WO2025057671A1 - Ball screw - Google Patents

Abstract

This ball screw includes a circulation member 5 which is attached to a fitting hole 6 provided in a nut 3 and which circulates a rolling ball. A pair of gaps 15 for inserting a jig 20 for positioning the circulation member 5 with respect to the fitting hole 6 are provided between the fitting hole 6 and the circulation member 5. The pair of gaps 15 are positioned respectively on one side and the other side in the extension direction of a screw shaft.

Description

Ball screw

The present invention relates to a ball screw equipped with a circulating member that circulates balls.

A ball screw used in general industrial machine tools or actuators for automobiles is known that includes a nut with a helical thread groove on its inner circumferential surface, a screw shaft with a helical thread groove on its outer circumferential surface, a number of balls that are rollably housed between the thread grooves of the nut and the screw shaft that is inserted into the nut, and a circulation member that circulates the balls.

For example, Patent Document 1 (Patent Publication No. 4756645) discloses a method of fixing a circulation member within a fitting hole provided in a nut. In this case, the circulation member is inserted into the fitting hole, and then the convex engagement portion provided on the circulation member is tilted outward to engage (crimp) with the edge of the fitting hole. This fixes the circulation member within the fitting hole and prevents the circulation member from falling off the nut. In addition, when the circulation member is fixed in the fitting hole, adjacent thread grooves of the nut are connected by the connecting groove of the circulation member, so that the balls are guided along the connecting groove to circulate in the thread groove.

Patent No. 4756645

In the configuration in which the circulation member described above is attached to the fitting hole of the nut, the fitting hole is formed slightly larger than the circulation member to make it easier to insert the circulation member into the fitting hole. As a result, when the circulation member is attached to the fitting hole, a gap is created between the connecting groove of the circulation member and the thread groove of the nut.

Such gaps become steps when the balls roll, so it is preferable for the gaps to be uniform in order for the balls to roll smoothly. However, if the positioning precision of the circulation member relative to the fitting hole is poor, there will be variation in the mounting position of the circulation member, which will also result in variation in the gaps. In that case, in places where the gaps are particularly large, the steps will also be large, which may hinder the smooth rolling of the balls.

The present invention aims to provide a ball screw that can accurately position the circulation member relative to the fitting hole and ensure smooth rolling of the balls.

In order to solve the above problems, the present invention provides a ball screw comprising a nut having a helical thread groove on its inner circumferential surface, a screw shaft having a helical thread groove on its outer circumferential surface, a number of balls rollably accommodated between the thread groove of the nut and the thread groove of the screw shaft inserted into the nut, and a circulation member that is fitted into a fitting hole provided in the nut and circulates the rolling balls, the ball screw being characterized in that a pair of gaps are provided between the fitting hole and the circulation member for inserting a jig for positioning the circulation member relative to the fitting hole, and the pair of gaps are located on one side and the other side in the extension direction of the screw shaft, respectively.

In this way, in the ball screw according to this embodiment, a pair of gaps are provided between the engagement hole and the circulation member, into which a jig for positioning the circulation member can be inserted, and the circulation member can be positioned with high precision by inserting a jig into this gap. As a result, it is possible to reduce the variation in the gap between the circulation member and the nut, thereby ensuring smooth rolling of the balls. Here, the one side and the other side in the extension direction of the screw shaft refer to one side and the other side when the direction in which the axis of the screw shaft extends is taken as the axial direction.

It is preferable that the center of the circulation member is positioned so that it coincides with the center of the fitting hole. By attaching the circulation member so that the center of the circulation member coincides with the center of the fitting hole, the gap between the circulation member and the nut becomes uniform, allowing the balls to roll more smoothly.

The circulation member may also have a non-planar contact surface that contacts the portion of the jig that is inserted into the pair of gaps.

The present invention allows the circulation member to be positioned accurately relative to the fitting hole, ensuring smooth ball rolling.

FIG. 1 is a plan view of a ball screw according to an embodiment of the present invention. FIG. 2 is a vertical sectional view of the ball screw according to the embodiment. FIG. 2 is a vertical cross-sectional view of the nut according to the embodiment. FIG. 4 is a cross-sectional perspective view showing a state before a circulation member is attached to the nut according to the embodiment. 13 is a diagram showing a state in which the center of the circulation member coincides with the center of the fitting hole. FIG. 13 is a diagram showing a state in which the center of the circulation member is offset from the center of the fitting hole. FIG. FIG. 2 is a perspective view of a jig according to the present embodiment. FIG. 2 is a side view of the jig according to the embodiment. 9 is a cross-sectional view of the jig according to the present embodiment taken along line AA in FIG. 8. 11A and 11B are diagrams for explaining a method of fixing the circulation member. 11A and 11B are diagrams for explaining a method of fixing the circulation member. FIG. 13 is a perspective view of a circulation member and a jig according to another embodiment of the present invention. 13 is a diagram showing a state in which a circulation member is positioned by a jig according to another embodiment of the present invention. FIG.

Below, an embodiment of the present invention will be described with reference to the attached drawings. In each drawing for explaining the present invention, components such as parts or components having the same function or shape will be given the same reference numerals as far as they can be distinguished. For this reason, explanations of components that have already been explained will be omitted.

The overall configuration of a ball screw according to one embodiment of the present invention will be described with reference to Figures 1 to 4. Figure 1 is a plan view of the ball screw according to this embodiment, and Figure 2 is a longitudinal cross-sectional view of the ball screw. Figure 3 is a longitudinal cross-sectional view of a nut provided on the ball screw, and Figure 4 is a cross-sectional perspective view showing the state before a circulation member is attached to the nut.

As shown in Figures 1 and 2, the ball screw 1 according to this embodiment includes a screw shaft 2, a nut 3, a number of balls 4, and a circulation member 5.

The screw shaft 2 has a helical screw groove 2a on its outer circumferential surface, and is inserted into a cylindrical nut 3. On the other hand, the nut 3 has a helical screw groove 3a on its inner circumferential surface that faces the screw groove 2a of the screw shaft 2. A number of balls 4 are housed between these screw grooves 2a, 3a in a rollable manner.

The cross-sectional shape of each screw groove 2a, 3a may be a circular arc shape or a gothic arc shape. In this embodiment, each screw groove 2a, 3a is formed in a gothic arc shape that allows a large contact angle with the ball 4 and a small axial gap. This increases the rigidity of each screw groove 2a, 3a against axial loads and suppresses the occurrence of vibration.

The nut 3 also has a circular fitting hole 6 that penetrates from its inner circumferential surface to its outer circumferential surface and cuts out a portion of the screw groove 3a. A circulation member 5 with a substantially circular cross section is inserted into this fitting hole 6.

The circulation member 5 has a connecting groove 5a that connects adjacent screw grooves 3a of the nut 3 for one revolution. Therefore, as shown in FIG. 3, when the circulation member 5 is inserted into the fitting hole 6, the S-shaped connecting groove 5a connects adjacent screw grooves 3a of the nut 3, and the connecting groove 5a and the approximately one revolution portion of the screw groove 3a form a rolling path for the balls 4. As a result, the multiple balls 4 are guided by the connecting groove 5a of the circulation member 5, and are returned to the adjacent screw groove 3a by climbing over the threads of the screw shaft 2. The multiple balls 4 then circulate by rolling again along the screw grooves 2a and 3a. The depth of the connecting groove 5a is set to a depth that allows the balls 4 to climb over the threads of the screw shaft 2 within the connecting groove 5a.

Also, as shown in FIG. 3, the circulation member 5 is provided with a pair of arm portions 9 that protrude in opposite directions. When the circulation member 5 is inserted into the fitting hole 6 of the nut 3, each arm portion 9 of the circulation member 5 fits into the thread groove 3a of the nut 3, thereby positioning the circulation member 5 in the axial direction relative to the nut 3 and preventing the circulation member 5 from falling off in the direction of the outer diameter of the nut. Each arm portion 9 engages with the thread groove 3a in which the balls 4 do not roll so as not to impede the rolling of the balls 4.

Also, as shown in FIG. 1, a pair of engagement portions 12 are provided on the outer diameter side of the nut of the circulation member 5 so as to protrude in the outer diameter direction. When the circulation member 5 is inserted into the fitting hole 6 of the nut 3, each engagement portion 12 is pressed down outward (in the direction away from each other) and tightened, so that each engagement portion 12 engages with the edge of the fitting hole 6. This fixes the circulation member 5 to the nut 3.

Here, in the configuration in which the circulation member 5 is mounted in the fitting hole 6 of the nut 3 as in the above embodiment, the positioning accuracy of the circulation member 5 relative to the fitting hole 6 affects the rolling properties of the balls 4. That is, as in the example shown in FIG. 5, when the circulation member 5 is mounted so that the center O of the circulation member 5 coincides with the center P of the fitting hole 6, the gaps S1 and S2 between the connecting groove 5a of the circulation member 5 and the thread groove 3a of the nut 3 can be made uniform. However, as in the example shown in FIG. 6, when the center O of the circulation member 5 is shifted from the center P of the fitting hole 6 and the circulation member 5 is mounted offset, the gaps S1 and S2 between the connecting groove 5a of the circulation member 5 and the thread groove 3a of the nut 3 vary (S1>S2). In this way, when the gaps S1 and S2 vary, the step between the connecting groove 5a of the circulation member 5 and the thread groove 3a of the nut 3 becomes large, especially in the area where the gap is large (gap S1 in FIG. 6), and there is a risk that the smooth rolling of the balls 4 may be hindered.

In the ball screw according to this embodiment, therefore, in order to accurately position the circulation member 5 relative to the fitting hole 6, the following jig is used to fix the circulation member 5. Below, the configuration of the jig used in this embodiment and the method of fixing the circulation member 5 using the jig (the manufacturing method of the ball screw) are explained.

FIG. 7 is a perspective view of the jig used in this embodiment, FIG. 8 is a side view of the jig, and FIG. 9 is a cross-sectional view of the jig taken along line A-A in FIG. 8.

As shown in Figures 7 to 9, the jig 20 has a cylindrical main body 21, a pair of positioning portions 22, and a pair of crimping portions 23. The pair of positioning portions 22 and the pair of crimping portions 23 are each provided to protrude in the longitudinal direction from one end of the main body 21 in the longitudinal direction. The pair of positioning portions 22 protrude more than the crimping portions 23 and are disposed at a distance from each other. On the other hand, the pair of crimping portions 23 protrude less than the positioning portions 22 and are disposed at a distance from each other in a direction intersecting or perpendicular to the direction in which the positioning portions 22 face each other.

In addition, each fastening portion 23 has an inclined surface 23a that is inclined toward the center line L (see FIG. 9) of the main body portion 21 toward its tip. This inclined surface 23a functions as a pressing portion that presses the engaging portion 12 when the engaging portion 12 of the circulation member 5 is fastened.

On the other hand, the pair of positioning portions 22 are formed in a D-shaped cross section consisting of an arc portion and a straight portion in a cross section perpendicular to the center line L of the main body portion 21. That is, each positioning portion 22 has a flat portion 22a arranged to face the center line L side (inside) of the main body portion 21, and an arc surface portion 22b arranged to face the opposite side to the center line L side (outside).

To attach the circulation member 5 to the nut 3 using the jig 20 according to the present embodiment, first, insert the circulation member 5 into the fitting hole 6 from the inner diameter side of the nut 3, and then insert the positioning portion 22 of the jig 20 into the gap 15 between the circulation member 5 and the fitting hole 6, as shown in FIG. 10.

In this embodiment, as shown in Figures 1 and 3, the circulation member 5 has a pair of flat surfaces 5b facing in opposite directions, and when the circulation member 5 is inserted into the fitting hole 6, a gap 15 with a D-shaped cross section is formed between these flat surfaces 5b and the inner surface of the fitting hole 6. Then, a positioning portion 22 with the same D-shaped cross section is inserted into this D-shaped gap 15.

In this manner, in this embodiment, D-shaped gaps 15 are provided between the fitting hole 6 and the circulation member 5 on one side and the other side in the extension direction of the screw shaft 2, and the circulation member 5 can be positioned in the fitting hole 6 by inserting a pair of positioning portions 22 into these gaps 15. That is, as shown in FIG. 10, when the positioning portions 22 are inserted into the gaps 15, the flat surface portion 22a of the positioning portion 22 contacts the flat surface portion 5b of the circulation member 5, and the arc surface portion 22b of each positioning portion 22 contacts the inner peripheral surface of the fitting hole 6, so that the displacement (misalignment) of the circulation member 5 in the fitting hole 6 is restricted by the pair of positioning portions 22. As a result, the circulation member 5 is positioned with high precision relative to the fitting hole 6.

Then, with the circulation member 5 positioned, the jig 20 is pushed further into the fitting hole 6, so that the pair of engagement portions 12 of the circulation member 5 are pressed by the inclined surfaces 23a of the pair of crimping portions 23, as shown by the two-dot chain lines in FIG. 11, and each engagement portion 12 is pressed down (crimped) outward. As a result, each engagement portion 12 engages with the edge of the fitting hole 6, and the circulation member 5 is fixed to the nut 3.

As described above, in this embodiment, the gap 15 between the fitting hole 6 and the circulation member 5 is used as a gap for inserting a jig 20 (positioning portion 22) for positioning the circulation member 5, thereby enabling the circulation member 5 to be positioned with high precision relative to the fitting hole 6. This allows the center O of the circulation member 5 to coincide with the center P of the fitting hole 6, as shown in FIG. 5, and makes the gaps S1 and S2 between the connecting groove 5a of the circulation member 5 and the thread groove 3a of the nut 3 equal, ensuring smooth rolling of the balls.

The position of the center O of the circulation member 5 does not necessarily have to coincide with the center P of the fitting hole 6. Even in such a case, by using the jig 20 according to this embodiment, the positional deviation of the circulation member 5 relative to the fitting hole 6 can be reduced, improving the positioning accuracy and allowing the balls to roll smoothly.

The pair of flat surfaces 5b of the circulation member 5 are preferably machined surfaces such as cut or ground. In this case, each flat surface 5b can be more accurately aligned with the surface of the positioning portion 22, improving positioning accuracy. In addition, because each flat surface 5b is formed in a direction approximately perpendicular to the axial direction of the screw shaft 2, the presence and degree of misalignment of the circulation member 5 can be easily confirmed by appearance.

Furthermore, it is preferable that the jig 20 is a jig having the positioning portion 22 and the crimping portion 23 integrally as in the above embodiment. By having the positioning portion 22 and the crimping portion 23 integrally, the positioning and fixing (crimping) of the circulation member 5 relative to the fitting hole 6 can be performed using a single jig 20, improving work efficiency. Furthermore, in the above embodiment, each engagement portion 12 is formed at a position perpendicular to the position of the gap 15 (flat portion 5b) so that the positioning and fixing (crimping) of the circulation member 5 can be performed simultaneously using a single jig 20.

In addition, in the above-mentioned method, the circulation member 5 is inserted into the fitting hole 6, and then the positioning portion 22 of the jig 20 is inserted. However, the procedure for positioning the circulation member 5 is not limited to the above-mentioned method. For example, the positioning portion 22 may be inserted into the fitting hole 6 before the circulation member 5, and then the circulation member 5 may be inserted into the fitting hole 6 to position it.

The above describes an embodiment of the present invention, but the present invention is not limited to the above embodiment and can be modified as appropriate without departing from the gist of the invention.

For example, as shown in the example in Figure 12, a convex portion 220 having a semicircular cross section may be provided on the planar portion 22a of each positioning portion 22 of the jig 20, and a concave portion 50 having a semicircular cross section may be provided on each planar portion 5b of the circulation member 5. In this case, as shown in Figure 13, when the positioning portions 22 of the jig 20 are inserted on both sides of the circulation member 5, the convex portion 220 of the positioning portion 22 fits into the concave portion 50 of the circulation member 5, thereby positioning the circulation member 5 within the fitting hole 6. In this way, the convex portion 220 and the concave portion 50 that fit into each other may be provided on the planar portion 22a of the positioning portion 22 and the planar portion 5b of the circulation member 5, to position the circulation member 5. That is, the circulation member 5 and the jig 20 may have non-flat contact surfaces (protrusions 220 and recesses 50) that contact each other between the portion of the jig 20 (positioning portion 22) inserted into the gap located on one side and the other side in the extension direction of the screw shaft 2 between the fitting hole 6 and the circulation member 5 and the circulation member 5. In addition, the shapes of the protrusions 220 and the recesses 50 may be shapes other than semicircular in cross section, and contrary to the examples of Figures 12 and 13, the jig 20 may be provided with a recess, and the circulation member 5 may be provided with a protrusion that fits into the recess.

REFERENCE SIGNS LIST 1 ball screw 2 screw shaft 2a screw groove 3 nut 3a screw groove 4 ball 5 circulation member 5a connecting groove 6 fitting hole 15 gap 20 jig 21 main body 22 positioning portion 23 crimping portion

Claims (3)

A nut having a helical thread groove on its inner circumferential surface;
A screw shaft having a helical screw groove on an outer circumferential surface thereof;
A plurality of balls rollably accommodated between the screw groove of the nut and the screw groove of the screw shaft inserted into the nut;
A ball screw including a circulation member that is attached to a fitting hole provided in the nut and circulates the rolling balls,
A ball screw characterized in that a pair of gaps are provided between the fitting hole and the circulation member, into which a jig for positioning the circulation member relative to the fitting hole is inserted, and the pair of gaps are respectively located on one side and the other side of the extension direction of the screw shaft. The ball screw according to claim 1, wherein the center of the circulation member is arranged to coincide with the center of the fitting hole. The ball screw according to claim 1 or 2, wherein the circulation member has a non-flat contact surface that contacts the portion of the jig that is inserted into the pair of gaps.

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