Friction transmission speed reducer

Abstract

According to the friction transmission speed reducer, at least two stages of friction transmission assemblies are sequentially and coaxially arranged in a shell in a sleeved mode from inside to outside, each stage of assembly comprises a rotating inner ring, a fixed outer ring and a retainer, and a laminated cascade structure that the inner side retainer in every two adjacent stages drives the outer side inner ring is adopted; a connection mode that a first-stage inner ring is connected with a power source and a last-stage retainer is connected with an output component is matched, so that a traditional axial series connection layout is changed. The friction transmission speed reducer adopting the radial nesting design effectively solves the problem that the axial size of a multi-stage speed reducer is too long while keeping the characteristics of no return difference and low noise of friction transmission, greatly improves the space utilization rate, realizes the miniaturization effect of a large reduction ratio and extremely compact volume, and is suitable for large-scale popularization and application. And high-end precision transmission scenes with limited space, such as robot joints, are perfectly adapted.

Description

TECHNICAL FIELD

[0001] The present application relates to a speed reducer, in particular to a friction drive speed reducer. BACKGROUND

[0002] As a core component in mechanical transmission systems, precision speed reducers are widely used in industrial robot joints, aerospace equipment, precision medical devices, and high-end optical instruments. In these application scenarios, speed reducers are mainly used to reduce the high speed of power sources (such as motors) and increase the output torque to achieve precise control of the actuator. With the rapid development of intelligent manufacturing and micro-electromechanical systems, the market requirements for transmission devices are increasingly stringent, not only requiring high-precision transmission capability, smooth running characteristics, and low noise levels, but also urgently needing to achieve high-performance power transmission in limited installation space, i.e., high requirements for miniaturization, lightweight, and high power density of speed reducers.

[0003] Current speed reduction transmission technologies mainly include gear transmission and friction transmission (traction transmission). Although traditional planetary gear reducers have strong load capacity, they are difficult to avoid backlash and vibration due to the side clearance of gear meshing, and have high noise at high speed, which makes it difficult to meet the demand for ultra-precision smooth transmission. In contrast, friction transmission based on rolling contact uses friction between contact surfaces to transmit torque, with significant advantages such as no backlash, smooth operation, overload slip protection, and low noise. However, the reduction ratio provided by single-stage friction transmission is usually small, and in order to obtain a larger reduction ratio, existing technologies usually use a multi-stage series connection. Traditional friction transmission components are usually arranged in series along the axial direction, or the components are independently set and connected through a shaft coupling. This structural layout results in an excessively long axial size and a bulky overall volume, and a loose structure.

[0004] However, in micro-sized application scenarios such as robot finger joints, miniature gimbals, or portable medical devices, there are strict limitations on space, requiring the speed reducer to provide a large reduction ratio to drive the load, while strictly limiting the axial length and radial volume of the speed reducer. Due to the structural layout of existing multi-stage friction transmission reducers, it is difficult to balance the contradiction between large reduction ratio and miniaturization: if the number of stages is increased to achieve a large reduction ratio, the volume and length will significantly increase, making it impossible to adapt to micro-sized spaces; if the volume is forcibly reduced, the reduction stages or load capacity are often sacrificed. Therefore, it is urgent to propose a new type of friction transmission speed reducer to solve the above problems. SUMMARY

[0005] The present application aims to provide a friction transmission speed reducer that not only ensures compact structure and improves space utilization, but also achieves a large reduction ratio in a very small volume.

[0006] The technical solution adopted by the present invention to solve the above problems is: a friction drive reducer, comprising: case; At least two stages of friction drive assemblies are coaxially sleeved within the housing from the inside out, with the innermost friction drive assembly being the first stage and the outermost friction drive assembly being the final stage; each stage of the friction drive assembly includes: The inner ring that rotates with the input of power; The outer ring is fixedly connected to the housing; A cage located between the inner ring and the outer ring; A plurality of rolling elements are disposed on the cage, the rolling elements respectively engaging in rolling friction with the outer wall of the inner ring and the inner wall of the outer ring; Output components.

[0007] In the two adjacent stages of the friction drive assembly, the cage of the friction drive assembly located in the inner stage is connected to the inner ring of the friction drive assembly located in the outer stage, so that the revolution of the cage located in the inner stage serves as the rotation input of the inner ring located in the outer stage; and the inner ring of the first stage friction drive assembly is connected to the output end of an external power source, and the cage of the final stage friction drive assembly is connected to the output component.

[0008] Preferably, in the two adjacent stages of the friction drive assembly, the cage located at the inner stage is connected to the inner ring located at the outer stage via an annular connector; the annular connector extends radially outward, causing the inner ring located at the outer stage to rotate synchronously with the cage located at the inner stage.

[0009] Preferably, the outer surface of the inner ring of the friction transmission assembly located at the innermost level has two annular inner raceways symmetrically formed on a mid-plane that passes through the midpoint of its own axis and is perpendicular to its own axis. The cage located at the innermost level has two rows of symmetrically arranged rolling elements, which respectively cooperate with the two inner raceways. The outer ring of the friction transmission assembly located at the innermost level includes two symmetrically arranged split rings along the axis. The two split rings are located on both sides of the annular connector, and the inner walls of the two split rings are respectively formed with outer raceways that cooperate with the two rows of rolling elements.

[0010] Preferably, there is an axial gap between the two separate rings; one end of the annular connector is connected to the middle of the retainer located at the inner level, and the other end of the annular connector passes through the axial gap and is connected to the inner wall of the inner ring located at the outer level; the inner diameter of the inner ring located at the outer level is larger than the outer diameter of the outer ring located at the inner level, so as to form a stacked nested structure.

[0011] Preferably, in at least two stages of the friction drive assembly, the outer surface of the inner ring of each stage is symmetrically provided with two annular inner raceways; the cage of each stage of the friction drive assembly is provided with two rows of symmetrically arranged rolling elements; the outer ring of each stage of the friction drive assembly is composed of two symmetrically arranged split rings; each stage of the friction drive assembly is provided with a drive connecting member passing through the gap between the two split rings; wherein, the drive connecting member located in the inner stage is the annular connector, and one end of the drive connecting member located in the outermost final stage of the friction drive assembly is connected to the cage of the final stage of the friction drive assembly, and the other end is connected to the output component.

[0012] Preferably, the contact surfaces of the inner ring, the outer ring, and the rolling element are all smooth, continuous curved surfaces, and the torque is transmitted between each contact surface only through the contact friction force generated by the preload force; the friction drive reducer is configured such that when the load torque borne by the output component exceeds a preset safety threshold, the rolling element slips and spins freely in the inner raceway or the outer raceway.

[0013] Preferably, at least two stages of the friction drive assembly are configured radially from the inside out, with the maximum static friction torque that each stage of the friction drive assembly can transmit increasing progressively; and the preload and friction contact parameters of the last stage friction drive assembly are configured such that the maximum static friction torque of the last stage friction drive assembly is less than the product of the maximum static friction torque of the next inner stage friction drive assembly and the reduction ratio between the two stages, so that under overload conditions, the slippage of the rolling element relative to the raceway occurs in the last stage friction drive assembly before other stages of the friction drive assembly.

[0014] Preferably, the outer ring of each stage of the friction drive assembly is a stator component, and the side or end face of the outer ring of each stage of the friction drive assembly is connected to the housing through a heat-conducting medium, so that the outer ring, the heat-conducting medium and the housing together form a heat-conducting channel from the friction drive assembly to the housing.

[0015] Preferably, the friction drive reducer is a three-stage transmission structure, including a first-stage friction drive assembly, a second-stage friction drive assembly, and a third-stage friction drive assembly coaxially sleeved from the inside out; wherein, the first-stage friction drive assembly is the innermost friction drive assembly, the second-stage friction drive assembly is the outermost friction drive assembly relative to the first-stage friction drive assembly, and the second-stage friction drive assembly also serves as the innermost friction drive assembly relative to the third-stage friction drive assembly.

[0016] Preferably, the third-stage friction transmission assembly is the final-stage friction transmission assembly; the transmission connecting member of the third-stage friction transmission assembly is an output connector; one end of the output connector is connected to the cage of the third-stage friction transmission assembly, and the other end passes through the gap between the two separate rings of the third-stage friction transmission assembly and is connected to the output component.

[0017] The beneficial effects of the embodiments of the present invention are as follows: 1. By employing a technique that involves coaxially mounting at least two stages of friction transmission components from the inside out within the housing, and using a cage located on the innermost stage to drive the inner ring on the outermost stage for cascaded transmission, this technology changes the existing structural layout where multi-stage transmission components are typically arranged in series along the axial direction or connected by couplings. Therefore, it effectively solves the technical problem that existing multi-stage friction transmission reducers, due to their excessively long axial dimensions and loose structure, cannot achieve both a large reduction ratio and a compact size in miniaturized applications. This allows for a significant improvement in space utilization within extremely limited installation space through radial nesting. While maintaining the backlash-free and low-noise characteristics of friction transmission, it greatly reduces the axial length and overall volume of the reducer, resulting in a miniaturized reducer that combines a large reduction ratio, high power density, and an extremely compact structure. This makes it suitable for high-end precision transmission applications with extremely strict space constraints, such as robotic finger joints and micro medical devices.

[0018] 2. By employing a symmetrical transmission structure based on a double-track inner ring, a double-row ball bearing cage, and a split double outer ring in each stage of at least two stages of friction transmission components, and configuring connecting components that transmit power through the gap between the double outer rings, the system effectively solves the cantilever beam effect caused by unilateral input or output in existing conventional planetary transmission structures. This results in uneven load distribution on the cage, easy overturning moment, and uneven ball bearing. Furthermore, it achieves the structural advantage of using intermediate output and support on both sides, enabling the axial force and radial overturning moment of each stage of the cage to be self-balanced during torque transmission. This not only eliminates the vibration hazards under high-speed operation and ensures smooth operation at high speeds, but also significantly extends the service life of the reducer.

[0019] 3. By employing a technique that designs the contact surfaces of each stage of the components as smooth, continuous curved surfaces to achieve pure friction transmission, and precisely configures the preload and friction contact parameters of each stage based on multi-stage serial logic, and forces the maximum static friction torque of the final stage friction transmission component to be less than the product of the maximum static friction torque of its adjacent inner stage component and the reduction ratio between the two stages, the technical problem of existing high reduction ratio precision reducers being prone to destructive failures such as tooth breakage and flexible gear breakage when encountering unexpected overload, rigid impact, or output end jamming is effectively solved. This achieves the technical effect of non-destructive slippage and freewheeling of the rolling elements in the final stage component bearing the maximum shear force under overload conditions. This built-in safety clutch mechanism, naturally formed through structural parameter configuration, can automatically cut off power transmission to protect the internal transmission chain without adding extra components, thus giving the reducer a flexible impact resistance and extremely high safety in use, which is not available in traditional rigid gear transmissions.

[0020] 4. By employing a technique where the outer ring of each stage of the friction drive assembly is designed as a fixed, non-rotating stator component, and the side or end face of each outer ring is directly connected to the housing via a heat-conducting medium, a radial heat conduction channel is constructed from the inner friction drive assembly to the outer housing using all the outer rings and the housing. This effectively solves the technical problem of severe internal heat accumulation caused by concentrated heat generation at internal friction contact points, enclosed space, and difficulty in effectively dissipating heat through rotating components in existing compact multi-stage nested transmission devices. Furthermore, by utilizing the stator thermal bridge effect, an excellent radial passive heat dissipation path is provided for the deep nested structure without the need for a complex coolant circulation system. This allows the internally generated frictional heat to be rapidly conducted to the housing and dissipated, thus significantly improving the thermal stability and continuous high-load operation capability of the reducer within an extremely compact space. Attached Figure Description

[0021] Figure 1 A schematic cross-sectional view of a friction drive reducer according to an embodiment of the present invention is shown.

[0022] The components are: 1. Housing; 2. Friction transmission assembly; 210. Inner ring; 220. Outer ring; 230. Cage; 240. Rolling element; 3. Output component; 4. Annular connector; 5. Transmission connection component; 6. Heat transfer medium; 7. External power source; 710. Output shaft. Detailed Implementation

[0023] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0024] In the description of this application, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting the scope of protection of this application. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0025] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art will understand the specific meaning of the above terms in this application based on the specific circumstances.

[0026] Currently, friction drive reduction technology using rolling contact utilizes the friction between contact surfaces to transmit torque, offering significant advantages such as zero backlash, smooth operation, overload slippage protection, and low noise. However, the reduction ratio provided by a single-stage friction drive is typically small. To obtain a larger reduction ratio, existing technologies usually employ a multi-stage series approach, arranging each stage of the friction drive component 2 sequentially along the axial direction, or setting each stage of the component independently and connecting them via couplings.

[0027] However, this traditional structural layout is often unsuitable for miniaturized applications with extremely strict space constraints, such as robotic finger joints, miniature gimbals, or portable medical devices, which require the reducer to provide a huge reduction ratio to drive the load, while also strictly limiting the axial length and radial volume of the reducer.

[0028] Figure 1 A schematic cross-sectional view of a friction drive reducer according to an embodiment of the present invention is shown.

[0029] Therefore, in order to solve the above problems, a preferred embodiment of this application proposes a novel friction drive reducer. Please refer to [link to relevant documentation]. Figure 1The friction drive reducer includes a housing 1, at least two stages of friction drive assemblies 2 coaxially sleeved within the housing 1 from the inside out, and an output component 3. The innermost friction drive assembly 2 is the first-stage friction drive assembly 2, and the outermost friction drive assembly 2 is the final-stage friction drive assembly 2. Each stage of the friction drive assembly 2 includes an inner ring 210 that rotates with the power input, an outer ring 220 fixedly connected to the housing 1, a cage 230 located between the inner ring 210 and the outer ring 220, and a plurality of rolling elements 240 disposed on the cage 230. The rolling elements 240 respectively engage in rolling friction with the outer wall of the inner ring 210 and the inner wall of the outer ring 220. In the two adjacent stages of the friction transmission assembly 2, the retainer 230 of the friction transmission assembly 2 located on the inner stage is connected to the inner ring 210 of the friction transmission assembly 2 located on the outer stage, so that the revolution of the retainer 230 located on the inner stage serves as the rotation input of the inner ring 210 located on the outer stage; and the inner ring 210 of the first stage friction transmission assembly 2 is connected to the output end of the external power source 7, and the retainer 230 of the final stage friction transmission assembly 2 is connected to the output component 3.

[0030] Specifically: The housing 1, serving as the supporting foundation and external protective component of the entire reducer, is typically made of high-rigidity metal, providing a stable mounting reference for the internal components. Within the internal space of the housing 1, at least two stages of friction drive assemblies 2 are housed. This arrangement is not the traditional linear arrangement along the axial direction, but rather a layered structure where components are coaxially nested from the inside out. That is, the first-stage friction drive assembly 2 is located on the innermost side, the second stage surrounds the first stage, and so on, until the final stage friction drive assembly 2 is located on the outermost side. This interlocking nested layout makes excellent use of radial space.

[0031] Each stage of the friction transmission assembly 2 is structurally similar and includes the following core units: The inner ring 210 serves as the input element for this stage of transmission, and its outer surface is a smooth friction rolling surface.

[0032] The outer ring 220, as the stator element of this stage of transmission, also has a smooth friction rolling surface on its inner surface. Crucially, the outer ring 220 of each stage is fixedly connected to the housing 1 and remains stationary during the operation of the reducer.

[0033] The cage 230 is an annular member located between the inner ring 210 and the outer ring 220, serving as the output element of this stage of transmission.

[0034] Several rolling elements 240 (such as balls or rollers) are constrained on a cage 230 and distributed between an inner ring 210 and an outer ring 220. The rolling elements 240 form a tight rolling friction fit with the outer wall of the inner ring 210 and the inner wall of the outer ring 220, respectively (usually through an interference fit or a preload device to generate contact pressure).

[0035] In terms of the connection between each stage, this embodiment adopts a unique cascaded drive method. For two adjacent friction transmission components 2, the cage 230 located in the inner stage (i.e., the upper stage) is connected to the inner ring 210 located in the outer stage (i.e., the lower stage). This is a rigid power transmission connection, which allows the revolution motion of the inner stage cage 230 to be directly converted into the rotation input of the outer stage inner ring 210.

[0036] In terms of overall input and output, the inner ring 210 of the innermost first-stage friction transmission assembly 2 is connected to the external power source 7 (such as the output shaft 710 of a micro motor) to receive the original high-speed power. Meanwhile, the cage 230 of the outermost final-stage friction transmission assembly 2 is connected to the output component 3 to output the low-speed, high-torque power after final deceleration to the load.

[0037] The operation of this friction drive reducer is based on the principle of planetary friction drive, and the specific working process is as follows: When the external power source 7 is started, it drives the inner ring 210 of the first-stage friction transmission assembly 2 to start rotating at high speed.

[0038] The inner ring 210 of the first stage drives the first-stage rolling element 240 to rotate through friction. Since the outer ring 220 of the first stage is fixed to the housing 1, the rolling element 240, while rotating on its own axis, is forced to revolve along the annular track between the inner ring 210 and the outer ring 220. This revolve motion of the rolling element 240 drives the first-stage cage 230 to rotate accordingly. According to the principle of planetary transmission, the rotational speed of the cage 230 is much lower than that of the inner ring 210, thus achieving first-stage speed reduction.

[0039] The rotation of the first-stage cage 230 is directly transmitted to the inner ring 210 of the second-stage (outer first-stage) cage connected to it. At this time, the output speed of the first-stage cage 230 becomes the input speed of the second-stage inner ring 210.

[0040] The second-stage friction drive assembly 2 repeats the above process, using the fixed second-stage outer ring 220 to force the second-stage rolling element 240 to drive the second-stage cage 230 to rotate at a lower speed. If there are more stages, this process continues, with the speed gradually reduced and the torque gradually amplified through a nested structure. Finally, the cage 230 of the final-stage friction drive assembly 2 drives the output component 3 to rotate stably at the designed low speed, driving the external load.

[0041] The technical solution of this embodiment is particularly suitable for miniaturized applications with extreme space constraints and extremely high requirements for transmission accuracy and stability. These include, but are not limited to, dexterous hand joints of bionic robots, drive mechanisms for miniature optical gimbals, end effectors for portable medical surgical instruments, and miniature adjustment devices in the aerospace field. It is also suitable for applications requiring zero-backlash positioning, low-noise operation, and overload slippage protection. Due to the use of friction transmission, this device is more suitable for use in clean, oil-free (or enclosed) environments to ensure a stable coefficient of friction.

[0042] To adapt to different engineering needs, this technical solution offers a degree of flexibility: although the embodiment describes at least two stages, in actual manufacturing, it can be designed as a nested structure with two, three, or even more stages, depending on the required reduction ratio. The more stages, the greater the final output reduction ratio. The rolling element 240 can be selected from spherical balls, cylindrical rollers, or tapered rollers depending on the load-bearing capacity. Spherical balls are suitable for light-load, high-speed applications requiring flexible operation; rollers are suitable for applications with higher load-bearing requirements.

[0043] In this embodiment, by employing a technique of coaxially mounting at least two stages of friction transmission components 2 from the inside out within the housing 1, and using the retainer 230 located on the inner stage to drive the inner ring 210 located on the outer stage for cascaded transmission, the technical problem of excessively long axial dimensions and large volume caused by the axial series layout of multi-stage friction transmission reducers in the prior art, which makes them unsuitable for miniaturized applications, is effectively solved. Thus, without sacrificing the number of reduction stages and transmission performance, the axial length of the reducer is significantly reduced by making full use of the radial space, resulting in a miniature transmission device with an extremely compact structure, high power density, and both a large reduction ratio and high stability.

[0044] Furthermore, to achieve power transmission between the multi-stage friction transmission components 2, a dedicated annular connector 4 is provided between adjacent friction transmission components 2. This annular connector 4 serves as the core bridging component for inter-stage transmission, acting as a link between the stages. The retainer 230 located at the inner stage is connected to the inner ring 210 located at the outer stage via the annular connector 4; the annular connector 4 extends radially outward, causing the inner ring 210 located at the outer stage to rotate synchronously with the retainer 230 located at the inner stage.

[0045] Specifically, the annular connector 4 is located between the inner first-stage friction transmission assembly 2 and the outer first-stage friction transmission assembly 2. Structurally, one end of the annular connector 4 is firmly connected to the retainer 230 located in the inner first stage. The connection method can be mechanical fastening (such as bolt connection, riveting), interference fit or key connection, and even in some integrated designs, the annular connector 4 can be directly formed by the radial extension of the retainer 230 in the inner first stage, with the two being a single integral structure.

[0046] The other end of the annular connector 4 extends radially outward, spanning the interstage gap, and is fixedly connected to the inner wall or side of the inner ring 210 located at the outermost stage. Similarly, this connection must also ensure a rigid connection to prevent relative slippage.

[0047] Geometrically, the annular connector 4 is typically disc-shaped or spoked, and its material is usually a high-strength and high-rigidity metal (such as alloy steel or stainless steel) to withstand the torque transmitted between stages and prevent torsional deformation under load. This structure establishes a rigid drive chain consisting of the inner cage 230, the annular connector 4, and the outer inner ring 210.

[0048] This part operates according to the principle of rigid synchronous transmission. When the reducer is working, the power is transmitted through the preceding stage to the cage 230 located on the inner stage, causing it to carry the rolling elements 240 of that stage in a revolution motion. Since the annular connector 4 is fixedly connected to the inner stage cage 230, the annular connector 4 then follows the cage 230 in a coaxial and same-speed rotational motion.

[0049] As the annular connector 4 rotates, the driving torque is directly transmitted to the outermost stage because it extends radially outward and locks the inner ring 210 located at the outermost stage. At this time, the inner ring 210 located at the outermost stage is no longer a stationary component, but is forced to rotate along with the annular connector 4.

[0050] Throughout the process, the annular connector 4 acts as a rigid coupler, forcing the inner ring 210 located on the outer stage to rotate synchronously with the cage 230 located on the inner stage. That is, the output speed and direction of the inner cage 230 are completely equivalent to the input speed and direction of the inner ring 210 on the outer stage, realizing lossless (no speed ratio change) transmission of speed and torque between stages, and completing a smooth transition from the output of the previous stage to the input of the next stage.

[0051] In this embodiment, by employing an annular connector 4 extending radially outward between adjacent friction transmission components 2, and rigidly fixing the retainer 230 located on the inner stage to the inner ring 210 located on the outer stage, the technical problem of excessively long axial dimensions, loose structure, and large cumulative assembly errors caused by complex couplings or long shaft transmissions required for inter-stage connections in multi-stage reducers in the prior art is effectively solved. This achieves short-distance, high-rigidity direct transmission of power between stages, ensuring that the outer inner ring 210 rotates precisely and synchronously with the inner retainer 230. While greatly reducing the axial length of the reducer, the overall rigidity and transmission accuracy of the transmission chain are improved.

[0052] To further improve the stress stability and operating accuracy of the transmission system, in some embodiments, a double-row symmetrical layout is adopted in the friction transmission assembly 2 located at the inner level. The outer surface of the inner ring 210 of the friction transmission assembly 2 located at the inner level has two annular inner raceways symmetrically formed on a plane of symmetry passing through the midpoint of its own axis and perpendicular to its own axis. The cage 230 located at the inner level has two rows of symmetrically arranged rolling elements 240, which respectively engage with the two inner raceways. The outer ring 220 of the friction transmission assembly 2 located at the inner level includes two symmetrically arranged split rings along the axial direction. The two split rings are located on both sides of the annular connector 4, and the inner walls of the two split rings each have outer raceways corresponding to the two rows of rolling elements 240.

[0053] Specifically, the outer surface of the inner ring 210 is precision machined, and two annular inner raceways are precisely symmetrically formed on the midpoint of its own axis, which is perpendicular to its own axis. These two inner raceways are arranged in parallel, and their depth and radius of curvature are consistent.

[0054] To complement this, the cage 230 is also designed with two rows of symmetrically arranged rolling element holes to accommodate the two rows of rolling elements 240. These two rows of rolling elements 240 correspond one-to-one with the two inner raceways of the inner ring 210, ensuring that each row of rolling elements 240 can run accurately within its corresponding raceway.

[0055] Most importantly, the outer ring 220 of this friction transmission assembly 2 is not a traditional integral ring, but is designed to include two separate rings symmetrically arranged along the axial direction. These two separate rings are spatially independent but coaxially arranged, respectively on both sides of the annular connector 4. Each separate ring has an annular outer raceway on its inner wall, which corresponds to and mates with one of the two rows of rolling elements 240.

[0056] This structure naturally creates an axial gap between the two split rings, which is precisely reserved for the passage of the aforementioned annular connector 4. One end of the annular connector 4 is connected to the axial center of the cage 230 (i.e., between the two rows of rolling elements 240), and the other end extends outward through the gap between the two split rings.

[0057] During operation, when the power drives the inner ring 210 to rotate, the inner ring 210 simultaneously drives the two rows of rolling elements 240 through two inner raceways. Due to the high symmetry of the structure, the two rows of rolling elements 240 simultaneously undergo pure rolling friction motion between the inner raceway and the outer raceway.

[0058] At this point, the two rows of rolling elements 240 are respectively subjected to reaction forces from the two separate rings (stator), and these forces converge through the cage 230. Since the power output point (the connection root of the annular connector 4) is located on the geometric center plane of the cage 230, and the two rows of rolling elements 240 are located on both sides of the output point, the radial pressure and axial component force (if a contact angle exists) generated during the transmission process form a pair of balanced force systems on the cage 230.

[0059] When the cage 230 rotates carrying the annular connector 4, it is actually rotated between the two rows of rolling elements 240. The power is smoothly derived from the center of mass of the structure, rather than from one side end face.

[0060] This structure is particularly suitable for high-speed, high-load transmission environments that are extremely sensitive to vibration. It is also suitable for applications where traditional single-row bearings or single-sided output structures are prone to bearing wear or cage misalignment due to cantilever effects. It is especially suitable for robot joints or precision gimbals, scenarios requiring the reducer to maintain extremely high axial and radial stiffness during frequent starts, stops, and reversals.

[0061] In this embodiment, by employing the technical means of symmetrically opening double raceways on the surface of the inner ring 210, setting double rows of symmetrical rolling elements 240 on the cage 230, and configuring split double outer rings 220 on both sides of the annular connector 4, the technical problems of the conventional planetary transmission in the prior art caused by the "cantilever beam" effect due to unilateral input or output, the overturning moment caused by the uneven load on the cage 230, and the wear aggravated by uneven force on the balls are effectively solved. Thus, the self-balancing transmission effect of "central output and two-sided support" is achieved, so that the axial force and radial overturning moment of the cage 230 are perfectly balanced when transmitting torque. This not only eliminates the vibration risk at high speeds, but also significantly extends the service life of the reducer and improves the smoothness of operation.

[0062] Furthermore, to achieve a compact radial nested drive, the core design involves constructing a power transmission channel that can pass through the fixed stator (outer ring 220). In one embodiment, there is an axial gap between the two separate rings; one end of the annular connector 4 is connected to the middle of the cage 230 located at the inner level, and the other end of the annular connector 4 passes through the axial gap and is connected to the inner wall of the inner ring 210 located at the outer level; the inner diameter of the inner ring 210 located at the outer level is larger than the outer diameter of the outer ring 220 located at the inner level, to form a stacked nested structure.

[0063] Specifically, the stator portion of the friction drive assembly 2 located on the inner stage is not a continuously closed cylinder, but rather an assembly composed of two separate rings. These two separate rings are aligned axially during assembly, but a predetermined axial gap is reserved between their mating end faces. This axial gap is continuous in the circumferential direction, forming an annular open channel.

[0064] The annular connector 4, which is used in conjunction with the power output, is designed as a bridging component. One end of the annular connector 4 is fixedly connected to the middle position of the cage 230 located on the inner first stage (typically located on the center plane between the two rows of rolling elements 240). The body of the annular connector 4 extends radially outward, and its thickness is less than the width of the aforementioned axial gap, so that it can extend to the outside without interference through the axial gap.

[0065] In terms of external structure, the inner ring 210 of the outermost stage is arranged around the periphery of the innermost stage component. To achieve a nested structure, the inner diameter of the inner ring 210 of the outermost stage is designed to be larger than the maximum outer diameter of the stator (i.e., the outer ring 220) of the innermost stage. The other end of the annular connector 4, passing through the gap, is directly and rigidly connected to the inner wall of the inner ring 210 of the outermost stage. Thus, the innermost stage component is completely enclosed in the internal cavity of the outermost stage component, forming a compact ring-within-a-ring layout.

[0066] During the operation of the reducer, the inner stage retainer 230, which serves as the power output end of that stage, revolves. The annular connector 4, fixed in the middle of the retainer 230, rotates synchronously.

[0067] The key motion process occurs in the area where the annular connector 4 passes through the stator: although the two separate rings (outer ring 220) are fixed and connected to the housing 1, the rotating annular connector 4 can rotate freely within the gap without contacting the end face of the separate rings due to the reserved axial gap.

[0068] The annular connector 4 passing through the gap transmits torque to the inner ring 210 located on the outermost level. Due to the radial gap (formed by the diameter difference) between the outer inner ring 210 and the inner outer ring 220, the outer inner ring 210 can rotate independently around the stationary inner outer ring 220 with the support of the outer rolling element 240, thus completing the power relay transmission from the enclosed interior to the enclosing exterior.

[0069] In this embodiment, by employing a technique of reserving an axial gap between the two separate rings of the outer ring 220 and configuring an annular connector 4 with one end connected to the middle of the inner cage 230 and the other end passing through the gap to connect to the outer large-diameter inner ring 210, the technical problem of the planetary friction transmission structure in the prior art, where the power of the inner cage 230 is difficult to be directly exported radially outward due to the fixation of the outer ring 220, thus making it difficult to achieve multi-stage coaxial compact nesting, is effectively solved. This allows for the transmission of power between stages through a layered nesting method without increasing the axial length, greatly improving the space utilization and structural compactness of the reducer.

[0070] To ensure the consistency of force and system rigidity of the entire reducer during multi-stage transmission, in another embodiment, each stage of at least two stages of friction transmission assemblies 2 uniformly adopts a double-row symmetrical transmission architecture. The outer surface of the inner ring 210 of each stage of the at least two stages of the friction transmission assemblies 2 is symmetrically provided with two annular inner raceways; the cage 230 of each stage of the friction transmission assembly 2 is provided with two rows of symmetrically arranged rolling elements 240; the outer ring 220 of each stage of the friction transmission assembly 2 is composed of two symmetrically arranged split rings; each stage of the friction transmission assembly 2 is equipped with a transmission connecting member 5 passing through the gap between the two split rings; wherein, the transmission connecting member 5 located in the inner stage is the annular connector 4, and one end of the transmission connecting member 5 located in the outermost final stage of the friction transmission assembly 2 is connected to the cage 230 of the final stage of the friction transmission assembly 2, and the other end is connected to the output component 3.

[0071] Specifically, both the primary transmission assembly located on the inner side and the final transmission assembly located on the outermost side have two annular inner raceways on their outer surface, with the midpoint of their shaft length and perpendicular to their own axis as the symmetry reference. These two inner raceways are evenly distributed in the axial position and are responsible for bearing twice the contact load.

[0072] Correspondingly, each stage of the friction transmission assembly 2 also has two rows of symmetrically arranged rolling elements 240 on its cage 230. These two rows of rolling elements 240 correspond one-to-one with the two inner raceways of the inner ring 210, forming a double-support structure.

[0073] To accommodate this dual-row layout and facilitate power delivery, the outer ring 220 of each stage of the friction drive assembly 2 is designed to consist of two symmetrically arranged split rings. These two split rings are fixed to the housing 1 as stators, and a physical gap is reserved between their mating end faces for the transmission components to pass through.

[0074] Based on this, each stage of the friction drive assembly 2 is equipped with a drive connection member 5. This member is located at the axial center of the cage 230 and extends outward through the gap between the two split rings.

[0075] For the component located at the inner level, the transmission connection member 5 is specifically embodied as a ring connector 4, which connects to the inner ring 210 of the next level to realize inter-stage transmission.

[0076] For the outermost final stage friction drive assembly 2, the function of its transmission connection member 5 has changed. One end of this member is connected to the final stage retainer 230, and the other end passes through the gap of the final stage outer ring 220 and is directly rigidly connected to the output component 3 of the reducer (such as the output flange or output shaft 710), thereby guiding the final reduced torque to the outside of the reducer.

[0077] The working principle of this embodiment reflects the characteristics of full-level symmetry and center output.

[0078] As power is transmitted stage by stage, each stage of the friction drive assembly 2 follows the same mechanical behavior: the inner ring 210 drives the double-row rolling elements 240 to rotate, and the rolling elements 240 roll on the inner wall of the fixed split ring (outer ring 220), causing the cage 230 to revolve. Because each stage adopts a double-row symmetrical structure, the radial pressure and overturning moment generated during the transmission process are self-balanced on the cage 230 of each stage, and no stage exhibits a cantilever phenomenon with unilateral force.

[0079] For interstage transmission, the transmission connecting member 5 (annular connector 4) of the inner stage drives the next stage through the gap. For the final output, when power is transmitted to the last stage, the last stage cage 230 carries the last stage transmission connecting member 5 to rotate at a low speed. This member, like a bridge, passes through the gap of the last stage fixed outer ring 220, driving the output component 3 to rotate. This design cleverly solves the problem of how to bring the rotational motion deeply embedded inside the fixed housing to the outside in a structure where the outer ring 220 is fixed and the cage 230 outputs power.

[0080] The connection method between the final stage transmission connecting component 5 and the output component 3 can be flexibly designed according to load requirements. It can be a flange connection for easy installation of the robotic arm, or a keyway shaft connection for easy installation of gears or pulleys. In some designs, the final stage transmission connecting component 5 can be designed as an integral structure with the output component 3, passing directly through the gap of the final stage outer ring 220 as a single part, in order to improve the end output stiffness.

[0081] In this embodiment, by employing a symmetrical structure in which a double inner raceway, a double row of rolling elements 240, and a split double outer ring 220 are uniformly deployed in each stage of the friction transmission assembly 2, and by utilizing the transmission connection component 5 passing through the gap of the split outer ring 220 to realize the cascaded drive of the intermediate stage and the power output of the final stage, the technical problems of rigidity differences caused by the inconsistency of the structure of each stage in the existing multi-stage reducer, and the difficulty in smoothly exporting the power of the final stage under the fixed outer ring 220 structure, are effectively solved. This achieves self-balancing and uniformity of the force on the entire system, ensuring that each layer of the transmission chain from the input stage to the output stage has extremely high anti-overturning ability and smooth operation, and successfully achieves reliable output of large torque in a compact closed stator structure.

[0082] To achieve high safety and built-in overload protection in the transmission system, the contact interfaces and mechanical parameters of each stage of the friction transmission components 2 are specially configured in some embodiments. The contact surfaces of the inner ring 210, the outer ring 220, and the rolling element 240 are all smooth continuous curved surfaces, and torque is transmitted between the contact surfaces only through the contact friction force generated by the preload force. The friction transmission reducer is configured such that when the load torque borne by the output component 3 exceeds a preset safety threshold, the rolling element 240 slips and rotates freely in the inner raceway or the outer raceway. At least two stages of the friction drive assembly 2 are configured radially from the inside out, with the maximum static friction torque that each stage of the friction drive assembly 2 can transmit increasing progressively; and the preload and friction contact parameters of the last stage friction drive assembly 2 are configured such that the maximum static friction torque of the last stage friction drive assembly 2 is less than the product of the maximum static friction torque of the next inner stage friction drive assembly 2 and the reduction ratio between the two stages, so that under overload conditions, the slippage and freewheeling of the rolling element 240 relative to the raceway occurs in the last stage friction drive assembly 2 before the other stages of the friction drive assembly 2.

[0083] Structurally, all key components involved in the transmission, namely the inner ring 210, outer ring 220, and rolling elements 240, have their contact surfaces machined into smooth, continuous curved surfaces. This means that rigid meshing structures such as gears, keyways, or ratchet wheels are completely eliminated in the entire transmission chain. There is no mechanical interlocking between the contact surfaces; power transmission relies entirely on the preload generated between the components and the resulting contact friction (traction) at the contact points to transmit torque.

[0084] In the parameter configuration of multi-stage transmission, the reducer follows the design principle of progressively increasing load capacity radially from the inside to the outside. Since the reducer's speed decreases progressively while its torque amplifies progressively during operation, at least two stages of friction transmission components 2 are configured such that the maximum static friction torque (i.e., the limit torque before slippage) that each component can transmit increases radially from the inside to the outside. This is typically achieved by increasing the contact radius of the outer components, increasing the size of the rolling elements 240, or increasing the preload, to ensure that each stage can reliably transmit the amplified torque from the previous stage under normal operating conditions.

[0085] Under normal operating conditions, the frictional torque generated by the preload is greater than the load torque, and the components at each stage maintain a pure rolling state, achieving the predetermined reduction ratio transmission.

[0086] The core of this embodiment lies in the overload protection triggering logic. To ensure that the risk of damage is minimized in the event of an accidental impact or jamming, the system is configured to trigger a slippage mechanism when the load torque borne by the output component 3 exceeds a preset safety threshold.

[0087] The specific control logic is achieved through the special parameter configuration of the final stage friction transmission assembly 2. Although the final stage assembly has the largest absolute load-bearing capacity in the entire system, its preload and friction contact parameters (such as friction coefficient and contact pressure) are precisely adjusted to satisfy a specific mechanical inequality: the maximum static friction torque of the final stage friction transmission assembly 2 < (the maximum static friction torque of its adjacent inner stage friction transmission assembly 2 × the reduction ratio between the two stages).

[0088] This means that although the theoretical output capacity of the inner stage (amplified by the reduction ratio) is sufficient to drive a larger load, the final stage component is configured to be unable to transmit this full theoretical torque. Therefore, when the external load increases abnormally (such as in an overload condition), the friction interface of the final stage component will reach its limit first. At this time, the rolling element 240 will slip relative to each other in the inner or outer raceway of the final stage (slippage).

[0089] This embodiment effectively solves the technical problems of existing high reduction ratio reducers (such as gears) being prone to tooth breakage and lacking an intrinsic protection mechanism when subjected to overload or rigid impact at the output end. By designing all transmission contact surfaces as smooth continuous curved surfaces to achieve pure friction transmission, and configuring the maximum static friction torque of each stage to increase progressively from the inside to the outside, while forcibly setting the maximum static friction torque of the final stage component to be less than the theoretical driving torque amplified by the previous stage, this embodiment ensures that under overload conditions, slippage and idling will preferentially occur in the final stage transmission component that bears the maximum shear force. This naturally forms a non-destructive built-in safety clutch, which protects the precision transmission components inside the reducer from damage, as well as the external load and the safety of the operators, greatly improving the reliability and safety of the equipment.

[0090] It should be noted that in this embodiment, the inequality "maximum static friction torque of the final stage friction transmission assembly 2 < (maximum static friction torque of its immediately adjacent inner stage friction transmission assembly 2 × reduction ratio between the two stages)" ensures that the final stage (output stage) slips preferentially because it is based on the principle of torque amplification and the concept of equivalent torque conversion. Simply put, the essence of this inequality is: although the final stage itself is very strong, it is designed to be slightly weaker relative to the transmission capacity of the previous stage, thus making it the first part of the transmission chain to break down. Specifically, as follows: Torque transmission in multi-stage reduction gears. In a multi-stage reducer, power is transmitted from the input to the output, following the principle that as speed decreases, torque increases. Assumption: It represents the last level (the outermost level).

[0091] It represents the level immediately inside the last level (the penultimate level).

[0092] Represents the reduction ratio between two stages ( ).

[0093] According to the law of conservation of energy (ignoring minimal efficiency losses), if the previous level ( Output a torque Then it is passed to the last stage ( When this happens, the torque will be amplified. Times. That is: .

[0094] However, to determine which stage slips first, one cannot directly compare the absolute frictional torque values ​​of the two stages; instead, one must compare their ability to resist external loads. Therefore, all capabilities need to be uniformly converted to the same reference frame (usually the output shaft 710 side).

[0095] Suppose the output (final stage) suddenly freezes, or the load... Infinitely increase: For the final stage It directly bears the load. Its maximum resistance (threshold) is its own static friction torque: .

[0096] Slip condition A: When At that time, the final stage slipped.

[0097] For the previous level (Stage) It does not directly bear the burden. Instead, it is through the reduction ratio To exert an effect. Due to the torque amplification effect of the reducer ( Conversely, external load When the torque is transmitted back to the previous stage, it decreases. However, for ease of comparison, we magnify the "ability of the next higher level". Compare the projections to the output. The maximum support that the previous stage can provide is... After the reduction ratio After amplification, the load it can effectively withstand at the output is: .

[0098] Slippage condition B: When Only when the previous level can't hold on will it slip.

[0099] At this point, the final threshold is: .

[0100] The next higher equivalent threshold: .

[0101] When load Starting from 0 and gradually increasing (e.g., during overload or impact), it will first touch the threshold with the smaller value. To protect the internal structure, it is desirable for the last stage to slip first. That is, the threshold of the last stage must be lower than the equivalent threshold of the previous stage. Mathematically, this can be expressed as: .

[0102] This is the origin of the above inequality.

[0103] The physical essence of this inequality in this embodiment is the reverse application of the barrel effect (or shortest-plank protection design). Conventional design principles typically involve making components thicker and stronger towards the final stage, aiming for an indestructible final stage. However, the design approach in this embodiment ensures that while the final stage has a large physical size and high load-bearing capacity (large absolute value), its frictional torque is intentionally limited by adjusting the preload or friction coefficient, making it the safest link in the entire torque amplification chain relative to its theoretical load-bearing requirements. The underlying principle is that in the event of an overload, the overload energy is released at the very end of the transmission chain, preventing external impact forces from being transmitted back to the precision internal components (such as the high-speed bearings in the first and second stages), thus achieving protection.

[0104] To address the challenge of heat dissipation within multi-level nested structures, a highly efficient heat conduction system based on a full stator structure is constructed in some embodiments. The outer ring 220 of each stage of the friction drive assembly 2 is a stator component, and the side or end face of the outer ring 220 of each stage is connected to the housing 1 via a heat-conducting medium 6. This forms a heat conduction channel from the friction drive assembly 2 to the housing 1, through the outer ring 220, the heat-conducting medium 6, and the housing 1.

[0105] Specifically, in terms of structural layout, the outer ring 220 of each of the at least two-stage friction transmission components 2 is designed as a stator component. This means that whether it is the outer ring 220 of the first stage located in the deepest layer, or the outer ring 220 located in the middle layer or the outermost layer, it remains absolutely stationary relative to the housing 1 during the operation of the reducer and does not undergo rotational motion.

[0106] In order to establish an effective heat conduction path, the side (i.e. outer cylindrical surface) or end face of the outer ring 220 of each stage friction transmission component 2 is not simply suspended or fixed by point contact, but is tightly connected to the housing 1 or the fixed seat that is thermally connected to the housing 1 through a layer of heat-conducting medium 6.

[0107] The thermally conductive medium 6 here can be a physical entity or a filling material with high thermal conductivity. In some embodiments, the thermally conductive medium 6 is a thermally conductive silicone grease or a phase change thermally conductive pad coated between the contact surfaces to fill microscopic gaps; in other high-rigidity embodiments, the thermally conductive medium 6 is embodied as a metal contact layer formed by an interference fit, or a thermally conductive potting compound or thermally conductive metal ring specifically filled in the gap between the stator outer ring 220 and the inner wall of the housing 1 to enhance thermal conductivity.

[0108] Thus, the outer ring 220, the heat-conducting medium 6, and the shell 1 are physically closely fitted together, forming a radial heat-conducting channel that runs from the internal friction transmission components 2 to the external shell 1.

[0109] During operation, the friction drive reducer generates significant frictional heat due to high-pressure contact and microscopic slippage between the rolling elements 240 and the raceway. In a multi-stage nested structure, the innermost component is often the area with the highest heat concentration. This embodiment utilizes the stator thermal bridge effect. Since the outer rings 220 of each stage are non-rotating stators, they become stable heat sinks. When heat is generated internally, it is first conducted through the contact points to the outer rings 220 of each stage. Due to the low thermal resistance channel constructed by the heat-conducting medium 6 between the outer rings 220 and the housing 1, heat does not need to cross the rotating air gap but is directly conducted radially from the innermost outer ring 220 through the heat-conducting medium 6 to the housing 1, or layer by layer outwards (if there is contact between the outer rings 220). Ultimately, all the heat accumulated internally converges onto the housing 1, which has a larger surface area, and is dissipated through heat exchange between the surface of the housing 1 and the external environment (natural convection or forced air cooling). The entire process is a passive and continuous physical heat conduction process that does not require external power to drive it, and the heat conduction efficiency will automatically increase as the temperature difference increases.

[0110] This thermal management solution is particularly suitable for enclosed, high-power-density applications where it is difficult to implement active cooling systems. It is ideal for optical instrument drive units that are extremely sensitive to thermal deformation, ensuring uniformity of the internal temperature field of the reducer by rapidly dissipating heat and reducing accuracy drift caused by thermal stress. It is especially suitable for long-term continuous operation under heavy loads, preventing grease failure or metal adhesion due to internal heat buildup.

[0111] In this embodiment, by designing the outer ring 220 of each stage of friction transmission component 2 as a fixed, non-rotating stator component, and by using a heat-conducting medium 6 to tightly connect each stage of the outer ring 220 to the housing 1 to construct a radially direct heat conduction channel, the technical problem of existing compact multi-stage nested reducers, where the internal components are wrapped layer by layer, makes it difficult to dissipate heat and easily forms local high temperatures, thus affecting transmission accuracy and lifespan, is effectively solved. This achieves the technical effect of using the full stator structure as an efficient thermal bridge to rapidly conduct deep frictional heat radially to the outer housing 1, significantly improving the thermal stability and continuous load capacity of the miniaturized reducer without the need to add a complex liquid cooling or air cooling circulation system.

[0112] Based on the above embodiments, the technical solution of this application is not merely a simple superposition of multi-stage reduction structures, but rather an organic integration of a double-row symmetrical self-balancing structure, multi-stage friction series transmission, and a coaxial nested full stator layout, constructing a highly self-consistent system in terms of mechanical performance, space utilization, and thermodynamic stability. These three technologies combine to create a significant synergistic effect, producing a super-superposition effect that cannot be predicted by individual improvements in existing technologies. First, the mechanical synergy between the double-row symmetrical self-balancing structure and the multi-stage friction series transmission achieves high-precision zero-backlash transmission under large preload.

[0113] In existing technologies, friction drives require a large radial preload on the rolling contact surface to ensure high torque output without slippage. In conventional single-row or cantilever planetary structures, this large preload can cause the cage 230 and bearings to overturn and deform, resulting in severe uneven wear, which leads to a rapid decrease in transmission accuracy and a shortened lifespan.

[0114] In one of the above embodiments, a double-row symmetrical and intermediate drive design is introduced. By utilizing the two symmetrical raceways of the inner ring 210 and the split structure of the outer ring 220, the huge frictional preload is spatially decomposed into symmetrical couples.

[0115] This achieves the following technical effects: The enormous radial preload is symmetrically distributed between the two rows of balls, so that when the cage 230 transmits torque, the radial overturning moment it experiences cancels out each other, achieving zero deformation operation under high preload.

[0116] This synergistic effect allows the reducer to maintain the rotational accuracy of a double-row bearing even when subjected to extreme frictional torque, resolving the contradiction between high load and high precision that is difficult to achieve simultaneously in traditional friction drives.

[0117] Secondly, the combination of the double-row symmetrical self-balancing structure and the coaxial nested full stator layout achieves the ultimate power density without additional support.

[0118] In existing technologies, multi-stage coaxial nesting typically faces extremely complex concentricity maintenance issues. To prevent interference or runout between the multiple inner rings 210, existing technologies usually require the addition of independent thin-walled bearings as supports between each stage. This greatly wastes valuable radial space, leading to difficulties in miniaturization, i.e., the volume is small but the structural strength is insufficient.

[0119] The double-row symmetrical ball bearing arrangement essentially constitutes a high-rigidity double-row angular contact ball bearing. The above embodiment cleverly utilizes the transmission components themselves (balls and raceways) as support components, achieving integration of transmission and support.

[0120] This achieves the following technical effects: Because each level has self-centering and self-supporting functions, no additional auxiliary support bearings are needed when multiple levels are nested. Each level is directly suspended above the level above it and is extremely rigid.

[0121] This synergy results in almost no wasted space inside the reducer. With the same volume, the load-bearing capacity and reduction ratio of this application far exceed those of existing solutions that require additional bearings.

[0122] Furthermore, the synergy between multi-stage friction series transmission and coaxial nested full stator layout enables sustainable overload protection under deep nesting.

[0123] Existing technologies provide slippage protection, but frictional slippage generates a large amount of heat instantly. In a coaxial nested stator structure, the heat in the innermost layer is extremely difficult to dissipate. If slippage occurs, the accumulated heat can instantly cause the internal grease to fail or even lead to metal adhesion, turning the protection into destruction.

[0124] This application provides a direct heat conduction short-circuit channel for the frictional heat generation of multi-stage friction series drives by designing the outer ring 220 of the full stator in a coaxial nested full stator layout.

[0125] This achieves the following technical effects: All outer raceways (outer ring 220) that generate frictional heat are directly connected to housing 1. When the multi-stage friction series drive triggers overload protection (slippage) and generates instantaneous high heat, the heat does not need to cross the rotating air gap, but is radially discharged directly to housing 1 through a fixed metal path.

[0126] This thermal architecture ensures that overload protection is truly available in the deeply nested structure, avoiding the awkward situation of one-time protection due to overheating, and significantly improving the reliability of the equipment under extreme operating conditions.

[0127] In summary, the technical solution of this application is not a simple combination of three technical solutions: double-row symmetrical self-balancing structure, multi-stage friction series transmission, and coaxial nested full stator layout, but rather achieves this through: The geometric symmetry of the double-row symmetrical self-balancing structure solves the mechanical preload problem of multi-stage friction series transmission. The spatial nesting problem of coaxial nested full stator layout is solved by utilizing the self-supporting characteristics of the double-row symmetrical self-balancing structure. The thermal failure problem of multi-stage friction series drive was solved by utilizing the thermal conductivity characteristics of a coaxial nested full stator layout.

[0128] These three technical solutions support and influence each other, collectively forming a highly rigid, ultra-compact, and thermally stable self-balancing friction transmission system. This holistic system architecture innovation produces synergistic effects that no single improvement in existing technologies can achieve, demonstrating outstanding substantive characteristics and significant progress.

[0129] In one specific embodiment, the friction drive reducer has a three-stage transmission structure, including a first-stage friction drive assembly 2, a second-stage friction drive assembly 2, and a third-stage friction drive assembly 2 coaxially sleeved from the inside out; wherein, the first-stage friction drive assembly 2 is the innermost friction drive assembly 2, the second-stage friction drive assembly 2 is the outermost friction drive assembly 2 relative to the first-stage friction drive assembly 2, and the second-stage friction drive assembly 2 also serves as the innermost friction drive assembly 2 relative to the third-stage friction drive assembly 2. The third-stage friction drive assembly 2 is the final-stage friction drive assembly 2; the transmission connecting member 5 of the third-stage friction drive assembly 2 is an output connector; one end of the output connector is connected to the retainer 230 of the third-stage friction drive assembly 2, and the other end passes through the gap between the two split rings of the third-stage friction drive assembly 2 and connects to the output component 3. This embodiment specifically demonstrates a three-stage friction drive reducer with extremely high reduction ratio and power density.

[0130] In terms of overall layout, the reducer adopts a coaxial sleeve structure that wraps around the inside out, mainly composed of a first-stage friction transmission assembly 2, a second-stage friction transmission assembly 2, and a third-stage friction transmission assembly 2. These three stages share a central axis and are arranged sequentially in radial space.

[0131] The first-stage friction transmission assembly 2 is located at the core of the reducer, i.e., the innermost part. It directly receives input from an external high-speed power source.

[0132] The second-stage friction drive assembly 2 is located outside the first-stage friction drive assembly 2, and is simultaneously enclosed inside the third-stage friction drive assembly 2. This special intermediate layer position determines its dual identity: relative to the first-stage assembly, it is the outermost stage, responsible for receiving the output of the first stage; while relative to the third-stage assembly, it is the innermost stage, responsible for providing input to the third stage.

[0133] The third-stage friction drive assembly 2 is located on the outermost layer of the reducer, i.e., the final-stage friction drive assembly 2. It is the end point of the entire deceleration process and is responsible for outputting the final high-torque, low-speed power.

[0134] The structural focus of this embodiment lies in the output structure design of the final stage (third stage). Since the outer ring 220 (split ring) of the third stage is a stator fixed to the housing 1, the retainer 230 of the third stage, as a rotating component, is enclosed internally. To deliver power, the third stage friction drive assembly 2 is equipped with a dedicated output connector (i.e., the final stage drive connection member 5).

[0135] One end of the output connector is securely connected (e.g., by welding, bolting, or integral molding) to the cage 230 of the third-stage friction drive assembly 2.

[0136] The other end of the output connector extends outward, passing through the axial gap between the two split rings of the third-stage friction drive assembly 2.

[0137] After passing through the gap, the output connector is rigidly connected to the output component 3 (such as the output flange, output shaft 710, or flexible interface) located outside the reducer.

[0138] The three-stage reducer operates according to the logic of progressively reducing speed and progressively amplifying torque. The power first passes through the first-stage reduction gear, and the first-stage cage 230 drives the second-stage inner ring 210; then it passes through the second-stage reduction gear, and the second-stage cage 230 drives the third-stage inner ring 210. In this process, the second-stage component plays a crucial role in connecting the first and third stages. It is both the load of the first stage and the drive source of the third stage, ensuring the continuity of the power chain in the radially nested structure.

[0139] When power is transmitted to the third-stage inner ring 210, it drives the third-stage rolling element 240 to roll within the fixed third-stage outer ring 220, thereby causing the third-stage cage 230 to rotate at the lowest speed in the entire system.

[0140] At this time, the output connector connected to the third-stage cage 230 rotates. Although the outer ring 220 of the third stage is stationary, the output connector cleverly utilizes the gap (clearance) reserved in the split structure of the outer ring 220 to transmit the rotational motion to the outside of the reducer without mechanical interference, thus driving the output component 3 to work.

[0141] This three-stage transmission scheme is suitable for applications requiring extremely high reduction ratios and with very strict size constraints. Due to the use of three stages in series, if the reduction ratio of each stage is N, the total reduction ratio can reach N cubed (for example, if the single stage is 10, the three stages can reach 1000). It is particularly suitable for miniature winches, precision regulating valves, or medical robot joints that require direct low-speed, high-torque from a high-speed motor.

[0142] In some alternative embodiments, the output connector and output component 3 can be designed as an integrated structure, for example, directly made into a disc with a splined shaft, which passes through the gap and directly serves as the power output shaft 710. Although the three-stage structure is the same, the single-stage reduction ratios of the first, second, and third stages can be made different by adjusting the diameters of the inner rings 210 and rolling elements 240 of each stage, so as to optimize the overall transmission efficiency and load-bearing capacity distribution. Typically, it is designed so that the final stage has the smallest reduction ratio but the largest load-bearing capacity.

[0143] In this embodiment, by employing a first-stage, second-stage, and third-stage friction transmission assembly 2 coaxially nested from the inside out, and utilizing the second-stage assembly as an intermediate bridge to achieve cascaded transmission, and by configuring an output connector with one end connected to the final-stage retainer 230 and the other end passing through the gap of the final-stage split outer ring 220 to connect to the output component 3, the technical problem of high reduction ratio devices in the prior art being typically bulky and having difficulty extracting the final-stage power in multi-stage nested structures is effectively solved. This allows for three-stage reduction to be completed within an extremely compact radial space, achieving a huge transmission ratio and output torque, and successfully solving the power extraction problem under a fully enclosed stator structure, significantly improving the power density and integration of the micro reducer.

[0144] The above description is merely illustrative of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, as long as they do not depart from the content of this specification or exceed the scope defined by the claims, all of which should fall within the protection scope of this invention.

Claims

1. A friction drive reducer, characterized in that, include: case; At least two stages of friction drive assemblies are coaxially sleeved within the housing from the inside out, with the innermost friction drive assembly being the first stage and the outermost friction drive assembly being the final stage; each stage of the friction drive assembly includes: The inner ring that rotates with the input of power; The outer ring is fixedly connected to the housing; A cage located between the inner ring and the outer ring; A plurality of rolling elements are disposed on the cage, the rolling elements respectively engaging in rolling friction with the outer wall of the inner ring and the inner wall of the outer ring; Output components; In the two adjacent stages of the friction drive assembly, the cage of the friction drive assembly located in the inner stage is connected to the inner ring of the friction drive assembly located in the outer stage, so that the revolution of the cage located in the inner stage serves as the rotation input of the inner ring located in the outer stage; and the inner ring of the first stage friction drive assembly is connected to the output end of an external power source, and the cage of the final stage friction drive assembly is connected to the output component.

2. The friction drive reducer according to claim 1, characterized in that, In the two adjacent stages of the friction drive assembly, the cage located in the inner stage is connected to the inner ring located in the outer stage via an annular connector; the annular connector extends radially outward, causing the inner ring located in the outer stage to rotate synchronously with the cage located in the inner stage.

3. The friction drive reducer according to claim 2, characterized in that, The outer surface of the inner ring of the friction transmission assembly located at the innermost level has two annular inner raceways symmetrically formed on a mid-plane that passes through the midpoint of its own axis and is perpendicular to its own axis. The cage located at the innermost level has two rows of symmetrically arranged rolling elements, which respectively cooperate with the two inner raceways. The outer ring of the friction transmission assembly located at the innermost level includes two symmetrically arranged split rings along the axis. The two split rings are located on both sides of the annular connector, and the inner walls of the two split rings are respectively formed with outer raceways that cooperate with the two rows of rolling elements.

4. The friction drive reducer according to claim 3, characterized in that, There is an axial gap between the two separate rings; one end of the annular connector is connected to the middle of the cage located at the inner level, and the other end of the annular connector passes through the axial gap and is connected to the inner wall of the inner ring located at the outer level; the inner diameter of the inner ring located at the outer level is larger than the outer diameter of the outer ring located at the inner level, so as to form a stacked nested structure.

5. The friction drive reducer according to claim 3, characterized in that, In at least two stages of the friction drive assembly, the outer surface of the inner ring of each stage is symmetrically provided with two annular inner raceways; the cage of each stage of the friction drive assembly is provided with two rows of symmetrically arranged rolling elements; the outer ring of each stage of the friction drive assembly is composed of two symmetrically arranged split rings; each stage of the friction drive assembly is provided with a drive connecting member passing through the gap between the two split rings; wherein, the drive connecting member located in the inner stage is the annular connector, and one end of the drive connecting member located in the outermost final stage of the friction drive assembly is connected to the cage of the final stage of the friction drive assembly, and the other end is connected to the output component.

6. The friction drive reducer according to any one of claims 3 to 5, characterized in that, The contact surfaces of the inner ring, the outer ring, and the rolling element are all smooth, continuous curved surfaces, and torque is transmitted between each contact surface only through the contact friction force generated by the preload force; the friction drive reducer is configured such that when the load torque borne by the output component exceeds a preset safety threshold, the rolling element slips and spins freely in the inner raceway or the outer raceway.

7. The friction drive reducer according to claim 6, characterized in that, At least two stages of the friction drive assembly are configured radially from the inside out, with the maximum static friction torque that each stage of the friction drive assembly can transmit increasing progressively; and the preload and friction contact parameters of the last stage friction drive assembly are configured such that the maximum static friction torque of the last stage friction drive assembly is less than the product of the maximum static friction torque of the next inner stage friction drive assembly and the reduction ratio between the two stages, so that under overload conditions, the slippage of the rolling element relative to the raceway occurs in the last stage friction drive assembly before the other stages of the friction drive assembly.

8. The friction drive reducer according to claim 1, characterized in that, The outer ring of each stage of the friction drive assembly is a stator component, and the side or end face of the outer ring of each stage of the friction drive assembly is connected to the housing through a heat-conducting medium, so that the outer ring, the heat-conducting medium and the housing together form a heat-conducting channel from the friction drive assembly to the housing.

9. The friction drive reducer according to claim 5, characterized in that, The friction drive reducer is a three-stage transmission structure, including a first-stage friction drive assembly, a second-stage friction drive assembly, and a third-stage friction drive assembly coaxially arranged from the inside out; wherein, the first-stage friction drive assembly is the innermost friction drive assembly, the second-stage friction drive assembly is the outermost friction drive assembly relative to the first-stage friction drive assembly, and the second-stage friction drive assembly also serves as the innermost friction drive assembly relative to the third-stage friction drive assembly.

10. The friction drive reducer according to claim 9, characterized in that, The third-stage friction transmission assembly is the final-stage friction transmission assembly; the transmission connection member of the third-stage friction transmission assembly is an output connector; one end of the output connector is connected to the cage of the third-stage friction transmission assembly, and the other end passes through the gap between the two split rings of the third-stage friction transmission assembly and is connected to the output component.

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