JP2003343565A - Linear motion apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a linear motion apparatus operating favorably for a long stretch of time by using a separator with high corrosion, high wear and high burn-in resistances. <P>SOLUTION: The separator inside the linear motion apparatus is made of titanium or a titanium alloy, and includes a plurality of recess portions independent from each other in its surface. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a linear motion device used for industrial machines and the like, and more specifically to a lightweight and high-strength separator which is refurbished between rolling elements that roll along a rolling element groove and circulate. The present invention relates to a linear motion device that can maintain good operability for a long time by having high corrosion resistance. In particular, the present invention relates to a linear motion device used for special environment applications such as food machinery and semiconductor manufacturing equipment.

[0002]

2. Description of the Related Art A machine tool such as a machining center or an industrial robot uses a ball or a roller as a rolling element in order to smoothly convert a rotary motion into a straight motion and a straight motion of a work table without friction loss. The device is heavily used. A full-ball type ball screw, which is a type of linear motion device, has balls (generally steel balls) as rolling elements between the screw shaft and the nut, which causes almost no friction loss during operation. Since it can be ignored, it has an extremely high driving efficiency, and because the relative rotation between the screw shaft and the nut does not involve sliding, the wear of the constituent elements is extremely small.

A full-ball type ball screw has a screw shaft formed with an external thread groove on its outer circumference, a nut formed with an internal thread groove facing the male thread groove on its inner circumference, and a male screw groove and an internal thread groove. And a circulation passage (tube, top, etc.) formed in the nut for moving the ball from one end side to the other end side of the female thread groove. When the screw shaft and the nut rotate relative to each other, the ball rolls with respect to the male screw shaft and the female screw shaft, and moves from one end side to the other end side of the female screw groove through the circulation passage.

In the above-described full ball type ball screw, when balls rolling in the same direction contact each other between the thread grooves, relative sliding occurs at the contact surface at a speed twice as high as the rolling speed. In particular, when the driving speed of the ball screw is increased in order to improve the performance of the machine, various problems such as wear of the ball surface, torque fluctuation, and noise increase occur.

Japanese Patent Application No. 11-315835 discloses a linear motion device in which a separator made of synthetic resin is interposed between adjacent balls. This linear motion device prevents contact between balls without significantly reducing the number of balls (suppressing reduction in load capacity).

[0006]

However, the separator made of synthetic resin may be worn by slipping with the ball or may be pinched by the ball at the time of starting and stopping and deformed by receiving compressive stress. If the gap between the ball and the separator becomes large due to wear or deformation, the separator falls down and the linear motion device is locked, so that the separator made of a synthetic resin has a limit of usage conditions. Since the separator made of synthetic resin expands due to the lubricating oil, there is a problem that the clearance between the separator and the ball becomes too small and the separator wears abnormally.

Although the synthetic resin material has excellent corrosion resistance, it is necessary to use a metallic separator in order to solve the above problems. Austenitic stainless steel is mentioned as a metal material having excellent corrosion resistance. But,
Austenitic stainless steel has insufficient corrosion resistance when applied to equipment such as semiconductor manufacturing equipment that is extremely corrosive, and also has a large specific gravity, which increases the operating torque of linear motion equipment. There are also problems.

The present invention has been made in view of the above problems, solves various problems caused by a separator, and uses a separator having high corrosion resistance, abrasion resistance and seizure resistance for a long time. It is an object of the present invention to provide a linear motion device that works well in crossing.

[0009]

In order to achieve the object of the present invention, a linear moving body which is fitted onto a shaft and linearly moves along the shaft, and an outer surface of the shaft and an inner surface of the linear moving body are formed. A plurality of balls held in a ball groove formed in the ball groove and rolling between the ball groove and the shaft; and a circulation formed in the linear motion body to move the ball from one end side to the other end side of the ball groove. In a linear motion device having a passage and a separator interposed between the balls, the separator is made of titanium or a titanium alloy and has a plurality of recesses independent of each other on the surface of the separator. A linear motion device is provided.

According to this linear motion device, a plurality of dents are provided on the surface of the separator made of titanium having high corrosion resistance. Lubricants such as grease and lubricating oil collect in the recesses to improve the lubrication between the separator and the rolling elements. Therefore, the corrosion resistance and wear resistance of the separator are improved, and problems such as seizure can be solved.

The recess of the separator is formed by injection molding a mixture of titanium or titanium alloy powder and a binder, removing the binder from the mixture, and sintering the mixture. Titanium separators manufactured by this so-called metal powder injection molding have much higher wear resistance and seizure resistance than titanium separators manufactured by melting, etc. Can be further increased.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows a ball screw (linear motion device) 10 according to a first embodiment of the present invention. Ball screw 1
0 is a screw shaft 11 having a male screw groove 12 formed on the outer periphery thereof.
And a cylindrical nut 13 having a female thread groove facing the male thread groove 12 formed on the inner circumference thereof, and a large number of balls 21 (rolling elements) interposed between the male thread groove 12 and the female thread groove. It is a component.

FIG. 2 is a sectional view taken along the line AA in FIG. As shown in FIG. 2, an internal thread groove 18 that is a ball groove that opposes the external thread groove 12 of the screw shaft 11 is spirally formed on the inner circumference (inner surface side) of the nut 13. Nut 13
A flange 14 for fixing to a table or the like (not shown) is formed at one axial end of the. A part of the outer peripheral surface of the nut 13 (upper side in FIG. 2) has a flat surface portion (notched surface).
15 is cut. A pair of steel tubes 17, 17 are fixed to the flat surface portion 15 by axially arranging them by means of a tube holder 16 screwed. Dustproof plastic seals 19 and 20 are fixed to both axial sides of the female thread groove 18.

Between the female thread groove 18 and the male thread groove 12,
A large number of balls 21 are interposed. A steel ball can be used as the ball 21. A separator 22 is arranged between each of the balls 21. One end portion and the other end portion of each of the tubes 17 and 17 have a male thread groove 12
The ball 21 and the separator 22 are circulated by the tubes 17 and 17 when the ball 21 and the separator 22 have rotated 3.5 times on the male screw groove 12 of the screw shaft 11 at a position corresponding to 3.5 rotations on the spiral line. .

FIG. 3 is a sectional view taken along the internal thread groove 18 and the external thread groove 12. The separator 22 interposed between the balls 21 is made of titanium, which is a softer metal material than the female thread groove 18, the male thread groove 12 and the balls 21, as a raw material.
It is formed in a substantially cylindrical shape. One end and the other end of the separator 22 have concave spherical ball contact surfaces 22a, 22 which are in surface contact with the ball 21 with a relatively small area.
b are formed respectively.

Titanium is a metal that is light, strong and has strong corrosion resistance, and forms an alloy with almost all metals.
On the other hand, since it is a very active metal, it tends to cause adhesion when it comes into contact with other metals, and is inferior in wear resistance and seizure resistance to steel. Therefore, when titanium is used as the separator 22, there is a risk that the separator 22 may be worn or seized due to sliding friction caused by contact with the balls 21. Generally, titanium is subjected to a surface treatment to improve wear resistance and seizure resistance. However, since this surface treatment is special, it causes an increase in the manufacturing cost of the separator 22.

Separator 2 made of titanium according to the present invention
2 has a plurality of independent fine recesses (recesses) on its surface. The recess holds the lubricant injected between the external thread and the internal thread. In particular, the lubricant retained in the depressions formed in the contact surfaces 22a and 22b of the separator 22 with the balls 21 has a function of significantly improving the lubricity of the separator 22 and the balls 21. As a result, a titanium alloy separator having excellent wear resistance and seizure resistance can be obtained.

Separator 2 having a depression on the surface of the present invention
2 is manufactured using a powder metallurgy method such as a powder compaction-sintering method and a metal powder injection molding method. The metal powder injection molding method is a manufacturing method in which a metal powder and a binder are mixed, the mixture is injection-molded, the binder is evaporated and removed (defatted) from the mixture, and the final molded product is obtained by sintering.

In the metal powder injection molding method, first, titanium powder and a binder are mixed to prepare a mixture. As titanium powder, gas atomized powder or hydrogenation / dehydrogenation (H
DH) powder can be used. These titanium powders are
Since the oxygen content is high, the final molded product after sintering has a higher oxygen concentration than the molten titanium material. The binder is a thermoplastic synthetic resin. The mixing ratio of metal powder and binder is
It is preferably performed in the range of about 6: 4 to 7: 3.

Then, the mixture is put into an injection molding machine and injection molding is performed. The injection molding machine used at the time of injection molding may be a conventional plastic injection molding machine. In the metal powder injection molding method, the injection temperature of the mixture of the metal powder and the binder is higher than that of plastic, and the injection pressure is lower,
Then, the injection speed is slow.

The molded product molded by injection molding is put into the gas phase of an organic solvent and extracted and degreased. The degreasing conditions are
For example, the molded product is held in a gas phase of hexane for 20 to 40 minutes at an ambient temperature of 50 to 70 #C, depending on the kinds of the metal powder and the binder.

The molded product subjected to the extraction degreasing is 450 to 60
It is held for 20 to 40 minutes in a nitrogen atmosphere of 0 # C to perform heat degreasing. After degreasing by heating, the molded product is subjected to temporary sintering under vacuum for about 1 hour. Temporary sintering temperature is 1050
It is about 1150 # C. The binder is removed from the molded product through these degreasing processes.

After the degreasing is completed, the molded product is finally sintered to obtain a final molded product. Main sintering temperature is 1100 #
It is C or higher and lower than the melting point of titanium constituting the molded product.
The main sintering is performed in an atmospheric furnace adjusted within this temperature range. By the main sintering, adjacent particles are firmly bonded to each other, and the strength is increased. The size of the final molded product thus obtained is appropriately adjusted by cutting or the like to obtain a final separator. A plurality of dents are formed on the surface of the final molded product produced by this method.

The separator obtained by this metal powder injection molding has substantially the same mechanical properties as the separator manufactured by the melting method or the like. Furthermore, the separator produced according to this method has a higher oxygen concentration than the melted titanium material. Also, because it is made using a binder, the separator contains more carbon than usual.

Generally, in titanium, interstitial solid solution elements such as hydrogen, oxygen, carbon, nitrogen, etc. act as impurities, and mechanical properties, particularly ductility, are remarkably deteriorated. Efforts are being made to eliminate as much as possible. However, in the metal powder injection molding method, these interstitial solid solution elements (oxygen, carbon, etc.) are positively utilized as solid solution strengthening elements. Therefore, the obtained titanium separator is a separator having excellent rigidity.

The size of the depressions formed on the surface of the separator 22 is 2 μm or more and 30 μm or less in average diameter, and preferably 2 μm or more and 10 μm or less. If the average diameter of the depressions is less than 2 μm, the amount of lubricant retained in each depression is reduced, so that the wear resistance of the separator,
The seizure resistance will decrease. On the other hand, the average diameter of the depressions is 3
If it exceeds 0 μm and becomes too large, when the contact stress is intensively applied to the separator surface, the dent on the separator surface may be deformed. Here, the average diameter of the depressions is obtained by observing and photographing the surface of the work with an optical microscope and subjecting the obtained image to image processing.

The existence ratio (porosity) of the depressions formed on the surface of the separator 22 is 2% of the surface area of the separator.
It is above and 10%. When the porosity is less than 2%, the number of depressions becomes insufficient, and it becomes impossible to sufficiently retain the lubricant and improve the lubricity of the separator. On the other hand, when the porosity exceeds 10%, the titanium is not sufficiently sintered, and the individual depressions are not independent but are connected to each other, so that the depressions hold the lubricant. Does not function as an oil sump. Here, the porosity is measured using the Archimedes method. Specifically, the volume and weight of the object to be measured are measured, and the ratio of the calculated density and the theoretical density is the porosity.

Further, in order to improve the strength of the separator 22, instead of titanium, a separator made of a titanium alloy is used. As a titanium alloy, Ti-6Al-4
V, Ti-8Al-1V-1Mo, Ti-6Al-2Sn-4Zr-6Mo, Ti-6Al-6V-2S
n, Ti-11Sn-5Zr-2.5Al-1Mo-0.25Si, Ti-13V-11Cr-3Al,
Ti-11.5Mo-4.5Sn-6Zr, Ti-4Mo-8V-6Cr-3Al-4Zr, Ti-15M
o-5Zr, Ti-15Mo-5Zr-3Al, Ti-8Mo-8V-2Fe-3Al, Ti-22V-
It is possible to use 6Al, Ti-15V-3Cr-3Sn-3Al, etc.

The separator made of titanium alloy is manufactured by the metal powder injection molding method as in the case of titanium. In the case of a titanium alloy, a method of using a powder of a titanium alloy in advance and a method called an elementary powder mixing method can be used. The method of preparing from alloy powder is not preferable because the cost of the alloy powder itself is high.

On the other hand, in the elementary powder mixing method, a predetermined amount of powder of each alloying element is mixed so as to obtain an alloy composition, which is mixed with a binder, injection molded and degreased, and then sintered to obtain a surface. It is a method of obtaining an alloy having a depression. The elementary powder mixing method is preferable because it can be performed at a low cost as compared with the method of preparing from alloy powder. Furthermore, it is preferable to use the elementary powder mixing method because a titanium alloy can be produced with a desired elemental composition ratio.

In the ball screw 10 as described above, when the screw shaft 11 is rotationally driven by a motor (not shown) or the like, the nut 13 screwed to the screw shaft 11 via the ball 21 is in the left-right direction in FIG. The screw shaft 11 is screwed forward and backward.
Since the male thread groove 12 on the side and the female thread groove 18 on the side of the nut 13 relatively rotate in the reverse rotation direction, each of the balls 21 rolls with respect to the male thread groove 12 and the female thread groove 18.
When each of the balls 21 rolls, the separators 22 prevent the balls 21 from colliding with each other, and at the same time, the relative sliding speed between the balls 21 and the separator 22 is also relative to each other in the total ball type ball screw. It becomes 1/2 of the sliding speed. Therefore, the wear of the balls 21 is extremely reduced, and the initial (desired) performance is maintained even when a long-term operation is performed.

Further, in this ball screw 10, since the width of the central portion of the separator 22 is relatively small, the number of balls 21 does not decrease so much as compared with the case where a spacer ball is used, which results in load capacity and rigidity. Can be suppressed. The separator 22 has a ball contact surface 2
Since the radius of curvature R1 of the balls 2a and 22b is larger than the radius R2 of the ball 21, the sliding resistance of the ball 21 is relatively small, and the gap between the ball contact surfaces 22a and 22b and the ball 21 is lubricated with grease or the like. The agent easily penetrates, and as a result, the driving resistance of the screw shaft 11 decreases.

The separator 22 produced by the metal powder injection molding method is made of titanium or titanium alloy. The separator 22 has substantially the same mechanical properties as the separator manufactured by the melting method. Furthermore, since the separator 22 formed by the metal powder injection molding method has fine and independent dents on the surface, it can hold the lubricant. Therefore, the separator 22 has excellent wear resistance and seizure resistance with respect to the balls 21.

In general, the titanium separator manufactured by the melting method is manufactured by using a special melting method, so that the cost is increased. Further, since titanium is a difficult-to-cut material, the cost for cutting is high. However, the separator of the present embodiment, by the metal powder injection molding method,
Since near net shape molding is performed, it is possible to reduce the cutting process. As a result, the yield of the material is increased, and the cost can be reduced.

Next, a ball screw using the separator according to the embodiment of the present invention was prepared and a durability test was conducted under the following conditions to confirm the effect of the invention. As an example, prepared by using powder injection molding, pure titanium, a separator made of Ti-6Al-4V, which is a typical titanium alloy, respectively, and a separator made by compressing and sintering titanium powder are prepared. did. For comparison, separators made of titanium and synthetic resin prepared by melting were also prepared. The separator made of titanium by melting has no fine dents on the surface. <Test conditions> Preload: 2kN Stroke: 700mm Rotation speed: 3000min-1 Lubrication: Grease lubrication test temperature: 80 ° C

The results of the above tests are shown in Table 1.

[Table 1]

The ball screws using the separators of Comparative Examples 1 and 2 were damaged at the time of running at 3250 km and 2650 km, and the running became impossible. On the other hand, the ball screws using the separators of Examples 1 to 3 operated well without being damaged even after traveling for 4000 km.

As described above, in the present embodiment in which titanium and titanium alloy are used for the separator, compared with the conventional ball screw using the synthetic resin for the separator, 100
It can be seen that it is possible to favorably operate a long distance of about 0 km to 3000 km, and the durability is significantly improved. Further, a separator made of titanium produced by a powder compaction-sintering method, particularly a powder metallurgy method such as metal powder injection molding has a better durability than a separator made of titanium produced by a melting method. It can be seen that it has the property.

The present invention is not limited to the above-described embodiment, but can be appropriately modified and improved. For example, the ball screw 10 of the present invention can be applied to the linear guide 50 shown in FIG.

[0040]

As described above, according to the present invention,
Since titanium is used as a material between the balls of the rolling device and a separator having fine dents on the surface is used, the corrosion resistance, wear resistance and seizure resistance of the separator are improved. Furthermore, by incorporating this separator, it is possible to provide a rolling device that operates well for a long period of time, and it is possible to improve the performance of equipment incorporating this rolling device.

[Brief description of drawings]

FIG. 1 is a plan view of a first embodiment.

FIG. 2 is a sectional view taken along the line AA of FIG.

FIG. 3 is a sectional view taken along a female screw groove and a male screw groove in the first embodiment.

FIG. 4 is an external perspective view of a linear guide to which the present invention is applied.

[Explanation of symbols]

10 Ball screw (direct acting device) 11 screw shaft 12 Male thread groove 13 Nut (direct acting body) 17 tube (circulation passage) 18 Female thread groove (ball groove) 21 balls 22 Separator

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 3J062 AA21 AA38 AB22 AC07 BA17                       BA32 CD06 CD63                 3J101 AA03 AA33 AA42 AA44 AA64                       AA71 BA13 BA14 BA20 DA20                       EA75 FA08 FA31 FA33 GA31                       GA55                 3J104 AA03 AA19 AA23 AA36 AA65                       AA69 AA74 BA15 BA80 CA01                       CA33 DA06 DA14 EA01 EA04                       EA06                 4K018 AA06 CA29 DA03 DA21 HA07                       KA02

Claims (5)

[Claims] 1. A linear motion body which is fitted onto a shaft and linearly moves along the shaft, and a ball groove formed on an outer surface of the shaft and an inner surface of the linear motion body, and the ball groove and the shaft. A plurality of balls rolling between the balls, a circulation passage formed in the linear motion body for moving the balls from one end side to the other end side of the ball groove, and a separator interposed between the balls. The linear motion device of claim 1, wherein the separator is made of titanium or a titanium alloy, and has a plurality of independent recesses on the surface of the separator. 2. The linear motion device according to claim 1, wherein the separator has the plurality of recesses on a contact surface with the balls. 3. The linear motion device according to claim 1, wherein the average diameter of the plurality of recesses is 2 μm or more and 30 μm or less. 4. The recess of the separator is formed by injection-molding a mixture of titanium or titanium alloy powder and a binder, removing the binder from the mixture, and sintering the mixture. The linear motion device according to any one of items 1 to 3. 5. The linear motion device according to claim 4, wherein the sintering is performed at a temperature of 1100 # C or higher and lower than the melting point of titanium.