A screw nut pair, a method for reducing pitch error of the screw nut pair, and a method for eliminating backlash of the screw nut pair

Abstract

The present application provides a screw-nut pair, comprising a screw and a spliced transmission nut; the spliced transmission nut comprises at least two single-turn nut units; the single-turn nut unit comprises a single-turn thread and a cylindrical outer tube independent of the single-turn thread, the single-turn thread has a starting face and a terminal face at two ends along the thread circumference; when two adjacent single-turn nut units are spliced and matched with the screw, the starting face of one single-turn thread and the terminal face of the other single-turn thread form a first opposite face, and the two cylindrical outer tubes form a second opposite face along the end faces of the two cylindrical outer tubes on the same side along the cylinder axis; a gap is formed between the first opposite faces. The present application also provides a method for reducing the pitch error of the screw-nut pair and a method for eliminating the backlash of the screw-nut pair.

Description

Technical Field

[0001] This invention relates to the field of machining equipment. Background Technology

[0002] In a conventional lead screw, the screw and nut are directly engaged via a trapezoidal thread; in a ball screw, the screw and nut are engaged via balls positioned within helical grooves. Because there is a gap between the thread teeth, when the lead screw rotates from one direction to the other, a backlash occurs between the teeth and the corresponding grooves, affecting transmission accuracy. Furthermore, during transmission, the moving parts are in direct contact, making them prone to wear and resulting in low accuracy retention in the lead screw transmission.

[0003] As CNC machine tools continue to develop towards high speed, heavy load, and precision, the ball screw pair, which is most widely used in this field, has gradually revealed some inherent defects due to its own structure, such as contact wear, heavy load pitting, low speed crawling, high speed limitation, reverse cross-flow, and poor accuracy retention. Moreover, the difficulty and cost of solving these problems are increasing.

[0004] Because of the pressure oil film between the screw and nut thread surfaces of the hydrostatic screw pair, it possesses advantages such as high load-bearing capacity, high rigidity, high vibration resistance, near-frictionless motion, and no creep, making it a highly competitive transmission form for heavy-duty, high-speed, long-life, and precision applications. However, the hydrostatic oil cavity on the helical surface of the nut thread and the numerous complex small-diameter oil supply channels arranged inside the nut result in extremely high processing and implementation difficulties.

[0005] To address the aforementioned technical problems, Chinese patent CN116066535A provides a spliced ​​nut, which solves the difficulty in machining hydrostatic nuts by splitting the nut into multiple single-turn nut units and then splicing them together. However, this introduces new problems: machining errors in the lead screw and the helical surfaces of each single-turn nut unit will lead to:

[0006] (1) The pitch of each single-turn nut unit is not consistent, and the uniformity of the pitch of the nut assembled from multiple single-turn nut units is poor;

[0007] (2) After the nut and the screw are engaged, the gaps on the two sides of the helical surface are not consistent. That is, there is a situation where the gap on one side is large on one turn of the helical surface and small on the other turn, while the gap on the other side is small on one turn of the helical surface and large on the other turn.

[0008] To address the aforementioned issues, Chinese patent CN116066535A uses shims to adjust the pitch, but this solution still has problems:

[0009] ① For example Figure 1A coordinate system is established with the horizontal axis as "circumferential" and the vertical axis as "axial". The adjacent two single-turn nut units are unfolded along the thread pitch diameter d. Although the pitch P and helix angle φ of the two single-turn nut units have no error, a pitch error "-ΔP" is generated after splicing due to the position error. Figure 2 This diagram illustrates how to eliminate errors by adding a shim of thickness ΔP between two single-turn nuts. The positional error ΔP caused by normal machining errors is generally no more than tens of micrometers, meaning the thickness of the shim should also be no more than tens of micrometers. In actual production, machining the shim to achieve this is impractical, and the shims at both points on the stepped semi-cylinder between the two single-turn nut units must have equal thickness and equal deformation after splicing; otherwise, additional errors will be introduced, leading to coaxiality errors in the nuts.

[0010] ② If the pitch error after splicing is "+ΔP", it cannot be adjusted by adding shims.

[0011] ③ If there is an error in the pitch or helix angle between two single-turn nut units, i.e., P and φ, the problem mentioned in ① and ② above will still exist when adjusting with shims.

[0012] ④ Each single-turn nut unit needs to be assembled with shims before it can be screwed into the screw for testing. If there are errors and it cannot fit well with the screw thread surface, each single-turn nut unit needs to be repeatedly disassembled to prepare and adjust the shims. Summary of the Invention

[0013] The main technical problem to be solved by the present invention is to provide a lead screw and nut pair that allows users to adjust the clearance to correct pitch error or eliminate backlash, optimize lubrication conditions, and improve transmission accuracy and stability.

[0014] To solve the above-mentioned technical problems, the present invention provides a lead screw and nut assembly, comprising: a lead screw and a spliced ​​transmission nut;

[0015] The spliced ​​transmission nut includes at least two single-turn nut units;

[0016] The single-turn nut unit includes a single-turn thread and a cylindrical outer cylinder independent of the single-turn thread. The two ends of the single-turn thread along the circumferential direction are the starting face and the ending face of the single-turn thread, respectively. When two adjacent single-turn nut units are spliced ​​together and cooperate with the lead screw, the starting face of one single-turn thread and the ending face of the other single-turn thread are opposite to form a first opposing face, and the two cylindrical outer cylinders are opposite to each other along the axial direction of the cylinder to form a second opposing face.

[0017] A gap is formed between the first opposing surfaces.

[0018] In a preferred embodiment: the starting surface and the ending surface are planes extending radially along the cylindrical outer cylinder, and the central angle formed by the radial planes containing the starting surface and the ending surface is 2θ.

[0019] In a preferred embodiment: the height of the cylindrical outer cylinder along the axial direction is not less than the pitch p of the single turn of the thread.

[0020] In a preferred embodiment: the spliced ​​transmission nut further includes an axial washer disposed between two adjacent single-turn nut units, so that the two adjacent single-turn nut units form an intermittent thread.

[0021] The present invention also provides a method for reducing the pitch error of the lead screw and nut pair as described above, by rotating two adjacent single-turn nut units relative to each other in the circumferential direction to change the gap between the first opposing surfaces.

[0022] In a preferred embodiment: when the pitch of the thread after connecting two adjacent single-turn nut units is less than 2p, the gap between the first opposing surfaces is reduced, where p is the pitch of the single-turn thread.

[0023] In a preferred embodiment: when the pitch of the thread after connecting two adjacent single-turn nut units is greater than 2p, the gap between the first opposing surfaces is increased, where p is the pitch of the single-turn thread.

[0024] In a preferred embodiment: when the gap between the first opposing surfaces increases or decreases by Δ, the resulting pitch change is ΔP, which satisfies Δ=ΔP / tan(φ), where φ is the helical lift angle of a single turn of the thread.

[0025] The present invention also provides a method for eliminating the backlash of the lead screw and nut pair as described above, characterized in that: a portion of the single-turn nut unit of the spliced ​​transmission nut is fitted with one helical surface of the lead screw, and another portion is fitted with the other helical surface of the lead screw.

[0026] In a preferred embodiment: each single-turn nut unit in the spliced ​​transmission nut is divided into two groups, and the two groups of single-turn nut units are arranged at intervals along the length of the lead screw, with one group of single-turn nut units fitting one side of the spiral surface of the lead screw and the other group of single-turn nut units fitting the other side of the spiral surface of the lead screw.

[0027] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0028] 1. The spliced ​​transmission nut consists of at least two single-turn nut units. Each single-turn nut unit has a cylindrical outer cylinder independent of its own thread, allowing the nut to be machined in sections, reducing the overall machining and assembly difficulty, and facilitating mass production and precision control. Each single-turn thread has a starting and ending face at both ends along its circumference. When adjacent single-turn nut units are spliced, they form a first opposing face with a pre-reserved gap between them. The gap can be changed by the relative circumferential rotation of adjacent single-turn nut units, achieving in-situ fine-tuning of the pitch error without the need for additional high-precision adjusting shims, making adjustment convenient and highly accurate.

[0029] 2. The single-turn nut unit is divided into two groups and respectively fits into the helical surfaces on both sides of the lead screw. This allows the two groups of single-turn nut units to bear the load separately when the lead screw switches between forward and reverse directions. There is no idle travel on the threaded mating surface, which eliminates transmission backlash from a structural perspective, avoids reverse cross-flow, and significantly improves transmission positioning accuracy and repeatability.

[0030] 3. An axial washer is placed between adjacent single-turn nut units to form an intermittent thread between adjacent single-turn threads. On the one hand, this reduces the machining and assembly requirements of the thread meshing surface. On the other hand, a lubrication cavity is formed between the axial washer and the lead screw, which can hold lubricating oil or grease, effectively improving the lubrication conditions of the thread mating surface, reducing friction and wear, and improving transmission life and accuracy retention.

[0031] 4. The axial height of the cylindrical outer cylinder is set to be equal to the pitch of the single-turn thread, ensuring that the structure is regular and the axial positioning is reliable after the single-turn nut unit is spliced. It is convenient for circumferential rotation adjustment and subsequent fixing, and the overall structure is compact, the force is uniform, and the transmission is stable. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the error before adjustment using shims in the prior art;

[0033] Figure 2 This is a schematic diagram of the error after adjustment using shims in the prior art;

[0034] Figure 3 This is a schematic diagram of the hydrostatic screw pair in the preferred embodiment 1 of the present invention;

[0035] Figure 4 This is a schematic diagram of the hydrostatic nut in preferred embodiment 1 of the present invention;

[0036] Figure 5 This is a cross-sectional view of the hydrostatic nut in preferred embodiment 1 of the present invention;

[0037] Figure 6 This is a partial schematic diagram of the hydrostatic nut in the preferred embodiment 1 of the present invention;

[0038] Figure 7This is a cross-sectional view of the single-turn nut unit in the preferred embodiment of the present invention along the axial direction of its oil inlet hole;

[0039] Figure 8 This is a schematic diagram of the single-turn nut unit in the preferred embodiment 1 of the present invention;

[0040] Figure 9 This is a schematic diagram showing the positional error between the two single-turn nut units in the preferred embodiment 1 of the present invention;

[0041] Figure 10 for Figure 9 A schematic diagram after error elimination;

[0042] Figure 11 This is a schematic diagram illustrating the shape error between the two single-turn nut units in the preferred embodiment of the present invention;

[0043] Figure 12 for Figure 11 A schematic diagram after error elimination;

[0044] Figure 13 This is a schematic diagram of the lead screw pair in preferred embodiment 2 of the present invention;

[0045] Figure 14 This is a schematic diagram of the single-turn nut unit in preferred embodiment 2 of the present invention;

[0046] Figure 15 This is a schematic diagram showing the back gap between single-turn nuts in a preferred embodiment of the present invention;

[0047] Figure 16 This is a schematic diagram of the preferred embodiment 2 of the present invention for eliminating backlash between single-turn nuts;

[0048] Figure 17 This is a schematic diagram of a preferred embodiment 2 of the present invention, in which a single-turn nut eliminates backlash using an axial washer. Detailed Implementation

[0049] refer to Figure 1 The diagram shows a hydrostatic screw and nut assembly provided in the embodiment, including a screw 1 and a hydrostatic nut 2. Figure 2 The diagram shows the structure of the hydrostatic nut 2 of this invention. The hydrostatic nut 2 consists of retaining rings 2.1 at both ends and multiple single-turn nut units 2.2 in the middle. The number of single-turn nut units 2.2 can be configured according to the load-bearing requirements. The retaining rings 2.1 and single-turn nut units 2.2 can be assembled by welding or other methods. After assembly, the internal thread helical surface is precision machined, including enlarging the four oil inlet holes 2.4 on one of the single-turn nut units 2.2 and machining the four main oil return holes 2.3 on the opposing surfaces of the other two single-turn nut units 2.2.

[0050] The four oil inlets 2.4 on the single-turn nut unit 2.2, which has undergone reaming, are the main oil inlets. The four oil inlets 2.4 on the other single-turn nut units 2.2 are sealed by welding or other methods. Figure 3 As shown.

[0051] Figure 4 To remove the hydrostatic nuts after removing the retaining rings 2.1 at both ends, four sets (or other sets) of internal feedback throttling bearing units 2.5 are evenly distributed on both sides of each spiral surface. High-pressure oil is distributed through the four enlarged main oil inlets 2.4 to the axial oil inlets 2.6 located on the outer cylinder of each throttling unit, and then enters each internal feedback throttling bearing unit 2.5. A return oil groove 2.7 is provided between each adjacent internal feedback throttling bearing unit 2.5. Low-pressure oil enters the axial return oil hole 2.8 through the return oil groove 2.7 from the thread top gap, etc., and then flows out from the main return oil hole 2.3.

[0052] Single internal feedback throttling bearing unit 2.5 Figure 5 and 6 As shown, it includes an annular boss oil-sealing surface 2.5.1, a fan-shaped groove pressure-bearing area 2.5.2 and a feedback oil inlet 2.5.6 located therein, a fan-shaped oil-sealing boss 2.5.3 inside the pressure-bearing area, a waist-shaped groove throttling area 2.5.4 and a cylindrical boss 2.5.5 with an oil inlet located therein, and a feedback oil outlet 2.5.7 located in the throttling area. The oil in the feedback oil inlet 2.5.6 flows out through the feedback oil outlet on the other side of the spiral surface, and the oil outlet 2.5.7 feeds the oil back to the feedback oil inlet on the other side of the spiral surface.

[0053] like Figure 7 The diagram shows a cross-sectional view of the single-turn nut unit 2.2 along the axial direction of its oil inlet hole 2.4. The axial oil inlet hole 2.6 distributes high-pressure oil to the four oil inlets 2.4 in each turn, and the oil inlets 2.4 then distribute the oil to the oil inlets on the cylindrical bosses 2.5.5 on the opposing sides of the spiral surface of the throttling bearing unit.

[0054] like Figure 8As shown, in this embodiment, the thread of the single-turn nut unit 2.2 is a separate feature, and its outer cylinder 2.2.1 is independent of the thread, serving functions such as connection, oil passage, positioning, and adjustment of pitch and helical surface clearance. Specifically, the single-turn nut unit 2.2 includes a single-turn thread and a cylindrical outer cylinder 2.2.1 independent of the single-turn thread. The two ends of the single-turn thread along the circumferential direction are the starting face and the ending face of the single-turn thread, respectively. When two adjacent single-turn nut units 2.2 are spliced ​​together and cooperate with the lead screw 1, the starting face of one single-turn thread and the ending face of the other single-turn thread face each other to form a first opposing face, and the two cylindrical outer cylinders face each other along the opposite side of the cylindrical axis to form a second opposing face; a gap is formed between the first opposing faces. Furthermore, the height of the outer cylinder 2.2.1 is equal to the pitch P of the unit thread. As a simple alternative, the height of the outer cylinder 2.2.1 can also be greater than the pitch P of the unit thread.

[0055] The method for adjusting the screw pitch using the outer cylinder is as follows:

[0056] In this embodiment, rotating the outer cylinder 2.2.1 of the single-turn nut unit 2.2 can eliminate the pitch error caused by the positional error between the two single-turn nut units 2.2. For example... Figure 9 As shown, there is a positional error between the two single-turn nut units 2.2, and the assembly causes a pitch error "-ΔP". The starting and ending face 2.2.2 of the thread of each single-turn nut unit 2.2 is provided with an included angle of 2θ. Then, in the unfolded diagram of the mean diameter d, the circumferential length of each single-turn nut unit 2.2 after unfolding is (π-θ)d, and there is a gap of θd between two adjacent single-turn nut units 2.2.

[0057] like Figure 10 As shown, by moving (rotating) the second single-turn nut unit 2.2 in the forward direction, the gap of the single-turn nut unit 2.2 is reduced to θd-Δ, thus eliminating the pitch error. Here, Δ = ΔP / tan(φ). φ is typically 3°-5°, so Δ can magnify the ΔP value by more than ten times, making adjustment convenient and providing high resolution. Furthermore, Δ corresponds to the thread pitch diameter d, and since the outer diameter of the outer cylinder 2.2.1 is larger, the magnification is even higher, making adjustment more convenient and providing higher resolution. On the other hand, during rotational adjustment, the impact of Δ error caused by operation or reading on ΔP is reduced by more than ten times, which is highly beneficial for actual production.

[0058] Similarly, when the pitch error caused by assembly is "+ΔP", it can be eliminated by moving (rotating) the second single-turn nut unit 2.2 in the opposite direction.

[0059] Besides positional error, in this embodiment, rotating the outer cylinder 2.2.1 of the single-turn nut unit 2.2 can also homogenize and reduce the pitch error caused by shape error in the two single-turn nut units 2.2. For example... Figure 11As shown, there is a shape error between the two single-turn nut units 2.2, that is, there is an error in the pitch P and the helix angle φ. When P1 < P2 and φ1 < φ2, the assembly of the two single-turn nut units 2.2 will cause a pitch error "+ΔP".

[0060] like Figure 12 As shown, by moving (rotating) the second single-turn nut unit 2.2 in the opposite direction, the gap between the two turns is increased to θd+Δ, which can equalize and reduce the pitch error, reducing the pitch error of the assembled unit by about 1 / 2.

[0061] Similarly, when the pitch error caused by assembly is "-ΔP", it can be made smaller and more uniform by moving (rotating) the second single-turn nut unit 2.2 in the forward direction.

[0062] Example 2

[0063] like Figure 13 As shown, the difference between this embodiment and Embodiment 1 is that the nut 2 in this embodiment is a common transmission nut, not a hydrostatic nut. Therefore, the single-turn nut unit in Embodiment 2 does not need to be machined with the oil flow channel and the internal feedback throttling bearing unit found in hydrostatic nuts, such as... Figure 14 As shown. The method and principle for adjusting the pitch error of the transmission nut are the same as in Example 1, and will not be repeated here.

[0064] Traditional transmission nuts and lead screws will have backlash after assembly, that is, a gap will be formed between the threaded mating surfaces (as shown in the shaded area in Figure 15).

[0065] While the backlash in a conventional lead screw drive can be eliminated through circumferential misalignment adjustment of the combined nut, a right-side helical surface clearance still exists between the first, third, and fifth single-turn nut units and the lead screw along the axial direction from left to right. The second, fourth, and sixth single-turn nut units, on the other hand, have a left-side helical surface clearance, making complete elimination of the backlash on both sides of the thread impossible. However, because the lead screw is only supported by the single-turn nut unit with the right-side clearance during forward drive and only by the single-turn nut unit with the left-side clearance during reverse drive, there is no idle travel or axial movement during switching between forward and reverse directions. Therefore, although the backlash on both sides of the thread still exists, the transmission backlash has been completely eliminated.

[0066] In this embodiment, by placing an axial washer between two adjacent single-turn nut units, the adjacent single-turn threads are separated axially, forming an intermittent thread structure, thereby fundamentally eliminating the aforementioned thread fit clearance. Simultaneously, the intermittent area between the single-turn threads can accommodate lubricating oil or grease, significantly improving the lubrication conditions of the thread meshing surface, reducing transmission friction and wear, and enhancing transmission accuracy and service life.

[0067] The above is only one specific embodiment of the present invention, but the design concept of the present invention is not limited thereto. Any non-substantial modifications made to the present invention using this concept shall be deemed as infringing the protection scope of the present invention.

Claims

1. A lead screw and nut assembly, characterized in that... include: Lead screw and spliced ​​transmission nut; The spliced ​​transmission nut includes at least two single-turn nut units; The single-turn nut unit includes a single-turn thread and a cylindrical outer cylinder independent of the single-turn thread. The two ends of the single-turn thread along the circumferential direction are the starting face and the ending face of the single-turn thread, respectively. When two adjacent single-turn nut units are spliced ​​together and cooperate with the lead screw, the starting face of one single-turn thread and the ending face of the other single-turn thread are opposite to form a first opposing face, and the two cylindrical outer cylinders are opposite to each other along the axial direction of the cylinder to form a second opposing face. A gap is formed between the first opposing surfaces.

2. The lead screw and nut assembly according to claim 1, characterized in that... The starting surface and the ending surface are planes extending radially along the cylindrical outer cylinder, and the central angle formed by the radial planes containing the starting surface and the ending surface is 2θ.

3. A lead screw and nut assembly according to claim 1, characterized in that... The height of the cylindrical outer cylinder along the axial direction is not less than the pitch p of the single-turn thread.

4. A lead screw and nut assembly according to claim 1, characterized in that... The spliced ​​transmission nut also includes an axial washer disposed between two adjacent single-turn nut units, so that the two adjacent single-turn nut units form an intermittent thread.

5. A method for reducing the pitch error of the lead screw and nut pair according to any one of claims 1-4, characterized in that: The gap between the first opposing surfaces is changed by rotating two adjacent single-turn nut units relative to each other in the circumferential direction.

6. The method for reducing the pitch error of the lead screw and nut pair according to claim 5, characterized in that: When the pitch of the connected two adjacent single-turn nut units is less than 2p, the gap between the first opposing surfaces is reduced, where p is the pitch of the single-turn thread.

7. The method for reducing the pitch error of the lead screw and nut pair according to claim 5, characterized in that: When the pitch of the connected two adjacent single-turn nut units is greater than 2p, the gap between the first opposing surfaces is increased, where p is the pitch of the single-turn thread.

8. The method for reducing the pitch error of the lead screw and nut pair according to claim 5, characterized in that: When the gap between the first opposing surfaces increases or decreases by Δ, the resulting pitch change is ΔP, and the two satisfy Δ=ΔP / tan(φ), where φ is the helical lift angle of a single turn of the thread.

9. A method for eliminating backlash in a lead screw and nut pair according to any one of claims 1-4, characterized in that: A portion of the single-turn nut unit of the spliced ​​transmission nut is attached to one helical surface of the lead screw, and the other portion is attached to the other helical surface of the lead screw.

10. The method for eliminating backlash in a lead screw and nut pair according to claim 9, characterized in that: The single-turn nut units in the spliced ​​transmission nut are divided into two groups. The two groups of single-turn nut units are arranged at intervals along the length of the lead screw, and one group of single-turn nut units is attached to one side of the spiral surface of the lead screw, while the other group of single-turn nut units is attached to the other side of the spiral surface of the lead screw.

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