers are incorporated as reinforcing fibers into the base resin. Various resin materials can be used for the base resin, such as PEEK or POM. If the reinforcing fibers contained in the resin material are not tied together in a cloth-like manner, the resin material can be injection molded or compression molded. If the material contained in the resin material is tied together in a cloth-like or strip-like manner, the resin material can be compression molded.

[0029] To ensure lubrication of the moving parts, a lubricant J is sealed in the internal space S of the reduction gear 10.

[0030] The characteristic configuration of the reduction gear 10 of the embodiment will be described with reference to Figures 2 and 3. Figure 2 is a view of the first output member 26 from the input side. Figure 3(A) shows a cross-section of the first output member 26 along line AA, and Figure 3(B) shows a cross-section of the first output member 26 along line BB.

[0031] It is conceivable to use resin materials for components of the speed reducer. Resin components undergo a creep phenomenon, where the surrounding area deforms over time when a certain load is applied. Furthermore, because resin materials are self-lubricating, the fastening structure may loosen in combination with the creep phenomenon. In particular, in screw fastening parts with resin female threads, excessive tightening torque may lead to shear failure or creep failure of the female threads. To reduce the effects of creep, it is conceivable to insert molded metal female threads, but this would be disadvantageous in terms of manufacturing cost and could lead to a decrease in accuracy.

[0032] To suppress the loosening phenomenon of screw fastenings over time, the reduction gear 10 is a reduction gear having output members 26 and 27 to which a driven member 50 is connected. The output members 26 and 27 are made of resin and have a plurality of bottomed first screw holes H1 into which fine-threaded screws B1 for connecting the driven member 50 are screwed. The output members 26 and 27 are provided with weight-reducing portions 28 between the plurality of first screw holes H1 in the circumferential direction. As shown in Figure 3(A), the first screw holes H1 and the weight-reducing portions 28 are provided alternately in the circumferential direction from opposite directions in the axial direction. In this example, the first screw holes H1 are circular holes that are recessed from the opening on the non-input side toward the input side. The first screw holes H1 may be provided with taps (female threads). In the example of Figure 3, the circumferential width of the weight-reducing portion 28 is greater than the circumferential width of the first screw hole H1.

[0033] With this configuration, the fine-pitch screw B1 is less prone to loosening due to its small lead angle, and requires less torque to loosen, thus suppressing the phenomenon of loosening of the screw fastening part over time. Furthermore, compared to a standard screw of the same size, the fine-pitch screw B1 has a larger effective diameter, resulting in higher yield strength, and its larger effective cross-sectional area makes it resistant to external forces in the shear direction. In addition, the fine-pitch screw B1 can obtain the required axial force with less torque than a standard screw. As a result, damage to the first screw hole H1 can be reduced. Since the first screw hole H1 is bottomed, there is a low possibility of lubricant J leaking from the first screw hole H1.

[0034] In the example shown in Figure 2, multiple (e.g., 16) first screw holes H1 are provided at predetermined intervals in the circumferential direction. The multiple first screw holes H1 may be arranged at equal intervals in the circumferential direction. Multiple (e.g., 12) weight-reducing portions 28 are provided between two adjacent first screw holes H1 in the circumferential direction. The weight-reducing portions 28 have a fan-shaped or rectangular contour when viewed from the input side. The weight-reducing portions 28 are recesses that are recessed from the opening on the input shaft side toward the opposite input side, and are provided as non-penetrating bottomed holes. By having the weight-reducing portions 28, it is expected that the cooling rate of the first output member 26 during resin molding will be made uniform and shape accuracy will be ensured. Since the weight-reducing portions 28 are bottomed, there is little possibility of lubricant J leaking from the weight-reducing portions 28.

[0035] While it is possible to integrally form the output members 26 and 27 by resin molding, this would complicate the mold structure and potentially increase the number of steps involved in resin molding. Therefore, in the reduction gear 10 of this embodiment, the output members 26 and 27 are configured by connecting a first output member 26 and a second output member 27, and each has a second screw hole H2 into which a connecting bolt B2 for connecting the first output member 26 and the second output member 27 is screwed. In this case, the manufacturing of the output members 26 and 27 becomes easier. The second output member 27 also functions as a cover that covers the non-input side of the input shaft bearing 30.

[0036] As an example, the second screw hole H2 is located in the circumferential direction between one screw hole H1(A) and another screw hole H1(B) from a plurality of first screw holes H1. The one screw hole H1(A) and the other screw hole H1(B) are two first screw holes H1 that are adjacent to each other in the circumferential direction from the plurality of first screw holes H1. In the example in Figure 2, a plurality of second screw holes H2 (for example, four) are provided at predetermined intervals in the circumferential direction. The second screw hole H2 is located in the center between one screw hole H1(A) and another screw hole H1(B) in the circumferential direction. The radial position of the second screw hole H2 is the same as the radial position of the first screw hole H1. In this example, the second screw hole H2 is a circular hole that is recessed from the opening on the non-input side toward the input side. The second screw hole H2 may be provided with a tap (female thread).

[0037] From the viewpoint of suppressing the loosening phenomenon over time, it is desirable to build up the area around the first screw hole H1 to maintain rigidity. Therefore, in this embodiment, as shown in Figure 2, the first output member 26 does not have a weight-reducing portion 28 between one screw hole H1(A) and another screw hole H1(B) in the circumferential direction. In other words, in the circumferential direction, an upper cover portion 29 is provided at a position corresponding to the weight-reducing portion between one screw hole H1(A) and another screw hole H1(B) adjacent to each other with the second screw hole H2 in between. As shown in Figure 3(B), since the second screw hole H2 is formed in the upper cover portion 29 from the non-input side, a thick-walled portion is hardly formed, and the cooling rate of the first output member 26 during resin molding is made uniform.

[0038] The connecting bolt B2 supports the second output member 27 and bears a smaller load than the first screw hole H1, so it is desirable that it be inexpensive. Therefore, in this embodiment, the connecting bolt B2 is a coarse thread, and the second screw hole H2 is bottomed. In this case, it is more cost-effective than a fine thread. Also, because it is bottomed, there is a low possibility of lubricant J leaking from the second screw hole H2.

[0039] Since a large load is applied between the first output member 26 and the first internal gear 16 during the torque transmission process, it is desirable that the two have a high coupling strength. Therefore, as mentioned above, the first output member 26 is integrally formed with the first internal gear 16, and the first output member 26 is the internal gear 16. In this case, a greater coupling strength can be achieved than when the first output member 26 and the first internal gear 16 are formed separately and then coupled.

[0040] In this embodiment, the second output member 27 functions as a bearing housing in which a bearing 30 supporting the input shaft 11 is located. In this case, the number of parts is reduced compared to providing a dedicated member to support the input shaft 11, which is advantageous in terms of miniaturization, cost, and reliability.

[0041] As described above, the system includes vibrators 12 and 13, external gears 14 and 15 that flex and deform due to the vibrators 12 and 13, and a first internal gear 16 and a second internal gear 17 that mesh with the external gears 14 and 15. In this embodiment, the first output member 26 is the first internal gear 16, and the second output member 27 functions as a bearing housing in which a bearing 30 supporting the vibrators 12 and 13 is arranged. In this case, the number of parts is reduced compared to the case where a dedicated member is provided to support the vibrators 12 and 13, which is advantageous in terms of miniaturization, cost, and reliability.

[0042] The embodiments of the present invention have been described in detail above. The embodiments described above are merely examples of how to implement the present invention. The contents of the embodiments do not limit the technical scope of the present invention, and many design changes, such as changes, additions, and deletions of components, are possible as long as they do not depart from the spirit of the invention as defined in the claims. In the embodiments described above, such design changes are described with notations such as "of the embodiments" or "in the embodiments," but this does not mean that design changes are not permitted for contents without such notations. Furthermore, the hatching applied to the cross-sections in the drawings does not limit the material to which the hatching is applied.

[0043] The following describes modified examples. In the drawings and descriptions of the modified examples, components and members that are the same as or equivalent to those in the embodiments are denoted by the same reference numerals. Descriptions that overlap with those in the embodiments will be omitted as appropriate, and the descriptions will focus on the configurations that differ from those in the embodiments.

[0044] In the description of the embodiment, an example was shown in which the reduction gear 10 is a cylindrical flexible mesh type gear device, but the present invention is not limited thereto. The reduction gear may be of other types. Examples of such other types of gear devices include flexible mesh type gear devices such as cup type and top hat type, eccentric oscillating type gear devices such as center crank type and split type, and simple planetary gear type gear devices.

[0045] In the description of the embodiment, an example was shown in which the weight-reducing portion 28 has a shape that is recessed from the opening on the input shaft side toward the opposite input side, but the present invention is not limited thereto. For example, the weight-reducing portion may have a shape that is recessed from the opening on the opposite input shaft side toward the input side.

[0046] In the description of the embodiment, an example was shown in which no ribs are provided in the weight-reducing portion 28, but the present invention is not limited thereto. For example, ribs may be provided in the weight-reducing portion.

[0047] In the description of the embodiment, an example was shown in which the circumferential width of the weight-reducing portion 28 is greater than the circumferential width of the first screw hole H1, but the present invention is not limited to this. The circumferential width of the weight-reducing portion may be less than or equal to the circumferential width of the first screw hole.

[0048] In the description of the embodiments, examples were shown in which the weight-reducing portion 28 has a fan-shaped or rectangular contour when viewed from the axial direction, but the present invention is not limited thereto. For example, the weight-reducing portion may have a circular, elliptical, polygonal, or other contour when viewed from the axial direction.

[0049] Each of the above-described modifications produces the same functions and effects as the embodiments.

[0050] Any combination of the components and modifications of the embodiments described above is also useful as an embodiment of the present invention. The new embodiments resulting from these combinations possess the combined effects of both the combined embodiments and the modifications. [Explanation of symbols]

[0051] B1 Fine thread, B2 Connecting bolt, H1 First screw hole, H2 Second screw hole, 10 Reduction gear, 11 Input shaft, 12 First vibrator, 13 Second vibrator, 14 First external gear, 15 Second external gear, 16 First internal gear, 17 Second internal gear, 26 First output member, 27 Second output member, 28 Weight reduction section, 30 First input shaft bearing, 50 Driven member.

Claims

1. A reduction gear having an output member to which a driven member is connected, The output member is made of resin and has a plurality of bottomed first screw holes into which fine-threaded screws for connecting the driven member are screwed. The plurality of first screw holes are provided in the built-up portion, The output member is a reduction gear provided with, in the circumferential direction, a reduction gear having a shorter axial length than the build-up portion between the build-up portion where the plurality of first screw holes are provided.

2. The output member is configured by connecting a first output member and a second output member, and has a second screw hole into which a connecting bolt for connecting the first output member and the second output member is screwed. The second screw hole is positioned in the circumferential direction between one of the plurality of first screw holes and another screw hole. The reduction gear according to claim 1, wherein the output member does not have a weight-reducing portion between the one screw hole and the other screw hole in the circumferential direction.

3. The reduction gear according to claim 2, wherein the connecting bolt is a coarse thread and the second screw hole is bottomed.

4. The reduction gear according to claim 1, wherein the weight-reducing portion is a recess that opens to the bottomed end side of the first screw hole and is recessed toward the open end side of the first screw hole.

5. The reduction gear according to claim 2, comprising a vibrator, an external gear that is deformed by the vibrator, and a first internal gear and a second internal gear that mesh with the external gear, wherein the first output member is the first internal gear, and the second output member is a bearing housing on which a bearing supporting the vibrator is disposed.

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