Harmonic reducer

Abstract

Embodiments of the present disclosure relate to a harmonic reducer (1). The invention relates to a harmonic reducer (1) comprising a power shaft (10), a wave generator (40) mounted on the power shaft (10), a steel wheel (20) comprising internal teeth, a flexspline (30) comprising external teeth and configured to receive the wave generator (40) to gradually engage the external teeth with the internal teeth when the wave generator (40) rotates, where the harmonic reducer (1) further comprises a bearing system configured to support the power shaft (10), and the bearing system comprises at least a first bearing (52) and a second bearing (54) located at a first side of the wave generator (40).

Description

Technical Field

[0001] The embodiments of this disclosure generally relate to a harmonic reducer, and more particularly to a harmonic reducer for industrial robots. Background Technology

[0002] Harmonic drives (also known as harmonic reducers) are increasingly used due to their superior torque-increasing performance. Harmonic drives can be used to increase the output torque of gears used in various engineering fields, such as in milling, manufacturing, and machines using robotic arms.

[0003] Harmonic reducers mainly consist of a flexure, a steel wheel, and a wave generator. The steel wheel has internal teeth that mesh with the external teeth on the flexure. The wave generator is typically elliptical and is arranged inside the flexure. The rotation of the wave generator causes the flexure to mesh with the steel wheel, usually at a fixed point, gradually engaging at points of opposite diameter. Thus, the flexure is driven to rotate to drive the load. Using a single harmonic reducer, the input speed to output speed ratio can reach over 320. This harmonic reducer is lighter, smaller, and more efficient than conventional high-ratio drives. However, traditional harmonic reducers are unsatisfactory in terms of lifespan, and further improvements are needed. Summary of the Invention

[0004] Exemplary embodiments of this disclosure provide a harmonic reducer with increased support stiffness, resulting in improved lifespan.

[0005] In a first aspect of this disclosure, a harmonic reducer is provided. The harmonic reducer includes a drive shaft, a wave generator mounted on the drive shaft, a steel wheel including internal teeth, and a flexible wheel including external teeth and configured to receive the wave generator so that the external teeth gradually mesh with the internal teeth as the wave generator rotates. The harmonic reducer also includes a bearing system configured to support the drive shaft, and the bearing system includes at least one first bearing and a second bearing located on a first side of the wave generator. Providing at least two bearings on one side can effectively improve support stiffness without increasing bearing size, and improve the rotational stability of the drive shaft and the force distribution in the bearing system.

[0006] In some embodiments, the first bearing may be axially spaced from the second bearing by a first gap on a first side. Force distribution can be further improved.

[0007] In some embodiments, the harmonic reducer may further include a first end flange configured to close a first end of an inner cavity in which a wave generator is located, wherein first and second bearings are mounted to the drive shaft by an interference fit, and the first bearing is located further away from the wave generator than the second bearing. The first end flange may help seal the inner cavity.

[0008] In some embodiments, the bearing system may further include a first washer located between the outer ring of the first bearing and the outer ring of the second bearing to transfer axial load from the outer ring of the second bearing to the outer ring of the first bearing. This arrangement further prevents external axial loads from being transmitted to the wave generator.

[0009] In some embodiments, the bearing system may further include a second washer located between the inner ring of the first bearing and the inner ring of the second bearing, wherein the second inner diameter of the second washer is lower than the first inner diameter of the first washer. Using the second washer, the first and second bearings can be reliably held axially in place.

[0010] In some embodiments, the section of the power shaft between the first bearing and the second bearing may have the same outer diameter.

[0011] In some embodiments, the first end flange may be fixed to the steel wheel and include a stepped portion configured to axially support the first bearing.

[0012] In some embodiments, the first end flange may be fixed to the flange portion of the flexure, and the outer ring of the first bearing is axially supported by a pre-tensioned portion disposed between the outer ring of the first bearing and the inner surface of the first end flange.

[0013] In some embodiments, the pretensioned portion may include a spring or multiple laminates.

[0014] In some embodiments, the bearing system may further include at least one third bearing located on the second side of the wave generator opposite to the first side.

[0015] In some embodiments, the harmonic reducer may further include a second end flange configured to close the second end of the cavity in which the wave generator is located, wherein a third bearing is mounted to the drive shaft by an interference fit.

[0016] In some embodiments, the bearing system may further include a fourth bearing located on the second side of the wave generator and axially spaced from the third bearing by a second gap, and the third bearing being located further away from the wave generator than the fourth bearing and axially supported by a second end flange. The support rigidity of the power shaft can be further improved.

[0017] In some embodiments, the bearing system may further include a third washer located between the outer ring of the third bearing and the outer ring of the fourth bearing to transfer axial load from the outer ring of the fourth bearing to the outer ring of the third bearing.

[0018] In some embodiments, the bearing system may further include a fourth washer located between the inner ring of the third bearing and the inner ring of the fourth bearing; and the fourth inner diameter of the fourth washer is lower than the third inner diameter of the third washer.

[0019] In a second aspect of this disclosure, an industrial robot is provided. The industrial robot includes: a harmonic reducer as described in any of the first aspects of this disclosure; a first arm connected to a steel wheel; and a second arm connected to a flexible wheel.

[0020] It should be understood that this overview is not intended to identify key or essential features of the embodiments of this disclosure, nor is it intended to limit the scope of this disclosure. Other features of this disclosure will become clear from the following description. Attached Figure Description

[0021] The above and other objects, features, and advantages of the exemplary embodiments disclosed herein will become more readily understood from the following detailed description with reference to the accompanying drawings. In the drawings, several exemplary embodiments disclosed herein will be described by way of example and non-limiting manner, wherein:

[0022] Figure 1 This is a perspective view of a harmonic reducer according to an example embodiment of the present disclosure;

[0023] Figure 2 This is a cross-sectional view of a harmonic reducer according to a first exemplary embodiment of the present disclosure;

[0024] Figure 3 yes Figure 2 An exploded perspective view of the harmonic reducer shown.

[0025] Figure 4 This is a cross-sectional view of a harmonic reducer according to a second exemplary embodiment of the present disclosure; and

[0026] Figure 5 This is a cross-sectional view of a harmonic reducer according to a third exemplary embodiment of the present disclosure.

[0027] In all the accompanying drawings, the same or similar reference numerals are used to denote the same or similar elements. Detailed Implementation

[0028] The principles of this disclosure will now be described with reference to several exemplary embodiments illustrated in the accompanying drawings. Although exemplary embodiments of this disclosure are shown in the drawings, it should be understood that these embodiments are described merely to enable those skilled in the art to better understand and implement this disclosure, and not to limit the scope of this disclosure in any way.

[0029] The terms “comprises” or “includes” and their variations shall be interpreted as open-ended terms meaning “including but not limited to”. The term “or” shall be understood as “and / or” unless the context explicitly indicates otherwise. The term “based on” shall be understood as “at least partially based on”. The term “operably” means a function, action, movement, or state achievable through operation caused by a user or external agency. The terms “one embodiment” and “embodiment” shall be understood as “at least one embodiment”. The term “another embodiment” shall be understood as “at least one other embodiment”. The terms “first,” “second,” etc., may refer to different or the same objects. Other explicit and implicit definitions may be included below. Unless the context explicitly indicates otherwise, the definitions of terms are consistent throughout the specification.

[0030] Figure 1 A perspective view of a harmonic reducer 1 according to an exemplary embodiment of the present disclosure is shown. Figure 1 As shown, the harmonic reducer 1 includes a drive shaft 10, a wave generator 40, a steel wheel 20, and a flexible wheel 30. The drive shaft 10 can be connected to a power source, such as a motor, pulley drive, etc. The wave generator 40 is mounted on the drive shaft 10 and configured to rotate as the drive shaft 10 rotates. The steel wheel 20 may include a cylindrical body with internal teeth thereon. The flexible wheel 30 may include external teeth on the cylindrical body, which are configured to mesh with the internal teeth on the steel wheel 20. The flexible wheel 30 may include a thin wall defining an internal space, and the wave generator 40 can be arranged within the internal space. The external teeth are provided on the outer surface of the thin wall. The wave generator 40 may be elliptical. When the wave generator 40 rotates, the external teeth on the flexible wheel 30 gradually mesh with the internal teeth on the steel wheel 20 at radially opposite points. In this way, the flexible wheel 30 is driven to rotate accordingly. The flexible wheel 30 may also be fixed to a supporting member. The supporting member then rotates.

[0031] Figure 2 and Figure 3 Cross-sectional and exploded perspective views of a harmonic reducer according to a first exemplary embodiment of the present disclosure are shown. In the example shown, the flexure 30 is in the form of a cap including a cylindrical portion 32 and a flange portion 34. The external teeth are the cylindrical portion of the flexure 30. The flange portion 34 can be connected to a load-bearing member. It should be understood that the example shown is merely illustrative, and the flexure 30 may have other suitable shapes.

[0032] like Figure 2 and Figure 3As shown, the harmonic reducer 1 may further include a first end flange 60. The first end flange 60 is configured to close the first end of the cavity 15 in which the wave generator 40 is located. The first end flange 60 may be secured to the steel wheel 20 by fasteners (e.g., screws). The harmonic reducer 1 may further include a second end flange 70, which may be part of a load-bearing member. The second end flange 70 is configured to close the opposite second end of the cavity 15. The second end flange 70 may be secured to the flexible wheel 30, for example, at the flange portion 34 by fasteners (e.g., screws). Lubricating oil may be disposed within the cavity 15.

[0033] like Figure 2 and Figure 3 As shown, the harmonic reducer 1 may further include a support bearing 80. The outer ring of the support bearing 80 can be secured to the flange portion 34 and the second end flange 70 by fasteners. The inner ring of the support bearing 80 can be secured to the steel wheel 20 and the first end flange 60 by fasteners. The support bearing is configured to withstand output axial / radial loads and bending moments.

[0034] like Figure 2 and Figure 3 As shown, the harmonic reducer 1 also includes a bearing system configured to support the power shaft 10. The bearing system includes at least one first bearing 52 and a second bearing 54 located on one side of the wave generator 40. In the illustrated example, the first bearing 52 and the second bearing 54 are located on the power input side, i.e., on the side where the first end flange 60 is located in the illustrated example. As shown, the first bearing 52 and the second bearing 54 are single-row deep groove ball bearings. It should be understood that other types of bearings, such as double-row angular contact ball bearings, can be used for the first bearing 52 and the second bearing 54. The first bearing 52 and the second bearing 54 can be of the same type or different types.

[0035] During operation of the harmonic reducer 1, various undesirable loads (e.g., external axial / radial loads) caused by various factors, such as installation tolerances between components, thermal expansion of components, and external turbulence from the surrounding environment, can be applied to the drive shaft 10 and then transmitted to the wave generator 32. The toothed section of the flexure 30 typically has a thin wall, which is highly sensitive to external turbulent loads. The lifespan of the flexure 30 (and the harmonic reducer 1) is greatly affected by its support stiffness. When undesirable loads from the drive shaft 10 are transmitted to the wave generator 32, the wave generator 32 often fails before its design life. The stiffness of the bearing system is crucial to the reliability and lifespan of the harmonic reducer. When the support stiffness is insufficient, the wave generator 32 will be subjected to additional external forces / vibrations, which may severely shorten its lifespan.

[0036] Increasing the diameter of the drive shaft 10 is effective in increasing the stiffness of the bearing system. However, this method has many drawbacks. Increasing the diameter of the drive shaft 10 results in a larger size of the harmonic reducer, which is undesirable in many applications. Moreover, a larger diameter of the drive shaft 10 means higher manufacturing costs. In addition, it increases the risk of oil leakage from the internal cavity. According to this disclosure, a novel system is proposed in which at least two bearings 52, 54 are disposed on one side of the wave generator 40 to increase the stiffness of the bearing system. At least two bearings 52, 54 are disposed on one side of the wave generator 40. Distributing two bearings 52, 54 on one side of the wave generator 40 can improve the stiffness of the bearing system. Therefore, undesirable loads can be prevented from being transmitted from the drive shaft 10 to the wave generator 32.

[0037] In some embodiments, such as Figure 2 and Figure 3 As shown, two bearings 52 and 54 are provided on the first side (i.e., the right side in the figure, and also corresponding to the power input side), and one bearing 56 is provided on the power input side (i.e., the left side in the figure, and also corresponding to the load side). Bearing 54 can first be mounted to the power shaft 10 by an interference fit. An axial positioning device, such as an axial step 18, can be provided on the power shaft 10 to axially position bearing 54. The outer ring of bearing 54 can be separated from the inner surface of the housing 61 of the end flange 60 by a clearance. After bearing 54 is mounted to the power shaft 10, another bearing 52 can similarly be mounted to the power shaft 10, for example, by an interference fit. Similarly, the outer ring 524 of bearing 52 can be separated from the inner surface of the housing 61 by a clearance. Bearing 52 can be located further away from the wave generator 40 than bearing 52. In some embodiments, bearing 54 can be adjacent to bearing 52. In some embodiments, bearing 52 can be axially spaced from bearing 54 by a clearance on the first side.

[0038] In some embodiments, such as Figure 2 and Figure 3As shown, the bearing system may further include an outer washer 64 located between the outer ring 524 of bearing 52 and the outer ring 544 of bearing 54. One end of the outer washer 64 abuts against the axial end face of the outer ring 544 of bearing 54. The opposite end of the outer washer 64 abuts against the axial end face of the outer ring 524 of bearing 52. Bearing 52 may also be axially positioned by the housing 61 of the end flange 60, for example by a step 67 provided on the inner surface of the housing 61 of the end flange 60. Therefore, during the rotation of the drive shaft 10, undesirable loads, such as radial loads, can be transmitted between bearings 52 and 54. In particular, the axial load from the outer ring 544 of bearing 54 can be transmitted to the outer ring 524 of bearing 52 and further to the end flange 60. Since the single-sided double bearing support stiffness is the sum of the two bearings, the support stiffness can be effectively increased without increasing the bearing size, thereby improving the rotational stability of the drive shaft and the force distribution in the bearing system.

[0039] In some embodiments, such as Figure 2 and Figure 3 As shown, the bearing system may further include an inner washer 62 located between the inner ring 522 of bearing 52 and the inner ring 542 of bearing 54. The inner diameter of washer 62 is smaller than the inner diameter of outer washer 64. One end of inner washer 62 abuts against the axial end face of inner ring 542 of bearing 54. The opposite end of inner washer 62 abuts against the axial end face of inner ring 522 of bearing 52. In the example shown, inner washer 62 is configured to axially restrict the movement of the inner rings of bearings 52 and 54. It should be understood that the example shown is merely illustrative, and other suitable means may be used to limit the relative torque between the inner ring 524 of bearing 52 and the inner ring 542 of bearing 54.

[0040] In some embodiments, such as Figure 2 and Figure 3As shown, a bearing 56 is disposed on the load side. A locating ring 14 can be arranged around the drive shaft 10 on the left side of the wave generator 40. The bearing 56 can be mounted to the drive shaft 10 via an interference fit. The outer ring 564 of the bearing 56 can be separated from the inner surface of the end flange 70 by a clearance. The inner ring 562 of the bearing 56 can abut against the locating ring 14. The outer ring 562 of the bearing 56 can be axially supported by a pre-tensioning portion 69. The pre-tensioning portion 69 is disposed between the outer ring 562 of the bearing 56 and the inner surface of the circumferential extension 71 of the end flange 70. When the drive shaft 10 and the assembled bearings 52, 54, 56 are assembled into the cavity 15, the pre-tensioning portion 69 can be pre-tensioned. The pre-tensioning portion 69 can be of various forms. In some embodiments, the pre-tensioning portion 69 can be made of a spring. In some embodiments, the pre-tensioning portion 69 can be made of a laminate. With this arrangement, both sides of the wave generator 40, namely one side adjacent to the end flange 70 and the opposite side adjacent to the end flange 60, can be reliably supported by bearings 52, 54, 56.

[0041] In the example shown, the power shaft 10 has substantially the same outer diameter at the locations where bearings 52, 54, and 56 are provided. It should be understood that the example shown is merely illustrative, and the outer diameter of the power shaft 10 can vary depending on the bearing positions. In the example shown, two bearings 52 and 54 are provided on one side adjacent to the end flange 60 (i.e., the power input side). It should be understood that more than two bearings 52 and 54, such as three, four, or more, can be provided on the power input side.

[0042] Figure 4 This is a cross-sectional view of a harmonic reducer 1 according to a second exemplary embodiment of the present disclosure. Figure 4 The harmonic reducer 1 shown is basically the same as Figure 2 The harmonic reducer shown is the same. The difference is that, in Figure 4 In this embodiment, two bearings 52 and 54 are provided on the load side, and one bearing 56 is provided on the power input side. The configuration of these bearings is consistent with reference to... Figure 2 The descriptions are essentially the same, therefore detailed descriptions of them are omitted. For example... Figure 4 As shown, bearings 52 and 54 can have the same dimensions, while bearing 56 can have different dimensions from bearings 52 and 54. It should be understood that the examples shown are merely illustrative, and bearings 52, 54, and 56 can be any other suitable type.

[0043] Figure 5 This is a cross-sectional view of a harmonic reducer 1 according to a third exemplary embodiment of the present disclosure. Figure 5 The harmonic reducer 1 shown is basically the same as Figure 2 and Figure 4The harmonic reducer shown is the same. The difference is that, in Figure 5 In this embodiment, two bearings 52 and 54 are provided on the power input side, and two bearings 56 and 58 are provided on the load side. The configuration of the bearings 52 and 54 on the power input side is as follows: Figure 2 Bearings 52 and 54 are described as essentially the same. Their detailed descriptions are omitted.

[0044] The two bearings 56 and 58 on the load side are similarly arranged. For example... Figure 5 As shown, the bearing system may further include an outer washer 68 located between the outer rings of bearing 56 and bearing 58. One end of the outer washer 68 abuts against the axial end face of the outer ring of bearing 56. The opposite end of the outer washer 68 abuts against the axial end face of the outer ring of bearing 58. Bearing 56 may also be axially positioned by a circumferential extension 71 of the end flange 70. Therefore, during rotation of the drive shaft 10, undesired loads, such as radial loads, can be transmitted between bearings 56 and 58 on the load side. In particular, axial loads from the outer ring of bearing 58 can be transmitted to the outer ring of bearing 56 and further to the end flange 70.

[0045] In some embodiments, such as Figure 5 As shown, the bearing system may further include an inner washer 66 located between the inner rings of bearing 56 and bearing 58. The inner diameter of washer 66 is smaller than the inner diameter of outer washer 68. One end of inner washer 66 abuts against the axial end face of the inner ring of bearing 56. The opposite end of inner washer 66 abuts against the axial end face of the inner ring of bearing 58. In the example shown, inner washer 62 is configured to axially restrict the movement of the inner rings of bearings 56 and 58. It should be understood that the example shown is merely illustrative, and other suitable means may be used to limit the relative torque between the inner rings of bearing 56 and bearing 58.

[0046] According to this disclosure, the harmonic reducer 1 can be used in various engineering fields. The steel wheel 20 of the harmonic reducer 1 can be fixed to a first component. For example, the first component can be fixed to the end flange 60 of the steel wheel 20 (see...). Figure 1 and Figure 2 The first component can be a fixed component or a movable component. A drive, such as a motor or pulley drive, can be mounted on the first component. The flexure 30 of the harmonic reducer 1 can be fixed to the second component. For example, the second component can be fixed to the end flange 70 of the flexure 30 (see...). Figure 1 and Figure 2Thus, when the drive is operating, the second component can be actuated by the harmonic reducer 1. In some embodiments, the harmonic reducer 1 can be used in an industrial robot. In particular, the harmonic reducer 1 can be used as a connector. In this case, the first component can be the robot arm of the industrial robot. The second component can be an adjacent robot arm of the industrial robot.

[0047] According to this disclosure, by providing at least two bearings on the power input side and / or the load side, the support stiffness of the bearing system can be increased without substantially modifying the structure of the harmonic reducer. Undesirable external loads, particularly radial and / or axial loads, can be prevented from being transmitted from the power shaft to the wave generator, resulting in an increased service life of the harmonic reducer.

[0048] Various embodiments of the invention have been described for illustrative purposes, but are not intended to be exhaustive or limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein has been chosen to best explain the principles of the embodiments, practical applications, or technical improvements to technologies found in the market, or to enable those skilled in the art to understand the embodiments disclosed herein.

Claims

1. A harmonic reducer (1), comprising: Power shaft (10). A wave generator (40) is mounted on the power shaft (10). Steel wheel (20), the steel wheel including a plurality of internal teeth, A flexible wheel (30) comprising a plurality of external teeth and configured to receive the wave generator (40) such that the external teeth gradually engage with the internal teeth as the wave generator (40) rotates. The harmonic reducer (1) further includes a bearing system configured to support the power shaft (10), and the bearing system includes at least one first bearing (52) and a second bearing (54) located on a first side of the wave generator (40).

2. The harmonic reducer (1) according to claim 1, wherein the first bearing (52) is axially spaced from the second bearing (54) by a first gap on the first side.

3. The harmonic reducer (1) according to claim 2 further includes a first end flange (60) configured to close a first end of the cavity in which the wave generator (40) is located, wherein the first bearing (52) and the second bearing (54) are mounted to the power shaft (10) by an interference fit, and the first bearing (52) is located further away from the wave generator (40) than the second bearing (54).

4. The harmonic reducer (1) according to claim 3, wherein the bearing system further comprises a first washer (64) located between the outer ring (524) of the first bearing (52) and the outer ring (544) of the second bearing (54) to transfer axial load from the outer ring of the second bearing (54) to the outer ring of the first bearing (52).

5. The harmonic reducer (1) according to claim 3 or 4, wherein the bearing system further comprises a second washer (62) located between the inner ring (522) of the first bearing (52) and the inner ring (542) of the second bearing (54), and The second inner diameter of the second washer (62) is lower than the first inner diameter of the first washer (64).

6. The harmonic reducer (1) according to any one of claims 2-5, wherein the power shaft (10) has the same outer diameter in the section between the first bearing (52) and the second bearing (54).

7. The harmonic reducer (1) according to any one of claims 3-6, wherein the first end flange (60) is fixed to the steel wheel (20) and includes a stepped portion (67) configured to axially support the first bearing (52).

8. The harmonic reducer (1) according to any one of claims 3-6, wherein the first end flange is fixed to the flange portion (34) of the flexure (30), and The outer ring of the first bearing is axially supported by a pre-tensioned portion (69) disposed between the outer ring of the first bearing and the inner surface of the first end flange.

9. The harmonic reducer (1) according to claim 8, wherein the pre-tensioned portion (69) comprises a spring or a plurality of laminates.

10. The harmonic reducer (1) according to any one of claims 1-9, wherein the bearing system further comprises at least one third bearing (56) located on a second side of the wave generator (40) opposite to the first side.

11. The harmonic reducer (1) according to claim 10 further includes a second end flange (70) configured to close a second end of the cavity therein of the wave generator (40), wherein the third bearing (56) is mounted to the power shaft (10) by an interference fit.

12. The harmonic reducer (1) according to claim 10 or 11, wherein the bearing system further comprises a fourth bearing (58) located on the second side of the wave generator (40) and axially spaced from the third bearing (56) by a second gap, and The third bearing (56) is located further away from the wave generator (40) than the fourth bearing (58) and is axially supported by the second end flange (70).

13. The harmonic reducer (1) according to claim 12, wherein the bearing system further comprises a third washer (68) located between the outer ring (562) of the third bearing (56) and the outer ring (582) of the fourth bearing (58) to transfer axial load from the outer ring (582) of the fourth bearing (58) to the outer ring (562) of the third bearing (56).

14. The harmonic reducer (1) according to claim 12 or 13, wherein the bearing system further comprises a fourth washer (66) located between the inner ring (562) of the third bearing (56) and the inner ring (582) of the fourth bearing (58); and The fourth inner diameter of the fourth washer (66) is lower than the third inner diameter of the third washer (68).

15. An industrial robot, comprising Harmonic reducer (1) according to any one of claims 1-14; The first arm is connected to the steel wheel (20); and The second arm is connected to the flexible wheel (30).

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