JPH0341248A - Preloading device for ball screw - Google Patents

Abstract

PURPOSE:To heighten the rigidity of a preloading device, eliminate a preload- weakening-phenomenon, and to lengthen the high-accuracy-continuance by incorporating balls, which are preloaded in a contact state, in between a ball screw groove of a nut and a ball screw groove of a screw shaft. CONSTITUTION:Balls B0, which are preloaded in a 4-point contact state, are incorporated in between a ball screw groove of a first nut 3 and a ball screw groove of a screw shaft 1. In addition, balls Bs, which are preloaded in a 2-point state, are incorporated in between a ball screw groove of a second nut 4 and a ball screw groove of the screw shaft 1. Meanwhile, two sets of belleville springs 5A as elastic members are interposed between both nuts 3 and 4. With this contrivance, regarding both directions of compression and tension, the regidity of the device can be heightened, a preload-weakening-phenomenon can be eliminated, and the high-accuracy-continuance of the device can be lengthened.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a preload device for a ball screw used as a feed screw in a high-precision positioning device that involves swinging, such as a stepper, and particularly to a preload device for a ball screw that is used as a feed screw for a high-precision positioning device that involves swinging, such as a stepper. This is an improvement on the drop.

[Conventional technology]

Generally, when performing high-precision positioning using a ball screw,
A preload is applied to the ball screw as a means to reduce the axial clearance of the ball screw to zero, further reduce the amount of elastic displacement in response to an axial load, and increase rigidity.

There are two preload methods: a single nut method and a double nut method. The former uses only one nut to apply preload, and the latter uses two nuts to apply preload.

In the case of a single nut system, a preload is applied by using a ball larger than the ball groove space, or by partially making the lead of the screw on the nut side larger than on the shaft side to create a negative clearance between the ball and the ball. Therefore, it has rigidity in both the compression and tension directions, has excellent torque characteristics during rocking motion, and is suitable for high frequency control.

The double nut system includes a fixed position preload system and a constant pressure preload system. In the case of the fixed position preload method, a spacer is inserted between both nuts screwed onto a common screw shaft to apply a load in the tensile or compressive direction to provide preload. There are similar benefits.

On the other hand, in the case of the double NAND method with constant pressure preload,
A preload is applied by inserting a spring into both nuts screwed onto a common screw shaft and applying a load in the tensile direction. Since the wear of the ball and thread groove can be absorbed by the elastic displacement of the spring,
This has the advantage that there is almost no deterioration in accuracy.

[Problem to be solved by the invention]

The above-mentioned conventional single nut system and fixed position preload double nut system are used in applications where swinging operation is repeated, such as in a stethoscope, but if the ball or thread groove wears out, there will be a gap between the ball and the groove surface. 1. This is because a phenomenon occurs after a so-called preload due to a gap. There was a problem that the accuracy life was short.

On the other hand, in the double nut system with constant pressure preload, the nut rigidity is smaller than that in the single nut system or the double nut system with fixed position preload, but this phenomenon does not occur after preload.

Therefore, the present invention has been made by focusing on the above-mentioned conventional problems, and its purpose is to provide high rigidity,
It is an object of the present invention to provide a preloading device for a ball screw that has excellent torque characteristics during rocking, has no phenomenon after preloading, and has a long accuracy life.

[Means to solve the problem]

In order to achieve the above object, a first aspect of the present invention includes a first nut and a second nut that are screwed onto a common screw shaft through a number of balls, and prevents relative rotation of both nuts. and a preload device for a ball screw which applies a preload by inserting an elastic member into both nuts, the ball screw groove having a diameter of 4 mm between the ball screw groove of the first nut and the ball screw groove of the screw shaft. A ball preloaded in a point contact state is installed, and a ball preloaded in a two point contact state is installed between the ball screw groove of the second nut and the ball screw groove of the screw shaft.

Further, the second invention has a first nut and a second nut that are screwed onto a common screw shaft through a plurality of balls, and prevents relative rotation of both nuts, and also includes an elastic member on both nuts. A preloading device for a ball screw that is inserted into the ball screw to apply a preload, wherein the lead of the screw is shifted by a predetermined amount near the center position of the first nut in the Bonyl thread groove of the first nut. A preloaded ball is installed between the ball screw groove and the ball screw groove of the screw shaft in a state of two-point contact with load support lines in different directions with respect to the center of the groove,
A preloaded ball is installed in a two-point contact state between the ball screw groove of the second NAND and the ball screw groove of the screw shaft.

(Function) When wear progresses to the balls and ball screw grooves of the first nut, and as a result, preload release occurs, at that point, the elastic force of the springs inserted in the first nut and the second nut causes The nut is displaced and automatically switches to a double nut with constant pressure preload. In this way, the occurrence of gaps due to wear is prevented, and the phenomenon after preloading is prevented, and the accuracy life can be extended.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a longitudinal section showing a first embodiment of the present invention. A first NAND 3 is connected to a common screw shaft 1 through a large number of balls B.
and a second slot 4 are screwed together, and two flat panels 5A serving as elastic members are inserted between both nuts 3 and 4.

The first NAND 3 has a mounting flange 6 on the end side,
A sleeve 7 for guiding the countersunk spring 5A is fixed to the other end.

This sleeve 7 is provided with a plurality of sliding grooves 8 in the axial direction, and a detent pin 9 is engaged with these grooves. The anti-rotation pin 9 is implanted at one end of the second nut 4, so that both nuts 34 are prevented from relative rotation.

The screw grooves of the screw shaft 1 and the nuts 3 and 4 have a Gothic arch groove shape. In other words, two with different centers
It is a groove formed in a V-shape with two arcuate surfaces. In the first nut 3, a steel ball (oversized ball) Bo that is slightly larger than the ball groove space is used as the ball B, and is made into a so-called oversized ball by making four points contact with the Gothic arch ball groove surface. A preload is applied using this method (Figure 4). In this case, in order to improve operability,
Small diameter spacer balls may be alternately inserted into the rows of oversized balls Bo in the nut 3.

On the other hand, the second nut 4 uses a ball Bs that is slightly smaller than the ball groove space and makes two-point contact with the ball groove surface.

The one shown in FIG. 2 is a modification of the one shown in FIG. 1, in which a compression coil spring 5B is used in place of the disc spring 5A as the elastic member.

Moreover, what is shown in FIG. 3 is yet another modification, in which a urethane rubber member 5C is used as the elastic member. Note that 10 is a housing having a keyway 11, and 12 is a housing having a keyway 11.
is a detent key.

In the first embodiment and its modifications, the elastic members 5A, 5B, and 5C are compressed and attached, and the fourth embodiment
As shown in the figure, a constant preload force Fao is applied between both nuts 3 and 4 in the tensile direction. In addition, the chain line J in the figure represents a load support line, and the arrow mark F represents the preload force synthesized by the spring force of the elastic member. Even if the preload force F on the second nut 4 side is excessive, it is absorbed by the elastic member 5B, so that the balls Bo of the three first nuts can maintain four-point contact.

In this way, the first nut 3 is initially driven with the amount of preload set by the oversized ball Bo. In other words, the ball Bo is in contact with the full surface of the ball at four points, so the nut has high rigidity and no directionality, so each nut 3
, 4 repeats rocking motion with respect to the screw shaft l, excellent torque characteristics can be obtained without causing a low torque state at the time of reversal.

However, if the ball Bo or the entire ball surface wears out,
A gap is created between the ball Bo and the ball groove surface.
Point contact cannot be maintained. In the case of the conventional oversized ball method, the amount of preload cannot be applied properly due to the phenomenon, and the accuracy life ends. However, in this case, the fifth
As shown in the figure, the first nut 3 is moved relative to the screw shaft 1 by the elastic force of the elastic member 5B (5A, 5C). As a result, the ball BO of the first nut 3 and the ball Bs of the second nut 4 are brought into contact at two points on the entire surface of each ball, a preload Fao in the tensile direction is applied, and the system is automatically switched to the spring preload method. Therefore, the accuracy of the preload amount is prevented from deteriorating due to phenomena, and the life can be significantly extended.

A second embodiment is shown in FIGS. 6 and 7.

In this embodiment, the oversized ball preload method of the first embodiment is changed to an offset lead preload method.

In other words, ■ The ball used for the first nut 3 is the ball used for the second nut 3.
The ball Bs was made slightly smaller than the ball groove space, similar to that used in the nut 4.

And, ■ By making the screw thread l of the first nut 3 slightly thicker (E+α) only near the center position,
The thread groove surface was shifted left and right as shown in FIG. The ball screw groove of the first nut 3 and the ball screw groove of the screw shaft 1 are preloaded in a two-point contact state with load support lines J, , J2 in different directions with respect to the center of the groove. A ball Bs is incorporated.

In this way, a load f in the tensile direction is applied to the two-point contact ball BS of the first nut 3, and a preload is applied to the ball screw, so that, as with the oversized ball system, the nut has high rigidity and Even when each nut 3.4 repeatedly oscillates with respect to the screw shaft 1, excellent torque characteristics can be obtained without causing a low torque state during reversal.

If the ball Bs or the ball groove surface of the first nut 3 is worn out, an appropriate preload cannot be applied after the preload is applied. Then, as in the case of the first embodiment, a preload Fao in the tensile direction is applied between the ball Bs of the first nut 3 and the ball Bs of the second nut 4 by the elastic force of the elastic member 5B (5A, 5C). automatically switches to a constant pressure spring preload method. Therefore, after preloading, deterioration in accuracy due to phenomena is prevented, and the service life can be significantly extended.

Note that the elastic members 5B (5A, 5
C) insertion position and 1. The direction of the load support line J of the ball in each second nut 3.4 is not limited to the example, and for example, FIG. 8(a), middle), (C),
Various modifications as schematically shown in (d) and (e) are possible. 15 is a guide shaft on which the elastic member is attached.

[Effects of the Invention] As explained above, the present invention provides a double-nut type ball screw NAND, in which one nut uses an oversized ball type or an offset lead type similar to the single nut preload type, and the ball or ball groove is worn out. At this time, a constant preload in the tensile direction was applied to the balls of both nuts by the elastic force of the elastic member. Therefore,
The characteristics of the single nut preload system are fully demonstrated, including rigidity in both the compression and tension directions, excellent torque characteristics during return motion, and suitability for high frequency control. This has the effect of preventing deterioration and providing a ball screw nut preloading method that is optimal for high-precision positioning methods that involve rocking.

[Brief explanation of drawings]

FIG. 1 is a vertical sectional view of the first embodiment of the present invention, FIG.
The figure is a side view of a modified example, FIGS. 4 and 5 are schematic sectional views explaining the functions of the components shown in FIGS. 1 to 3, FIG. 6 is a longitudinal sectional view of the second embodiment, and FIG. The figure is a schematic cross-sectional view explaining the effect, Figure 8 (a) (b), (C), (d),
(e) is a schematic sectional view of a main part explaining another aspect of each of the above embodiments. 1 is the screw shaft, 3 is the first nut, 4 is the second nut,
5A, 5B, 5C are elastic members, B, B. S is for ball.

Claims (2)

[Claims] (1) It has a first nut and a second nut that are screwed onto a common screw shaft through a number of balls, and the relative rotation of both nuts is prevented, and an elastic member is inserted in both nuts to apply a preload. A ball screw preload device configured to apply a preload to a ball screw, wherein balls used in a four-point contact state are incorporated between a ball screw groove of the first nut and a ball screw groove of the screw shaft, and A preloading device for a ball screw, characterized in that a ball utilized in a two-point contact state is incorporated between a ball screw groove of the second nut and a ball screw groove of the screw shaft. (2) It has a first nut and a second nut that are screwed onto a common threaded shaft through a number of balls, and the relative rotation of both nuts is prevented and an elastic member is inserted in both nuts. The ball screw preload device is configured to apply a preload to the ball screw groove of the first nut, wherein the lead of the screw is shifted by a predetermined amount near the center position of the nut, and the ball screw groove of the first nut and the ball screw groove of the first nut are A preloaded ball is installed between the ball screw groove of the screw shaft and the ball screw in a two-point contact state with load support lines in different directions with respect to the center of the groove, and the ball screw groove of the second nut and the screw A preloading device for a ball screw, characterized in that a preloaded ball is installed in two-point contact with a ball screw groove of a shaft.