JP3208138U - Ball screw - Google Patents

Abstract

The present invention provides a ball screw capable of making the load distribution of the ball screw uniform and reducing stress concentration generated in a ball at a specific position. A screw shaft 2 having a first screw groove 2a on an outer peripheral surface, a nut 3 having a second screw groove facing the first screw groove 2a formed on an inner peripheral surface, and a first screw groove. And a plurality of balls accommodated in a spiral passage formed by the second thread groove, and three or more balls, each attached to the nut 3 and forming a circulation path connecting two portions of the spiral passage In the ball screw including the circulation members 5, 6, and 7, at least one ball circulation member 6 is arranged at a circumferential position different from the other ball circulation members 5 and 7. [Selection] Figure 1

Description

  The present invention relates to a ball screw that converts rotational motion into linear motion. In particular, the present invention relates to a technique for extending the life of a ball screw used for high load applications.

  The shape of the screw shaft and nut thread groove of the conventional ball screw is formed so that the initial contact angle between the thread groove and the ball is about 45 ° and the maximum contact angle is about 65 °. This takes into account the balance of processability, operability, load capacity, and the like.

  The ball screw with multiple circuits is designed to arrange the mounting positions of multiple circulation tubes in the axial direction at the same circumferential position, that is, the design where all of the multiple circulation tubes are arranged in a line in the axial direction on the outer periphery of the nut Was normal. This is to reduce the number of processing steps. For example, as shown in FIG. 7, in the case of a tube circulation system having three circuits, the attachment positions of the circulation tubes 50a, 50b, and 50c in each circuit are the same circumferential position.

  When a ball screw is applied to various mechanical devices, the selection of the ball screw is performed after setting a large safety factor so as to sufficiently withstand the use conditions of the ball screw. At this time, in order to increase the safety factor, it is effective to increase the diameter of the ball screw, that is, the diameter of the screw shaft 52. However, when the ball screw shaft diameter cannot be increased, the number of circuits through which the ball circulates is increased and the number of balls is increased. Alternatively, the problem has been solved by increasing the lead of the thread groove and using a ball having a large diameter.

  In the above conventional selection, the following measures are usually taken, including the case of increasing the shaft diameter of the ball screw. As for the load condition at the time of selecting the ball screw, it is assumed that all the balls rolling between the screw shaft 52 and the nut 51 are equally loaded. The load applied to each ball in this case is obtained by dividing the load applied to the entire ball screw by the number of effective balls in the nut 51. Here, the effective ball is a ball that is actually rolling between the screw shaft 52 and the nut 51. That is, the balls in the circulation path such as the circulation tube are not included in the effective balls. The contact surface pressure between the thread groove and the ball is calculated based on the assumed load. An appropriate ball screw is selected by comparing the value of the contact surface pressure with a database of the function and life of the ball screw obtained through experiments or the like.

Akira 61-131553 Shokai 53-138085 JP 54-113762 A Japanese Utility Model Hei 04-110255

  Actually, the load is not equally applied to all of the effective balls. Due to the elastic deformation of the screw shaft 52 and the nut 51 when subjected to a load, the axial load distribution in the nut 51 varies. When the axial load Fa in the axial direction is applied to the nut 51 of the ball screw and the axial load Fa ′ is applied to the screw shaft 52 in the direction as shown in FIG. , 52a, the distribution of elastic displacement along the axial direction is represented by an arrow in the figure. Depending on the amount of elastic displacement of the screw shaft 52 and the amount of elastic displacement of the nut 51, stress is concentrated at the contact points between the balls located near both ends of the nut 51 and the screw grooves 51a and 52a that contact the balls. Can be seen. For example, this tendency is remarkable when a processing table for heavy cutting is supported by a ball screw on the processing table.

  As the screw shaft 52 and the nut 51 rotate relative to each other, the balls are sequentially lifted up from the thread grooves 51 a and 52 a to the circulation tube 50 and circulate through the circulation tube 50. Therefore, there is a portion where there is no ball on the track of the screw shaft 52 facing the nut 51. For this reason, the load distribution varies in the circumferential direction, and a high load is applied to a part of the effective balls. As shown in FIG. 9, the ball 1 of each circuit in the nut 51 circulates by passing through the circulation tube 50 from the thread groove. FIG. 10 schematically shows this state as viewed from the axial direction. β is an angle formed by two straight lines connecting the central axis of the screw shaft 52 and both ends of the circulation tube 50. By referring also to FIG. 9, it can be seen that the number of balls in the range of the β angle in the circumferential direction is relatively small. Since the number of balls is relatively small, the load applied to the balls within the range of the β angle is relatively large.

  In the conventional ball screw, as described above, there is a concern that the stress concentration at the contact portion between the ball and the screw groove at both ends of the nut 51 and the load on the ball within a specific range increase. Therefore, the conventional ball screw has a problem that unless the safety factor at the time of design is set large, the surface of each screw groove 51a, 52a of the screw shaft 52 or the nut 51 is prematurely peeled off or abnormal wear occurs. It was.

  In particular, in high load applications, if the safety factor is set to be large, the ball screw becomes large, resulting in a problem that the target specification is not met or the cost is increased.

  The present invention has been made paying attention to the above-described problems, and an object of the present invention is to provide a ball screw that can make the load distribution of the ball screw uniform and reduce the stress concentration generated in the ball at a specific position. To do.

In order to solve the above problems, the ball screw of the present application is
A screw shaft having a first thread groove on the outer peripheral surface;
A nut having a second thread groove on the inner peripheral surface facing the first thread groove;
A plurality of balls housed in a spiral passage formed by the first thread groove and the second thread groove;
In each of the ball screws provided with three or more ball circulation members attached to the nut and forming a circulation path connecting two portions of the spiral passage,
It is assumed that at least one of the ball circulation members is disposed at a circumferential position different from the other ball circulation members.

Preferably, at least two of the ball circulation members are arranged at the same position in the circumferential direction,
It is assumed that the at least one ball circulation member is disposed between the at least two ball circulation members in the axial direction.

  Preferably, the at least one ball circulation member and the two ball circulation members are arranged at positions different from each other by 180 ° in the circumferential direction.

  Preferably, a portion of the second screw groove that constitutes a circuit in which the ball circulates together with the at least one ball circulation member includes a circuit in which the ball circulates together with the at least two ball circulation members. It is assumed that the preload is generated by shifting in the axial direction from a position equidistant from the two portions of the second thread groove to be configured.

Preferably, it has a support member that rotatably supports the screw shaft at one end portion of the screw shaft,
The nut has a flange extending radially outward at an end opposite to the support member.

Preferably, the ball circulation member is
An outer scooping portion that scoops up the ball in the spiral passage on the radially outer side, and an inner scooping portion that scoops up the ball in the spiral passage on the radially inner side. A pair of scooping passages,
A ball feed path connecting the pair of scooping paths,
The outer scooping part and the inner scooping part constitute a recess recessed from the tip side to the ball feed passage side between them,
The ball circulation member is composed of two components separated from a portion of the recess located closest to the ball feed passage by a dividing surface along the path of the ball.

  Preferably, when viewed in the axial direction, the dividing surface is disposed closer to the inner scooping portion than the locus of the center of the ball passing through the ball circulation member in the vicinity of the recess. Shall.

  Preferably, the first thread groove has a curvature which is smoothly continuous at both ends in a cross section perpendicular to the traveling direction of the ball, and has a curvature not less than 1/2 and not more than twice the radius of the ball. An arc part having a radius is provided.

  Preferably, a value obtained by subtracting the maximum radius of the screw shaft from the distance from the central axis of the screw shaft to the center of the ball in the first screw groove is 10% or less of the diameter of the ball. Shall.

Preferably, the seal has a contact portion attached to an end portion of the nut and contacting the screw shaft,
The contact portion has a curved surface with an arc-shaped cross section at least on the screw shaft side.

  As described above, when the ball screw of the present invention is employed, the load distribution for a plurality of balls rolling between the screw shaft and the nut is averaged by simple means. That is, the stress concentration generated in some balls is reduced. Therefore, there is an effect that the load capacity becomes larger than before without increasing the outer diameter of the ball screw.

  Further, since the load capacity increases without increasing the size of the ball screw, the application to a high load application (for example, an injection molding machine, a molding, a power cylinder) is further facilitated.

FIG. 1 is a side view showing a ball screw according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view for explaining the configuration of the ball screw according to the embodiment of the present invention. FIG. 3 is a cross-sectional view showing the shape of the thread groove according to the embodiment of the present invention. FIG. 4 is a diagram showing the relationship between the contact angle and the contact ellipse. FIG. 5 is a diagram showing the effect of the characteristic arrangement in the axial direction of the circuit of the present invention by comparing the distribution of the axial load ignoring the variation in the circumferential load distribution. FIG. 6 is a diagram showing the effect of the circuit inversion of this embodiment by comparing the axial load distribution in consideration of the axial variation and the circumferential load distribution variation. FIG. 7 is a view showing a conventional ball screw. FIG. 8 is a diagram showing the amount of elastic displacement that causes variations in axial load. FIG. 9 is a diagram showing ball circulation in one circuit. FIG. 10 is a view taken in the direction of the arrow 10-10 in FIG. FIG. 11 is a plan view illustrating a case where the present embodiment is applied to a double nut type ball screw. FIG. 12 is a view showing a state where the ball screw according to the embodiment of the present invention is used in a cantilever support structure. FIG. 13A, FIG. 13B, FIG. 13C, and FIG. 13D are diagrams for explaining operations and effects when the ball screw according to the embodiment of the present invention is used in a cantilever support structure. 13A shows the action state of the axial load, FIG. 13B shows the load distribution of the ball when the screw shaft is assumed to be a rigid body, and FIG. 13C shows the load distribution of the ball when the nut is assumed to be a rigid body. Shows the load distribution of the ball in consideration of the elastic deformation of the screw shaft and nut. 14A, 14B, 14C, and 14D are diagrams for explaining the influence on the load distribution of the ball by the ratio of the cross-sectional area of the screw shaft and the cross-sectional area of the nut according to the second embodiment of the present invention. 14A and 14B show a case where both cross-sectional areas are made equal, and FIG. 14C shows a case where the cross-sectional area on the nut side is relatively large. It is the figure which looked at the nut periphery of the ball screw which concerns on the 1st modification of embodiment of this invention in radial direction. It is the figure which looked at the ball screw which concerns on the 1st modification of embodiment of this invention to the axial direction. FIG. 17 is an arrow view in the 17 direction shown in FIG. 16 and shows the nut before the side cap is mounted. FIG. 18 is an arrow view in the 18 direction shown in FIG. 16 and shows a state after the side cap is mounted. FIG. 19 is a perspective view showing a side cap according to a first modification of the embodiment of the present invention. FIG. 20 is a perspective view showing a side cap constituent member according to a first modification of the embodiment of the present invention. FIG. 21 is an explanatory view showing, in an enlarged manner, a portion indicated by a circle 21 in FIG. 20 of the side cap according to the first modification of the embodiment of the present invention. FIG. 22 is a cross-sectional view for explaining the combined state of the peripheral walls at the scooping base end portion according to the second modification of the embodiment of the present invention. FIG. 23 is a perspective view for explaining a combined state of the peripheral walls at the scooping base end portion according to the second modification of the embodiment of the present invention. FIG. 24 is a view of a ball screw according to a modification of the embodiment of the present invention as seen from the radial direction. FIG. 25 is a perspective view of a side cap of a comparative example of a modification of the embodiment of the present invention. FIG. 26 is an explanatory diagram showing, in an enlarged manner, the main part of the comparative example in which the dividing line of the modification of the embodiment of the present invention is matched to the trajectory of the ball center. FIG. 27 is a perspective view showing a side cap component of a comparative example in which the side cap is aligned with the locus of the ball center. FIG. 28 is a cross-sectional view of the ball groove of the screw shaft according to the embodiment of the present invention. FIG. 29 is a continuous plot of the ball collision position on the ball groove indicated by the arrow 29 in FIG. The case where the ball motion trajectory is ideal is shown. FIG. 30 is a continuous plot of the ball collision position on the ball groove indicated by arrow 29 in FIG. The case where the ball motion trajectory is realistic is shown. FIG. 31 is a continuous plot of the ball collision position on the ball groove in a conventional ball screw. The case where the ball motion trajectory is realistic is shown. FIG. 32 is a sectional view of a ball groove of a screw shaft according to a conventional example. FIG. 33 is a plan view of a tube-type ball screw according to a conventional example. It is 34-34 sectional drawing shown in FIG. FIG. 35 is a sectional view of a ball groove of a screw shaft according to another conventional example. FIG. 36 is a perspective view of a top circulating ball screw. FIG. 37 is a front view of the seal 15 according to the embodiment of the present invention. 38 is a 38-38 sectional view of the seal 15 of FIG. FIG. 39 is an enlarged cross-sectional view of the seal 15 according to the embodiment of the present invention. 40 is an enlarged view of the contact portion 15b of the seal 15 shown in FIG. FIG. 41 is a cross-sectional view of a circulating tube type ball screw nut cut in the axial direction. FIG. 42 is a front view of a conventional seal. 43 is a cross-sectional view taken along line 43-43 shown in FIG. FIG. 44 is an enlarged cross-sectional view of another prior art seal. FIG. 45 is a further enlarged view of the seal piece 5d of the seal 5 of FIG.

  Embodiments of the present invention will be described with reference to the drawings. First, the configuration will be described. As shown in FIG. 1, in the ball screw according to this embodiment, a nut 3 is screwed onto the outer periphery of a screw shaft 2 via a plurality of balls. The nut 3 linearly moves relative to the screw shaft 2 by the relative rotation of the screw shaft 2 and the nut 3.

  As shown in FIG. 2, a male screw-like screw groove 2 a is provided on the outer peripheral surface of the screw shaft 2 as a first screw groove. Also, on the inner peripheral surface of the nut 3, a female thread-like thread groove 9 is provided as a second thread groove at a position facing the thread groove 2 a of the screw shaft 2 in the radial direction. Both the screw grooves 2a and 9 form a spiral passage, in which a plurality of balls 1 (shown by hatching in FIG. 2) are accommodated. The ball 1 rolls and circulates along the thread groove 2a as the screw shaft 2 and the nut 3 rotate relative to each other.

  The ball screw of this embodiment is a tube type ball screw having three circuits through which the ball circulates. As shown in FIG. 2, the thread groove 9 of the nut 3 is divided into three sections along the axial direction. Both ends of the thread groove 9 in each section are connected by circulation tubes 5, 6, and 7, which are ball circulation members. As a result, three circuits in which the ball circulates are formed. For convenience of explanation, the first circuit X, the second circuit Y, and the third circuit Z are referred to from the left side in FIGS.

  In the present embodiment, the circulation tube 6 of the second circuit Y is inverted 180 ° in the circumferential direction as shown in FIG. 1 with respect to the attachment positions of the circulation tubes 5 and 7 of the first circuit X and the third circuit Z. Provided in position.

  In the present embodiment, the circuit of the second circuit Y is arranged closer to the third circuit Z side by several tens of μm than the normal position. That is, the lead La between the screw groove 9a of the first circuit X and the screw groove 9b of the second circuit Y in the nut 3 is larger by several tens of μm (α) than the lead L of each of the screw grooves 9a, 9b, 9c. Set (La = L + α). At the same time, the lead Lb between the screw groove 9b of the second circuit Y and the screw groove 9c of the third circuit Z is set smaller than the lead L by several tens of μm (α) (Lb = L−α). . The leads of the screw groove 2a on the screw shaft 2 side are equally spaced over the entire length.

  In order to increase the load capacity of the ball screw, it is desired to increase the size of the contact angle of the ball 1 and the radius of curvature of the thread grooves 2a and 9 as much as possible. However, when an axial load is applied with the contact angle being excessively large as shown in FIG. 4, the end of the contact ellipse F indicating the range where the ball 1 and the screw groove 2a are in contact is the screw groove 2a. , And protrudes from the end of the groove 9. When a part of the contact ellipse F is cut, the stress increases and the life of the ball screw is extremely deteriorated. For this reason, in this embodiment, as shown in FIG. 3, the initial contact angle D is set to 50 ° to 55 °, and the maximum contact angle E is set to 75 °.

  Preferably, the initial contact angle is 51 ° or more and 54 ° or less, and the maximum contact angle is 72 °.

For each ball 1, the ball 1 having a ball diameter Da having the following relationship with respect to the lead L of the thread groove 9 is used.
0.7 ≦ (Da / L)
Conventionally, when Da / L is set to 0.7 or more, there is a possibility that the outer diameter portion of the circulation tube may interfere with the adjacent thread groove, so Da / L was set to less than 0.7. . On the other hand, in this embodiment, Da / L can be set to 0.7 or more by increasing the angle in the axial direction of the scooping portion of the ball 1 from the thread groove to the tube. Yes.

  Next, functions and effects of the ball screw configured as described above will be described. By placing the second circuit Y position closer to the third circuit Z, a preload is applied to the ball in the thread groove 9b of the second circuit Y portion. Therefore, the elastic displacement amount of the thread groove 9b when the axial load Fa is applied to the nut 3 is larger than that when the position of the second circuit Y is not arranged near the third circuit Z, and the contact area with the ball Will increase. As a result, the load sharing amount by the balls in the second circuit Y arranged closer to the third circuit Z increases, and the first circuit X and the third circuit which are the circuits on the nut end side where stress concentration occurs in a normal case. The load sharing amount of the circuit Z decreases. Therefore, the axial load distribution in the nut 3 is averaged, and variation is reduced.

  The attachment position of the circulation tube 6 of the second circuit Y is reversed 180 ° in the circumferential direction with respect to the attachment positions of the circulation tubes 5 and 7 of the first circuit X and the third circuit Z. As a result, it is avoided that a portion where the number of effective balls in the first circuit X and the third circuit Z in the circumferential direction is small and a portion where the number of effective balls in the second circuit Y is small overlap in the circumferential direction. . That is, dispersion of the load distribution with respect to each effective ball 1 in the circumferential direction can be suppressed by dispersing the no-load zone (portion where the ball 1 does not exist) in the circumferential direction.

  As described above, the load distribution in the axial direction and the circumferential direction with respect to the effective ball (the ball 1 rolling between the screw shaft 2 and the nut 3) is made more uniform than in the past. Therefore, the load distribution with respect to each effective ball, and further the load distribution with respect to each screw groove 2a, 9 of the screw shaft 2 and nut 3 in contact with the ball are averaged to increase the load capacity.

  In the present embodiment, the initial contact angle E and the maximum contact angle F of the ball 1 are made larger than before, and Da / L is set to 0.7 or more, thereby further increasing the load capacity. .

The configuration of the present embodiment is also effective when the ball diameter is 10 mm or more. In the case of a ball screw for an electric injection molding machine, a ball screw having a relation of the following formula is preferable.
0.7 ≦ (Da / L) ≦ 0.9 (ie, Da is 70 to 90% of L)

  In this embodiment, only the attachment position of the circulation tube 6 of the second circuit Y is inverted by 180 ° with respect to the attachment position of the circulation tube 5 of the first circuit X. The attachment position of 7 may be reversed 180 ° with respect to the attachment position of the circulation tube 5 of the first circuit X. Alternatively, the first circuit X and the second circuit Y may be set to the same circumferential position, and only the third circuit Z may be inverted by 180 °. Furthermore, the circulation tube does not necessarily need to be inverted by 180 °, and the circumferential position of the plurality of circulation tubes should be set so that the distribution of the number of effective balls in the circumferential direction is uniform or close to uniform. That's fine.

  In the above description, as shown in FIG. 2, when the axial load Fa to the nut 3 is loaded from the first circuit X side, the thread groove 9b of the second circuit Y is disposed closer to the third circuit Z. An embodiment is given. However, when the axial load on the nut 3 is applied from the third circuit Z side, the thread groove 9b of the second circuit Y is arranged closer to the first circuit X. That is, the thread groove of the circuit at a position sandwiched between a plurality of circuits may be shifted from the position equidistant from both adjacent circuits in the same direction as the axial load applied to the nut 3.

  In the present invention, the distribution of the amount of elastic displacement in the axial direction of the nut is averaged by disposing a part of the plurality of circuits in the axial direction in accordance with the direction of the axial load. . Thereby, the effect of averaging the load distribution in the axial direction with respect to the ball and increasing the load capacity as a whole is obtained. Instead, for example, the diameter of the ball 1 used in the second circuit Y in the present embodiment is made larger than the diameter of the ball 1 used in the first circuit X and the third circuit Z. The same effect as described above can also be obtained by changing the diameter of the ball loaded in the circuit. That is, by increasing the diameter of the ball 1 of the second circuit Y, a preload is applied to the ball in the thread groove 9b of the second circuit Y portion. As a result, the amount of elastic displacement of the thread groove 9b when the axial load Fa is applied to the nut 3 becomes larger than when the diameter of the ball 1 is not increased, and the contact area with the ball increases. Then, the load sharing amount by the balls in the circuit Y in which the diameter of the ball is increased is increased, and the first circuit X and the third circuit which are circuits on the nut end side where stress concentration occurs in a state where the diameter of the ball 1 is not increased. Since the load sharing amount in the circuit Z decreases, the load distribution in the axial direction in the nut 3 is averaged, and variation is reduced. As a result, the axial load shared by the ball 1 of the second circuit Y is increased as compared with the prior art, and the same effects as described above are exhibited.

  The thread groove 9 of the second circuit Y is arranged closer to the first circuit X or the third circuit Z, and the diameter of the ball 1 of the second circuit Y is set to the diameter of the ball 1 of the first circuit X and the third circuit Z. You may set so that it may become larger.

  In the present embodiment, both the inversion of the circuit by 180 ° and the disposition of the thread groove 9 of the second circuit Y closer to the third circuit Z are employed, but the load distribution of only one of the two is adopted. The variation is reduced and the load capacity is increased as compared with the conventional case.

  The ball screw according to the present invention having the above-described configuration and the ball having the same specifications as the conventional one in which the three circulation tubes 5, 6, and 7 are attached at the same circumferential position and the circuit of the second circuit Y is not arranged near the third circuit Z. When the load distribution state was analyzed for the screw (comparative example), results as shown in FIGS. 5 and 6 were obtained.

  FIG. 5 shows the distribution of the axial load applied to the effective ball 1 when the variation in the load distribution in the circumferential direction is ignored and only the variation in the axial direction is considered. A is the ball screw of the present invention, and B is the ball screw of the comparative example. As can be seen from FIG. 5, in the ball screw according to the present invention, the load in the second circuit Y increases and the load in the first circuit X and the third circuit Z decreases, so that the load distribution in the axial direction is reduced. Averaged.

  FIG. 6 shows the axial load applied to each effective ball 1 along the thread groove 9 when the variation in the axial direction and the load distribution in the circumferential direction are taken into consideration. A (solid line) is the ball screw of the present invention, and B (broken line) is the ball screw of the comparative example. As can be seen from FIG. 6, in the ball screw according to the present invention, the amplitude of the load along the thread groove 9 is smaller, and the load distribution in the circumferential direction is averaged.

  Actually, in the ball screw A according to the present invention, it was confirmed that the load capacity increased by about 20% from the load capacity of the ball screw B of the comparative example without changing the outer diameter.

  The ball screw to which the present invention can be applied is not limited to the tube circulation type as shown in the embodiment. For example, a so-called deflector circulation system as described in FIG. 1 of Japanese Utility Model Publication No. 5-35228 (guide having a ball return groove for communicating a plurality of sets of ball communication paths with each other and attached to the outer periphery of the nut. A circulation path is configured by a plate and a ball lifting member that is arranged on the inner side of each ball communication path and sequentially guides a group of balls interposed between the screw grooves of the ball screw shaft and the nut to the ball communication path side. It is also applicable to those that are). Also, a guide plate circulation system described in the prior art in FIG. 15 of the same publication (the ball communication path is connected to the guide plate attached to the outer periphery of the nut having a ball return groove for communicating the ball communication paths with each other). A guide piece to be inserted and projected is formed, an outer ball guide surface is formed on the inner surface side of the guide piece, and the outer ball guide surface is substantially formed between both ends of the ball return groove and each ball communication path. It is also applicable to those that are configured to change the direction of the ball. Further, the above feature can be applied to a side cap type ball screw. The side cap type ball screw will be described later as a first modified example and a second modified example.

  In the present embodiment, the ball screw in which the circuit in which the ball 1 circulates is described as three circuits of the first (X), the second (Y), and the third (Z), but the present invention is limited to three circuits. Instead, it can be applied to a circuit having four or more circuits. Moreover, it is not limited to one provided with three or more circuits in one nut, but may be a total of three or more circuits in total using two or more nuts as in the double nut type described later.

  Further, in the present embodiment, the so-called single nut type having one nut is described, but in addition, for example, two or more as in the so-called double nut type using two nuts 3A and 3B shown in FIG. It is also applicable to those using the nut. In the case of such a multi-nut type, for example, in the case of the double nut type shown in FIG. 11, one of the two nuts 3A, 3B (for example, 3A) may be inverted 180 °, or each nut 3A One of the two circuits 10, 11 and 12, 13 provided in 3B (for example, the circuit 10 and the circuit 12) may be inverted by 180 °. Further, regarding the arrangement of the circuits in the axial direction, not only the circuit in one nut is shifted from the normal position in the axial direction but also a spacer 14 is interposed between the two nuts 3A and 3B. Then, the respective circuits (the set of circuits 10 and 11 and the set of circuits 12 and 13) provided in each nut may be arranged so as to be shifted in the axial direction from the normal position.

  Next, other features of the present embodiment will be described with reference to the drawings. The ball screw device according to this embodiment may have a cantilever support structure as shown in FIG. The one axial end 101a side shown on the right side in FIG. 12 is rotatably supported by a support unit 103 which is a support member. As a support bearing for the ball screw used in the support unit 103, for example, a thrust angular ball bearing can be used. The support unit 103 is fixed to the fixing member 104.

  A pulley 105 is attached to one end of the screw shaft 101 in the axial direction. As the pulley 105 rotates, the screw shaft 101 rotates. The rotation of the nut 102 is limited, and the nut 102 is configured to move linearly by the rotation of the screw shaft 101.

  Further, the nut 102 is provided with a flange portion 107a at an axial end opposite to the support unit 103 side. The flange portion 107 a constitutes the attachment portion 107. An attachment member 108 driven by the nut 102 is attached to the attachment portion 107 with bolts. The mounting portion 107 constitutes an axial load acting portion.

  In the ball screw device configured as described above, as shown in FIG. 13A, when an axial load F1 acts on the mounting portion 107 of the nut 102 from the mounting member 108, the axial load is transmitted from the nut 102 to the screw shaft 101. An opposite axial load F2 is generated as a reaction force at the fixed side end.

  At this time, when the screw shaft 101 is assumed to be a rigid body as in the prior art and the elastic deformation of the nut 102 is taken into consideration, the load distribution of the ball along the axial direction is represented by the position of the mounting portion 107 as shown in FIG. 13B. The load becomes the largest and gradually decreases toward the other end (support unit 103 side).

  On the other hand, the nut 102 is assumed to be a rigid body, and elastic deformation of the screw shaft 101 is considered. Then, as shown in FIG. 13C, the load distribution of the ball along the axial direction has the largest load on the support unit 103 side (axial end portion 101a side of the screw shaft 101), and the other end portion (nut It gradually becomes smaller toward the mounting portion 107) of 102.

  Actually, both the nut 102 and the screw shaft 101 are elastically deformed in the axial direction. Therefore, when the elastic displacement of both the members 101 and 102 is taken into consideration, a uniform load distribution as shown in FIG. 13D is obtained. That is, in this embodiment, by providing the nut mounting portion 107 at the end of the nut 102 opposite to the support unit 103, the portion where the load is concentrated due to the elastic deformation of the nut 102 and the elastic deformation of the screw shaft 101. The part where the load is concentrated is separated in the axial direction. As a result, the load distribution along the axial direction of the nut is relatively large at both ends and relatively small at the center, but the difference between the maximum value and the minimum value is small. That is, the load on the ball is made uniform. Therefore, the screw shaft 101 and the nut 102 are preferably elastically deformed to the same extent.

  Here, the cross-sectional area of the screw shaft 101, that is, the area of the cross section obtained by cutting the screw shaft 101 in the direction perpendicular to the axial direction, and the cross-sectional area of the nut 102, that is, the nut 102 cut in the direction perpendicular to the axial direction. The operation when the cross-sectional areas are made equal will be described. When both the cross-sectional areas are equal, as shown in FIGS. 14A and 14B, the load on the ball becomes substantially the same at both ends in the axial direction, and the screw shaft load acting side and the nut load acting side are balanced, Maximum load can be suppressed. On the other hand, for example, when the cross-sectional area of the nut 102 is made larger than the cross-sectional area of the screw shaft 101 as in the conventional case, it is disadvantageous compared to the case where the cross-sectional area of the screw shaft 101 is equal to the cross-sectional area of the nut 102. Become. This is because, by making the cross-sectional area of the nut 102 larger than the cross-sectional area of the screw shaft 101, there is a difference in deformation amount between the screw shaft load acting side and the nut load acting side, and as shown in FIG. This is because the maximum load on the ball on the load acting side 101 (the side opposite to the mounting portion 107, that is, the support unit side) is increased.

  14A and 14B is obtained by changing the cross-sectional areas of the screw shaft 101 and the nut 102. That is, FIG. 14A shows a case where the cross sectional area of both is increased, and FIG. 14B shows a case where the cross sectional area of both is reduced. That is, the larger the cross-sectional area of the screw shaft 101 and the nut 102, the less the influence of elastic deformation. Therefore, the cross-sectional area of the screw shaft 101 and the nut 102 is desirably as large as possible. When the screw shaft 101 and the nut 102 are compared, the cross-sectional area of the screw shaft 101 on the inner side inevitably tends to be smaller than the cross-sectional area of the nut 102. Therefore, it is preferable to make the cross-sectional area of the screw shaft 101 larger than usual so as to be approximately equal to the cross-sectional area of the nut 102. The cross-sectional area ratio between the screw shaft 101 and the nut 102 is preferably within a range in which the load applied to the ball can be balanced to some extent in consideration of the elastic deformation of the screw shaft 101 and the nut 102. Therefore, it is preferable that the cross-sectional area of one is not more than twice the cross-sectional area of the other.

(First modification)
Hereinafter, a first modification of the present embodiment will be described with reference to the drawings as appropriate. The ball screw device according to this modification is a side cap type ball screw in which the circulation tube of the above embodiment is replaced with a side cap. FIG. 15 is a view of a ball screw according to a modification of the embodiment of the present invention as seen in the radial direction. FIG. 16 is a view of a ball screw according to a modification of the embodiment of the present invention when viewed in the axial direction. FIG. 17 is an arrow view in the 17 direction shown in FIG. 16 and shows the nut before the side cap is mounted. FIG. 18 is an arrow view in the 18 direction shown in FIG. 16 and shows a state after the side cap is mounted.

  As shown in FIGS. 15 to 16, the ball screw 10 includes a screw shaft 12 and a nut 14. The screw shaft 12 has a helical thread groove 11 on the outer peripheral surface. The nut 14 has a helical thread groove 13 corresponding to the thread groove 11 of the screw shaft 12 on the inner peripheral surface. The nut 14 is fitted to the screw shaft 12, and the screw groove 13 of the nut 14 and the screw groove 11 of the screw shaft 12 face each other. A spiral passage 8 is formed between the thread groove 13 and the thread groove 11. In the spiral passage 8, a plurality of balls 215 as rolling elements are loaded so as to be able to roll.

  Moreover, as shown in FIG. 17, the nut 14 has a side cap attachment surface 16 formed of a rectangular flat surface on the outer peripheral surface thereof. A pair of long holes 20 are formed in the side cap mounting surface 16. The long hole 20 is drilled through to the spiral passage 8 formed between the thread grooves 11 and 13. Then, as shown in FIG. 18, a side cap 17 as a ball circulation member is attached to the side cap attachment surface 16. As shown in FIG. 19, the side cap 17 has a pair of leg portions 19, and the pair of leg portions 19 are inserted into the long holes 20 formed in the side cap mounting surface 16 of the screw shaft 12. It can be fitted with almost no gap from the direction perpendicular to the axial direction (see FIG. 15). Then, as shown in FIG. 18, the entire side cap 17 is attached to the side cap mounting surface 16 by a lid-shaped side cap cover 26 that covers the side cap 17. The side cap cover 26 is screwed to the nut 14 with a set screw 18.

  Here, a ball scooping (returning) passage 21 is formed in the side cap 17 inside the leg portion 19 (see FIG. 16). The ball scooping (returning) passage 21 is formed to be inclined with respect to the outer peripheral wall surface of the leg portion 19. This ball scooping passage 21 is continuous with the ball feeding passage 22. The ball feed passage 22 and the pair of ball scooping passages 21 constitute a circulation path 27.

  The side cap 17 has a structure in which the leg portion 19 can be easily fitted into the long hole 20 formed in the side cap mounting surface 16. Further, the traveling direction of the ball 215 in the ball scooping passage 21 formed in the leg portion 19 can be scooped up in a direction substantially tangential to the screw shaft 12 and substantially coincident with the lead angles of both the screw grooves 11 and 13. It has a three-dimensional configuration. Therefore, the processing of the nut 14 is simplified, and the degree of freedom in design of the circulation path 27, that is, the ball scooping path 21 and the ball feed path 22 can be improved. The circulation path 27 and the spiral path 8 constitute a circuit in which the balls 215 circulate infinitely.

  Next, the divided structure of the side cap 17 will be described in detail. FIG. 19 is a perspective view of a side cap, and FIG. 20 is a perspective view showing one side cap constituent member obtained by dividing the side cap.

  The side cap 17 is manufactured by resin molding, and is formed by combining a pair of side cap constituent members 23 and 23 formed by molding a resin material, for example. The side cap constituent members 23 and 23 have the same shape. A line indicated by a symbol PL in FIG. 19 indicates a dividing line that divides the side cap 17 into the side cap constituent members 23.

  As shown in FIG. 20, a circulation path 27 including a ball scooping path 21 and a ball feed path 22 is formed inside the side cap 17. The side cap 17 is formed point-symmetrically with the center point as a symmetric point when viewed from the upper side of FIG. And as shown in FIG. 20, it is comprised from the two side cap structural members 23 which formed the boundary surface 23d along the advancing direction of the ball | bowl 215. As shown in FIG.

  Next, the dividing line PL (or dividing surface 23d) between the side cap constituent members 23 will be described in more detail. FIG. 21 is an explanatory view showing, in an enlarged manner, a main part (a periphery of a part surrounded by a circle 21 in FIG. 20) of the dividing line of the side cap. In the same figure, the division example in the scooping base end part of the inner side ball scooping part which concerns on a present Example is shown.

  By the way, as shown in FIG. 21, the side cap 17 has an inner ball scooping portion 24 at the tip of the ball scooping passage 21 of the side cap 17. The inner ball scooping portion 24 is directed from the ball scooping passage 21 toward the screw groove 11 in order to smoothly scoop the ball 215 rolling in the spiral passage 8 from the spiral passage 8 to the ball scooping passage 21. And has a tongue shape to be inserted into the screw groove 11 of the screw shaft 12. A tongue-shaped outer scooping portion 28 is also formed in the thread groove and on the leg portion 19 of the other side cap constituting member 23. Therefore, a V-shaped concave portion 25 having an acute angle is formed between the inner ball scooping portion 24 and the outer scooping portion 28.

  Here, in the side cap 17 according to the present embodiment, as shown in FIG. 21, the dividing line PL extends from the deepest portion of each recess 25 of the pair of leg portions 19. That is, the dividing line PL that divides the side cap 17 into the two side cap constituent members 23, 23 is set at a position where the concave portion 25 is divided at the V-shaped apex.

  Further, the dividing line PL passing through each concave portion 25 has an arc-shaped portion in the vicinity of the scooping base end portion 24a, as indicated by reference numeral 23f in FIG. Further, the arc and the dividing line PL thereon are set so as to be connected gently. As shown in FIG. 21, the split surface 23d of the side cap component member 23 has a ball in the vicinity of the scooping base end portion 24a (portion surrounded by a circle 21 in FIG. 20) when viewed in the axial direction. An overhang portion 23f that protrudes toward the inner ball scooping portion 24 with respect to the locus BCD (shown in FIG. 21) at the center of 215 is provided. In accordance with this, the scooping base end portion 24a is formed away from the track BCD when viewed in the axial direction. Thereby, since the scooping base end part 24a has a gentle shape, the stress concentration at the scooping base end part 24a can be preferably alleviated. In addition, the code | symbol Z of the figure has shown the scooping point which scoops up the ball | bowl 215. FIG. Further, in the division performed over the entire side cap 17, the dividing line PL in a portion other than the vicinity of the scooping base end portion 24 a is aligned with the locus of the center of the ball 215, and the two side cap constituting members 23, 23 are set so as to surround the circumference of the ball almost equally to each other. Thereby, the performance which restrains ball 215 can be stabilized.

  Next, the effect of the ball screw 10 and the side cap 17 in this embodiment is demonstrated. In this ball screw 10, the ball 215 that has rolled between the screw grooves 11 and 13 is scooped up in the lead angle direction of the screw grooves 11 and 13 by the ball scooping passage 21 of the side cap 17 and into the ball feed passage 22. Guided smoothly. Therefore, in this ball screw 10, even if the leads of the thread grooves 11 and 13 become large, the traveling direction of the ball 215 is not suddenly bent. Therefore, the ball 215 is damaged or noises when the ball 215 is lifted up. Can be suppressed. Furthermore, unlike the end cap type ball screw, for example, there is no restriction that the number of ball circulation circuits is limited to the number of thread grooves, so load capacity can be increased without increasing the number of balls (number of turns) per circuit. Can be increased.

  Further, in this ball screw 10, the side cap 17 is composed of a pair of side cap constituting members 23, 23 divided into two along the traveling direction of the ball 215. Therefore, it is possible to easily form the circulation path 27 in the side cap 17 by resin molding or the like by scooping up the ball 215 in the direction matching the lead angle of the thread grooves 11 and 13 and returning it to the spiral path 8 again.

  Further, in this ball screw 10, the side cap 17 can be molded with a single mold by combining the side cap 17 with a pair of side cap components 23, 23 having the same shape. Thereby, the side cap 17 can be manufactured more easily.

  Further, in this ball screw 10, the split surface 23 d that divides the side cap 17 into the side cap constituent members 23, 23 has a recess 25 formed between the inner ball scooping portion 24 and the outer ball scooping portion 28. Dividing at the deepest part of the recess 25. Conventionally, as shown in FIG. 27, the shape of the base end portion 240a is complicated, which causes stress concentration. In the ball screw 10 according to the present embodiment, the scooping base end portion 24a has a gentle and simple shape due to the above-described configuration. Therefore, an impact caused by the ball 215 circulating in the side cap 17 acts on the side cap constituent member 23. Even in this case, there is almost no risk of fatigue failure starting from the scooping base end 24a or the vicinity of the scooping base end 24a. Therefore, according to the present embodiment, the high-speed operation performance and durability performance of the ball screw can be improved.

  As described above, if the dividing line PL starts (and ends) from the deepest portion of the recess 25, that is, the side cap 17 prevents the deepest portion of the recess 25 from being formed on the scooping base end 24a. , The stress concentration at the scooping base end portion 24a can be preferably alleviated. However, as a side effect thereof, the split surface of the ball circulation member constituting member 23 is shifted toward the inner ball scooping portion 24 with respect to the ball trajectory drawn by the center of the ball 215. The performance of restraining the ball 215 by the peripheral wall in the vicinity of 24a may become unstable.

(Second modification)
Therefore, as a second modified example, a shape that can relieve stress concentration at the scooping base end and stabilize ball restraining performance in the vicinity of the scooping base end will be described. FIG. 22 and FIG. 23 are diagrams for explaining the combined state of the peripheral walls in the vicinity of the scooping base end portion by the pair of side cap constituent members 23, 23 according to the present embodiment. As described above, the side cap 17 includes the two side cap constituent members 23, and the pair of side cap constituent members 23 and 23 each have a split surface (mating surface) 23d (see FIG. 20). .

  Note that the second modification differs from the side cap 17 of the first modification described above only in the shape of the overhang portion 23f, and the other configuration is the same as that of the first modification. Therefore, only the shape of the overhang portion 23f will be described here, and the other description will be omitted.

  In the side cap 17 of the second modified example, unlike the side cap 17 of the first embodiment, as shown in FIG. 22, the overhanging portion 23 f is used as a scooping base end portion 24 a of the other side cap constituting member 23. It is formed so as to cover the outside.

  As a result, the dividing position of the two side cap constituent members 23, 23 is different between the two side cap constituent members 23, 23 in the ratio of the peripheral wall surrounding the ball in the vicinity of the scooping base end portion 24a. In addition, the ball restraining performance by the peripheral wall in the vicinity of the scooping base end portion 24a can be stabilized. Note that the symbol O in the figure indicates the center position of the ball 215.

  Thus, in the side cap 17 of the second modified example, it is possible to stabilize the ball restraining performance by the peripheral wall in the vicinity of the scooping base end portion 24a while preventing stress concentration at the scooping base end portion 24a. .

  As described above, according to the ball screw 10 according to the first and second modifications, the ball circulating member is used as the side cap 17 and the weakly raised base end portion 24a having the configuration of the above-described embodiment. By improving the strength of the ball screw 10, it is possible to provide the ball screw 10 with improved high-speed driving performance and durability performance.

  In addition, the ball screw which concerns on this invention is not limited to said each modification, A various deformation | transformation is possible within the range which does not deviate from the meaning of this invention.

  For example, each of the above modifications may further include a protruding portion and a hole portion as positioning portions for mutual alignment with respect to the dividing surface (mating surface) 23d. Further, the side cap 17 may have a structure in which a side cap attachment hole for directly passing the set screw 18 is formed.

  Further, in each of the above-described modifications, in the division performed over the entire side cap 17, the dividing line PL has two side cap components 23 along the trajectory of the center of the ball except for the scooping base end portion 24 a. However, the present invention is not limited to this, and the dividing line does not have to be at an equally divided position. However, since the performance of restraining the ball is stabilized by each of the side cap constituent members 23 and 23 surrounding the ball substantially equally with respect to the ball, the side cap component members 23 and 23 are arranged at portions other than the vicinity of the scooping base end portion. The dividing line PL is preferably set evenly according to the trajectory of the ball center.

  Alternatively, for example, the side cap 17 may be configured to be completely integrated. Or the side cap 17 may be comprised combining the side cap structural member divided | segmented into three or more.

  For example, in each of the above modifications, the example in which the shape of the recess 25 is a V-shaped groove having an acute angle has been described. However, the shape of the recess 25 is not limited to the V-shaped groove. In other words, the recess includes a “dent” such as a notch or a groove, and the shape of the recess may be U-shaped or semicircular.

  Further, for example, in each of the above-described modifications, the ball screw 10 has been described as an example in which the side cap 17 (side cap constituent members 23 and 23) is formed of a resin. However, for example, the side cap 17 is formed by metal molding, for example, sintered steel. It may be formed of a sintered material such as, or may be formed by metal injection molding (MIM). By setting it as such a structure, it can be used also on the high temperature conditions which are not suitable for use of resin.

  This is the end of the description of the modification of the embodiment of the present application. Hereinafter, the embodiment of the present application will be described again with reference to the drawings. Here, still another feature of the present embodiment will be described. This embodiment is applied to a tube-type ball screw having a screw shaft diameter of 40 mm, a lead of 25 mm, and a ball diameter of 7.1438 mm. FIG. 28 shows a cross-sectional shape of the ball groove 2 a of the screw shaft 2. The outer diameter portion (land portion) 4 of the screw shaft 2 and the substantially semicircular ball rolling portion 35 of the ball groove 2a are connected by an arc portion 311 chamfered in an arc shape. In this embodiment, the radius of curvature R of the arc portion 311 is substantially equal to the radius r of the ball 1 = 3.57 mm. The arc portion 311 is formed smoothly and continuously with the curve of the ball rolling portion 35.

  The upper portion of the arc portion 311 is adjacent to the land portion 4 at the intersection P2. Further, in this embodiment, the difference Y between the distance from the center axis of the screw shaft 2 to the center of the ball 1 in the screw groove 2a and the distance from the center axis of the screw shaft 2 to the surface of the land portion 4 is calculated as follows. 1 is set to be smaller than 10% of the diameter. In order to reduce the stress concentration due to the impact of the ball collision, it is desirable to make the radius of curvature R of the arc portion 311 as large as possible. However, as the radius of curvature R increases, the position of the intersection point P2 between the arc portion 311 and the land portion 4 approaches the groove center and the shape becomes a sharp protrusion. If the radius of curvature R exceeds the limit, the ball has an opportunity to collide with the vicinity of the point P2, and at the same time, the stress concentration at the time of the collision increases, and the risk of damage to the shoulder of the land portion increases. Therefore, it is necessary to provide an upper limit to the radius of curvature R of the arc portion 311 to avoid the danger.

  The inventor plots the position where the ball 1 first collides with the surface of the ball groove 2a when the ball 1 passes through the ball circulation tube and is fed toward the ball groove 2a of the screw shaft 2. The upper limit of the radius of curvature R of the arc portion 311 is defined by analyzing the obtained diagram. 29 to 31 are diagrams in the case where the results of continuously plotting the ball collision positions are looked down from the top of FIG. In each figure, when the ball center position comes to the height of the uppermost point E1, the ball collides with the surface of the ball groove 2a at the point E2 shown directly below E1.

  FIG. 29 shows a case where the trajectory of the ball 1 being fed into the ball groove 2a is ideal and there is no variation. In this case, the ball 1 collides only with the ball rolling portion 35 regardless of the radius of curvature R of the arc portion 311. Therefore, the upper limit of the radius of curvature R of the arc portion 311 does not matter. However, in actual cases, the locus of the ball inevitably varies within a certain range depending on the use conditions such as processing and assembly errors of the ball screw and operation speed. FIG. 30 and FIG. 31 show the analysis results when considering the dimensional accuracy of the ball screw and the deviation of the ball trajectory estimated from the experimental results.

  FIG. 30 shows the ball groove shape of the present embodiment shown in FIG. 28, and the point E2 where the ball collides with the surface of the ball groove 2a is in the arc portion 311. However, since the radius of curvature R of the arc portion 311 is formed to be approximately equal to the ball radius, the possibility of damage from there is very small. When the radius of curvature R of the arc portion 311 is further increased, the ball collision position approaches the protruding boundary line L between the arc portion 311 and the screw shaft outer diameter portion (land portion) 4. When the curvature radius R exceeds a predetermined value, there is a risk that the ball collides with the boundary line L and damages the land shoulder. The present inventor performs the above analysis for various changes in the radius of curvature R of the arc portion 311, and based on the result, the arc does not collide with the boundary line L between the arc portion 311 and the land portion 4. The upper limit value of the radius of curvature R of the portion 311 could be obtained. Its value is twice the radius of the ball. That is, the radius of curvature R of the arc portion 311 may be set to be twice or less the radius of the ball.

  On the other hand, when the radius of curvature R of the arc portion 311 is less than ½ of the radius of the ball, it was recognized that the arc portion 11 was damaged by the ball collision. FIG. 31 shows the case of the conventional ball groove shape shown in FIG. 32 (in which the shoulder portion of the land portion is connected by a chamfered portion 36 having an inclined surface). In this case, the point E2 where the ball collides with the surface of the ball groove 2a is on the boundary line between the ball rolling part 35 and the chamfered part 36, and the boundary line is a projection, so that damage is caused from there. It was observed to occur.

  The difference Y between the distance from the central axis of the screw shaft 2 to the center of the ball 1 in the screw groove 2a and the distance from the central axis of the screw shaft 2 to the surface of the land portion 4 is set to 0 or 10 of the ball diameter. In the ball groove shape set as small as less than%, the ball collision on the boundary line L between the arc portion 311 and the land portion 4 can be prevented even if the radius of curvature R of the arc portion 311 is set larger. Therefore, it is possible to further alleviate the stress concentration at the time of collision.

  In the present embodiment, an example in which the present invention is applied to a tube circulation type ball screw has been described. However, the above-described features can be similarly applied to other ball screws. For example, the above-described feature can be applied to a top-circulating ball screw as shown in FIG.

  As described above, in this embodiment, in the cross-sectional shape of the ball groove of the screw shaft of the ball screw, an arc portion is provided between the outer diameter portion of the screw shaft and the substantially semicircular ball rolling portion of the ball groove. And the radius of curvature of the arc part is ½ or more and twice or less than the radius of the ball rolling in the ball groove, and at least the ball rolling part is continuously connected with a smooth curve. did. Thereby, even if the impact force of the collision of the ball is applied in the vicinity of the arc portion, the stress concentration is relaxed, and damage to the shoulder portion of the screw shaft can be prevented even at high speed operation. The difference Y between the distance from the central axis of the screw shaft 2 to the center of the ball 1 in the screw groove 2a and the distance from the central axis of the screw shaft 2 to the surface of the land portion 4 is set to 0 or 10 of the ball diameter. By setting it as small as less than%, even if the radius of curvature of the arc portion is increased, it is possible to prevent the ball from colliding with the intersection of the arc portion and the land portion, so that the life of the ball screw can be extended. 33 to 35 show a tube-type ball screw according to a conventional example. In the conventional example shown in FIG. 35, arc portions are formed on both sides of the ball rolling portion 35, but the radius of curvature R of the arc portion is 40% or less of the radius of the ball 1. There is a risk that damage will occur by performing high-speed driving for a long time.

  Finally, other features of the embodiment of the present application will be described. FIG. 37 is a front view of the seal 15 according to the embodiment of the present application. FIG. 38 is a view of the seal 15 of FIG. 37 taken along line 38-38 and viewed in the direction of the arrow. The seal 15 includes an annular seal body 15c that expands in the radial direction, and a seal piece 15d that refracts from the inside of the seal body 15c to one side in the axial direction over the entire circumference and extends radially inward. The seal piece 15d forms an annular contact portion 15b having a circular cross section at the inner edge thereof.

  The inside of the contact portion 15b is an opening 15a corresponding to the cross-sectional shape of the screw shaft 2. The seal body 15c, the seal piece 15d, and the contact portion 15b, which are attachment portions for attaching the outer periphery to the nut 3, are integrally formed from a resin or rubber having wear resistance and flexibility.

  39 is an enlarged cross-sectional view of the periphery of the seal piece 15d of the seal 15 according to the present embodiment, and FIG. 40 further enlarges the contact portion 15b of the seal 15 of FIG. 39, and a thread groove (two-dot chain line). It is the figure which showed the contact state with. The contact portion 15b has a shape like an O-ring having a circular cross section as shown in the figure.

  In FIG. 39, a two-dot chain line indicates the position (15A to 15G) of the contact portion 15b of the seal 15 that contacts the screw shaft 2 and is displaced according to the relative angle between the seal 15 and the screw shaft 2. As apparent from FIG. 40, the contact point 15 e (contact region) of the contact portion 15 b is displaced on the contact portion 15 b according to the position in contact with the peripheral surface of the screw shaft 2.

  According to the contact part 15b, even if it contacts any peripheral surface of the screw shaft 2, the normal line of the contact surface passes through the center of the cross section of the contact part 15b as shown in FIG. Therefore, regardless of the contact position, the contact relationship between the seal 15 and the screw shaft 2 is maintained constant, so that a sealing function can be secured. For example, in the case of the prior art seal 5 shown in FIG. 44, an unstable contact is caused such that the left side surface 5f or the right side surface 5g contacts the screw shaft 2 before the tip portion 5e contacts. There is a fear. However, according to the present embodiment, as shown in FIG. 39, the contact portion 15b is always in contact with the peripheral surface of the screw shaft at any position from 5A to 5G, so that a stable sealing function of the seal is ensured. it can.

  The present invention has been described above with reference to the embodiments. However, the present invention should not be construed as being limited to the above-described embodiments, and modifications and improvements can be made as appropriate. For example, the cross-sectional shape of the contact portion 5b described last may be a semicircular shape.

  In addition, as for the characteristics of the ball screw described in the embodiment and the first and second modified examples, any one of the characteristics may be applied to the ball screw, or any of a plurality of characteristics may be applied to the ball screw. You may apply and all the characteristics may be applied to a ball screw.

1 Ball 2 Screw shaft 2a Screw groove 3 Nut 5, 6, 7 Circulating tube 9 Screw groove 17 Side cap

Claims (10)

A screw shaft having a first thread groove on the outer peripheral surface;
A nut having a second thread groove on the inner peripheral surface facing the first thread groove;
A plurality of balls housed in a spiral passage formed by the first thread groove and the second thread groove;
In each of the ball screws provided with three or more ball circulation members attached to the nut and forming a circulation path connecting two portions of the spiral passage,
At least one said ball circulation member is arrange | positioned in the position of the circumferential direction different from the said other ball circulation member, The ball screw characterized by the above-mentioned. At least two of the ball circulation members are arranged at the same position in the circumferential direction;
2. The ball screw according to claim 1, wherein the at least one ball circulation member is disposed between the at least two ball circulation members in an axial direction.   3. The ball screw according to claim 2, wherein the at least one ball circulating member and the two ball circulating members are disposed at positions that are different from each other by 180 ° in a circumferential direction.   The second thread groove portion constituting a circuit in which the ball circulates together with the at least one ball circulation member constitutes a circuit in which the ball circulates together with the at least two ball circulation members. 4. The ball screw according to claim 3, wherein a preload is generated by shifting in an axial direction from a position equidistant from two portions of the screw groove. A support member that rotatably supports the screw shaft at one end of the screw shaft;
5. The ball screw according to claim 1, wherein the nut has a flange extending radially outward at an end portion opposite to the support member. 6. The ball circulation member is
An outer scooping portion that scoops up the ball in the spiral passage on the radially outer side, and an inner scooping portion that scoops up the ball in the spiral passage on the radially inner side. A pair of scooping passages,
A ball feed path connecting the pair of scooping paths,
The outer scooping part and the inner scooping part constitute a recess recessed from the tip side to the ball feed passage side between them,
5. The ball circulating member is composed of two components separated from a portion of the concave portion located closest to the ball feeding passage by a dividing surface along the path of the ball. The ball screw according to claim 1.   When viewed in the axial direction, the dividing surface is disposed closer to the inner scooping portion than the locus of the center of the ball passing through the ball circulation member in the vicinity of the recess. The ball screw according to claim 6.   In the cross section perpendicular to the traveling direction of the ball, the first screw groove is smoothly continuous at both ends, and has an arc portion having a radius of curvature that is equal to or more than one-half and less than twice the radius of the ball. The ball screw according to any one of claims 1 to 4, further comprising:   A value obtained by subtracting the maximum radius of the screw shaft from the distance from the central axis of the screw shaft to the center of the ball in the first screw groove is 10% or less of the diameter of the ball. The ball screw according to claim 8. A seal attached to an end of the nut and having a contact portion that contacts the screw shaft;
The ball screw according to any one of claims 1 to 4, wherein the contact portion has a curved surface having an arcuate cross section at least on the screw shaft side.

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