JP2007285379A - Ball screw device and method of manufacturing ball circulating member for ball screw - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To restrain a fatigue crack caused by stress concentration from being generated in a ball scooping-up part of a ball circulating member. <P>SOLUTION: This ball screw device has a ball return tube 14 having a circular arc-shaped connecting surface 16 as a circular arc-shaped processing part on both right-left sides of a tongue part 15. When forming the tongue part 15 and the circular arc-shaped connecting surface 16 by processing both end parts of the ball return tube 14 by a rotary processing tool 18, the tongue part 15 and the circular arc-shaped connecting surface 16 are formed so that a generating processing flaw 18a of the processing tool 18 becomes a shape in the substantially right-angled direction to the action direction of ball impact force applied to the tongue part 15. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a ball screw device used in, for example, a machine tool as a machine part that converts rotational motion into linear motion. The present invention also relates to a method for manufacturing a ball circulation member used for a ball screw.

  A ball screw device used in a machine tool or the like generally includes a screw shaft and a nut formed in a cylindrical shape with an inner diameter larger than the outer diameter of the screw shaft, and a ball formed on the outer peripheral surface of the screw shaft. A large number of balls are rollably provided between the screw groove and the ball screw groove formed on the inner peripheral surface of the nut. These balls roll between the screw shaft and the ball screw groove of the nut as the screw shaft or nut rotates, and the nut rolls between the screw shaft and the ball screw groove of the nut. A ball return tube for returning the ball between the ball screw grooves is mounted as a ball circulation member.

  In such a ball screw device, a ball rolled between a screw shaft and a ball screw groove of a nut collides with a tongue portion formed as a ball scooping portion formed at an end portion of the ball return tube to enter the ball return tube. be introduced. For this reason, when the screw shaft or the nut is rotated at a high speed, the impact force of the ball applied to the tongue portion increases, so that excessive stress concentration occurs in the tongue portion, causing damage to the ball return tube. Therefore, there is a ball screw device that suppresses the occurrence of excessive stress concentration by forming arc-shaped notches formed by cutting a part of the end face of the ball return tube into an arc shape on both left and right sides of the tongue. It has been proposed (see, for example, Patent Document 1).

By the way, when manufacturing a ball return tube of such a ball screw device, conventionally, as shown in FIG. 9, both end portions of a tubular body 17 made of metal are turned by a ball end mill 21, and FIG. A ball return tube 14 as shown in FIG. 6 is manufactured. In FIG. 9, reference numeral 15 denotes a tongue portion of the ball return tube 14, and reference numeral 20 denotes arcuate notches formed on the left and right sides of the tongue portion 15.
JP 2003-269568 A

  However, in the above-described method, when both ends of the tubular body 17 are turned by the ball end mill 21, the both ends of the tubular body 17 are placed with the rotation axis of the ball end mill 21 parallel to the central axis of the tubular body 17. Turning. For this reason, the processing flaws (processing marks) 21b (see FIG. 10) of the ball end mill 21 generated when turning both ends of the tubular body 17 have a shape along the axial direction of the tubular body 17. The fatigue crack 22 as shown in FIG.

In addition, if the radius of curvature of the arcuate cutout portion 20 formed on both the left and right sides of the tongue portion 15 is too large, the ball is likely to be caught at that portion, and the smooth rolling motion of the ball may be hindered.
The present invention has been made paying attention to the above-mentioned problems, and the purpose thereof is a ball screw device capable of suppressing the occurrence of fatigue cracks caused by stress concentration in the ball scooping portion of the ball circulation member, and It is providing the manufacturing method of a ball | bowl circulation member.

  In order to solve the above problems, a ball screw device according to the invention of claim 1 of the present invention includes a screw shaft, a nut formed in a cylindrical shape with an inner diameter larger than an outer diameter of the screw shaft, and the screw shaft. A plurality of balls provided between ball screw grooves formed on an outer peripheral surface of the nut and an inner peripheral surface of the nut, and a ball circulating member mounted on the nut, and the ball circulating member is a ball A ball screw device having a scooping portion at both ends and an arc-shaped processing portion machined in a circular arc shape on both left and right sides of the ball scooping portion, wherein both end portions of the ball circulation member are moved by a rotary processing tool. One that is substantially perpendicular to the direction of action of the ball impact force applied to the ball scooping portion due to processing flaws of the processing tool generated when the ball scooping portion and the arc-shaped processing portion are formed by processing. Wherein the ball scooping portions so as to be shaped and the arcuate working portion is formed along the.

The ball screw device according to a second aspect of the present invention is the ball screw device according to the first aspect, wherein the ball circulating member is a ball return tube, the ball scooping portion is a tongue portion, and The arcuate processed part is an arcuate notch.
The ball screw device according to a third aspect of the present invention is the ball screw device according to the second aspect, wherein the inner diameter of the ball return tube is D and the width of the tongue portion along the circumferential direction of the ball return tube. Is the curvature radius of the arc-shaped notch, where R is the radius of curvature of the arc-shaped notch, and H is the height from the end surface of the ball return tube to the bottom of the arc-shaped notch. The radius is w + 4R ≦ πD × 3/4 (1)
And the ratio of the height from the end surface of the ball return tube to the bottom surface of the arcuate notch and the radius of curvature of the arcuate notch is H / R ≧ 1 ( 2)
It is set to the value which satisfy | fills.

The ball screw device according to a fourth aspect of the present invention is the ball screw device according to the third aspect, wherein a height from an end surface portion of the ball return tube to a bottom surface portion of the arcuate notch is set to the tongue. It is characterized by having the same height on both the left and right sides of the part.
The invention according to claim 5 of the present invention is a method of manufacturing a ball circulating member for a ball screw having an arc-shaped processed portion processed into an arc shape on both the left and right sides of the ball scooping portion, and both end portions of the ball circulating member Are processed by a rotary processing tool to form the ball scooping portion and the arc-shaped processing portion so that the rotation axis of the processing tool is substantially perpendicular to the central axis of the ball circulation member. Both ends of the ball circulation member are processed by the processing tool while maintaining the posture of the processing tool.

According to the ball screw device of the first and second aspects of the present invention, the processing flaw of the processing tool generated when the ball scooping portion and the arc-shaped processing portion are processed has a shape along the axial direction of the ball circulation member. Therefore, it is possible to suppress the occurrence of fatigue cracks due to stress concentration in the ball scooping portion of the ball circulation member.
According to the ball screw device of the third aspect of the invention, since the ball is not easily caught in the arc-shaped notch portion of the ball return tube, in addition to the above-described effects, a smooth rolling motion of the ball is ensured and the operability is improved. Improvements can be made.

According to the ball screw device of the invention of claim 4, since the balance between the stress generated on the left side of the tongue portion and the stress generated on the right side of the tongue portion is improved, the stress concentration can be further reduced.
According to the method for manufacturing a ball circulating member according to the invention of claim 5, the processing scratches (processing marks) of the processing tool generated when both ends of the ball circulating member are processed are along the circumferential direction of the ball circulating member. It becomes a shape. Thereby, even if the impact force of the ball applied to the tongue portion increases, fatigue cracks are less likely to occur, so that a ball return tube having excellent impact resistance can be manufactured.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a schematic configuration of a ball screw device according to a first embodiment of the present invention. The ball screw device shown in the figure includes a screw shaft 11 and a nut 12 formed in a cylindrical shape with an inner diameter larger than the outer diameter of the screw shaft 11, and is formed on the outer peripheral surface of the screw shaft 11. A large number of balls 13 are provided between the ball screw groove 11 a and the ball screw groove 12 a formed on the inner peripheral surface of the nut 12 so as to be able to roll.

These balls 13 roll between the ball screw grooves 11a and 12a as the screw shaft 11 or the nut 12 rotates, and the nut 12 rolls between the ball screw grooves 11a and 12a. A metal ball return tube (ball circulation member) 14 for returning the ball 13 between the ball screw grooves 11a and 12a is mounted.
The ball return tube 14 has tongue portions 15 (see FIG. 2) as ball scooping portions at both ends, and the balls 13 rolling between the ball screw grooves 11a and 12a collide with the tongue portions 15 to return the ball return. It is introduced into the tube 14.

Further, the ball return tube 14 is formed by forming a tubular body made of metal into a substantially U shape. At both ends of the ball return tube 14, as shown in FIG. Arc-shaped connection surfaces 16 that smoothly connect 15 a and the end surface portion 14 a of the ball return tube 14 are formed on both the left and right sides of the tongue portion 15.
The arc-shaped connecting surface 16 and the tongue 15 serving as the arc-shaped machined portion are caused by the processing scratches of the turning tool that occur when both ends of the ball return tube 14 are turned by a rotary turning tool such as a ball end mill. It is formed so as to have a shape along a direction substantially perpendicular to the acting direction of the ball impact force applied to the portion 15.

  When manufacturing such a ball return tube 14, first, as shown in FIG. 4A, a metal tubular body 17 which is a tube material of the ball return tube 14 is prepared. Then, both end portions of the tubular body 17 are turned by a rotary turning tool 18 such as a ball end mill to form the tongue portion 15 and the arc-shaped connecting surface 16, and FIG. 4B and FIG. ), When turning both ends of the tubular body 17 with the turning tool 18, the turning axis 18a of the turning tool 18 is turned so that it is substantially perpendicular to the central axis 17a of the tubular body 17. Both ends of the tubular body 17 are turned while the posture of the tool 18 is maintained.

  In this way, when both ends of the tubular body 17 are turned in a state where the posture of the turning tool 18 is maintained such that the rotation axis 18a of the turning tool 18 is substantially perpendicular to the central axis 17a of the tubular body 17. As shown in FIG. 5, the processing scratches (processing marks) 18 a of the turning tool 18 generated when both ends of the tubular body 17 are turned have a shape along the circumferential direction of the tubular body 17. Thereby, even if the impact force of the ball applied to the tongue portion 15 increases, fatigue cracks are less likely to occur, so that a ball return tube having excellent impact resistance can be manufactured.

In the first embodiment described above, the arcuate connection surface that smoothly connects the side surface portion of the tongue portion and the end surface portion of the ball return tube is illustrated as not being recessed from the end surface portion of the ball return tube. The present invention can be applied even when the connection surface 17 is recessed from the end surface portion 14a of the ball return tube 14, that is, when the arc-shaped connection surface 17 is an arc-shaped notch.
Further, in the first embodiment described above, a case where a rotary turning tool such as a ball end mill is used when the tongue 15 of the ball return tube 14 or the arcuate connection surface 16 continuous to the tongue is formed is illustrated. However, a grinding tool may be used instead of the turning tool.

Next, a second embodiment of the present invention will be described with reference to FIGS.
As shown in FIG. 6, the ball return tube 14 of the ball screw device according to the second embodiment of the present invention introduces a ball rolled between the ball screw grooves of the screw shaft and the nut into the ball return tube 14. A tongue portion 15 is provided at both ends, and on both the left and right sides of the tongue portion 15, in order to reduce the stress generated in the tongue portion 15, an arc-shaped cutout portion 20 (see FIG. 7) as an arc-shaped processed portion. ) Is formed adjacent to the tongue 15.

These arc-shaped notches 20 are formed by turning the end surface portion 14a of the ball return tube 14 into an arc shape by a rotary cutting tool such as a ball end mill. When the width of the tongue 15 along the circumferential direction of the return tube 14 is w, the radius of curvature R of the arcuate notch 20 is
w + 4R ≦ πD × 3/4 (1)
It is set to a value that satisfies
Further, as shown in FIG. 7, assuming that the height from the end surface portion 14 a of the ball return tube 14 to the bottom surface portion of the arc-shaped notch 20 is H, the arc-shaped notch from the end surface 14 a of the ball return tube 14. The ratio of the height H to the bottom surface portion of 20 and the radius of curvature R of the arc-shaped notch portion 20 is
H / R ≧ 1 (2)
It is set to a value that satisfies

  According to such a configuration, when the ball rolled between the ball screw grooves of the screw shaft and the nut collides with the tongue portion 15 and enters the ball return tube 14, the ball is caught by the arcuate cutout portion 20. It becomes difficult. Thereby, even if the screw shaft or the nut is rotated at a high speed, the ball is not caught by the arc-shaped notch 20 of the ball return tube 14, so that a smooth rolling motion of the ball is ensured and the operability is improved. be able to.

In the second embodiment described above, the height H from the end surface portion 14a of the ball return tube 14 to the bottom surface portion of the arcuate cutout portion 20 is exemplified on the left and right sides of the tongue portion 15, but this is not limitative. It is not something that can be done. For example, as in the third embodiment shown in FIG. 8, the height H from the end surface portion 14 a of the ball return tube 14 to the bottom surface portion of the arc-shaped cutout portion 20 is made the same on both the left and right sides of the tongue portion 15. May be.
As described above, when the height H from the end surface portion 14a of the ball return tube 14 to the bottom surface portion of the arcuate cutout portion 20 is the same on both the left and right sides of the tongue portion 15, the stress generated on the left side of the tongue portion 15 Since the balance between the stress generated on the right side of the tongue portion 15 is improved, the stress concentration can be further reduced.

It is sectional drawing which shows schematic structure of the ball screw apparatus which concerns on the 1st Embodiment of this invention. It is a figure showing a ball return tube of a ball screw device concerning a 1st embodiment of the present invention. It is a figure which shows a part of ball return tube of the ball screw apparatus which concerns on the 1st Embodiment of this invention. It is explanatory drawing for demonstrating the manufacturing method of the ball | bowl circulation member for ball screws which concerns on this invention. It is explanatory drawing for demonstrating the effect by the manufacturing method of the ball | bowl circulation member for ball screws which concerns on this invention. It is a figure which shows the ball | bowl return tube of the ball screw apparatus which concerns on the 2nd Embodiment of this invention. It is a figure which shows a part of ball return tube of the ball screw apparatus which concerns on the 2nd Embodiment of this invention. It is a figure which shows a part of ball return tube of the ball screw apparatus which concerns on the 3rd Embodiment of this invention. It is explanatory drawing for demonstrating the manufacturing method of the conventional ball return tube. It is explanatory drawing for demonstrating the subject which this invention tends to solve.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Screw shaft 11a Ball screw groove 12 Nut 12a Ball screw groove 13 Ball 14 Ball return tube 15 Tongue part 16 Arc-shaped connection surface 17 Tubular body 18 Turning tool 20 Arc-shaped notch

Claims (5)

A screw shaft, a nut formed in a cylindrical shape with an inner diameter larger than the outer diameter of the screw shaft, and a plurality of ball screw grooves provided between an outer peripheral surface of the screw shaft and an inner peripheral surface of the nut And a ball circulation member attached to the nut, and the ball circulation member has a ball scooping portion at both ends and is processed into an arc shape on both the left and right sides of the ball scooping portion. A ball screw device having a processing portion,
Ball impact force applied to the ball scooping portion by a processing flaw of the processing tool generated when both ends of the ball circulation member are processed by a rotary processing tool to form the ball scooping portion and the arc-shaped processing portion. The ball screw device is characterized in that the ball scooping portion and the arc-shaped processing portion are formed so as to have a shape along a direction substantially perpendicular to the acting direction.   2. The ball screw device according to claim 1, wherein the ball circulation member is a ball return tube, the ball scooping portion is a tongue portion, and the arc-shaped processed portion is an arc-shaped notch portion. The inner diameter of the ball return tube is D, the width of the tongue portion along the circumferential direction of the ball return tube is w, the radius of curvature of the arc-shaped notch is R, and the arc shape extends from the end surface of the ball return tube. When the height of the notch to the bottom is H, the radius of curvature of the arcuate notch is w + 4R ≦ πD × 3/4 (1)
And the ratio of the height from the end surface of the ball return tube to the bottom surface of the arcuate notch and the radius of curvature of the arcuate notch is H / R ≧ 1 ( 2)
The ball screw device according to claim 2, wherein the ball screw device is set to a value satisfying   4. The ball screw device according to claim 3, wherein a height from an end surface portion of the ball return tube to a bottom surface portion of the arc-shaped cutout portion is the same height on both right and left sides of the tongue portion. apparatus. A method of manufacturing a ball circulating member for a ball screw having an arc-shaped processed portion processed into an arc shape on both left and right sides of a ball scooping portion, wherein both ends of the ball circulating member are processed by a rotary processing tool, In forming the ball scooping portion and the arc-shaped processing portion, the ball is kept in a state where the posture of the processing tool is maintained so that the rotation axis of the processing tool is substantially perpendicular to the central axis of the ball circulation member. A method of manufacturing a ball circulating member for a ball screw, wherein both ends of the circulating member are processed by the processing tool.

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