Patent Publication Number: US-2015082764-A1

Title: Laser hardened knife guard

Description:
FIELD OF THE INVENTION 
     This invention generally relates to a laser hardened knife guard for a sickle bar assembly. 
     BACKGROUND OF THE INVENTION 
     Knife guards are used in sickle style cutting systems. They act as the stationary surface for moving sickle blades to cut against or at least to protect or cover the sickle blades. Examples are shown in U.S. Pat. Nos. 6,962,040, 4,660,361, 7,478,522, and 8,464,506 the disclosures of which are incorporated by reference as the present invention may be applied and/or incorporated into these examples in various embodiments. 
     Knife guards are primarily constructed of steel and manufactured in a variety of ways including forging, casting, welded fabrication of stamped components, and machining. In some instances, a hardened plate is assembled into the guard to create a surface known as a ledger plate that the sickle runs on and the edge. Past efforts to improve the hardness of the ledger plate and the edge have included hardening via quench and temper or austemper, carborizing or carbonitriding, induction hardening, flame hardening, or boronizing. In some cases, more than one of these treatments is performed on the part in order to impart varying properties within the knife guard. 
     With the exception of induction hardening, the remaining treatments are high heat processes of over 1500° F. and require the entire part to be raised into these temperature ranges. The knife guard in its original state contains internal stresses. Accordingly, distortion of the part is a factor with these processes. Distortion is not desirable where the knife guard provides a bearing surface supporting sliding movement and reciprocation of a sickle bar. The result is often additional machining or straightening processes to bring the part back within specification. These additional steps increase cost. 
     In the case of induction hardening, typically very elaborate induction coils and quenching processes are required to perform the process in a repeatable and predictable manner. Induction heat is a resistance type of heating. The result of this process along with flame hardening a heat affected zone which is driven deep into the part. In order to achieve the desired microstructure in knife guard material, a quench process must be used to reduce the internal temperature of the knife guard quickly enough to create the proper metallurgical transformation. In addition, the induction process focuses the energy in the thinner section of the knife guard edge resulting in the risk of melting the material at the edge. The depth of the heat affected zone also creates a similar situation to the previously mentioned treatments in that it causes stresses in the part to be relieved often resulting in distortion of the part. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is generally directed towards laser hardening the knife guard in one or more select regions. Laser hardening may be done to the ledger plate and edges to produce hardened areas on the ledger bar of the knife guard and may be done along edges of the knife guard so as to maintain the sharpness of the edges of the knife guard. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein. 
     In one aspect, the invention provides for a knife guard that comprises a guard body that further comprises a base material. The base material includes a mounting bar that defines at least one bolt hole and at least one tine projecting forward from the mounting bar. The base material has a first hardness. A laser treated material is formed into or in the base material. The laser treated material comprises a second hardness greater than the first hardness. 
     The knife guard include a ledger surface that is adapted to bear against or at least face a sickle bar assembly. The ledger surface includes a region of laser hardened layer formed integrally with an outer surface of the base material to provide for the laser treated material. 
     The base material may be steel and the laser hardened layer may be at least 0.5 millimeter in depth thickness along the base material and less than 3 millimeters. 
     The tines can comprise a central protrusion and a pair of flank surfaces on either side of the protrusion that extend from the bottom surface toward the bearing surface. The flank surfaces intersect the bearing surface at a shearing edge. The region of the laser hardened layer may include at least one portion formed above the flanks along ledger surface that forms part of the shearing edge. 
     The knife guard may further comprise a free region of base material that is not a laser hardened layer. The free region may be disposed above the central protrusion along the ledger surface and between first and second portions of laser hardened layer. The first and second portions are formed above the flanks along ledger surface and form part of the shearing edge. 
     An advantage of laser hardening select regions and limited regions leaving free regions is that distortion can be prevented or minimized reducing or eliminating post machining or straightening steps along bearing surfaces. 
     The knife guard may further include a trash bar. The trash bar extends perpendicularly to an extension direction of the at least one tine. The trash bar connects adjacent tines of the at least one tine. The free region extends along the ledger surface that extends along a trash bar portion of the ledger surface defined by the trash bar. The trash bar is free of the laser hardened layer. 
     The mounting bar can include a ledger bar that extends perpendicularly to an extension direction of the at least one tine. The ledger bar defines a ledger bar portion of the ledger surface. The ledger bar portion forms part of the region of laser hardened layer along the length thereof. 
     In one embodiment more than 40% of the ledger surface is free of the region of laser hardened layer. The laser hardened layer may be between 0.5 millimeter and 3 millimeter in depth thickness along the base material at the shearing edge. During erosion of the flank surfaces, the laser hardened layer sharpens into the laser hardened layer. 
     The at least one portion formed above the flanks along ledger surface that forms part of the shearing edge may be formed in a non-linear oscillation profile to provide a serrated pattern for serrated cutting performance. 
     In one embodiment over 85% of an outer surface of the knife guard may form an untreated region of base material. The laser treated material may be limited to less than 15% of the outer surface. The base material may have a hardness of less than 50 HRC, and the laser treated material can have a hardness between 50 and 70 HRC and preferably between 50 to 65 HRC. The laser treated material has a hardness at least 5 HRC points higher than the base material and typically 10 HRC points or more higher than the base material. 
     In another aspect, the invention provides that the knife guard may include at least one tine that comprises a plurality of tines with valleys between the tines. The at least one bolt hole may comprise a plurality of bolt holes. The bolt holes may have respective bolt mounting centers aligned along an mounting axis that extends perpendicularly relative to a forward extending axis direction of the tines. The bolt holes may be formed in mounting bosses formed along the mounting bar. A connecting trashbar may extend perpendicularly relative to the forward extending axis direction and connect adjacent tines. The mounting bar can include a ledger bar. The ledger bar and the tines define a ledger surface that extends in a plane. A sickle clearance channel is formed between the ledger bar and the trash bar. Ribs at a bottom of the sickle clearance channel connect the ledger bar and the trash bar. 
     The ledger bar may project from a mounting plate portion of the mounting bar. Mounting bosses may be formed into the mounting plate. 
     In yet another aspect, the invention provides for a cutter bar assembly that can include a linear array of a plurality of the knife guards. The cutter bar assembly can include a cutter bar support having a mounting flange that extends in parallel relation to the linear array. The sickle bar assembly may extend in a longitudinal direction in parallel relation with the cutter bar support in order to reciprocate back and forth in the longitudinal direction for cutting. The sickle bar assembly can include a sickle bar frequently referred to as a knife back and a plurality of sickle knives mounted to the sickle bar. The knife guards may be arranged in side by side relation. The sickle knives may be arranged in side by side relation. The knife guards and sickle knives may be arranged in a vertically overlapping relation wherein the knife guards may be over the sickle knives or wherein the sickle knives may be over the knife guards. 
     The sickle bar slides along the knife guards along a region of laser hardened layer formed integrally with an outer surface of the base material to provide for the laser treated material. 
     Another aspect of the present invention is directed toward a method of forming a knife guard. The knife guard can comprise a guard body. The guard body may comprise a base material that includes a mounting bar that defines at least one bolt hole and at least one tine projecting forward from the mounting bar. The method comprises hardening with a laser a region of the base material to provide a second hardness greater than the first hardness. 
     The hardening with the laser can include using at least one of the following lasers CO2, YAG, Diode and Fiber. The hardening may comprise targeting and confining the application of the laser to the region of an outer surface of the guard body. The region may be less than 20% of an area of the outer surface. 
     The laser hardening can be conducted without a liquid quenchant. The base material of the guard body operates as a heat sink to allow the part to quench to a hardened microstructure in said region. No further tempering operation is conducted after the hardening with the laser. 
     The laser hardened region may be formed along a ledger surface that forms a sliding interface with a sickle bar assembly that reciprocates relative to the knife guard in use. 
     Part of the ledger surface may be free and untreated with the laser with an at least 30% untreated region. Distortion may be eliminated or reduced such that subsequent machining or straightening operations are not conducted on the ledger surface after said hardening. The laser hardened region can be formed along a shearing edge formed along opposing sides of the at least one tine. 
     Other aspects, objectives and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings: 
         FIG. 1A  is a schematic top view of a first portion of a knife guard according to an embodiment of the present invention with the laser hardened regions emphasized. 
         FIG. 1B  is a section view taken about area A in  FIG. 1A  and illustrating with emphasis the laser hardened regions above the flanks of the knife guard. 
         FIG. 2  is an isometric view of a knife guard according to an embodiment of the present invention. 
         FIG. 3  is a side view of the knife guard of  FIG. 3 . 
         FIG. 4  is an enlarged side view of the area taken about the sickle clearance channel of the knife guard of  FIG. 3 . 
         FIG. 5  is a schematic illustration of at least two portions of knife guards and sickle blades of an embodiment of the present invention, the distance between knife guards being potentially exaggerated (e.g. trash bars of adjacent knife guards my abut or almost abut each other at less than 1 cm in spacing.) 
         FIG. 6  is a schematic illustration of an embodiment of a knife guard of the present invention with a non-linear oscillation profile showing the laser hardening tool movement and application to the knife guard. 
         FIG. 7  is a schematic illustration of an embodiment of fabricated knife guard of the present invention with the laser hardening tool angularly positioned to laser treat the ledger and or bearing surfaces of the tines. 
         FIG. 8  is a schematic illustration of an embodiment of a knife guard of the present invention with the laser hardening tool angularly positioned to laser treat the ledger and or bearing surfaces of the tines. 
     
    
    
     While the invention will be described in connection with certain preferred embodiments, there is no intent to limit it to those embodiments. On the contrary, the intent is to cover all alternatives, modifications and equivalents as included within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in  FIGS. 1A and 1B , a laser hardened knife guard  10  according to an embodiment of the present invention is illustrated. A knife guard  10  comprises a guard body  12  and is comprised of a base material  14  such as steel material, that includes a mounting bar  16 , which defines at least one bolt hole  18  and at least one tine  20  projecting forward  56  from the mounting bar  16 . The base material  14  has a first hardness  22  and a laser treated material  24  is formed into or in the base material. The laser treated material  24  comprises a second hardness  26 , greater than the first hardness  22 . 
     The knife guard  10  includes a ledger surface  28  that is adapted to bear against or at least face a sickle bar assembly  30 . Typically the ledger surface  28  will come into contact with the sickle bar assembly  30  to guide or maintain linear reciprocating movement of the sickle bar assembly  30 .  FIG. 5  illustrates an embodiment of the present invention wherein the sickle bar assembly  30  moves over the ledger surface  28  of a knife guard  10 . The ledger surface  28  includes a region of laser hardened layer  26  formed integrally with in outer surface of the base material  14  to provide for the laser treated material  26 . As shown in  FIG. 3  the ledger surface  28  may be provided by respective coplanar regions of ledger bar portion  80   a  and bearing surface portion  36  of the of tines  20 . 
     The base material  14  may be steel and the laser hardened layer  26  is at least 0.5 millimeters and less than 3 millimeters in depth thickness  48  along the base of the material. 
       FIG. 1B  illustrates a tine  20  comprising a bottom surface  33  that includes a central protrusion  32  and a pair of flank surfaces  34  on either side of the central protrusion  32  extending toward a bearing surface  36 . A portion of the flank  34  that extends toward the bearing surface  36  acts as a cutting support surface  86 . The cutting support surfaces  86  of the flank surfaces  34  intersect the bearing surface  36  at a shearing edge  38 . The region of laser hardened layer  26  includes at least one portion  48  formed above the flanks along the ledger surface  28  and along the cutting support surfaces  86  and forms part of the shearing edge  38 . 
       FIG. 1B  illustrates an angle of 90° between the laser hardened bearing surface portion  36  and the cutting support surface  86  of the flanks  34 . For the system to perform at an optimum level, the guard  10  should preferably maintain a sharp corner between the ledger face  28  that the sickle blades  78  that run on the cutting support surface  86 . Often, the cutting support surface  86  of each tine  20  is undercut in order to allow for an angle between these two surfaces of less than 90 degrees as shown for example in  FIG. 2  about the area of character reference  24 . Thus the cutting support surface  86  may be a beveled edge under the shearing edge  38  running generally from the tip of the tine to the start of the trash bar  44 , or in those embodiments wherein there is no trash bar  44 , to the end of the tine&#39;s bearing surface  36 . 
     The knife guard  10  may further comprise a free region  42  of base material  14  that is not a laser hardened layer. As illustrated in  FIG. 1B , the free region  42  may be disposed under the central protrusion  32  along the bearing surface portion  36  and between first and second portions  40   a ,  40   b  of a laser hardened layer  26 . The first and second portions  40   a ,  40   b  being formed along the bearing surface portion of the ledger surface  28  and cutting support surfaces  86  and includes the shearing edges  38 . The free region  42  can limit distortion and cost associated with laser hardening operations. 
       FIG. 2  illustrates that the knife guard  10  may further comprise a trash bar  44  that extends perpendicularly to an extension direction  56  of the at least one tine  20  and connecting adjacent tines of the at least one tine  20 . The free region  42  may extend along the bearing surface portion  36  of ledger&#39;s surface  28  that extends along trash bar  44 . The trash bar  44  may be free of the laser hardened layer  26 . All (90% or more) of the ledger bar portion  80   a  may be heat treated while half or more of the bearing surface portion  36  may be laser heat treated. As can be readily appreciated not every embodiment of tine  10  has a trash bar  44  with associated ledger portion  80   a . For example, as shown in  FIG. 7  tine  10  does not have a trash bar, and this embodiment may be configured without the trash bar. 
     The mounting bar  16  includes a ledger bar  80  that extends perpendicularly to an extension direction  56  of the at least one tine  20 . The ledger bar  80  defines a ledger bar portion  80   a  of the ledger surface  28  wherein the ledger bar portion  80   a  forms part of the region of laser hardened layer  26  along the length thereof. More than 30% of the overall ledger surface  28  may be free of the region of laser hardened layer  26 . As illustrated in  FIG. 7  not every embodiment of a laser treated guard has a ledger bar and thus would not have a ledger bar portion  80   a  that would be part of the laser hardened layer  26  or form part of ledger surface  28 . 
     The laser hardened layer  26  may be between 0.5 millimeter and 3 millimeter in depth thickness  48  along the base material  14  at the shearing edge  38 . During erosion of the flank surfaces  34  of the untreated base material  14 , the cutting support surface  86  that is part of the laser hardened layer  26  may be sharpened along its lower edge  88  relative to bearing surface  36 . This self-sharpening effect may result from the erosion of the softer base material  14  above the hardened zone  24 ,  26  (as shown for example in  FIG. 1B ) along the flanks  34  due to the interaction with the crop material during the cutting motion and in conjunction with the forward motion of the unit through the field. The erosion of the softer based material  14  along the flanks  34  exposes the harder edges  38 ,  88  of the cutting support surfaces  86  allowing them to protrude and thus maintaining the shearing edges  38 ,  88 . 
     The laser hardening process, due to its fast interaction with the material, can produce compressive stresses at the surface of the heat treated zone, which increases the fatigue properties of the part in certain cases. 
     The laser hardened portions  40   a  and  40   b  formed above the flanks  34  along the ledger surface  28  that forms part of the shearing edge  38  may be formed in a non-linear oscillation profile  50  (which indicates the laser tool application path) that provides for a serrated pattern for serrating cutting performance as shown in  FIG. 6 . As erosion of the softer base material  14  occurs during operation of the knife guard  10  the serrated pattern along the cutting support surfaces  86  of the flanks  34  and the bearing surface  36  results in self-sharpening of the serrated cutting edges  38 ,  88 . 
     Over 85% of the outer surface of the knife guard  10  may form an untreated region of base material  14 . The laser treated material  24  may be limited to less than 15% of the outer surface of the knife guard  10  and as shown, formed preferably only along the ledger surface  28 . The base material  14  may have a hardness of less than 50 HRC and the laser treated material  24  may have a hardness between 50 and 70 HRC, less than 50 HRC, and the laser treated material can have a hardness between 50 and 70 HRC and preferably between 50 to 65 HRC. The laser treated material has a hardness at least 5 HRC points higher than the base material and typically 10 HRC points or more higher than the base material. 
     The at least one tine  20  may comprise plurality of tines  20  with, as shown for example in  FIG. 6 , valleys  52  between the tines. The at least one bolt hole  18  may comprise a plurality of bolt holes  18  having respective bolt hole mounting centers aligned along a mounting axis  54 , as shown if  FIG. 1A , that extends perpendicularly relative to a forward extending axis direction  56  of the tines  20 . The bolt holes  18  may be formed in mounting bosses  60  formed along the mounting bar  16 . A connection trash bar  44  extends perpendicularly relative to the forward extending axis direction  56  and connecting adjacent tines  20 . The mounting bar  16  includes a ledger bar  80 . The ledger bar  80  and the tines  20  define a ledger surface  28  that extends in a plane wherein a sickle clearance channel  62  is formed between the ledger bar  80  and the trash bar  44 . Ribs  64  at a bottom of the sickle clearance channel  62  connect the ledger bar  80  and the trash bar  44 . The ledger bar  80  projects from a mounting plate portion  66  of the mounting bar  16 . The mounting bosses  60  are formed into the mounting plate  66 . 
       FIGS. 3 and 4  show in greater detail the ledger surface  28  comprising the ledger bar portion  80   a  and the bearing surface  36  of a tine  20 . The ledger bar portion  80   a  of ledger bar  80  may be of laser treated material  24  forming a second hardness  26  relative to the base material  14  of a first hardness  22 . Further illustrated is the depth thickness  48  of the laser treated material  24  on both the ledger bar  80  and the flank surface  34  of the tine  20 . The free region  42  is the region that has not been laser treated and remains of the first hardness  22  of the base material  14 . 
       FIG. 5  illustrates a cutter bar assembly  68  that includes a linear array of a plurality of knife guards  10  of an embodiment of the present invention. A cutter bar support  72  has a mounting flange  74  that extends in parallel relation to the linear array of knife guards. A sickle bar assembly  30  extends in a longitudinal direction  70  and parallel relation with a cutter bar support  72  in order to reciprocate back and forth in a longitudinal direction  70  for cutting. The sickle bar assembly  30  includes a sickle bar also commonly referred to in the art as a knife back  82  and a plurality of sickle knives  78  mounted to the sickle bar  82 . The sickle knives  78  are arranged in side by side relation. The knife guards  10  are arranged in side-by-side relation. The sickle knives  78  are in a vertically overlapping relation to the knife guards  10 . A portion of the sickle bar  82  rides inside the sickle clearance channel  62  while a surface of each of the sickle knives  78  rides over the ledger surface  28  of the knife guards  10 . 
     An embodiment of the present invention showing two portions of tines  20  is shown in  FIG. 5 . The trash bar  44  of each portion of tines  20  as shown here meets the next portion with no overlap. However, as can be readily appreciated, the tines may be mounted such that the trash bar  44  of one portion may overlap the trash bar  44  of a second portion. As can be readily appreciated not every embodiment of knife guard has a trash bar or ledger bar and yet other embodiments as shown in  FIG. 7  have a retainer portion over a base portion of the tine either portion or both of which may be laser treated with an angular approach of the laser tool as depicted in  FIGS. 7 and 8 . Thus about the edges and along the bearing surfaces on either side of the tines and on either or both the cover and the bottom a laser hardened area is formed just as in the other embodiments heretofore described. 
     The laser used to harden the base material  14  may include using at least one of the following lasers; CO2, YAG, Diode and fiber. The laser beam consists of a column of light energy of similar wave length. These different types of lasers produce different wave lengths of light. These lasers each have their own unique characteristics, but all work well in heat treating applications. 
     The laser hardening of the knife guard  10  results in a hardened area along the edge of the guard  10  necessary to maintain the sharpness of the edge  38  defined by the hardened portion of the ledger surface portions  40   a  and  40   b  and the cutting supports surfaces  86 . The method of using the laser to laser harden the knife guard  10  has the advantage over other processes currently in use of involving a smaller heat effected zone that is created with the laser. The smaller heat affected zone results in less distortion of the part and minimal disruption to the microstructure of the base part, which allows better material properties in the base part after laser hardening. In some cases, it is desirable to heat treat the base part to a lower hardness to allow for a mixture of strength and toughness. This lower heat effected zone maintains the prior heat treatment and a greater percentage of the base part will compare to induction or flame hardening. 
     The lower distortion eliminates subsequent machining and/or straightening operations, thus reducing processing time and costs. The process of heat treating the base material  14  for strength and toughness, then machining the surface (if necessary) for the section to ride on, then laser hardening can be performed easily. This process of hardening the edge after heat treat is difficult to perform without distortion or the risk of melting the edge material. 
     However, with the laser hardening process, the body of the part acts as a heat sink to allow the part to quench to the proper microstructure. With other heat treatment processes, the part must be submerged in a quench (oil, air, water, polymer solution, molten salt, etc.) The rapid quenching by submersion results in a rapid transformation of the part, which can impart internal stresses causing distortion. Oftentimes with other heat treatment processes, a secondary tempering process is necessary to relieve these internal stresses, thus adding another opportunity for the part to deform along with adding additional process steps and costs. 
       FIG. 6  illustrates that the precision of the laser heat treatment zone and the precision of the laser motion system allows for non-linear heat treat patterns  50  that would enhance the performance of the part. An oscillation profile  50  would result in the part eroding in a serrated pattern  50 , which would improve cutting performance. Thus, the precision of the laser heat treat zone and precision of the laser motion system allows the heat treatment to be applied in specific areas, which allows for other critical structures in the knife guard  10  to perform as designed with different material properties. 
       FIG. 7  illustrates a fabricated embodiment of a laser hardened knife guard  10  of the present invention. The knife guard  10  of this embodiment does not have a ledger bar or a trash bar. The knife guard  10  is comprised of two tines  20  with each tine  20  further comprised of a retainer portion  96 A and a base portion  98 A. The bottom surface  90 A of the retainer portion  96 A of each tine  20  acts as a bearing surface under which passes a sickle blade  100 . The two edges of the bottom surface  90 A of the retainer portion  96 A act as cutting edges against the knife blade  100  and may be beveled and or serrated. 
     Still with reference to  FIG. 7 , the top surface  92 A of each base portion  98 A of each tine  20  acts as and provides a bearing surface for the sickle blade  100 . The two edges of the top surface  92 A of the base portion  98 A act as cutting edges against the knife blade  100  and may be beveled or serrated. 
     A laser tool  94  makes an angular approach to laser harden along the length of the bearing surfaces  90 A,  92 A of the retainer portion  96 A and base portion  98 A from the cutting edges inwardly towards the center of the bearing surfaces  90 A,  92 A. Thus, in this two tine  20  embodiment there are eight cutting edges and thus eight portions of laser hardened areas on the bearing surfaces  90 A,  92 A extending from the cutting edges thereof. It can be readily appreciated as with the previous embodiments only a portion of the bearing surfaces are laser hardened along the cutting edges in order to obtain the same advantages heretofore discussed in the other embodiments, for example, self-sharpening of the cutting edges and decreased wear of the bearing surfaces  90 A,  92 A of the knife guard  10 . 
       FIG. 8  illustrates yet another embodiment of a laser hardened knife guard  10  of the present invention. As with  FIG. 7  the tine  20  of this embodiment has a retainer portion  96 B and a base portion  98 B. The bottom surface  90 B of the retainer portion  96 B acts as a bearing surface for a knife blade and thus with an angular approach of the laser tool  94  laser hardening may be accomplished on the bearing surface  90 B along the edges thereof. Further, the top surface  92 B of the base section  98 B acts as a bearing surface for the knife blade  100  and thus with an angular approach of the laser tool  94 , laser hardening may be accomplished on the bearing surface  92 B along the edges thereof for all the same advantages heretofore discussed. 
     All references, including publications, patent applications, and patents cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. 
     The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) is to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. 
     Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.