Ball screw

Abstract

This invention provides a ball screw that absorbs the misalignment between the central axis of the circulating tube and the trajectory of the ball in the load zone, thereby mitigating the impact caused by collisions between the ball and the circulating tube, and suppressing deterioration of operation, noise, vibration, and damage to the circulating tube. [Solution] The ball screw 10 comprises a screw shaft 20 having an outer circumference screw groove 21, a nut 30 having an inner circumference screw groove 31 and a through hole 33, a plurality of balls 12, a circulation component (circulation tube) 40 forming a ball circulation passage 13, a circulation component retainer 50 that prevents radial movement of the circulation component 40 relative to the nut 30, and an elastic member 60 disposed between the through hole 33 and the circulation component 40 to support the circulation component 40 so that it can be elastically displaced in the axial direction.

Description

Technical Field

[0001] The present invention relates to a ball screw, and more particularly to a ball screw provided with a circulation component for circulating balls.

Background Art

[0002] As shown in FIGS. 5 and 6, a conventional ball screw 10A includes a screw shaft 20 having a spiral outer screw groove 21 formed on its outer peripheral surface, a nut 30 having a spiral inner screw groove 31 formed on its inner peripheral surface facing the outer screw groove 21 of the screw shaft 20, a large number of balls 12 rotatably interposed in a ball rolling path 11 formed by the outer screw groove 21 and the inner screw groove 31, and a substantially U-shaped circulation tube 40.

[0003] The circulation tube 40 has a ball circulation passage 13 inside thereof and circulates the balls 12 rolling in the ball rolling path 11. The circulation tube 40 is fixed to a notch plane 32 formed on the outer peripheral surface of the nut 30 by a set screw 55 via a circulation component retainer 50.

[0004] Generally, as shown in FIG. 6, the circulation tube 40 is designed such that the central axis C1 of the ball orbit near the inlet and outlet of the circulation tube 40 (hereinafter also referred to as the central axis C1 of the circulation tube 40) intersects with the central axis C2 of the ball orbit near the inlet and outlet of the ball rolling path 11, so that the balls 12 can smoothly enter and exit the circulation tube 40.

[0005] However, as shown in FIGS. 7(a) and (b), during the operation of the ball screw 10A, due to the influence of sliding friction generated between the balls 12 and the outer screw groove 21 and the inner screw groove 31, the balls 12 move within the ball orbit. The direction of movement varies depending on the direction of motion. As shown in FIG. 7(a), when the moving direction A of the nut 30 and the load P are in the same direction (hereinafter also referred to as reverse operation), the balls 12 move in the lower right direction (arrow C direction) in the figure. As shown in FIG. 7(b), when the moving direction B of the nut 30 and the load P are in opposite directions (hereinafter also referred to as forward operation), the balls 12 move in the upper left direction (arrow D direction) in the figure.

[0006] The cause of the misalignment between the central axis C1 of the circulation tube 40 and the ball trajectory 15 in the load zone is the gap inside the ball screw and the preload applied to the ball screw. Generally, ball screws are provided with a margin for the screw shaft or nut to move radially or axially, and such movable dimensions in the radial or axial direction are called radial clearance or axial clearance. Figures 8(a) and (b) are diagrams to illustrate radial clearance, with Figure 8(a) showing the screw shaft at the top of the diagram and Figure 8(b) showing the screw shaft at the bottom of the diagram. As shown in Figures 8(a) and (b), the ball screw 10A has radial clearance L. Figures 9(a) and (b) are diagrams to illustrate axial clearance, with Figure 9(a) showing the screw shaft at the leftmost part of the diagram and Figure 9(b) showing the screw shaft at the rightmost part of the diagram. As shown in Figures 9(a) and (b), the ball screw 10A has axial clearance M.

[0007] Furthermore, the required accuracy, such as lead error, and allowable backlash (axial clearance M) of ball screws vary depending on the application, such as for conveying, machine tools, semiconductor manufacturing equipment, electric injection molding, and electric presses. For example, in applications requiring high rigidity, such as precision positioning or machine tools, preload is applied to eliminate the clearance inside the ball screw. Methods of applying preload include double-nut preload, which uses two nuts with a spacer inserted between them, and offset preload, which increases the lead near the axial center of the nut by a predetermined offset amount. When preload is applied, elastic displacement occurs due to the applied preload load in addition to the clearance, which further increases the misalignment between the central axis C1 of the circulating tube 40 and the ball's trajectory 15 in the load zone, thus increasing the risk of noise and damage to circulating components as described above.

[0008] As described above, since the ball 12 moves to different positions during forward and reverse operation, a misalignment occurs between the central axis C1 of the circulation tube 40 and the trajectory 15 of the balls rolling near the inlet and outlet of the ball rolling path 11 during forward and reverse operation (hereinafter also referred to as the trajectory 15 of the balls in the load zone). Furthermore, the misalignment between the central axis C1 of the circulation tube 40 and the trajectory 15 of the balls in the load zone may become even larger due to the machining accuracy when machining the insertion hole for the circulation tube 40 in the nut 30 and the mounting accuracy of the circulation tube 40.

[0009] If there is a large discrepancy between the central axis C1 of the circulation tube 40 and the trajectory 15 of the ball in the load zone, the ball 12 will not enter the circulation tube 40 smoothly, and the frequency and load of collisions between the inlet / outlet of the circulation tube 40 and the ball 12 will increase. This may lead to deterioration of operation, noise, vibration, and damage to the inlet / outlet of the circulation tube 40 and the grooves near them.

[0010] Patent Document 1 discloses a ball screw device in which a cushioning material more flexible than the material of the screw shaft is placed on the ball restraining surface on the nut side, extending from the ball scooping point to the load region between the two screw grooves. This absorbs the kinetic energy when the ball hits the cushioning material, preventing peeling and wear of the screw shaft and nut near the ball scooping point, and also reduces vibration and noise.

[0011] Furthermore, Patent Document 2 discloses a ball screw comprising a passage-forming member having a groove that constitutes part of the ball return passage and is inserted into a through hole that penetrates the outer and inner surfaces of a nut, and an elastic member fixed to the through hole and elastically supporting the passage-forming member, wherein the step difference between the groove of the passage-forming member and the ball groove of the nut is absorbed by the elastic member to suppress ball jamming. [Prior art documents] [Patent Documents]

[0012] [Patent Document 1] Japanese Patent Publication No. 2005-83522 [Patent Document 2] Japanese Patent Publication No. 2023-139832 [Overview of the project] [Problems that the invention aims to solve]

[0013] The misalignment between the central axis C1 of the aforementioned circulating tube 40 and the ball trajectory 15 in the load zone occurs not only in the radial direction but also in the axial direction. In the ball screws described in Patent Documents 1 and 2, since the elastic body is arranged only in the radial direction, radial misalignment can be absorbed, but axial misalignment cannot.

[0014] This invention has been made in view of the aforementioned problems, and its purpose is to provide a ball screw that can absorb the misalignment between the central axis of the circulating tube and the trajectory of the ball in the load zone, thereby mitigating the impact caused by collisions between the ball and the circulating tube, and suppressing deterioration of operation, noise, vibration, and damage to the circulating tube. [Means for solving the problem]

[0015] Therefore, the above objective of the present invention is achieved by the following configuration [1] relating to a ball screw. [1] A screw shaft having a helical outer thread groove formed on its outer surface, A nut having a spiral inner thread groove formed on its inner surface so as to be opposite to the outer thread groove, and a plurality of through holes formed so as to communicate the outer surface and the inner thread groove, A plurality of balls that roll along a ball rolling path formed by the outer circumferential screw groove and the inner circumferential screw groove, At least one circulating component, the end of which is inserted into the through hole, to form a ball circulation passage for circulating the balls that roll along the ball rolling path, A ball screw equipped with, A circulating part retainer is fixed to the nut and prevents radial movement of the circulating part relative to the nut, An elastic member disposed between the inner peripheral surface of the through hole of the nut and the outer peripheral surface of the circulation component, and supporting the circulation component so as to be elastically displaced in the axial direction of the circulation component; A ball screw comprising.

Advantages of the Invention

[0016] According to the ball screw of the present invention, the deviation between the central axis of the circulation tube and the orbit of the ball in the load zone can be absorbed, the impact caused by the collision between the ball and the circulation tube can be mitigated, and the deterioration of operability, noise, vibration, damage to the circulation tube, etc. can be suppressed.

Brief Description of the Drawings

[0017] [Figure 1] FIG. 1 is a plan view of a ball screw according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a perspective view showing the extraction of a circulation tube, a circulation component retainer, and an elastic member from the ball screw shown in FIG. 1. [Figure 3] FIG. 3 is a perspective view of a circulation tube, a circulation component retainer, and an elastic member of a ball screw according to a second embodiment of the present invention. [Figure 4] FIG. 4 is a perspective view of a circulation tube, a circulation component retainer, and an elastic member of a ball screw according to a third embodiment of the present invention. [Figure 5] FIG. 5 is a perspective view of a conventional ball screw. [Figure 6] FIG. 6 is a cross-sectional view showing the relationship between the ball rolling path and the ball circulation passage of a conventional ball screw. [Figure 7] FIG. 7(a) is an explanatory diagram for explaining the moving direction of the ball when the moving direction of the nut and the load are in the same direction, and FIG. 7(b) is an explanatory diagram for explaining the moving direction of the ball when the moving direction of the nut and the load are in the opposite direction. [Figure 8] FIGS. 8(a) and (b) are diagrams for explaining the radial clearance. FIG. 8(a) is a diagram in which the screw axis is arranged at the uppermost part in the drawing, and FIG. 8(b) is a diagram in which the screw axis is arranged at the lowermost part in the drawing. [Figure 9]Figures 9(a) and 9(b) are diagrams illustrating the axial clearance. Figure 9(a) shows the screw shaft positioned at the leftmost part of the diagram, while Figure 9(b) shows the screw shaft positioned at the rightmost part of the diagram. [Modes for carrying out the invention]

[0018] Hereinafter, each embodiment of the ball screw according to the present invention will be described in detail with reference to the drawings.

[0019] (First Embodiment) The ball screw 10 of this embodiment will be described with reference to Figures 1 and 6. Figure 6 is a cross-sectional view showing a conventional ball screw 10A, but the conventional ball screw 10A and the ball screw 10 of this embodiment are generally similar except for the elastic member 60 which will be described later, so please refer to Figure 6 as appropriate.

[0020] The mechanism comprises a screw shaft 20 with a helical outer screw groove 21 formed on its outer surface, a nut 30 with a helical inner screw groove 31 formed on its inner surface opposite to the outer screw groove 21 of the screw shaft 20 and which screws onto the screw shaft 20, a number of balls 12 rotatably interposed in a ball rolling path 11 formed by the outer screw groove 21 of the screw shaft 20 and the inner screw groove 31 of the nut 30, a circulation tube 40 which is a circulation component that circulates the balls 12 rolling in the ball rolling path 11, a circulation component retainer 50 that fixes the circulation tube 40 to the nut 30, and an elastic member 60, and converts rotational motion into linear motion. In this embodiment, the lead of the internal thread groove 31 is the same as that of the external thread groove 21 along the entire axial length of the nut 30. However, the lead near the axial center of the nut 30 may be increased by a predetermined amount, and preload may be applied.

[0021] The nut 30 has a notched plane 32 in which a portion of its outer circumferential surface is cut out, and a plurality of through holes 33 are formed in the notched plane 32, which connect the notched plane 32 to the inner circumferential screw groove 31 (ball rolling path 11). The through holes 33 are formed in pairs of two through holes 33, 33 formed on both sides in the circumferential direction, straddling the central axis of the nut 30, and in the embodiment shown in the figure, there are four pairs (eight through holes 33). The paired through holes 33, 33 are spaced apart in the axial direction of the nut 30. Each through hole 33 has an inner diameter larger than the diameter of the circulation tube 40. Also, the through holes 33 extend perpendicular to the notched plane 32.

[0022] Multiple circulation tubes 40 (four in the embodiment shown in the figure) are attached to the nut 30 for returning the balls 12 that have rolled along the ball track 11 back to their predetermined positions in the ball track 11.

[0023] As shown in Figure 2, the circulation tube 40 is made of a pipe member and has a roughly U-shape with both axial ends bent at approximately 90°. The circulation tube 40 has a pair of legs 41, 41 which serve as ends inserted into the through holes 33, and a connecting portion 42 which connects the pair of legs 41, 41 to form the bottom of the U-shape. The circulation tube 40 has a ball circulation passage 13 inside for circulating the balls 12.

[0024] The circulation component retainer 50 has a retaining portion 51 provided in the center, a pair of side walls 52, 52 formed at approximately 90° bends at both ends of the retaining portion 51, and a pair of flange portions 53, 53 formed projecting away from each other from the ends of each side wall 52. Screw holes 54 are provided in the flange portions 53. The circulation component retainer 50 is positioned so that a pair of legs 41, 41 cover the circulation tube 40 inserted into the through hole 33 from above, and the circulation tube 40 is fixed to the notched plane 32 by set screws 55 inserted through the screw holes 54.

[0025] In this case, the pressing portion 51 of the circulating component holder 50 extends in a direction perpendicular to the axial direction (X direction) of the circulating tube 40 (Y direction) so as to cover the connecting portion 42 of the circulating tube 40. The pair of side walls 52, 52 are formed at both ends of the pressing portion 51 in the Y direction. The circulating component holder 50 is approximately U-shaped, rotated approximately 90° in the XY plane relative to the approximately U-shape of the circulating tube 40. Therefore, the displacement of the circulating tube 40 in the axial direction (X direction) is not prevented by the circulating component holder 50.

[0026] The height H from the bottom surface of the flange portion 53 to the inner surface of the retaining portion 51 is the same as the diameter of the circulating tube 40. Therefore, the upper end of the connecting portion 42 of the circulating tube 40 abuts against the inner surface of the retaining portion 51 of the circulating component retainer 50, preventing radial movement of the circulating tube 40 relative to the nut 30, or in other words, preventing it from coming out of the through hole 33.

[0027] The inner dimension L of the pair of side walls 52, 52 is larger than the diameter of the circulating tube 40, and a gap is provided between both sides of the circulating tube 40 and the pair of side walls 52 of the circulating component retainer 50. Therefore, the displacement of the circulating tube 40 in the direction perpendicular to the axial direction (X direction) of the circulating tube 40 (Y direction) is not prevented by the circulating component retainer 50.

[0028] Furthermore, the inner surface roughness of the pressing portion 51 of the circulating component retainer 50 is smooth so that it can smoothly slide against the circulating tube 40.

[0029] The elastic member 60 is formed in an annular shape from a material with low rigidity and easy elastic deformation, such as rubber, foamed resin, foamed rubber, metal leaf spring material, elastomer material, or cork material. As will be described later, when the elastic member 60 is assembled to the ball screw 10, the lower side surface on the screw shaft 20 side is beveled to form an inclined surface 61 in order to prevent interference with the screw shaft 20.

[0030] The elastic member 60 is fitted into the gap between the through hole 33 of the nut 30 and the leg portion 41 of the circulating tube 40 inserted into the through hole 33, thereby supporting the circulating tube 40 so that it can be elastically displaced relative to the nut 30.

[0031] In the ball screw 10 configured in this way, when the screw shaft 20 is rotated, the balls 12 rolling in the ball rolling path 11 move in and out of the circulation tube 40, circulating between the ball rolling path 11 and the ball circulation passage 13.

[0032] As mentioned above, when the ball 12 enters and exits the circulation tube 40, if there is a misalignment between the central axis C1 of the circulation tube 40 and the trajectory 15 of the ball in the load zone, the ball 12 may collide with the inlet and outlet of the circulation tube 40, which can cause deterioration of operation, noise, vibration, and damage to the inlet and outlet of the circulation tube 40 and the grooves nearby.

[0033] However, in this embodiment, the ball screw 10 has a circulating tube 40 (leg portion 41) that is supported by an elastic member 60 so as to be elastically displaceable relative to the nut 30. Therefore, when the ball 12 collides with the inlet or outlet of the circulating tube 40, the elastic member 60 elastically deforms, causing the circulating tube 40 to be elastically displaced in the axial direction (X direction) and in the direction perpendicular to the axial direction (Y direction).

[0034] This absorbs the misalignment between the central axis C1 of the circulation tube 40 and the ball's trajectory 15 in the load zone, mitigates the impact caused by the collision between the ball 12 and the circulation tube 40, and suppresses vibration, noise, and damage to the inlet and outlet of the circulation tube 40 and the grooves nearby.

[0035] Furthermore, since the inner surface of the pressing portion 51 of the circulating component retainer 50 that slides against the circulating tube 40 has a smooth surface roughness, the circulating tube 40 can be displaced smoothly. Also, as described above, in this embodiment, a gap is provided between both sides of the circulating tube 40 and the pair of side walls 52 of the circulating component retainer 50, so the circulating tube 40 can be elastically displaced in the Y direction as well.

[0036] In this context, the axial direction (X direction) of the circulating tube 40 refers to the direction in which the connecting portion 42 of the circulating tube 40 extends, and is inclined relative to the axial direction of the nut 30. Therefore, the axial displacement (X-direction displacement) of the circulating tube 40 can be decomposed into an axial component and a circumferential component relative to the nut 30, so it can also be said that the circulating tube 40 undergoes elastic displacement in both the axial and circumferential directions of the nut 30.

[0037] (Second Embodiment) The ball screw 10 of this embodiment differs from the ball screw 10 of the first embodiment in the shape of the circulating component retainer 50. Specifically, as shown in Figure 3, the circulating component retainer 50 of this embodiment has a height H from the bottom surface of the flange portion 53 to the inner surface of the retaining portion 51 and an inner dimension L of the pair of side walls 52 that are approximately the same as the outer diameter of the circulating tube 40. That is, the top surface and both sides of the circulating tube 40 are held in place by the circulating component retainer 50, and radial displacement and displacement in the X direction are prevented by the circulating component retainer 50. Therefore, the circulating tube 40 of this embodiment can only be displaced in the axial direction (X direction).

[0038] In this case as well, when the ball 12 collides with the inlet or outlet of the circulation tube 40, the circulation tube 40, which is supported by the elastic member 60 so as to be elastically displaceable, is displaced in the axial direction (X direction). As a result, the misalignment between the central axis C1 of the circulation tube 40 and the trajectory 15 of the ball in the load zone is absorbed, thereby suppressing vibration, noise, and damage to the inlet and outlet of the circulation tube 40 and the grooves in their vicinity.

[0039] (Third embodiment) The ball screw 10 of this embodiment differs from the ball screw 10 of the second embodiment in the shape of the elastic member 60. Specifically, as shown in Figure 4, while the elastic member 60 of the second embodiment is annular, the elastic member 60 of this embodiment is formed in a semi-annular shape and is positioned on the axially outer side of the circulation tube 40.

[0040] Thus, since there is no elastic member 60 on the axially inner side of the circulating tube 40 (leg portion 41) which may interfere with the screw shaft 20, it can be easily assembled without having to consider interference with the screw shaft 20. In addition, material costs are reduced, making it possible to manufacture at a low cost.

[0041] Furthermore, the present invention is not limited to the embodiments described above, and can be modified, improved, etc., as appropriate. For example, although the embodiments described above used a circulation tube as an example of a circulation component, it is not limited to a circulation tube and can be similarly applied to three-dimensional circulation components made of resin or other materials, achieving similar effects.

[0042] As described above, the following matters are disclosed in this specification: (1) A screw shaft having a helical outer thread groove formed on its outer surface, A nut having a spiral inner thread groove formed on its inner surface so as to be opposite to the outer thread groove, and a plurality of through holes formed so as to communicate the outer surface and the inner thread groove, A plurality of balls that roll along a ball rolling path formed by the outer circumferential screw groove and the inner circumferential screw groove, At least one circulating component, the end of which is inserted into the through hole, to form a ball circulation passage for circulating the balls that roll along the ball rolling path, A ball screw equipped with, A circulating part retainer is fixed to the nut and prevents radial movement of the circulating part relative to the nut, An elastic member is disposed between the inner circumferential surface of the through hole of the nut and the outer circumferential surface of the circulating component, and supports the circulating component so that it can be elastically displaced in the axial direction of the circulating component. A ball screw equipped with a ball screw. This configuration absorbs the discrepancy between the central axis of the circulating component and the trajectory of the ball in the load zone, mitigating the impact caused by collisions between the ball and the circulating component, and suppressing deterioration of operation, noise, vibration, and damage to the circulating component.

[0043] (2) The elastic member supports the circulating component so that it can be elastically displaced in a direction perpendicular to the axial direction of the circulating component. (1) The ball screw described above. This configuration effectively absorbs the discrepancy between the central axis of the circulating component and the trajectory of the ball in the load zone, mitigating the impact caused by collisions between the ball and the circulating component, and suppressing deterioration of operation, noise, vibration, and damage to the circulating component.

[0044] (3) The elastic member is formed in an annular shape, (1) or (2) the ball screw described above. This configuration allows the circulating component to be supported in a stable state within the through-hole in an elastically displaceable manner, and can absorb the deviation between the central axis of the circulating component and the trajectory of the ball in the load zone.

[0045] (4) The elastic member is formed in a semicircular shape, (1) or (2) the ball screw described above. This configuration eliminates the need to consider interference between the elastic member and the screw shaft, making assembly of the elastic member easier. Furthermore, material costs are reduced, allowing for inexpensive manufacturing. [Explanation of Symbols]

[0046] 10 Ball screws 11 Ball Rolling Path 12 balls 13 Ball circulation passage 20 Screw shaft 21 Outer circumference thread groove 30 nuts 31 Internal thread groove 32 Notch plane (outer surface) 33 Through hole 40 Circulation tubes (circulation components) 41 Leg (end) 50 Circulation part retainer 60 Elastic members

Claims

1. A screw shaft having a helical outer thread groove formed on its outer surface, A nut having a spiral inner thread groove formed on its inner surface so as to be opposite to the outer thread groove, and a plurality of through holes formed so as to communicate the outer surface and the inner thread groove, A plurality of balls that roll along a ball rolling path formed by the outer circumferential screw groove and the inner circumferential screw groove, At least one circulating component, the end of which is inserted into the through hole, to form a ball circulation passage for circulating the balls that roll along the ball rolling path, A ball screw equipped with, A circulating part retainer is fixed to the nut and prevents radial movement of the circulating part relative to the nut, An elastic member is disposed between the inner circumferential surface of the through hole of the nut and the outer circumferential surface of the circulating component, and supports the circulating component so that it can be elastically displaced in the axial direction of the circulating component. A ball screw equipped with a ball screw.

2. The elastic member supports the circulating component so that it can be elastically displaced in a direction perpendicular to the axial direction of the circulating component. The ball screw according to claim 1.

3. The elastic member is formed in an annular shape. The ball screw according to claim 1 or 2.

4. The elastic member is formed in a semi-annular shape. The ball screw according to claim 1 or 2.

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