JP2003329099A - Ball screw device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the workability and extend the life-time by avoiding a ball passage change generated in a ball circulating tube and a torque fluctuation and a torque increase generated by a ball competing, etc., and carrying out the ball entering from the ball circulating tube into a load orbit smoothly. <P>SOLUTION: A ball screw device is provided with a screw shaft 3 having a spiral groove 2 on the outer perimeter, a ball nut 6 having a screw groove 4 corresponding to the screw groove 2 on the inner perimeter and fitted in the screw shaft 3 with clearance, many balls 5 rotatably loaded between both screw grooves 2 and 4, and a ball circulating tube 10 fixed in the ball nut 6 for infinitely rolling the balls 5 rolling between both screw grooves 2 and 4. The sectional shape of the ball screw tube 10 is made elliptical to change the ellipticity of the elliptical section in the axial direction. <P>COPYRIGHT: (C)2004,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor manufacturing apparatus,
The present invention relates to a ball screw device used for a feed mechanism of various devices such as an injection molding machine and an industrial robot. 2. Description of the Related Art As a conventional ball screw device of this type, for example, the one shown in FIG. 7 is known. In this ball screw device 1, a ball nut 6 having a helical thread groove 4 on an inner peripheral surface is loosely fitted on a screw shaft 3 having a helical thread groove 2 on an outer peripheral surface and extending in an axial direction. . The screw groove 4 of the ball nut 6 and the screw groove 2 of the screw shaft 3 are opposed to each other to form a helical passage between them, and the helical passage has a number of balls as rolling elements. 5 is rollably mounted. The rotation of the screw shaft 3 causes the ball nut 6 to move linearly through the rolling of the ball 5. The ball nut 6
When the ball 5 moves linearly, the ball 5 moves while rolling in the spiral path formed by the two screw grooves 2 and 4. However, in order to continuously move the ball nut 6, the ball 5 Must be cycled infinitely. For this purpose, for example, a part of the outer peripheral surface of the ball nut 6 is made flat, and a set of two holes 7 communicating with the two screw grooves 2, 4 are formed in this flat part so as to straddle the screw shaft 3. And
By fitting both ends of a U-shaped ball circulation tube 8 into this set of holes 7, an infinite circulation path of the ball 5 is formed by the spiral passage between the two screw grooves 2 and 4 and the ball circulation tube 8. I have. The cross-sectional shape of the ball circulation tube 8 is a perfect circle from the inlet to the outlet as shown in FIGS. 8 to 10. When a circulation path as shown in FIG. The ball 5 moves in the tube along the staggered state in the straight section and along the outside in the curved section. Therefore, when the ball 5 moves from the straight portion to the curved portion or from the curved portion to the straight portion of the ball circulation tube 8, the ball 5
In this case, the ball fluctuates, causing competition between the balls, which causes torque fluctuation. Further, in the curved portion of the ball circulation tube 8, the balls are arranged in a line along the outside of the path, so that the balls compete with each other and cause an increase in torque. [0006] Incidentally, in an attempt to solve the above problems, there is a technique described in Japanese Patent Application No. 2001-217162 previously proposed by the present applicant.
According to this technique, the ball has a shape (such as an elliptical shape) in which the amount of movement of the ball in the direction perpendicular to the axis of the ball circulation tube is larger than the amount of movement in the direction perpendicular thereto. The balls are arranged in a staggered manner in the longitudinal direction of the tube cross section. Therefore, the balls can smoothly pass through the circulation path while rolling without competing with each other. [0007] However, Japanese Patent Application No. 2001-21716.
In the ball circulation tube described in the specification of No. 2,
As shown in FIG. 1, since the shape of the outlet portion of the ball circulation tube suddenly changes from an elliptical shape having a large area (FIG. 11B) to a perfectly circular shape (FIG. 11A), the load from the ball circulation tube is reduced. When the ball enters the track, there is a problem that the ball easily collides with a screw shaft or a shoulder of a land portion of a ball nut. The present invention has been made in order to solve such inconveniences, and it is possible to avoid a fluctuation in a path of a ball generated in a ball circulation tube, a fluctuation in a torque caused by a competition between balls, and an increase in torque. Needless to say, it is an object of the present invention to provide a ball screw device capable of smoothly moving a ball from a ball circulation tube into a load track to improve operability and extend the life. In order to achieve the above object, the invention according to claim 1 is directed to a screw shaft having a helical screw groove on an outer peripheral surface, and a screw shaft of the screw shaft. A ball nut having a thread groove formed on the inner peripheral surface thereof and being loosely fitted to the screw shaft; a number of balls rotatably mounted between the thread grooves; and rolling between the thread grooves. In a ball screw device having a ball circulation tube fixed to the ball nut for infinite circulation of a ball, the cross-sectional shape of the ball circulation tube is made elliptical, and the ellipticity of the elliptical cross section is changed in the axial direction. It is characterized by. Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory cross-sectional view for explaining a ball circulation tube of a ball screw device which is an example of an embodiment of the present invention. FIG. FIG. 3 (a) is a longitudinal sectional view of an outlet portion of the ball circulation tube of FIG. 1, FIG. 3 (b) is a longitudinal sectional view of an inlet portion, and FIG. FIG. 5 is an explanatory cross-sectional view for explaining a modified example of the tube. FIG. 5 is a cross-sectional view taken along a radial direction at a plurality of positions in the axial direction from an inlet to an outlet of the ball circulation tube in FIG. 6) is a longitudinal sectional view of an outlet portion of the ball circulation tube of FIG. 4, and FIG. 6 (b) is a longitudinal sectional view of an inlet portion. In this embodiment, only the ball circulation tube is different from the ball screw device described with reference to FIG. 7, and therefore only the ball circulation tube will be described. As shown in FIGS. 1 to 3, the cross section of the ball circulating tube 10 has an elliptical shape at a substantially central portion in the axial direction. The ellipticity (the ratio of the length of the major axis to the length of the minor axis) decreases to include the target or stepwise, and the cross-sectional shapes of the outlet and the inlet at both ends of the tube are perfectly circular. In the conventional (see FIGS. 8 to 10) ball circulating tube 8 having a perfect circular cross section, the balls 5 connected in the tube are staggered at a straight portion, but are staggered at a curved portion. Because of this, competition between the balls is inevitable. On the other hand, in this embodiment, since the inner diameter of the ball circulation tube 10 is elliptical, the balls 5 are arranged in a staggered manner in the longitudinal direction of the tube cross section regardless of the linear portion or the curved portion. Competition of balls is avoided, whereby it is possible to avoid a variation in the path of the ball generated in the ball circulation tube, a variation in torque caused by the competition between the balls, and an increase in torque. The elliptical cross section of the ball circulation tube 10 has a gradually decreasing ellipticity as it goes from the substantially central portion in the axial direction to the outlet and the inlet at both ends of the tube, and the outlet and the inlet have a perfect circular cross section. Therefore, when the ball 5 enters the load track from the ball circulation tube 10, the ball 5 can be prevented from colliding with the screw shaft or the shoulder of the land portion of the ball nut. The ball 5 can smoothly enter the load track from the tube 10, thereby improving operability and extending the life. The inner diameter of the ball circulation tube 10 is
In order to absorb the manufacturing error of the ball 5 and the tube, it is necessary to make the ball circulation tube 10 slightly larger than the ball diameter. In this embodiment, since the cross-sectional shape of the ball circulation tube 10 is elliptical, the diameter of the ellipse is the smallest. The length (diameter) of the portion, that is, the minor axis of the ellipse is 1.1 times or more the ball diameter. On the other hand, if the length of the long axis exceeds twice the short axis, the balls are arranged in two rows in the ball circulation tube 10. Therefore, it is indispensable to reduce the number of balls. Therefore, the ratio of the long axis to the short axis is 1.5 or less, and the ratio of the ball diameter to the inner diameter of the ball circulation tube 10 is 0.1.
8 to 0.99. The material of the ball circulation tube 10 is as follows:
Conventionally used metal materials and resin materials can be applied. Here, the ball 5 that moves in the ball circulation tube 10 moves while rolling in the tube without competing with each other, so that the load applied to the tube and the friction of the tube surface are smaller than those in the related art. Therefore, in the ball circulation tube 10 of this embodiment, even if a resin material is used, the ball circulation tube 10 can sufficiently withstand the strength, thereby facilitating processing and manufacturing a tube having a complicated shape at low cost. At the same time, the noise generated in the tube can be reduced. Further, the ball 5 of the ball circulation tube 10
Various methods can be applied as a method of scooping, such as using a tongue, scooping up in the tangential direction without using the tongue, and scooping up in the lead direction. In addition, the ball circulation tube 10 of the above embodiment
In, the wall thickness of the tube is constant, and the outer diameter section is shaped like an ellipse similar to the inner diameter section to approach a perfect circle, but instead, the outer diameter section remains a perfect circle, only the inner diameter section May be applied so as to change gradually. FIGS. 4 to 6 show modified examples of the ball circulation tube. The ball circulation tube 20 has an elliptical cross-section at the entrance, and the elliptic cross-section gradually decreases in ellipticity toward the exit, and the cross-section at the exit is a perfect circle. In normal ball screw device applications,
Since the ball nut reciprocates along the screw axis, the inlet portion of the ball circulation tube changes to the outlet portion and the outlet portion changes to the inlet portion according to the change in the forward and backward strokes. Therefore, usually, as in the above embodiment, the outlet portion side and the inlet side are symmetrical shapes as a base point at the central portion of the ball circulation tube, but depending on the use of the ball screw device, only when moving in one direction. May require high performance. For example, when a ball screw device is used in an injection molding machine or the like, a high load is applied in the direction in which the member is pressed, but a large load does not act when the member is returned. Therefore, particularly high performance of the ball screw device is required in one direction. The ball circulating tube 20 is to be incorporated in a ball screw device requiring high performance in only one direction. The effect of forming the cross section at the outlet portion into a perfect circular shape is different from that of the above embodiment. Similarly, since the cross-sectional area of the ball circulation tube 20 is increased at the entrance, the ball 5 can smoothly enter the ball circulation tube 20 from the load track. As is apparent from the above description, according to the ball screw device of the present invention, the fluctuation of the path of the ball generated in the ball circulation tube, the fluctuation of the torque generated by the competition between the balls and the like, and the increase of the torque are prevented. Since the ball can be avoided and the ball can smoothly enter the load track from the ball circulation tube, the operability can be improved and the life can be extended.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory sectional view for explaining a ball circulation tube of a ball screw device which is an example of an embodiment of the present invention. FIG. 2 is a cross-sectional view of the ball circulation tube of FIG. 1 cut along a radial direction at a plurality of positions in an axial direction from an inlet portion to an outlet portion. 3A is a longitudinal sectional view of an outlet portion of the ball circulation tube of FIG. 1, and FIG. 3B is a longitudinal sectional view of an inlet portion. FIG. 4 is an explanatory sectional view for explaining a modification of the ball circulation tube. 5 is a cross-sectional view of the ball circulation tube of FIG. 4 cut along a radial direction at a plurality of positions in an axial direction from an inlet portion to an outlet portion. 6 (a) is a longitudinal sectional view of an outlet portion of the ball circulation tube of FIG. 4, and FIG. 6 (b) is a longitudinal sectional view of an inlet portion. FIG. 7 is an explanatory sectional view for explaining a ball screw device. FIG. 8 is an explanatory sectional view illustrating a ball circulation tube of a conventional ball screw device. 9 is a cross-sectional view of the ball circulation tube of FIG. 8 cut along a radial direction at a plurality of axial locations from an inlet to an outlet. 10A is a longitudinal sectional view of an outlet portion of the ball circulation tube of FIG. 9, and FIG. 10B is a longitudinal sectional view of an inlet portion. 11A and 11B are explanatory cross-sectional views for explaining a conventional problem, in which FIG. 11A is a cross-sectional view of a perfect circular portion of an outlet portion of a ball circulation tube, and FIG. It is sectional drawing. [Explanation of Symbols] 2 ... thread groove 3 ... screw shaft 4 ... screw groove 5 ... ball 6 ... ball nut 10, 20 ... ball circulation tube

Claims (1)

Claims: 1. A screw shaft having a spiral screw groove on an outer peripheral surface, and a screw groove corresponding to the screw groove of the screw shaft on an inner peripheral surface, and is loosely fitted to the screw shaft. And a ball circulation tube fixed to the ball nut to infinitely circulate the balls rolling between the two screw grooves, and a number of balls rollably loaded between the two screw grooves. A ball screw device comprising: a ball circulation tube, wherein a cross-sectional shape of the ball circulation tube is elliptical, and an ellipticity of the elliptical cross section is changed in an axial direction.