JP2004028317A - Linear motion mechanism - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a linear motion mechanism to be used for a member for manufacturing a semiconductor manufacturing device wherein a retainer fitted to the inner peripheral surface of an outer cylinder moving along a shaft holds a plurality of steel balls and these steel balls are brought in contact with a shaft for rotation to reduce the friction to be generated with the motion and wherein even if a flash is generated with metal injection molding in a window part formed in the retainer to expose the held steel balls toward the shaft side, discrimination is facilitated to expand tolerance for occurrence of flash. <P>SOLUTION: A current taper shape of a tip is cut by a cross section of an edge of a window part 13 formed in the retainer 7 to form a bluff-like part 15. Thickness of this bluff-like part 15 is formed larger than the thickness of the flash 17 to be usually generated. for example, several times of 6 % of the diameter of the steel ball or more. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a linear motion mechanism used as a member when manufacturing a semiconductor manufacturing apparatus, a transport apparatus, and the like, and more particularly, to a shape of a part called a retainer that constitutes a linear motion mechanism and holds a steel ball that reduces friction.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a member called a linear motion mechanism for an operation of repeatedly performing a linear motion is used as a member when manufacturing a semiconductor manufacturing device, a transport device, or the like. In this linear motion mechanism, a retainer attached to the inner peripheral surface of an outer cylinder that moves along a shaft holds a plurality of steel balls, and the steel balls rotate in contact with the shaft. The friction associated with it is reduced.
[0003]
There are a plurality of types of linear motion bodies, and a steel ball travels in a groove formed in the longitudinal direction of the shaft, so that not only linear motion but also torque around the shaft can be loaded. By eliminating the directivity of the holding form on the plane (plane in contact with the position of the shaft where the steel ball contacts), not only linear movement but also movement around the shaft is possible, with emphasis on linear movement only There are a designed one, an outer cylindrical body having a columnar shape, a rectangular parallelepiped shape, and the like.
In any case, since the steel ball is exposed to the shaft side, a window is formed in the retainer.
[0004]
The retainer has a complicated shape due to the formation of a plurality of windows and the like, and is generally manufactured by metal injection molding. That is, the paste into which the metal powder of the material is kneaded is injected into the mold by injection molding, the mold is opened, the molded body is taken out, and sintered.
[0005]
[Problems to be solved by the invention]
However, in order to manufacture a large number of retainers, the mold must be opened and closed many times, and as the number of shots indicating the number of times increases, the mold is worn and burrs occur. Also, even if the number of shots is small, burrs may be unavoidable depending on the type and shape of the retainer.
[0006]
Such burrs must be removed because they affect the performance of the retainer, particularly when they occur in windows where precise dimensions are required. However, conventionally, the cross-sectional shape of the edge of the window portion has an edge shape having a sharp tapered tip, so that even if burrs are generated, it is difficult to distinguish the edge from the edge of the window portion.
[0007]
For example, as shown in FIGS. 5A and 5B, a window 105 formed in a retainer 103 which is disposed on the outer peripheral side of the shaft 101 and holds the steel ball 102 has a tapered edge having a sharp cross section. And the most advanced thickness t1 was less than 1% of the steel ball diameter. As shown in FIG. 4C, when the burr 107 is generated at the tip, the thickness t2 of the burr 107 is 0 to several percent of the steel ball diameter, and it is difficult to distinguish the edge of the window 105 from the burr 107. Was.
[0008]
Immediately after the generation of the large burr 107, the exposure of the steel ball 102 becomes insufficient or the movement of the steel ball is hindered by the burr, so that the performance of the retainer 103 is not satisfied.
The present invention has been made in order to solve the above problems, and even if burrs are generated on the edge of the window portion of the retainer, the burrs can be easily distinguished and removed, and the allowable amount satisfying the performance of the retainer is increased. It is an object of the present invention to provide a linear motion mechanism that can perform the motion.
[0009]
[Means for Solving the Problems]
In order to solve the above problems, a first invention is directed to a shaft that guides a linear motion, an outer cylinder that moves along the shaft, and a metal injection molding attached to the inner peripheral surface of the outer cylinder. A steel ball held by the retainer and rotating in contact with the shaft; a loop-shaped groove for holding the steel ball so that a row of steel balls can move endlessly; and a loop-shaped groove. A window portion formed at two corner portions and one straight portion for exposing the steel ball to the shaft side, and a straight portion continuous with the two corner portions and each of these corner portions of the window portion. The cross-sectional shape of the edge in a part, the cliff-shaped portion formed by cutting the tapered tip, and the thickness of the burr that usually occurs at the edge of the window when the retainer is subjected to metal injection molding. The thickness of the sufficiently large the Gakejo moiety is a linear movement mechanism, characterized in that it comprises a.
Further, the second invention is a linear motion mechanism, characterized in that the thickness of the cliff portion is several times or more of 6% of the diameter of the steel ball.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention is shown in FIGS.
As shown in FIG. 2A, in the linear motion mechanism 1 of this embodiment, an outer cylinder 5 having a columnar outer shape linearly moves along a shaft 3 having a circular cross section. Rotational movement around the shaft 3 is also possible, but it is designed mainly with emphasis on linear movement only.
[0011]
As shown in FIGS. 2B and 2C, the cross-sectional shape of the inner peripheral surface of the outer cylinder 5 is a non-circular shape in which the corners of the square are largely rounded, similarly to the outer cross-sectional shape of the retainer 7. Thus, the positioning of the retainers 7 with respect to the outer cylinder 5 is performed by positioning the both 5 and 7 in the circumferential direction, and by performing positioning in the axial direction by other means (not shown).
[0012]
On the outer peripheral surface of the retainer 7, a groove 11 in which a plurality of steel balls 9 can move in an endless state while rotating in a line, that is, a steel ball infinite circulation path is formed in a loop shape. The four grooves 11 are formed at regular intervals in the circumferential direction of the retainer 7.
[0013]
Each loop-shaped groove 11 has a shape in which two straight portions 11A and 11B are connected to two corner portions 11C and 11D, like a track and a track for athletics. The window portion 13 is formed on one straight portion 11B and on the corner portions 11C and 11D continuous with both ends of the straight portion, since a portion under each of the steel balls 9 arranged in a line is exposed to the shaft 3 side. , Formed and become a load part to receive a load. The exposed steel balls 9 rotate in contact with the shaft 3 to reduce friction with the shaft 3. The other straight portion 11A is a no-load portion.
[0014]
In the groove 11 of FIG. 2B, a portion where burrs are particularly likely to occur is indicated by oblique lines. This portion is a part of two corner portions of the window portion and a straight line portion continuing to each of these corner portions.
[0015]
As shown in FIGS. 1 (A) and 1 (B), the window 13 formed in the retainer 7 has a tapered portion 15 (see FIG. 5 of the conventional example) cut at the tip in the cross-sectional shape of the edge. Is formed. As a result, a cliff-like portion 15 is present around the edge of the window portion 13 as an annular, nearly vertical surface.
[0016]
As shown in FIG. 1C, it is assumed that the cut thickness T is sufficiently larger than the thickness t of the burr 17. This size is set so that the thickness T of the cliff-like portion 15 is sufficiently larger than the thickness t of the burr 17 which usually occurs at the edge of the window portion 13 when the retainer 7 is subjected to metal injection molding. It is set to be several times or more the thickness t of the seventeenth embodiment. That is, the burrs can be distinguished if they are at least two times or more, and if possible three times or more, preferably four times or more.
[0017]
As shown in FIG. 3, as the number of shots for opening and closing the mold for manufacturing the retainer 7 increases, the burrs 17 generated on the edge of the window 13 grow larger due to wear of the mold. At this time, for example, stainless steel powder is used as the material of the retainer 7, the mold clamping force is 250 to 500 kN, and the injection filling pressure is 50 to 150 MPa.
[0018]
When the number of shots at which the mold is discarded reaches around 100,000, the burr 17 becomes close to 6% of the steel ball diameter. Therefore, by setting the thickness T of the cliff portion 15 to be more than 6% of the diameter of the steel ball, even when the mold is worn and the burr 17 grows large, the cliff portion 15 and the burr are not formed. The distinction becomes easy. In order to make this distinction clear, it is desirable that the thickness T be several times or more of 6% of the steel ball diameter.
[0019]
(Operation and Effect of Embodiment)
As shown in FIGS. 1 (C) and 1 (D), the thickness T of the cliff-shaped portion 15 formed by cutting is sufficiently larger than the thickness t of the burr 17 to be generated. 17 becomes easy. Therefore, burrs can be easily removed.
[0020]
As shown in FIG. 4, by cutting the edge of the window 13, the width of the window (the width of the window, the same applies hereinafter) can be increased. Since it can be satisfied, the allowable amount can be increased.
[0021]
That is, generally, when the window width becomes 50% or less of the steel ball diameter, the exposure of the steel ball becomes insufficient, and the movement of the steel ball 9 is hindered, so that the function of reducing friction (bearing function) cannot be performed. Further, when it becomes 92.5% or more, the edge of the window portion 13 is shaved due to abrasion with the steel ball 9, and the steel ball 9 may fall.
[0022]
In the conventional (old shape), the edge of the window 13 has an edge shape (see FIG. 5), and the window width is only 70% of the steel ball diameter (in a state where no burr occurs). When 10% or more of the steel ball diameter 9 is generated (20% or more in total on both sides of the window), the substantial window width becomes 50% or less. Therefore, when the number of shots increases and burrs grow, the bearing function is not immediately fulfilled.
[0023]
On the other hand, in this embodiment (new shape), by cutting the edge of the window portion 13, the window width can be made 85%, so that even if the burr 17 grows to 17% of the steel ball diameter (window (A total of 34% on both sides of the part 13), the effective window width is 50% or more, and performs a bearing function. This means that even when the burrs 17 are removed, the burrs 17 cannot be completely removed, so that the allowable amount allowed even if the removal is incomplete is increased.
[0024]
(Other embodiments)
In the above embodiment, four loop-shaped grooves 11 are formed at regular intervals in the circumferential direction of the retainer 7, but in other embodiments, the grooves are formed at irregular intervals. Alternatively, three or more than five may be formed.
[0025]
In the above embodiment, the linear motion mechanism 1 is designed with emphasis on linear motion only, and the outer shape of the outer cylinder 5 is cylindrical. In the, the steel ball can travel in the groove formed in the longitudinal direction of the shaft and load the torque around the shaft, but the movement around the shaft is also possible by eliminating the direction of the holding form of the steel ball The outer cylinder may have a rectangular parallelepiped outer shape.
[0026]
【The invention's effect】
As described above, according to the first or second aspect of the present invention, the retainer is formed into a cliff-shaped portion having a cross-sectional shape of an edge of a window portion holding a steel ball and having a tip cut. Even if burrs are generated in the portion, the burrs can be easily distinguished and thus easily removed.
[0027]
In addition, the exposed steel ball is enough for the cut, and even if a certain amount of burr occurs, it does not hinder the movement of the steel ball and satisfies the performance of the retainer. Can be larger.
[Brief description of the drawings]
FIG. 1A is an enlarged cross-sectional view showing a main part of a linear motion mechanism according to an embodiment of the present invention, and FIG. 1B is an enlarged view of a portion B in FIG. (C) is an enlarged view of a portion C in a state where burrs of (A) are generated.
FIG. 2A is an overall perspective view of a linear motion mechanism according to an embodiment of the present invention, and FIG. 2B is an enlarged side view showing only a retainer constituting the linear motion mechanism of FIG. () Is a CC cross-sectional view of (B).
FIG. 3 is a graph showing a relationship between the number of shots for opening and closing a mold for manufacturing the retainer of FIG. 2 (B) by metal injection molding and the growth of burrs generated at the edge of a window. .
FIG. 4 is a graph illustrating a state in which the window width of the retainer is reduced according to the amount of burr generated (grows with the number of shots).
FIG. 5
(A) is an enlarged cross-sectional view showing a main part of a conventional linear motion mechanism, (B) is an enlarged view of (B) in a state where no burr is generated in (A), and (C) is a burr of (A). FIG. 6 is an enlarged view of a portion C in a state where the occurrence of the occurs.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Linear motion mechanism 3 Shaft 5 Outer cylinder 7 Retainer 9 Steel ball 11 Looped groove 11A, B Linear part 11C, D Corner part 13 Window part 15 Cliff-shaped part T Cliff-shaped part thickness 17 Burr-thickness Sa

Claims (2)

A shaft that guides linear motion, an outer cylinder that moves along the shaft, a retainer that is attached to the inner peripheral surface of the outer cylinder and that is formed by metal injection molding, and that is held by the retainer and contacts the shaft. A steel ball that rotates in a row, a loop-shaped groove for holding the steel ball so that the row of steel balls can move endlessly, and a steel groove formed in two corner portions and one straight portion of the loop-shaped groove. The tapered shape at the tip is cut off at the window for the sphere to be exposed to the shaft side, and at the cross-sectional shape of the edges of the two corners and a part of the straight line continuous to each of these corners of the window. A cliff portion formed as a result, and a thickness of the cliff portion that is sufficiently larger than a thickness of a burr that normally occurs at an edge of the window portion when the retainer is subjected to metal injection molding. Linear movement mechanism, characterized in that. The linear motion mechanism according to claim 1, wherein the thickness of the cliff-shaped portion is set to be several times or more of 6% of the diameter of the steel ball.

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