Abstract:
The present invention has a frame, two articulating structures, a drag link and a linear drive assembly. Each articulating structure has a rigid support, a serpentine support and a caster support. The rigid supports are pivotally connected to the frame and to the caster supports. The serpentine supports are pivotally connected to the frame, the rigid support and the caster support. The drag link makes the first and second articulating structures cooperate. The linear drive assembly is connected to the rigid support of one articulating structure and to the drag link. The linear drive assembly causes the bed to rise by acting in two directions, one to directly push the drag link in a first direction and the second to redirect the linear drive assembly force to indirectly push the drag link in the first direction by rotating the first rigid structure away from the frame.

Description:
This application claims priority on US Provisional Application having application No. 60/585,424, filed on Jul. 2, 2004, the entire disclosure of which is hereby incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a support frame, and more particularly to a vertically adjustable support frame that is selectably raised and lowered by extending and retracting at least one articulating structure. 
   2. Description of the Related Art 
   Typically, height and angle adjustable beds are used by medical institutions, such as hospitals and nursing homes. The beds usually include a bed frame and an articulating mechanism for lowering the bed frame to a low position and raising the bed frame to a high position so that it may be used as a gurney or at any height in between. As a result, a patient can be transferred by merely sliding the patient from one gurney to another or a chair. 
   It is known to have height and angle adjustable beds that may be lowered to a fully lowered position near the floor; however, such beds usually require a mechanical or hydraulic compression assist mechanism or high-power hydraulic lift mechanisms to lift the bed from the fully lowered position. For example, U.S. Pat. No. 6,405,393 (“the &#39;393 patent”) incorporated by reference herein, discloses a spring assist mechanism that allows a height adjustable bed to raise from a fully lowered position. The &#39;393 patent describes the increase in force necessary to raise the bed from the fully lowered position. This is because as the angle between the linear actuator and the bed frame in the bed shown in the &#39;393 patent approaches zero, the cosine of that angle also approaches zero. As the cosine of the angle approaches zero, the resultant lift component, or vertical component, of the actuator force also approaches zero. The actuator is therefore at a mechanical disadvantage when the cosine of the angle approaches zero. One way to overcome such a limitation is to use multiple actuators, or an actuator having a relatively large force. Such an approach can be undesirably expensive. 
   Further, a mechanical or hydraulic compressive assist mechanism may be used to overcome the mechanical disadvantage. However, such components may fail unexpectedly. In addition, when such mechanisms fail, time delay, damage or injury may occur. Thus, it would be desirable to eliminate any need for mechanical and hydraulic compressive assist mechanisms. 
   Presently, to achieve a low bed position, one must also accept a mechanical disadvantage. Further, elimination of the mechanical disadvantage requires that the cosine of the angle between the actuator and bed frame not approach zero, and accordingly that the bed not be lowered to the desired position. Thus it would be desirable to achieve a low bed position while simultaneously avoiding a situation where the cosine of the angle between the bed frame and linear actuator approaches zero. 
   A still further disadvantage yet of some existing angle adjustable beds that have two motors is that the motors can get out of synchronization. In this regard, either motor may raise or lower a respective end of the bed at a different rate. This could jeopardize the health and safety of any person on the bed. Further, such a drawback could make transport during raising and lowering of the bed impractical and hazardous. 
   A still further disadvantage yet of existing angle adjustable beds is that they may require an undesirably large amount of swing to reposition the bed from the lowered position to the raised position. The swing occurs as a result of the support frame of the bed moving forward or rearward relative to the wheels. A large swing is disadvantageous for several reasons. First, having bed frame move forward or rearward relative to the wheels changes the center of gravity of the bed. The larger the swing, the larger the change in the center of gravity of the bed. Second, with the ever increasing pressure to reduce room size and to fit more items into existing rooms, there is a sizable disadvantage to a bed that requires a relatively large amount of swing to raise to the raised position. 
   A still further drawback yet is that some beds require three or more casters at each end of the bed to provide a stable structure. This leads to an undesirable number of components. Alternatively, some beds have a stabilizing rod extending between the casters from the front to the rear of the bed. These stabilizing rods can interfere with and limit the use of items such as over bed tables, patient lifts and the like. 
   Thus there exists a need for a support frame that solves these and other problems. 
   SUMMARY OF THE INVENTION 
   One embodiment of the present invention has a frame, two articulating structures, a drag link and a linear drive assembly. Several brackets can extend down from the frame. Each articulating structure can have a rigid support with two arms connected with a tube, and can have a serpentine support with three members. A caster support can be at the bottom of each articulating structure for supporting a pair of casters. The rigid supports are pivotally connected to the frame and to the caster supports. The serpentine supports are pivotally connected to the frame, the rigid support and the caster support. A drag link can be present for making the first and second articulating structures act in cooperation. The linear drive assembly can be connected to the rigid support of one articulating structure and to the drag link. Action of the linear drive assembly causes the bed to raise from a low position to a high position. This is accomplished by the linear drive assembly acting in two directions, one to directly push the drag link in a first direction and the second to indirectly push the drag link in the first direction by rotating the first rigid structure away from the frame. 
   According to one advantage of the present invention, the articulating structures collapse to a compact orientation when the bed is lowered to a low position. Yet, the longitudinal axis of the actuator of the linear drive assembly is maintained at an angle relative to the plane of the frame that is substantially greater than zero. Because this angle does not approach zero, the cosine of this angle also does not approach zero. Accordingly, the vertical lift component of the actuator force never approaches zero, even when the bed is at the fully lowered position. 
   According to another advantage of the present invention, the geometry of the rigid support provides a mechanical advantage to the linear drive assembly. This is advantageously accomplished by having both ends of the linear drive assembly move in opposite directions relative to the frame during operation. The first end of the linear drive assembly applies a force to push the drag link from the first articulating structure towards the second articulating structure. The second end of the linear drive assembly applies force to the rigid member of the first articulating structure to cause the second end of the first articulating structure to rotate away from the frame. This rotation causes the first end of the rigid member of the articulating structure to apply a redirected force against the drag link to also force the drag link towards the second articulating structure. 
   Due to the described mechanical advantage achieved, there is no need for mechanical or hydraulic compressive assist mechanisms. Advantageously, elimination of the mechanical and hydraulic compressive assist mechanisms eliminates a potential for undesirable consequences that may occur as a result of the failure of the assist mechanisms. 
   Related, a single linear drive assembly can be used to raise the bed from a lowered position to a raised position. Using a single linear drive assembly and a drag link to simultaneously raise and lower two articulating structures eliminates the risk that two sides of the bed could move at different rates. 
   A still further advantage of the present invention is that the bed is raised from a low position to a high position with a relatively low amount of swing, or movement of the frame relative to the casters. Accordingly, the center of gravity of the bed is maintained at an acceptable point during the entire movement of the bed. Further, less space is required for operation of the bed. 
   A still further advantage yet of the present invention is that only two casters are needed at each end of the bed. This is accomplished by use of a serpentine support in each articulating structure. The serpentine supports, combined with the rigid support, the frame and the caster supports comprise a structure resembling a split parallelogram. In this regard, the casters can be oriented at a selected orientation with respect to the ground and the frame can be oriented parallel to the ground throughout the entire range of motion of the bed. 
   Other advantages, benefits, and features of the present invention will become apparent to those skilled in the art upon reading the detailed description of the invention and studying the drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a preferred embodiment of the present invention in a raised position. 
       FIG. 2  is an alternative perspective view of a preferred embodiment of the present invention in a raised position. 
       FIG. 3  is a close-up perspective view of a preferred embodiment shown in a raised position. 
       FIG. 4  is a side view of a preferred embodiment shown in a raised position. 
       FIG. 5  is a close-up perspective view of a preferred embodiment shown in an intermediate position. 
       FIG. 6  is a side view of a preferred embodiment shown in an intermediate position. 
       FIG. 7  is a close-up perspective view of a preferred embodiment shown in a lowered position. 
       FIG. 8  is a side view of a preferred embodiment shown in a lowered position. 
       FIG. 9  is an end view of a preferred embodiment shown in a lowered position. 
       FIG. 10  is a profile of the articulating structures of the present invention illustrated functionally as lines and nodes shown in a raised position. 
       FIG. 11  is a profile of the articulating structures of the present invention illustrated functionally as lines and nodes shown in an intermediate position. 
       FIG. 12  is a profile of the articulating structures of the present invention illustrated functionally as lines and nodes shown in a lowered position. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   While the invention will be described in connection with referred embodiments, it will be understood that it is not intended to limit the invention to those embodiments. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims. 
   The preferred embodiments of the present invention are shown and described in relation with a bed  5  having four casters  6 . The casters  6  of the bed  5  preferably rest on a floor  1  lying in a plane  2 . In a preferred embodiment, the bed  5  has a frame  10 , a first articulating structure  20 , a second articulating structure  120 , a drag link  200  and a linear drive assembly  210 . The bed frame  10  is understood to include deck assemblies and the like, however, for the sake of clarity, the frame  10  will be described as a single structure. Of course, the principles of the present invention are applicable to beds having frames with different structures, and the scope of the present invention is not limited to the structure of the illustrated frame. 
   The frame  10  has a top surface  11  lying in a plane  12 , as is shown in  FIG. 4 . It is preferably that the top surface plane  12  be parallel to the floor  1  having a plane  2 . However, any desired orientation of the top surface plane  12  can be achieved. Turning now to  FIGS. 1 and 2 , it is seen that four brackets  13 ,  14 ,  15 , and  16 , respectively depend from the frame  10  for connection with other components of the bed  5 , as later described herein. 
   A first articulating structure  20  is provided. The first articulating structure is preferably comprised of a rigid support  25 , a serpentine support  50  and a caster support  70 . The components are generally and preferably shown to be hollow components having varying shapes and sizes. However, other structures, such as solid members could alternatively be used without departing from the broad aspects of the present invention. 
   The rigid support  25  of the first articulating structure  20  preferably comprises a tube  30 . The tube  30  has a longitudinal axis that preferably lies generally parallel to the top surface plane  12 . The tube  30  has a first end  31  and an opposed second end  32 . Four brackets  33 ,  34 ,  35  and  36 , respectively, are preferably welded or otherwise rigidly connected to the tube  30 . Bracket  33  is preferably pivotally connected to bracket  13  of the frame  10 . Bracket  36  is preferably pivotally connected to bracket  15  of the frame  10 . 
   A first arm  40  is provided and has a first end  41  and a second end  42 . The first end  41  is preferably rigidly connected to the first end  31  of tube  30 . A second arm  45  is also provided, and has a first end  46  and a second end  47 . The first arm  40  and second arm  45  are preferably connected to the tube  30  at a right angles, and as such, are parallel to each other. The tube  30 , first arm  45  and second arm  50  preferably form a generally U shaped structure. 
   It is understood that the first rigid support  25  has many ends, including the pivot points at the second ends  42  and  47  of respective arms  40  and  45 , as well as the pivot points at the ends of the brackets  33 ,  34 ,  35  and  35  rigidly connected to the tube  30 . 
   The first articulating structure  20  also preferably comprises a serpentine support  50 . In a preferred embodiment, the serpentine structure  50  comprises three members, or pieces. The first piece  55  has a first end  56  and a second end  57 . The second piece  60  has a first end  61  and a second end  62 . The third piece  65  has a first end  66  and a second end  67 . The first end  56  of the first piece  55  is preferably pivotally connected to the frame  10 . The second end  57  of the first piece  55  is preferably pivotally connected to the first end  61  of the second piece  60 . The second piece  60 , at a location intermediate the first end  61  and the second end  62 , is preferably pivotally connected to bracket  35  on the tube  30 . The second end  62  of the second piece  60  is preferably pivotally connected to the first end  66  of the third piece  65 . 
   Further, the first articulating structure  20  also preferably comprises a caster support  70 . The caster support  70  preferably comprises a base  71  having a front  72 , a rear  73 , a first end  74  and a second end  75 . The base  71  can be a bent base, such that it dips between the ends  74  and  75 , as shown in  FIGS. 1 and 2 . A first upright  76  is at the first end  74  of the base  71 . A second upright  77  is at the second end  75  of the base  71 . A third upright  78  can be connected to the base  71  intermediate the first and second ends  74  and  75 . The second end  42  of the first arm  40  is preferably pivotally connected to the first upright  76 . The second end  47  of the second arm  45  is preferably pivotally connected to the second upright  77 . The second end  67  of the third piece  65  of the serpentine support  50  is preferably pivotally connected to the third upright  78 . 
   Starting at a low position, the first articulating support  20  rises as the second end of the first rigid support, or the second ends  42  and  47  of the arms  40  and  45 , respectively rotate away from the frame  10 . The pivot point for this rotation is at the pivoting connections between the brackets  13  and  15  of the frame and  33  and  36  of the tube  30 , respectively. Rotation of the tube  30  caused by the pivoting of the first rigid support causes the serpentine support  50  to straighten, and accordingly elongate. Elongation of the serpentine support  50  and rotation of the rigid structure cause the frame  10  to rise relative to the castor support  70 . 
   Looking now to  FIGS. 10-12 , it is shown that in profile, the first articulating structure  20  resembles a split parallelogram. In  FIG. 10 , point A represents the pivot point between the second end  42  of the first arm  40  and the upright  76 . Point B represents the pivot point between the bracket  13  of the frame  10  and bracket  33  of the tube  30 . Point C represents the longitudinal axis of the tube  30 . Point D represents the pivot point between the first end  66  of the second piece  65  of the serpentine support  50  and the second end  57  of the second piece  55  of the serpentine support  50 . Point E represents the pivot point between the second end  67  of the third piece  65  of the serpentine support  50  and the third upright  78  of the base. Point F represents pivot point between the first end  61  of the second piece  60  of the serpentine support  50  and the second end  57  of the first piece  55  of the serpentine support  50 . Point G represents the pivot point between the first end  56  of the first piece  55  of the serpentine support  50  at the connection to the frame  10 . 
   Line segments between points are rigid members, although not necessarily along central axis of the respective members. In this regard, line segment AB corresponds to the rigid support  25 , line segment AE corresponds to the caster support  70 , line segment DE corresponds to the third piece  65  of the serpentine support  50 , line segment DF corresponds to the second piece  60  of the serpentine support  50 , line segment FG corresponds to the first piece  55  of the serpentine support  50 , and line segment GB corresponds to the frame  10 . The split or double parallelogram structure allows the caster support  70 , and hence the casters  6 , to be in a selected orientation relative to the frame  10  no matter whether the frame  10  is in a high position, a low position, or at any position there between. A preferred orientation of the casters  6  is normal to the floor plane  2 . However, it will be understood that other orientations of the casters  6  may be used without departing from the broad aspects of the present invention. 
   A raised, or high, position of the frame  10  is shown in  FIGS. 3 and 4 , and is represented by line segments in  FIG. 10 . An intermediate position of the frame  10  is shown in  FIGS. 5 and 6 , and is represented by line segments in  FIG. 11 . A low position of the frame is shown in  FIGS. 7-9 , and is represented by line segments in  FIG. 12   
   A second articulating structure  120  is provided. The second articulating structure  120  is preferably comprised of a rigid support  125 , a serpentine support  150  and a caster support  170 . The components are generally and preferably shown to be hollow components having varying shapes and sizes. However, other structures, such as solid members could alternatively be used without departing from the broad aspects of the present invention. 
   The rigid support  125  of the second articulating structure  120  preferably comprises a tube  130 . The tube  130  has a longitudinal axis that preferably lies generally parallel to the top surface plane  12 . The tube  130  has a first end  131  and an opposed second end  132 . Four brackets  133 ,  134 ,  135  and  136 , respectively, are preferably welded or otherwise rigidly connected to the tube  130 . Bracket  133  is preferably pivotally connected to bracket  14  of the frame  10 . Bracket  136  is preferably pivotally connected to bracket  16  of the frame  10 . 
   A first arm  140  is provided and has a first end  141  and a second end  142 . The first end  141  is preferably rigidly connected to the first end  131  of tube  130 . A second arm  145  is also provided, and has a first end  146  and a second end  147 . The first arm  140  and second arm  145  are preferably connected to the tube  130  at a right angles, and as such, are parallel to each other. The tube  130 , first arm  145  and second arm  150  preferably form a generally U shaped structure. 
   It is understood that the second rigid support  125  has many ends, including the pivot points at the second ends  142  and  147  of respective arms  140  and  145 , as well as the pivot points at the ends of the brackets  133 ,  134 ,  135  and  135  rigidly connected to the tube  130 . 
   The second articulating structure  120  also preferably comprises a serpentine support  150 . In a preferred embodiment, the serpentine structure  150  comprises three members, or pieces. The first piece  155  has a first end  156  and a second end  157 . The second piece  160  has a first end  161  and a second end  162 . The third piece  165  has a first end  166  and a second end  167 . The first end  156  of the first piece  155  is preferably pivotally connected to the frame  10 . The second end  157  of the first piece  155  is preferably pivotally connected to the first end  161  of the second piece  160 . The second piece  160 , at a location intermediate the first end  161  and the second end  162 , is preferably pivotally connected to bracket  134  on the tube  130 . The second end  162  of the second piece  160  is preferably pivotally connected to the first end  166  of the third piece  165 . 
   Further, the second articulating structure  120  also preferably comprises a caster support  170 . The caster support  170  preferably comprises a base  171  having a front  172 , a rear  173 , a first end  174  and a second end  175 . The base  171  can be a bent base, such that it dips between the ends  174  and  175 , as shown in  FIGS. 1 and 2 . A first upright  176  is at the first end  174  of the base  171 . A second upright  177  is at the second end  175  of the base  171 . A third upright  178  can be connected to the base  171  intermediate the first and second ends  174  and  175 . The second end  142  of the first arm  140  is preferably pivotally connected to the first upright  176 . The second end  147  of the second arm  145  is preferably pivotally connected to the second upright  177 . The second end  167  of the third piece  165  of the serpentine support  150  is preferably pivotally connected to the third upright  178 . 
   Starting at a low position, the first articulating support  120  rises as the second end of the second rigid support  125 , or the second ends  142  and  147  of the arms  140  and  145 , respectively rotate away from the frame  10 . The pivot point for this rotation is at the pivoting connections between the brackets  14  and  16  of the frame  10  and  133  and  136  of the tube  130 , respectively. Rotation of the tube  130  caused by the pivoting of the second rigid support  125  causes the serpentine support  150  to straighten, and accordingly elongate. Elongation of the serpentine support  150  and rotation of the rigid support  125  cause the frame  10  to rise relative to the castor support  170 . 
   Looking now to  FIGS. 10-12 , it is shown that in profile, the first articulating structure  20  resembles a split parallelogram. The split parallelogram of the second articulating structure  120  is highly similar or identical to the geometry of the first articulating structure  20 , described above. Point A′ represents the pivot point between the second end  142  of the first arm  140  and the upright  176 . Point B′ represents the pivot point between the bracket  113  of the frame  10  and bracket  133  of the tube  130 . Point C′ represents the longitudinal axis of the tube  130 . Point D′ represents the pivot point between the first end  166  of the second piece  165  of the serpentine support  150  and the second end  157  of the second piece  155  of the serpentine support  150 . Point E′ represents the pivot point between the second end  167  of the third piece  165  of the serpentine support  150  and the third upright  178  of the base. Point F′ represents pivot point between the first end  161  of the second piece  160  of the serpentine support  150  and the second end  157  of the first piece  155  of the serpentine support  150 . Point G′ represents the pivot point between the first end  156  of the first piece  155  of the serpentine support  150  at the connection to the frame  10 . 
   Line segments between points are rigid members, although not necessarily along central axis of the respective members. In this regard, line segment A′B′ corresponds to the rigid support  125 , line segment A′E′ corresponds to the caster support  170 , line segment D′E′ corresponds to the third piece  165  of the serpentine support  150 , line segment D′F′ corresponds to the second piece  160  of the serpentine support  150 , line segment F′G′ corresponds to the first piece  155  of the serpentine support  150 , and line segment G′B′ corresponds to the frame  10 . 
   In this regard, the split or double parallelogram structure of the second articulating structure  120  allows the caster support  170 , and hence the casters  6 , to be in a selected orientation relative to the frame  10  no matter whether the frame  10  is in a high position, a low position, or at any position there between. A preferred orientation of the casters  6  is normal to the floor plane  2 . However, it will be understood that other orientations of the casters  6  may be used without departing from the broad aspects of the present invention. 
   A raised, or high, position of the frame  10  is shown in  FIGS. 3 and 4 , and is represented by line segments in  FIG. 10 . An intermediate position of the frame  10  is shown in  FIGS. 5 and 6 , and is represented by line segments in  FIG. 11 . A low position of the frame is shown in  FIGS. 7-9 , and is represented by line segments in  FIG. 12   
   Optionally, a rigid base structure (not shown) could be alternatively used instead of the serpentine structures to achieve the desired orientation of the caster supports  70  and  170 . 
   According to another preferred aspect of the present invention, a drag link  200  is provided. The drag link  200  has a first end  201  and a second end  202 . The drag link first end  201  is preferably pivotally connected to bracket  34  of the tube  30 . The drag link second end  202  is preferably pivotally connected to bracket  135  of tube  130 . The drag link  200  ensures that the first articulating structure  20  and the second articulating structure act cooperatively at the same rate to achieve the same amount of lift of the frame  10 . 
   According to yet another preferred aspect of the present invention, a linear drive assembly  210  is provided. The linear drive assembly  210  has a motor  211  and an actuator  212  that can selectably extend from the housing containing the motor  211 . The actuator has a distal end  213  and defines a longitudinal axis  214 . 
   According to a preferred embodiment, the housing can be rotatably connected to the rigid support  25  of the first articulating structure  20 . More particularly, the motor  212  and housing are preferably connected to the tube  30  of the first articulating structure  20 . The distal end  213  of the actuator  212  of the linear drive assembly  210  is preferably pivotally connected to the drag link  200  at a location intermediate the drag link first end  201  and the drag link second end  202 , as shown in  FIGS. 1 and 2 . As illustrated in  FIGS. 4 ,  6 , and  8 , the angle between the longitudinal axis  214  of the actuator  212  and the plane  12  of the frame never approaches zero no matter the position of the frame  10 . The minimum preferred angle of the longitudinal axis  214  is approximately between 10 and 20 degrees. In this regard, even at the low bed position, there is still a vertical lift resultant force component of the overall actuator force. 
   Returning attention to  FIGS. 10-12 , it is shown that the location of the motor  211  of the linear drive assembly  210  is at a point that is a fixed distance from points B and C. In this regard, it is understood that the linear drive assembly is rotatably connected to the rigid frame  25  of the first articulating structure  20 . 
   During operation of the linear drive assembly  210 , the linear drive assembly operates, or moves in two directions. In this regard, the distal end  213  of the actuator  212  operates against the drag link  200  to move the drag link towards the second articulating structure  120 . Simultaneously, the housing and motor  211  move to force the second end of the first rigid structure  25  to rotate away from the frame  10 . Rotation of the second end of the first rigid structure  25  away from the frame  10  causes the frame to lift relative to the caster support  70 . Also, rotation of the first rigid structure  25  includes rotation of the tube  30  and bracket  34 . Bracket  34 , being pivotally connect to the drag link first end  201 , redirects the rotational force within the first rigid member  25  to move the drag link  200  towards the second articulation structure  120 . 
   Moving the drag link towards the second articulating structure  120  causes the rigid support  125  of the second articulating structure  120  to pivot, such that the second end of the rigid support  125  of the second articulating structure  120  rotates away from the frame  10  at the same rate as the second end of the rigid support  25  of the first articulating structure  20 . 
   The geometry of the structure of the articulating structures  20  and  120  described above, and particularly the location of the pivots between the articulating structures  20  and  120 , and the frame  10 , respectively, results in minimal swing of the frame  10  as it is raised from the low position to the high position. From the low position, it is preferably that the frame  10  moves laterally approximately less than 5 inches relative to the casters  6 . 
   In the preferred embodiment, a total stroke length of approximately between 7 and 15 inches in the linear drive assembly  210  produces a lift in the frame  10  of at least 10 inches. At any given point along the stroke length of the actuator  212 , there is a preferred maximum ratio of stroke length to frame lift of 1:2. That is, for each 1 inch of stroke, the frame lifts a maximum of 2 inches. The minimum preferred angle of the longitudinal axis  214  of the actuator  212  relative to the frame plane  12  is approximately between 10 and 20 degrees. 
   Thus it is apparent that there has been provided, in accordance with the invention, a supported frame with articulating structures that fully satisfies the objects, aims and advantages as set forth above. While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims.