Planetary roller screw

Abstract

The invention relates to the technical field of planetary roller lead screws, and particularly discloses a planetary roller lead screw which comprises a lead screw, a sun gear, a planet carrier and a gear ring which are sequentially arranged from inside to outside, a hollow hole is formed in the sun gear, an internal thread matched with the lead screw is machined on the inner wall of the hollow hole, and an external gear part is arranged on the periphery of the sun gear; the planet wheel carrier is rotatably connected between the sun wheel and the gear ring, the planet wheel carrier comprises an annular retainer and a plurality of planet wheels which are uniformly distributed in the circumferential direction of the sun wheel, each planet wheel is rotatably connected to the retainer, each planet wheel is in tooth meshing with the outer gear part of the sun wheel and the inner gear part of the gear ring at the same time, and the tooth type of tooth meshing is helical teeth or straight teeth. According to the scheme, the problems of motion interference, high machining cost and insufficient transmission stability caused by thread phase difference existing in a traditional ball screw in the prior art are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of planetary roller screws, and in particular to a planetary roller screw. Background Art

[0002] With the widespread application of planetary roller screws in industrial automation, robotics and other fields, their importance as high-precision linear-to-rotational motion conversion mechanisms has become increasingly prominent. Traditional planetary roller screws consist of a central screw, rollers surrounding the screw, and a nut that encloses the rollers. The rollers, screw, and nut are all machined with threads, which are used to achieve fit, ensuring that when the screw rotates, the nut moves axially, or by controlling the rotation of the nut, the screw moves axially. However, existing planetary roller screw technology still has several key issues that need to be addressed in practical applications: First, the thread fit accuracy of planetary roller screws is difficult to guarantee. Because the structure contains multiple precision components such as threaded rollers, nuts, and screws, differences in the thread phase angles between the various parts can lead to axial position deviations after assembly. When the pitch is large, this deviation can cause helical interference, seriously affecting the positioning accuracy and operational smoothness of the system. More critically, the thread pitch diameters of the various components are inherently different, resulting in differences in thread lead angles. This negative impact is further amplified by manufacturing variations (precision errors such as angle differences, axial taper differences, head splitting errors, and helical line differences occur during the machining process), making it difficult for the system to achieve theoretical design performance.

[0003] Secondly, controlling the axial clearance of planetary roller screws presents a significant challenge. The structural complexity of planetary roller screws leads to numerous parameters affecting axial clearance, including the thread phase angle of each component, meshing clearance, and preload. Precise control of these parameters requires extremely high manufacturing precision and assembly process technology. In actual production, achieving ideal tolerances is often difficult, resulting in difficult component selection and unstable performance.

[0004] Finally, the complexity and cost of the manufacturing process severely restrict the widespread application of this technology. Planetary roller screws involve the machining of the internal thread of the nut, the threaded roller, and the external thread of the screw. To ensure the proper thread alignment of the nut, screw, and roller, high demands are placed on the grinding equipment used for thread machining. This requires both specialized equipment and the skills of the machining personnel. The procurement cost of a dedicated grinding machine alone exceeds 10 million yuan per unit, making the production cost of this type of high-precision ball screws high. Furthermore, the entire production and assembly process places stringent demands on the technical personnel, further increasing the difficulty of mass production and the cost of application, making it difficult to achieve large-scale application in areas such as industrial robots that require mass production.

[0005] These challenges collectively limit the breadth and depth of planetary roller screw applications in high-end equipment manufacturing, necessitating innovation to overcome existing technical bottlenecks. Developing planetary roller screws with higher performance, lower cost, and improved manufacturability is particularly important in applications such as servo motors, electric cylinders, and robotic joints, which require extremely high motion precision, response speed, and reliability. Summary of the Invention

[0006] The present invention aims to provide a planetary roller screw to solve the problems of conventional ball screws in the prior art, such as motion interference caused by thread phase difference, high processing costs and insufficient transmission stability.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions: A planetary roller screw comprises a screw, a sun gear, a planetary gear carrier and a ring gear arranged in sequence from the inside to the outside. The sun gear is provided with a hollow hole, the inner wall of the hollow hole is processed with an internal thread that cooperates with the screw, an external gear portion is provided on the outer periphery of the sun gear, and the planetary gear carrier is rotatably connected between the sun gear and the ring gear. The planetary gear carrier comprises an annular retaining frame and a plurality of planetary gears uniformly distributed around the circumference of the sun gear. Each planetary gear is rotatably connected to the retaining frame, and each planetary gear is simultaneously meshed with the external gear portion of the sun gear and the internal gear portion of the ring gear. The tooth profile of the meshing teeth is helical or straight.

[0008] The principle and advantages of this solution are: the gear meshing method of the planetary gear, the sun gear and the ring gear replaces the thread matching method in the traditional roller screw, which fundamentally solves the motion interference problem caused by the phase difference of the thread. In the traditional solution, there are inevitable phase angle differences in the threads of the roller, the screw and the nut, which leads to axial position deviations of the parts during assembly. When the pitch is large, helical interference will occur, seriously affecting the positioning accuracy and running smoothness. In the gear meshing transmission of the planetary gear, the sun gear and the ring gear of this solution, even the helical gears will not produce helical interference problems similar to threads. By designing the helical angles of the helical teeth of the ring gear, the planetary gear and the sun gear to be the same value, the synchronization of motion transmission is ensured. Gear processing adopts the hobbing, shaping and other forming methods. The tool and the workpiece are continuously rotated and meshed, and multiple teeth are involved in cutting at the same time, so that the pitch error is evenly distributed and does not accumulate, so that high transmission accuracy requirements can be achieved with conventional processing accuracy.

[0009] In terms of processing economy, this solution only requires high-precision grinding of the lead screw and sun gear internal threads. This threading process only involves the screw-nut fit, eliminating the traditional threading of rollers and lead screws, or rollers and nuts. Therefore, machining accuracy is more easily guaranteed. Standard gear machining equipment can be used to process the sun gear external teeth, planetary gears, and ring gear. Because gear machining precision control is simpler and more reliable, overall manufacturing costs are significantly reduced.

[0010] In terms of transmission performance, helical gear meshing offers higher load capacity and impact resistance than straight gearing. The progressive meshing of helical gears increases the number of teeth simultaneously participating in the transmission, resulting in a smoother transmission process. Compared to traditional hub bearing structures (which feature an inner ring, double-row balls, and an outer ring), this solution achieves power transmission through gear meshing, eliminating rolling element and ball slippage. This significantly reduces friction loss and noise levels, meeting the requirements of high-precision transmission applications.

[0011] Preferably, as an improvement, outer raceways are respectively provided on the outer periphery of both axial ends of the sun gear, and inner raceways are provided at corresponding positions on the inner periphery of the retaining frame; a row of balls is provided between the outer raceway at each end of the sun gear and the inner raceway at the corresponding end of the retaining frame, and the outer raceway of the sun gear, the inner raceway of the retaining frame and the balls arranged therebetween together form a double-row ball bearing structure.

[0012] Preferably, as an improvement, each of the planetary wheels is provided with an outer raceway at both axial ends, and an inner raceway is provided at a corresponding position on the retaining frame; a row of balls is provided between the outer raceway at each end of the planetary wheel and the corresponding inner raceway of the retaining frame, and the planetary wheel outer raceway, the retaining inner raceway and the balls arranged therebetween together form a double-row ball bearing structure.

[0013] Preferably, as an improvement, outer raceways are respectively provided on the outer periphery of the two axial ends of the retaining frame, and inner raceways are provided at corresponding positions on the inner periphery of the gear ring; a row of balls is provided between the outer raceway at each end of the retaining frame and the inner raceway at the corresponding end of the gear ring, and the outer raceway of the retaining frame, the inner raceway of the gear ring and the balls arranged therebetween together form a double-row ball bearing structure.

[0014] Preferably, as an improvement, the double-row ball bearing structure is a double-row angular contact bearing structure.

[0015] Preferably, as an improvement, the retaining frame includes end covers at both ends and a plurality of support rods connecting the end covers at both ends in series, and both ends of the support rods are fixedly connected to the end covers on the corresponding sides.

[0016] Preferably, as an improvement, the plurality of support rods are evenly distributed about the center of the sun gear.

[0017] Preferably, as an improvement, the support rod is connected to the end cover via screws.

[0018] Preferably, as an improvement, the internal thread of the sun gear has multiple thread starts.

[0019] Preferably, as an improvement, the number of the planetary gears is 6.

[0020] Other technical effects of the present invention: 1. In the present invention, a double-row ball bearing structure is formed between the sun gear and the planetary gear carrier, and a double-row ball bearing structure is also formed between the planetary gear carrier and the ring gear. On the planetary gear carrier, each planetary gear has a double-row ball structure with the retaining frame. This design greatly improves the load-bearing performance of the entire planetary roller screw. The design of the double-row angular contact bearing structure also greatly improves the axial impact resistance of the solution of the present invention. The load-bearing performance and impact resistance are far superior to those of existing planetary roller screws.

[0021] 2. The present invention replaces the previous contact mode with the rolling friction of the balls, so the noise during operation is also smaller.

[0022] 3. The annular retainer of the present invention is composed of two end covers and multiple support rods in the middle, which not only facilitates assembly, but also helps to ensure the center distance between the planetary gear and the sun gear, ensuring the ease of installation of the planetary gear frame and the structural stability during operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the three-dimensional structure of an embodiment of the present invention.

[0024] Figure 2 for Figure 1 Schematic diagram of the axial section.

[0025] Figure 3 for Figure 2 AA cross-sectional view.

[0026] Figure 4 Schematic diagram of the three-dimensional structure of the screw rod according to an embodiment of the present invention.

[0027] Figure 5 for Figure 4 Left view of .

[0028] Figure 6 Schematic diagram of the three-dimensional structure of the sun gear according to an embodiment of the present invention.

[0029] Figure 7 for Figure 6 Right view of .

[0030] Figure 8 for Figure 6 Schematic diagram of the axial section.

[0031] Figure 9 Schematic diagram of the three-dimensional structure of the planetary gear according to an embodiment of the present invention.

[0032] Figure 10 Schematic diagram of the three-dimensional structure of the end cover according to an embodiment of the present invention.

[0033] Figure 11 for Figure 10Rotated section view cut at the countersunk hole location.

[0034] Figure 12 Schematic diagram of the three-dimensional structure of the ring gear according to an embodiment of the present invention.

[0035] Figure 13 for Figure 12 Schematic diagram of the axial section.

[0036] The reference numerals in the drawings of the specification include: ring gear 1, first row of balls 2, end cover 3, countersunk hole 31, planetary gear 4, second row of balls 5, third row of balls 6, screw 7, sun gear 8, support rod 9, screw 10, oil filling hole 11. DETAILED DESCRIPTION

[0037] The following is further described in detail through specific implementation methods: The embodiment is basically as shown in the attached Figures 1 to 13 shown.

[0038] Combine Figures 1 to 3 A planetary roller screw comprises a coaxially arranged screw rod 7, a sun gear 8, a planetary wheel carrier and a ring gear 1; the sun gear 8 is provided with an axially through-hole, the inner wall of the hollow hole is provided with an internal thread that matches the thread of the screw rod 7, and the outer periphery of the sun gear 8 is processed with a first external gear portion; The planetary wheel carrier includes an annular retainer and at least three circumferentially evenly distributed planetary wheels 4, both ends of each planetary wheel 4 being rotatably connected to the retainer; the planetary wheels 4 are processed with a second external gear portion that meshes with the first external gear portion; The inner wall of the ring gear 1 is machined with an internal gear portion that meshes with the second external gear portion of the planetary gear 4; The teeth of the first, second, and internal gears are all helical or spur. In the drawings of this embodiment, helical teeth are used. The teeth on the second external gear of the planetary gear 4 and the first external gear of the sun gear 8 are top-cut. This top-cut ensures that the major and minor diameter centers of the first external gear are coaxial with the center of the sun gear 8. Similarly, the major and minor diameter centers of the second external gear are coaxial with the center of the sun gear and the planetary gear 4. Furthermore, to avoid interference and noise during meshing, the teeth of the external gears on the outer peripheries of the planetary gears 4 and sun gear 8 are ground on the opposite side, with a grinding depth of 0.04-0.06 mm.

[0039] To improve load-bearing performance and impact resistance, outer raceways are provided on the outer circumference of each axial end of sun gear 8, and inner raceways are provided at corresponding locations on the inner circumference of the cage. A row of balls, referred to as the third row of balls 6 in the accompanying drawings, is located between the outer raceways at each end of sun gear 8 and the inner raceways at the corresponding end of the cage. The outer raceways at both ends of sun gear 8 and the inner raceways at both ends of the cage are retained by steel balls and connected with sealing rings to form a double-row angular contact bearing structure. In this embodiment, all the balls are steel balls.

[0040] Each planetary gear 4 is provided with an outer raceway at both axial ends, and an inner raceway is provided on the mounting hole of the retaining frame for mounting the planetary gear 4; a row of balls is provided between the outer raceway at each end of the planetary gear 4 and the corresponding inner raceway of the retaining frame, and this row of balls is called the second row of balls 5. The outer raceway of the planetary gear 4, the inner raceway of the retaining frame and the balls arranged therebetween together form a double-row angular contact bearing structure.

[0041] An outer raceway is provided on the outer periphery of each axial end of the cage, and an inner raceway is provided at the corresponding position on the inner periphery of the ring gear 1; a row of balls is provided between the outer raceway at each end of the cage and the inner raceway at the corresponding end of the ring gear 1. This row of balls is called the first row of balls 2 in the accompanying drawings. The outer raceway of the cage, the inner raceway of the ring gear 1 and the balls arranged therebetween together form a double-row angular contact bearing structure.

[0042] To facilitate lubrication of the meshing position of the planetary gears 4, multiple oiling holes 11 are circumferentially provided on the central outer periphery of the ring gear 1. The oiling holes penetrate the wall thickness of the ring gear 1. The inner wall of the ring gear 1 corresponding to the oiling holes 11 is provided with an annular groove. The annular groove divides the internal gear portion of the ring gear 1 into two axial sections. The annular groove is formed by reducing the height of the teeth in the annular region in the middle of the internal gear portion after machining the internal gear portion of the ring gear 1. Therefore, the annular groove still contains a number of drainage teeth with the same root as the internal gear portion of the ring gear 1 and connected to each other. The tooth top height of the drainage teeth is less than the tooth top height of the internal gear portion. The drainage teeth are the teeth left after a certain height is cut off from the original tooth top of the internal gear portion. When lubricating oil is added to the oiling hole 11, the lubricating oil will move circumferentially along the annular groove and simultaneously extend axially along the rotational direction of the tooth root, facilitating lubrication of the entire gear meshing area.

[0043] The cage includes end caps 3 at both ends and multiple support rods 9 connecting the end caps 3 in series. Both ends of the support rods 9 are fixedly connected to the end caps 3 on the corresponding side. The multiple support rods 9 are evenly distributed about the center of the sun gear 8. In this embodiment, there are three support rods 9. The end caps 3 at both ends have the same structure.

[0044] Each end cover 3 is provided with a countersunk hole 31 , and the support rod 9 is connected to the two end covers 3 on the countersunk hole 31 by screws 10 .

[0045] The internal thread of the sun gear 8 has multiple thread starts, and in this embodiment, has four thread starts.

[0046] The number of planetary gears 4 is 6.

[0047] The planetary roller screw of this embodiment adopts a unique structure combining a helical planetary gear system (a combination of sun gear 8, planetary gears 4, and ring gear 1) with a threaded pair (the combination of screw rod 7 and the internal thread of sun gear 8). Motion conversion is achieved by integrating the internal thread and the combination of helical sun gear 8 and screw rod 7. The hub-like structure formed by the combination of sun gear 8, planetary gears 4, and ring gear 1 enables the planetary roller screw of the present invention to combine the low friction and high load-bearing characteristics of a hub bearing with the stability and speed-changing function of the transmission system. This structure can significantly improve transmission efficiency and reduce system inertia, and is particularly suitable for high-precision applications such as servo motor-driven electric cylinder robot joints.

[0048] Furthermore, the planetary roller screw of this embodiment offers low operating noise and high load-bearing capacity, effectively resolving issues such as insufficient impact tolerance, excessive operating noise, and severe friction loss under high-torque conditions. This improves the effectiveness of the planetary roller screw in high-speed, high-precision applications, particularly in robotic joints that require frequent starts and stops or fluctuating loads.

[0049] In addition, the planetary roller screw of this embodiment breaks the original planetary roller screw's multiple thread matching scheme, and instead adopts a thread matching scheme only for the screw rod 7 and the sun gear 8 internal thread, which greatly reduces the precision requirements for thread processing matching and the expensive equipment requirements, and can avoid the motion interference problem caused by the thread phase difference. On the basis of greatly reducing the processing cost, it can also ensure the operation stability of the planetary roller screw (the helical gear matching will not have the problem of motion interference of matching parts, and the screw rod 7 and the sun gear 8 internal threads are in the same thread phase, so there will be no motion interference).

[0050] The above is only an embodiment of the present invention, and the common knowledge such as the specific technical solutions and / or characteristics in the solution are not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several variations and improvements can be made, which should also be regarded as the scope of protection of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the description can be used to interpret the content of the claims.

Claims

1. A planetary roller screw, characterized in that: It includes a screw, a sun gear, a planetary gear carrier and a ring gear arranged in sequence from the inside to the outside. The sun gear is provided with a hollow hole, and the inner wall of the hollow hole is processed with an internal thread that cooperates with the screw. An external gear part is provided on the outer periphery of the sun gear. The planetary gear carrier is rotatably connected between the sun gear and the ring gear. The planetary gear carrier includes an annular retaining frame and multiple planetary gears evenly distributed around the circumference of the sun gear. Each planetary gear is rotatably connected to the retaining frame. Each planetary gear is simultaneously meshed with the external gear part of the sun gear and the internal gear part of the ring gear. The tooth profile of the tooth meshing is helical teeth or straight teeth.

2. A planetary roller screw according to claim 1, characterized in that: The sun gear is provided with outer raceways at both axial ends, and inner raceways are provided at corresponding positions on the inner periphery of the cage. A row of balls is provided between the outer raceway at each end of the sun gear and the inner raceway at the corresponding end of the cage. The outer raceway of the sun gear, the inner raceway of the cage and the balls arranged therebetween together form a double-row ball bearing structure.

3. The planetary roller screw according to claim 1, characterized in that: Each of the planetary wheels is provided with an outer raceway at both axial ends, and an inner raceway is provided at a corresponding position on the retaining frame; A row of balls is provided between the outer raceway of each end of the planetary gear and the corresponding inner raceway of the retainer. The outer raceway of the planetary gear, the inner raceway of the retainer and the balls arranged therebetween together form a double-row ball bearing structure.

4. The planetary roller screw according to claim 1, characterized in that: The outer circumferences of the two axial ends of the retainer are respectively provided with outer raceways, and the inner circumference of the gear ring is provided with inner raceways at corresponding positions; A row of balls is provided between the outer raceway at each end of the cage and the inner raceway at the corresponding end of the gear ring. The outer raceway of the cage, the inner raceway of the gear ring and the balls arranged therebetween together form a double-row ball bearing structure.

5. A planetary roller screw according to any one of claims 2 to 4, characterized in that: The double-row ball bearing structure is a double-row angular contact bearing structure.

6. A planetary roller screw according to any one of claims 1 to 4, characterized in that: The retaining frame includes end covers at both ends and a plurality of support rods connected in series with the end covers at both ends, and both ends of the support rods are fixedly connected to the end covers at the corresponding sides.

7. A planetary roller screw according to claim 6, characterized in that: The plurality of support rods are evenly distributed about the center of the sun gear.

8. The planetary roller screw according to claim 7, characterized in that: The support rod is connected to the end cover through screws.

9. A planetary roller screw according to any one of claims 1-4, 7-8, characterized in that: The internal thread of the sun gear has multiple thread starts.

10. A planetary roller screw according to any one of claims 1-4, 7-8, characterized in that: The number of the planetary gears is 6.

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