JP2023119334A - Ball screw and machine tool using the same - Google Patents

Abstract

To provide a ball screw which can maintain high rigidity by imparting a proper amount of a preload between a screw shaft having a multi-thread screw groove and a nut, and a machine tool using the same.SOLUTION: In a ball screw having a screw shaft at which a multi-thread external peripheral screw groove is formed at an external peripheral face, a nut which is arranged around the screw shaft, and in which a multi-thread internal peripheral screw groove is formed at an internal peripheral face while opposing the external peripheral screw groove, and a plurality of balls accommodated in a rolling path which is formed of the external peripheral screw groove and the internal peripheral screw groove which oppose each other, at least one-thread external peripheral screw groove is the same in a lead between a first region of the screw shaft and a second region which is arranged in an axial direction of the screw shaft with respect to the first region, and at least one-thread external peripheral screw groove differs in the lead between the first region and the second region.SELECTED DRAWING: Figure 3

Description

The present invention relates to a ball screw and a machine tool using the same.

Linear motion devices such as ball screws and linear guides are used in machine tools, and in order to improve machining accuracy, it is necessary to ensure high rigidity of the linear motion devices.

In general, the ball screw has the advantage that it is easy to suppress the backlash between the nut and the thread groove, thereby ensuring high rigidity. In order to suppress the backlash of the ball screw, a method of reducing the axial clearance is usually used, and for this purpose, a preload is applied between the nut and the thread groove. On the other hand, if a preload is applied, heat generation increases during rapid feed after machining, and the shaft may elongate, making it impossible to maintain good machining accuracy.

In Patent Document 1, the lead of the rolling element rolling groove formed on the outer peripheral surface of the screw shaft or the pitch circle diameter of the rolling element on the screw shaft side is changed continuously or partially to change the connection between the screw shaft and the nut. A ball screw is disclosed that provides a preload therebetween.

Japanese Patent Application Laid-Open No. 2004-036702

The technique disclosed in Patent Literature 1 aims to adjust the preload between the screw shaft and the nut so that the preload is applied only to portions where rigidity and accuracy need to be increased.

However, the technology disclosed in Patent Document 1 is intended for a single-start ball screw, and is difficult to apply to a multi-start ball screw. Furthermore, in the ball screw disclosed in Patent Document 1, the amount of movement of the nut per rotation of the screw shaft changes in areas where the lead differs. There is also the problem of being unwieldy.

The present invention has been made in view of the above problems, and provides a ball screw capable of ensuring high rigidity by applying an appropriate amount of preload between a screw shaft having multiple thread grooves and a nut. The purpose is to provide a machine tool using

The ball screw of the present invention is
a screw shaft having a multi-threaded outer peripheral thread formed on its outer peripheral surface;
a nut disposed around the screw shaft and having multiple inner peripheral thread grooves formed on an inner peripheral surface facing the outer peripheral thread groove;
a plurality of balls accommodated in a rolling path formed by the outer peripheral thread groove and the inner peripheral thread groove facing each other;
A ball screw having
The at least one outer peripheral thread groove has the same lead in a first region in the screw shaft and in a second region arranged in the axial direction of the screw shaft with respect to the first region. ,
The at least one outer peripheral thread groove is characterized in that the first region and the second region have different leads.

ADVANTAGE OF THE INVENTION According to the present invention, it is possible to provide a ball screw that can ensure high rigidity by applying an appropriate amount of preload between a screw shaft having multiple thread grooves and a nut, and a machine tool using the ball screw. can.

FIG. 1 is a cross-sectional view of a two-start ball screw. FIG. 2 is a side view of the screw shaft of the ball screw according to the first embodiment; FIG. 3 is a side view showing the screw shaft of the ball screw according to the first embodiment together with a schematic cross section of the nut. FIG. 4 is a side view showing a screw shaft of a ball screw according to a second embodiment together with a schematic cross section of a nut.

An embodiment according to the present invention will be described in detail below with reference to the drawings. In the present embodiment, the term "multi-start thread" means that a thread groove of N threads (where N is an integer equal to or greater than 2) is formed in one pitch, and the lead (progress in one rotation) is formed compared to a single thread. distance) is N times. Here, a double thread will be described as an example, but the thread is not limited to the double thread.

FIG. 1 is a perspective view of a ball screw 100 according to this embodiment.
The ball screw 100 includes a screw shaft 11 , a nut 13 arranged around the screw shaft 11 , and a plurality of balls 15 .

The outer peripheral surface of the screw shaft 11 is formed with helical outer peripheral thread grooves 17A and 17B. The outer peripheral thread grooves 17A and 17B are multi-threaded (two threads in the illustrated example) thread grooves.

The nut 13 is arranged around the screw shaft 11 . The inner peripheral surface of the nut 13 has inner peripheral thread grooves 19A and 19B spirally formed with a peripheral length of less than one turn, and circulation grooves (irregular grooves) to which both ends of the inner peripheral thread grooves 19A and 19B are respectively connected. shown) and

The inner peripheral thread groove 19A is formed corresponding to the outer peripheral thread groove 17A of the screw shaft 11 , and the inner peripheral thread groove 19B is formed corresponding to the outer peripheral thread groove 17B of the screw shaft 11 . The inner peripheral thread grooves 19A, 19B and the outer peripheral thread grooves 17A, 17B are formed to a depth approximately equal to the radius of the ball 15, respectively. A plurality of balls 15 are accommodated in the rolling paths formed by the outer peripheral thread grooves 17A, 17B and the inner peripheral thread grooves 19A, 19B.

A single closed annular rolling groove is formed by connecting both ends of the inner peripheral thread groove 19A to the circulation groove. Similarly, by connecting both ends of the inner peripheral thread groove 19B to the circulation groove, one closed annular rolling groove is formed. That is, the nut 13 has a plurality of annularly formed rolling grooves.

A circulation circuit in which a plurality of balls 15 are rotatably accommodated is defined between the rolling groove composed of the inner peripheral thread groove 19A and the circulation groove and the outer peripheral thread groove 17A. Further, a circulation circuit in which a plurality of balls 15 are rotatably accommodated is also defined between the rolling groove including the inner peripheral thread groove 19B and the circulation groove, and the outer peripheral thread groove 17B.

As the screw shaft 11 rotates relative to the nut 13, the plurality of balls 15 circulate in the circulation circuit, thereby linearly moving the nut 13 relative to the screw shaft 11 in the axial direction of the screw shaft 11. It is possible to

[First embodiment]
FIG. 2 is a side view of the screw shaft 11 of the ball screw 100 according to the first embodiment, showing the pitch of the screw groove partially exaggerated. FIG. 3 is a side view showing the screw shaft 11 of the ball screw 100 according to this embodiment together with a schematic cross section of the nut 13. As shown in FIG.

As shown in FIG. 2, along the axial direction of the screw shaft 11, a region C (first region) and a region P (second region) are separated with a boundary BD as a base point. The lead of the outer peripheral thread grooves 17A and 17B in the region C is L, and the pitch of the thread groove is L/2. On the other hand, the lead of the outer peripheral thread groove 17A in the region P is (Ld), but the lead of the outer peripheral thread groove 17B is still L. Note that d is a value other than 0, and may be a negative value without being limited to a positive value.

On the other hand, the lead of the inner peripheral thread grooves 19A and 19B of the nut 13 is L, and the pitch of the thread groove is L/2.

According to the ball screw 100 of this embodiment, when the nut 13 is positioned in the region P of the screw shaft 11, the lead L of the outer peripheral thread groove 17B is equal to the lead L of the inner peripheral thread groove 19B of the nut 13, while the lead L of the inner peripheral thread groove 19B of the nut 13 Since the lead (L−d) of the thread groove 17A is different from the lead L of the inner peripheral thread groove 19A of the nut 13, a preload corresponding to the lead difference of the thread groove is applied as shown in FIG. An offset preload (Fa0) is applied between the screw shaft 11 and the nut 13 . This increases the nut rigidity and improves the positioning accuracy.

Therefore, when the ball screw 100 of the present embodiment is applied to a machine tool, the state in which the nut 13 is positioned in the region P of the screw shaft 11 (the outer peripheral thread grooves 17A and 17B in the region P are aligned with the inner peripheral thread grooves 19A and 19B). By machining the workpiece in a state where they face each other, high-precision machining can be achieved.

On the other hand, when the nut 13 is positioned in the region C of the screw shaft 11 (that is, when the nut 13 is not positioned in the region P of the screw shaft 11), the leads L of the outer thread grooves 17A, 17B and the inner thread grooves 19A, 19B Since the lead L of 19B becomes equal, the inter-row offset preload Fa0 disappears, and the frictional heat generated when the nut 13 moves can be reduced.

Therefore, when the ball screw 100 of the present embodiment is applied to a machine tool, the state in which the nut 13 is positioned in the region C of the screw shaft 11 (the outer peripheral thread grooves 17A and 17B in the region C are aligned with the inner peripheral thread grooves 19A and 19B). In this state, the nut 13 can be rapidly fed, for example, and the total machining time can be shortened. Since the lead L of the outer peripheral thread groove 17B is constant in the regions C and P, the feed amount of the nut 13 with respect to the rotation of the screw shaft 11 can be made constant in both regions.

[Second embodiment]
FIG. 4 is a side view showing the screw shaft 11 of the ball screw 100 according to the second embodiment together with a schematic cross section of the nut 13. As shown in FIG. In this embodiment, only the nut 13 differs from the first embodiment.

As shown in FIG. 4, along the axial direction of the screw shaft 11, the area C and the area P are separated with the boundary BD as a base point. Also in this embodiment, the lead of the outer peripheral thread grooves 17A and 17B in the region C is L (the pitch of the thread groove is L/2). On the other hand, the lead of the outer peripheral thread groove 17A in the region P is (Ld), but the lead of the outer peripheral thread groove 17B is L.

On the other hand, the lead of the inner peripheral thread grooves 19A and 19B of the nut 13 is (L+d), and the pitch of the thread groove is (L+d)/2. That is, the leads (L+d) of the inner peripheral thread grooves 19A and 19B of the nut 13 are the leads L of the outer peripheral thread grooves 17A and 17B in the region C, and the leads (L−d) and the outer thread of the outer peripheral thread groove 17A in the region P. It differs from the lead L of the groove 17B.

According to the ball screw 100 of this embodiment, when the nut 13 is positioned in the region C of the screw shaft 11, the lead L of the outer peripheral thread grooves 17A and 17B and the lead (L+d) of the inner peripheral thread grooves 19A and 19B are Therefore, as shown in FIG. 4, a thread-to-thread offset preload Fa1 corresponding to the lead difference of the thread groove is applied between the screw shaft 11 and the nut 13 via the balls 15 .

Furthermore, when the nut 13 is located in the region P of the screw shaft 11, the lead difference between the lead (L−d) of the outer peripheral thread groove 17A and the lead (L+d) of the inner peripheral thread groove 19A is much different. As shown in FIG. 4 , a row-to-row offset preload Fa2 larger than the row-to-row offset preload Fa1 in the region C is applied between the screw shaft 11 and the nut 13 via the balls 15 . This can further increase the nut stiffness.

In the case of a ball screw including a screw shaft having three or more outer peripheral thread grooves, in region C, for example, when the lead of the three outer peripheral thread grooves is L in common, in region P, at least one thread is formed. Let L be the lead of the outer peripheral thread groove, and let (Ld) be the lead of the remaining outer peripheral thread groove. In this case, the positions where the leads of the two or more outer peripheral thread grooves are (Ld) may be the same or different in the axial direction.

The invention is not limited to the embodiments described above. Variations of any of the components of the above-described embodiments are possible within the scope of the invention. Also, arbitrary components can be added or omitted in the above-described embodiments. For example, the present invention can be applied to various ball screws such as circulating top type ball screws, tube type ball screws, deflector type ball screws, and end cap type ball screws.

100 ball screw 11 screw shaft 13 nuts 17A, 17B outer thread grooves 19A, 19B inner thread grooves

Claims (4)

a screw shaft having a multi-threaded outer peripheral thread formed on its outer peripheral surface;
a nut disposed around the screw shaft and having multiple inner peripheral thread grooves formed on an inner peripheral surface facing the outer peripheral thread groove;
a plurality of balls accommodated in a rolling path formed by the outer peripheral thread groove and the inner peripheral thread groove facing each other;
A ball screw having
The at least one outer peripheral thread groove has the same lead in a first region in the screw shaft and in a second region arranged in the axial direction of the screw shaft with respect to the first region. ,
A ball screw, wherein at least one of said outer peripheral thread grooves has a different lead between said first region and said second region. 2. The ball screw of claim 1, wherein the lead of said inner peripheral thread of said nut is equal to the lead of said outer peripheral thread in said first region. 2. The ball screw according to claim 1, wherein the lead of said inner peripheral thread groove is different from the lead of said outer peripheral thread groove in said first region and said second region. A machine tool using the ball screw according to claim 2 or 3,
A machine tool, wherein a workpiece is machined when the inner peripheral thread groove of the nut faces the outer peripheral thread groove of the second region.

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