Abstract:
A battery power supply with extended shelf-life is composed of a plurality of batteries connected in series with a switching element and voltage booster. The switching element is composed of a transistor in parallel with a passive component that produces a voltage drop when the transistor is off. The voltage booster maintains an output voltage at set value when battery capacity deteriorates. A micro-controller is used to monitor voltage potentials to detect the presence of an external load. When no load is detected, all active components are disabled to conserve energy and avoid self-discharge.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation-in-Part of prior pending U.S. patent application Ser. No. 12/747,513 to Simon B. Johnson filed Jun. 10, 2010 based on PCT application PCT/US08/86301 filed Dec. 10, 2008 which claims the benefit of provisional patent application No. 61/012,700 filed Dec. 10, 2007; and is a Continuation-in-Part of prior pending U.S. patent application Ser. No. 13/218,336 filed Aug. 25, 2011 which claims the benefit of provisional patent application No. 61/377,089 filed Aug. 25, 2010. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     FIELD OF THE INVENTION 
     The present invention relates generally to battery powered supplies for electronic devices and more particularly, to a means of improving battery shelf life by eliminating self-discharge of battery powered supplies. 
     BACKGROUND OF THE INVENTION 
     Many of the devices we come to depend on today are battery powered: cell phones, tablets, mp3 players, etc. These typically have a battery power supply that can be recharged, and can typically be recharged from either an AC power source using an adapter or a powered USB port for charging the battery power supply. Conventional devices of this type typically require a +5 volt DC source for charging the battery power supply. 
     A common issue facing all battery powered devices is they need to re-charge—sometimes when a suitable charging port is not available. To this end, there have been a number of auxiliary supplies sold that consist of a battery source that, when connected to a cell phone, provide extended operation. 
     Batteries do not, by their nature, provide a consistent voltage at the anode. For example, an alkaline battery might start at 1.6 volts when purchased, but will fade to about 0.9 volts when it is determined depleted. This means that any 5 volt supply generated from a set of four such batteries would benefit from having an internal voltage booster capable of compensating for a drifting supply in order to prolong the interval between recharging of the batteries (in the case of rechargeable batteries) or replacement of the batteries (in the case of disposable batteries). 
     Most backup supplies of the type discussed above that are sold on the market come equipped with a switch for activating their internal voltage booster. This internal voltage booster requires additional power for operation. Even with no load, an auxiliary power supply is susceptible to self-discharge. The user must remember to turn off the unit when disconnecting a load. Failure to do so means the auxiliary power source may not be available when needed in the future. 
     An example of a prior art device of the type described above is a Duracell Instant USB charger for cell phones. Booster circuitry within this charger draws current whether powering an external load or whether powering nothing. It is like the electronics in a typical PC computer—it consumes power whether the PC computer is in use or whether the user has left the room and the PC computer sits idle. 
     SUMMARY OF THE INVENTION 
     The present invention provides a battery power supply apparatus that is an auxiliary battery powered source capable of generating a substantially fixed voltage source for powering connected devices. In this apparatus, a battery—which can include a plurality of batteries connected in series—is provided that is a voltage source that fluctuates as battery capacity diminishes. Thus, the battery voltage may diminish with time, and this is referred to herein as battery drift. The present invention provides a voltage booster to compensate for this battery drift, for the purpose of providing a constant output voltage. 
     A switch, in parallel with a passive component, is used for the detection of a load. With the switch off, a load draws current through the passive component creating a voltage drop. At a predetermined threshold, a micro-controller is activated that triggers a voltage booster to provide a fixed voltage at the output. The switch is then turned ON, providing a zero resistance path to the voltage booster. 
     By monitoring the voltage potential at the battery and across the passive component, the micro-processor is able to determine when a load has been disconnected or has been turned off. Upon determination that a load no longer exists, the switch is turned off, the voltage booster is disabled, and the micro-controller waits for the connection of a load. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an apparatus for a battery power supply apparatus having a battery portion and an electrical circuit connected to the battery portion. 
         FIG. 2  is a state transition diagram for the battery power supply of the apparatus of  FIG. 1  showing four operating states together with conditions for a change of state between the four operating states. 
         FIGS. 3A-3D  schematically show equivalent circuits associated with each of the four states shown in  FIG. 2 . 
         FIG. 4  is an expanded schematic circuit diagram of a voltage booster in the apparatus of FIG.  1 . 
         FIG. 5  is a flow chart illustrating operation of the apparatus of  FIGS. 1-4 , according to the present invention. 
         FIG. 6  schematically depicts the micro-controller and its internal components and connections of the device of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a schematic diagram of a battery power supply apparatus  100  having a battery portion  101  and an electrical circuit (discussed further hereunder) which has an output  112  for connection to a load. The battery portion  101  includes one or more batteries  12 , and for the example shown and described herein the battery portion  101  includes four identical batteries  12  connected in series. This battery arrangement with four batteries  12  is typical of many practical devices. 
     The above-mentioned electrical circuit includes a first circuit path  20  connected to a positive terminal of the battery portion  101  having a voltage indicated as Vbat  111  in  FIG. 1 , and continuing to a positive side of the output  112 . The first circuit path  20 , going in direction from the positive battery terminal indicated at Vbat  111  in  FIG. 1 , includes a MOSFET  104  having an integral body diode  105  (one specific example of a MOSFET having an integral body diode is a model no. NTGS3443), an inductor  106 , and a diode  113 . The inductor  106  and diode  113  are controlled by a voltage booster  107 . The above-mentioned electrical circuit also includes a second circuit path  30 , which is connected between a negative terminal of the battery portion  101  and continuing to a negative side of the output  112 . 
     It is noted that the circuit elements which include the MOSFET  104  and the integral body diode  105  taken together form a controllable ON-OFF portion, the term “controllable ON-OFF portion” being a designation used herein for the function of these circuit elements. However, although the MOSFET  104  and the integral body diode  105  form the preferred embodiment, the present invention is not limited to use of a MOSFET circuit element, and other circuit arrangements can be used which would perform similar functions, as discussed further below. 
     Examples follow of equivalent types of circuits which are contemplated for use for the controllable ON-OFF portion (defined above), and which could be used in place of the MOSFET  104  and the body diode  105 . More specifically, the following are examples of equivalent circuits for the “controllable ON-OFF portion”: 
     First example: a bipolar transistor (not shown) with discrete diode connected between collector and emitter. The voltage drop can be detected across the discrete diode when the bipolar transistor is turned OFF. Turning the bipolar transistor ON removes that diode from the current path. 
     Second example: a bipolar transistor (not shown) with a resistor connected between the collector and emitter. The voltage drop can be detected across the resistor with the bipolar transistor OFF. Turning the bipolar transistor ON effectively removes the resistor from the current path. 
     Third example: either a discrete diode (not shown) or a resistor connected across a relay (not shown). A voltage drop is detected across the relay in the open state. Closing the relay effectively removes both passive components from the current path. 
     In general, the MOSFET  104  provides two important features: 
     When OFF, it provides a means of sensing current by creating a voltage drop that is detected by the sense inputs  102  and  103  when current passes through the internal body diode  105 . 
     When ON, it provides a short circuit eliminating the voltage drop created by current sensing mechanism in  1 . 
     The examples above provide an alternate means of accomplishing approximately the same thing. 
     It is contemplated that any one having skill in the circuit design arts would understand how to implement these example replacement circuits, as well as any other arrangements which perform the same functions as are required of the MOSFET  104  and body diode  105  in the present invention as discussed hereinabove. 
     The above-mentioned electrical circuit includes a third circuit path  40  connecting the first circuit path  20  with the second circuit path  30 , the third circuit path  40  having one end thereof connected between the MOSFET  104  and the positive terminal of the battery portion  101  and having the other end thereof connected to the second circuit path  30 . The third circuit path  40  includes a first resistor  42  and a second resistor  44 . A sense  102  is shown in dashed outline in  FIG. 1  positioned to sense voltage between the first resistor  42  and the second resistor  44 . 
     The battery power supply apparatus  100  also includes a fourth circuit path  50  connecting the first circuit path  20  with the second circuit path  30 , the fourth circuit path  50  having one end thereof connected between the MOSFET  104  and the inductor  106 , and having the other end thereof connected to the circuit path  30 . The circuit path  50  includes a third resistor  52  and a fourth resistor  54 . A sense  103  is shown in dashed outline in  FIG. 1  positioned to sense voltage between the third resistor  52  and the fourth resistor  54 . The third circuit path  40  and the fourth circuit path  50  together with the resistors ( 42 ,  44 ) and ( 52 ,  54 ) constitute voltage dividers, and the resistors ( 42 ,  44 ) and ( 52 ,  54 ) are voltage divider resistors. 
     The above-mentioned electrical circuit further includes a booster control portion  60 , which includes a micro-controller  109 , a voltage booster  107 , and a regulated voltage  108  connected to the micro-controller  109 . The micro-controller  109  supplies an FET control signal  110  (shown in dashed outline in  FIG. 1 ) to control the MOSFET  104 , and also supplies a booster enable signal  114  to control operation of the booster  107 . The regulated voltage  108  is connected to the voltage Vbat  111  providing power to the micro-controller  109  and establishing a reference voltage for which sense  102  and  103  are measured. 
     The regulated voltage  108  provides a dual function: it powers the micro-controller  109  and also supplies a fixed reference voltage for the sense  102  and the sense  103 . The micro-controller  109  receives analog values from sense  102  and  103  and converts to digital values. This is a standard feature of micro-controllers with analog to digital (A/D). The PIC16F506, from Microchip is an example of such a controller. There are many other examples currently on the market. 
     The A/D values are relative to the supply voltage of the micro-controller  109 . Therefore, it is important to establish a reference voltage via the regulated voltage  108 . As an example, say the regulated voltage  108  is fixed at 3.3 volts. This means the resistor values creating the sense  102  and  103  must be chosen such that neither the sense  102  nor the sense  103  exceed 3.3 volts. Also, since Vbat  111  can range anywhere from 4 volts to 6 volts, the regulated voltage  108  supplies a constant 3.3 volts allowing the micro-controller  109  to differentiate between a fully charged state and a discharged state. 
     The operation of the battery power supply apparatus  100  is as follows.  FIG. 1  schematically depicts a battery power supply apparatus which provides an extended operational life and extended shelf-life. The series of batteries  12  forming the battery portion  101  provides the power source. In the embodiment shown, four series batteries  12  provide a cumulative potential (Vbat  111 ) that ranges from 3.6 volts when batteries are low to 6.4 volts when batteries are fully charged. For the sake of discussion, it will be assumed that each battery  12  is a typical Alkaline AA battery, however the invention is not limited thereto but contemplates use of other battery types and other battery chemistries, such as NiCd and NiMH, among others which will be apparent to any one having skill in the battery power arts. 
     The MOSFET  104  provides several functions, as follows: 
     a) When turned OFF, its internal body diode  105  provides a means of sensing current; 
     b) When turned ON, it provides a zero ohm path for power delivery; 
     c) When turned OFF, the internal body diode  105  provides a voltage drop when Vbat  111  exceeds the nominal value at output  112   
     As shown in  FIG. 1 , the voltage divider resistors ( 42 ,  44 ) and ( 52 ,  54 ) are placed on either side of the MOSFET  104  to create sense potentials  102  and  103 . When the MOSFET  104  is turned OFF, sense  102  and sense  103  are equivalent when the output  112  has no load. However, when a load is present, the body diode  105  will conduct providing a standard diode drop which is typically in the range of Vf=0.8 volts. With a load present, the sense  102  will be greater than the sense  103 . The FET control signal  110  is used to turn the MOSFET  104  OFF and ON. When MOSFET  104  is turned off, current flows through the body diode  105 . Combined with the forward voltage drop across diode  113  of 0.2 volts, a 1 volt drop occurs between Vbat  111  and output  112 . When MOSFET  104  is turned ON, it is effectively a short circuit created between the anode and cathode of body diode  105 . This is consistent with the paragraph above. 
     The purpose of the voltage booster  107  is to provide a fixed voltage (i.e., fixed to be within a predetermined target output voltage range) at the output  112 . Therefore, whenever the battery voltage Vbat  111  drops below 4.5 volts, for example, the voltage booster  107  is turned on by the micro-controller  109  via the booster enable signal  113  to increase the voltage output at the output  112  to an approximately constant 5 volts. 
     Voltage boosters exist, for example a NCP1415A (which is commercially available), that typically generate a fixed voltage within 2.5% accuracy of the desired output; in this case, 5.0 volts. 
     Known voltage boosters usable in the present invention are of the type having the external inductor  106  and operate such that, when switched at a specified frequency, creates a higher potential on the + side of the inductor  106  compared to the − side of the inductor  106 . The inductor  106  has the added advantage of passing DC current. Therefore, when the voltage booster  107  is disabled, the inductor  106  acts as a short circuit passing current from the MOSFET  104  to the output  112 . 
     The micro-controller  109  functions to monitor the voltages received by the sense  102  and the sense  103 . Depending on the absolute and relative values of sense  102  and sense  103 , the micro-controller  109  can determine the specific state in which the battery power supply  100  should operate. These states are shown and discussed below with reference to  FIGS. 2 and 3 . A regulated voltage source  108  powers the micro-controller  109  in order to establish a reference for measuring the sense  102  and the sense  103 . For example, if the battery portion  101  produces a Vbat  111  of 3.6 volts when “dead”, then it makes sense to provide a regulated voltage  108  of 3.3 volts to assure proper operation of the micro-controller  109 . 
     Micro-controllers operate within a range of voltages. The 16F506 mentioned earlier operates from as low as 2 volts to as high as 5.5 volts. There is nothing special about this, and it is considered that most or even all micro-controllers operate in this way. 
       FIG. 2  is a state transition diagram for the battery power supply of the apparatus of  FIG. 1  showing four operating states  201 ,  202 ,  203  and  204 , together with conditions for a change of state between these four operating states. More specifically,  FIG. 2  is a state transition diagram showing how internal control is affected by an external load and by the battery voltage level of the battery portion  101 . The following discussion will also reference  FIG. 3  which shows the equivalent circuits for each of the above-mentioned four states. 
     The process starts with state  201 , in which:
         No load connected to the output  112 : output is floating.   the MOSFET  104  is OFF: with no load, there is no voltage drop across the body diode  105     the voltage booster  107  is OFF: the inductor  106  acts as a short circuit for DC   the output  112 =Vbat  111     the sense  103 &gt;4.7 volts: assuming fully charged batteries  12  in the battery portion  101     Equivalent circuit is shown in  FIG. 3A         

     State  201  is a state consuming micro-amps, inasmuch as the micro-controller  109  is in a sleep mode. The resistance of the voltage divider resistors must be selected to be high enough to limit current needed for the sense  102  and the sense  103 . 
     The resistances of the resistors  42 ,  44 ,  52 , and  54  are referred to in the following as R 42 , R 44 , R 52 , and R 54 , respectively. The resistances R 42  and R 44  could for example be  100  ohms. That means the current across the path  40  will be 5 volts/200 ohms=25 mA. The sense  102  will have a value of 2.5 volts. While the sense  102  is within an acceptable range, 25 mA is excessive and adds additional burden on the batteries which will result in a shorter lifespan. Now, let R 42  and R 44  be chosen to be 100K ohms each. Then the sense  102  will still have a value of 2.5 volts, but the quiescent current drawn on path  40  is now 5 volts/200K ohms=25 micro-amps (0.025 mA)—a much better choice for preserving batteries and extending battery life. 
     Thus, the values for R 42 , R 44 , R 52 , and R 54  are somewhat arbitrary, and one having ordinary skill in the battery powered circuit arts would be able to select suitable resistances; there are almost an unlimited number of values one could choose and still have this circuit work properly. 
     When a load, such as a cell phone  90 , is connected to the output  112 , the circuit begins to conduct and the battery power supply  100  transitions to a state  202 , wherein the state  202  is as follows:
         the MOSFET  104  is OFF: a voltage drop is now detected across the body diode  105     the voltage booster  107  is off: inductor  106  acts as a short circuit for DC   the output  112  &lt;Vbat  111 : due to voltage drop across the body diode  105     if R 52  and R 54  are of equal value, sense  103 &gt;2.35 volts which translates to 4.7 volts at the cathode of body diode  105 : this value also appears at output  112  (less the forward bias of Schottky diode  113 ) and is within the bounds of a +5 volt supply   Equivalent circuit is shown in  FIG. 3B         

     A cell phone will typically charge itself when provided a supply voltage  112  between 4.5 and 5.5 volts. Output  112  may fluctuate as we transition from one state to the next, but it&#39;s all within the bounds of what a cell phone might expect. 
     Another aspect of the body diode  105  is that it acts as a voltage drop when a fully charged set of batteries  101  creates a Vbat of &gt;5 volts. For example, if Vbat=6 volts, the voltage drop across the body diode  105  (assuming forward voltage drop=0.8 volts and assuming 0.2 volt forward drop across diode  113 ) creates an output voltage  112  of 5 volts. Every diode has a forward voltage drop associated with it. 
     As the load continues to draw current, the voltage Vbat  111  will diminish as battery capacity diminishes. At some point, the voltage at sense  103  will drop below 2.25 volts (4.5 volts at cathode of body diode  105 ) and the battery power supply  100  transitions from the state  201  to a state  203 , wherein the state  203  is as follows:
         the MOSFET  104  is ON: there is no longer a voltage drop across body diode  105     Voltage booster  107  is OFF: inductor  106  acts as a short circuit to DC   Output  112 =Vbat  111 : there is now effectively a short circuit between load and batteries   Sense  103 &gt;4.7 volts: have not yet reached the threshold for enabling voltage booster  107     Equivalent circuit is shown in  FIG. 3C         

     As the load continues to draw even more current, Vbat  111  will drop below 4.5 volts as reflected at the sense  102 =2.25 (if R 42  and R 44  are equal) and the battery power supply  100  transitions to a state  204 , in which the state  204  is as follows:
         the MOSFET  104  is ON: there is no longer a voltage drop across the body diode  105     the Voltage booster  107  is ON: the + side of the inductor  106  has a higher potential than its − side   Output  112 &gt;Vbat  111 : the voltage booster  107  provides +5 volts to the load   Sense  103 &lt;2.35 (4.7 volts at cathode of body diode  105 ): this condition will persist until the load is disconnected   Equivalent circuit is shown in  FIG. 3D         

     Disconnecting the load  90  will cause the voltage Vbat  111  to rise. That is because batteries inherently provide a higher potential under light or no loads as compared with heavier or full loads. Typically, the heavier the load, the more downward pressure there is on the battery output voltage. Because the micro-controller  109  is able to detect a rise in the voltage at sense  102 , it can determine whether the load has been disconnected or attached load is fully charged. This can be confirmed by momentarily turning off MOSFET  104 , and the micro-processor can optionally be programmed to do this. If sense  102 =sense  103 , the micro-processor  109  determines that the load has been disconnected. The battery power supply  100  then transitions back to the state  201  wherein current consumption returns to micro-amps. 
       FIG. 4  is an expanded schematic circuit diagram of the voltage booster  107  which is used in the apparatus of  FIG. 1 . In  FIG. 4 , a pulse width modulation (PWM) DC-DC controller  404  is used to switch a switch transistor  402 . When the switch transistor  402  is on, the current ramps up in the inductor  106 , storing energy in a magnetic field associated therewith. When the external power to the switch transistor  402  is OFF, the energy stored in the magnetic field is transferred to an output storage capacitor  401 . A diode  113  is used to block current flowing back into the inductor  106 . A capacitor  403  is used to filter output to the monitor pin of PWM controller  404 . When PWM controller  404  is enabled, a potential of 5 volts is maintained at an output  112  independent of load when the battery  101  potential falls below a minimum. 
     Another way of saying the above is that one gets 5 volts at output  112  with a 50 mA load, a 100 mA load, a 200 mA load, or no load. i.e. one gets 5 volts independent of load. The diagram of  FIG. 4  represents a conventional circuit that would be understood by any one having skill in the voltage booster art, and therefore the diagram of  FIG. 4  requires no further explanation. 
       FIG. 5  is a flow chart of firmware contained within the micro-controller  109 . For the sake of discussion, it is assumed that the output voltage  112  will deliver 5 volts, plus or minus 10%: for example, 4.5 to 5.5 volts with 5.0 volts being the ideal output. 
     The process starts at step  501  when sense  102  and sense  103  inputs are sampled. If those inputs are equivalent, as in decision block  502 , it can be concluded there is no load at output  112 . The MOSFET  104  and the voltage booster  107  are turned OFF as shown in block  503  and the micro-controller  109  is put into a sleep state to conserve power. The equivalent circuit is depicted in the aforementioned  FIG. 3A . An interrupt caused by a change in the sense  103  causes the controller  109  to wake and proceed with block  501  again. 
     If decision block  502  indicates there is a difference in potential between the voltages at sense  102  and sense  103 , then the path proceeds to a decision block  506 . If the voltage at the sense  102  is greater than 5.5 volts, then the MOSFET  104  and the voltage booster  107  are turned OFF in block  509 . The voltage drop across the body diode  105  and the diode  113  are used to create an output voltage  112  that is near 5 volts. The equivalent circuit is shown in the aforementioned  FIG. 3B . 
     If the decision block  506  determines that the voltage at the sense  102  is below 5.5 volts, the path then proceeds to a decision block  507 . If the voltage at the sense  102  is greater than 4.7 volts, then the MOSFET  104  is turned ON, thereby removing the body diode  105  from the circuit. Current is still passing through the diode  113 . The drop across the diode  113  is 0.2 volts if the Schottky variety is used. The equivalent circuit is depicted in the aforementioned  FIG. 3C . 
     If the decision block  507  determines that the voltage at the sense  102  is below 4.7 volts, then the MOSFET  104  and voltage booster  107  are turned ON. The voltage booster  107  is now taking a voltage which is at a relatively lower potential from the battery portion  101  and boosting that voltage to 5.0 volts at the output  112 . The equivalent circuit is shown in the aforementioned  FIG. 3D . 
       FIG. 6  schematically depicts the micro-controller  109  and its internal components, described below, as well as its connections which are also described below, which is used in the device  100  of  FIG. 1 . As shown in  FIG. 6 , the micro-controller  109  includes an A/D converter  603 , a comparator  601 , an I/O port  605 , and firmware  607 . The A/D converter  603  and the comparator  601  both receive inputs from the sense  102  and the sense  103 . The output of the A/D converter provides ADC counts  604  to the firmware  607 . The output of the comparator  601  provides an interrupt  602  to the firmware  607 . 
     The firmware  607  provides a digital I/O  606  to the I/O port  605 . The I/O port  605  provides two outputs, an FET control  110  and a booster enable  114 . In  FIG. 6 , the regulated voltage  108  provides a fixed power source Vdd  608  which is supplied to the micro-controller  109  in order to keep the micro-controller  109  powered at all times. The firmware  607  performs the functions which are shown in  FIG. 5  and which are described hereinabove with reference to  FIG. 5 . 
     The sense  102  and the sense  103  are connected to Analog to Digital Converter (ADC) pins. A simple ADC represents an input voltage by ADC counts  604 . The counts are in the range of 0 to 255 for an 8 bit ADC and thus translates a detected voltage potential into a binary value. For example, if Vdd is 3.3 volts and the sense  102  is at 1 volt, the ADC count for the sense  102  would be (1/3.3*255)=4 D (hex). 
     The comparator  601  is used to wake the micro-controller  109  from a sleep state. When entering the sleep state, the sense  102  and the sense  103  are equal. The sense  102  is used to set a reference voltage. When a load begins to draw current, the sense  103  will decrease in value and cause the comparator  601  to change state causing the creation of a wake interrupt  602  which is supplied to the firmware  607 . The wake interrupt  602  thereby causes the micro-controller  109  to enter an awake state. 
     As shown in  FIGS. 1 and 6 , the micro-controller  109  supplies the FET control  110  and the booster enable  114  as digital outputs that change state when the firmware  607  writes data to the I/O port  605 . 
     The foregoing embodiments are described in sufficient detail to enable those skilled in the art to make and use the invention, and it is to be understood that other embodiments would be evident based on the present disclosure and that process or mechanical changes may be made without departing from the scope of the present invention. 
     In the foregoing description, numerous specific details are given to provide a thorough understanding of the invention. However, it will be apparent that the invention may be practiced without these specific details. In order to avoid obscuring the present invention, some well-known circuits, system configurations, and process steps are not shown in detail and would be understood by any one having skill in the relevant art. 
     Likewise, the drawings showing embodiments of the apparatus/device are semi-diagrammatic and not to scale and, particularly, some of the dimensions are for clarity of presentation and may be shown greatly exaggerated in the drawings. 
     While the invention has been described in conjunction with a specific preferred embodiment which is considered to be the best mode, it is to be understood that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description and accompanying drawings. Accordingly, it is intended to embrace all such alternatives, modifications, and variations that fall within the scope of the included claims. All matters hithertofore set forth herein or shown in the accompanying drawings are to be interpreted in an illustrative and non-limiting sense.