Ball screw device

Abstract

The present invention is provided with: a plurality of balls; a screw shaft (110) in which rolling grooves (111) for the balls are formed in a spiral shape on the outer peripheral surface; and a nut member (120) having a through-hole through which the screw shaft (110) passes, having a return groove (210) for circulating the plurality of balls around the screw shaft (110) only one circle on the inner peripheral surface (240) of the through-hole, and being screwed to the screw shaft (110) by means of the plurality of balls, the return groove (210) having: a load rolling groove (121) for rolling a load on the screw shaft (110); the guide rail (110) is opposite to a part of a rolling groove (111) of the screw shaft (110); and a circulation groove (220) that crosses the screw thread of the screw shaft (110) and connects both ends of the load rolling groove (121), the return groove (210) being provided adjacent to the opening edge of the through-hole of the nut member (120). An inclined portion (230) is provided at a corner portion where an inner peripheral surface (240) of the through-hole intersects with an axial end surface of the nut member (120), the inclined portion (230) being formed by cutting the corner portion (310) at a non-uniform width in the circumferential direction of the through-hole.

Description

Technical Field

[0001] The present invention relates to a ball screw device in which a nut member is provided with a ball endless circulation path corresponding to one circumference of a screw shaft. Background Art

[0002] A ball screw device is a mechanical element that can convert rotational motion and linear motion into each other. It is widely used in various machine tools, handling devices, industrial robots, etc. for the purpose of converting the rotational motion generated by a servo motor into linear motion. The ball screw device includes a screw shaft having a spiral rolling groove, a plurality of balls rolling in the rolling groove, and a nut member having a through hole for the screw shaft to pass through and an infinite circulation path for the plurality of balls to roll. The screw shaft and the nut member are screwed together via the plurality of balls. As a conventional ball screw device, various types of infinite circulation paths with different structures are known. Patent document 1 discloses a ball screw device having an infinite circulation path with a plurality of loops provided in the nut member, and the infinite circulation path sets one loop as one circle around the screw shaft.

[0003] In the ball screw device of patent document 1, a load rolling groove opposite to a part of the rolling groove of the screw shaft is formed on the inner peripheral surface of the through hole of the nut member, and a circulation groove connecting the beginning and the end of the load rolling groove is provided. The load rolling groove constitutes a load passage by being opposite to the rolling groove of the screw shaft, and the ball rolls in the load passage while carrying a load between the screw shaft and the nut member. On the other hand, the circulation groove is a load-free passage in which the ball rolls in a state free from the load, and an infinite circulation path of the ball is constructed by connecting the two ends of the load passage. The circulation groove allows the ball that reaches the end of the load passage to disengage from the rolling groove of the screw shaft and return to the beginning of the load passage over the thread teeth. That is, the circulation groove enables the ball rolling in the load passage to recover the amount of one lead of the rolling groove of the screw shaft, thereby the infinite circulation path provided in the nut member constitutes a loop of one week around the screw shaft.

[0004] In the ball screw device of Patent Document 1, the load rolling groove and the circulation groove are directly formed on the inner peripheral surface of the nut member, and in particular, the latter circulation groove is formed by cutting the inner peripheral surface of the nut member using a tool such as an end mill. In this cutting process, the tool is inserted from the axial direction relative to the through hole of the nut member, and the tool is used to cut into the inner peripheral surface of the through hole of the nut member in the radial direction, and the cutting depth is controlled to form the circulation groove.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2015-24471 Summary of the invention

[0008] Problems to be solved by the invention

[0009] As described above, the circulation groove allows the ball to disengage from the rolling groove of the screw shaft and pass over the thread teeth of the screw shaft. The circulation groove is not a passage separated from the screw shaft, but is formed as a passage open to the screw shaft.

[0010] Therefore, the balls rolling on the circulation grooves are likely to come into irregular contact with the threads of the screw shaft, and there is a concern that smooth ball circulation in the infinite circulation path may be hindered.

[0011] Taking into account preventing the balls rolling in the circulation groove from contacting the screw shaft as much as possible and ensuring that the balls move smoothly from the rolling groove of the screw shaft to the circulation groove, it is considered to provide an embracing portion at the opening edge of the circulation groove along the moving direction of the balls so that the opening width of the circulation groove open toward the screw shaft is narrower than the diameter of the balls.

[0012] Regarding this point, in patent document 1, when processing the nut member, a tool is inserted axially relative to the through hole of the nut member, and the tool is used to cut into the inner circumferential surface of the through hole of the nut member along the radial direction to form the circulation groove, so it is difficult to form the embracing portion at the opening edge of the circulation groove.

[0013] Solutions to Solve Problems

[0014] The present invention has been made in view of such a problem, and an object thereof is to provide a ball screw device that can realize smooth ball circulation in an endless circulation path even when a circulation groove is formed on the inner peripheral surface of a nut member by cutting.

[0015] The nut member is a block diagram of a block diagram of a screw shaft according to claim 1, wherein the nut member is a block diagram of a screw shaft having a plurality of rollers disposed on the nut member. The nut member is a block diagram of a screw shaft having a plurality of rollers disposed on the nut member. The block diagram of the screw shaft comprises a plurality of rollers disposed on the nut member. The nut member is a block diagram of a screw shaft having a plurality of rollers disposed on the nut member. The nut member is a block diagram of a screw shaft having a plurality of rollers disposed on the nut member.

[0016] Effects of the Invention

[0017] The ball screw device of the present invention has an inclined portion formed by cutting off the corner with an uneven width along the circumference of the through hole at the corner where the inner circumferential surface of the through hole formed in the nut member intersects with the axial end face of the nut member. Therefore, when the nut member is cut, the insertion angle of the cutting tool relative to the inner circumferential surface of the through hole will not be limited by the distance between the circulation groove and the axial end face, and the circulation groove can be cut at any insertion angle corresponding to the uneven width of the inclined portion. As a result, sufficient embrace can be formed in the circulation groove, and the ball that passes over the thread can be guided. Therefore, according to the ball screw device of the present invention, even if the circulation groove is formed by cutting on the inner circumferential surface of the nut member, smooth infinite circulation of the rolling balls can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a perspective view showing a ball screw device according to one embodiment of the present invention.

[0019] Figure 2 It is a cross-sectional view showing a nut member according to one embodiment of the present invention.

[0020] Figure 3 is a cross-sectional view showing the circulation groove.

[0021] Figure 4 It is a perspective view showing a nut member according to one embodiment of the present invention.

[0022] Figure 5 It is a perspective view showing a state where a nut member is being cut.

[0023] Figure 6This is a diagram showing a state in which a nut member according to an embodiment of the present invention is viewed from the axial direction.

[0024] Figure 7 It is an enlarged cross-sectional view of a nut member according to one embodiment of the present invention.

[0025] Figure 8 : is a graph showing the relationship between the cut-out width w of the inclined portion and the position θ in the circumferential direction.

[0026] Fig. 9 Graph showing the relationship between the surface depth h of the inclined portion and the circumferential position θ.

[0027] Fig.10 : is a graph showing the distance s of the circulation groove and the position θ in the circumferential direction.

[0028] Fig.11 yes Figure 6 Cross-sectional view along line III-III.

[0029] Fig.12 It is a cross-sectional view showing a state where the nut member is being cut.

[0030] Fig.13 It is an enlarged cross-sectional view showing the circulation groove when the nut member is cut.

[0031] Fig.14 This is a perspective view of a conventional nut member being cut.

[0032] Fig.15 This is an enlarged cross-sectional view showing a circulation groove when a conventional nut member is cut. DETAILED DESCRIPTION

[0033] Hereinafter, the ball screw device of the present invention will be described in detail with reference to the drawings.

[0034] Figure 1 1 is a perspective view showing a ball screw device 100 according to an embodiment of the present invention. The ball screw device 100 includes a screw shaft 110 having a rolling groove 111 for balls formed in a spiral shape on the outer peripheral surface, and a nut member 120 having a through hole for the screw shaft 110 to pass through and being screwed with the screw shaft 110 by means of a plurality of balls. The balls roll in a spiral shape between the screw shaft 110 and the nut member 120, so that when the screw shaft 110 is rotated relative to the nut member 120, the nut member 120 moves in the axial direction of the screw shaft 110, or when the nut member 120 is rotated relative to the screw shaft 110, the screw shaft 110 moves in the axial direction of the nut member 120.

[0035] Figure 2It is a cross-sectional view obtained by cutting the nut member 120 along the axial direction. A return groove 210 is provided on the inner circumferential surface 240 of the through hole of the nut member 120 so that the ball can circulate infinitely around the screw shaft 110. In the present embodiment, a pair of return grooves 210 are provided adjacent to the opening edge of the through hole of the nut member 120, and each return groove 210 is around the inner circumferential surface 240 of the through hole of the nut member. The return groove 210 includes a load rolling groove 121 formed on the inner circumferential surface 240 of the through hole of the nut member 120 and a circulation groove 220 connecting the two ends of the load rolling groove 121. It should be noted that, in the present embodiment, the return grooves 210 are provided at the opening edges at both ends of the axial direction in the through hole, but it can also be a structure in which the return groove 210 is provided only at the opening edge of either side.

[0036] The load rolling groove 121 is formed in a spiral shape opposite to a part of the rolling groove of the screw shaft 110, and the load rolling groove 121 is formed to have a length less than one circumference of the screw shaft. The load rolling groove 121 is opposite to the rolling groove 111 of the screw shaft 110 to form a load passage, and the ball rolls in the load passage while carrying a load between the screw shaft and the nut member.

[0037] On the other hand, the circulation groove 220 and the load rolling groove 121 are continuously formed on the inner circumferential surface 240 of the nut member 120, and the circulation groove 220 is formed by a groove deeper than the load rolling groove 121 in order to allow the ball to disengage from the rolling groove 111 of the screw shaft 110 and pass over the thread of the screw shaft 110. That is, the circulation groove 220 connects one end of the load rolling groove 121 with the other end in a manner that crosses the thread of the screw shaft 110. When the ball enters the circulation groove 220 from the load rolling groove 121, it is freed from the load and becomes a no-load state, and when it enters the load rolling groove 121 from the circulation groove 220, it is loaded again. That is, the circulation groove 220 is a no-load passage for the ball, and the two ends of the load passage are connected by the no-load passage to form an infinite circulation path around the screw shaft 110. Therefore, the nut member 120 in this embodiment has an infinite circulation path for the ball with two circuits.

[0038] Connecting parts (not shown) for connecting the balls with the load rolling groove 121 are provided at both ends of the circulation groove 220. The connecting parts are gently inclined relative to the circulation groove 220, so that the balls rolling in the load rolling groove 121 are freed from the load and gradually separated from the rolling groove of the screw shaft 110. Thus, the balls rolling in the load rolling groove 121 can smoothly enter the circulation groove 220 and pass over the thread teeth of the screw shaft 110.

[0039] Figure 3 It is a cross-sectional view of the circulation groove 220. Protrusions 221 continuously formed along the length direction of the circulation groove 220 are provided at both ends in the width direction of the circulation groove 220. The protrusions 221 are in a shape protruding toward the inner side of the circulation groove 220. The opening width of the embraced portion 222 formed by the pair of protrusions 221 is set to be narrower than the diameter of the ball. Therefore, when the ball that enters the circulation groove 220 from the end of the load rolling groove 121 passes over the thread teeth of the screw shaft 110, it is embraced by the embraced portion 220 and can pass over the thread teeth while avoiding contact with the thread teeth.

[0040] like Figure 2 as well as Figure 4 As shown, at the corner 310 where the inner circumferential surface 240 of the through hole intersects with the axial end face of the nut member 120, an inclined portion 230 is formed by a curved surface along the circumference of the through hole. The inclined portion 230 is used when the circulation groove 220 is cut on the nut member. The inclined portion 230 is formed by cutting the corner 310 with an uneven width. The inclined portion 230 is at least arranged at a position 180 degrees opposite to the formation position of the circulation groove 220 in the circumference of the through hole of the nut member 120. The uneven width of the inclined portion 230 includes the cutting width w and the surface depth h described later.

[0041] Figure 5 1 is a diagram showing a state in which a recirculation groove 220 is processed on a nut member 120 using a ball end mill 400 as a cutting tool. The ball end mill 400 uses a ball end mill with a thin neck root, and a spherical head 410 is formed at the front end of the shank 420 of the ball end mill 400. When the recirculation groove 220 is cut using the ball end mill 400, a temporary groove is pre-formed at the position where the recirculation groove 220 is formed. The cutting process applied to the recirculation groove 220 is performed by inserting the spherical head 410 of the ball end mill 400 into the temporary groove.

[0042] Figure 6 The state obtained by observing the nut member 120 from the axial direction is shown. The dotted line shows the circulation groove 220 formed in the nut member 120. The angle formed by the end 211 of one side of the circulation groove 220 and the end 212 of the other side relative to the center of the through hole is approximately 90 degrees. The circulation groove 220 connects the two ends of the load rolling groove formed in a spiral shape, so that the end 211 of one side of the circulation groove is closer to the axial end face of the nut member 120 than the end 212 of the other side (refer to Figure 4 ). Therefore, in Figure 6In the circulation groove 220 , the balls moving from one end 211 to the other end 212 gradually move away from the axial end surface of the nut member 120 .

[0043] Figure 7 Yes Figure 2 A magnified view of a portion of Figure 6 as well as Figure 7 As shown in FIG. 1 , the inclination angle of the inclined portion 230 relative to the axial end face of the nut member 120 is determined by the cut width w and the surface depth h of the inclined portion 230. Therefore, the inclination angle of the inclined portion 230 at a portion where the cut width w is wide and the surface depth h is small is relatively small. The cut width w and the surface depth h of the inclined portion 230 are adjusted according to the distance between the circulation groove 220 and the axial end face of the nut member 120.

[0044] exist Figure 6 In the example of FIG. 1 , the cut width w and the surface depth h of the inclined portion 230 at a position substantially 180 degrees opposite to the end 211 of one side of the circulation groove 220 in the circumferential direction of the through hole of the nut member are wider and the surface depth h is greater than that of other positions of the inclined portion 230 (refer to FIG. 1 ). Figure 7 ). That is, the cut-out width w and the surface depth h of the inclined portion 230 are maximum at a position 180 degrees opposite to the position of the circulation groove 220 closest to the axial end face of the nut member 120 in the circumferential direction of the through hole of the nut member 120. It should be noted that in the present embodiment, the cut-out width w and the surface depth h of the inclined portion 230 are maximum at a position 180 degrees opposite to the position of the circulation groove 220 closest to the axial end face, but it is not limited to this. As long as the cut-out width w and the surface depth h change continuously along the circumferential direction of the through hole of the nut member 120, the design can be appropriately changed. However, if Figure 7 As shown in FIG. 1 , the surface depth h of the inclined portion 230 is set to a size such that the inclined portion 230 does not interfere with the load rolling groove 121 .

[0045] Figure 8 as well as Fig. 9 is a graph showing the circumferential position θ of the nut member 120 (see Figure 6 ) is a graph showing the relationship between the cut-out width w and the surface depth h of the inclined portion 230. In addition, Fig.10 : is a graph showing the relationship between the circumferential position θ of the nut member 120 and the distance s of the return groove 210 relative to the axial end surface of the nut member 120. Figure 7 As shown in FIG. 1 , the distance s refers to the formation position of the return groove 210 including the circulation groove 210 from the axial end surface. Fig.10The dashed line represents the load rolling groove 121 as a part of the return groove 210, and the part outside the dashed line represents the circulation groove 220. As shown in these diagrams, the cut-out width w and the surface depth h of the inclined portion 230 are maximum at approximately the same circumferential position θ. The position where the cut-out width w and the surface depth h of the inclined portion 230 are maximum is approximately 180 degrees opposite to the position of the axial end face of the return groove 210 closest to the nut member 120 in the circumferential direction of the nut member 120.

[0046] In addition, with respect to the circumferential position θ of the nut member 120, the inclined portion 230 is disposed at a position 180 degrees opposite to the circulation groove 220, and on the other hand, is not disposed at a position overlapping the circulation groove 220. In addition, with respect to the circumferential position θ, the cut-out width w and the surface depth h of the inclined portion 230 decrease as it approaches the formation position of the circulation groove 220. That is, the cut-out width w and the surface depth h of the inclined portion 230 continuously change along the circumference of the nut member 120.

[0047] Fig.11 yes Figure 6 The sectional view is a III-III line view showing a state where the end 211 of one side of the circulation groove 220 is being cut. At this time, since the cutting width w and the surface depth h of the inclined portion 230 at a position approximately 180 degrees opposite to the end 211 are formed large, the ball end mill 400 can be erected to a nearly vertical state relative to the inner peripheral surface 240 of the nut member 120. Fig.12 The figure shows a state where the middle position of the circulation groove 220 is being cut. The processing of the middle position of the circulation groove 220 is performed by inserting the spherical head 410 deeper into the inner peripheral surface of the nut member 120 than when processing the end 211 of one side of the circulation groove 220 .

[0048] Fig.13 1 is an enlarged view showing the circulation groove 220 when cutting is performed using a ball end mill 400. The inner peripheral surface of the nut member 120 is cut using the ball end mill 400, and a circulation groove 220 having the same curvature as the spherical head 410 is formed on the inner peripheral surface 240 of the nut member 120. In addition, as described above, an embracing portion 222 formed by a pair of protrusions 221 is formed in the circulation groove 220.

[0049] In this regard, the inclined portion 230 is not provided in the conventional nut member, and when the nut member is cut, the shank 420 of the ball end mill 400 contacts the corner portion 310 of the nut member (see Fig.14). Therefore, in the conventional nut member, the ball end mill 400 cannot be inserted in a state close to vertical relative to the inner peripheral surface 240 during the cutting process of the circulation groove 220. In addition, the rising angle μ of the ball end mill 400 relative to the inner peripheral surface 240 cannot be sufficiently ensured, resulting in the incorporation portion 222 not being formed in the circulation groove 220.

[0050] On the other hand, the ball screw device 100 of the present invention is provided with an inclined portion 230 formed by cutting off the corner portion 310 with an uneven width along the circumference of the through hole at the corner portion 310 where the inner circumferential surface 240 of the through hole in the nut member 120 intersects with the axial end face of the nut member. Therefore, the ball screw device 100 can set the rising angle μ of the ball end mill 400 relative to the inner circumferential surface 240 to be larger when processing the circulation groove 220, and can perform cutting processing using the ball end mill 400 in a state close to vertical relative to the inner circumferential surface 240. As a result, the embracing portion 222 can be formed in the circulation groove 220, and the circulation groove 220 can guide the ball that passes over the thread. Therefore, according to the ball screw device 100 of the present invention, even if the circulation groove is formed on the inner circumferential surface of the nut member by cutting, the smooth infinite circulation of the rolling ball can be achieved.

Claims

1. A ball screw device (100), characterized in that: The ball screw device (100) comprises: Multiple balls; A screw shaft (110) having a rolling groove (111) for the ball formed in a spiral shape on its outer peripheral surface; and A nut member (120) having a through hole through which the screw shaft (110) passes, and having a return groove (210) on the inner circumferential surface (240) of the through hole so that the plurality of balls circulate only once around the screw shaft (110), and being threadedly engaged with the screw shaft (110) by means of the plurality of balls rolling in the return groove (210). The return slot (210) has: a load rolling groove (121) which is opposed to a portion of the rolling groove (111) of the screw shaft (110); and A circulation groove (220) that crosses the thread of the screw shaft (110) and connects both ends of the load rolling groove (121). The return groove (210) is arranged adjacent to the opening edge of the through hole of the nut member (120). A sloped portion (230) is provided at a corner portion (310) where the inner circumferential surface (240) of the through hole intersects with the axial end surface of the nut member (120), the sloped portion (230) being cut away from the corner portion (310) with an uneven width along the circumferential direction of the through hole.

2. The ball screw device (100) according to claim 1, characterized in that: The inclined portion (230) is provided at least at a position opposite to the formation position of the circulation groove (220) in the circumferential direction of the through hole of the nut member (120).

3. The ball screw device (100) according to claim 2, characterized in that: The cut-off width of the inclined portion (230) and the inclination angle relative to the axial end surface of the nut member continuously change along the circumferential direction of the through hole of the nut member (120).

4. The ball screw device (100) according to claim 3, characterized in that: The cut-off width of the inclined portion (230) is largest at a position opposite to a position of the circulation groove (220) closest to the axial end surface of the nut member (120) in the circumferential direction of the through hole of the nut member (120).

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