Patent Publication Number: US-2007124529-A1

Title: Subrack with front and rear insertion of AMC modules

Description:
RELATED APPLICATION  
      Related subject matter is disclosed in U.S. patent application entitled “MONOLITHIC BACKPLANE HAVING A FIRST AND SECOND PORTION” having application Ser. No. ______ and filed on the same date herewith and assigned to the same assignee.  
     BACKGROUND OF INVENTION  
      The PCI Industrial Computer Manufacturers Group (PICMG®) Micro Telecommunications Architecture (MicroTCA™) defines the requirements for a system that uses PICMG Advanced Mezzanine Card (AMC) modules directly on a backplane (PICMG® MicroTCA.0 Draft 0.6—Micro Telecom Compute Architecture Base Specification). MicroTCA may serve as a platform for telecommunications and enterprise computer network equipment as well as consumer premises equipment. MicroTCA is complimentary to PICMG3 Advanced Telecommunications Computing Architecture (AdvancedTCA®, or PICMG3). While ATCA is optimized for high capacity, high performance applications, MicroTCA addresses cost-sensitive and physically smaller applications with lower capacity, performance and less-stringent availability requirements.  
      In the prior art MicroTCA systems, all modules are inserted from one side of the subrack or chassis (i.e. the front of the subrack), resulting in all input/output (I/O) forced to be from the front of the subrack. This has the disadvantage in that all I/O cabling is in the front of the subrack, which blocks maintenance personnel from easily accessing the subrack and creates a hazardous and cluttered area where many subracks are present.  
      There is a need, not met in the prior art, to have a MicroTCA subrack where modules may be inserted from the front and the rear and where rear I/O is available to allow better access and more efficient routing of external cables. Accordingly, there is a significant need for an apparatus that overcomes the deficiencies of the prior art outlined above. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Representative elements, operational features, applications and/or advantages of the present invention reside inter alia in the details of construction and operation as more fully hereafter depicted, described and claimed—reference being made to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout. Other elements, operational features, applications and/or advantages will become apparent in light of certain exemplary embodiments recited in the Detailed Description, wherein:  
       FIG. 1  representatively illustrates a prior art carrier card;  
       FIG. 2  representatively illustrates a prior art MicroTCA subrack;  
       FIG. 3  representatively illustrates a computer system in accordance with an exemplary embodiment of the present invention; and  
       FIG. 4  representatively illustrates another computer system in accordance with an exemplary embodiment of the present invention. 
    
    
      Elements in the Figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the Figures may be exaggerated relative to other elements to help improve understanding of various embodiments of the present invention. Furthermore, the terms “first”, “second”, and the like herein, if any, are used inter alia for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. Moreover, the terms “front”, “back”, “top”, “bottom”, “over”, “under”, and the like in the Description and/or in the Claims, if any, are generally employed for descriptive purposes and not necessarily for comprehensively describing exclusive relative position. Any of the preceding terms so used may be interchanged under appropriate circumstances such that various embodiments of the invention described herein may be capable of operation in other configurations and/or orientations than those explicitly illustrated or otherwise described.  
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
      The following representative descriptions of the present invention generally relate to exemplary embodiments and the inventor&#39;s conception of the best mode, and are not intended to limit the applicability or configuration of the invention in any way. Rather, the following description is intended to provide convenient illustrations for implementing various embodiments of the invention. As will become apparent, changes may be made in the function and/or arrangement of any of the elements described in the disclosed exemplary embodiments without departing from the spirit and scope of the invention.  
      For clarity of explanation, the embodiments of the present invention are presented, in part, as comprising individual functional blocks. The functions represented by these blocks may be provided through the use of either shared or dedicated hardware, including, but not limited to, hardware capable of executing software. The present invention is not limited to implementation by any particular set of elements, and the description herein is merely representational of one embodiment.  
      Software blocks that perform embodiments of the present invention can be part of computer program modules comprising computer instructions, such control algorithms that are stored in a computer-readable medium such as memory. Computer instructions can instruct processors to perform any methods described below. In other embodiments, additional modules could be provided as needed.  
      A detailed description of an exemplary application is provided as a specific enabling disclosure that may be generalized to any application of the disclosed system, device and method for a MicroTCA subrack in accordance with various embodiments of the present invention.  
       FIG. 1  representatively illustrates a prior art carrier card  102 . Conventional subrack-based, modular computer systems have slots for the insertion of payload cards that add functionality to the computer system. Payload cards are designed to plug direction into the backplane of a chassis. These payload cards may include processors, memory, storage devices, wireless communication modules, I/O ports, and the like. Carrier cards are payload cards that are designed to have one or more mezzanine cards plugged into them to add even more modular functionality to the computer system. Mezzanine cards are different from payload cards in that mezzanine cards are not coupled to physically connect directly with the backplane, whereas payload cards function to physically directly connect with the backplane.  
      For example, carrier card  102  may include a backplane connector  110  to interface with the backplane in a conventional subrack, modular computer system for instance an AdvancedTCA subrack as defined in the PICMG 3.0 AdvancedTCA specification. Carrier card  102  further includes connectors for coupling mezzanine cards to the carrier card  102 . Mezzanine cards can also add functionality to a computer system and may include central switching devices, processors, memory, storage devices, wireless communication modules, I/O ports, and the like. In the particular prior art example illustrated in  FIG. 1 , carrier card  102  includes Advanced Mezzanine Card (AMC) connector  106  for coupling an AMC module  104  to carrier card  102 . AMC module  104  may include one or more I/O ports  108  for providing an external link to carrier card  102  and the computer system to which carrier card  102  is coupled. The Advanced Mezzanine Card Base Specification (PICMG® AMC.0 RC1.1) defines the AMC module  104  that is coupled to the carrier card  102 . AMC modules  104  may lie parallel to and are integrated into carrier card  102  via AMC connector  106 .  
      AMC modules  104  can be single-width, double-width, full-height, half-height modules or any combination thereof as defined by the AMC specification. Carrier card  102  may be conventional, cutaway or hybrid carrier cards as defined in the AMC specification. AMC connector  106  may be a B connector, AB connector, basic connector, extended connector or any combination thereof. B connectors may be used with conventional carrier cards and support single layer and full-height AMC modules. AB connectors may be used on cutaway carrier cards and support a stacked configuration of two half-height AMC modules. All AMC connectors  106  use a card edge connection style, where conductive traces at the edge of the AMC module  104  printed circuit board (PCB) act as male pins, which mate to a female portion in the AMC connector  106 . A basic connector style is equipped to interface with an AMC module  104  having traces on one side of the PCB. An extended connector is equipped to interface with an AMC module  104  having traces on both sides of the PCB.  
       FIG. 2  representatively illustrates a prior art MicroTCA subrack  201 . Details on MicroTCA subrack design and configurations can be found in PICMG® MicroTCA.0 Draft 0.6—Micro Telecom Compute Architecture Base Specification. The prior art MicroTCA system is a collection of interconnected elements including at least one AMC module  204 , at least one virtual carrier manager (VCM)  203  and the interconnect, power, cooling and mechanical resources need to support them. A typical prior art MicroTCA system may consist of twelve AMC modules  204 , one (and optionally two for redundancy) virtual carrier managers  203  coupled to a backplane  205 , and a subrack  201 .  
      A VCM  203  acts as a virtual carrier card which emulates the requirements of the carrier card defined in the Advanced Mezzanine Card Base Specification (PICMG® AMC.0 RC1.1) to properly host AMC modules. Carrier card functional requirements include power delivery, interconnects, Intelligent Platform Management Interface (IPMI) management, and the like. VCM  203  combines the control and management infrastructure, interconnect fabric resources and the power control infrastructure for the AMC module(s)  204  into a single unit. VCM  203  comprises these common elements that are shared by all AMC modules  204  and is located on the backplane  205 , on one or more AMC modules, or a combination thereof.  
      In the prior art, all AMC modules  204  and the VCM  203  are inserted in the subrack  201  from the front face  202  to interface with only one side of the backplane as shown. No AMC modules  204  are inserted from the rear of the chassis or interface with the other side of the backplane  205 . Consequently, any I/O ports on the AMC modules  204  require external connections to be routed from the front face  202  of the subrack  201 . Although  FIG. 2  depicts a shelf implementation of a MicroTCA subrack, other prior art MicroTCA subracks (a cube implementation, and the like) are also limited to insertion of AMC modules though a single side (front) of the subrack and connection to a single side of the backplane.  
       FIG. 3  representatively illustrates a computer system  300  in accordance with an exemplary embodiment of the present invention. In the embodiment shown, subrack  301  includes a backplane  305  of a midplane type design having a first side  372  and a second side  374  opposite to each other, where AMC modules  304 ,  307  may be connected to both the first side  372  and the second side  374 .  
      For example, subrack  301  may have a front side  312  with one or more first slots  370  coupled to receive a first AMC module  304  inserted via the front side  312 , where the first AMC module  304  connects directly to the first side  372  of the backplane  305 . Subrack  301  may also have a rear side  314  with one or more second slots  371  coupled to receive a second AMC module  307  inserted via the rear side  314 , where second AMC module  307  connects directly to the second side  374  of the backplane  305 .  
      Subrack  301  is illustrated in plan view with first AMC module  304  and second AMC module  307  mounted horizontally. In an embodiment, the form factor of subrack  301  is 1U, where as known in the art, “U” and multiples of “U” can refer to the depth of a subrack or chassis. In an embodiment, “U” can measure approximately 1.75 inches. This is not limiting of the invention as subrack  301  may be orientated such that first AMC module  304  and second AMC module  307  may be mounted vertically or any combination of horizontally and vertically. Further, subrack  301  may have a form factor other than 1U and be within the scope of the invention, for example and without limitation, 3U, 6U and 9U.  
      The Advanced Mezzanine Card Base Specification (PICMG® AMC.0 RC1.1) defines AMC modules  304 ,  307 , which may add functionality to a computer system  300  and may include central switching devices, processors, memory, storage devices, wireless communication modules, I/O ports, and the like. First AMC module  304  and second AMC module  307  can be single-width, double-width, full-height, half-height modules or any combination thereof as defined by the AMC specification. AMC modules  304 ,  307  are not payload modules, but instead are mezzanine modules, particularly AMC modules, that connect directly to the backplane  305 . This differentiates computer system  300  and subrack  301  from other conventional midplane designs where typical payload cards connect to a backplane.  
      In an embodiment, an AMC connector  306  at each of first slot  370  and second slot  371  is coupled to directly connect the first AMC module  304  and the second AMC module  307  to the first side  372  and the second side  374  of the backplane  305  respectively. AMC connector  306  may be a B connector, AB connector, basic connector, extended connector or any combination thereof, where the types of AMC connectors  306  are defined in the AMC specification and the MicroTCA specification. AMC connectors  306  may use a card edge connection style, where conductive traces at the edge of the AMC module  304 ,  307  printed circuit board (PCB) act as male pins, which mate to a female portion in the AMC connector  306 . A basic AMC connector style is equipped to interface with an AMC module  304 ,  307  having traces on one side of the PCB. An extended AMC connector style is equipped to interface with an AMC module  304 ,  307  having traces on both sides of the PCB. AMC connector  306  may include both the basic AMC connector style and the extended AMC connector style.  
      In an embodiment, computer system  300  includes virtual carrier manager (VCM)  303 . In subrack  301 , a VCM  303  acts as a virtual carrier card which emulates the requirements of the carrier card defined in the Advanced Mezzanine Card Base Specification (PICMG® AMC.0 RC1.1) to properly host AMC modules  304 ,  307 . Carrier card functional requirements include power delivery, interconnects, Intelligent Platform Management Interface (IPMI) management, and the like. VCM  303  may combine the control and management infrastructure, interconnect fabric resources and the power control infrastructure for the AMC module(s)  304 ,  307  into a single unit. VCM  303  comprises these common elements that are shared by all AMC modules  304 ,  307  and may be on the backplane  305 , on one or more AMC modules  304 ,  307 , or a combination thereof. Although VCM  303  is depicted on both an AMC module and on the backplane, this is not limiting of the invention. VCM  303  may be situated on the backplane  305 , on one or more AMC modules  304 ,  307 , or a combination thereof.  
      In an embodiment, VCM  303  includes control management function  366 , which acts as a central authority in a computer system  300  by monitoring and controlling AMC modules  304 ,  307 . In an embodiment, computer system  300  with VCM  303  is a MicroTCA computer system and subrack  301  is a MicroTCA subrack. The control management function  366  may make use of Intelligent Platform Management Interface (IPMI) links to each AMC module  304 ,  307 , as well as presence detect, enable and geographic address signals. The control and management function  366  may also include the common overhead functions of clock distribution and test support. In an embodiment, three clock signals may be distributed to each AMC module  304 ,  307  from each VCM  303  in order to provide network grade synchronization to computer system  300 . A set of JTAG test pins permit advanced testing of complete computer system  300 , as well as individual elements.  
      In an embodiment, VCM  303  includes central switching function  364 , such that a switched fabric  350  provides the main connectivity among the AMC modules  304 ,  307  in a computer system. This switched fabric  350  includes a central switch and a number of high speed serial lanes radiating to each slot and hence to each AMC module  304 ,  307 . Lanes may be half duplex, differential high speed serial interconnects, with bandwidth capacities of at least 3.125 Gb/s. In another embodiment, these bit rates may be up to and beyond 10 Gb/s per lane. The central switching function  364  of VCM  303  is the hub of a star or a dual star network. In another embodiment, there may be supplementary paths directly from each AMC module  304 ,  307  to other AMC modules  304 ,  307  permitting the construction of supplemental mesh interconnects in addition to the star or dual star configurations. Clocking may be provided for the entire computer system  300  by a synchronization subcircuit on the VCM  303 . It has the ability to receive a reference clock from one of the AMC modules  304 ,  307  it manages, use it to create a set of master synchronization clocks, and distribute these clocks across the backplane  305  to the AMC modules  304 ,  307 .  
      In an embodiment, switched fabric  350  may be implemented by using one or more of a plurality of switched fabric network standards, for example and without limitation, InfiniBand™, Advanced Switching, Serial RapidIO™, FibreChannel™, Ethernet™, Gigabit Ethernet, PCI Express™, Hypertransport™, and the like. Switched fabric  350  is not limited to the use of these switched fabric network standards and the use of any switched fabric network standard is within the scope of the invention.  
      In an embodiment, VCM  303  includes power control function  362 , which may function to supply and control the power to the AMC modules  304 ,  307 . In an embodiment, a single 12V main power feed is routed to each AMC module  304 ,  307 . The power infrastructure may take its supply bus (either 48V nominal, or AC mains) and convert it to one 12V distribution conductor to provide a radial payload power port to each AMC module  304 ,  307 . Management power for all AMC modules  304 ,  307  may also be supplied by the power control function  362 , which may also perform sequencing, protection and isolation functions.  
      In an embodiment, second AMC module  307  inserted via the rear side  314  of subrack  301  and connected to the second side  374  of backplane  305  may comprise an I/O port  354  to provide an external link  352  from subrack  301  and computer system  300 . I/O port  354  and external link  352  may be coupled to extend switched fabric  350  outside of subrack  301 , to facilitate transfer of data to/from computer system  300 , and the like. In an embodiment, AMC modules  304  inserted via the front side  312  and connected to the first side  372  of backplane  305  may omit an I/O port and external link. In these embodiments, cabling associated with external link  352  may be run from the rear side  314  of subrack  301 , thereby freeing up valuable space on the front side  312  and facilitating safer and more efficient routing of cables to/from subrack  301 .  
       FIG. 4  representatively illustrates another computer system  400  in accordance with an exemplary embodiment of the present invention. In the embodiment shown, subrack  401  includes a monolithic backplane  405  having a first portion  482  and a second portion  484 , where the first portion  482  runs substantially along a front side  412  of the subrack  401  and the second portion  484  runs substantially along the rear side  414  of the subrack  401 . The first portion  482  and the second portion  484  of monolithic backplane  405  are monolithic, meaning they form one unitary and functional backplane, but are not linearly aligned or linearly continuous as shown in  FIG. 4 . The first portion  482  and the second portion  484  are linearly discontinuous over the length of the subrack  401 . In another embodiment, first portion  482  and second portion  484  may be linearly discontinuous over the height of subrack  401 , or linearly discontinuous over both the length and height of subrack  401 . AMC modules  404 ,  407  may be connected to both the first portion  482  and the second portion  484 .  
      In an embodiment, subrack  401  may have a front side  412  with one or more first slots  470  coupled to receive a first AMC module  404  inserted via the front side  412 , where the first AMC module  404  connects directly to the second portion  484  of monolithic backplane  405 . Subrack  401  may also have a rear side  414  with one or more second slots  471  coupled to receive a second AMC module  407  inserted via the rear side  414 , where second AMC module  407  connects directly to the first portion  482  of monolithic backplane  405 .  
      Subrack  401  is illustrated in plan view with first AMC module  404  and second AMC module  407  mounted horizontally. In an embodiment, the form factor of subrack  401  is 1U, where as known in the art, “U” and multiples of “U” can refer to the depth of a subrack or chassis. In an embodiment, “U” can measure approximately 1.75 inches. This is not limiting of the invention as subrack  401  may be orientated such that first AMC module  404  and second AMC module  407  may be mounted vertically or any combination of horizontally and vertically. Further, subrack  401  may have a form factor other than 1U and be within the scope of the invention, for example and without limitation, 3U, 6U and 9U.  
      The Advanced Mezzanine Card Base Specification (PICMG® AMC.0 RC1.1) defines AMC modules  404 ,  407 , which may add functionality to a computer system  400  and may include central switching devices, processors, memory, storage devices, wireless communication modules, I/O ports, and the like. First AMC module  404  and second AMC module  407  can be single-width, double-width, full-height, half-height modules or any combination thereof as defined by the AMC specification. AMC modules  404 ,  407  are not payload modules, but instead are mezzanine modules, particularly AMC modules, that connect directly to the monolithic backplane  405 . This differentiates computer system  400  and subrack  401  from other conventional midplane designs where typical payload cards connect to a backplane.  
      In an embodiment, an AMC connector  406  at each of first slot  470  and second slot  471  is coupled to directly connect the first AMC module  404  and the second AMC module  407  to the first portion  482  and the second portion  484  of the monolithic backplane  405  respectively. AMC connector  406  may be a B connector, AB connector, basic connector, extended connector or any combination thereof, where the types of AMC connectors  406  are defined in the AMC specification and the MicroTCA specification. AMC connectors  406  may use a card edge connection style, where conductive traces at the edge of the AMC module  404 ,  407  printed circuit board (PCB) act as male pins, which mate to a female portion in the AMC connector  406 . A basic AMC connector style is equipped to interface with an AMC module  404 ,  407  having traces on one side of the PCB. An extended AMC connector style is equipped to interface with an AMC module  404 ,  407  having traces on both sides of the PCB. AMC connector  406  may include both the basic AMC connector style and the extended AMC connector style.  
      In an embodiment, computer system  400  includes virtual carrier manager (VCM)  403 . In subrack  401 , a VCM  403  acts as a virtual carrier card which emulates the requirements of the carrier card defined in the Advanced Mezzanine Card Base Specification (PICMG® AMC.0 RC1.1) to properly host AMC modules  404 ,  407 . Carrier card functional requirements include power delivery, interconnects, Intelligent Platform Management Interface (IPMI) management, and the like. VCM  403  may combine the control and management infrastructure, interconnect fabric resources and the power control infrastructure for the AMC module(s)  404 ,  407  into a single unit. VCM  403  comprises these common elements that are shared by all AMC modules  404 ,  407  and may be on the monolithic backplane  405 , on one or more AMC modules  404 ,  407 , or a combination thereof. Although VCM  403  is depicted on both an AMC module and on the backplane, this is not limiting of the invention. VCM  403  may be situated on the backplane  405 , on one or more AMC modules  404 ,  407 , or a combination thereof.  
      In an embodiment, VCM  403  includes control management function  466 , which acts as a central authority in a computer system  400  by monitoring and controlling AMC modules  404 ,  407 . In an embodiment, computer system  400  with VCM  403  is a MicroTCA computer system and subrack  401  is a MicroTCA subrack. The control management function  466  may make use of Intelligent Platform Management Interface (IPMI) links to each AMC module  404 ,  407 , as well as presence detect, enable and geographic address signals. The control and management function  466  may also include the common overhead functions of clock distribution and test support. In an embodiment, three clock signals may be distributed to each AMC module  404 ,  407  from each VCM  403  in order to provide network grade synchronization to computer system  400 . A set of JTAG test pins permit advanced testing of complete computer system  400 , as well as individual elements.  
      In an embodiment, VCM  403  includes central switching function  464 , such that a switched fabric  450  provides the main connectivity among the AMC modules  404 ,  407  in a computer system. This switched fabric  450  includes a central switch and a number of high speed serial lanes radiating to each slot and hence to each AMC module  404 ,  407 . Lanes may be half duplex, differential high speed serial interconnects, with bandwidth capacities of at least 3.125 Gb/s. In another embodiment, these bit rates may be up to and beyond 10 Gb/s per lane. The central switching function  464  of VCM  403  is the hub of a star or a dual star network. In another embodiment, there may be supplementary paths directly from each AMC module  404 ,  407  to other AMC modules  404 ,  407  permitting the construction of supplemental mesh interconnects in addition to the star or dual star configurations. Clocking may be provided for the entire computer system  400  by a synchronization subcircuit on the VCM  403 . It has the ability to receive a reference clock from one of the AMC modules  404 ,  407  it manages, use it to create a set of master synchronization clocks, and distribute these clocks across the monolithic backplane  405  to the AMC modules  404 ,  407 .  
      In an embodiment, switched fabric  450  may be implemented by using one or more of a plurality of switched fabric network standards, for example and without limitation, lnfiniBand™, Advanced Switching, Serial RapidlO™, FibreChannel™, Ethernet™, Gigabit Ethernet, PCI Express™, Hypertransport™, and the like. Switched fabric  450  is not limited to the use of these switched fabric network standards and the use of any switched fabric network standard is within the scope of the invention.  
      In an embodiment, VCM  403  includes power control function  462 , which may function to supply and control the power to the AMC modules  404 ,  407 . In an embodiment, a single 12V main power feed is routed to each AMC module  404 ,  407 . The power infrastructure may take its supply bus (either 48V nominal, or AC mains) and convert it to one 12V distribution conductor to provide a radial payload power port to each AMC module  404 ,  407 . Management power for all AMC modules  404 ,  407  may also be supplied by the power control function  462 , which may also perform sequencing, protection and isolation functions.  
      In an embodiment, second AMC modules  407  inserted via the rear side  414  of subrack  401  and connected to the first portion  482  of monolithic backplane  405  may comprise an I/O port  454  to provide an external link  452  from subrack  401  and computer system  400 . I/O port  454  and external link  452  may be coupled to extend switched fabric  450  outside of subrack  401 , to facilitate transfer of data to/from computer system  400 , and the like. In an embodiment, AMC modules  404  inserted via the front side  412  and connected to the second side  484  of monolithic backplane  405  may omit an I/O port and external link. In these embodiments, cabling associated with external link  452  may be run from the rear side  414  of subrack  401 , thereby freeing up valuable space on the front side  412  and facilitating safer and more efficient routing of cables to/from subrack  401 .  
      In the foregoing specification, the invention has been described with reference to specific exemplary embodiments; however, it will be appreciated that various modifications and changes may be made without departing from the scope of the present invention as set forth in the claims below. The specification and figures are to be regarded in an illustrative manner, rather than a restrictive one and all such modifications are intended to be included within the scope of the present invention. Accordingly, the scope of the invention should be determined by the claims appended hereto and their legal equivalents rather than by merely the examples described above.  
      For example, the steps recited in any method or process claims may be executed in any order and are not limited to the specific order presented in the claims. Additionally, the components and/or elements recited in any apparatus claims may be assembled or otherwise operationally configured in a variety of permutations to produce substantially the same result as the present invention and are accordingly not limited to the specific configuration recited in the claims.  
      Benefits, other advantages and solutions to problems have been described above with regard to particular embodiments; however, any benefit, advantage, solution to problem or any element that may cause any particular benefit, advantage or solution to occur or to become more pronounced are not to be construed as critical, required or essential features or components of any or all the claims.  
      As used herein, the terms “comprise”, “comprises”, “comprising”, “having”, “including”, “includes” or any variation thereof, are intended to reference a non-exclusive inclusion, such that a process, method, article, composition or apparatus that comprises a list of elements does not include only those elements recited, but may also include other elements not expressly listed or inherent to such process, method, article, composition or apparatus. Other combinations and/or modifications of the above-described structures, arrangements, applications, proportions, elements, materials or components used in the practice of the present invention, in addition to those not specifically recited, may be varied or otherwise particularly adapted to specific environments, manufacturing specifications, design parameters or other operating requirements without departing from the general principles of the same.