JP2005114066A - Ball screw - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ball screw capable of stably supplying the lubricant for a long period and effectively inhibiting the generation of dust. <P>SOLUTION: This ball screw comprises a screw shaft 1, a plurality of rolling elements 2, a nut 3 and a circulation passage 4 for circulating the rolling elements 2. A cylindrical body 21 composed of a porous member impregnated with the lubricant in vacuum, is inserted into the circulation passage 4. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a ball screw that is used in a semiconductor manufacturing apparatus or a liquid crystal manufacturing apparatus, for example.

  Conventionally, a ball screw has been used as a positioning means in a semiconductor manufacturing apparatus. This ball screw may be used in a high-temperature vacuum environment, and a plurality of rollers that roll along a screw shaft, a nut that is externally mounted on the screw shaft, and a spiral groove that is provided on both the screw shaft and the nut. A rolling element and a circulation path through which the rolling element circulates, and the plurality of rolling elements roll along the spiral groove of the screw shaft and the nut and circulate through the circulation path, so that the screw shaft The rotational movement around the axis can be converted into the linear movement of the nut in the axial direction.

In such a ball screw, since the ball rolls while receiving the force around the axis of the screw shaft and the axial force, both rolling contact and sliding contact occur between the ball and both spiral grooves. For this reason, in order to roll a rolling element stably over a long period of time, how to perform lubrication is important.
Under such circumstances, a technique has been proposed in which a solid film made of a fluorine-based polymer component is formed on the contact surface, and an oil film made of a fluorine-based oil component is further formed on the surface of the solid film (for example, Patent Document 1). reference).

  However, the technique of Patent Document 1 has a problem that the fluorine-based oil component supplied from the oil film tends to become fine particles and become a dust-generating component, and it is particularly difficult to apply to a semiconductor manufacturing apparatus or the like that requires a clean room. . In addition, since the oil film is formed on the surface of the spiral groove via a solid film, the oil film is less likely to peel compared to the case where the oil film is directly formed on the surface of the spiral groove, but when using a ball screw for a long time, There is also a problem that the oil film is peeled off and it is difficult to meet the demand for a longer life.

  On the other hand, in a linear motion bearing in which a slider moves linearly along a track rail via a plurality of balls, a porous body obtained by sintering ultra-high molecular weight polyethylene fine particles into a passage hole through which the ball passes. A technique has been proposed in which a sleeve formed by dipping a lubricant into a hole is inserted (see, for example, Patent Document 2). However, in the above technique, since the lubricant is impregnated by dipping, the lubricant adheres to the inner and outer peripheral surfaces of the sleeve, or the porous body is insufficiently impregnated with the lubricant. To do. For this reason, even if this technique is diverted to a ball screw, there is a problem that it is not sufficient in terms of low dust generation and lubricity. Moreover, in said technique, since polyethylene is used, there also exists a problem that heat resistance is low.

JP 2000-205278 A (2nd page, 3rd page, FIG. 1) JP 2001-82469 A (page 7)

  The present invention has been made in view of such circumstances, and an object thereof is to provide a ball screw capable of stably supplying a lubricant over a long period of time and effectively suppressing dust generation. Another object of the present invention is to provide a ball screw with excellent heat resistance.

A first ball screw according to the present invention includes a screw shaft having a spiral groove on an outer peripheral surface, and a nut having a spiral groove corresponding to the spiral groove of the screw shaft on the inner peripheral surface. A plurality of rolling elements that are freely rollable between the spiral groove of the screw shaft and the spiral groove of the nut; and the plurality of rolling elements between the spiral groove of the screw shaft and the spiral groove of the nut. A ball screw provided with a circulation path for circulating the rolling elements, wherein a cylindrical body made of a porous body that is vacuum impregnated with a lubricant is inserted into the circulation path. .
According to the above configuration, since the cylindrical body composed of the porous body in which the lubricant is vacuum-impregnated is inserted into the circulation path, the vacuum impregnation is performed when the rolling element rolls in the cylindrical body. Thus, a trace amount of lubricant can be oozed out from the cylinder holding an appropriate amount of lubricant. Further, since the bleeding of the lubricant is caused by the capillary phenomenon of the porous body, the lubricant supply is not excessive, and the excessive lubricant is effectively prevented from generating dust (scattering).

A second ball screw according to the present invention includes a screw shaft having a spiral groove on the outer peripheral surface, and a nut that is arranged movably along the screw shaft and has a spiral groove corresponding to the spiral groove of the screw shaft on the inner peripheral surface. A plurality of rolling elements that are freely rollable between the spiral groove of the screw shaft and the spiral groove of the nut; and the plurality of rolling elements between the spiral groove of the screw shaft and the spiral groove of the nut. A ball screw provided with a circulation path for circulating the rolling elements, wherein a cylindrical body made of a porous body impregnated with a lubricant is inserted into the circulation path, and the porous The porosity of the body is set in the range of 10 to 30%, and the impregnation rate of the lubricant is set in the range of 90 to 100% with respect to the space volume inside the porous body. It is characterized by.
According to the above configuration, the cylindrical body in which the porous body having a predetermined porosity is impregnated with the lubricant at the predetermined impregnation rate is inserted into the circulation path, so that the rolling element rolls in the cylindrical body. In this case, a small amount of lubricant can be oozed out from the cylinder holding an appropriate amount of lubricant. Further, since the bleeding of the lubricant is caused by the capillary phenomenon of the porous body, the lubricant supply is not excessive, and the excessive lubricant is effectively prevented from generating dust (scattering). Further, the cylindrical body has an advantage that it has sufficient mechanical strength to be inserted into the circulation path and the rolling element rolls, and is impregnated with an appropriate amount of lubricant.

  In the first and second ball screws, a fluorine-based polymer thin film having a functional group is provided on at least one of the rolling element contact surface of the screw shaft, the rolling element contact surface of the nut, and the surface of the rolling element. Preferably it is formed. In this case, since the lubricant is also supplied from the fluoropolymer thin film when the rolling element contacts the screw shaft or the nut, the rolling element can be stably rolled over a long period of time. In particular, when the functional group of the fluorine-based polymer thin film is a functional group having adhesion to metals and lubricants, the functional group adheres to the metal screw shaft and the fluorine-based polymer thin film. And the adhesion to the lubricant supplied to the surface of the rolling element is also increased, so that the lubricant can be further prevented from dusting (scattering). Further, since the lubricant impregnated and held in the cylindrical body can be replenished to the fluoropolymer thin film by circulating the rolling elements, the linear motion bearing can be used more stably over a long period of time. Have advantages.

In the first and second ball screws, the lubricant preferably has a vapor pressure at 20 ° C. of 10 ⁻⁹ torr or less. In this case, outgas can be suppressed.
Furthermore, in the first and second ball screws, the lubricant is preferably a fluorinated oil. In this case, heat resistance can be improved.
In the first and second ball screws, the porous body is preferably made of a fluororesin. In this case, the heat resistance can be improved and the dust generation life can be improved. In addition, when the lubricant is a fluorinated oil and the porous body is formed of a fluorinated resin, the fluorinated oil is easily adapted to the fluorinated resin, so that the impregnation rate is easily increased and the heat resistance is also improved. It has the advantage of becoming an excellent ball screw.

  Furthermore, in the first and second ball screws, it is preferable that the fluorine-based polymer thin film having the functional group is a gel-like thin film. In this case, since it is not a hard thin film, there is an advantage that even if the rolling element rolls on the surface, abrasion powder is hardly generated.

  According to the ball screw of the present invention, the lubricant can be stably supplied to the rolling elements over a long period of time, and dust generation can be effectively suppressed. Further, when a cylindrical body in which a porous body made of a fluororesin is impregnated with a fluorine-based oil is used, a ball screw excellent in heat resistance can be provided.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a partial longitudinal sectional view showing an embodiment of the ball screw of the present invention. This ball screw is, for example, incorporated in a positioning means in a semiconductor manufacturing apparatus and used in a high temperature vacuum environment, and includes a screw shaft 1, a plurality of balls (rolling elements) 2, and a plurality of balls on the screw shaft 1. 2 and a circulator tube (circulation path) 4 through which a plurality of balls 2 circulate.

The screw shaft 1 is formed using, for example, a metal material such as SUS440, SUS440C, SUS630, or SUS304, and a spiral groove 1a is formed on the outer peripheral surface thereof. The spiral groove 1a is formed by forming a groove having a concave cross section (for example, Gothic arch shape, arc shape) in a spiral shape with a predetermined pitch so that a plurality of balls 2 can roll without dropping. It has become. The screw shaft 1 is connected to a drive device (not shown) and is configured to rotate around the shaft.
The ball 2 is formed in a true spherical shape with a metal material such as SUS440, SUS440C, SUS630, or SUS304. All the balls 2 are formed in substantially the same size.

  The nut 3 is formed using a metal material such as SUS440, SUS440C, SUS630, SUS304, or the like, and a spiral groove 3a corresponding to the spiral groove 1a of the screw shaft 1 is formed on the inner peripheral surface thereof. . Like the spiral groove 1a of the screw shaft 1, the spiral groove 3a is formed by forming a groove having a concave section (for example, Gothic arch shape, arc shape) in a spiral shape with a predetermined pitch. Can roll without falling off. When the plurality of balls 2 roll between the spiral grooves 1a and 3a, the rotational motion of the screw shaft 1 is converted into the linear motion of the nut 3, and the nut 3 moves in the axial direction of the screw shaft 1. Can do.

  The circulator tube 4 is used to circulate the ball 2 that rolls by the rotational motion around the axis of the screw shaft 1, and is attached to the outer side of the nut 2. The circulator tube 4 has, for example, a substantially circular cross section, a central portion is arranged in parallel to the axial direction, both end portions are bent and penetrate the nut 3, and the spiral groove 1 a of the screw shaft 1 and the spiral of the nut 3 are arranged. The ball 2 that rolls between the grooves 3a can be circulated.

  A cylindrical body 21 separate from the circulator tube 4 is inserted into the circulator tube 4 along the inner peripheral surface thereof. The outer diameter of the cylindrical body 21 is substantially the same as the inner diameter of the circulator tube 4, and the inner diameter is set to be almost the same as or slightly larger than the diameter of the ball 2. The cylindrical body 21 is not particularly limited as long as it can be inserted into the circulator tube 4 and the ball 2 can roll. However, the cylindrical body 21 is usually formed in a hollow cylindrical shape (circular cross section).

  The cylindrical body 21 is composed of, for example, a porous body formed into a hollow cylindrical shape and a lubricant filled in the pores of the porous body. Here, the porosity of the porous body is set within a range of 10 to 30%. This is because if it is less than 10%, the space volume for filling the lubricant is too small, and even if the space volume is filled with the lubricant, there is a possibility that a sufficient lubricating effect cannot be exhibited. On the other hand, if it exceeds 30%, the mechanical strength may be insufficient, or the amount of lubricant supplied to the ball 2 may be too large to effectively suppress dust generation. Further, the pore size in the porous body is preferably about several tens of μm in average pore diameter, and more preferably 30 to 70 μm. Furthermore, the filling rate of the lubricant is set within a range of 90 to 100% with respect to the space volume inside the porous body. This is because if the filling rate of the lubricant is small, the lubricant may not be stably supplied over a long period of time.

  The porous body can be produced, for example, by preparing a molding composition containing a synthetic resin and a known pore forming agent and extruding the composition into a cylinder. As the synthetic resin, a fluororesin such as a tetrafluoroethylene polymer, polyethylene, polypropylene, or the like can be used. In particular, a porous material obtained using a fluororesin has heat resistance (for example, 260 ° C.), and even when the lubricant is depleted, the porous body is lubricated by adhering abrasion powder generated by contact with the ball to the ball. There is an advantage that cutting can be effectively suppressed. The porous body can also be produced by filling a predetermined mold with heat-molded ultra-high molecular weight synthetic resin fine particles, for example, and heat-molding the porous body thus obtained. Since a quality sintered resin body is inferior in mechanical strength to an extruded product, it is preferable to produce it by extrusion molding.

The lubricant filled in the pores of the porous body as described above has a kinematic viscosity (20 ° C.) in the range of 500 to 1000 cSt and a vapor pressure (20 ° C.) of 10 ⁻⁹ torr or less, preferably A fluorine-based oil within a range of 10 ⁻¹² to 10 ⁻⁹ is preferably used. Since the fluorinated oil is excellent in heat resistance (for example, 300 ° C.) and chemical stability, it is particularly suitable as a ball screw for a semiconductor manufacturing apparatus used in a high temperature environment.
When the vapor pressure (20 ° C.) of the lubricant exceeds 10 ⁻⁹ torr, the lubricant easily volatilizes, and there is a possibility that the ball screw cannot be used stably over a long period of time. If the kinematic viscosity (20 ° C.) of the lubricant is less than 500 cSt, a liquid film (oil film) having an appropriate thickness may not be formed on the surface of the ball 2, or the formed liquid film (oil film) may not be maintained. As a result, the lubricant may scatter or the lubricant may become fine particles and generate dust. On the other hand, if it exceeds 1000 cSt, it is difficult to supply an appropriate amount of lubricant from the porous body to the surface of the ball 2, and there is a possibility that a sufficient lubricating action cannot be obtained.

  The cylinder 21 can be manufactured by vacuum impregnating the porous body with a lubricant. Specifically, the porous body is introduced into a vacuum impregnation apparatus and decompressed, and the impregnation is performed by adding a lubricant, or the porous body is immersed in the lubricant bath, and the pressure is reduced and impregnated as it is. It can manufacture by the method to make. Adopting vacuum impregnation as a method for impregnating the porous body with the lubricant has an advantage that the impregnation rate into the pores of the porous body can be easily increased. The conditions for vacuum impregnation are appropriately set according to the porosity of the porous body, the type of lubricant, etc., but the vacuum impregnation is performed under the condition that the entire space inside the porous body is filled with the lubricant. It is preferable.

In the ball screw provided with the cylindrical body 21, a very thin fluoropolymer thin film having a functional group is formed on the entire surface of the screw shaft 1 and the nut 3. Specifically, as shown in FIGS. 3 and 4, the entire surface of the screw shaft 1 including the surface (rolling body contact surface) of the spiral groove 1 a of the screw shaft 1 and the surface (rolling surface) of the nut 3. On the entire surface of the nut 3 including the moving body contact surface), a fluoropolymer thin film 11 having a functional group and a thickness of the order of submicron is formed. The fluorine-based polymer thin film 11 is a gel-like thin film having a three-dimensional network structure, extremely low frictional resistance, and fluidity that does not easily generate wear powder due to rolling of the ball 2. Such a fluorine-based polymer thin film 11 can be formed using one or more compounds having a plurality of fluorine atoms, such as a fluoropolyether compound and a polyfluoroalkyl compound. Here, fluoropolyether _compound (the X 1 to 4 integer) -C _x F 2x -O- is a compound having a structural unit represented by the number average molecular weight (Mn) is 1,000 It is about 50,000. The polyfluoroalkyl compound is a compound having a fluoroalkyl group in which a plurality of hydrogen atoms in the alkyl group are substituted with fluorine atoms, and the number average molecular weight (Mn) is about 1,000 to 50,000. It is.

  The compound having a plurality of fluorine atoms, such as the above-mentioned fluoropolyether compound and polyfluoroalkyl compound, is one or more kinds of functional groups having high adhesion to the metal and the lubricant that are the constituent materials of the screw shaft 1 and the nut 3. It is preferable to have. Examples of such functional groups include alcohol groups, epoxy groups, amino groups, carboxyl groups, hydroxyl groups, mercapto groups, isocyanate groups, sulfone groups, ester groups, and the like.

  Preferred examples of the fluoropolyether compounds include compounds represented by the following chemical formulas (a1) to (a10). In addition, preferable examples of the polyfluoroalkyl compound include compounds represented by the following chemical formulas (b1) to (b13).

  More specifically, Fomblin Y Standard, Fomblin Emulsion (FE20, EMO4, etc.), Fomblin Z Derivatives (FONBLIN Z DEAC, FONBLIN Z DIAC, FONBLIN Z DISOC, FONBLIN Z DOL, FONBLIN Z DOLTX2000, manufactured by Montecatini, FONBLIN Z TETRAOL) is preferably used. Moreover, a thing with a kinematic viscosity (20 degreeC) in the range of 1000-2200cSt is preferable.

  The fluorine-based polymer thin film 11 can be formed, for example, as follows. That is, first, a coating solution is prepared in which a compound having a plurality of fluorine atoms is dispersed in a solvent. Here, the concentration of the coating solution is set to a low concentration of 10% by weight or less, preferably 5 to 10% by weight. Subsequently, the screw shaft and nut are immersed in the immersion tank filled with the obtained coating solution and rotated several times. As a result, a coating liquid film is formed on the surfaces of the screw shaft and the nut. In addition, you may form a coating liquid film not only by immersion but by spray application etc. Further, when it is desired to form the coating liquid film only on a specific portion, masking or the like is performed, and then immersion, spray coating, or the like is performed. Furthermore, the coating liquid film may be formed on a site where the coating liquid film is to be formed using, for example, a syringe capable of microinjection. Thereafter, the solvent in the coating liquid film is removed by heating, for example, at 40 to 50 ° C. for 3 minutes. Subsequently, for example, heating is performed at a temperature of 80 to 180 ° C. for 15 to 70 minutes. In this way, a fluorine-based polymer thin film having a thickness of submicron order (preferably 0.1 to 0.4 μm, for example 0.2 μm) can be formed. In order to obtain a desired film thickness, the above-described series of film forming steps may be performed a plurality of times.

  The ball screw according to the present embodiment configured as described above has an impregnation rate of 90 to 100% by vacuum impregnation into a porous body having a porosity of 10 to 30% in the circulation path 4 through which the ball 2 circulates. Since the cylindrical body 21 made of a porous body impregnated with a lubricant at a high impregnation rate is inserted, the porous body constituting the cylindrical body 21 while the ball 2 rolls in the cylindrical body 21 is inserted. The lubricant begins to ooze due to capillary action, and a small amount of lubricant can be supplied to the ball 2. In addition, since a large amount of lubricant is supplied, it can be effectively suppressed that excessive lubricant generates dust (scatters). Furthermore, since the fluorine-based polymer thin film 11 having a functional group is formed on the surfaces of the spiral groove 1a of the screw shaft 1 and the spiral groove 3a of the nut 3, the lubricant is also supplied from the fluorine-based polymer thin film 11. The ball 2 can be rolled stably over a long period of time. In particular, when the functional group of the fluorine-based polymer thin film 11 is a functional group having adhesiveness with a metal, the adhesiveness between the metal screw shaft 1 and the like and the fluorine-based polymer thin film 11 is increased, and the fluorine-based polymer thin film 11 There is an advantage that the polymer thin film 11 is difficult to peel off. Further, when the functional group having adhesiveness with the lubricant impregnated and held in the cylindrical body 21 is exposed on the surface of the fluoropolymer thin film 11, dust generation (scattering) of the lubricant is effectively suppressed. be able to. Furthermore, since the lubricant impregnated and held in the cylinder 21 can be replenished to the fluoropolymer thin film 11 by circulation of the ball 2, the ball 2 can be rolled more stably over a long period of time. . In addition, when the fluororesin porous body is impregnated with fluorine-based oil, the fluorine-based oil is easy to adjust to the fluororesin because the fluorine-based oil is easy to adjust to the fluororesin, and the heat resistance (200 ° C. or more) is also improved. It has the advantage of being excellent. Furthermore, in this embodiment, even if the nut 3 and the screw shaft 1 come into contact with each other when the nut 3 moves in the axial direction of the screw shaft 1, the nut 3 and the screw shaft 1 including the contact surface are all over the surface. Since the fluorine-based polymer thin film 11 is formed, there is an advantage that dust generation and wear caused by contact other than the contact with the ball 2 can be effectively suppressed.

  The present invention is not limited to the above embodiment. For example, the cylindrical body 21 may be divided into a plurality of parts and inserted into the circulation path 4. Further, the fluorine-based polymer thin film 11 having a functional group may be formed on the surface of the ball 2. Furthermore, it goes without saying that the ball screw of the present invention can be used other than the positioning means of a semiconductor manufacturing apparatus used in a high temperature vacuum environment.

It is a partial longitudinal cross-sectional view which shows one Embodiment of the ball screw of this invention. It is sectional drawing which shows the part enclosed by the broken line A of FIG. It is sectional drawing which shows the part enclosed with the broken line B of FIG.

Explanation of symbols

1 Screw shaft 2 Ball (rolling element)
3 Nut 4 Circulation Path 11 Fluoropolymer Thin Film Having Functional Group 21 Cylindrical Body

Claims (7)

A screw shaft having a spiral groove on the outer peripheral surface, a nut that is movably disposed along the screw shaft, and has a spiral groove on the inner peripheral surface corresponding to the spiral groove of the screw shaft, and a spiral groove of the screw shaft; A plurality of rolling elements which are arranged so as to roll between the spiral grooves of the nut, and a circulation path for circulating the plurality of rolling elements between the spiral grooves of the screw shaft and the spiral grooves of the nut; A ball screw with
A ball screw comprising a cylindrical body made of a porous body, which is vacuum-impregnated with a lubricant, is inserted into the circulation path. A screw shaft having a spiral groove on the outer peripheral surface, a nut that is movably disposed along the screw shaft, and has a spiral groove on the inner peripheral surface corresponding to the spiral groove of the screw shaft, and a spiral groove of the screw shaft; A plurality of rolling elements which are arranged so as to roll between the spiral grooves of the nut, and a circulation path for circulating the plurality of rolling elements between the spiral grooves of the screw shaft and the spiral grooves of the nut; A ball screw with
A cylindrical body composed of a porous body impregnated with a lubricant is inserted into the circulation path, and the porosity of the porous body is set within a range of 10 to 30%. The ball screw is characterized in that an impregnation rate of the lubricant is set in a range of 90 to 100% with respect to a space volume inside the porous body.   The fluorine polymer thin film having a functional group is formed on at least one of the rolling element contact surface of the screw shaft, the rolling element contact surface of the nut, and the surface of the rolling element. Ball screw. The ball screw according to any one of claims 1 to 3, wherein a vapor pressure of the lubricant at 20 ° C is set to 10 ^-9 torr or less.   The ball screw according to any one of claims 1 to 4, wherein the lubricant is a fluorinated oil.   The ball screw according to any one of claims 1 to 5, wherein the porous body is made of a fluororesin.   The ball screw according to claim 3, wherein the fluorine-based polymer thin film having a functional group is a gel-like thin film.

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