Abstract:
An electrode mask for electrowinning a metal is provided. An example technique forms openings in a solid nonconductive sheet, such as vinyl, polyvinyl chloride (PVC), or other plastic and adheres the sheet as a solid to a cathode surface as a mask. The mask protects the cathode surface from electrical interaction with an electrolyte, while the openings allow controlled electrodeposition of a metal in harvestable rounds, which can be stripped from the cathode. The electrode mask is reusable, and easily removed for recycling and replacement. A matrix design engine calculates pattern and sizes for the openings in the mask to optimize electrodeposition of the metal based on multiple parameters including the metal to be deposited, ions present in an electrolyte, electrolyte concentration, pH level, voltage, electrical current density, solution temperature, electrode temperature, or plating time.

Description:
RELATED APPLICATIONS 
       [0001]    This patent application claims the benefit of priority to U.S. Provisional Patent Application No. 61/692,114 to Valentine, filed Aug. 22, 2012 and entitled, “Electrode Mask for Electrowinning a Metal,” which is incorporated herein by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    Electrowinning is the process of electrodeposition of metal from a metal-bearing electrolyte, reducing metal ions in solution by the application of direct current electric power and is a primary technology in hydrometallurgical extraction of various metals. 
       BACKGROUND 
       [0003]    A technical paper entitled, “Development of a Cathode Mandrel for Production of Nickel and Cobalt Rounds,” by Douglas J. Robinson, Dremco Inc., presented at the Alta 2000 Nickel/Cobalt-6 conference in Perth, Australia May 15-18, 2000 presents some background information: 
         [0004]    “Nickel and cobalt, purified by electrolysis, are often used in a cut or fragmented form in subsequent electroplating cells and alloy melting furnaces. Nickel cathodes, with their Face Centered Cubic (FCC) crystal form, lend themselves to shearing into squares, while cobalt with its more brittle Body Centered Tetragonal (BCT) crystal form tends to shatter if sheared, so has been fragmented by grinding and tumbling equipment. An alternative method of obtaining sectioned products has been to produce “rounds” deposits, with an approximately 20-50 mm diameter and an approximately 2-5 mm thickness. These deposits are formed on full sized cathode blanks, where point or circular “islands” have been exposed on an otherwise insulated surface” (Robinson, supra). 
         [0005]    An electrowinning process was developed by INCO LIMITED (Toronto) in Canada, and subsequently by FALCONBRIDGE LIMITED (Toronto) for its plant in Norway. Inco produces rounds in two sizes for nickel and a third size for cobalt. The Falconbridge product is termed a “crown,” and is nominally 12 mm in diameter. It is intentionally thicker than the round and is claimed as a superior product by its producer. These two companies enjoy a premium price for the nickel products, and so have chosen to maintain the details of their methods as proprietary, not available to competitor companies. 
         [0006]    A recent development in electrowinning (electrodepositing) technology has been an innovation of isolating either the anodes or cathodes from the bulk electrolyte for the purpose of better controlling the acidity (measured as pH) of the electrolyte solution in direct contact with the cathode, which is where the metal is deposited. 
         [0007]    This is accomplished by encasing the electrodes, either the anodes or the cathodes, in a box or frame equipped with a permeable membrane such that solution either flows primarily out of the cathode frame into the bulk electrolyte or from the bulk electrolyte into the anode frame. 
         [0008]    Elevated acidity in the solution at the point of plating has detrimental effect on product metal quality and the current efficiency. The ability to maintain the solution around the cathodes at a desirable moderate pH, while allowing the solution around the anodes to become more acidic through the normal anodic chemical reactions, facilitates greater efficiencies in the overall downstream metal recovery process. 
         [0009]    In the case of cobalt electrowinning, full sheet cathode deposits have high internal stresses and frequently separate partially from the cathode blank and curl up, thus growing faster toward the anode and penetrating the membrane. During this process, or at harvesting, the membrane is torn and the more acidic solution is no longer contained. This results in contaminating the bulk solution, thus compromising quality, and necessitates the replacement of the torn anode bags. 
         [0010]    Producing electrowinning rounds greatly reduces the hazard of shorting through curling deposits and is thus another advantage over making full size deposits. Also, harvesting cobalt rounds is easier than harvesting the full size cathode, being generally easier to release the rounds. 
         [0011]    There are various designs used to produce rounds. For example, U.S. Pat. No. 3,668,081 to Borner describes a thermoset epoxy ink or heat curing paint to create a reusable resist matrix on a repeatedly reusable cathode or mandrel. The epoxy ink coating lasts approximately four plating and harvesting cycles until wear and tear necessitates replacement. The removal of the epoxy ink coating utilizes a process involving hash chemicals, such as hydrofluoric acid, thus creating a waste stream. 
         [0012]    Canadian Patent No. 1,066,657 to Parkinson describes a reusable integrated cathode unit with surface array of metal islands. This technology uses a non-conductive cathode support slab with embedded conductive metal assembly having projections at spaced intervals that penetrate the surface of the slab thereby forming an array of solid, conductive metal islands being flush with or raised above the slab separated from each other sufficiently for the electrodeposition of metal deposits. 
       SUMMARY 
       [0013]    An electrode mask for electrowinning a metal is provided. An example technique forms openings in a solid nonconductive sheet, such as vinyl, polyvinyl chloride (PVC), or other plastic and adheres the sheet as a solid to a cathode surface as a mask. The mask protects the cathode surface from electrical interaction with an electrolyte, while the openings allow controlled electrodeposition of a metal in harvestable rounds, which can be stripped from the cathode. The electrode mask is reusable, and easily removed for recycling and replacement. A matrix design engine calculates pattern and sizes for the openings in the mask to optimize electrodeposition of the metal based on multiple parameters including the metal to be deposited, ions present in an electrolyte, electrolyte concentration, pH level, voltage, electrical current density, solution temperature, electrode temperature, or plating time. 
         [0014]    This summary section is not intended to give a full description of an electrode mask for electrowinning a metal. A detailed description with example embodiments follows. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a diagram of example test cathodes with an example electrode masking film applied. 
           [0016]      FIG. 2  is a diagram of an example test cathode with metal rounds deposited at openings in the example electrode masking film. 
           [0017]      FIG. 3  is a diagram of an example matrix or pattern of openings in the example electrode masking film, with dimension in units of inches, for example. 
           [0018]      FIG. 4  is a flow diagram of an example method of preparing a cathode for electrowinning a metal. 
           [0019]      FIG. 5  is a flow diagram of an example method of processing a used electrode masking film. 
           [0020]      FIG. 6  is a block diagram of an example matrix design engine hosted by a computing device and controlling a plotter to make pattern of holes. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    This application describes electrode masks for electrowinning metals. Example masking films described herein provide an improvement on the conventional processes of painting or coating a liquid, non-conductive, i.e., insulating material, on the face of the cathode blank  104 , which then sets or dries to define a layer of insulation on the cathode  104  that has conductive islands (openings in the insulation layer). The example masking films described herein have pre-formed holes in an insulating masking film to be applied to a cathode surface  104 , thereby insulating the cathode  104  against the electrolyte solution, except for the intentional holes (the conductive islands or openings) though which the cathode makes contact with the electrolyte solution. The example electrode masking films and application techniques provide more cost-effective, more durable, and easier-to-use materials and processes than conventional methods. 
         [0022]    In an implementation, as shown in  FIG. 1 , an example technique applies a solid masking sheet (“electrode masking film  100 ”) of non-conductive material with a pattern of holes  102  that are in a preferred shape and arrangement, directly to the cathode face  104 . The electrode masking film  100  can be made from a variety of materials, such as polyvinyl chloride (PVC), other plastics, or other materials with insulating properties, and can be manufactured in a variety of thicknesses, densities, and flexibilities as best suited to the application. In an implementation, equipment to create a pattern of holes  102  in the example electrode masking film  100  is relatively inexpensive and has been well-developed from use in other technological arts, and likewise equipment that can apply the electrode masking film  100  to the surface of a cathode sheet  104  is also available from other technologies. Compared to silk-screening equipment and various types of thermal curing equipment required for conventional epoxy ink technology, the example electrode masking film  100  provides significant savings in required capital equipment, energy, process labor, and necessary plant floor space. The example electrode masking film  100  can be applied to many cathode materials, such as stainless steel, titanium, aluminum, iron, steel, and so forth. 
         [0023]    Referring to  FIG. 2 , the example holes  102  in the solid electrode masking film  100 , and the pattern of the holes  102  defining the arrangement of conductive islands or openings  102 , can all be adjusted in size, shape and configuration to provide the best electrowinning performance and to create metal deposits  200 , such as the illustrated rounds or crowns, that have optimal properties for a specific application. The openings  102  and their pattern of arrangement can be varied to suit changing conditions in a process. Such optimizing adjustment may benefit the electrodeposited metal  200 , including the product quality and shape of the metal deposit  200 , as achieved, for example, through manipulation of current density. Such optimizing adjustment can be easily achieved without replacing any equipment or hardware, because the holes  102  can be milled in the electrode masking film  100  with machines that are calibrated by computer-aided drawings and software programming, so that adjustments to hole size and hole patterns can be made by changing simple programming parameters and do not require buying or retooling manufacturing stencils, molds, and other equipment. 
         [0024]    Example electrode masking film materials may be obtained with adhesive already attached on one side, so that application can be, for example, a peel-and-stick operation, again with relatively inexpensive equipment. The adhesive to be used can be adjusted for the best performance in a specific operation. The adhesive does not necessarily need to be pre-applied to the film, although such is a simple method. 
         [0025]    In various implementations, many materials can be used as the electrode masking film  100  and applied to a conductive cathode surface  104  by various means of adhesion, including thermal treatment. 
         [0026]    Cost is often a driving force in decision making. The cost of a PVC embodiment of the electrode masking film  100  is approximately equal to the cost of the conventional epoxy ink used in the conventional process. The advantages of the electrode masking film  100  start with a simpler initial application step, in which the electrode masking film  100  can be applied with a roller machine to each side of the cathode  104 , which may take only a few minutes, and the cathode  104  is then ready for edge strip installation and return to service. The conventional epoxy ink technique, on the other hand, requires screen-printing the epoxy ink onto the cathode face  104 , then transporting the cathode into a curing oven without smearing the wet ink, and then curing the epoxy ink at high temperature for several minutes. The cost of the screen printing equipment alone can be approximately $500,000 USD in current values, and approximately $1,000,000 to $2,000,000 USD for an entire printing, heat-curing and material-handling equipment package for a small operation. A plotting machine capable of producing the example electrode masking films  100 , on the other hand, may cost approximately $5,000 USD in current value, and an application roller machine can be obtained for less than $3,000 USD. Additionally, the needed operational working area and manpower is reduced by using an example electrode masking films  100  and associated application and removal techniques, as are the associated energy costs also reduced for an example electrowinning operation. 
         [0027]    Eventually, masking materials wear and must be replaced. The conventional methods require dissolving or loosening the epoxy masking using harsh chemicals such as hydrofluoric acid. By comparison, example removal of the PVC or plastic film of the electrode masking film  100 , when necessary for replacement, also provides advantages over previous technology, for example, the removal and replacement is simpler and creates no hazardous waste. An obsolete electrode masking film  100  can be removed with grit blasting, precise wire brushing, water blasting, or by heating and scraping. Grit blasting with non-abrasive media effectively removes the electrode masking film  100  from the cathode without detrimentally impacting the cathode surface  104 . Water blasting with a simple pressure washer at 3,000 psi effectively removes the electrode masking film  100 , and leftover residue adhesive can be removed with a solvent. The electrode masking film  100  can also be removed by heating with a simple hand held hot air gun, scraped, and when performed correctly, most of the adhesive is removed with the film and any residue adhesive can be removed with solvent. With these methods, and depending upon the film material used, the removed material is not a hazardous waste. In the case of poly vinyl chloride, the material can be recycled, although to date, such a recycling industry for this waste is immature and yet to be widely developed. 
         [0028]    An example plastic electrode masking film  100  is more durable and lasts longer than conventional epoxy ink electrode coatings. The example electrode masking film  100  does not break down chemically in an electrochemical cell. The electrode masking film  100  is a robust insulating material and is usually only damaged because of handling outside the cell, not inside the cell during a plating or electrowinning operation. So, when a cathode with the electrode masking film  100  is handled properly, it can have a service life several times greater than the conventional epoxy ink. 
         [0029]    To summarize to this point, an example electrode masking film  100  is more durable and longer lasting than conventional materials used for electrowinning processes, less expensive to use because application and removal are simple steps that produce no hazardous materials, requires less labor and plant floor space area, and the cost of the associated equipment is greatly reduced. 
         [0030]    The electrode masking film  100  described herein provides an efficient and cost effective improvement within electrowinning and electrorefining technology. In an implementation as shown in  FIG. 3 , a thin plastic film is utilized, manufactured with a pattern  300  of holes  102 , and applied with adhesive onto cathode sheets to create a background of insulated area on the cathode face  104 ; and via the hole pattern  300 , to create a matrix of exposed bare metal shapes (the holes  102 ) where the cathode surface  104  is exposed through the insulation for purposes of electroplating, electrowinning or electrorefining metal from a solution. The electrode masking film  100  with pattern  300  of holes  102  results in electrodeposited metal pieces  200 , such as rounds or crowns, produced with specific shape and size. 
         [0031]    In an implementation, the electrode masking film  100  is similar to a vinyl film used to coat traffic signs. This material technology is very well developed and the thin plastic material is often a polyvinyl chloride (PVC)-based material. Such a film withstands continuous outside exposure in the elements for years, and there are a variety of materials to choose from. Polyvinyl chloride (PVC) is a material widely used in the electrochemical industry because of its properties of chemical resistance and stability at normal operating temperatures for electrochemical processes, which can be at least as high as 160° F. Other materials may be used for the electrode masking film  100 , depending upon specific chemistry in the electrochemical cell and operating conditions, and are within the scope of the invention. 
         [0032]    The electrode masking film  100  can be machine cut to produce a matrix pattern  300  of open spaces in many shapes and configurations, and the pattern  300  can be easily modified because an example plotting and cutting machine can be CNC (computer numerical controlled) programmed which converts a CAD (Computer Aided Design) into the machining procedure. The patterns  300  cut with such machines are easily modified via programming or changing a parameter value, thus requiring no conventional hardware or equipment such as stencils that each become obsolete with design changes. 
         [0033]    A typical cathode for use in electrowinning is approximately one meter (about 40 inches) square, and a plotting machine capable of producing such a size may cost approximately $5,000 USD in current value, as opposed to the cost of the conventional screen printing epoxy equipment, which is approximately $1,000,000 to $2,000,000 for the entire printing, heat curing, and material handling equipment package for a small operation, as introduced above. Larger conventional production operations may invest up to five times these amounts. 
         [0034]    The pattern  300  of holes  102  cut into the electrode masking film  100  can be of many patterns  300  of hole shapes and hole arrangements. Traditionally, round shaped holed  102  provide preferred performance because they produce even patterns of deposition, thus the metal deposits  200  grow uniformly. This is an advantage for producing smooth deposits with minimal inclusion of contaminants, whereas square shapes have been shown to produce concentrated metal deposit at the corners, which is undesirable. Any shape for the holes  102  can be made in the electrode masking film  100 , however, though circular holes  102  arranged in staggered rows have proven to produce a uniform product of deposited metal  200  and also utilize the plating area most efficiently. An example plotting machine can cut many patterns  300  and many sizes and shapes of the holes  102  as desired and the holes  102  and patterns  300  can be changed with simple programming adjustment. 
         [0035]    In an implementation, the pattern  300  consisting of a matrix of holes  102 , which provides the bare plating areas, ends a small distance from the edges of a cathode blank in order to allow installation of edge strips on the sides and bottom if desired, and also at the top of the cathode blank to avoid incomplete plating patterns on the deposits at the top when there are fluctuations in the electrolyte level or the interference of floating acid mist containment materials. When such is not an operational concern, the holes  102  can extend in the pattern  300  above the solution line to provide maximum plating area. Typically, an area of the electrode masking film  100  with no holes  102  would extend above the solution line to avoid plating any irregular metal deposits above the uniform matrix pattern  300 . 
         [0036]    Application of the electrode masking film  100  can be performed manually by hand with simple tools or with a roller application machine, which may cost approximately $3,000. For example, an example machine can be obtained from Highway Handyman (Eagan, Minn.). 
         [0037]    Stainless steel or titanium cathode blanks can withstand many cycles of application and removal of the electrode masking film  100 . The plating surfaces of cathode blanks are maintained to certain standards to assure good performance as a mandrel for electrodepositing metal from solutions. The surface roughness must be within limits set by standard to strike a balance of providing sufficient roughness for the electrodeposited metal  200  to adhere throughout the plating cycle, while not dislodging under its own weight, called pre-stripping. But the cathode surface  104  must not be overly rough, so that the metal deposit  200  can release when harvesting the deposited metal  200  during stripping at the end of the plating cycle. Nicks, gouges and pitting can cause the deposited metal  200  to attach, or mechanically key, onto the cathode blank and then become stubborn or impossible to release during normal harvesting operations. So it is important that the electrode masking film  100  not alter the cathode surface  104  during application or removal. 
         [0038]    Prior to application of the electrode masking film  100 , the cathode blank is inspected for surface damage, which can be repaired at that time. The blank is cleaned and dirt, oil, and organic waste removed, then the cathode blank surface  104  is allowed to dry. If the electrode masking film  100  is not applied by hand, the in an implementation, the cathode is positioned at the roller application machine and the electrode masking film  100  is applied first to one side, then the other. The cathode is then fitted with plastic edge strips to insulate the edges from electrolyte and from electrical current so that the metal is deposited only on the flat sides of the cathode and does not wrap around the edges. The electrode masking film  100  can be manufactured such that it overlaps the cathode blank and can be installed to cover the edges, which then insulates the cathode blank from the electrolyte. In such a scenario, the edge strips serve primarily to protect the electrode masking film  100 . Electroplating insulation tape is commonly applied to the cathode edges under the edge strips, and can also be utilized in this an example application, overlapping the electrode masking film  100  on either side to assist the function of sealing the cathode edges from the electrolyte. As with any electrowinning or electrorefining process, it is best to keep the cathode blank surfaces free of dirt and contamination prior to inserting into the cells. 
         [0039]    At harvesting, the cathodes are withdrawn from the cells, washed, and the metal deposits  200  are removed manually or mechanically. If any part of the insulating matrix is damaged so as to allow electrolyte to leak onto an unintended part of the cathode surface  104  and create an errant deposit, often called a nodule in reference to the typical random round shape of the metal deposit  200 , the errant nodule can be removed and a small patch applied to the damaged spot to extend the service life of the electrode masking film  100 . If damage has occurred to a circle boundary of a hole  102 , a round patch can be applied to reinforce the boundary of the original circular hole  102  or a patch of slightly smaller diameter applied to create a deposit area (hole  102 ) with a fresh edge. Either repair procedure is intended to extend the life of the electrode masking film  100  at least a few more plating cycles. Otherwise, the cathodes are taken out of service for film replacement on a regular interval based on performance at the individual electrorefining plant. The electrode masking film  100  can be a robust insulating material and is damaged primarily through handling outside the cell. The electrode masking film  100  is an effective barrier to plating metal under the edges of the of the bare areas of the cathode surfaced  104 , but when this does occur, the harvesting procedure can loosen part of the electrode masking film  100  and cause subsequent plating with each cycle until the cathode is removed from service and the electrode masking film  100  replaced. 
       Example Methods 
       [0040]      FIG. 4  shows an example method  400  of preparing a cathode for electrowinning a metal. In the flow diagram, operations are shown in individual blocks. The example method  400  may be performed by various hardware components, such as a plotting machine, cutting device, an application roller machine, and a matrix design engine  602 . 
         [0041]    At block  402 , openings are formed in a nonconductive sheet. The openings, or holes  102 , can be formed when the nonconductive sheet or film is being manufactured. Alternatively, the openings or holes  102  can be cut into the nonconductive sheet or film after manufacture, e.g., by a plotting machine or cutting device. The nonconductive sheet or film may be a plastic, such as vinyl or a PVC film or sheet. 
         [0042]    At block  406 , the nonconductive sheet is adhered to a cathode for electrorefining a metal. The nonconductive sheet may be applied by hand or by an application roller machine, for example. The resulting cathode with the electrode masking film  100  applied is ready to submerge in an electrolyte and receive deposition of a metal from the electrolyte by electron exchange with the electrolyte at the holes  102  in the electrode masking film  100 . 
         [0043]      FIG. 5  shows an example method of  500  of processing used electrode masking film  100 . In the flow diagram, operations are shown in individual blocks. Parts of the example method  500  may be performed by various hardware components for removing a plastic film that has been adhered to a metal surface. 
         [0044]    At block  502 , an electrode masking film  100  is removed from a cathode. 
         [0045]    At block  504 , the electrode masking film  100  is recycled to make subsequent masking film, via plastic recycling. 
       Example Matrix Design Engine 
       [0046]      FIG. 6  shows an example computing device  600  hosting a matrix design engine  602  that can be implemented to design, modify, calculate, and/or optimize a matrix of holes or openings to be cut, formed, or placed in a plastic or nonconductive film, layer, or sheet used as an electrode masking film  100  for electrowinning, electrorefining, or electrodepositing a metal. Thus the computing device  600  and matrix design engine  602  increases, optimizes, or maximizes an electrodeposition of a metal  200 , or optimizes the efficiency of electrodepositing the metal  200 . The computing device  600  can also control a plotter, cutter, or other device for making holes  102  in a solid or semi-solid electrode masking film  100 . 
         [0047]    The example computing device  600  is only one example of a computer, controller, or computing apparatus, and is not intended to suggest any limitation as to scope of use or functionality of the computing device  600  or its possible architectures. Neither should computing device  600  be interpreted as having any dependency or requirement relating to one or a combination of the components illustrated in the example computing device  600 . 
         [0048]    Computing device  600  includes one or more processors  604  or processing units, one or more memory  606  and/or volatile storage components, one or more input/output (I/O) devices  608 , and a bus  610  that allows the various components and devices to communicate with one another. Bus  610  represents one or more of any of several types of bus structures, including a memory bus or memory controller, a peripheral bus, an accelerated graphics port, and a processor or local bus using any of a variety of bus architectures. Bus  610  can include wired and/or wireless buses. 
         [0049]    The memory  606  can be volatile media, such as random access memory (RAM), or read-only memory (ROM), for example. The example computing device  600  may also include nonvolatile data storage media  612 , such as a hard drive, internal flash memory, and so forth. Data storage component  612  can include a media drive interface  614  to receive removable media  616 , such as an optical disk, flash memory drive, removable hard drive, magnetic disks, and so forth. 
         [0050]    One or more input/output devices  608  controlled by a user interface controller  618  allow a user to enter commands and information to computing device  600 , and also allow information to be presented to the user on a display and audio equipment. Examples of input devices include a keyboard, a cursor control device (e.g., a mouse), a microphone, a scanner, and so forth. Examples of output devices include a display device (e.g., a monitor or projector), speakers, a printer, a network card, and so forth. 
         [0051]    A network interface  620  allows the example matrix design engine  602  to communicate with external hardware, such as a plotter  622 . The matrix design engine  602  can determine the configuration and pattern  300  of holes  102  to be formed of cut in the electrode masking film  100 . An example matrix design engine  602  can optimize the size (and sometimes shape) of the holes  102 , as well as the geometry of the pattern  300 , including layout, angles, and spacing of the holes relative to each other and to the pattern  300 , and the overall extent of the pattern on an electrode surface  104 . The matrix design engine  602  can control the total amount of bare electrode area to be exposed to an electrolyte solution, for example. The holes  102  and the pattern  300  may be varied by the matrix design engine  602  to optimize metal deposition onto a cathode. The matrix design of holes  102  and pattern  300  implemented by the matrix design engine  602  can be created and varied depending on multiple parameters, such as the particular metal(s) and associated metal ions being deposited, electrolyte concentrations, pH levels, electrical voltages, electrical current densities, solution temperatures, electrode temperatures, and plating time, for example. 
         [0052]    The example matrix design engine  602  and various other techniques may be described herein in the general context of software or program modules. Generally, software includes routines, programs, objects, components, data structures, and so forth that perform particular tasks or implement particular abstract data types. An implementation of these modules and techniques, such as the example matrix design engine  602 , may be stored on or transmitted across some form of tangible computer-readable data storage media, for example local data storage  612  or removable media  616 . Computer readable media can be any available tangible medium or media that can be accessed by a computing device. 
         [0053]    Computer storage media include volatile and non-volatile, removable and non-removable tangible media implemented in a method or technology for storage of information, such as computer readable instructions, data structures, program modules, or other data. Computer storage media include, but are not limited to, RAM, ROM, EEPROM, flash memory, and other memory technology; CD-ROM, digital versatile disks (DVD), or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, and other tangible media that can be used to store the desired information and which can be accessed by a computer. 
       CONCLUSION 
       [0054]    Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from the subject matter. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures. It is the express intention of the applicant not to invoke 35 U.S.C. §112, paragraph 6 for any limitations of any of the claims herein, except for those in which the claim expressly uses the words ‘means for’ together with an associated function.