Abstract:
A system and method for digital management and control of power conversion from battery cells. The system utilizes a power management and conversion module that uses a CPU to maintain a high power conversion efficiency over a wide range of loads and to manage charge and discharge operation of the battery cells. The power management and conversion module includes the CPU, a current sense unit, a charge/discharge unit, a DC-to-DC conversion unit, a battery protection unit, a fuel gauge and an internal DC regulation unit. Through intelligent power conversion and charge/discharge operations, a given battery type is given the ability to emulate other battery types by conversion of the output voltage of the battery and adaptation of the charging scheme to suit the battery.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This Application claims priority to U.S. Provisional Patent Applications, Ser. No. 60/868,851, filed Dec. 6, 2006, and titled “Distributed Solar Array Monitoring, Management and Maintenance,” Ser. No. 60/868,893, filed Dec. 6, 2006, and titled “Distributed Power Harvesting System for Distributed Power Sources,” 60/868,962, filed Dec. 7, 2006, and titled “System, Method and Apparatus for Chemically Independent Battery,” Ser. No. 60/908,095, filed Mar. 26, 2007, and titled “System and Method for Power Harvesting from Distributed Power Sources,” and Ser. No. 60/916,815, filed May 9, 2007, and titled “Harvesting Power From Direct Current Power Sources,” the entire content of which is incorporated herein by reference. Further, this Application is related to ordinary U.S. patent application Ser. No. 11/950,224, filed Dec. 4, 2007, titled “Current Bypass for Distributed Power Harvesting Systems Using DC Power Sources,” patent application Ser. No. 11/950,271, filed Dec. 4, 2007, titled “Distributed Power Harvesting Systems Using DC Power Sources,” patent application Ser. No. 11/950,307, filed Dec. 4, 2007 titled “A Method for Distributed Power Harvesting Using DC Power Sources,” patent application Ser. No. 11/951,419, filed Dec. 6, 2007, titled “Monitoring of Distributed Power Harvesting Systems Using DC Power Sources,” and patent application Ser. No. 11/951,485, filed Dec. 6, 2007, titled “Removal Component Cartridge for Increasing Reliability in Power Harvesting Systems,” and incorporates the entire content of these applications by this reference. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to power management, power conversion and batteries and, more particularly, to power conversion for batteries. 
         [0004]    2. Related Arts 
         [0005]    Most of the electronic devices today are configured for specific battery types and chemistries. The selection of which chemistry to use is usually based upon an assessment of, among other considerations, the device&#39;s environmental conditions and expected lifetime, and the price of the battery at time of design. 
         [0006]    Different batteries have different chemistries, each having their own properties, advantages and challenges. One conventional type of battery, that is used extensively especially in lower-end products, uses a Nickel-Cadmium (Ni—Cd) chemistry. A Ni—Cd battery has numerous drawbacks and limitations: it allows only moderate energy density (45-80 Wh/Kg); has a high rate of self-discharge of approximately 20% per month; and requires charging maintenance in the form of periodic charge/discharge cycles in order to prevent memory-effects which limit the usable capacity of the battery. Furthermore, the compounds used in its production are highly toxic and cause environmental problems. Cells of this chemistry have an output voltage of approximately 1.25 volts. The Nickel-Metal-Hydride (NiMH) chemistry is a variation of Ni-Cad and shares many of the Ni-Cad properties. It provides a slightly higher energy density 60-120 Wh/Kg. 
         [0007]    In the recent years, Lithium-ion (Li-ion) batteries have become prevalent, especially in devices which require high energy densities such as laptops, medical devices and cell-phones. This chemistry provides high energy density (150-190 Wh/Kg) and is environmentally friendly. However, it also suffers from numerous drawbacks. It has a limited life and after 300-500 cycles the battery&#39;s capacity drops to 80% of the rated capacity. It has very low tolerance to overcharging, and if mistreated might become thermally unstable and hazardous. In order to maintain the battery&#39;s safety, it is essential to have charge/discharge monitoring and protection circuits that prevent over-discharge, monitor the charging process and stop the charging before over-charge. Cells of this chemistry have a maximum output voltage of approximately 4.1V but will provide efficient power at approximately 3.6V, and their voltage shouldn&#39;t drop under 2.5V-3V, depending on the kind of Li-ion used. 
         [0008]    There is continuous progress in increasing the capacity of different types of the Li-ion chemistry and new battery technologies, such as spinnel and Li-Polymer, keep emerging. These technologies, while similar to the regular Li-ion technology, may require adaptation of the hosting devices due to slightly different voltages or charge procedures. 
         [0009]    Finally, there are radically new battery technologies in the making, such as nano-tube based batteries, which hold the promise of much higher charge capacities. However, because these batteries will have electronic properties different from the currently common batteries, the current electronic products would need an adaptation circuit in order to benefit from such batteries. 
         [0010]    As set forth above, most electronic devices are configured for a specific battery type. Locking the design of an electronic device into one specific battery type prevents the device owners from enjoying the benefits of new battery technologies, price reductions and other advances. In order to enjoy such benefits, the device must be re-designed in order to fit the new batteries. This is not desirable for the buyer. 
         [0011]    Furthermore, if problems are found in the battery management circuits, a recall may have to be made in order to fix the problem. Recalls, that happen not infrequently, are costly to the device manufacturer. 
         [0012]    Energy efficiency in analog conversion circuits is greatly dependant upon the current consumption. The conversion efficiency will usually be high for the designed load and current consumption, but as the load changes the efficiency drops. Thus, if good energy efficiency is desired, the conversion circuit must be specifically designed for the host device. Building a voltage-converting circuit to fit many different products and, thus, many different loads, is complicated and results in a large converter that is not suitable for a small battery. 
       SUMMARY 
       [0013]    The following summary of the invention is included to provide a basic understanding of some aspects and features of the invention. This summary is not an extensive overview of the invention, and as such it is not intended to particularly identify key or critical elements of the invention, or to delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented below. 
         [0014]    Aspects of the invention provide circuitry that may be incorporated in the battery itself or outside of the battery. The circuitry is programmed to output the voltage required by the load, and monitors the power drawn from the battery according to the battery&#39;s characteristics, e.g., type, temperature, age, shelf life, etc. 
         [0015]    According to an aspect of the invention, an intelligent battery power delivery apparatus is provided, comprising: input terminals receiving power from one or more battery cells; output terminal for providing power to a load; and, a conversion module programmable to maintain output power characteristics at the output terminals according to programmed characteristics, and programmable to control power draw at the input terminals according to programmed characteristics. The conversion module may comprise an integrated circuit. The conversion module may comprise a DC/DC converter. The conversion module may comprise a buck converter and a boost converter and wherein one of the buck converter and the boost converter is engaged depending on the type of the battery cell. The conversion module may further comprise a battery protection unit. The battery protection unit may comprise a fuel gauging unit for monitoring the state of charge of the one or more battery cells. The conversion module may further comprise a current sensor. The conversion module may further comprise telemetry terminals for communicating operation data. The apparatus may further comprise a casing, and wherein the conversion module and the one or more battery cells are housed within the casing and form an integral intelligent battery. The conversion module may comprise a digital circuit, the digital circuit comprising: a DC to DC voltage conversion unit; a current sense unit; a fuel gauge; and a central processing unit; wherein the DC to DC voltage conversion unit is adapted to provide a desirable voltage to the load, wherein the current sense unit is adapted to obtain a sensed current from the battery module and to utilize the sensed current for functioning of the fuel gauge unit, wherein the fuel gauge unit monitors a state of charge of the one or more battery cells and reports the state of charge to the central processing unit to prevent overcharge or over-discharge of the one or more battery cells, and wherein the central processing unit manages the digital power conversion. The conversion unit may comprise: a charge/discharge unit; a battery protection unit; and an internal DC regulation unit, wherein the charge/discharge unit is adapted to provide over-current protection during discharge and to control charging schemes used by the intelligent battery, wherein the battery protection unit is adapted to monitor voltage, the sensed current and battery module charge and to alert the central processing unit of potentially hazardous conditions, and wherein the internal voltage regulation unit regulates a voltage required by each of the power management and conversion units. The conversion module may further comprise telemetry terminals for communicating with an outside device, and wherein the central processing unit communicates with the outside device via the telemetry port. 
         [0016]    According to aspects of the invention, an intelligent battery is provided, comprising: a casing; one or more battery cells housed within the casing; and a conversion circuit housed within the casing, the conversion circuit adapted to perform digital power conversion; wherein the conversion circuit controls a voltage conversion to convert a voltage of the battery cells to a voltage level corresponding to load requirement, and wherein the conversion circuit controls a charging of the battery cells to provide an external DC voltage to the battery cells according to charging requirements of the battery cells. The conversion circuit may further comprise programming means enabling the conversion circuit to provide output power characteristic of at least one of an alkaline battery, a lithium ion battery, a metal hydride battery, a Nickel-Cadmium battery, and a Nickel-Metal-Hydride battery, regardless of the type of one or more battery cells housed within the casing. The conversion circuit may comprise a digital integrated circuit. The conversion circuit may comprise a charge/discharge unit; a battery protection unit; and an internal DC regulation unit. 
         [0017]    According to aspects of the invention, a method for utilizing a first type battery in an application designed for a second type battery is provided, the method comprising: converting a first power from the first type battery to a second power corresponding to the second type battery using digital power conversion; and converting a charging voltage from a charger corresponding to the second type battery to a charging voltage appropriate for the first type battery. The converting a first power may comprise digitally converting the first power. The method may further comprise monitoring charging voltage applied to the first battery type to protect from overcharging and under charging. The method may further comprise tracking battery status by monitoring charge condition in the first battery type. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The accompanying drawings, which are incorporated in and constitute a part of this specification, exemplify the embodiments of the present invention and, together with the description, serve to explain and illustrate principles of the invention. The drawings are intended to illustrate major features of the exemplary embodiments in a diagrammatic manner. The drawings are not intended to depict every feature of actual embodiments nor relative dimensions of the depicted elements, and are not drawn to scale. 
           [0019]      FIG. 1  shows an integral intelligent battery according to aspects of the invention. 
           [0020]      FIG. 2  shows a modular intelligent battery according to aspects of the invention. 
           [0021]      FIG. 3  is a block diagram of components of an intelligent battery according to aspects of the invention. 
           [0022]      FIG. 4  is a plot of conversion efficiency versus load and shows a comparison between conversion efficiency of an analog conversion scheme and a digital conversion scheme. 
           [0023]      FIG. 5  is a block diagram of a power management and conversion module used in an intelligent battery according to aspects of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    Aspects of the present invention are directed to an intelligent battery including one or more battery cells together with digital power management and conversion electronics. The intelligent battery provides a substantially constant voltage required by the hosting device and manages the charge/discharge operations. As a result, the hosting device may be simplified and different battery chemistries may be made compatible with a particular hosting device. 
         [0025]    In one aspect of the invention, a single package is provided, which includes both battery cell or cells and a power management integrated circuit (IC). In one aspect of the invention, the package includes two separate modules, one including the battery cells and the other including the power management IC such that the battery cells may be replaced. The power management IC that is used may be included in the host device, thus enabling the host device to use different battery cells. In one aspect, a safety circuit monitors the battery to prevent misuse and a charge circuit correctly charges the battery in an adequate manner. Fuel-gauging may be used to provide data about the state-of-charge of the battery and monitoring may be used to provide data about the state-of-health of the battery. The battery cells used in various aspects of the invention may include chemical battery cells, fuel-cells, photovoltaic cells and the like. 
         [0026]    Aspects of the invention also provide a method for utilizing a first type of battery in an application and a circuit that is designed for a second type of battery. A power conversion scheme is used to convert the power output from the first type of battery to the power that would be output from the second type of battery. The power conversion scheme may be implemented digitally, due to its greater versatility and higher efficiencies over large load variations. Also, when a charger corresponding to the second type of battery is being used to charge the first type of battery, the charging voltage is adjusted by the digital power conversion scheme to a level appropriate for charging the first battery. Digital power conversion schemes are used because they maintain a more uniform efficiency over a wider range of loads when compared to analog power conversion schemes that are efficient only near their design load. 
         [0027]      FIG. 1  shows an integral intelligent power-converting battery  100 , according to aspects of the invention. The battery  100  shown in  FIG. 1  includes one or more battery cells  102  and a power management and conversion unit  104  that are encased in the same casing. The battery  100  also includes an anode terminal  106  and debug, telemetry and upgrade terminals  108  at the power management and conversion unit  104 , and a cathode terminal  110  at the one or more battery cells  102 . The debug and telemetry terminals  108  are optional. 
         [0028]    The casing interfaces to external components and a host device via the anode  106  and the cathode  110  terminals. Through the anode and the cathode terminals  106 ,  110 , energy from the battery may be supplied to a hosting device and external voltage may be applied to the battery in order to charge the battery. 
         [0029]    The power management and conversion unit  104  may provide the power conversion, battery charge/discharge and communication functionality. The power management and conversion unit  104  may be implemented in a PCB with discrete components soldered to it. Alternatively, the power management and conversion unit  104  may be implemented in a single component IC. 
         [0030]    The power management and conversion unit  104  controls the power delivered to the load and the power extracted from the batteries. As for the power delivery to the load, unit  104  may be programmed with the parameters of the load, e.g., voltage and current requirements. The programming can be done beforehand in the factory, and may also be done by user programming or by “learning” the requirements from interaction with the load. As for power extracted from the battery, here too unit  104  may be programmed in the factory for a certain type of cell, but may have means for modifying this programming or for programming in the field by user or by “learning” the cell&#39;s characteristics. For example, unit  104  could learn what battery-cell it is coupled to based on sensing the output voltage, performing short-circuit for a very short time to determine the maximum current, see how long it takes to drain to gather capacity, etc. Using this information unit  104  provides the required output power to the load, but extracts power according to the requirements of the battery or cells. In this manner, any type of battery may be connected to any type of device. 
         [0031]    The optional debug and telemetry terminals  108  are used for ascertaining status information about the intelligent battery or for providing the intelligent battery with operating instructions. Status information about the intelligent battery may be the state of charge (SoC) of the enclosed cell  102 , state of health (SoH), internal temperature, and various statistics regarding the cell  102  that may be logged in the power management and conversion unit  104 . This statistics include date of production, number of charge cycles to date, type of cells, cell output voltage, and regulated output voltage. Operating instructions to the intelligent battery may include requests for wanted regulator output voltage, current and voltage limiting, and various charge parameters. The charge parameters include the charging scheme parameters, amount of charge parameters and safety parameters. The charging schemes include constant current, constant voltage, trickle, and the like. The amount of charge parameters include the maximal and the minimal charge allowed. The safety parameters include the maximum allowed temperature. 
         [0032]    Communications to and from the debug and telemetry terminals  108  may be implemented by various protocols. In one aspect of the invention, an asynchronous serial communication bus may be used, in other embodiments synchronous communications may be used such as SPI or I2C. Other protocols such as PMBus or SMBus may be used. Both point-to-point and bus topologies may be suitable for this type of communication. The communication may be wireless, either in active form by use of IR or RF transceivers, or in passive form by use of RFID or similar devices. 
         [0033]      FIG. 2  shows a modular intelligent power-converting battery according to aspects of the invention. The modular intelligent battery  200  includes two separate and connectable modules. A battery module  212  that includes the battery cells  213  and a conversion module  214  that includes a power management and conversion unit  215 . In the modular intelligent battery  200  shown in  FIG. 2 , replacement of the battery cell or battery cells  213  is possible. 
         [0034]    The battery module  212  includes an external battery cathode  217  and terminals  219  to the conversion module  214 . The conversion module  214  includes an external battery anode  221 , optional debug, telemetry and upgrade terminals  223  and terminals  225  to the battery module  212 . The battery module  212  and the conversion module  214  may be connected through the terminals  219  and  225 . The conversion module  214  may operate as unit  104  to ensure proper power output and proper power extraction from the battery module  212 . 
         [0035]    The conversion module may be implemented as application specific module or a generic module. When it is designed as application specific module, it is designed for a specific type of battery and a specific type of load. In such a case, its input and output power requirements are preprogrammed at the factory for the specific battery and specific load. On the other hand, if it is made as a generic module, means for programming different input and output power characteristics are provided, so that the conversion module  214  may be connected to any type of load and be used with any type of battery. Various methods for programming the required output and input may be implemented. For example, the unit may be coupled to a computer via a charger, USB, etc, and the required programming downloaded via the Internet. Also, means may be provided for a user to input a code when the battery type or load is changed. 
         [0036]    In the modular intelligent battery  200 , the battery cells  212  may be replaced when they malfunction or reach the end of their life. The modular intelligent battery  200 , however, may require a larger casing or may be less reliable than the integral intelligent battery  100  of  FIG. 1 . 
         [0037]      FIG. 3  is a block diagram of components of an intelligent battery according to aspects of the invention.  FIG. 3  shows the coupling between a battery module  302  including one or more battery cells and a power management and conversion module  305  in an intelligent battery  300 . The two modules  302 ,  305  are coupled via voltage input terminals  308 ,  314 . The voltage input terminals  308 ,  314  are respectively providing a battery Vcc and a battery ground. The battery module  302  and the conversion module  305  may also be connected by one or more sensors  312 . These sensors may be temperature or pressure sensors but they may be any other sensor deemed appropriate. 
         [0038]    Voltage output terminals  310  and  316  are provided at the conversion module  305  and may also be used for charging the battery module  302 . Optionally, a debug and telemetry terminal  318  may be present to provide the functionality discussed above. 
         [0039]    In one aspect of the invention, the conversion module  305  includes an IC  304  and external components. In  FIG. 3 , the external components are respectively an inductor  306  and a capacitor  320 . The integration of the elements into the IC  304  provides digital power conversion and permits the conversion module  305  to include fewer external components. 
         [0040]      FIG. 4  is a plot of conversion efficiency versus load and shows a comparison between conversion efficiency of an analog conversion scheme and a digital conversion scheme. In  FIG. 4 , a load being supplied by a battery through a conversion module is shown on the horizontal axis and the percent efficiency of the conversion is shown on the vertical axis. A load for which an analog conversion circuit is designed is shown at  402 . An efficiency curve  404  using an analog conversion and another efficiency curve  406  using a digital conversion are superimposed. 
         [0041]    Analog power conversion schemes usually imply a linear control algorithm. These linear loops take a relatively long time to adapt to changes in current consumption by the load or the host. Thus, if the host suddenly starts to take more current, while the loop is adjusting, the voltage may drop. Large external capacitors and inductors are used to prevent the drop and maintain the required voltage until the loop adjusts. When digital conversion is used, the loop feedback may not be linear. As a result the convergence time may be much faster. Thus, smaller components may be used. This could be beneficial in mobile applications that require batteries. 
         [0042]    As described above, and as depicted in  FIG. 4 , the analog conversion circuitry is usually designed for a specific load such as the load  402 . At this load, the analog conversion is quite efficient and the efficiency is shown at 95%. However, efficiency of the analog conversion  404  drops at loads far from the design target load  402 . As a result, it is difficult to design an efficient conversion circuit when the host device is unknown. 
         [0043]    On the contrary, when digital power conversion schemes are used, efficient conversion could be achieved for a wider array of load conditions. As seen in  FIG. 4 , the efficiency curve  406  for digital conversion stays near and above 95% efficiency over a large range of loads. Therefore, an intelligent battery using digital power conversion is suitable for many different applications. The digital power conversion circuits are managed by a CPU such as a CPU  514  shown in  FIG. 5 . 
         [0044]      FIG. 5  is a block diagram of a power management and conversion module used in an intelligent battery according to aspects of the invention.  FIG. 5  shows internal units in an exemplary IC  504  of a power management and conversion module according to aspects of the invention. The IC  504  includes a charge/discharge unit  505 , a DC to DC conversion unit  506 , a current sense unit  508 , a battery protection unit  510 , a fuel gauge  512 , the CPU  514 , and an internal DC regulation unit  516 . The IC  504  engages in digital power management and conversion and therefore may operate over a large range of loads with substantially high efficiency. 
         [0045]    The charge/discharge unit  505  is provided to prevent a load or a host device from extracting too much energy from the battery cells during discharge and to provide over-current protection. The charge/discharge unit  505  also disconnects the battery cells when they are empty in order to prevent over-discharge. During charge, the unit  505  controls the charging schemes used. Such schemes may be constant charge ratio, constant current, constant voltage and trickle charge. Because the charging of the battery cells may be software controllable, other schemes may also be implemented. 
         [0046]    The DC to DC voltage conversion unit  506  is included to provide the host device with the desired voltage. The conversion unit  506  may be a buck, boost, buck/boost or Cuk converter. The conversion may be done substantially inside the IC  504  with field effect transistors (FETs) and drivers fabricated on the silicon substrate and only minimal external components such as an inductor and a capacitor may be used in addition to the circuits existing on the IC  504 . The use of buck-boost or cascaded buck boost may be useful where the cell output voltage may drop below the desired output voltage. For example, if a Li-ion cell is used and a 3.3V output voltage is desired, because fully charged Li-ion cells provide 3.6V to 4.1V, a buck conversion is needed when the battery is fully charged. The buck conversion provides a step down conversion from 3.6V or 4.1V to the desirable 3.3V output voltage. However, Li-ion cells may drop to 2.5V and to fully utilize the charge contained in these cells, a boost conversion is performed to raise the output voltage. 
         [0047]    The battery protection unit  510  is included such that proper charge and discharge conditions are applied. Monitoring of cell parameters such as temperature or pressure may be achieved via connection  526  to cell sensors located in a battery module such as the battery module  302  of  FIG. 3 . Other critical data such as voltage, current and charge is obtained from the internal units within the IC  504 . If the protection unit  510  finds a potentially hazardous situation it may alert the CPU  514 . The CPU may take action to minimize the risk and it may also alert the host device via the telemetry terminals. 
         [0048]    The fuel gauging unit  512  may be present to monitor the state of charge of the battery cell. This information is reported to the CPU  514  and may be transferred to the host device. This information may also be used to prevent overcharge or over-discharge of the cell. Both overcharge and over-discharge conditions may prove dangerous to certain cell chemistries. 
         [0049]    The current sense unit  508  is used to sense the current. The sensed current is used for the functioning of both the protection unit  510  and the fuel gauge unit  512 . This current sensing may be done by monitoring the voltage drop across a sense resistor such as a resistor  517  shown in  FIG. 5 . Current sensing may be achieved by using a current loop, or by using other methods. The current sense unit  508  may be shared by both the battery protection unit  510  and the fuel gauge unit  512 , thus lowering costs and reducing board space. 
         [0050]    The CPU  514  is used for digital power conversion management. The CPU  514  may be implemented via a micro-processor, for ease of development, or via a state-machine, which may provide lower current consumption. The CPU  514  monitors various parameters, such as an input voltage  518  and an output voltage  520  to the IC  504 , and controls the various internal units of the IC  504  that are described above. The CPU  514  also may communicate with outside devices via the debug and telemetry port. 
         [0051]    The internal voltage regulation unit  516  regulates the voltage required by each of the other internal units. The internal voltage regulation unit  516  may receive voltage from the battery cells, and may also receive voltage from the host device in case the cells are exhausted and need to be charged. 
         [0052]    One exemplary aspect of the present invention may be embodied in an intelligent battery casing that looks like a regular AA battery, in a manner similar to the battery depicted in  FIG. 1 . This battery has an internal Li-ion cell, which provides energy density greater than the energy density of Ni—Cd or Ni-MH batteries. However, the cell provides an output voltage of 3.6V instead of 1.5V, and requires different charge schemes. Part of the casing includes a small power management and conversion circuit. This circuit contains an IC and a few external components. The IC converts the voltage of the cell from 3.6V to 1.5V so it would seem like a regular Alkaline or Ni—Cd battery to any device that takes AA batteries. Providing an external DC voltage to the intelligent battery would cause the enclosed circuit to charge the cell in a manner favorable to Li-ion. This voltage could originate from a Ni—Cd charger, a dedicated intelligent battery charger, or a simple voltage source, for example, USB port of a computer. The described intelligent battery provides the advantages of a Li-ion battery to devices that were designed for Ni—Cd AA batteries. Obviously, this conversion may prove beneficial for other devices and batteries as well. 
         [0053]    The present invention has been described in relation to particular examples, which are intended in all respects to be illustrative rather than restrictive. Those skilled in the art will appreciate that many different combinations of hardware, software, and firmware will be suitable for practicing the present invention. Moreover, other implementations of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims and their equivalents.