Abstract:
The present invention is directed to a roll-up partition comprising a rolling shutter, a shutter assembly, a flexible strap and a tensioner. The tensioner includes a locking mechanism that is configured to lock and unlock the flexible strap and a quick release mechanism configured to release the locking mechansim, thus allowing the rolling shutter to change positions. The invention also includes a strap recoiler with a locking mechanism and a quick release mechanism, wherein activation of the quick release mechanism causes the release of the locking mechanism, thus allowing the roll-up partition to change positions. The invention also includes a method of exiting an enclosed space partially bounded by a portal protected by a roller shutter. The method includes operating the quick release mechanism, waiting for the shutter to retract and exiting the space through the portal.

Description:
FIELD OF THE INVENTION 
   The present invention is directed to a roll-up partition system assembly having a protective partition for covering a window or door opening that may be rolled up into a housing when not in use. More particularly, the present invention is directed to an assembly implementing a strap box and having an emergency opening mechanism. 
   BACKGROUND OF THE INVENTION 
   Roll-up partition systems protect portals such as windows and doors from break-ins or from wind gusts and flying debris in heavy storms. One type of roll-up partition system is a rolling protective shutter. Rolling protective shutters are conventional and are used to provide protection against extreme weather conditions and to deter theft, for example. Rolling shutters illustratively comprise a plurality of elongate slats that are interconnected by a plurality of hinges. When not in use, the shutter may be retracted into a casing that is usually situated either above or beside the portal, illustratively a window or door. Retracting involves rolling up the shutter onto a roller tube. The shutter is composed of a number of elongated slats that are articulated along their long edges. Forming the shutter out of articulated slats enables the shutter to be retracted compactly yet be strong enough to deter burglary and provide protection against flying debris. 
   Roll-up partitions in general, and rolling protective shutters in particular, sometimes incorporate one or more torsion spring assemblies to assist in rolling and unrolling the shutters manually or by a powered opening device. In one illustrative arrangement, the assembly is a self-contained modular unit having a spring shaft surrounded by a coiled torsion spring. One end of the spring shaft includes a spring shaft support that is rotatable about the spring shaft, and a spring plate rigidly fixed to the spring shaft and to the proximate end of the torsion spring to prevent rotation of the end of the torsion spring relative to the spring shaft. The other end of the spring shaft includes a spring drive that is rotatable about the spring shaft and rigidly fixed to the other end of the torsion spring. The assembly is inserted into the shutter support member with one end of the spring shaft rigidly fixed to the shutter housing. The spring shaft support and spring drive engage the interior of and rotate with the shutter support member. When the shutter is unrolled, the torsion spring is wound tighter, thereby providing for controlled deployment and providing additional torque to assist in lifting and rolling the shutter onto the shutter support member. During normal operation of the rolling protective shutters, the torsion spring exerts a minimum torque when the shutter is in the rolled position and a maximum torque when the shutter is in the unrolled position. 
   Taking as an example a shutter for a window opening with a casing located above the window, as the shutter is unrolled the weight of the deployed portion of the shutter tends to cause unrolling to accelerate uncontrollably. To prevent such uncontrolled deployment, with the accompanying noise and potential for injury, the torsion spring biases the roller tube toward the fully retracted position. Rotation of the roller tube about the spring shaft in the direction for deployment tightens the torsion spring, which resists further motion in the direction of rotation, thereby at least partially compensating for the accelerating effect of the ever increasing weight of the unrolled portion of the shutter as it is being deployed. When the roller tube is rotated in the opposite direction to retract the shutter, the bias force of the torsion spring assists the motive force to lift the shutter, and the assistance diminishes as rolling of the shutter onto the roller tube progresses. The degree of bias is determined by the choice of spring and/or any pretensioning there may be when the shutter is fully retracted. The degree of bias, in turn, determines whether a shutter of a predetermined weight will remain deployed or will retract when there is no braking force on the roller tube to prevent rotation. For safety reasons, roller shutters may be equipped with a sufficiently strong torsion spring to fully retract the shutter when there is no braking force applied to the roller tube. 
   The motive force behind retraction and deployment of the shutter may be provided manually, e.g. by an operator pulling a strap, or electro-mechanically, e.g. by a motor. 
   Some building code regulations require that manual and electro-mechanical shutters be able to be opened very quickly in the case of an emergency, such as during a fire. A safety mechanism enabling quick release of a roller tube that is engaged to an electric motor is discussed in commonly-assigned U.S. Pat. Nos. 5,975,185 and 6,244,325, the teachings of which are herein incorporated by reference. 
   In manually operated shutters employing a strap, there is typically a pulley at one end of the roller tube. Illustratively, the pulley is attached to the shutter support member, and the strap is connected between the pulley and a strap recoiler (or “strap box” mounted to one of the shutter tracks or to the wall surrounding the opening. The strap recoiler includes a take-up roll upon which the excess strap is stored and a locking mechanism with a brake tab that locks the strap in place when the strap is pulled tight between the pulley and the strap recoiler. The locking mechanism of the strap recoiler is configured to facilitate retraction and deployment of the strap to roll and unroll the shutter. Illustratively, to roll the shutter to the retracted position, the strap is pulled outwardly away from the shutter track and opening and pulled downwardly toward the strap recoiler. As the strap is pulled outwardly, the locking mechanism releases the strap and allows the force of a torsion spring within the take-up roll to wind the excess strap onto the take-up roll. At the same time, the control strap is unrolled from the pulley, thereby rolling the shutter onto the shutter support member. When the strap is released, the weight of the shutter rotates the pulley and pulls the strap tight between the pulley and the strap recoiler, thereby locking the locking mechanism. To unroll the shutter to the deployed position, the strap is pulled outwardly away from the shutter track and opening and pulled upwardly toward the pulley and shutter housing. As the strap is pulled outwardly, the locking mechanism releases the strap and allows the strap to unwind from the take-up roll. At the same time, the control strap is rolled onto the pulley as the shutter support member rotates due to the weight of the shutter. When the strap is released, the weight of the shutter and the tension in the torsion spring pull the strap tight between the pulley and the strap recoiler, thereby locking the locking mechanism. 
   To improve the safety of manually operated roller shutters for doors and windows and to meet regulatory objectives, it would be highly desirable to have a quick release mechanism for a manually operated roller shutter employing a strap recoiler. 
   SUMMARY OF THE INVENTION 
   The present invention provides a roller shutter having a quick release feature that the roller shutter to move to a desired position. 
   One embodiment of the present invention is a roll-up partition comprising: 
   a) a shutter assembly comprising:
         i) a shutter assembly housing adapted to be mounted to a wall above or beside a portal,   ii) a roller tube rotatably mounted in the shutter assembly housing, and   iii) a rolling shutter connected to the roller tube and configured to move between a retracted position in which the rolling shutter is wrapped around the roller tube and an open position in which the rolling shutter is deployed within the portal,       

   b) a flexible strap having a proximal end and a distal end, the proximal end connected to the roller tube, 
   c) a tensioner external to the shutter assembly housing, the tensioner connected to the distal end of the flexible strap and comprising a locking mechanism configured to releasably lock the flexible strap in place and a quick release mechanism configured to release the locking mechanism upon activation of the quick release mechanism, to allow the rolling shutter to change positions. 
   Illustratively, the locking mechanism is a brake tab, and the quick release mechanism changes the angle between the strap and the brake tab or otherwise releases the brake tab from a bearing surface. In various embodiments, the quick release mechanism is a pin, the removal of which permits the tensioner to pivot toward the roller tube, thereby releasing the locking mechanism. In other embodiments, the quick release mechanism is a lever or knob operatively connected to the locking mechanism, the movement of which releases the locking mechanism. 
   In illustrative embodiments, the roll-up partition further comprises a torsion spring connected to the roller tube, the torsion spring biasing the roller tube to move the rolling shutter toward the retracted position, and wherein operation of the quick release mechanism results in the rolling shutter moving toward the retracted position. 
   Another aspect of the invention is directed to a strap recoiler for use with a roller shutter, the strap recoiler comprising a housing, a take-up roll mounted in the housing, the take-up roll configured for wrapping a strap there-around, a torsion spring biasing the take-up roll in a direction to wrap the strap around the take-up roll, a first mounting bracket connected to the housing configured for pivotally mounting the strap recoiler to a support, and a second mounting bracket connected to the housing configured for releasably mounting the strap recoiler to the support. 
   Yet another aspect of the invention comprises strap recoiler for use with a roller shutter comprising a housing, take-up roll mounted in the housing, the take-up roll configured for wrapping a strap there-around, a torsion spring biasing the take-up roll in a direction to wrap the strap around the take-up roll, a locking mechanism configured to lock the strap in place, and a quick release mechanism configured to release the locking mechanism upon activation of the quick release mechanism. Various quick release mechanisms are within the scope of this invention. 
   Additional features of the present invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a first embodiment of a rolling shutter assembly that can implement the present invention; 
       FIG. 2  is a fragmentary perspective view of a portion of the shutter of the shutter assembly of  FIG. 1 ; 
       FIG. 3  is a partial cross-sectional side view of the strap recoiler of  FIG. 1  in the locked position; 
       FIG. 4  is a partial cross-sectional side view of the strap recoiler of  FIG. 1  in the unlocked position; 
       FIG. 5  is a partial cross-sectional side view of the strap recoiler of  FIG. 1  in the with the quick release mechanism deployed; 
       FIG. 6  is an isometric view of a strap recoiler of  FIG. 1 ; 
       FIG. 7  is a cross-sectional view of the strap recoiler of  FIG. 6  along line  7 - 7 ; 
       FIG. 8  is an isometric view of a take-up roll for the strap recoiler of  FIGS. 3-6 ; 
       FIG. 9  is a partial cross-sectional side view of another strap recoiler in the locked position; 
       FIG. 10  is an isometric view of a strap recoiler of  FIG. 9 ; and 
       FIG. 11  is an isometric view of an alternative embodiment of a strap recoiler of  FIG. 9 . 
   

   DETAILED DESCRIPTION 
   Directional terms like “above” and “below” and “upper” and “lower” may be used in the description of the roller shutter and tensioner according to the invention. The spatial relationships of the elements are determined by the design and construction of the roller shutter and the portal it protects. Thus, these terms are not intended to limit the invention to a vertical arrangement of elements. 
   The embodiments disclosed herein illustrated the various aspects of the present invention applied to one particular type of roll-up partition system: rolling protective shutters formed from a plurality of interconnected slats. It will be apparent to those of ordinary skill in the art that the present invention has application in other systems wherein a partition member is coupled to and rolls up onto a support member within a housing, such as roll-up doors, roll-up grills, roll-up gates, fire doors and the like. The application of the present invention to the various types of roll-up partition systems is contemplated by the inventor. 
   One type of a rolling shutter assembly  10  that may implement the present invention is shown in  FIGS. 1-2 . Referring to  FIG. 1 , the shutter assembly  10  has a shutter housing  8  that includes a top wall  12 , a pair of side walls  14 , and a front wall  16 . A shutter support member  20  is mounted for rotation within the shutter housing. The support member  20  includes a generally cylindrical central roller tube  22  and a plurality of mounting members  24  fixed to the roller tube  22 . 
   The upper end of a rolling shutter  30  is coupled to the mounting members  24 . The shutter  30  is composed of a plurality of individual, elongate slats  32 . One example of a configuration of slats  32  is illustrated in  FIG. 2 . The slats  32 , each of which is substantially flat, having two substantially planar side portions, and may be composed of steel, are interconnected by a plurality of hinges  34 , each of which joins together a pair of adjacent slats  32 . Each of the slats  32  includes an upward projection  35  extending longitudinally along the upper edge of the slat  32  and having a rearwardly and downwardly extending hook  36  at the top. Each of the slats  32  further includes a downward facing U-shaped recess  37  extending longitudinally along the lower edge of the slat  32  and having a forward horizontal projection  38  formed on the rear edge of the recess  37 . The hook  36  of a lower slat  32  and the recess  37  and projection  38  of an upper slat  32  interlock to form each hinge  34 . Other configurations of slats  32  and interconnecting hinges  34  are well known in the art and are contemplated by the inventor as having use with the present invention. Several such examples of configurations of slats  32  are illustrated in co-pending U.S. patent application Ser. Nos. 10/802,385 and 10/802,257, the disclosures of which are herein incorporated by reference. 
   Referring back to  FIG. 1 , a torsion spring assembly  26  is provided to assist roll-up of the shutter. Further details on an exemplary torsion spring assembly are found in U.S. Pat. No. 5,975,185, already incorporated by reference. However, other torsion spring configurations, as are known in the art, are within the scope of this invention. Illustratively, torsion spring  26  is sufficiently strong to fully retract shutter  30  when no braking force is applied. Still referring to  FIG. 1 , the ends of the slats  32  are disposed within a pair of shutter tracks  40 . The shutter assembly  10  has a pulley housing  42  that interconnects the rotatable roller tube  22  to one end of a strap  44  via a conventional pulley (not shown). The other end of the strap  44  is attached to a strap recoiler  46 , which is mounted to track  40  via mounting bracket  76 . When mounted to protect a window or other opening, the shutter tracks  40  of the shutter assembly  10  are positioned on either side of the opening and the shutter housing is positioned over the top of the opening. Alternatively, in some applications, the side tracks  40  and shutter housing are positioned within the opening. 
   An illustrative strap recoiler  46  is shown in greater detail in  FIGS. 3-5 . Referring to  FIG. 3 , the strap  44  enters the housing  48  of the recoiler  46  through an opening  50  in the top  51 . The strap  44  is attached to a take-up roll  52  disposed within the housing  48 . The take-up roll  52  is rotatably coupled to the housing  48  by a central shaft (not shown) and includes a torsion spring  27  that applies torque that rotates the take-up roll  52  counter-clockwise as shown in  FIG. 3 , to wrap the strap  44  around the take-up roll  52 . 
   The strap recoiler  46  of  FIG. 3  includes a locking mechanism formed by a brake tab  56  and a bearing surface, illustratively bearing pin  58 . The brake tab  56  is pivotally mounted to the housing  48  by a pivot pin  60 . The brake tab  56  pivots about the pivot pin  60  between a locked position ( FIG. 3 ) wherein the brake tab  56  bears upon the bearing pin  58 , and an unlocked position ( FIG. 4 ) wherein the brake tab  56  does not bear upon the bearing pin  58 . When the shutter  30  is partially or fully unrolled, the torsion spring tends to rotate the shutter support member  20  in the direction that rolls the shutter  30 . This results in a force on the strap  44  in the direction of the shutter housing as indicated by the arrow F. The tension on the strap  44  exerts a force on a tip  62  of the brake tab  56  that rotates an engagement surface  63  at the opposite end of the brake tab  56  into engagement with the bearing pin  58 . In this position, the frictional force between the engagement surface  63 , the bearing pin  58  and the strap  44  is sufficient to retain the strap  44  and prevent the shutter  30  from rolling or unrolling, depending on the weight of the shutter and relative strengths of the torsion spring in torsion spring assembly  26  and the torsion spring provided in strap recoiler  46 . 
   During normal operation of the shutter assembly  10 , the locking mechanism automatically releases the strap  44  when the strap  44  is pulled out to raise or lower the shutter  30 , as illustrated in  FIG. 4 . In an embodiment employing a torsion spring sufficiently strong enough to retract the shutter fully, to unroll the shutter  30  to the deployed position, the strap  44  is pulled outwardly away from the shutter track  40  and the opening and downwardly toward the strap recoiler  46 , in the general direction of the arrow F′. As the strap  44  is pulled outwardly and downwardly, the upward force exerted on the tip  62  of the brake tab  56  decreases and the brake tab  56  pivots toward the unlocked position. The strap  44  is released and the force of the torsion spring within the take-up roll  52  winds the excess strap  44  onto the take-up roll  52 . At the same time, the strap  44  is unrolled from the roller tube  22 , thereby unrolling the shutter  30  from the shutter support member  20 . When the strap  44  is released, the tension of the torsion spring  27  rotates the roller tube  22  and pulls the strap  44  tight between the roller tube  22  and the strap recoiler  46 , thereby pivoting the brake tab  56  to the locked position of  FIG. 3  and securing the strap  44  to prevent the shutter  30  from rolling or unrolling. 
   To roll the shutter  30  onto the shutter support member  20 , the strap  44  is pulled outwardly away from the shutter track  40  and the opening and upwardly away from the strap recoiler  46 , in the general direction of the arrow F″. As the strap  44  is pulled outwardly and upwardly, the upward force exerted on the tip  62  of the brake tab  56  decreases and the brake tab  56  pivots toward the unlocked position shown in  FIG. 4 . The strap  44  is released and the tension of the torsion spring  27  rotates the shutter support member  20  and the excess strap  44  winds onto the roller tube  22 . At the same time, the strap  44  is unrolled from the take-up roll  52 . When the strap  44  is released, the tension in the torsion spring pulls the strap  44  tight between the roller tube  22  and the strap recoiler  46 , thereby pivoting the brake tab  56  to the locked position of  FIG. 3  and securing the strap  44  to prevent the shutter  30  from rolling or unrolling. It is understood that the direction the strap is moved to effect rolling and unrolling is opposite that of a configuration where the shutter is deployed due to gravity, and the torsion spring (if any) merely assists with retraction. 
   In certain circumstances, it would be desirable to have a quick release mechanism to release brake tab  56  from bearing pin  58  and permit torsion spring  27  to roll shutter  30 , without the need to pull the strap  44  outwardly during the entire rolling process. In various embodiments, the quick release mechanism alters the angle the brake tab  56  and the strap  44 , to release the strap  44 . In other embodiments, the quick release mechanism moves the brake tab  56  from contact with the bearing pin  58 , thereby releasing strap  44 . 
   One such embodiment is illustrated in  FIGS. 3-7 . As shown in  FIGS. 3-5 , the housing  48  is mounted to a top mounting bracket  54  and a bottom mounting bracket  55 . Optionally, the housing  48  is pivotally connected to brackets  54  and  55 , which permits the strap recoiler  46  to rotate from side-to-side if the strap  44  is pulled outwardly at an acute angle with respect to the opening and the wall. A mounting track  76  is also provided. The mounting track  76  may be mounted on shutter track  40 , as shown in  FIG. 1 , or may be mounted on a nearby portion of wall or any other nearby surface. Illustratively, top mounting bracket  54  is pivotally connected to mounting track  76  at pivot point  70 . As shown, a pin  73  extends through mounting track  76  at opening  71  and through top mounting bracket  54 . However, it is understood that other hinges and devices for pivotally connecting the housing  48  to the mounting track  76  are within the scope of this invention. 
   As illustrated in  FIGS. 3-5 , bottom mounting bracket  55  is removably attached to mounting track  76  by way of a removable pin  74  that extends through pin hole  72  in mounting track  76  and pin hole  72 A (as shown in  FIG. 5 ) in bottom of mounting bracket  55 . Removal of removable pin  74 , illustratively by pulling pull ring  78 , allows the housing  48  to rotate on pivot point  70  upward, as shown in  FIG. 5 . Once the housing  48  rotates upward, as shown in  FIG. 5 , the strap is released from the locked position, and the torsion spring assembly  26  attached to roller tube  22  and the torsion spring  27  in the housing  48  can then work together to roll the strap  44  into the housing  48  and roll the rolling shutter  30  into shutter housing  8 . Such a configuration provides for rapid retraction of the shutter with only the removal of a single pin. Conversely, in certain situations where it may be desirous to seal off a portion of the building, the rolling shutter assembly  10  may be provided with weaker torsion springs or without a torsion spring connected to roller tube  22 . In this alternative embodiment, removal of the pin  74  would allow rolling shutter  30  to open, thereby closing off the opening in which the rolling shutter  30  is mounted. 
   It is understood, however, that other means of releasably restraining bottom mounting bracket  55  to mounting track  76  are possible and are within the scope of this invention. Various clips, pins, and other quick release mechanisms may be employed, as are known in the art, such that the quick release mechanism may be easily activated illustratively by pulling a ring or ribbon, or by pressing a button or twisting a handle. It is further understood that while brackets  54  and  55  are shown as separate parts that are connected to housing  48 , brackets  54  and  55  may be formed integrally with housing  48 . Alternatively, an opening  71 A for pivot point  70  may be provided through an upper section of housing  48  and pin hole  72 A may be provided in a lower section of housing  48 . 
     FIGS. 6 and 7  illustrate more detail of the mounting track  76  and the connection between the mounting track  76  and the strap recoiler  48 . As best seen in  FIG. 7 , mounting track  76  is U-shaped, with a first side  80 , a second side  81 , and a bottom  82 . Top mounting bracket  54  sits within the U-shaped mounting track  76 , and is retained by pin  73 . Pin  73  extends through hole  72  in the first side  80  of mounting track  76 , through hole  72 A in top mounting bracket  54 , and through hole  72 ′ in the second side  81  of mounting track  76 . It is understood that bottom mounting bracket  55  is similarly retained in mounting track  76 , except that pull ring  78  allows easy removal of removable pin  74 . 
   As previously discussed, the take-up roll  52  in the strap recoiler  46  includes a torsion spring  27  that provides torque to roll up the excess strap  44  when the shutter  30  is opened.  FIG. 8  illustrates the take-up roll  52 , removed from housing  48 . The strap  44  is omitted from the figure for the sake of clarity, but it is understood that the strap is wound around take-up roll  52 , and the take-up roll  52  is shown with a portion of the wall removed to expose a torsion spring  90 . The take-up roll  52  includes a central shaft  92  that is rotatable with respect to the take-up roll  52 . One end of the torsion spring  90  is connected to the take-up roll  52  and the other end is connected to the shaft  92  such that the tension in the torsion spring  90  increases as the strap  44  is unrolled (clockwise rotation of the roll  52 ) and decreases as the strap  44  is rolled up (counter-clockwise rotation of the roll  52 ). When the take-up roll  52  is disposed within the housing  48 , the shaft  92  is held in a fixed position within the housing  48  and is not permitted to rotate within housing  48 . The tension in the torsion spring  90  may be adjusted either by rotating the take-up roll  52  or by varying the amount of the strap  44  that is unrolled from the roll  52 . 
   The quick release mechanism of  FIGS. 3-7  includes a pivoting connection between mounting track  76  and strap recoiler  48 , wherein the strap recoiler housing pivots to release the locking mechanism. However, other configurations that release the locking mechanism to provide a quick release mechanism are within the scope of the present invention. Illustratively, any mechanism that changes the angle between the brake tab  56  and the strap  44  or otherwise disengages brake tab  56  from bearing pin  58 , to release the strap  44 , is within the scope of this invention. 
   Illustrative embodiments of alternative configurations for a quick release mechanism are shown in  FIGS. 9-11 . In these embodiments, rather than moving the strap recoiler  46  to change the angle between the brake tab  56  and strap  44 , these embodiments change the angle by moving the brake tab  56 . In  FIG. 9  a lever  96  is provided and is connected to brake tab  56 . Lever  96  and brake tab  56  may be formed integrally, or lever  96  may be connected to brake tab  56 . Movement of lever  96  in the direction shown by arrow G moves brake tab  56  away from bearing pin  58  and into the unlocked position. As shown in  FIG. 10 , lever  96  may extend through a slot  97  or other opening in housing  48 , to provide a user with easy access to lever  96  to move lever  96  in the direction shown by arrow G. A notch  98 , provided in slot  97  allows the user to secure lever  96  in position, thereby securing brake tab  56  in the unlocked position. Other mechanisms for retaining lever  96  in the locked or unlocked position are possible. 
   In  FIG. 10 , lever  96  extends through curved slot  97   a  and is attached to a knob  99 . Rotation of knob  99  in the direction shown by arrow H moves lever  96  in curved slot  97   a  and moves brake tab  56  to the unlocked position. A notch  98   a  may be provided to secure lever  96  in position, thereby securing brake tab  56  in the unlocked position. Another notch  98   b  at the opposite end of slot  97   a  may be provided to secure lever  96  in position such that brake tab  56  is secured in the locked position. Other configurations for securing knob  99  or lever  96  are within the scope of this invention. 
   Additionally, it is understood that lever  96  could be placed near tip  62  of brake tab  56 , with movement of lever  96  in a direction opposite to that shown by G in  FIG. 9 , to move brake tab  56  to the unlocked position. Alternatively, a magnet may be placed on the outside of housing  48  to move brake tab  56 . In yet another alternative embodiment, engagement surface  63  may be moved to change the angle between brake tab  56  and strap  44 . In yet another embodiment, the quick release mechanism is a lever, magnet, or other device that moves bearing pin  58  away from brake tab  56  to release strap  44 . Other configurations are possible that move the brake tab  56  to an unlocked position to provide a quick release mechanism. 
   Other modifications and alternative embodiments of the invention will be apparent to those skilled in the art in view of the foregoing description. This description is to be construed as illustrative only, and is for the purpose of teaching those skilled in the art the best mode of carrying out the invention. The details of the structure and method may be varied substantially without departing from the spirit of the invention, and the exclusive use of all modifications which come within the scope of the appended claims is reserved.