JP4426389B2 - Ball screw nut - Google Patents

Description

  The present invention relates to a ball screw nut that is screw-coupled to a screw shaft via a plurality of balls that roll on a helical male screw groove formed on the screw shaft.

  The ball screw is constituted by a screw shaft and a ball screw nut, and the ball screw nut is screwed to the screw shaft via a plurality of balls that roll on the male screw groove of the screw shaft. Ball screws are widely used in various measuring instruments and machine tools because of their low rolling friction resistance between the screw shaft and ball screw nut and easy removal of backlash. It is used to drive a member constituting a machine tool or the like by converting it into a linear reciprocating motion of a ball screw nut that is screwed to the machine tool. The ball screw nut, that is, the nut is formed with a female screw groove for forming a meshing passage with a male screw groove formed on the outer surface of the screw shaft, and a return passage for communicating both ends of the meshing passage is formed. ing. As a result, the ball that has reached one end of the meshing passage through the rotation of the screw shaft enters the meshing passage from the other end through the return passage, and the ball has a loop-like shape between the meshing passage and the return passage. It circulates in the circulation path formed in a row and rolls, that is, rolls and moves.

In a conventional nut, a meshing passage is provided between the screw shaft and the nut over an angle of 360 degrees or more in the rotation direction of the screw shaft so that the ball rolls in the male screw groove for a plurality of turns. In order to return the ball to the meshing passage, a return pipe is attached to the outside of the nut, or end caps are attached to both ends of the nut to form a return passage in the nut between the end caps. Like to do.
JP 2003-156118 A

  For this reason, conventionally, since it is necessary to form the return passage outside the meshing passage so as to straddle the plurality of meshing passages, the diameter of the nut becomes large, and there is a limit to downsizing the nut.

  On the other hand, in the conventional ball screw, the nut itself cannot hold the ball. Therefore, the engagement passage and the return passage formed by the male screw groove and the female screw groove in a state where the nut is fitted to the screw shaft. A predetermined number of balls are incorporated therein, and in order to assemble the ball screw, it is necessary to perform the operation of assembling the ball into the nut while the nut is assembled to the screw shaft. Therefore, the ball cannot be incorporated in the nut under the condition that the nut is separated from the screw shaft. Further, when the nut is removed from the screw shaft, the ball falls off from the nut, so it is necessary to provide a stopper on the screw shaft to regulate the movement stroke of the nut.

  An object of the present invention is to provide a small ball screw nut.

  Another object of the present invention is to provide a ball screw nut that can be mounted on a screw shaft in a state where the ball is assembled.

The ball screw nut of the present invention is a ball screw nut that is assembled to a screw shaft having a male screw groove, and has a cylindrical body with a partition projection extending in the axial direction and formed on the outer peripheral surface. An inner case formed with a ball-holding slit that extends and is formed in the cylindrical body so that both ends reach the partition projection , a ball guide surface that extends along the slit and that is connected to the slit, and the inner case; A small-diameter inner peripheral surface that is incorporated outside the case and forms a female thread groove for guiding a plurality of balls by the slit, and a return passage for returning the ball from one end of the slit to the other end. And an outer case provided with a large-diameter inner peripheral surface formed by the guide surface.

  The ball screw nut of the present invention is characterized in that the slit has a spiral shape corresponding to the male screw groove.

  The ball screw nut of the present invention is characterized in that the inner case is provided with an engaging claw protruding into the slit, and the ball is held in the female screw groove.

  The ball screw nut of the present invention is characterized in that an arcuate groove on which the ball in the slit rolls is formed on the inner surface of the small diameter.

The ball screw nut according to the present invention has a reversing projection that forms a reversing passage for guiding the ball between the both ends of the slit and the both ends of the outer peripheral surface by the partitioning projecting portion. It is characterized by providing in.

  The ball screw nut of the present invention is characterized in that an engagement groove into which the partition projection is inserted is provided in the outer case.

  In the ball screw nut of the present invention, a plurality of nut assemblies formed by the inner case, the outer case, and the ball are coaxially incorporated in the housing, and a preload is applied to each nut assembly in the axial direction. It is characterized by that.

  According to the present invention, the ball holding slit is formed in the circumferential direction with the partition protrusion formed on the outer peripheral surface of the cylindrical body extending in the axial direction, and the slit is fitted to the inner case and the outer side thereof. An internal thread groove for holding a ball that rolls into the external thread groove of the screw shaft and a return passage are formed between the outer case and the outer case to be matched with the portions on both sides in the circumferential direction of the partition projection. Therefore, it is not necessary to provide a reversing passage for reversing from one end of the female screw groove to the return passage and a reversing passage for reversing from the return passage to the other end of the female screw groove so as to straddle the female screw groove, Even if the outer diameter of the ball screw nut is reduced, the ball can be circulated and moved with the rotational movement of the screw shaft relative to the ball screw nut. Thereby, a ball screw nut can be reduced in size.

  The ball screw nut has an inner case and an outer case, and a return passage and a female screw groove for circulating and moving the ball are formed in both cases, so that the ball is held by an engaging claw in the slit. By doing so, the ball is held between both cases, and the ball does not fall off the ball screw nut without attaching the ball nut to the screw shaft. As a result, the ball screw nut can be easily replaced with another screw shaft.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a cross-sectional view showing a ball screw having a ball screw nut of the present invention, and FIG. 2 is a perspective view showing an inner case and an outer case constituting the nut shown in FIG.

  A ball screw 10 shown in FIG. 1 includes a screw shaft 12 in which a helical male screw groove 11 is formed and two nut assemblies, that is, ball screw nuts 13. It is incorporated coaxially inside. The housing 14 is formed with a circular accommodation hole 15 for accommodating the two nuts 13, and C-shaped rings 16 are attached to both ends of the housing 14 to prevent the nuts 13 from coming out of the housing 14. ing. A wave washer 17 is incorporated between the two nuts 13 in order to apply axially opposite preloads in the axial direction to the two nuts 13, and the screw member 18 screwed to the housing 14 is a nut. The nut 13 is prevented from rotating by being pressed against the outer peripheral surface of the nut 13.

  The nut 13 is a combination of an inner case 21 that is generally cylindrical, that is, an inner case 21, and an outer case 22 that is fitted to the outside of the inner case 21 and is generally cylindrical. It is formed by. In the illustrated case, the inner case 21 is manufactured using a resin material, and the outer case 22 is manufactured using a metal material. However, the inner case 21 may also be manufactured using a metal material.

  3 (A) is a front view of the inner case 21, FIG. 3 (B) is a right side view of FIG. 3 (A), and FIG. 3 (C) is a line 3C-3C in FIG. 3 (B). It is sectional drawing which follows. FIG. 4A is a front view of the inner case 21 in a state where a ball is incorporated, and FIG. 4B is a rear view of the inner case in a similar state.

  The inner case 21 is formed by a cylindrical body 24 provided with a flange portion 23 at one end, and the outer diameter of the cylindrical body 24 is smaller than that of the flange portion 23. A partition projection 25 is provided on the outer peripheral surface of the cylindrical body 24 so as to project outward in the radial direction and extend from the flange 23 side toward the other end of the cylindrical body 24. The outer surface of the partition projection 25 is It inclines toward the other end part from the flange part 23. FIG. However, it may be formed straight so that the outer surface is parallel to the center axis without inclining the outer surface of the partition projection 25. A spiral ball holding slit 26 is formed on the distal end side of the cylindrical body 24 so that both ends thereof reach the partitioning projections 25. The slit 26 penetrates the inner surface and the outer surface of the cylindrical body 24 and is circumferential. It is formed over a range of angles slightly larger than 270 degrees in the direction. A steel ball, that is, a ball 27 is arranged in the slit 26, and the ball 27 rolls along the slit 26. The thickness of the cylindrical body 24 is set to a value smaller than the diameter of the ball 27 so that the ball 27 protrudes from the inner surface and the outer surface of the cylindrical body 24, and the lead angle β of the spiral slit 26 is the screw shaft 12. Corresponds to the lead angle.

  On the rear end side of the cylindrical body 24, a ball guide surface 28 that is shifted in the axial direction with respect to the slit 26 and reaches both ends of the partition projection 25, substantially corresponds to the slit 26 along the slit 26 and the flange portion 23. A ball 27 is disposed on the ball guide surface 28, and the ball 27 rolls along this surface. The outer peripheral surface of the ball guide surface 28 has substantially the same outer diameter as the outer peripheral surface of the cylindrical body 24. The inner case 21 is provided with an engaging claw 29 projecting into the slit 26, and the ball 27 disposed in the slit 26 is prevented from falling toward the inner side in the radial direction of the inner case 21. . The engaging claws 29 are provided on both end faces of the slit 26 in the axial direction, but may be provided on one end face.

  A substantially semi-circular reversing surface 31 for guiding the ball 27 between one end of the slit 26 and one end of the ball guide surface 28 is formed on one side in the circumferential direction of the partition projection 25. On the other circumferential side of the portion 25, a substantially semicircular reversing surface 32 for guiding the ball 27 is formed between the other end of the slit 26 and the other end of the ball guiding surface 28. As shown in FIGS. 4A and 4B, one end of the slit 26 is closer to the flange portion 23 side than the other end of the slit 26, so that one inversion surface 31 is more than the other inversion surface 32. The radius is small. In order to form the reversing passages 33 and 34 for guiding the ball 27 between the slit 26 and the ball guiding surface 28 between the reversing surfaces 31 and 32, the cylindrical body 24 has a reversing projection 35, 36 is provided projecting radially outward. The bottom surfaces of the respective reversing passages 33 and 34 are connected to the ball guide surface 28 from the inner peripheral surface of the cylindrical body 24 serving as the end of the slit 26, and radially outward from the slit 26 toward the ball guide surface 28. Inclined towards. 4A and 4B are diagrams showing the ball 27 and the inner case 21 in a state where they are assembled between the inner case 21 and the outer case 22, for convenience. Unless the outer case 22 is fitted, the ball 27 cannot be held on the outer surface of the inner case 21.

  5 (A) is a front view of the outer case 22, FIG. 5 (B) is a left side view of FIG. 5 (A), and FIG. 5 (C) is taken along line 5C-5C in FIG. 5 (B). It is sectional drawing which follows. FIG. 6 is a cross-sectional view showing a ball screw nut assembled by incorporating a plurality of balls 27 in a state in which the inner case 21 and the outer case 22 are fitted, and FIG. 8 is a sectional view taken along line 8-8 in FIG. 6, and FIG. 9 is a sectional view taken along line 9-9 in FIG.

  As shown in FIG. 5C, the outer case 22 fitted to the outer side of the inner case 21 has a small-diameter inner peripheral surface 37 corresponding to the slit 26 and a large-diameter inner peripheral surface 38 corresponding to the ball guide surface 28. And have. A female screw groove 41 that holds and guides the ball 27 is formed by the small-diameter inner peripheral surface 37 and the slit 26, and the ball 27 positioned in the female screw groove 41 engages with the male screw groove 11 of the screw shaft 12. The meshing passage is formed by the female thread groove 41 and the male thread groove 11. On the other hand, the large-diameter inner peripheral surface 38, the ball guide surface 28, the flange portion 23, and the radial step surface 39 are used to move the ball 27 from one end portion of the slit 26 to the other end portion of the reverse passage 33, 34. A return passage 42 is formed through the return passage. An arcuate groove 43 that engages with the ball 27 disposed in the female thread groove 41 corresponding to the slit 26 is formed in the small-diameter inner peripheral surface 37.

  As shown in FIG. 5C, an engagement groove 44 into which the partition projection 25 of the inner case 21 enters when the inner case 21 and the outer case 22 are fitted is formed on the inner surface of the outer case 22. Has been. Reversing protrusions 35 and 36 are engaged with the end faces 45 and 46 in the radial direction of the engaging groove 44, respectively. As shown in FIG. An angle θ is formed with respect to the central axis of the outer case 22, and an engagement groove 44 is formed in the range of the angle θ. This angle θ is approximately 90 degrees.

When the outer case 22 is fitted to the outer side of the inner case 21, a female screw groove 41 is formed between both the cases 21 and 22 by the slit 26 of the inner case 21 and the small-diameter inner peripheral surface 37 of the outer case 22. A return passage 42 is formed by the ball guide surface 28 of the inner case 21, the flange portion 23, the large-diameter inner peripheral surface 38 of the outer case 22, and the step surface 39, and the reverse passage on both sides of the partition projection 25. 33 and 34 are formed. As shown in FIG. 5C, the outer case 22 is formed with a ball insertion hole 47 that communicates with the large-diameter inner peripheral surface 38. In a state where the outer case 22 is fitted to the outer side of the inner case 21, the female screw groove 41, the return passage 42 and the reverse passages 33 and 34 formed by both the cases 21 and 22 from the ball insertion hole 47. By incorporating a plurality of balls 27, a plurality of balls 27 can be arranged in a loop in these. When the incorporation of the ball 27 is completed, the ball insertion hole 47 is closed by a plug 48 made of a screw member or the like. An annular groove 49 is formed on the outer peripheral surface of the outer case 22 so as to correspond to the ball insertion hole 47 to which the plug 48 is attached, and the screw member 18 is pressed against the bottom surface of the annular groove 49 as shown in FIG. It has become.

  Since the nut assembly, that is, the ball screw nut 13 protrudes into the slit 26 and the engagement claw 29 provided in the inner case prevents the ball 27 in the slit 26 from dropping from the slit 26, the inner case 21 and the outer case 22. Can be assembled without attaching the inner case 21 to the screw shaft 12. However, when the engagement claw 29 is not provided in the slit 26, the assembly is performed with the inner case 21 mounted on the screw shaft 12.

The screw shaft 12 and the ball screw nut 13 constituting the ball screw shown in FIG. 1 are right-handed screws. For example, when the screw shaft 12 is rotated clockwise as viewed from the right as shown by an arrow in FIG. The ball screw nut 13 moves to the right in FIG. With this rotation, the ball 27 held in the slit 26 rolls while being guided by the slit 26, the male thread groove 11 and the arc-shaped groove 43, and from the end of the slit 26 to the reversing surface 31 and the reversing projection 35. The reversing passage 33 is scooped up and enters the return passage 42 through the reversing passage 33. The ball 27 entering the return passage 42 rolls to the other inversion passage 34 as the screw shaft 12 rotates, and enters the slit 26 from the other end through the inversion passage 34. When the screw shaft 12 is rotated in the opposite direction, each ball 27 rolls in a direction opposite to the direction described above with respect to the nut 13.

  In this way, the ball 27 enters the male screw groove 11 of the screw shaft 12 in a continuous state within a range of about 270 degrees in the rotational direction as shown in FIG. The outer diameter of the ball guide surface 28 is reduced to such an extent that the ball 27 rolling in the return passage 42 and the ball 27 rolling in the female screw groove 41 overlap in the radial direction without straddling the radially outer side. Therefore, the ball 27 can be circulated and moved in the passage formed between the inner case 21 and the outer case 22 without increasing the outer diameter of the ball screw nut 13. Therefore, the outer diameter of the nut corresponding to the outer diameter of the screw shaft 12 can be made smaller than that of the conventional ball screw nut, and the ball screw nut can be reduced in size.

In the illustrated case, the female thread groove 41 is formed in a range of about 270 degrees in the circumferential direction. However, if the dimension in the circumferential direction of the partition projection 25 is smaller than that illustrated, the female thread groove 41 is at least 270 degrees. The female thread groove 41 can be formed in the range. Incidentally, projections 35, 36 for the inversion to form an inverted communication path 3 3,34 is provided integrally with the inner casing 21, without providing the inner case 21, as provided in the outer case 22 May be.

  The ball screw shaft shown in FIG. 1 has two nut assemblies, that is, ball screw nuts 13 incorporated in a housing 14, and the two ball screw nuts 13 are incorporated so that both ends are opposite to each other. The ball screw nuts 13 are 180 degrees out of phase with each other in the circumferential direction. As a result, the nut 13 is screw-coupled to the single screw shaft 12 by the two nuts 13 at the portion of 360 degrees or more in the rotational direction via the ball 27, and the nut is moved by rotating the screw shaft 12. The accuracy can be maintained at a desired accuracy.

  As shown in FIG. 1, a wave washer 17 is incorporated between the two nuts 13, and a preload is applied between the screw shaft 12 and the nut 13 in the direction in which the two nuts 13 are separated, that is, in the opposite direction. The occurrence of backlash when the rotation direction of the screw shaft 12 changes can be prevented, and the positioning accuracy of the nut 13 can be increased.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention. For example, the housing 14 shown in FIG. 1 incorporates two nut assemblies or ball screw nuts 13, but only one, or three or more ball screw nuts 13 are incorporated into the housing 14. May be. In the case shown in FIG. 1, the threaded shaft 12 is rotated to move the member to be transported attached to the housing 14 in the linear direction. However, if the lead angle of the screw is made larger than the illustrated case, the housing The screw shaft 12 can be rotated by moving 14 in the axial direction.

It is sectional drawing which shows the ball screw which has the ball screw nut of this invention. It is a perspective view which shows the inner side case and outer side case which comprise the nut shown by FIG. (A) is a front view of the inner case, (B) is a right side view of FIG. 3 (A), and (C) is a cross-sectional view taken along line 3C-3C in FIG. 3 (B). (A) is a front view of the inner case in a state where a ball is incorporated, and (B) is a rear view of the inner case in a similar state. (A) is a front view of an outer case, (B) is a left side view of FIG. 5 (A), and (C) is a cross-sectional view taken along line 5C-5C in FIG. 5 (B). It is sectional drawing which shows the ball screw nut assembled by incorporating a some ball | bowl under the state which fitted the inner side case and the outer side case. It is sectional drawing which follows the 7-7 line in FIG. It is sectional drawing which follows the 8-8 line in FIG. It is sectional drawing which follows the 9-9 line in FIG.

Explanation of symbols

10 Ball screw 11 Male thread groove 12 Screw shaft 13 Ball screw nut (nut assembly)
14 Housing 15 Housing Hole 16 C-Shaped Ring 17 Wave Washer 18 Screw Member 21 Inner Case 22 Outer Case 23 Flange 24 Cylindrical Body 25 Partitioning Projection 26 Slit 27 Ball 28 Ball Guide Surface 29 Engagement Claws 31 and 32 Reverse Surface 33 , 34 Reversing passages 35, 36 Reversing projections 37 Small diameter inner circumferential surface 38 Large diameter inner circumferential surface 39 Step surface 41 Female thread groove 42 Return passage 43 Arc-shaped groove 44 Engaging grooves 45, 46 End face 47 Ball insertion hole 48 Plug 49 Annular groove

Claims (7)

A ball screw nut assembled to a screw shaft having a male screw groove,
A partition protrusion having a cylindrical body extending in the axial direction and formed on the outer peripheral surface; and a ball holding slit extending in the circumferential direction to be formed in the cylindrical body and having both ends reaching the partition protrusion ; An inner case formed with a ball guide surface along the slit and having both ends connected to the slit,
A small-diameter inner peripheral surface that is incorporated outside the inner case and forms a female thread groove that guides a plurality of balls by the slit, and a return passage that returns the ball from one end of the slit to the other end. A ball screw nut comprising: an outer case provided with a large-diameter inner peripheral surface formed by the ball guide surface.   2. The ball screw nut according to claim 1, wherein the slit has a spiral shape corresponding to the male screw groove.   3. The ball screw nut according to claim 1, wherein an engagement claw that protrudes into the slit is provided in the inner case, and the ball is held in the female screw groove.   The ball screw nut according to any one of claims 1 to 3, wherein an arc-shaped groove on which the ball in the slit rolls is formed on the inner peripheral surface of the small diameter. 5. The ball screw nut according to claim 1, wherein an inversion path that guides the ball between the both ends of the slit and the both ends of the outer peripheral surface is formed by the partition projection. A ball screw nut, characterized in that a reversing protrusion is provided on the inner case.   The ball screw nut according to any one of claims 1 to 5, wherein an engagement groove into which the partition projection is inserted is provided in the outer case. The ball screw nut according to any one of claims 1 to 6, wherein a plurality of nut assemblies formed by the inner case, the outer case, and the ball are coaxially incorporated in a housing and each of the nut assemblies is formed. A ball screw nut characterized by preloading a nut assembly in an axial direction.

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