JP6449717B2 - Ball screw nut and ball screw - Google Patents

Description

  The present invention relates to a ball screw nut and a ball screw, and more particularly to a nut structure used for a non-circulating ball screw.

  Generally, the ball screw includes a circulation type ball screw and a non-circulation type ball screw. As a non-circulating ball screw, a ball screw having a lead screw, a nut, and a cage (retainer) is generally known. The lead screw has a spiral lead groove on its outer peripheral surface. The nut has a circular holding groove on its inner peripheral surface, and a lead screw is inserted through the nut. The cage (retainer) has a ball holding hole for holding the ball so that it can roll, and the ball is interposed between the lead screw and the nut and rolls between the inner lead groove and the outer holding groove. To do.

  Patent Documents 1 to 3 are the above-mentioned non-circular ball screws. In either case, a structure in which the nut having a circular holding groove and a cage having a ball holding hole are fixed is disclosed. Thus, by fixing the nut and the cage, the cage and the ball held by the cage are prevented from spinning between the lead screw and the nut. Thereby, it is possible to accurately perform the conversion between the rotational motion and the linear motion by the ball screw.

Japanese Patent No. 2661789 Japanese Utility Model Publication No.57-41489 Japanese Utility Model Publication No. 55-145747

Upper Symbol acyclic ball screw has a relatively simple structure. That is, the circulating ball screw has a structure in which a nut having a circular holding groove and a cage having a ball holding hole are fixed to each other. When the nut and the cage are fixed to each other, the position of the circumferential holding groove provided in the nut and the position of the holding hole provided in the cage may not slightly match in the axial direction. . If the position of the nut and the position of the cage do not coincide with each other in the axial direction, the size of the space in which the ball is accommodated is not secured. It makes sliding contact without rolling contact. As a result, the ball, the ball holding hole, and the like are worn due to sliding contact, causing problems such as malfunction, and insufficient durability and poor operation accuracy.

  Therefore, the present invention solves the above-described problems, and an object thereof is to realize a non-circular ball screw that can ensure durability and operation accuracy.

  In view of such circumstances, the ball screw nut of the present invention is a ball screw nut to be attached to a lead screw having a spiral lead groove, and the ball fitted into the lead groove, A holding body having a cylindrical holding portion provided with a holding hole that is held so as to be able to roll, and mounted on the outer peripheral surface of the holding portion in a manner in which the position is not restrained in the axial direction on the holding body, And a sleeve having a single circular holding groove into which the ball held in the holding hole is fitted.

  In the present invention, the holding portion includes the first holding hole and the second holding hole provided at different positions in the axial direction, and the sleeve is held in the first holding hole as the sleeve. A first sleeve provided with the holding groove that fits into the ball; and a second sleeve provided with the holding groove that fits into the ball held in the second holding hole. It is preferable that the first sleeve and the second sleeve are attached to the holding portion in a state where the positions are not restrained from each other. Note that the number of holding holes and the number of sleeves provided at different positions in the axial direction are not limited to two, and may be three or more.

In the present invention, in order to improve the posture stability and position accuracy of the nut with respect to the lead screw, the holding portion includes a hole row in which a plurality of holding holes are arranged in the circumferential direction, and a plurality of holes belonging to the hole row are provided. It is preferable that a plurality of balls held in the holding hole are fitted in the single holding groove.

  As described above, in the case where the holding portion includes a hole row in which a plurality of holding holes are arranged in the circumferential direction, the holding portion has the plurality of holding pieces arranged in the circumferential direction as the hole row. A first hole row made of holes, and a second hole row made of the plurality of holding holes arranged in a circumferential direction at a position shifted in the axial direction with respect to the first hole row. The sleeve having the holding groove that fits into the ball held in the plurality of holding holes belonging to the first hole row, and the sleeve belonging to the second hole row. A second sleeve having the holding groove that fits into the ball held in a plurality of holding holes, and the first sleeve and the second sleeve are not restrained in position relative to each other. It is preferable that it is attached to the holding part. The number of the hole rows and the number of sleeves formed in the axial direction are not limited to two and may be three or more.

  In the present invention, the holding groove is preferably a circular groove having an arc-shaped cross section corresponding to the shape of the ball. The holding groove may be a V-shaped groove having a V-shaped cross section or a trapezoidal groove having a trapezoidal cross section as long as it corresponds to the shape of the ball. The groove shape of the holding groove is not limited to the above, and various shapes used for the ball screw can be used. Further, the shape of the lead groove of the lead screw can have various cross-sectional shapes as described above.

  In this invention, it is preferable that the said holding body has an external attachment part which can be attached to another member. The external mounting portion can be, for example, a flange portion that protrudes in the axial direction and the radial direction with respect to the holding portion. Further, the other member is configured to be relatively movable in the axial direction of the lead screw, and the other member is mounted by fixing the external mounting portion of the holding body to the other member. It is possible to drive the lead screw in the axial direction. In this case, the sleeve is mounted on the outer peripheral surface of the holding portion in a manner that the position of the sleeve is not restrained in the axial direction, and the sleeve held in the holding hole is fitted. One circular holding groove is provided. Further, the position of the sleeve is not restricted by the other member. The external attachment portion can be provided with various attachment means for fixing other members such as a through hole, a screw hole, a notch, and a boss.

  In the present invention, it is preferable that the holding portion is formed in a cylindrical shape, and the sleeve is attached to the holding portion so as to be rotatable in a circumferential direction.

  In the present invention, it is preferable that a thickness Tr of the holding portion corresponding to a penetration depth of the holding hole is larger than a depth Dg of the holding groove of the sleeve.

  In the present invention, the maximum contact angle α of the ball with respect to the holding groove along the axial direction is preferably larger than the lead angle β of the lead groove.

  In the present invention, the lead screw includes n lead grooves (n is a natural number of 2 or more), and the holding portions are n pieces arranged in a circumferential direction corresponding to each of the n lead grooves. The n number of balls respectively held in the holding holes are fitted in the lead grooves of the n strips, and are fitted together in the single holding groove of the sleeve. It is preferable.

  According to the present invention, the sleeve is mounted on the outer peripheral surface of the holding portion of the holding body. The sleeve is mounted on the holding portion in such a manner that its position is not restrained in the axial direction, so that the circumferential holding groove of the sleeve is fitted to the ball held in the holding hole, and the sleeve is positioned by the ball. Therefore, it is not necessary to secure or position the accuracy between the position of the holding hole and the position of the holding groove of the sleeve, and it is possible to avoid the poor durability and operational accuracy due to the lack of accuracy between the two positions. Can have an effect.

It is sectional drawing which shows the structure of the ball screw of 1st Embodiment which concerns on this invention in the cross section along an axial direction. It is sectional drawing which shows the structure of the ball screw of 1st Embodiment in the cross section (II-II cross section of FIG. 1) orthogonal to an axial direction. It is a perspective view which shows the shape of the holding part of the nut of 1st Embodiment. It is a perspective view which shows the shape of the holding part of the nut of 2nd Embodiment. It is an expanded sectional view showing the engagement structure of the lead screw, holding body, and sleeve of the first and second embodiments. It is an expanded fragmentary sectional view which expands and shows a part of engagement structure of the lead screw of 3rd Embodiment, a holding body, and a sleeve. It is sectional drawing (a) and (b) which shows the structure and operation | movement aspect of an electric actuator using the ball screw of 1st-3rd embodiment.

  Next, the configuration of the embodiment of the present invention will be described in detail with reference to the accompanying drawings. First, the first embodiment according to the present invention will be mainly described with reference to FIGS. 1 to 3, the second embodiment will be described with reference to FIG. 4, and the third embodiment will be described with reference to FIG. 6. An embodiment will be described.

  The ball screw 1 of the first embodiment includes a lead screw 10 and a nut 20. The lead screw 10 includes spiral lead grooves 10a to 10d on the outer peripheral surface thereof. In the illustrated example, four lead grooves 10a, 10b, 10c, and 10d are provided, but only one lead groove may be provided. However, the engagement accuracy and operation accuracy of the nut 20 can be improved by providing two or more lead grooves. In the figure, the lead angle of the lead groove is indicated by β.

  The nut 20 includes a holding body 21, sleeves 22 </ b> A and 22 </ b> B, and a ball 23. The holding body 21 has a cylindrical holding portion 21A and an external mounting projecting in the axial direction (the direction of the axis 10x of the lead screw 10) and the radial direction (the radial direction perpendicular to the axis 10x) with respect to the holding portion 21A. And a flange portion 21B. The holding portion 21A is formed with a plurality of holding holes 21a and 21b penetrating in the radial direction, and a spherical ball 23 is rotatably held in each holding hole 21a and 21b.

  In the present embodiment, a plurality of first holding holes 21a are provided in the circumferential direction (a direction around the axis line 10x). In the illustrated example, four first holding holes 21a are provided in the holding portion 21A at equiangular (90 degrees) intervals in the circumferential direction. In the present embodiment, the four balls 23 held so as to be able to roll in the plurality of first holding holes 21a (first hole rows) are respectively formed in the four lead grooves 10a to 10d. Mate one by one. A plurality of second holding holes 21b provided at different positions in the axial direction with respect to the first holding hole 21a are also provided in the circumferential direction. In the illustrated example, four second holding holes 21b are provided in the holding portion 21A at equal angular intervals (90 degrees) in the circumferential direction. In the case of the present embodiment, the balls 23 are held in the plurality of second holding holes 21b (second hole rows) so as to be capable of rolling, and one ball 23 is provided in each of the four lead grooves 10a to 10d. Fit one by one.

  In the illustrated example, the first holding hole 21a and the second holding hole 21b adjacent to each other in the axial direction are arranged at the same angular position. However, like the holding body 21 ′ (holding portion 21A ′) of the second embodiment shown in FIG. 4, the first holding hole 21a and the second holding hole 21b ′ are in positions shifted from each other in the circumferential direction. It may be arranged. The second embodiment is different from the first embodiment only in the relative circumferential positional relationship between the first holding hole 21a and the second holding hole 21b '. is there.

  In order to ensure the rigidity of the flange portion 21B as an external mounting portion, the thickness dimension in the axial direction and the radial direction are both larger than the thickness dimension of the holding portion 21A. A through hole 21c is formed in the flange portion 21B, and the through hole 21c functions as an attaching means for attaching to another member. In the illustrated example, four through holes 21c are formed at equal angular intervals in the circumferential direction. The attachment means is not limited to the through hole 21c, and various structures such as a screw hole, a notch, and a boss can be used.

  The sleeves 22A and 22B are mounted on the outer peripheral surface of the holding portion 21A. In the present embodiment, two sleeves 22A and 22B are mounted adjacent to each other in the axial direction.

  Each of the sleeves 22A and 22B has a cylindrical shape corresponding to the outer peripheral surface shape (cylindrical surface) of the holding portion 21A. On the inner peripheral surfaces of the sleeves 22A and 22B, one holding groove 22a and 22b each having a shape that circulates in the circumferential direction is formed. That is, only the single holding groove 22a is formed in the first sleeve 22A, and only the single holding groove 22b is formed in the second sleeve 22B. These holding grooves 22a and 22b have a groove shape. A part of the ball 23 protrudes from the holding holes 21a and 21b of the holding portion 21A to the outer peripheral side, and fits into groove-shaped holding grooves 22a and 22b. The holding grooves 22 a and 22 b are circular grooves, and the radius of the holding grooves 22 a and 22 b corresponds to the radius of the ball 23. However, as will be described later, the holding groove may be any groove structure that can be fitted to the balls 23 arranged in the above-described manner. For example, it may be a V-shaped groove having a V-shape like a holding groove 22a ′ formed in the sleeve 22A ′ of the third embodiment shown in FIG.

  The sleeves 22 </ b> A and 22 </ b> B are fitted to the balls 23 held in the holding holes 21 a and 21 b without being restricted by the holding body 21 in the axial direction, and are positioned in the axial direction by the balls 23. Accordingly, there is no difference between the axial position of the holding holes 21a and 21b and the axial position of the holding grooves 22a and 22b, and therefore, the abnormal wear of the ball 23 due to the difference does not occur. Here, the sleeves 22A and 22B are attached to the holding body 21 in such a manner that their positions are not restrained in the axial direction. When the ball 23 is not interposed, the sleeves 22A and 22B move in the axial direction on the holding portion 21A. It means that the shapes and dimensions of the sleeves 22A and 22B and the holding body 21 are set so that they can be freely set. In the present embodiment, the positions of the sleeves 22 </ b> A and 22 </ b> B in the axial direction are not directly positioned by the holding body 21, but are positioned by fitting the holding grooves 22 a and 22 b with the balls 23. Furthermore, in this embodiment, the positions of the sleeves 22A and 22B are not constrained to each other, that is, do not interfere with each other. The sleeves 22 </ b> A and 22 </ b> B are positioned relative to each other only through the holding body 21 and the ball 23 as a result of the balls 23 interposed between the holding bodies 21. However, when there is a variation in the position in the axial direction between the plurality of balls 23 held in the circumferentially arranged state (that is, there is a variation in the axial direction at the positions of the holding holes 21a and 21b of the holding body 21). In this case, there may be a difference in operation mode between the balls 23 arranged in the circumferential direction when the plurality of balls 23 are fitted to the single holding grooves 22a and 22b. This is only a problem of the holding body 21, and can be avoided by increasing the alignment accuracy of the hole rows formed in the holding portion 21 </ b> A, and the degree of wear is not large. Moreover, as will be described later, it reduces backlash and backlash. Also useful.

  Note that the gap dimension between the holding portion 21A (holding holes 21a and 21b) and the sleeves 22A and 22B is not zero but has a slight gap. Therefore, the sleeves 22 </ b> A and 22 </ b> B are positioned in the axial direction and the radial direction by fitting with the balls 23. When the ball screw 1 is operated, the holding body 21 is attached to another external member via an external attachment portion such as a flange portion 21B, but the sleeves 22A and 22B are provided as described above. The holding portion 21A of 21 is maintained in a state of being fitted and positioned only on the ball 23 in a state where the position is not restricted in the axial direction.

  Here, in the illustrated example, the holding portion 21A is formed in a cylindrical shape and the sleeve 22 is formed in a cylindrical shape, and each hole row of holding holes 21a and 21b holding the ball 23 and the corresponding holding grooves 22a, Since 22b is formed along a plane (virtual plane P described later) orthogonal to the axis 10x, the position of the sleeve 22 is not restricted by the holding portion 21A not only in the axial direction but also in the circumferential direction. It is mounted rotatably. However, the holding portion 21A may be in a cylindrical shape. For example, when the outer peripheral surface of the holding portion 21A has a non-cylindrical shape such as a rectangular tube shape, the sleeves 22A and 22B have a corresponding non-cylindrical shape. There may be. In this case, the sleeves 22A and 22B are attached to the holding portion 21A in such a manner that their positions are not restricted in the axial direction, but their positions are restricted in the circumferential direction (circumferential direction) and do not rotate. Become.

  In the present embodiment, the ball 23, the lead screw 10 having the lead grooves 10 a to 10 d having the groove shape corresponding to the ball 23, and the circular holding grooves 22 a and 22 b having the groove shape corresponding to the ball 23 are provided. The sleeves 22 </ b> A and 22 </ b> B are made of metal that can easily secure rigidity, and the holding body 21 having holding holes 21 a and 21 b that hold the balls 23 in a rollable manner is made of a synthetic resin having a low coefficient of friction. . As the synthetic resin, for example, polyacetal resin (POM) is preferable because it has high mechanical strength, wear resistance, slidability, and the like. However, any member is not limited to the material of these metals or synthetic resins, and can be made of an appropriate material according to various required characteristics corresponding to the application.

  In the first and second embodiments, as shown in FIG. 5, the driving force F generated when the lead screw 10 rotates in the circumferential direction R moves the nut 20 in the axial direction. At this time, it is preferable that the thickness Tr of the holding portion 21A of the holding body 21 is larger than the depth Dg of the circumferential holding grooves 22a and 22b of the sleeves 22A and 22B. This is to increase the rigidity of the holding portion 21A that holds the ball 23 and to easily secure the positional accuracy of the holding holes 21a and 21b. This is also for facilitating the mounting of the sleeves 22A, 22B to the holding body 21 during assembly of the ball screw 1 while ensuring the fitting accuracy of the sleeves 22A, 22B to the balls 23. For example, the sleeve 22A and 22B may be mounted after the ball 23 is inserted and disposed in the holding holes 21a and 21b in a state where the lead screw 10 is not inserted at least inside the holding portion 21A of the holding body 21. 22A and 22B are carried out in the axial direction on the outer peripheral surface of the holding portion 21A. Thereafter, the assembly of the ball screw 1 is completed by inserting the lead screw 10 while rotating it inside the holding portion 21A so that the lead grooves 10a to 10d are screwed into the ball 23.

  Further, in the present embodiment, the maximum contact angle α with respect to the inner surfaces of the holding grooves 22a and 22b of the sleeves 22A and 22B measured in the direction along the axial direction with respect to the virtual plane P orthogonal to the axis 10x is the lead screw 10. The lead grooves 10a to 10d are set to be larger than the lead angle β. Here, the maximum contact angle α can be contacted around the center of the ball 23 with respect to the inner surfaces of the holding grooves 22a and 22b on a plane (paper surface in FIG. 5) along an axial direction orthogonal to the virtual plane P. Indicates the angle range. In this embodiment, the depth Dg of the holding grooves 22a and 22b is smaller than the thickness Tr of the holding portion 21A for the reason described above, but if the depth Dg is too small, the sleeves 22A and 22B This is because it is preferable to keep the maximum contact angle α at a certain large value because the degree of engagement with the ball 23 in the axial direction is weakened to cause problems. That is, the sleeves 22 </ b> A and 22 </ b> B are mounted on the holding body 21 so that the positions thereof are not restricted in the axial direction but are restricted only in the axial direction and the radial direction via only the balls 23. When a force is applied between the sleeves 22A, 22B and the ball 23 during acceleration / deceleration of the nut 20 due to, the nut structure for holding the ball 23 becomes unstable due to elastic deformation or vibration of the sleeves 22A, 22B. In some cases, the sleeves 22A and 22B may come off the ball 23 on the holding portion 21A. When such a situation occurs, the radial positioning function of the sleeves 22A and 22B with respect to the ball 23 is deteriorated or lost, which significantly affects the durability and operation accuracy of the ball screw. Since the acceleration / deceleration in the axial direction has a positive correlation with the lead angle β of the lead screw 10, it is possible to ensure the performance of the ball screw 1 by making the maximum contact angle α larger than the lead angle β. Become.

  FIG. 6 is a cross-sectional view showing a fitting structure between the holding grooves 22a and 22b of the sleeves 22A and 22B and the balls 23 according to the third embodiment. This third embodiment differs from the previous first and second embodiments in that the holding grooves 22a and 22b are V-shaped in cross section, but other structures are different. Is common to the first and second embodiments. In the third embodiment, since the ball 23 contacts the inner surfaces of the holding grooves 22a and 22b, which are V-shaped grooves, at two points before and after the axial direction, if an effective viewpoint is emphasized, the holding groove 22a ' The depth Dg may be considered as the thickness of the portion disposed inside the holding groove 22a ′ of the ball 23 in a state where two points are in contact with each other as illustrated. On the other hand, the maximum contact angle α of the ball 23 with respect to the holding groove 22a ′ may be considered as an angle along the axial direction with respect to the virtual plane P of the straight line from the center point of the ball 23 to the contact point.

  In the ball screw 1 of the present embodiment, as shown in FIG. 1, the first sleeve 22A and the second sleeve 22B are disposed adjacent to each other in the axial direction on the outer peripheral surface of the holding portion 21A. Since the axial lengths of the sleeves 22A and 22B are shorter than the pitch of the holding holes 22a and 22b of the holding portion 21A, the first sleeve 22A and the second sleeve 22B are adjacent to each other via a gap. . That is, since the first sleeve 22A and the second sleeve 22B do not contact each other, the positions in the axial direction do not interfere with each other. Further, since the first sleeve 22A has a gap also between the adjacent flange portions 21B, the first sleeve 22A is not positioned in the axial direction by the flange portions 21B. The sleeves 22A and 22B are positioned in the axial direction by the ball 23, and are not positioned in the axial direction by anything other than the ball.

  With the above configuration, the first sleeve 22A is positioned in the axial direction and the radial direction on the holding portion 21A only by the fitting action between the holding groove 22a and the ball 23 corresponding thereto, and the second sleeve 22B is also The holding groove 22b and the ball 23 corresponding to the holding groove 22b are only positioned in the axial direction and the radial direction on the holding portion 21A. That is, the first sleeve 22A is automatically positioned with respect to the holding hole 21a, that is, the holding portion 21A by the fitting action of the holding groove 22a and the ball 23 corresponding thereto. Similarly, the second sleeve 22B is automatically positioned with respect to the holding hole 21b, that is, the holding portion 21A by the fitting action of the holding groove 22b and the ball 23 corresponding thereto. Therefore, the axial position of the holding groove 22a, the axial position of the holding hole 21a, and the axial position of the ball 23 are automatically positioned at the optimum positions. There is no risk of lowering durability and operating accuracy due to increased friction.

  In the present embodiment, a plurality of balls 23 arranged in the circumferential direction are fitted into the single holding grooves 22 a and 22 b provided in each sleeve 22. The plurality of balls 23 are positioned and held by a plurality of holding holes 21 a and 21 b provided in the holding portion 21 </ b> A of the holding body 21. In the illustrated example, four balls 23 are respectively held in the four first holding holes 22a constituting the first hole row. Similarly, the four balls 23 are respectively held in the four second holding holes 22b constituting the second hole row. As described above, the plurality of balls 23 held in each hole row are fitted into the common holding grooves 22a and 22b, so that the positions in the axial direction between the plurality of circumferential holding holes 22a and 22b, The backlash and backlash of each part resulting from the dispersion | variation in the holding | maintenance position and shape of the axial direction between the some ball | bowl 23 hold | maintained by this are reduced.

  In the present embodiment, the plurality of balls 23 arranged in the circumferential direction as described above are fitted into the lead grooves 10a to 10d, respectively. By configuring in this way, a plurality of balls 23 are fitted into the circumferential holding grooves 22a and 22b formed in the circumferential direction along the virtual plane P. Therefore, the stability of the axial and radial positioning states of the sleeves 22A and 22B is ensured. Moreover, the conversion performance and conversion accuracy of the motion conversion function as a ball screw are ensured, and the nut structure is configured compactly.

  In the holding portion 21A, the first hole row and the second hole row are provided at different positions in the axial direction. Each set of the plurality of balls 23 held in each hole row is fitted into a single common holding groove 22a, 22b. Here, each of the sleeves 22A and 22B has only a single holding groove 22a and 22b, respectively, and is fitted and positioned only on the plurality of balls 23 of each of the above sets. Therefore, it is only necessary to form a single holding groove 22a, 22b in one sleeve 22A, 22B. Furthermore, it is only necessary to ensure the shape accuracy of the single holding groove. When a plurality of holding grooves are formed in the axial direction with respect to one sleeve 22A, 22B, the pitch in the axial direction of the plurality of holding grooves needs to coincide with the pitch of the lead grooves 10d. On the other hand, in the present invention, since the single holding grooves 22a and 22b are processed into one sleeve 22A and 22B, for example, it is not necessary to set the interval between the holding grooves, the holding groove with respect to the sleeves 22A and 22B is formed. The advantage of easy processing is obtained.

  Further, the first sleeve 22A and the second sleeve 22B are individually attached to the holding portion 21A of the holding body 21 and are fitted to the plurality of balls 23 held in the corresponding hole rows. Thus, not only can the friction increase due to the slight difference in position between the corresponding holding hole and the holding groove as described above be avoided, but also the first holding hole 21a provided at a different position in the axial direction. Dimensional error between each hole row of the second holding hole 21b, fitting mode of the ball 23 held in each hole row to the first holding groove 22a and the lead grooves 10a to 10d, and the second holding The backlash between the lead screw 10 and the holding body 21 is reduced as a whole because the backlash at each place is compensated for each other due to the difference in the fitting mode with respect to the groove 22b and the lead grooves 10a to 10d.

  FIG. 7 is a longitudinal sectional view showing an electric actuator using the ball screw 1 of the first to third embodiments. The electric actuator includes a motor 2, a lead screw 10, and a nut 20 that is screwed into the lead screw 10. The lead screw 10 is connected to the output shaft 2 a of the motor 2 through the shaft coupling 3 and the joint rod 5 supported by the bearing 4. The flange portion 21B of the holding body 21 of the nut 20 is fixed to the base end of the cylindrical drive shaft 8 guided by the guide structure such as the bush 7 using the fixing screw 6 inserted through the through hole 21c. . The drive shaft 8 is guided so as to be movable only in the axial direction of the lead screw 10 and is guided so as not to rotate in the circumferential direction, so that the drive shaft 8 is driven in the axial direction by the ball screw 1. Here, since the inner surface of the shaft hole of the drive shaft 8 and the sleeves 22A and 22B are not in contact with each other, the sleeves 22A and 22B are not subjected to external axial and radial restraining forces.

The lead of the ball screw 1 of the first embodiment is set to 15 mm, incorporated in the electric actuator, the weight of 0.5 kg is indirectly mounted on the drive shaft 8, the axial direction is fixed in the vertical direction, and the drive shaft The controller 2 controls the motor 2 so that the moving stroke of 8 is 56 mm, the maximum speed is 180 mm / s, and the maximum acceleration is about 0.2 G (2014 mm / s ² ), and the reciprocating operation is continuously performed 5 million times. I was able to. The total travel distance was 560 km. At this time, abnormal wear of each part was not observed.

In addition, a weight of 1.5 kg is indirectly mounted on the drive shaft 8 of the same electric actuator as described above, the axial direction is fixed horizontally, the travel stroke of the drive shaft 8 is 56 mm, the maximum speed is 180 mm / s, the maximum The motor 2 was controlled by the controller so that the acceleration was about 0.2 G (2014 mm / s ² ), and the reciprocating operation could be continuously performed 5 million times. The total travel distance was 560 km. At this time, abnormal wear of each part was not observed.

  As described above, it was confirmed that the ball screw 1 of the present embodiment has durability enough to withstand 5 million tests. Further, when the repetition accuracy of the moving distance when moving the 10 lead (150 mm) of the drive shaft 8 was measured continuously for four days and nights, as a result of removing the temperature factor, the width of the variation of the moving distance was within 5 μm, and the average It became about 3 μm. Therefore, it was confirmed that the ball screw 1 of this embodiment has sufficient operation accuracy.

  In addition, the ball screw nut and the ball screw of the present invention are not limited to the above-described illustrated examples, and it is needless to say that various modifications can be made without departing from the scope of the present invention. For example, in each of the embodiments described above, the lead groove formed in the lead screw 10 is an R groove (circular groove), but any suitable groove such as a trapezoidal groove or a V-shaped groove can be used as long as the ball 23 is fitted. It may have a shape. Moreover, although it is preferable not only to have four lead grooves 10a to 10d as in the above embodiment, but to have two or more lead grooves, it may have an arbitrary number of one or more lead grooves. Good. Furthermore, the holding grooves 22a and 22b may have any shape that circulates in the circumferential direction, and need not be formed completely along the virtual plane P orthogonal to the axis 10x as in the illustrated example.

DESCRIPTION OF SYMBOLS 1 ... Ball screw, 2 ... Motor, 3 ... Shaft coupling (coupling), 4 ... Joint rod, 5 ... Bearing, 6 ... Fixing screw, 7 ... Bush, 8 ... Drive shaft, 10 ... Lead screw, 10a-10d ... Lead groove, 20 ... nut, 21 ... holding body, 21A ... holding portion, 21B ... flange portion, 21a, 21b ... holding hole, 21a ... first (hole row) holding hole, 21b ... second (hole row) ) Holding hole, 22A ... first sleeve, 22B ... second sleeve, 22a, 22b ... holding groove, 23 ... ball

Claims (11)

A nut for a ball screw attached to a lead screw having a spiral lead groove,
A ball that fits into the lead groove;
A holding body having a cylindrical holding portion having a holding hole for holding the ball in a rollable manner;
The holding body is mounted on the outer peripheral surface of the holding portion in a manner in which the position is not restrained in the axial direction, and has a single circular holding groove into which the ball held in the holding hole is fitted. A sleeve having
The holding portion includes the first holding hole and the second holding hole provided at different positions in the axial direction,
As the sleeve, a first sleeve having the holding groove that fits into the ball held in the first holding hole, and the holding that fits into the ball held in the second holding hole. A second sleeve with a groove,
The first sleeve and the second sleeve are adjacent to each other through a gap;
The ball screw nut, wherein the first sleeve and the second sleeve are attached to the holding portion in a state where the positions are not restrained from each other. The holding portion includes a hole row in which a plurality of holding holes are arranged in a circumferential direction,
The ball screw nut according to claim 1, wherein a plurality of balls held in a plurality of holding holes belonging to the hole row are fitted in the single holding groove. The holding portion is provided as a first hole row composed of the plurality of holding holes arranged in the circumferential direction as the hole row, and at a position shifted in the axial direction with respect to the first hole row. And a second hole row comprising the plurality of holding holes arranged in the circumferential direction,
The first sleeve has the holding groove fitted to the ball held in the plurality of holding holes belonging to the first hole row,
The second sleeve has the holding groove that fits into the ball held in the plurality of holding holes belonging to the second hole row,
The ball screw nut according to claim 1.   The ball screw nut according to any one of claims 1 to 3, wherein the balls are fitted one by one into the plurality of holding holes.   3. The ball screw nut according to claim 1, wherein the holding body has an external mounting portion having mounting means that can be mounted on another member.   The external mounting portion is a flange portion that protrudes in an axial direction and a radial direction with respect to the holding portion on a side opposite to the side on which the second sleeve is disposed with respect to the first sleeve, The ball screw nut according to claim 5, wherein the flange portion is adjacent to the first sleeve via a gap.   The ball screw according to any one of claims 1 to 6, wherein a thickness Tr of the holding portion corresponding to a penetration depth of the holding hole is larger than a depth Dg of the holding groove of the sleeve. Nuts. A ball screw comprising: the ball screw nut according to any one of claims 1 to 7; and a lead screw to which the ball screw nut is attached and having a lead groove into which the ball is fitted. And
A ball screw, wherein a maximum contact angle α of the ball with respect to the holding groove along the axial direction is larger than a lead angle β of the lead groove. A ball screw comprising: the ball screw nut according to any one of claims 1 to 6; and a lead screw to which the ball screw nut is attached and having a lead groove into which the ball is fitted. And
The lead screw has n lead grooves (n is a natural number of 2 or more),
The holding portion includes n holding holes arranged in a circumferential direction corresponding to each of the n-shaped lead grooves,
The n number of balls respectively held in the n number of holding holes are fitted in each of the n number of lead grooves, and are fitted together in the single holding groove of the sleeve. Ball screw to play. A ball screw comprising a lead screw having a spiral lead groove, and a ball screw nut attached to the lead screw,
The nut for the ball screw is
A ball that fits into the lead groove;
A cylindrical holding portion having a holding hole for holding the ball in a rollable manner, and an external mounting portion fixedly attached to another member that is movable relative to the lead screw in the axial direction. Holding body,
The holding body is mounted on the outer peripheral surface of the holding portion in a manner in which the position is not restrained in the axial direction, and has a single circular holding groove into which the ball held in the holding hole is fitted. has, seen including a, a sleeve not being bound to the other member,
The holding portion includes the first holding hole and the second holding hole provided at different positions in the axial direction,
As the sleeve, a first sleeve having the holding groove that fits into the ball held in the first holding hole, and the holding that fits into the ball held in the second holding hole. A second sleeve with a groove,
The first sleeve and the second sleeve are adjacent to each other through a gap;
The ball screw, wherein the first sleeve and the second sleeve are attached to the holding portion in a state where the positions are not restrained from each other . The length of the first sleeve and the second sleeve, respectively, claim 8-10, characterized in that less than the pitch between the first holding hole and the second retaining hole The ball screw according to one item.

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