Abstract:
A fluidic coupler assembly ( 10 ) for use in a light-guided flow cell comprises a coupler body ( 12 ) having a sealing face ( 10   a ), a tubular insert such as an optical fibre ( 16 ) passing through a through bore ( 14 ) of the coupler body and through a ferrule ( 18 ) located adjacent the sealing face of the coupler body. A backing plug ( 20 ) holds the ferrule in position within the coupler body.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims benefit of and is a continuation of to U.S. Provisional Application No. 61/288,915, filed Dec. 22, 2009. The contents of these applications are expressly incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to a fluidic coupler assembly which accurately locates a tubular insert, such as an optical fibre and is particularly, although not exclusively, useful in a light guided flow cell of a chromatography system. 
       SUMMARY OF THE INVENTION 
       [0003]    The coupler assembly of the present invention is less sensitive to manufacturing tolerances than previous constructions and permits more sealing force to be applied so that the assembly can withstand higher fluidic pressures. Moreover, the assembly aligns a tubular insert such as an optical fibre precisely on the axial centreline of a main body of the coupler. A fluidic seal is also created and maintained at a sealing surface of the coupler body. 
         [0004]    One aspect of the present invention provides a fluidic coupler assembly for use in a light-guided flow cell which coupler comprises a coupler body having a sealing face, at least one tubular insert passing through a through bore of the coupler body and through a ferrule located adjacent the sealing face of the coupler body and means to hold the ferrule in position within the coupler body. 
         [0005]    According to a feature of this aspect of the invention, the holding means may comprise a backing plug which abuts the ferrule within the coupler body remote from said sealing face and through which body the or each tubular bodyextends. 
         [0006]    According to another feature of this aspect of the invention, the ferrule may have a frusto-conical nose which abuts a complementary frusto-conical portion of said through bore. Preferably, the through bore of the coupler body has a reduced diameter portion disposed between the frusto-conical portion of the coupler body and the sealing face. 
         [0007]    According to a further feature of this aspect of the invention, the cone angle of the frusto-conical portion of the coupler body may be substantially larger than the complementary cone angle of the ferrule nose. Preferably, the cone angle of the frusto-conical portion of the coupler body is substantially 40° and the complementary cone angle of the ferrule nose is substantially 29°. 
         [0008]    According to a still further feature of this aspect of the invention, the coupler body may be formed from a material which is harder and/or less compliant than that of the ferrule. Preferably, the backing plug is formed from material similar to that of the coupler body. 
         [0009]    According to yet another feature of this aspect of the invention, the ferrule may be formed from a chemically inert polymer such as PEEK or fluropolymers including the various grades of Teflon AF. 
         [0010]    According to another feature of this aspect of the invention a plurality of coaxial tubular inserts may pass through the through bore of the coupler body and through the ferrule. In some constructions the or each tubular insert may be capillary, and optionally the or each tubular insert may be an optical fibre. 
         [0011]    According to a still further feature of this aspect of the invention the coupler body may have a sealing face at each of its opposite axial ends, wherein at least one tubular insert passes through a through bore of the coupler body and through a ferrule located adjacent each of the opposed sealing faces of the coupler body and wherein said holding means comprises a backing plug within the couple body between, and providing a sealing face for, each of the ferrules. 
         [0012]    Another aspect of the invention provides a method of assembling a fluidic coupler for use in a light guided flow cell, which method comprises threading a tubular insert through a through bore of a coupler body, threading a ferrule onto the tubular insert and inserting the ferrule into the through bore of the coupler body until complementary faces of the ferrule and the through bore are in abutment adjacent a sealing face of the coupler body, threading a backing plug onto the tubular insert and bringing the backing plug into abutment with the ferrule remote from said complementary faces, causing the backing plug to exert sufficient force on the ferrule that a portion of the ferrule is extruded from the sealing face of the coupler body. 
         [0013]    According to a feature of this aspect of the invention, a further ferrule accommodated within a further coupler body may be threaded onto the or each tubular insert protruding from the backing plug remote from said sealing face and connecting together the coupler bodies so that a portion of the further ferrule is extruding from a sealing face of the further coupler body. According to a further feature of this aspect of the invention, the method may further comprise the step of trimming any excess tubular insert protruding from each sealing face and grinding, in each case the tubular insert, the extruded ferrule portion and the sealing face of each coupler body so that those respective components at each end of the assembly are flush. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0014]    Embodiments of the invention will now be described with reference to the accompanying drawings, in which: 
           [0015]      FIG. 1  is a vertical cross-section through a fluidic coupler assembly according to the invention; 
           [0016]      FIG. 2  is a vertical cross-section through a main coupler body of the assembly shown in  FIG. 1 ; 
           [0017]      FIG. 3  is a vertical cross-section through a ferrule of the assembly; 
           [0018]      FIG. 4  is a vertical cross-section through a backing plug of the assembly 
           [0019]      FIG. 5  is a vertical cross-section through the coupler assembly prior to grinding and polishing during the course of its manufacture. 
           [0020]      FIG. 6  is a vertical cross-section through a coupler assembly which depicts a dual-ferruled captivation arrangement, and while  FIG. 6   a  is a vertical cross-section of the central tubular an alternative structure which comprises two coaxial tubes contained within a ferrule. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0021]    Referring to the drawings, a coupler assembly  10  comprises a coupler body  12  which is machined from a suitable metal such as stainless steel but other materials are possible as long as the chosen material is harder or less compliant than the ferrule material. The assembly of this embodiment of the invention is described as incorporating an optic fibre  16  but other tubular inserts of various materials such as glass, metal and ceramics may be used. The coupler body has a generally cylindrical through bore  14  which at one end of the body has a frusto-conical portion  14   a  which terminates at a sealing face  10   a  of the coupler in a reduced diameter cylindrical portion  14   b . This feature assures proper centering of the optical fibre  16 . The coupler body incorporates a frusto-conical ferrule  18  which has a frusto-conical nose cone  18   a  which is complementary to the frusto-conical portion  14   a  of the through bore  14 . The ferrule material must be softer or more compliant than the material of the coupler body  12 . Such material may include but is not limited to chemically inert materials such as PEEK or fluoropolymers, including the various grades of Teflon AR The ferrule has a cylindrical through bore  18   b  which is slightly larger in diameter than the diameter of the optical fibre  16  which it is to receive. The cone angle machined into the coupler body is larger than the ferrule cone angle. In one arrangement the cone angle of the coupler body is 40° and the cone angle of the ferrule is 29° in order to concentrate deformation of the tip of the ferrule nose cone near the reduced diameter portion  14   b  of the coupler body. 
         [0022]    The frusto-conical ferrule  18  will seal and accurately locate the optical fibre  16  in the coupler body  12 . The ferrule is held in place within the coupler by a compression screw (not shown) or more preferably by means of a pressed-in cylindrical backing plug  20  having a through bore  20   a . The backing plug has a slightly larger outside diameter than the inside diameter of the coupler body which creates an interference fit between the plug  20  and body  12  along the diameter  14 . Depending upon the overall length of the body  12 , it may be advantageous to make bore  14  slightly larger than diameter  20   b  of the backing plug but followed by the reduced diameter  14   c  which will now create the interference fit with plug  20 . The diameter of the through bore  20   a  is sufficiently larger than the diameter of the optical fibre  16  so as to prevent damage to the optical fibre during assembly. The backing plug  20  is made from a material similar to the coupler body but sufficiently different in alloy composition as to reduce galling during assembly. 
         [0023]    In assembling the coupler, the optical fibre  16  is threaded through the through bore  14  of the coupler body  12  whereafter the ferrule  18  is threaded onto the optical fibre with its frusto-conical nose cone facing the frusto-conical end  14   b  of through bore  14   a  and the ferrule is then pushed into the coupler body. The backing plug  20  is then threaded onto the optical fibre  16  and is pressed into place within the through bore  14  or  14   c  as the situation requires, causing a small amount  22  ( FIG. 5 ) of the ferrule to extrude through the reduced diameter portion  14   b  of the coupler bore at the coupler sealing face  10   a , as shown in  FIG. 5 . Any excess fibre beyond the extruded portion of the ferrule is trimmed and the optical fibre, the ferrule and the sealing face are then ground and polished so that they are completely flush with the coupler sealing face. It can be appreciated that the final compressive loading around and along the fiber may be controlled by the extent to which the plug  20  is pressed into the bore  14  against the ferrule, the strength of the ferrule material and the specific tapered surfaces of both the ferrule,  18   a , and body,  14   a.    
         [0024]    The foregoing method for securing an optical fiber within the body  12  may also be applied to other cylindrically-shaped objects; these could include glass, metal or polymeric capillaries or tubes, or wires. In the case of tubular inserts, it is oftentimes beneficial to install a sacrificial material such as a wax that can be easily removed after final processing, into the lumen of the tube prior to polishing. This provides a measure of mechanical support for the tube&#39;s inner diameter, minimizing edge chips or wall fractures. 
         [0025]    In an alternative embodiment of the invention, a double-ended seal may be effected using the captivation method described above.  FIG. 6  depicts a two-part coupler comprising coupler bodies  12   a  and  12   b , each having a frusto-conical portion for receiving a ferrule  18 ,  19  respectively. As shown, the complete assembly has already been polished at each end to remove by means of grinding and polishing the extruded ferrule material and, in this instance, a glass capillary  16   a . The plug  20  is pressed flushe to surface  12   c  of coupler  12   a  by which point the desired extrusion of ferrule  18  has been realized. Ferrule  19  is then threaded onto tube  16   a  followed by coupler body  12   a  which is held in concentric relationship to  12   a  through well-known means such as dowel pins in part  12   b  engaging a hole and a slot in face  12   c  of  12   b . Fastening means such as screws are then employed for joining body  12   b  to  12   a  so that surfaces  12   d  of part  12   b  and  12   c  of part  12   a  are flush. This joining process necessarily serves to extrude ferrule  19  beyond the exterior surface of  12   b  in like manner to that of pressing plug  20  against ferrule  18 . The amount of ferrule compression may be controlled by well-known means such as the use of physical features such as stops in the coupler body. Axially aligning body part  12   b  to  12   a  may also be effected by fabricating the same bore in  12   a  used to contain plug  20  part way into  12   b . Adjustments of the length of the plug  20  can accommodate a wide range of ferrule and coupler lengths  12   a  and  12   b  making it possible to fabricate complete couplers of lengths from a few millimetres to tens of centimeters. It is not always necessary to have an interference fit between the plug  20  and its receiving bore; in these cases there is a simultaneous loading and extrusion of each ferrule as the two coupler parts are brought and permanently fastened to one another. 
         [0026]    In yet a further embodiment of this assembly method,  FIG. 6   a  illustrates an axial cylindrical structure that may consist of more than one tubular insert; for example, a glass tube  16   a  contained within a polymeric tube  16   b . In many cases it is difficult if not impossible to find commercially available tubes having the requisite outside and inside diameters. This ferruling method permits some slight gap between the two coaxial tubes which is then eliminated during the ferrule extrusion process.