BALL SCREW

Abstract

In a ball screw with a circulation element 5, which is attached to a fitting hole 6 provided in a nut 3 for circulating rolling balls, a pair of slots 15, into which a (positioning) device 20 for positioning the circulation element 5 with respect to the fitting hole 6 is inserted, are provided between the fitting hole 6 and the circulation element 5, and wherein the pair of slots 15 is arranged on one side and on the other side in an extension direction of a spindle shaft.

Description

TECHNICAL FIELD The present invention relates to a ball screw with a circulation element that circulates a ball. STATE OF THE ART A ball screw used for general industrial machine tools, motor vehicle actuators and the like is known to comprise: a nut with a helical spindle groove on an inner circumferential surface; a spindle shaft with a helical spindle groove on an outer circumferential surface; a plurality of balls which are rollably received between the respective spindle grooves of the nut and the spindle shaft inserted into the nut; and a circulation element which circulates the balls. For example, patent literature 1 (Japanese patent no. 4756645) discloses a method for securing a circulation element in a pilot hole provided in a nut. In this case, after the circulation element has been inserted into the pilot hole, a convex engagement portion provided on the circulation element is tilted outwards to engage (countersink) an edge of the pilot hole. This secures the circulation element in the pilot hole and prevents it from falling out of the nut. Furthermore, when the circulation element is secured in the pilot hole, adjacent spindle grooves of the nut are connected by a connecting groove of the circulation element, so that the ball is guided along the connecting groove to circulate through the spindle groove. QUOTES PATENT LITERATURE Patent literature 1: Japanese patent no. 4756645 SUMMARY OF THE INVENTION TECHNICAL TASKS In the configuration described above, where the circulation element is installed in the nut's locating hole, the locating hole is slightly larger than the circulation element to facilitate its insertion. Therefore, when the circulation element is installed in the locating hole, a gap forms between the circulation element's connecting groove and the nut's spindle groove. Since such a gap results in a height difference when the ball rolls, it is advantageous for the gap to be uniform so that the ball can roll smoothly. However, if the positioning accuracy of the circulation element relative to the mounting hole is poor, the mounting position of the circulation element varies, and consequently, so does the gap. In this case, the height difference is particularly large at points where the gap is large, potentially hindering the smooth rolling of the ball. Therefore, an objective of the present invention is to provide a ball screw capable of accurately positioning a circulation element with respect to a pass hole and ensuring smooth rolling of a ball. SOLUTIONS TO THE TASKS To solve the aforementioned problem, the present invention provides a ball screw comprising: a nut with a spindle groove having a helical shape on an inner circumferential surface; a spindle shaft with a spindle groove having a helical shape on an outer circumferential surface; a plurality of balls which are rollably received between the spindle groove of the nut and the spindle groove of the spindle shaft inserted into the nut; and a circulation element which is attached to a fitting hole provided in the nut in order to allow the rolling balls to circulate, wherein a pair of slots is provided between the fitting hole and the circulation element, into which a (positioning) device is inserted which serves to position the circulation element with respect to the fitting hole, and wherein the pair of slots is located on one side and on the other side in an extensional direction of the spindle shaft. In this way, in the ball screw according to the present embodiment, the circulation element can be precisely positioned by inserting the (positioning) device into the gap, since the pair of gaps into which the (positioning) device is inserted for positioning the circulation element is provided between the locating hole and the circulation element. This reduces the deviation of the gap between the circulation element and the nut, thus ensuring smooth rolling of the ball. Here, one side and the other side in the direction of extension of the spindle shaft are one side and the other side with respect to one side, in the case where a direction in which an axial center of the spindle shaft extends is an axial direction. The circulation element is preferably arranged such that its center coincides with the center of the fitting hole. When the circulation element is mounted so that its center coincides with the center of the fitting hole, the gap between the circulation element and the nut becomes uniform, allowing the ball to roll more smoothly. Furthermore, the circulation element may have a non-planar contact surface that comes into contact with part of the (positioning) device inserted into the pair of columns. ADVANTAGES OF THE INVENTION According to the present invention, it is possible to position the circulation element precisely in relation to the pass hole and to ensure smooth rolling of the ball. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a top view of a ball screw according to an embodiment of the present invention. Fig. 2 is a longitudinal sectional view of the ball screw according to the present embodiment. Fig. 3 is a longitudinal sectional view of a nut according to the present embodiment. Fig. 4 is a perspective cross-sectional view showing a state before the mounting of a circulation element on the nut according to the present embodiment. Fig. 5 is a view showing a state in which the center of the circulation element coincides with the center of a locating hole. Fig. 6 is a view showing a state in which the center of the circulation element is offset from the center of the locating hole. Fig. 7 is a perspective view of a (positioning) device according to the present embodiment. Fig. 8 is a side view of the (positioning) device according to the present embodiment.Figure 9 is a cross-sectional view of the (positioning) device according to the present embodiment along line AA in Figure 8. Figure 10 is a view illustrating a method for attaching the circulation element. Figure 11 is a view illustrating a method for attaching the circulation element. Figure 12 is a perspective view of a circulation element and a (positioning) device according to a further embodiment of the present invention. Figure 13 is a view showing a state in which a circulation element is positioned by a (positioning) device according to a further embodiment of the present invention. DESCRIPTION OF THE EXECUTION FORM An embodiment of the present invention is described below with reference to the accompanying drawings. It should be noted that, in the individual drawings used to illustrate the present invention, components such as elements or parts with the same function or shape are designated with the same reference numerals, insofar as a distinction is possible. Therefore, a description of the components already described is omitted. A complete configuration of a ball screw according to an embodiment of the present invention is described with reference to Figures 1, 2, 3 to 4. Figure 1 is a top view of the ball screw according to the present embodiment, and Figure 2 is a longitudinal sectional view of the ball screw. Furthermore, Figure 3 is a longitudinal sectional view of a nut contained in the ball screw, and Figure 4 is a perspective sectional view showing a state before the attachment of a circulation element to the nut. As shown in Fig. 1 and Fig. 2, a ball screw 1 according to the present embodiment comprises a spindle shaft 2, a nut 3, a plurality of balls 4 and a circulation element 5. The spindle shaft 2 has a helical groove 2a on its outer circumferential surface and is inserted into the cylindrical nut 3. The nut 3, on the other hand, has a helical groove 3a on its inner circumferential surface, which is opposite the groove 2a of the spindle shaft 2. The several balls 4 are mounted so as to roll between the grooves 2a and 3a. The cross-sectional shape of each of the spindle grooves 2a and 3a can be a circular arc or a Gothic arc. In the present embodiment, each of the spindle grooves 2a and 3a is formed in a Gothic arc shape, in which a large contact angle with respect to the sphere 4 can be achieved and a small axial gap can be set. This increases the stiffness against an axial load of each of the spindle grooves 2a and 3a, and the occurrence of vibrations can be suppressed. Additionally, the nut 3 is provided with a circular locating hole 6 that extends from the inner circumferential surface to an outer circumferential surface and cuts out part of the spindle groove 3a. The circulation element 5, which has a substantially circular cross-section, is then inserted into the locating hole 6. The circulation element 5 has a connecting groove 5a that connects adjacent single-threaded sections of the spindle groove 3a of the nut 3. Therefore, when the circulation element 5 is inserted into the fitting hole 6, as shown in Fig. 3, the adjacent spindle grooves 3a of the nut 3 are connected to each other by the S-shaped connecting groove 5a, and a rolling track for the balls 4 is formed by the connecting groove 5a and a substantially single-threaded section of the spindle groove 3a. Consequently, the majority of the balls 4 are guided through the connecting groove 5a of the circulation element 5, pass through the spindle thread of the spindle shaft 2, and are returned to the adjacent spindle groove 3a. The majority of the balls 4 then circulate again by rolling along the spindle grooves 2a and 3a. The depth of the connecting groove 5a is set so that the ball 4 can protrude beyond the spindle thread of the spindle shaft 2 in the connecting groove 5a. Additionally, the circulation element 5, as shown in Fig. 3, is provided with a pair of arm sections 9 projecting in opposite directions. When the circulation element 5 is inserted into the fitting hole 6 of the nut 3, each of the arm sections 9 of the circulation element 5 engages in the spindle groove 3a of the nut 3, thereby positioning the circulation element 5 axially with respect to the nut 3 and preventing it from falling towards the outer diameter of the nut. It should be noted that each of the arm sections 9 engages in the spindle groove 3a, in which the ball 4 does not roll, so as not to impede the rolling of the ball 4. Additionally, as shown in Fig. 1, a pair of engagement parts 12 are provided on the nut's outer diameter side of the circulation element 5, projecting in the direction of the outer diameter. When the circulation element 5 is inserted into the locating hole 6 of the nut 3, the individual engagement parts 12 are displaced and compressed (away from each other in one direction), causing them to engage with an edge of the locating hole 6. This secures the circulation element 5 to the nut 3. Here, as in the embodiment described above, in a configuration where the circulation element 5 is attached to the locating hole 6 of the nut 3, the positioning accuracy of the circulation element 5 with respect to the locating hole 6 affects the rolling performance of the balls 4. That is, as in the example shown in Fig. 5, if the circulation element 5 is mounted such that a center point O of the circulation element 5 coincides with a center point P of the locating hole 6, the gaps S1 and S2 between the connecting groove 5a of the circulation element 5 and the spindle groove 3a of the nut 3 can be made uniform. However, if, as in the example shown in Fig.In the example shown in Fig. 6, if the center point O of the circulation element 5 is offset from the center point P of the fitting hole 6 and the circulation element 5 is mounted under preload, deviations occur in the gaps S1 and S2 between the connecting groove 5a of the circulation element 5 and the spindle groove 3a of the nut 3 (S1 > S2). Therefore, if deviations occur in the gaps S1 and S2, the height difference between the connecting groove 5a of the circulation element 5 and the spindle groove 3a of the nut 3 increases, particularly at a point where the gap is large (the gap S1 in Fig. 6), so that the smooth rolling of the ball 4 can be impeded. Therefore, in the ball screw according to the present embodiment, the circulation element 5 is fixed using a (positioning) device as described below in order to precisely position the circulation element 5 with respect to the locating hole 6. The following describes a configuration of a (positioning) device used in the present embodiment and a method for fixing the circulation element 5 using the (positioning) device (method for manufacturing a ball screw). Fig. 7 is a perspective view of the (positioning) device used in the present embodiment, Fig. 8 is a side view of the (positioning) device and Fig. 9 is a sectional view of the (positioning) device along line AA in Fig. 8 . As shown in Figures 7, 8 to 9, a (positioning) device 20 comprises a cylindrical main part 21, a pair of positioning parts 22, and a pair of pressing parts 23. The pair of positioning parts 22 and the pair of pressing parts 23 are each arranged such that they project longitudinally from one end of the main part 21. The pair of positioning parts 22 projects further than the pressing part 23 and are spaced apart from each other. The pair of pressing parts 23, on the other hand, has a smaller projection than the positioning part 22 and is spaced apart in a direction that intersects or is orthogonal to the direction in which the positioning parts 22 are opposite each other. Furthermore, the press parts 23 each have inclined surfaces 23a, which are inclined towards their respective distal ends to approximate a center line L (see Fig. 9) of the main part 21. This inclined surface 23a acts as a pressure element that presses the engagement part 12 at the time of compression of the engagement part 12 of the circulation element 5. The pair of positioning parts 22, on the other hand, is designed such that it has a D-shaped cross-section comprising an arcuate section and a straight section, in a cross-section orthogonal to the centerline L of the main part 21. That is, each of the positioning parts 22 has a flat surface section 22a, which is arranged so that it faces the centerline L-side (inside) of the main part 21, and an arcuate surface section 22b, which is arranged so that it faces a side opposite the centerline L-side (outside). In order to attach the circulation element 5 to the nut 3 using the (positioning) device 20 according to the present embodiment, the circulation element 5 is first inserted into the fitting hole 6 from the inside of the nut 3 and then, as shown in Fig. 10, the positioning part 22 of the (positioning) device 20 is inserted into the gap 15 between the circulation element 5 and the fitting hole 6. In the present embodiment, as shown in Figs. 1 and 3, the circulation element 5 has a pair of flat surface sections 5b oriented in opposite directions. Therefore, when the circulation element 5 is inserted into the fitting hole 6, a gap 15 with a D-shaped cross-section is formed between the flat surface sections 5b and the inner circumferential surface of the fitting hole 6. The positioning element 22, with the same D-shaped cross-section, is then inserted into the D-shaped gap 15. Since, in the present embodiment, the D-shaped slots 15 are provided at positions on one side and the other side in the direction of extension of the spindle shaft 2 between the locating hole 6 and the circulation element 5, the circulation element 5 can be positioned in the locating hole 6 by inserting the pair of positioning parts 22 into these slots 15. That is, as shown in Fig. 10, when the positioning part 22 is inserted into the slot 15, the flat surface section 22a of the positioning part 22 comes into contact with the flat surface section 5b of the circulation element 5, and the arcuate surface section 22b of each of the positioning parts 22 comes into contact with the inner circumferential surface of the locating hole 6, so that a displacement (positional displacement) of the circulation element 5 in the locating hole 6 is regulated by the pair of positioning parts 22.As a result, the circulation element 5 is positioned precisely in relation to the pass hole 6. When the (positioning) device 20, in the state in which the circulation element 5 is positioned, is further pressed into the locating hole 6, the pair of engagement parts 12 of the circulation element 5 is pressed through the inclined surfaces 23a of the pair of press parts 23, as shown by the catenary line marked with two dots in Fig. 11, and each of the engagement parts 12 is pushed outwards (compressed). This causes the engagement parts 12 to engage with the edges of the locating holes 6, and the circulation element 5 is fastened to the nut 3. In this embodiment, the gap 15 between the locating hole 6 and the circulation element 5 is used as a gap into which the (positioning) device 20 (positioning part 22) is inserted to position the circulation element 5, thereby allowing the circulation element 5 to be precisely positioned with respect to the locating hole 6. As shown in Fig. 5, this allows the center point O of the circulation element 5 and the center point P of the locating hole 6 to be aligned, and the gaps S1 and S2 between the connecting groove 5a of the circulation element 5 and the spindle groove 3a of the nut 3 can be uniformly shaped to ensure smooth rolling of the ball. It should be noted that the position of the center point O of the circulation element 5 does not necessarily have to coincide with the center point P of the fitting hole 6. Even in such a case, by using the (positioning) device 20 according to the present embodiment, the positional displacement of the circulation element 5 with respect to the fitting hole 6 can be reduced, thus improving the positioning accuracy and achieving smooth rolling of the ball. The two flat surface sections 5b contained in the circulation element 5 are preferably surfaces obtained by machining, such as cutting or grinding. In this case, each of the flat surface sections 5b can be more precisely aligned with a surface of the positioning part 22, thus further improving the positioning accuracy. Since each of the flat surface sections 5b is a surface formed in a direction substantially perpendicular to the axial direction of the spindle shaft 2, the presence or absence and the degree of positional displacement of the circulation element 5 can be easily verified by its appearance. Furthermore, the (positioning) device 20 is preferably a (positioning) device that, as in the embodiment described above, integrally comprises the positioning part 22 and the pressing part 23. Since the (positioning) device 20 integrally comprises the positioning part 22 and the pressing part 23, the positioning and fastening (upsetting) of the circulation element 5 with respect to the locating hole 6 can be carried out with a single (positioning) device 20, thereby improving work efficiency. In the embodiment described above, each of the engagement parts 12 is formed at a position perpendicular to a position of the gap 15 (flat surface section 5b), so that the positioning and fastening (pressing) of the circulation element 5 can be carried out simultaneously with one (positioning) device 20. Furthermore, the procedure described above includes an example case in which the positioning part 22 of the (positioning) device 20 is inserted after the circulation element 5 has been inserted into the fitting hole 6. However, the procedure for positioning the circulation element 5 is not limited to the procedure described above. For example, the positioning part 22 can be inserted into the fitting hole 6 before the circulation element 5, and then the circulation element 5 can be inserted into the fitting hole 6 to be positioned. Although the embodiment of the present invention has been described above, the present invention is not limited to the embodiment described above and can be modified in a suitable manner without departing from the essence of the invention. For example, as shown in Fig. 12, a convex section 220 with a semicircular cross-section can be provided in the flat surface section 22a of each of the positioning parts 22 of the (positioning) device 20, and a concave section 50 with a semicircular cross-section can be provided in each of the flat surface sections 5b of the circulation element 5. In this case, as shown in Fig. 13, when the positioning parts 22 of the (positioning) device 20 are inserted on both sides of the circulation element 5, the convex section 220 of the positioning part 22 and the concave section 50 of the circulation element 5 are aligned, thereby positioning the circulation element 5 in the pass hole 6.In this way, the flat surface section 22a of the positioning part 22 and the flat surface section 5b of the circulation element 5 can be provided with the convex section 220 and the concave section 50, which fit together to position the circulation element 5. That is, the circulation element 5 and the (positioning) device 20 can have non-planar contact surfaces (the convex section 220 and the concave section 50) that come into contact with each other between the circulation element 5 and a section (the positioning part 22) of the (positioning) device 20, which is inserted in slots on one side and the other side in the direction of extension of the spindle shaft 2 between the locating hole 6 and the circulation element 5.Furthermore, the shapes of the convex section 220 and the concave section 50 can have a different shape than the semicircular cross-section, or a concave section can be provided in the (positioning) device 20 and a convex section that fits into the concave section can be provided in the circulation element 5, which is the opposite of the examples in Fig. 12 and Fig. 13. LIST OF REFERENCE MARKS 1 Ball screw 2 Spindle shaft 2a Spindle groove 3 Nut 3a Spindle groove 4 Ball 5 Circulation element 5a Connecting groove 6 Dowel hole 15 Gap 20 (Positioning) device 21 Main part 22 Positioning part 23 Dowel part QUOTES INCLUDED IN THE DESCRIPTION This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature JP 4756645 [0003, 0004]

Claims

Ball screw comprising: a nut with a spindle groove having a helical shape on an inner circumferential surface; a spindle shaft with a spindle groove having a helical shape on an outer circumferential surface; a plurality of balls which are rollably received between the spindle groove of the nut and the spindle groove of the spindle shaft inserted into the nut; and a circulation element which is attached to a fitting hole provided in the nut for circulating the rolling balls, wherein a pair of slots is provided between the fitting hole and the circulation element, into which a (positioning) device is inserted, the (positioning) device serving to position the circulation element with respect to the fitting hole, and wherein the pair of slots is located on one side and on the other side in an extension direction of the spindle shaft. Ball screw according to claim 1, wherein the circulation element is arranged such that a center point of the circulation element coincides with a center point of the pass hole. Ball screw according to claim 1 or 2, wherein the circulation element has a non-planar contact surface which comes into contact with a part of the (positioning) device inserted into the pair of slots.

Images