Abstract:
An electrosurgical generator includes: a power supply configured to output a DC waveform; a power converter coupled to the power supply and configured to generate a radio frequency waveform based on the DC waveform; an active terminal coupled to the power converter and configured to couple to a first electrosurgical instrument and a second electrosurgical instrument; at least one sensor coupled to the power converter and configured to sense at least one property of the radio frequency waveform; and a controller coupled to the power converter. The controller is configured to: determine a first impedance associated with a first electrosurgical instrument and a second impedance associated with a second electrosurgical instrument based on the at least one property of the radio frequency waveform; and adjust at least one parameter of the radio frequency waveform based on the first impedance and the second impedance.

Description:
BACKGROUND 
     Technical Field 
       [0001]    The present disclosure relates to systems and methods for simultaneous activation of two or more electrosurgical instruments powered by a single electrosurgical generator. In particular, the present disclosure relates to an electrosurgical generator configured to prevent power surges during simultaneous activation and deactivation of multiple electrosurgical instruments. 
       Background of Related Art 
       [0002]    Electrosurgery involves application of high radio frequency (“RF”) electrical current to a surgical site to cut, ablate, desiccate, or coagulate tissue. In monopolar electrosurgery, a source or active electrode delivers radio frequency alternating current from the electrosurgical generator to the targeted tissue. A patient return electrode is placed remotely from the active electrode to conduct the current back to the generator. 
         [0003]    In bipolar electrosurgery, return and active electrodes are placed in close proximity to each other such that an electrical circuit is formed between the two electrodes (e.g., in the case of an electrosurgical forceps). In this manner, the applied electrical current is limited to the body tissue positioned between the electrodes. Accordingly, bipolar electrosurgery generally involves the use of instruments where it is desired to achieve a focused delivery of electrosurgical energy between two electrodes positioned on the instrument, e.g. forceps or the like. 
         [0004]    Some conventional electrosurgical generators allow for use of two or more electrosurgical instruments coupled to a single output rail of the electrosurgical generator. Thus, the electrosurgical generator splits the output from the single output rail to each of the instruments. This allows multiple surgeons to operate using a single generator. However, for a selected power setting, if both instruments were activated simultaneously, each of the instruments receives only a portion of the power, dependent on impedance of the tissue. Thus, if both instruments are operating simultaneously on the tissue having the same impedance, then each instrument only receives half of the selected power setting. In some instances, due to different impedances encountered by each of the electrosurgical instruments, some of the instruments may receive too much or too little power, as the conventional electrosurgical generators are incapable of calculating power output at each channel. Moreover, when the power flow to one of the instruments is deactivated, then the other instrument experiences a power surge as the electrosurgical generator supplies the full amount of power previously supplied to two instruments to a single instrument. Accordingly, there is a need for an electrosurgical generator configured to prevent power surges that occur during simultaneous deactivation of one of the multiple electrosurgical instruments. 
       SUMMARY 
       [0005]    The present disclosure provides an electrosurgical generator including a non-resonant power converter having one or more switching elements controlled by a switching waveform (e.g., a pulse-width modulated waveform) generated by a controller. The generator also includes one or more sensors configures to measure voltage and current of the power output by the power converter. The electrosurgical generator includes an advanced simultaneous operational mode, during which the electrosurgical generator is set to a common power setting for two or more electrosurgical instruments coupled to a single output rail. While one of the electrosurgical instruments is used, e.g., a first electrosurgical instrument, the electrosurgical generator operates in a standard power control mode, during which the power is held constant within applicable impedance range and voltage and current limits. During this mode, impedance encountered by the first electrosurgical instrument is continuously calculated and averaged over a period of time, which may be from about 500 milliseconds (“ms”) to about 1,000 ms. Once the second electrosurgical instrument is activated, simultaneously with the first electrosurgical instrument, the impedance encountered by the second electrosurgical instrument is in parallel with the impedance encountered by the first electrosurgical instrument, which results in a parallel impedance. At this point, the electrosurgical generator also calculates the total parallel impedance. Using the previously calculated first impedance and the total parallel impedance, the generator estimates and/or calculates the second impedance. The electrosurgical generator then adjusts the voltage supplied to one of the first or second electrosurgical instrument having the lower impedance to the selected power setting. The other electrosurgical instrument, the one having the higher impedance, receives higher power. Thus, the electrosurgical generator according to the present disclosure allows for simultaneous activation of multiple electrosurgical instruments based on measured impedance without drastic power changes. 
         [0006]    According to one embodiment of the present disclosure, an electrosurgical generator is provided. The electrosurgical generator includes: a power supply configured to output a DC waveform; a power converter coupled to the power supply and configured to generate a radio frequency waveform based on the DC waveform; an active terminal coupled to the power converter and configured to couple to a first electrosurgical instrument and a second electrosurgical instrument; at least one sensor coupled to the power converter and configured to sense at least one property of the radio frequency waveform; and a controller coupled to the power converter. The controller is configured to: determine a first impedance associated with a first electrosurgical instrument and a second impedance associated with a second electrosurgical instrument based on the at least one property of the radio frequency waveform; and adjust at least one parameter of the radio frequency waveform based on the first impedance and the second impedance. 
         [0007]    According to one aspect of the above embodiment, the electrosurgical generator also includes a user interface coupled to the controller, the user interface configured to receive a user input. 
         [0008]    According to one aspect of the above embodiment, the controller is further configured to adjust the at least one parameter of the radio frequency waveform based on the user input. 
         [0009]    According to one aspect of the above embodiment, the electrosurgical generator also includes a return terminal coupled to the power converter, wherein the return terminal is configured to couple to at least one return electrode pad. The active terminal is further configured to couple to a first monopolar electrosurgical instrument and a second monopolar electrosurgical instrument. 
         [0010]    According to one aspect of the above embodiment, the at least one property is power. 
         [0011]    According to one aspect of the above embodiment, the controller is further configured to adjust the power of the radio frequency waveform such that the power delivered to each of the first electrosurgical instrument and the second electrosurgical instrument is between 50% and 100% of the adjusted power. 
         [0012]    According to another embodiment of the present disclosure, an electrosurgical system is disclosed. The electrosurgical system includes: a first electrosurgical instrument; a second electrosurgical instrument; and an electrosurgical generator. The electrosurgical generator includes a power supply configured to output a DC waveform; a power converter coupled to the power supply and configured to generate a radio frequency waveform based on the DC waveform; an active terminal coupled to the power converter and configured to couple to the first electrosurgical instrument and the second electrosurgical instrument; at least one sensor coupled to the power converter and configured to sense at least one property of the radio frequency waveform; and a controller coupled to the power converter. The controller configured to: determine a first impedance associated with the first electrosurgical instrument and a second impedance associated with the second electrosurgical instrument based on the at least one property of the radio frequency waveform; and adjust power of the radio frequency waveform based on the first impedance and the second impedance. 
         [0013]    According to one aspect of the above embodiment, electrosurgical generator further includes a user interface coupled to the controller, the user interface is configured to receive a user input. 
         [0014]    According to one aspect of the above embodiment, the controller is further configured to adjust the power of the radio frequency waveform based on the user input. 
         [0015]    According to one aspect of the above embodiment, the electrosurgical generator further includes a return terminal coupled to the power converter, the return terminal is configured to couple to at least one return electrode pad. 
         [0016]    According to one aspect of the above embodiment, the active terminal is further configured to couple to a first monopolar electrosurgical instrument and a second monopolar electrosurgical instrument. 
         [0017]    According to one aspect of the above embodiment, the first electrosurgical instrument is activated prior to the second electrosurgical instrument. 
         [0018]    According to one aspect of the above embodiment, the at least one sensor is configured to measure the first impedance prior to activation of the second electrosurgical instrument. 
         [0019]    According to one aspect of the above embodiment, the at least one sensor is configured to measure total impedance after activation of the first electrosurgical instrument and the second electrosurgical instrument. 
         [0020]    According to one aspect of the above embodiment, the controller is configured to determine the second impedance based on the total impedance and the first impedance. 
         [0021]    According to one aspect of the above embodiment, the controller is further configured to adjust the power such that the power delivered to one of the first electrosurgical instrument or the second electrosurgical instrument having a lower impedance does not exceed the adjusted power. 
         [0022]    According to one aspect of the above embodiment, the controller further configured to adjust the power such that the power delivered to one of the first electrosurgical instrument or the second electrosurgical instrument having a higher impedance is more than half of the adjusted power. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    The present disclosure may be understood by reference to the accompanying drawings, when considered in conjunction with the subsequent, detailed description, in which: 
           [0024]      FIG. 1  is a perspective view of an electrosurgical system according to an embodiment of the present disclosure; 
           [0025]      FIG. 2  is a front view of an electrosurgical generator of the electrosurgical system of  FIG. 1  according to an embodiment of the present disclosure; 
           [0026]      FIG. 3  is a schematic diagram of the electrosurgical system of  FIG. 1  according to an embodiment of the present disclosure; 
           [0027]      FIG. 4  is a flow chart of a method for controlling the electrosurgical generator  FIG. 2  according to an embodiment of the present disclosure; and 
           [0028]      FIG. 5  is an impedance and power plot for simultaneously activating two electrosurgical instruments according to an embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    Particular embodiments of the present disclosure will be described below with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail to avoid obscuring the present disclosure in unnecessary detail. Those skilled in the art will understand that the present disclosure may be adapted for use with any electrosurgical instrument. It should also be appreciated that different electrical and mechanical connections and other considerations may apply to each particular type of instrument. 
         [0030]    Briefly, an electrosurgical generator according to the present disclosure may be used in monopolar and/or bipolar electrosurgical procedures, including, for example, cutting, coagulation, ablation, and vessel sealing procedures. The generator may include a plurality of outputs for interfacing with various electrosurgical instruments (e.g., monopolar instruments, return electrode pads, bipolar electrosurgical forceps, footswitches, etc.). Further, the generator includes electronic circuitry configured to generate radio frequency energy specifically suited for powering electrosurgical instruments operating in various electrosurgical modes (e.g., cut, blend, coagulate, division with hemostasis, fulgurate, spray, etc.) and procedures (e.g., monopolar, bipolar, vessel sealing). 
         [0031]    Referring to  FIG. 1  an electrosurgical system  10  is shown which includes one or more monopolar electrosurgical instruments  20 ′ and  20 ″ having one or more active electrodes  23 ′ and  23 ″ (e.g., electrosurgical cutting probe, ablation electrode(s), etc.) for treating tissue of a patient. Electrosurgical alternating RF current is supplied to the instruments  20 ′ and  20 ″ by a generator  200  via supply lines  24 ′ and  24 ″, respectively, that are connected to an active terminal  230  ( FIG. 3 ) of the generator  200 , allowing the instruments  20 ′ and  20 ″ to cut, coagulate, and/or otherwise treat tissue. The alternating RF current is returned to the generator  200  through a return electrode pad  26  via a return line  28  at a return terminal  232  ( FIG. 3 ) of the generator  200 . The system  10  may include a plurality of return electrode pads  26  that, in use, are disposed on a patient to minimize the chances of tissue damage by maximizing the overall contact area with the patient. In addition, the generator  200  and the return electrode pads  26  may be configured for monitoring tissue-to-patient contact to ensure that sufficient contact exists therebetween. In embodiments, the system  10  may also include one or more bipolar electrosurgical instruments, for example, a bipolar electrosurgical forceps (not shown), having one or more electrodes for treating tissue of a patient. In further embodiments, the generator  200  according to the present disclosure may also be configured to simultaneously activate bipolar electrosurgical instruments in a manner described below. 
         [0032]    With reference to  FIG. 2 , a front face  240  of the generator  200  is shown. The generator  200  may include a plurality of ports  250 - 262  to accommodate various types of electrosurgical instruments. The generator  200  includes a user interface  241  having one or more display screens  242 ,  244 ,  246  for providing the user with variety of output information (e.g., intensity settings, treatment complete indicators, etc.). Each of the screens  242 ,  244 ,  246  is associated with a corresponding port  250 - 262 . The generator  200  includes suitable input controls (e.g., buttons, activators, switches, touch screen, etc.) for controlling the generator  200 . The screens  242 ,  244 ,  246  are also configured as touch screens that display a corresponding menu for the instruments (e.g., more monopolar electrosurgical instruments  20 ′ and  20 ″, electrosurgical forceps, etc.). The user then adjusts inputs by simply touching corresponding menu options. 
         [0033]    Screen  242  controls monopolar output and the instruments connected to the ports  250  and  252 . Port  250  is configured to couple to a monopolar electrosurgical instrument (e.g., electrosurgical instruments  20 ′ and  20 ″) and port  252  is configured to couple to a foot switch (not shown). The foot switch may be used to provide for additional inputs (e.g., replicating inputs of the generator  200 ). Screen  244  controls monopolar and bipolar output and the instruments connected to the ports  256  and  258 . Port  256  is configured to couple to other monopolar instruments. Port  258  is configured to couple to a bipolar instrument (not shown). 
         [0034]    Screen  246  controls the electrosurgical forceps that may be plugged into one of the ports  260  and  262 , respectively. The generator  200  outputs energy through the ports  260  and  262  suitable for sealing tissue grasped by the electrosurgical forceps. In particular, screen  246  outputs a user interface that allows the user to input a user-defined intensity setting for each of the ports  260  and  262 . The user-defined setting may be any setting that allows the user to adjust one or more energy delivery parameters, such as power, current, voltage, energy, etc. or sealing parameters, such as energy rate limiters, sealing duration, etc. The active and return terminals  230  and  232  ( FIG. 3 ) may be coupled to any of the desired ports  250 - 262 . In embodiments, the active and return terminals  230  and  232  may be coupled to the ports  250 - 262 . 
         [0035]    With reference to  FIG. 3 , the generator  200  includes a controller  224 , a power supply  227 , and a power converter  228 . The power supply  227  may be a high voltage, DC power supply connected to an AC source (e.g., line voltage) and provides high voltage, DC power to the power converter  228 , which then converts high voltage, DC power into RF energy and delivers the energy to the active terminal  230 . The energy is returned thereto via the return terminal  232 . In particular, electrosurgical energy for energizing the monopolar electrosurgical instruments  20 ′ and  20 ″ coupled to ports  250  and  256  is delivered through the active terminal  230  and returned through the return electrode pad  26  coupled to the port  254 , which in turn, is coupled to the return terminal  232 . The active and return terminals  230  and  232  are coupled to the power converter  228  through an isolation transformer  229 . The isolation transformer  229  includes a primary winding  229   a  coupled to the power converter and a secondary winding  229   b  coupled to the active and return terminals  230  and  232 . 
         [0036]    The generator  200  also includes a DC-DC buck converter  301  coupled to the power supply  227 . Furthermore, an inductor  303  is electrically coupled to the DC-DC buck converter  301  and the power converter  228 . The inductor  303  may have a relatively large inductance which smoothes the current supplied to the power converter  228 , such that the inductor  303  is configured to supply relatively constant current to the power converter  228 . The output of power converter  228  transmits current through an isolation transformer  229  to the load e.g., tissue being treated. 
         [0037]    The power converter  228  is configured to operate in a plurality of modes, during which the generator  200  outputs corresponding waveforms having specific duty cycles, peak voltages, crest factors, etc. It is envisioned that in other embodiments, the generator  200  may be based on other types of suitable power supply topologies. Power converter  228  may be a resonant RF amplifier or a non-resonant RF amplifier, as shown. A non-resonant RF amplifier, as used herein, denotes an amplifier lacking any tuning components, i.e., conductors, capacitors, etc., disposed between the power converter and the load, e.g., tissue. 
         [0038]    The controller  224  includes a processor (not shown) operably connected to a memory (not shown), which may include one or more of volatile, non-volatile, magnetic, optical, or electrical media, such as read-only memory (ROM), random access memory (RAM), electrically-erasable programmable ROM (EEPROM), non-volatile RAM (NVRAM), or flash memory. The processor may be any suitable processor (e.g., control circuit) adapted to perform the operations, calculations, and/or set of instructions described in the present disclosure including, but not limited to, a hardware processor, a field programmable gate array (FPGA), a digital signal processor (DSP), a central processing unit (CPU), a microprocessor, and combinations thereof. Those skilled in the art will appreciate that the processor may be substituted for by using any logic processor (e.g., control circuit) adapted to perform the calculations and/or set of instructions described herein. 
         [0039]    The controller  224  includes an output port that is operably connected to the power supply  227  and/or power converter  228  allowing the processor to control the output of the generator  200  according to either open and/or closed control loop schemes. A closed loop control scheme is a feedback control loop, in which a plurality of sensors measure a variety of tissue and energy properties (e.g., tissue impedance, tissue temperature, output power, current and/or voltage, etc.), and provide feedback to the controller  224 . The controller  224  then controls the power supply  227  and/or power converter  228 , which adjusts the DC and/or power supply, respectively. 
         [0040]    The generator  200  according to the present disclosure may also include a plurality of sensors  310 . In the embodiment illustrated in  FIG. 3 , the sensors  310  are coupled to a rail  305 , which couples the power converter  228  to the primary winding  229   a  of the transformer  229 . Thus, the sensors  310  are configured to sense voltage, current, and other electrical properties of energy supplied to the active and return terminals  230  and  232  through the rail  305 . 
         [0041]    In further embodiments, the sensors  310  may be coupled to the power supply  227 , DC-DC buck converter  301 , and/or the inductor  303 , and may be configured to sense properties of DC current supplied to the power converter  228 . The controller  224  also receives input signals from the input controls of the generator  200  and/or the instruments  20 ′ and  20 ″, and/or electrosurgical forceps  30 . The controller  224  utilizes the input signals to adjust power outputted by the generator  200  and/or performs other control functions thereon. 
         [0042]    The DC-DC buck converter  301  includes a switching element  301   a  and power converter  228  includes a plurality of switching elements  228   a - 228   d  arranged in an H-bridge topology. In embodiments, power converter  228  may be configured according to any suitable topology including, but not limited to, half-bridge, full-bridge, push-pull, and the like. Suitable switching elements include voltage-controlled devices such as transistors, field-effect transistors (FETs), combinations thereof, and the like. In embodiments, the FETs may be formed from gallium nitride, aluminum nitride, boron nitride, silicone carbide, or any other suitable wide bandgap materials. 
         [0043]    The controller  224  is in communication with both DC-DC buck converter  301  and power converter  228 , in particular, the switching elements  301   a  and  228   a - 228   d , respectively. Controller  224  is configured to output control signals, which may be a pulse-width modulated (“PWM”) signal, to switching elements  301   a  and  228   a - 228   d . In particular, controller  224  is configured to modulate a control signal d 1  supplied to switching element  301   a  of DC-DC buck converter  301  and control signal d 2  supplied to switching elements  228   a - 228   d  of power converter  228 . Additionally, controller  224  is configured to calculate power characteristics of generator  200 , and control generator  200  based at least in part on the measured power characteristics including, but not limited to, current passing through the inductor  303 , DC output of the DC-DC buck converter  301 , and the voltage and current at the output of power converter  228 . 
         [0044]    With reference to  FIG. 4 , a method  400  according to the present disclosure for controlling the generator  200  during simultaneous activation of electrosurgical instruments  20 ′ and  20 ″ is described. Method  400  is also described below concurrently with  FIG. 5 , which shows a combined plot of impedance encountered by each of the electrosurgical instruments  20 ′ and  20 ″ and power delivered thereto. 
         [0045]    Initially, the electrosurgical instruments  20 ′ and  20 ″ are coupled to the active terminal  230  of the generator  200  through the ports  250  and  256 . The user may select a desired electrosurgical mode (e.g., cut, blend, coagulate, division with hemostasis, fulgurate, spray, etc.). The user also selects the power/intensity setting at which the electrosurgical instrument  20 ′ is operated through the user interface  241 . Thereafter, the electrosurgical instrument  20 ′ is activated by signaling the generator  200  to supply electrical power. In response, electrosurgical energy is supplied to the electrosurgical instrument  20 ′, during which the sensors  310  continually monitor electrical properties of the supplied energy, such as voltage and current. The monitored voltage and current values are supplied to the controller  224 , which calculates the impedance encountered by the electrosurgical instrument  20 ′ during treatment. In embodiments, the controller  224  may continuously calculate impedance based on the measured voltage and current values to obtain first instrument impedance Z1 (e.g., impedance of the electrosurgical instrument  20 ′) as shown in  FIG. 5 . The calculated impedance may be averaged to provide a moving average over a defined time period. The time period for the moving impedance average may be from about 100 milliseconds (ms) to about 2,000 ms, in embodiments, the time period may be from about 500 ms to about 1,000 ms. 
         [0046]    The second electrosurgical instrument  20 ″ may be activated simultaneously with or after the first electrosurgical instrument  20 ′. As the second electrosurgical instrument  20 ″ contacts tissue, the tissue impedance encountered by the second electrosurgical instrument  20 ″, Z2, is in parallel with impedance Z1 of the first electrosurgical instrument  20 ′. As described above, the sensors  310  measure voltage and current through the rail  305 , which supplies energy to the active terminal  230 , to which both of the first and second electrosurgical instrument  20 ′ and  20 ″ are coupled. Accordingly, the sensors  310  are capable of determining voltage and current for the combined power supplied to the first and second electrosurgical instruments  20 ′ and  20 ″. The controller  224  calculates the total impedance, Ztotal, based on the total measured voltage and current. The Ztotal value is based on the parallel combination of Z1 and Z2. Accordingly, the controller  224  is configured to calculate Z2, which cannot be measured directly by the sensors  310  as the first and second electrosurgical instruments  20 ′ and  20 ″ share a common output, namely the active terminal  230  through the rail  305 . In particular, the controller  224  is configured to calculate Z2 based on the following formulas (I) and (II): 
         [0000]        Z total= Z 1* Z 2/( Z 1+ Z 2)  (I)
 
         [0000]        Z 2= Z 1 *Z total/ Z 1 −Z total)  (II)
 
         [0047]    In formulas (I) and (II), Z1 is the impedance calculated based on measured voltage and current when only one electrosurgical instrument (e.g., first electrosurgical instrument  20 ′) is activated, Ztotal is the impedance calculated based on measured voltage and current when both electrosurgical instruments  20 ′ and  20 ″ are activated, and Z2 is the impedance encountered by the second electrosurgical instrument  20 ″. 
         [0048]    Once the controller  224  calculates Z2, both Z1 and Z2 are known, the controller  224  adjusts the power output of the power converter  228  based on the selected power setting and the impedance of both of the electrosurgical instruments  20 ′ and  20 ″. In particular, the controller  224  adjusts the power to provide for a change in impedance due to addition of the impedance encountered by the second electrosurgical instrument  20 ″. However, power is adjusted not to exceed the initial power setting and to ensure that the electrosurgical instrument with the lower impedance receives the power at the initial power setting. The power is also adjusted such that the other electrosurgical instrument receives more than half of the selected power setting. 
         [0049]    The power and impedance plots for each of the electrosurgical instruments  20 ′ and  20 ″ are described in further detail below with respect to  FIG. 5 . In particular, plots P1 and Z1 illustrate exemplary power delivered to and the measured impedance encountered by the first electrosurgical instrument  20 ′, respectively. The electrosurgical instrument  20 ′ is activated at the selected power setting of about 40 watts and the impedance is constant at about 2,000 ohms. At about 3 seconds, the second electrosurgical instrument  20 ″ is activated and the controller  224  determines that the impedance of the second electrosurgical instrument  20 ″ is about 1,500 ohms, based on the total impedance, Ztotal. Since the addition of another electrosurgical instrument in parallel results in decrease in impedance, the controller  224  signals the power converter to adjust its output such that the second electrosurgical instrument  20 ″, which has the lower impedance, receives the power at the selected setting of about 40 watts. Based on that setting, the first electrosurgical instrument  20 ′ receives about 30 watts, which is larger than 50% of the initial setting of 40 watts. This calculation and adjustment in power prevents large swings in power, such that when the first electrosurgical instrument  20 ′ is deactivated at about 8 seconds, the second electrosurgical instrument  20 ″ continues to receive power at the initial power setting of about 40 watts, rather than receiving the higher combined power for both of the electrosurgical instruments  20 ′ and  20 ″. 
         [0050]    In embodiments, the generator  200  may include individual rails for each of the ports  250  and  256  and the sensors  310  may be coupled to each of the rails to monitor current and voltage therein. The controller  224  may then calculate power for each rail individually and signal the power converter  228  to adjust the power dynamically to match the set power on each of the rail as described above with respect to the embodiment of  FIG. 3 . In particular, the controller  224  signals the power converter  228  to adjust the power dynamically at the rail having the highest current not to exceed the power setting. 
         [0051]    While several embodiments of the disclosure have been shown in the drawings and/or described herein, it is not intended that the disclosure be limited thereto, as it is intended that the disclosure be as broad in scope as the art will allow and that the specification be read likewise. Therefore, the above description should not be construed as limiting, but merely as exemplifications of particular embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.