Abstract:
A ferrule holder for holding a ferrule in a grinding apparatus, wherein said holder is e.g., substantially spherical in shape or provided with a cardanic mounting device. The ferrule holder has a cut face, a holder recess in the cut face adapted to accept the ferrule, and an attachment mechanism for attaching the ferrule within the holder recess. Moreover, a ferrule grinding apparatus is disclosed with at least one grinding plate for grinding the surface of a ferrule, at least one ferrule holder adapted to hold the ferrule and at least one ferrule positioning mechanism, wherein the ferrule holder and the said ferrule positioning mechanism cooperate together to position dynamically the ferrule such that the face of the ferrule is parallel to the surface of the grinding plate.

Description:
The invention relates to a ferrule holder for holding a ferrule in a grinding apparatus. The invention furthermore relates to a grinding and polishing apparatus for a ferrule with at least one grinding plate for grinding the surface of a ferrule, at least one ferrule holding means adapted to hold the ferrule and at least one ferrule positioning means. 
     Ferrules for use in fiber-optic interconnects are known, for example, from the German Patent Application DE-A-44 23 842 (Moser et al.) assigned to IMM Institut für Mikrotechnik GmbH. Such ferrules have a series of grooves into which the individual strands of the fiber-optic cables can be laid. In an interconnect for fiber-optic cables, it is crucial to ensure that the ends of the fiber-optic strands in the two halves of the interconnect are aligned. For this purpose, the ferrule disclosed in the &#39; 842  patent application contains alignment holes into which alignment pins can be inserted. 
     In order to achieve optimum coupling between the two halves of the fiber-optic interconnect, it is also necessary to ensure that the matching faces of the complementary ferrules in the fiber-optic interconnect are smoothly polished and that the ends of the strands of the fiber-optic cables are planar with the surface of the ferrule. It is particularly important to ensure that when the two ferrules are connected together, the axes of the strands of the fiber optic cables in one ferrule are substantially parallel to the axes of the strands of the fiber optic cable in the other ferrule. This is difficult to achieve in conventional ferrule grinding and polishing means since it is difficult to ensure that the face of the ferrule is ground in a plane that is exactly perpendicular to the axes of the strands of the fiber-optic cable. Even slight angular deviations can lead to mismatching of the strands of the fiber-optic cable and thus to loss of signal. 
     The object of the invention is therefore to develop an improved holder for a ferrule which allows use in a grinding and polishing apparatus. 
     It is furthermore an object of the invention to produce a ferrule with a face plane substantially perpendicular to the axes of the strand of the fiber-optic cable. 
     It is furthermore an object of the invention to produce a ferrule holder which allows dynamic positioning of the ferrule within said grinding and polishing means. 
     It is furthermore an object of the invention to produce a ferrule holder which allows the use of the alignment pins within the ferrule to position the ferrule holder within the grinding and polishing apparatus. 
     These and other objects of the invention are solved by using a ferrule holder with a cut face and having a holder recess in said cut face adapted to-accept the ferrule and furthermore having attachment means for attaching the ferrule within said recess. Preferably the ferrule holder is substantially spherical in shape. The use of such substantially spherical ferrule holder allows dynamic adjustment of the ferrule to be carried out when the ferrule is mounted within the polishing and grinding apparatus. 
     Preferably the holder recess is a hole cut through said ferrule holder. This allows ease of mounting of the ferrule within the ferrule holder since it can be mounted through the side of the ferrule holder opposite from the cut face. In order to ensure that the surface of the ferrule is cut in a plane which is substantially perpendicular to that of the axes of the strands of the fiber-optic cable, the axis of the recess is substantially perpendicular to the plane of the cut face. 
     The ferrule can be attached within the ferrule holder by attachment means comprising a spring-loaded plate adapted to push the ferrule against one side of the recess. This spring-loaded plate is provided with a compressible surface to avoid damage to the ferrule. 
     In one embodiment of the invention, the spring-loaded plate is activated by a feather spring with a first end and a second end which first end is in contact with the spring-loaded plate and which second end is activated by a sledge. The sledge is mounted in a recess through the holder and is slid by means of a screw attached to one end of said sledge. The use of the sledge and screw allow very fine adjustments to be made to the pressure exerted on the ferrule and thus ensure that sufficient pressure is applied to hold the ferrule within the holder recess but not to damage the ferrule. 
     The objects of the invention are further solved by providing a ferrule grinding apparatus with 
     at least one grinding plate for grinding the surface of the ferrule, at least one ferrule holding means adapted to hold the ferrule and at least one ferrule positioning means, wherein 
     the said ferrule holding means and the said ferrule positioning means cooperate together to position dynamically the ferrule such that the face of the ferrule is parallel to the surface of the grinding plate. 
     The positioning means of the ferrule grinding apparatus preferably includes at least one guide pin which cooperates with at least one ferrule recess within said ferrule to position said ferrule. If the ferrule holder is of spherical shape, said shape of the ferrule holder allows the ferrule to be pivoted freely within the ferrule grinding apparatus. If the shape of the ferrule holder is not spherical, e.g. a cardanic mounting might be provided in order to achieve the necessary degrees of freedom with respect to pivotal movements of the ferrule holder necessary for obtaining the cooperation of the ferrule holder and said positioning means. A particularly suitable grinding apparatus has an arm with a recess in which the ferrule holder can freely rotate. In particular, as the ferrule holder is moved down onto the guide pin by the ferrule grinding apparatus, it can rotate to assume a position in which the face of the ferrule is in a plane perpendicular to the axis of the guiding pin. Since the ferrule is manufactured with the axes of the ferrule recesses—or alignment holes—substantially parallel to the axes of the strands of the fiber-optic cables, then the ferrule is positioned in an optimum polishing and grinding position. 
     Although the invention is described with reference to ferrules for fiber-optic cables, it should be noted that it can also find application in the grinding of ferrules for conventioal wire-cables. 
    
    
     DESCRIPTION OF THE FIGURES 
     FIG. 1 show an overview of the ferrule holder according to the invention. 
     FIG. 2 shows a more detailed diagram of the internal mechanism of the ferrule holder according to the invention. 
     FIG. 3 shot the grinding and polishing apparatus with positioning means in an open position. 
     FIG. 4 shows the grinding and polishing apparatus with positioning means in an closed position. 
     FIG. 5 shoes the arrangement of the recesses in the arm for positioning the ferrule holder. 
     FIG. 6 is a diagram illustrating the rotation of the ferrule holder within the grinding and polishing apparatus. 
     FIG. 7 shows, the grinding and polishing apparatus with positioning means in a closed position. 
     FIG. 8 shows a ferrule holder equipped with an air bearing operating with pressurized air. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An overview of a ferrule holder  10  for holding a ferrule in a polishing and grinding machine is shown in FIG.  1 . The ferrule holder  10  is substantially spherical in shape with a cut face  20  on a first side of the ferrule holder  10 . In the disclosed embodiment, the ferrule holder  10  is provided with a groove  30  on a second side of the ferrule holder  10  and with a hole  40  passing through the ferrule holder  10  from the first side of She ferrule holder  10  to the second side of he ferrule holder  10 . The hole  40  is adapted to allow a ferrule (not shown in this figure) to be inserted through the hole such that the face of the ferrule which is to be ground protrudes from the face  20  of the ferrule holder  10 . The ferrule holder  10  according to this invention is made from stainless steel of a hardness similar to that used to make ball bearings supplied by Kugelfischer AG. The ferrule holder  10  could, however, be made of other materials such as very hard plastics or other hard metals. 
     FIG. 2 shows a cross-sectional view through the ferrule holder  10 . The FIG. shows a ferrule  50  attached to a fiber-optic or other cable  55  which is inserted through the hole  40  in the ferrule holder  10 . The fiber-optic cable  55  is surrounded by a protective sheath  57 . The ferrule face  60  which is to be ground on a grinding and polishing machine (not shown) protrudes from end of the hole  40  as is shown on the figure. The ferrule  50  is designed with a rim  70  which matches with a stop  80  machined within the hole  40  of the ferrule holder  10  to prevent the ferrule  50  from passing completely through the hole  40 . 
     The ferrule  50  is held in position within the hole  40  by means of a plate  90  which pushes the ferrule  50  against a hole wall  85 . The plate  90  is depicted as comprising a first layer  100  mounted on a support  110 . The first layer  100  and the support  110  could be made of the same materials. Preferably, however, the first layer  100  is made of a compressible material such as rubber or a soft plastic and the support  110  is made of a hard material such as metal or a hard plastic. The purpose of the first layer  100  is to prevent damage to the ferrule  50  due to the force exerted on the ferrule  50  when it is pushed against the hole wall  85 . It does this by ensuring that the force of exertion is spread out over the whole surface of the ferrule  50  even if there are irregularities in the surface of the ferrule  50 . 
     The plate  90  is preferably provided with a recess  120  in the side facing away from the ferrule  50  into which a first ball bearing  130  is placed. A leaf spring  140  contacts on its first surface  142  the other side of the first ball bearing  130  and exerts force on the first ball bearing which consequently exerts force on the plate  90  and thus pushes the ferrule  50  against the hole wall  85 . One end of the leaf spring  140  is held fast within the ferrule  50  by means of an attachment at a leaf spring support  145 . Approximately at the other end of the leaf spring  145  a first pin  160  contacts the second side  147  of the leaf spring  145 . The first pin  160  is mounted within a sledge  150  as will be described later. The sledge  150  is mounted in the groove  30  of the ferrule holder  10  and can be slid transversely to the axis of the hole  40 . In the illustrated embodiment the sledge  150  is provided with holes  165   a  and  165   b  which contain the pin  160 . 
     The arrangement of the leaf spring  140 , first ball bearing  130 , first pin  160  is merely illustrative and could be replaced by other arrangements known to a skilled person. For example, the first ball bearings  130  and the first pin  160  could be removed altogether. Alternatively, the ball bearing  130  and the pin  160  could be replaced by protrusions on the surface of the plate  90  and sledge  150 . Alternatively, the first pin  60  could be replaced by a second ball bearing and the first ball bearing by a pin. 
     The sledge  150  is moved through the groove by means of a screw  170 . The screw  170  and sledge  150  are provided with matching thread  175  and the end of the screw  170  is held against a wall  180  within the ferrule holder  10 . Turning the screw  170  will consequently move the sledge  140  within the groove  30  of the ferrule holder  10 . The sledge  150  could be also moved within the groove  30  by other means such as pushing the sledge  150 . However, providing a screw  170  is the preferred method as it allows a fine adjustment of the force exerted by the leaf spring  140  on the plate  90 . 
     The manner in which the ferrule  50  is mounted within the ferrule holder  10  will now be described. In a first step, the sledge is slid into a position such that the second ball bearing  160  is not touching the second surface  147  of the leaf spring  140 . The leaf spring  140  is thus in a position shown by the dotted line in the figure. In this position, no force is exerted by means of the first ball bearing  130  against the plate  90 . The ferrule  50  is then mounted into the hole through an opening opposite to the cut face  20  of the ferrule holder  10 . The ferrule  50  is slid through the hole until the rim  70  hits the stop  80  and the ferrule  50  cannot then be pushed further into the hole  40 . At this point, the face  60  of the ferrule  50  should protrude slightly from the cut face  20  of the ferrule holder  10 . Since the plate  90  is exerting no force on the ferrule  50 , it is easy to maneuver the ferrule within the hole  40 . 
     The sledge  150  is then moved to the right of the figure by turning the screw  170  such that the pin  160  deflects the leaf spring  140  to the position shown by the solid line in the figure. At this point the leaf spring  140  exerts a force on the first ball bearing  130  which consequently exerts a force on the plate  90  and thus on the ferrule  50  against the hole wall  85 . The ferrule  50  is held securely within the hole  40 . 
     Release of the ferrule  50  from the ferrule holder  10  is achieved in an opposite manner. The screw  170  is adjusted such that the leaf spring  140  exerts no pressure on the ferrule  50  which can thus be removed from the hole  40  by pulling on the protective sheath  57  of the fiber optic cable  55 . In the illustrated embodiment, the screw  170  is preferably an M3 screw which has an end having a diameter of 5 mm and thus suitable for turning by hand. 
     FIG. I shows the design of the sledge  150 . In this figure like parts are numbered in the same manner as in the previous figures. The sledge  150  comprises a runner element  200  and a sealing element  210 . The runner element  200  is provided with two first holes  165   a  and  165   b  through which the first pin  160  passes. The sledge  150  is furthermore provided with two second holes  230   a ,  230   b  through which second pins  220   a ,  220   b  pass. The second pins  220   a ,  220   b  cooperate with sealing element recesses  240  to hold the sealing element  210  in place in the groove  30  of the ferrule holder  10 . 
     The sledge  150  is mounted within the groove  30  of the ferrule holder  10  by sliding the runner element  200  into the groove  30  from the right hand side (in the depicted embodiment) of the ferrule holder  10  and then mounting the sealing element  200  onto the runner element  200  by means of the second pins  200   a ,  200   b . 
     FIG. 3 shows a polishing holder  250  of a polishing and grinding machine which comprises an arm  260  into which a first arm recess  270   a  and a second arm recess  270   b  are constructed. The arm recesses  270   a ,  270   b  are so constructed such that the ferrule holder  10  can rotate freely within the arm recesses  270   a ,  270   b . The arm recesses  270   a ,  270   b  are also provided with securing means (not shown) which can secure the ferrule holder  10  in place such that the ferrule holder  10  can no longer rotate freely within the arm recesses  270   a ,  270   b . The polishing holder  250  furthermore includes a positioning element  280  which has two protruding guide pins  290 . These guide pins  290  are positioned such that they exactly match the ferrule recesses casa  52 ; c.f. FIG.  4 . 
     FIG. 5 shows an exploded drawing of the end of the arm  260  in which the arm recesses  270   a ,  270   b  are depicted together with the positioning element  280  and the guide pins  290 . 
     The arm  260  of the polishing holder  250  is shown in FIG. 6 in the open position. In this position the ferrule holder  10  can be freely mounted between the arm recesses  270   a ,  270   b  and is able to rotate within the arm recesses  270   a ,  270   b  freely. The polishing holder  250  in FIG. 7 is shown in the closed position in which the arm is lowered such that the guide pins  290  pass into the ferrule recesses  52 . The ferrule holder  10  rotates within the arm recesses  270  until the ferrule face  60  is positioned exactly planar to the positioning holder  280 . At this point, the securing means are activated to ensure that the ferrule holder  10  can no longer rotate within the arm recesses  270  so that it is held firmly in place. Such means could include the application of a vacuum to hold the ferrule holder  10  in place or by providing an additional mechanical arm which holds the ferrule holder  10  within the arm  260 . 
     FIGS. 6 and 7 show diagrammatically how the ferrule holder  10  is correctly mounted within the arm  260 . Suppose the ferrule holder  10  is mounted within the arm  260  such that the ferrule face  55  is not planar to the face of the positioning element  280 . This is depicted in FIG.  6 . As the arm  260  of the polishing holder  250  is lowered, the guide pins  290  are inserted within the corresponding ferrule recess  52 . Since the ferrule holder may rotate freely within the arm recesses  270 , the ferrule holder  10  rotates until the ferrule face  60  is planar to the face of the positioning holder  280  as is shown in FIG.  7 . As mentioned above the ferrule holder  10  is then fixed within the arm  260  and lifted off from the positioning holder  280 . 
     The polishing holder  250  can then move the arm  260  in a position to allow the ferrule face  55  to be brought into contact with a polishing and grinding surface (not shown) to polish the ferrule face  55 . As has been mentioned, the ferrule  50  is made of plastic and the ferrule holder  10  of stainless steel. The polishing surface used for polishing the ferrule face  60  is chosen so that only the plastic from which the ferrule is made is ground away and the stainless steel of the ferrule holder  10  is not affected. 
     FIG. 8 shows a ferrule holder  10  equipped with an air bearing means  310  operated with pressurized air supplied by tubes  320 . The ferrule holder  10  is of spherical shape and pressurized air flows around it, the flow of pressurized air supporting the ferrule holder  10  and thereby minimizing any slip-stick effects with regard to the movement of the ferrule holder  10 .