Patent Publication Number: US-6213750-B1

Title: Guide block assembly for aligning bore forming pins during molding of multi-fiber optical connector ferrules

Description:
This application is a divisional application of serial number 09/096,971, filed Jun. 12, 1998 and now U.S. Pat. No. 6,071,442, which in turn is a continuation of serial number 08/627,639, filed Apr. 4, 1996 and now U.S. Pat. No. 5,786,002. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to an apparatus and method for aligning and retaining bore forming pins that extend through a mold cavity for molding multi-fiber optical connector ferrules. In one aspect, the present invention relates to a guide block assembly and method that retain and align each bore forming pins in a respective bore defined in a respective block. 
     BACKGROUND OF THE INVENTION 
     The present invention is directed to one aspect of the molding process used to mold multi-fiber optical fiber ferrules of the type described in U.S. Pat. No. 5,214,730 to Nagasawa et al. The reference numerals  2 ,  3 ,  4  and  6  used in the Background of the Invention section are the same as those used in the Nasasawa patent. The multi-fiber ferrule is generally indicated by reference numeral  3  in FIG. 1 of Nagasawa. The term ferrule is used herein instead of the term “plug assembly” used in Nagasawa. “Ferrule” is a term of art that refers to the structure that receives the end of an optical fiber or fibers and then is abutted against an opposing ferrule to precisely align optical fibers for transmission of an optical signal. With reference to FIG. 1 of Nagasawa, the multi-fiber ferrule includes an array of optical fibers  2  disposed therein and guide bores  4  for receiving guide pins  6  to align two ferrules during the mating of the two ferrules. 
     In the typical molding of ferrules  3 , bore forming pins extend through the mold cavity to create the guide bores  4  and the bores that receive optical fibers  2  from ribbon cable  1 . After the ferrule is molded, then ribbon cable  1  is appropriately stripped and the individual fibers  2  are inserted into the fiber bores. Various techniques are used to fix the fibers in the molded ferrule and then the face  5  of the ferrule and the ends of the fibers  2  are polished. 
     As is known in the art, there is a premium placed on precise alignment of opposing optical fibers in a connector to minimize connection loss which diminished the qualify of the optical transmission through the connector. The issue of precisely aligning opposing optical fibers becomes even more sensitive with multi-fiber ferrules because of the need to precisely align all the optical fibers relative to each other and relative to the guide pin bores within the molded ferrule. 
     The prior art presently used a series of V-grooves machined into a block to retain bore forming pins extending through the mold cavity. FIG. 1 herein shows a cross-section of an example V-groove geometry where fiber bore forming pins  7  and guide bore forming pins  8  are shown disposed in V-grooves  9 . The disadvantages of this or similar open groove constructions are many. 
     First, there is a tendency of the pins to float within the V-groove in the direction of arrow A during the molding process. This float contributes to imprecise alignment of the bores formed in the molded ferrule. Additionally, after repeated used of a mold cavity with the groove construction, flash begins to build up in areas indicated by B. This flash build up requires frequent cleaning of the V-grooves. Also, as can be seen, the pins contact the V-grooves along two lines of contact and thus all the friction forces of the repeated insertion and removal of the pins into the V-grooves are imparted along these two lines of contact thereby causing wear along the sides of the V-groove. This causes the alignment of the pins to become progressively more imprecise. Another disadvantage is that preciseness in the construction of the V-groove block in inherently limited. The V-grooves are machined into a stock piece without the ability to adjust the relationship of the grooves to each other. 
     Therefore a need exists for a guide block to retain the bore forming pins that reduces float of the pins during the molding process and improves wear resistance of the guide block. Additionally, a guide block is needed that eliminates the need to clean the guide block after each mold to remove flash. Additionally, a guide block is needed that allows the relationships between the bore forming pins to be continually adjusted during construction of the guide block to allow a more precise guide block to be constructed. Additionally, a need exists for a guide block that can be adjusted after it is constructed to account for gradual shifts in the bore pin relationships caused by repeated use of the guide. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention is a guide block assembly for aligning and retaining a plurality of fiber bore forming pins and at least one guide bore forming pin in precise relation to each other during molding of a multi-fiber optical connector ferrule. The assembly comprises a plurality of fiber bore blocks each of which defines a fiber bore therethrough sized for retaining a fiber bore forming pin. The fiber bore blocks are arranged together in an array such that the fiber bores are generally parallel defining an axial direction. Adjoining surfaces are defined between adjacent fiber bore blocks in the array. 
     The guide block assembly also comprises at least one guide bore block that defines bore therethrough sized for retaining one of the guide bore forming pins. The guide bore block is assembled with the array of fiber bore blocks such that the guide bore is oriented generally parallel with the fiber bores. Adjoining surfaces are defined between the at least one guide block adjacent fiber bore blocks. 
     Another aspect of the present invention is a method of aligning and retaining a plurality of fiber bore forming pins and at least one guide bore forming pin in precise relation to each other during molding of a multi-fiber ferrule. The method comprises the step of retaining each of the fiber bore forming pins in a respective fiber bore which is formed through a respective fiber bore block. Another step is adjoining the plurality of fiber bore blocks together in an array such that the fiber bores are parallel to each other defining an axial direction and defining adjoining surfaces between adjacent fiber bore blocks. Another step is retaining each of the guide bore forming pins in a respective guide bore which is formed through a respective guide bore block. Another step is adjoining the guide bore blocks to the array of fiber bore blocks such that the guide bores are parallel with the fiber bores and wherein adjoining surfaces are defined between the guide bore blocks and the array of fiber bore blocks. Another step is machining the adjoining surfaces between the fiber bore blocks and between the guide bore blocks and the array of fiber bore blocks such that when the fiber bore blocks and the guide bore blocks are assembled together, the desired relationships between successive fiber bores and between the fiber bores and the guide bores are achieved. 
     Another aspect of the present invention is a method of manufacturing a fiber bore block for use in a guide block assembly that is used for aligning and retaining fiber bore forming pins and guide bore forming pins in precise relation to each other during molding of a multi-fiber ferrule around such pins. The method comprises the step of machining in a first radial direction against a cylindrical ferrule until a first planar surface is formed along the length of the ferrule. The cylindrical ferrule already defines a precisely machined bore extending therethrough in the axial direction. Another step is machining in a second radial direction against the cylindrical ferrule until a second planar surface is formed along the length of the ferrule that is opposite of and generally with the first planar surface. 
     Another aspect of the present invention is a guide block assembly for aligning and retaining a plurality of fiber bore forming pins in precise relation to each other during molding of a multi-fiber ferrule. The guide block assembly comprises a plurality of fiber bore blocks. Each fiber bore block defines a fiber bore therethrough for retaining one of the fiber bore forming pins. The plurality of fiber bore blocks are assembled together in an array such that the fiber bores are generally parallel defining an axial direction and such that adjoining surfaces are defined between adjacent fiber bore blocks in the array. The adjoining surfaces are readily machinable when the fiber bore blocks are disassembled to allow precise positioning of the fiber bores relative to each other when assembled. 
     The assembly and methods of the present invention allow for the more precise construction of a guide block for retaining the bore forming pins during molding of the multi-fiber ferrules. Float of pins during the molding process is reduced, and the use of bores eliminates the build up of flash that needs to be removed after each molding. The guide block also has better wear resistance due to the frictional forces being distributed over the entire interior surface of the bores as opposed to lines of contacts as the V-groove. 
     Moreover, the relationships between the fiber bores and the guide bores are adjustable during construction of the assembly to achieve the desired preciseness. The relationships are also adjustable after the initial assembly is constructed to respond to shifts in the relationships between bores caused by the repeated use of the guide block assembly in the molding process. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-section of a prior art V-groove geometry used for guide blocks to retain bore forming pins; 
     FIG. 2 is a perspective view of a representative arrangement of a mold cavity environment depicting the preferred embodiment of the guide block assembly of the present invention in relation thereto; 
     FIG. 3 is an exploded partial view of the preferred embodiment of the guide block assembly of the present invention; 
     FIG. 4 is an end view of the preferred embodiment of the guide block assembly of the present invention; 
     FIG. 5 is a perspective view of the preferred embodiment of the fiber bore block used in the present invention; 
     FIG. 6 is a longitudinal cross-section of the fiber bore block of FIG. 5; 
     FIG. 7 is a perspective view of cylindrical ferrule used in a method of the present invention to manufacture the fiber bore block of FIG. 5; 
     FIG. 8 is a side view of the guide block assembly of the present invention; 
     FIG. 9 is an end view of an alternative embodiment of the guide block assembly of the present invention; and 
     FIG. 10 is an end view of another alternative embodiment of the guide block assembly of the present invention. 
    
    
     DETAILED DESCRIPTION 
     With reference to FIGS. 2-8, the preferred embodiment of the guide block assembly  10  of the present invention is shown. FIG. 2 partially depicts a mold cavity  12  to illustrate the environment for guide block assembly  10 . Assembly  10  has mold face  14  which can serve as one of the walls  16  which define part of mold cavity  12 . Making up assembly  10  is an array  20  of fiber bore blocks  22   a-h  more particularly referenced in FIGS. 3-7. Guide bore blocks  24   a  and  24   b  confine array  20  in the lateral direction. Top spacer block  26   a  and bottom spacer  26   b  confine array  20  in the vertical direction. It should be understood that any number and configuration of fiber bore blocks  22  can be used. For example, two rows of eight blocks or four rows of four blocks may be used. 
     Assembly  10  is configured to retain a plurality of fiber bore forming pins  30  received in fiber bores  32   a-h  in fiber blocks  22   a-h , respectively, and retain guide bore forming pins  33  in guide bores  34   a-b  in guide bore blocks  24   a-b , respectively. Any suitable jig, not shown, can be used to translate pins  30  and  33  into and out of bores  32  and  34 . During molding of a multi-fiber ferrule, the pins are inserted into the bores and the molding material flows around the pins. After the mold has set, the pins can be retracted to leave behind a plurality of molded bores. The fiber bore forming pins will create small inner diameter molded bores sized to receive an individual optical fiber in close tolerance. Fiber bore forming pins  30  may be the actual fibers when the connector will be molded directly around the fibers. The guide bore forming pins will create typically larger diameter molder bores sized to receive guide pins to mate two opposed multi-fiber ferrule in precise alignment. 
     The present invention is directed to an apparatus and method of being able to precisely arrange the fiber bore forming pins and the guide bore forming pins relative to each other in such away that the precision is repeatable over a large number of molding cycles. As discussed in the background of the invention, the method of arranging the bore forming pins with V-grooves such as shown in FIG. 1 suffers from floating of pins, flash build up, premature wear of the guide block, and the limits on preciseness of the relationships between the grooves as a result of machining the grooves in a single stock piece. By using bores in an array of blocks, float is reduced, wear is reduced, flash build up is eliminated and the relationships between the bore forming pins in the bore blocks is more precise. Specifically, bores  32  and  34  provide less room for floating of the bore forming pins  30  and  33  during the molding process. By having a cylindrical bore  32  or  34 , the contact of the bore forming pin to the bore is spread across a larger surface area thereby decreasing wear of the bore compared to V-grooves which have only lines of contact with the bore forming pins which lend themselves to faster wear. 
     Another advantage of the present invention is that having an array of blocks allows the guide block assembly to be fine tuned until the relationship of the bores are extremely precise. Once the precise guide block is made, it is used repeatedly in the molding process and can be adjusted from time to time to account for shifts in the relationships caused by repeated use. This feature of adjustability can best be described with reference to FIG. 3 which is a partially exploded perspective of guide block assembly  10 . The adjoining fiber bore blocks  22   a-h , guide bore blocks  24   a-b , and spacer blocks  26   a-b  define adjoining surfaces  40  which can be precisely machined and polished. Each block has at least one critical distance which is defined as the distance between the centerline of the bore in such block in a normal direction to any adjoining surface  40  of such block. For example, guide bore block  24   a  has one critical distance  42  between the centerline of guide bore  34   a  and adjoining surface  40  which adjoins against fiber bore block  22   a . Distance  42  is critical because it contributes to establishing a precise relationship between guide bore  34   a  and the remainder of the bores. If not enough material is removed from adjoining surface  40  of guide bore block  24   a  in the initial construction of the blocks for a guide block assembly, then a measurement is taken of guide bore block  24   a  to determine the amount of machining or polishing that is needed to achieve critical distance  42 . The critical distance can be precisely approached by iterations of these steps. 
     If too much material is removed from adjoining surface  40  of guide bore block  24 , then the block is either discarded to start over with another block, or some type of shim or plating technique is used to make up the critical distance. The preferred construction of guide block assembly involves iterations of machining, measuring and machining to approach the desired critical distance  42 . This same methodology may be used on each critical distance  42 . 
     However, there are some short cuts that may apply to precisely constructing guide block assembly  10 . For example, fiber bore blocks  22   a-h  may be initially machined close to the critical distance. Then, two or more of fiber bore blocks  22   a-h  can be rearranged in different orders in an attempt to find an order that achieves the desired preciseness of the relationship between fiber bores  32   a-h.    
     With additional reference to FIGS. 5-7, fiber bore blocks  22   a  is generally rectilinear and defines fiber bore  32   a  extending therethrough in a direction defined as the axial direction. A representative fiber bore forming pin  30  is shown in position to be inserted into fiber bore  32   a . FIG. 6 shows a longitudinal cross-section of fiber bore block  22   a  with fiber bore forming pin  30  having distal end  58  disposed in fiber bore  54  and mold zone  60  of fiber bore forming pin  30  disposed outside of fiber bore block  22  where resin or plastic used in the molding process will form around mold zone  60  of fiber bore forming pin  30 . 
     All of the four planar surfaces parallel with the axial direction are adjoining surfaces  40  for fiber bore block  22   a . Therefore, fiber bore block  22   a  has four critical distances  42  extending from the centerline of fiber bore  32   a  in a normal direction to each adjoining surface  40 . To aid in achieving critical distances in the minimum amount of iterations, fiber bore block  22   a  is preferably machined from commercially available cylindrical ceramic ferrule  48  which is supplied with precisely machined bore  32  as shown in FIG.  7 . Machining operations are applied against the ferrule in four different radial directions to create the rectilinear wafer structure of fiber bore blocks  22   a-h . One aspect of the present invention is this method of manufacturing a fiber bore block. 
     Alternatively, ceramic ferrule  48  may be machined to have only two or three planar surfaces. The top and/or bottom may remain arcuate with spacer blocks  26  adjoining against such arcuate surfaces. As another alternative, the use of shims or plating techniques may be incorporated with the present invention. For example, metal shims may be placed between one or more adjoining surfaces to aid in achieving the critical distances. In such an example, either the shim, the adjoining surfaces or both may be machined to adjust the guide block assembly. 
     The ceramic material lends itself to precise machining as is known in the ceramic ferrule art. Because cylindrical ceramic ferrules have long been used in optical fiber connectors, suppliers have been producing ceramic ferrules with precise bores as required by optical fiber connectors. Kyocera Industrial Ceramics Corp. is an example of suppliers of such ceramic ferrules. By being able to use a readily available, precisely bored ferrule as starting stock for the fiber bore blocks, the iterations needed to create a sufficiently precise fiber bore block are minimized. Fiber bore blocks  22  may also be made of sapphire, other suitable jewel, or metal. 
     By using readily available, precisely bore ferrules, the advantages discussed above with regards to using a cylindrical bore as opposed to a V-groove are even more significant because the already established preciseness of the ceramic ferrule bore eliminates the need to machine bores  32  and  34  in constructing guide block assembly  10 . In contrast, a V-groove guide block requires that the V-grooves be machined into a piece of stock. Additionally, machining all the V-grooves into one piece of stock does not allow critical distances to be precisely obtained through iterations of machining and measuring. 
     Guide bore blocks  24   a, b  and spacer blocks  26   a, b  are preferably made from hardenable mold steel. The guide bore blocks and spacer blocks may be eliminated from the guide block assembly. For example, multifiber ferrules may be designed with a sleeve instead of guide pins to align the two ferrules. In such a case, there is no need for guide bore blocks. 
     Another aspect of the present invention is a method of aligning and retaining a plurality of fiber bore forming pins and at least one guide bore forming pin generally in accordance with the operation of the guide block assembly discussed above. The plurality of bore forming pins are retained in fiber bores that extend through fiber bore blocks arranged in an array between two guide bore blocks. Two guide bore forming pins are retained in a respective guide bore formed in a respective guide bore block. All the bores are oriented parallel to each other. The guide bore blocks and fiber bore blocks define adjoining surfaces between adjacent blocks. The adjoining surfaces are machined such that when the blocks are assembled together, the desired relationships between successive fiber bores and between the fiber bores and the guide bores are achieved. 
     The various blocks of the guide block assembly can be held together in a variety of ways. The preferred embodiment of such attachment is shown in FIGS. 4 and 8. Four continuous passageways  70  are located as shown, each of which comprises passageway  70   a  bored through guide bore block  24   a , passageway  70   b  bored through bottom spacer block  26   b , and passageway  70   c  bored into guide bore block  24   b . Some type of self tapping bolt  72  may be threaded through passageways  70  to pull guide bore blocks  24   a  and  24   b  toward each other thereby clamping the array of fiber bore blocks in the lateral direction. Alternatively, passageway  70   c  may extend through guide bore block  24   b  so that any type of nut and bolt arrangement can be used. Furthermore, additional passageways similar to passageways  70  may be located elsewhere through the blocks of the guide block assembly if more balanced clamping or bolting forces are desired. Alternatively, the blocks of guide block assembly may be retained together merely by walls  16  of the mold thereby eliminating the need for bolts  72 . 
     The arrangement of the blocks of guide block assembly is only one of a variety of possible arrangements. FIGS. 9-10 illustrate alternative block arrangements of fiber bore blocks  22  and guide bore blocks  24  with and without spacer blocks  26 . FIG. 9 does not include spacer blocks and only includes four fiber bore blocks for the molding of a four fiber ferrule. 
     Although the present invention has been described with respect to certain embodiments, it should be understood that various changes, substitutions and modifications may be suggested to one skilled in the art, and it is intended that the present invention encompass such changes, substitutions and modifications as fall within the scope of the appended claims.