Slotted planetary roller screw

Abstract

This invention discloses a slotted planetary roller screw, comprising: a screw, a nut, rollers, a cage, a reversing key, and a locating pin. The nut has a circumferential notch. The rollers are evenly distributed circumferentially between the screw and the nut, and their outer surfaces have multiple rows of arc-shaped annular grooves. The cage is sleeved on the outer circumference of the screw and located inside the nut. The cage has a vertical groove parallel to the screw axis. The rollers are rotatably placed in the vertical groove and constrained to always engage with the screw and the nut simultaneously. The reversing key is embedded in the notch and fixed to the nut by the locating pin. The reversing key has a groove, which smoothly connects with the nut's internal thread on both sides of the notch to form a closed channel for roller circulation. The mean diameter curve of the groove is constructed as a quintic parabola. The slotted planetary roller screw of this invention allows the reversing key groove to constrain the rollers during roller circulation, connecting the nut thread with a quintic parabola, reducing impact and noise, and improving the smoothness of roller circulation.

Description

Technical Field

[0001] This invention belongs to the field of ball screw technology, specifically relating to a slotted planetary ball screw. Background Technology

[0002] Currently, planetary roller screws are increasingly widely used due to their high lifespan and high efficiency. Among them, the recirculating planetary screw, unlike the standard and reverse types, has no specific head ratio, offering greater space flexibility and allowing for smaller leads. Furthermore, it boasts higher transmission accuracy compared to differential planetary roller screws. However, the discontinuous thread connection of the nut return groove in the recirculating planetary roller screw causes impact during operation, preventing its application in high-speed, high-dynamic applications and severely hindering its development. Referring to existing patents, because the cage is located on both sides without parallel constraint on the rollers, the rollers twist and tilt during high-speed rotation and high-dynamic processes, leading to uneven movement. Summary of the Invention

[0003] This invention provides a slotted planetary roller screw to solve the aforementioned technical problems, specifically employing the following technical solution:

[0004] A slotted planetary roller screw includes: a screw, a nut, rollers, a cage, a reverse key, and a locating pin. The nut has an internal thread with the same direction of rotation and lead as the screw, and a circumferential notch. The rollers are evenly distributed circumferentially between the screw and the nut, and their outer surfaces have multiple rows of arc-shaped annular grooves. The cage is fitted around the screw and located inside the nut, and has vertical grooves parallel to the screw axis. The rollers are rotatably placed within these vertical grooves and constrained to always engage simultaneously with both the screw and the nut. The reverse key is embedded in the notch and fixed to the nut by the locating pin. The reverse key has grooves on its inner surface facing the screw, with the opposite direction of rotation and the same number of threads as the nut's internal thread. The grooves smoothly connect to the nut's internal thread on both sides of the notch to form a closed channel for roller circulation. The mean diameter curve of the grooves is constructed as a quintic parabola.

[0005] Furthermore, taking the lead screw axis as the y-axis, the plane of symmetry of the reverse key as the xOz plane, and the xOy plane as a plane perpendicular to the z-axis, the equation of the quintic parabola in the xOy plane is:

[0006]

[0007] Among them, the coefficients A, B and C are uniquely determined by the continuity condition of the roller at the helical access point F, so that the center trajectory of the roller remains continuous in terms of curvature, tangential direction and axial velocity throughout the entire cycle of the roller from the nut thread through the groove and back to the nut thread.

[0008] Furthermore, the coefficients A, B, and C are determined by the following formula:

[0009]

[0010] Where, x F Let d be the x-coordinate of the junction F. p Where P is the center diameter of the roller shaft, and P is the lead of the roller screw pair.

[0011]

[0012]

[0013]

[0014] Where λ is the helix angle.

[0015] Furthermore, the distance ρ from the groove mid-diameter curve to the lead screw shaft varies along the return trajectory, and satisfies:

[0016] When the roller is located at the center of the screw tooth tip, ρ takes its maximum value ρ0.

[0017]

[0018] Where d is the outer diameter of the lead screw and r is the outer radius of the roller.

[0019] When the roller meshes with the lead screw tooth profile, ρ takes its minimum value. min

[0020]

[0021] Within the axial span of the reverse key, ρ changes continuously with the axial deviation v, and the relationship between ρ and v is defined piecewise as follows:

[0022] Straight segment at the tooth crest:

[0023] ρ=ρ0

[0024] Corresponding to v b ≤v≤P / 2.

[0025] Tooth crest rounded corner segment:

[0026]

[0027] Corresponding to v e ≤v≤v b .

[0028] Tooth profile arc segment:

[0029]

[0030] Corresponding to v a ≤v≤v e .

[0031] Tooth profile bevel section:

[0032]

[0033] Corresponding to 0≤v≤v a .

[0034] in:

[0035] v is the axial deviation, r is the outer diameter radius of the roller, r0 is the pitch diameter radius of the roller, r1 is the tip radius of the screw tooth fillet, r2 is the tip radius of the roller tooth fillet, α is the half-angle radius of the tooth profile, d is the outer diameter of the screw, d0 is the pitch diameter of the screw, v a v e and v b These are the critical deviations for each segment, used to define the boundaries between different segments.

[0036] Furthermore, the critical deviation v b v e v a Determined by the following formula:

[0037]

[0038]

[0039] .

[0040] Furthermore, the working width ϕ of the reverse key satisfies:

[0041]

[0042] Where n is the number of rollers, d0 is the lead screw pitch diameter, and r0 is the roller pitch diameter radius.

[0043] The width ϕ′ of the reverse key body satisfies:

[0044]

[0045] Where t takes the value of 2-3 mm.

[0046] Furthermore, the spatial coordinates of the contact point F are determined by the following formula:

[0047]

[0048] Where, d p λ is the center diameter of the roller shaft, P is the lead of the roller screw pair, and λ is the helix angle.

[0049] Furthermore, the lead screw has a single-start external thread.

[0050] The advantage of this invention lies in the provision of a slotted planetary roller screw, which, during roller circulation, uses a reverse key groove to constrain the rollers, connecting the nut thread with a five-fold parabolic curve. This reduces impact and noise, improves the smoothness of roller circulation, and allows for application in high-speed, high-dynamic scenarios. Furthermore, it significantly improves transmission efficiency and reduces impact noise. This overcomes the limitation of ordinary circulating planetary roller screws, which cannot be used in high-speed, high-dynamic motion applications. Attached Figure Description

[0051] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0052] Figure 1 This is a schematic diagram of the slotted planetary roller screw of this application;

[0053] Figure 2 This is a cross-sectional view of the slotted planetary roller screw of this application;

[0054] Figure 3 This is a schematic diagram of the slot-type planetary roller screw of this application after the nut has been removed;

[0055] Figure 4 This is a schematic diagram of the nut in this application;

[0056] Figure 5 This is a schematic diagram of the reverse key in this application;

[0057] Figure 6 This is a schematic diagram of the tooth profile of the lead screw roller;

[0058] Figure 7 It is xOy vision Figure 5 Schematic diagram of the parabola;

[0059] 1. Lead screw; 2. Nut; 21. Notch; 3. Roller; 31. Arc-shaped annular groove; 4. Cage; 41. Vertical groove; 5. Reverse key; 51. Groove; 6. Locating pin. Detailed Implementation

[0060] Embodiments of the present invention are described in detail below. Examples of these embodiments are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0061] like Figure 1-5The diagram shows a slotted planetary roller screw 100 according to this application, comprising: a screw 1, a nut 2, rollers 3, a cage 4, a reverse key 5, and a locating pin 6. This application is used in high-speed, high-dynamic applications. The screw 1 has a single-start external thread, and the nut 2 has an internal thread with the same direction of rotation and lead as the screw 1, and a circumferential notch 21. The rollers 3 are evenly distributed circumferentially between the screw 1 and the nut 2, and their outer surfaces are provided with multiple rows of arc-shaped annular grooves 31. The cage 4 is sleeved on the outer circumference of the screw 1 and located inside the nut 2. A vertical groove 41 parallel to the screw axis is provided on the cage 4, and the rollers 3 are rotatably placed within the vertical groove 41 and constrained to always engage simultaneously with the screw 1 and the nut 2. The reverse key 5 is embedded in the notch 21 and fixed to the nut 2 by the locating pin 6. The reverse key 5 has a groove 51 on its inner surface facing the lead screw 1, which has the opposite direction of the internal thread of the nut and the same number of threads. The groove 51 and the internal thread of the nut smoothly connect on both sides of the notch 21 to form a closed channel for the roller 3 to circulate. The mean diameter curve (i.e., the reverse curve) of the groove 51 is constructed as a quintic parabola.

[0062] Taking the y-axis as the helix axis, the equation of the helix in the o-xyz coordinate system is:

[0063]

[0064] Where θ is the parametric angle, in rad. p is the center diameter of the roller shaft, in mm. P is the lead of the planetary roller screw pair.

[0065] like Figure 6 The figure shows the cross-section of the lead screw surface within the z0y section of the thread. The coordinate z passes through the center of the thread crest, meaning the z-axis is taken as the axis of symmetry for the reverse key. Therefore, when designing the pitch diameter curve, it is natural to take the z-axis as the axis of symmetry. The projection of the pitch diameter curve onto the xOy plane is symmetrical about the origin, as shown below. Figure 7 The FOF' shown is used for calculation. Therefore, when designing and calculating coordinates, only FO needs to be calculated. As for 0F', it can be obtained by reversing the signs of x and y.

[0066] From a geometric perspective, a fifth-order parabolic cylinder with the z-axis as its axis of symmetry, that is, a fifth-order parabolic cylinder perpendicular to the axial plane xOy (the lead screw axis is y), intersects with the equidistant curved surface on the lead screw surface where the roller center is located to form the mean diameter curve.

[0067] If we take the lead screw helical axis as y, according to the right-hand coordinate system, the above equidistant surface can be expressed by parametric equations as follows:

[0068] x=ρcos

[0069] y=y

[0070] z=ρsin

[0071] The fifth-order parabolic cylinder can be expressed by the equation:

[0072] x=x

[0073] y=Ax+Bx 3 +Cx 5

[0074] z=z

[0075] Combining the two equations, we obtain the equation for the median diameter curve:

[0076] x=ρcos

[0077] y=Ax+Bx 3 +Cx 5

[0078] z=ρsin

[0079] In the formula, y is a parameter variable. Let x be the distance from the pitch diameter curve to the leadscrew shaft. For ease of calculation and production, x is used as a parameter. The equation of the pitch diameter curve is:

[0080]

[0081] y=Ax+Bx 3 +Cx 5

[0082]

[0083] The remaining question is how to determine the coefficients A, B, C, and the distance. .

[0084] Specifically, with the lead screw axis as the y-axis, the plane of symmetry of the reverse key is the xOz plane, and the xOy plane is a plane perpendicular to the z-axis. The fifth-order parabolic curve in the xOy plane has the same y, y′, and y″ values ​​as the helix of the nut thread at the contact point F, ensuring a smooth transition of the roller during the cycle. This reduces impact and noise, achieving smooth transmission under high speed and high dynamic conditions.

[0085] The equation of the quintic parabola in the xOy plane is:

[0086]

[0087] Among them, the coefficients A, B and C are uniquely determined by the continuity condition of the roller at the helical access point F, so that the center trajectory of the roller remains continuous in terms of curvature, tangential direction and axial velocity throughout the entire cycle of the roller from the nut thread through the groove and back to the nut thread.

[0088] The determination of coefficients A, B, and C begins with defining the boundary conditions of the median diameter curve:

[0089] The median diameter curve is symmetrical about the z-axis, and its intersection with the z-axis is:

[0090] x=0

[0091] y=0

[0092]

[0093] r is the outer radius of the roller, d is the outer diameter of the lead screw, and ρ0 is... The maximum value of ρ. When the roller meshes with the lead screw tooth profile, ρ takes its minimum value. min

[0094]

[0095] Therefore:

[0096]

[0097] The mean diameter curve and the helix at F0(x) F y F , z F Connect the two sides and make the quintic parabola y = Ax + Bx 3 +Cx 5 In F(x) F y F The projection of the point and the spiral onto the x0y plane Tangent to each other, and requiring that the y, y', and y'' values ​​of the two curves are equal at point F, ensures that the curvature of the median diameter curve is continuous at point F, in order to determine the three coefficients A, B, and C. Rewrite the helix equation as an equation with x as a parameter:

[0098]

[0099] If we take positive values ​​of x upwards, then,

[0100]

[0101] According to the boundary conditions, when x=x F hour:

[0102]

[0103] in,

[0104]

[0105]

[0106]

[0107] λ is the helix angle, measured in rad.

[0108] Therefore, the coefficients A, B, and C are determined by the following formula:

[0109]

[0110] Where, x F Let d be the x-coordinate of the junction F. p Where is the center diameter of the roller shaft, and P is the lead of the roller screw pair.

[0111] Where λ is the helix angle.

[0112] Within the axial span of the reverse key, ρ varies continuously with the axial deviation v. The deviation v represents the axial (y-direction) distance from a point on the median diameter curve to point F.

[0113]

[0114]

[0115]

[0116]

[0117] The distance ρ from the groove mid-diameter curve to the lead screw shaft varies along the return trajectory and satisfies:

[0118] When the roller is located at the center of the lead screw tooth tip, v = v max =P / 2 (within the xOy plane). ρ takes its maximum value ρ0.

[0119]

[0120] Where d is the outer diameter of the lead screw and r is the outer radius of the roller.

[0121] When the roller meshes with the lead screw tooth profile, v=0, and ρ takes its minimum value. min

[0122]

[0123] The relationship between ρ and v is defined piecewise as follows:

[0124] Straight segment at the tooth crest:

[0125] ρ=ρ0

[0126] Corresponding to v b ≤v≤P / 2.

[0127] Tooth crest rounded corner segment:

[0128]

[0129] Corresponding to v e ≤v≤v b .

[0130] Tooth profile arc segment:

[0131]

[0132] Corresponding to v a ≤v≤v e .

[0133] Tooth profile bevel section:

[0134]

[0135] Corresponding to 0≤v≤v a .

[0136] in:

[0137] v is the axial deviation, r is the outer diameter radius of the roller, r0 is the pitch diameter radius of the roller, r1 is the tip radius of the screw tooth fillet, r2 is the tip radius of the roller tooth fillet, α is the half-angle radius of the tooth profile, d is the outer diameter of the screw, d0 is the pitch diameter of the screw, v a v e and v b These are the critical deviations for each segment, used to define the boundaries between different segments.

[0138] Critical deviation v b v e v a Determined by the following formula:

[0139]

[0140]

[0141]

[0142] In this embodiment of the application, the working width ϕ of the reverse key satisfies:

[0143]

[0144] Where n is the number of rollers, d0 is the lead screw pitch diameter, and r0 is the roller pitch diameter radius.

[0145] The width ϕ′ of the reverse key body satisfies:

[0146]

[0147] Where t takes the value of 2-3 mm.

[0148] Furthermore, the spatial coordinates of the contact point F are determined by the following formula:

[0149]

[0150] Where, d p λ is the center diameter of the roller shaft, P is the lead of the roller screw pair, and λ is the helix angle.

[0151] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the above embodiments do not limit the present invention in any way, and all technical solutions obtained by equivalent substitution or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A slotted planetary roller screw, characterized in that, include: The system comprises a lead screw, a nut, rollers, a cage, a reverse key, and a locating pin. The lead screw has an external thread, and the nut has an internal thread with the same direction of rotation and lead as the lead screw, and a circumferential notch. The rollers are evenly distributed circumferentially between the lead screw and the nut, and their outer surfaces have multiple rows of arc-shaped grooves. The cage is fitted around the outer circumference of the lead screw and located inside the nut. The cage has a vertical groove parallel to the axis of the lead screw, and the rollers are rotatably placed in the vertical groove and constrained to always engage with the lead screw and the nut simultaneously. The reverse key is embedded in the notch and fixed to the nut by the locating pin. The reverse key has a groove on its inner surface facing the lead screw, with the opposite direction of rotation and the same number of threads as the nut's internal thread. The grooves smoothly connect with the nut's internal thread on both sides of the notch to form a closed channel for roller circulation. The mean diameter curve of the groove is constructed as a quintic parabola. The distance ρ from the groove mid-diameter curve to the lead screw shaft varies along the return trajectory and satisfies: When the roller is located at the center of the screw tooth tip, ρ takes its maximum value ρ0: Where d is the outer diameter of the lead screw and r is the outer radius of the roller. When the roller meshes with the lead screw tooth profile, ρ takes its minimum value. min : Within the axial span of the reverse key, ρ changes continuously with the axial deviation v, and the relationship between ρ and v is defined piecewise as follows: Straight segment of tooth crest: ρ=ρ0 Corresponding to v b ≤v≤P / 2; Tooth crest rounded corner segment: Corresponding to v e ≤v≤v b ; Tooth-shaped curved surface segment: Corresponding to v a ≤v≤v e ; Tooth profile bevel section: Corresponding to 0≤v≤v a ; in: v is the axial deviation, r is the outer diameter radius of the roller, r0 is the pitch diameter radius of the roller, r1 is the tip radius of the screw tooth fillet, r2 is the tip radius of the roller tooth fillet, α is the half-angle radius of the tooth profile, d is the outer diameter of the screw, d0 is the pitch diameter of the screw, v a v e and v b These are the critical deviations for each segment, used to define the boundaries between different segments; The critical deviation v b v e v a Determined by the following formula: 。 2. The slotted planetary roller screw according to claim 1, characterized in that, With the lead screw axis as the y-axis, the plane of symmetry of the reverse key is the xOz plane, and the xOy plane is a plane perpendicular to the z-axis. The equation of the fifth-order parabola in the xOy plane is: Among them, the coefficients A, B and C are uniquely determined by the continuity condition of the roller at the helical access point F, so that the center trajectory of the roller remains continuous in terms of curvature, tangential direction and axial velocity throughout the entire cycle of the roller from the nut thread through the groove and back to the nut thread.

3. The slotted planetary roller screw according to claim 2, characterized in that, The coefficients A, B, and C are determined by the following formula: Where, x F Let d be the x-coordinate of the junction F. p Where P is the center diameter of the roller shaft, and P is the lead of the roller screw pair. Where λ is the helix angle.

4. The slotted planetary roller screw according to claim 1, characterized in that, Reverse key working width satisfy: Where n is the number of rollers, d0 is the lead screw pitch diameter, and r0 is the roller pitch diameter radius; Reverse key body width satisfy: Where t takes the value of 2-3 mm.

5. The slotted planetary roller screw according to claim 4, characterized in that, The spatial coordinates of contact point F are determined by the following formula: Where, d p λ is the center diameter of the roller shaft, P is the lead of the roller screw pair, and λ is the helix angle.

6. The slotted planetary roller screw according to claim 1, characterized in that, The lead screw has a single-start external thread.

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