Differential roller screw drive assembly

Abstract

The invention provides a differential roller screw transmission assembly, which comprises a nut, a screw, a plurality of rollers and a retainer group, the nut is provided with an inner hole penetrating in the axial direction, and an annular tooth section is arranged on the inner circumferential face. The threaded rod is arranged in the inner hole in a penetrating mode, a thread structure is arranged on the peripheral face of the threaded rod, the thread structure is provided with M thread lines, and M is an integer larger than one. The plurality of rollers are arranged between the nut and the screw. Each roller has a uniform pitch diameter, the periphery of each roller is provided with an annular tooth groove structure with a plurality of tooth grooves, and the annular tooth groove structures are meshed with the thread structure of the screw rod and the annular tooth section of the nut. The number of the plurality of rollers is N, and N is a factor greater than one of M. The retainer group is arranged at two ends of the roller. And the spiral angle of each thread line of the screw is matched with the circumferential distance of the plurality of rollers, so that the axial distance between any thread line and the corresponding tooth groove between the two adjacent rollers is equal to the pitch of the annular tooth groove structure. Therefore, the part design and the manufacturing process are simplified, and the load sharing effect is improved.

Description

Technical Field

[0001] The present invention relates to a transmission assembly, and in particular to a differential roller screw transmission assembly which can convert rotational motion into axial linear motion and has differential transmission characteristics. Background Art

[0002] Differential roller-screw drive assemblies are widely used in equipment requiring high-load and high-rigidity linear drives, such as robotic arms, robotic systems, and automated devices. These assemblies typically consist of a screw, a nut, and multiple rollers. The rollers are positioned between the screw and nut. Through rolling contact between the rollers, the screw, and the nut, the screw's rotational motion is converted into axial linear motion relative to the nut, achieving a differential drive effect.

[0003] like Figure 1A As shown, existing differential roller screw transmission assemblies mostly use a roller structure with large and small diameter sections. The assembly includes a nut 12, a screw 11, and a plurality of rollers 13. The large diameter section 131 of each roller 13 meshes with the thread structure of the screw 11, while the small diameter section 132 meshes with the annular tooth section 120 on the inner circumference of the nut 12. Although this design can avoid tooth interference, the small diameter section only has a guiding or avoidance function, and the area actually involved in the meshing is limited to the large diameter section, resulting in a limited contact section between the roller and the nut, which limits the load-bearing capacity. To strengthen this defect, it is often necessary to lengthen the nut structure to increase the meshing length, resulting in an increase in the overall structural volume.

[0004] like Figure 1B and Figure 1C As shown, the screw 11 of the transmission assembly has two thread lines (not shown) and is equipped with six rollers 13. Since the ratio of the number of thread lines and rollers in the circumferential direction does not form an integer multiple correspondence, and each thread line has a helix angle, a fixed axial displacement will be generated on the rollers at different circumferential positions. The relationship between this axial displacement and the pitch of the roller tooth groove is also not an integer multiple, resulting in the thread line 11t having a non-integer multiple pitch offset at the corresponding position of the tooth groove on different rollers (13a, 13b, 13c). This offset phenomenon makes it impossible to achieve complete and precise meshing with rollers with a single tooth groove configuration. Therefore, existing designs often require individual adjustment of the axial starting position of the tooth groove for each roller to match the tooth profile distribution of the specific thread line at its corresponding circumferential position.

[0005] like Figure 1C The figure further illustrates the correspondence between one thread line 11t and three adjacent rollers 13a, 13b, and 13c. Due to the helix angle of the thread line 11t, the tooth profile heights corresponding to different roller positions will vary axially, indicated as displacement difference D in the figure. This displacement difference D is the cumulative axial offset between the multiple rollers caused by the circumferential expansion of the thread line.

[0006] To ensure that each roller accurately matches a specific thread profile, existing designs typically require individual adjustment of the axial position of the tooth grooves of each roller's large diameter section 131. For example, rollers 13a, 13b, and 13c shown in the figure are three roller assemblies with different tooth groove starting positions.

[0007] Although this type of design can meet the meshing requirements, it requires the development of multiple roller parts with different tooth groove configurations, which increases the number of parts, increases manufacturing and management costs, and adversely affects assembly efficiency and modular design.

[0008] Therefore, there is an urgent need to develop an improved differential roller screw transmission assembly to overcome the problems of manufacturing and assembly difficulties, reduced load efficiency, etc. caused by the diverse roller forms, insufficient engagement length and structural complexity in the existing design, while alleviating the design limitations of the large nut volume. Summary of the Invention

[0009] To solve the above problems, the present invention aims to provide a differential roller screw transmission assembly.

[0010] The present invention provides a differential roller screw transmission assembly, characterized by comprising:

[0011] A nut having an inner hole extending axially therethrough, wherein an inner circumferential surface of the nut is provided with an annular tooth section;

[0012] a screw rod, inserted into the inner hole, and having a threaded structure on its outer circumference, wherein the threaded structure has a plurality of thread lines, wherein the number of the plurality of thread lines is M, and M is an integer greater than one;

[0013] a plurality of rollers disposed between the nut and the screw, each roller having a uniform pitch diameter and an annular tooth groove structure disposed on its outer periphery. The annular tooth groove structure has a plurality of tooth grooves for engaging with the thread structure of the screw and the annular tooth section of the nut, wherein the number of the plurality of rollers is N, and N is a factor of M greater than one; and

[0014] A retaining member set is arranged at the axial ends of the plurality of rollers to maintain the circumferential spacing arrangement of the plurality of rollers.

[0015] In an embodiment of the present invention, the thread structure of the screw is provided with a predetermined helix angle, which cooperates with the circumferential spacing configuration of the rollers in the nut so that the axial distance between the tooth grooves corresponding to any thread line on two adjacent rollers is equal to the pitch of the annular tooth groove structure.

[0016] In an embodiment of the present invention, the annular tooth groove structure of the plurality of rollers is arranged in a continuous tooth shape along the axial direction.

[0017] In an embodiment of the present invention, the annular tooth groove structures of the plurality of rollers have a consistent tooth groove pitch.

[0018] In an embodiment of the present invention, the inner circumferential surface of the nut is further provided with an inner groove section, and the inner diameter of the inner groove section is larger than the inner diameter of the annular tooth section.

[0019] In an embodiment of the present invention, the retaining member assembly includes two annular components, which are sleeved on the screw and respectively arranged at two opposite axial ends of the plurality of rollers to jointly maintain the spacing arrangement of the plurality of rollers in the circumferential direction.

[0020] In an embodiment of the present invention, each annular component is provided with a plurality of positioning grooves, each positioning groove correspondingly accommodating an axial end portion of a roller.

[0021] In an embodiment of the present invention, a fixing member is further included. The fixing member is disposed in the inner hole of the nut and abuts against a side of the annular member facing away from the plurality of rollers.

[0022] This allows all rollers to have a uniform pitch diameter, eliminating the need to differentiate between large and small diameter segments or tooth groove position differences. This allows for a standardized roller assembly, simplifies the design and manufacturing process, improves load-bearing capacity, and simultaneously shortens the nut length, miniaturizing the overall structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1A It is a cross-sectional schematic diagram of an existing differential roller screw transmission assembly.

[0024] Figure 1B The figure is a schematic end-on cross-sectional view of the configuration of rollers on the circumference of the screw in a conventional differential roller screw transmission assembly.

[0025] Figure 1C Schematic diagram of the circumferential arrangement of some rollers in a conventional differential roller screw transmission assembly.

[0026] Figure 2 Schematic diagram of the main components of the differential roller screw transmission assembly according to an embodiment of the present invention.

[0027] Figure 3A Schematic cross-sectional view of a differential roller screw transmission assembly according to an embodiment of the present invention.

[0028] Figure 3B FIG2 is a schematic cross-sectional view of a differential roller screw transmission assembly according to another embodiment of the present invention.

[0029] Figure 3C Schematic end view of the cross-section of the rollers in the differential roller screw transmission assembly according to an embodiment of the present invention, arranged circumferentially along the screw.

[0030] Figure 4Schematic diagram of the structure and configuration of the retaining member assembly in an embodiment of the present invention.

[0031] Figure 5A 2 is a three-dimensional schematic diagram of one end portion of a screw according to an embodiment of the present invention.

[0032] Figure 5B FIG. 1 is an end view of one end of a screw according to an embodiment of the present invention.

[0033] Figure 6 FIG2 is a schematic diagram of a circumferential arrangement of some rollers in a differential roller screw transmission assembly according to an embodiment of the present invention.

[0034] Explanation of reference numerals: differential roller screw transmission assembly 1; nut 10; inner hole 100; flange portion 101; annular tooth section 102; inner groove section 103; groove 104; screw 11; thread line 11t; nut 12; annular tooth section 120; rollers 13, 13a, 13b, 13c; large diameter section 131; small diameter section 132; screw 20; thread structure 201; thread line 201t; first thread line 201t1; second thread line 201t2; first thread line 201t3; second thread line 201t4; first thread line 201t5; first thread line 201t6; first thread line 201t7; first thread line 201t8; first thread line 201t9; first thread line 201t10; first thread line 201t112; first thread line 201t123; first thread line 201t13 Third thread 201t3; fourth thread 201t4; fifth thread 201t5; sixth thread 201t6; roller 30; first roller 30a; second roller 30b; third roller 30c; annular tooth groove structure 301; tooth groove 301g; retainer assembly 40; annular member 40r; through hole 400; protrusion 401; positioning groove 402; fixing member 50; axial displacement difference D; reference plane horizontal line HL; number of thread threads M; number of rollers N; helix angle Tooth pitch P; distance L. DETAILED DESCRIPTION

[0035] The structure and functional characteristics of the differential roller screw transmission assembly proposed by the present invention will be described based on the preferred embodiments shown in the accompanying drawings.

[0036] See also Figure 2 、 Figure 3A 、 Figure 3B 、 Figure 3C 、 Figure 4 、 Figure 5A and Figure 5B shown.

[0037] An embodiment of the present invention provides a differential roller screw transmission assembly 1 , comprising: a nut 10 , a screw 20 , a plurality of rollers 30 , and a retaining member assembly 40 .

[0038] The nut 10 is a hollow cylindrical component with an inner hole 100 extending axially through both ends thereof. One end of the nut 10 may be provided with a radially outwardly expanding flange portion 101 to serve as a positioning reference or stop structure for the nut 10 during assembly and to allow the nut 10 to be fixed to an external component of the mechanism.

[0039] like Figure 3A As shown, in this embodiment, the inner circumference of the nut 10 is provided with an annular tooth section 102, which continuously extends along the predetermined meshing section. This design is particularly suitable for application scenarios with high requirements for structural rigidity.

[0040] In contrast, Figure 3B As shown, in another embodiment of the present invention, the inner circumference of the nut 10 is further provided with an inner groove section 103, and the inner groove section 103 can be, for example, arranged between the two annular tooth sections 102. The inner groove section 103 has a relatively large inner diameter, and its inner circumference is not provided with a tooth profile, and does not form contact with the roller 30. The setting of the inner groove section 103 is intended to provide an avoidance space, in particular to prevent the roller 30 from interfering with the nut 10 when slight deformation occurs due to manufacturing tolerances or thermal expansion and contraction during operation, thereby reducing the potential risk of interference and improving the smoothness of movement. This design is suitable for applications with high speeds or long-term operation, giving priority to movement stability and durability rather than maximizing the engagement length. The inner groove section 103 is an optional design, and whether it is provided depends on the needs of the specific application.

[0041] The screw 20 is a long rod-shaped member, such as a long cylindrical shaft, that passes through the inner hole 100 of the nut 10 and is coaxial with the nut 10. Both ends of the screw 20 extend outside the nut 10 to connect to a drive device or other external mechanism. A threaded structure 201 is formed on the outer circumference of the screw 20.

[0042] like Figure 5A and Figure 5B As shown, the thread structure 201 of the screw 20 is a multi-thread design, having M thread lines 201t, where M is an integer greater than 1, such as 2, 3, 4, 5, or 6, to achieve a multi-thread differential engagement function. This embodiment uses M as 6 (i.e., six thread lines) as an example for description. The thread structure 201 includes a first thread line 201t1, a second thread line 201t2, a third thread line 201t3, a fourth thread line 201t4, a fifth thread line 201t5, and a sixth thread line 201t6, each of which has a predetermined helix angle.

[0043] like Figure 3A 、 Figure 3B and Figure 3CAs shown, a plurality of rollers 30 are arranged between the nut 10 and the screw 20 at predetermined angular intervals along the circumferential direction of the screw 20. In this embodiment, each roller 30 has a uniform pitch diameter from one end to the other, and an annular tooth groove structure 301 is provided on its outer circumference. The annular tooth groove structure 301 is arranged in a continuous tooth profile along the axial direction of the roller 30, extending from one end to the other without interruption, forming a plurality of regularly arranged tooth grooves 301g with a uniform pitch. In this embodiment, each roller 30 has a consistent tooth groove configuration. The plurality of tooth grooves 301g intermesh with the thread structure 201 of the screw 20 and the annular tooth segment 102 of the nut 10. In this embodiment, all sections of the annular tooth groove structure 301 of each roller 30 intermesh with the annular tooth segment 102 of the nut 10 and the thread structure 201 of the screw 20.

[0044] The number of the plurality of rollers 30 is N, and N is a factor greater than 1 of the number of threads M of the screw 20. For example, in the present embodiment, the number of threads M of the screw 20 is 6, and N can be 2, 3, or 6 to ensure that the rollers 30 are evenly distributed in the multi-thread structure 201 of the screw 20, avoiding the circumferential uneven distribution caused when the number of rollers and the number of threads cannot form an integer ratio, thereby preventing meshing misalignment or uneven load. The embodiment of the present invention is described using N as 6 (i.e., six rollers) as an example. That is, in this embodiment, the six rollers 30 are evenly distributed according to a preset circumferential angle (e.g., adjacent 60 degrees), so that each roller corresponds to the six threads 201t of the screw 20, ensuring that each thread can form a corresponding meshing with a roller, thereby achieving stable and synchronous multi-point meshing between the screw 20 and the rollers 30.

[0045] like Figure 3A and Figure 4 As shown, the retaining element assembly 40 is disposed at the axial ends of the plurality of rollers 30 to maintain the circumferential spacing of the plurality of rollers 30. In this embodiment, the retaining element assembly 40 comprises two integrally formed annular members 40r, disposed at opposite axial ends of the rollers 30. The two annular members 40r are sleeved around the outer circumference of the screw 20 and engage the untoothed section of the nut 10. Each annular member 40r has a central through-hole 400 for the screw 20 to pass through.

[0046] The surface of the annular member 40r is circumferentially provided with a plurality of spaced-apart protrusions 401. These protrusions 401 define a corresponding number of positioning grooves 402. The groove profile of each positioning groove 402 matches the outer shape of the axial end of the roller 30, accommodating the end of the roller 30 and stabilizing it in a specific circumferential position. Through this design, the retaining assembly 40 spaced the rollers 30 between the screw 20 and the nut 10, ensuring consistent circumferential alignment during rolling motion.

[0047] like Figure 3AAs shown, the fixing member 50 is disposed within the inner bore 100 of the nut 10 and abuts against the side of the annular member 40r facing away from the roller 30. The fixing member 50 can be, for example, an annular elastic fastener embedded in a groove 104 on the inner circumference of the nut 10, forming a locking engagement with the annular member 40r to strengthen the positioning stability of the annular member 40r within the nut 10, preventing axial displacement within the inner bore 100 during prolonged operation or under external forces, thereby improving the structural stability of the entire transmission assembly. However, the fixing member 50 is an optional component and may be installed depending on the actual usage scenario and structural requirements.

[0048] See also Figure 6 As shown, Figure 6 This diagram illustrates the unfolded arrangement of some rollers around the screw in an embodiment of the present invention. Three adjacent rollers, designated first roller 30a, second roller 30b, and third roller 30c, are selected from the six rollers and displayed on a single plane to facilitate visualization of the correspondence between the screw thread and the roller tooth grooves. All rollers have a uniform pitch diameter and are equipped with an annular tooth groove structure with a uniform pitch P on their outer circumference.

[0049] Each thread line (201t1, 201t2, 201t3) of the screw has a preset helix angle The helix angle refers to the angle formed by the thread line at the pitch diameter and the horizontal line HL perpendicular to the screw axis. Figure 6 Three broken lines represent three of the six consecutive threads, labeled from bottom to top as the first thread 201t1, the second thread 201t2, and the third thread 201t3. Because the threads have helix angles, they exhibit consistent axial offset when applied to rollers at different circumferential positions.

[0050] To clearly illustrate the geometric correspondence of this embodiment, it is assumed that the tooth grooves 301g of the first roller 30a, the second roller 30b, and the third roller 30c are numbered in ascending order from bottom to top. Based on this hypothetical numbering, the correspondence between the first thread 201t1, the second thread 201t2, and the third thread 201t3 and the roller tooth grooves is as follows:

[0051] The first thread 201t1 meshes with the i-th tooth groove on the first roller 30a, the i+1th tooth groove on the second roller 30b, and the i+2th tooth groove on the third roller 30c. The second thread 201t2 meshes with the i+1th tooth groove on the first roller 30a, the i+2th tooth groove on the second roller 30b, and the i+3th tooth groove on the third roller 30c. The third thread 201t3 meshes with the i+2th tooth groove on the first roller 30a, the i+3th tooth groove on the second roller 30b, and the i+4th tooth groove on the third roller 30c. The remaining threads (not shown) from the fourth to the sixth thread are offset according to the same pattern, exhibiting a periodic and linear meshing relationship within a lead.

[0052] The distance L marked in the figure represents the axial displacement between the tooth grooves corresponding to any two adjacent rollers of any thread line. This distance L is exactly equal to the pitch P of the tooth groove.

[0053] It can be seen that the embodiment of the present invention is to make the helix angle of the screw thread line The circumferential spacing configuration of multiple rollers cooperates with each other to establish the geometric correspondence shown above. Specifically, the "cooperation" here means that under the premise that the tooth pitch P of the rollers is fixed and consistent, the circumferential spacing between the rollers is designed to correspond to the helix angle. The axial displacement caused by, or vice versa, by adjusting the helix angle The preset circumferential spacing between the corresponding rollers ensures that each thread line, starting from the first roller, moves axially by exactly one tooth pitch P each time it crosses a predetermined circumferential spacing (i.e., the spacing between two adjacent rollers). This ensures that each thread line forms a continuous and equidistant axial meshing relationship with each roller.

[0054] This geometrically matched design allows all rollers to utilize the same pitch diameter and tooth structure, eliminating the need for tooth start position modification or pitch compensation based on the helix angle. This ensures stable, synchronized, and complete multi-line differential rolling transmission between the thread lines and roller tooth grooves. This design not only simplifies roller machining and assembly, but also helps improve overall system assembly tolerances and motion accuracy, making it particularly suitable for precision transmission applications requiring high rigidity and synchronization.

[0055] In summary, the differential roller screw transmission assembly of the present invention utilizes a plurality of rollers having a uniform pitch diameter and a consistent tooth groove pitch, with the number N being a factor greater than one of the number of M threads provided on the screw, thereby forming a corresponding circumferential distribution. With this design, when each thread is wound around the outer circumference of the screw according to its helix angle, the tooth grooves corresponding to any two adjacent rollers of any thread can be spaced axially by exactly one tooth groove pitch, thereby ensuring that all threads can form consistent and stable meshing nodes with the rollers, achieving synchronous and continuous multi-line contact. Furthermore, the rollers can adopt a tooth groove structure that is continuously arranged along the entire axial length, so that they form a stable meshing with the screw and nut along the entire length. In addition to helping to balance the load and improve transmission stability, it also eliminates the need to configure multiple roller types to correspond to different meshing nodes, simplifying the manufacturing and assembly process, further promoting the shortening of the nut structure and the miniaturization of the overall transmission assembly.

[0056] The above description has provided a detailed description of the present invention. However, the above description is merely a preferred embodiment of the present invention and should not limit the scope of the present invention. In other words, all equivalent variations and modifications based on the present invention should still fall within the scope of the present invention.

Claims

1. A differential roller screw transmission assembly, characterized in that: include: A nut having an inner hole extending axially therethrough, wherein an inner peripheral surface of the nut is provided with an annular tooth section; a screw rod, inserted into the inner hole, and having a threaded structure on its outer circumference, wherein the threaded structure has a plurality of thread lines, wherein the number of the plurality of thread lines is M, and M is an integer greater than one; a plurality of rollers disposed between the nut and the screw, each roller having a uniform pitch diameter and an annular tooth groove structure disposed on its outer periphery. The annular tooth groove structure has a plurality of tooth grooves for engaging with the thread structure of the screw and the annular tooth section of the nut, wherein the number of the plurality of rollers is N, and N is a factor of M greater than one; and A retaining member set is arranged at the axial ends of the plurality of rollers to maintain the circumferential spacing arrangement of the plurality of rollers.

2. The differential roller screw transmission assembly according to claim 1, wherein: The multiple threads of the screw each have a helix angle, which is matched with the circumferential spacing of the multiple rollers so that the axial distance between the corresponding tooth grooves of any thread on two adjacent rollers is equal to the pitch of the annular tooth groove structure.

3. The differential roller screw transmission assembly according to claim 1, wherein: The annular tooth groove structure of the plurality of rollers is arranged in a continuous tooth shape along the axial direction.

4. The differential roller screw transmission assembly according to claim 1, wherein: The annular tooth groove structure of the plurality of rollers has a uniform tooth groove pitch.

5. The differential roller screw transmission assembly according to claim 1, wherein: The inner circumferential surface of the nut is further provided with an inner groove section, the inner diameter of the inner groove section is larger than the inner diameter of the annular tooth section.

6. The differential roller screw transmission assembly according to claim 1, wherein: The retaining component assembly includes two annular components, which are sleeved on the screw and respectively arranged at two opposite axial ends of the plurality of rollers to jointly maintain the spacing arrangement of the plurality of rollers in the circumferential direction.

7. The differential roller screw transmission assembly according to claim 6, wherein: Each annular component is provided with a plurality of positioning grooves, and each positioning groove corresponds to and accommodates an axial end portion of a roller.

8. The differential roller screw drive assembly according to claim 6, wherein: The invention also comprises a fixing piece which is arranged in the inner hole of the nut and stops at a side of the annular component which is away from the plurality of rollers.

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