Abstract:
The present invention relates to a portable adhesive dispensing appliance with adjustable duty cycle. Rather than applying power continuously to the heating element, the element power is intermittently switched over to a variable duty cycle. Savings are gained in three areas: extended life of the element; less heat lost to thermal radiation; and less adhesive waste due to dripping and overheating. The duty cycle may be adjusted manually or automatically based on the temperature of the adhesive in the melt chamber. Additionally, the voltage and/or current to the heating element may be adjusted, either manually or automatically, for more rapid recovery during high usage periods. Higher throughput is achieved by sensing the temperature, comparing the temperature to a desired temperature, and then increasing the duty cycle by either or both one of increasing the frequency of duty pulses and/or lengthening the duration of the duty pulses.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
   The present application is a continuation in part of and claims priority from the following U.S. patent applications: 
   U.S. patent application entitled “Portable Hair Dryer” having application Ser. No. 10/117,776, and filed on Apr. 5, 2002, now U.S. Pat. No. 6,718,651, which is a divisional of U.S. Ser. No. 09/662,860 now U.S. Pat. No. 6,449,870 entitled “Portable Hair Dryer” and filed on Sep. 15, 2000. The above-identified applications are incorporated by reference herein in their entirety. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates in general to a hot glue dispenser or “glue gun.” More specifically, the present invention is related to a hot glue dispenser and a voltage regulating circuit to control the heat produced by the element, but also has a power control circuit that allows the heating element to obtain fill heat and then pulses it to maintain the set heat which reduces the power consumption. 
   2. Description of Related Art 
   A hot glue dispenser, or gun, is an appliance for liquefying and dispensing thermoplastic materials such as hot melt adhesives and glues from their solid phase through the controlled application of heat energy. The liquefied glue, or “melt,” is then in a readily usable form for application to a workpiece. Typically, prior art glue guns are comprised of three major parts: the body; the electrical power circuit components, e.g., the heating element(s) and control(s); and the mechanical components, e.g., the glue path and application mechanism. The mechanical components associated with a typical glue gun are described in U.S. Pat. No. 4,523,705 issued to Belanger et al. entitled “Mechanism for Glue Gun,” which is incorporated herein by reference in its entirety. Normally, the type of glue selected is dictated by the particular type of glue gun used for dispensing the gun. One popular form of glue is the hot melt “glue stick” which is elongated cylindrically shaped thermoplastic material which is received in a portable hot melt glue gun at a similarly shaped receiving end in the glue path. Further along the glue path is the melt chamber which is surrounded by one or more electrical heating elements for communicating radiant heat energy to the melt chamber and thermoplastic material therein. A mechanical feed mechanism is typically provided within the body for applying pressure to the solid portion of the flexible thermoplastic rod for forcing it along the glue path, into the melt chamber and finally dispensing the melt through an exit nozzle onto, for instance, a workpiece. The glue may also be of the “cool” melt type which liquefies at a lower temperature than hot melt type glue. Hot melt adhesives are appropriate for high temperature glue guns that typically operate at approximately 380° F. (193° C.) and are used for most bonding applications, craft projects, floral arrangements, repairs, and on most materials such as paper, wood, plastics, etc. The melting point of a hot melt adhesive is lower than 380° F. to ensure that the glue is melted and dispensable from a 380° F. chamber. Cool melt adhesives, on the other hand, are appropriate for low temperature glue guns that typically operate at approximately 225° F. (107° C.) and are recommended for use on heat sensitive materials such as styrofoam, balloons, and fabrics. A typical prior art glue gun is permanently configured for either hot or cool melt applications, although some prior art glue guns have dual temperature switching capability. 
   The temperature of the glue in the melt chamber is determined by three basic factors: heat energy in, i.e., the amount and time heat is applied to the chamber; heat energy out, i.e., the heat loss of the gun, glue path and amount of glue dispensed; and heat energy absorbed, i.e., the thermal properties of the glue enabling it to change phases. A distinction should be understood between the temperature and heat energy. Temperature is a measure of the average amount of motion per molecule, or concentration of heat, while heat energy is a quantity of heat. Temperature is graduated in degrees and heat in calories such that one calorie is the quantity heat energy required to raise the temperature of one gram of water one degree C. 
   Prior art glue guns generally rely on a relatively uncomplicated electrical power circuit for regulating the heat of the glue, the most simple of which utilizes a fixed temperature heating element operating at a predetermined fixed temperature, say 380° F. (193° C.), which is electrically coupled to a power source. However, two heating elements may operate at the identical fixed temperature and still produce different levels of heat energy, e.g., by employing high capacity heating elements. For example, two glue guns with heating elements operating at the identical fix temperature of 380° F. might, but if one has a larger capacity heating element, it will be capable of liquefying more glue in the same time period. 
   Other prior art glue gun power circuits are only slightly more complicated than that described above. One exemplary power circuit used a thermostat, or other heat-sensing device, for regulating electrical power to the heating element. That power circuit consists of an optional switch connected between a power source and a thermostat, and a heating element electrically coupled between the thermostat and power source. With a thermostat protecting the glue from overheating, heating elements may be employed which operate at a much higher temperature. The combination of higher operating temperature and larger capacity elements enables higher volumes of glue to be emulsified and dispersed in a comparable time period. 
   Throughput, the volume of glue a gun is capable of liquefying and dispersing in a set time period is a continual problem plaguing glue gun manufacturers. Incorporating larger capacity heating elements in a gun increases throughput, but substantially increase the cost of the gun. Heating elements with higher operating temperatures are also more expensive and have the added disadvantage of reacting with thermoplastics that cannot tolerated a higher temperature in the melt chamber. This is especially true for colored adhesives. 
   One solution for increasing throughput is described by U.S. Pat. No. 4,059,204 issued to Duncan et al. entitled “System for Dispensing and Controlling the Temperature of Hot Melt Adhesive.” Duncan discloses a hot melt glue gun which includes an electronic circuit enabling the gun operator to set a desired temperature to which the glue is heated. The set point is automatically raised to a predetermined amount when the glue is flowing in order to compensate for the drop in temperature caused by the loss of heat to the glue and atmosphere. 
   Another solution for increasing throughput and lowering the glue gun costs is by incorporating a head sink in the melt chamber. The heat sink absorbs latent heat which would otherwise be exhausted to the ambient air when the melt chamber is at higher temperatures, for instance during idle periods when glue is not passing through the glue path, and then releases the heat energy back into the melt chamber when the glue passing through it is at a lower temperature than the sink, such as during active periods when large volumes of glue are passing through the glue path. Other improvements to the melt chamber are disclosed in U.S. Pat. No. 5,462,206 issued to Kwasie entitled “Melting Assembly for Thermoplastic Materials,” which is incorporated herein by reference in its entirety. While the heat sink increases throughput somewhat, with only a marginal increase in cost, additional operation costs can easily surpass initial savings in gun costs. This happens because with the addition of the sink, the surface area of the high temperature portion of the gun is also increased, thereby increasing the area of the gun exposed to the cooler ambient air, and increasing heat loss. Additionally, heat losses result from transferring the heat energy from the element to the sink, then to the chamber and, then finally to the glue which decreases the overall efficiency of the gun. Thus, while the sink may lower the initial glue gun cost through the use of smaller capacity and/or lower operating temperature heating elements, the guns are considerably inefficient. 
   Other prior art references describe increasing the efficiency of glue guns by identifying areas of high heat loss and insulating them, thereby increasing efficiency of heat energy transfer into and retained in the melt adhesive, such as U.S. Pat. No. 6,142,207 issued to Richardot entitled “Hot Melt Glue Applicator and Glue Stick for Use Therein,” which is incorporated herein by reference in its entirety. However, each prior art glue gun suffers from a paradox, attempting to increase throughput results in more expensive initial costs and substantially higher operating expenses, due to the inherent inefficiencies of the gun. While, setting for lower throughput results in higher lag times, which in turn increases operating expenses due to the operator&#39;s increased idle time. 
   SUMMARY OF THE INVENTION 
   The present invention relates to an adhesive dispensing appliance with adjustable duty cycle. Rather that applying power continuously to the heating element, the element power is intermittently switched over a variable duty cycle. Savings are gained in three areas: extended life of the element; less heat lost to thermal radiation; and less adhesive waste due to dripping and overheating. The duty cycle may be adjusted manually, or automatically based on the temperature of the adhesive in the melt chamber. Additionally, the voltage and/or current to the heating element may be adjusted, either manually or automatically, for more rapid recovery during high usage periods. Higher throughput is achieved by sensing the temperature, comparing the temperature to a desired temperature, and then increasing the duty cycle by either or both one of increasing the frequency of duty pulses and/or lengthening the duration of the duty pulses. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features believed characteristic of the present invention are set forth in the appended claims. However, the invention itself, as well as a preferred mode of use, further objectives and advantages thereof, will be best understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings wherein: 
       FIG. 1  is a perspective view of the novel hot adhesive dispenser appliance for liquefying and dispensing thermoplastic materials in accordance with exemplary embodiments of the present invention; 
       FIG. 2  is a perspective view of the novel battery that can be attached to the adhesive dispenser appliance as shown in  FIG. 1  in accordance with an exemplary embodiment of the present invention; 
       FIG. 3  is a schematic representation of a converter for supplying either AC or DC power 0to the battery for charging thereof in accordance with an exemplary embodiment of the present invention; 
       FIG. 4A  is a block diagram of the control circuit for controlling the power to the blower fan and to the heating element in accordance with an exemplary embodiment of the present invention; 
       FIG. 4B  is a circuit illustrating one circuit embodiment for quickly heating the heating element and then supplying pulsed current or voltage to maintain the heat in accordance with an exemplary embodiment of the present invention; 
       FIG. 4C  illustrates the details of the pulsing circuit illustrated in  FIG. 4B  in accordance with an exemplary embodiment of the present invention; 
       FIG. 4D  illustrates in waveform  1  the oscillator output, and in waveform  2  the output of a circuit illustrating a 1:4 ratio for applying pulses to the heating element in accordance with an exemplary embodiment of the present invention; 
       FIG. 4E  is a schematic illustration of the output circuit with a manual switch control being set to high, medium and low to provide pulses and pulse ratios to the power transistor that supplies voltage and current to the heating element in accordance with an exemplary embodiment of the present invention; 
       FIG. 4F  illustrates a circuit for supplying pulses to the power transistor to automatically maintain a desired heater temperature utilizing an innovative control circuit in accordance with an exemplary embodiment of the present invention; 
       FIG. 4G  illustrates a circuit for stepping up the voltage or current only during the time the pulses are applied to the heating element in accordance with an exemplary embodiment of the present invention; and 
       FIG. 4H  illustrates the stepped-up voltage pulses that are applied to the heating element by the circuit of  FIG. 4G  in accordance with an exemplary embodiment of the present invention. 
   

   Other features of the present invention will be apparent from the accompanying drawings and from the following detailed description. 
   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  is a perspective view of novel adhesive dispensing appliance  10  including body portion  12 , handle portion  14  and battery base portion  16 . It will be noted that mass center line  18  of each of hollow body portion  12 , handle  14 , and battery base  16  are all in alignment thus allowing unit  10  to be balanced and enables the adhesive dispensing appliance to stand alone on base  16 . In addition, by the alignment of the mass center lines of elongated hollow body portion  12 , handle  14  and base  16 , and proper weight distribution of hollow body portion  12  and base  16  as can be done by those skilled in the art, balance is provided to enable the unit to be used with minimum strain on the arm and hand of the user. 
   Contained within hollow body portion  12  are the electrical power circuit components for heating the adhesive and the mechanical components for dispensing the melted adhesive. In accordance with an exemplary embodiment of the present invention, the electrical power circuit components comprise heating element  20 , pulsing circuit  24  and temperature sensor  68 . With particular regard to the exemplary depicted as adhesive dispensing appliance  10 , a portable type of “glue gun” which utilizes hot melt glue sticks, elongated cylindrically shaped thermoplastic glue stick material  1  is received at opening  2  of glue path  6 . Further along glue path  6  is melt chamber  7  which is surrounded by one or more electrical heating element  20  for communicating radiant heat energy to melt chamber  7  and thermoplastic material  1  therein. Optionally, mechanical feed mechanism  4  is shown generally within body portion  12  for applying pressure to the solid portion of flexible thermoplastic rod  1  for forcing it along glue path  6 , into melt chamber  7  and finally dispensing the melt through exit nozzle  8 . 
   Handle  14  also has switch control pedestal  30  and mechanism  32 , well known in the art, for locking battery/base unit  16  to handle  14 . Switch pedestal  30  includes diode light  34 , usually of green color but which may be of any desired color, switch  36  (S 1 ) that controls power only to heating element  20 , via sensor  23 , as will be described in greater specificity below, while switch  38  (S 2 ) increases the duty cycle or pulse widths from control circuit  24  to accommodate higher adhesive throughput. Manual control switch  40 , which will be explained in detail hereafter, has multiple positions such as low, medium and high (or alternative are preset activate pre-set temperature levels) that can be selected by the user to designate the heat desired to be produced by heating element  20 . Alternative, the positions on manual control switch  40  are preset for predetermined melts, for instance one position preset to correspond with 380° F. (193° C.) for using hot melt adhesives and another position on manual control switch  40  are preset to correspond to 225° F. (107° C.) for using cool melt adhesives. 
     FIG. 2  depicts an exemplary base/power unit  16  which includes battery  42  and stem  44  that can be inserted into handle  14  of dispensing appliance  10  shown in FIG.  1  and electrical terminals  46  to be received by appropriate terminals (not shown) in the handle  14  of the dispensing appliance  10  illustrated in FIG.  1 . The battery/base  16  may be constructed such that stem  44  can be inserted in handle  14  in only one direction. This may take many different forms such as slot  48  on one side of connectors  46 . Other versions could be to shape the cross-sectional area of stem  44  to be inserted in a corresponding receptacle shape in handle  14  as shown in FIG.  1 . Battery/base  16  may include connector jack  50  for receiving a charging connector from the device in FIG.  3 . As stated previously, that charging connector may be an AC voltage from an alternating current source if battery/base  16  has rectifier unit  52 . This would allow a unit to be charged while it is mounted on blower/dryer  10  as well as an additional separate unit that can be charged at the same time. Moreover, dispensing appliance  10  is operable in on three modes: as portable unit using battery  42  as a power source; as a wired unit connected to an AC current source and using rectified AC current from rectifier unit  52  as a power source; or finally, as a wired unit connected to an AC current source but using battery  42  as a power source while simultaneously rectifying AC current from rectifier unit  52  and charging battery  42 . 
   Note in  FIG. 3  that plug-in unit  54  could generate either AC or DC power output voltage on jacks  56  and  58 . If the battery unit has its own rectifier unit  52 , then jacks  56  and  58  in  FIG. 3  may generate AC voltage. If the battery unit is selected that does not have rectifier  52 , then plug-in unit  54  must be an AC to DC converter and jacks  56  and  58  would generate DC voltage. Here it should be understood that battery  42  may be any known, or heretofore unknown, type of power source without departing from the intended scope of the present invention. For example, battery  42  may be any of a dry cell, wet cell, alkaline, nickel-cadmium (Ni-Cad), fuel cell or any other chargeable or disposable portable source of AC or direct current (DC) power. Moreover, the power source need not be portable, but instead may be connection (wired) to any regulated source of AC or DC power, such as a typical 110 volt (60 hz) US standard wall outlet or equivalent 220 volt (50 hz) international standard outlet. The power may originate from any generation source whatsoever. The weight of base  16  is in balance with the weight of the elongated body portion. Such balance can be easily achieved by those skilled in the art. 
   It will be noted in  FIG. 1  that handle portion  14  has a longitudinal axis extending substantially transversally from and along mass center line  18  of elongated body portion  12 . Again, base unit  16  in  FIG. 1  also has a mass center line that, when attached to the handle portion, lies substantially along the longitudinal axis of mass center line  18  such that (I) power can be supplied to manual controls  30  and (2) flat base  16  may provide a structure for enabling the adhesive dispensing appliance to stand alone. 
     FIG. 4A  discloses the basic electrical circuit for controlling power to the heating element. Basic circuit  62  includes battery base portion  16  with battery cells  42  therein and, if desired, rectifier unit  52 . It also has jack  50  for connecting a charger thereto. When the unit is plugged into a power source, the power is immediately supplied to LED  34  which indicates that the battery has sufficient power to operate the unit. When switch button  36  (S 1 ) is depressed, power is coupled to heating element  20  through a pulsing circuit  64 , if desired. Switch button  38  (S 2 ) is a “super button.” By depressing switch button  38  (S 2 ), the duty cycle or pulse widths from control circuit pulsing circuit  64  is increased for accommodate higher usage rates. Pulsing circuit  64  will be described hereafter. 
   Pulsing circuit  64  is shown in detail in FIG.  4 B. When the unit is first turned on and switch  36  (S 1 ) is depressed, the heating element is energized and it is desired that the heating element heat as quickly as possible. Thus, as shown in  FIG. 4B , when switch  36  is closed, conductor  39  is coupled directly to the input of transistor  66 . The temperature of heating element  20  is monitored by a temperature sensor, such as a thermocouple or thermistor. Temperature sensor  68  is coupled to comparator  70 . Another voltage reference  72  is coupled to the other input of the comparator representing the proper or maximum heating temperature of element  20 . Since there is no heat at first, there is no output from comparator  70 . That lack of signal is detected by inverting diode  73  which generates an output signal on line  76  that is coupled to base  78  of power transistor  66  causing it to conduct. Transistor  66  is turned on by the signal on output line  76 . Thus, full voltage is applied to heating element  20  to provide maximum heating in minimum time. As soon as the element is heated to the desired temperature, and that is sensed by sensor  68 , an output signal is generated by comparator  70  that causes inverting diode  73  to remove its signal on output line  76  thus removing the continuous signal from the base  78  of transistor  66 . At this time, pulser circuit  80 , which is isolated from inverting diode  73  by isolating diode  82 , provides pulses to base  78  of transistor  66  to maintain the heat attained by heating element  20  without having a continuous voltage applied thereto. 
   Pulser circuit  80  is shown in detail in  FIG. 4C  in accordance with one exemplary embodiment of the present invention. Oscillator  84  applies pulses to circuit  86  that could be a shift register, a timer, a counter, or a divider circuit as shown in U.S. Pat. No. 4,571,588, which is incorporated herein by reference in its entirety. The duty cycle is the percentage of time a unit is used, or the ratio of operation time to shutdown time. If device capable of only fixed length pulses is used for controlling the duty cycle, then ration can be adjusted only by designating more or less pulses as operation pulses. If, however, the period of the pulses can also be altered, then the duty cycle can be altered by either increasing the ratio of the operation pulses to shutdown pulses, or by lengthening the duration of the operation pulses in the cycle. Thus, selecting a device having output pulse width modulation capability allows for adjusting the duration of the operation period as well as the ratio of operation periods. Many types of times and shift registers known in the art have pulse width modulation capabilities. In accordance with one exemplary embodiment, circuit  86  may be a 4-bit shift register as depicted in FIG.  4 C. Input switch  40  is used for selecting select low, medium and high heat, causes a selected bit from one stage of circuit  86  to be connected to base  78  of transistor  66  thus causing transistor  66  to be pulsed on and off at a given rate. An example is illustrated in FIG.  4 D. The oscillator is shown to have 5 pulses in waveform “ 1  ” of  FIG. 4D  while circuit  86  generates an output pulse only once for every four input pulses as shown in waveform “2” which means there is a 4:1 ratio of the operating time of transistor  66 . For every four pulses received by circuit  86 , only one is gated to transistor  66  allowing transistor  66  to power heating element  20  only one-fourth of the time possible for heating (i.e., one-fourth of the duty cycle). The duty cycle may be increased by adding pulses or by increasing the pulse width of output of circuit  86 . 
   Other ratios could be selected as illustrated by the circuit in  FIG. 4E  where oscillator  84  is feeding the pulses to circuit  86 . At the output of each of the four stages or dividers of circuit  86 , a switch (S 1 -S 5 ) is connected to base  78  of transistor  66 . If, for instance, switch S 1  is selected as the high heat position, then circuit  86 , at stage  87 , will produce an output with every pulse received and applied to base  78  of transistor  66 . If stage  88  is selected by closing switch (S 3 ) or placing switch  40  in the medium position, then third stage  88  will be selected and a pulse will be generated through switch S 3  to base  78  of transistor  66  with every third pulse of the oscillator or a 1:3 ratio. In like manner, if stage  90  is selected with selector position switch  40  in the low position, then every fourth pulse presented to circuit  86  will be counted and be produced through switch S 5 , the low position, to base  78  of transistor  66  thus having a 1:4 heating ratio. It can be readily seen that such a circuit cannot only control the amount of heat generated by heating element  20 , but also maintain the heat with less power requirements since it simply adds enough heat at periodic intervals to maintain a given heat. Thus, power is saved and the unit is more economically efficient and the battery life is prolonged. Implementing a duty cycle has an additional benefit that is not immediately apparent, that is, extending appliance life. Because the heating element is not operating the full time period the appliance is switched on, the useful life of the heating element is extended. 
   In accordance with still another exemplary embodiment of the present invention, automatic temperature control of heating element  20  is achieved through the circuit depicted in FIG.  4 F. As can be seen in  FIG. 4F , an integrated circuit controller  92  is added as an integrated circuit chip with memory  94  that stores a table comparing detected temperature versus counter  86  output. When hand controller  40  is set to a position of low, medium or high, that position is detected by integrated circuit controller  92  which then compares the temperature table with the actual temperature received from sensor  68  and through line  96  causing the proper output of counter  86  to be applied to the base of transistor  66  to supply the proper voltage or current to heating element  20  to cause it to reach the set temperature. The table in memory  94  stores temperature to count maps for each position on manual control switch  40 . For example, one position preset to correspond with 380° F. (193° C.) for using hot melt adhesives and another position on manual control switch  40  are preset to correspond to 225° F. (107° C.)for using cool melt adhesives. Alternatively, table in memory  94  may store temperature to count map-biased on the desired temperature associated with each position on manual control switch  40 . In that case, the greater the differential between the actual temperature, as detected by sensor  68 , and the desired temperature, as indicted by the position of manual control switch  40 , the longer the duty cycle. This allows for rapid recovery for higher usage and substantially increases throughput. 
   In accordance with another exemplary embodiment of the present invention, current or voltage to the heating element may be increased during the time the pulse is applied through the transistor  66 . Thus, in  FIG. 4G , each time pulser circuit  80  applies a pulse to base  78  of transistor  66 , it also applies a pulse to a voltage or current step-up device  98  to increase the current or voltage to heating element  20 . Such voltage step-up device could be, for instance, a piezoelectric device, well known in the art, that, when voltage is applied to the device in one direction, causes a step-up voltage that may be detected in another direction of the piezoelectric device. Voltage and current step-up devices are well known in the art and will not be described in any further detail here. Optionally, device  98  may be selectively activated by couples a switch, such as switch  36  (S 2 ) between pulser  80  and device  98 , thereby activating voltage and current step-up device  98  only after manual intervention by the operator. Alternatively, device  98  may be activated automatically based on the temperature of melt chamber  7  as sensed by sensor  68 . 
     FIG. 4H  illustrates how the pulse is increased in magnitude. Normally the pulse is at height  100 , but a step-up to height  102  is caused by step-up unit  98 . This increases the speed of heating of the element to the desired temperature. Further, to maintain a desired heat with such increased pulse could mean that a higher pulse ratio could be used. That is, for example only, one pulse out of five instead of one pulse out of three or four could be used. 
   While the present invention has been described with reference to an exemplary portable adhesive dispensing appliance which dispenses melt adhesive from “glue sticks,” one of ordinary skill level in the relevant art would readily understand that the principles and concepts discussed herein are equally relevant for other types of appliances. One such appliance is an industrial adhesive dispensing appliance which holds bulk adhesives in a melt reservoir and forces the hot melt to the dispensing gun through an insulated hose. The techniques described herein with regard to the present invention may be incorporated in the melt reservoir of such an appliance. Moreover, often the dispensing gun contains a secondary heating element for re-heating the melt to the ideal temperature for application onto a workpiece. In those cases, both the primary heating element of the melt reservoir and the secondary heating element in the dispensing gun may be controlled by pulse circuits as described herein above. 
   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.