Planetary gear reducer and robot joint

Abstract

The application discloses a planetary gear reducer and a robot joint, and the reducer comprises an input sun gear, a plurality of double planetary gears, an output inner gear ring and a fixed inner gear ring, the double planetary gears are distributed in the periphery of the input sun gear in a circumferential direction, each double planetary gear comprises a first planetary gear and a second planetary gear, the first planetary gear and the second planetary gear are coaxially arranged along the axial direction of the input end to the output end of the reducer, the number of teeth of the first planetary gear is different from that of the second planetary gear, and the input sun gear is engaged with the plurality of first planetary gears; the inner side of the output inner gear ring is engaged with the plurality of second planetary gears; and the inner side of the fixed inner gear ring is engaged with the plurality of first planetary gears. The two planetary gears of the double planetary gear are designed as a structure with a tooth difference, so that large transmission ratio transmission is realized while the structure is compact, and all gaps in the movement direction of the reducer are eliminated through the flexible support scheme of the two intersecting installations at the two ends of the double planetary gear.

Description

Technical Field

[0001] This invention belongs to the field of robot joint technology, specifically relating to a planetary gear reducer and a robot joint. Background Technology

[0002] The reducer is a core component of a robot joint, and its transmission performance significantly impacts the overall performance of the robot. Compared to traditional harmonic reducers, planetary gear reducers offer advantages such as high rigidity, high bidirectional transmission efficiency, and good reverse transmission performance. Compared to RV reducers, they are smaller and lighter. These advantages make planetary gear reducers particularly suitable for collaborative robots and rehabilitation robots with high requirements for human-robot interaction. However, traditional gear drives suffer from backlash, and gears enter a dead zone during reversal. Furthermore, due to the cumulative error in the transmission chain, planetary gear reducers have a larger transmission backlash, which not only reduces transmission accuracy but also increases the difficulty of high-precision position control. Therefore, the application of planetary gear reducers in precision transmission scenarios, especially in robot joints, still faces significant challenges.

[0003] Currently, methods for eliminating planetary gear backlash generally fall into two categories: First, using redundant transmission chains. For example, in patent CN110925409A, entitled "A Planetary Gear Elastic Backlash-Eliminating Reducer," a combination of fixed and floating internal gear rings is used, with the phase angle difference between the two internal gear rings ensuring backlash-free contact with both sides of the planetary gears. Second, adjusting the center distance eliminates backlash. For instance, in patent CN113757349A, entitled "A Planetary Transmission Device Containing a Variable Planetary Carrier System," an expansion-type flexible planetary carrier is used to reduce backlash by adjusting the center distance between the planetary gears and the internal gear ring. However, the first method requires adding redundant transmission chains to achieve backlash elimination, increasing the size and weight of the reducer. The second method only eliminates the backlash of the internal meshing pair, failing to address the backlash of both internal and external meshing, resulting in residual backlash.

[0004] How to provide a planetary gear reducer that simultaneously has a large transmission ratio, compact structure, and zero backlash is an urgent problem to be solved. Summary of the Invention

[0005] The main objective of this invention is to provide a planetary gear reducer that simultaneously features a large transmission ratio, a compact structure, and zero backlash characteristics, thereby overcoming the shortcomings of the prior art.

[0006] To achieve the aforementioned objective, the technical solution adopted by this invention includes: a planetary gear reducer, comprising:

[0007] Input the sun gear;

[0008] A plurality of double planetary gears are circumferentially distributed around the input sun gear. Each double planetary gear includes a first planetary gear and a second planetary gear. The first planetary gear and the second planetary gear are coaxially arranged along the axis from the input end to the output end of the reducer. The number of teeth of the first planetary gear is not equal to the number of teeth of the second planetary gear. The input sun gear meshes with all of the first planetary gears.

[0009] An output internal gear ring is located outside the double planetary gears and close to the output end of the reducer, and the inner side of the output internal gear ring meshes with several second planetary gears.

[0010] A fixed internal gear ring is located outside the double planetary gears and close to the input end of the reducer, and the inner side of the fixed internal gear ring meshes with several of the first planetary gears.

[0011] In a preferred embodiment, the transmission ratio of the planetary gear train backlash elimination device based on double-sided cross flexible support is:

[0012]

[0013] Where i is the transmission ratio, z s , z p1 , z p2 , z r , z g These represent the number of teeth in the input sun gear, the first planet gear, the second planet gear, the fixed internal gear ring, and the output internal gear ring, respectively.

[0014] In a preferred embodiment, the reducer further includes an output-end flexible planetary carrier and a fixed-end flexible planetary carrier. The output-end flexible planetary carrier and the fixed-end flexible planetary carrier are located at the two ends of the double planetary gear and are staggered and intersected in the circumferential direction, driving the second planetary gear and the first planetary gear on both sides to move in opposite directions in the circumferential direction, thereby eliminating the backlash in the double planetary gear transmission.

[0015] In a preferred embodiment, the output-end flexible planetary carrier includes an output-end central bearing housing and a plurality of output-end planetary bearing housings circumferentially distributed around the output-end central bearing housing, the same number as the second planetary gears. Each output-end central bearing housing has an output-end central bearing hole concentrically arranged with the input sun gear, and each output-end planetary bearing housing has an output-end bearing hole concentrically arranged with the second planetary gears. The fixed-end flexible planetary carrier includes a fixed-end central bearing housing and a plurality of fixed-end planetary bearing housings circumferentially distributed around the fixed-end central bearing housing, the same number as the first planetary gears. Each fixed-end central bearing housing has a fixed-end central bearing hole concentrically arranged with the input sun gear, and each fixed-end planetary bearing housing has a fixed-end bearing hole concentrically arranged with the first planetary gears.

[0016] In a preferred embodiment, the output-end flexible planetary carrier further includes at least one output-end adjustment component, each of which is disposed between two adjacent output-end planetary bearing seats and is used to adjust the angle between the two output-end planetary bearing seats, thereby driving the corresponding two second planetary gears to move in the circumferential direction; the fixed-end flexible planetary carrier further includes at least one fixed-end adjustment component, each of which is disposed between two adjacent fixed-end planetary bearing seats and is used to adjust the angle between the two fixed-end planetary bearing seats, thereby driving the corresponding two first planetary gears to move in the circumferential direction.

[0017] In a preferred embodiment, the output end adjustment assembly includes an output end adjustment bracket, an output end adjustment screw, and an output end preload spring. The output end adjustment bracket is located between two adjacent output end planetary bearing seats. The output end adjustment screw is radially installed inside the output end adjustment bracket. The output end preload spring is fitted onto the output end adjustment screw. By changing the radial connection depth of the output end adjustment screw within the output end adjustment bracket, the output end preload spring is compressed, thereby adjusting the angle between the two output end planetary bearing seats, and thus driving the corresponding two second planetary gears to move circumferentially. Alternatively, the output end adjustment assembly includes an output end adjustment bracket, an output end adjustment screw, and an output end preload spring. The fixed end adjustment bracket is located between two adjacent fixed end planetary bearing seats. The fixed end adjustment screw is radially installed inside the fixed end adjustment bracket. The fixed end preload spring is fitted onto the fixed end adjustment screw. By changing the radial connection depth of the fixed end adjustment screw within the fixed end adjustment bracket, the fixed end preload spring is compressed, thereby adjusting the angle between the two fixed end planetary bearing seats, and thus driving the corresponding two first planetary gears to move circumferentially.

[0018] In a preferred embodiment, an output end bearing coaxial with the corresponding second planetary gear is installed in each of the output end bearing holes, and a fixed end bearing coaxial with the corresponding first planetary gear is installed in each of the fixed end bearing holes.

[0019] In a preferred embodiment, both the output flexible planetary carrier and the fixed flexible planetary carrier are integrally molded.

[0020] In a preferred embodiment, the output end adjustment component and the output end flexible planetary carrier are integrally molded, and the fixed end adjustment component and the fixed end flexible planetary carrier are also integrally molded.

[0021] The present invention also discloses a robot joint comprising the aforementioned planetary gear reducer.

[0022] Compared with the prior art, the beneficial effects of the present invention are at least as follows:

[0023] 1. The present invention designs the two planetary gears of the double planetary gear set as having a tooth difference structure, so as to achieve a large transmission ratio while maintaining a compact structure.

[0024] 2. This invention uses two intersecting flexible support schemes at both ends of the double planetary gear set up so that the two ends of the double planetary gear receive circumferential elastic support forces in opposite directions, so that there is a small angle between the double planetary gear and the original axis within the gap range. This ensures that the two planetary gears of the double planetary gear keep in contact with the input sun gear, the fixed internal gear ring and the output internal gear ring in the front and rear rows at the same time. At the same time, the adjacent planetary gears generate shaft deflection angles in opposite directions, ensuring that the reducer can maintain a backlash-free meshing state in both forward and reverse rotation. All backlashes in the direction of motion can be eliminated by the deflection of a single double planetary gear.

[0025] 3. The double-sided planetary carrier support provided by the present invention improves the radial support stiffness of the planetary gears and improves the load conditions of the planetary gears. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a front view of the overall assembly structure of the planetary gear reducer according to one embodiment of the present invention;

[0028] Figure 2 This is a left view of the overall assembly structure of the planetary gear reducer according to one embodiment of the present invention;

[0029] Figure 3 This is an exploded view of the overall assembly structure of the planetary gear reducer according to one embodiment of the present invention;

[0030] Figure 4 This is a transmission principle diagram of a planetary gear reducer according to one embodiment of the present invention;

[0031] Figure 5 This is an assembly diagram of a fixed-end flexible planetary carrier according to one embodiment of the present invention;

[0032] Figure 6 This is a schematic diagram of the axle-side assembly of the flexible planetary carrier and the double planetary gears in one embodiment of the present invention;

[0033] Figure 7 This is a schematic diagram of the load on the double planetary gear under the double-sided cross flexible planetary carrier in one embodiment of the present invention;

[0034] Figure 8a , 8b This is an abstract schematic diagram illustrating the transmission gap elimination principle in one embodiment of the present invention, wherein... Figure 8a This is the initial state. Figure 8b It is in a gap-free state;

[0035] Figure label:

[0036] 1. Input sun gear; 2. Double planetary gears; 201. First planetary gear; 202. Second planetary gear; 3. Output internal gear ring; 4. Fixed internal gear ring; 50. Output end flexible planetary carrier; 501. Output end center bearing housing; 502. Output end planetary bearing housing; 503. Output end center bearing hole; 504. Output end bearing hole; 505. Output end bearing; 60. Fixed end flexible planetary carrier; 601. Fixed end center bearing housing; 602. Fixed end planetary bearing housing; 603. Fixed end center bearing hole; 604. Fixed end bearing hole; 605. Fixed end bearing; 70. Output end adjusting assembly; 80. Fixed end adjusting assembly; 801. Fixed end adjusting bracket; 802. Fixed end adjusting screw; 803. Fixed end preload spring; F 50 The elastic force F exerted by the flexible planetary carrier at the output end on the double planetary gears. 60 The elastic force applied by the fixed-end flexible planetary carrier to the double planetary gears. Detailed Implementation

[0037] The invention will be more fully understood through the following detailed description, which should be read in conjunction with the accompanying drawings. Detailed embodiments of the invention are disclosed herein; however, it should be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, the specific functional details disclosed herein should not be construed as limiting, but rather as the basis for the claims and as intended to teach those skilled in the art to employ the representative basis of the invention in different ways in any suitable detailed embodiment.

[0038] The planetary gear reducer and robot joint disclosed in this invention use two intersecting flexible planetary carriers at both ends of a double planetary gear set up. The deflection angle generated by the axis of the double planetary gear within the gap range drives the two planetary gears to deflect in opposite directions. All backlash in the direction of motion can be eliminated by relying on the deflection of a single double planetary gear.

[0039] Combination Figures 1-4 As shown in the embodiment of the present invention, a planetary gear reducer includes an input sun gear 1, a plurality of double planetary gears 2, an output internal gear ring 3, a fixed internal gear ring 4, an output flexible planetary carrier 50, and a fixed flexible planetary carrier 60.

[0040] In this embodiment, the input sun gear 1 is located at the innermost edge, and several double planetary gears 2 are evenly distributed around the input sun gear 1. In practice, the number of double planetary gears 2 can be 2n, where n is an integer greater than or equal to 1. In this embodiment, there are 4 double planetary gears 2, which are evenly distributed around the input sun gear 1.

[0041] Each double planetary gear 2 includes two planetary gears, defined as a first planetary gear 201 and a second planetary gear 202. The first planetary gear 201 and the second planetary gear 202 are arranged on the same axis along the axial direction (left and right direction in the figure) from the input end to the output end of the reducer, and the number of teeth of the first planetary gear 201 and the number of teeth of the second planetary gear 202 are not equal.

[0042] The output internal gear ring 3 is located outside the double planetary gear 2 and close to the output end of the reducer, and the inner side of the output internal gear ring 3 meshes with all four second planetary gears 202; the fixed internal gear ring 4 is located outside the double planetary gear 2 and close to the input end of the reducer, and the inner side of the fixed internal gear ring 4 meshes with all four first planetary gears 201, and all four first planetary gears 201 also mesh with the input sun gear 1.

[0043] In this embodiment of the invention, the transmission ratio of the planetary gear reducer is:

[0044]

[0045] Where i is the transmission ratio, zs , z p1 , z p2 , z r , z g These represent the number of teeth in the input sun gear 1, the first planetary gear 201, the second planetary gear 202, the fixed internal gear ring 4, and the output internal gear ring 3, respectively.

[0046] Preferably, the output-end flexible planetary carrier 50 and the fixed-end flexible planetary carrier 60 are respectively installed at both ends of the double planetary gear 2. Specifically, the output-end flexible planetary carrier 50 is installed at the output end of the planetary gear reducer, i.e., near the second planetary gear 202 of the double planetary gear 2, and the fixed-end flexible planetary carrier 60 is installed at the fixed end of the planetary gear reducer, i.e., near the first planetary gear 201 of the double planetary gear 2. In this embodiment, the output-end flexible planetary carrier 50 and the fixed-end flexible planetary carrier 60 have the same structure. Preferably, both the output-end flexible planetary carrier 50 and the fixed-end flexible planetary carrier 60 are integrally molded.

[0047] Specifically, the output-end flexible planetary carrier 50 includes an output-end central bearing seat 501 and a plurality of output-end planetary bearing seats 502 circumferentially distributed around the output-end central bearing seat 501, the same number as the second planetary gears 202. That is, in this embodiment, the number of output-end planetary bearing seats 502 is also four. An output-end central bearing hole 503 is formed within the output-end central bearing seat 501, concentrically and coaxially arranged with the input sun gear 1. Each output-end planetary bearing seat 502 has an output-end bearing hole 504 concentrically and coaxially arranged with the second planetary gear 202. An output-end bearing 505 is installed within each output-end bearing hole 504, and the output-end bearing 505 is also concentrically and coaxially arranged with the corresponding second planetary gear 202.

[0048] Similarly, such as Figure 5 As shown, the fixed-end flexible planetary carrier 60 includes a fixed-end central bearing seat 601 and a plurality of fixed-end planetary bearing seats 602 circumferentially distributed around the fixed-end central bearing seat 601, the same number as the first planetary gears 201. That is, in this embodiment, the number of fixed-end planetary bearing seats 602 is also four. A fixed-end central bearing hole 603 is formed within the fixed-end central bearing seat 601, concentrically and coaxially arranged with the input sun gear 1. Each fixed-end planetary bearing seat 602 has a fixed-end bearing hole 604 concentrically and coaxially arranged with the first planetary gear 201. A fixed-end bearing 605 is installed within each fixed-end bearing hole 604, and the fixed-end bearing 605 is also concentrically and coaxially arranged with the corresponding first planetary gear 201.

[0049] Since the above-mentioned output end flexible planetary carrier 50 and fixed end flexible planetary carrier 60 are respectively concentrically and coaxially arranged with the corresponding end second planetary gear 202 and first planetary gear 201, and the number of teeth of the first planetary gear 201 and the second planetary gear 202 are not equal, the output end flexible planetary carrier 50 and fixed end flexible planetary carrier 60 are staggered and cross-arranged in the circumferential direction.

[0050] Preferably, both the output-end flexible planetary carrier 50 and the fixed-end flexible planetary carrier 60 are provided with adjustment components. These adjustment components drive the second planetary gears 202 and the first planetary gears 201 on both sides to move in opposite directions circumferentially, thereby eliminating the backlash in the transmission of the double planetary gears 2. Specifically, the output-end flexible planetary carrier 50 includes at least one output-end adjustment component 70. In practice, the number of output-end adjustment components 70 can be n, where n is an integer greater than or equal to 1. In this embodiment, two output-end adjustment components 70 are provided, spaced apart between two adjacent output-end planetary bearing seats 502. For example, in this embodiment, there are four output-end planetary bearing seats 502, numbered 1 to 4 for ease of description. One of the two output-end adjustment components 70 is positioned between two adjacent output-end planetary bearing seats 502 numbered 1 and 2, and the other is positioned between two adjacent output-end planetary bearing seats 502 numbered 3 and 4, used to adjust the angle between the two output-end planetary bearing seats 502, thereby driving the corresponding two second planetary gears 202 to move circumferentially. Similarly, the fixed-end flexible planetary carrier 60 includes at least one fixed-end adjustment component 80. In practice, the number of fixed-end adjustment components 80 can be n, where n is an integer greater than or equal to 1. In this embodiment, the number of fixed-end adjustment components 80 is two, which are respectively arranged at intervals between two adjacent fixed-end planetary bearing seats 602. For example, in this embodiment, there are four fixed-end planetary bearing seats 602, which are numbered 1 to 4 for ease of description. One of the two fixed-end adjustment components 80 is arranged between two adjacent fixed-end planetary bearing seats 602 numbered 1 and 2, and the other is arranged between two adjacent fixed-end planetary bearing seats 602 numbered 3 and 4. It is used to adjust the angle between the two fixed-end planetary bearing seats 602, thereby driving the corresponding two first planetary gears 201 to move in the circumferential direction.

[0051] In this embodiment, the output end adjustment assembly 70 and the fixed end adjustment assembly 80 have the same structure. Specifically, the output end adjustment assembly 70 includes an output end adjustment bracket (not shown), an output end adjustment screw (not shown), and an output end preload spring (not shown). The output end adjustment bracket is located between two adjacent output end planetary bearing seats 502. The output end adjustment screw is radially installed inside the output end adjustment bracket, and the output end preload spring is fitted onto the output end adjustment screw. By changing the radial thread connection depth of the output end adjustment screw inside the output end adjustment bracket, the output end preload spring is compressed, further pushing the output end adjustment bracket to undergo elastic deformation. Under the constraint of the output end preload spring, the angle between the two output end planetary bearing seats 502 is adjusted, while the distance from the output end planetary bearing seat 502 to the output end central bearing seat 501 remains unchanged, thereby driving the corresponding two second planetary gears 202 to move circumferentially. Preferably, the output end adjustment assembly 70 and the output end flexible planetary carrier 50 are integrally molded.

[0052] The fixed-end adjustment assembly 80 includes a fixed-end adjustment bracket 801, a fixed-end adjustment screw 802, and a fixed-end preload spring 803. The fixed-end adjustment bracket 801 is located between two adjacent fixed-end planetary bearing seats 602. The fixed-end adjustment screw 802 is radially installed inside the fixed-end adjustment bracket 801. The fixed-end preload spring 803 is fitted onto the fixed-end adjustment screw 802. By changing the radial thread depth of the fixed-end adjustment screw 802 within the fixed-end adjustment bracket 801, the fixed-end preload spring 803 is compressed, further pushing the fixed-end adjustment bracket 801 to undergo elastic deformation. Under the constraint of the fixed-end preload spring 803, the angle between the two fixed-end planetary bearing seats 602 is adjusted, while the distance from the fixed-end planetary bearing seat 602 to the fixed-end center bearing seat 601 remains unchanged, thereby driving the corresponding two first planetary gears 201 to move circumferentially. Preferably, the fixed-end adjustment assembly 80 and the fixed-end flexible planetary carrier 60 are integrally molded.

[0053] The flexible planetary carrier 50 at the output end and the flexible planetary carrier 60 at the fixed end of the double planetary gear 2, as disclosed in this invention, are respectively installed at both ends in a staggered manner in the circumferential phase. According to the structural design of the adjustment assembly, its elastic deformation will generate a thrust along the tangential direction of the planetary gear reducer on the double planetary gear 2. Due to the staggered installation, the thrust generated by the flexible planetary carrier 50 at the output end and the flexible planetary carrier 60 at the fixed end are in opposite directions, namely elastic force F50 and elastic force F60, respectively, thereby forming a bending moment that causes the axis of the double planetary gear 2 to deflect.

[0054] By adopting the above structural design, the double planetary gear 2 is subjected to the thrust of the flexible planetary carrier installed on both sides in a cross pattern, such as... Figure 6 As shown. Furthermore, Figure 7The core principle of this invention for eliminating backlash is described. By utilizing the deflection angle generated by the axis of the double planetary gear 2 within the backlash range, the two planetary gears are driven to deflect in opposite directions circumferentially. The deflection of a single double planetary gear 2 is sufficient to eliminate all backlash in the direction of motion. Because the axes of adjacent double planetary gears 2 will generate deflection angles in opposite directions, even when the direction of motion of the reducer changes, it is ensured that one motion chain remains in a backlash-free meshing state. Figure 8a , 8b These are abstract schematic diagrams illustrating the transmission gap elimination principle in one embodiment of the present invention, wherein... Figure 8a This is the initial state. Figure 8b It is in the state of eliminating gaps.

[0055] The planetary gear reducer described in this embodiment can be used in various composite planetary gear systems, further improving the transmission accuracy of high-ratio planetary gear reducers. Furthermore, the planetary gear reducer can be applied in multiple fields. For example, in one application case, the planetary gear reducer can be used in the joint of a collaborative robot to improve the joint's bidirectional driving capability and force transmission while maintaining high positioning accuracy.

[0056] Correspondingly, the present invention also discloses a robot joint, including the aforementioned planetary gear reducer. The specific structure of the planetary gear reducer can be referred to the above description, and will not be repeated here.

[0057] This invention has the following advantages: 1. This invention designs the two planetary gears of the double planetary gear set with a tooth difference structure, achieving a large transmission ratio while maintaining a compact structure. 2. The double-sided cross-flexible support scheme provided by this invention ensures that the two ends of the double planetary gear set receive circumferential elastic support forces in opposite directions, creating a small angle between the gears and the original axis within the clearance range. This ensures that the two planetary gears of the double planetary gear set maintain contact with the input sun gear, the fixed internal gear ring, and the output internal gear ring in both the front and rear rows. Simultaneously, adjacent planetary gears generate shaft offset angles in opposite directions, ensuring a backlash-free meshing state in both forward and reverse rotation of the reducer. 3. The double-sided planetary carrier support provided by this invention improves the radial support stiffness of the planetary gears and enhances their load-bearing capacity.

[0058] All aspects, embodiments, features, and examples of this invention are to be regarded as illustrative in all respects and are not intended to limit the invention, the scope of which is defined only by the claims. Other embodiments, modifications, and uses will become apparent to those skilled in the art without departing from the spirit and scope of the invention as claimed.

[0059] The use of headings and sections in this invention is not intended to limit the invention; each section can be applied to any aspect, embodiment or feature of the invention.

Claims

1. A planetary gear reducer, characterized in that, The speed reducer includes: Input the sun gear; A plurality of double planetary gears are circumferentially distributed around the input sun gear. Each double planetary gear includes a first planetary gear and a second planetary gear. The first planetary gear and the second planetary gear are coaxially arranged along the axis from the input end to the output end of the reducer. The number of teeth of the first planetary gear is not equal to the number of teeth of the second planetary gear. The input sun gear meshes with all of the first planetary gears. An output internal gear ring is located outside the double planetary gears and close to the output end of the reducer, and the inner side of the output internal gear ring meshes with several second planetary gears. A fixed internal gear ring is located outside the double planetary gears and close to the input end of the reducer, and the inner side of the fixed internal gear ring meshes with several of the first planetary gears; The reducer also includes an output flexible planetary carrier and a fixed flexible planetary carrier. The output flexible planetary carrier and the fixed flexible planetary carrier are located at the two ends of the double planetary gear and are staggered and intersected in the circumferential direction. This causes the second planetary gear and the first planetary gear on both sides to move in opposite directions in the circumferential direction, thereby forming a bending moment that causes the axis of the double planetary gear to deflect and eliminates the backlash of the double planetary gear transmission. The output-end flexible planetary carrier includes several output-end planetary bearing seats and at least one output-end adjustment component. Each output-end adjustment component is disposed between two adjacent output-end planetary bearing seats and is used to adjust the angle between the two output-end planetary bearing seats, thereby driving the corresponding two second planetary gears to move in the circumferential direction. The fixed-end flexible planetary carrier includes several fixed-end planetary bearing seats and at least one fixed-end adjustment component. Each fixed-end adjustment component is disposed between two adjacent fixed-end planetary bearing seats and is used to adjust the angle between the two fixed-end planetary bearing seats, thereby driving the corresponding two first planetary gears to move in the circumferential direction.

2. The planetary gear reducer according to claim 1, characterized in that: The transmission ratio of the planetary gear reducer is: ； in, The transmission ratio is... These represent the number of teeth in the input sun gear, the first planet gear, the second planet gear, the fixed internal gear ring, and the output internal gear ring, respectively.

3. A planetary gear reducer according to claim 1, characterized in that: The output-end flexible planetary carrier further includes an output-end central bearing housing. A plurality of output-end planetary bearing housings are circumferentially distributed around the output-end central bearing housing and are the same number as the second planetary gears. An output-end central bearing hole concentrically arranged with the input sun gear is formed within the output-end central bearing housing. Each output-end planetary bearing housing also has an output-end bearing hole concentrically arranged with the second planetary gear. The fixed-end flexible planetary carrier further includes a fixed-end central bearing housing. A plurality of fixed-end planetary bearing housings are circumferentially distributed around the fixed-end central bearing housing and are the same number as the first planetary gears. A fixed-end central bearing hole concentrically arranged with the input sun gear is formed within the fixed-end central bearing housing. Each fixed-end planetary bearing housing also has a fixed-end bearing hole concentrically arranged with the first planetary gear.

4. A planetary gear reducer according to claim 3, characterized in that: The output end adjustment assembly includes an output end adjustment bracket, an output end adjustment screw, and an output end preload spring. The output end adjustment bracket is located between two adjacent output end planetary bearing seats. The output end adjustment screw is radially installed inside the output end adjustment bracket. The output end preload spring is fitted onto the output end adjustment screw. By changing the radial connection depth of the output end adjustment screw within the output end adjustment bracket, the output end preload spring is compressed, thereby adjusting the angle between the two output end planetary bearing seats, and thus driving the corresponding two second planetary gears to move circumferentially. The fixed end adjustment assembly includes a fixed end adjustment bracket, a fixed end adjustment screw, and a fixed end preload spring. The fixed end adjustment bracket is located between two adjacent fixed end planetary bearing seats. The fixed end adjustment screw is radially installed inside the fixed end adjustment bracket. The fixed end preload spring is fitted onto the fixed end adjustment screw. By changing the radial connection depth of the fixed end adjustment screw within the fixed end adjustment bracket, the fixed end preload spring is compressed, thereby adjusting the angle between the two fixed end planetary bearing seats, and thus driving the corresponding two first planetary gears to move circumferentially.

5. A planetary gear reducer according to claim 3, characterized in that: An output end bearing coaxial with the corresponding second planetary gear is installed in each of the output end bearing holes, and a fixed end bearing coaxial with the corresponding first planetary gear is installed in each of the fixed end bearing holes.

6. A planetary gear reducer according to claim 1, characterized in that: Both the output-end flexible planetary carrier and the fixed-end flexible planetary carrier are integrally molded designs.

7. A planetary gear reducer according to claim 1, characterized in that: The output end adjustment component and the output end flexible planetary carrier are integrally molded, and the fixed end adjustment component and the fixed end flexible planetary carrier are also integrally molded.

8. A robot joint, characterized in that... Includes the planetary gear reducer as described in any one of claims 1-7.

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