Axial pre-tightening device for retainer of roller screw

Abstract

The utility model provides an axial pre-tightening device for a retainer of a pin roller screw. The axial pre-tightening device comprises a screw, a nut, a pin roller group, a retainer group and a pre-tightening part group, the pin roller group is provided with a plurality of first pin rollers and second pin rollers which are arranged in a staggered mode, and the periphery of each pin roller is provided with annular teeth which are meshed with a thread structure of the screw and an annular groove section in the nut. The retainer group is arranged at the two ends of the roller group, and a first gap and a second gap which are staggered are formed by utilizing the axial length difference between the two ends of the first roller and the second roller. The pre-tightening piece set penetrates through the retaining piece set in the axial direction and exerts adjustable fastening force, so that the retaining piece set clamps the roller set, then adjustable axial pre-pressing force opposite in direction is exerted on the first roller and the second roller respectively, and the staggered two-way pre-pressing effect is achieved. By means of the design, back clearance can be eliminated, pure rolling contact is guaranteed, transmission stability is improved, the service life is prolonged, retaining rings are omitted, space is saved, and friction is avoided.

Description

Technical Field

[0001] This utility model relates to a transmission component, and more particularly to a cage axial preload device for a roller screw that can generate adjustable axial preload on the rollers to improve rolling stability. Background Technology

[0002] Planetary roller screws utilize multiple rollers that synchronously roll and mesh between the screw and nut to efficiently convert rotary motion into linear motion. They possess high load capacity, high rigidity, and high positioning accuracy, and are widely used in machine tools, servo actuators, and aerospace control systems.

[0003] like Figure 1A As shown, a conventional planetary roller screw drive includes a screw 11, a nut 12, a plurality of rollers 13, and a cage assembly 14. The screw 11 has an external thread structure, and the nut 12 has an inner hole 120 to accommodate the rollers 13, and an annular tooth structure 12t on its inner circumference to form rolling contact with the annular teeth of the rollers 13. The cage assembly 14 is located at both ends of the plurality of rollers 13 to limit their circumferential spacing and angular distribution and maintain their positioning. To prevent axial displacement of the cage assembly 14 during movement, the nut 12 has two internal grooves 121 to accommodate a retainer 15 (such as a C-shaped retainer or annular retainer) in each groove. The retainer 15 is located on the outside of the cage assembly 14 and contacts it to fix its axial position and prevent it from dislodging.

[0004] However, traditional designs still have several problems. For example... Figure 1B and Figure 1C As shown, the geometric fit between roller 13, screw 11, and nut 12 is extremely precise. However, due to manufacturing tolerances and assembly errors, a small gap G is generated between roller 13 and screw 11 / nut 12, causing the actual contact position of roller 13 to deviate from the designed pitch circle radius. If this complex fit gap G is not effectively compensated, there will be insufficient friction between roller 13 and nut 12 during operation, making it easy to slip or spin, making it difficult to maintain pure rolling contact and generating sliding friction. This results in greater wear on roller 13, reducing the overall structural lifespan. Similarly, insufficient contact may also cause slippage between roller 13 and screw 11, thereby disrupting the deceleration and propulsion effects of planetary motion, resulting in a decrease in linear propulsion efficiency and positioning accuracy.

[0005] Although the cage assembly 14 can control the angle and spacing of the rollers 13, it only has a mechanical positioning function and cannot provide preload compensation or guide the preload direction of the rollers. It also cannot effectively improve the sliding offset problem caused by the clearance G. More importantly, the actual contact between the cage assembly 14 and the retaining ring 15 generates frictional resistance. When the cage assembly 14 rotates with the rollers 13, relative sliding occurs between it and the retaining ring 15, resulting in wear and resistance. This affects the consistency and smoothness of the rollers 13's movement, causing a decrease in transmission efficiency and a deterioration in accuracy. Furthermore, the embedded groove 121 structure required for the retaining ring 15 occupies valuable axial space in the nut 12, limiting the miniaturization and compact design of the overall transmission assembly. This restricts applications requiring minimal space or high structural integration.

[0006] Therefore, how to effectively improve the stability of the contact between the roller 13 and the nut 12 without increasing structural complexity and manufacturing cost, and strengthen the rolling engagement between the roller 13 and the screw 11, so as to ensure that the screw 11, roller 13 and nut 12 maintain stable rolling motion, is an important issue that needs to be overcome in this field. Utility Model Content

[0007] The purpose of this invention is to provide an axial preload device for the retainer of a roller screw that effectively solves the aforementioned technical problems. This device can compensate for the fit clearance caused by machining errors and apply axial preloads in opposite directions with adjustable preload to the staggered first and second rollers, thereby preventing sliding friction between the roller assembly and the screw / nut, ensuring rolling contact, and thus improving overall lifespan. It also effectively eliminates backlash, enhances transmission stability and positioning accuracy, and eliminates the need for the traditional design of fixing the axial position of the retainer with a retainer ring, simplifying the structure, saving axial space, and avoiding additional friction caused by retainer ring contact.

[0008] To achieve the above objectives, this utility model provides an axial preload device for the cage of a roller screw, characterized in that it comprises:

[0009] A screw, the outer circumferential surface of which is provided with a threaded structure;

[0010] A nut having an inner hole for housing the screw, the inner side of which has at least one annular groove section;

[0011] A roller assembly is disposed between the screw and the nut, having a plurality of first rollers and a plurality of second rollers arranged in an alternating pattern. Each first roller and second roller has a plurality of annular teeth on its outer circumferential surface, which respectively mesh with the thread structure and the annular groove section.

[0012] A retainer assembly is disposed within the nut and located at both ends of the roller assembly. It has a first retainer and a second retainer. The first retainer is connected to one end of the plurality of first rollers and second rollers, and the second retainer is connected to the other end of the plurality of first rollers and second rollers. A first gap is provided between one end of the plurality of first rollers and the first retainer, and a second gap is provided between one end of the plurality of second rollers and the second retainer. The plurality of first gaps and second gaps are arranged at opposite ends of the roller assembly and are staggered.

[0013] A preload assembly is disposed between the first retainer and the second retainer, generating an adjustable clamping force to bring the first retainer and the second retainer closer together and clamp the roller assembly. In conjunction with the staggered first gap and the second gap, axial preloads with opposite directions and adjustable preload amounts are applied to the plurality of first rollers and the plurality of second rollers, so that the roller assembly forms staggered bidirectional axial preloads to reduce the backlash between the screw and the nut and maintain pure rolling contact of the rollers.

[0014] The roller screw retainer axial preload device, wherein: the preload assembly includes at least two preload screws, respectively disposed between the first retainer and the second retainer, and parallel to the plurality of first rollers and the plurality of second rollers; each preload screw has a threaded end and a head end, the threaded end being threaded into one of the first retainer and the second retainer, and the head end abutting against the other of the first retainer and the second retainer.

[0015] The roller screw cage axial preload device, wherein:

[0016] The first retainer is provided with a plurality of first positioning grooves and at least one first mating part. The plurality of first positioning grooves are used to accommodate one end of the plurality of first rollers and the plurality of second rollers. The at least one first mating part is used to accommodate the threaded end of the preload screw and is provided with an internal thread that mates with the threaded end.

[0017] The second retainer is provided with a plurality of second positioning grooves and at least one second mating part. The plurality of second positioning grooves are used to accommodate the other ends of the plurality of first rollers and the plurality of second rollers. The at least one second mating part corresponds to the head end of the pre-tightening screw.

[0018] The roller screw cage axial preload device, wherein:

[0019] The axial length of one end of the first roller housed in the first positioning groove is less than the length of its other end, and it does not contact the bottom of the first positioning groove, thereby forming the first gap; and

[0020] The axial length of one end of the second roller housed in the second positioning groove is less than the length of the other end, and it does not contact the bottom of the second positioning groove, so as to form the second gap.

[0021] The roller screw retainer axial preload device comprises: a first retainer having a plurality of first positioning grooves and at least one first mating part; a second retainer having a plurality of second positioning grooves and at least one second mating part; and a preload screw having a threaded end passing through the second mating part of the second retainer and being threaded to the first mating part of the first retainer, with the head end abutting against the outside of the second mating part of the second retainer; and a preload screw having a threaded end passing through the first mating part of the first retainer and being threaded to the second mating part of the second retainer, with the head end abutting against the outside of the first mating part of the first retainer.

[0022] The roller screw retainer axial preload device, wherein: the first retainer and the second retainer are respectively provided with an internal thread at the first mating part and the second mating part corresponding to the screw end to mate with the screw end.

[0023] This invention effectively compensates for the clearance between the screw and nut, and guides the preload transmission direction through a staggered clearance design, ensuring that the rollers stably conform to the rolling tooth surfaces of the screw and nut, preventing slippage and free rotation, and improving rolling stability and service life. Furthermore, the adjustable preload screw assembly allows for the application of adjustable tightening force between the two retaining members, applying axial pressure in opposite directions and with adjustable preload to different rollers, creating a bidirectional preload effect. The overall design eliminates the need for retaining rings to limit the axial position of the retaining members, simplifying the structure, saving space, reducing frictional losses, and achieving a high-precision, high-efficiency, and high-reliability transmission system. Attached Figure Description

[0024] Figure 1A This is a schematic diagram of an existing planetary roller screw drive.

[0025] Figure 1B for Figure 1A Schematic diagram of the meshing contact relationship between the middle roller and the nut;

[0026] Figure 1C for Figure 1A Schematic diagram of the meshing contact relationship between the middle roller and the screw;

[0027] Figure 2 This is an exploded perspective view of an embodiment of the present utility model;

[0028] Figure 3A This is an axial sectional view of an embodiment of the present utility model;

[0029] Figure 3B for Figure 3A Showing a magnified schematic diagram of the meshing area;

[0030] Figure 3C for Figure 3A The cross-section shows a schematic diagram of the roller and retainer configuration;

[0031] Figure 4 This is a schematic diagram showing the difference in axial length between the first roller and the second roller at opposite ends in an embodiment of this utility model.

[0032] Figure 5 This is a schematic diagram illustrating the application of force by the pre-tightening assembly in an embodiment of the present invention, causing the retaining assembly to clamp the roller assembly.

[0033] Figure 6 This is a cross-sectional view of the direction of pre-pressure transmission guided by the staggered first and second gaps in an embodiment of the present invention;

[0034] Figure 7A for Figure 6 A magnified view of the first gap in the middle;

[0035] Figure 7B for Figure 6 A magnified view of the second gap in the middle;

[0036] Figure 8A A magnified view of a portion of the preload contact formed by the first roller towards the screw;

[0037] Figure 8B A magnified view of a portion of the preload contact formed by the first roller towards the nut side;

[0038] Figure 9A A magnified view of a portion of the preload contact formed by the second roller towards the screw side;

[0039] Figure 9B A magnified view of a portion of the preload contact formed by the second roller toward the nut side;

[0040] Figure 10 A schematic diagram of applying axial clamping force to a pre-tightening screw from a relative direction.

[0041] Explanation of reference numerals in the attached drawings: 21-Screw; 211-Threaded structure; 22-Nut; 220-Inner hole; 221-Annular groove section; 221g-Annular groove; 223-Allowing groove section; R-Roller assembly; 23-First roller; 231-First meshing section; 232-Second meshing section; 233 end; 234 end; 23t-Annular tooth; 24-Second roller; 241-First meshing section; 242-Second meshing section Section; End 243; End 244; 24t - Ring tooth; K - Retaining component assembly; 25 - First retaining component; 251 - First positioning groove; 252 - First mating part; 26 - Second retaining component; 261 - Second positioning groove; 262 - Second mating part; P - Preload assembly; 27 - Preload screw; 271 - Screw end; 272 - Head end; 31 - First clearance; 32 - Second clearance; L1~L4 - Axial length; G - Clearance. Detailed Implementation

[0042] The structure and functional characteristics of this utility model's bidirectional axial preload structure for roller screws will be described with reference to the preferred embodiment shown in the accompanying drawings.

[0043] Please see Figure 2 , Figures 3A-3C , Figure 4 and Figure 5 As shown, a preferred embodiment of the present invention provides an axial preload device for a roller screw cage, comprising: a screw 21, a nut 22, a roller assembly R, a retainer assembly K, and a preload assembly P.

[0044] Nut 22 is a hollow cylindrical component with an axially extending inner bore 220. The inner circumferential surface of the inner bore of nut 22 has two annular groove sections 221 for rolling engagement with the roller assembly R. These multiple annular groove sections 221 provide circumferential guidance and contact restraint, allowing the roller assembly R to roll stably within nut 22 in a planetary manner, preventing axial disengagement. The annular groove sections 221 have a plurality of annular grooves 221g distributed circumferentially (e.g., ...). Figure 3B (As shown).

[0045] In addition, between the two annular groove sections 221, the inner circumferential surface of the inner hole of the nut 22 is provided with a radial clearance groove section 223. The inner diameter of the clearance groove section 223 is larger than that of other parts to provide sufficient space to avoid interference between the roller assembly R and the inner wall. The specific function will be described later.

[0046] The screw 21 is a long rod-shaped component, coaxially arranged within the inner hole 220 of the nut 22 along the axial direction, and extends to the outside of the nut 22 to facilitate connection to a drive device or installation on other external mechanisms. The outer circumferential surface of the screw 21 has a threaded structure 211 (also called a helical groove or helical teeth), which can be a multi-start thread. In actual operation, the screw 21 can be driven to rotate by an external power source (not shown in the figure), and through the double-sided meshing between the threaded structure 211 and the roller assembly R, the roller assembly R simultaneously rotates and revolves between the screw 21 and the nut 22, forming planetary rolling. This motion mechanism converts the rotational motion of the screw 21 into axial linear motion.

[0047] Please refer to the following: Figure 2 , Figures 3A-3C and Figure 4 As shown, the roller assembly R is disposed in the inner hole 220 of the nut 22 and is located between the nut 22 and the screw 21. It includes a plurality of staggered first rollers 23 and second rollers 24. The plurality of first rollers 23 and second rollers 24 are arranged around the outer periphery of the screw 21, and are staggered and spaced apart along the circumferential direction. In this embodiment, the number of first rollers 23 and second rollers 24 is even, and they are symmetrically arranged at different circumferential angle positions on the outer periphery of the screw 21, and form rolling engagement with the corresponding thread structure 211.

[0048] The first roller 23 and the second roller 24 are cylindrical members extending axially, and have a plurality of annular teeth 23t and 24t on their outer circumferential surfaces for meshing with corresponding structures on the screw 21 and nut 22. Specifically, each first roller 23 and second roller 24 is divided axially into at least one first meshing section 231 and 241 and at least one second meshing section 232 and 242, wherein the diameter of the first meshing section 231 and 241 is larger than the diameter of the second meshing section 232 and 242. The annular teeth 23t and 24t of the first meshing sections 231 and 241 are used for rolling meshing with the thread structure 211 of the screw 21, and the annular teeth 23t and 24t of the second meshing sections 232 and 242 are used for rolling meshing with the annular groove 221g of the annular groove section 221 of the nut 22 (e.g., ...). Figure 3B (As shown).

[0049] like Figure 3A and Figure 4 As shown, the first engagement sections 231 and 241 are located in the axial middle section of the first roller 23 and the second roller 24, respectively, and each end of the first engagement section 232 and 242 is provided with a second engagement section 232 and 242, thereby forming a double-sided rolling engagement relationship with the screw 21 and the nut 22. Furthermore, to avoid interference between the first engagement sections 231 and 241 and the inner wall of the nut 22, these sections are correspondingly arranged in the clearance groove section 223 of the nut 22, providing sufficient radial space so that they only contact the screw 21 and participate in rolling.

[0050] The ends 233, 234, 243, and 244 of the first roller 23 and the second roller 24 do not have annular teeth 23t and 24t, and are fitted with retainer assembly K. The axial length L1 of one end 233 of the first roller 23 is less than the axial length L2 of the other end 234. The axial length L4 of one end 244 of the second roller 24 is less than the axial length L3 of its corresponding end 243. Thus, an axial length difference is formed between the ends 233, 234, 243, and 244 of the first roller 23 and the second roller 24. The purpose of this design will be further explained below.

[0051] Please refer to the following: Figure 2 and Figure 3A and Figure 6 As shown, the retaining member assembly K includes a first retaining member 25 and a second retaining member 26, respectively disposed at both ends of the roller assembly R and fixed inside the nut 22. The first retaining member 25 has a plurality of first positioning grooves 251 and at least one first mating part 252. The plurality of first positioning grooves 251 are used to accommodate one end 233, 243 of the plurality of first rollers 23 and second rollers 24. The second retaining member 26 has a plurality of second positioning grooves 261 and at least one second mating part 262. The plurality of second positioning grooves 261 are used to accommodate corresponding ends 234, 244. The first mating parts 252 and second mating parts 262 are used to cooperate with the preload assembly P described later. The groove depths of the first and second positioning grooves 251 and 261 can be set to be the same, to accommodate the difference in axial length of the two ends 233, 234, 243, 244 of the first and second rollers 23 and 24, thereby forming a selective preload configuration. In other implementations, the difference in groove depth between the first and second positioning grooves 251 and 261 can be used to form the first and second gaps 31 and 32 by matching the same axial length between the two ends 233, 234, 243 and 244 of the first roller 23 and the second roller 24, thereby achieving a selective preload configuration.

[0052] like Figure 4 , Figure 6 , Figure 7A and Figure 7B As shown, this embodiment utilizes the difference in axial length between the two ends of the first and second rollers 23 and 24 to form a first gap 31 and a second gap 32 between the first and second retainers 25 and 26, respectively. Specifically, the axial length L1 of one end 233 of the first roller 23, which is pivotally connected to the first positioning groove 251, is less than the groove depth of the first positioning groove 251 and less than the axial length L3 of one end 243 of the second roller 24 (e.g., ...). Figure 4 (As shown). That is, one end 233 of the first roller 23 cannot be inserted into the bottom of the first positioning groove 251, and a first gap 31 is formed between it and the first retainer 25 (as shown). Figure 6 , Figure 7A(As shown). Furthermore, the axial length L4 of one end 244 of the second roller 24, which is pivotally connected to the second positioning groove 261, is less than the groove depth of the second positioning groove 261 and less than the axial length L2 of the other end 234 of the first roller 23 on the same side (as shown). Figure 4 (As shown). That is, one end 244 of the second roller 24 cannot be inserted into the bottom of the second positioning groove 261, and a second gap 32 is formed between it and the second retainer 26 (as shown). Figure 6 , Figure 7B (As shown). The two gaps 31 and 32 are staggered at opposite ends of the roller assembly R, so that the force directions of different rollers are opposite, establishing a guideable preload transmission direction (as shown). Figure 6 (As shown).

[0053] Please see Figure 2 and Figure 5 As shown, the preload assembly P includes a plurality of preload screws 27, for example, at least two, respectively disposed between the first retainer 25 and the second retainer 26, and at an angle offset from the roller assembly R. Each preload screw 27 has a threaded end 271 and a head end 272 at both ends. The threaded end 271 passes through the second mating portion 262 (e.g., through hole) of the second retainer 26 and is threaded to the first mating portion 252 of the first retainer 25, which has an internal thread that engages with the threaded end 271. The head end 272 abuts against the outside of the second mating portion 262 of the second retainer 26. By tightening the preload screws 27, the axial clamping force is adjusted to bring the first and second retainers 25 and 26 closer together, thereby clamping the roller assembly R.

[0054] like Figure 5 , Figure 6 , Figure 7A and Figure 7BAs shown, when the preload screw 27 is tightened, an axial clamping force is generated, causing the first retainer 25 and the second retainer 26 to approach each other and apply a clamping force to the roller assembly R. Due to the existence of the first gap 31 and the second gap 32, the axial preload generated by each preload screw 27 is selectively transmitted to the non-gap ends of the first and second rollers 23 and 24. Specifically, there is a gap 31 between the first roller 23 and the first retainer 25 at one end 233, so the preload of the first retainer 25 will not act on the first roller 23, but will be directly transmitted from the second retainer 26, which is in close contact with the first roller 23, thereby pushing the first roller 23 to the left in the figure (towards the first retainer 25). The second roller 24 has a second gap 32 between its end 244 and the second retainer 26. Therefore, the preload of the second retainer 26 will not act on the second roller 24, but will be directly transmitted from the first retainer 25, which is in close contact with the second roller 24, thereby pushing the second roller 24 to the right in the figure (towards the second retainer 26). In this way, the different rollers are subjected to opposite forces, achieving a bidirectional axial preload effect, ensuring that each of the first and second rollers 23 and 24 can stably and tightly adhere between the screw 21 and the nut 22, maintaining pure rolling contact and avoiding slippage and free rotation.

[0055] Therefore, as Figure 6 and Figure 8A and Figure 8B As shown, the first roller 23, which is pushed to the left (towards the first retainer 25), has its annular teeth 23t abutting against the right side of the thread structure 211 of the screw 21 and the right side of the annular groove 221g of the nut 22, thus generating a stable meshing contact.

[0056] Similarly, such as Figure 6 , Figure 9A and Figure 9B As shown, the second roller 24, pushed to the right (towards the second retainer 26), has its annular teeth 24t facing the left side of the threaded structure 211 of the screw 21 and abutting the left side of the annular groove 221g of the nut 22, achieving stable contact on both sides with the screw 21 and the nut 22. This forms a stable rolling engagement, effectively preventing slippage and freewheeling. Thus, it not only compensates for the clearance G caused by manufacturing tolerances (see [reference]...) Figure 1B and Figure 1C As shown in the figure, it can also suppress any loosening that may occur due to initial assembly, ensuring that the roller movement reaches a stable state as soon as it starts.

[0057] Although the foregoing embodiment indicates that the two preloaded screws 27 are locked from the second retainer 26 toward the first retainer 25, it is not limited thereto. Please refer to [further details]. Figure 10As shown, the two preload screws 27 can also apply axial clamping forces to the first and second retainers 25 and 26 from opposite directions. Specifically, the threaded end 271 of one preload screw 27 passes through the second mating portion 262 (e.g., through hole) of the second retainer 26 and is screwed to the first mating portion 252 of the first retainer 25. The first mating portion 252 has an internal thread that engages with the threaded end 271. The head end 272 abuts against the outside of the second mating portion 262 of the second retainer 26. The threaded end 271 of the other preload screw 27 passes through the first mating portion 252 (e.g., through hole) of the first retainer 25 and is screwed to the second mating portion 262 of the second retainer 26. The second mating portion 262 has an internal thread that engages with the threaded end 271. The head end 272 abuts against the outside of the first mating portion 252 of the first retainer 25. By tightening the preload screw 27 in the opposite direction to adjust its axial clamping force, the first and second retainers 25 and 26 are brought closer to each other, thereby clamping the roller assembly R, thereby achieving the above-mentioned function and effect.

[0058] In summary, this invention, by directly applying the preload assembly P between the two retaining members 25 and 26, uses the preload screw 27 to generate an adjustable tightening force, replacing the traditional elastic element or retaining ring method. This not only allows for precise adjustment of the applied pressure but also simplifies component configuration and axial structural design. The structure of this invention eliminates the need for an additional retaining ring to fix the axial position of the retaining member assembly K, thereby eliminating friction between the retaining member assembly K and the retaining ring. This avoids efficiency loss and roller instability caused by friction interference, contributing to improved system reliability and lifespan. Furthermore, by combining the axial length differences between the two ends 233, 234, 243, 244 of the first and second rollers 23 and 24, or the groove depth differences between the first and second positioning grooves 251, 261 of the first and second retainers 25 and 26, staggered first and second gaps 31 and 32 are formed between the first and second rollers 23 and 24 and the first and second retainers 25 and 26. This guides the axial preload to selectively act on specific rollers, thereby establishing a staggered bidirectional force application mechanism. This structure can not only effectively compensate for the gaps caused by machining tolerances and eliminate initial backlash, but also stabilize the movement trajectory of the first and second rollers 23 and 24, ensuring they always maintain a pure rolling state, effectively suppressing sliding friction and freewheeling, and improving rolling stability and overall transmission accuracy.

[0059] The above description is a detailed account of the preferred embodiments of this utility model. Any equivalent or similar modifications made based on the specification and drawings disclosed in this utility model shall naturally be included within the protection scope of this utility model patent.

Claims

1. An axial preload device for the cage of a roller screw, characterized in that, include: A screw, the outer circumferential surface of which is provided with a threaded structure; A nut having an inner hole for housing the screw, the inner side of which has at least one annular groove section; A roller assembly is disposed between the screw and the nut, having a plurality of first rollers and a plurality of second rollers arranged in an alternating pattern. Each first roller and second roller has a plurality of annular teeth on its outer circumferential surface, which respectively mesh with the thread structure and the annular groove section. A retainer assembly, disposed within the nut and located at both ends of the roller assembly, includes a first retainer and a second retainer. The first retainer is connected to one end of a plurality of first and second rollers, and the second retainer is connected to the other end of the plurality of first and second rollers. A first gap is provided between one end of the plurality of first rollers and the first retainer, and a second gap is provided between one end of the plurality of second rollers and the second retainer. The plurality of first and second gaps are arranged in the roller assembly. The roller assembly is arranged in a staggered manner at opposite ends; a preload assembly is disposed between the first retainer and the second retainer, generating an adjustable clamping force to bring the first retainer and the second retainer closer together and clamp the roller assembly, and in conjunction with the staggered first gap and the second gap, applies axial preload in opposite directions and with adjustable preload to the plurality of first rollers and the plurality of second rollers respectively, so that the roller assembly forms a staggered bidirectional axial preload to reduce the backlash between the screw and the nut and maintain pure rolling contact of the rollers.

2. The axial preload device for the cage of the roller screw as described in claim 1, characterized in that: The preload assembly includes at least two preload screws, which are respectively disposed between the first retainer and the second retainer and are parallel to the plurality of first rollers and the plurality of second rollers. Each preload screw has a threaded end and a head end. The threaded end is threaded to one of the first retainer and the second retainer, and the head end abuts against the other of the first retainer and the second retainer.

3. The axial preload device for the cage of the roller screw as described in claim 2, characterized in that: The first retainer is provided with a plurality of first positioning grooves and at least one first mating part. The plurality of first positioning grooves are used to accommodate one end of the plurality of first rollers and the plurality of second rollers. The at least one first mating part is used to accommodate the threaded end of the preload screw and is provided with an internal thread that mates with the threaded end. The second retainer is provided with a plurality of second positioning grooves and at least one second mating part. The plurality of second positioning grooves are used to accommodate the other ends of the plurality of first rollers and the plurality of second rollers. The at least one second mating part corresponds to the head end of the pre-tightening screw.

4. The axial preload device for the cage of the roller screw as described in claim 3, characterized in that: The axial length of one end of the first roller housed in the first positioning groove is less than the length of its other end, and it does not contact the bottom of the first positioning groove, thereby forming the first gap; and The axial length of one end of the second roller housed in the second positioning groove is less than the length of the other end, and it does not contact the bottom of the second positioning groove, so as to form the second gap.

5. The axial preload device for the cage of the roller screw as described in claim 2, characterized in that: The first retainer is provided with a plurality of first positioning grooves and at least one first mating part, and the second retainer is provided with a plurality of second positioning grooves and at least one second mating part; and the threaded end of one of the pre-tightening screws passes through the second mating part of the second retainer and is screwed to the first mating part of the first retainer, and the head end abuts against the outside of the second mating part of the second retainer; the threaded end of another pre-tightening screw passes through the first mating part of the first retainer and is screwed to the second mating part of the second retainer, and the head end abuts against the outside of the first mating part of the first retainer.

6. The axial preload device for the cage of the roller screw as described in claim 5, characterized in that: The first retainer and the second retainer each have an internal thread at the first mating portion and the second mating portion corresponding to the threaded end to mate with the threaded end.

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