JP2004138214A - Ball screw equipment and manufacturing method of the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To adjust the preload quantity of a ball screw equipment with ease and low cost. <P>SOLUTION: This equipment has a screw shaft 3 having a spiral screw groove 2 to the outer circumference, a nut 6 having a screw grove 4 corresponding to the screw groove 2 at inner circumference face and being fit with idle and many balls 51, 52 that are loaded so that the rolling movement can be done to the spiral load raceway formed between both screw grooves 2, 4. In the ball screw equipment that gives the pre-load so that the contact direction to the screw groove 2, 4 of the ball 51 on the center left and the contact direction to the screw groove 2, 4 of the ball 52 on the center right are faced in the reverse direction respectively by changing the lead of the screw groove 4 of the nut 6 around the center of the shaft direction of the nut 6, the preload quantity is adjusted by making the ball diameter of the left side of balls 51 of the above center different from the ball diameter of the right side balls 52 of the above center. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a ball screw device used for a feed mechanism of various devices.
[0002]
[Prior art]
FIG. 3 shows an example of a conventional ball screw device of this type. The ball screw device 1 has a screw shaft 3 having a single spiral thread groove 2 on the outer peripheral surface and extending in the axial direction, and a spiral screw groove 4 corresponding to the thread groove 2 on the inner peripheral surface. The nut 6 is loosely fitted. The screw groove 4 of the nut 6 and the screw groove 2 of the screw shaft 3 are opposed to each other to form a spiral load track between them, and a number of balls 5 as rolling elements are rolled on the load track. It is movably loaded. The rotation of the screw shaft 3 (or the nut 6) causes the nut 6 (or the screw shaft 3) to move in the axial direction through the rolling of the ball 5.
[0003]
When the nut 6 (or the screw shaft 3) moves in the axial direction, the ball 5 moves while rolling on the load track formed between the two screw grooves 2 and 4. In order to continuously move the shaft 3), it is necessary to circulate the ball 5 infinitely.
For this reason, for example, a part of the outer peripheral surface of the nut 6 is flattened, and a pair of holes 7 communicating with the load track is formed on the flat surface so as to straddle the screw shaft 3. By inserting both ends of a U-shaped ball circulating tube 8 as a ball circulating member into the ball circulating tube, the ball 5 rolling on the load trajectory between the two screw grooves 2 and 4 moves at a point A (or a point B). 8 and is returned from the point B (or point A) to the load orbit through the tube 8 and rolls on the load orbit to reach the point A (point B) so as to perform an infinite circulation. It has become. In addition, in order to form the infinite circulation path of the ball, besides a ball circulation tube type, a top type, an end cap type and other types are also adopted.
[0004]
By applying a preload to the ball screw device, the rigidity can be improved by eliminating the gap between the screw groove and the ball. As an example of such a preload applying method, as shown in FIG. , The lead L of the thread groove 4 of the nut 6 is slightly increased (L + α) at a portion where the ball 5 does not roll substantially at the center of the nut 6 in the axial direction, thereby offsetting the thread groove of the left and right balls 5. The directions of contact (preload direction) are opposite to each other (see FIGS. 4 and 5), and a ball 5 having a ball diameter dimension appropriately adjusted and selected according to the amount of preload is installed between the left and right thread grooves. Thus, a method of applying a preload is known.
[0005]
[Problems to be solved by the invention]
In the above-mentioned conventional ball screw device, the diameter of the ball 5 is selected according to a preset amount of preload. However, the same diameter is selected for all the balls 5 incorporated in the nut 6.
In this case, if the dimensions of the screw shaft 3 and the nut 6 are ideal, a predetermined amount of preload can be given by incorporating the ball 5 having a predetermined ball diameter. Are varied within the processing tolerance, so that when a predetermined amount of preload is applied to the ball screw device, the diameter of the ball 5 is selected according to the combination of the screw shaft 3 and the nut 6. Therefore, in order to finely adjust the amount of preload, many balls 5 having slightly different ball diameters are required.
[0006]
More specifically, it is assumed that three types of balls 5 having ball diameters D0, D0 + Δ, and D0 + 2Δ are prepared, and when the ball 5 having the ball diameter D0 is incorporated, the gap 0 and the preload amount are also 0. .
Here, since the ball diameter of all the balls 5 is the same, by using these three types of balls, the ball diameter is D0 and the preload is 0, and if the ball diameter is D0 + Δ, the preload of Δ is equivalent to the ball diameter. When the ball diameter is D0 + 2Δ, it is possible to adjust 2Δ preload and three types of preload amounts corresponding to the ball diameter. Since the resolution of the adjustment of the preload amount is determined by the jump of the ball diameter dimension Δ, in the assembly of a normal ball screw device, balls of about 20 kinds of ball diameter dimensions of 1 μm jump are required.
[0007]
As described above, in order to finely adjust the amount of preload, it is necessary to prepare balls 5 having a very large ball diameter, which has been a factor of cost increase.
In particular, in recent years, the use of a ball screw device in a vacuum environment or a non-magnetic environment has increased, and the use of ceramic balls has been increasing. However, ceramic balls are expensive, and moreover, ordinary steel balls are used. Because it has a higher Young's modulus and a smaller elastic displacement than a ball, it is extremely difficult to obtain a large amount of various types of balls with different ball diameters, despite the need for a ball with a smaller dimensional difference than a steel ball. However, there is a problem that it is difficult to finely adjust the preload amount.
[0008]
The present invention has been made to solve such a problem, and an object of the present invention is to provide a ball screw device capable of performing preload adjustment easily and at low cost.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1 includes a screw shaft having a spiral screw groove on an outer peripheral surface, and a screw groove corresponding to a screw groove of the screw shaft on an inner peripheral surface. A nut loosely fitted on a screw shaft, and a number of balls rotatably mounted on a spiral load track formed between the two screw grooves, and a part of the plurality of balls. A ball screw device that applies a preload by directing the contact direction of the remaining groove and the contact direction of the remaining ball to the screw groove in directions opposite to each other.
The ball diameter of some of the balls is different from the ball diameter of the remaining balls.
[0010]
According to a second aspect of the present invention, in the ball screw device according to the first aspect, the two thread grooves are one thread groove, and the lead of the thread groove of the nut is changed at a substantially central portion in the axial direction of the nut. Accordingly, the contact directions of the partial ball and the remaining ball with respect to the screw groove are made opposite to each other.
The ball screw device according to claim 3 is the ball screw device according to claim 1, wherein the two screw grooves are an even number of screw grooves, and the pitch between the screw grooves of the nut is changed, so that the part of the balls and the The directions of contact of the remaining balls with the screw grooves were reversed.
[0011]
According to a fourth aspect of the present invention, in any one of the first to third aspects, the ball is made of ceramic.
The invention according to claim 5 is that a nut having a screw groove corresponding to the screw groove of the screw shaft is screwed into a screw shaft having a helical screw groove on an outer peripheral surface via a number of balls, A method of manufacturing a ball screw device in which a preload is applied by directing a contact direction of some of the balls to the screw groove and a contact direction of the remaining balls to the screw groove in opposite directions. At
The ball diameter of some of the balls is different from the ball diameter of the remaining balls.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an example of an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an explanatory cross-sectional view illustrating a ball screw device according to a first embodiment of the present invention, and FIG. 2 is an explanatory diagram illustrating a ball screw device according to a second embodiment of the present invention. FIG. In the ball screw device of the first embodiment shown in FIG. 1, the configurations of the screw shaft, nut and ball circulation tube are the same as those of the conventional ball screw device described with reference to FIG. The description is omitted by attaching reference numerals.
[0013]
First, a ball screw device according to a first embodiment of the present invention will be described with reference to FIG. 1. In this ball screw device 10, similarly to a conventional example, a lead L of a screw groove 4 of a nut 6 is connected. The nut 5 is slightly increased (L + α) and offset at a portion where the ball 5 substantially does not roll in the center of the nut 6 in the axial direction. The contact directions (preloading directions) of the balls 51 and 52 incorporated between the balls 2 and 4 with the screw grooves 2 and 4 are opposite to each other (see FIGS. 4 and 5).
[0014]
Here, in this embodiment, the diameter of the ball 51 to be incorporated between the two thread grooves 2 and 4 on the left side in the axial center of the nut 6 is the same as that between the two thread grooves 2 and 4 on the right side of the central part. The diameters of the balls 52 are different. All the balls 51 have the same diameter, and all the balls 52 have the same diameter.
Thus, for example, assuming that the ball diameter of the left ball 51 in FIG. 1 is D0 and the ball diameter of the right ball 52 is D0 + Δ, the preload amount is approximately Δ / 2 equivalent to the ball diameter. Assuming that the ball diameter of the ball 51 is D0 + Δ and the ball diameter of the right ball 52 is D0 + 2Δ, the ball diameter is equivalent to 1. The preload amount is 5 Δ, and as a result, the resolution of the preload amount adjustment of the ball screw device can be set to の of the jump Δ of the ball diameter. Although the contact angle slightly changes due to the difference in the ball diameter of the balls 51 and 52, the difference Δ between the ball diameters of the balls 51 and 52 is at most 10 μm or less, usually 5 μm or less. The change in angle is small and its effect is negligible.
[0015]
As described above, in this embodiment, the resolution of the preload adjustment of the ball screw device can be reduced to 1/2 of the jump Δ of the ball diameter, so that a finer adjustment of the preload can be performed as compared with the related art. In other words, if it is not necessary to finely adjust the resolution of the preload adjustment, the types of balls having different diameters required for the adjustment of the preload can be reduced to about half of the conventional type. The adjustment of the preload amount can be performed easily and at low cost, and it can be particularly suitable when using a ceramic ball which is expensive and difficult to secure a ball having a small diameter difference.
[0016]
Next, a ball screw device according to a second embodiment of the present invention will be described with reference to FIG.
The ball screw device 20 includes a screw shaft 13 having two thread grooves 12a and 12b on an outer peripheral surface and extending in an axial direction, and a two thread groove 14a corresponding to the screw grooves 12a and 12b on an inner peripheral surface. , 14b are fitted. The screw grooves 14a, 14b of the nut 16 and the screw grooves 12a, 12b of the screw shaft 13 are opposed to each other to form a load track between them, and the load track between the screw grooves 12a, 14a and the both screw grooves. A large number of balls 53 and 54 are rotatably mounted on the load track between 12b and 14b, respectively. The rotation of the screw shaft 13 (or the nut 16) causes the nut 16 (or the screw shaft 13) to move along the axial direction through the rolling of the balls 53 and 54.
[0017]
The nut 16 has ball return passages 17, 18 penetrating in the axial direction to form an endless circulation path of the balls 53, 54. An end cap 19 is provided for communicating the load track between the screw grooves 12a and 14a and for connecting the ball return path 18 and the load track between the screw grooves 12b and 14b.
[0018]
The lead of the screw shaft 13 is L, and the pitch between the two thread grooves 12a and 12b is P = L / 2. On the other hand, the nut 16 is formed with two thread grooves 14a and 14b of the same lead as the screw shaft 13, but the pitch P between the two thread grooves 14a and 14b is offset by α, and As shown, the pitch-to-pitch dimensions on the left and right are P + α and P-α. Due to this offset, the contact direction (preload direction) of the ball 53 incorporated into the load track between the two screw grooves 12a and 14a and the ball 54 incorporated into the load track between the two screw grooves 12b and 14b. The contact directions (preload direction) with respect to the thread grooves 12b and 14b are opposite to each other.
[0019]
In this embodiment, if the ball diameter of the ball 53 incorporated in the load track between the two screw grooves 12a and 14a is different from the ball diameter dimension of the ball 54 incorporated in the load track between the two screw grooves 12b and 14b. The balls 53 are all the same diameter, and the balls 54 are all the same diameter. Thereby, the same operation and effect as those of the first embodiment can be obtained.
Note that the present invention is not limited to the above-described embodiments, and can be appropriately changed without departing from the spirit of the present invention.
[0020]
【The invention's effect】
As is clear from the above description, according to the present invention, the resolution of the preload adjustment of the ball screw device can be set to 1/2 of the jump Δ of the ball diameter, so that the adjustment of the preload is simple and low. The effect can be obtained at a low cost, and in particular, the effect can be obtained when using a ceramic ball that is expensive and difficult to secure a ball having a small diameter difference.
[Brief description of the drawings]
FIG. 1 is an explanatory cross-sectional view illustrating a ball screw device according to a first embodiment of the present invention.
FIG. 2 is an explanatory sectional view illustrating a ball screw device according to a second embodiment of the present invention.
FIG. 3 is an explanatory sectional view for explaining a conventional ball screw device.
FIG. 4 is an explanatory diagram for explaining a preload applying method.
FIG. 5 is a partial detailed view of FIG. 4;
[Explanation of symbols]
2: Screw groove (screw shaft side)
3 ... screw shaft 4 ... screw groove (nut side)
6 nut 10 ball screw device 51, 52 ball

Claims (5)

A screw shaft having a helical screw groove on the outer peripheral surface, a nut having a screw groove corresponding to the screw groove of the screw shaft on the inner peripheral surface and being loosely fitted to the screw shaft, between the two screw grooves; A plurality of balls rollably mounted on a spiral load track to be formed, and a contact direction of some of the plurality of balls with respect to the thread groove and a remaining ball with respect to the thread groove. In a ball screw device that applies a preload by directing the contact directions in opposite directions,
A ball screw device characterized in that the ball diameter of some of the balls is different from the ball diameter of the remaining balls. The two thread grooves are a single thread groove, and the lead of the thread groove of the nut is changed at a substantially central portion in the axial direction of the nut, whereby the thread of the partial ball and the remaining ball is changed. 2. The ball screw device according to claim 1, wherein the contact directions with respect to the grooves are opposite to each other. The two screw grooves are an even number of screw grooves, and by changing the pitch between the screw grooves of the nut, the contact directions of the partial balls and the remaining balls with respect to the screw grooves are opposite to each other. The ball screw device according to claim 1. The ball screw device according to any one of claims 1 to 3, wherein the ball is made of ceramic. A nut having a screw groove corresponding to the screw groove of the screw shaft is screwed onto a screw shaft having a spiral screw groove on the outer peripheral surface via a number of balls, and one of the balls is screwed. In a method for manufacturing a ball screw device, a preload is applied by directing a contact direction of a portion of the ball to the thread groove and a contact direction of the remaining ball to the thread groove in opposite directions.
A method of manufacturing a ball screw device, wherein the ball diameter of the part of the balls is different from the ball diameter of the remaining balls.

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