Planetary roller lead screw pair convenient to machine

Abstract

The utility model relates to a planetary roller lead screw pair convenient to machine, belongs to the field of precision mechanical transmission, reduces the radius of an addendum circle of a gear part of a roller, avoids mutual contact between the gear part of the roller and a thread of a lead screw, improves the stress condition on the roller, and prolongs the service life of the planetary roller lead screw pair. Meanwhile, threaded teeth are changed into the straight spur gears, and the straight spur gears can be directly machined in a hobbing or gear shaping mode, so that the machining procedures of complex tooth profiles are reduced, the machining cost is reduced, and the machining precision and quality of the gears are more easily guaranteed; and the constraint on gear parameters is also reduced, so that the gear part of the roller can have more parameter choices.

Description

Technical Field

[0001] The utility model belongs to the field of precision mechanical transmission, and in particular relates to a planetary roller screw pair that is easy to process. Background Art

[0002] In today's precision machine tool manufacturing, the feed system is crucial for achieving precise tool movement and ultimately high-quality part processing. The planetary roller screw mechanism (PRSM), with its superior performance, has been widely used in feed systems for precision machine tools.

[0003] Precision machine tools are designed to manufacture high-precision parts that meet demanding industrial needs through precise control and efficient motion control. In this process, planetary roller screws, with their high precision, high load capacity, and high transmission efficiency, meet the stringent linear motion requirements of precision machine tools. They enable fast and accurate position control, improving production efficiency and product quality. The operating principle of a planetary roller screw is similar to that of a planetary gear system. The screw acts as the sun gear, the rollers as the planetary gears, and the nut as the inner ring gear of a planetary gear system. As the screw rotates, the rollers roll between the screw and nut, converting the screw's rotational motion into linear motion of the nut. Specifically, the rollers rotate while orbiting the screw. Because the rollers are in rolling contact with both the screw and the nut, frictional resistance is minimal, enabling efficient transmission.

[0004] However, due to the special shape of the screw thread in the planetary roller screw pair, a high-precision fit is required between the roller and the screw, and between the roller and the nut. This places high demands on processing equipment and process technology, which undoubtedly increases the difficulty and cost of processing. In addition, the threaded teeth of the rollers of the planetary roller screw pair are also faced with extremely complex stress conditions. The coupling of multiple loads has a significant impact on its structural integrity and service life. Specifically, the threaded teeth of the rollers are subject to multiple loads from different aspects during operation. On the one hand, there is an impact load between the threaded tooth surface of the roller and the inner ring gear. On the other hand, the threaded tooth surface of the roller also bears the circumferential load between the roller and the screw. Under the complex coupling of multiple loads, the probability of wear and damage on the threaded tooth surface of the roller is increased, which seriously affects the overall working performance of the planetary roller screw pair and greatly reduces the service life of the overall structure.

[0005] Therefore, in order to increase the service life of the planetary roller screw pair and reduce the processing cost, a new planetary roller screw pair structure is needed. Utility Model Content

[0006] In order to solve the above problems existing in the prior art, the present invention provides a planetary roller screw pair that is easy to process. The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0007] The utility model provides a planetary roller screw pair that is easy to process, comprising: a screw, a nut, a roller, an inner gear ring and a retaining frame; the nut is coaxially sleeved on the screw, and two inner gear rings are relatively arranged at the axial ends of the nut; a plurality of rollers are evenly arranged around the screw, and the axial ends of the plurality of rollers are respectively fixed between the two retaining frames; a threaded portion is provided in the middle of each roller, and gear portions are provided at both ends of the threaded portion; the threaded portion of each roller is respectively engaged with the screw and the nut thread; the two gear portions of each roller are respectively engaged with the corresponding gears of the two inner gear rings, and the gear portions and the screw do not contact each other; wherein the gear portion is a spur gear, and the tooth top circle radius of the gear portion is smaller than the tooth top circle radius of the standard involute spur gear.

[0008] In one embodiment of the present invention, the thread profile and number of thread starts of the lead screw and the nut are equal.

[0009] In one embodiment of the present invention, the thread profiles of the lead screw and the nut are both trapezoidal, and the thread profile angles of the lead screw and the nut are both 90°.

[0010] In one embodiment of the present invention, each roller is symmetrical about its axial center at both ends, and each roller is sequentially provided with a threaded portion, a gear portion and an axial end from the middle outward, wherein the axial end is the optical axis.

[0011] In one embodiment of the present invention, the threaded portion of each roller is a single-start thread.

[0012] In one embodiment of the present invention, the thread profile of the threaded portion is a double arc shape.

[0013] In one embodiment of the present invention, the gear portion of each roller has the same module and pressure angle as the inner gear ring.

[0014] In one embodiment of the present invention, each retaining frame is provided with a plurality of circular holes for supporting the shaft ends of a plurality of rollers.

[0015] In one embodiment of the present invention, each roller is positioned and fixed on the retaining frame along the axial direction through a spring retaining ring.

[0016] In one embodiment of the present invention, the tooth tip circle diameter of the gear portion is smaller than the thread pitch diameter of the thread portion.

[0017] Compared with the prior art, the beneficial effects of the present invention are:

[0018] This easy-to-process planetary roller screw pair reduces the addendum radius of the roller gear portion, preventing contact between the roller gear portion and the screw thread, improving the stress on the rollers and increasing the lifespan of the planetary roller screw pair. Furthermore, the threaded teeth are replaced with spur gears. Since spur gears can be directly processed using hobbing or shaping, the number of machining steps for complex tooth profiles is reduced, lowering processing costs and making it easier to ensure gear processing accuracy and quality. This also reduces constraints on gear parameters, allowing for a wider range of parameter options for the roller gear portion.

[0019] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention, it can be implemented in accordance with the contents of the specification. In addition, in order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, the following preferred embodiments are specifically cited and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic structural diagram of a planetary roller screw pair that is easy to process, provided by an embodiment of the utility model;

[0021] Figure 2 This is a schematic structural diagram of a roller provided by an embodiment of the present utility model;

[0022] Figure 3 It is a partial cross-sectional view of a planetary roller screw pair that is easy to process provided by an embodiment of the utility model.

[0023] Reference numerals: 1 - screw; 2 - nut; 3 - roller; 31 - threaded portion; 32 - gear portion; 4 - inner ring gear; 5 - cage. DETAILED DESCRIPTION

[0024] In order to further illustrate the technical means and effects adopted by the present invention to achieve the predetermined purpose of the utility model, the following is a detailed description of a planetary roller screw pair that is easy to process according to the present invention, in combination with the accompanying drawings and specific implementation methods.

[0025] The aforementioned and other technical contents, features, and effects of the present invention are clearly presented in the following detailed description of the specific embodiments in conjunction with the accompanying drawings. Through the description of the specific embodiments, a more in-depth and specific understanding of the technical means and effects adopted by the present invention to achieve the intended purpose can be obtained. However, the accompanying drawings are for reference and illustration purposes only and are not intended to limit the technical solutions of the present invention.

[0026] Example 1

[0027] like Figures 1 to 3As shown, this embodiment provides a planetary roller screw pair that is easy to process, including: a screw 1, a nut 2, a roller 3, an inner gear ring 4 and a retaining frame 5; the nut 2 is coaxially sleeved on the screw 1, and the two inner gear rings 4 are relatively arranged at the axial ends of the nut 2; a number of rollers 3 are evenly arranged around the screw 1, and the axial ends of the several rollers 3 are respectively fixed between the two retaining frames 5; a threaded portion 31 is provided in the middle of each roller 3, and a gear portion 32 is provided at both ends of the threaded portion 31; the threaded portion 31 of each roller 3 is respectively threadedly engaged with the screw 1 and the nut 2; the two gear portions 32 of each roller 3 are respectively engaged with the corresponding gears of the two inner gear rings 4, and the gear portion 32 and the screw 1 do not contact each other; wherein, the gear portion 32 is a spur gear, and the tooth top circle radius of the gear portion 32 is smaller than the tooth top circle radius of the standard involute spur gear.

[0028] The principle is that the screw 1, acting as the input end, rotates. The screw 1 is threaded externally, while the nut 2 is threaded internally. Driven by the threaded transmission, the rollers 3 simultaneously revolve around the axis of the screw 1 and rotate about their own axes, creating a planetary motion. Driven by the rollers 3, the nut 2 undergoes linear motion along the axis of the screw 1. The gears 32 at each end of each roller 3 mesh with the internal gear ring 4, ensuring synchronization of the meshing transmission between the screw 1, nut 2, and rollers 3. The gears 32 at each end of each roller 3 are spur gears. These spur teeth eliminate the effect of the helix angle of the screw 1 on the tilting torque of the rollers 3. Furthermore, the spur teeth mesh with the internal gear ring 4 to ensure that the axes of the rollers 3 are parallel to the axis of the screw 1 and roll in a rolling motion. A cage 5 secures the position of the rollers 3, ensuring uniform distribution of the rollers 3 along the circumference.

[0029] It is worth noting that the gear portion 32 is provided with a spur gear. Since the tooth profile of the spur gear is a straight line, the tooth surface contact during meshing is more stable, with higher transmission precision, and can better maintain transmission accuracy. Moreover, since the processing of spur gears is simpler than that of threaded gears, they can be processed using ordinary gear processing equipment, such as hobbing machines or gear shaping machines. The movement trajectory of the tool during processing is also relatively simple, making it easier to control the processing precision. In contrast, the processing of threaded gears requires two processing steps, and the processing precision is not easy to guarantee. In addition, due to the simple processing technology, the processing cost of spur gears is also relatively low. Considering the cost of processing equipment, the cost of cutting tools, and processing time, the use of spur gears is more advantageous than helical gears, which helps to reduce the overall production cost of planetary roller screw pairs.

[0030] In this embodiment, the module and pressure angle of the gear portion 32 of each roller 3 are equal to those of the inner gear ring 4 .

[0031] It is noteworthy that the gear portion 32 of the roller 3 is provided with an equal module and pressure angle to the inner gear ring 4, and is consistent in size ratio. When performing structural design, a unified standard can be followed, making the calculation process simpler and more unified, reducing the complexity of design variables and calculations, and reducing the possibility of errors. Standardized processing technology and processing equipment can also be used to reduce processing costs. Since the size ratios of each component are fixed, the tool selection and cutting parameter settings during the processing can be more standardized and unified, thereby improving production efficiency and processing accuracy. The standardized manufacturing process can also reduce production costs and reduce the time and resource waste caused by the need to frequently adjust processing equipment for components with different modules. At the same time, it is also convenient to achieve mass production and improve product consistency and quality stability.

[0032] In addition, during the transmission process, after setting equal modules and pressure angles, the clearance and fit of each meshing part are also more uniform, which helps to reduce the phenomenon of meshing instability caused by parameter differences, improves transmission accuracy and repeatability, and the friction loss is relatively small, which helps to improve transmission efficiency and reduce energy loss. Especially in high-speed and high-load application scenarios, it is beneficial for the planetary roller screw pair to maintain high efficiency during long-term operation. The distribution of contact stress is also more uniform, which improves the load-bearing capacity of the planetary roller screw pair and enables it to withstand greater axial and radial loads. In heavy-load applications, the same pressure angle helps to ensure the structural strength and stability of the planetary roller screw pair.

[0033] Setting equal modules and pressure angles also makes assembly more convenient and faster. Because the dimensions of each component are proportionally consistent, installers can more easily position and assemble the components, reducing the likelihood of installation errors. During equipment commissioning and maintenance, parameter adjustments and fault diagnosis are easier. Because the performance and characteristics of each component are consistent, commissioning personnel can more accurately identify problems and take appropriate measures to adjust and repair them.

[0034] In an optional embodiment, the thread profile and number of thread starts of the lead screw 1 and the nut 2 are equal.

[0035] Exemplarily, the thread profiles of the lead screw 1 and the nut 2 may both be trapezoidal, and the thread profile angles of the lead screw 1 and the nut 2 may both be 90°.

[0036] In an optional embodiment, each roller 3 is symmetrical about its axial center at both ends, and each roller 3 is provided with a threaded portion 31, a gear portion 32 and an axial end in sequence from the middle to the outside, wherein the axial end is the optical axis.

[0037] Exemplarily, the threaded portion 31 of each roller 3 may be a single-start thread.

[0038] For example, the thread profile of the threaded portion 31 can be a double arc. By machining the top surface of the thread profile of the threaded portion 31 into a spherical surface, load capacity can be increased, friction can be reduced, and efficiency can be improved. This ensures that when the roller 3 and the nut 2 engage with each other, only pure rolling occurs without relative axial displacement.

[0039] In an optional embodiment, each retaining frame 5 is provided with a plurality of circular holes for supporting the axial ends of a plurality of rollers 3 .

[0040] Exemplarily, each roller 3 is positioned and fixed on the retaining frame 5 in the axial direction via a spring retaining ring.

[0041] The geometric parameters of the planetary roller screw pair are shown in Table 1. First, the module m and the number of teeth Z of the gear are preliminarily selected. r 、Number of teeth of the inner ring gear Z g , pressure angle α, tooth top height coefficient h a * , head clearance coefficient C * , and determine whether undercutting occurs:

[0042] Z min =2h a * / sin 2 α; (1)

[0043] Among them, Z min is the minimum number of teeth without undercutting; sin is the cosine function.

[0044] If the number of teeth of the gear is Z r Less than Z min , then it is necessary to adjust the tooth height coefficient h a * , and calculate the displacement coefficient x:

[0045]

[0046] Then, whether to adopt height displacement is determined according to the size of the displacement coefficient x. When the displacement coefficient x is small, it means that slight root cutting is allowed, and height displacement may not be adopted; when x is large, height displacement is required.

[0047] After it has been determined that undercutting does not occur, the addendum diameter R of the gear portion 32 is calculated. ra :

[0048] R ra =m(Z r +2ha * ); (3)

[0049] In order to avoid the gear portion 32 from contacting the thread of the screw 1, the tooth tip diameter Rra Smaller than the thread diameter d of the threaded portion 31 rf Then select the module in descending order and calculate the number of teeth Z of the gear under the module. r and the number of teeth of the inner ring gear Z g , and according to the number of teeth Z of the gear r and the number of teeth of the inner ring gear Z g Calculate the overlap ε:

[0050]

[0051] Where α′ is the engagement angle.

[0052] To ensure continuous transmission, the overlap ε must be greater than 1; if the overlap ε is less than or equal to 1, the module is gradually reduced until the parameter selection is completed.

[0053] Table 1 Geometric parameters of planetary roller screw pair

[0054] symbol meaning parameter symbol meaning parameter <![CDATA[d s ]]> Screw thread pitch diameter 19.5mm Screw thread rotation direction Left-handed <![CDATA[d sf ]]> Screw thread diameter 18.45mm Nut thread direction Left-handed <![CDATA[d sa ]]> Screw thread major diameter 20.07mm Roller thread rotation direction right-handed <![CDATA[d r ]]> Roller thread pitch diameter 6.5mm Thread profile angle 90° <![CDATA[d rf ]]> Roller thread diameter 5.81mm Screw thread profile Trapezoid <![CDATA[d ra ]]> Roller thread major diameter 7.43mm Roller thread profile Double arc <![CDATA[d n ]]> Nut thread diameter 32.5mm Nut thread profile Trapezoid <![CDATA[d nf ]]> Nut thread diameter 31.98mm R Roller thread profile arc radius 2.5mm <![CDATA[d na ]]> Nut thread major diameter 33.55mm N Number of rollers 10 <![CDATA[r r ]]> Roller gear center diameter 5.0mm <![CDATA[z r ]]> Roller gear teeth 12 <![CDATA[r rf ]]> Roller gear diameter 4.2mm <![CDATA[z g ]]> Number of teeth on the inner ring gear 70 <![CDATA[r ra ]]> Roller gear major diameter 5.8mm m Modulus 0.35 P Pitch 2mm <![CDATA[h * ]]> Addendum coefficient 0.8 <![CDATA[n s ]]> Number of screw threads 5 α pressure angle 20° <![CDATA[n r ]]> Number of roller thread starts 1 x Displacement coefficient 0.41 <![CDATA[n n ]]> Number of nut threads 5 <![CDATA[P s ]]> Screw thread lead 10mm <![CDATA[P n ]]> Nut thread lead 10mm

[0055] It is worth noting that when the planetary roller screw pair is running, the gear portion 32 of the roller 3 mainly bears the impact load between the inner ring gear 4. Although the impact load still exists when using spur gears, the force condition on the roller 3 is greatly simplified compared to the previous complex situation of multiple load coupling. The use of spur gear structure can effectively disperse and absorb impact force, thereby reducing the risk of structural damage caused by complex and variable loads, and thus increasing the fatigue life of the roller 3. With the increase in fatigue life, the reliability of the overall structure of the planetary roller screw pair during long-term work has also been significantly improved, and it can complete various work tasks more stably and efficiently. At the same time, this improvement also brings great convenience in the assembly process.

[0056] Furthermore, by reducing the tooth tip radius of the gear portion 32 of the roller 3, axial contact between the gear portion 32 and the thread of the screw 1 is avoided. The roller 3 only engages with the inner ring gear 4 to perform planetary motion, simplifying the processing technology of the roller 3. This makes the shape of the roller 3 simpler, reduces processes such as complex tooth profile processing, reduces the processing difficulty and the reliance on high-precision processing equipment, thereby saving processing costs and time. The processing of the gear portion 32 at both ends of the roller 3 is also relatively independent and not restricted by the structure of the screw 1. It is easier to ensure the processing accuracy and quality of the gear portion 32, making the processing process easier to control and adjust. At the same time, since direct contact points are reduced, friction and wear between the gear portion 32 of the roller 3 and the screw 1 are avoided, energy loss caused by friction is reduced, and transmission efficiency is improved. This helps to reduce heat generation and extend the service life of the planetary roller screw pair, especially under high-frequency and long-term use, the effect is more significant.

[0057] Furthermore, during assembly, since roller 3 and lead screw 1 only contact each other through the threads, the complexity and difficulty of assembly are reduced. This makes the assembly process more flexible and efficient, reduces assembly time and the potential for error, and improves production efficiency. For large-scale production, this design facilitates more efficient assembly line operations, further improving production efficiency and reducing production costs.

[0058] This easy-to-process planetary roller screw pair reduces the addendum radius of the roller gear portion, preventing contact between the roller gear portion and the screw thread, improving thread stress and increasing the lifespan of the planetary roller screw pair. Furthermore, the threaded teeth are replaced with spur gears. Since spur gears can be directly processed using hobbing or shaping, the number of machining steps for complex tooth profiles is reduced, lowering processing costs and making it easier to ensure gear processing accuracy and quality. This also reduces constraints on gear parameters, allowing for a wider range of parameter options for the roller gear portion.

[0059] It should be noted that, in this document, relational terms such as first and second are used solely to distinguish one entity or operation from another, and do not necessarily require or imply any actual relationship or order between these entities or operations. Furthermore, the terms "comprise," "include," or any other variations thereof are intended to encompass non-exclusive inclusion, such that an article or device comprising a list of elements includes not only those elements but also other elements not explicitly listed. Without further limitation, elements defined by the phrase "comprising a..." do not preclude the presence of additional identical elements in the article or device comprising the elements. Terms such as "connected" or "connected" are not limited to physical or mechanical connections but may include electrical connections, whether direct or indirect. References to directions or positional relationships, such as "upper," "lower," "left," and "right," are based on the directions or positional relationships shown in the accompanying drawings and are intended solely for ease of description and simplification of the present invention. They do not indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limitations on the present invention.

[0060] The above content is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention cannot be considered to be limited to these descriptions. For those skilled in the art of the present invention, without departing from the concept of the present invention, several simple deductions or substitutions can be made, which should be considered to fall within the scope of protection of the present invention.

Claims

1. A planetary roller screw pair that is easy to process, characterized in that: include: Screw (1), nut (2), roller (3), inner gear ring (4) and cage (5); The nut (2) is coaxially sleeved on the lead screw (1), and the two inner gear rings (4) are arranged oppositely at the axial ends of the nut (2); A plurality of rollers (3) are evenly arranged around the lead screw (1), and the shaft ends of the plurality of rollers (3) are respectively fixed between the two retaining frames (5); A threaded portion (31) is provided in the middle of each roller (3), and gear portions (32) are provided at both ends of the threaded portion (31); the threaded portion (31) of each roller (3) is threadedly engaged with the lead screw (1) and the nut (2) respectively; the two gear portions (32) of each roller (3) are respectively engaged with corresponding gears of the two inner gear rings (4), and the gear portions (32) and the lead screw (1) do not contact each other; The gear portion (32) is a spur gear, and the tooth top circle radius of the gear portion (32) is smaller than the tooth top circle radius of a standard involute spur gear.

2. The easy-to-process planetary roller screw pair according to claim 1, characterized in that: The thread profile and number of thread starts of the lead screw (1) and the nut (2) are equal.

3. The planetary roller screw pair that is easy to process according to claim 2, characterized in that: The thread profiles of the lead screw (1) and the nut (2) are both trapezoidal, and the thread profile angles of the lead screw (1) and the nut (2) are both 90°.

4. The planetary roller screw pair that is easy to process according to claim 1, characterized in that: Each roller (3) is symmetrical at both ends about its axial center. Each roller (3) is provided with a threaded portion (31), a gear portion (32) and an axial end in sequence from the middle outward, wherein the axial end is an optical axis.

5. The easy-to-process planetary roller screw pair according to claim 1, characterized in that: The threaded portion (31) of each roller (3) is a single-start thread.

6. The easy-to-process planetary roller screw pair according to claim 1, characterized in that: The thread profile of the threaded portion (31) is a double arc shape.

7. The easy-to-process planetary roller screw pair according to claim 1, characterized in that: The module and pressure angle of the gear portion (32) of each roller (3) are equal to those of the inner gear ring (4).

8. The easy-to-process planetary roller screw pair according to claim 1, characterized in that: Each of the retaining frames (5) is provided with a plurality of circular holes for supporting the shaft ends of the plurality of rollers (3).

9. The easy-to-process planetary roller screw pair according to claim 1, characterized in that: Each roller (3) is positioned and fixed on the retaining frame (5) along the axial direction via a spring retaining ring.

10. The easy-to-process planetary roller screw pair according to claim 1, characterized in that: The tooth tip diameter of the gear portion (32) is smaller than the thread pitch diameter of the thread portion (31).

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