Small series-connection variable-stiffness elastic driver based on differential gear train

Abstract

The invention discloses a differential gear train-based small series variable stiffness elastic driver, and belongs to the technical field of drivers, the differential gear train-based small series variable stiffness elastic driver comprises an input end cover, an output end cover and a shell, and two sides of the shell are respectively connected with the input end cover and the output end cover; a driving structure, a differential gear train structure, an elastic force transmission structure and a variable stiffness structure are arranged in the shell, a double-power-source structure is arranged on one side of the input end cover, the double-power-source structure is connected with the driving structure through the input end cover, the differential gear train structure is connected with the driving structure, the elastic force transmission structure is connected with the differential gear train structure, and the variable stiffness structure is connected with the double-power-source structure. And the variable stiffness structure is connected with the elastic force transmission structure and the output end cover. By the adoption of the structure, rigidity adjustment of the variable-rigidity adjusting structure and decoupling and accurate control of output displacement are achieved through differential control over the planet carrier and the sun gear in the differential gear train through the double-power-source structure.

Description

Technical Field

[0001] The present invention relates to the technical field of drivers, and in particular to a small series variable-rigidity elastic driver based on a differential gear train. Background Art

[0002] The rapid development of robotics has led to a growing number of robotic applications and increasingly complex environments. Joint actuators, as core components for robotic motion execution, have a direct impact on the robot's dynamic response, energy efficiency, environmental adaptability, and interactive safety. While traditional rigid actuators offer high precision and high load capacity, their rigidity can easily lead to energy accumulation during dynamic interactive tasks, resulting in decreased system stability and potential safety hazards. Series elastic actuators, by introducing a fixed-stiffness elastic element between the rigid drive motor and the load, enable the actuator to cushion the impact of the operating environment to protect the motor, store potential energy during cyclic motion for use by the robot, and release this stored potential energy in a very short period of time during explosive movements to achieve high acceleration. This significantly improves the system's compliance and safety, and to a certain extent enhances the robot's drive performance. However, series elastic actuators cannot dynamically adjust their stiffness to balance precise motion and smooth interaction.

[0003] The invention of the variable stiffness elastic actuator aims to solve the problem of the inability to adjust stiffness. However, existing variable stiffness elastic actuators have the following problems:

[0004] (1) The number of elastic elements is large, and a single group of antagonistically arranged springs is used, which results in low space utilization and a small adjustable stiffness range of the elastic actuator;

[0005] (2) The main stiffness adjustment methods are to use a cam mechanism with an Archimedean spiral groove, a ball screw mechanism, a planetary gear train mechanism with a diameter ratio of 2:1, etc. The cam mechanism with an Archimedean spiral groove is complicated to process, and the number of grooves on the cam plate is limited. When the number increases, the strength of the cam plate will be reduced, resulting in plastic deformation under heavy loads, affecting the stiffness adjustment accuracy; the ball screw mechanism occupies a large space, which is not conducive to the compact design of the drive, and has a slow response speed, which is not conducive to the rapid adjustment of stiffness; the planetary gear train mechanism with a diameter ratio of 2:1 has high requirements on the strength of the pivot fixed to the planetary gear, and there is also a hidden danger of insufficient strength under heavy loads, which in turn affects the stiffness adjustment accuracy. Summary of the Invention

[0006] The purpose of the present invention is to provide a small series variable stiffness elastic driver based on a differential gear train to solve the problems mentioned in the background art.

[0007] To achieve the above-mentioned objectives, the present invention provides a small series variable-stiffness elastic driver based on a differential gear train, comprising an input end cover, an output end cover and an outer shell, wherein the two sides of the outer shell are respectively connected to the input end cover and the output end cover, and a driving structure, a differential gear train structure, an elastic force transmission structure and a variable stiffness structure are arranged in the outer shell, a dual power source structure is arranged on one side of the input end cover, the dual power source structure is connected to the driving structure through the input end cover, the differential gear train structure is connected to the drive structure, the elastic force transmission structure is connected to the differential gear train structure, the variable stiffness structure is connected to the elastic force transmission structure, and the variable stiffness structure is connected to the output end cover.

[0008] Preferably, the driving structure includes a guide shaft, a spur gear I, a spur gear II, a spur gear III and a first internal gear. The guide shaft is rotatably connected to the input end cover through a bearing I, and the guide shaft is located at the center of the input end cover. The spur gear III is mounted on the guide shaft. The spur gear I and the spur gear II are both axially positioned by the input end cover. The spur gear III is meshed with the spur gear II, and the first internal gear is meshed with the spur gear I. The spur gear I is arranged on the inner side of the first internal gear, and the first internal gear is axially positioned by the input end cover. A planetary carrier assembly is fixedly connected to one side of the first internal gear. The guide shaft passes through the planetary carrier assembly and is connected to the planetary carrier assembly through the bearing assembly I.

[0009] Preferably, a bearing II is provided on the outside of the planetary carrier assembly, and the outer side of the bearing II is connected to the outer shell to ensure coaxiality. The planetary carrier assembly includes a planetary carrier I and a planetary carrier II fixedly connected to the planetary carrier I, the planetary carrier I is fixedly connected to the first internal gear, and the bearing assembly I includes a sleeve I and bearings III and IV arranged on both sides of the sleeve I.

[0010] Preferably, the differential gear system includes a second internal gear, and the second internal gear is provided with meshing planetary gears I, II, III and IV. A sun gear is provided between the planetary gears I, II, III and IV and meshes with the sun gear. The sun gear is sleeved on the guide shaft, and the planetary gears I, II, III and IV are connected to the planet carrier II through elastic retaining rings.

[0011] Preferably, the elastic torque conversion mechanism includes an output shaft arm, and the elastic torque conversion rod I and the elastic torque conversion rod II are symmetrically fixedly connected on both sides of the output shaft arm. The output shaft is fixedly connected to the output shaft at the center position of the output shaft arm, and the output shaft wall is arranged on one side of the second internal gear.

[0012] Preferably, the elastic force transmission structure includes a spring seat platform, which passes through the elastic torque conversion rod I, the elastic torque conversion rod II and the output shaft and is arranged on one side of the output shaft arm; a first linear guide and a second linear guide are symmetrically arranged on the spring seat platform; a first spring action slider and a second spring action slider are respectively connected to the first linear guide and the second linear guide; a first spring stop and a second spring stop are arranged on both sides of the first spring action slider; a first spring is arranged between the first spring action slider and the first spring stop; a second spring is arranged between the first spring action slider and the second spring stop; a third spring stop and a fourth spring stop are arranged on both sides of the second spring action slider; a third spring is arranged between the second spring action slider and the third spring stop; and a fourth spring is arranged between the second spring action slider and the fourth spring stop.

[0013] Preferably, the first spring stop, the second spring stop, the third spring stop and the fourth spring stop are all fixedly connected to the spring seat platform, the output shaft is connected to the spring seat platform through a bearing V, and the spring seat platform is connected to the planet carrier II through bolts.

[0014] Preferably, the variable stiffness structure includes a lever assembly and a crank slider assembly, the lever assembly includes a first lever and a second lever, one side of the first lever and the second lever are respectively connected to the elastic torque conversion rod I and the elastic torque conversion rod II via a circlip, and the other side is floatingly connected to the first spring action slider and the second spring action slider respectively;

[0015] The crank slider assembly includes a second internal gear and a common crank connecting block, a common crank, a first connecting rod, a second connecting rod and a common crank connecting block, the common crank and the common crank connecting block are fixedly connected, the common crank and the common crank connecting block are rotatably connected to the output shaft through a bearing assembly II, a first connecting plate and a second connecting plate are symmetrically arranged on the common crank connecting block, the first connecting plate and the second connecting plate are fixedly connected to the second internal gear and the common crank connecting block, the first connecting rod and the second connecting rod are connected to the common crank connecting block through a cotter pin, and the pivots in the first connecting rod and the second connecting rod are respectively placed in the first lever and the second lever.

[0016] Preferably, the second internal gear is fixedly connected to the common crank connecting block and the second internal gear, the bearing assembly II includes a sleeve II and bearings VI and VII arranged on both sides of the sleeve II, the bearing VI is connected to the common crank, the bearing VII is connected to the common crank connecting block, and a bearing VIII is provided on the outside of the common crank connecting block and is placed in the bearing seat of the output end cover.

[0017] Preferably, the dual power source structure includes a first power source and a second power source, the first power source includes a first motor and a first reducer connected to the first motor, the second power source includes a second motor and a second reducer connected to the second motor, and the output shafts of the first reducer and the second reducer pass through the input end cover and are respectively connected to the spur gear I and the spur gear II.

[0018] Therefore, the present invention adopts the above-mentioned small series variable stiffness elastic driver based on the differential gear train, which has the following beneficial effects:

[0019] (1) The dual-power source structure achieves decoupling and precise control of the stiffness adjustment and output displacement of the variable stiffness adjustment structure by controlling the differential speed of the planetary carrier and the sun gear in the differential gear system.

[0020] (2) A common crank is used to drive two connecting rods to control the fulcrum movement position of the two levers. Under the constraint of a small external size of the driver, the crank slider mechanism can make the mechanism composition simpler and the processing cost lower;

[0021] (3) Two sets of antagonistically arranged springs are symmetrically placed in the driver, which can improve the space utilization inside the driver and enable the driver to have a larger stiffness adjustment range in a smaller volume.

[0022] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 An exploded schematic diagram of the power transmission portion of a variable stiffness elastic actuator according to an embodiment of the present invention;

[0024] Figure 2 An exploded schematic diagram of the elastic force conversion portion of a variable stiffness elastic actuator according to an embodiment of the present invention;

[0025] Figure 3 This is an overall schematic diagram of a small series variable stiffness elastic actuator according to an embodiment of the present invention;

[0026] Reference numerals

[0027] 1. First motor; 2. First reducer; 3. Second motor; 4. Second reducer; 5. Input end cover; 6. Bearing I; 7. Spur gear I; 8. Spur gear III; 9. Spur gear II; 10. First internal gear; 11. Planet carrier I; 12. Bearing II; 13. Guide shaft; 14. Bearing III; 15. Bushing I; 16. Bearing IV; 17. Planet carrier II; 18. Second internal gear; 19. Planet gear I; 20. Planet gear II; 21. Planet gear III; 22. Planet gear IV; 23. Sun gear; 24. Connecting block between second internal gear and common crank; 25. Output shaft arm; 26. Elastic torque conversion rod I; 27. Elastic torque conversion rod II; 28. Spring seat platform; 29 , bearing V; 30, first linear guide; 31, second linear guide; 32, first spring; 33, second spring; 34, third spring; 35, fourth spring; 36, first spring stop; 37, second spring stop; 38, first spring-acting slider; 39, third spring stop; 40, fourth spring stop; 41, second spring-acting slider; 42, first lever; 43, second lever; 44, first connecting rod; 45, second connecting rod; 46, common crank; 47, bearing VI; 48, bushing II; 49, bearing VII; 50, output shaft; 51, common crank connecting block; 52, first connecting plate; 53, second connecting plate; 54, bearing VIII; 55, output end cover; 56, housing. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings herein can be arranged and designed in various different configurations. In the description of the present invention, it should be noted that the orientation or position relationship indicated by the terms "upper", "lower", "inside", "outside", etc. is based on the orientation or position relationship shown in the drawings, or is the orientation or position relationship in which the product of the invention is usually placed when in use. It is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0029] Example

[0030] Reference Figure 1-Figure 3The present invention discloses a small series variable-stiffness elastic actuator based on a differential gear train, comprising an input end cap 5, an output end cap 55, and a housing 56. The housing 56 is connected to the input end cap 5 and the output end cap 55 on both sides, respectively. The housing 56 houses a drive structure, a differential gear train structure, an elastic force transmission structure, and a variable-stiffness structure. A dual-power source structure is provided on one side of the input end cap 5. The dual-power source structure is connected to the drive structure via the input end cap 5, the differential gear train structure is connected to the drive structure, the elastic force transmission structure is connected to the differential gear train structure, the variable-stiffness structure is connected to the elastic force transmission structure, and the variable-stiffness structure is connected to the output end cap 55. The housing 56 ensures that all structures except the dual-power source structure are enclosed in a sealed environment, preventing dust and impurities from entering and affecting the actual operation of the actuator.

[0031] The drive structure includes a guide shaft 13, a spur gear I7, a spur gear II9, a spur gear III8, and a first internal gear 10. The guide shaft 13 is rotatably connected to the input end cap 5 via a bearing I6 and is located at the center of the input end cap 5. The spur gear III8 is sleeved on the guide shaft 13 and circumferentially positioned by a flat key. The spur gears I7 and II9 are both axially positioned by the input end cap 5. The spur gears III8 and II9 mesh with each other. The first internal gear 10 meshes with the spur gear I7. The spur gear I7 is disposed inside the first internal gear 10. The first internal gear 10 is axially positioned by the input end cap 5. A planetary carrier assembly is fixedly connected to one side of the first internal gear 10. The guide shaft 13 passes through the planetary carrier assembly and is connected to the planetary carrier assembly via the bearing assembly I.

[0032] The planetary carrier assembly is equipped with a bearing II12 on its outer side, which is connected to the outer shell 56 to ensure coaxiality. The planetary carrier assembly includes a planetary carrier I11 and a planetary carrier II17 fixedly connected to planetary carrier I11 by bolts. Planetary carrier I11 is also fixedly connected to the first internal gear 10 by bolts to ensure torque transmission. Bearing assembly I includes a sleeve I15 and bearings III14 and IV16 arranged on either side of sleeve I15. Bearing assembly I is axially positioned on the guide shaft 13 by a shoulder and a circlip. The dual-bearing configuration minimizes deflection of the guide shaft 13 and simultaneously ensures circumferential motion of planetary carrier I11 and planetary carrier II17.

[0033] The differential gear system includes a second internal gear 18, inside which are arranged meshing planetary gears I19, II20, III21 and IV22. A sun gear 23 is arranged between the planetary gears I19, II20, III21 and IV22 and meshes with the sun gear 23. The sun gear 23 is connected to the guide shaft 13 through a flat key, a bolt and an elastic retaining ring. The planetary gears I19, II20, III21 and IV22 are connected to the four short shafts on the planet carrier II17 through elastic retaining rings.

[0034] The elastic torque conversion mechanism includes an output shaft arm 25, with elastic torque conversion rods I26 and II27 symmetrically fixedly connected on both sides of the output shaft arm 25. The output shaft arm 25 is fixedly connected to the output shaft 50 at its center. The output shaft wall 25 is located on one side of the second internal gear 18. The elastic torque conversion rods I26, II27, and output shaft 50 are all connected to the output shaft arm 25 by bolts.

[0035] The elastic force transmission structure includes a spring seat platform 28, which passes through the elastic torque conversion rod I26, the elastic torque conversion rod II27, and the output shaft 50 and is located on one side of the output shaft arm 25. The output shaft 50 is connected to the spring seat platform 28 via a bearing V29. The spring seat platform 28 is bolted to the four long shafts of the planetary carrier II17. A first linear guide 30 and a second linear guide 31 are fixedly bolted to the spring seat platform 28, and the first and second linear guides 30 and 31 are arranged symmetrically. A first spring action slider 38 and a second spring action slider 41 are connected to the first and second linear guides 30 and 31, respectively. Both the first linear guide 30 and the second linear guide 31 consist of a slide rail and a slider. The first spring-acting slider 38 and the second spring-acting slider 41 are fixedly connected to the sliders of the first linear guide 30 and the second linear guide 31 by bolts. A first spring stop 36 and a second spring stop 37 are provided on either side of the first spring-acting slider 38. A first spring 32 is provided between the first spring-acting slider 38 and the first spring stop 36, and a second spring 33 is provided between the first spring-acting slider 38 and the second spring stop 37. A third spring stop 39 and a fourth spring stop 40 are provided on either side of the second spring-acting slider 41. A third spring 34 is provided between the second spring-acting slider 41 and the third spring stop 39, and a fourth spring 35 is provided between the second spring-acting slider 41 and the fourth spring stop 40. The first spring 32 and the second spring 33 form a pair of antagonistically arranged springs, while the third spring 34 and the fourth spring 35 form another pair of antagonistically arranged springs. The maximum deformation of each spring is determined by the gap between the spring-acting slider and the end face of the spring stop. The first spring stop 36, the second spring stop 37, the third spring stop 39, and the fourth spring stop 40 are all bolted to the spring seat platform 28. To accommodate heavy loads, the working length of each set of springs is within a range of 0.3-0.7 of the maximum deformation length to ensure constant stiffness and reduce errors caused by possible stiffness variations in the compression springs.

[0036] The variable stiffness structure includes a lever assembly and a crank slider assembly. The lever assembly includes a first lever 42 and a second lever 43. One side of the first lever 42 and the second lever 53 are respectively connected to the elastic torque conversion rod I26 and the elastic torque conversion rod II27 through a retaining spring, and the other side is floatingly connected to the first spring action slider 38 and the second spring action slider 41, respectively, and is responsible for converting the elastic torque generated by the spring into the torque of the output shaft.

[0037] The slider crank assembly includes a second internal gear and common crank connecting block 24, a common crank 46, a first connecting rod 44, a second connecting rod 45, and a common crank connecting block 51. The second internal gear and common crank connecting block 24 are fixedly connected to the second internal gear 18, the common crank 46 is fixedly connected to the common crank connecting block 51, and the common crank 46 and the common crank connecting block 51 are rotationally connected to the output shaft 50 via a bearing assembly II. A first connecting plate 52 and a second connecting plate 53 are symmetrically provided on the common crank connecting block 51. The first connecting plate 52 and the second connecting plate 53 are respectively fixedly connected to the second internal gear and the common crank connecting block 24 to ensure accurate transmission of torque of the second internal gear 18. The first connecting rod 52 and the second connecting rod 53 are connected to the common crank connecting block 51 via a cotter pin, and the pivots in the first connecting rod 52 and the second connecting rod 53 are respectively placed in the first lever 42 and the second lever 43 to act as fulcrums.

[0038] It should be noted that the lever assembly of the present invention can be expanded from two to four according to needs. When a larger deflection angle is required, a two-lever solution is adopted; when a smaller deflection angle is required, a four-lever solution is adopted.

[0039] The bearing assembly II includes a sleeve II48 and bearings VI47 and VII49 arranged on both sides of the sleeve II48. The bearing VI47 is connected to the common crank 46, and the bearing VII49 is connected to the common crank connecting block 51. A bearing VIII54 is arranged on the outside of the common crank connecting block 51 and is placed in the bearing seat of the output end cover 55 to ensure coaxiality and axial positioning.

[0040] The dual power source structure includes a first power source and a second power source. The first power source includes a first motor 1 and a first reducer 2 connected to the first motor 1. The second power source includes a second motor 3 and a second reducer 4 connected to the second motor 3. The first reducer 2 and the second reducer 4 are fixedly connected to the input end cover 5 by bolts. The output shafts of the first reducer 2 and the second reducer 4 pass through the input end cover 5 and are respectively connected to the spur gear I7 and the spur gear II9.

[0041] Working principle: The variable stiffness elastic driver of the present invention is provided with two power flow transmission paths, and a displacement control mode and a stiffness control mode are provided based on the two power flow transmission paths.

[0042] The two power flow transfer paths include:

[0043] The first power flow transmission path includes: the first power source drives the spur gear I7 via a flat key, which drives the first internal gear 10 through internal meshing, thereby driving the planetary carrier assembly to rotate. The planetary carrier II17 is connected to the spring seat platform 28, achieving synchronous rotation of the spring seat platform 28. The second power flow transmission path includes: the second power source drives the spur gear II9 via a flat key, which in turn drives the spur gear III8 through external meshing, drives the sun gear 23 through the guide shaft 13, and then drives the second internal gear 18. The common crank is driven by the second internal gear and the common crank connecting block 24, the first connecting plate 52, the second connecting plate 53, and the common crank connecting block 51, thereby driving the first connecting rod 44 and the second connecting rod 45 to rotate, thereby controlling the position of the pivots on the first connecting rod 44 and the second connecting rod 45 in the first lever 42 and the second lever 43.

[0044] Displacement Control Mode: In this mode, the second power source must maintain the output shaft position, keeping the slider-crank mechanism stationary. This means the pivots on the first and second connecting rods 44 and 45 remain in the same position within the levers. The first power flow transmission path transfers the power of the first power source to the spring seat platform 28. During rotation, the spring seat platform 28 drives two sets of antagonistically arranged springs to respectively drive the first and second levers 42 and 43. These two levers deflect and rotate around the pivots on the first and second connecting rods 44 and 45, causing the other sides of the first and second levers 42 and 43 to drive the elastic torque conversion rods I26 and II27, respectively. This in turn drives the output shaft arm 25, and thus the output shaft 50, to rotate. Because the springs are not fully compressed, both sets of antagonistically arranged springs undergo a certain degree of compression during rotation, achieving flexible drive.

[0045] Stiffness Control Mode: In this mode, the output shaft of the first power source must be kept stationary, keeping the planetary carrier stationary, that is, the spring seat platform stationary. The second power flow transmission path transmits the power of the second power source to the common crank 46 through the variable stiffness mechanism. The common crank 46 drives the first connecting rod 44 and the second connecting rod 45 to rotate, causing the pivots on the first connecting rod 44 and the second connecting rod 45 to change their positions in the first lever 42 and the second lever 43. This in turn adjusts the lever arm ratio between the antagonistic spring group and the elastic torque conversion rod I26 and the elastic torque conversion rod II27 on the first lever 42 and the second lever 43, achieving different proportions of changing the elastic torque generated by the springs, that is, achieving stiffness control.

[0046] In addition, the driver achieves passive protection through two sets of antagonistically arranged springs. Specifically, the first power source composed of the first motor 1 and the first reducer 2, and the second power source composed of the second motor 3 and the second reducer 4 remain stationary (i.e., the driver output shaft moves to a specified position). If an external impact load acts on the output shaft 50, the output shaft 50 drives the output shaft arm 25, the elastic torque conversion rod I26, and the elastic torque conversion rod II27, which act on the first lever 42 and the second lever 43, respectively. The two levers deflect, respectively driving the first spring action slider 38 and the second spring action slider 41, and then acting on the first spring 32 and the second spring 33, the third spring 34 and the fourth spring 35, respectively, causing the springs to deform and absorb impact energy. Within the maximum deformation range of the springs, the two power sources are guaranteed not to be subjected to reverse loads, that is, the function of protecting the power source under impact loads is achieved.

[0047] Therefore, the present invention adopts the above-mentioned small series variable stiffness elastic driver based on the differential gear train, adopts two levers as elastic force transmission mechanisms and is simultaneously connected to the load, and utilizes two sets of antagonistically arranged springs to act on the spring load points of the two levers respectively, thereby increasing the adjustable stiffness range and improving the space utilization of the driver.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A small series variable stiffness elastic actuator based on a differential gear train, characterized by: It includes an input end cover, an output end cover and an outer shell, and the two sides of the outer shell are respectively connected to the input end cover and the output end cover. A driving structure, a differential gear train structure, an elastic force transmission structure and a variable stiffness structure are arranged in the outer shell. A dual power source structure is arranged on one side of the input end cover, and the dual power source structure is connected to the driving structure through the input end cover, the differential gear train structure is connected to the driving structure, the elastic force transmission structure is connected to the differential gear train structure, the variable stiffness structure is connected to the elastic force transmission structure, and the variable stiffness structure is connected to the output end cover.

2. A small series variable stiffness elastic actuator based on a differential gear train according to claim 1, characterized in that: The driving structure includes a guide shaft, a spur gear I, a spur gear II, a spur gear III and a first internal gear. The guide shaft is rotatably connected to the input end cover through a bearing I, and the guide shaft is located at the center of the input end cover. The spur gear III is installed on the guide shaft. The spur gear I and the spur gear II are both axially positioned by the input end cover. The spur gear III is meshed with the spur gear II, and the first internal gear is meshed with the spur gear I. The spur gear I is arranged on the inner side of the first internal gear, and the first internal gear is axially positioned by the input end cover. A planetary carrier assembly is fixedly connected to one side of the first internal gear. The guide shaft passes through the planetary carrier assembly and is connected to the planetary carrier assembly through the bearing assembly I.

3. A small series variable stiffness elastic actuator based on a differential gear train according to claim 2, characterized in that: A bearing II is provided on the outside of the planetary carrier assembly, and the outside of the bearing II is connected to the outer shell to ensure coaxiality. The planetary carrier assembly includes a planetary carrier I and a planetary carrier II fixedly connected to the planetary carrier I. The planetary carrier I is fixedly connected to the first internal gear. The bearing assembly I includes a sleeve I and bearings III and IV arranged on both sides of the sleeve I.

4. A small series variable stiffness elastic actuator based on a differential gear train according to claim 3, characterized in that: The differential gear system includes a second internal gear, and the second internal gear is provided with meshing planetary gears I, II, III and IV. A sun gear is provided between the planetary gears I, II, III and IV and meshes with the sun gear. The sun gear is sleeved on the guide shaft, and the planetary gears I, II, III and IV are connected to the planet carrier II through a circlip.

5. A small series variable stiffness elastic actuator based on a differential gear train according to claim 4, characterized in that: The elastic torque conversion mechanism includes an output shaft arm, and elastic torque conversion rods I and II are symmetrically fixedly connected on both sides of the output shaft arm. The output shaft is fixedly connected to the output shaft at the center position of the output shaft arm, and the output shaft wall is arranged on one side of the second internal gear.

6. A small series variable stiffness elastic actuator based on a differential gear train according to claim 5, characterized in that: The elastic force transmission structure includes a spring seat platform, which passes through the elastic torque conversion rod I, the elastic torque conversion rod II and the output shaft and is arranged on one side of the output shaft arm. A first linear guide and a second linear guide are symmetrically arranged on the spring seat platform. The first linear guide and the second linear guide are respectively connected to a first spring-action slider and a second spring-action slider. A first spring stop and a second spring stop are arranged on both sides of the first spring-action slider. A first spring is arranged between the first spring-action slider and the first spring stop. A second spring is arranged between the first spring-action slider and the second spring stop. A third spring stop and a fourth spring stop are arranged on both sides of the second spring-action slider. A third spring is arranged between the second spring-action slider and the third spring stop. A fourth spring is arranged between the second spring-action slider and the fourth spring stop.

7. A small series variable stiffness elastic actuator based on a differential gear train according to claim 6, characterized in that: The first spring stop, the second spring stop, the third spring stop and the fourth spring stop are all fixedly connected to the spring seat platform, the output shaft is connected to the spring seat platform via a bearing V, and the spring seat platform is connected to the planet carrier II via bolts.

8. A small series variable stiffness elastic actuator based on a differential gear train according to claim 7, characterized in that: The variable stiffness structure includes a lever assembly and a crank slider assembly, wherein the lever assembly includes a first lever and a second lever, wherein one side of the first lever and the second lever are respectively connected to the elastic torque conversion rod I and the elastic torque conversion rod II via a circlip, and the other side is respectively connected to the first spring action slider and the second spring action slider in a floating manner; The crank slider assembly includes a second internal gear and a common crank connecting block, a common crank, a first connecting rod, a second connecting rod and a common crank connecting block, the common crank and the common crank connecting block are fixedly connected, the common crank and the common crank connecting block are rotatably connected to the output shaft through a bearing assembly II, a first connecting plate and a second connecting plate are symmetrically arranged on the common crank connecting block, the first connecting plate and the second connecting plate are fixedly connected to the second internal gear and the common crank connecting block, the first connecting rod and the second connecting rod are connected to the common crank connecting block through a cotter pin, and the pivots in the first connecting rod and the second connecting rod are respectively placed in the first lever and the second lever.

9. A small series variable stiffness elastic actuator based on a differential gear train according to claim 8, characterized in that: The second internal gear is fixedly connected to the common crank connecting block and the second internal gear. The bearing assembly II includes a sleeve II and bearings VI and VII arranged on both sides of the sleeve II. The bearing VI is connected to the common crank, and the bearing VII is connected to the common crank connecting block. A bearing VIII is provided on the outside of the common crank connecting block and is placed in the bearing seat of the output end cover.

10. The small series variable stiffness elastic actuator based on a differential gear train according to claim 2, characterized in that: The dual power source structure includes a first power source and a second power source, the first power source includes a first motor and a first reducer connected to the first motor, the second power source includes a second motor and a second reducer connected to the second motor, the output shafts of the first reducer and the second reducer pass through the input end cover and are respectively connected to the spur gear I and the spur gear II.

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