JP4244610B2 - Ball screw device and method of manufacturing the device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a ball screw device used for a feeding mechanism of various devices.
[0002]
[Prior art]
As a conventional ball screw device of this type, for example, the one shown in FIG. 3 is known. The ball screw device 1 has a spiral thread groove 4 corresponding to the thread groove 2 on an inner peripheral surface of a screw shaft 3 having a spiral thread groove 2 on the outer peripheral surface and extending in the axial direction. A 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 raceway between which a plurality of balls 5 as rolling elements are rolled. It is loaded movably. The nut 6 (or the screw shaft 3) is moved in the axial direction through the rolling of the ball 5 by the rotation of the screw shaft 3 (or the nut 6).
[0003]
When the nut 6 (or screw shaft 3) moves in the axial direction, the ball 5 moves while rolling on the load track formed between the screw grooves 2 and 4, but the nut 6 (or screw) 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 made flat and a set of two 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 circulation tube 8 as a ball circulation member into the ball, the ball 5 that rolls on the load trajectory between both screw grooves 2 and 4 is at the point A (or point B). 8 is passed through the tube 8 and returned from the point B (or point A) to the load trajectory and rolls along the load trajectory to reach point A (point B). It has become. In addition to the ball circulation tube type, a top type, an end cap type, and other methods are also used to form the infinite circulation track of the ball.
[0004]
By applying a preload to the ball screw device, the clearance between the screw groove and the ball can be eliminated and the rigidity can be improved. 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 the portion where the substantially central ball 5 in the axial direction of the nut 6 does not roll to be offset, whereby the thread grooves of the left and right balls 5 are offset. The direction of contact (preloading direction) with respect to is opposite to each other (see FIG. 4 and FIG. 5), and a ball 5 having a ball diameter dimension appropriately adjusted and selected according to the amount of preload is incorporated between the left and right screw grooves. Thus, a method for applying a preload is known.
[0005]
[Problems to be solved by the invention]
In the above conventional ball screw device, the diameter of the ball 5 is selected according to a preset amount of preload, but 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 dimensions, a predetermined preload amount can be given by incorporating the ball 5 having a predetermined ball diameter. Therefore, when a predetermined amount of preload is applied to the ball screw device, the diameter of the ball 5 is selected in accordance with the combined size of the screw shaft 3 and the nut 6. For this reason, in order to finely adjust the amount of preload, a large number of balls 5 having slightly different ball diameters are required.
[0006]
More specifically, it is assumed that three types of balls 5 having a ball diameter of D0, D0 + Δ, and D0 + 2Δ are prepared, and when the ball 5 having a ball diameter of D0 is incorporated, the clearance is 0 and the preload amount is 0. .
Here, since the ball diameter dimensions of all the balls 5 are the same, by using these three kinds of balls, the ball diameter dimension is D0 and the preload is 0, and the ball diameter dimension is D0 + Δ and the ball diameter is equivalent to a preload of Δ. When the ball diameter is D0 + 2Δ, it is possible to adjust the preload of 2Δ and three kinds of preload amounts corresponding to the ball diameter. Since the resolution of the preload adjustment is determined by the ball diameter dimension jump Δ, assembly of a normal ball screw device requires about 20 types of balls having a ball diameter dimension of about 1 μm.
[0007]
As described above, in order to finely adjust the preload amount, it is necessary to prepare the balls 5 having a large number of ball diameters, which causes an increase in cost.
In particular, in recent years, the use of ball screws in vacuum and non-magnetic environments has increased, and the use of ceramic balls has increased, but ceramic balls are also expensive and made of ordinary steel. Because the Young's modulus is higher than the ball and the elastic displacement is small, it is extremely difficult to obtain many types of balls with different ball diameters, despite the need for balls with smaller dimensional differences than steel balls. There is a problem that it is difficult to adjust the fine preload amount.
[0008]
The present invention has been made in order to eliminate such inconveniences, 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 helical thread groove on an outer peripheral surface, and a thread groove corresponding to the screw groove of the screw shaft on the inner peripheral surface. A nut that is loosely fitted to the screw shaft, and a plurality of balls that are slidably loaded on a spiral load raceway formed between the screw grooves, and the contact directions of the balls with respect to the screw grooves are opposite to each other. In a ball screw device that applies a preload by directing in a direction,
When a ball in one contact direction is a part of the ball and a ball in the other contact direction is the remaining ball,
The ball diameter dimension of the part of the balls and the ball diameter dimension of the remaining balls are different from each other.
A ball screw device according to a second aspect is the ball screw device according to the first aspect, wherein the two screw grooves are one screw groove, and the lead of the screw groove of the nut is changed at a substantially central portion in the axial direction of the nut. Thus, the contact directions of the part of the balls and the remaining balls with respect to the thread grooves are opposite to each other.
A ball screw device according to a third aspect is the ball screw device according to the first aspect, wherein the two screw grooves are even-numbered screw grooves, and the pitch between the screw grooves of the nut is changed to change the pitch of the part of the balls and The contact directions of the remaining balls with respect to the thread grooves were opposite to each other.
[0011]
The invention according to claim 4, in any one of claims 1 to 3, wherein the ball is Ru ceramic der.
[0012]
DETAILED DESCRIPTION OF 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 sectional view for explaining a ball screw device according to a first embodiment of the present invention, and FIG. 2 is an explanation for explaining a ball screw device according to a second embodiment of the present invention. FIG. The ball screw device according to the first embodiment shown in FIG. 1 has the same configuration as that of the conventional ball screw device described with reference to FIG. Reference numerals are assigned and explanations thereof are omitted.
[0013]
First, a ball screw device according to a first embodiment of the present invention will be described with reference to FIG. 1. This ball screw device 10 is provided with a lead L of a thread groove 4 of a nut 6 as in the conventional example. The ball 6 at the substantially central portion in the axial direction of the nut 6 is offset by slightly increasing (L + α) at the portion where the ball 6 does not roll, whereby both the left and right screw grooves at the central portion in the axial direction of the nut 6 are offset. The contact directions (preloading load directions) of the balls 51 and 52 incorporated between 2 and 4 with respect to the thread grooves 2 and 4 are opposite to each other (see FIGS. 4 and 5).
[0014]
Here, in this embodiment, the ball diameter dimension of the ball 51 incorporated between the screw grooves 2 and 4 on the left side of the central portion in the axial direction of the nut 6 is integrated between the screw grooves 2 and 4 on the right side of the center portion. The ball 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, if the ball diameter dimension of the left ball 51 in FIG. 1 is D0 and the ball diameter dimension of the right ball 52 is D0 + Δ, the preload amount is approximately Δ / 2 corresponding to the ball diameter. When the ball diameter dimension of the ball 51 is D0 + Δ and the ball diameter dimension of the right ball 52 is D0 + 2Δ, 1. As a result, the resolution of adjusting the preload amount of the ball screw device can be ½ of the ball diameter dimension jump Δ. Although a slight change in the contact angle occurs due to the difference in the ball diameter of the balls 51 and 52, the difference Δ in the ball diameter of the balls 51 and 52 is 10 μm or less, usually 5 μm or less at most. The change of the angle is small and its influence can be ignored.
[0015]
As described above, in this embodiment, the resolution of the preload adjustment of the ball screw device can be reduced to ½ of the ball diameter dimension jump Δ, so that the preload can be adjusted more finely than in the past. In other words, if the resolution for adjusting the preload amount is not required to be fine, the types of balls having different diameters required for adjusting the preload amount can be reduced to about half of the conventional ball screw device. The preload amount can be adjusted easily and at low cost, and can be particularly suitable for the case of using ceramic balls that are 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 has two screw grooves 12a and 12b on the outer peripheral surface and a screw shaft 13 extending in the axial direction, and two screw grooves 14a corresponding to the screw grooves 12a and 12b on the inner peripheral surface. , 14b are fitted. The thread grooves 14a, 14b of the nut 16 and the thread 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 both screw grooves are formed. A large number of balls 53 and 54 are slidably loaded on the load track between 12b and 14b. The nut 16 (or the screw shaft 13) is moved along the axial direction through the rolling of the balls 53 and 54 by the rotation of the screw shaft 13 (or the nut 16).
[0017]
The nut 16 is formed with ball return passages 17 and 18 penetrating in the axial direction so as to form an infinite circulation track of the balls 53 and 54. An end cap 19 is attached which communicates the load track between the thread grooves 12a and 14a and communicates the load path between the ball return passage 18 and the thread 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, As shown, the left-right pitch dimensions are P + α and P-α. Due to this offset, the contact direction (preloading direction) of the ball 53 incorporated in the load track between the screw grooves 12a and 14a with respect to the screw groove 12a and 14a and the ball 54 incorporated in the load track between the screw grooves 12b and 14b. The contact directions (preloading load directions) with respect to the thread grooves 12b and 14b are opposite to each other.
[0019]
Here, in this embodiment, the ball diameter dimension of the ball 53 incorporated in the load raceway between both screw grooves 12a and 14a is different from the ball diameter dimension of the ball 54 incorporated in the load raceway between both screw grooves 12b and 14b. In addition, all the balls 53 have the same diameter, and all the balls 54 have the same diameter. Thereby, the same effect as the first embodiment can be obtained.
The present invention is not limited to the embodiments described above, and can be appropriately changed without departing from the gist of the present invention.
[0020]
【The invention's effect】
As is apparent from the above description, according to the present invention, the resolution of the preload adjustment of the ball screw device can be halved by the jump Δ of the ball diameter dimension. This is advantageous in that it can be carried out at a low cost, and can be particularly suitable when using a ceramic ball that is difficult to secure a ball having a ball diameter with a small dimensional difference.
[Brief description of the drawings]
FIG. 1 is an explanatory sectional view for explaining a ball screw device according to a first embodiment of the present invention.
FIG. 2 is an explanatory cross-sectional view for explaining a ball screw device according to a second embodiment of the present invention.
FIG. 3 is an explanatory cross-sectional view for explaining a conventional ball screw device.
FIG. 4 is an explanatory diagram for explaining a preload application method;
FIG. 5 is a partial detail view of FIG. 4;
[Explanation of symbols]
2 ... Thread groove (screw shaft side)
3 ... Screw shaft 4 ... Thread groove (Nut side)
6 ... nut 10 ... ball screw device 51, 52 ... ball

Claims (4)

A screw shaft having a helical thread groove on the outer peripheral surface, a nut having a thread groove corresponding to the screw groove of the screw shaft on the inner peripheral surface and loosely fitted on the screw shaft, and the two screw grooves In a ball screw device comprising a plurality of balls that are slidably loaded on a spiral load raceway that is formed, and applying a preload by directing contact directions of the balls with respect to the screw grooves in opposite directions to each other ,
When a ball in one contact direction is a part of the ball and a ball in the other contact direction is the remaining ball,
2. A ball screw device according to claim 1, wherein the ball diameter of the part of the balls is different from the ball diameter of the remaining balls. The both screw grooves are a single thread groove, and by changing the lead of the screw groove of the nut at a substantially central portion in the axial direction of the nut, the screws of the part balls and the remaining balls The ball screw device according to claim 1, wherein contact directions with respect to the grooves are opposite to each other. The two screw grooves are even-numbered screw grooves, and by changing the pitch between the screw grooves of the nut, the contact directions of the some 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.

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