Abstract:
A machine arrangement, including at least one bearing ring, wherein a glass fiber is connected with the machine arrangement. To allow a proper measurement of stresses even at curved surfaces of the machine arrangement as it is typical in the case of bearing rings, the connection between the glass fiber and the machine arrangement is established by a metallic material which metal material is connected by material bonding with the machine arrangement as well as with the glass fiber.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a National Stage Application claiming the benefit of International Application Number PCT/EP2013/062137 filed on 12 Jun. 2013, which claims the benefit of European Patent Application Serial Number PCT/EP2012/061347 filed on 14 Jun. 2012, both of which are incorporated herein by reference in their entireties. 
     TECHNICAL FIELD 
     The invention relates to a machine arrangement, comprising or being at least one bearing ring, wherein a glass fiber is connected with the machine arrangement. 
     BACKGROUND 
     It is known in the art to equip a machine part of this kind with a glass fiber element to allow the measurement of different physical parameters. By doing so, a survey of the parameters becomes possible by using the fiber Bragg grating (FBG) method. By this method temperatures as well as strains of the machine arrangement can be monitored. 
     For doing so it is necessary to connect a glass fiber with the component. For surveying temperatures it is essential that a thermal coupling between the glass fiber and the machine arrangement is established. For monitoring strains it is necessary to mechanically connect the glass fiber with the component to be monitored. 
     Specifically in the latter case problems arise because the glass fiber is normally equipped with a plurality of coaxially arranged cover layers. A typical construction employs a cladding arranged around the glass fiber (core) itself; the cladding is coated by a coating layer. Then, strengthening fibers (made e. g. from aramid) are arranged at the outer circumference of the coating. Finally the strengthening fibers are cased by a hollow cylindrical cable jacket. 
     When a glass fiber element of this type is connected with the component a certain elasticity is inherent between the glass core and the component. Thus, specifically the measurement of strains is problematic due to the elasticity. This is specifically a problem when the component is not even or flat but if it has a spherical shape. This is typical in the case of a part of a bearing, specifically of a roller bearing. 
     It is an object of the present invention to propose a machine arrangement of the above mentioned kind which is designed in such a manner that a contact is established between the glass fiber core and the component which is as stiff as possible. By doing so it is aimed to monitor physical properties, especially of strains in the component, with a high degree of precision. Thus, specifically a proper measurement of stresses should become possible even at curved surfaces of the machine arrangement as is typical in the case of bearing rings. 
     SUMMARY OF THE INVENTION 
     A solution according to the invention is characterized in that the connection between the glass fiber and the machine arrangement is established by a metallic material which metal material is connected by material bonding with the machine arrangement as well as with the glass fiber. 
     The glass fiber is basically free from any layer as described above. An exception can be that the glass fiber is encased by a reflective cover material to ensure the conduction of light through the glass fiber. 
     The metallic material preferably consists of at least two different metallic materials, wherein a first metallic material encases the glass fiber and wherein a second metallic material connects the first metallic material with the machine arrangement by material bonding. 
     The material bonded connection between the metallic material and the machine arrangement can be established by a welding process using the metallic material. 
     The material bonded connection between the metallic material and the glass fiber can also be established by a welding or melting process using the metallic material. 
     The mentioned first metallic material can be a single metal element. In this case a preferred embodiment proposes that the first metallic material is chromium (Cr). An alternative suggests nickel (Ni) as the first metallic material. 
     The second metallic material can be a metal alloy. In this case the second metallic material can be an alloy of chromium (Cr) and nickel (Ni). 
     In a preferred embodiment of the invention, a cladding of nickel (Ni) which encases the glass fiber is provided; this cladded glass fiber it then coated with a nickel-chromium-alloy. 
     The second metallic material can have at least partially a thickness measured in the direction perpendicular to the longitudinal axis of the glass fiber of at least 0.3 mm, preferably of at least 0.5 mm. 
     The glass fiber can be arranged on a curved surface of the machine arrangement, especially on a cylindrical surface of a bearing ring. 
     Thereby, the glass fiber can be attached to a cylindrical surface of the machine arrangement. Also, it is possible to locate the glass fiber in a groove which is machined for the glass fiber into the machine arrangement. 
     By the proposed design a stiff and direct connection is established between the glass fiber and the component to be monitored so that physical parameters—especially temperatures and strains—can be detected in a precise way. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings show embodiments of the invention. 
         FIG. 1  shows in a perspective view a section of an outer bearing ring of a roller bearing, on which a glass fiber is fixed, 
         FIG. 2 a    shows a glass fiber connected to a bearing ring by a metallic material,  FIG. 2 b    shows the cross section A-A according to  FIG. 1 , 
         FIG. 3  shows a perspective view of a glass fiber which is fixed at a bearing ring similar to  FIG. 2   b,    
         FIG. 4  shows a front view of a glass fiber which is fixed at a bearing ring, similar to  FIG. 3 , 
         FIG. 5  shows a perspective view of a glass fiber which is fixed in a groove of a bearing ring, 
         FIG. 6  shows a front view of a glass fiber which is fixed in a groove of a bearing ring, similar to  FIG. 5 , 
         FIG. 7 a    shows the process of fixing a glass fiber in a groove of a bearing ring in a first, early state, 
         FIG. 7 b    shows the process of fixing a glass fiber in a groove of a bearing ring in a second, later state. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In  FIG. 1  a machine arrangement  1  being an outer bearing ring of a roller bearing is shown. The bearing ring  1  has an outer spherical surface which is to be monitored with respect to strains which act in the machine part. The survey of those strains is carried out by the fiber Bragg grating (FBG) method which is known as such. Reference is made e. g. to U.S. Pat. No. 6,923,048 B2 where this technology is explained in more detail. 
     For doing so a glass fiber  2  is securely fixed on the spherical, i. e. cylindrical outer circumference of the bearing ring  1 . The glass fiber  2  has a longitudinal direction L which extends in the circumferential direction of the bearing ring  1 . 
     Details concerning the fixation of the glass fiber  2  at the bearing ring  1  can be seen from  FIG. 2 . 
     In  FIG. 2 a   , it can be seen that the glass fiber  2  is basically the pure glass element-possibly covered only by a reflective coating to ensure proper light conduction within the glass fiber-which is then connected with the bearing ring  2  by means of metallic material  3 . 
     In  FIG. 2 b   , two different metallic materials are employed: 
     A first metallic material  3 ′ coats the glass fiber  2  itself. The preferred material is chromium (Cr). 
     The first metallic material  3 ′ it then connected with a second metallic material  3 ″. This material is preferably an alloy, preferably from chromium (Cr) and nickel (Ni). 
     Thus, a material bonding is established between the glass fiber  2  and the machine part  1  to be monitored. This means, all strains in the machine part  1  are directly transferred into the glass fiber  2 . Thus, the precondition is assured for a precise measurement of physical parameters of the machine part  1 . 
     In  FIG. 3  a further embodiment of the invention is shown. Here, the glass fiber  2  is provided with a cladding  3 ′ from a first metallic material being nickel (Ni). This cladding is embedded in a second metallic material  3 ″ being a nickel-chromium-alloy. The second metallic material  3 ″ is fixed on the bearing ring  1  by means of welding or brazing  4 . 
     In  FIG. 4  a similar solution is shown. Here, the glass fiber  2  is again embedded in a cladding of nickel  3 ′. This cladding is covered by a coating  3 ″ of a nickel-chromium-alloy. This coating  3 ″ is fixed with the bearing ring  1  by means of welding or brazing  4 . 
     In  FIG. 5  an alternative is shown. Here the bearing ring  1  has a groove  5 , in which the glass fiber  1  is inserted and securely fixed. For doing so, the glass fiber  1  is cladded with a cover  3 ′ from nickel. Then, the covered glass fiber  2  is fixed on the bearing ring  1  by a nickel-chromium-alloy  3 ″which fills up the groove  5 . 
     A similar solution is shown in  FIG. 6 . Here, the bearing ring  1  again has a groove  5  in which the glass fiber  2  is inserted. The glass fiber  2  is embedded in a nickel cladding  3 ′. The cladding  3 ′ is embedded by a nickel-chromium-alloy  3 ″. The fixation of the coating of nickel-chromium-alloy  3 ″ is fixed in the groove  5  by means of welding or brazing  4 . 
     In  FIG. 7 a    and  FIG. 7 b    a process is depicted by which a fixation as shown in  FIG. 6  can be realized. Here, a container  7  is arranged at the bearing ring  1  when the embedded glass fiber  2  (coated again by a nickel layer  3 ′ and a layer form a nickel-chromium-alloy  3 ″) is arranged in a groove  5  in the bearing ring  1 . The container  7  is filled with braze paste  6 . This is shown in  FIG. 7   a.    
     Heating elements  8  being inductive heaters are arranged near the container  7 . Due to the heat produced by the inductive heaters  8  the braze paste  6  melts and forms the brazing  4  which is shown in  FIG. 7 b   . Afterwards, the container  7  is removed. 
     The proposed connection technology can be used to fix a glass fiber  2  firmly between two points on the bearing ring  1  to use the fiber Bragg grating (FBG) method for measurement of specific data. 
     For the cladding of the glass fiber  2  itself, pure material—specifically nickel (Ni) or chromium (Cr)—is preferred. This gives a very dense and defect free coating. 
     For the outer coating a selection can be made from suitable alloys between nickel (Ni) and chromium (Cr) with or without additional elements such as B, Fe, Mn, Si, Ti, which can be selected to obtain a harder or more ductile coating and/or to reduce the melting temperature for the coating or later brazing or welding to be applied. 
     Beside pure nickel also nickel can be used which is alloyed with a maximum of 2 weight-% titan (Ti), 1 weight-% silizium (Si) or a nickel-alloy with a maximum of 3.5 weight-% boron (B), 4.5 weight-% silizium (Si), between 5 and 7 weight-% chromium (Cr) and about 4 weight-% ferrum (Fe). 
     For the outer coating  3 ″ pure chromium (Cr) can be employed but also chromium alloyed with a maximum of 20 to 60 weight-% nickel (Ni). The outer coating has preferably between 0.2 to 0.5 mm wall thickness in order to enable microlaser welding or brazing, 
     Here, a nickel-chromium-alloy is preferred with 20 to 80 weight-% nickel (Ni) and a balance of chromium (Cr). Also, an alloy has been found suitable with 20 to 70 weight-% nickel (Ni), 1 to 5 weight-% mangan (Mn), a maximum of 1 weight-% silizium (Si) and a balance of chromium (Cr). Also the addition of copper (Cu) can be beneficial. 
     REFERENCE NUMERALS 
     
         
           1  Machine arrangement (bearing ring) 
           2  Glass fiber 
           3  Metallic material 
           3 ′ First metallic material 
           3 ″ Second metallic material 
           4  Welding/Brazing 
           5  Groove 
           6  Braze paste 
           7  Container 
           8  Heating element (induction heating element) 
         L Longitudinal axis