Abstract:
A method for producing a holding configuration for at least one sheathed optical fiber conductor, which includes forming a holding body with a through-channel having a first channel section expanded over an expansion region into a second channel section opening into an outlet opening having a rounded rim. The method further includes applying a fixing compound from the outlet opening into the expansion region for fixing a section of an optical fiber conductor introduced into the first channel section, dimensioning a width of the first channel section for exerting capillary forces on the fixing compound contributing to filling a gap between the optical fiber conductor and the first channel section, and dimensioning a width of the second channel section for maintaining the fixing compound in the second channel section free of capillary forces, and metering the fixing compound for permitting the optical fiber conductor to emerge through the outlet opening with radial freedom of movement and free of fixing compound.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This is a division of U.S. application Ser. No. 09/067,073, filed Apr. 27, 1998, which was a continuation of International Application No. PCT/DE96/02024, filed Oct. 18, 1996, which designated the United States.  
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    Field of the Invention  
           [0003]    The invention relates to a method for producing a holding configuration for at least one sheathed optical fiber conductor.  
           [0004]    Such holding configurations are used, for example, for connecting an optical fiber conductor end to an electrooptical module, or for coupling to corresponding plug connectors. Holding configurations, as an end piece which can be coupled, can directly terminate the optical fiber conductor, which is sheathed by a protective sheath, or can surround a section of the optical fiber conductor located in front of the end, so that the optical fiber conductor runs on both sides of the holding configuration. In each case, the holding configuration has at least one end (which is called an outlet opening in the following text) of a through-channel for holding the optical fiber conductor, from which end the optical fiber conductor emerges.  
           [0005]    U.S. Pat. No. 4,984,865 discloses a holding configuration for an optical fiber conductor which emerges from a cable sheath end together with ends of a strain relief device in the form of strands (aramide fibers). The cable sheath end is inserted into a plug connector housing, which is filled with a thermoplastic. It is not possible for unacceptably small bending radii of the optical fiber conductor to occur in the case of that known holding configuration, since the optical fiber conductor is completely surrounded by the thermoplastic and runs in a fixed manner within the holding part.  
           [0006]    German Patent DE 27 11 670 C2 discloses a holding configuration in the form of a detachable plug connector, in which two optical fibers to be coupled are each bonded by their end region into a centering insert. The latter is inserted into one end of a tube, which is used as a guide body and can be inserted with the corresponding coupling partner into an adjustment capillary, in order to make contact at the end.  
           [0007]    In the case of the holding configuration of the type mentioned initially, which is known from German Published, Non-Prosecuted Patent Application DE 43 03 737 A1, corresponding to U.S. Pat. No. 5,574,819, a cable end, which has been freed at the end of its cable sheath revealing strain relief device ends and two optical fiber conductor ends which are sheathed by one protective sheath (buffer) in each case, enters an inlet opening of a receptacle. A spreading sleeve is inserted into the cable sheath end and expands the sheath beyond the inlet opening width. The optical fiber conductors pass through a through-channel which runs from the inlet opening to an outlet opening, and leave the receptacle with radial freedom of movement. The receptacle is partially filled with a fixing compound. That surface of the cured fixing compound which is close to the outlet opening (filling level) is located vertically at a distance below the outlet opening in the longitudinal axis direction when the configuration is oriented vertically.  
           [0008]    If the cable end, once it has been provided with the holding configuration, is handled incorrectly or carelessly in the rest of the production or assembly process, there is a risk of the optical fiber conductors being bent over the comparatively sharp-edged contact line to the surface of the fixing compound.  
           [0009]    That problem is exacerbated if fixing compounds are used which raise up the optical fiber conductors due to adhesion effects and capillary forces. Specifically, in practice, it has been found with through-channels having a cross section which is dimensioned to be only slightly greater than the cross section of the sheathed optical fiber conductor, that the fixing compound, when in the flowing state, rises to an undesirably high extent above the desired filling level due to capillary effects, and consequently forms sharp edges which lie against the optical fiber conductor, closely underneath the outlet opening. On one hand, if optical fiber conductors are bent beyond their critical bending radii, they can be irreversibly damaged. Such damage may temporarily remain concealed by the protective sheath in a disadvantageous manner, and not be detected until final inspection or initial operation. On the other hand, comparatively narrow through-channels are desirable in order to achieve adequate adhesion forces, the necessary amount of fixing compound and its curing time.  
           [0010]    In order to overcome that problem, production and assembly have until now had to be carried out extraordinarily carefully, with the optical fiber conductors temporarily being fixed in appropriately constructed production holders at least until additional, permanent structural elements (for example separate kink protection elements) or appropriate housings with guides were fitted.  
         SUMMARY OF THE INVENTION  
         [0011]    It is accordingly an object of the invention to provide a method for producing a holding configuration for at least one sheathed optical fiber conductor, which overcome the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and which, even immediately after fitting and curing of a fixing compound, and without any additional apparatuses, ensure reliable protection of the sheathed optical fiber conductor against unacceptably small bending radii.  
           [0012]    With the foregoing and other objects in view there is provided, in accordance with the invention, a holding configuration, comprising a fixing compound; a receptacle for receiving the fixing compound, the receptacle having an inlet opening for receiving an end of an optical fiber cable stripped at the end to expose an optical fiber conductor, and the receptacle having an outlet opening through which the optical fiber conductor emerges with radial freedom of movement and free of the fixing compound fixing a section of the optical fiber conductor; and a spreading body at least partially inserted into an end of a cable sheath of the optical fiber cable, the spreading body bounding a through-channel expanded from a first cable section closely surrounding the optical fiber conductor to a second cable section opening into the outlet opening, the second cable section having a cross section dimensioned relative to a cross section of the optical fiber conductor for maintaining the fixing compound in the second cable section substantially free of capillary forces.  
           [0013]    While capillary force effects on the fixing compound are achieved in the first, narrower section, in order to fix the optical fiber conductor safely while using little material, as long as the fixing compound is still a low-viscosity liquid, the deliberate expansion of the through-channel results in the capillary effects in the second section being suppressed in a defined manner. On one hand, the amount of fixing compound to be introduced can thus be considerably reduced in an advantageous manner since it is necessary to fill only a comparatively narrow gap between the optical fiber conductor and the wall of the first section. Since, on the other hand, the expansion reliably prevents the fixing compound, which can still flow, from flowing on or rising undesirably in the direction of the outlet opening, the amount of fixing compound can be dimensioned and introduced without so much care being required in particular with regard to capillary effects. The amount of fixing compound is preferably dimensioned in such a way that the optical fiber conductor remains largely free of fixing compound in the second section. In consequence, the optical fiber conductor has radial mobility even at the start of the expanded section, and that has a positive influence on the bending geometry, which is governed by the last fixing point, close to the outlet opening, of the optical fiber conductor. The expansion allows the distance between the fixing point and the outlet opening to be set as planned, and to be easily controllable.  
           [0014]    The maximum angles or bending radii of the optical fiber conductor which occur during the production and assembly processes (without deliberate overbending) are automatically kept comparatively gentle in conjunction with rounding of the rims or edges of the outlet opening which may come into contact with the optical fiber conductor. The maximum angle which can occur on its own, without deliberate action, between the longitudinal axis of the holding configuration and the optical fiber conductor is preferably less than 45°.  
           [0015]    In accordance with another feature of the invention, the second channel section expands to approximately twice the width of the first channel section. This provides a particularly preferred cross-sectional ratio of the channel sections.  
           [0016]    In accordance with a further feature of the invention, the expansion from the first channel section to the second channel section is constructed like a step, which permits a specially defined control of the capillary effects according to a preferred development of the invention.  
           [0017]    In accordance with an added feature of the invention, the spreading body has two essentially parallel webs which extend radially outward as far as the rim of the receptacle and bound the outlet opening. The spreading mandrel, in combination with the receptacle, forms an outlet opening with its webs which is specifically constructed for the optical fiber conductor and has a size and contour that can be dimensioned in order to reliably avoid bending radii less than the minimum.  
           [0018]    As a supplementary function, the webs according to an advantageous version of the invention can interact with at least one positioning projection on the holding part side, which produces a defined position and secures the spreading body against twisting.  
           [0019]    In accordance with still another feature of the invention, the spreading body has a shaft.  
           [0020]    In accordance with an additional feature of the invention, the narrow channel section is formed by an axial groove in the spreading body, so that the optical fiber conductor is guided particularly exactly along the spreading body.  
           [0021]    In accordance with yet another feature of the invention, a ratio of the diameter of the optical fiber conductor including the sheath, to the width of the second channel section and to a distance between the expansion and the outlet opening, is approximately 1:2:5. This has been found to be particularly advantageous with regard to the physical structure. In practical tests, with the sheathed optical fiber conductor having a diameter of 1 mm, it has been found to be particularly advantageous for the distance between the expansion and the outlet opening to be at least 5 mm.  
           [0022]    With the objects of the invention in view there is also provided a method for producing a holding configuration for at least one sheathed optical fiber conductor, which comprises forming a holding body with a through-channel having a first channel section expanded over an expansion region into a second channel section opening into an outlet opening having a rounded rim; applying a fixing compound from the outlet opening into the expansion region for fixing a section of an optical fiber conductor introduced or to be fitted into the first channel section; dimensioning a width of the first channel section for exerting capillary forces on the fixing compound contributing to filling a gap between the optical fiber conductor and the first channel section, and dimensioning a width of the second channel section for maintaining the fixing compound in the second channel section free of capillary forces; and metering the fixing compound for permitting the optical fiber conductor to emerge through the outlet opening with radial freedom of movement and free of fixing compound.  
           [0023]    Other features which are considered as characteristic for the invention are set forth in the appended claims.  
           [0024]    Although the invention is illustrated and described herein as embodied in a method for producing a holding configuration for at least one sheathed optical fiber conductor, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.  
           [0025]    The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]    [0026]FIGS. 1 and 2 are diagrammatic, sectional views of a holding configuration produced by using the method according to the invention; and  
         [0027]    [0027]FIGS. 3 and 4 are sectional views of a holding configuration according to the invention.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]    Referring now to the figures of the drawings in detail and first, particularly, to FIGS. 1 and 2 thereof, there is seen a holding or support configuration which includes a holding body  1  with an inlet opening  2  and an outlet opening  3 , between which a through-channel  4  runs, in order to hold a section of an optical fiber conductor  5 . The optical fiber conductor  5  includes an outer protective sheath (“buffer”)  6 , an inner protective sheath (“coating”)  7  and an optical fiber  8  as a signal conductor, having an exposed end  9  which passes through the inlet opening  2 . Depending on the application, the holding configuration may be constructed as a plug connector for coupling to corresponding plug connector parts or for flange connection to a module housing as illustrated, in which case it is possible in each case to position and fix the end  9  of the optical fiber  8  precisely with the aid of the holding configuration.  
         [0029]    The through-channel  4  is divided into at least first and second mutually adjacent channel sections  10 ,  11 . The first section  10  is constructed to be narrower and encloses the protective sheath  6  of the optical fiber conductor  5  except for a narrow gap, which allows the insertion of the optical fiber conductor, and assists the capillary penetration of a fixing compound  12 . The second section  11  is expanded considerably in comparison. The curable potting compound or fixing compound  12  which is applied from the outlet opening  3  surrounds the end of the narrower section  10  close to the inlet opening and the region of an expansion  14 , and fills a gap between the optical fiber conductor  5  and an inner wall surface of the section  10 . The fixing compound  12  is preferably applied before the insertion of the optical fiber conductor, so that when the optical fiber conductor is inserted, fixing compound also passes into a front region  15  close to the inlet opening, in order to fix the inner protective sheath  7  and the optical fiber  8 .  
         [0030]    One aspect that is essential to the invention is that the through-channel  4  expands from the narrower first section  10  to the second section  11  which is close to the outlet opening. The optical fiber conductor  5  runs free of fixing compound  12  in the second section  11 . No capillary forces act on the fixing compound  12  on the outlet opening side after the expansion  14  in the section  11 . If need be, adhesion forces can lead to the fixing compound being drawn up slightly on the protective sheath  6  toward the outlet opening  3 . The through-channel  4  preferably expands in the second section  11  to a width W which is at least approximately twice a width w of the first section  10 . This reliably avoids any capillary effects in the second section  11 , so that undesirable wetting and fixing of the optical fiber conductor  5  in the second section  11  are reliably prevented. The optical fiber conductor  5  thus has radial freedom of movement in the second section  11 , in which case, in the event of radial movement, the optical fiber  8  is prevented from being kinked or being bent on a radius less than a minimum bending radius  23  at a contact point  18  next to the outlet opening, between the optical fiber conductor  5  or its outer protective sheath  6  and the fixing compound  12 .  
         [0031]    A rim  20  of the outlet opening  3  which comes into contact with the optical fiber conductor  5  is rounded, thus reliably preventing bending radii less than the minimum bending radius in the event of radial movement of the optical fiber conductor  5 . (This consideration ignores arbitrary, deliberate bending back of the optical fiber conductor over the rim  20  toward the side having the inlet opening  2 ). The combination of the effects of the structure of the through-channel  4  and the rounding of the rim  20  ensure that the contact point  18 , which is critical for radial mobility and the bending radii that occur, is constructed in a controlled manner, that can be predetermined, and is at a sufficient distance  22  from the outlet opening  3 , on the inside of the holding body. By preventing capillary effects, the contact point  18  cannot become undesirably close to the outlet opening. The position of the contact point  18  can be adjusted by the metering of the amount of fixing compound, which can be carried out with a considerable amount of tolerance.  
         [0032]    The ratio of the width w of the first section  10  to the width W of the second section  11  and to a distance  24  between the outlet opening  3  and the expansion  14  is preferably approximately 1:2:5.  
         [0033]    [0033]FIGS. 3 and 4 show a holding or support configuration according to the invention for the preparation of ends of optical cables. This holding configuration includes a receptacle  30  and a spreading body  31 , which complement one another to form a holding body  32 . One end  33  of an optical fiber cable  34  enters the receptacle  30 . The optical fiber cable has a cable sheath  35  that is removed at one end, as a result of which two optical fiber conductors  40 ,  42 , which are each surrounded by an individual protective sheath  36 ,  37 , and ends  43  of a strain-relief device  44  in the form of strands aramide fibers, for example, are exposed, as is seen in FIG. 4. The ends  43  and the end of the cable sheath  35  are potted in an interior  51  of the receptacle  30  with fixing compound  50 , up to a filling level  52 .  
         [0034]    A spreading mandrel  53  is used to insert the spreading body  31  into the end of the cable sheath  35  until the cable sheath end is expanded beyond the width of an inlet opening  54  in the receptacle  30  and is consequently secured from being pulled out axially. Inwardly pointing ribs  56 , which are raised from the base of the receptacle  30  and reduce the unobstructed width of the receptacle interior, run in the interior  51  of the receptacle  30 , close to the inlet opening. The end of the cable sheath  35  is additionally supported and is secured against rotation with respect to the receptacle  30  by interacting with the spreading body  31  and the fixing compound  50 . The ribs  56  also allow undisturbed potting, or fixing compound flow, as far as the inlet opening  54 . The receptacle  30  has a flange attachment  58  through the use of which the holding configuration can be introduced in a manner that is known per se (German Published, Non-Prosecuted Patent Application DE 43 03 737 A1, corresponding to U.S. Pat. No. 5,574,819), and in such a way that it is protected against twisting, into a duplex connector housing, which dissipates the tensile stresses absorbed by the strain relief device  44 . The receptacle  30  and the spreading body  31  are preferably composed of transparent material, which allows substances that are cured by light to be used as the fixing compound.  
         [0035]    The spreading body  31  has continuous grooves  60 ,  61  at the sides, running in the axial direction A. The grooves  60 ,  61  interact with the receptacle  30  and the cable sheath  35  in each case to form a first section  62  of a through-channel  63  for the optical fiber conductors  40 ,  42 . The axial grooves  60 ,  61  each have an expansion step  65 , at which a width w 1  of the section  62  (which is matched to the respective optical fiber conductor cross section) increases by approximately twice to a width W 1 , providing a radial boundary of a subsequent, second section  66 .  
         [0036]    The spreading body  31  for each optical fiber conductor has two essentially parallel webs  70 ,  71  and  72  (the web which is opposite and parallel to the web  72  cannot be seen due to the representation in the drawing). The webs extend radially outward to beyond a rim  75  of the receptacle  30 . Each of those edges  76 ,  77 ,  78  of the webs which face the optical fiber conductors  40 ,  42  are rounded, so that the optical fiber conductors cannot be kinked at sharp edges. The rim  75 , a rounded edge  79  of the receptacle  30  and the webs  70 ,  71 ,  72  together form an individual outlet opening  80 ,  81  for each optical fiber conductor. The axial grooves  60 ,  61  in the spreading body  31  interact with the cable sheath  35  to define a respective individual inlet opening  84 ,  85  for each optical fiber conductor.  
         [0037]    The rim  75  of the receptacle  30  has projections  90 ,  91  which act as positioning projections and are constructed as an axial extension. When the spreading mandrel  31  is inserted, the positioning projections  90 ,  91  move between the webs (for example  70 ,  71 ) and thus position the spreading body  31  in such a way that it cannot twist. This prevents the cable sheath  35  from being torsioned, and the optical fiber conductors  40 ,  42  from being twisted around one another. In order to make handling easier, the spreading body  31  has a shaft  96 , along which the axial grooves  60 ,  61  continue.  
         [0038]    The broadening of the grooves  60  of the expansion step  65  prevents any further rise of the fixing compound  50 , due to the capillary effect, in the axial direction A beyond the expansion toward the outlet openings  80 ,  81  since no capillary forces are exerted on the fixing compound  50  in the second section  66  of the through-channel  63  due to the presence of an adequate gap. While the capillary effect is desirable in order to penetrate the region located underneath the expansion step, for embedding the optical fiber conductors, the strain relief device and the cable sheath, the formation of fixing compound contacts with the optical fiber conductors above the expansion is deliberately prevented. A distance α between the outlet openings  80 ,  81  and the expansion, or the filling level  52 , is preferably dimensioned to be five times the width w 1 . A width W 2 , which is illustrated in FIG. 4 for clarity and is at right angles to the width W 1  shown in FIG. 3, is preferably dimensioned in a corresponding manner to the width W 1 .  
         [0039]    In the case of a practical implementation with an optical fiber conductor diameter d of 1 mm, the width W 1 , which results from the distance between the webs  70 ,  71 , is preferably dimensioned to be 2 mm. The width w 1  is dimensioned to be approximately equal to the optical fiber conductor diameter, and is thus about 1 mm. The distance α is 5 mm.  
         [0040]    A resin system which can be activated or cured by light is preferably used as the fixing compound. Such known resin systems (for example the resin system which can be activated by light and is known by the trademark KATIOBOND 050 from the company DELO) allow deliberate activation of the potting compound. Two-component epoxy resins can also be used as an alternative.