A mass production method of a double-toothed nut for a planetary roller screw

Abstract

The application discloses a batch manufacturing method of a double-toothed nut for a planetary roller screw, and relates to the technical field of planetary roller screws, which comprises the following steps: machining a workpiece from a forged blank and performing spheroidizing annealing treatment; performing quenching and tempering treatment after rough machining of the workpiece, and then performing high-frequency quenching treatment after semi-finishing machining; manufacturing a gear shaping fixture and machining a flange positioning disc on the outer circumference of the workpiece to assemble a tooth position reference; machining a first inner gear ring and a second inner gear ring which are symmetrically arranged, and controlling the azimuth angle difference P of the central axes of the first inner gear ring and the second inner gear ring to be within the range of-0.015mm to +0.015mm in terms of the arc length L at a tooth division circle; machining an inner thread part in the workpiece in the axial direction; and machining the flange positioning disc to be removed to form the double-toothed nut. The application increases the process structure, designs the gear shaping fixture and changes the heat treatment method, thereby completing integrated manufacturing of the inner gear ring and the inner thread part, and improving the overall strength and assembly precision.

Description

Technical Field

[0001] This invention relates to the field of planetary roller screw technology, and in particular to a method for mass production of double-toothed nuts for planetary roller screws. Background Technology

[0002] Planetary roller screws are a new type of transmission device that can convert rotary motion into linear motion. Planetary roller screws have higher impact resistance than traditional ball screws, and can achieve higher rotational speeds and accelerations.

[0003] A standard planetary roller screw consists of a screw, a nut, and rollers. The screw's outer circumferential surface has an external thread, the nut's inner circumferential surface has an internal thread with the same number of starts and tooth profile as the external thread, and the rollers have a single-start thread with the same tooth profile as the external thread. The tooth profiles of the external, internal, and single-start threads are, for example, triangular. The nut is fitted onto the screw, and several rollers are evenly distributed along the screw's circumference. When the screw rotates, the rollers revolve around the screw's axis and also rotate on their own axes. The internal and external threads have the same helix angle, ensuring pure rolling without axial displacement when the rollers mesh with the nut. This type of planetary roller screw requires very high thread precision; however, in existing technologies, the threads gradually deform due to insufficient strength after a period of operation, affecting performance.

[0004] In addition, some planetary roller screws are also equipped with internal gear rings. In order to cooperate with the rollers, the tooth grooves at both ends of the two internal gear rings must be aligned during assembly. The conventional practice is to use tooling and experience to determine the installation position of the internal gear rings at both ends of the nut. Once the position is determined, a cylindrical shaft is used to fix the position of the two internal gear rings. If the position of the internal gear rings is deviated, it will affect the smoothness of the planetary roller screw pair operation. At the same time, the separate structure of the internal gear rings and the nut will reduce the strength of the entire assembly.

[0005] Finally, due to the limitations of the nut structure, the thread diameter of the nut is the same as the pitch circle of the internal teeth of the internal gear ring. It is impossible to complete the machining of the internal teeth structure at both ends of the double-tooth nut in one clamping by drawing or shaping the teeth. Usually, the internal gear ring is machined separately, and then the internal gear ring and the nut are assembled and fixed together by tooling and matching pins, which makes the assembly extremely difficult. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, the present invention provides a mass manufacturing method for a double-tooth nut for planetary roller screws, which changes the separate manufacturing of the internal gear ring and nut of the planetary roller screw, thus avoiding the assembly difficulties caused by the need for matching the upper and lower internal gear rings and the matching of the cylindrical shaft during the assembly stage. This method reduces the minimum outer diameter of the planetary roller screw nut, improves the overall strength of the nut for planetary roller screws, and enhances the assembly accuracy of the planetary roller screw pair.

[0007] To address the aforementioned problems, the primary objective of this invention is to provide a method for mass manufacturing double-toothed nuts for planetary roller screws, comprising the following steps:

[0008] S1: The workpiece is machined from the forging blank and then subjected to spheroidizing annealing treatment;

[0009] S2: After rough machining of the workpiece, it is heat treated, then semi-finished, and then the area to be machined into the internal thread is subjected to high-frequency quenching.

[0010] S3: Fabricate a gear hobbing fixture and machine a flange positioning plate on the outer circumference of the workpiece. The assembly of the gear hobbing fixture and the flange positioning plate forms a machining tooth position reference.

[0011] S4: Using the machining tooth position reference, a first internal gear ring and a second internal gear ring symmetrically arranged are machined inside both ends of the workpiece, and the azimuth angle difference P between the central axes of the first internal gear ring and the second internal gear ring is controlled to have an arc length L at the tooth pitch circle within the range of -0.015mm to +0.015mm.

[0012] S5: After the first and second internal gear rings are machined, continue to machine the internal thread portion along the axial direction between the first and second internal gear rings of the workpiece;

[0013] S6: Machining removes the flange positioning plate to form a double-toothed nut.

[0014] Furthermore, in step S1, the workpiece material is GCr15, and the spheroidizing annealing treatment reaches HB179-207.

[0015] Furthermore, in step S2, the tempering treatment is carried out until the hardness reaches HRC38-42; the hardness of the high-frequency quenching treatment is as follows: the hardness depth is between 0.433 times the diameter of the tangent circle D of the middle diameter of the internal thread cross section, which is the high hardness zone, and the hardness in the high hardness zone is between 655-745 HV. The hardness of the effective hardened layer zone with a layer depth of 1-1.2 times the diameter of the tangent circle D is HV550.

[0016] Furthermore, in step S3, the flange positioning plate is machined with a pair of symmetrical vertical through pin holes and a plurality of evenly distributed threaded through holes, and the pin holes and threaded through holes are arranged alternately.

[0017] The gear-shaping fixture manufactured includes:

[0018] The connecting base is fixedly connected to the processing platform of the gear shaper;

[0019] The positioning cylinder seat is coaxially and integrally connected to the upper surface of the connecting base. The upper surface of the positioning cylinder seat is provided with a cylindrical pin and an internal hexagonal head screw respectively corresponding to the pin hole and the threaded through hole. The pin hole is adapted to the cylindrical pin and the threaded through hole is adapted to the internal hexagonal head screw.

[0020] The flange positioning disc is adapted to be positioned and connected to the upper surface of the positioning cylinder seat by the cylindrical pin and the internal hexagonal head screw, and the workpiece is located in the lower half of the flange positioning disc and suspended inside the positioning cylinder seat.

[0021] Furthermore, before machining the first and second internal gear rings, symmetrically arranged internal snap ring grooves and gear retraction grooves are machined inside both ends of the workpiece; the internal snap ring grooves and the gear retraction grooves are located at both ends of the first and second internal gear rings.

[0022] Furthermore, in step S3, controlling the azimuth angle difference P between the central axes of the first internal gear ring and the second internal gear ring to have an arc length L at the pitch circle within the range of -0.015mm to +0.015mm specifically includes:

[0023] Place the double-toothed nut on the tooth-shaping fixture. Fix the radial position and tooth position of the double-toothed nut by assembling two pin holes with two cylindrical pins. At the same time, fix the axial position of the double-toothed nut by assembling three threaded through holes with three internal hexagonal head screws.

[0024] Machining the first internal gear ring of the double-tooth nut;

[0025] After completing the machining of the first internal gear ring, remove and flip the double-tooth nut so that the second internal gear ring without teeth faces upward;

[0026] The second internal gear ring is fixed and machined, and the azimuth angle difference P between the first and second internal gear rings under the current installation state is detected.

[0027] Based on the detected azimuth angle difference P, the azimuth angle difference P is compensated at the starting point of the workpiece spindle;

[0028] Based on the compensated starting point coordinates of the workpiece spindle, double-tooth nuts are mass-produced.

[0029] Furthermore, in step S4, the thread width of the internal thread portion is equal to the axial length of the double-tooth nut - 2 * (width of the first internal gear ring + width of the internal snap ring groove and width of the tooth shearing groove).

[0030] Furthermore, in step S5, the gear parameters of the first internal gear ring and the second internal gear ring are the same.

[0031] The second objective of this invention is to provide a double-tooth nut for planetary roller screws, employing the aforementioned method for mass production of the double-tooth nut for planetary roller screws, comprising:

[0032] The nut body has an internal retaining spring groove, an internal gear ring, a toothed relief groove, and an internal thread portion symmetrically arranged along the axial direction inside the nut body. The internal retaining spring groove is located at both ends of the nut body, the internal gear ring is located between the internal retaining spring groove and the toothed relief groove, and the internal thread portion is located between the two toothed relief grooves.

[0033] A third objective of this invention is to provide a planetary roller screw, comprising a double-tooth nut, rollers, and a screw manufactured by the mass production method of the planetary roller screw using a double-tooth nut as described above, wherein the screw is located at the central axis of the double-tooth nut, the double-tooth nut is sleeved on the outside of the screw, and the rollers mesh with the double-tooth nut and the screw respectively.

[0034] Compared with the prior art, the present invention has significant advantages and beneficial effects, specifically reflected in the following aspects:

[0035] The mass production method of the double-tooth nut for planetary roller screws in this invention is as follows: A workpiece is machined from a forged blank and subjected to spheroidizing annealing; after rough machining, the workpiece undergoes quenching and tempering, followed by semi-finishing and high-frequency quenching of the area to be machined into the internal thread portion; a gear-shaping fixture is fabricated, and a flange positioning plate is machined on the outer circumference of the workpiece; the assembly of the gear-shaping fixture and the flange positioning plate forms a machining tooth position reference; based on the machining tooth position reference, a first internal gear ring and a second internal gear ring symmetrically arranged are machined axially at both ends of the workpiece, and the azimuth angle difference P between the central axes of the first and second internal gear rings is controlled to have an arc length L at the tooth pitch circle within the range of -0.015mm to +0.015mm; after the first and second internal gear rings are machined, the internal thread portion is machined axially between the first and second internal gear rings of the workpiece; the flange positioning plate is removed to form the double-tooth nut. By adding a flange positioning plate to the outer circumference of the workpiece, designing a gear-shaping fixture for positioning and connection with the flange positioning plate, and changing the workpiece heat treatment method, the mass production of the integrated structure of the internal gear ring and nut of the planetary roller screw can be completed. While ensuring the overall performance of the planetary roller screw pair, the cost of the entire workpiece will not increase significantly. This method changes the traditional method where the internal gear ring and nut of the planetary roller screw need to be manufactured separately, and the assembly difficulties of matching the upper and lower internal gear rings and matching the cylindrical shaft are required during the assembly stage. It also reduces the minimum outer diameter of the nut for the planetary roller screw, improves the overall strength of the nut for the planetary roller screw, and enhances the assembly accuracy of the planetary roller screw pair. Attached Figure Description

[0036] Figure 1 This is a schematic flowchart of the mass production method of the double-tooth nut for planetary roller screws in an embodiment of the present invention.

[0037] Figure 2 This is a three-dimensional structural diagram of the double-toothed nut in an embodiment of the present invention;

[0038] Figure 3 This is a side view of the double-toothed nut in an embodiment of the present invention;

[0039] Figure 4 for Figure 3 Schematic diagram of the cross-sectional structure at point AA;

[0040] Figure 5 This is a schematic diagram of the main top view of the workpiece in an embodiment of the present invention;

[0041] Figure 6 This is a schematic diagram of the internal structure of the workpiece after it is assembled with the gear hobbing fixture in an embodiment of the present invention;

[0042] Figure 7 This is a schematic diagram of the structure of the workpiece after the internal gear ring has been machined in an embodiment of the present invention;

[0043] Figure 8 This is a schematic diagram of the structure of the workpiece after the internal gear ring and internal thread portion have been machined in an embodiment of the present invention;

[0044] Figure 9 This is a three-dimensional structural schematic diagram of the planetary roller screw in an embodiment of the present invention;

[0045] Figure 10 This is a schematic diagram of the internal cross-sectional structure of the planetary roller screw in an embodiment of the present invention;

[0046] Figure 11 for Figure 10 Schematic diagram of the cross-sectional structure at point BB;

[0047] Figure 12 for Figure 10 A schematic diagram of the cross-sectional structure at the CC section;

[0048] Figure 13 for Figure 10 Schematic diagram of the cross-sectional structure at point DD;

[0049] Figure 14 for Figure 10 A schematic diagram of the cross-sectional structure at point NN;

[0050] Figure 15 This is a three-dimensional structural diagram of the lead screw in an embodiment of the present invention;

[0051] Figure 16 This is a schematic diagram of the reference position of the workpiece tooth position in an embodiment of the present invention;

[0052] Figure 17 This is a schematic diagram showing the deviation of the central axis between the first internal gear ring and the second internal gear ring in an embodiment of the present invention;

[0053] Figure 18 This is an enlarged view of the cross-section of the internal thread portion in an embodiment of the present invention.

[0054] Explanation of reference numerals in the attached figures:

[0055] 1-Double-tooth nut; 11-First internal gear ring; 12-Second internal gear ring; 13-Internal thread portion; 14-Internal snap ring groove; 15-Gear shearing groove;

[0056] 2-Gear clamp; 21-Connecting base; 22-Positioning sleeve seat; 221-Cylindrical pin; 222-Internal hexagonal head screw;

[0057] 3-Workpiece; 31-Cylinder structure; 32-Flange positioning plate; 321-Pin hole; 322-Threaded through hole; 3221-First threaded through hole; 3222-Second threaded through hole; 3223-Third threaded through hole;

[0058] 4-Lead screw; 5-Roller; 6-Cage; 7-Snap ring. Detailed Implementation

[0059] 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. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0060] It should be noted that when a component is referred to as "fixed to," "set on," or "located on" another component, it can be directly on or indirectly on that other component. When a component is referred to as "connected to" another component, it can be directly connected to or indirectly connected to that other component.

[0061] Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0062] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installed," "connected," "linked," and "equipped with" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0063] Please see Figure 1-8 As shown, this embodiment of the invention provides a method for mass manufacturing of double-tooth nuts for planetary roller screws, the method comprising the following steps:

[0064] S1: Machining workpiece 3 from the forging blank and performing spheroidizing annealing treatment;

[0065] In this step, forged blanks are used to save raw materials, whereas conventional bar stock processing would waste materials.

[0066] S2: After rough machining of the workpiece, it is heat treated, then semi-finished, and then the area to be machined into the internal thread is subjected to high-frequency quenching.

[0067] In this step, after the semi-finishing is completed, the size of workpiece 3 does not reach the finished size, and there is usually a 0.3mm margin. Then, high frequency quenching is performed. It is particularly important to note that only the internal thread part 13 is subjected to high frequency quenching treatment. The axial hardening part is only in the internal thread part 13, and the first internal gear ring 11 and the second internal gear ring 12 must not be hardened. This is to ensure the tool life during gear hobbing. The remaining parts are subjected to quenching and tempering treatment.

[0068] S3: Make a gear hobbing fixture 2 and machine a flange positioning plate 32 on the outer circumference of the workpiece 3. The assembly of the gear hobbing fixture 2 and the flange positioning plate 32 forms a machining tooth position reference.

[0069] In this step, since the double-tooth nut 1 to be mass-produced is a cylindrical structure, there is no usable machining tooth reference, so it is necessary to design a custom machining tooth reference.

[0070] S4: Using the machining tooth position reference, the first internal gear ring 11 and the second internal gear ring 12, which are symmetrically arranged, are machined inside both ends of the workpiece, and the azimuth angle difference P between the central axes of the first internal gear ring 11 and the second internal gear ring 12 is controlled to have an arc length L at the tooth pitch circle ranging from -0.015mm to +0.015mm.

[0071] It should be noted that the azimuth difference P is the difference in azimuth angle between the central axis of the first internal gear ring 11 and the second internal gear ring 12.

[0072] Additionally, it should be noted that because the pitch diameter of the internal teeth in the planetary roller screw and the pitch diameter of the internal thread on the nut must be consistent, the two internal gear rings cannot be machined in one go. Due to the structural limitations of the planetary roller screw, in order to ensure that the difference in the azimuth angle of the central axis of the inner double gear rings (first internal gear ring 11 and second internal gear ring 12) meets the design requirements, two clamping and two machining operations are required. Therefore, the radial reference for the two machining operations must be the same.

[0073] For example, when machining the second internal gear ring 12 in this embodiment, there must be a tooth position reference and a flipping shaft M. The tooth position reference positions the first internal gear ring 11 to ensure that the teeth of the second internal gear ring 12 have a definite phase relationship with the first internal gear ring 11, that is, the azimuth angle difference P between the central axis of the first internal gear ring 11 and the second internal gear ring 12.

[0074] Considering that the arc length L of the same azimuth angle difference P is the same at different pitch circles, the arc length L of the azimuth angle difference at the pitch circle is the standard for judging whether the tool and fixture are qualified. Therefore, the azimuth angle difference P is a parameter required when adjusting the machining machine.

[0075] Please see Figure 16 As shown, the flipping shaft M is the shaft that flips the workpiece 3 after the first internal gear ring 11 is machined. The function of the flipping shaft M is that, in mass production, if the flipping shaft M is different, multiple phase relationships will be generated between the first internal gear ring 11 and the second internal gear ring 12.

[0076] Because of the randomness of the clamping of workpiece 3 and the gear shaper cutter, it is impossible to determine the azimuth angle difference P between the centerlines of the teeth at both ends during the two gear shaping operations. However, by using the tooth position reference and the flip axis M, the azimuth angle difference P of the subsequently processed workpiece 3 can be fixed to a value within the same small range. Therefore, it is necessary to define the tooth position reference and the flip axis M. At the same time, after processing, the tool spindle and workpiece spindle of the gear shaper need to return to the starting point of the previous processing. In this way, we can ensure that the tooth groove will appear in the same place each time the same end of workpiece 3 is processed. When processing the other end of workpiece 3, by using the test workpiece made in the first piece, the azimuth angle difference P between the centerlines of the teeth at both ends of the test workpiece is detected, and this angle difference is compensated to the starting position of the workpiece spindle when processing the second end. This ensures that the azimuth angle difference P between the centerlines of the teeth at both ends meets the design requirements.

[0077] For the gear inspection of the first internal gear ring 11 and the second internal gear ring 12, this embodiment uses a gear precision inspection instrument, which has the function of inspecting upper and lower double gears. The gear precision inspection instrument uses probes to detect the tooth profile and tooth direction parameters of the first internal gear ring 11 and the second internal gear ring 12 to determine the central axis of the first internal gear ring 11 and the second internal gear ring 12, and then evaluates the error of the two central axes.

[0078] S5: After the first internal gear ring 11 and the second internal gear ring 12 are processed, the internal thread portion 13 is further processed axially between the first internal gear ring 11 and the second internal gear ring 12 of the workpiece 3.

[0079] S6: Machining removes flange positioning disc 32 to form double toothed nut 1.

[0080] Therefore, this embodiment of the invention achieves mass production of the integrated structure of the internal gear ring and nut of the planetary roller screw by adding a flange positioning plate 32 to the outer circumference of the workpiece, designing a gear-shaping fixture 2 for positioning connection with the flange positioning plate 32, and changing the heat treatment method of the workpiece. While ensuring the overall performance of the planetary roller screw pair, the cost of the entire workpiece will not increase significantly. This changes the traditional method of manufacturing the internal gear ring and nut of the planetary roller screw separately, and the assembly risk of matching the upper and lower internal gear rings and the matching cylindrical shaft during the assembly stage. It also reduces the minimum outer diameter of the nut for the planetary roller screw, improves the overall strength of the nut for the planetary roller screw, and improves the assembly accuracy of the planetary roller screw pair.

[0081] Specifically, in the embodiments of the present invention, in step S1, the material of workpiece 3 is GCr15, and the spheroidizing annealing treatment requires HB179-207.

[0082] In this step, GCr15 is generally used to manufacture all parts of the planetary roller screw pair. Therefore, in this embodiment of the invention, GCr15 is also selected as the preferred material for the double tooth nut 1, and the workpiece 3 is subjected to spheroidizing annealing treatment to achieve HB179-207, thereby reducing the hardness of the blank, improving the cutting performance, extending the service life of the tool, and improving the machinability of the steel.

[0083] Specifically, in the embodiments of the present invention, in step S2, after rough machining of the workpiece 3, it undergoes heat treatment, and then semi-finishing, the area to be machined into the internal thread portion 13 is subjected to high-frequency quenching treatment, specifically including:

[0084] Workpiece 3 is rough-machined, and after rough machining, workpiece 3 is quenched and tempered until the hardness reaches HRC38-42.

[0085] Then, workpiece 3 is semi-finished, and the area to be machined into the internal thread part 13 is subjected to high-frequency quenching.

[0086] In this step, workpiece 3 is first rough-machined and then semi-finished, which is a conventional machining method. Different treatments are performed at different stages. In the rough-machine stage, in order to improve the machining speed and tool life, tempering is used to reduce the material hardness and increase the rough-machine speed. In the semi-finishing stage, since the size of workpiece 3 has not yet reached the finished size, there is generally a 0.3mm allowance. Then, high-frequency quenching is performed, and high-frequency quenching is only performed on the internal thread part 13 to increase the hardness and prevent accidents such as tooth breakage in the internal thread part 13.

[0087] Please see Figure 5 , 6As shown, in a specific embodiment of the present invention, in step S3, the flange positioning plate 32 is machined with a pair of symmetrical vertical through pin holes 321 and a plurality of evenly distributed threaded through holes 322, and the pin holes 321 and threaded through holes 322 are arranged alternately; the gear hobbing fixture 2 includes a connecting base 21 and a positioning cylinder seat 22, wherein the connecting base 21 is fixedly connected to the processing platform of the gear hobbing machine; the positioning cylinder seat 22 is coaxially and integrally connected to the upper surface of the connecting base 21, and the upper surface of the positioning cylinder seat 22 is provided with There are cylindrical pins 221 and internal hexagonal head screws 222 corresponding to pin holes 321 and threaded through holes 322, respectively. The pin holes 321 are adapted to be connected with the cylindrical pins 221, and the threaded through holes 322 are adapted to be connected with the internal hexagonal head screws 222. The flange positioning plate 32 is adapted to be positioned and connected to the upper surface of the positioning cylinder seat 22 by the cylindrical pins 221 and internal hexagonal head screws 222, and the cylindrical structure 31 of the workpiece 3 located below the flange positioning plate 32 is suspended inside the positioning cylinder seat 22.

[0088] In this step, a disc-shaped structure (i.e., flange positioning disc 32) is designed at the axial center of the double toothed nut 1. Two vertically penetrating pin holes 321 are distributed on the surface of the flange positioning disc 32. Correspondingly, cylindrical pins 221 are provided on the upper surface of the positioning cylinder seat 22. When the first internal gear ring 11 is machined, the two pin holes 321 and the two cylindrical pins 221 are connected to each other to fix the radial and tooth position of the entire double toothed nut 1. In addition, since the flange positioning disc 32 is positioned on the positioning cylinder seat 22 of the gear-shaping fixture 2, the flange positioning disc 32 fixes the axial position of the double toothed nut 1.

[0089] During the machining process, the double tooth nut 1 is fixed on the gear-shaping fixture 2 by the engagement of the threaded through hole 322 and the internal hexagonal head screw 222, thereby machining the first internal gear ring 11.

[0090] After machining the first internal gear ring 11, remove the double-tooth nut 1 and flip it over. Here, the flipping axis M is defined as the line connecting the threaded through hole 322 and the center. With the un-toothed second internal gear ring 12 facing upward, adjust the spatial position of the first internal gear ring 11 during the second clamping based on the machining tooth position reference of the first internal gear ring 11, and further complete the machining of the second internal gear ring 12.

[0091] It should be specifically noted that the so-called machining tooth position reference is the reference for positioning the first internal gear ring 11 when machining the second internal gear ring 12. By machining the tooth position reference, the spatial position of the first internal gear ring 11 is kept fixed each time it is clamped. Of course, the machining tooth position reference can be the first internal gear ring 11 itself, or a structure that has a positional relationship with the first internal gear ring 11.

[0092] Please see Figure 7 , 8As shown, in a specific embodiment of the present invention, before machining the first internal gear ring 11 and the second internal gear ring 12, symmetrically arranged internal retaining spring grooves 14 and gear retraction grooves 15 are machined inside both ends of the workpiece; the internal retaining spring grooves 14 and gear retraction grooves 15 are both located at both ends of the first internal gear ring 11 and the second internal gear ring 12.

[0093] In this step, the inner retaining spring grooves 14 are located on both sides of the inner wall of the double toothed nut 1. The inner retaining spring 7 is provided in the inner retaining spring groove 14. The retainer 6 is installed and fixed through the retaining spring 7, and the roller 5 is supported through the retainer 6. When machining the first internal gear ring 11 and the second internal gear ring 12, due to the position of the first internal gear ring 11 and the second internal gear ring 12 on the inner wall of the double toothed nut 1, considering the feed position of the cutting tool for the gear shaping, it is also necessary to machine a cutting tool relief groove 15 on the side of the first internal gear ring 11 and the second internal gear ring 12 that are close to each other. The inner diameter of the cutting tool relief groove 15 is larger than the root circle diameter of the first internal gear ring 11 and the second internal gear ring 12, so that the first internal gear ring 11 and the second internal gear ring 12 of the required width can be completely machined without tool interference.

[0094] Please see Figure 16 , 17 As shown, specifically in the embodiment of the present invention, in step S3, controlling the azimuth angle difference P between the central axes of the first internal gear ring 11 and the second internal gear ring 12 to have an arc length L at the pitch circle within the range of -0.015mm to +0.015mm specifically includes:

[0095] First, place the double-toothed nut 1 on the tooth-shaping fixture 2. Fix the radial position and tooth position of the double-toothed nut 1 by assembling the two pin holes 321 with the two cylindrical pins 221. At the same time, fix the axial position of the double-toothed nut 1 by assembling the three threaded through holes 322 (first threaded through hole 3221, second threaded through hole 3222 and third threaded through hole 3223) with the three internal hexagonal head screws 222.

[0096] At this point, the radial reference is assumed to be the distribution circle containing the two pin holes 321, the tooth position reference is the two pin holes 321, and the flip axis M is the line connecting the threaded through hole 322 and the center of the circle.

[0097] In this embodiment, the double-tooth nut 1 is fixed to the gear-shaping fixture 2 using three internal hexagon head screws 222, which provides more accurate positioning. However, in practice, it has been found that during the mass production of the double-tooth nut 1, the three pin holes 321 are prone to misalignment of the flip axis M, resulting in errors in the azimuth angle difference P of the workpiece 3. Therefore, to prevent mistake-proofing, the workpiece 3 is designed to have only one flip axis M to avoid errors during clamping.

[0098] After positioning, the first internal gear ring 11 of the double-tooth nut 1 is machined; after the machining of the first internal gear ring 11 is completed, the double-tooth nut 1 is removed and flipped so that the second internal gear ring 12 without teeth faces upward, and the line connecting one of the threaded through holes 322 and the center is defined as the flipping axis M; then the second internal gear ring 12 is fixed and machined, and the azimuth angle difference P between the first internal gear ring 11 and the second internal gear ring 12 in the current installation state is detected; then, based on the detected azimuth angle difference P, the azimuth angle difference P is compensated at the starting point of the spindle of the workpiece 3; finally, the double-tooth nut 1 is mass-produced according to the coordinates of the starting point of the spindle of the workpiece 3 after compensation.

[0099] It should be noted that when the central axis of the first internal gear ring 11 coincides with the line connecting the center of the pin hole 321, the central axes of the first internal gear ring 11 and the second internal gear ring 12 coincide. However, this is an ideal state. Under normal machining error conditions, the central axes of the first internal gear ring 11 and the second internal gear ring 12 do not coincide. In this case, it is necessary to adjust the workpiece position.

[0100] When batch processing double-tooth nuts 1, the first double-tooth nut 1 can be used as a test workpiece. By using the test workpiece, the azimuth angle difference P between the first internal gear ring 11 and the second internal gear ring 12 in the current installation state of the tool and the gear shaping fixture 2 during the machining process can be detected. Then, the azimuth angle difference P is compensated at the starting point of the spindle of the workpiece. After completing the above operations, the internal tooth structure of the double-tooth nut 1 is completed.

[0101] For the tooth-cutting process at both ends of the double-tooth nut 1, the requirement that the difference in azimuth angle P between the central axes of the two teeth is within ±0.015mm of the arc length L at the tooth pitch circle is acceptable. For the machining of the internal thread portion 13, existing processes can be used for both grinding and turning.

[0102] It is particularly important to note that when inspecting and debugging the workpiece in this embodiment of the invention, the first internal gear ring 11 should be used as the inspection reference. The detected azimuth difference value P is relative to the central axis of the first internal gear ring 11. At this time, it is sufficient to inspect one tooth of each of the first internal gear ring 11 and the second internal gear ring 12.

[0103] Please see Figure 4 As shown, in a specific embodiment of the present invention, in step S4, the thread width of the internal thread portion 13 is equal to the axial length L of the double-tooth nut - 2 * (width of the first internal gear ring + width of the internal snap ring groove and width of the tooth shearing groove).

[0104] As a result, the inner hole axis of the double toothed nut 1 is completely filled with the internal tooth ring and internal thread, so that the double toothed nut 1 meshes evenly and smoothly with the roller 5 and the lead screw 4.

[0105] Specifically, in the embodiments of the present invention, in step S5, the specific requirements for the high-frequency quenching treatment of the internal thread portion 13 are as follows: the hardness depth is between 0.433 times the diameter of the tangent circle D of the mid-diameter of the internal thread cross-section, which is a high hardness zone; the hardness in the high hardness zone is between 655-745 HV; and the hardness of the effective hardened layer zone with a layer depth of 1-1.2 times the diameter of the tangent circle D is HV550.

[0106] It should be noted that, please refer to Figure 18 As shown, the tangent circle of the mean diameter of the thread cross section is 90° for the nut of the planetary roller screw, which is different from the 60° or 55° of the metric thread. Therefore, its cross section is an isosceles right triangle, and the tangent circle of the mean diameter of the cross section is the circle tangent to the right-angled side of the isosceles right triangle. The tangent point is the intersection of the mean diameter of the thread and the right-angled side.

[0107] Please see Figure 7 , 8 As shown in Figure 9, this embodiment of the invention also provides a double-tooth nut 1 for planetary roller screws. The double-tooth nut 1 is manufactured using the mass production method for the double-tooth nut for planetary roller screws described above. In this embodiment, the double-tooth nut 1 is composed of a nut body. The nut body has an internal retaining groove 14, an internal gear ring, a tooth relief groove 15, and an internal thread portion 13 symmetrically arranged along the axial direction. The internal retaining groove 14 is located at both ends of the nut body and is used to support the positioning retainer 6. The internal gear ring is composed of a first internal gear ring 11 and a second internal gear ring 12, and the first internal gear ring 11 and the second internal gear ring 12 are symmetrically arranged along the inner wall of the double-tooth nut 1. The first internal gear ring 11 and the second internal gear ring 12 are both located between the internal retaining groove 14 and the tooth relief groove 15 on the corresponding side, while the internal thread portion 13 is located between the two tooth relief grooves 15.

[0108] In this embodiment, the internal thread portion 13 in the middle of the inner wall of the double toothed nut 1 is a multi-start thread. There are internal tooth rings (i.e., the first internal tooth ring 11 and the second internal tooth ring 12) on both sides of the inner wall of the double toothed nut 1. There is a tooth removal groove 15 between the internal tooth ring and the internal thread portion 13 to facilitate tooth removal. The outermost sides of both sides of the inner wall of the double toothed nut 1 are internal retaining spring grooves 14, which makes the structure of the entire double toothed nut 1 very compact. The thickness difference between the tooth tip circle of the internal thread portion 13 and the outer wall thickness of the double toothed nut 1 is about 4mm.

[0109] Please see Figure 9-15 As shown, this embodiment of the invention also provides a planetary roller screw, which includes a double-toothed nut 1, rollers 5 and a screw 4, wherein the screw 4 is located at the central axis of the double-toothed nut 1, the double-toothed nut 1 is sleeved on the outside of the screw 4, and the rollers 5 mesh with the double-toothed nut 1 and the screw 4 respectively.

[0110] The effect of the planetary roller screw in this embodiment is the same as that of the mass production method of the double tooth nut for planetary roller screw described above, and will not be described in detail here.

[0111] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of this disclosure, and all such changes and modifications will fall within the scope of protection of this invention.

Claims

1. A method for mass manufacturing of a double-tooth nut for a planetary roller screw, characterized in that, Includes the following steps: S1: The workpiece is machined from the forging blank and then subjected to spheroidizing annealing treatment; S2: After rough machining of the workpiece, it is heat treated, then semi-finished, and then the area to be machined into the internal thread is subjected to high-frequency quenching. S3: Fabricate a gear hobbing fixture and machine a flange positioning plate on the outer circumference of the workpiece. The assembly of the gear hobbing fixture and the flange positioning plate forms a machining tooth position reference. In step S3, the flange positioning plate is machined with a pair of symmetrical vertical through pin holes and a plurality of evenly distributed threaded through holes, and the pin holes and threaded through holes are arranged alternately. The manufactured gear-shaping fixtures include: The connecting base is fixedly connected to the processing platform of the gear shaper; The positioning cylinder seat is coaxially and integrally connected to the upper surface of the connecting base. The upper surface of the positioning cylinder seat is provided with a cylindrical pin and an internal hexagonal head screw respectively corresponding to the pin hole and the threaded through hole. The pin hole is adapted to the cylindrical pin and the threaded through hole is adapted to the internal hexagonal head screw. The flange positioning plate is adapted to be positioned and connected to the upper surface of the positioning cylinder seat by the cylindrical pin and the internal hexagonal head screw, and the lower half of the workpiece is located below the flange positioning plate and suspended inside the positioning cylinder seat. S4: Using the machining tooth reference, a first internal gear ring and a second internal gear ring symmetrically arranged along the axial direction are machined inside both ends of the workpiece, and the azimuth angle difference P between the central axes of the first internal gear ring and the second internal gear ring is controlled to have an arc length L at the tooth pitch circle ranging from -0.015mm to +0.015mm. In step S4, the azimuth angle difference P between the central axes of the first internal gear ring and the second internal gear ring is controlled to have an arc length L at the pitch circle within the range of -0.015mm to +0.015mm, specifically including: Place the double-toothed nut on the tooth-shaping fixture. Fix the radial position and tooth position of the double-toothed nut by assembling two pin holes with two cylindrical pins. At the same time, fix the axial position of the double-toothed nut by assembling three threaded through holes with three internal hexagonal head screws. Machining the first internal gear ring of the double-tooth nut; After completing the machining of the first internal gear ring, remove and flip the double-tooth nut so that the second internal gear ring without teeth faces upward; The second internal gear ring is fixed and machined, and the azimuth angle difference P between the first and second internal gear rings under the current installation state is detected. Based on the detected azimuth angle difference P, the azimuth angle difference P is compensated at the starting point of the workpiece spindle; Based on the compensated starting point coordinates of the workpiece spindle, double-tooth nuts are mass-produced. S5: After the first and second internal gear rings are machined, continue to machine the internal thread portion along the axial direction between the first and second internal gear rings of the workpiece; S6: Machining removes the flange positioning plate to form a double-toothed nut; Before machining the first and second internal gear rings, symmetrically arranged internal snap ring grooves and gear retraction grooves are machined inside both ends of the workpiece; the internal snap ring grooves and the gear retraction grooves are located at both ends of the first and second internal gear rings.

2. The method for mass manufacturing of double-tooth nuts for planetary roller screws according to claim 1, characterized in that, In step S1, the workpiece material is GCr15, and the spheroidizing annealing treatment reaches HB179-207.

3. The method for mass manufacturing of double-tooth nuts for planetary roller screws according to claim 1, characterized in that, In step S2, the tempering treatment is carried out until the hardness reaches HRC38-42; the hardness of the high-frequency quenching treatment is as follows: the hardened layer depth is between 0.433 times the diameter of the tangent circle D of the middle diameter of the internal thread cross section, which is the high hardness zone, and the hardness in the high hardness zone is between 655-745 HV. The hardness of the effective hardened layer zone with a layer depth of 1-1.2 times the diameter of the tangent circle D is HV550.

4. The method for mass manufacturing of double-tooth nuts for planetary roller screws according to claim 1, characterized in that, In step S5, the thread width of the internal thread portion = axial length of the double-tooth nut - 2 * (width of the first internal gear ring + width of the internal snap ring groove + width of the tooth shearing groove).

5. The method for mass manufacturing of double-toothed nuts for planetary roller screws according to claim 1, characterized in that, In step S5, the gear parameters of the first internal gear ring and the second internal gear ring are the same.

6. A double-tooth nut for planetary roller screws, comprising a mass production method for the double-tooth nut for planetary roller screws as described in any one of claims 1 to 5, characterized in that, include: The nut body has an internal retaining spring groove, an internal gear ring, a toothed relief groove, and an internal thread portion symmetrically arranged along the axial direction inside the nut body. The internal retaining spring groove is located at both ends of the nut body, the internal gear ring is located between the internal retaining spring groove and the toothed relief groove, and the internal thread portion is located between the two toothed relief grooves.

7. A planetary roller screw, characterized in that, The invention includes a double-tooth nut, rollers, and a lead screw manufactured by the mass production method of the double-tooth nut for planetary roller screws as described in any one of claims 1-5, wherein the lead screw is located at the central axis of the double-tooth nut, the double-tooth nut is sleeved on the outside of the lead screw, and the rollers respectively mesh with the double-tooth nut and the lead screw.

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