JP6550740B2 - Method of setting axial clearance with ball screw nut alone and method of manufacturing ball screw using the same - Google Patents

Description

  The present invention relates to a ball screw.

  In a feeding device of a machine tool such as a machining center, a circular motion accuracy test (see Non-Patent Document 1) is performed for motion accuracy evaluation. When a circular motion accuracy test is performed with a feeding device that controls two linear motion axes simultaneously to make a circular motion, when the circular motion quadrant is switched (the feed direction of one axis changes from + to-or from-to +) It is known that a projection error and a step error (hereinafter also referred to as “quadrant projection error” and “quadrant step error”, respectively) occur at four points where the quadrant changes. There is a concern that the machining accuracy of the workpiece may be reduced due to the quadrant protrusion error and the quadrant step error generated in the feeding device of the machine tool.

  Quadrant protrusion errors can be compensated by control techniques (see, for example, Non-Patent Document 2). For example, a mathematical model that can approximate the hysteresis loop of the friction torque of the feed system is constructed based on the nonlinear friction characteristics of the ball screw, rolling linear motion guide or rolling bearing that constitutes the feeding device, and this is used as servo information. What is necessary is just to input into the controller of a feeder.

JP 2002-023852 A

JIS B 6190-4, Machine tool test method general rules-Part 4: Circular motion accuracy test by numerical control Tsutsumi Masaomi: “Friction Characteristics of Ball Screws and Linear Motion Guides that Control the Accuracy of Machine Tool Motion”, Precision Engineering Society Rolling Machine Element Special Committee Lecture (June 7, 2013), p. 33. Maeda Ueda, Hirokazu Shimoda: “Ball behavior and lost motion of ball screw (3rd report)”, Journal of Japan Society for Precision Engineering (2011), Vol. 77, no. 2, p. 183.

  On the other hand, when a ball screw is used for the feeder, even if the quadrant protrusion error is compensated by the control technology, the circular motion trajectory has a quadrant step of submicron to micron order due to the lost motion when the driving direction of the ball screw is reversed. An error will occur. On the other hand, a mathematical model that can approximate the nonlinear friction characteristic of the feed system can be constructed and corrected for quadrant step error as well as the compensation method of quadrant protrusion error at the time of circular motion quadrant switching (for example, patent Reference 1).

  However, it is necessary to construct a mathematical model while repeating adjustment by trial and error using an actual machine (see, for example, Non-Patent Document 2). For this reason, there is a problem that it takes too much cost and labor to build a mathematical model using an actual machine, and this is an improvement in preventing reduction in workpiece machining accuracy due to lost motion when the ball screw drive direction is reversed. There is room for it.

In recent years, in order to solve such a problem, investigation and research have been carried out analytically and experimentally regarding the cause of the lost motion when the driving direction of the ball screw is reversed (for example, see Non-Patent Document 3). According to Non-Patent Document 3, a lost motion of a ball screw is a biting motion of a ball revolving in a nut into a thread groove of a screw shaft or a thread groove of a nut at the time of reversing a drive direction It is clarified that it is caused by
Therefore, the present invention has been made paying attention to such problems, and a method of setting an axial clearance with a single nut of a ball screw capable of reducing or preventing lost motion, and manufacture of a ball screw using the same It is an object to provide a method .

Here, as shown in FIG. 21, in the case of a ball screw on which an axial load Fx acts (see FIG. 21A), the ball 3 usually has two screw grooves 101k and 102k of the screw shaft 101 and the nut 102. (Refer to reference numerals M and B in FIG. 5B) (refer to FIG. 5B), mainly due to elastic contact deformation at the contact points M and B, the screw shaft 101 and the nut. An axial displacement δ _x occurs between the two 102 (see (a) in the figure). In the same figure, the symbol m is the center of the ball 3, α is the contact angle, δ _M , δ _B is the amount of elastic contact deformation at the contact points M and B, and P is the contact load (hereinafter, FIG. 21 to FIG. The same in 23).

Now, when turning the screw shaft 101 in a counterclockwise direction while restraining the rotation of the nut 102, nut 102, as shown in FIG. 22, the direction of the axial load F _x moves in the opposite direction (such This is called “forward operation”). At this time, as shown in FIG. 4B, the ball 3 bites in a wedge shape in a direction perpendicular to the rolling direction, and the contact state between the ball 3 and the track formed by the opposing screw grooves 101k and 102k is It changes from a two-point contact to a three-point contact (locations with symbols M, M ′, and B). Therefore, changes as [delta] _xF from the relative displacement also [delta] _x between the screw shaft 101 and the nut 102.

Then, when the direction of rotation of the screw shaft 101 is reversed, the direction of movement of the nut 102 is also reversed (this operation state is referred to as “reverse operation”). Therefore, as shown in FIG. 23, the direction of biting of the ball 3 with respect to the track is also reversed (see FIG. _23B ), and the relative displacement between the screw shaft 101 and the nut 102 is δ _× B. Therefore, the lost motion Δe _p generated when the driving direction of the ball screw is reversed can be expressed by the following (Expression 1).
Δe _p = δ _xF −δ _xB (Formula 1)

As shown in (Equation 1), the lost motion Δe _p generated at the time of reversing the driving direction of the ball screw suppresses the difference between the axial displacement δ _xF at the time of forward operation and the axial displacement δ _xB at the time of reverse operation. if, it is possible to reduce or minimize .DELTA.e _p. The inventor of the present invention has completed the present invention as a result of earnest study based on such consideration.

That is, in order to solve the above problems , an axial clearance setting method using a single nut of a ball screw according to the first aspect of the present invention includes a screw shaft, a nut, and a plurality of balls, and the screw shaft Rolling through which the plurality of balls revolve by a spiral thread groove formed on the outer peripheral surface of the screw shaft and a spiral thread groove formed on the inner peripheral surface of the nut. a method for setting the axial clearance in the nut single ball screw road is formed, as the ball screw, the screw groove of the screw shaft and the nut are both a gothic arch groove, double nut preload It is used by applying preload by the method or constant pressure preload method, and the ball screw load is only the above-mentioned preload, and its magnitude is 3 to 5% of the dynamic rated load, and there is no nut clearance. Contact angle 40 ° to 50 ° when the groove R ratio from 0.54 to 0.56, and, chamfering start angle of the land ends of the screw shaft to target shall be the 65 ° to 75 °, The ball on the bottom of the groove of each screw groove so as not to cause the ball to ride on the land chamfered portion of each screw groove of the screw shaft and the nut due to the ball biting behavior during operation. so as not to cause the ride down of, based on the results of simulation analysis, an axial clearance in the nut itself, that you set relative to the ball diameter of the ball used in a range satisfying the following (equation 2) It features. Here, sa is the axial clearance of the nut alone, and Da is the ball diameter of the ball used.
0.17% <sa / Da ≦ 3.6% (Formula 2)

Further, in order to solve the above problems , an axial clearance setting method using a single nut of a ball screw according to a second aspect of the present invention includes a screw shaft, a nut, and a plurality of balls. Rolling through which the plurality of balls revolve by a spiral thread groove formed on the outer peripheral surface of the screw shaft and a spiral thread groove formed on the inner peripheral surface of the nut. a method for setting the axial clearance in the nut single ball screw road is formed, as the ball screw, the screw groove of the screw shaft and the nut are both a gothic arch groove, double nut preload If the ball screw load is only the preload, and the size is 3 to 5% of the dynamic load rating, and there is no clearance between nuts. The contact angle 40 ° to 50 °, the groove R ratio from 0.52 to 0.54, and, chamfering start angle of the land ends of the screw shaft to target shall be the 60 ° to 65 °, working So that the ball does not ride on the land chamfered portion of each screw groove of the screw shaft and the nut due to the ball biting behavior in the middle and the ball of the ball to the groove bottom of the screw groove during reverse operation so as not to cause the ride down, based on the results of simulation analysis, an axial clearance in the nut itself, characterized that you set relative to the ball diameter of the ball used in a range satisfying the following (equation 3) I assume . Here, sa is the axial clearance of the nut alone, and Da is the ball diameter of the ball used.
0.17% <sa / Da ≦ 1.66% (Formula 3)

In order to solve the above-mentioned problem, a method for manufacturing a ball screw according to an aspect of the present invention includes:
A ball screw is manufactured using the axial clearance setting method of the ball screw nut alone according to the first or second aspect.
Here, in the present invention, as shown in FIG. 2, the axial clearance sa of the nut alone is shown in FIG. 2 (b) from the relationship between the nut 1, the screw shaft 2 and the ball 3 in FIG. The axial movement (see FIG. 2C) of the screw shaft 1 and the nut 2 when the state shown in FIG. 2 is defined is defined as the axial clearance sa. Since the ball screw has a lead angle, the axial clearance sa cannot be simply written in FIGS. 2A and 2B, whereas the axial clearance sa is smaller than the nut clearance ΔDa. In the present invention, it is defined using an axial clearance sa of a nut alone, as it can be easily measured from the device. In the present specification, sa / Da is also simply referred to as “gap / ball diameter ratio” hereinafter.

According to the axial clearance setting method for a single nut of a ball screw according to an aspect of the present invention, the axial clearance sa of the single nut is set to a ball diameter Da of the ball to be used. In the ball screw according to the second embodiment, the gap / ball diameter ratio is 0.17% <sa / Da ≦ 3.6%, and the gap / ball diameter ratio is 0.17% <sa / Da. It was set as ≦ 1.66% . Therefore, according to the ball screw manufactured using the axial clearance setting method for the ball screw nut alone according to the first or second aspect, the initial contact angle during preloading can be increased by increasing the internal clearance. As the axial rigidity increases, the axial rigidity increases, and as apparent from the results of simulation analysis described later, the difference between the axial displacement δxF in forward operation and the axial displacement δxB in reverse operation can be reduced. it can. Therefore, it is possible to reduce or minimize the lost motion that occurs when the driving direction of the ball screw is reversed.

Here, in the axial clearance setting method for the ball screw nut alone according to one aspect of the present invention, the thread of the screw shaft or the nut of the ball revolving in the nut when the driving direction is reversed When the biting into the screw groove is called “ball biting behavior” , the axial clearance setting method for the ball screw nut alone according to one aspect of the present invention is based on the ball biting behavior. It is preferable to target only those in which the thread groove is in contact with the ball at three points. The double nut fixed position preloaded ball screw used in the feed system of the machine tool is usually driven under preloaded conditions such that 3% ≦ Fa / Ca ≦ 5%.

As described above, according to the present invention, it is possible to provide a method of setting an axial clearance of a ball screw nut alone which can reduce or minimize lost motion, and a method of manufacturing a ball screw using the same .

It is a figure which shows one Embodiment of the ball screw which concerns on 1 aspect of this invention, The figure (a) shows a nut in the cross section along an axial direction, (b) is orthogonal to the axis line of a screw shaft. A cross section is shown. BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram explaining the axial clearance which prescribes | regulates the ball screw which concerns on this invention, The figure (a) shows the cross section of a rolling path typically, (b) is only the clearance gap between a ball | bowl and a screw groove. The cross section of the rolling path of the state moved to the axial direction is shown typically, (c) has shown typically the top view of the nut single-piece | unit of the state of (b). BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1A and 1B are schematic views (a) and (b) of a cross section of a rolling path for explaining the relationship between an internal clearance, a ball and a track of an embodiment of a ball screw according to the present invention (hereinafter also referred to as “invention product”). It is a schematic diagram (a), (b) of the rolling path cross section explaining the internal clearance of the conventional ball screw (it is also called the following "normal goods") shown as a comparative example, a ball, and a track. It is a graph explaining the relationship between the axial direction displacement of invention, and a lost motion. Clearance / ball diameter ratio (s a _{/ D a)} and a graph for explaining the relationship of the lost motion (a), is (b). It is a schematic diagram ((a)-(c)) explaining the relationship between the increase in the axial clearance and the ride in the normal product. It is a schematic diagram ((a)-(c)) explaining the relationship between the increase in the axial clearance and the ride in the invention. It is a principal part enlarged view explaining the riding-up state (at the time of forward direction action | operation) to the land chamfering part formed in the land edge part of the screw shaft in invention. Is a graph illustrating relationship _{(F a / C a = 5} %) of the ride-down rate to axial clearance and the land chamfer (ride-down when the value is positive). As an example, it is a graph explaining _a relation (F _a / C _a = 5%) for _a gap and three types of ball screws. As an example, a graph illustrating the relationship between rate ride with axial clearance _{(F a / C a = 5} %) for three of the ball screw. It is a graph explaining the relationship ( _Fa / _Ca = 5%) of an axial clearance gap and a lost motion with respect to three types of thread groove shape as an Example. As an example, for the 3 types of screw groove shape is a graph illustrating the relationship between axial clearance between ride rate _{(F a / C a = 5} %). As an Example, it is a graph explaining the relationship ( _Fa / _Ca = 5%) of an axial clearance gap and a lost motion with respect to three types of contact angles. As an example, a graph illustrating relative three of the contact angle, the relationship of the axial gap between ride rate _{(F a / C a = 5} %). It is a graph explaining the relationship ( _Fa / _Ca = 5%) of an axial clearance gap and a lost motion with respect to three types of groove | channel R ratio as an Example. As an example, for the three types of grooves R ratio is a graph illustrating the relationship between axial clearance between ride rate _{(F a / C a = 5} %). As an example, it is a graph explaining the relation (F _a / C _a = 5%) of the axial clearance and the lost motion to the groove R ratio when the screw shaft chamfering start angle is changed. As an example, graphs (a) and (b) illustrating the analysis result (F _a / C _a = 5%) of the ball screw that is most likely to be mounted. It is a figure explaining a lost motion, The figure is a two-point contact state at the time of a stop, The figure (a) is a top view which shows a ball screw typically, (b) is a cross section of a rolling path FIG. It is a figure explaining a lost motion, The figure is a three-point contact state produced at the time of forward operation | movement, The figure (a) is a top view which shows a ball screw typically, (b) is a rolling path. It is a figure which shows a cross section typically. It is a figure explaining a lost motion, The figure is a three-point contact state which arises in a reverse operation, The figure (a) is a top view which shows a ball screw typically, (b) is a rolling path. It is a figure which shows a cross section typically.

Hereinafter, an embodiment of a ball screw according to an aspect of the present invention will be described with reference to the drawings as appropriate.
As shown in FIG. 1, the ball screw 10 has a screw shaft 1 and a nut 2 screwed to the screw shaft 1 via a ball 3.
In the nut 2, the first nut 2A and the second nut 2B arranged in the axial direction and the spacer 9 interposed between the two nuts 2A and 2B are integrally configured. One nut 2A is formed with an annular flange 31 at the end. Between the inner peripheral part of the flange 31 and the screw shaft 1 and between the other axial end of the second nut 2B and the screw shaft 2 are closed by a dustproof seal 32. The two nuts 2A and 2B are positioned in the rotational direction by a key (not shown) inserted in the key groove 5 so that the phase in the rotational direction is not shifted.

  A helical thread groove 11 is formed on the outer peripheral surface of the screw shaft 1. The two nuts 2A, 2B are respectively formed with spiral thread grooves 21 facing the thread grooves 11 of the screw shaft 1 on the inner peripheral surfaces of the nuts 2A, 2B. Further, ball return passages 4a and 4b are formed in the nuts 2A and 2B along the axial direction of the nuts 2A and 2B. A pair of end deflectors 6a and 6b are fitted into both ends of the nuts 2A and 2B so as to communicate with both ends of the ball return passages 4a and 4b of the nuts 2A and 2B, respectively.

  The plurality of balls 3 are arranged in a circulation path including a rolling path formed by opposing screw grooves 11 and 21 and a ball return path. That is, the ball 3 rolling on the rolling path is moved up to one end of the rolling path of each nut 2A, 2B, and then scooped up by one end deflector 6a and passes through the ball return paths 4a, 4b to the opposite side. Is formed, and a circulation path is formed in which the other end deflector 6b returns to the rolling path again. The screw shaft 1 and the nut 2 move relative to each other via a plurality of balls 3 rolling (moving while rotating in a loaded state) in the rolling path while circulating through the circulation path. .

  When preload is applied to the ball screw 10, the nut 9A is clamped between the two nuts 2A, 2B and tightened in the axial direction, and an opposite axial force is applied to each nut 2A, 2B. Thus, a preload is applied to the ball 3 in the rolling path. The amount of preload is adjusted by the thickness of the spacer 9. Thereby, each ball 3 contacts at one point of one point of the screw groove 21 of the nuts 2A, 2B and one point of the screw groove 11 of the screw shaft 1 at a position opposite to this.

  That is, this ball screw 10 adopts a double nut spacer preload system as a preload application system, and applies a preload by shifting the lead between the left and right rolling paths, thereby making contact between the ball 3 and the rolling path. It is a two-point contact type. However, in this embodiment, when the nut 2 and the screw shaft 2 are moved relative to each other in the axial direction via the rolling of the ball 4, the groove type is such that the third contact occurs due to the ball biting behavior. It is set.

  In the present embodiment, an example of a fixed position preload that employs a double nut spacer preload method as a preload addition method has been shown, but the present invention is not limited to this, and if a preload is applied by a double nut preload method, A constant pressure preload may be used. The ball screw 10 is used by applying a preload by a double nut preloading method or a constant pressure preloading method, and the ball screw load is only the preload, and the magnitude thereof is 3 to 5% of the dynamic load rating.

FIG. 2 shows a cross-sectional shape of the rolling path formed by the opposed screw grooves 11 and 21 at a right angle to the groove.
In the ball screw 10, the screw groove 11 of the screw shaft 1 and the screw groove 21 of the nut 2 are both gothic arc grooves. That is, the cross-sectional shapes of the screw groove 11 of the screw shaft 1 and the screw groove 21 of the nut 2 are substantially V-shaped in which two identical circular arcs having different centers of curvature are combined. Here, in this embodiment, the groove R ratio (the radius of curvature R of the thread groove cross section / the outer diameter Da of the ball) is a value in the range of 0.52 to 0.54 or 0.54 to 0.56. It is set to.

  A land chamfer 7 that smoothly connects to the land 12 of the screw shaft 1 is formed outside the screw groove 11 of the screw shaft 1 (both edges of the land 12), and the substantially V-shaped screw groove 11 is formed. The bottom of the groove 11d is formed with a groove bottom. Similarly, the land chamfered portion 8 that smoothly connects to the inner peripheral surface of the nut 2 is formed on the land outer side (both edges) of the screw groove 21 of the nut 2, and the substantially V-shaped screw groove 21. The bottom of the groove is formed with a groove bottom relief 21d.

Hereinafter, the rolling path of the ball screw 10 will be described in more detail.
In the ball screw 10 of the present embodiment, as shown in FIG. 3, the opposing flanks of the groove shape of the ball screw 10 are respectively the grooves F1 and F2 and the contact angle when the single clearance is zero is α, and the initial contact angle is α ₀ ((FIG. 5B)), the chamfering start angle of the land chamfer 7 of the screw shaft 1 is defined as β _1B , and the groove bottom relief start angle of the screw shaft 1 is defined as β _2B .

In FIG. 3A, a ball 3 (ball diameter φD _a ) drawn by a broken line represents a case where the single clearance is zero, and at this time, the ball 3 is a Gothic arc groove (screw groove) of the screw shaft 1 and the nut 2. 11 and 21) and contact each other at a contact angle α at a load angle of zero at a total of four locations. Here, in the present embodiment, the contact angle α when there is no single nut clearance is set in the range of 40 ° to 50 °.

However, it is more reasonable to consider that the condition as shown in the figure can hardly occur in practice due to the dimensional error of each part of the ball screw and the like. Therefore, in the ball screw of this embodiment (in particular, a ball screw used in a region where the preload load Fa is 3 to 5% of the dynamic rated load Ca), as shown by the solid line 3 in FIG. It is considered that there is _a slight clearance (ΔD _a ) between the ball 3 and the screw grooves 11 and 21.

In other words, a normal ball screw has _a clearance (ΔD _a ) between the ball and the track, and as a result, in a two-point contact ball screw, relative displacement (axial clearance, diameter) between the screw shaft 1 and the nut 2 is caused. Direction gap) occurs. If the screw shaft 1 and the nut 2 are moved in the axial direction by the clearance (ΔD _a ) between each of the screw grooves 11 and 21 and the ball 3, as shown in FIG. , 21) can be considered to be in two-point contact with zero load. At this time, the contact angle between the ball 3 and the orbit changes from the contact angle α when the single clearance is zero to the initial contact angle α ₀ , and the axial direction between the screw shaft 1 and the nut 2 at this time relative displacement, as shown in FIG. 2, defined in the present invention, the axial clearance s _a of a nut alone.

Here, in the first aspect of the present embodiment, when the groove R ratio is from 0.54 to 0.56, the chamfer start angle beta _1B of the screw shaft 1 is a 65 ° to 75 °, further axial clearance _{s a} Is set to satisfy the range of 0.17% <s _a / D _a ≦ 3.6% with respect to the ball diameter φD _a of the ball 3 used.
Further, in the second aspect of the present embodiment, when the groove R ratio is from 0.52 to 0.54, the chamfer start angle beta _1B of the screw shaft 1 is a 60 ° to 65 °, further axial clearance _{s a} is It is set to satisfy the range of 0.17% <s _a / D _a ≦ 1.66% with respect to the ball diameter φD _a of the ball 3 to be used.

In general, as shown in FIG. 4, the internal clearance ΔD _a of _a normal ball screw is set to a small value (axial clearance s _{a for} the purpose of reducing backlash and suppressing the biting behavior of the ball. is _{s a} / _D a ≦ _0.17% with respect to the ball diameter _{D a} of the ball to be used _{(s a / D a ≦ 1} /600)).

On the other hand, the ball screw 10 of the present embodiment has a considerably larger internal clearance ΔD _a than that of a normal product as shown in FIG. Therefore, the relationship between the ball 3 and the raceway (screw groove 11, 21), as shown in FIG. (B), by increasing the internal clearance [Delta] D _a, conventional initial contact angle alpha ₀ is, as shown in FIG. 4 The axial rigidity is also increased, and lost motion can be reduced or minimized.

Hereinafter, the ball screw 10 of the above-described embodiment will be described in more detail based on examples.
Table 1 shows the specifications of a ball screw for machine tools (ball screw manufactured by NSK Ltd., model: BS3610). Table 1 shows the specifications of the ball screw (normal ball screw (comparative example) and the product of the present invention) which is the basis of the simulation analysis in the first embodiment.

  The first embodiment uses the normal ball screw (comparative example) shown in Table 1 and the product of the present invention, and when the actual contact state (FIG. 3 (b), FIG. 4 (b)) is reached, It is a simulation analysis which reduced or minimized the lost motion at the time of reversal of the drive direction of a screw. The relationship between axial displacement and lost motion when the preloaded ball screw shown in Table 1 is operated is shown in FIG.

As shown in FIG. 5, when the clearance / ball diameter ratio s _a / D _a is larger than the clearance / ball diameter ratio s _a / D _a of the normal product, the axial rigidity of the ball screw increases, and the operation is in progress. It can be seen that the displacements δ _xF (positive direction operation) and δ _xB (reverse direction operation) between the screw shaft and the nut of the above are reduced. Also, the difference in displacement [delta] _xF and [delta] _xB between the screw shaft and the nut in operation (area indicated by hatching), i.e., lost motion _{Δe p = | δ xF -δ xB} | but also have decreased ascertained . In order to form the present invention product, only the internal clearance ΔD _{a with} respect to a normal product ball screw so as to obtain a desired internal clearance (a clearance / ball diameter ratio s _a / D _a > 0.2%). It is only necessary to incorporate a small ball 3.

Next, the relationship between the examples in various internal clearances (clearance / ball diameter ratio s _a / D _a ) and the landing / lowering of the ball 3 on the land chamfered portion 7 will be described in detail.
Against the preload ball screw of the first embodiment shown in Table 1, the lost motion and its reduction rate in the case of changing the axial clearance s _a to various _{(0% ≦ s a / D} a ≦ 10%) The analysis results are shown in FIGS. 6 (a) and (b), respectively.

From Figure 6, an increase in the axial clearance s _a, and decreased lost motion reduction rate Rep and lost motion delta _ep together, it can be seen that the higher the effect of reducing the lost motion. However, as the axial clearance s _a is increased, the contact angle is not only increased as shown schematically in FIG. 7 and FIG. 8 in particular, but in particular, reference symbols A and B in FIGS. In the part shown by, the ball biting behavior during operation makes it easy for the shoulders of the screw grooves 11 and 21 to run on the land chamfers 7 and 8 (see the enlarged view of the main part in FIG. 9).

  As shown in an enlarged view in FIG. 9, when the ball 3 rides on the land chamfered portion 7, there is a concern that early breakage may occur due to the edge surface pressure at the shoulder portion of the screw groove 11. Further, when the operation direction of the ball screw 10 is reversed, the direction of biting of the ball is also reversed. Therefore, when the operation is performed in the reverse direction, the screw shaft 1 rides on the groove bottom 1d, and the nut 2 enters the chamfered portion 8 of the land. There is concern about getting on board.

Therefore, axial clearance s _a screw shaft 1 and riding rate to land chamfer 7,8 of the nut 2 of the ball screw 10 of the present inventions, shown in Table 1, the groove bottom relief 1d, the ride down rate to 2d If it analyzes, it will become like each of FIG. 10 (a)-(d).
However, in the product of the present invention, the riding up / down rate of the ball 3 is defined as (Equation 4) below, and it is shown that the riding up / down occurs when these symbols are positive. There is. Although contact points with the balls 3 do not have an oval shape as shown in FIG. 9 when riding on the land chamfered portion 7 occurs, the land chamfered portion 7 does not have an oval shape as shown in FIG. The analysis was performed ignoring the edge surface pressure.

As shown in FIGS. 10 (a) and 10 (b), the land chamfers 7, 8 of the screw shaft 1 and the nut 2 are made in the region where the clearance / ball diameter ratio s _a / D _a is s _a / D _a > 6%. It can be seen that the ride of
On the other hand, as shown in FIGS. 10C and 10D, when the screw shaft 1 and the nut 2 are lowered onto the groove bottom dented portions 1d and 2d, the lowering rate is considerably smaller than the rising rate, and the clearance / ball diameter ratio s. _{In a} region where a 1 / D _a exceeds about 1.6%, the boarding rate further decreases. Therefore, it is apparent that the upper limit of the clearance / ball diameter ratio s _a / D _a when the axial clearance s _a is increased is determined by the influence of the screw shaft on the land chamfered portion.

Meanwhile, as shown in FIG. 10 (a) ~ (d) , looking at the ride rate or ride down ratio during operation of the ball screw 10, the gap / ball diameter ratio _s a / _{D a} is at 1.8% near You can see that it has an inflection point. Furthermore, in 0% ≦ s _a / D _a <1.8%, riding up / down is shown in the groove F2 (that is, the non-load side thread groove flank) during forward or reverse operation.

This is because in the region of 0% ≦ s _a / D _a <1.8%, the ball 3 which is in contact at two points at rest becomes three-point contact due to the ball biting behavior during operation of the ball screw 10 If the ball diameter ratio s _a / D _a exceeds 1.8%, even if the ball biting behavior occurs, the axial clearance s _a is large, so the biting is saturated before the three-point contact. Further, from FIG. 6, the lost motion in the region of 0% ≦ s _a / D _a <1.8% and in the region of the gap / ball diameter ratio s _a / D _a of s _a / D _a > 1.8% When the reduction effects are compared, it can be confirmed that the reduction effect is larger in the former region. Further, as shown in FIGS. 10A to 10D, the two-point contact state in the region where the clearance / ball diameter ratio s _a / D _a is 0.5% ≦ s _a / D _a ≦ 1.8%. It turns out that it is not.

Next, _a preferred range of the axial clearance sa applied to the product of the present invention will be described in detail based on examples.
As mentioned earlier, increasing the axial clearance s _a, it is possible to reduce the lost motion. However, if the set value of the axial clearance s _a exceeds a certain upper limit, the ball 3 may run onto the land chamfered portion 7 of the screw shaft 1. Here, the upper limit of the gap / ball diameter ratio s _a / D _a is about s _a / D _a <0.2% in the case of a normal ball screw, but in the present invention, the region greatly exceeds this value Used in Therefore, in order to determine the upper limit of the axial clearance s _a which may be applied to the present invention product, the internal design value of various ball screw and the screw groove shape, the runs on the land chamfer of the lost motion reduction rate and the screw shaft Examined.

In order to confirm the range of more effective clearance / ball diameter ratio s _a / D _a applied to the present invention, the ball screw in the embodiment of the present invention shown in FIG. 6 and FIG. Analyzes were conducted on different ball screws. As shown in Table 2, the ball screw used in the analysis is, in addition to the ball screw (BS 3610) in the first embodiment, a small diameter ball screw (BS 1004) as the second embodiment, as shown in Table 2. In addition, there are three types of large-diameter ball screws (BS6316) as a third embodiment.

Based on the specifications of Table 2, in the case of changing the axial clearance s _a variously above three and lost motion reduction ratio Re _p to the ball screw, the screw shaft 1 and the nut 2 land chamfered portions 7 and 8 The climbing rates ε _1B and ε _1M are shown in FIGS. 11 and 12, respectively.

Than the lost motion reduction rate Re _p shown in FIG. 11, when the specifications of the ball screw 10 is also different, is verified can be lost motion reduced by increasing the axial clearance s _a.
Next, with regard to the run-up on the land chamfered portions 7 and 8 of the screw shaft 1 and the nut 2, with a large diameter ball screw such as BS6316, the groove R ratio is 52%, which is smaller than that of the normal size. There is a concern about riding on land chamfers 7 and 8 of the However, as shown in Table 2, in the large-diameter ball screw such as BS 6316, the chamfering start angle is set to be larger than the others, so as shown in FIG. 12, the clearance / ball diameter ratio s _a / D _a It can be seen that the ride has begun in an area exceeding 6%.

Next, examples in the case of different screw groove shapes will be described.
As described with reference to FIGS. 6 and 11, the lost motion reduction effect of the present invention is established regardless of the specifications and size of the ball screw. However, as described above, the range of axial clearance s _a capable established advantages of the present invention product is limited by the riding of balls 3 to the land chamfer 7 during operation of the ball screw 10. Accordingly, based on the first embodiment, the effectiveness of the present invention was analytically investigated for three types of ball screws having different contact angles and chamfering start angles. Table 3 shows the specifications of the three ball screws used in the analysis.

Based on the specifications of Table 3, in the case of changing the gap / ball diameter ratio s _{a /} D _a variously 3 types of lost motion reduction ratio Re _p from the screw groove shape K1 for K3 of the ball screw 13 Also, FIG. 14 shows a running rate ε _{1B of} the screw shaft 1 on the land chamfered portion 7 and a running rate ε _{1M of the} nut 2 on the land chamfered portion 8, respectively.
It can be seen from FIG. 13 that in the case of the thread groove shapes K1 and K2, there is no difference with respect to the lost motion because the thread groove shape is different only in the land chamfering start angle β _{1 B} and the nib start angle. In the screw groove shape K3, the contact angle α is different from the other lands chamfered start angle beta _1B and relief start angle, although differences appearing in lost motion reduction ratio Re _p, in any of the thread groove shape, the as is apparent from the lost motion reduction rate Re _p of FIG validity is verified against lost motion reduction products of the present invention.

Next, referring to FIG. 14, when comparing the thread groove shapes with respect to the landing of the ball 3 on the land chamfered portion 7, the chamfering start angle β _1B of the screw shaft 1 is slightly different between the thread groove shape K 1 and the thread groove shape K 2. It is smaller than the thread groove shape K2. For this reason, it can be seen that the clearance / ball diameter ratio s _a / D _{a at} which the ball 3 starts to ride is lower than the thread groove shape K1.
Further, although the screw groove shape K3 has a chamfering start angle β _1B of the screw shaft 1 smaller than that of the other two screw groove shapes K1 and K2, the contact angle α is α = 40 °, which is higher than that of the other screw groove shapes. Since the ball 3 is also small, the value of the clearance / ball diameter ratio s _a / D _a at which the riding of the ball 3 starts does not decrease significantly.

On the other hand, although the difference in chamfering start angle β _1M of the nut 2 is small in the thread groove shapes K1 to 3 from the nut climbing rate ε _1M shown in FIG. 14B, only the thread groove shape K3 has a different contact angle α. The value of the clearance / ball diameter ratio s _a / D _a at which the riding of the ball 3 starts is high, since the screw groove shape K1, K2 is smaller than the above. In any case, from the analysis result of the thread groove shape K3 of the riding ratio ε _1B of the screw shaft 1 shown in FIG. 14, the gap / ball diameter ratio s _a / D _a is in the range of s _a / D _a <4.8% In this case, it is confirmed that the effectiveness of the present invention for reducing the lost motion is established.

Next, an embodiment in the case where the contact angle α is changed will be described.
The contact angle of the ball screw 10 of the first embodiment shown in Table 1 α = 40 °, 45 ° , prepared three different 50 °, with respect to these, various gaps / ball diameter ratio _s a / _{D a} 15 and FIG. 15 show the analysis results of the lost motion reduction rate Re _p , the climb rate ε _1B to the land chamfered portion 7, and the climb rate ε _1M of the nut 2 to the land chamfered portion 8, respectively. It is shown in 16.

As shown in FIG. 15, it can be seen that the effect of reducing lost motion is reduced when the contact angle α is increased. Further, as shown in FIG. 16, it is confirmed that when the contact angle α is increased, the clearance at which the ball 3 starts to climb is reduced.
Thus, in the present invention product, by taking large axial clearance s _a ball screw 10, since the initial contact angle alpha ₀ is also increased axial stiffness increases, aimed at reducing the lost motion as a result It is a thing. However, in practice, it has been clarified that simply increasing the contact angle α to increase the rigidity of the ball screw has no significant effect on reducing the lost motion.

The reason is that, as seen in FIG. 16, the curve of the riding ratio has an inflection point in the vicinity of the gap / ball diameter ratio s _a / D _a = 1.0 to 1.1% when α = 50 °. On the other hand, when α = 40 °, there is an inflection point in the vicinity of s _a / D _a = 2.0%. That is, by reducing the contact angle α, the area of the axial clearance s _a (clearance / ball diameter ratio s _a / D _a ) that can be contacted at three points is increased. For this reason, since the lost motion reduction effect is increased in the region where the three-point contact occurs (0% <s _a / D _a <2%), the smaller the contact angle α, the higher the effectiveness of the product of the present invention. It is thought that it became.

That is, by increasing the axial clearance s _a as in the present invention product, as well as axial stiffness increases due to an increase in the initial contact angle alpha _0, from multiple factors by expanding the gap region capable three-point contact, lost motion reduction effect It is thought that was demonstrated.
From the above, the contact angle of the gothic arch groove alpha is, for alpha ≦ 50 ° to become such a ball screw, axial clearance s _a is a gap / ball diameter ratio s _{a /} D _a ≦ 3.6% Then, the effectiveness of the lost motion reduction effect was confirmed.

Next, a description will be given of an embodiment in the case of changing the groove R ratio f _p.
The groove R ratio f _p of the ball screw 10 of the first embodiment shown in Table 1 is prepared in three ways of f _p = 0.52, 0.54, and 0.56, and the gap / ball diameter ratio with respect to these is prepared. in the case where a s _{a /} D a is changed variously, the lost motion reduction rate Re _p in FIG. 17, also rides ratio epsilon _1M to ride rate epsilon _1B and nut chamfer _8, to the land chamfer 7 The results of analyzing are shown in FIG.

As shown in FIG. 17, reducing the groove R ratio f _p, as is apparent from the lost motion reduction rate Re _p, it can be seen that the improved effect of reducing the lost motion. However, from FIG. 18, reducing the groove R ratio f _p, it is confirmed that gap ride begins balls 3 is small.
This, reducing the groove R ratio f _p, but is suppressed ball bite behavior is the lost motion is reduced, since the major axis radius of the contact ellipse is increased, presumably because that is easily ride the ball 3. The large-diameter ball screw high load for, for the purpose of reducing the contact surface pressure, but in many cases to design the groove R ratio f _p 0.52, the area to which the present invention can be applied is narrowed.

Next, an example in which the land chamfering start angle β _1B of the screw shaft 1 is changed will be described.
The land chamfering start angle β _1B of the ball screw 10 of the first embodiment shown in Table 1 is prepared in four ways of β _{1 B} = 60 °, 66 °, 70 °, 75 °, and with respect to these, clearance / ball FIG. 19 shows the result of analyzing the lost motion reduction rate Re _p and the climbing rate ε _1B to the land chamfer 7 when the diameter ratio s _a / D _a is changed variously. As shown in the figure, it can be seen that the area of the gap / ball diameter ratio s _a / D _a applicable as the present invention becomes smaller if the land chamfering start angle β _{1 B} is made smaller.

Next, an embodiment will be described in the case where the run-up of the ball 3 on the land chamfered portion 7 of the screw shaft 1 is most concerned.
That is, based on the analysis results described above, when the present invention is applied, the ball screw 10 that is most concerned about the climbing of the screw shaft 1 onto the land chamfered portion 7 is the large-diameter ball screw (BS 6316, groove R ratio f _p = It is 0.52), and land chamfering start angle beta _{1B of} screw axis 1 is composition of beta _1B = 60 degrees (however, contact angle = 40 degrees) (refer Table 4).

Therefore, with respect to the ball screw as the specifications as described above, a gap / ball diameter ratio s in the case where the _{a /} D _a is changed variously, the lost motion reduction ratio Re _p, land chamfered portion of the screw shaft 1 As a result of analysis of the climbing rate ε _1B to 7, the results shown in FIGS. 20 (a) and 20 (b) were obtained. As shown in the figure, it was confirmed that the present invention is applicable if the gap / ball diameter ratio s _a / D _a satisfies s _a / D _a ≦ 1.66%.

As described above in detail based on the embodiments and examples for the present invention, according to the ball screw 10 according to one aspect of this embodiment, the axial clearance s _a of nuts alone, the balls used In the ball screw according to the first aspect with respect to the ball diameter φD _a , the gap / ball diameter ratio is set to 0.17% <s _a / D _a ≦ 3.6%, and the ball according to the second aspect In the case of a screw, the clearance / ball diameter ratio is set to 0.17% <s _a / D _a ≦ 1.66%, so by increasing the internal clearance, the lost motion generated when the ball screw is reversed can be reduced or It can be minimized. The ball screw according to the present invention is not limited to the above embodiment and examples, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

1 screw shaft 2 nut 3 ball 7 screw shaft land chamfered portion 8 nut land chamfered portion 11 screw shaft screw groove 12 screw shaft land 21 nut screw groove

Claims (3)

It has a screw shaft, a nut and a plurality of balls, and the screw shaft penetrates the nut and is formed on a helical thread groove formed on an outer peripheral surface of the screw shaft and an inner peripheral surface of the nut A method of setting an axial clearance of a nut of a ball screw in which a rolling path in which the plurality of balls revolve is formed by a spiral screw groove,
As the ball screw, the screw groove of the screw shaft and the nut are both a gothic arch groove is used to impart a preload by double nut preloading or constant pressure preloading, only the ball screw load the preload The size is 3 to 5% of the dynamic rated load, the contact angle is 40 ° to 50 ° when there is no nut clearance alone, the groove R ratio is 0.54 to 0.56, and the screw chamfering start angle of the land ends of the shaft to target shall be the 65 ° to 75 °,
The ball on the bottom of the groove of each screw groove so as not to cause the ball to ride on the land chamfered portion of each screw groove of the screw shaft and the nut due to the ball biting behavior during operation. so as not to cause the ride down of, based on the results of simulation analysis, an axial clearance in the nut itself, characterized that you set in a range satisfying the following (expression) relative to the ball diameter of the ball used How to set the axial clearance of a single ball screw nut .
0.17% <sa / Da ≦ 3.6% (Formula)
Here, sa is the axial clearance of the nut alone, and Da is the ball diameter of the ball used. It has a screw shaft, a nut and a plurality of balls, and the screw shaft penetrates the nut and is formed on a helical thread groove formed on an outer peripheral surface of the screw shaft and an inner peripheral surface of the nut A method of setting an axial clearance of a nut of a ball screw in which a rolling path in which the plurality of balls revolve is formed by a spiral screw groove,
As the ball screw, the screw groove of the screw shaft and the nut are both a gothic arch groove is used to impart a preload by double nut preloading or constant pressure preloading, only the ball screw load the preload Have a size of 3 to 5% of the dynamic rated load, a contact angle of 40 ° to 50 °, a groove R ratio of 0.52 to 0.54, and the screw when there is no single nut clearance. chamfering start angle of the land ends of the shaft to target shall be the 60 ° to 65 °,
The ball on the bottom of the groove of each screw groove so as not to cause the ball to ride on the land chamfered portion of each screw groove of the screw shaft and the nut due to the ball biting behavior during operation. so as not to cause the ride down of, based on the results of simulation analysis, an axial clearance in the nut itself, characterized that you set in a range satisfying the following (expression) relative to the ball diameter of the ball used How to set the axial clearance of a single ball screw nut .
0.17% <sa / Da ≦ 1.66% (Formula)
Here, sa is the axial clearance of the nut alone, and Da is the ball diameter of the ball used.   A ball screw is manufactured using the method of setting an axial clearance of a ball screw nut alone according to claim 1 or 2, wherein the ball screw is manufactured.

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