Miniature circulating type planetary roller screw rod pair

Abstract

The invention relates to the technical field of high-precision transmission, and particularly discloses a miniature circulating planetary roller screw rod pair which is applied to compact spaces such as a robot end effector and a precision machine tool, and comprises a screw rod, a nut, a pair of retainers, a plurality of rollers and a pair of end surface composite cams, the radial thickness of a radial lifting convex part of the end face composite cam is gradually reduced in the direction away from an axial reset convex part, and the radial height of a radial lifting face is obliquely reduced in the direction away from the axial reset convex part. The free end of the roller is provided with a gradually-shrinking section which is gradually shrunk towards the size, and the gradually-shrinking section is used for being in contact fit with the radial lifting face. According to the structure, the radial contact stroke and the matching envelope size between the pin roller and the radial lifting convex part are obviously reduced, the structural space required by radial motion is reduced, more compact layout and smaller radial size of the circulating type planetary pin roller lead screw pair are favorably realized, and key support is provided for miniaturization and even microminiaturization design of a system.

Description

Technical Field

[0001] This invention relates to the field of high-precision transmission technology, specifically to a miniature circulating planetary roller screw pair applicable to compact spaces such as robot end effectors and precision machine tools. Background Technology

[0002] The circulating planetary roller screw pair is a high-performance linear drive component widely used in robots, spacecraft and precision transmission devices. It achieves high load capacity, high precision and long service life by circulating multiple rollers in the threaded channel between the screw and nut.

[0003] As the roller rolls within the threaded channel, axial relative displacement occurs due to the discrepancy between its helix angle and that of the nut. Each time the lead screw rotates once, the roller moves axially by one lead relative to the lead screw. To achieve cyclic motion, when the roller reaches the notch area of ​​the nut, the end face cams located at both ends of the nut apply an axial thrust to the roller. Under this action, the roller rises along the thread angle direction, thus bypassing the major diameter section of the lead screw and completing its stroke reset, re-entering the threaded channel to continue its operation.

[0004] An existing type of circulating planetary roller screw pair has an axial reset cam and a radial lifting cam integrated on the end face cam. When the roller runs to the notch area of ​​the nut, the end face cam needs to apply an axial thrust (to make the roller retract by one lead) and a radial lifting force (to make the roller disengage from the screw thread).

[0005] However, in this type of recirculating planetary roller screw assembly, when the screw lead is reduced to a miniaturized size of 0.5 mm or even smaller, the geometry of the end face cam is extremely small, and the radial lifting cam exhibits a cantilever structure with a thickness of only about 0.2 mm and an arm length of about 0.4 mm. Such a small radial lifting cam, due to its extremely thin cantilever, suffers from insufficient strength and is prone to elastic deformation or breakage. Furthermore, the rollers and the radial lifting cam often contact at the root fillet, which can easily lead to interference and jamming, severely affecting the operational stability and lifespan of the screw assembly. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to address the risks of insufficient strength, elastic deformation or fracture, and interference jamming caused by the extremely thin cantilever of the radial lifting protrusion in the miniaturized structure of the existing circulating planetary roller screw pair after miniaturization. In addition, the roller and the radial lifting protrusion often come into contact at the root fillet, which seriously affects the operating stability and life of the screw pair.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a miniature circulating planetary roller screw pair, comprising a screw, a nut, a pair of oppositely arranged cages, multiple rollers, and a pair of end-face composite cams disposed on the outer side of the cages; the end face of the end face composite cams is provided with an axial reset protrusion and a radial lifting protrusion, the axial end face of the axial reset protrusion forms an axial reset guide surface, and the radial outer surface of the radial lifting protrusion forms a radial lifting surface; the radial thickness of the radial lifting protrusion gradually decreases in the direction away from the axial reset protrusion, and the radial height of the radial lifting surface decreases obliquely in the direction away from the axial reset protrusion; the free end of each roller is provided with a tapered section that gradually decreases in size, the tapered section being used to contact and engage with the radial lifting surface.

[0008] In a preferred embodiment, the lead screw is provided with an external thread, the nut is provided with an internal thread, and the roller is disposed between the lead screw and the nut.

[0009] In a preferred embodiment, the inner wall of the nut is provided with an axially extending relief groove that penetrates the internal thread, and the axial reset protrusion and the radial lifting protrusion are located at positions corresponding to the relief groove.

[0010] In a preferred embodiment, the cage is provided with a plurality of roller guide grooves evenly distributed along the circumferential direction, and the roller guide grooves extend radially along the cage.

[0011] In a preferred embodiment, the roller includes a threaded section and smooth sections located at both ends of the threaded section, and the tapered section is disposed at the free end of the smooth section.

[0012] In a preferred embodiment, the contact point between the outer surface of the tapered section and the radially raised surface is located at the axial center of the radially raised surface or on a side away from the axially resetting protrusion.

[0013] In a preferred embodiment, the outer surface of the tapered section is a conical surface.

[0014] In a preferred embodiment, the inclination angle of the conical surface is greater than the inclination angle of the radially raised surface.

[0015] In a preferred embodiment, the outer surface of the tapering section is a drum-shaped arc surface.

[0016] Compared with the prior art, the miniature circulating planetary roller screw pair of this embodiment has the following advantages:

[0017] (1) The progressive slope of the radial lifting surface and the precise fit design of the roller tapering section significantly reduce the radial contact stroke and fit envelope size between the roller and the radial lifting protrusion, reducing the structural space required for radial movement. This is conducive to achieving a more compact layout and smaller radial size for the circulating planetary roller screw pair, providing key support for the miniaturization and even micro-miniaturization design of the system.

[0018] (2) The radially raised cam adopts an innovative structure with gradually varying thickness, and its root thickness is significantly increased, which effectively improves the bending section modulus and load-bearing capacity. This design is particularly beneficial for the miniaturization and micro-miniaturization of cyclic planetary roller screw pairs: with the background of size reduction, the root of the radially raised cam can still maintain excellent strength and rigidity, significantly reducing the risk of fatigue or cantilever fracture caused by stress concentration, and improving the reliability and service life of the end face composite cam under long-term cyclic load.

[0019] (3) By designing the inclination angle of the conical surface to be greater than that of the radial lifting surface, and optimizing the arrangement of the contact points between the drum-shaped arc surface and the radial lifting surface, the contact position between the roller and the radial lifting protrusion is made more biased towards the outer region of the radial lifting surface. This design can effectively prevent interference or even jamming between the roller and the root of the radial lifting protrusion, while reducing stress concentration at the root. As a result, the roller experiences more uniform force and moves more smoothly during reversal, significantly reducing the risk of impact and jamming, thereby improving the stability and reliability of the transmission system. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the internal structure of the circulating planetary roller screw pair in this embodiment; Figure 2 This is a schematic diagram of the internal three-dimensional structure of the circulating planetary roller screw pair in this embodiment; Figure 3 This is a schematic diagram of the end-face compound cam in this embodiment; Figure 4 This is a cross-sectional view of the composite cam in this embodiment. Figure 5 This is a schematic diagram of the roller structure of the first embodiment in this example; Figure 6 for Figure 5 The diagram shows the fit between the roller and the end face compound cam. Figure 7 This is a schematic diagram of the roller structure of the second embodiment in this example; Figure 8 for Figure 7 The diagram shows the fit between the roller and the end face composite cam. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0022] In the description of this invention, it should be understood that the terms "upper", "lower", "front", "rear", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention 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. Therefore, they should not be construed as limitations on this invention.

[0023] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation", "connection" and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, an integral connection, or a detachable connection; they can refer to the internal connection of two components; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0024] like Figure 1 , Figure 2 As shown, a miniature circulating planetary roller screw assembly of this embodiment includes a screw 20, a nut 30, a cage 50, rollers 40, and a face composite cam 10. The screw 10 has external threads, and the nut 30 has internal threads. The inner wall of the nut 30 has an axially extending clearance groove 31 that penetrates the internal threads. Multiple rollers 40 are disposed between the screw 10 and the nut 30, and the positions of the rollers 40 are held by the cages 50 on both sides.

[0025] In this embodiment, the cage 50 is provided with a plurality of roller guide grooves 51 evenly distributed along the circumferential direction, and the roller guide grooves 51 extend radially along the cage. In this embodiment, as shown... Figure 5 , Figure 7 As shown, the roller 40 includes a threaded section 41 and smooth sections 42 located at both ends of the threaded section. The smooth sections 42 pass through the roller guide groove 51, so that the roller 40 has space for radial displacement.

[0026] In this embodiment, the end-face compound cam 10 is disposed on the outer side of the cage 50. The structure of the end-face compound cam 10 is as follows: Figures 3-4As shown, the cam body 11 has an axial reset protrusion 12 on its end face, and the axial end face of the axial reset protrusion 12 forms an axial reset guide surface 13. A radial lifting protrusion 14 is integrally formed at the radial bottom of the axial reset protrusion 12. The height of the radial lifting protrusion 14 protruding from the end face of the cam body is higher than the protrusion height of the axial reset protrusion 12, and the radial outer surface of the radial lifting protrusion 14 forms a radial lifting surface 15.

[0027] In this embodiment, the axial reset protrusion 12 and the radial lifting protrusion 13 are located at positions corresponding to the clearance groove 31.

[0028] The working principle of the circulating planetary roller screw pair in this embodiment is as follows: When the lead screw 20 rotates one revolution, the roller 40 moves axially by one lead relative to the lead screw 20. When the roller 40 runs to the clearance groove 31 of the nut 30, the smooth section 42 of the roller 40 contacts and engages with the radial lifting surface 15 of the radial lifting protrusion 14, driving the roller 40 to move radially and pass over the tooth crest of the lead screw 20; at the same time, the free end face of the smooth section 42 of the roller 40 contacts and engages with the axial reset guide surface 13 of the axial reset protrusion 12, guiding the roller 40 to axial reset, thus realizing the coordinated movement of radial lifting and axial reset of the roller during the reversing process.

[0029] As a special feature of this embodiment, such as Figure 3 , Figure 4 As shown, the radial thickness of the radially lifting protrusion 14 gradually decreases in the direction away from the axially resetting protrusion 12, and the radial height of the radially lifting surface 15 decreases at an angle away from the axially resetting protrusion. In this embodiment, the radially lifting protrusion 14 adopts an innovative structure with a gradually varying thickness, and its root thickness is significantly increased, effectively improving the bending section modulus and load-bearing capacity. This design is particularly beneficial for the miniaturization and micro-miniaturization of cyclic planetary roller screw pairs: with reduced size, the root of the radially lifting protrusion 14 can still maintain excellent strength and rigidity, significantly reducing the risk of fatigue or cantilever fracture caused by stress concentration, and improving the reliability and service life of the end face composite cam 10 under long-term cyclic loads.

[0030] Furthermore, in this embodiment, as Figure 5 , Figure 7As shown, the free end of the smooth section 42 on the roller 40 is provided with a radially tapered section 43, which is used to contact and engage with the radially raised surface 15. In this embodiment, the precise fit between the progressive slope of the radially raised surface 15 and the tapered section 43 of the roller significantly reduces the radial contact stroke and engagement envelope size between the roller 40 and the radially raised protrusion 14, thereby reducing the structural space required for radial movement. This facilitates a more compact layout and smaller radial size for the cyclic planetary roller screw pair, providing key support for the miniaturization and even micro-miniaturization of the system design.

[0031] As a preferred embodiment, the roller 40 of the first structural form is, for example... Figure 5 , Figure 6 As shown, the outer surface of the tapered section 43 is a drum-shaped arc surface 44, and the contact point A between the drum-shaped arc surface 44 and the radial lifting surface 15 is located on the side of the radial lifting surface 15 that is biased away from the axial reset protrusion 12. It should be noted that the contact point A is usually designed at the axial center of the radial lifting surface 15, or biased away from the axial reset protrusion 12.

[0032] As a preferred embodiment, the roller 40 of the first structural form is, for example... Figure 7 , Figure 8 As shown, the outer surface of the tapered section 43 is a conical surface 45. Furthermore, in this embodiment, the inclination angle of the conical surface 45 is greater than the inclination angle of the radially lifting surface 15. This arrangement aims to make the contact point A between the roller 40 and the radially lifting protrusion 14 more biased towards the outer region of the radially lifting surface 15.

[0033] In this embodiment, the contact position between the roller and the radially raised protrusion is more biased towards the outer region of the radially raised surface. This design effectively prevents interference or even jamming between the roller and the root of the radially raised protrusion, while reducing stress concentration at the root. As a result, the roller experiences more uniform force and moves more smoothly during reversal, significantly reducing the risk of impact and jamming, thereby improving the stability and reliability of the transmission system.

[0034] In summary, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A miniature circulating planetary roller screw assembly, comprising a screw, a nut, a pair of opposing cages, a plurality of rollers, and a pair of end-face composite cams disposed on the outer side of the cages; wherein the end faces of the end faces of the composite cams are provided with axial return protrusions and radial lifting protrusions, the axial end face of the axial return protrusions forming an axial return guide surface, and the radial outer surface of the radial lifting protrusions forming a radial lifting surface; characterized in that, The radial thickness of the radial lifting protrusion gradually decreases in the direction away from the axial reset protrusion, and the radial height of the radial lifting surface decreases at an angle in the direction away from the axial reset protrusion; the free end of the roller is provided with a tapered section that gradually decreases in size, and the tapered section is used to contact and cooperate with the radial lifting surface.

2. The miniature circulating planetary roller screw assembly according to claim 1, characterized in that, The lead screw is provided with an external thread, the nut is provided with an internal thread, and the roller is provided between the lead screw and the nut.

3. The miniature circulating planetary roller screw assembly according to claim 2, characterized in that, The inner wall of the nut is provided with an axially extending relief groove that penetrates the internal thread, and the axial reset protrusion and the radial lifting protrusion are located at positions corresponding to the relief groove.

4. The miniature circulating planetary roller screw assembly according to claim 1, characterized in that, The cage is provided with a plurality of roller guide grooves evenly distributed along the circumferential direction, and the roller guide grooves extend radially along the cage.

5. The miniature circulating planetary roller screw assembly according to claim 1, characterized in that, The roller includes a threaded section and smooth sections located at both ends of the threaded section, and the tapered section is located at the free end of the smooth section.

6. The miniature circulating planetary roller screw assembly according to claim 1, characterized in that, The contact point between the outer surface of the tapering section and the radially raised surface is located at the axial center of the radially raised surface or on the side away from the axially resetting protrusion.

7. The miniature circulating planetary roller screw assembly according to claim 6, characterized in that, The outer surface of the tapered section is a conical surface.

8. The miniature circulating planetary roller screw assembly according to claim 7, characterized in that, The inclination angle of the conical surface is greater than the inclination angle of the radially raised surface.

9. The miniature circulating planetary roller screw assembly according to claim 6, characterized in that, The outer surface of the tapering section is a drum-shaped arc surface.

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