Harmonic speed reducer with double rigid wheels

Abstract

The utility model discloses a double-rigid-gear harmonic speed reducer. The double-rigid-gear harmonic speed reducer comprises a static rigid gear, a rear cover, a front cover, a dynamic rigid gear, a flexible gear and a wave generator. A rear cover and a front cover are arranged on the two sides of the static rigid wheel respectively. The rear cover comprises an annular sheet body and a cylindrical structure, and one side of the annular sheet body protrudes to form the cylindrical structure. And the dynamic rigid gear and the flexible gear are arranged between the front cover and the rear cover. The wave generator includes a flexible bearing, a connecting member, and an outer rotor motor. The connecting component comprises an annular bottom, and one side of the annular bottom protrudes to form an annular wall. The annular wall, the outer side of the cylindrical structure and the annular sheet body jointly form a containing space. The outer rotor motor is arranged in the containing space, the outer rotor is fixed to the annular bottom, and the inner stator and the rear cover are fixed to each other. The outer rotor can drive the connecting component to rotate, and the connecting component can drive the flexible bearing to rotate.

Description

Technical Field

[0001] The present application relates to a harmonic speed reducer, in particular to a double-rigid-ring harmonic speed reducer. Background Art

[0002] After an existing common double-rigid-ring harmonic speed reducer is assembled with a motor, there is a problem that it is difficult to reduce the overall thickness. Utility Model Content

[0003] The present application discloses a double-rigid-ring harmonic speed reducer, which is mainly used to improve the problem that it is difficult to reduce the overall thickness of the existing double-rigid-ring harmonic speed reducer.

[0004] One embodiment of the present application discloses a double-rigid-ring harmonic speed reducer, which includes: a static rigid ring, with its opposite two sides respectively defined as a front side and a rear side; a rear cover, which includes an annular sheet body and a cylindrical structure, a cylindrical structure is formed by protruding from one side of the annular sheet body, the annular sheet body has a perforation, the cylindrical structure has a hollow channel, and one end of the hollow channel communicates with the perforation; the annular sheet body is fixed to the rear side of the static rigid ring; a front cover, which is fixedly arranged on the front side of the static rigid ring, the front cover includes an opening, and the inner diameter of the opening is larger than the outer diameter of the cylindrical structure; a dynamic rigid ring, which is fixedly connected to the front cover, and the dynamic rigid ring is located between the front cover and the rear cover; a flexspline, which is arranged between the rear cover and the front cover, and the static rigid ring and the dynamic rigid ring can mesh with the flexspline; a wave generator, which includes: a flexible bearing, which is connected to the flexspline; a connecting member, which includes an annular bottom and an annular wall, the annular wall is formed by extending from the periphery of the annular bottom to one side, the annular bottom has a through hole, and the through hole penetrates the annular bottom; the inner diameter of the through hole is larger than the outer diameter of the cylindrical structure, and the through hole can be sleeved on the outside of the cylindrical structure; the annular wall is pivotally connected to the front cover and is also pivotally connected to the rear cover, the connecting member is connected to the flexible bearing, and the annular wall, the outside of the cylindrical structure and the annular sheet body together form an accommodating space; an outer-rotor motor, which is arranged in the accommodating space, the outer-rotor motor includes an outer rotor and an inner stator, the outer rotor is fixedly connected to the connecting member, and the inner stator is fixedly connected to the rear cover; wherein, the wave generator is arranged around the cylindrical structure, and the hollow channel penetrates the double-rigid-ring harmonic speed reducer, and the hollow channel is used to accommodate at least one electric wire; wherein, the length from the outer side surface of the front cover along an axial direction to the outer side surface of the rear cover is defined as a total length; the length of the outer-rotor motor along the axial direction is less than the length of the annular wall along the axial direction, and the length of the annular wall along the axial direction is less than the total length.

[0005] Optionally, an annular oil seal structure is further arranged between the through hole and the outside of the cylindrical structure, and the annular oil seal structure is used to seal the gap between the through hole and the cylindrical structure.

[0006] Optionally, the rear cover further includes a rear annular convex structure that is disposed around the cylindrical structure, and the inner diameter of the rear annular convex structure is greater than the outer diameter of the annular wall of the connecting member; the wave generator further includes a rear bearing that is located between the rear annular convex structure and the annular wall, and the connecting member can rotate relative to the rear cover through the rear bearing; the rear bearing, the connecting member, the annular oil seal structure, and the rear cover jointly enclose the accommodating space so that the accommodating space is not communicated with the space where the flexible bearing is located.

[0007] Optionally, a front annular convex structure is formed around the opening of the front cover; the wave generator further includes a front bearing that is located between the front annular convex structure and the connecting member, and the connecting member can rotate relative to the front cover through the front bearing.

[0008] Optionally, an annular boss is formed on the outer side of the annular wall of the connecting member, and the thickness of the annular wall at the annular boss is greater than that at other positions. The flexible bearing is connected to the annular boss, and the rear bearing and the front bearing are respectively located on both sides of the annular boss; the front bearing, the rear bearing, the annular boss, the flexible bearing, the front annular convex structure, the rear annular convex structure, the front cover, the rear cover, the dynamic rigid gear, and the static rigid gear jointly form a closed space that is not communicated with the accommodating space.

[0009] Optionally, the static rigid gear has an outer ring side wall, and the double rigid gear harmonic speed reducer further includes an outer annular oil seal structure that is located between the outer ring side wall and the outer side wall of the dynamic rigid gear, and the outer annular oil seal structure is used to assist in enclosing the closed space.

[0010] Optionally, the front bearing is a rubber-covered bearing, and the rubber-covered bearing can assist in enclosing the closed space.

[0011] Optionally, the rear bearing is a rubber-covered bearing, and the rubber-covered bearing can assist in preventing the closed space from communicating with the accommodating space.

[0012] Optionally, the annular bottom of the connecting member has a plurality of mounting holes that are used to cooperate with a plurality of mounting parts so that the outer rotor is fixed to the annular bottom.

[0013] Optionally, the front cover and the annular bottom are located on one side of the double rigid gear harmonic speed reducer, and the rear cover is located on the other side of the double rigid gear harmonic speed reducer; the rear cover or the cylindrical structure further includes at least one wire outlet hole that is used to provide an outlet for the wires of the outer rotor motor.

[0014] In summary, through the design of the connecting member included in the wave generator and the outer rotor motor of the present application, and in combination with the design of arranging the outer rotor motor in the accommodating space, the double rigid gear harmonic speed reducer of the present application can have a relatively thin overall thickness.

[0015] To further understand the features and technical content of this application, please refer to the following detailed description and drawings of this application. However, these descriptions and drawings are only used to illustrate this application and do not impose any limitations on the scope of protection of this application. Description of the Drawings

[0016] Figure 1 and Figure 2 are schematic diagrams of different perspectives of the double-rigid-ring harmonic reduction gear of this application respectively.

[0017] Figure 3 is Figure 1 a schematic cross-sectional view of the double-rigid-ring harmonic reduction gear of this application along the section line III-III.

[0018] Figure 4 is Figure 3 a partially enlarged schematic diagram.

[0019] Figures 5 to 9 are respectively partially disassembled schematic diagrams of the double-rigid-ring harmonic reduction gear of this application. Detailed Implementation Modes

[0020] In the following description, if specific drawings are pointed out or as shown in specific drawings, it is only used to emphasize that in the subsequent description, most of the relevant content mentioned appears in that specific drawing, but it does not limit that only that specific drawing can be referred to in the subsequent description.

[0021] Please refer to Figures 1 to 9 , Figure 1 and Figure 2 which are respectively schematic diagrams of different perspectives of the double-rigid-ring harmonic reduction gear of this application, Figure 3 is Figure 1 a schematic cross-sectional view of the double-rigid-ring harmonic reduction gear of this application along the section line III-III, Figure 4 is Figure 3 a partially enlarged schematic diagram, Figures 5 to 9 are respectively partially disassembled schematic diagrams of the double-rigid-ring harmonic reduction gear of this application.

[0022] As Figures 1 to 4 shown, the double-rigid-ring harmonic reduction gear 100 of this application includes a static rigid ring 1, a front cover 2, a dynamic rigid ring 3, a flexible gear 4, a wave generator 5 and a rear cover 6. The two opposite sides of the static rigid ring 1 are respectively defined as a front side 1A and a rear side 1B.

[0023] As Figure 7As shown, the static rigid gear 1 includes an annular body 11, an outer ring side wall 12, and a rigid gear body 13. An outer ring side wall 12 is formed on one side around the annular body 11. The annular body 11 has a plurality of mounting holes 111, and each mounting hole 111 penetrates through the annular body 11. The rigid gear body 13 is located on the side of the annular body 11 where the outer ring side wall 12 is formed. A plurality of first inner toothed structures 131 are formed on the inner side of the rigid gear body 13.

[0024] As Figure 8 and Figure 9 shown, the rear cover 6 includes an annular sheet body 61, a cylindrical structure 62, and a rear annular convex structure 63. The annular sheet body 61 has a perforation 611 that penetrates through the annular sheet body 61. A cylindrical structure 62 and a rear annular convex structure 63 are convexly formed on one side of the annular sheet body 61. The annular sheet body 61 can be fixed to the rear side 1B of the static rigid gear 1 by cooperating a plurality of screws Q with the plurality of mounting holes 111 of the annular body 11, and the annular sheet body 61 will shield the rear side 1B of the static rigid gear 1.

[0025] As Figure 8 and Figure 9 shown, the cylindrical structure 62 has a hollow channel 621, and one end of the hollow channel 621 communicates with the perforation 611. The rear annular convex structure 63 is disposed around the cylindrical structure 62. The rear annular convex structure 63 is along an axial direction (for example, along the direction of the axis AX shown Figure 3 ), and is less than the length of the cylindrical structure 62 along the axial direction.

[0026] As Figures 3 to 5 shown, the front cover 2 is fixed to the dynamic rigid gear 3 by a plurality of screws Q, and the front cover 2 and the dynamic rigid gear 3 are fixedly disposed on the front side 1A of the static rigid gear 1, and the dynamic rigid gear 3 is located between the front cover 2 and the rear cover 6. The front cover 2 includes an opening 21, and the inner diameter of the opening 21 is greater than the outer diameter of the cylindrical structure 62. The front cover 2 forms a front annular convex structure 22 around the opening 21.

[0027] A plurality of second inner toothed structures 31 are formed on the inner side of the dynamic rigid gear 3. The dynamic rigid gear 3 and the rigid gear body 13 of the static rigid gear 1 are also connected to a crossed roller bearing 9, and the crossed roller bearing 9 is located between the outer ring side wall 12 and the dynamic rigid gear 3 and the rigid gear body 13. In practical applications, the crossed roller bearing 9 can also be a four-point contact ball bearing.

[0028] As Figures 3 to 6As shown, the flexible gear 4 is disposed within the static rigid gear 1 and is located between the rear cover 6 and the front cover 2. The outer side of the flexible gear 4 has a plurality of first tooth-shaped structures 41 and a plurality of second tooth-shaped structures 42, and there is a groove 43 between the first tooth-shaped structures 41 and the second tooth-shaped structures 42. The plurality of first tooth-shaped structures 41 and the plurality of second tooth-shaped structures 42 are respectively used to mesh with a plurality of first inner tooth-shaped structures 131 of the static rigid gear 1 and a plurality of second inner tooth-shaped structures 31 of the dynamic rigid gear 3. Among them, the number of teeth of the first inner tooth-shaped structures 131 included in the static rigid gear 1 is the same as the number of teeth of the first tooth-shaped structures 41 included in the flexible gear 4, and the number of teeth of the second inner tooth-shaped structures 31 included in the dynamic rigid gear 3 is different from the number of teeth of the second tooth-shaped structures 42 included in the flexible gear 4.

[0029] As Figure 3 , Figure 4 , Figures 7 to 9 shown, the wave generator 5 includes: a flexible bearing 51, a connecting member 52, an outer rotor motor 53, a front bearing 54, and a rear bearing 55. The flexible bearing 51 is connected to the flexible gear 4. The connecting member 52 includes an annular bottom 521 and an annular wall 522. The annular bottom 521 has a plurality of mounting holes 5211, and the plurality of mounting holes 5211 are used to cooperate with a plurality of mounting members (such as screws Q) so that the outer rotor 531 is fixed to the annular bottom 521. The periphery of the annular bottom 521 extends to one side to form the annular wall 522, and the annular bottom 521 has a through hole 5212, and the through hole 5212 penetrates the annular bottom 521. The inner diameter of the through hole 5212 is greater than the outer diameter of the cylindrical structure 62, and the through hole 5212 can be sleeved on the outer side of the cylindrical structure 62. The annular wall 522 is pivotally connected to the front cover 2 and is pivotally connected to the rear cover 6. The connecting member 52 is connected to the flexible bearing 51, and the annular wall 522, the outer side of the cylindrical structure 62, and the annular sheet 61 together form an accommodation space SP1.

[0030] In practical applications, the front bearing 54 is located between the front annular convex structure 22 and the connecting member 52, and the connecting member 52 can rotate relative to the front cover 2 through the front bearing 54. The rear bearing 55 is located between the rear annular convex structure 63 and the annular wall 522, and the connecting member 52 can rotate relative to the rear cover 6 through the rear bearing 55.

[0031] An annular boss 5221 protrudes from the outer side of the annular wall 522 of the connecting member 52, and the thickness of the annular wall 522 at the annular boss 5221 is greater than the thickness at other positions. The inner diameter of the rear annular convex structure 63 is greater than the outer diameter of the annular boss 5221 of the annular wall 522 of the connecting member 52, and the inner diameter of the front annular convex structure 22 is greater than the outer diameter of the annular boss 5221 of the annular wall 522 of the connecting member 52.

[0032] As Figure 3 and Figure 4As shown, in the cross-sectional view of the double-rigid-ring harmonic speed reducer 100, the annular boss 5221 of the connecting member 52 generally presents a structure similar to a convex shape. The flexible bearing 51 is connected to the annular boss 5221, and the rear bearing 55 and the front bearing 54 are respectively located on both sides of the annular boss 5221. By designing the thickness of the annular boss 5221 to be greater than the thickness of the remaining positions of the connecting member 52, and in combination with the design of placing the rear bearing 55 and the front bearing 54 on both sides of the annular boss 5221, the annular boss 5221 can assist in restricting the movement range of the rear bearing 55 and the front bearing 54 in the axial direction.

[0033] As Figure 3 and Figure 4 shown, in the cross-sectional view of the double-rigid-ring harmonic speed reducer 100, the front bearing 54 is disposed between one side of the front annular protrusion structure 22 and the annular boss 5221 of the connecting member 52, and the rear bearing 55 is disposed between the other side of the rear annular protrusion structure 63 and the annular boss 5221 of the connecting member 52. The annular boss 5221 of the connecting member 52, the front annular protrusion structure 22, and the rear annular protrusion structure 63 are designed to jointly hold the front bearing 54 and the rear bearing 55.

[0034] The front bearing 54, the rear bearing 55, the annular boss 5221, the flexible bearing 51, the front annular protrusion structure 22, the rear annular protrusion structure 63, the front cover 2, the rear cover 6, the dynamic rigid ring 3, and the static rigid ring 1 jointly form a closed space SP2, and the closed space SP2 is not connected to the accommodation space SP1. In an alternative embodiment, the front bearing 54 can be a rubber-covered bearing, and the rubber-covered bearing can assist in closing the closed space SP2; the rear bearing 55 can also be a rubber-covered bearing, and the rubber-covered bearing can assist in blocking the communication between the closed space SP2 and the accommodation space SP1.

[0035] In practical applications, between the through hole 5212 (as Figure 8 shown) and the outer side of the cylindrical structure 62, an annular oil seal structure 7 is further provided, and the annular oil seal structure 7 is used to seal the gap between the through hole 5212 and the cylindrical structure 62. The rear bearing 55, the connecting member 52, the annular oil seal structure 7, and the rear cover 6 jointly seal the accommodation space SP1, so that the accommodation space SP1 is not connected to the closed space SP2. Since lubricating oil is provided in the closed space SP2, by designing the accommodation space SP1 and the closed space SP2 not to communicate with each other, it can effectively prevent the lubricating oil located in the accommodation space SP1 from flowing into the accommodation space SP1. If the lubricating oil flows into the accommodation space SP1, it may cause damage to the outer rotor motor 53.

[0036] In practical applications, the dual-rigid harmonic reduction device 100 may further include an outer annular oil seal structure 8, which is located between the outer ring side wall 12 and the outer side wall of the dynamic rigid wheel 3. The outer annular oil seal structure 8 is used to assist in sealing the closed space SP2 to prevent the lubricating oil in the closed space SP2 from leaving the closed space SP2.

[0037] like Figure 3 , Figures 7 to 9 As shown, the outer rotor motor 53 is disposed in the accommodation space SP1. The outer rotor motor 53 includes an outer rotor 531 and an inner stator 532. The outer rotor 531 and the connecting member 52 are fixed to each other, and the inner stator 532 and the rear cover 6 are fixed to each other. In one embodiment, the rear cover 6 may also include at least one outlet hole (not shown), which passes through the rear cover 6, and the outlet hole is used to provide the wires of the outer rotor motor 53 to pass through. The shape of the outlet hole and its setting position can be designed according to actual needs and are not limited here.

[0038] like Figures 1 to 3 As shown, the front cover 2 and the annular bottom 521 are located on one side of the dual-rigid harmonic reduction device 100, and the rear cover 6 is located on the other side of the dual-rigid harmonic reduction device 100. When the dual-rigid harmonic reduction device 100 is in operation, the dynamic rigid wheel 3 and the connecting member 52 located on the same side will rotate, while the rear cover 6 will be stationary. Therefore, by locating the wire outlet hole on the rear cover 6, the wires can be prevented from being caught in the rotating dynamic rigid wheel 3 or the connecting member 52.

[0039] In different embodiments, the outlet hole can also be generated in the cylindrical structure 62. Since the hollow channel 621 is used to provide wires for passing through, directly generating the outlet hole in the cylindrical structure 62 can facilitate the arrangement of wires by relevant personnel. In the example where the outlet hole is generated in the cylindrical structure 62, since no wires will pass through the rear cover 6, and the rear cover 6 will not rotate when the dual-rigid-wheel harmonic reduction device 100 is in operation, when the relevant personnel install the dual-rigid-wheel harmonic reduction device 100 in a device such as a robot arm, there is basically no need to reserve space around the rear cover 6. For this reason, it is convenient for relevant personnel to plan the installation position of the dual-rigid-wheel harmonic reduction device 100 in the robot arm.

[0040] like Figure 3 and Figure 4As shown, in one of the practical applications, the length from the outer side surface of the front cover 2 to the outer side surface of the rear cover 6 in the axial direction is defined as a total length 100L. The length 6L from the outer side surface of the rear cover 6 to the end face of the cylindrical structure 62 in the axial direction is not greater than the total length 100L. And the length 53L of the outer rotor motor 53 in the axial direction is less than the length of the annular wall 522 in the axial direction, and the length 522L of the annular wall 522 in the axial direction is less than the total length 100L. The outer rotor motor 53 is arranged in the connecting member 52 and is located between the front cover 2 and the rear cover 6. With such a design, the overall double-ring gear harmonic reduction device 100 can have a relatively small width (i.e., the total length 100L), so that the double-ring gear harmonic reduction device 100 can be better applied to various occasions, such as various mechanical arms with different sizes.

[0041] When the outer rotor motor 53 is driven, the outer rotor 531 will rotate relative to the inner stator 532, and the outer rotor 531 will drive the connecting member 52 to rotate. The connecting member 52 will drive the flexible bearing 51 to flexibly deform repeatedly. And a part of the plurality of first tooth-shaped structures 41 of the flexspline 4 will mesh with a part of the plurality of first inner tooth-shaped structures 131 of the static ring gear 1. Since the number of the first inner tooth-shaped structures 131 included in the static ring gear 1 is the same as the number of the first tooth-shaped structures 41 included in the flexspline 4, when the flexspline 4 flexibly deforms repeatedly, the flexspline 4 will not rotate relative to the static ring gear 1. And a part of the second tooth-shaped structures 42 of the flexspline 4 that flexibly deforms repeatedly will mesh with a part of the second inner tooth-shaped structures 31 of the dynamic ring gear 3. Since the number of the second tooth-shaped structures 42 included in the flexspline 4 is different from the number of the second inner tooth-shaped structures 31 of the dynamic ring gear 3, the dynamic ring gear 3 will be driven by the flexspline 4 that flexibly deforms repeatedly to rotate. Thus, the high-speed power input by the outer rotor motor 53 will be output by the dynamic ring gear 3 at a relatively low speed, achieving the purpose of speed reduction.

[0042] As described above, for the double-ring gear harmonic reduction device 100 of the present application, through the design of making the wave generator 5 include the connecting member 52 and the outer rotor motor 53, and cooperating with the design of the cylindrical structure 62 of the rear cover 6, etc., the wave generator 5 can be accommodated between the front cover 2 and the rear cover 6, so that the overall double-ring gear harmonic reduction device 100 can have a relatively thin thickness. That is to say, the double-ring gear harmonic reduction device 100 of the present application can meet the requirement of being thin.

[0043] It should be emphasized that in the existing double-rigid-wheel harmonic reducer, an inner-rotor motor is adopted. Therefore, it is difficult to reduce the overall thickness of the double-rigid-wheel harmonic reducer, and the requirement of thinning cannot be achieved. In addition, since there are interlocking relationships among the various components included in the double-rigid-wheel harmonic reducer, in practice, the inner-rotor motor cannot be directly modified into an outer-rotor motor. When attempting to modify the inner-rotor motor into an outer-rotor motor, it is necessary to redesign the interlocking relationships among all the components included in the double-rigid-wheel harmonic reducer in order to achieve the original function. During the process of redesigning the double-rigid-wheel harmonic reducer by relevant technical personnel, the relevant technical personnel will plan and design the interlocking relationships of the various components according to the target they want to connect (such as a robotic arm, a self-driving vehicle, etc.). Therefore, in practice, the installation positions and shapes of the various components may vary according to actual requirements.

[0044] Therefore, for those skilled in the art to which this case pertains, referring to the existing double-rigid-wheel harmonic reducer with an inner-rotor motor, unless there is a clear teaching or motivation, it is impossible for relevant technical personnel to think of modifying the inner-rotor motor into an outer-rotor motor. Because if the inner-rotor motor is to be modified into an outer-rotor motor, the entire double-rigid-wheel harmonic reducer must be redesigned. That is to say, for those skilled in the art, modifying a harmonic reduction device with an inner-rotor motor into an outer-rotor motor is not common knowledge, let alone a commonly used technical means. On the contrary, in the existing common double-rigid-wheel harmonic reducers, the design with an inner-rotor motor is the commonly used technical means.

[0045] The above are only optional and feasible embodiments of this application, and do not limit the patent scope of this application. Therefore, all equivalent technical changes made by using the content of the specification and drawings of this application are included in the protection scope of this application.

Claims

1. A double rigid wheel harmonic reduction device, characterized in that: The double rigid wheel harmonic reduction device comprises: a static rigid wheel, wherein two opposite sides of the static rigid wheel are respectively defined as a front side and a rear side; A rear cover, comprising an annular sheet and a cylindrical structure, wherein one side of the annular sheet protrudes to form the cylindrical structure, the annular sheet has a through hole, the cylindrical structure has a hollow channel, one end of the hollow channel is connected to the through hole; the annular sheet is fixed to the rear side of the static rigid wheel; A front cover, fixedly disposed on the front side of the static rigid wheel, the front cover comprising an opening, the inner diameter of the opening being larger than the outer diameter of the cylindrical structure; A dynamic rigid wheel, which is fixed to the front cover, and the dynamic rigid wheel is located between the front cover and the rear cover; A flexible wheel is disposed between the rear cover and the front cover, and the static rigid wheel and the dynamic rigid wheel can mesh with the flexible wheel; A wave generator, including: a flexible bearing connected to the flexible wheel; and A connecting member, comprising an annular bottom and an annular wall, the periphery of the annular bottom extends to one side to form the annular wall, the annular bottom has a through hole, the through hole penetrates the annular bottom; the inner diameter of the through hole is greater than the outer diameter of the cylindrical structure, and the through hole can be sleeved on the outer side of the cylindrical structure; the annular wall is pivotally connected to the front cover, and the annular wall is pivotally connected to the rear cover, the connecting member is connected to the flexible bearing, and the annular wall, the outer side of the cylindrical structure and the annular sheet jointly form an accommodating space; an outer rotor motor, disposed in the accommodating space, the outer rotor motor comprising an outer rotor and an inner stator, the outer rotor and the connecting member are fixed to each other, and the inner stator and the rear cover are fixed to each other; Wherein, the wave generator is arranged around the cylindrical structure, and the hollow channel is arranged through the double rigid wheel harmonic reduction device, and the hollow channel is used to accommodate at least one wire; Among them, the length from the outer side surface of the front cover to the outer side surface of the rear cover along an axial direction is defined as a total length; the length of the outer rotor motor along the axial direction is smaller than the length of the annular wall along the axial direction, and the length of the annular wall along the axial direction is smaller than the total length.

2. The double rigid wheel harmonic reduction device according to claim 1, characterized in that: An annular oil seal structure is also provided between the through hole and the outer side of the cylindrical structure, and the annular oil seal structure is used to seal the gap between the through hole and the cylindrical structure.

3. The double rigid wheel harmonic reduction device according to claim 2, characterized in that: The rear cover also includes a rear annular protrusion structure, which is arranged around the cylindrical structure, and the inner diameter of the rear annular protrusion structure is larger than the outer diameter of the annular wall of the connecting member; the wave generator also includes a rear bearing, which is located between the rear annular protrusion structure and the annular wall, and the connecting member can rotate relative to the rear cover through the rear bearing; the rear bearing, the connecting member, the annular oil seal structure and the rear cover jointly close the accommodating space so that the accommodating space is not connected to the space where the flexible bearing is located.

4. The double rigid wheel harmonic reduction device according to claim 3, characterized in that: The front cover forms a front annular protrusion structure around the opening; the wave generator also includes a front bearing, which is located between the front annular protrusion structure and the connecting member, and the connecting member can rotate relative to the front cover through the front bearing.

5. The double rigid wheel harmonic reduction device according to claim 4, characterized in that: The outer side of the annular wall of the connecting member protrudes to form an annular boss, the thickness of the annular wall at the annular boss is greater than the thickness at other positions, the flexible bearing is connected to the annular boss, and the rear bearing and the front bearing are respectively located on both sides of the annular boss; the front bearing, the rear bearing, the annular boss, the flexible bearing, the front annular protrusion structure, the rear annular protrusion structure, the front cover, the rear cover, the dynamic rigid wheel and the static rigid wheel together form a closed space, and the closed space is not connected to the accommodating space.

6. The double rigid wheel harmonic reduction device according to claim 5, characterized in that: The static rigid wheel has an outer ring side wall, and the double rigid wheel harmonic reduction device also includes an outer ring oil seal structure, which is located between the outer ring side wall and the outer side wall of the dynamic rigid wheel, and is used to assist in closing the closed space.

7. The double rigid wheel harmonic reduction device according to claim 5, characterized in that: The front bearing is a rubber-covered bearing, and the rubber-covered bearing can assist in closing the closed space.

8. The double rigid wheel harmonic reduction device according to claim 5, characterized in that: The rear bearing is a rubber-covered bearing, and the rubber-covered bearing can assist in preventing the closed space and the accommodating space from being connected to each other.

9. The double rigid wheel harmonic reduction device according to claim 1, characterized in that: The annular bottom of the connecting member has a plurality of mounting holes, and the plurality of mounting holes are used to cooperate with a plurality of mounting members so as to fix the outer rotor and the annular bottom to each other.

10. The double rigid wheel harmonic reduction device according to claim 1, characterized in that: The front cover and the annular bottom are located on one side of the double-rigid harmonic reduction device, and the rear cover is located on the other side of the double-rigid harmonic reduction device; the rear cover or the cylindrical structure also includes at least one wire outlet hole, and the wire outlet hole is used to provide the wires of the outer rotor motor to pass through.

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