Abstract:
An optical component bowing device is configured to include a bending moment generating structure that generates a bending moment in a supported portion of an optical component that reflects or shapes a light beam.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2006-232518 filed on Aug. 29, 2006. 
   BACKGROUND 
   1. Technical Field 
   The present invention relates to an optical component bowing device, an optical device, an optical scanning device, and an image forming apparatus. 
   2. Related Art 
   In an optical scanning device that emits a light beam, a cylindrical lens or the like is caused to bow to correct the scanning position in a direction orthogonal to the scanning direction of the light beam on a photoconductor. 
   SUMMARY 
   An optical component bowing device of a first aspect of the invention includes a bending moment generating structure that generates a bending moment in a supported portion of an optical component that reflects or shapes a light beam. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein: 
       FIG. 1  is a general configural diagram of an image forming apparatus disposed with an optical scanning device pertaining to a first exemplary embodiment of the invention; 
       FIG. 2  is a diagram schematically showing, in plan view, relevant portions of the optical scanning device pertaining to the first exemplary embodiment of the invention; 
       FIG. 3A  is a perspective diagram showing a cylindrical mirror, and  FIG. 3B  is a plan diagram showing a state where the cylindrical mirror is bowed; 
       FIG. 4  is a diagram schematically showing, in plan view, relevant portions of an optical scanning device pertaining to a second exemplary embodiment of the invention; 
       FIG. 5  is a diagram schematically showing, in plan view, relevant portions of an optical scanning device pertaining to a third exemplary embodiment of the invention; 
       FIG. 6  is a perspective diagram schematically showing relevant portions of an optical scanning device pertaining to a fourth exemplary embodiment of the invention; and 
       FIG. 7A  and  FIG. 7B  are explanatory diagrams describing bow correction. 
   

   DETAILED DESCRIPTION 
   In  FIG. 1 , there is shown the general configuration of an image forming apparatus  12  disposed with an optical scanning device  14  pertaining to a first exemplary embodiment of the present invention. The image forming apparatus  12  is a tandem full-color image forming apparatus where plural photoconductors are juxtaposed, toner images of respective colors are formed on the photoconductors, and then the respective color toner images are superposed to form a full-color toner image. 
   Below, when members are to be distinguished by color, the letters C (cyan), M (magenta), Y (yellow), and Bk (black) will be added to reference numerals representing those members. When it is not particularly necessary to distinguish between the members by color, the letters C, M, Y, and Bk will be omitted. Further, the direction in which light beams scan optical components will be referred to as a scanning direction. 
   The optical scanning device  14  includes a box-shaped optical box  50 . Housed inside the optical box  50  are various kinds of optical components such as light source members  18 C,  18 M,  18 Y, and  18 Bk, plane mirrors  20 , plane mirrors  22 , a rotating polygon mirror  24 , an fθ lens group  26 , plane mirrors  28 C,  28 M,  28 Y, and  28 Bk, and cylindrical mirrors  30 C,  30 M,  30 Y, and  30 Bk having an imaging function in a direction orthogonal to the scanning direction. 
   A semiconductor laser  32 , a collimator lens  34 , an aperture  36 , and a cylindrical lens  38  having an imaging function in one direction are disposed inside each of the light source members  18 C,  18 M,  18 Y, and  18 Bk (in  FIG. 1 , just the components of the light source member  18 C are shown). A light beam is emitted from the semiconductor laser  32  in correspondence to image information of each color and is shaped by the collimator lens  34  having a light beam shaping function. The beam width of the light beam is made into a predetermined width by the aperture  36 , and the light beam is focused by the cylindrical lens  38  in a direction corresponding to the direction in which the light beam moves in the circumferential direction with the rotation of a later-described photoconductor  40 . 
   The light beams emitted from the light source members  18 M and  18 Y are reflected by the plane mirrors  20  and the plane mirrors  22  and made incident on a mirror surface  24 R of the rotating polygon mirror  24 . Further, the light beams emitted from the light source members  18 C and  18 Bk are reflected by the plane mirrors  22  and made incident on the mirror surface  24 R of the rotating polygon mirror  24 . 
   The rotating polygon mirror  24  is disposed in the center portion of the optical box  50  such that its rotational axis Y coincides with the vertical direction (the direction of gravitational force), and the rotating polygon mirror  24  is rotated about the rotational axis Y by an unillustrated rotary drive device. The light beams made incident on the mirror surface  24 R of the rotating polygon mirror  24  are deflected by the movement of the mirror surface  24 R resulting from the rotation of the rotating polygon mirror  24 . 
   The light beams deflected by the rotating polygon mirror  24  are transmitted through the fθ lens group  26  having an imaging function, are respectively reflected by the plane mirrors  28 C,  28 M,  28 Y, and  28 Bk corresponding to each color, and are further reflected by the cylindrical mirrors  30 C,  30 M,  30 Y, and  30 Bk. It will be noted that arrow S represents the scanning direction in which the light beams scan the cylindrical mirrors  30 C,  30 M,  30 Y, and  30 Bk. 
   Surfaces of photoconductors  40 C,  40 M,  40 Y, and  40 Bk corresponding to each color and disposed below the optical scanning device  14  are exposed to the light. At this time, due to the rotation of the rotating polygon mirror  24  and the fθ lens group  26 , the light beams scan the surfaces of the photoconductors  40 C,  40 M,  40 Y, and  40 Bk at substantially uniform velocities in the axial direction. 
   It will be noted that, when seen in plan view, the cylindrical mirrors  30 C,  30 M,  30 Y, and  30 Bk are disposed juxtaposed in a single row parallel to each other (see  FIG. 2 ). 
   The photoconductors  40 C,  40 M,  40 Y, and  40 Bk are shaped like drums, and their longitudinal directions (axial directions of the drums) coincide with the scanning direction. When the image forming apparatus  12  is seen from the side in the scanning direction, the photoconductors  40 C,  40 M,  40 Y, and  40 Bk are disposed juxtaposed in a single line with predetermined intervals interposed therebetween. 
   The surfaces of the photoconductors  40 C,  40 M,  40 Y, and  40 Bk are charged by charging devices (not shown). When the photoconductors  40 C,  40 M,  40 Y, and  40 Bk rotate, the light beams to which the surfaces of the photoconductors  40 C,  40 M,  40 Y, and  40 Bk are exposed (scanned) relatively move in the circumferential direction. Electrostatic latent images are formed on the surfaces of the photoconductors  40 C,  40 M,  40 Y, and  40 Bk as a result of the surfaces of the photoconductors  40 C,  40 M,  40 Y, and  40 Bk being exposed to the light beams in this manner. 
   The electrostatic latent images on the photoconductors  40 C,  40 M,  40 Y, and  40 Bk are made visible by developing devices (not shown) corresponding to each color, whereby toner images of the respective colors are formed on the photoconductors  40 C,  40 M,  40 Y, and  40 Bk. 
   The color toner images formed on the respective photoconductors  40 C,  40 M,  40 Y, and  40 Bk are sequentially transferred to an intermediate transfer body such as an endless intermediate transfer belt (not shown), and the four colors are superposed to form a full-color image on the intermediate transfer belt. Then, the full-color image formed on the intermediate transfer belt is transferred all at once to a recording medium and fixed by a fixing device (not shown) to the recording medium, so that a desired full-color image can be obtained on the recording medium. 
   Next, the cylindrical mirrors  30 C,  30 M,  30 Y, and  30 Bk will be described. Because the cylindrical mirrors  30 C,  30 M,  30 Y, and  30 Bk corresponding to the respective colors all have the same configuration, they will be described without distinguishing between them by color. 
   As shown in  FIG. 3A , a reflective surface  102  of each of the cylindrical mirrors  30  has power just in a direction orthogonal to the scanning direction (arrow S) (i.e., a direction corresponding to the direction in which the light beam moves in the circumferential direction with the rotation of the photoconductor  40 ), and the reflective surface  102  corrects variations in the scan line resulting from optical face tangle error in the mirror surface  24 R (see  FIG. 1 ) of the rotating polygon mirror  24  (optical face tangle error correction). The cylindrical mirror  30  includes a quadrangular prism-shaped mirror body  104  disposed with the reflective surface  102  on one side. It will be noted that the longitudinal direction of the mirror body  104  coincides with the scanning direction represented by arrow S. Further, in  FIG. 3A  and  FIG. 3B , the orientation of the reflective surface  102  is shown oppositely from the orientation shown in  FIG. 1  and  FIG. 2  (i.e., in  FIG. 1  and  FIG. 2 , the reflective mirror  102  faces down). 
   Extension members  150 A and  150 B that extend toward mutually opposite sides in a direction substantially orthogonal to the longitudinal direction (scanning direction) when seen in plan view in a direction orthogonal to the reflective surface  102  are disposed on an end portion on one longitudinal direction side (scanning start side) of the mirror body  104  (when it is not necessary to distinguish between the two, they will be referred to simply as the extension members  150 ). Similarly, extension members  160 A and  160 B are also disposed on the end portion on the other side (scanning end side) (similarly, when it is not necessary to distinguish between the two, they will be referred to simply as the extension members  160 ). Thus, each of the end portions on the one side and on the other side of the cylindrical mirror  30  is shaped like a T when seen in plan view in the direction orthogonal to the reflective surface  102 . It will be noted that the extension members  150  and  160  are disposed further outside in the scanning direction than the reflective surface  102 . 
   Further, by “substantially orthogonal” is meant an angular range of an angle of 90°±3°. It will be noted that it is alright even if the extension members  150  and  160  are not substantially orthogonal to the longitudinal direction. It suffices as long as the extension members extend in a direction intersecting the longitudinal direction (scanning direction). It is also alright even if the extension member  150 A and the extension member  150 B (and the extension member  160 A and the extension member  160 B) are not formed on the same straight line. For example, the extension member  150 A and the extension member  150 B (and the extension member  160 A and the extension member  160 B) may also form an angle (like an L shape). Further, the extension members may also be curved rather than being straight. Moreover, it is alright even if just one of the extension member  150 A and the extension member  150 B (and the extension member  160 A and the extension member  160 B) is disposed. 
   In the present exemplary embodiment, after the mirror body  104  and the extension members  150  and  160  have been formed as separate components, the mirror body  104  and the extension members  150  and  160  are joined together by adhesion or some other method so that the mirror body  104  and the extension members  150  and  160  are integrally configured. It will be noted that the mirror body  104  and the extension members  150  and  160  may also be formed as an integral mold. 
   Support holes  110  and  112  are formed in the longitudinal direction center sides of the end portions of the one side and the other side of the mirror body  104 . Either one of the support holes  110  and  112  is an elongate hole whose longitudinal direction coincides with the longitudinal direction (scanning direction) of the cylindrical mirror  30 . In the present exemplary embodiment, the support hole  110  on the one side is an elongate hole. Support pins  111  and  113  fixed to the optical box  50  (see  FIG. 1 ) respectively pass through these two support holes  110  and  112  so that the cylindrical mirror  30  is supported in the optical box  50 . 
   Further, through holes  120 A,  120 B,  130 A, and  130 B that penetrate the extension members  150 A,  150 B,  160 A, and  160 B are formed in longitudinal direction center sides from the end portions (in the vicinities of the end portions) of the extension members  150 A,  150 B,  160 A, and  160 B. 
   Additionally, as represented by arrow F 1  in  FIG. 3B , when a load is applied from the outsides to the insides of the extension members  150 A and  160 A to cause the extension members  150  and  160  to be displaced in the scanning direction, a bending moment is generated in the portions of the support holes  110  and  112 . The cylindrical mirror  30  is caused by this bending moment to bow (in order to make it easier to understand, in  FIG. 3B  the cylindrical mirror  30  is shown as being bowed more greatly than in actuality). It will be noted that, as represented by arrow F 2 , a load may also be applied from the insides to the outsides of the extension members  150 B and  160 B to cause the extension members  150  and  160  to be displaced. 
   Further, when a load that is opposite from the directions of arrows F 1  and F 2  is applied, the cylindrical mirror  30  bows oppositely from that shown in  FIG. 3B  (i.e., with respect to  FIG. 3B , the cylindrical mirror  30  would bow such that its convex side faces up). 
   As shown in  FIG. 2 , both longitudinal direction end portions of each of the cylindrical mirrors  30 Bk,  30 Y,  30 M, and  30 C project from windows  56 Bk,  56 Y,  56 M, and  56 C formed in side surface portions  52  and  54  of the optical box  50 . In other words, the extension members  150 Bk,  150 Y,  150 M, and  150 C are exposed to the outside of the optical box  50 . It will be noted that the gaps between the windows  56 Bk,  56 Y,  56 M, and  56 C and the cylindrical mirrors  30 Bk,  30 Y,  30 M, and  30 C are sealed with a sealing member (not shown) such that external dust or the like does not enter into the optical box  50 . 
   As shown in  FIG. 3A  and  FIG. 3B , the through holes  120 A,  120 B,  130 A, and  130 B are formed in the longitudinal direction (scanning direction) in both end portions of the extension members  150  and  160  of each of the cylindrical mirrors  30 . Screws  125  are passed through the through holes  120 A,  120 B,  130 A, and  130 B and screwed into screw holes (not shown) in the side surface portions  52  and  54  of the optical box  50 . 
   By adjusting how much the screws  125  are screwed into the screw holes in the side surface portions  52  and  54 , the extension members  150  and  160  are displaced in the scanning direction and the cylindrical mirror  30  bows (see  FIG. 3B ). It will be noted that the bowing direction (i.e., the direction that the convex side of the cylindrical mirror  30  faces) may be either up or down in  FIG. 2 . 
   As mentioned above, the image forming apparatus  12  of the present exemplary embodiment superposes respective color toner images to form a full-color image. Thus, when the respective color toner images are not precisely superposed, color misregistration occurs. 
   One cause of color misregistration is, as shown in  FIG. 7A , when scan lines (BOW(Bk) to BOW(C)) of the light beams scanning the photoconductors  40 Bk,  40 Y,  40 M, and  40 C become bowed in the direction orthogonal to the scanning direction (i.e., the direction in which the light beams move in the circumferential direction with the rotation of the photoconductors  40 ) with respectively different curvatures. For this reason, as shown in  FIG. 7B , bow correction for correcting and matching up the bowing of the scan lines (BOW(Bk) to BOW(C)) is performed to correct color misregistration. 
   Additionally, in the image forming apparatus  12  of the present exemplary embodiment, bow correction is performed (see  FIG. 3B ) by adjusting how much the screws  125  are screwed into the screw holes in the side surface portions  52  and  54  of the optical box  50  and adjusting the scanning direction displacement amounts of the extension members  150 Bk,  150 Y,  150 M, and  150 C of the cylindrical mirrors  30 Bk,  30 Y,  30 M, and  30 C—that is, the bending moment generated in the support holes  110  and  112  in each of the cylindrical mirrors  30 Bk,  30 Y,  30 M, and  30 C—to adjust the bowing amounts of the cylindrical mirrors  30 Bk,  30 Y,  30 M, and  30 C. 
   In the present exemplary embodiment, as shown in  FIG. 2 , the extension members  150  and  160  of each of the cylindrical mirrors  30  are exposed from the side surface portions  52  and  54  of the optical box  50 , but the invention is not limited to this. The extension portions  150  and  160  of the cylindrical mirrors  30  may also be disposed inside the optical box  50 . 
   Further, the screws  125  are screwed into screw holes in the side surface portions  52  and  54  to cause the extension members  150  and  160  of the cylindrical mirrors  30  to be displaced, but the invention is not limited to this. Screw holes may also be formed in sites other than the optical box  50  and screws may be screwed into those screw holes to cause the extension members  150  and  160  to be displaced. 
   Next, an optical scanning device  214  of a second exemplary embodiment pertaining to the present invention will be described. It will be noted that description that is redundant with the description of the first exemplary embodiment will be omitted. 
   As shown in  FIG. 4 , extension members  250  and  260  are alternately disposed on either one of the one side (scanning start side) and the other side (scanning end side) of adjacent cylindrical mirrors  230 . Specifically, an extension member  250 Bk is disposed on the end portion on the one side of a cylindrical mirror  230 Bk, an extension member  260 Y is disposed on the end portion on the other side of a cylindrical mirror  230 Y, an extension member  250 M is disposed on the end portion on the one side of a cylindrical mirror  230 M, and an extension member  260 C is disposed on the end portion on the other side of a cylindrical mirror  230 C. 
   Additionally, the extension members  250  and the extension members  260  of the cylindrical mirrors  230  that are adjacent when seen in the scanning direction (arrow S) are disposed so as to overlap each other. 
   Further, the extension members  250  and  260  of the cylindrical mirrors  230  are exposed from side surface portions  272  and  274  of an optical box  270 . Screws  125  are screwed into screw holes in the side surface portions  272  and  274  to cause the extension members  250  and  260  of the cylindrical mirrors  230  to be displaced in the scanning direction. 
   It will be noted that in the present exemplary embodiment also, similar to the first exemplary embodiment, the extension members  250  and  260  of the cylindrical mirrors  230  may also be disposed inside the optical box  270 . Further, screw holes may be disposed in sites other than the optical box  270  and the screws  125  may be screwed into these screw holes to cause the extension members  250  and  260  to be displaced. 
   Next, an optical scanning device  314  of a third exemplary embodiment pertaining to the present invention will be described. It will be noted that description that is redundant with the description of the first exemplary embodiment will be omitted. 
   As shown in  FIG. 5 , extension members  350  and  360  of cylindrical mirrors  330  are exposed from side surface portions  352  and  354  of an optical box  370 . 
   The extension members  350  on the one side (scanning start side) of the cylindrical mirrors  330  and the extension members  360  on the other side (scanning end side) of the cylindrical mirrors  330  are coupled together by linear members  332  such as wires or piano wires. Additionally, the lengths of the linear members  332  are adjusted (shortened)—that is, the distances between the extension members  350  on the one side of the cylindrical mirrors  330  and the extension members  360  on the other side of the cylindrical mirrors  330  are adjusted (shortened)—to cause the extension members  350  and  360  to be displaced and to cause the cylindrical mirrors  330  to bow. 
   Further, the linear expansion coefficients of the linear members  332 Bk,  332 Y,  332 M, and  332 C are caused to vary, for example, in response to differences in temperature change and differences in length. For example, the linear expansion coefficients of the linear members  332 Bk,  332 Y,  332 M, and  332 C are selected in accordance with differences in temperature rises in places where the cylindrical mirrors  330 Bk,  330 Y,  330 M, and  330 C are disposed. In other words, the linear expansion coefficients are made smaller in places where the temperature rise is greater. For example, the linear expansion coefficients of the linear members  332  are selected in accordance with the distance from a heat source such as the fixing device that fixes the full-color toner image to the recording medium. For example, assuming that the cylindrical mirror  330 Bk is the closest to the heat source and that the cylindrical mirror  330 C is the farthest from the heat source, then the linear expansion coefficient of the linear member  332 Bk is made the smallest, and the linear expansion coefficients are made greater from there on in the order of the linear member  332 Y, the linear member  332 M, and the linear member  332 C. 
   Examples of materials for the linear members  332  whose linear expansion coefficients are different include the following. 
   stainless steel wires (according to Japan Industrial Standards (JIS)) 
   SUS304: 1.73(×10 −5 ) 
   SUS316: 1.60(×10 −5 ) 
   SUS430: 1.04(×10 −5 ) 
   phosphor bronze wires: 1.80(×10 −5 ) 
   hard steel wires: 1.20(×10 −5 ) 
   It will be noted that because the linear members  332  such as wires or piano wires can only cause the extension members  350  and  360  to be displaced in the direction in which the distances between the extension members  350  and the extension members  360  are narrowed, the extension member  350 A and the extension member  360 A, or the extension member  350 B and the extension member  360 B, are coupled together on the opposite side of the direction in which one wishes the cylindrical mirrors  330  to bow in convex shapes. In  FIG. 5 , the cylindrical mirror  330 Bk and the cylindrical mirror  330 Y bow in convex shapes downward in  FIG. 5 , and the cylindrical mirror  330 M and the cylindrical mirror  330 C bow in convex shapes upward in  FIG. 5 . 
   In the present exemplary embodiment, the extension members  350  on the one side of the cylindrical mirrors  330  and the extension members  360  on the other side of the cylindrical mirrors  330  are coupled together by the linear members  332  such as wires or piano wires, but the invention is not limited to this. It suffices as long as coupling members couple together the extension members  350  on the one side and the extension members  360  on the other side and have lengths that are adjustable. For example, rod-shaped coupling members may also be used. In the case of rod-shaped coupling members, the distances between the extension members  350  and the extension members  360  may be increased to cause the extension members  350  and  360  to be displaced. 
   Further, in the present exemplary embodiment also, similar to the first exemplary embodiment and the second exemplary embodiment, the extension members  350  and  360  of the cylindrical mirrors  330  may also be disposed inside the optical box  370 . 
   Next, an optical scanning device  414  of a fourth exemplary embodiment of the present invention will be described. 
   As shown in  FIG. 6 , a resin cylindrical lens  430  for performing optical face tangle error correction is disposed in the optical scanning device  414 . In  FIG. 6 , just one cylindrical lens  430  is shown, but in actuality, similar to the first exemplary embodiment, four are disposed in correspondence to the respective colors. 
   As shown in  FIG. 6 , a lens body  432  of the cylindrical lens  430  has a quadrangular prism shape whose longitudinal direction coincides with the scanning direction. Convex portions  440  and  442 , in which support holes  441  and  443  are formed in a direction orthogonal to the scanning direction (i.e., a direction corresponding to the direction in which the light beam moves in the circumferential direction in accompaniment with the rotation of the photoconductor  40 ), are integrally formed on the end portions on the one side (scanning start side) and the other side (scanning end side) of the lens body  432 . Shaft portions  452  and  462  of torsion bar springs  450  and  460  are inserted into the support holes  441  and  443  in the convex portions  440  and  442 . The shaft portions  452  and  462  are configured so as to not rotate inside the support holes  441  and  443 . 
   The torsion bar springs  450  and  460  include, from the top portions of the shaft portions  452  and  462 , plate-shaped adjustment portions  454  and  464  whose longitudinal direction coincides with the direction orthogonal to the shaft portions  452  and  462 . When the adjustment portions  454  and  464  are rotated about the shaft portions  452  and  462 , the shaft portions  452  and  462  twist, and a bending moment is generated in the convex portions  440  and  442  because of the reaction force. Additionally, due to this bending moment, the cylindrical lens  430  bows. 
   Pins  501  and  502  are inserted into plural adjustment holes  498  and  499  formed in a fixed portion  496  disposed spanning the distance between a side surface portion  492  and a side surface portion  494  of an optical box  490 , and the adjustment portions  454  and  464  of the torsion bar springs  450  and  460  are caught on the pins  501  and  502 . The adjustment holes  498  and  499  are plurally formed in a circle around the support holes  441  and  443  (the shaft portions  452  and  462  of the torsion bar springs  450  and  460 ) in the cylindrical lens  430 . Additionally, by changing the adjustment holes  498  and  499  into which the pins  501  and  502  are to be inserted, the rotation amount of the adjustment portions  454  and  464  of the torsion bar springs  450  and  460 —that is, the bending moment generated in the convex portions  440  and  442  of the cylindrical lens  430 —can be adjusted to adjust the bowing amount of the cylindrical lens  430 . 
   The present invention is not limited to the preceding exemplary embodiments and can be implemented in various aspects in a range that does not depart from the gist of the invention. 
   For example, in the preceding exemplary embodiments, four light beams to which the four photoconductors  40 Bk,  40 Y,  40 M, and  40 C are exposed were emitted from one optical scanning device  14 ,  214 ,  314 , or  414 , but the invention is not limited to this. For example, the image forming apparatus may also be disposed with one optical scanning device for each of the photoconductors (for a total of four optical scanning devices). 
   Further, in the preceding exemplary embodiments, the image forming apparatus was disposed with the four photoconductors  40 Bk,  40 Y,  40 M, and  40 C, but the invention is not limited to this. The image forming apparatus may also be disposed with three or less or five or more photoconductors. 
   Further, in the preceding exemplary embodiments, as examples of optical components to which the invention may be applied, the invention was applied to the cylindrical mirrors  30 ,  230 , and  330  and to the cylindrical lens  430 , but the invention is not limited to this. The invention can also be applied to optical components that reflect or shape light beams, such as other lenses and mirrors of an optical scanning device. 
   Moreover, in the preceding exemplary embodiments, the invention was applied to optical components of an optical scanning device of an image forming apparatus, but the invention is not limited to this. The invention can also be applied to optical components that reflect or shape light beams, such as lens and mirrors used in other optical devices. For example, the invention can be applied to optical components used in barcode reading apparatus. 
   The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The exemplary embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.