Patent Publication Number: US-2019198834-A1

Title: Telecommunications equipment cabinets including isolated and removable battery box assemblies

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit and priority of U.S. Provisional Application No. 62/609,099, filed on Dec. 21, 2017. The entire disclosure of the above application is incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to telecommunications equipment cabinets including isolated and removable battery box assemblies. 
     BACKGROUND 
     This section provides background information related to the present disclosure which is not necessarily prior art. 
     In telecommunications equipment cabinets, batteries can release hydrogen gas during operation. A fan/filter cooling system is often used to allow hydrogen gas to escape the cabinet through abundant open area ventilation. However, abundant open area ventilation increases the risk of corrosion for significant electrical components stored inside the cabinet. Further, a fan/filter cooling system may not be sufficient to meet thermal requirements of electrical components intended for use within the cabinet, especially in warm climate areas. 
     In some cases, a separate battery base cabinet may be used in combination with an equipment only cabinet. The equipment only cabinet may be installed on top of the battery base cabinet, or the two cabinets can be deployed side by side. The equipment only cabinet can utilize a cooling system (e.g., air conditioner, heat exchanger, etc.) sufficient to meet thermal requirements of the equipment, without needing to account for hydrogen outgassing because the hydrogen outgassing would be contained within the battery base cabinet. However, this approach necessitates two separate cabinets, which requires more deployment space than may be desired and does not allow for equipment expansion without introducing additional enclosure(s). 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     According to one aspect of the present disclosure, a telecommunications equipment cabinet includes a cabinet housing, and at least one equipment chamber defined within the cabinet housing. The equipment chamber has one or more electrical components disposed therein. The telecommunications equipment cabinet also includes a battery box removably positioned in the cabinet housing. The battery box includes at least one battery, and the battery box is isolated from the equipment chamber to inhibit hydrogen gas from escaping the battery box into the at least one equipment chamber. 
     According to another aspect of the present disclosure, a telecommunications equipment cabinet includes a cabinet housing having multiple vents, and at least one equipment chamber defined within the cabinet housing. The at least one equipment chamber has one or more electrical components disposed therein. The telecommunications equipment cabinet also includes multiple battery boxes removably positioned in the cabinet housing, and each battery box includes at least one battery. Each battery box is vented through a distinct one of the multiple vents of the cabinet housing to inhibit hydrogen gas from escaping said battery box into the at least one equipment chamber. 
     According to yet another aspect of the present disclosure, a method of exchanging components in a telecommunications equipment cabinet is disclosed. The telecommunications cabinet includes at least one equipment chamber defined within the cabinet housing and multiple battery boxes positioned in the cabinet housing. The at least one equipment chamber has one or more electrical components disposed therein. Each battery box includes at least one battery and is isolated from the at least one equipment chamber to inhibit hydrogen gas from escaping the battery box into the at least one equipment chamber. The method includes removing one of the multiple battery boxes from the cabinet housing to define a space previously occupied by said one of the multiple battery boxes, and inserting another electrical component into the space previously occupied by said one of the multiple battery boxes while maintaining isolation between the inserted electrical component and the other battery box(es) remaining in the cabinet housing to inhibit hydrogen gas from escaping the other battery box(es) to the inserted electrical component. 
     Further aspects and areas of applicability will become apparent from the description provided herein. It should be understood that various aspects of this disclosure may be implemented individually or in combination with one or more other aspects. It should also be understood that the description and specific examples herein are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG. 1  is a block diagram of a perspective view of a telecommunications equipment cabinet, according to one example embodiment of the present disclosure. 
         FIG. 2  is a perspective view of the telecommunications equipment cabinet of  FIG. 1 , with a cabinet door in an open position. 
         FIG. 3  is a perspective view of a telecommunications equipment cabinet including an air conditioner, according to another example embodiment of the present disclosure. 
         FIG. 4  is a perspective view of the telecommunications equipment cabinet of  FIG. 3 , with a cabinet door in an open position. 
         FIG. 5  is a front isometric exploded view of a battery box assembly of the telecommunications equipment cabinet of  FIG. 2 . 
         FIG. 6  is a front isometric exploded view of the battery box assembly of  FIG. 5 , including additional components. 
         FIG. 7  is a rear isometric view of the battery box assembly of  FIG. 5 . 
         FIG. 8  is a front isometric view of the battery box assembly of  FIG. 5 . 
         FIG. 9  is an enlarged view of a portion of the telecommunications equipment cabinet of  FIG. 2 . 
         FIG. 10  is a front isometric exploded view of the battery box assembly of  FIG. 5 , including floor reinforcement brackets. 
         FIG. 11  is a bottom isometric view of the battery box assembly of  FIG. 5 , including a strip gasket. 
         FIG. 12  is an enlarged view of a portion of the telecommunications equipment cabinet of  FIG. 2 . 
         FIG. 13  is an enlarged view of a portion of the telecommunications equipment cabinet of  FIG. 4 . 
         FIG. 14  is an exploded enlarged view of a portion of the telecommunications equipment cabinet of  FIG. 2 . 
         FIG. 15  is an exploded enlarged view of a portion of the telecommunications equipment cabinet of  FIG. 4 . 
         FIG. 16  is a perspective view of the telecommunications equipment cabinet of  FIG. 4  including two battery box assemblies having SAFT batteries. 
         FIG. 17  is a perspective view of the telecommunications equipment cabinet of  FIG. 2  including two battery box assemblies having VRLA batteries. 
     
    
    
     Corresponding reference numerals indicate corresponding features throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     Example embodiments will now be described more fully with reference to the accompanying drawings. 
     Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. 
     The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
     Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments. 
     Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     A telecommunications equipment cabinet according to one example embodiment of the present disclosure is illustrated in  FIGS. 1 and 2 , and indicated generally by reference number  100 . As shown in  FIGS. 1 and 2 , the telecommunications equipment cabinet  100  includes a cabinet housing  102  and at least one equipment chamber  104  defined within the cabinet housing  102 . One or more electrical components (not shown) are disposed within the equipment chamber  104 . 
     The equipment cabinet  100  includes two battery boxes  106  (e.g., battery box assemblies) removably positioned in the cabinet housing  102 . Each battery box  106  includes at least one battery. Each battery box  106  is isolated from the equipment chamber  104  to inhibit hydrogen gas from escaping the battery box  106  into the equipment chamber  104 . Although  FIG. 2  illustrates two battery boxes  106 , other embodiments may include more or less battery boxes  106 . 
     As described above, the telecommunications equipment cabinet  100  incorporates individual battery boxes  106  that are isolated from the equipment chamber  104 , and are removable. This allows a user to separate (e.g., isolate) the equipment chamber  104  of the telecommunications equipment cabinet  100  from the batteries inside the battery boxes  106  to reduce (e.g., eliminate) a risk of potential hydrogen outgassing issues from the batteries. For example, dangerous hazards can arise when batteries outgas hydrogen into the equipment chamber  104  of the telecommunications equipment cabinet  100 . 
     The telecommunications equipment cabinet  100  also allows the battery boxes  106  to be removed if the user desires to place electrical component(s) in a space previously occupied by a removed battery box, to expand the electrical component capacity of the telecommunications equipment cabinet  100 , etc. For example, use of removable battery boxes  106  (e.g., as opposed to permanent members of the telecommunications equipment cabinet  100 ), allows a user to replace a battery box  106  with additional equipment in that space if desired. In this manner, the removable battery boxes  106  can allow for equipment expansion in the event multiple battery strings are deemed unnecessary, etc. A user can increase (e.g., optimize) deployment space available in the telecommunications equipment cabinet, which can reduce long term costs. 
     The telecommunications equipment cabinet  100  includes a combination heat exchanger  108  and thermoelectric cooler (TEC)  110  cooling system. The heat exchanger  108  is configured to provide sufficient thermal cooling to cool electronic components in the equipment chamber  104  of the telecommunications equipment cabinet  100 . 
     TECs  110  within a TEC shroud  112  of the telecommunications equipment cabinet  100  are configured to provide sufficient thermal cooling for the battery boxes  106 . As shown in  FIG. 1 , the heat exchanger  108 , TECs  110  and TEC shroud  112  are positioned on a cabinet door  114  (e.g., cabinet door assembly) of the telecommunications equipment cabinet  100 . 
       FIGS. 3 and 4  illustrate a telecommunications equipment cabinet  200  according to another example embodiment of the present disclosure. The telecommunications equipment cabinet  200  is similar to the telecommunications equipment cabinet  100  of  FIGS. 1 and 2 , but includes a cooling system having an air conditioner  216  and vent shrouds  218  instead of the heat exchanger  108 , TECs  110  and the TEC shroud  112 . 
     The air conditioner  216  and vent shrouds  218  are positioned on a cabinet door  214 , which is coupled to cabinet housing  202 . The telecommunications equipment cabinet  200  includes an equipment chamber  204 , and two battery boxes  206 . 
     As shown in  FIG. 5 , the battery boxes  106  include a top panel  320 , a back wall  322 , a left wall  324 , a right wall  326 , and a floor panel  328 . The panels  320  and  328 , and the walls  322 ,  324  and  326 , may be formed of steel (e.g., sixteen gauge painted steel) components that are riveted and bolted together. 
     In other embodiments the panels  320  and  328 , and the walls  322 ,  324  and  326 , may be formed of other suitable materials (e.g., plastic), and may be coupled together using other suitable fastening approaches. For example, the panels  320  and  328 , and the walls  322 ,  324  and  326 , may be welded together, may be die-cast as a one-piece box, etc. Gaps and seams in the panels  320  and  328 , and the walls  322 ,  324  and  326 , can be sealed with an adhesive silicone (e.g., to form an air-tight seal). 
     The battery box  106  may include side restraint brackets  330  to align and restrain one or more batteries in the battery box  106 . For example, each battery box  106  may include one or more batteries in any suitable configuration, such as a string of four valve-regulated lead-acid (VRLA) batteries, one SAFT battery, etc. In the case of a string of four VRLA batteries, the side restraint brackets  330  may be adapted to restrain the outer two VRLA batteries. 
     The battery box  106  can include a removable sealed access panel assembly  332  at the rear of the battery box  106 , which allows a user to open the battery box  106  if necessary. In some embodiments, the rear of the telecommunications equipment cabinet  100  may also provide rear access to a user (e.g., to access a battery box  106  inside the telecommunications equipment cabinet  100 ). The access panel assembly  332  includes a stop bracket  334  that sets a depth of batteries in the battery box  106 . 
     In the case of a string of VRLA batteries, the access panel assembly  332  may also include restraint brackets  336  (e.g., “in-between” restraint brackets) for use with the VRLA string of batteries. A front brace assembly  338  can also include restraint brackets  336  for use with a string of VRLA batteries. The restraint brackets  336  may be removed in embodiments that include only one battery (e.g., one SAFT battery), etc. 
     In some embodiments, the front brace assembly  338  can mount to forward side restraint brackets  330 . The forward side restraint brackets  330  may be adjustable in their depth position. This can allow for accommodation of different battery depths. 
     The battery box  106  may include a circuit breaker bracket  340 . The circuit breaker bracket  340  can mount any suitable circuit breaker as specified by a user (e.g., a 250 Amp F series circuit breaker, etc.), to provide desired battery protection. The circuit breaker bracket  340  can include switch guards to inhibit accidental tripping of the circuit breaker. 
     As shown in  FIGS. 6 and 7 , the battery box  106  can include cable management brackets  342  and exit ports  344  for routing cables (e.g., battery cables, circuit breaker cables, etc.), out of the battery box  106 . The exit ports  344  may include industry standard liquid-tight-fittings (LTFs) sized to fit the cables exiting the battery box  106 . In the event the LTFs do not fully seal the exit port opening, adhesive silicone may be used to complete the seal. 
     The battery box  106  may include any suitable fasters for coupling the battery box  106  to the telecommunications equipment cabinet  100 , including but not limited to insulation studs  346 , internal frame mounting features  348 , external frame mounting features  350 , a cabinet mounting access panel  352 , a wind latch stud  354 , etc. 
     These mounting features can allow for mounting the battery box  106  to internal and/or external frames of the telecommunications equipment cabinet  100  (e.g., using machine bolts, etc.). Mounting of the battery box  106  to the telecommunications equipment cabinet  100  can improve the rigidity and structural integrity of the telecommunications equipment cabinet  100 , and the use of optional machine bolts allows for the battery box  106  to be disassembled from the telecommunications equipment cabinet  100 . 
     Referring back to  FIG. 8 , a NOMEX material  356  (e.g., a flame-resistant meta-aramid polymer material), may be affixed (e.g., via rivets) to an inside roof of the battery box  106  to inhibit (e.g., prevent) battery posts from coming in direct contact with sheet metal of the roof of the battery box  106 . 
     The roof of the battery box  106  may include one or more perforations  358 . The perforation(s)  358  can allow airflow between multiple battery boxes  106 . The perforation(s)  358  may be used to facilitate removal of hydrogen gas from multiple battery boxes  106 , to transfer heat out of multiple battery boxes  106 , etc. If more battery boxes  106  are desired, additional perforations  358  can be included between each battery box  106 . 
     In other embodiments, multiple battery boxes  106  may not include any perforation(s)  358 . In that case, each of the multiple battery boxes  106  may be isolated from each other battery box  106  to inhibit hydrogen gas from moving between multiple battery boxes  106 , to inhibit hydrogen gas escaping to the equipment chamber  104  if one of the multiple battery boxes  106  is removed from the telecommunications equipment cabinet  100 , etc. 
     As shown in  FIGS. 6 and 9 , a lower battery box  106  can be assembled onto internal and/or external frames of the telecommunications equipment cabinet  100 . The lower battery box  106  includes a mounting stud  354  for a door wind resistant bracket, and access panels  352  for providing access to locations where the telecommunications equipment cabinet  100  can be assembled to a concrete pad, installation frame, etc. 
     As shown in  FIGS. 9 and 10 , the upper battery box  106  can also assemble to internal and/or external frames of the telecommunications equipment cabinet  100 , and can incorporate a double floor  360  with reinforcement brackets  362  to support the batteries inside the battery box  106 . 
     In some embodiments, the battery box  106  may include mounting features for thermal insulation. For example,  FIG. 9  illustrates thermal insulation  364  positioned along the battery boxes  106 . Thermal insulation along the battery box  106  may be more desirable when a combination heat exchanger  108  and TEC  110  cooling system is used with the telecommunications equipment cabinet  100 , but less necessary when an air conditioner  216  cooling system is used with the telecommunications equipment cabinet  100 . 
       FIG. 11  illustrates an adhesive strip gasket  366  along the bottom panel  328  (e.g., a bottom surface) of the battery box  106 . The adhesive strip gasket can facilitate assembly of two battery boxes  106  to one another, provide a seal between two battery boxes  106 , etc. 
     The cabinet door  114  may include features that supplement (e.g., complete) isolation of the battery boxes  106  from the equipment chamber  104 , and provide an airflow (e.g., venting) rate sufficient to meet hydrogen outgassing requirements. As shown in  FIGS. 12 and 13 , an adhesive strip gasket  468  may be placed on an inside surface of the cabinet door  114 , to align with a perimeter of an opening of each battery box  106 . The adhesive strip gasket  468  may be also be used to seal the cabinet door  114 . 
     Although  FIGS. 12 and 13  illustrate an adhesive strip gasket  468  placed on an inside surface of the cabinet door  114  to align with a perimeter of an opening of each battery box  106 , other embodiments may not include an adhesive strip gasket  468  on the cabinet door  114 . In those cases, the cabinet door  114  may directly contact the perimeter of an opening of each battery box  106  to facilitate isolation of each battery box  106  from the equipment chamber  104 . 
     In other embodiments, the openings of the battery boxes  106  may contact a surface of the cabinet housing  102  other than the door. For example, openings of the battery boxes  106  may contact side walls, rear walls, etc. of the cabinet housing  102  to facilitate isolation of each battery box  106  from the equipment chamber  104 . 
     Referring again to  FIGS. 12 and 13 , when the battery boxes  106  are assembled in the telecommunications equipment cabinet  100 , the battery boxes  106  may have their front edges in alignment with the lead edges of the external frame of the telecommunications equipment cabinet  100 . When the cabinet door  114  is closed, the front edges of the battery boxes  106  can interface with the strip gasket  468  to effectively isolate (e.g., seal) the battery boxes  106  from the rest of the telecommunications equipment cabinet  100 . 
     As shown in  FIGS. 12 and 13 , an open area ventilation design is utilized to address the battery hydrogen outgassing requirement. Specifically, open area vents  470  are spaced apart from one another (e.g., as far apart vertically as possible). In some embodiments, a minimum open area size for each open area vent  470  may optionally be about a 1.375 inch diameter circle. 
     In the telecommunications equipment cabinet  100  including the heat exchanger  108  and TEC  110  cooling system, a lowest open area vent  470  may be positioned directly under the lower TEC  110  via rectangular slots  472  that exceed the required open area. Additional open area vents  470  can be positioned at higher (e.g., highest) points within the perimeters of the openings of the battery boxes  106 . Similar open area vent configurations can be used on the telecommunications equipment cabinet  200  including the air conditioner  216  cooling system. 
     Although  FIGS. 12 and 13  illustrate the vents  470  positioned on the cabinet door  114 , other embodiments may include vents positioned on other surfaces of the cabinet housing  102 . For example, vents may be positioned on a side wall of the cabinet housing  102 , a rear wall of the cabinet housing  102 , top or bottom panels of the cabinet housing  102 , etc. 
     The location of the vents can correspond to an orientation of battery boxes  106 . For example, if the battery boxes  106  have openings contacting a side wall of the cabinet housing  102 , the side wall of the cabinet housing  102  may include vents for venting hydrogen gas from the openings of the battery boxes  106 . In some cases, each battery box  106  may correspond to a distinct vent, to facilitate isolation of each battery box  106  from the other battery boxes  106  and the equipment chamber  104 . 
     In order to protect the telecommunications equipment cabinet  100  from unwanted water entry, the open area vents  470  can be positioned on an external side of the cabinet door  114  by water guards including plates  474  and/or shrouds  476 , that cover the open area vents  470  as shown in  FIGS. 14 and 15 . In some embodiments, the shrouds  476  on the outside of the cabinet door  114  may include perforations  478  to allow for airflow into the battery boxes  106 . 
     On the inside of the cabinet door  114 , drip pans  480  may be used to catch any water that enters through the open area vents  470 . The drip pans  480  may then drain the water back out of the front of the cabinet door  114  via drip tubes  482  that are incorporated into the drip pans  480 . 
     On an external side of the cabinet door  114 , angled air deflector plates  484  may be used utilized to direct warm return air from the TECs  110  away from the open area vents  470 . This inhibits (e.g., prevents) the warm return air from the TECs  110  from entering the telecommunications equipment cabinet  100 . 
     The battery boxes  106  can be designed work with both heat exchanger/TEC (HEX/TEC) cooling systems and air conditioner cooling systems, which can make the base cabinet (e.g., the telecommunications equipment cabinet  100  not including the cabinet door  114 ) essentially independent of the cooling system the end user decides to use. For example, different cabinet doors  114  may incorporate either a heat exchanger/TEC cooling system or an air conditioner system, and either cabinet door  114  could be used with the same base cabinet. This can help manage cabinet configuration requirements, reduce part number management, improve overall manufacturability of the telecommunications equipment cabinets, etc. 
       FIG. 16  illustrates an example embodiment of a telecommunications equipment cabinet  500  including an air conditioning cooling system  516  and two battery boxes  506 . Each battery box  506  houses one SAFT battery  586 . 
       FIG. 17  illustrates an example embodiment of a telecommunications equipment cabinet  600  including a HEX/TEC cooling system  688  and one battery box  606 . The battery box  606  houses a string of VRLA batteries  690 . 
     The telecommunications equipment cabinets described herein may be used in any suitable applications, such as telecommunications network electrical equipment cabinets, etc. The telecommunications equipment cabinets may have any suitable size (e.g., about 84 inches, etc.). 
     According to another example embodiment, a telecommunications equipment cabinet includes a cabinet housing having multiple vents, and at least one equipment chamber defined within the cabinet housing. The at least one equipment chamber has one or more electrical components disposed therein. 
     The telecommunications equipment cabinet also includes multiple battery boxes removably positioned in the cabinet housing, and each battery box includes at least one battery. Each battery box is vented through a distinct one of the multiple vents of the cabinet housing to inhibit hydrogen gas from escaping said battery box into the at least one equipment chamber. 
     Each vent may be positioned within the perimeter of the opening of the corresponding battery box from which the vent passes hydrogen gas. The cabinet housing may include a strip gasket corresponding to the perimeter of the opening of the battery box to seal the perimeter of the opening of the battery box. 
     In some embodiments, the cabinet housing includes a cabinet door, and the cabinet door contacts the perimeter of the opening when the cabinet door is in a closed position. The battery box may include multiple walls that are riveted or bolted together with seams between the multiple walls sealed with an adhesive silicone, the battery box may include multiple walls that are welded together, the battery box may include a one-piece die-cast box, etc. 
     According to another example embodiment, a method of exchanging components in a telecommunications equipment cabinet is disclosed. The telecommunications cabinet includes at least one equipment chamber defined within the cabinet housing and multiple battery boxes positioned in the cabinet housing. The at least one equipment chamber has one or more electrical components disposed therein. Each battery box includes at least one battery and is isolated from the at least one equipment chamber to inhibit hydrogen gas from escaping the battery box into the at least one equipment chamber. 
     The method includes removing one of the multiple battery boxes from the cabinet housing to define a space previously occupied by said one of the multiple battery boxes, and inserting another electrical component into the space previously occupied by said one of the multiple battery boxes while maintaining isolation between the inserted electrical component and the other battery box(es) remaining in the cabinet housing to inhibit hydrogen gas from escaping the other battery box(es) to the inserted electrical component. 
     In some embodiments, removing one of the multiple battery boxes includes removing one of the multiple battery boxes from the cabinet housing without moving any of the one or more electrical components disposed in the at least one equipment chamber. The cabinet housing may include an internal frame or an external frame. In those cases, removing one of the multiple battery boxes can include removing machine bolts to decouple said one of the multiple battery boxes from the internal frame or the external frame. 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.