Abstract:
A function generator is introduced into a stack light in the form of a compatible modular element that fits between the base and a light module. By centralizing the operation of the function generator, fewer components must be separately stocked and a cost savings may be realized through the centralized function generator.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to “stack lights”, a visual display used to convey operation and warning information in an industrial environment and, in particular, to a stack light that includes a modular power converter serving to greatly reduce the number of stocked components needed to provide different stack light configurations. 
         [0002]    Stack lights provide a short tower of different colored lamps, such as may be attached to, or placed in close proximity to, operating industrial equipment to provide a visible indication of the equipment operating status. The tower structure ensures good visibility of the beacon lights over a range of angles and locations in the operating environment. Different colors of the lights allow multiple types of information to be communicated at a distance in a possibly noisy environment. For example, a red light may indicate a machine failure or emergency, a yellow light may indicate a warning such as over-temperature or over-pressure and green may indicate machine operation, etc. 
         [0003]    Stack lights are typically constructed of modular components that may be flexibly interconnected to produce stack lights with different colors, color order and stack heights. Beacon modules, each providing a single color lamp, may be stacked one on top of another, the bottom beacon module supported on a modular base unit. 
         [0004]    Each beacon module includes an electric light source (for example an incandescent or LED assembly) held within a transparent housing, for example a cylindrical tube of colored plastic, through which the light source may be viewed. Upper and lower mechanical connectors on each beacon module allow the beacon modules to be joined into the tower described above. Each beacon module also includes an upper and lower mechanical connector and internal electrical conductors that communicate electrical signals from the bottom of the module to its top. The connectors and conductors operate so that when the beacon modules are assembled together, electrical continuity is established along the height of the tower between the base and the various modules without the need for separate wiring operations. 
         [0005]    As noted the multiple beacon modules are supported on a lower base module. The base module may provide a wire terminal block receiving electrical wiring from an externally switched power source intended to control the lighting of the different beacon modules. The externally switched power source may, for example, be provided by an I/O module or other programmable industrial control unit. Important status information developed during the execution of a control program on the industrial control unit may be relayed to the stack light through the I/O module for display to human operators. 
         [0006]    In normal wiring practices, the base module of the stack light receives a power “common” together with multiple “signal lines” each identified to one of the different beacon modules. A given beacon module is turned on when its corresponding signal line is energized. The electrical continuity as established by the electrical connector and conductor system of the beacon modules, described above, routes each signal line from the base module to a single beacon module input. 
         [0007]    The usefulness and popularity of stack lights has led to a wide variety of configurations of the basic stack light components. As a starting point, the modular components may be offered in different tower diameters (e.g. 30 mm, 40 mm, 50 mm, 60 mm, 70 mm and 100 mm). In each of these diameter classes, a variety of different base modules are normally offered to permit mounting of the tower to different surfaces, for example to a horizontal surface to extend upward therefrom or to the side of a vertical wall or the like. Different base heights are also normally provided as well as different mechanical attachment structures. Also in each diameter class, the beacon module may be offered in different colors (e.g. green, red, amber, blue, clear, and yellow), with different lamp types (LED/incandescent/strobe), different function capabilities (e.g. flashing, rotation) and power supply requirements (12 V. 24 V, 120 V, 250 volt, AC or DC). 
         [0008]    While modularity of the stack light instruction is intended to provide a customer with the ability to rapidly fabricate a wide variety of different stack light types out of readily available (stocked) components, the large number of component variations can undercut this goal by leading to an impractically large number of different modules. For example, in order to provide the customer with each of the choices described above, with colors, voltages, dimensions etc., many hundreds of different types of pre-manufactured modules may be necessary. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention provides a modular function generator providing flashing and other animation effects to stack light beacons. Providing the function generator in a freestanding module, separate from the base or beacon modules which it controls, reduces the number of variations of bases and/or beacon modules that must be stocked to obtain a full range of functions and further permits functions to be synchronized among multiple beacon modules. When multiple beacon modules need function affects, centralized function circuitry reduces costs. Power for centralized function modules may be obtained by scavenging power from various control signals. The centralized function module may be combined with a centralized voltage converter to obtain additional advantages in reduced cost and in reducing the variety of stocked components. 
         [0010]    Specifically then, the present invention provides a function generator for use in a stack light of the type providing a set of beacon modules interlocking to each other and to a base unit by means of interlocking mechanical connectors and interfitting electrical connectors positioned at a top and bottom of each beacon module and at a top of the base unit together allowing multiple beacon modules and one base to be mechanically and electrically assembled into a tower with electrical communication between the base and each beacon module. The function generator includes housing having first and second mechanical connectors positioned at a top and bottom of the housing and adapted to releasably interlock with corresponding mechanical connectors of beacon modules and a base. The top and bottom of the housing also provide first and second electrical connectors adapted to releasably interface with corresponding electrical connectors of beacon modules and a base. A function generation circuit is positioned within the housing to receive electrical power from the second electrical connector and to generate a time-modulation signal to provide time-modulated electrical power to the first electrical connector based on that time-modulated signal. 
         [0011]    It is thus a feature of at least one embodiment of the invention to segregate the functional capabilities of the stack light into a centralized modular component eliminating or reducing the proliferation of different stack light components necessary to provide a range of functions (or no function). 
         [0012]    The function generator may include an oscillator providing a time reference for the time-modulation signal. 
         [0013]    It is thus a feature of at least one embodiment of the invention to reduce stack light costs by sharing a common time source. 
         [0014]    The function generator may include a switch communicating with the function generator circuit to change the time-modulated signal. 
         [0015]    It is thus a feature of at least one embodiment to leverage a centralization of function generation to provide a more sophisticated multi-modulation unit having switch selectivity. 
         [0016]    The time-modulated electrical power may be provided to multiple different conductors of the first electrical connector adapted to communicate with different beacon modules and the switch may select which of the different electrical connectors receive modulated electrical power based on the time-modulated signal. 
         [0017]    It is thus a feature of at least one embodiment of the invention to provide centralization of function generation capabilities while still allowing individual selection of functions on individual beacons. 
         [0018]    The time-modulation signal may provide synchronized modulation to the different conductors of the first electrical connector. 
         [0019]    It is thus a feature of at least one embodiment of the invention to permit synchronization among generated functions across beacons for additional visual impact. 
         [0020]    The time-modulation signal may provide synchronized different modulation to the different conductors of the first electrical connector. 
         [0021]    It is thus a feature of at least one embodiment of the invention to provide for sophisticated modulation techniques such as flashing that proceeds through the beacons in order, either with equal flash on times or “stacked” flash times where the beacons have different on times and the same off time. 
         [0022]    The housing may further include a power conversion circuit positioned within the housing and receiving electrical power from the second electrical connector having a parameter of at least one of voltage and mode to provide converted power to the function generator circuit for generation of the time-modulated electrical power. 
         [0023]    It is thus a feature of at least one embodiment of the invention to permit the generation of power for the function generator as derived from the signal lines received by the stack light. 
         [0024]    The first and second electrical connectors may be of a same connector type such as would permit inter-engagement of the separated first and second electrical connectors and the first and second mechanical connectors are of a same connector type such as would permit entry engagement of the separated first and second mechanical connectors. 
         [0025]    It is thus a feature of at least one embodiment of the invention to provide a modular function generator conforming to the order-free connect system of a conventional stack light so as to permit the power converter to be integrated into an existing stack light systems when function generation is desired or omitted from a given stack light system when function generation is not required. 
         [0026]    The housing may be substantially cylindrical and have a diameter substantially between 30 and 100 mm. 
         [0027]    It is thus a feature of at least one embodiment of the invention to provide a function generator that visually integrates into conventional stack light towers. 
         [0028]    The housing may be substantially opaque and electrically insulating. 
         [0029]    It is thus a feature of at least one embodiment of the invention to provide function generation separate from the beacon modules where issues of light transmission would limit circuitry options. 
         [0030]    The power conversion circuit may receive signal lines from the second electrical connector and provide a source of electrical power derived from the signal lines to the function circuitry of the power conversion circuit, the function circuitry further modulating power on at least one signal line provided to the first electrical connector. 
         [0031]    It is thus a feature of at least one embodiment of the invention to permit a centralized function generator without the presence of a consistent power signal received by the stack light. 
         [0032]    These particular features and advantages may apply to only some embodiments falling within the claims and thus do not define the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]      FIG. 1  is a perspective view of a stack light assembled of several beacon modules, a power-converter/function module and a base module, juxtaposed with alternative unassembled modules; 
           [0034]      FIG. 2  is a fragmentary, exploded, elevational cross-section of the stack light of  FIG. 1  showing mechanical and electrical connection of the various modules; 
           [0035]      FIG. 3  is a schematic representation of the circuitry of  FIG. 2  showing principal functional blocks of the power-converter/function module including a power converter circuit and modulation function circuit; 
           [0036]      FIG. 4  is a detailed block diagram of the function module of  FIG. 3  including a timing state machine and AND-gate modulator; 
           [0037]      FIGS. 5   a  and  5   b  are timing diagrams of the outputs of the timing state machine of  FIG. 4  for two modes of operation in which lamps from different beacon modules are synchronized; and 
           [0038]      FIG. 6  is a schematic similar to that of  FIG. 3  showing an alternative configuration power converter circuit with direct power supply access. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0039]    Referring now to  FIG. 1 , a stack light  10  constructed according to the present invention may be assembled of multiple interlocking beacon modules  12   a ,  12   b ,  12   c , a power-converter/function module  14 , and a base module  16 . 
         [0040]    In one embodiment, the lowest most element of the base module  16  may provide a lower flange  19  having one or more openings  20  for receiving machine screws  22  or the like to fasten the flange  19  and hence the base module  16  to a surface  24  of a machine or the like. Alternative base module  16 ′ and  16 ″ may provide for different flanges  19 ′ and  19 ″ respectively (for example for mounting the vertical surfaces) or for accommodating different base constructions. 
         [0041]    The upper surface of the base module  16  may expose a centered electrical connectors  26  (visible in  FIG. 1  only on base module  16 ′ and  16 ″) that may be received by a corresponding electrical connector  26  (not visible in  FIG. 1 ) on the lower surfaces of each of the beacon modules  12 , power-converter/function module  14  and audio alarm module  18 . Similar connectors  26  exist on the upper surface of each of the other modules the beacon modules  12 , and power-converter/function module  14  (visible in  FIG. 1  only on beacon module  12 ). Inter-engagement of these electrical connectors  26  in the assembled stack light  10  provide electrical communication between each of the base module  16  beacon modules  12 , power-converter/function module  14  and audio alarm module  18  as will be described. 
         [0042]    The upper end of the base module  16  also provides a portion of a mechanical interlocking system in the form of radially extending tabs  28  (visible in  FIG. 1  only on base module  16 ′ and  1   6 ″). These radially extending tabs  28  may be received by a second portion of the mechanical interlocking system in the form of twist type bayonet rings  30  rotatably affixed to the lower surfaces of each of the beacon modules  12 , and power-converter/function module  14 . Such bayonet rings  30 , as generally understood in the art, provide features on their inner diameter that may capture the radially extending tabs  28  against a helical flange in the manner of inter-engaging threads while providing a slight pocket at the end of rotation forming a detent that locks the tabs  28  and bayonet rings  30  into predetermined compression, 
         [0043]    Similar radially extending tabs  28  exist at the upper end of each of the other modules the beacon modules  12 , power-converter/function module  14  and audio alarm module  18  (visible in  FIG. 1  only on beacon module  12 ′). Inter-engagement of these tabs  28  and bayonet rings of other modules in the assembled stack light  10  provide permit mechanical interconnection between any of the base module  16 , the beacon modules  12 , and the power-converter/function module  14  into the stack light  10 . 
         [0044]    As assembled the base module  16 , the beacon modules  12 , the power-converter/function module  14  and the audio alarm module  18  provide a tower extending generally upward from the base module  16  through power-converter/function module  14 , then through one or more beacon modules  12  each of which may independently controlled to display a predetermined color illumination. 
         [0045]    As depicted in  FIG. 1 , the tower may be capped by a plastic dome  17  also having a bayonet ring  30  but no electrical connector  26 . Alternatively, an audio alarm module  18  operating in a manner similar to that of the beacon modules  12  but providing an audible alarm through sound ports  21  rather than an illuminated signal may replace the final beacon module  12   c . Like the other modules, the audio alarm module  18  may include a bayonet ring  30  on its lower end for attachment to a lower module, and an electrical connector  26  on its lower surface for electrical interconnection to an earlier lower module. Desirably, the audio alarm module  18  may have a dome top without a connector  26  or tabs  28  on its top surface for attachment to later modules, thereby providing a finished appearance to the top of the tower. 
         [0046]    Referring now to  FIG. 2 , base module  16  may provide a housing  32 , for example, constructed of electrically insulating and opaque thermoplastic. The housing  32  may provide a cylindrical periphery in diameter generally matching the diameter of corresponding housings of the beacon modules  12 , power-converter/function module  14  and audio alarm module  18 . Standard diameters for stack lights  10  include 30 mm, 40 mm, 50 mm, 60 mm, 70 mm and 100 mm. 
         [0047]    A terminal block  34  may be positioned within the housing  32  of the base module  16 , for example, providing screw terminals, to receive conductors  36  from a remote switching device as will be discussed below. Each of the conductors  36 , when attached to the terminal block  34 , will be routed to the electrical connector  26   a  exposed at an upper surface of the base module  16 . This electrical connector  26   a  receives a downwardly extending connector  26   b  from power-converter/function module  14  when it is connected to base module  16 . Electrical connectors  26   a  and  26   b , for example, may be male and female versions of the same connector to be mechanically inter-engageable or may be identical connector reoriented as in the case of hermaphrodite connector systems. 
         [0048]    For simplicity, the electrical connectors  26   a  and  26   b  (and all connectors  26  in  FIG. 2 ) are depicted with only four conductive inserts  42  (for example, conductive pins or sockets) or which may each receive a separate conductor  36 . As is understood in the art, each conductive insert  40  provides an electrically independent conductive paths within mating electrical connectors  26 . 
         [0049]    As noted, the upper edge of the base module  16  provides for radially extending tabs  28  that may be received by a bayonet ring  30  rotatably attached to the bottom of power-converter/function module  14 . In this way the base module  16  may be electrically and mechanically attached to the power-converter/functional module  14  with connectors  26   a  and  26   b  joined. An O-ring seal  44  may be provided at the junction between the upper surface of base module  16  and the lower surface of power-converter/function module  14  to reduce the ingress of environmental contamination when the two are connected. 
         [0050]    Referring still to  FIG. 2 , power-converter/function module  14  may provide for a opaque housing  48  supporting at its upper surface connector  26   c  being substantially identical connector  26   a  and exposed to receive a connector  26   d  when beacon module  12   a  is attached to the upper surface of the power-converter/function module  14 . As described above this connection may be by means of radially extending tabs  28  at the upper edge of power-converter/function module  14  received by a corresponding bayonet ring  30  of beacon module  12   a.    
         [0051]    As will be discussed in greater detail below, power-converter/function module  14  includes power converter/function circuitry  56  that receives electrical power from connector  26   b  to convert this electrical power into a backbone voltage for use with the later beacon modules  12  and audio alarm module  18 . In this way beacon modules  12  and audio alarm modules  18  having common voltage parameters (e.g. the same voltage and the same voltage mode of either AC or DC) can be used with stack lights  10  receiving any operating voltage. Power converter/function circuitry  56  further provides for the ability to impose modulation functions such as lamp flashing or module sequencing on the later beacon modules  12  and audio alarm module  18  by modulating the power received by those modules. This eliminates the need for those modules to each include circuitry for modulation functions. 
         [0052]    In various configurations that will be discussed below, the power converter/function circuitry  56  will receive operating electrical power and multiple signal lines through electrical connector  26   b  as derived from conductors  36 . From this, the power converter/function circuitry  56  establishes a backbone ground reference on “common” conductor  68  and multiple signal voltages for control of beacon modules  12  or audio alarm module  18  on conductors  75   a - 75   c  (typically up to seven conductors although only three are shown for clarity in this example). The common conductor  68  and signal conductors  75  are connected to electrical connector  26   c , for example, as depicted in right to left order of signal conductors  75   a ,  75   b ,  75   c  and common conductor  68 . 
         [0053]    Referring still the  FIG. 2 , connector  26   d  in subsequent beacon module  12   b , may connect to connector  26   c  and may be attached, for example, to a printed circuit board  60  carrying on it multiple light emitting diodes (LEDs)  62 . As shown, LEDs  62  are connected between common conductor  68  and signal conductor  75   a  occupying the extreme left and right positions of the connector  26   d . Accordingly power on signal conductor  75   a  will energize the LEDs  62  of beacon module  12   b  so that the light may be viewed through transparent housing  63 . The housing  63  may have a tint to provide a desired light color and/or the LEDs  62  may be selected for a desired color. 
         [0054]    Although the LEDs  62  are shown connected in parallel, series connections are also possible. Current sharing resistances for each LED  62  have been omitted for clarity. 
         [0055]    The upper edge of the circuit board  60  may communicate with connector  26   e  being identical to connector  26   c  and  26   b . Circuit traces on a printed circuit board  60  provide common conductor  68  join an identical location of connectors  26   d  and  26   e  (in the leftmost position as shown in  FIG. 1 ). Signal conductor  75   a  used to control the LEDs  62  of beacon module  12   a  does not pass to connector  26   e , however, and signal conductors  75   b  and  75   c  are shifted one connector position to the right so that signal conductor  75   b  is now at the rightmost conductive insert  42  of connector  26   e.    
         [0056]    It will be understood then that beacon module  12   b  being constructed of electrically and mechanically identical to beacon module  12   a  may then be attached to beacon module  12   a  in the same way that beacon module  12   a  was attach the power-converter/function module  14  and that signal conductor  54   b  will now be connected to its LEDs  62 . 
         [0057]    The system illustrated for beacon module  12   a  and beacon module  12   b  may be continued to beacon module  12   c  (not depicted in  FIG. 2 ) so that signal conductors  75   a ,  75   b , and  75   c  will control the first second and third beacon modules  12  according to their order in the stack and in a manner indifferent to the exact beacon module  12  and without the need for adjustment of the internal wiring of the beacon modules  12   a  or the setting of internal addresses or the like. The number of conductive inserts  42  in the connector  26  and signal conductors  75  determine the limit of the number of modules  12  may be stacked in this manner. 
         [0058]    Referring now to  FIG. 3 , in a first wiring mode of the stack light  10 , conductors  36  received by the base module  16  do not provide to the base module  16  direct connections to an external power supply  67  that provides the operating voltage of the stack light  10 . This external power supply  67  is normally provided by a customer and may vary in voltage between 12 and 240 V (e.g. 12 V 24 V 120 V 240 V) and may be either AC or DC voltage (termed herein the power supply “mode”). In this wiring mode, the base module  16  receives only a power supply common  52  and multiple switched signal lines  54   a - 54   c  representing power from the external power supply  67  only after it has been switched by external switch system  64 . The external switch system  64  may be, for example, relays or programmable logic controller I/O module referenced through a power supply  67  to the common  52 . 
         [0059]    In this embodiment, the power power-converter/function module  14  taps the signal conductors  54  to obtain power for its operation when it least one signal conductor  54  is active. This may be done by attaching a full wave rectifier  66  between each the signal conductors  54  and a common DC bus input line  71 . Each full wave rectifier  66  is /configured to steer either DC or AC current is applied to the signal conductors  54  independently from any of the signal conductors  54  to a filter capacitor  70  reference to a backbone common  68  while preventing crosstalk between signal conductors  54 . 
         [0060]    The filter capacitor  70  is made therefore provide a source of DC voltage regardless of whether AC or DC voltage is provided by the supply  67  for any time a beacon module  12  is to be activated. The effective filter time constant provided by capacitor  70  is chosen to prevent the imposition of any meaningful delay in the generation necessary power once a signal present on anyone of the signal conductors  54 . Nevertheless, voltage of the power on capacitor  70  will vary substantially according to the operating voltage of the power supply  67 . Accordingly the voltage on the capacitor  70  may then be provided to a voltage regulator  72  uniformly converting that voltage to a least common denominator voltage (e.g. 12 VDC) of local backbone power  74 . The voltage regulator  72  may be of any design including, for example, a switched mode regulator is well known in the art. By using a boost mode converter, the voltage of the local backbone power  74  may be in fact higher than 12 V by allowing 12 V power supply voltages of power supply  67  to be boosted appropriately. 
         [0061]    The backbone power  74  and backbone common  68  provide power to the modulation function circuit  58  as will be described below in defines the voltage level of the active signal conductors  75  connecting to the beacon modules  12 . 
         [0062]    As well as scavenging power from the signal conductors  54 , the power-converter/function module  14  also extracts the information content on the signal conductors  54  by passing them through optoisolators  78  (one for each conductor  54 ) which isolate the operating voltage of power supply  67  (in common  52 ) from the backbone power  74  (and backbone common  68 ) optically isolated electrical signals  80   a ,  80   b , in  80   c  (each corresponding to one of conductors  54   a ,  54   b  and  54   c  respectively) are then provided to the modulation function circuit  58  which may modulate those signals when present according to a desired pattern set by user for example, through a dip switch  82  providing signals to modulation function circuit  58 . 
         [0063]    Referring now momentarily to  FIG. 4 , modulation function circuit  58  may implemented in a variety of different ways including a microcontroller, programmable gate array or discrete logical circuitry and generally includes a modulation clock  84 , for example, providing a base modulation frequency. The modulation clock  84  may for example be a conventional RC oscillator and divider circuit to provide a modulation frequency of 1 Hz. The output of the modulation clock is then received by programmable timing state machine  86  whose particular programming (and hence the modulation pattern) is set by switches  82 . In one example, three outputs  85   a ,  85   b , and  85   c  from the timing state machine  86  (for example, such as may control the modulation of signals to beacon modules  12   a ,  12   b , in  12   c ) may provide identical square waves at the frequency of the clock  84 . Each of these outputs may be received by an AND gate  88  whose other input is one of the signals  80   a - 80   c  output from the optoisolators  78  indicating the state of activation of the signal conductors  54 . This modulation pattern would provide synchronized flashing of any active beacon modules  12 . In this case, the modulation pattern would be synchronized and identical among beacon modules  12 . 
         [0064]    Another modulation provided by switches  82  may provide for steady high state output on each of the four signals  80   a - 80   e  of the timing state machine  86  essentially providing no function blinking of the beacon modules  12  when they are activated. It will be understood that some settings of the switches  82 , may likewise provide modulation on only some of the signals  80   a - 80   c , so that selected beacons may be modulated and other beacons not modulated. Different modulation patterns (for example frequencies) may be applied to different of the signals  80   a - 80   c.    
         [0065]    Alternatively as shown in  FIG. 5   a , the output signals  80   a - 80   c  of the timing state machine  86  may alternately turn high in a round-robin “marquee” pattern so that when multiple beacon modules  12  are activated their illumination expresses an animation, for example, of an upwardly rising single point of illumination that passes successively through each colored beacon. 
         [0066]    In contrast, as shown in  FIG. 5   b , a “stacked” pattern may be implemented in which, for example, an upwardly rising animation is generated but with the lowermost beacon remaining on as successively higher beacons are illuminated until all are ultimately illuminated and then extinguished together and this pattern repeated. 
         [0067]    In all of these examples, the flashing of different beacon modules  12  is synchronized in a way that is difficult when the timing circuitry for flashing is localized in the individual beacons themselves. This latter modulation provides modulation patterns that are also synchronized but are not identical. Another similar synchronized but different set of modulation patterns might provide different frequencies for each beacon module  12  but are nevertheless phase synchronized. 
         [0068]    Referring now to  FIG. 6 , it will be appreciated that the present invention may also work with a dedicated power supply line  90  from the external power supply  67 , for example, introduced through a separate screw terminal so that the base module  16  has direct access to constant electrical power through power supply common  52  and power supply line  90 . In this case, power may be directed from this power supply line to a single full wave rectifier  66  providing current to capacitor  70 . 
         [0069]    It will be appreciated that the LEDs  62  may be replaced with incandescent lamps according to well-understood techniques. 
         [0070]    Certain terminology is used herein for purposes of reference only, and thus is not intended to be limiting. For example, terms such as “upperu, plower”, “above”, and “below” refer to directions in the drawings to which reference is made. Terms such as “front”, “back”, “rear”, “bottom” and “side”, describe the orientation of portions of the component within a consistent but arbitrary frame of reference which is made clear by reference to the text and the associated drawings describing the component under discussion. Such terminology may include the words specifically mentioned above, derivatives thereof, and words of similar import. Similarly, the terms “first”, “second” and other such numerical terms referring to structures do not imply a sequence or order unless clearly indicated by the context. 
         [0071]    When introducing elements or features of the present disclosure and the exemplary embodiments, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of such elements or features. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements or features other than those specifically noted. It is further to be understood that 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. 
         [0072]    It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein and the claims should be understood to include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims. All of the publications described herein, including patents and non-patent publications, are hereby incorporated herein by reference in their entireties. 
         [0073]    It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein and the claims should be understood to include modified forms of those embodiments, including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims.