JPH06341503A - Ball screw - Google Patents

Abstract

PURPOSE:To adjust pre-load while the ball screw is being left over as is built in a machine without being removed when the aforesaid ball screw having physical properties such as rigidity and the like, which are identical to those of a former in-place pre-load ball screw, is reduced in pre-load because of wear. CONSTITUTION:A first screw section 2a is formed in one part 2 of paired nuts 2 and 2', and concurrently a second screw section 2'a which is different in pitch or reverse in twist, from the first screw section 2a, is formed in the other part 2' of the nuts, and a ring 10 formed with screw sections 10a and 10b to be engaged with the first and second screw sections 2a and 2'a, are provided therein, so that the amount of per-load is thereby changed with the relative angular position of the ring 10 changed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ball screw used in a machine tool or the like, and more specifically, it is an improved ball screw preload mechanism.

[0002]

2. Description of the Related Art A ball screw shown in FIG. 4 has a shaft (1) having a thread groove formed on the outer circumference thereof, a nut (2, 2 ') having a thread groove formed on the inner circumference thereof, and a space between the thread grooves. A ball (not shown) placed, a return tube (4) for circulating the ball in each nut (2, 2 '), and a nut (2) and a nut (2') for preloading. It is composed of a spacer (5) sandwiched between them and a preload fixing key (6) for fixing the spacer (5) to the nut.

[0003]

The demand for higher precision is increasing year by year in the feed system of machine tools and the like, and preload is applied to the ball screw in order to improve the positioning accuracy of the feed system, axial rigidity, and the like. Is widely practiced. Although there are various methods of applying the preload, the fixed position preload in which the spacer is sandwiched between the two nuts as shown in FIG. 4 is most often used. However, in this method, the preload is gradually released compared to the initial stage due to wear of the screw grooves and balls of the shaft and nut due to long-time use of the ball screw, and in the worst case, play may occur. In many cases, the required accuracy cannot be obtained due to an early decrease in preload.In such a case, the conventional ball screw disassembles the ball screw from the machine to perform preload readjustment. Disassembly,
Adjustment of the ball screw and reassembly of the machine are required, which requires a lot of man-hours.

The ball screw includes a constant pressure preload ball screw in which the preload reduction hardly occurs due to the wear of the screw groove or the ball. This is replaced by a coil spring, a disc spring or the like instead of the spacer (5) in FIG. Since it is used, it is inferior to the fixed position preload ball screw in terms of rigidity, and its application is limited.

Therefore, an object of the present invention is to have a function equivalent to that of a conventional fixed position preload ball screw such as rigidity, and when the preload decreases due to wear, adjust the preload without disassembling it from the machine. It is to be able to do.

[0006]

According to the present invention, there is provided a screw shaft having a spiral inner raceway surface formed on an outer peripheral surface thereof, and a ball nut composed of a pair of nuts having a spiral outer raceway surface formed on an inner peripheral surface thereof. A ball having a plurality of balls arranged in a spiral circulation path formed between the inner and outer raceways and a circulation member connecting the spiral circulation paths to form a series of ball circulation paths In the screw, while forming a first threaded portion on one nut of the pair of nuts and a second threaded portion having a pitch different from the first threaded portion or the twisting direction is opposite to the other nut on the other nut. A ring having a threaded portion which is formed and which is screwed into the first and second threaded portions is provided, and the amount of preload is changed by changing the relative angular position of the ring.

[0007]

The pair of nuts are locked with a key so that relative movement is possible only in the axial direction. Therefore, if the relative angular position of the ring with respect to the nut is changed, the pitch is different or the twisting direction is opposite. Due to the screw connection, the pair of nuts move in a direction toward or away from each other. As a result, the amount of elastic displacement of the sphere changes and the amount of preload changes.

[0008]

EXAMPLE As shown in FIG. 1 (a), a ball screw comprises a screw shaft (1) having a spiral inner raceway surface formed on an outer peripheral surface,
A ball nut (2, 2 ') having a spiral outer raceway surface formed on the inner peripheral surface, and a plurality of balls (3) arranged in a spiral circulation path formed between the inner and outer raceway surfaces, And a circulation member (4) for connecting a spiral circulation path to form a series of ball circulation paths.

A pair of nuts (2, 2 ') adjacent to each other in the axial direction and forming a ball nut are detented by a preload fixing key (6) so as not to rotate relatively. However, the key (6) is fixed only to one nut (2) (Fig. 1 (b)), so that the key (6) can move axially in the key groove of the nut (2 '). ing.
Male threads (2a, 2'a) on the ends of the nuts (2, 2 ')
Is formed, and the ring (10) is screwed onto this male screw with female screws (10a, 10b) formed on the inner diameter side. Two screw parts (2a10a; 2'a, 10
In b), the twist direction is opposite. That is, in the case of this embodiment, the threaded portions (2a, 10a) are right-handed threads, but the threaded portions (2'a, 10b) are left-handed threads. In the structure illustrated in the drawings, a female screw, a nut (2,
Although a male screw is formed on the 2 ') side, conversely, a male screw may be formed on the ring (10) side and a female screw may be formed on the nut (2, 2') side (FIG. 3).

As shown in FIG. 2 (a), the nut (2) has a tapped hole (2b) machined therein. This tapped hole (2b)
A bolt (9) is screwed on and can be tightened or loosened from the outside. On the other hand, a notch (10c) is provided on the outer diameter portion of the ring (10) so as to make surface contact with the tip of the bolt (9).

When the bolt (9) is further tightened from the state shown in FIG. 2 (a), the ring (10) rotates clockwise relative to the nut (2). The ring (10) and the nuts (2, 2 ') have different screw directions (2a, 10).
b; 2'a, 10a), the nuts (2, 2 ') move toward or away from each other as the ring (10) rotates. Nuts (2,
If you turn the bolt (9) in the direction that 2 ') separate from each other,
Axial force is transmitted to the shaft (1) via the ball (3),
Finally, the amount of elastic displacement of the ball (3) increases and the amount of preload increases. In this way, the amount of preload can be adjusted by adjusting the tightening amount of the bolt (9).

FIG. 2 (b) shows the bolt (9) of FIG. 2 (a).
An example in which a spring element such as a compression coil spring (9 ′) is used instead of the compression coil spring (9 ′) is shown. The compression coil spring (9 ′) is inserted into the through hole (2c) and the tip thereof is a notch (10c) of the ring (10). Abutted against. In addition, plug (2d)
The plug (2) can be omitted by making a blind hole. If the balls (3) and the thread grooves (raceways) are worn, the amount of preload will decrease as it is. In this embodiment, the compression coil spring (9 ') pushes the ring (10) accordingly and the nut (2). ) Rotate the ring (10) relative to
This allows the nuts (2, 2 ') to move away from each other, that is, the ball (3) in the same direction as when the bolt (9) described above in connection with the embodiment of FIG. 2 (a) is tightened. It moves in the direction of increasing the elastic displacement. Therefore, the predetermined amount of preload is always maintained.

[0013]

In the conventional fixed position preload ball screw, when the ball groove, the nut, or the thread groove surface of the shaft is worn and the initial preload is lowered or slipped out, the ball screw is disassembled, adjusted, and reassembled. However, according to the present invention, the preload can be easily adjusted by changing the relative angular position of the ring without disassembling the ball screw from the machine.

Further, not only when the preload is reduced or when the preload is removed, the preload adjustment for changing the rigidity of the feeding system can be easily performed.

[Brief description of drawings]

FIG. 1 is a half sectional view in the axial direction of a ball screw showing an embodiment of the present invention (a) and a plan view of a key portion (b).

2 is a sectional view (a) taken along the line II-II of FIG. 1 and a partial view (b) showing another embodiment.

FIG. 3 is an axial half sectional view similar to FIG. 1 showing a modified example.

FIG. 4 is a plan view showing a conventional example.

[Explanation of symbols]

 1 Screw shaft 2, 2'Nut (ball nut) 2a, 2'a Male screw 2b Tap hole 3 Ball 4 Return tube (circulating member) 6 Preload fixing key 9 Bolt 9'Compression coil spring (spring element) 10 Ring 10a, 10b Female screw 10c cutout

Claims (1)

[Claims] 1. A ball nut consisting of a screw shaft having a spiral inner raceway surface formed on an outer peripheral surface, a pair of nuts having a spiral outer raceway surface formed on an inner peripheral surface, and the inner and outer raceway surfaces. In a ball screw having a plurality of balls arranged in a spiral circulation path formed in, and a circulation member forming a series of ball circulation paths by connecting the spiral circulation path, Forming a first threaded portion on one of the nuts and forming a second threaded portion on the other nut with a pitch different from the first threaded portion or with a twist direction opposite to each other; and A ball screw, characterized in that a ring formed with a screw part that is respectively screwed into the second screw part is provided, and the amount of preload is changed by changing the relative angular position of the ring.