Patent Publication Number: US-2013247734-A1

Title: Apparatus for Manufacturing Cut Glass Fibres

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of European Patent Application No. 12 160 715.4 filed Mar. 22, 2012, incorporated by reference herein in its entirety. 
     BACKGROUND OF THE INVENTION 
     The present invention generally relates to an apparatus for manufacturing cut glass fibres. 
     BRIEF SUMMARY OF THE INVENTION 
     In one embodiment there is an apparatus for manufacturing cut glass fibres comprising: at least one first cot wheel and at least one second cot wheel, a first cutter head and a second cutter head, whereby the apparatus is configured such that the apparatus is operable in at least one first operation mode in which at least one of the cot wheels and at least one of the cutter heads are capable to cut inline glass fibres from a yarn, preferably from an endless yarn. In one embodiment, the first cot wheel and the second cot wheel are mounted on a cot turret, whereby the cot turret is movable from a first position to a second position and from the second position to the first position. In one embodiment, the first position of the cot turret is a position, in which the first cot wheel is in an operating position for cutting glass fibres inline and/or that the second position of the cot turret is a position, in which the second cot wheel is in an operating position for cutting glass fibres inline. 
     In one embodiment, the first position of the cot turret is a position, in which the second cot wheel is in a non-operating position and detachable and/or that the second position of the cot turret is a position, in which the first cot wheel is in a non-operating position and detachable, whereby preferably in the first position of the cot turret the second cot wheel is accessible through at least one safety door and/or whereby preferably in the second position of the cot turret the first cot wheel is accessible through the at least one safety door. In one embodiment, the cot turret is rotatable around a cot turret axis and that the first cot wheel is rotatable around a first cot wheel axis and the second cot wheel is rotatable around a second cot wheel axis, whereby the cot turret axis, the first cot wheel axis and the second cot wheel axis are substantially parallel. 
     In one embodiment, the first cutter head and the second cutter head are mounted on a cutterhead turret, whereby the cutterhead turret is movable from a first position to a second position and from the second position to the first position. In one embodiment, the first position of the cutterhead turret is a position, in which the first cutter head is in an operating position for cutting glass fibres inline and/or that the second position of the cutterhead turret is a position, in which the second cutter head is in an operating position for cutting glass fibres inline. In one embodiment, the first position of the cutterhead turret is a position, in which the second cutter head is in a non-operating position and detachable and/or that the second position of the cutterhead turret is a position, in which the first cutter head is in a non-operating position and detachable, whereby preferably in the first position of the cutterhead turret the second cutter head is accessible through at least one safety door and/or whereby preferably in the second position of the cutterhead turret the first cutter head is accessible through the at least one safety door. 
     In one embodiment, the cutterhead turret is rotatable around a cutterhead turret axis and that the first cutter head is rotatable around a first cutter head axis and the second cutter head is rotatable around a second cutter head axis, whereby the cutterhead turret axis, the first cutter head axis and the second cutter head axis are substantially parallel. In one embodiment, the apparatus comprises at least one idler, whereby the idler is configured such that the yarn can be guided by means of the idler. In one embodiment, the apparatus comprises at least one movable idler being movable from at least a first position to a second position and backwards. In one embodiment, the movable idler is configured such that by moving from the first position to the second position the yarn is guided into the cot wheel being in the non-operating position, preferably during the automatic change-over process when changing from the first cot wheel to the second cot wheel or from the second cot wheel to first cot wheel and/or that the movable idler is configured such that by moving from the first position to the second position the yarn is guided into the cot wheel being in the operating position for cutting glass fibres inline, preferably during the automatic starting of the insertion and cutting process of the yarn. 
     In one embodiment, the apparatus comprises at least one set of at least two pulley wheels, whereby the pulley wheels are configured such that the pulley wheels are capable to pull the yarn, preferably during the automatic starting of the insertion and cutting process of the yarn. In one embodiment, the apparatus comprises at least one movable press roller being movable from at least a first position to a second position and backwards, whereby preferably the movable press roller is configured such that by moving from the first position to the second position the yarn is guided into the cot wheel being in the operating position for cutting glass fibres inline, preferably during the automatic starting of the insertion and cutting process of the yarn. In one embodiment, the apparatus comprises at least one oscillating comb, which is configured such that the incoming yarn is guided by the oscillating comb. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The foregoing summary, as well as the following detailed description of embodiments of the apparatus for manufacturing cut glass fibres, will be better understood when read in conjunction with the appended drawings of an exemplary embodiment. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. 
       In the drawings: 
         FIG. 1  is a schematic drawing of a chopper according to the present invention; 
         FIG. 2  is a schematic drawing of the arrangement of the cutting head and the cot wheel of the chopper according to the present invention; 
         FIG. 3  is a further schematic drawing of the arrangement of the cutting head and the cot wheel of the chopper according to the present invention; 
         FIG. 4  is a further schematic drawing of the chopper according to the present invention; 
         FIG. 5  is a further schematic drawing of the chopper according to the present invention during the automatic application of a first strand in a first step; 
         FIG. 6  is a further schematic drawing of the chopper according to the present invention during the automatic application of a first strand in a second step; 
         FIG. 7  is a further schematic drawing of the chopper according to the present invention during the automatic application of a first strand in a third step; 
         FIG. 8  is a further schematic drawing of the chopper according to the present invention during the cutting in operation; 
         FIG. 9  is a further schematic drawing of the chopper according to the present invention during the automatic application of a strand in a first step; 
         FIG. 10  is a further schematic drawing of the chopper according to the present invention during the automatic application of a strand in a second step; 
         FIG. 11  is a further schematic drawing of the chopper according to the present invention during the automatic application of a strand in a third step; 
         FIG. 12  is a further schematic drawing of the chopper according to the present invention during the automatic application in a first step; 
         FIG. 13  is a further schematic drawing of the chopper according to the present invention during the automatic application in a second step; 
         FIG. 14  is a further schematic drawing of the chopper according to the present invention during the automatic application in a third step; 
         FIG. 15  is a further schematic drawing of the chopper according to the present invention during the automatic application in a fourth step; 
         FIG. 16  is a further schematic drawing of the chopper according to the present invention during exchange of the cutter head and the cot wheel during operation; 
         FIGS. 17   a, b  are schematic drawings illustrating details of the cot wheel; and 
         FIG. 18  is a schematic drawing of an alternative embodiment which comprises engine-driven cutter heads. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     For the inline manufacturing of cut glass fibres machines are used, which are equipped with a cot wheel (drive wheel) and a cutting head. These machines are so-called choppers. 
     The cutter head is driven by the rotating cot wheel by means of friction. At least one glass fibre yarn is fed from a glass yarn spinning machine to the chopper, handled by the machine by means of several cylinders and/or wheels and cut by the cutter head. 
     Since the cutter head and the cot wheel are subject to abrasive wear due to the kind of actuation of the cutter head and due to the normal wear caused by the cutting procedure of the glass fibres, the cutter head and the cot wheel have to be exchanged from time to time. Both the cutter head and the cot wheel are the most prominent wear parts of the chopper, since these parts are directly involved in the cutting process and thus subject to extensive wear and loads. 
     During an exchange process of the cot wheel and the cutter head the whole machine has to be stopped and thus the production process of manufacturing cut glass fibres has to be interrupted. 
     It is therefore an object of the present invention to improve an apparatus for manufacturing cut glass fibres in particular in that the exchange of the cot wheel and the cutter head is simplified and that the interruption time of the chopper during exchange of the cot wheel and the cutter head is reduced. 
     An apparatus for manufacturing cut glass fibres is provided, whereby the apparatus comprises at least one first cot wheel and at least one second cot wheel, a first cutter head and a second cutter head, whereby the apparatus is configured such that the apparatus is operable in at least one first operation mode in which at least one of the cot wheels and at least one of the cutter heads are capable to cut inline glass fibres from a yarn, preferably from an endless yarn. 
     The apparatus for manufacturing cut glass fibres can be a so-called chopper, for instance preferably an inline chopper that automatically runs along for manufacturing cut glass fibres more or less directly after the spinning nozzle of the spinning machine. The machines are so-called choppers and the cut glass fibres are so-called chopped glass fibres. 
     Thereby, the advantage is achieved that at least one pair of a cot wheel and a cutter head is capable to operate and to be used for cutting of a yarn. The other pair of cot wheel and cutter head is in a non-operating state and can thus be exchanged easily. It is possible that the cot wheel und cutter head being in operation can be changed, so that the cot wheel und cutter head being not in operation can be used for the cutting process. 
     The yarn or, as it is also possible, a plurality of yarns can be provided by at least one spinning machine comprising one or more spinning nozzles. Especially, the exchange of the cot wheel and the cutter head is simplified and the interruption time of the apparatus for manufacturing of cut glass fibres during exchange of the cot wheel and the cutter head is reduced. 
     It is especially possible that the first cot wheel and the second cot wheel are mounted on a cot turret, whereby the cot turret is movable from a first position to a second position and from the second position to the first position. By means of the cot turret the exchange of the positions of the first and second cot wheel is simplified. 
     Moreover, the first position of the cot turret may be a position, in which the first cot wheel is in an operating position for cutting glass fibres inline and/or that the second position of the cot turret may be a position, in which the second cot wheel is in an operating position for cutting glass fibres inline. 
     Additionally, it is possible that the first position of the cot turret is a position, in which the second cot wheel is in a non-operating position and detachable and/or that the second position of the cot turret is a position, in which the first cot wheel is in a non-operating position and detachable, whereby preferably in the first position of the cot turret the second cot wheel is accessible through at least one safety door and/or whereby preferably in the second position of the cot turret the first cot wheel is accessible through the at least one safety door. The safety door(s) may be e.g. interlinked with a control means of the apparatus, which is configured such that in an unsafe state for opening the safety door is locked, e.g. during the rotation of the cot turret. 
     Furthermore, it is possible that the cot turret is rotatable around a cot turret axis and that the first cot wheel is rotatable around a first cot wheel axis and the second cot wheel is rotatable around a second cot wheel axis, whereby the cot turret axis, the first cot wheel axis and the second cot wheel axis are substantially parallel. 
     Moreover, it is possible that the first cutter head and the second cutter head are mounted on a cutterhead turret, whereby the cutterhead turret is movable from a first position to a second position and from the second position to the first position. 
     It is further possible that the first position of the cutterhead turret is a position, in which the first cutter head is in an operating position for cutting glass fibres inline and/or that the second position of the cutterhead turret is a position, in which the second cutter head is in an operating position for cutting glass fibres inline. 
     Preferably, the first position of the cutterhead turret may be a position, in which the second cutter head is in a non-operating position and detachable and/or that the second position of the cutterhead turret may be a position, in which the first cutter head is in a non-operating position and detachable, whereby preferably in the first position of the cutterhead turret the second cutter head is accessible through at least one safety door and/or whereby preferably in the second position of the cutterhead turret the first cutter head is accessible through the at least one safety door. 
     Additionally, it is possible that the cutterhead turret is rotatable around a cutterhead turret axis and that the first cutter head is rotatable around a first cutter head axis and the second cutter head is rotatable around a second cutter head axis, whereby the cutterhead turret axis, the first cutter head axis and the second cutter head axis are substantially parallel. 
     Furthermore, it is possible that the apparatus comprises at least one idler, whereby the idler is configured such that the yarn can be guided by means of the idler. 
     Moreover, the apparatus may comprise at least one movable idler being movable from at least a first position to a second position and backwards. 
     It is possible that the movable idler is configured such that by moving from the first position to the second position the yarn is guided into the cot wheel being in the non-operating position, preferably during the automatically change-over process when changing from the first cot wheel to the second cot wheel or from the second cot wheel to first cot wheel and/or that the movable idler is configured such that by moving from the first position to the second position the yarn is guided into the cot wheel being in the operating position for cutting glass fibres inline, preferably during the automatic starting of the insertion and cutting process of the yarn. 
     Furthermore, it is possible that the apparatus comprises at least one set of at least two pulley wheels, whereby the pulley wheels are configured such that the pulley wheels are capable to pull the yarn, preferably during the automatic starting of the insertion and cutting process of the yarn. 
     Additionally, the apparatus may comprise at least one movable press roller being movable from at least a first position to a second position and backwards, whereby preferably the movable press roller is configured such that by moving from the first position to the second position the yarn is guided into the cot wheel being in the operating position for cutting glass fibres inline, preferably during the automatic starting of the insertion and cutting process of the yarn. 
     It is further possible that the apparatus comprises at least one oscillating comb, which is configured such that the incoming yarn is guided by the oscillating comb. 
       FIG. 1  shows a schematic drawing of an apparatus  10  for manufacturing of cut glass fibres CG (see also e.g.  FIG. 4 ), in particular an automatic shifting chopper  10  according to the present invention. 
     A plurality of glass fibre yarns Y, which is produced by several spinning machines  1  comprising e.g. common spinning nozzles  5 , is transferred to and fed into the automatic inline chopper  10  for the cutting process. 
     As can be derived from  FIGS. 2 and 3 , the apparatus  10  comprises at least one first cot wheel  20  and at least one second cot wheel  30 , a first cutter head  50  and a second cutter head  60 , whereby the apparatus  10  is configured such that the apparatus is operable in at least one first operation mode in which at least one of the cot wheels  20 ,  30  and at least one of the cutter heads  50 ,  60  are capable to cut inline glass fibres CG from the endless yarn Y produced by the spinning machines  1 . 
     As shown in  FIG. 2 , the cot wheel  20  being in the operating position is engaged with the cutting head  50  also being in the operating position. The cutting head is rotated by means of friction and the rotation of the cot wheel  20 . 
       FIG. 3  shows that the cot wheel  20  may be driven by a spindle drive  22  and that the cot wheel  30  may be driven by the spindle drive  32 . The power supply to the spindle drives  22 ,  32  is established via a slip ring  43 . 
     The first cot wheel  20  and the second cot wheel  30  are mounted on a cot turret  40 , whereby the cot turret  40  is movable from a first position to a second position and from the second position to the first position. 
     The first position of the cot turret  40 , which is shown in  FIGS. 2 and 3 , is a position, in which the first cot wheel  20  is in an operating position for cutting glass fibres CG inline. The cot turret  40  can be rotated by means of a servomotor, here a turret drive  47  with a belt. The cot turret  40  can be rotated and there is a second position of the cot turret  40 , in which the second cot wheel  30  is in an operating position for cutting glass fibres CG inline. The cot turret axis, the first cot wheel axis and the second cot wheel axis are substantially parallel. To determine the actual cot turret position an index bolt  45  is provided. 
     Moreover, the first position of the cot turret  40  is a position, in which the second cot wheel  30  is in a non-operating position and detachable and the second position of the cot turret  40  is a position, in which the first cot wheel  20  is in a non-operating position and detachable. 
       FIG. 4  shows a further schematic drawing of the chopper  10  according to the present invention. 
     As shown in  FIG. 4 , in the first position of the cot turret  40  the second cot wheel  30  is accessible through a safety door  80  and in the second position of the cot turret  40  the first cot wheel  20  is accessible through the safety door  80 . The safety door  80  can be opened during operation of the chopper  10  to unmount or exchange the cot wheel located behind the safety door  80 . 
     The first cutter head  50  and the second cutter head  60  are mounted on a cutterhead turret  70 , whereby the cutterhead turret  70  is rotatable from a first position to a second position and from the second position to the first position. The cutterhead turret  70  is rotatable around a cutterhead turret axis and the first cutter head  50  is rotatable around a first cutter head axis and the second cutter head  60  is rotatable around a second cutter head axis, whereby the cutterhead turret axis, the first cutter head axis and the second cutter head axis are substantially parallel. 
     The first position of the cutterhead turret  70  is a position, in which the first cutter head  50  is in an operating position for cutting glass fibres CG inline and the second position of the cutterhead turret  70  is a position, in which the second cutter head  60  is in an operating position for cutting glass fibres CG inline. 
     The first position of the cutterhead turret  70  is a position, in which the second cutter head  60  is in a non-operating position and detachable and the second position of the cutterhead turret  70  is a position, in which the first cutter head  50  is in a non-operating position and detachable. In the first position of the cutterhead turret  70  the second cutter head  60  is accessible through the safety door  90  and in the second position of the cutterhead turret  70  the first cutter head  50  is accessible through the safety door  90 . 
     The chopper  10  comprises an oscillating comb  150 , which is configured such that the incoming yarn Y is guided by the oscillating comb  150 . Moreover, the chopper  10  comprises idlers  100 ,  110 ,  120 ,  130 , whereby the idlers  100 ,  110 ,  120 ,  130  are configured such that the yarn Y can be guided by means of the idler  100 ,  110 ,  120 ,  130 . The idlers  110 ,  130  are movable idlers  110 ,  130  and are movable from at least a first position to a second position and vice versa. 
     Furthermore, a set of two pulley wheels  140 ,  142  is provided, whereby the pulley wheels  140 ,  142  are configured such that the pulley wheels  140 ,  142  are capable to pull the yarn Y, preferably during the automatic application of the yarn Y. Additionally, the chopper  10  comprises one movable press roller  160  being movable from a first position to a second position and vice versa, whereby the movable press roller  160  is configured such that by moving from the first position to the second position the yarn is guided into the cot wheel  20 ,  30  being in the operating position for cutting glass fibres CG inline, i.e. during the automatic starting of the application and cutting process of the yarn Y (cf.  FIGS. 5 to 7 ). 
       FIGS. 5 to 7  show schematic drawings of the automatic chopper  10  according to the present invention during the automatic application of a first strand, respectively the first yarn Y to be introduced into the chopper  10 . 
       FIG. 5  shows the automatic application of the first strand in a first step. The yarn Y is guided through the oscillating comb  150  and guided by the idlers  100 ,  110  around the movable idler  130  and around the idler  120  down to the pulley wheels  140 ,  142 . The pulley wheels  140 ,  142  cause a transportation of the yarn sheet into a trash chute. 
     As can be derived from  FIGS. 6 and 7 , the movable idler  130  is configured such that by moving from the first position to the second position the yarn Y is guided into the cot wheel  20  being in the operating position for cutting glass fibres CG inline, preferably during the automatic starting of the insertion and cutting process of the yarn Y. 
       FIG. 6  shows the automatic laying of a first strand in a second step. The linearly movable idler  130  is moved along its guidance rail  132  from the first position shown in  FIG. 5  to a second position shown in  FIG. 6 . This second position is above the first cot wheel  20  and the yarn Y is initially introduced into the cot wheel  20  by moving the movable idler  130  into the second position. 
       FIG. 7  shows the automatic laying of a first strand in a third step. The movable idler  130  is diverted from the second position shown in  FIG. 6  towards the first cot wheel  20 , thereby laying the yarn Y onto the cot wheel  20 . To support this laying, the movable press roller  160  is diverted towards the first cot wheel  20  by also laying the yarn Y onto the cot wheel  20 . 
     Thereby, the yarn Y is automatically transported to the cutter head  50  ( 60 ) and the cutting process begins. 
       FIG. 8  shows the chopper  10  during the cutting process. When cutting is in operation, the yarn Y is guided by the oscillating comb  150 , the idler  100  and the movable press roller  160 . The yarn Y is laid onto the cot wheel  20 , which is in operation and engaged with the first cutter head  50 . The yarn Y is cut into cut glass fibres CG by passing through the engaged cot wheel  20  and the cutter head  50 . 
       FIGS. 9 to 11  show schematic drawings of the automatic chopper  10  according to the present invention during the automatic application of a yarn sheet during the cutting. 
       FIG. 9  shows the automatic winding during the cutting process in a first step. A first yarn Y is cut as shown and described with respect to  FIG. 8 . A second yarn Y 1  is applied automatically, similar to the first strand shown in  FIGS. 5 to 7 , however with little differences as described in the following. 
     The second yarn Y 1  is guided through the oscillating comb  150  and guided by the idler  100 , around the movable press roller  160 , around the movable idler  130  and around the idler  120  down to the pulley wheels  140 ,  142 . The pulley wheels  140 ,  142  provide an automatic discharge into the trash chute. 
       FIG. 10  shows the automatic application of a yarn sheet during the cutting process in a second step. The linearly movable idler  130  is moved along its guidance rail  132  from the first position shown in  FIG. 9  to a second position shown in  FIG. 10 . This second position is above the first cot wheel  20  and the yarn Y 1  is initially applied onto the cot wheel  20  by moving the movable idler  130  into the second position. 
     The movable idler  130  is deflected from the second position shown in  FIG. 10  towards the first cot wheel  20 , thereby applying the yarn Y onto the cot wheel  20  as can be derived from  FIG. 11 . Thus,  FIG. 11  shows the automatic applying or laying during the cutting process of a first strand in a third step. 
     After the steps shown in  FIGS. 9 to 11 , the chopper  10  is again operated as shown in  FIG. 8 , i.e. in the cutting mode operation. 
       FIG. 12  shows the chopper  10  according to the present invention during automatic change over from the first cot wheel  20  to the second cot wheel  30  in a first step. Thereby, the second cot wheel  30  is running with production speed, i.e. in particular the speed of the first cot wheel  20 . 
     The movable idler  110  is configured such that by moving from the first position to the second position the yarn Y is guided into the cot wheel  30 , which is running with production speed, being in the non-operating position during the automatic change-over process when changing from the first cot wheel  20  to the second cot wheel  30  as shown in  FIGS. 12 to 15 . 
     The movable idler  110  is moving down along its guidance rail  112 , thereby initially applying the yarn Y onto the second cot wheel  30 . Thus, the yarn Y is guided through the oscillating comb  150 , the idler  110 , the cot wheel  30 , then guided by the movable press roller  160  being engaged with the first cot wheel  20 . The yarn is then guided by the first cot wheel to cutter head  50  which is in operation and cuts the yarn Y into cut glass fibres CG. 
       FIG. 13  shows the chopper  10  during automatic change over in a second step. The yarn Y is wound around the second cot wheel  30  to remove the first cot wheel from operation. Therefore, the yarn push off back one  135  is moving the yarn Y to a catcher  35  and the catcher  35  (see also  FIGS. 17   a, b ) is catching the yarn Y and the yarn Y is then running on the second cot wheel  30 . 
       FIG. 14  shows the chopper  10  during automatic change over in a third step. Thereby, the movable press roller  160  and the cutterhead turret  70  with its cutter heads  50 ,  60  is swinging out of the collision circle of the rotating cot wheel turret  30  with the cot wheel  30  and the cot wheel  20 . The idler  110  is moved in its upper position and the cot wheel  30  is transferred into the operating position. 
       FIG. 15  shows the chopper  10  during automatic change over in a fourth step, whereby both turrets  40  and  70  are now in the right position for operation. The front yarn push off  137  moves the yarn Y into the normal operating position. The press roller  160  and the cutter head  50  swing back into the working position. 
     In a further schematic drawing  FIG. 16  shows the chopper  10  after the automatic change over process of  FIGS. 12 to 15 . As is shown in  FIG. 16 , the cutting process is in operation and the safety door  80  is opened to change the first cot wheel  20 . Meanwhile, the yarn Y is cut by means of the second cot wheel  30  and the cutter head  50 . It is possible that during the third step of the automatic change over process as shown in  FIG. 14  the first and the second cutter head  50 ,  60  exchange their positions, so that the first cutter head  50  can be exchanged also in the situation shown in  FIG. 16 . 
       FIG. 17   a  shows a front view of the cot wheel  30 , whereby it is to be noted that the cot wheel  20  is identical. As can be seen in  FIG. 17  a, the cot wheel  30  comprises two catchers  35 , which are used in the automatic change over (see  FIG. 13 ). The catchers  35  are cast of the boundary of the cot wheel  30  without a covering wall  37  of the border wall  36 .  FIG. 17   b  shows the cot wheel  30  of  FIG. 17   a  in a side view. 
       FIG. 18  shows an alternative embodiment of the drives  55 ,  65  of the cutting heads  50 ,  60 . The difference compared to the embodiments shown in  FIGS. 2 to 16  is that the embodiment of  FIG. 18  comprises two small servo motors  55 ,  65 , which drive the cutting heads  50 ,  60 . 
     In one embodiment, the apparatus includes one or more computers having one or more processors and memory (e.g., one or more nonvolatile storage devices). In some embodiments, memory or computer readable storage medium of memory stores programs, modules and data structures, or a subset thereof for a processor to control and run the various systems and methods disclosed herein. In one embodiment, a non-transitory computer readable storage medium having stored thereon computer-executable instructions which, when executed by a processor, perform one or more of the methods disclosed herein. 
     It will be appreciated by those skilled in the art that changes could be made to the exemplary embodiments shown and described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the exemplary embodiments shown and described, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the claims. For example, specific features of the exemplary embodiments may or may not be part of the claimed invention and features of the disclosed embodiments may be combined. Unless specifically set forth herein, the terms “a”, “an” and “the” are not limited to one element but instead should be read as meaning “at least one”. 
     It is to be understood that at least some of the figures and descriptions of the invention have been simplified to focus on elements that are relevant for a clear understanding of the invention, while eliminating, for purposes of clarity, other elements that those of ordinary skill in the art will appreciate may also comprise a portion of the invention. However, because such elements are well known in the art, and because they do not necessarily facilitate a better understanding of the invention, a description of such elements is not provided herein.