Retainer, retainer assembly and reverse planetary roller lead screw pair

Abstract

The invention discloses a retainer, a retainer assembly and a reverse planetary roller screw pair, the retainer is an annular elastic element, is provided with an axial predetermined bulge or recess, and can continuously provide axial compensation force like a spring after being assembled and pressed; the retainer assembly is combined with the rigid positioning frame to respectively achieve the backlash compensation function and the pin roller positioning function; when being applied to a lead screw pair, the axial clearance generated by abrasion can be automatically and dynamically compensated through the design, the zero-clearance or micro-clearance transmission state is kept for a long time, and therefore the positioning precision and the operation stability are remarkably improved, and noise and impact abrasion are reduced.

Description

Technical Field

[0001] This invention relates to the field of mechanical transmission technology, and in particular to a cage, a cage assembly, and a reverse planetary roller screw pair. Background Technology

[0002] Reverse planetary roller screw pairs are high-precision, high-load-bearing transmission mechanisms that convert rotary motion into linear motion. They offer advantages such as compact structure, high transmission efficiency, high rigidity, and long service life, and are widely used in demanding fields such as industrial robots, CNC machine tools, aerospace actuators, and precision presses. However, during long-term operation, wear inevitably occurs on the meshing thread surfaces of the screw, rollers, and nut. This wear leads to axial clearance between the meshing pairs, causing a series of problems such as transmission return error, decreased motion positioning accuracy, and increased operating noise, severely affecting the overall performance and control stability of the equipment.

[0003] To address the aforementioned axial clearance issue, existing technologies commonly employ an adjustment mechanism added to the nut section, such as a double-nut configuration with adjusting shims. By tightening the double nuts or replacing the shims with those of different thicknesses, the clearance can be manually eliminated or adjusted. However, this solution has significant drawbacks: First, the preload is set once during assembly and cannot dynamically compensate for the clearance that increases due to wear during use. Once the wear exceeds the initial preload, the clearance will reappear. Second, when the clearance exceeds the allowable limit due to wear, the machine must be stopped, the entire transmission component disassembled, and the preload readjusted by replacing or grinding the shims—a time-consuming, labor-intensive process with high maintenance costs. Third, excessive initial preload increases sliding friction between the rollers and raceways, leading to decreased transmission efficiency, faster temperature rise, and potentially accelerated wear.

[0004] In a reverse planetary roller screw assembly, the primary function of the cage is to separate and guide the rollers, preventing them from colliding and tilting. Currently, rigid integral cages or parallel segmented cages are widely used. These traditional cages are purely rigid structures, their function limited to geometric positioning and guidance, lacking any elastic compensation capability and completely unable to adapt to changes in the meshing pair's dimensional chain caused by wear. When clearance occurs, play will also appear between the cage and the rollers in this type of traditional structure, not only failing to suppress clearance but also potentially exacerbating wear due to the impact motion of the rollers. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a cage, a cage assembly and a reverse planetary roller screw pair to solve the above-mentioned technical problem.

[0006] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: A cage for a planetary roller screw assembly includes a cage body, the cage body being an annular elastic element, wherein, in a free and unconstrained state, at least a portion of the cage body has a predetermined bulge or depression in the axial direction to form an axial compensation portion, the axial compensation portion being used to elastically deform after assembly compression to continuously apply an axial compensation force to the rollers of the planetary roller screw assembly.

[0007] The cross-section of the axial compensation part is a continuous or discontinuous arc shape.

[0008] The cage body is a disc spring made of spring steel.

[0009] The cage body has an inner hole at its center for screw assembly with a planetary roller screw pair and multiple radial slots for accommodating the rollers of the planetary roller screw pair, the number of which is equal to the number of rollers.

[0010] After assembly, the cage provides a continuous axial compensation force through axial elastic deformation, which is used to compensate for the meshing clearance caused by the wear of the planetary roller screw assembly parts.

[0011] A cage assembly for a planetary roller screw pair includes a positioning base and an elastic compensation component, wherein the elastic compensation component is a cage as described above, and the positioning base is a rigid cage; the elastic compensation component and the positioning base are arranged side by side along the axial direction.

[0012] The rigid cage is a parallel cage, and the two axially opposite end faces of the parallel cage are parallel flat end faces.

[0013] A reverse planetary roller screw pair includes: Lead screw; A nut is fitted onto the outside of the lead screw; Multiple rollers are disposed between the lead screw and the nut, and the threaded sections of the rollers respectively engage with the threads of the lead screw and the nut; And at least one cage assembly as described above, the cage assembly being mounted on the lead screw, wherein the rigid cage is used to position the rollers, and the elastic compensator is used to apply an axial compensating force.

[0014] The lead screw is provided with two cage assemblies, which are located on both sides of the threaded section of the lead screw.

[0015] The bulges or depressions of the two elastic compensation members are oriented in the same direction.

[0016] Compared with the prior art, the advantages of the present invention are as follows: (1) It achieves adaptive, dynamic, and sustainable compensation for axial clearance, specifically: The cage body, as a ring-shaped elastic element, has an axial compensation part (bulge / depression) that generates pre-compression deformation after assembly, continuously applying axial force to the roller like a spring. This force can automatically adapt to the micro-dimensional chain changes that gradually increase due to wear of the thread surface. The compensation force is continuously present and acts in real time during operation. As long as the deformation of the elastic element has not reached the limit (i.e., the wear is within the preset compensation stroke), the gap will be compensated immediately once it is generated, thus realizing dynamic online compensation. This compensation mechanism is applied throughout the product's lifespan during the compensation stroke, requiring no manual intervention and significantly extending the maintenance time of high-precision operation. (2) Significantly improves transmission performance and reliability, specifically: By using continuous and dynamic preload, the threaded meshing pairs of the rollers, lead screw, and nut are always kept in a state of zero or minimal clearance, effectively eliminating the backlash error caused by clearance, thus maintaining the high positioning accuracy of the transmission pair over a long period of time. It eliminates the impact and collision of rollers caused by clearance during reversal or load changes, making the transmission operation smoother, effectively reducing noise and vibration, and improving the operating quality of the equipment. It avoids impact loads caused by gaps, reducing impact wear and fatigue damage; The elastic compensation element in this design ensures good contact between the rollers and the cage, reducing relative impact and thus improving the durability of the cage. (3) Optimize the preload setting to balance efficiency and lifespan, specifically: This solution allows for the setting of a moderate and reasonable initial preload. A moderate initial preload can ensure transmission stiffness, reduce unnecessary sliding friction, maintain high transmission efficiency, and reduce temperature rise, thereby forming a virtuous cycle of low initial friction and long-term gapless operation, which optimizes the performance and lifespan of the transmission pair as a whole. (4) Significantly reduced maintenance costs and downtime, specifically: Within the wear compensation stroke designed for the product, there is no need to stop the machine, disassemble, replace the shims, or adjust the nuts; even if the wear exceeds the compensation stroke after long-term use and adjustment is required, only the relatively low-cost elastic cage assembly needs to be replaced, rather than disassembling the entire nut assembly or regrinding the high-precision shims, which greatly simplifies the maintenance process. (5) It has a clever structure, high integration, and is easy to implement, specifically: The two core functions of roller positioning and backlash compensation are cleverly integrated into a single component through a combination of a rigid cage (positioning base component) and an elastic compensation component. The structure is compact and does not require any changes to the main design of the planetary roller screw pair. The cage assembly is assembled on the lead screw as a standard component. The assembly process is similar to that of a traditional cage, which makes it easy to apply in new products and also convenient to upgrade and replace in the maintenance of existing equipment. Attached Figure Description

[0017] Figure 1 This is a three-dimensional structural diagram of the cage in this invention; Figure 2 This is a cross-sectional view of the cage structure in this invention; Figure 3 This is an exploded structural diagram of the cage assembly in this invention; Figure 4 This is a cross-sectional view of the cage assembly in this invention; Figure 5 This is a cross-sectional view of the reverse planetary roller screw pair in this invention. Figure 6 A magnified structural diagram of point A in the middle. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0019] As shown in the figure, a cage for a planetary roller screw assembly includes a cage body 1, which is an annular elastic element. In a free and unconstrained state, at least a portion of the cage body 1 has a predetermined bulge or depression in the axial direction to form an axial compensation portion 11. The axial compensation portion 11 is used to undergo elastic deformation after being compressed during assembly to continuously apply an axial compensation force to the rollers 5 of the planetary roller screw assembly.

[0020] In this specific embodiment, the cross-section of the axial compensation part 11 is a continuous or discontinuous arc shape.

[0021] In this specific embodiment, the cage body 1 is a disc spring made of spring steel, forming a disc spring type cage. Therefore, the axial compensation part 11 of the cage body 1 based on the disc spring structure is specifically manifested as the entire conical spring area.

[0022] In this specific embodiment, the cage body 1 has an inner hole 12 at its center for assembly with the lead screw 3 of the planetary roller screw pair. The cage body 1 has multiple radial slots 13 evenly spaced along its circumference, the number of which is equal to the number of rollers 5 in the planetary roller screw pair. With these radial slots 13, the function of the axial compensation part 11 is further refined into multiple elastic arms formed by the slots, capable of independent or coordinated elastic deformation, each elastic arm corresponding to and constraining one roller 5.

[0023] The working principle of the cage is as follows: after being assembled into the planetary roller screw pair and axially constrained, its axial compensation part 11 (i.e., the butterfly spring area / each elastic arm) is forced to undergo compressive elastic deformation. This deformation will store elastic potential energy and generate a continuous axial compensation force directed towards restoring the original shape. This force is intended to be transmitted to the roller 5 to compensate for the meshing clearance caused by long-term wear of the transmission pair.

[0024] As shown in the figure, a cage assembly for a planetary roller screw pair includes a positioning base and an elastic compensation component. The elastic compensation component is the cage as described above, and the positioning base is a rigid cage 2. The elastic compensation component and the positioning base are arranged side by side along the axial direction.

[0025] In this specific embodiment, the rigid cage 2 is a parallel cage. The parallel cage is a rigid ring structure as a whole. Its two opposite end faces along the axial direction are parallel flat end faces. It also has a central inner hole 21 and radial opening slots 22 equal in number to the rollers 5. However, its structure does not have axial elasticity.

[0026] During assembly, the parallel cage is first fitted onto the cage section of the lead screw 3. Then, the disc spring cage is installed with one end face tightly fitted to the corresponding end face of the parallel cage, allowing them to combine into a functional unit with virtually no axial clearance. This tight-fitting assembly effectively ensures that the radial openings (13, 22) on the two cages are aligned axially, forming a series of precise and stable roller 5 receiving grooves, providing reliable radial and circumferential positioning references for the rollers 5. In the overall assembly, the core function of the parallel cage is to provide rigid positioning support, ensuring precise indexing and guidance of the rollers 5 on the circumference; the core function of the disc spring cage is to provide axial elastic compensation force, which is efficiently and losslessly transmitted through its direct contact surface with the parallel cage.

[0027] As shown in the figure, a reverse planetary roller screw pair includes: The lead screw 3 has a lead screw retainer section 32, which is used to assemble the retainer assembly. Nut 4 is a long nut that is fitted onto the outside of lead screw 3, and its inner wall is machined with internal threads; Multiple rollers 5 are positioned between the lead screw 3 and the nut 4. Each roller 5 sequentially comprises a front gear section 51, a roller cage section 52, a roller thread section 53, a roller cage section 54, and a rear gear section 55. The threads of the roller thread section 53 simultaneously mesh with the threaded section of the lead screw 3 and the internal threads of the nut 4, with the threads of the roller 5 and the lead screw 3 having opposite directions of rotation and equal helix angles to achieve reverse transmission. The gear sections at both ends of the roller 5 mesh with the corresponding gear sections on the lead screw 3 to achieve synchronized movement. The cage assembly as described above: In this embodiment, there are two cage assemblies, which are respectively mounted on two lead screw cage sections 32. The bulging direction of the two disc spring type cages (i.e. the protruding direction of the axial compensation part 11) is set to be the same to provide the same preload compensation force.

[0028] After all the above components are assembled and initial preload is applied (which can be achieved through system structure or assembly tooling), the axial compensation parts 11 (conical springs / elastic arms) of the two disc spring cages are axially compressed, generating a continuous elastic thrust pointing towards the rollers 5. This force is transmitted through the components, so that the threaded surfaces of all rollers 5 and the threaded surfaces of the lead screw 3 and nut 4 establish a tight, gapless or micro-gap engagement state.

[0029] During long-term operation, when wear occurs on the meshing thread surfaces of the lead screw 3, roller 5, and nut 4, the original tight fit may loosen. At this time, the pre-compressed disc spring cage will release its stored elastic potential energy due to the slight relaxation of the constraint, resulting in further axial recovery deformation. This deformation pushes the cage assembly and the roller 5 constrained by it to follow a slight axial displacement, thereby automatically and in real time compensating for the increase in axial clearance caused by wear. As long as the total wear is within the preset elastic compensation stroke of the disc spring cage, this automatic compensation mechanism will remain effective, thereby ensuring that the transmission pair maintains high-precision, low-noise, and stable operation throughout its entire life cycle, completely avoiding the cumbersome maintenance required by traditional structures, such as stopping the machine to disassemble and replace shims.

Claims

1. A cage for a planetary roller screw assembly, characterized in that... Includes a cage body, which is an annular elastic element. In a free and unconstrained state, at least a portion of the cage body has a predetermined bulge or depression in the axial direction to form an axial compensation portion. The axial compensation portion is used to undergo elastic deformation after being compressed during assembly to continuously apply axial compensation force to the rollers of the planetary roller screw pair.

2. A retainer as described in claim 1, characterized in that... The cross-section of the axial compensation part is a continuous or discontinuous arc shape.

3. A retainer as described in claim 2, characterized in that... The cage body is a disc spring made of spring steel.

4. A retainer as described in claim 1, characterized in that... The cage body has an inner hole at its center for screw assembly with a planetary roller screw pair and multiple radial slots for accommodating the rollers of the planetary roller screw pair, the number of which is equal to the number of rollers.

5. A retainer as described in claim 1, characterized in that... After assembly, the cage provides a continuous axial compensation force through axial elastic deformation, which is used to compensate for the meshing clearance caused by the wear of the planetary roller screw assembly parts.

6. A cage assembly for a planetary roller screw pair, characterized in that... It includes a positioning base and an elastic compensation component, wherein the elastic compensation component is a retainer as described in any one of claims 1 to 5, and the positioning base is a rigid retainer; the elastic compensation component and the positioning base are arranged side by side along the axial direction.

7. A cage assembly as claimed in claim 6, characterized in that... The rigid cage is a parallel cage, and the two axially opposite end faces of the parallel cage are parallel flat end faces.

8. A reverse planetary roller screw pair, characterized in that... include: Lead screw; A nut is fitted onto the outside of the lead screw; Multiple rollers are disposed between the lead screw and the nut, and the threaded sections of the rollers respectively engage with the threads of the lead screw and the nut; And at least one cage assembly as described in claim 6 or 7, the cage assembly being mounted on the lead screw, wherein the rigid cage is used to position the rollers, and the elastic compensator is used to apply an axial compensating force.

9. A reverse planetary roller screw pair as described in claim 8, characterized in that... The lead screw is provided with two cage assemblies, which are located on both sides of the threaded section of the lead screw.

10. A reverse planetary roller screw pair as described in claim 9, characterized in that... The bulges or depressions of the two elastic compensation members are oriented in the same direction.

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