Ball screw

Abstract

A ball screw includes: a screw shaft having a first helical screw groove provided on the outer peripheral surface; a nut attached to the outer peripheral side of the screw shaft, having a helical second screw groove provided on the inner peripheral surface, movable in the longitudinal direction of the screw shaft, and having a long hole passing through in the radial direction; a plurality of balls rolling on a rolling path formed between the first screw groove and the second screw groove; and a top member attached to the nut so as to cover the long hole, and provided with a circulation path for guiding the balls so that the balls pass over the screw thread of the first screw shaft and enter the adjacent rolling path. The top member includes: a first member provided with a first recessed groove constituting a part of the circulation path; a second member that is provided with a second recessed groove constituting a part of the circulation path, and that forms a circulation path by being combined with the first member; a grease-feeding member having a contact part that is exposed to the circulation path side and that comes into contact with the balls; and a third member for holding the grease-feeding member so as to cover the outer-diameter side of the grease-feeding member.

Description

ball screw

[0001] The present disclosure relates to a ball screw.

[0002] BACKGROUND ART Ball screws are known that include a screw shaft, a nut, a plurality of balls, and a bearing member that circulates the balls (see, for example, Patent Documents 1, 2, 3, and 4).

[0003] JP 2002-54710 A JP 2015-232346 A JP 2018-40455 A JP 2010-71411 A

[0004] Ball screws are required to ensure smooth ball rolling and circulation over a long period of time, and also to improve workability during maintenance and assembly.

[0005] Therefore, one of the objects is to provide a ball screw that can improve workability while ensuring smooth rolling and circulation of balls over a long period of time.

[0006] A ball screw according to the present disclosure comprises a threaded shaft having a first helical thread groove on its outer peripheral surface, a nut attached to the outer peripheral side of the threaded shaft, having a second helical thread groove on its inner peripheral surface, and having an elongated hole extending radially therethrough, movable in the longitudinal direction of the threaded shaft, a plurality of balls that roll in rolling paths formed between the first and second thread grooves, and a bearing member attached to the nut so as to cover the elongated hole and provided with a circulation path that guides the balls so that they climb over the threads of the first threaded shaft and enter adjacent rolling paths. The bearing member includes a first member provided with a first groove that forms a part of the circulation path, a second member provided with a second groove that forms a part of the circulation path and combined with the first member to form the circulation path, a lubrication member having a contact portion exposed on the circulation path side that contacts the balls, and a third member that holds the lubrication member so as to cover the outer diameter side of the lubrication member.

[0007] According to the above-described ball screw, it is possible to ensure smooth rolling and circulation of the balls over a long period of time, while improving workability.

[0008] FIG. 1 is a schematic perspective view of a ball screw according to a first embodiment of the present disclosure. FIG. 2 is a schematic side view of the ball screw shown in FIG. 1. FIG. 3 is a schematic cross-sectional view of a portion taken along the line III-III in FIG. 1. FIG. 4 is a schematic perspective view of a nut included in the ball screw. FIG. 5 is a schematic perspective view of the exterior of a link member. FIG. 6 is an exploded perspective view of the link member. FIG. 7 is a schematic cross-sectional view of a portion of the link member cut away. FIG. 8 is a schematic perspective view of the link member as viewed from the inner diameter side of the nut. FIG. 9 is a schematic perspective view of a first member and a second member combined together. FIG. 10 is a schematic perspective view of a first member and a second member combined together. FIG. 11 is a schematic perspective view of the first member. FIG. 12 is a schematic perspective view of the second member. FIG. 13 is a schematic perspective view of a third member.

[0009] [Summary of the embodiment] A ball screw of the present disclosure includes a threaded shaft having a first helical thread groove on its outer peripheral surface, a nut attached to the outer peripheral side of the threaded shaft, having a second helical thread groove on its inner peripheral surface, and having an elongated hole extending radially therethrough, movable in the longitudinal direction of the threaded shaft, a plurality of balls that roll in rolling paths formed between the first and second thread grooves, and a bearing member attached to the nut so as to cover the elongated hole and provided with a circulation path that guides the balls so that they climb over the threads of the first threaded shaft and enter adjacent rolling paths. The bearing member includes a first member provided with a first groove that forms a part of the circulation path, a second member provided with a second groove that forms a part of the circulation path and combined with the first member to form the circulation path, a lubrication member having a contact portion exposed on the circulation path side that contacts the balls, and a third member that holds the lubrication member so as to cover the outer diameter side of the lubrication member.

[0010] According to the ball screw of the present disclosure, the bearing member is not composed of a single component, but is composed of a first member, a second member, a third member, and a lubrication member. The circulation path is formed by combining the first groove and the second groove. This allows components other than the lubrication member to be selected and combined from appropriate materials and shapes depending on the functionality required of the circulation path, ease of installation, and the like. The lubrication member has a contact portion exposed to the circulation path that contacts the balls, allowing lubrication to be applied to the balls passing through the circulation path via this contact portion. This ensures smooth ball rolling and circulation over a long period of time. Furthermore, the third member is positioned to cover the outer diameter side of the lubrication member, preventing the lubrication member from being exposed to the outer diameter side, thereby preventing the lubrication member from drying out. Because the lubrication member is held by the third member, the third member can be removed from the nut when replacing the lubrication member. This allows the lubrication member to be replaced without removing the first and second members from the nut, thereby reducing the risk of an increase in assembly steps and improving workability. As described above, the ball screw can improve workability while ensuring smooth ball rolling and circulation over a long period of time.

[0011] In the ball screw, the greasing member may be plate-shaped. This allows the greasing member to be disposed with its thickness oriented in the radial direction of the ball screw, thereby preventing the greasing member from becoming too large in volume, particularly in the radial direction, and allowing a relatively large amount of lubricating oil to be impregnated into the greasing member. Furthermore, the greasing member can be made easier to handle.

[0012] In the above-described ball screw, the grease supply member may be held so as to be sandwiched between the third member and the second member. This allows the position of the grease supply member to be stably maintained within the bearing member. Therefore, the balls can be greased more stably for a long period of time.

[0013] In the above-described ball screw, the contact portion may have a protruding region that protrudes toward the circulation path. The second member may be provided with a housing groove that houses the protruding region. This allows lubricating oil to gradually seep out from the protruding region and grease the balls. In this case, since the protruding region is housed in the housing groove, it is possible to stably hold the protruding region and prevent displacement of the grease supply position. Therefore, it is possible to more reliably grease the balls over a long period of time.

[0014] In the above-described ball screw, the protruding length of the protruding region may be 30% to 70% of the diameter of the ball. This ensures reliable contact between the ball and the protruding region. Therefore, the ball can be more reliably lubricated. More preferably, the protruding length of the protruding region is selected to be 40% to 60% of the diameter of the ball.

[0015] In the above-described ball screw, the third member may be provided with an accommodating recess for accommodating the grease supply member. This allows the grease supply member to be fitted into the accommodating recess provided in the third member, thereby enabling the grease supply member to be held more stably. Furthermore, the third member can be attached by fitting the grease supply member into the accommodating recess, improving workability.

[0016] In the above-described ball screw, the first member and the third member may each be attached to the nut by a screw. The second member may be sandwiched between the first member and the third member. This allows the first member and the third member to be securely fixed to the nut by the screw, and the first member and the third member to be removed by turning the screw. Furthermore, since the second member is sandwiched between the first member and the third member, it can be more securely fixed to the nut. In other words, adopting such a configuration makes it easy to attach and detach the bridge member. This also makes it easy to replace the grease supply member, etc. Therefore, workability can be further improved.

[0017] In the above-mentioned ball screw, a plurality of bearing members may be provided at intervals in the circumferential direction. In this way, the plurality of balls can be smoothly circulated by the plurality of bearing members. Therefore, the balls can be circulated more smoothly.

[0018] [Specific Example of Embodiment] Next, an example of a specific embodiment of the ball screw of the present disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding parts are designated by the same reference numerals, and description thereof will not be repeated.

[0019] (Embodiment 1) First, embodiment 1, which is an embodiment of the present disclosure, will be described. Fig. 1 is a schematic perspective view of a ball screw in embodiment 1 of the present disclosure. Fig. 2 is a schematic side view of the ball screw shown in Fig. 1. Fig. 2 is a view seen in the opposite direction to the direction of arrow Y shown in Fig. 1. Fig. 3 is a schematic cross-sectional view of a portion when cut at the cross section indicated by III-III in Fig. 1. In Fig. 1 and the subsequent figures, the direction indicated by arrow Z is the longitudinal direction of the screw shaft, which will be described later, and the directions indicated by arrow X and arrow Y are radial directions. The direction indicated by arrow X and the direction indicated by arrow Y are orthogonal to each other.

[0020] 1, 2, and 3, a ball screw 10a according to the first embodiment includes a screw shaft 11a, a nut 12a, a plurality of balls 13a as rolling elements, and a plurality of, in this embodiment, three, top members 14a. The balls 13a may be, for example, steel balls. The screw shaft 11a has a shape extending in the longitudinal direction (Z direction). A first spiral screw groove 16a is provided on the outer peripheral surface of the screw shaft 11a over the entire longitudinal area. When the ball screw 10a is viewed from the side, a first screw thread 17a is disposed between adjacent first screw grooves 16a.

[0021] Figure 4 is a schematic perspective view showing the nut 12a included in the ball screw 10a. Also referring to Figure 4, the nut 12a is attached to the outer periphery of the screw shaft 11a. The nut 12a includes a hollow cylindrical tubular portion 21a and a flange portion 22a disposed on one longitudinal side of the tubular portion 21a. The flange portion 22a has a rectangular shape when viewed from the thickness direction, which is the longitudinal direction of the screw shaft 11a, specifically, a square shape with four chamfered corners. The nut 12a has a shape in which the tubular portion 21a and the flange portion 22a are connected in the longitudinal direction.

[0022] The nut 12a, specifically the cylindrical portion 21a included in the nut 12a, is provided with a plurality of radially penetrating elongated holes 23a, 23b, and 23c (three in this embodiment). The cylindrical portion 21a is provided with three recesses 24a, each recessed inward on the outer circumferential surface, at intervals of 120 degrees in the circumferential direction. The elongated holes 23a, 23b, and 23c are provided in the regions where the three recesses 24a are located. The elongated holes 23a are each provided at intervals in the circumferential direction. In this embodiment, the elongated holes 23a, 23b, and 23c are also provided at intervals in the axial direction (longitudinal direction (Z direction)). The elongated holes 23a, 23b, and 23c are each provided at an angle to the axial direction. Each of the elongated holes 23a, 23b, and 23c opens so as to straddle two adjacent first screw grooves 16a when viewed from the outer diameter side when the nut 12a is attached to the outer periphery of the screw shaft 11a. The two first screw grooves 16a straddled by the elongated holes 23a, 23b, and 23c are offset by one. A ball member 14a that circulates the balls 13a is attached to each of the elongated holes 23a, 23b, and 23c. This will be described in detail later. A plurality of threaded holes for attaching the ball members 14a are provided around the elongated holes 23a, 23b, and 23c. Four through-holes are provided near the four corners of the flange portion 22a for attaching other components to the nut 12a.

[0023] A second helical screw groove 18a is provided on the inner peripheral surface of the nut 12a. A plurality of balls 13a are arranged in a rolling path 19a formed between the first screw groove 16a and the second screw groove 18a. The balls 13a roll in the rolling path 19a. The nut 12a is movable in the longitudinal direction of the screw shaft 11a as the balls 13a circulate while rolling. The nut 12a is capable of linear reciprocating motion relative to the screw shaft 11a.

[0024] The nut 12a includes a first annular seal ring 25a attached to one longitudinal side where the cylindrical portion 21a is located, and a second annular seal ring 26a attached to the other longitudinal side where the flange portion 22a is located. The first seal ring 25a is fitted into a first fitting recess 27a provided on the inner periphery of the cylindrical portion 21a, and the second seal ring 26a is fitted into a second fitting recess 28a provided on the inner periphery of the flange portion 22a. The inner periphery of the first seal ring 25a and the second seal ring 26a is formed with a thread groove that engages with the first thread groove 16a of the screw shaft 11a.

[0025] Next, the configuration of the bearing member 14a will be described. As described above, the bearing member 14a is attached to the nut 12a so as to cover each of the three elongated holes 23a, 23b, and 23c provided in the nut 12a. The bearing member 14a is provided with a circulation path 29a that guides the balls 13a in a given first screw groove 16a so that the balls 13a move over the threads of the screw shaft 11a and enter the adjacent first screw groove 16a. The ball screw 10a is provided with a rake 15a that sequentially supplies the balls 13a from the rolling path 19a to the circulation path 29a.

[0026] The support member 14a includes a first member 31a, a second member 32a, a third member 33a, and a greasing member 34a. The first member 31a, the second member 32a, and the third member 33a are made of rigid materials, such as metal. Specifically, the first member 31a, the second member 32a, and the third member 33a are made of at least one of a resin such as polyacetal, carbon steel, and stainless steel.

[0027] FIG. 5 is a schematic perspective view showing the appearance of the top member 14a. FIG. 6 is an exploded perspective view of the top member 14a. FIG. 7 is a schematic cross-sectional view of a portion of the top member 14a. FIG. 8 is a schematic perspective view of the top member 14a as seen from the inner diameter side of the nut 12a. FIGS. 9 and 10 are schematic perspective views showing the first member 31a and the second member 32a assembled together. FIGS. 9 and 10 are views seen from different angles. FIG. 11 is a schematic perspective view of the first member 31a. FIG. 12 is a schematic perspective view of the second member 32a. FIG. 13 is a schematic perspective view of the third member 33a. For ease of understanding, FIGS. 5, 7, and 8 also show a plurality of rolling balls 13a, and FIG. 9 also shows the first screw 42a.

[0028] 5 to 13, the first member 31a is provided with a first groove 36a that constitutes part of the circulation path 29a. The first member 31a also has a first contact surface 37a that comes into contact with the second member 32a when combined with the second member 32a. The second member 32a is provided with a second groove 38a that constitutes part of the circulation path 29a. The second member 32a has a second contact surface 39a that comes into contact with the first member 31a when combined with the first member 31a. The shape of the second contact surface 39a corresponds to the shape of the first contact surface 37a. By combining the first member 31a and the second member 32a so that the first contact surface 37a and the second contact surface 39a come into contact with each other, the circulation path 29a, which is composed of the first groove 36a and the second groove 38a, is formed.

[0029] The first member 31a has a first mounting hole 41a for mounting the first member 31a to the nut 12a. The first mounting hole 41a is circular. The first mounting hole 41a has a shape with a portion of a different diameter for receiving the body of a first mounting screw 42a and the head of the first screw 42a. The first screw 42a and a second screw 47a (described later) are, for example, flat head screws. The first screw 42a is configured so that the head of the first screw 42a fits within the first mounting hole 41a when the first screw 42a is inserted into the first mounting hole 41a and tightened. The second member 32a also has a receiving groove 43a for receiving a protruding region 53a of a contact portion 52a of a lubrication member 34a (described later).

[0030] The grease supply member 34a is plate-shaped. More specifically, the grease supply member 34a is flat. The grease supply member 34a is also called an oil-retaining member. The grease supply member 34a is made of, for example, a member impregnated with lubricating oil. Specifically, the grease supply member 34a may be made of, for example, a porous sintered resin member that has been heat-molded and impregnated with a lubricant. Alternatively, a solid lubricant may be used that has been obtained by mixing a powder of a sintered resin member with a lubricant and then heat-molding the mixture.

[0031] The grease supply member 34a includes a flat plate portion 51a and a contact portion 52a exposed on the circulation path 29a side and contacting the ball 13a. The flat plate portion 51a is polygonal when viewed in the thickness direction. The contact portion 52a has a protruding region 53a protruding from the flat plate portion 51a toward the circulation path 29a side. Lubricating oil is supplied to the ball 13a by seeping out from the protruding region 53a. The lubricating oil impregnated in the flat plate portion 51a is gradually supplied to the protruding region 53a. In this embodiment, the protruding length L of the protruding region 53a is 30% to 70% of the diameter D of the ball 13a. In this embodiment, the protruding length L of the protruding region 53a is 40% to 60% of the diameter D of the ball 13a (see particularly FIGS. 5 and 6 ). In addition, in this embodiment, the protruding length of the protruding region 53a toward the circulation path 29a, as indicated by the arrow P in Figure 7, is, for example, 40% to 60% of the protruding length L of the protruding region 53a in Figure 6.

[0032] The third member 33a holds the grease supply member 34a by covering the outer diameter side of the grease supply member 34a. The third member 33a has a storage recess 45a that stores the grease supply member 34a. The storage recess 45a is recessed to conform to the outer shape of the plate-shaped grease supply member 34a, mainly the outer shape of the flat plate portion 51a. The third member 33a has a second mounting hole 46a that mounts the third member 33a to the nut 12a. The second mounting hole 46a is circular. Similar to the first mounting hole 41a, the second mounting hole 46a has a shape with a different diameter portion so that the body of the second mounting screw 47a passes through and the head of the second mounting screw 47a is engaged. The third member 33a also has a third contact surface 48a that contacts the first contact surface 37a of the first member 31a during mounting.

[0033] The first member 31a is attached to the nut 12a with a first screw 42a. The third member 33a is attached to the nut 12a with a second screw 47a. The second member 32a is sandwiched between the first member 31a and the third member 33a. The grease supply member 34a is sandwiched between the second member 32a and the third member 33a.

[0034] The installation of the above-mentioned link member 14a can be briefly explained as follows. The first member 31a and the second member 32a are assembled so that the first contact surface 37a and the second contact surface 39a are in contact with each other, and the first member 31a is fixed to the nut 12a using the first screw 42a. In this case, the body of the first screw 42a is passed through the first mounting hole 41a, and the first screw 42a is attached using a threaded hole provided in the nut 12a to fix the first member 31a. Next, the grease supply member 34a is accommodated in the accommodation recess 45a, and the third member 33a is attached from the outer diameter side so that the protruding region 53a of the contact portion 52a is accommodated in the accommodation groove 43a of the second member 32a. Alternatively, the grease supply member 34a is placed from the outer diameter side so that the protruding region 53a of the contact portion 52a is received in the receiving groove 43a of the second member 32a, and the third member 33a is attached from the outer diameter side so that the grease supply member 34a is received in the receiving recess 45a. In these cases, the grease supply member 34a is sandwiched radially between the second member 32a and the third member 33a. Then, the third member 33a is fixed to the nut 12a using the second screw 47a so that the first contact surface 37a and the third contact surface 48a are in contact with each other. In this case, the barrel of the second screw 47a is passed through the second mounting hole 46a, and the second screw 47a is attached using a threaded hole provided in the nut 12a to fix the third member 33a.

[0035] In the ball screw 10a configured as described above, the ball member 14a is not composed of a single component, but is composed of a first member 31a, a second member 32a, a third member 33a, and a grease supply member 34a. The circulation path 29a is formed by combining the first groove 36a and the second groove 38a. This allows components other than the grease supply member 34a to be selected and combined with appropriate materials and shapes depending on the functionality and ease of installation required for the circulation path 29a. The grease supply member 34a has a contact portion 52a exposed to the circulation path 29a and in contact with the balls 13a, allowing grease to be supplied to the balls 13a passing through the circulation path 29a via this contact portion 52a. This ensures smooth rolling and circulation of the balls 13a for a long period of time. Furthermore, the third member 33a is positioned to cover the outer diameter side of the grease supply member 34a, preventing the grease supply member 34a from being exposed to the outer diameter side, thereby preventing the grease supply member 34a from drying out. Because the grease supply member 34a is held by the third member 33a, the third member 33a can be removed from the nut 12a when replacing the grease supply member 34a. This allows the grease supply member 34a to be replaced without removing the first member 31a and the second member 32a from the nut 12a, reducing the risk of an increase in assembly man-hours and improving workability. As described above, the ball screw 10a can improve workability while ensuring smooth rolling and circulation of the balls 13a over a long period of time.

[0036] In this embodiment, the grease supply member 34a is plate-shaped. Therefore, by arranging the thickness of the grease supply member 34a in the radial direction of the ball screw 10a, it is possible to impregnate the grease supply member 34a with a relatively large amount of lubricating oil while suppressing an increase in volume, particularly in the radial direction. This also makes the grease supply member 34a easier to handle.

[0037] In this embodiment, the grease supply member 34a is held between the third member 33a and the second member 32a. This allows the grease supply member 34a to maintain a stable position within the block member 14a. This allows the ball 13a to be greased more stably over a long period of time.

[0038] In this embodiment, the contact portion 52a has a protruding region 53a that protrudes toward the circulation path 29a. The second member 32a has a housing groove 43a that houses the protruding region 53a. Therefore, lubricating oil gradually seeps out from the protruding region 53a and can be supplied to the ball 13a. In this case, since the protruding region 53a is housed in the housing groove 43a, the protruding region 53a can be stably held and the misalignment of the lubrication position can be suppressed. Therefore, the ball 13a can be more reliably lubricated over a long period of time.

[0039] In this embodiment, the protruding length L of the protruding region 53a is 30% to 70% of the diameter D of the ball 13a. This allows the ball 13a to be in contact with the protruding region 53a more reliably. This allows the ball 13a to be greased more reliably.

[0040] In this embodiment, the third member 33a is provided with an accommodating recess 45a that accommodates the grease supply member 34a. Therefore, the grease supply member 34a can be fitted into the accommodating recess 45a provided in the third member 33a and accommodated therein, thereby enabling the grease supply member 34a to be held more stably. Furthermore, the grease supply member 34a can be fitted into the accommodating recess 45a when attaching the third member 33a, thereby improving workability.

[0041] In this embodiment, the first member 31a and the third member 33a are attached to the nut 12a by screws 42a and 47a, respectively. The second member 32a is sandwiched between the first member 31a and the third member 33a. Therefore, the first member 31a and the third member 33a can be securely fixed to the nut 12a by the screws 42a and 47a, and the first member 31a and the third member 33a can be removed by turning the screws 42a and 47a. Furthermore, because the second member 32a is sandwiched between the first member 31a and the third member 33a, it can be more securely fixed to the nut 12a. In other words, adopting this configuration facilitates the attachment and detachment of the link member 14a. This also facilitates the replacement of the grease supply member 34a, etc., thereby further improving workability.

[0042] In this embodiment, a plurality of the ball members 14a are provided at intervals in the circumferential direction, so that the plurality of balls 13a can be circulated smoothly by the plurality of the ball members 14a, thereby enabling the balls 13a to circulate more smoothly.

[0043] (Other embodiments) In the above embodiment, three elongated holes and three top members are provided, but this is not limited to this, and the ball screw may have two elongated holes and two top members, or four or more elongated holes and two top members.

[0044] Furthermore, in the above embodiment, the contact portion and the rolling surface of the ball are in contact on the outer diameter side of the ball, but this is not limited to this, and the contact portion and the rolling surface of the ball may be in contact on one side of the axial direction of the ball.

[0045] In the above embodiment, the grease supply member is plate-shaped, but is not limited to this. The grease supply member may be, for example, block-shaped or spherical.

[0046] Furthermore, in the above embodiment, the first member and the third member are attached to the nut side with screws, but this is not limited thereto, and the first member and the third member may be attached to the nut side by, for example, a snap fit.

[0047] The present invention is intended to cover a wide range of applications, including those related to the present invention, including those related to the present invention.

[0048] 10a ball screw, 11a screw shaft, 12a nut, 13a ball, 14a bearing member, 15a scoop, 16a first screw groove, 17a first screw thread, 18a second screw groove, 19a rolling path, 21a cylindrical portion, 22a flange portion, 23a, 23b, 23c elongated hole, 24a recess, 25a first seal ring, 26a second seal ring, 27a first fitting recess, 28a second fitting recess, 29a circulation path, 31a first member, 32a second member, 33a third member, 34a greasing member, 36a first groove, 37a first contact surface, 38a second groove, 39a second contact surface, 41a first mounting hole, 42a screw (first screw), 43a accommodation groove, 45a Accommodating recess, 46a; second mounting hole, 47a; screw (second screw); 48a; third contact surface, 51a; contact portion, 52a; protruding region.

Claims

a nut attached to the outer periphery of the threaded shaft, the nut having a second spiral groove on its inner periphery, the nut being movable in the longitudinal direction of the threaded shaft and having an elongated hole passing through in the radial direction; a plurality of balls rolling in a rolling path formed between the first screw groove and the second screw groove; and a top member attached to the nut so as to cover the elongated hole, the top member having a circulation path for guiding the balls in a given first screw groove so that the balls pass over the threads of the threaded shaft and enter the adjacent first screw groove, the top member including: a first member having a first groove forming a part of the circulation path; a second member having a second groove forming a part of the circulation path and combining with the first member to form the circulation path; a lubrication member having a contact portion exposed to the circulation path side and contacting the balls; and a third member holding the lubrication member so as to cover the outer diameter side of the lubrication member.

2. The ball screw according to claim 1, wherein the greasing member is plate-shaped.

3. A ball screw according to claim 1 or 2, wherein the greasing member is held by being sandwiched between the third member and the second member.

4. A ball screw as described in any one of claims 1 to 3, wherein the contact portion has a protruding region that protrudes toward the circulation path, and the second member is provided with an accommodating groove that accommodates the protruding region.

5. The ball screw according to claim 4, wherein the protruding length of said protruding region is equal to or greater than 30% and equal to or less than 70% of the diameter of said ball.

6. A ball screw as set forth in any one of claims 1 to 5, wherein the third member is provided with a receiving recess for receiving the greasing member.

7. A ball screw as claimed in any one of claims 1 to 6, wherein the first member and the third member are each attached to the nut by a screw, and the second member is sandwiched between the first member and the third member.

8. A ball screw according to any one of claims 1 to 7, wherein a plurality of the top members are provided at intervals in the circumferential direction.

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