Abstract:
The invention provides a ball screw lubricative sealing device having a simplified lubrication mechanism. It is attachable to an installed standard ball screw nut, capable of retaining larger amount of lubricant and long supply of lubricant to the contacting screw parts, and further includes a sealing function. It includes: generally cylindrical case members having attachment part to be attached to both ends of a screw nut, respectively; plural thin seal plates made of lubricating oil impregnated felt-like fiber material which is a three-dimensionally crosslinked plastic fiber and resilient rubber members, and having a hole each and fitted inside said case member in such a state that they circumferentially overlap with each other, the hole having a shape corresponding to a lateral cross-sectional shape of a screw groove of ball screw shaft; and a plastic wiper fitted with a space from the thin seal plates inside each of the case member.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS AND CLAIM FOR PRIORITY 
     This application is a divisional of application Ser. No. 11/254,471, filed Oct. 20, 2005, now issued as U.S. Pat. No. 7,857,100 on Dec. 28, 2010, entitled BALL SCREW LUBRICATIVE SEALING DEVICE, the priority of which is claimed herein, which application Ser. No. 11/254,471 was based upon and claimed the benefit of priority from Japanese Patent Application No. 2004-306994, filed on Oct. 21, 2004, the priority of which is also claimed in the present divisional application, and said application Ser. No. 11/254,471 having been based also upon Japanese Patent Application No. 2003-392279, filed on Nov. 21, 2003, the entire contents of which applications are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a lubricative sealing device which provides lubrication to rolling parts of ball screws, particularly between the screw groove of the ball screw shaft or the ball screw nut and the balls, and enables the ball screw to be used for a long time without replenishment of oil. 
     2. Description of the Related Art 
     Various sealing devices of this type have been proposed so far (see, for example, Japanese Unexamined Patent Application Publication No. 10-2395 and Japanese Patent No. 3288961). 
     Japanese Unexamined Patent Application Publication No. 10-2395 discloses a structure in which a lubricant-impregnated rubber or synthetic resin ring is attached to the end of a ball nut with a pressing member which has projections to apply a preload to the ring in a circumferential direction. 
     Japanese Patent No. 3288961 discloses a sealing device that is attached to sliding members such as nuts similarly to Japanese Unexamined Patent Application Publication No. 10-2395. The lubricating oil applying member is made of polyester/wool blend felt, sintered resin, or the like, which has the merit of being able to absorb and hold more lubricant, as described in the specification. 
     Another structure for the sealing device is known, as described in Japanese Examined Utility Model Application Publication No. 5-43310. In this sealing device, thin seal plates having holes of shapes that correspond to the lateral cross-sectional shape of the screw groove of the ball screw shaft are circumferentially displaced and overlapped, and held in a frame-shaped ring to be attached to the end of the ball nut. This structure is effective as a sealing device. 
     A sealing device that can be used on any installed standard ball screw nuts by attaching to both ends of the ball screw nut is also known (see, for example, Japanese Unexamined Patent Application Publication No. 2002-147561). 
     In the structure disclosed in Japanese Unexamined Patent Application Publication No. 10-2395, however, pressure is constantly applied to the lubricant supplying member making contact with the balls serving as rolling elements, to keep their contact for a long time. This accordingly causes a problem of complexing lubrication mechanism. 
     With the structure of Japanese Patent No. 3288961, while the member that makes contact with the rolling elements, or balls, to apply oil can absorb and hold a large amount of oil, it requires a lubricating oil reservoir member (tank function) that supply oil in order to achieve constant lubricating effect. Another problem is that the lubricating oil applying and retaining member loses its resiliency in the areas contacting the balls as time passes, which leads to its plastic deformation, and as the surfaces contacting the rolling balls deteriorate, the lubricating effect may be reduced. Also, since felt materials usually have large pores, absorbed oil can readily flow out. Therefore, the structure needs to be modified such as provision of a flow rate control valve between the oil reservoir member and the oil application member, as described in the specification. 
     Further, the device shown in Japanese Examined Utility Model Application Publication No. 5-43310 uses a common seal material, and therefore, while it has good sealing properties, it lacks a lubricating function and is unable to supply lubricating oil stably for a long time. 
     Furthermore, with the device shown in Japanese Unexamined Patent Application Publication No. 2002-147561, the built-in lubricant holding member is made of a porous sintered resin material. Therefore, similar to the other conventional devices described above, the lubricating oil applying and retaining member loses its resiliency as time passes in the areas contacting the balls, which leads to its plastic deformation, and as the surfaces contacting the rolling balls deteriorate, the lubricating effect can be reduced. Accordingly, the device shown in this fourth patent document requires an oil replenishing member attached to one side, which is provided in addition to the lubricant applying member that contacts the screw groove, so that lubricant is replenished constantly from outside to the rolling parts of the screw. 
     SUMMARY OF THE INVENTION 
     The present invention has been made to solve these problems in the conventional techniques. The object is thereof to eliminate the complexity of the lubrication mechanism and provide a ball screw lubricative sealing device which is externally attachable to an installed standard ball screw nut. The ball screw lubricative sealing device is capable of retaining larger amount of lubricant and long supply of lubricating oil to the contacting screw parts, and it further includes a sealing function. 
     Another object of the present invention is to provide a ball screw lubricative sealing device which can be attached externally to the side face of a standard ball screw. 
     Yet another object of the present invention is to provide a ball screw lubricative sealing device which can be attached externally to the side face of a standard ball screw without any additional work. 
     A lubricative sealing device according to a first aspect of the invention includes generally cylindrical case members having attachment parts to be attached to both ends of a screw nut, respectively, a plurality of thin seal plates having a hole each and fitted inside each of the case members in such a state that they are circumferentially displaced and overlap with each other, the hole having a shape corresponding to a lateral cross-sectional shape of a screw groove of a ball screw shaft, and a plastic wiper fitted with a space from the this seal plates inside each of the case members, in which the plurality of thin seal plates are made of a lubricating oil impregnated felt-like material formed of a fiber material which is made of a three-dimensionally crosslinked plastic fiber and resilient rubber members. 
     In the first aspect of the invention, preferably, outer circumferential surfaces of the plurality of thin seal plates circumferentially displaced are fixed to an inner circumferential surface of each of the case members using an adhesive. Preferably, the plurality of thin seal plates are impregnated with lubricating oil after they are inserted and fixed inside each of the case members in circumferentially displaced manner. 
     With the first aspect of the invention, because the resilient force of the resilient rubber member exerts on the screw groove surface, the thin seal plates can provide long lubricating effect as compared to other common felt materials. Moreover, unlike the conventional devices, they can achieve effective lubrication without a mechanism such as applying pressure from an outer circumference side. 
     Since only the outer circumferential surface of the thin seal plates are bonded and fixed to the inner circumferential surface of each of the case members, the thin seal plates can hold sufficient amount of lubricating oil. Besides, they can move freely to follow the screw grove inside the inner circumference, so that good seal performance and effective lubricating oil application are achieved. 
     Further, because the thin seal plates are formed of resilient rubber members, the felt material contained therein is less likely to peel off as compared to other common felt materials. Also, the thin seal plates are capable of catching contaminants from outside in their oil-holding spaces, thereby also providing a sealing function. 
     Further, since the plastic wiper is located outermost of each of the case members, and the lubricant supplying thin seal plates are located with a space from the plastic wiper, contaminants from outside are removed by the plastic wiper, and small contaminants that have entered are pushed through into the next space and kept there, or caught in the lubricant supplying thin seal plates. Thus, the entry of contaminants to the inside is prevented reliably. 
     A lubricative sealing device according to a second aspect of the invention includes: generally cylindrical case members to be attached to both ends of a screw nut of a ball screw, respectively, using fastening bolts; a thin cap inserted and fixed inside each of the case members, a plurality of thin seal plates placed inside the thin cap and made of a lubricating oil-impregnated felt-like material formed of a fiber material which is made of a three-dimensionally crosslinked plastic fiber and resilient rubber member, and a grease reservoir space formed inside each of the case members between the plurality of thin seal plates and one end of the screw nut. 
     With the second aspect of the invention, because the lubricant-impregnated seal members and the grease reservoir space are placed inside each of the case members, the lubricative sealing device can be used without replenishing oil for a long time, and thus enables maintenance-free use of the ball screw. 
     Moreover, because of the structure in which the thin seal plates are placed inside the thin cap, the lubricative sealing device can be assembled easily. 
     A lubricative sealing device according to a third aspect of the invention includes either one of end caps and end covers attached to both ends of a screw nut of a ball screw, respectively, using fastening bolts each having a head with a concentric screw thread formed therein, a generally cylindrical case member to be attached to either one of the end caps and the end covers, respectively, using mounting bolts engaging them with the a concentric screw threads formed in the heads of the fastening bolts, a thin cap inserted and fixed inside each of the case members, a plurality of thin seal plates fitted inside the thin cap and made of a lubricating oil impregnated felt-like material formed of a fiber material which is made of a three-dimensionally crosslinked plastic fiber and resilient rubber members, and a grease reservoir space formed inside each of the case members between the plurality of thin seal plates and one end of the screw nut. 
     In either one of the second aspect and third aspect of the invention, each of the fastening bolts is preferably a bolt having a head with a hexagonal hole. Also, each of the mounting bolts is preferably a bolt having a head with a hexagonal hole. Further, outer circumferential surfaces of the plurality of thin seal plates circumferentially overlapped are preferably fixed to an inner circumferential surface of each of the case members using an adhesive. Also, the plurality of thin seal plates are preferably impregnated with lubricating oil after they are inserted and fixed inside each of the case members in the circumferentially overlapping manner. 
     With the third aspect of the invention, because of the lubricant-impregnated seal members and the grease reservoir space inside each of the case members, the lubricative sealing device can be used without replenishing oil for a long time, and thus enables maintenance-free use of the ball screw. 
     With the third aspect of the invention, the lubricative sealing device can be attached to a ball screw nut only with a devisal to the mounting screw and without any additional work to the ball screw structure, whereby a cost reduction can be achieved. 
     The double screw structure of each of the fastening bolts that attaches the component such as the end cap or the end cover having a concentric screw hole, provides a side advantage that the case member of the lubricative sealing device is firmly attached by the mounting screw fitted in the concentric screw hole of the fastening bolt. 
     Also, with the use of the fastening bolt having the above-described double screw structure that attaches a component of a standard ball screw such as an end cover, it is made unnecessary to do additional work to the ball screw or disassemble the ball screw at the time of installing the lubricative sealing device. Therefore, ball screw accuracy and assembling accuracy of the ball circulation parts will not be lowered. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The nature, principle, and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by identical reference numbers, in which: 
         FIG. 1  is a cross-sectional view of a ball screw lubricative sealing device  1  according to the first embodiment of the present invention, which is assembled to one end of a ball screw nut; 
         FIG. 2  is an exploded perspective view of the ball screw lubricative sealing device  1  according to the first embodiment of the present invention; 
         FIG. 3  is a cross-sectional view showing the relationship between each of thin seal plates  11 A,  11 B, and  11 C and a ball screw shaft  3  in the ball screw lubricative sealing device  1  according to the first embodiment of the present invention; 
         FIG. 4  is a partially cut-away side view of a ball screw lubricative sealing device according to the second embodiment of the present invention; 
         FIG. 5  is a front view of the case member of  FIG. 4 ; 
         FIG. 6  is a perspective view showing how the lubricative sealing part of  FIG. 4  is assembled; 
         FIG. 7  is a cross-sectional view illustrating the relationship between each of thin seal plates  27 A,  27 B, and  27 C and a ball screw shaft  22  of  FIG. 4 ; 
         FIG. 8  is a partially cut-away side view of a ball screw lubricative sealing device according to the third embodiment of the present invention; 
         FIG. 9  is an exploded cross-sectional view illustrating how the mounting screw of  FIG. 8  is connected; and 
         FIG. 10  is a cross section taken along the line A-A in  FIG. 9 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Various embodiments of the present invention shown in the drawings will be hereinafter described. 
     First Embodiment 
       FIG. 1  is a cross-sectional view of a ball screw lubricative sealing device  1  according to a first embodiment of the present invention which is assembled to one end of a ball screw nut,  FIG. 2  is an exploded perspective view of the ball screw lubricative sealing device  1  according to the first embodiment of the present invention, and  FIG. 3  is a cross-sectional view showing the relationship between each of thin seal plates  11 A,  11 B, and  11 C and a ball screw shaft  3  in the ball screw lubricative sealing device  1  according to the first embodiment of the present invention. 
     The ball screw lubricative sealing device  1  according to this embodiment includes: generally cylindrical case members  9  having attachment parts  9   d  to be connected to both ends of a screw nut  7 , respectively, which are threadably engaged with a ball screw shaft  3  having a helical groove  5 , with rolling elements such as steel balls (not shown) interposed therebetween; three thin seal plates  11 A,  11 B, and  11 C having holes  11   a ,  11   b , and  11   c  that correspond to the lateral cross-sectional shape of the helical groove  5  of the screw shaft  3  and set in a groove  9   a  of each of the case members  9  in such a state that they are circumferentially displaced and overlapping with each other; and a plastic wiper  13  set inside each of the case members  9  that accommodates the three thin seal plates  11 A,  11 B, and  11 C with a space  9   e  from the three thin seal plates  11 A,  11 B, and  11 C. The outer circumferential surfaces of the three overlapped thin seal plates  11 A,  11 B, and  11 C are fixed to the inner circumferential surface of each of the case members  9  using an adhesive. The three thin seal plates  11 A,  11 B, and  11 C are made of a felt-like material impregnated with a lubricating oil, the felt-like material being formed of a fiber material which is made of a three-dimensionally crosslinked plastic fiber and resilient rubber members. 
     Each of the case members  9  is generally cylindrical and has the same size as the outer shape of either end of the screw nut  7 . Each of the case members  9  has the attachment part  9   d  at one end, which is threadably engaged with a cavity  11   a  provided at either end of the screw nut  7 . Inside each of the case members  9  there are the groove  9   a  for setting the three thin seal plates  11 A,  11 B, and  11 C, an annular projection  9   c  for forming the space  9   e , and a groove  9   b  for setting the plastic wiper  13  by screwing or bonding. 
     The fiber material made of three-dimensionally crosslinked plastic fiber and the resilient rubber members, which forms the three thin seal plates  11 A,  11 B, and  11 C, is obtained by adhering molten rubber on the surfaces of thin polyester plastic fibers, in which the integrated fiber material has a multiplicity of spaces between the fibers. These spaces are filled with a lubricant such as grease to form a lubricant supply unit. Polyester resin is effectively used as the base resin of the plastic fiber, but the material is not limited to this. 
     Next, the mechanism of the thus structured embodiment of the ball screw lubricative sealing device  1  will be described. 
     Firstly, referring to  FIG. 1  and  FIG. 2 , the three lubricant-impregnated thin seal plates  11 A,  11 B, and  11 C are circumferentially displaced and overlapped in the groove  9   a  of the case member  9 . After they are fixedly bonded in the groove  9   a  of the case member  9 , the plastic wiper  13  is set in the outer groove  9   b  of the case member  9 . 
     Next, the attachment part  9   d  of the case member  9  is threadably engaged with the cavity  11   a  at either end of the screw nut  7 . 
     Next, the ball screw shaft  3  is inserted into the hole  13   a  of the plastic wiper  13  and the holes  11   a ,  11   b , and  11   c  of the three thin seal plates  11 A,  11 B, and  11 C. 
     Thereby, the holes  11   a ,  11   b , and  11   c  of the three thin seal plates  11 A,  11 B, and  11 C make contact with the screw groove  5  of the ball screw shaft  3 , as shown in  FIG. 3 . 
     The holes  11   a ,  11   b , and  11   c  of the three thin seal plates  11 A,  11 B, and  11 C make pressure contact with the surface of the screw groove  5  of the ball screw shaft  3  because of the resiliency of the resilient rubber member, whereby the thin seal plates provide lubricating effect for a longer time as compared to known felt materials. 
     Further, the plastic wiper  13  located on the outer side of the case member  9  removes most of the contaminants from outside. Small contaminants that have passed through the plastic wiper  13  are trapped in the space  9   e . Contaminants that proceed further inside are caught and kept in the interspaces between the fibers of the three thin seal plates  11 A,  11 B, and  11 C. Entrance of contaminants from outside is thus prevented reliably. 
     As described above, with this embodiment of the ball screw lubricative sealing device  1 , effective lubrication is achieved without any mechanism for applying pressure from an outer circumferential side as with the conventional device. 
     While the three thin seal plates  11 A,  11 B, and  11 C used in the above-described embodiment are preliminarily impregnated with a lubricating oil, this is not a requirement of the present invention and the thin seal plates  11 A,  11 B, and  11 C may be impregnated with a lubricating oil after they are fixedly set inside the case member  9 . 
     Also, while three thin seal plates  11 A,  11 B, and  11 C are used in the above-described embodiment, this is not a requirement of the present invention and the number of thin seal plates may be suitably selected according to needs. 
     Further, while the ball screw shaft  3  has a single-thread screw groove  5  in the above-described embodiment, this is not a requirement of the present invention and the screw shaft may have any number of threads. 
     Furthermore, while the case member  9  is attached to the screw nut  7  by threadably engaging the attachment part  9   d  with the cavity  11   a  at either end of the screw nut  7  in the above-described embodiment, this is not a requirement of the present invention and the case member may be attached by any other means. 
     Second Embodiment 
       FIG. 4  to  FIG. 7  show a ball screw lubricative sealing device  20  according to a second embodiment of the present invention. 
     This embodiment of the ball screw lubricative sealing device  20  includes: generally cylindrical case members  24  that is connected to both ends  21   a  of a screw nut  21  using fastening bolts (having a head with a hexagonal hole)  25  and screw holes  21   b  formed in both ends  21   a  of the screw nut  21 , which are threadably engaged with a ball screw shaft  22  having a helical groove  23 , with rolling elements such as steel balls (not shown) interposed therebetween; a thin cap  26  having a hole  26   a  which is large enough to allow the ball screw shaft  22  to extend through and being fixedly set in a seal accommodating hole  24   a  of each of the case members  24 ; three thin seal plates  27 A,  27 B, and  27 C having holes  27   a ,  27   b , and  27   c  that match the lateral cross-sectional shape of the helical groove  23  of the ball screw shaft  22  and being overlapped in a circumferentially displaced manner and set in the thin cap  26  as shown in  FIG. 6  and  FIG. 7 ; and a grease reservoir space  28  formed inside each of the case members  24  between the three thin seal plates  27 A,  27 B, and  27 C and the end  21   a  of the screw nut  21 . 
     The outer circumferential surfaces of the three overlapped thin seal plates  27 A,  27 B, and  27 C and the inner circumferential surface of the thin cap  26  have substantially the same area, and they are fixed to each other using an adhesive. The fiber material made of three-dimensionally crosslinked plastic fiber and resilient rubber members, which forms the three thin seal plates  27 A,  27 B, and  27 C, is obtained by adhering molten rubber on the surfaces of thin polyester plastic fibers, and the integrated fiber material has a multiplicity of spaces between the fibers. These spaces are filled with a lubricant such as a grease to form a lubricant supply unit. Polyester resin is effectively used as the base resin of the plastic fiber, but the material is not limited to this. 
     Each of the case members  24  is generally cylindrical and has the same size as the outer shape of the end  21   a  of the screw nut  21 . On the inner side next to the seal accommodating hole  24   a  is formed a hole  24   b  with a smaller diameter, and in the bottom of this hole, a hole  24   c  is formed which is large enough to allow the screw shaft  22  to extend through. Reference numeral  29  in the drawing shows a screw that plugs an opening  24   f  for supplying a lubricant such as grease into the grease reservoir space  28 . 
     As shown in  FIG. 5 , each of the case members  24  further includes deep spot face holes  24   d  at three equally distanced locations from the side of the hole  24   a  to as far as near the other end face  24   g , and concentric holes  24   e  that are bored from the bottom of these spot face holes, to form the mounting holes for the fastening bolts  25 . 
     Next, the mechanism of the thus structured ball screw lubricative sealing device  20  according to the embodiment will be described. 
     Referring to  FIG. 4  and  FIG. 6 , first, the three lubricant-impregnated thin seal plates  27 A,  27 B, and  27 C are circumferentially displaced and overlapped in the thin cap  26  and fixed in the thin cap  26  using an adhesive, after which the thin cap is set in the seal accommodating hole  24   a  of each of the case members  24  and fixed using an adhesive. 
     Next, three fastening bolts  25  are set in the holes  24   d  and  24   e  at three locations of each of the case members  24 , to secure the case members  24  to both ends  21   a  of the screw nut  21 . 
     Next, the ball screw shaft  22  is inserted into the hole  26   a  of the thin cap  26  and the holes  27   a ,  27   b , and  27   c  of the three thin seal plates  27 A,  27 B, and  27 C. 
     Thereby, the hole  26   a  of the thin cap  26  and the holes  27   a ,  27   b , and  27   c  of the three thin seal plates  27 A,  27 B, and  27 C make contact with the screw groove  23  of the ball screw shaft  22 , as shown in  FIG. 7 . 
     The holes  27   a ,  27   b , and  27   c  of the three thin seal plates  27 A,  27 B, and  27 C make pressure contact with the surface of the screw groove  23  of the ball screw shaft  22  because of the resiliency of the resilient rubber member, whereby the thin seal plates provide lubricating effect for a longer time as compared to known felt materials. 
     Further, the thin cap  26  located inside the seal accommodating hole  24   a  of each of the case members  24  removes most of the contaminants from outside. Small contaminants that have passed through the thin cap  26  and proceed further inside are caught and kept in the interspaces between the fibers of the three thin seal plates  27 A,  27 B, and  27 C. Entrance of contaminants from outside is thus prevented reliably. 
     As described above, with the ball screw lubricative sealing device  20  according to this embodiment, effective lubrication is achieved without any mechanism for applying pressure from an outer circumferential side as with the conventional device. 
     Moreover, the ball screw lubricative sealing device  20  according to this embodiment can be attached to the screw nut  21  by providing the screw holes  21   b  at the ends  21   a  of the screw nut  21 , and an end cover or the like need not be attached to the end faces of the screw nut  21 . 
     While the three thin seal plates  27 A,  27 B, and  27 C used in the above-described embodiment are preliminarily impregnated with a lubricating oil, this is not a requirement of the present invention and the thin seal plates  27 A,  27 B, and  27 C may be impregnated with a lubricating oil after they are fixedly set inside the thin cap  26 . 
     Also, while three thin seal plates  27 A,  27 B, and  27 C are used in the above-described embodiment, this is not a requirement of the present invention and the number of thin seal plates may be suitably selected according to needs. 
     Further, while the ball screw shaft  22  has a single-thread screw groove  23  in the above-described embodiment, this is not a requirement of the present invention and the screw shaft may have any number of threads. 
     Third Embodiment 
       FIG. 8  to  FIG. 10  illustrate a ball screw lubricative sealing device  20 A according to a third embodiment of the present invention. 
     The ball screw lubricative sealing device  20 A according to this third embodiment is different from the ball screw lubricative sealing device  20  according to the second embodiment in that end caps  39  is provided to both ends  21   a  of the screw nut  21  and the case members  24  are attached to these end caps  39 . 
     Therefore, the same elements as those of the ball screw lubricative sealing device  20  according to the second embodiment are given the same reference numerals and will not be described again. 
     Each of the end caps  39  is provided with screw holes  39   a  that are coaxial with the screw holes  21   b  of the screw nut  21 . Fastening bolts  40  are set in the screw holes  39   a . Each of the fastening bolts  40  has a head with a hexagonal hole as shown in  FIG. 9  and  FIG. 10  and includes a coaxial screw hole  40   b  bored in the bottom of the hexagonal hole  40   a . Not to mention, this screw hole  40   b  has a smaller diameter than the inner circle diameter of the hexagonal hole  40   a . While the screw hole has a bottom as it is bored only partway in the illustrated example, the screw hole may extend through to the bottom, or, the screw hole may be bored partway and connected to a clear hole that extends through to the bottom. 
     Each of the case members  24  is secured to the end cap  39  using mounting screws (bolts with a head having a hexagonal hole)  41  having a screw part that engages with the screw holes  40   b.    
     Next, the mechanism of the thus structured ball screw lubricative sealing device  20 A according to the embodiment will be described. 
     First, the end caps  39  are attached to both ends  21   a  of the screw nut  21  by the fastening bolts  40  set in the screw holes  39   a.    
     Next, as with the second embodiment, the lubricant-impregnated three thin seal plates  27 A,  27 B, and  27 C are circumferentially displaced and overlapped in the thin cap  26 , and fixed in the thin cap  26  using an adhesive, after which the thin cap is set into the seal accommodating hole  24   a  of each of the case members  24  and fixedly attached using an adhesive. 
     Next, three mounting screws  41  are set in the screw holes  40   b  of the fastening bolts  40  through the holes  24   d  and  24   e  formed at three locations of each of the case members  24 , to secure the case members  24  to both ends  21   a  of the screw nut  21 . 
     Next, the ball screw shaft  22  is inserted into the hole  26   a  of the thin cap  26  and the holes  27   a ,  27   b , and  27   c  of the three thin seal plates  27 A,  27 B, and  27 C. 
     Thereby, the hole  26   a  of the thin cap  26  and the holes  27   a ,  27   b , and  27   c  of the three thin seal plates  27 A,  27 B, and  27 C make contact with the screw groove  23  of the ball screw shaft  22 , as shown in  FIG. 7 . 
     The holes  27   a ,  27   b , and  27   c  of the three thin seal plates  27 A,  27 B, and  27 C make pressure contact with the surface of the screw groove  23  of the ball screw shaft  22  because of the resiliency of the resilient rubber member, whereby the thin seal plates provide lubricating effect for a longer time as compared to known felt materials. 
     Further, the thin cap  26  located inside the seal accommodating hole  24   a  of each of the case members  24  removes most of the contaminants from outside. Small contaminants that have passed through the thin cap  26  and proceed further inside are caught and kept in the interspaces between the fibers of the three thin seal plates  27 A,  27 B, and  27 C. Entrance of contaminants from outside is thus prevented reliably. 
     As described above, with the ball screw lubricative sealing device  20 A according to this embodiment, the device can be attached to the ball screw after the ball screw has been assembled. Therefore, the ball screw and the lubricative sealing device can be assembled separately, which improves work efficiency and enables simple attachment of the lubricative sealing device even after making adjustments to the assembled ball screw. This prevents accuracy deterioration of the ball screw, prevents deterioration of ball circulation performance that is caused by disassembling or the like, and eliminates the need of re-adjustments after the disassembling. 
     While this embodiment uses the end caps  39 , this is not a requirement of the present invention, and an end cover may also be used. 
     Further, each of the mounting screws  41  need not necessarily have a head with a hexagonal hole, and hexagonal bolts and any other screws may be used. 
     Furthermore, a plastic wiper, a lip seal, or the like may be set in the seal accommodating hole  24   a  of the case member  24  that is located outside and slightly spaced from the plurality of thin seal plates  27 A,  27 B, and  27 C fitted in the thin cap  26  that is fixedly set inside each of the case members  24 , to prevent entrance of contaminants from outside or grease leakage from inside. 
     The invention is not limited to the above embodiments and various modifications may be made without departing from the spirit and scope of the invention. Any improvement may be made in part or all of the components.