Patent Publication Number: US-2006002660-A1

Title: Two-piece nose assembly with solid sleeve for optical subassembly

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application claims priority to and the benefit of U.S. Provisional Patent Application Ser. No. 60/564,387, filed on Apr. 22, 2004, and entitled “Two Piece Nose Assembly With Solid Sleeve for Optical Subassembly”, which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION  
      1. The Field of the Invention  
      The present invention generally relates to the field of fiber optic couplers and, more specifically, to an at least two-piece nose assembly with a solid sleeve for joining to a ferrule containing an optical component or sub-assembly.  
      2. The Relevant Technology  
      Fiber optic technologies are increasingly used for transmitting voice and data signals. As a transmission medium, fiber optics provides a number of advantages over traditional electrical communication techniques. For example, light signals allow for extremely high transmission rates and very high bandwidth capabilities. Light signals also can be transmitted over greater distances without the signal loss typically associated with electrical signals on copper wire. These light signals are transmitted over optical waveguides, such as the optical fibers found in fiber optic cable.  
      To correct two adjacent optical waveguides or correct an optical waveguide with optical devices, such as, Ferrule-type plug/receptacle optical connectors are typically used to position two optical waveguides, such as optical fibers, so that light can propagate between the two waveguides. Alternatively, ferrule-type plug/receptacle optical connectors can be used between an optical waveguide and an optical component or subassembly. The ferrule-type connector is inserted into a sleeve that fixes the position of the optical fiber with respect to a laser, a photodiode, another optical fiber, or some other optical component. The sleeve is often inserted into a base that is fixed to a housing holding an optical component, such as, by way of example and not limitation, a transmitter optical sub-assembly (TOSA), a receiver optical sub-assembly (ROSA), a laser, a photodiode, or other optical components. The sleeve/base combination is sometimes referred to as a nose assembly. The ferrules and sleeves are manufactured to specific tolerances to ensure a proper friction fit between them, which allows the ferrule to be repeatedly removed and reconnected to the sleeve, while assuring proper alignment of the optical components.  
      There are a number of problems associated with the various connections between these components. One problem is that the material of the sleeve is typically a ceramic, plastic, or soft metal. As the ferrule is repeatedly inserted and removed from the sleeve during positioning of an optical fiber or component, portions of the sleeve material can adhere to the outside surface of the ferrule. Over time, this can cause a buildup of material on the outside surface of the ferrule, causing the ferrule to stick in the housing. This condition is sometimes known as “cold welding”. This can make it very difficult to insert and remove the ferrule. In extreme cases, parts that are “cold welded” together must be physically broken to separate the components. Additionally, the material particles would sometimes contaminate the optical components, thus degrading the optical signal. In some cases, the above mentioned problems have resulted in manufacturing losses of 30% or more (i.e. 30% of parts produced did not meet required tolerances).  
      Another problem associated with the interconnections of these components is the connection of the base to the housing. The base and housing are oftentimes both made of metal. The base has a hole in its center that allows for a light signal to pass from the fiber optic cable in the ferrule to/from the optical component within the housing. In previous configurations, the base has a smooth outside surface that is perpendicular to the surface of the housing. An alignment process ensures that the hole in the base provides an optical alignment between the optical fiber and the optical component. Once the base and housing are properly aligned, the base is welded to the housing using, for example, a laser welding apparatus.  
      There are several problems associated with this welding procedure. First, the laser does not always strike precisely at the junction between the base and the housing. Since the parts themselves act as heat sinks, this results in additional laser energy being used to sufficiently melt the housing and base to form the weld. This additional energy causes the components to become very hot and therefore take a long time to cool. During the cool down period, a lateral displacement of the base with respect to the housing can occur, known as post weld shift. The post weld shift can be sufficient to cause the optical components to be misaligned, thereby degrading the optical signal. This problem can be both expensive and time consuming to correct.  
      Additionally, if the laser is slightly misaligned, the beam melts only a portion of the base or a portion of the housing. The rest of the heat can dissipate into either the housing or the base. This results in no weld being formed, which can potentially cause the pieces to separate entirely. Such a break can result in an interruption of data signals, or even complete data loss.  
     BRIEF SUMMARY OF THE EMBODIMENTS  
      To overcome these and other problems, embodiments of the present invention provide a two piece nose assembly for optoelectronic devices. The assembly includes a first piece having a central bore and an annular alignment recess about the central bore. The first piece can be attached to a housing of the optoelectronic device. The assembly also includes an annular sleeve designed to receive an optical connector and having an outside surface designed to interference fit with an inside surface of the annular alignment recess in the first piece. The annular second piece has an inside surface having a hardness of at least 35 on the Rockwell “C” scale.  
      In exemplary embodiments, the first piece can have an annular groove on an outside surface thereof that defines a lip adjacent to the housing. The annular groove can have a tapered edge that facilitates an optimized angle of incidence for a laser beam used to weld the first piece to the housing. This design provides several advantages. First, the lip that receives the laser beam helps to reduce the heat loss to the greater mass of the whole metal body of the base. This allows fast pulse heating of the lip and metal housing of the optoelectronic device to the melting temperature, and a slow enough cooling phase change to a solid so as to not crystallize the weld nugget grain structure. This results in a weld that is both more uniform and stronger than previous designs.  
      Additionally, the area sacrificed from the edge on the base to form the weld puddle is more or less the same thickness laterally with respect to the weld angle of incidence. Thus, a radial shift towards the center of the part or away from it in the originally fixed laser weld beam alignment is less sensitive compared to the 90 degree cylinder edge of previous designs. This reduces or even eliminates the problem of post weld shift discussed above.  
      The hardening process for the inside surface of the annular sleeve alleviates the problem of ablation of the ferrule/sleeve that results in the cold welding problem discussed above. Ferrules can be inserted and removed as often as desired without significantly increasing the difficulty of inserting and removing the ferrule.  
      These and other objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      To further clarify the above and other advantages and features of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:  
       FIG. 1A  illustrates a side view of one exemplary embodiment of a two-piece nose assembly with a solid sleeve according to the present invention;  
       FIG. 1B  illustrates a cross-sectional side view of the two piece nose assembly of  FIG. 1A  along the lines B-B;  
       FIG. 1C  illustrates a perspective view of the two piece nose assembly of  FIGS. 1A and 1B  with the pieces joined together;  
       FIG. 1D  illustrates a perspective view of the two piece nose assembly of  FIGS. 1A-1C  with the pieces separated;  
       FIG. 1E  illustrates a close-up view of a portion of  FIG. 1D  showing the base and housing;  
       FIG. 2A  illustrates a side view of an alternate exemplary embodiment of a two-piece nose assembly with a solid sleeve according to the present invention;  
       FIG. 2B  illustrates a cross-sectional side view of the two piece nose assembly of  FIG. 2A  along the lines B-B;  
       FIG. 2C  illustrates a perspective view of the two piece nose assembly of  FIGS. 2A and 2B  with the pieces joined together;  
       FIG. 2D  illustrates a perspective view of the two piece nose assembly of  FIGS. 2A-2C  with the pieces separated; and  
       FIG. 2E  illustrates a close-up view of a portion of  FIG. 2D  showing the base and housing.  
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
      Embodiments of the present invention provide several solutions to the problems identified in the prior art. Specifically, embodiments of the present invention disclose a sleeve that receives a ferrule. The sleeve is constructed from a material that resists the ablation associated with previous sleeves. Additionally, a base is disclosed that is constructed in such a way as to minimize the amount of post weld shift that occurs when the base is attached to a housing.  
       FIGS. 1A-1E  illustrate different views of one exemplary embodiment of a two-piece nose assembly, designated generally as reference numeral  100 . In this exemplary embodiment, nose assembly  100  is designed to cooperate with a Lucent Connector (LC connector, not shown). However, those skilled in the art will realize that exemplary embodiments of the present invention can be constructed to work with almost any standard connector. Such connectors can include, by way of example and not limitation, ST, STII, FC, AFC, FDDI, ESCON, and SMA, or any other connector designed to receive a ferrule.  
      With reference to  FIG. 1A , in this exemplary embodiment, nose assembly  100  includes a sleeve  110  and a base  140 . This two piece construction makes machining and manufacturing the parts easier and more cost efficient. However, exemplary embodiments of the present invention can also be used with nose assemblies that have more than two parts. Such nose assemblies are also contemplated to fall within the scope of the exemplary embodiments. The invention is therefore not limited to the two piece construction shown in  FIGS. 1A-1E .  
      Turning to  FIGS. 1B and 1C , in this exemplary embodiment, sleeve  110  is an annular member sized and configured to i) be interference fit into base  140  and ii) receive a ferrule (not shown) containing an optical fiber (not shown). Sleeve  110  includes a first end  112  and a second end  114 . First end  112  can have a top surface  116 , an inside beveled edge  118 , and an outside beveled edge  120 . Beveled edge  118  makes it easier to insert a ferrule (not shown) into sleeve  110 , while beveled edge  120  can aid with placement of sleeve  110  relative to an optical component or other optical connector. It will be understood that second end  114  can also include one or more beveled edges. Although reference is made to the use of various beveled edges  118  and  120 , one will understand that the edges of sleeve  110  can have other configurations to aid with inserting a ferrule (not shown) into sleeve  110 . For instance, at least a portion of each edge  118  and  120  can have a tapered or curved profile.  
      In this exemplary embodiment, as illustrated in  FIG. 1C , sleeve  110  has an outside diameter D 1 , and an inside diameter D 2 . Outside diameter D 1  is chosen to allow sleeve  110  to fit into base  140 , such that an outside surface  124  can interference fit with a portion of base  140 . Additionally, inside diameter D 2  is chosen to allow an inside surface  122  to fit around a post member  154  that is internal to base  140 , such that inside surface  122  can interference fit about this post member, as will be discussed in more detail hereinafter. The inside diameter D 2  can be uniform for the entire length of sleeve  110 .  
      Sleeve  110  can also include a notch  126  in outer surface  124 . Notch  126  is located towards second end  114 . When sleeve  110  is fully inserted into base  140 , notch  126  is not visible, thus providing a visual indicator that sleeve  110  is fully inserted into base  140 . This notch  126  can extend around the entire periphery of sleeve  110  or can be at least partially disposed around the periphery of sleeve  110 . In other configurations, other visual indicators can be used to indicate when sleeve  110  is fully inserted into base  140 . For instance, a series of holes or recesses can be substituted for notch  126 . In still other configurations, visual markings can be applied to outer surface  124  without changing the generally planar configuration of outer surface  124  as occurs with formation of notch  126 . Various other structures or techniques for providing a visual indicator of the desired position of sleeve  110  relative to base  140  can be used and are known to those skilled in the art.  
      In order to overcome the problems associated with cold welding discussed above, one exemplary embodiment provides that sleeve  110  be made from metal and that inside surface  122  be heat treated. Heat treating hardens inside surface  122  so that portions of inside surface  122  do not scrape off when a ferrule (not shown) is repeatedly inserted and removed. In an exemplary embodiment, inside surface  122  is heat treated until it has a hardness of at least 35 on the Rockwell “C” scale.  
      In exemplary embodiments, sleeve  110  can be made from carbon steel, 416 steel, and other metals that can be heat treated or otherwise hardened to a Rockwell “C” hardness of at least 35. Materials with a Rockwell “C” hardness of at least 35 are sufficient to alleviate the problem with the ferrule ablating inside surface  122  of sleeve  110 . Additional surface treatments can also be applied after heat treating or instead of heat treating to further increase the hardness of inside surface  122 . For example, a hard coating can be applied to inside surface  122  to increase the hardness by a desired amount, to at least a Rockwell “C” hardness of 35. Such coatings can include, by way of example and not limitation, titanium nitrite, and other coatings known to those of skill in the art that provide a sufficient increase in hardness to inside surface  122 .  
      As mentioned above, sleeve  110  cooperates with base  140 . With reference to  FIG. 10 , the base  140  includes a central bore  146  that extends from a first end  142  toward a second end  144  having an annular alignment recess  148  ( FIG. 1B ) formed therein. The recess  148  ( FIG. 1B ) is centered about bore  146 . The recess  148  includes a bottom wall  150  and a sidewall  152 . A post member  154  extends from bottom wall  150  and towards a center of recess  148 , with bore  146  running through post member  154 . This post member  154  is configured to receive second end  114  of sleeve  110  and cooperate with inside surface  122  thereof. The post member  154  can, therefore, have various configurations so long as inside surface  122  and post member  154  are complementary and can, in one configuration, interference fit one with another. It will be understood that other techniques can be used to connect sleeve  110  to post member  154 .  
      As shown in  FIGS. 1A-1D , sidewall  152  of recess  148  has a height above bottom wall  150  that is greater than that of post member  154 . This is only one configuration of the present invention, and it can be understood by those skilled in the art that in some circumstances post member  154  can have a height generally the same as bottom wall  150  and even greater than bottom wall  150 . In still other configurations, no post member is required.  
      With specific reference to  FIG. 1E , base  140  also includes an annular groove  158  on an outside surface  156 . Annular groove  158  is located proximal first end  142 . Annular groove  158  defines a lip  160  immediately adjacent first end  142 , and a tapered portion  162  on the side of groove  158  away from first end  142 . With this configuration, lip  160  presents a limited quantity of material to be heated during the process of attaching base  140  to a housing  170  ( FIGS. 1B and 1E ). Further, with lip  160  in the presently illustrated configuration, the attachment process can occur more quickly than existing bases because a small quantity of material can be heated more quickly and hence melted more quickly to create the attachment bond.  
      In addition to the configuration of lip  160 , tapered portion  162  also aids with the attaching process. More specifically, tapered portion  162  and a tapered portion  163  of lip  160 , collectively provide clearance for equipment used during the attaching process. For instance, when a laser is used to create a weld between base  140  and housing  170 , tapered portion  162  and optionally the tapered portion  163  of lip  160 , collectively provide clearance for the laser beam.  
      Base  140  can be, by way of example and not limitation,  304  stainless steel, other stainless or non-stainless steels, or other metals known to those of skill in the art. Base  140  is welded to housing  170 , which can also be 304 stainless, other stainless or non-stainless steels, or other metals known to those of skill in the art.  
      The specific design of base  140  shown in  FIGS. 1A-1E  is useful in preparing base  140  to be welded to housing  170 . In one configuration, a laser beam  180 , shown in  FIG. 1E  (not to scale) is used to create the necessary heat to weld base  140  to housing  170 . Specifically, beam  180  can be directed to the edge of lip  160 . In exemplary embodiments, beam  180  is a pulsed beam about 50 microns across at the point of incidence upon base  140  and housing  170 . Although this is one diameter of laser beam  180 , other diameters greater and lesser than 50 microns are possible.  
      Since base  140  is itself a heat sink, it is advantageous to keep the heat loss to a minimum. The specific design of lip  160  keeps the heat from laser beam  180  from dissipating too quickly out of the heated weld area into the larger base material during the “weld heated molten metal phase” of the penetrating root nugget development that forms the weld after cooling. Lip  160  helps achieve this by reducing the amount of material heated both by laser beam  180  to form the weld, and by allowing this reduced amount of material to heat to the melting point more rapidly than occurs in previous processes. In one exemplary embodiment, lip  160  is approximately 0.0035 inches thick at the outside edge. However, greater or lesser thicknesses, in the range from about 0.0010 to about 0.0100, are also contemplated.  
      As mentioned above, tapered edge  162  is designed to provide clearance for incoming laser beam  180  that actually performs the weld. In exemplary embodiments, tapered edge  162  has an angle of about 60 degrees from the horizontal. However, angles between about 30 degrees and about 80 degrees are also possible.  
       FIGS. 2A-2E  illustrate different views of an alternate exemplary embodiment of a two-piece nose assembly, designated generally as reference numeral  200 . In this exemplary embodiment, nose assembly  200  is designed to cooperate with a subscriber connector (SC connector, not shown). However, those skilled in the art will realize that exemplary embodiments of the present invention can be constructed to work with almost any standard connector. Such connectors can include, by way of example and not limitation, ST, STII, FC, AFC, FDDI, ESCON, and SMA, or any other connector designed to receive a ferrule. While nose assembly  200  is shown as being two pieces, exemplary embodiments of the present invention will work with nose pieces that comprise two or more pieces. The invention is therefore not limited to the two piece construction shown if  FIGS. 2A-2E .  
      In this exemplary embodiment, nose assembly  200  includes a sleeve  210  and a base  240 . This two piece construction makes machining and manufacturing the parts easier and more cost efficient. However, exemplary embodiments of the present invention can also be used with nose assemblies that have more than two parts. Such nose assemblies are also contemplated to fall within the scope of the exemplary embodiments.  
      In this exemplary embodiment, sleeve  210  is an annular member sized and configured to i) be interference fit into base  240 , and ii) receive a ferrule (not shown) containing an optical fiber (not shown). Sleeve  210  includes a first end  212  and a second end  214 . First end  212  can have a top surface  216 , an inside beveled edge  218 , and an outside beveled edge  220 . Beveled edge  218  makes it easier to insert a ferrule (not shown) into sleeve  210 , while beveled edge  220  can aid with placement of sleeve  210  relative to an optical component or other optical connector. It will be understood that second end  214  can also include one or more beveled edges. Although reference is made to the use of various beveled edges  218  and  220 , one will understand that the edges of sleeve  210  can have other configurations to aid with inserting a ferrule (not shown) into sleeve  210 . For instance, at least a portion of each edge  218  and  220  can have a tapered or curved profile.  
      In this exemplary embodiment, as illustrated in  FIG. 2A , sleeve  210  has an upper outside diameter D 1 , a lower outside diameter D 2 , and an inside diameter D 3 . The lower outside diameter D 2  is chosen to allow sleeve  210  to fit snugly into base  240 . Additionally, inside diameter D 2  is chosen to allow an inside surface  222  to fit snugly around a post member  254  that is internal to base  220 , such that inside surface  222  can interference fit about this post member, as will be discussed in more detail hereinafter. The inside diameter D 3  can be uniform for the entire length of sleeve  210 .  
      In order to overcome the problems associated with cold welding discussed above, one exemplary embodiment provides that sleeve  210  be made from metal and that inside surface  222  be heat treated. Heat treating hardens inside surface  222  so that portions of inside surface  222  do not scrape off when a ferrule (not shown) is repeatedly inserted and removed. In an exemplary embodiment, inside surface  222  is heat treated until it has a hardness of at least 35 on the Rockwell “C” scale.  
      In exemplary embodiments, sleeve  210  can be made from carbon steel, 416 steel, and other metals that can be heat treated or otherwise hardened to a Rockwell “C” hardness of at least 35. Materials with a Rockwell “C” hardness of at least 35 are sufficient to alleviate the problem with the ferrule ablating inside surface  222  of sleeve  210 . Additional surface treatments can also be applied after heat treating, or instead of heat treating, to further increase the hardness of inside surface  222 . For example, a hard coating can be applied to inside surface  222  to increase the hardness by a desired amount, to at least a Rockwell “C” hardness of 35. Such coatings can include, by way of example and not limitation, titanium nitrite, and other coatings known to those of skill in the art that provide a sufficient increase in hardness to inside surface  222 .  
      As mentioned above, sleeve  210  cooperates with base  240 . The base  240  includes a central bore  246  that extends from a first end  242  toward a second end  244  having an annular alignment recess  248  formed therein. The recess  248  is centered about bore  246 . The recess  248  includes a bottom wall  250  and a sidewall  252 . A post member  254  extends from bottom wall  250  and towards a center of recess  248 , with bore  246  running through post member  254 . This post member  254  is configured to receive second end  214  of sleeve  210  and cooperate with inside surface  222  thereof. The post member  254  can, therefore, have various configurations so long as inside surface  222  and post member  254  are complementary and can, in one configuration, interference fit one with another. It will be understood that other techniques can be used to attach sleeve  210  to post member  254 .  
      A shown in  FIGS. 2A-2D , the sidewall  252  of recess  248  has a height above bottom wall  250  that is greater than that of post member  254 . This is only one configuration of the present invention, and it can be understood by those skilled in the art that in some circumstances post member  254  can have a height generally the same as bottom wall  250  and even greater than bottom wall  250 .  
      With specific reference to  FIG. 2E , base  240  also includes an annular groove  258  on an outside surface  256 . Annular groove  258  is located proximal first end  242 . Annular groove  258  defines a lip  260  immediately adjacent first end  242 , and a tapered portion  262  on the side of groove  258  away from first end  242 . With this configuration, lip  260  presents a limited quantity of material to be heated during the process of attaching base  240  to a housing  270  ( FIGS. 2B and 2E ). Further, with lip  260  in the presently illustrated configuration, the attachment process can occur more quickly than existing bases because a small quantity of material can be heated more quickly and hence melted more quickly to create the attachment bond.  
      In addition to the configuration of lip  260 , tapered portion  262  also aids with the attaching process. More specifically, tapered portion  262 , and a tapered portion  263  of lip  260 , collectively provide clearance for equipment used during the attaching process. For instance, when a laser is used to create a weld between base  240  and housing  270 , tapered portion  262  and optionally tapered portion  263  of lip  160 , collectively provide clearance for the laser beam.  
      Base  240  can be, by way of example and not limitation, 304 stainless steel, other stainless or non-stainless steels, or other metals known to those of skill in the art. Base  240  is welded to a housing  270  ( FIGS. 2B and 2E ), that can also be 304 stainless, other stainless or non-stainless steels, or other metals known to those of skill in the art.  
      The specific design of base  240  shown in  FIGS. 2A-2E  assists in preparing base  240  to be welded to housing  270 . In one configuration, a laser beam  280 , shown in  FIG. 2E  (not to scale) is used to create the necessary heat to weld base  240  to housing  270 . Specifically, beam  280  can be directed to the edge of lip  260 . In exemplary embodiments, beam  280  is a pulsed beam about 50 microns across at the point of incidence upon base  240  and housing  270 . Although this is one diameter of laser beam  280 , other diameters greater and lesser than 50 microns are possible.  
      Since base  240  is itself a heat sink, it is advantageous to keep the heat loss to a minimum. The specific design of lip  260  keeps the heat from laser beam  280  from dissipating too quickly out of the heated weld area into the larger base material during the “weld heated molten metal phase” of the penetrating root nugget development that forms the weld after cooling. Lip  260  helps achieve this by reducing the amount of material heated both by laser beam  280  to form the weld, and by allowing this reduced amount of material to heat to the melting point more rapidly than occurs in previous processes. In one exemplary embodiment, lip  260  is approximately 0.0035 inches thick at the outside edge. However, greater or lesser thicknesses, in the range from about 0.0010 to about 0.0100, are also contemplated.  
      As mentioned above, tapered edge  262  is designed to provide clearance for incoming laser beam  280  that actually performs the weld. In exemplary embodiments, tapered edge  262  has an angle of about 60 degrees from the horizontal. However, angles between about 30 degrees and about 80 degrees are also possible.  
      The exemplary embodiments discussed above provide some distinct advantages over previous designs. First, with respect to sleeves  110 ,  210 , the hardening process alleviates the problem of ablation of the ferrule/sleeve that results in the cold welding problem discussed above. Ferrules can be inserted and removed as often as desired without significantly increasing the difficulty of inserting and removing the ferrule.  
      With respect to base members  140 ,  240 , there are several advantages over previous designs having the base contacting the housing at a perpendicular angle. First, the lip that receives the laser beam helps to reduce the heat loss to the greater mass of the whole metal body of the base. This allows fast pulse heating to the melting temperature and a slow enough cooling phase change to a solid so as to not crystallize the weld nugget grain structure. This results in a weld that is both more uniform and stronger than previous designs.  
      Additionally, because the area sacrificed from the prep edge on the base to form the weld puddle is more or less the same thickness laterally with respect to the weld angle of incidence, a radial shift towards the center of the part or away from it in the originally fixed laser weld beam alignment is less sensitive compared to the 90 degree cylinder edge of previous designs. In the previous designs, if the laser beam moves a little towards the base wall, the melted area becomes just the base wall surface. If the laser beam moves a little away from the base wall, the melted area becomes only the perpendicular housing face. In either case, the two pieces are not reliably joined together. The present design is much less sensitive to these minor shifts in the laser beam placement.  
      The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.