JP2003314659A - Ball screw device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase the load capacity of a ball screw device by reducing the maximum contact pressure P<SB>max</SB>while keeping a ride-on rate τ down to 0.05 or lower. <P>SOLUTION: The ball screw device comprises a screw shaft 3 having a spiral screw groove 2 in the outer periphery face, a nut 6 having a screw groove 4 in the inner periphery face corresponding to the screw groove 2, loosely fitted to the screw shaft 3, and a number of balls 5 rollingly loaded in a spiral load raceway formed between both screw grooves 2, 4, both screw grooves 2, 4 being offset Gothic arch grooves. A groove radius ratio f=r/d<SB>a</SB>as the percentage of an offset Gothic arch groove radius r of the screw shaft 3 or the nut 6 to a ball diameter d<SB>a</SB>is set to 0.515≥f≥0.504. <P>COPYRIGHT: (C)2004,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thread groove and a thread groove of a screw shaft.
And nut thread grooves are offset gothic arch grooves
Ball screw devices, especially injection molding machines and presses
Ball screw device suitable for high-load applications such as
I do. [0002] 2. Description of the Related Art As a conventional ball screw device, for example,
The one shown in FIG. 14 is known. This ball screw device
1 has a spiral thread groove 2 on the outer peripheral surface and extends in the axial direction.
Screw shaft 3 having a helical thread groove 4 on its inner peripheral surface.
6 is loosely fitted. Screw groove 4 of nut 6 and screw shaft 3
And a spiral load between them.
A track is formed, and the load track has a large number of rolling elements.
A number of balls 5 are rollably mounted. And
The rotation of the spindle 3 causes the nut 6 to move through the rolling of the ball 5.
To move linearly. In addition, the screw groove 4 and the screw shaft 3 of the nut 6
The shape of the thread groove 2 is offset as shown in FIG.
Gothic arch grooves are often used.
Is the offset amount, h is the groove shoulder height, β is the rest angle,
r is the groove radius, d_aIs the ball diameter. In addition, nut 6
When the ball moves linearly, the ball 5 is formed by both thread grooves 2 and 4.
It moves while rolling on the spiral load trajectory formed,
In order to move the ball 6 continuously, the ball 5
Infinite circulation is required. For this reason, for example, a part of the outer peripheral surface of the nut 6
Into a flat surface and communicate with both screw grooves 2 and 4 on this flat surface.
A pair of two holes 7 are formed so as to straddle the screw shaft 3.
U-shaped circulation tube as a ball circulation member in the set of holes 7
By fitting both ends of the bush 8,
The ball 5 revolving along the load orbit is placed in the middle of the load orbit.
From the ball to the original load trajectory
Back, so that the ball 5 circulates infinitely
ing. [0005] The ball screw device is provided with a lubricant bearing.
In order to seal inside, or to remove dust from outside
Seal 9 is used to prevent entry into the running surface
Often. The seal 9 is, as shown in FIG.
And fitted into the thread groove 2 of the screw shaft 3 in the inner diameter part
Is generally provided with a protruding portion 9a.
The screw is screwed to the end of the slot 6 through the screw hole 9b,
A slight clearance on the sliding contact side, or
a has a lip and is in contact with the thread groove 2. [0006] Problems to be Solved by the Invention
With the trend toward injection, injection molding, which was conventionally driven by hydraulic equipment,
Forming machines and press machines tend to be electrified, and injection
Hydraulic devices replace drive mechanisms such as molding machines and press devices
Ball screw device with high mechanical efficiency is used
Examples are increasing. However, injection molding machines and press machines
What if the drive requires a particularly large load capacity?
Regarding the load capacity, the hydraulic drive
The load is received on the surface of the hydraulic piston, while the ball screw
The device loads multiple balls and nuts and the screw on the screw shaft
Due to the difference in the structure of receiving at the contact point with the groove, the ball screw
The device has the disadvantage that it is inferior to the hydraulic device. When the load is large, a plurality of balls
Contact at the point of contact between the nut and the thread groove of the nut or screw shaft
Pressure P_maxIs too high, the fatigue of the ball screw device
The life is shortened. Also, when the load is large, multiple baud
Angle α between the nut and the thread groove of the nut or screw shaft (see Fig. 17).
Large) and the contact ellipse also becomes large.
The contact ellipse protrudes from the thread groove of the screw or screw shaft and the thread groove
The ball easily rides on the shoulder. Ball is thread groove
When you get on the shoulder of the ball, an edge load occurs and the ball
The fatigue life of the same device is reduced. Therefore, the maximum contact pressure P_maxAnd FIG.
The running distance l of the ball 5 shown₀Major axis length of contact ellipse
Ride rate τ = 1, which is the ratio to 2a₀/ 2a is Bo
Dominant Constraints Determining the Maximum Load Capacity of a Screw Device
Becomes Here, the maximum contact pressure P_maxAnd ride
The maximum axial load that satisfies the two constraints
Load capacity F_{a max}And The present invention has been made in view of such a technical background.
And increased load capacity.
It is an object to provide a ball screw device. [0011] [MEANS FOR SOLVING THE PROBLEMS] To achieve the above object
In addition, the invention according to claim 1 has a spiral thread groove on the outer peripheral surface.
Having a screw shaft and a screw groove corresponding to the screw groove of the screw shaft
A nut having an inner peripheral surface and being loosely fitted to the screw shaft;
Rollable to spiral load track formed between both screw grooves
With many balls loaded, both screw grooves are off
Set gothic arch groove ball screw device smell
And the maximum contact pressure P_maxTo lower the screw
Offset Gothic arch groove radius of shaft and said nut
ball diameter d of r_aGroove radius ratio f = r
/ D_aIn the range of 0.515 ≧ f ≧ 0.504
It is characterized by. According to the above construction, the groove radius ratio f is set to 0.51.
By setting the range of 5 ≧ f ≧ 0.504, the conventional button
Contact pressure P compared to_maxWill be lower
And the load capacity F_{a max}Increase. Where the shoulder of the thread groove
Offset ball to prevent the ball from getting on
Ball diameter d of shoulder height h of thick arch groove_aRatio to
Groove shoulder height ratio λ = h / d_a0.50 ≧ λ ≧ 0.3
It is preferably within the range of 6. Thus, when the groove shoulder height ratio λ is 0.50 ≧ λ
If ≧ 0.36, the ride rate τ is 0.05 [-].
Since it does not exceed, the maximum contact pressure P_maxLoad with decline
Capacity F_{a max}Increase. Also, the shoulder to the thread groove
Four offset screws to prevent
51 ° ≧ β ≧ 17 °
It is preferable to set it in the range. Thus, the rest angle β is 51 ° ≧
If β ≧ 17 °, the ride rate τ (= ride of ball 5)
Lifting distance l₀/ Long axis length 2a of contact ellipse: see FIG. 17)
Does not exceed 0.05 [-], the maximum contact pressure P_max
Load capacity F_{a max}Increase. In addition, screws
To prevent the ball from climbing over the shoulder of the groove,
Al gap δ _rBall diameter d_aIs the ratio to
Gap ratio Δ = δ_r/ D_aIs 1.89 × 10^-3≧ Δ ≧ −
1.57 × 10^-3It is preferable to set it in the range. As described above, the radial gap ratio Δ is 1.89.
× 10^-3≧ Δ ≧ −1.57 × 10^-3If you get on
Since the rate τ does not exceed 0.05 [-], the maximum contact pressure P
_maxLoad capacity F_{a max}Increase. here
The groove radius ratio f, groove shoulder height ratio λ, and resting
Β and radial gap ratio Δ all satisfy the above range
Is most preferable, the groove radius ratio f, the groove shoulder height ratio λ,
At least the angle β and the radial gap ratio Δ
Even if one satisfies the above range, the load capacity F_{a max}of
Increase is possible. [0016] DESCRIPTION OF THE PREFERRED EMBODIMENTS The following is an example of the embodiment of the present invention.
Will be described with reference to the drawings. FIG. 1 shows an embodiment of the present invention.
Explanatory sectional view and diagram of a conventional ball screw device used for description
2 is the coordinate system used for numerical analysis of the ball screw device of FIG.
FIG. 3 is an explanatory view showing a ball according to an embodiment of the present invention.
To explain the thread groove shape of the nut and screw shaft
FIG. 4 shows the edge load ratio P._e/ P_hAnd ride
FIG. 4 is a graph showing a relationship with the deflection ratio τ. Note that FIG. 1 and FIG.
The ball screw device shown in FIG. 2 and FIG.
Since the basic configuration is almost the same as the
The description is omitted by attaching reference numerals. Maximum allowable contact pressure of the ball screw device
P_maxIs determined by the material that composes the ball screw device.
You. As an example of a conventional ball screw device for high load applications,
Outer diameter of shaft 100 [mm], pitch circle diameter 104 [mm],
Ball diameter (d_a) 19.05 [mm], per row
43 effective balls, effective number of turns per row 2. 5 volumes, number of columns
FIG. 1 shows a four-row ball screw device. In this example,
For ball screw equipment, use common materials such as carburized steel.
I assume. This ball screw device has a coordinate system
Each axis of x, y, z (the origin is the center of four rows) as shown in FIG.
And fix the left end (flange) of the nut 6 and
A tensile load is applied to the left end of the screw shaft 3 in the negative direction of the x-axis.
The loaded state is numerically analyzed and the rotational speed is 250 [min].^-1]
Calculate the size of constant load that gives 5000 hours life
1.65 × 10^Five[N]. At this time, the ball 5 and the load track (screw groove)
2,4) the maximum contact pressure generated between_maxIs 1.8
8 [GPa]. Therefore, the ball screw device
The maximum contact pressure P that can be tolerated by common materials_max
Is about 1.88 [GPa]. Ball 5 thread groove
The edge road that occurs at the part where
Peak pressure P_eIs the ride rate τ (= the ride of ball 5)
Distance l₀/ Long axis length 2a of contact ellipse: see FIG. 17)
Therefore, it changes. Edge load peak pressure P_eAnd ride
Maximum contact pressure P without raising_hRatio, that is,
Jiroth ratio P_e/ P_h Numerical solution of the relationship between
The results of the analysis are shown in FIG. As can be seen from FIG.
When the pressure is larger than 08 [-], the peak pressure P_eGot on
Contact pressure P in the absence of pressure_hWill be exceeded. baud
The fatigue life of the screw device is the peak pressure P_eOr ride
Maximum contact pressure P without raising_hWhichever is greater
Depends on Considering the groove tolerance,
If the ride rate τ is 0.05 [-] or less, the ride rate
τ does not affect fatigue life. As described above, the maximum contact pressure P_max
Is 1.88 [GPa] or less and the riding ratio τ is
Groove radius ratio while satisfying the condition of 0.05 [-] or less
f = r (groove radius) / d_a(Ball diameter), groove shoulder height ratio λ
= H (groove shoulder height) / d_a(Ball diameter), restoring
Β and radial gap ratio Δ = δ_r(Radial gap) /
d_aAt least one of the (ball diameter)
If selected, the load capacity F of the ball screw device_{a max}Increases
I do. Here, in this embodiment, the most suitable
As an example, the groove radius ratio f is set to 0.510 ≧ f ≧ 0.504.
And the groove shoulder height ratio λ is in the range of 0.50 ≧ λ ≧ 0.36.
And the rest angle β is in the range of 51 ° ≧ β ≧ 17 °
And the radial gap ratio Δ is 1.89 × 10^-3≧ Δ ≧ −
1.57 × 10^-3Load capacity of ball screw device as the range of
Quantity F_{a max}Is increasing. FIG. 3 shows that the groove radius ratio f = 0.50 within the above range.
5. Groove shoulder height ratio λ = 0.397, rest angle β = 2
5 °, radial gap ratio Δ = 5.25 × 10^-FourScrew
The shape of the grooves 2 and 4 is shown. And the shape of these thread grooves 2 and 4
And ball diameter d_aFigure 1 shows the number of balls, the number of turns, and the number of rows.
Negative value when the same as the conventional ball screw device shown
Load capacity F_{a max}Is 2.60 × 10^Five[N]
Load capacity F of ball screw device_{a max}= 1.65 × 10
^FiveIt increases 57.6 [%] compared to [N]. Next, the groove radius ratio f, the groove shoulder height ratio λ, the rest
Angle β and radial gap ratio Δ are determined within the above ranges.
Explain why. First, the range of the groove radius ratio f is determined.
You. The smaller the groove radius ratio f, the greater the maximum contact pressure P_maxDecreases
On the contrary, the smaller the groove radius ratio f, the larger the riding ratio τ.
Load capacity F_{a max}The largest groove half
There is a range of the diameter ratio f. A ball screw device having the same shaft diameter as that of FIG.
And the load capacity F when the groove radius ratio f is used as a parameter.
_{a max}And the load capacity F of the ball screw device of FIG._{a max0}Ratio
Load capacity ratio F_{a max}/ F_{a max0}Of the groove radius ratio f
The relation is shown in FIG. As can be seen from FIG. 5, 0.515 ≧ f
≥0.504 compared to conventional ball screw devices
Be F_{a max}Increases by 10% or more, and 0.510 ≧ f ≧
0.504 range compared to conventional ball screw device
F_{a max}Increases by 30% or more, especially 0.508 ≧ f
In the range of ≧ 0.504, the conventional ball screw device
Compare F_{a max}Increases by 50% or more. From the above, the range of the groove radius ratio f is 0.515
≧ f ≧ 0.504, preferably 0.510 ≧ f ≧
0.504, more preferably 0.508 ≧ f ≧ 0.50
And 4. Next, the range of the groove shoulder height ratio λ is determined. Groove shoulder
The larger the height ratio λ, the smaller the riding ratio τ
However, the ball screw device of the present invention is
Misalignment of screw shaft 3 caused by applying an axial load
Nut 6 and screw shaft 3 due to misalignment
The upper limit of the groove shoulder height ratio λ is
0.50. Conversely, the lower limit of the groove shoulder height ratio λ is half the groove
Minimize the diameter ratio f and minimize the rest angle β
Or reduce the radial gap ratio Δ to reduce the load
When the contact angle α is the smallest while receiving
And the ride rate τ is 0. From conditions not exceeding 05 [-]
Decided. FIG. 6 shows the load capacity of the ball screw device of the present invention.
The relationship between the running ratio τ and the groove shoulder height ratio λ when the weight ratio is 1.5
Show the person in charge. As shown in FIG. Over 05 [-]
The lower limit of the groove shoulder height ratio λ under the impossible condition is 0.36.
I understand. From the above, the range of the groove shoulder height ratio λ is 0.50 ≧ λ ≧
0.36. Next, the range of the rest angle β is determined.
You. The smaller the rest angle β, the greater the maximum contact pressure P_max
Becomes larger, the load capacity F_{a max}1.88 depending on
[GPa] ≧ P_maxThe minimum response that can satisfy the condition
Angle β exists. First, the load capacity F_{a max}Is 3
0% or more (load capacity ratio 1.3)
And the maximum contact pressure P_maxAnd the relationship between the rest angle β
As shown in FIG. FIG. 7 shows that the rest angle β is 17 ° or less.
When the maximum contact pressure P_maxExceeds 1.88 [GPa]
You. Therefore, the load capacity F_{a max}Increases by 30% or more
The lower limit of the rest angle β is 17 °.
You. Next, the load capacity F_{a max}Is 50% or more
Maximum contact when increasing (load capacity ratio 1.5)
Pressure P_maxFIG. 8 shows the relationship between and the rest angle β. Figure
Maximum contact when the rest angle β is less than 20 ° from 8
Pressure P_maxExceeds 1.88 [GPa]. Therefore, negative
Load capacity F_{a max}Increases by more than 50%.
Thus, the lower limit of the rest angle β is 20 °. Also, the larger the rest angle β,
Since the increase rate τ increases, the load capacity F_{a max}In response to the
Maximum response that can satisfy the condition of 0.05 [-] ≥ τ
Angle β exists. First, the load capacity F_{a max}Is 3
0% or more (load capacity ratio 1.3)
FIG. 9 shows the relationship between the riding ratio τ and the rest angle β.
Show. From FIG. 9, when the rest angle β is 51 ° or more,
Ride rate τ exceeds 0.05 [-]. Therefore, the load
Capacity F_{a max}Is increased by 30% or more,
The upper limit of the rest angle β is 51 °. Next, the load capacity F_{a max}Is 50% or more
In case of increase (load capacity ratio 1.5)
FIG. 10 shows the relationship between the ratio τ and the rest angle β. FIG.
Ride when the rest angle β is 30 ° or more from 0
The ratio τ exceeds 0.05 [-]. Therefore, the load capacity F
_{a max}Is increased by more than 50%
The upper limit of the angle β is 30 °. From the above, the load capacity F_{a max}Is less than 30 [%]
The range of the rest angle β that increases upward is 51 ° ≧ β ≧ 17
° and the load capacity F_{a max}Increase by more than 50%
The preferred range of the rest angle β is 30 ° ≧ β ≧ 20
°. Next, the range of the radial gap ratio Δ is determined.
Since the object of the present invention is to increase the load capacity, it is possible.
As long as the contact pressure between the ball 5 and the load track decreases
It is necessary to select the condition of the radial gap ratio Δ. When the radial clearance ratio Δ is negative, that is,
Prestressing load is applied if the clearance is
I don't. However, a load capacity ratio of 1.5 is realized.
When selecting such a groove radius ratio f, the conventional ball screw device
Even if a preload equivalent to 20% of the load capacity of
As a result, the load capacity increases by more than 30%.
Negative gaps can be said to be well tolerated. The ball screw device of the present invention has a radius
As the gap ratio Δ gradually decreases, the ball 5
Lower limit where it runs over the joint at the bottom of the rock arch groove
Is determined, and the value is −1.57 × 10^-3Becomes Follow
Therefore, the lower limit of the radial gap ratio Δ is −1.57 × 10^-3In
You. On the other hand, when the radial gap ratio Δ increases, the ball 5
It is easy to ride on the groove shoulder, but the ride rate τ is 0.05
Condition of the radial gap ratio Δ so that it is lower than [-].
It is necessary to select. FIG. 11 shows a ball screw device having a load capacity ratio of 1.5.
Ride when setting the groove radius ratio f as a parameter
6 shows the relationship between the ratio τ and the radial gap ratio Δ. From FIG.
As shown, the radial gap ratio Δ is 1.89 × 10^-3below
At this time, the riding ratio τ becomes 0.05 [−] or less. Follow
Therefore, the upper limit of the radial gap ratio Δ is 1.89 × 10^-3In
You. From the above, the range of the radial gap ratio Δ is 1.
89 × 10^-3≧ Δ ≧ −1.57 × 10^-3And In addition,
The ball screw device of the present invention is limited to the above embodiment.
Not within the spirit of the present invention.
It can be changed as appropriate. For example, in the above embodiment,
Example of applying the present invention to a ball type ball screw device
But is not limited to this, as shown in FIG.
The pocket 21 which holds the ball 5 so as to be able to roll is the ball 5
Provided with connection type holding pieces 20 formed according to the number of
Ball screw device, and as shown in FIG.
Circles on both sides facing the ball 5 interposed between
Arc, offset arc, parabolic or conical
With a detachable holding piece 30 having a concave surface 31
The present invention may be applied to a screw device. Ball screw device equipped with these holding pieces
The operation is higher than that of the all ball type ball screw device.
It is excellent in terms of performance, low noise, etc.
Suitable for high-speed and high-load environments
Used for [0038] As is clear from the above description, the present invention
According to the maximum contact rate while keeping the ride rate below 0.05
Contact pressure P_maxSo you can lower the ball
Effect that the load capacity of the same device can be increased
Is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory sectional view of a conventional ball screw device used for describing an embodiment of the present invention. FIG. 2 is an explanatory diagram showing a coordinate system used for numerical analysis of the ball screw device of FIG. FIG. 3 is an explanatory diagram for explaining a thread groove shape of a nut and a screw shaft of the ball screw device according to the embodiment of the present invention. 4 is a graph showing the relationship between rate ride and Etsujirodo ratio P _e / P _h τ. FIG. 5 is a graph showing a relationship between _a load capacity ratio _Famax / _Famax0 and a groove radius ratio f. FIG. 6 is a graph showing a relationship between a running ratio τ and a groove shoulder height ratio λ. FIG. 7 is a graph showing the results of numerical analysis of the relationship between the maximum contact pressure _Pmax and the rest angle β when the load capacity ratio is 1.3. FIG. 8 is a graph showing the results of numerical analysis of the relationship between the maximum contact pressure _Pmax and the rest angle β when the load capacity ratio is 1.5. FIG. 9: Load capacity ratio FIG. 7 is a graph showing a result of a numerical analysis of a relationship between the riding ratio τ and the rest angle β in the case of No. 3; FIG. 10 is a graph showing the results of numerical analysis of the relationship between the riding ratio τ and the rest angle β when the load capacity ratio is 1.5. FIG. 11 shows a load capacity ratio of 1. FIG. 7 is a graph showing a numerical analysis result of a relationship between a running ratio τ and a radial gap ratio Δ in the case of No. 5; FIG. 12 is a schematic perspective view of a connection type holding piece. 13A and 13B are views showing a separation type holding piece, wherein FIG. 13A is a view as viewed from an axial direction, and FIG. 13B is a cross-sectional view taken along the line AA of FIG. FIG. 14 is an explanatory sectional view for explaining a conventional ball screw device. FIG. 15 is an explanatory diagram for explaining an offset gothic arch groove. FIG. 16 is a perspective view for explaining a seal of a general ball screw device. FIG. 17 is an explanatory diagram for explaining the definition of the riding ratio τ. [Description of reference numerals] 2 ... screw groove (screw shaft side) 3 ... screw shaft 4 ... screw groove (nut side) 5 ... Ball 6 ... nut r ... offset Gothic arch groove radius d _a ... ball diameter f ... groove radius ratio 20 ... Connection type holding piece 30 ... Separation type holding piece

Claims (1)

Claims: 1. A screw shaft having a spiral screw groove on an outer peripheral surface, and a screw groove corresponding to the screw groove of the screw shaft on an inner peripheral surface, and is loosely fitted to the screw shaft. A ball screw device comprising: a plurality of balls rotatably mounted on a helical load track formed between the two screw grooves; and the two screw grooves are offset Gothic arch grooves. , characterized in that the screw shaft and the nut offset Gothic arch groove radius r ball diameter d _a groove radius ratio f = r / d _a a ratio is in a range of 0.515 ≧ f ≧ 0.504 And ball screw device.