CN113803434A

CN113803434A - Harmonic speed reducer

Info

Publication number: CN113803434A
Application number: CN202111150127.8A
Authority: CN
Inventors: 李亮; 关蕴奇; 史正良; 胡文祥; 李业林; 马啸昌
Original assignee: Gree Green Refrigeration Technology Center Co Ltd of Zhuhai
Current assignee: Gree Green Refrigeration Technology Center Co Ltd of Zhuhai
Priority date: 2021-09-29
Filing date: 2021-09-29
Publication date: 2021-12-17
Anticipated expiration: 2041-09-29
Also published as: CN113803434B

Abstract

The present invention provides a harmonic speed reducer, including: first rigid wheel, first flexible wheel and first flexible bearing, first flexible wheel includes first gear section, first drum section and first flange section, the inner periphery of first rigid wheel is worn to locate by first gear section, first flexible bearing's periphery is located to first gear section cover simultaneously, be provided with first oblique ripple structure on the periphery wall and/or the inner perisporium of first drum section, first oblique ripple structure is the protruding structure of protrusion in the periphery wall and/or the inner perisporium of first drum section, or first oblique ripple structure is for sinking in the groove structure of the periphery wall and/or the inner perisporium of first drum section. According to the invention, a certain torsional stress can be borne through the deformation of the oblique ripple shape when the flexible gear runs, so that the elastic deformation of the cylinder wall of the flexible gear is reduced, the problem of fatigue fracture failure of the cylinder wall part of the flexible gear caused by bearing a larger torsional stress is solved, and the service life of the flexible gear is effectively prolonged.

Description

Harmonic speed reducer

Technical Field

The invention relates to the technical field of speed reducers, in particular to a harmonic speed reducer.

Background

The harmonic reducer is a device for realizing power transmission by controlling elastic deformation of a flexible gear by a wave generator, has the advantages of small volume, light weight, high precision and the like, and is widely applied to the fields of robots, aerospace, automobiles and the like. In the failure modes of the harmonic reducer, the fatigue failure of the flexible gear is the main failure mode, and is the most main reason for influencing the service life of the harmonic reducer.

In the operation process of the harmonic reducer, the flexible gear bears the effects of torsional stress besides deformation, and the cylinder wall part is the main failure part of the flexible gear.

The harmonic reducer in the prior art is researched and designed because the technical problems that the cylinder wall part of a flexible gear of a part is easy to generate fatigue fracture failure and the like exist in the operation process of the harmonic reducer.

Disclosure of Invention

Therefore, the invention aims to overcome the defect that the harmonic reducer in the prior art is easy to generate fatigue fracture failure at the cylinder wall part of a flexible gear of a part, thereby providing the harmonic reducer.

In order to solve the above problems, the present invention provides a harmonic reducer including:

first rigid wheel, first flexbile gear and first flexible bearing, first flexbile gear includes first gear section, first cylinder section and first flange section, first gear section is worn to locate the internal week of first rigid wheel, simultaneously first gear section cover is located first flexible bearing's periphery, be provided with first oblique ripple structure on the periphery wall of first cylinder section and/or the internal perisporium, first oblique ripple structure for protrusion in the protruding structure of the periphery wall of first cylinder section and/or the internal perisporium, or first oblique ripple structure for recess in the groove structure of the periphery wall of first cylinder section and/or the internal perisporium.

In some embodiments, the first cylindrical section includes a first adjoining section adjoining the first gear section and a second adjoining section adjoining the first flange section in an axial direction of the first flexspline, and the first helical corrugation includes a first end adjoining the first adjoining section and a second end adjoining the second adjoining section, the first end being offset from the second end in the axial direction.

In some embodiments, the first oblique wave structure is a plurality of first oblique wave structures, and the first oblique wave structures are arranged at intervals along the circumferential direction of the first cylinder segment, and the directions of the first oblique wave structures which are offset are all the same.

In some embodiments, the first angled corrugation structure is an arcuately extending structure including a first segment connected to the first end, a second segment connected to the second end, and a third segment connected between the first segment and the second segment.

In some embodiments, the first segment is an arc segment having a concave surface opposite the first end; the second section is an arc section, and the concave surface of the arc section is opposite to the second end; the third section is an arc section, and the concave surface of the arc section is opposite to the first end or opposite to the second end.

In some embodiments, the radius of curvature of the third section is greater than the radius of curvature of the first section, and the radius of curvature of the third section is greater than the radius of curvature of the second section; and/or the radius of curvature of the first section is equal to the radius of curvature of the second section.

In some embodiments, the junction between the first gear segment and the first cylinder segment is a circular arc transition; the connecting position between the first flange section and the first cylinder section is also in arc cambered surface transition.

In some embodiments, a tangential direction of each location on the first helical corrugation is perpendicular to a torsional stress experienced by the first flexspline during operation; and/or the presence of a gas in the gas,

and the included angle between the connecting line between the first end and the second end and the plane of the first flange section is 35-55 degrees.

In some embodiments, the flexible gear transmission device further comprises a first cam assembly and an input shaft, wherein the first cam assembly is arranged on the inner periphery of the first flexible bearing in a penetrating mode so as to drive the first flexible bearing to rotate, and the first flexible bearing drives the first flexible gear to rotate;

the first cam component comprises a first cam, a first ratchet wheel and a first pawl, the first ratchet wheel is sleeved on the input shaft, the first pawl is arranged on the first cam, and the tip end of the first pawl is matched with saw teeth on the periphery of the first ratchet wheel, so that the first cam is driven to rotate when the input shaft can only rotate towards one direction, and the first cam cannot be driven to rotate when the input shaft rotates towards the other direction.

In some embodiments, a direction of a line connecting the first end to the second end, which is a sub-direction in the circumferential direction, coincides with a rotational direction in which the first ratchet drives the first cam.

In some embodiments, the device further comprises a second cam assembly, a second rigid gear, a second flexible gear and a second flexible bearing, wherein the second cam assembly comprises a second cam, a second ratchet wheel and a second pawl, the second ratchet wheel is sleeved on the input shaft, the second pawl is arranged on the second cam, the tip of the second pawl is matched with saw teeth on the periphery of the second ratchet wheel, and a second oblique corrugated structure is further arranged on the second flexible gear;

the first ratchet wheel and the second ratchet wheel are arranged in opposite circumferential directions, so that the input shaft can only drive the first ratchet wheel to drive the first cam to rotate when rotating towards one direction, and can only drive the second ratchet wheel to drive the second cam to rotate when rotating towards the other direction.

The harmonic reducer provided by the invention has the following beneficial effects:

1. the invention provides a harmonic reducer, which is characterized in that a first oblique corrugated structure is arranged on the outer peripheral wall and/or the inner peripheral wall of a first cylindrical section of a first flexible gear, the first oblique corrugated structure is a protruding structure protruding out of the outer peripheral wall and/or the inner peripheral wall of the first cylindrical section, or the first oblique corrugated structure is a groove structure recessed in the outer peripheral wall and/or the inner peripheral wall of the first cylindrical section, so that certain torsional stress can be borne by the oblique corrugated shape during the operation of the flexible gear, the elastic deformation of the cylindrical wall of the flexible gear is further reduced, the problem of fatigue fracture failure of the cylindrical wall part of the flexible gear due to the bearing of larger torsional stress is solved, and the service life of the flexible gear is effectively prolonged.

2. The two flexible gear/rigid gear component structures are arranged on one input shaft, and are driven by one shaft to form a double-flexible gear/rigid gear component structure, each flexible gear rotates in one direction, and the running directions are opposite, so that the flexible gears only bear periodic torsional stress in one direction, the service life of the flexible gears is further prolonged, and the maintenance cost of the speed reducer is reduced.

Drawings

FIG. 1 is an exploded view of a harmonic reducer of the present invention;

FIG. 2 is an assembled cross-sectional structural view of the harmonic reducer of the present invention;

FIG. 3 is a structural view of a flexspline having a skewed wave configuration according to the present invention;

FIG. 3a is a partial enlarged view of portion A of FIG. 3;

FIG. 4 is a cam assembly block diagram of the present invention;

FIG. 5 is a three-dimensional schematic of a harmonic reducer of the present invention.

The reference numerals are represented as:

100. a first flexspline/rigid spline assembly; 110. a first rigid bearing; 120. a first rigid wheel; 130. a first flexspline; 131. a first gear segment; 132. a first cylindrical section; 132a, a first phase connection section; 132b, a second interfacing section; 133. a first flange section; 134. a first angled corrugation structure; 134a, a first end; 134b, a second end; 134c, first section; 134d, a second section; 134e, third section; 140. a first compliant bearing; 150. a first cam assembly; 151. a first ratchet wheel; 152. a first pawl; 153. a first cam; 200. a second flexspline assembly; 210. a second rigid bearing; 220. a second rigid wheel; 230. a second flexspline; 234. a second oblique corrugated structure; 240. a second compliant bearing; 250. a second cam assembly; 251. a second ratchet wheel; 252. a second pawl; 253. a second cam; 300. an input end; 310. an input shaft; 320. a first pin; 330. a second pin.

Detailed Description

As shown in fig. 1 to 5, the present invention provides a harmonic reducer including:

first circular spline 120, first flexspline 130 and first flexible bearing 140, first flexspline 130 includes first gear section 131, first cylinder section 132 and first flange section 133, first gear section 131 wears to locate the internal week of first circular spline 120, simultaneously first gear section 131 cover is located first flexible bearing 140's periphery, be provided with first oblique ripple structure 134 on the periphery wall of first cylinder section 132 and/or the internal perisporium, first oblique ripple structure 134 for bulge in the protruding structure of the periphery wall of first cylinder section 132 and/or the internal perisporium, or first oblique ripple structure 134 for cave in the groove structure of the periphery wall of first cylinder section 132 and/or the internal perisporium.

The invention provides a harmonic reducer, which is characterized in that a first oblique corrugated structure is arranged on the outer peripheral wall and/or the inner peripheral wall of a first cylindrical section of a first flexible gear, the first oblique corrugated structure is a protruding structure protruding out of the outer peripheral wall and/or the inner peripheral wall of the first cylindrical section, or the first oblique corrugated structure is a groove structure recessed in the outer peripheral wall and/or the inner peripheral wall of the first cylindrical section, so that certain torsional stress can be borne by the oblique corrugated shape during the operation of the flexible gear, the elastic deformation of the cylindrical wall of the flexible gear is further reduced, the problem of fatigue fracture failure of the cylindrical wall part of the flexible gear due to the bearing of larger torsional stress is solved, and the service life of the flexible gear is effectively prolonged.

One of the core transmission parts of the robot is a harmonic reducer, which has the advantages of small volume, large reduction ratio, high transmission precision and the like. In the use process, a flexible gear serving as one of important parts of the harmonic reducer needs to be subjected to a large amount of torsional deformation and a large torsional stress during operation, and the flexible gear is often broken and fails. The invention solves the problem that the cylinder wall part of the flexible gear of a part is easy to generate fatigue fracture failure in the operation process of the harmonic reducer.

In view of the problems and deficiencies mentioned in the background above, the present invention is directed to a flexspline structure, wherein a cylinder wall of the flexspline has oblique corrugations, and the oblique corrugations can elastically deform when the flexspline is subjected to a torsional stress, so that the flexspline can be subjected to more stress strain, thereby prolonging a service life of a harmonic reducer.

The flexible gear section is connected with the input, the flexible gear flange section is connected with the output, when the flexible gear/rigid gear assembly operates and starts, the flexible gear can bear larger torsional stress, and the oblique corrugated structure of the cylinder section can release partial torsional stress through generating small deformation, so that the fatigue strength is improved, and the fatigue fracture failure is improved.

1. The oblique corrugation of the flexible gear is perpendicular or nearly perpendicular to the torsional stress borne by the flexible gear during operation, and the oblique corrugation can deform to bear a certain torsional stress, so that the elastic deformation of the cylinder wall of the flexible gear is reduced, and the service life of the flexible gear is prolonged.

2. The double-flexible wheel/rigid wheel assembly structure has the advantages that each flexible wheel rotates in one direction, the running directions are opposite, and the flexible wheels only bear periodic torsional stress in one direction, so that the service life of the flexible wheels is prolonged.

In some embodiments, in the axial direction of the first flexible gear 130, the first cylindrical section 132 includes a first connecting section 132a connected to the first gear section 131, and a second connecting section 132b connected to the first flange section 133, the first helical corrugation 134 includes a first end 134a connected to the first connecting section 132a, and a second end 134b connected to the second connecting section 132b, and the first end 134a is offset from the second end 134b in the axial direction. The oblique corrugated structure extends from the first connecting section to the second connecting section, the first end and the second end are offset in the axial direction, a structure capable of overcoming torsional stress along with rotation can be formed, the oblique corrugations of the flexible wheel are perpendicular or nearly perpendicular to the torsional stress borne by the flexible wheel during operation, a certain torsional stress can be borne through deformation of the oblique corrugations, elastic deformation of the cylinder wall of the flexible wheel is reduced, and the service life of the flexible wheel is prolonged.

In some embodiments, the first oblique wave structure 134 is a plurality of first oblique wave structures 134, and the first oblique wave structures 134 are spaced apart along the circumferential direction of the first cylindrical segment 132, and the offset directions of the first oblique wave structures 134 are the same. The arrangement of the plurality of oblique corrugated structures and the consistent deviation direction can play a role in strengthening and overcoming the torsional stress when the flexible gear rotates, further reduce the elastic deformation of the flexible gear and reduce the fatigue failure caused by the torsional stress.

In some embodiments, the first angled corrugation 134 is an arc-extending structure including a first segment 134c, a second segment 134d and a third segment 134e, wherein the first segment 134c is connected to the first end 134a, the second segment 134d is connected to the second end 134b, and the third segment 134e is connected between the first segment 134c and the second segment 134 d. The inclined corrugated structure is a preferable structural form of the inclined corrugated structure, and the structure extending in the arc line can enable the inclined corrugated structure to be in smooth transition at each position, so that the stress concentration on the inclined corrugated structure can be further reduced, the stress can be further reduced, and the condition of fatigue fracture failure of the flexible gear can be prevented.

The invention provides an oblique corrugated flexible gear structure, which can bear the torsional stress in the flexible gear operation process by generating elastic deformation after the oblique corrugated structure is used, so that the service life of the flexible gear is prolonged as much as possible. Meanwhile, one harmonic reducer uses two oblique corrugated flexible gears, the running directions are opposite, each flexible gear only bears the torsional stress in one direction, the service life of the flexible gears is further prolonged, and the maintenance cost of the reducer is reduced. Because the flexspline is inclined under the torsional stress, the circular arc-shaped inclined corrugated structure can better play a role, so that stress concentration is prevented, and failure fracture is further prevented.

The flexible gear is made of an iron-based material, and the iron-based material is at least one of alloy structural steel, high-speed steel or stainless steel.

In some embodiments, the first segment 134c is an arc segment having a concave surface opposite the first end 134 a; the second segment 134d is an arc segment, and the concave surface of the arc segment is opposite to the second end 134 b; the third segment 134e is an arc segment, and the concave surface of the arc segment is opposite to the first end 134a or opposite to the second end 134 b. The first section extends from the first end to the outer peripheral wall and/or the inner peripheral wall of the flexible wheel, the middle section is the third section, and the second section extends to the position connected with the second end, so that the tangential direction of each position of the extending direction of the first oblique corrugated structure is perpendicular to the torsional stress as much as possible, the effect of reducing the torsional stress is further improved, and the effect of preventing the fatigue failure of the flexible wheel is improved.

In some embodiments, the radius of curvature of the third section 134e is greater than the radius of curvature of the first section 134c, and the radius of curvature of the third section 134e is greater than the radius of curvature of the second section 134 d; and/or the radius of curvature of the first segment 134c is equal to the radius of curvature of the second segment 134 d. The curvature radius of the third section is larger than that of the first section, the curvature radius of the third section is larger than that of the second section, a structural form consistent with the torsion direction of the flexible gear can be effectively formed, and partial torsion stress is released by generating micro deformation, so that the fatigue strength is improved, and the fatigue fracture failure is improved.

In some embodiments, the junction between the first gear segment 131 and the first cylindrical segment 132 is a circular arc transition; the connection position between the first flange section 133 and the first cylinder section 132 is also in arc-arc transition. The structure through circular arc transition can effectively avoid stress concentration to lead to failure fracture.

In some embodiments, the tangential direction of each position on the first oblique wave structure 134 is perpendicular to the torsional stress experienced by the first flexspline during operation; according to the invention, the tangential directions of all positions on the oblique corrugated structure are set to be perpendicular to the torsional stress of the flexible gear, so that the torsional stress can be resisted to the greatest extent through the deformation of the oblique corrugated structure, and the fatigue failure is reduced. And/or the presence of a gas in the gas,

an included angle between a connecting line between the first end 134a and the second end 134b and a plane of the first flange section 133 is 35-55 degrees. Preferably 45. The invention can further form the structural form of the oblique corrugated structure consistent with the torsion direction of the flexible gear by the means, and further release partial torsion stress by generating micro deformation, thereby improving the fatigue strength and improving the fatigue fracture failure.

In some embodiments, the device further comprises a first cam assembly 150 and an input shaft 310, wherein the first cam assembly 150 is disposed through an inner circumference of the first flexible bearing 140 to drive the first flexible bearing 140 to rotate, and the first flexible bearing 140 drives the first flexible gear 130 to rotate;

the first cam assembly 150 includes a first cam 153, a first ratchet wheel 151, and a first pawl 152, the first ratchet wheel 151 is sleeved on the input shaft 310, the first pawl 152 is disposed on the first cam 153, and a tip of the first pawl 152 is engaged with a serration on an outer circumference of the first ratchet wheel 151, so that the first cam 153 is driven to rotate when the input shaft 310 can only rotate in one direction, and the first cam 153 cannot be driven to rotate when the input shaft 310 rotates in the other direction.

The first cam assembly and the input shaft can provide power for driving the first flexible gear to rotate, the first cam assembly comprises a first cam, a first ratchet wheel and a first pawl, and the first cam assembly can ensure that the cam can be driven to rotate only when the input shaft rotates towards one direction, so that the flexible gear only bears periodic torsional stress in one direction, the service life of the flexible gear is further prolonged, and the maintenance cost of the speed reducer is reduced.

In some embodiments, a direction of a line connecting the first end 134a to the second end 134b is divided into a circumferential direction and a rotational direction in which the first ratchet 151 drives the first cam 153. The invention can further form the structural form of the oblique ripple structure consistent with the torsion direction of the flexible gear by the means, further improve the generation of micro deformation, and improve the reduced torsion stress, thereby improving the fatigue strength and the fatigue fracture failure.

In some embodiments, the present invention further comprises a second cam assembly 250, a second rigid gear 220, a second flexible gear 230, and a second flexible bearing 240, wherein the second cam assembly 250 comprises a second cam 253, a second ratchet 251, and a second pawl 252, the second ratchet 251 is sleeved on the input shaft 310, the second pawl 252 is disposed on the second cam 253, and a tip of the second pawl 252 is engaged with a sawtooth on an outer circumference of the second ratchet 251, and a second oblique corrugated structure 234 is further disposed on the second flexible gear 230; the structural form of the second oblique corrugated structure is the same as that of the first oblique corrugated structure.

The first ratchet wheel 151 and the second ratchet wheel 251 are arranged in opposite circumferential directions, so that the input shaft 310 can only drive the first ratchet wheel 151 to rotate the first cam 153 when rotating in one direction, and can only drive the second ratchet wheel 251 to rotate the second cam 253 when rotating in the other direction.

The two flexible gear/rigid gear component structures are arranged on one input shaft, and are driven by one shaft to form a double-flexible gear/rigid gear component structure, each flexible gear rotates in one direction, and the running directions are opposite, so that the flexible gears only bear periodic torsional stress in one direction, the service life of the flexible gears is further prolonged, and the maintenance cost of the speed reducer is reduced. Two flexspline/rigid spline assemblies are mounted opposite each other on the input shaft to provide outputs in opposite directions.

At present, the harmonic reducer is not provided with an input shaft connected with two flexible wheel/rigid wheel assemblies, the two flexible wheel/rigid wheel assemblies cannot operate simultaneously, and the harmonic reducer has longer service life compared with the harmonic reducer provided with a single flexible wheel/rigid wheel assembly.

The flexspline all cooperates with flexible bearing, flexible bearing quantity is 2, and the shape is oval ring, and quantity is 2 because there are two flexspline rigid wheel subassemblies to need the cooperation.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention. The above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, several modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.

Claims

1. A harmonic reducer, characterized in that: the method comprises the following steps:

first rigid wheel (120), first flexbile gear (130) and first flexible bearing (140), first flexbile gear (130) includes first gear section (131), first cylinder section (132) and first flange section (133), first gear section (131) are worn to locate the internal week of first rigid wheel (120), simultaneously first gear section (131) cover is located the periphery of first flexible bearing (140), be provided with first oblique ripple structure (134) on the periphery wall of first cylinder section (132) and/or the internal perisporium, first oblique ripple structure (134) for protrusion in the protruding structure of the periphery wall of first cylinder section (132) and/or the internal perisporium, or first oblique ripple structure (134) for recess in the groove structure of the periphery wall of first cylinder section (132) and/or the internal perisporium.

2. The harmonic reducer of claim 1, wherein:

in an axial direction of the first flexspline (130), the first cylindrical section (132) includes a first connecting section (132a) connected to the first gear section (131) and a second connecting section (132b) connected to the first flange section (133), the first helical corrugation (134) includes a first end (134a) connected to the first connecting section (132a) and a second end (134b) connected to the second connecting section (132b), and the first end (134a) and the second end (134b) are offset in the axial direction.

3. The harmonic reducer of claim 2 wherein:

the first oblique corrugated structures (134) are arranged at intervals along the circumferential direction of the first cylindrical section (132), and the offset directions of the first oblique corrugated structures (134) are consistent.

4. A harmonic reducer according to claim 2 or 3 in which:

the first oblique corrugated structure (134) is an arc-extending structure and comprises a first section (134c), a second section (134d) and a third section (134e), wherein the first section (134c) is connected with the first end (134a), the second section (134d) is connected with the second end (134b), and the third section (134e) is connected between the first section (134c) and the second section (134 d).

5. The harmonic reducer of claim 4 wherein:

said first segment (134c) is an arc segment having a concave surface opposite said first end (134 a); the second section (134d) is an arc section, and the concave surface of the arc section is opposite to the second end (134 b); the third section (134e) is an arc segment, the concave surface of which is opposite to the first end (134a) or opposite to the second end (134 b).

6. The harmonic reducer of claim 4 wherein:

the radius of curvature of the third section (134e) is greater than the radius of curvature of the first section (134c), and the radius of curvature of the third section (134e) is greater than the radius of curvature of the second section (134 d); and/or the radius of curvature of the first segment (134c) is equal to the radius of curvature of the second segment (134 d).

7. The harmonic reducer of any one of claims 1-6 wherein:

the connection position between the first gear section (131) and the first cylinder section (132) is in arc surface transition; the connecting position between the first flange section (133) and the first cylinder section (132) is also in arc-arc surface transition.

8. The harmonic reducer of claim 2 wherein:

the tangential direction of each position on the first oblique corrugated structure (134) is vertical to the torsional stress borne by the first flexible gear during operation; and/or the presence of a gas in the gas,

an included angle between a connecting line between the first end (134a) and the second end (134b) and a plane of the first flange section (133) is 35-55 degrees.

9. The harmonic reducer of claim 2 wherein:

the first cam assembly (150) is arranged on the inner periphery of the first flexible bearing (140) in a penetrating mode to drive the first flexible bearing (140) to rotate, and the first flexible bearing (140) drives the first flexible gear (130) to rotate;

the first cam assembly (150) comprises a first cam (153), a first ratchet wheel (151) and a first pawl (152), the first ratchet wheel (151) is sleeved on the input shaft (310), the first pawl (152) is arranged on the first cam (153), and the tip of the first pawl (152) is matched with saw teeth on the periphery of the first ratchet wheel (151) so that the first cam (153) is driven to rotate when the input shaft (310) can only rotate towards one direction, and the first cam (153) cannot be driven to rotate when the input shaft (310) rotates towards the other direction.

10. The harmonic reducer of claim 9, wherein:

the direction of a connecting line from the first end (134a) to the second end (134b) in the circumferential direction is in accordance with the rotation direction of the first cam (153) driven by the first ratchet (151).

11. The harmonic reducer of claim 9, wherein:

the flexible gear mechanism is characterized by further comprising a second cam assembly (250), a second rigid gear (220), a second flexible gear (230) and a second flexible bearing (240), wherein the second cam assembly (250) comprises a second cam (253), a second ratchet wheel (251) and a second pawl (252), the second ratchet wheel (251) is sleeved on the input shaft (310), the second pawl (252) is arranged on the second cam (253), the tip end of the second pawl (252) is matched with saw teeth on the periphery of the second ratchet wheel (251), and a second oblique corrugated structure (234) is further arranged on the second flexible gear (230);

the first ratchet wheel (151) and the second ratchet wheel (251) are arranged in opposite circumferential directions, so that the input shaft (310) can only drive the first ratchet wheel (151) to drive the first cam (153) to rotate when rotating in one direction, and can only drive the second ratchet wheel (251) to drive the second cam (253) to rotate when rotating in the other direction.