JP7840218B2 - Gear unit, harmonic drive gear, robot, and method for manufacturing a gear unit - Google Patents

Description

This invention relates to a gear unit, a harmonic drive gear, a robot, and a method for manufacturing a gear unit.

Conventionally, harmonic drive gears comprising flexible gears and rigid gears are known. This type of harmonic drive gear is mainly used as a speed reducer. Conventional harmonic drive gears are disclosed, for example, in Japanese Patent Publication No. 2017-180486 and Japanese Patent Publication No. 2018-087611.

The flexible gear (3) in the gear apparatus (1) described in Japanese Patent Publication No. 2017-180486 and Japanese Patent Publication No. 2018-087611 has a cup shape with one end open, and external teeth (33) are formed on the open end. The flexible gear (3) also has a cylindrical body (31) around the axis (a) and a bottom (32) connected to the other end of the body (31) in the direction of the axis (a). This allows the end of the body (31) opposite to the bottom (32) to bend radially, achieving good flexible meshing of the flexible gear (3) with the rigid gear (2). An input shaft and an output shaft are connected to the bottom (32).

Furthermore, the flexible gear (3) is formed by performing an upsetting forging process and a deep drawing process on a cylindrical metal material (10). In the upsetting forging process, a disc-shaped plate (11) is formed by applying pressure to the material (10) in the axial direction (α). In the deep drawing process, a cylindrical body (12) having a body portion (31) and a bottom portion (32) is formed by deep drawing of the plate (11). Furthermore, external teeth (33) are formed on the cylindrical body (12) by rolling or the like.
Japanese Patent Publication No. 2017-180486 Japanese Patent Publication No. 2018-087611

However, when forming flexible gears, particularly by deep drawing, the thickness of the base becomes approximately constant due to the nature of the process. Therefore, when a harmonic drive gear is driven, the flexible gear flexes while meshing with the rigid gear, and as it rotates, stress due to deformation occurs locally in the flexible gear. In this case, prolonged operation of the harmonic drive gear may lead to deterioration of the flexible gear.

The objective of this invention is to provide a technology that improves the durability of flexible gears with substantially constant bottom thickness, thereby suppressing deterioration of flexible gears even when they bend and rotate while meshing with rigid gears over a long period of time.

The present invention relates to a gear unit used in a wave drive gear system, comprising a flexible gear, a bush and a spacer fixed to the flexible gear, wherein the flexible gear has a plate-shaped diaphragm portion extending perpendicular to a central axis, a bent portion that gradually curves axially in one direction from the radially outer end of the diaphragm portion toward the radially outer side, a cylindrical body portion extending axially in one direction from the axially outer end of the bent portion, and a plurality of external teeth provided on the outer circumferential surface of the body portion, the bush extends perpendicular to the central axis and has a first contact surface that contacts the axially outer surface of the diaphragm portion, the spacer extends perpendicular to the central axis and has a second contact surface that contacts the axially outer surface of the diaphragm portion, and the radially outer ends of the first contact surface and the radially outer ends of the second contact surface are located at the boundary between the diaphragm portion and the bent portion.

According to the present invention, by sandwiching the plate-shaped diaphragm portion forming the bottom of the flexible gear between the bush and the spacer, the deflection of the diaphragm portion during the operation of the harmonic drive gear can be suppressed. Furthermore, during the operation of the harmonic drive gear, stress due to the deformation of the flexible gear can be applied to the bent portion. This suppresses deterioration caused by stress concentration in the flexible gear.

Figure 1 is a longitudinal cross-sectional view of a harmonic drive gear apparatus according to an exemplary embodiment of the present invention. Figure 2 is a cross-sectional view of a harmonic drive gear device according to an exemplary embodiment of the present invention. Figure 3 is a partial longitudinal cross-sectional view of a gear unit according to an exemplary embodiment of the present invention. Figure 4 is a flowchart showing the manufacturing procedure of a gear unit according to an exemplary embodiment of the present invention. Figure 5 is a schematic diagram of an intermediate molded product according to an exemplary embodiment of the present invention. Figure 6 is a schematic diagram of the robot.

The following describes exemplary embodiments of this application with reference to the drawings. In this application, the direction parallel to the central axis of the harmonic drive gear is referred to as the "axial direction," the direction perpendicular to the central axis of the harmonic drive gear is referred to as the "radial direction," and the direction along the arc centered on the central axis of the harmonic drive gear is referred to as the "circumferential direction."

Furthermore, in this application, in Figures 1 and 3 described later, the axial direction is defined as the left-right direction, with the right side being the "one axial side" and the left side being the "other axial side," and the shapes and positional relationships of each part are explained accordingly. However, this definition of the left-right direction is not intended to limit the orientation of the harmonic drive gear including the gear unit according to the present invention during manufacturing or use. Also, in this application, "parallel directions" are not limited to cases where they are strictly parallel geometrically. They only need to be parallel to the extent that the effects of the invention are achieved. Similarly, in this application, "orthogonal directions" are not limited to cases where they are strictly orthogonal geometrically. They only need to be orthogonal to the extent that the effects of the invention are achieved.

<1. Configuration of the harmonic drive gear system>
The configuration of a harmonic drive gear 100 according to an exemplary embodiment of the present invention will be described below. Figure 1 is a longitudinal cross-sectional view of the harmonic drive gear 100 according to an exemplary embodiment of the present invention. Figure 2 is a transverse cross-sectional view of the harmonic drive gear 100 as seen from position II-II in Figure 1.

The harmonic drive gear 100 is a device that changes the speed of input rotational motion by utilizing the differential between a rigid gear 10 and a flexible gear 20, which will be described later. In this embodiment, the harmonic drive gear 100 is incorporated into, for example, an actuator and used as a speed reducer to reduce the power obtained from a motor. However, the harmonic drive gear 100 may also be incorporated into various devices such as the joints of a small robot to change the speed of various rotational motions.

As shown in Figures 1 and 2, the harmonic drive gear unit 100 comprises a rigid gear 10, a gear unit 19, and a wave generator 30. The harmonic drive gear unit 100 is also provided with an input shaft (not shown) for obtaining power from an external source. The input shaft is connected, for example, to the rotating part of a motor and extends cylindrically in the axial direction around a central axis C1. The input shaft rotates together with the rotating part of the motor around the central axis C1.

The rigid gear 10 is a member that extends in an annular shape around a central axis C1. The rigid gear 10 is positioned radially outward from the body portion 23 of the flexible gear 20 (described later). The rigidity of the rigid gear 10 is far greater than that of the second body portion 232 of the flexible gear 20 (described later), which is positioned radially inward from the rigid gear 10. Therefore, the rigid gear 10 can be considered substantially rigid. As shown in Figure 2, the rigid gear 10 has a plurality of internal teeth 11 on its inner circumferential surface. Each of the internal teeth 11 protrudes radially inward. Furthermore, the internal teeth 11 are arranged along the circumferential direction at a constant pitch. In this embodiment, the rigid gear 10 is fixed to the frame of the device on which the wave drive gear 100 is mounted.

Figure 3 is a partial longitudinal cross-sectional view of a gear unit 19 according to an exemplary embodiment of the present invention. As shown in Figures 1 to 3, the gear unit 19 includes a flexible gear 20, a bush 26, and a spacer 27. In this embodiment, the flexible gear 20, the bush 26, and the spacer 27 are each made of austenitic stainless steel. The flexible gear 20 has a plate-shaped diaphragm portion 21, a bent portion 22, a cylindrical body portion 23, and a plurality of external teeth 24. As will be described in detail later, the flexible gear 20 is formed by deep drawing. That is, the flexible gear 20 is a deep-drawn product.

The diaphragm portion 21 is a part that extends perpendicularly to the central axis C1. Furthermore, the diaphragm portion 21 expands in an annular and flat shape around the central axis C1. The diaphragm portion 21 has higher rigidity and is less prone to bending than the second body portion 232 of the body portion 23, which will be described later. Also, the axial thickness d1 of the diaphragm portion 21 (see Figure 3) is approximately constant throughout the entire diaphragm portion 21. The diaphragm portion 21 has a central hole 210 and a plurality of through holes 211. The central hole 210 penetrates the diaphragm portion 21 axially along the central axis C1. Each of the plurality of through holes 211 penetrates the diaphragm portion 21 axially, parallel to the central axis C1, radially outward from the central hole 210. Furthermore, the plurality of through holes 211 are formed at equal intervals in the circumferential direction around the central axis C1.

The bent portion 22 is the part of the diaphragm portion 21 that gradually bends axially in one direction as it extends radially outward from its radially outer end. In Figure 3, the boundary between the diaphragm portion 21 and the bent portion 22 is indicated by the dashed line B1.

The body portion 23 is a cylindrical part extending axially from one end of the bent portion 22. The body portion 23 extends cylindrically along the central axis C1 around the central axis C1. As shown in Figure 1, the body portion 23 includes a first body portion 231 and a second body portion 232.

The first body portion 231 is the part that extends from one axial end of the bent portion 22 toward the other axial end. In Figure 3, the boundary between the first body portion 231 and the bent portion 22 is shown by the dashed line B2. The second body portion 232 extends from one axial end of the first body portion 231 toward the other axial end and is located radially inward of the multiple external teeth 24. The second body portion 232 is also positioned radially inward of the rigid gear 10. Furthermore, the second body portion 232 is flexible and can bend radially.

Multiple external teeth 24 are provided on the outer circumferential surface of the body portion 23. Each of the multiple external teeth 24 protrudes radially outward. The multiple external teeth 24 are arranged along the circumferential direction at a constant pitch. The number of internal teeth 11 in the rigid gear 10 differs slightly from the number of external teeth 24 in the flexible gear 20.

The bush 26 is a member that extends perpendicularly to the central axis C1. The bush 26 has a flange portion 261 and a fixing portion 262. The flange portion 261 is a portion that extends in an annular and flat shape around the central axis C1. The flange portion 261 is positioned on one axial side of the diaphragm portion 21 and contacts the diaphragm portion 21. As a result, as shown in Figure 3, a first contact surface CS1 is formed in the bush 26 that contacts the axial side surface of the diaphragm portion 21. Furthermore, multiple through holes 260 are formed in the flange portion 261. Each of the multiple through holes 260 penetrates the flange portion 261 axially, parallel to the central axis C1. The multiple through holes 260 are also formed at equal intervals in the circumferential direction around the central axis C1.

Furthermore, as shown in Figure 3, a first curved surface CS3 is formed near the radially outer end of the bush 26. The first curved surface CS3 gradually curves axially in one direction as it extends radially outward from the radially outer end of the first contact surface CS1. That is, in this embodiment, the first curved surface CS3 is formed on the peripheral edge of the bush 26 that is close to the flexible gear 20, resulting in a smooth shape. Also, the radius of curvature of the first curved surface CS3 is smaller than the radius of curvature of the bent portion 22.

The fixing portion 262 is a cylindrical part that extends axially in the other direction along the central axis C1 from the radially inner end of the flange portion 261. The fixing portion 262 passes through the central hole 210 of the diaphragm portion 21 and the central hole 270 of the spacer 27 (described later). An output shaft (not shown) for extracting power after reduction is inserted radially into the fixing portion 262. For example, a male thread is formed on the outer circumferential surface of the output shaft. For example, a female thread is formed on the inner circumferential surface of the fixing portion 262. The output shaft is fixed to the inner circumferential surface of the fixing portion 262 by screw fastening.

The spacer 27 is a member that extends perpendicularly to the central axis C1. The spacer 27 is an annular and flat plate-shaped portion that extends around the central axis C1. The spacer 27 is positioned on the other axial side of the diaphragm portion 21 and contacts the diaphragm portion 21. As a result, as shown in Figure 3, a second contact surface CS2 is formed on the spacer 27, contacting the other axial side surface of the diaphragm portion 21. The spacer 27 also has a central hole 270 and a plurality of fastening holes 271. The central hole 270 penetrates the spacer 27 axially along the central axis C1. Each of the plurality of fastening holes 271 is formed radially outward from the central hole 270 and parallel to the central axis C1. Each of the plurality of fastening holes 271 is formed from one axial side of the spacer 27 toward the other side. Furthermore, the plurality of fastening holes 271 are formed at equal intervals in the circumferential direction around the central axis C1.

Furthermore, as shown in Figure 3, a second curved surface CS4 is formed near the radially outer end of the spacer 27. The second curved surface CS4 gradually curves in the other axial direction as it extends radially outward from the radially outer end of the second contact surface CS2. That is, in this embodiment, the peripheral edge of the spacer 27 adjacent to the flexible gear 20 has a second curved surface CS4, resulting in a smooth shape.

The diaphragm portion 21 is fixed to the bush 26 and spacer 27 by fastening multiple fastening members 28, which pass through each of the multiple through holes 211 and each of the multiple through holes 260 in the bush 26, to the multiple fastening holes 271 in the spacer 27. In other words, the bush 26 and spacer 27 are each fixed to the flexible gear 20 having the diaphragm portion 21. By fixing the diaphragm portion 21 between the bush 26 and spacer 27 in this way, deflection of the diaphragm portion 21 during the operation of the harmonic drive gear 100 can be suppressed. Note that the fastening holes 271 are, for example, "screw holes," and the fastening members 28 are, for example, "screws."

Furthermore, as described above, an output shaft (not shown) for extracting power after reduction is fixed to the radially inward side of the bush 26. This allows the flexible gear 20, including the diaphragm portion 21, the bush 26, and the spacer 27 to be fixed to the output shaft in a way that prevents relative rotation. A more detailed description of the structure and manufacturing method of the gear unit 19, including the flexible gear 20, bush 26, and spacer 27, will be described later.

The wave generator 30 is a mechanism for causing the flexible gear 20 to bend and deform. The wave generator 30 is positioned radially inward of the body 23 of the flexible gear 20. The wave generator 30 includes a non-circular cam 31 and a flexible bearing 32.

The non-circular cam 31 is a member that expands in an annular shape around the central axis C1. The non-circular cam 31 in this embodiment has an elliptical cam profile. That is, the non-circular cam 31 has different outer diameters depending on its circumferential position. As shown in Figures 1 and 2, the non-circular cam 31 is positioned radially inward of the second body portion 232 of the flexible gear 20. The input shaft (not shown) is fixed radially inward of the non-circular cam 31 so as to be unable to rotate relative to it. The input shaft and the non-circular cam 31 rotate at their pre-reduction speed by power obtained from an external motor or the like.

The flexible bearing 32 comprises an inner ring 321, a plurality of balls 322, and an elastically deformable outer ring 323. The inner ring 321 is fixed to the outer circumferential surface of the non-circular cam 31. In this embodiment, the outer ring 323 is fixed to the inner circumferential surface of the second body 232 of the flexible gear 20. The plurality of balls 322 are interposed between the inner ring 321 and the outer ring 323 and are arranged along the circumferential direction. The outer ring 323 elastically deforms (flexes) via the inner ring 321 and the balls 322 to reflect the cam profile of the rotating non-circular cam 31.

In the harmonic drive gear 100 with this configuration, when power is supplied to the input shaft, the input shaft and the non-circular cam 31 rotate together. Furthermore, as described above, the non-circular cam 31 has different outer diameters depending on its position in the circumferential direction. As a result, the inner circumferential surface of the second body 232 of the flexible gear 20 is pushed from the radially inward direction via the flexible bearing 32, causing the second body 232 to deform in an elliptical shape. As a result, as shown in Figure 2, the external teeth 24 and internal teeth 11 mesh at two points, at both ends of the major axis of the ellipse formed by the non-circular cam 31 and the second body 232. On the other hand, at phase positions other than these two points on the ellipse, the external teeth 24 and internal teeth 11 do not mesh. In other words, in this embodiment, the multiple external teeth 24 partially mesh with the multiple internal teeth 11 in the circumferential direction. That is, in this embodiment, a portion of the multiple external teeth 24 meshes with a portion of the multiple internal teeth 11.

When the non-circular cam 31 rotates, the position of the major axis of the ellipse formed by the non-circular cam 31 and the second body portion 232 moves in the circumferential direction, and therefore the meshing position between the internal teeth 11 and the external teeth 24 also moves in the circumferential direction. Here, as described above, the number of internal teeth 11 on the rigid gear 10 and the number of external teeth 24 on the flexible gear 20 are slightly different. Therefore, with each rotation of the non-circular cam 31, the meshing position between the internal teeth 11 and the external teeth 24 changes slightly. As a result, the flexible gear 20 rotates relative to the rigid gear 10 due to the difference in the number of teeth between the internal teeth 11 and the external teeth 24. This allows the wave drive gear 100 to reduce the power input to the wave generator 30 from an external motor or the like via the input shaft and output it from the output shaft fixed to the flexible gear 20.

<2. Detailed structure and manufacturing method of the gear unit>
Next, a more detailed description of the structure and manufacturing method of the gear unit 19, including the flexible gear 20, bushing 26, and spacer 27, will be given. Figure 4 is a flowchart showing the manufacturing procedure of the gear unit 19.

As shown in Figure 4, when manufacturing the flexible gear 20, first, a metal plate that will serve as the base material for the flexible gear 20 is prepared (Step S1). As described above, the flexible gear 20 is formed using austenitic stainless steel. That is, austenitic stainless steel material is used for the metal plate. Generally, these austenitic stainless steels have a face-centered cubic lattice crystal structure and are relatively low in hardness. However, when austenitic stainless steel is cold-worked, plastic deformation induces a transformation of austenite into martensite, resulting in work hardening. As a result, the strength increases after the formation of the martensite phase. Note that the amount of this transformation depends on the amount of deformation.

Furthermore, the n-value, which is the work hardening index of stainless steel, is 0.3 or higher. In other words, stainless steel with an n-value of approximately 0.3 or higher is used for metal sheets. Here, the n-value can be calculated from the slope when the true stress (σ) - true strain (ε) value is plotted on a log-log graph, using the index n-value obtained when the "true stress (σ) - true strain (ε) curve" obtained from the "load (tensile strength) - elongation curve" is approximately expressed as "σ = Fε ⁿ " by taking a "JIS No. 13B tensile test specimen" from each steel sheet to be measured in accordance with JIS Z 2253:2020 and conducting a tensile test. Generally, the larger the n-value, the better the formability, the easier it is for work hardening to occur, and the more uniform the deformation can be.

Next, as shown in Figure 4, the metal plate is subjected to a deep drawing process (step S2). During the deep drawing process, for example, a disc-shaped metal plate is attached to the tip surface of a cylindrical die and brought into contact with it under a predetermined pressure. As a result, a bottomed cylindrical intermediate molded product 60 is formed. Figure 5 is a schematic diagram of the intermediate molded product 60.

Furthermore, the flat plate-shaped portion 61 of the intermediate molded product 60 that was in contact with the front surface of the mold becomes the diaphragm portion 21 of the flexible gear 20 after subsequent processing such as the formation of holes (the central hole 210 and multiple through holes 211). Also, the portion 62 of the intermediate molded product 60 that was in contact with the side surface of the mold becomes the body portion 23 and multiple external teeth 24 of the flexible gear 20. Finally, the portion 63 of the intermediate molded product 60 that was in contact with the corner of the front surface of the mold becomes the bent portion 22 of the flexible gear 20.

Next, an external tooth forming roller (not shown) having an uneven shape is pressed against the tip portion 621 of portion 62 and rolled in the circumferential direction around the central axis of the mold to form (rolling) the external teeth 24 (step S3). However, the external teeth 24 may also be formed on portion 621 by another method such as cutting. As a result, portion 621 becomes a second body portion 232 with multiple external teeth 24 formed on its outer circumferential surface. Furthermore, the portion 622 located on the bottom (portion 61) side of portion 621 becomes the first body portion 231 of the flexible gear 20.

As described above, part 621 is pressed and deformed by the external tooth forming roller during the process of forming the external teeth 24. This causes plastic deformation of the austenite in the metal plate constituting part 621. This plastic deformation then induces a transformation of the austenite into martensite, leading to work hardening. As a result, the strength of part 621 increases.

Next, as shown in Figure 4, the flexible gear 20, after the external teeth 24 have been formed, is subjected to shot peening (step S4). Shot peening is a surface treatment that modifies the surface by impacting it with countless tiny spheres. In this embodiment, shot peening is applied to the body 23 and the bent portion 22, centering on the second body 232 where the external teeth 24 are located on the outer circumferential surface. After shot peening, the external teeth 24, body 23, and bent portion 22 each have multiple dimples (small round indentations) on their surfaces.

This causes plastic deformation of the austenite near the surface of the external teeth 24, body 23, and bent portion 22. This plastic deformation induces a transformation of the austenite into martensite, leading to work hardening. In other words, shot peening further enhances the martensite content of the surfaces of the external teeth 24, body 23, and bent portion 22. This further increases the strength of the external teeth 24, body 23, and bent portion 22, improving the durability of the flexible gear 20. As a result, even when the wave drive gear 100 is driven for a long period, causing the flexible gear 20 to flex and rotate while meshing with the rigid gear 10, deterioration of the external teeth 24, body 23, and bent portion 22 can be suppressed.

As described above, in this embodiment, in the process of forming the flexible gear 20 using a metal sheet made of austenitic stainless steel, first, the diaphragm portion 21, the bent portion 22, the first body portion 231, and the second body portion 232 are formed by deep drawing. Next, the external teeth 24 are formed on the outer circumferential surface of the second body portion 232 by tooth rolling. Furthermore, shot peening is applied to the external teeth 24, the body portion 23, and the bent portion 22. As a result, the proportion of the martensite phase contained in these materials increases with each step, leading to work hardening. Consequently, the residual stress in the formed flexible gear 20 increases, further enhancing its strength.

Furthermore, in this embodiment, by forming the flexible gear 20 using austenitic stainless steel with a high n-value, deformation during processes such as deep drawing, tooth rolling, and shot peening can be made uniform, thereby improving the accuracy of the final product.

As described above, in this embodiment, the bush 26 and spacer 27 are also formed from the same stainless steel as the flexible gear 20. During the process of forming the bush 26 and spacer 27, a tolerance of ±1% of the respective diameters of the bush 26 and spacer 27 is set. Then, as described above, the bush 26 and spacer 27 are fixed to the diaphragm portion 21 of the flexible gear 20 using a plurality of fastening members 28 (step S5).

In other words, the gear unit 19 used in the wave drive gear device 100 is manufactured through the following steps: a) a process of manufacturing a flexible gear 20, and b) a process of fixing a bush 26 and a spacer 27 to the flexible gear 20. In step a), the bent portion 22 and the body portion 23 are formed by drawing a metal plate. In step b), the first contact surface CS1, which is the other axial surface of the bush 26, is brought into contact with one axial surface of the diaphragm portion 21, and the second contact surface CS2, which is the other axial surface of the spacer 27, is brought into contact with the other axial surface of the diaphragm portion 21.

The output shaft is then fixed radially inward of the diaphragm portion 21, the bush 26, and the spacer 27. As a result, when the harmonic drive gear 100 is driven, the flexible gear 20 flexes while meshing with the rigid gear 10, and rotates together with the bush 26, spacer 27, and output shaft at a reduced rotational speed around the central axis C1. Furthermore, as described above, by sandwiching the diaphragm portion 21 between the bush 26 and the spacer 27, the amount of flexing of the diaphragm portion 21 during the driving of the harmonic drive gear 100 can be suppressed.

However, in this embodiment, when forming the flexible gear 20 by drawing, the diaphragm portion 21 of the flexible gear 20 becomes approximately constant in thickness due to the nature of the process. Therefore, when using a bush 26 and spacer 27 with a conventional structure, during the drive of the wave drive gear 100, the flexible gear 20 flexes and rotates while meshing with the rigid gear 10, resulting in localized stress concentration in the flexible gear 20 due to deformation. In particular, stress was locally concentrated at the portion of the diaphragm portion 21 that contacts the radially outer end of the first contact surface CS1 of the bush 26, and at the portion of the spacer 27 that contacts the radially outer end of the second contact surface CS2.

Therefore, in this invention, larger bushings 26 and spacers 27 are used in the radial direction than in conventional designs. The radially outer end of the first contact surface CS1 of the bushing 26 and the radially outer end of the second contact surface CS2 of the spacer 27 are positioned at the boundary between the diaphragm portion 21 and the bent portion 22 (see the dashed line B1 in Figure 3). However, the radially outer end of the first contact surface CS1 of the bushing 26 and the radially outer end of the second contact surface CS2 of the spacer 27 do not necessarily have to perfectly coincide with the boundary between the diaphragm portion 21 and the bent portion 22. For example, the radially outer end of the first contact surface CS1 of the bushing 26 and the radially outer end of the second contact surface CS2 of the spacer 27 may be offset by approximately ±1% from the boundary between the diaphragm portion 21 and the bent portion 22 with respect to the respective diameters of the bushing 26 and spacer 27.

Furthermore, in this invention, by using larger bushings 26 and spacers 27 in the radial direction than conventional designs, the stress caused by the deformation of the flexible gear 20 during the operation of the harmonic drive gear 100 can be applied to the bent portion 22. As described above, the bent portion 22 gradually bends axially in one direction as it extends radially outward. Therefore, when the flexible gear 20 bends and rotates while meshing with the rigid gear 10, the bent portion 22 deforms smoothly and has a shape that easily releases stress. In this embodiment, by applying stress to such a bent portion 22, deterioration of the flexible gear 20 due to stress can be suppressed. Also, as described above, the bent portion 22 of the flexible gear 20 becomes more martensitic and its strength is further increased during the process of formation through drawing and shot peening. As a result, the durability of the flexible gear 20 is improved, and deterioration of the flexible gear 20 can be further suppressed even when the flexible gear 20 bends and rotates while meshing with the rigid gear 10 over a long period of time.

Furthermore, as shown in Figure 3, the thickness of the bent portion 22 of the flexible gear 20 gradually decreases from the diaphragm portion 21 towards the first body portion 231. Also, the radial thickness d2 of the first body portion 231 is thinner than the axial thickness d1 of the diaphragm portion 21. This gradual change in the thickness of the bent portion 22 allows for further distribution of the stress acting on the bent portion 22 during the operation of the wave drive gear unit 100. As a result, deterioration of the flexible gear 20 due to stress can be further suppressed.

Furthermore, as described above, a first curved surface CS3 is formed on the peripheral edge of the bush 26 that is close to the flexible gear 20, resulting in a smooth shape. That is, no corners are formed at the radially outer end of the first contact surface CS1. Therefore, when the flexible gear 20 bends and rotates while meshing with the rigid gear 10, deterioration of the boundary between the diaphragm portion 21 and the bent portion 22 due to contact with corners can be prevented. Also, the radius of curvature of the first curved surface CS3 is smaller than the radius of curvature of the bent portion 22. This prevents interference between the bush 26 and the area near the boundary between the diaphragm portion 21 and the bent portion 22, which would hinder the rotation of the flexible gear 20, when the flexible gear 20 bends and rotates while meshing with the rigid gear 10.

Furthermore, as described above, a second curved surface CS4 is formed on the peripheral edge of the spacer 27 that is close to the flexible gear 20, resulting in a smooth shape. That is, no corners are formed at the radially outer end of the second contact surface CS2. Therefore, when the flexible gear 20 bends and rotates while meshing with the rigid gear 10, deterioration of the boundary between the diaphragm portion 21 and the bent portion 22 due to contact with corners can be prevented.

<3. Variations>
Although exemplary embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above.

In the above embodiment, deep drawing was used as an example of a method for forming the flexible gear 20. However, the method for forming the flexible gear 20 is not limited to this. The flexible gear 20 may be formed by other methods such as cutting, forging, casting, or press working.

Figure 6 is a schematic diagram of a robot 200 equipped with a harmonic drive gear 100, representing a modified example in which the harmonic drive gear 100 is incorporated. This modified robot 200 is a so-called industrial robot, used, for example, in an industrial product manufacturing line to perform tasks such as parts transport, processing, and assembly. As shown in Figure 6, the robot 200 comprises a base frame 201, an arm 202, a motor 203, and a harmonic drive gear 100.

The arm 202 is rotatably supported on the base frame 201. The motor 203 and the harmonic drive gear 100 are incorporated into the joint between the base frame 201 and the arm 202. When a drive current is supplied to the motor 203, rotational motion is output from the motor 203. This rotational motion output from the motor 203 is then reduced in speed by the harmonic drive gear 100 and transmitted to the arm 202. As a result, the arm 202 rotates relative to the base frame 201 at the reduced speed.

Furthermore, the detailed shapes of the harmonic drive gear, including the gear unit, may differ from those shown in the figures of the above embodiments.

<4. Summary>
Furthermore, this technology can be configured as follows:
(1): A gear unit used in a wave drive gear system,
Flexible gears and
A bush and spacer fixed to the aforementioned flexible gear,
It has,
The aforementioned flexible gear is
A plate-shaped diaphragm section that extends perpendicular to the central axis,
From the radially outer end of the diaphragm portion, a bent portion that gradually curves toward one side in the axial direction as it extends radially outward,
A cylindrical body extending from one end of the bent portion on one axial side to the other axial side,
Multiple external teeth provided on the outer circumferential surface of the body,
It has,
The aforementioned bush,
It extends perpendicularly to the central axis and has a first contact surface that contacts one axial side surface of the diaphragm portion,
The previous spacer is
It has a second contact surface that extends perpendicularly to the central axis and contacts the other axial surface of the diaphragm portion,
A gear unit in which the radially outer end of the first contact surface and the radially outer end of the second contact surface are located at the boundary between the diaphragm portion and the bent portion.

(2): The gear unit described in (1),
The aforementioned torso is,
A first body portion extending from one end of the bent portion on one axial side toward the other axial side,
A second body portion extends from one axial end of the first body portion to the other axial side and is located radially inward of the plurality of external teeth,
Includes,
The radial thickness of the first body is thinner than the axial thickness of the diaphragm portion.
A gear unit in which the thickness of the bent portion gradually decreases from the diaphragm portion toward the first body portion.

(3): A gear unit as described in (1) or (2),
The aforementioned bush,
The first contact surface further has a first curved surface that gradually curves toward one side in the axial direction as it extends radially outward from its radially outer end,
A gear unit in which the radius of curvature of the first curved surface is smaller than the radius of curvature of the bent portion.

(4): A gear unit as described in any one of (1) to (3),
The previous spacer is
A gear unit further having a second curved surface that gradually curves toward the other axial direction as it extends radially outward from the radially outer end of the second contact surface.

(5): A gear unit described in any one of (1) to (4),
The aforementioned flexible gear is a product of a drawing process, a gear unit.

(6): A gear unit as described in any one of (1) to (5),
The aforementioned flexible gear is a gear unit formed from austenitic stainless steel.

(7): The gear unit described in (6),
A gear unit in which the n-value, which is the work hardening index of the aforementioned stainless steel, is 0.3 or higher.

(8): A gear unit as described in any one of (1) to (7),
The bent portion is a gear unit having multiple dimples on its surface.

(9): A gear unit as described in any one of (1) to (8),
A wave generator positioned radially inward of the body portion,
A rigid gear positioned radially outward of the aforementioned body portion,
Equipped with,
The rigid gear has a plurality of internal teeth on its inner circumferential surface,
A wave drive gear device in which a portion of the plurality of external teeth meshes with a portion of the plurality of internal teeth.

(10): A robot equipped with the wave drive gear mechanism described in (9).

(11): A method for manufacturing a gear unit used in a wave drive gear,
a) A process for manufacturing a flexible gear,
b) The step of fixing the bush and spacer to the flexible gear,
It has,
The aforementioned flexible gear is
A plate-shaped diaphragm section that extends perpendicular to the central axis,
From the radially outer end of the diaphragm portion, a bent portion that gradually curves toward one side in the axial direction as it extends radially outward,
A cylindrical body extending from one end of the bent portion on one axial side to the other axial side,
Multiple external teeth provided on the outer circumferential surface of the body,
It has,
In step a), the bent portion and the body portion are formed by drawing the metal plate.
In step b) above,
The first contact surface, which is the other axial surface of the bush, is brought into contact with the axial surface of the diaphragm portion,
The second contact surface, which is the axial side surface of the spacer, is brought into contact with the axial side surface of the diaphragm portion.
A method for manufacturing a gear unit, wherein the radially outer end of the first contact surface and the radially outer end of the second contact surface are positioned at the boundary between the diaphragm portion and the bent portion.

This invention can be used in gear units, harmonic drive gears, robots, and methods for manufacturing gear units.

10 Rigid gear 11 Internal teeth 19 Gear unit 20 Flexible gear 21 Diaphragm section 22 Bent section 23 Body section 24 External teeth 26 Bushing 27 Spacer 30 Wave generator 31 Non-circular cam 32 Flexible bearing 100 Wave gear device 200 Robot 231 First body section 232 Second body section C1 Central axis CS1 First contact surface of bushing CS2 Second contact surface of spacer CS3 First curved surface of bushing CS4 Second curved surface of spacer d1 Axial thickness of diaphragm section d2 Radial thickness of first body section

Claims (11)

A gear unit used in a wave drive gear system,
Flexible gears and
A bush and spacer fixed to the aforementioned flexible gear,
It has,
The aforementioned flexible gear is
A plate-shaped diaphragm section that extends perpendicular to the central axis,
From the radially outer end of the diaphragm portion, a bent portion that gradually curves toward one side in the axial direction as it extends radially outward,
A cylindrical body extending from one end of the bent portion on one axial side to the other axial side,
Multiple external teeth provided on the outer circumferential surface of the body,
It has,
The aforementioned bush,
It extends perpendicularly to the central axis and has a first contact surface that contacts one axial side surface of the diaphragm portion,
The previous spacer is
It has a second contact surface that extends perpendicularly to the central axis and contacts the other axial surface of the diaphragm portion,
A gear unit in which the radially outer end of the first contact surface and the radially outer end of the second contact surface are located at the boundary between the diaphragm portion and the bent portion. A gear unit according to claim 1,
The aforementioned torso is,
A first body portion extending from one end of the bent portion on one axial side toward the other axial side,
A second body portion extends from one axial end of the first body portion to the other axial side and is located radially inward of the plurality of external teeth,
Includes,
The radial thickness of the first body is thinner than the axial thickness of the diaphragm portion.
A gear unit in which the thickness of the bent portion gradually decreases from the diaphragm portion toward the first body portion. A gear unit according to claim 1 or claim 2,
The aforementioned bush,
The first contact surface further has a first curved surface that gradually curves toward one side in the axial direction as it extends radially outward from its radially outer end,
A gear unit in which the radius of curvature of the first curved surface is smaller than the radius of curvature of the bent portion. A gear unit according to claim 1 or claim 2,
The previous spacer is
A gear unit further having a second curved surface that gradually curves toward the other axial direction as it extends radially outward from the radially outer end of the second contact surface. A gear unit according to claim 1 or claim 2,
The aforementioned flexible gear is a product of a drawing process, a gear unit. A gear unit according to claim 1 or claim 2,
The aforementioned flexible gear is a gear unit formed from austenitic stainless steel. The gear unit according to claim 6,
A gear unit in which the n-value, which is the work hardening index of the aforementioned stainless steel, is 0.3 or higher. A gear unit according to claim 1 or claim 2,
The bent portion is a gear unit having multiple dimples on its surface. A gear unit according to claim 1 or claim 2,
A wave generator positioned radially inward of the body portion,
A rigid gear positioned radially outward of the aforementioned body portion,
Equipped with,
The rigid gear has a plurality of internal teeth on its inner circumferential surface,
A wave drive gear device in which a portion of the plurality of external teeth meshes with a portion of the plurality of internal teeth. A robot equipped with a wave drive gear mechanism as described in claim 9. A method for manufacturing a gear unit used in a wave drive gear system,
a) A process for manufacturing a flexible gear,
b) The step of fixing the bush and spacer to the flexible gear,
It has,
The aforementioned flexible gear is
A plate-shaped diaphragm section that extends perpendicular to the central axis,
From the radially outer end of the diaphragm portion, a bent portion that gradually curves toward one side in the axial direction as it extends radially outward,
A cylindrical body extending from one end of the bent portion on one axial side to the other axial side,
Multiple external teeth provided on the outer circumferential surface of the body,
It has,
In step a), the bent portion and the body portion are formed by drawing the metal plate.
In step b) above,
The first contact surface, which is the other axial surface of the bush, is brought into contact with the axial surface of the diaphragm portion,
The second contact surface, which is the axial side surface of the spacer, is brought into contact with the axial side surface of the diaphragm portion.
A method for manufacturing a gear unit, wherein the radially outer end of the first contact surface and the radially outer end of the second contact surface are positioned at the boundary between the diaphragm portion and the bent portion.