JPH10153245A - Ball screw - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ball screw by which the small size and the high load capacity are realized without increasing the size of the ball screw by unifomizing variations of the load distribution of the ball screw and decreasing stress concentration to be generated on a ball in the specified position. SOLUTION: A ball screw is provided with a screw shaft 2 provided with ball screw grooves 2a on the outer surface, at least one ball nut 3 provided with ball screw grooves facing the ball screw grooves 2a on the inner surface, a spiral passage formed of the ball screw grooves of the ball nut 3 and the ball screw grooves 2a of the screw shaft 2, many balls to be circulated in the passage, and return passages 5, 6, 7 for the balls, and three or more circulation passages X, Y, Z formed of the return passages 5, 6, 7 for the balls provided on the above spiral passages and the ball nut 3 are provided. At least two circuits of the circulation passages X, Y, Z are made into the same phase in the circumferential direction, and the other circuit is reversed in the circumferential direction in relation to the two circuits by 180 deg..

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ball screw for converting a rotary motion into a linear motion, and more particularly to an improvement in a ball screw used for a high load application.

[0002]

2. Description of the Related Art In a conventional ball screw, workability,
From the balance of operability, load capacity, etc., it has been customary that the shape of the ball screw groove formed on the screw shaft or ball nut has an initial contact angle of about 45 degrees and a maximum contact angle of about 65 degrees.

In the case of a ball screw having a ball circulation path of a plurality of circuits, in order to reduce the number of machining steps, for example, in the case of a tube circulation system as shown in FIG. The design is usually such that the mounting positions of the plurality of circulation tubes 50a, 50b, 50c are arranged in the axial direction at the same phase position in the circumferential direction. FIG. 7 illustrates a circuit having three circuits.

When designing a ball screw, a relatively large safety factor is set, and a ball screw having a shaft diameter that can sufficiently withstand use conditions has been selected. At this time, when the shaft diameter of the ball screw cannot be increased, the number of circuits is increased by increasing the number of circuits of the ball nut 51, or the ball diameter is increased by increasing the lead of the ball screw groove. .

On the other hand, conventionally, when examining the load conditions when selecting a ball screw, a screw shaft 52 and a ball nut 5 are required.
Assuming that all the balls rolling between 1 and 2 are evenly loaded, the contact surface pressure is calculated by the average load obtained by dividing the load by the number of effective balls in the ball nut 51. Appropriate ball screws have been selected by comparing them with databases of ball screw functions and life obtained by experiments and the like.

[0006]

However, actually, the load is not uniformly applied to all of the so-called effective balls rolling between the screw shaft 52 and the ball nut 51, but the load is applied. Due to the elastic deformation of the screw shaft 52 and the ball nut 51 when received, the load distribution in the axial direction in the ball nut 51 varies. For example, such as when performing heavy cutting on a processing table supported by a ball screw, the ball nut 51 of the ball screw is used.
When an axial load Fa in the axial direction is applied to the screw shaft 52 and an axial load Fa ′ is applied to the screw shaft 52 in the direction shown in FIG. 8, the shafts at the positions of the ball nut grooves 51a and 52a of the ball nut 51 and the screw shaft 52 are formed. The distribution of the amount of elastic displacement along the direction is as indicated by the arrow mark in FIG. 8 above, and according to the amount of elastic displacement of the screw shaft 52 and the amount of elastic displacement of the ball nut 51, It can be seen that stress concentration occurs at the contact points with the balls at both ends of the.

The balls in each circulation path are sequentially scooped up from the ball screw grooves 51a and 52a by the circulation tube 50 and circulated through the tube 50, so that the orbit of the screw shaft 52 facing the ball nut 51. There is a part without a ball on the top. For this reason, the load distribution varies in the circumferential direction, and a high load is applied to a part of the effective ball. That is, the circulation of the ball in each circuit in the ball nut 51 is represented as shown in FIG. 9, but when the ball 1 is scooped up from the ball screw groove to the circulation tube 50, when viewed from the axial direction, As shown in FIG. 10, the number of balls in the range of the β angle in the circumferential direction becomes relatively small, and the load applied to the balls in the range of the β angle becomes relatively large.

Due to the fact that the stress is concentrated on the contact portions of the ball nut 51 at both ends with the ball and the load on the ball within a specific range of the ball circulation path is increased, the design of the conventional ball screw is If the safety factor at the time is small,
Each ball screw groove 51 of the screw shaft 52 or the ball nut 51
There has been a problem that the a, 52a surface is prematurely peeled off or abnormal wear is caused.

In addition, in a high-load application, if the safety factor is increased, the size of the ball screw becomes large, so that the ball screw does not meet the intended specifications or the cost increases.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems. The present invention has been made by making uniform the variation in load distribution of a ball screw and reducing the concentration of stress generated in a ball at a specific position. It is an object of the present invention to provide a ball screw that achieves a compact and high load capacity without increasing the size of the ball screw.

[0011]

According to another aspect of the present invention, there is provided a ball screw comprising: a screw shaft having a ball screw groove on an outer surface; and a ball screw groove facing the ball screw groove of the screw shaft. At least one ball nut having an inner surface thereof, a helical passage formed by the ball screw groove of the ball nut and the ball screw groove of the screw shaft, a number of balls circulating in the helical passage, A ball return path, wherein the helical path and the return path of the ball provided in the ball nut have three or more circuits. The circuit is characterized in that it has the same phase in the circumferential direction, and the remaining circuits are circumferentially inverted by 180 with respect to the other circuits.

Here, the number of the circulation paths is an even number of circuits, and half of the circulation paths have the same phase in the circumferential direction, and the remaining circulation paths are in the circumferential direction with respect to the other circulation paths. 18
It can be inverted by 0 degrees.

The circulation path has an odd number of circuits, of which (n / 2) +0.5 circuits (where n is the number of circuits in the circulation path) have the same phase in the circumferential direction. The remaining circuit may be circumferentially inverted by 180 degrees with respect to the other circuits.

Further, a ball screw according to a second aspect of the present invention includes a screw shaft having a ball screw groove on an outer surface, at least one ball nut having a ball screw groove on the inner surface facing the ball screw groove of the screw shaft, A helical passage formed by the ball screw groove of the ball nut and the ball screw groove of the screw shaft, and a number of balls circulating in the helical passage;
A ball screw having a number of ball return paths, and wherein the circulation path formed by the spiral path and the ball return path provided in the ball nut has three or more circuits, wherein at least two of the circulation paths are provided. The same phase in the circumferential direction, the remaining circuits are circumferentially inverted by 180 degrees with respect to other circuits, and at least one circuit in the entire circuit is axially offset with respect to the other circuits. It is characterized by.

According to the present invention, with respect to variations in the load distribution in the circumferential direction, at least two of the three or more circulating circuits have the same phase in the circumferential direction, and the remaining circuits are different from other circuits. By inverting 180 degrees in the circumferential direction, 1
A portion of the circuit having a small number of balls in the circumferential direction (a portion having a large load) and a portion of the other circuits having a small number of balls in the circumferential direction (a portion having a large load) are inverted 180 degrees in the circumferential direction. As a result, a portion having a small number of balls in the circumferential direction is dispersed and averaged, and the variation in the load distribution in the circumferential direction is reduced.

Since the range of the portion where the ball is small in each circuit falls within the angle range smaller than 180 degrees,
By inverting by 80 degrees, a portion of at least two circuits with less balls in the circumferential direction and a portion of the remaining circuits with less balls in the circumferential direction do not overlap in the circumferential direction.

With respect to variations in the axial load, at least one circuit among all the circulation paths in the ball screw having three or more circulation paths is provided in accordance with the axial direction of the axial load applied to the ball nut. Offset in the direction. By offsetting in this manner, a preload is applied to the ball in the ball screw groove circuit that has been offset on the ball nut side, and the amount of elastic displacement of the ball screw groove becomes larger than when no offset is performed. Since the load sharing by the balls in the offset circuit increases, and the load sharing at the circuit position on the nut end side where stress concentration occurs without offsetting decreases, the axial load on the ball nut is reduced. The distribution is averaged to reduce variations.

[0018]

Embodiments of the present invention will be described with reference to the drawings. First, the configuration will be described. As shown in FIG. 1, a ball nut 3 is screwed onto the outer periphery of the screw shaft 2 via a plurality of balls, and one of the screw shaft 2 and the ball nut 3 is relatively rotated. The ball nut 3 moves linearly with respect to the screw shaft 2.

That is, as shown in FIG. 2, which is a schematic configuration diagram, a female screw-shaped ball screw groove 2 is formed on the outer peripheral surface of the screw shaft 2.
a ball screw groove 9 is provided on the inner peripheral surface of the ball nut 3 at a position radially opposed to the ball screw groove 2 a of the screw shaft 2. A plurality of balls 1 (shown by oblique lines in FIG. 2) are interposed between 2a and 9 and the balls 1 are ball screw grooves 2
Rolls and circulates along a.

The ball screw according to the present embodiment is a tube-type ball screw having three ball circulation paths. That is, the ball screw groove 9 of the ball nut 3 is
As shown in FIG. 2 described above, the ball screw groove 9 is divided into three sections along the axial direction, and both ends of the ball screw groove 9 in each section are connected by circulation tubes 5, 6, 7 forming return paths. , Three ball circulation paths are formed.
For convenience of description, the first circuit X, the second circuit Y, and the third circuit Z are referred to from the left side in FIGS. 1 and 2.

However, in the present embodiment, as shown in FIG. 1, the mounting position of the circulation tube 6 of the second circuit Y is different from the mounting position of the circulation tubes 5 and 7 of the first and third circuits X and Z. , Are provided at positions that are inverted by 180 degrees in the circumferential direction.

Further, as shown in FIG. 2, the circulation path of the second circuit Y is offset in the axial direction so as to approach the third circuit Z side by several tens of μm. That is, the lead La between the ball screw groove 9a of the first circuit X and the ball screw groove 9b of the second circuit Y in the ball nut 3 is several tens of μm from the lead L of each of the ball screw grooves 9a, 9b, 9c ( .alpha.) (La = L + .alpha.), and at the same time, the lead Lb between the ball screw groove 9b of the second circuit Y and the ball screw groove 9c of the third circuit Z is several tens .mu.m (.alpha.) larger than the lead L. It is set small (Lb = L-α). In addition, naturally, the screw shaft 2
The leads of the ball screw groove 2a on the side are equally spaced.

Here, in order to increase the load capacity of the ball screw, the contact angle of the ball 1 and the ball screw groove 2
Although it is desired to increase the radius of curvature of a and 9 as much as possible, when an axial load is applied in a state where the contact angle is excessively increased as shown in FIG.
9 protrudes from the groove end and is cut off. When a part of the contact ellipse F is cut, the applied stress increases, and the life of the ball screw becomes extremely short. Therefore, in the present embodiment, as shown in FIG. 3, the initial contact angle D is 50 to 55 degrees,
The maximum contact angle E is 75 degrees.

Each of the balls 1 has a ball diameter Da having the following relationship with the lead L of the ball screw groove 9. 0.7 ≦ (Da / L) By the way, conventionally, when Da / L is set to 0.7 or more, since the outer diameter of the circulation tube may interfere with the adjacent ball screw groove, Da / L L is set to less than 0.7. On the other hand, in the present embodiment, by changing the angle in the axial direction of the portion for scooping up the ball 1 from the ball screw groove to the tube to a direction larger than the conventional one, Da /
L can be set to 0.7 or more.

Next, the operation and effect of the ball screw having the above configuration will be described. By offsetting the position of the circulation path of the second circuit Y toward the third circuit Z, a preload is applied to the ball in the ball screw groove 9b of the second circuit Y, so that an axial load is applied to the ball nut 3. The elastic displacement of the ball screw groove 9b when Fa is loaded is:
As compared with the case where the offset is not performed, the contact area with the ball increases. Then, the load sharing by the balls in the offset circuit Y increases, and the load sharing in the first circuit X and the third circuit Z, which are the circuits on the nut end side where the stress concentration occurs where no offset occurs, is achieved. Since the load is reduced, the load distribution in the axial direction of the ball nut 3 is averaged, and the variation is reduced.

The mounting position of the circulating tube 6 of the second circuit Y is reversed by 180 degrees in the circumferential direction with respect to the mounting position of the circulating tubes 5 and 7 of the first circuit X and the third circuit Z. In the direction, the portion where the number of effective balls is small in the first circuit X and the third circuit Z and the portion where the number of effective balls is small in the second circuit Y are prevented from overlapping in the circumferential direction. That is, since the no-load zone (the portion where the ball 1 does not exist) in the circumferential direction is dispersed, the variation in the load distribution on each effective ball 1 in the circumferential direction can be suppressed.

As described above, the axial and circumferential load distributions on the effective balls (the balls 1 rolling between the screw shaft 2 and the ball nut 3) are made more uniform than before, and Load distribution, and furthermore, each ball screw groove 2 of the screw shaft 2 and the ball nut 3 contacting the ball
The load distributions for a and 9 are averaged, and the load capacity increases.

Further, in this embodiment, the load capacity is further increased by increasing the initial contact angle E and the maximum contact angle F of the ball 1 and setting Da / L to 0.7 or more. It is planned.

In the above-described embodiment, only the mounting position of the circulation tube 6 of the second circuit Y is inverted by 180 degrees with respect to the mounting position of the circulation tube 5 of the first circuit X. The mounting position of the circulation tube 7 of Z may also be inverted by 180 degrees with respect to the mounting position of the circulation tube 5 of the first circuit X. Alternatively, the first circuit X and the second circuit Y may have the same phase in the circumferential direction, and only the third circuit Z may be inverted by 180 degrees.

In the above embodiment, when the axial load Fa to the ball nut 3 is applied to the first circuit X side, the ball screw groove 9 in the circulation path of the second circuit Y
b is offset to the third circuit Z side, but the axial load on the ball nut 3 is
In the case of the usage mode in which the ball screw groove 9b is loaded on the side of the second circuit Y, the ball screw groove 9b in the circulation path of the second circuit Y is offset toward the first circuit X.

According to the present invention, a part of the plurality of circulation paths is offset in the axial direction in accordance with the direction in which the axial load is applied as described above, so that the axial elastic displacement of the ball nut can be reduced. Instead of averaging the variation and averaging the axial load distribution on the ball to increase the overall load capacity, for example, the diameter of the ball 1 used in the second circuit Y in the embodiment may be changed as follows: The same operation and effect as described above can also be obtained by changing the diameter of the balls loaded in some of the circulation paths such that the diameter is relatively larger than the diameter of the balls 1 used in the first circuit X and the third circuit Z. Can be obtained. That is, by increasing the diameter of the ball 1 of the second circuit Y, a preload is applied to the ball in the ball screw groove 9b of the second circuit Y, and therefore, the axial load Fa is applied to the ball nut 3.
When the load is applied, the amount of elastic displacement of the ball screw groove 9b is larger than when the ball diameter is not increased, and the contact area with the ball increases. The first circuit X and the third circuit, which are circuits on the nut end side, in which the load sharing by the balls in the circuit Y having the increased diameter of the ball increases and stress concentration occurs without increasing the diameter of the ball. Since the load sharing amount in Z is reduced, the load distribution in the axial direction of the ball nut 3 is averaged, and the variation is reduced. As a result, the axial load shared by the ball 1 of the second circuit Y is increased as compared with the conventional case, and the same effect as described above is exerted.

Of course, the ball screw groove 9 of the second circuit Y is
The ball 1 of the second circuit Y may be set to be larger than the diameter of the ball 1 of the first circuit X and the third circuit Z while being offset toward the circuit X or the third circuit Z.

As described above, in the above embodiment, both the inversion of the circulation path by 180 degrees and the offsetting are adopted, but the inversion of the circulation path by 180 degrees alone can reduce the variation in the load distribution. However, the load capacity is increased as compared with the related art.

[0034]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The state of the load distribution with respect to a ball screw (comparative example) having the same specifications as the conventional one in which the mounting positions of the two circulation tubes 5, 6, 7 are set in the same phase in the circumferential direction and the circulation path of the second circuit Y is not offset. Fig. 5
And the result as shown in FIG. 6 was obtained.

FIG. 5 shows the distribution of the axial load applied to the effective ball 1 when the variation in the load distribution in the circumferential direction is ignored and only the variation in the axial direction is considered. Is the ball screw of the present invention, and B is the ball screw of the comparative example. As can be seen from FIG. 5, in the ball screw according to the present invention, the load in the second circuit Y increases and the loads in the first circuit X and the third circuit Z decrease. Averaged.

FIG. 6 shows the axial load applied to each effective ball 1 along the ball screw groove 9 in consideration of the variation in the axial direction and the load distribution in the circumferential direction. A (solid line) is for the ball screw of the present invention, and B (dashed line) is for the ball screw of the comparative example.
As can be seen from FIG. 6, in the ball screw according to the present invention, the amplitude of the load along the ball screw groove 9 is smaller, and the load distribution state in the circumferential direction is averaged.

Actually, it was confirmed that the load capacity of the ball screw A according to the present invention was increased by about 20% from the load capacity of the ball screw B of the comparative example without changing the outer diameter.

The ball screw to which the present invention can be applied is:
The present invention is not limited to the tube circulation type as shown in the embodiment. For example, as shown in FIG. 1 of Japanese Utility Model Publication No. 5-35228, a so-called deflector circulation system (having a ball return groove for communicating a plurality of sets of ball communication passages with each other and being attached to the outer peripheral portion of a ball nut). The circulation path is formed by a guide plate and a ball scooping member that is disposed on the inner side of each ball communication path and sequentially guides a group of balls interposed between the screw grooves of the ball screw shaft and the ball nut to the ball communication path. Is configured). A guide plate circulation system described in the prior art in FIG. 15 (which has a ball return groove communicating the ball communication passages with each other and is attached to an outer peripheral portion of a ball nut). A guide piece inserted into the passage protrudes, an outer ball guide surface is formed on the inner surface side of the guide piece, and the outer ball guide surface substantially defines the space between both ends of the ball return groove and each ball communication passage. It is configured to perform a typical ball direction change.)

In the above embodiment, the circulation circuit is the first circuit.
Although the ball screw having three circuits of (X), second (Y), and third (Z) has been described, the ball screw of the present invention is not limited to three circuits, and a circulation path of three or more circuits is provided. It is also applicable to those having. In addition, three ball nuts
The circuit is not limited to the one provided with the circuits or more, but may be a circuit having two or more ball nuts and a total of three or more circuits in all nuts, such as a double nut type described later.

In the embodiment, the so-called single nut type having one ball nut has been described. In addition, for example, a so-called double nut type or two ball nut using two ball nuts 3A and 3B shown in FIG. The present invention is also applicable to those using more than one ball nut. In the case of such a multi-nut type, for example, in the case of a double nut type shown in FIG.
One of the two ball nuts 3A and 3B (for example, 3
A) may be inverted by 180 degrees, or each ball nut 3
A, 3B, two circuits 10, 11, and 1, respectively.
One of the circuits 2 and 13 (for example, circuit 10
And the circuit 12) may be inverted by 180 degrees. Further, regarding the offset, instead of offsetting the circuit in one ball nut, two ball nuts 3A, 3B
Each circuit (for example, a set of circuits 10 and 11 and a circuit 1) provided on each ball nut with a spacer 14 interposed therebetween.
2, 13) may be offset.

[0041]

As described above, when the ball screw of the present invention is employed, the load distribution on a plurality of balls rolling between the screw shaft and the ball nut is averaged by simple means, That is, the concentrated load generated on some of the balls is reduced. Therefore, there is an effect that the load capacity becomes larger than before without increasing the outer diameter of the ball screw.

That is, the load capacity can be increased without increasing the size of the ball screw, and can be used for high-load applications (eg, injection molding machine, molding, power cylinder)
There is an effect that the width of is increased.

[Brief description of the drawings]

FIG. 1 is a side view showing a ball screw according to an embodiment of the present invention.

FIG. 2 is a schematic diagram for explaining a configuration of a ball screw according to the embodiment of the present invention.

FIG. 3 is a sectional view showing a shape of a ball screw groove according to the embodiment of the present invention.

FIG. 4 is a diagram showing a relationship between a contact angle and a contact ellipse.

FIG. 5 is a diagram showing the offset effect of the circulation path of the present invention by comparing the load distribution in the axial direction ignoring the variation in the load distribution in the circumferential direction.

FIG. 6 is a diagram showing the reversal effect of the circulation path of the present invention by comparing the distribution of load in the axial direction in consideration of the variation in the axial direction and the variation in the load distribution in the circumferential direction.

FIG. 7 is a view showing a conventional ball screw.

FIG. 8 is a diagram showing an elastic displacement amount that causes a variation in an axial load.

FIG. 9 is a diagram showing circulation of a ball in one circulation path.

FIG. 10 is a view taken along the line XX in FIG. 9 and showing a portion with a small number of balls in the circumferential direction, as viewed from the axial direction.

FIG. 11 is a plan view illustrating a case where the present invention is applied to a double nut type ball screw.

[Explanation of symbols]

 X 1st circuit Y 2nd circuit Z 3rd circuit 1 Ball 2 Screw shaft 2a Ball screw groove (of screw shaft) 3 Ball nut 5 Circulation path of 1st circuit 6 Circulation path of 2nd circuit 7 Circulation path of 3rd circuit 9 Ball screw groove (of ball nut) 9a Ball screw groove of first circuit 9b Ball screw groove of second circuit 9c Ball screw groove of third circuit

Claims (2)

[Claims] 1. A screw shaft having a ball screw groove on an outer surface,
At least one ball nut having on its inner surface a ball screw groove facing the ball screw groove of the screw shaft; a helical passage formed by the ball screw groove of the ball nut and the ball screw groove of the screw shaft; A ball having a large number of balls circulating in the spiral passage and a return path for the large number of balls, wherein the spiral path and the ball return path provided in the ball nut have three or more circuits. In the screw, at least two circuits of the circulation path have the same phase in the circumferential direction, and the remaining circuits have the same phase in the circumferential direction with respect to the other circuits.
A ball screw characterized by being inverted by 0 degrees. 2. A screw shaft having a ball screw groove on an outer surface,
At least one ball nut having on its inner surface a ball screw groove facing the ball screw groove of the screw shaft; a helical passage formed by the ball screw groove of the ball nut and the ball screw groove of the screw shaft; A ball having a large number of balls circulating in the spiral passage and a return path for the large number of balls, wherein the spiral path and the ball return path provided in the ball nut have three or more circuits. In the screw, at least two circuits of the circulation path have the same phase in the circumferential direction, and the remaining circuits have the same phase in the circumferential direction with respect to the other circuits.
A ball screw characterized by being inverted by 0 degrees and at least one circuit of the entire circulation path is axially offset with respect to another circuit.