Patent Publication Number: US-11644008-B1

Title: Vertical axis wind turbine having vertical rotor apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a Continuation of U.S. application Ser. No. 17/557,187, now allowed, having a filing date of Dec. 21, 2021 which is a Continuation of U.S. application Ser. No. 17/156,772, now U.S. Pat. No. 11,236,725, having a filing date of Jan. 25, 2021 which is a Continuation of U.S. application Ser. No. 16/364,790, now U.S. Pat. No. 10,927,810, having a filing date of Mar. 26, 2019. 
    
    
     STATEMENT REGARDING PRIOR DISCLOSURE BY THE INVENTORS 
     Aspects of this technology are described in “A Straight-Bladed Variable-Pitch VAWT Concept for Improved Power Generation,” by Yann Staelens, et al., AIAA Paper 2003-0524, AIAA (American Institute of Aeronautics and Astronautics), Jan. 7, 2003, incorporated herein by reference. 
     BACKGROUND 
     Field of the Invention 
     The invention described herein is related to vertical axis rotors that rotate under influence of a moving fluid, such as wind or water. More specifically, this disclosure relates to vertical axis rotors of vertical axis wind turbines. 
     Discussion of the Related Art 
     As the debate regarding the benefits and shortcomings of converting fossil fuels into other forms of energy continues, much research and development has been devoted towards alternative energy conversion techniques. Converting energy from a moving fluid such as wind or water is one such technique. The wind turbine, whether it be a horizontal axis wind turbine (HAWT) or a vertical axis wind turbine (VAWT) offers a practical way to convert wind energy into other forms of energy. 
     A VAWT is a type of wind turbine where the main rotor shaft is set vertically transverse to the wind direction. One main advantage of the VAWT is in its omnidirectional character, i.e., a VAWT does not need to be pointed into the wind. The omnidirectional character, therefore, eliminates the need for orientation mechanisms that position the turbine based on wind direction, such as those required for HAWTs. 
       FIG.  1    illustrates an example of a rotor assembly  100  of a conventional straight-bladed VAWT. The primary components of rotor assembly  100  are turbine shaft  110  to transfer mechanical energy from the rotor to a device that can do work (generator, pump, etc.). Rotor assembly  100  further includes rotor blades  130   a  and  130   b , representatively referred to herein as rotor blade(s)  130 , to capture the wind energy and struts  120   a - 120   d , representatively referred to herein as strut(s)  120 , to attach rotor blades  130  to turbine shaft  110 . In the example illustrated, the pitch of rotor blades  130  is fixed and the blades cannot rotate or twist freely about their attachment points. As these blades revolve about the turbine rotor axis under the influence of the aerodynamic forces, they undergo a cyclic variation of pitch angle (angle of attack), defined as the relative angle between the rotor blade&#39;s tangential velocity vector and the wind direction vector. The magnitude of this cyclic pitch variation is a direct function of the turbine rpm and the wind speed. One artifact of this cyclic variation is that, at some point in the cycle when the pitch angle is at a critical angle, rotor blades  130  exhibit stall. The stall manifests itself as diminished rotor power compared to that achievable when blade stall is not encountered. 
     Accordingly it is an object of the invention to provide a vertical axis wind/water turbine rotor that improves power generation by avoiding rotor blade stall. 
     SUMMARY 
     In a vertical rotor apparatus that rotates in response to a moving fluid, a shaft defines an axis of rotor rotation. Rotor blades are longitudinally aligned in parallel with the shaft and each rotor blade defines an axis of blade rotation. A sensor determines whether any of the rotor blades are within rotor azimuthal angles of blade stall regions. A controller provides blade pitch information for the blade stall regions and an actuator, which is mechanically coupled to each of the rotor blades, alters blade pitch about the axis of blade rotation in accordance with the blade pitch information. 
     In one aspect, the sensor comprises a fluid vane mechanically coupled to an uneven swashplate having an incline formed thereon that provides the blade pitch information as a function of fluid flow direction. 
     In another aspect, the actuator comprises an even swashplate mechanically coupled to the uneven swashplate through a plurality of input rods and mechanically coupled to the rotor blades through a plurality of blade pitch link rods that impart a force on the rotor blades in accordance with spatial orientation of the incline formed on the uneven swashplate. 
     In another aspect, the sensor comprises a fluid vane configured to indicate fluid direction. Contact wires of the sensor are connected to the fluid vane and displaced with rotation thereof, where the contact wires define the blade stall regions as a function of fluid direction. A contact sensor mounted proximally to the shaft and moving through azimuthal angles therewith generates the signal in response to contacting the contact wires. 
     In yet another aspect, a plurality of struts mechanically connect the rotor blades to the shaft and the contact sensor is mounted on the struts. 
     In another aspect, the actuator is mounted on the struts. 
     In another aspect, the sensor comprises a rotary encoder. 
     In yet another aspect, a photovoltaic power source provides power to the rotary encoder. 
     In another aspect, the blade pitch information includes a blade pitch profile that defines a pitch angle as a function of azimuthal angle of rotor rotation 
     In another aspect, the blade pitch profile is constant at a predetermined blade pitch for all azimuthal angles. 
     In yet another aspect, the blade pitch profile is constant at a predetermined blade pitch for azimuthal angles corresponding to the blade stall regions. 
     In another aspect, the blade pitch profile is a sinusoid. 
     In still another aspect, the actuator is internal to each of the rotor blades and rotates the corresponding blade about the axis of blade rotation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG.  1    is a diagram of a conventional vertical axis wind turbine. 
         FIGS.  2 A and  2 B  are schematic diagrams of a vertical axis wind turbine for defining parameters of embodiments of the present invention. 
         FIGS.  3 A- 3 C  are schematic diagrams of a vertical axis wind turbine by which the present invention can be embodied. 
         FIG.  4    is a schematic diagram of a vertical axis wind turbine by which the present invention can be embodied. 
         FIG.  5    is a schematic diagram of a vertical axis wind turbine by which the present invention can be embodied. 
         FIG.  6    is a schematic diagram of another vertical axis wind turbine by which the present invention can be embodied. 
         FIG.  7 A  is a graph depicting a blade pitch profile with which the present invention can be embodied. 
         FIGS.  7 B- 7 C  are graphs depicting tangential force and torque, respectively, of a vertical axis wind turbine operating under the blade pitch profile of  FIG.  7 A . 
         FIG.  8 A  is a graph depicting another blade pitch profile with which the present invention can be embodied. 
         FIGS.  8 B- 8 C  are graphs depicting tangential force and torque, respectively, of a vertical axis wind turbine operating under the blade pitch profile of  FIG.  7 A . 
         FIG.  9 A  is a graph depicting another blade pitch profile with which the present invention can be embodied. 
         FIGS.  9 B- 9 C  are graphs depicting tangential force and torque, respectively, of a vertical axis wind turbine operating under the blade pitch profile of  FIG.  8 A . 
         FIG.  10    is a graph of output power of a vertical axis wind turbine operating under different blade pitch profiles. 
         FIG.  11    is a flow diagram of a turbine blade control process by which the present invention can be embodied. 
     
    
    
     DETAILED DESCRIPTION 
     The present inventive concept is best described through certain embodiments thereof, which are described in detail herein with reference to the accompanying drawings, wherein like reference numerals refer to like features throughout. It is to be understood that the term invention, when used herein, is intended to connote the inventive concept underlying the embodiments described below and not merely the embodiments themselves. It is to be understood further that the general inventive concept is not limited to the illustrative embodiments described below and the following descriptions should be read in such light. 
     Additionally, the word exemplary is used herein to mean, “serving as an example, instance or illustration.” Any embodiment of construction, process, design, technique, etc., designated herein as exemplary is not necessarily to be construed as preferred or advantageous over other such embodiments. Particular quality or fitness of the examples indicated herein as exemplary is neither intended nor should be inferred. 
       FIG.  2 A  is a schematic diagram of an example VAWT rotor for purposes of indicating certain parameters that are discussed herein. In the example illustrated, space is defined in cylindrical coordinates by a triplet (r, θ, z), where r is the distance from a chosen reference axis (radius), θ is a direction from the chosen reference axis relative to a chosen reference direction (azimuthal angle), and z is the distance from a chosen reference plane perpendicular to the chosen reference axis (height). In this disclosure, the reference axis is the axis of rotation of the rotor that coincides with the z-axis and the reference plane is at z=z EQ , i.e., the equatorial plane of the rotor. Two rotor blades are situated at (R, 0, z R ) and (R, π, z R ), where, as illustrated in  FIG.  2 A , z R  is the distance from the lowest point on the rotor blades to a reference ground where the wind speed V(z) is at a minimum. Each rotor blade is 2H in longitudinal length. In certain embodiments, the rotor blades are matching National Advisory Committee for Aeronautics (NACA) airfoils, e.g., NACA 0015 airfoils, and are fixed in space relative to the rotor axis by a mechanical connection, such as by a strut or similar mechanism (not illustrated in  FIG.  2 A ) connected to a shaft or similar mechanism (not illustrated in  FIG.  2 A ) situated on the rotor axis. It is assumed that the blades revolve about the z-axis at an angular velocity ω under aerodynamic forces imparted by the wind. 
       FIG.  2 B  is an overhead view of the VAWT rotor of  FIG.  2 A  in the equatorial plane (z=z EQ ) to define further parameters related to embodiments of the invention. Primed indicators refer to the downwind cycle (where the blade is leeward of the turbine shaft (z-axis)) and non-primed indicators refer to the upwind cycle (where the blade is windward of the turbine shaft (z-axis)). In the figure, V(z) is the z-dependent wind velocity vector, ω is the turbine angular velocity, θ is the azimuthal angle, α is the rotor blade angle of attack, Rω is the rotor blade tangential velocity vector, W is the apparent wind velocity vector, F T  is the tangential force vector, F N  is the normal force vector, L is the lift force vector and D is the drag force vector. As illustrated, the wind is directed into the turbine at 0° azimuthal angle. 
     As the blades revolve about the rotor axis under the influence of the aerodynamic forces, they undergo a cyclic variation of pitch angle α, defined as the relative angle between the tangential velocity vector Rω and the wind direction vector V.  FIG.  2 B  shows a typical variation in the blade pitch angle α for different locations in terms of the azimuthal angle θ in the equatorial plane. The variation in the resultant velocity vectors W at four different azimuthal locations θ are also shown in terms of vector addition of the tangential velocity vectors Rω and the wind direction vectors V. The magnitude of the cyclic pitch variation is a direct function of the turbine rpm and the wind speed. 
       FIG.  3 A  is an illustration of an example VAWT rotor  300  by which the present invention can be embodied. Exemplary rotor  300  includes a plurality of rotor blades  310   a  and  310   b , representatively referred to herein as rotor blade(s)  310 , revolving about a rotor shaft  320 . Exemplary rotor  300  further includes struts  315   a - 315   d , representatively referred to herein as strut(s)  315  fixed at one end to shaft  320  and fixed at an opposing end to attachment points  312   a  and attachment points  312   b , representatively referred to herein as attachment point(s)  312 , of rotor blades  310 . Attachment points  312  serve as the blade rotational axes and, in certain embodiments, are located quarter-chord from the blade leading edge It is to be noted that the center of pressure is not a good choice for attachment points because the center of pressure location is not fixed but changes with the blade pitch. A better location for attachment points adopted by embodiments of the present invention is at the aerodynamic center which is defined as the location where the blade moment is independent of the blade pitch. The aerodynamic center is located at the quarter-chord location for most blade profiles employing NACA profile sections. It is to be understood, however, that the invention is not limited to the quarter-chord attachment point discussed herein and can be practiced with blade profiles other than those standardized by NACA 
     Unlike the fixed-bladed VAWT described above, rotor blades  310  are free to rotate about their blade axes located at attachment points  312 . In the example illustrated, the blade axes are parallel to the axis defined by turbine shaft  320 , although other blade configurations are possible. 
     Exemplary VAWT rotor  300  includes a sensor  330  by which wind direction and rotor angular velocity (which is dependent on wind velocity) are determined. To that end, exemplary sensor  330  comprises a wind vane  340 , contact wires  332   a  and  332   b , representatively referred to herein as contact wire(s)  332 , and controllers  334   a  and  334   b , representatively referred to herein as controller(s)  334 . As rotor  300  rotates about its axis, contact wires  332  come into contact with controllers  334  and, responsive thereto, a signal is generated, which may be used to control respective actuators  350   a  and  350   b , representatively referred to herein as actuator(s)  360 . Actuators  360  are mechanically coupled to respective rotor blades  310  at attachment points  354  through suitable linkages  352  that compel the corresponding rotor blade  310  to rotate about its blade axis  312 . 
     As illustrated in  FIG.  3 A , actuator  350  may be implemented by a motor  355  mechanically affixed to strut  315  by suitable connection hardware. Motor  355  may include a gear  356  that engages with a gear portion  356  of linkage  352 . Motor  355  may be a stepper or servo motor and may provide the necessary torque to motivate blade  310  about its blade axis and to retain blade  310  in position against the aerodynamic forces imparted thereon. However, it is to be understood that the motor arrangement of  FIG.  3 A  is but one example of an actuator that can be used in embodiments of the invention. Other actuator implementations, including pneumatic or hydraulic implementations, can be realized in embodiments of the invention without departing from the spirit and intended scope thereof. 
       FIG.  3 B  is a diagram illustrating an example sensor mechanism that can be incorporated in embodiments of the present invention. As illustrated in the figure, contact wires  332  are attached to wind vane  340  at locations defining a stall region  390 . The location of the stall regions are determined from analysis of forces described with reference to  FIG.  2 A- 2 B . The position of wind vane  340  provides the wind direction; thus, the position of contact wires  332  depends only on wind direction. As shaft  320  rotates, actuators  350  pass under wind vane  340  and make contact with contact wires  332 . The rate at which such contact occurs as the rotor rotates can be used to determine the turbine angular velocity ω. 
       FIG.  3 C  is an overhead view of VAWT rotor  300  illustrating an example pitch actuation sequence. At point A, the wind vane location is sensed to serve as a reference and the angular velocity of the shaft is sensed. At point B, the pitch actuation is initiated based on a programmed increment from the reference point (wind vane location). After another programmed increment in azimuthal angle θ, i.e., point C, the blade pitch is reset back to its initial value. Contact wires  332  may be positioned on wind vane  340  to effectuate this sequence. Because the stall locations depend only on the wind direction, the contact wire activation/deactivation may be fixed. As the rpm changes, the activation amplitude and frequency can be changed to correspond to the rpm. This may be pre-programmed in the sensor that activates the servo or stepper motor. 
     Referring once again to  FIG.  3 A , controller  334  may include a contact switch  362  that indicates contact with contact wires  332 , such as by sensing the pressure of contact wire  332  thereon. Contact switch  362  may provide an indication of the contact to a processor  365 , which may execute programmed instructions stored in memory  367 . Processor  365  may be so programmed to realize a controller that controls actuator  350  based on the azimuthal angles θ of stall region  390  and rotor angular velocity ω determined by sensor  330 . e.g., by location of contact wires  332  on wind vane  340  (to define the stall region based on wind direction) and the rate at which contact wires  332  make contact with controller  334  (to establish rotor angular velocity ω). Processor  365  may determine the amount of rotor rotation from the turbine angular velocity ω. An interface  368  may be provided to convert processor level signals to a motor drive signal  369  that compels motor  355  to rotate an amount specified by processor  365 . 
     In  FIGS.  3 A- 3 C , processor  365 , memory  367  and interface  368  are illustrated as residing in the same housing as contact switch  362 . However, the present invention is not so limited. Indeed, in certain embodiments, these components are contained in the same housing as motor  355 . The distribution of components is left to the designer. 
       FIG.  4    is a diagram illustrating an example VAWT rotor  400  by which the present invention can be embodied. Rotor  400  is similar in construction to rotor  300  and, thus, rotor  400  includes a plurality of rotor blades  410   a  and  410   b , representatively referred to herein as rotor blade(s)  410 , revolving about a turbine shaft  420  and fixed thereto by struts  415   a - 415   d , representatively referred to herein as strut(s)  415 . Rotor blades  410  are free to rotate about respective blade axes located at attachment points  412   a  and  412   b , representatively referred to as attachment points  412 . The blade axes may be parallel to the axis defined by turbine shaft  420 , but, again, the present invention is not so limited. 
     Exemplary VAWT rotor  400  includes controllers  450   a  and  450   b , representatively referred to herein as controller(s)  450 , that control respective actuators  460   a  and  460   b , representatively referred to herein as actuator(s)  460 . As with VAWT rotor  300 , actuators  460  are mechanically coupled to respective rotor blades  410  through suitable linkages that compel the corresponding rotor blade  410  to rotate about its blade axis under control of the corresponding controller  450  as the rotor blade  410  revolves about the rotor axis defined by turbine shaft  420 . VAWT turbine  400  may utilize any of the actuator implementations discussed herein. 
     Exemplary VAWT rotor  400  includes a sensor  430  by which the wind direction and turbine angular velocity ω can be ascertained. Sensor  430  may include a wind vane  440  by which the wind direction is determined and a rotary encoder indicates the relative wind direction. Another rotary encoder  432  can determine both the angular velocity of shaft  420  and its azimuthal angle relative to some reference angle. Absolute and incremental rotary encoders may be used in embodiments of the invention. In one embodiment, rotary encoder  432  is attached to a fixed point on the turbine, such as on a mast (not illustrated) and to the turbine shaft  420 . A battery or photovoltaic power source  470  may be used to provide power to rotary encoder  432 . 
       FIG.  5    is a diagram illustrating an example VAWT rotor  500  by which the present invention can be embodied. VAWT rotor  500  includes a shaft  520  to which are connected a plurality of rotor blades  510   a - 510   c , representatively referred to herein as rotor blade(s)  510 . Rotor blades  510  may be connected to shaft  520  through struts  515   a - 515   f , representatively referred to herein as strut(s)  515 . Each rotor blade  510  has internally installed a housing  512 , which may be tubular, that contains a controller  550  and an actuator  560 . Housing  512  and turbine blade  510  are mechanically coupled such that activation of actuator  560  results in rotation of rotor blade  510  about an axis. Housing  512  may be mechanically connected to struts  515  to be rotated by actuator  560  under control of controller  550 . In the illustrated embodiment, actuator  560  includes a motor  562  moving a gear  564 . Gear  564  may be engaged to a gear  566 , such that actuation of motor  562  causes turbine blade  510  to rotate about its connection point with strut  515 . In one embodiment, each turbine blade  510  has a mounting flange  532  or similar structure that may be fixedly attached to strut  515  with suitable hardware, such as bolts  534 . Such could keep motor stationary to apply sufficient torque to turbine blade  510  to hold it steady against the torque applied by aerodynamic forces. 
       FIG.  6    is a diagram illustrating an example VAWT rotor  600  by which the present invention can be embodied. In this example, blades  601   a - 601   b , representatively referred to herein as blade(s)  601 , are mechanically coupled to shaft  650  to revolve about an axis  601  defined by the center of shaft  650 . Blade pitch link rods  605   a - 605   d , representatively referred to herein as blade pitch link rod(s)  605 , are activated by the tilt of the upper portion  621  of even swashplate  620  that rotates with the blades  601  and shaft  650 . Its lower part  623  below the bearings  622  is connected to the uneven or tilted swashplate  625  via input link rods  624   a - 624   b , representatively referred to herein as input link rod(s)  624 . A wind vane  630  is also connected to the uneven or tilted swashplate  625 . The wind vane  630 , the uneven or tilted swashplate  625 , the input link rods  624  and the lower part  623  of the even swashplate  620  rotate together as one part about shaft  650  and align according to the wind direction independently from the blades  601 , shaft  650  and the upper portion  621  of even swashplate  623 . The uneven height or the tilt of the uneven or tilted swashplate  625  is predetermined according to the design and prebuilt into the mechanism by an incline  626 . The input link rods  624  of equal length connected to the lower part  623  of even swashplate  620  causes the even swashplate  620  to have the same tilt as the incline  626  of uneven swashplate  625 . Since the blade pitch link rods  605  are attached to hinges  615   a - 615   b , representatively referred to herein as hinge(s)  615 , that are fixed to the upper strut-shaft collar  610 , the tilt of the swashplate pushes the blade link rods  605  up or down as it rotates. This push and pull of the blade pitch link rods  605  results in an increase or decrease in the blade pitch according to a predetermined and preset amount thus achieving a passively controlled variable pitch action. 
     As indicated above, embodiments of the invention enhance turbine performance by preventing the rotor blades from undergoing stall by actively modifying the pitch angle of the blades as they enter the stall regions. In certain embodiments, a local pitch change Δα e  is added to the local pitch angle α to realize a local effective pitch angle α e =α+Δα e . The curve defined by the local effective pitch angle over the 360° azimuthal angles θ is referred to herein as a pitch angle profile. 
       FIG.  7 A  is a graph illustrating a pitch angle profile, referred to herein as pitch angle profile 1, of one embodiment of the present invention. Here, the local rotor blade angle of attack α is kept just below the local stall angle at all points along the revolution cycle, i.e., for every azimuthal angle θ. Essentially, the local geometric blade angle of attack α is increased/decreased by Δα e  to the local static stall angle value and as such the blade never experiences stall since it avoids the stall region altogether.  FIG.  7 B  is a graph illustrating the tangential force under the pitch angle profile 1 and  FIG.  7 C  is a graph illustrating torque under pitch angle profile 1. 
       FIG.  8 A  is a graph illustrating another pitch angle profile, referred to herein as pitch angle profile 2, of an embodiment of the present invention Here, the local effective angle of attack α e  is kept at the blade stall angle during the revolution cycle only when the geometric angle of attack exceeds the static stall angle value α stall . As illustrated in  FIGS.  8 B and  8 C , the tangential force and torque undergo a more gradual change or smoother transition at θ=−π/2 and π/2 than in the blade pitch angle profile 1 case. 
       FIG.  9 A  is a graph illustrating another pitch angle profile, referred to herein as pitch angle profile 3, of an embodiment of the present invention Here, the evolution of the local angle of attack correction Δα e  is implemented in a smooth continuous function such as a sinusoid. The maximum amplitude of the sinusoidal correction function is set equal to the maximum difference between the local geometric angle of attack α and the blade static stall angle α stall . As a consequence, the local effective angle of attack α e  is also sinusoidal. In this embodiment, the blade experiences dynamic stall at a few locations during the revolution cycle, which can be avoided by decreasing the maximum value of the correction function until the dynamic stall condition is avoided altogether yielding a smooth and continuous variation in tangential and normal forces and torque. A smooth and continuous correction function Δα e  is more practical to implement.  FIGS.  9 B and  9 C  illustrate the tangential force and torque curves, respectively, under pitch angle profile 3. 
       FIG.  10    is a graph illustrating output power of the VAWT rotor as a function of wind velocity under the different blade pitch profiles described above. As is illustrated, power output of these embodiments increases linearly with wind speed. Moreover, the increase in power output at high wind speeds is significantly higher than the case where static or dynamic stall or both are encountered by the blade. 
       FIG.  11    is a flow diagram of an example turbine blade control process  1100  by which the present invention can be embodied. As indicated at block  1105 , process  1100  is provided with turbine speed and wind direction data, such as by the techniques described above. In operation  1110 , azimuthal angles are determined at which stall occurs by a turbine blade. In operation  1115 , it is determined whether the turbine blade at a particular azimuthal angle enters a stall region. If so, process  1100  transitions to operation  1120 , by which the pitch angle of the turbine blade is modified to avoid stall, In certain embodiments, the pitch angle is modified in accordance with a pitch angle profile, such as those described above. In operation  1125 , it is determined whether the turbine blade at a particular azimuthal angle is leaving the stall region. If so, process  1100  transitions to operation  1130 , whereby the pitch angle of the turbine blade is reset to its original position. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, 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 features, integers, steps, operations, elements, components, and/or groups thereof. 
     The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated. 
     The descriptions above are intended to illustrate possible implementations of the present inventive concept and are not restrictive. Many variations, modifications and alternatives will become apparent to the skilled artisan upon review of this disclosure. For example, components equivalent to those shown and described may be substituted therefore, elements and methods individually described may be combined, and elements described as discrete may be distributed across many components. The scope of the invention should therefore be determined not with reference to the description above, but with reference to the appended claims, along with their full range of equivalents.