A pull bar screen apparatus and system in which screen is mechanically attached directly to a pull bar. Weld-less friction-lock cold-joining of screen and pull bar provides an improved pull-bar screen apparatus used in retractable pull screens. The pull bar screen apparatus and system remove the need for attaching a vinyl strip to the screen. Instead, the screen is flattened to retain its form and structural integrity. On one elongated end of the screen, an upper and lower lock bar are placed on either side of the screen. Corrugated ridges in the lock bars pinch the screen and hold it in place. A lock bar casing is placed under pressure around the upper and lower lock bars which hold the lock bars in position and thereby retain the screen.

BACKGROUND 
     I. Field of the Invention 
     The present invention relates generally to the field pull bar screens and more particularly to a pull bar screen apparatus and system. 
     II. Description of the Related Art 
     Fixed frame screens have been used for seasonal placement typically to prevent insects from entering into houses while having windows open. Fixed frame screens are either left in place permanently or are taken out in the off-season for storage in attics, basements and the like. The fixed frame screens typically represent perpetual maintenance problems because they are frail. In contrast, retractable screen systems are housed in a cassette that is permanently mounted to a portion of either a door or window frame and never need to be removed for storage. When not in use, they simply retract into the permanently mounted cassette. Retractable screens have also increased in popularity for use as sun screens. 
     In manufacturing retractable screens, there are several flaws that reduce the overall quality and structural integrity of the retractable screen product. Typically, high frequency welding is used to connect a screen sheet between two flaps of a vinyl strip, which is pre-positioned within a channel of an extruded pull-bar. The high frequency welding applies electronically controlled quantities of heat and pressure to weld one side of the screen to the vinyl strip. The sheet of screen is welded after the positioning of the vinyl strip.  FIG. 1  illustrates a top exploded view the constituent components of a prior art pull bar apparatus  50 . As described above, the apparatus  50  generally includes a cassette holder  55  in which the retractable screen material  60  is held. A vinyl strip  70  is welded to a lower end of the screen  60 . A high frequency weld  65  is used to connect the screen  65  and the vinyl strip. In general, a pull bar  75  is then connected to the vinyl strip and a portion of the screen  60  to cover the weld  65 . 
     In general, it is appreciated that imperfect positioning of the unsupported sheet of screen often occurs. In addition, there are uneven expansion factors between the screen and the strip thereby causing unsightly wave patterns in the screen. Therefore, the vinyl strip is typically the flaw of present retractable pull screens. However, in order to retain aesthetic appearance, this process continues to be used. 
     SUMMARY 
     In general, the invention features a pull bar screen apparatus and system in which screen is mechanically attached directly to a pull bar. The invention features weld-less friction-lock cold-joining of screen and pull bar that provides an improved pull-bar screen apparatus used in retractable pull screens. The present invention removes the need for attaching a vinyl strip to the screen. Instead, the screen is flattened to retain its form and strength. On one elongated end of the screen, an upper and lower lock bar are placed on either side of the screen. Corrugated ridges in the lock bars pinch the screen and hold it in place. A lock bar casing is placed under pressure around the upper and lower lock bars which hold the lock bars in position and thereby retain the screen. 
     In general, the invention features a pull-screen apparatus, including a sheet of screen, a first lock bar, a second lock bar placed in opposition to the first lock bar, wherein an end of the sheet of screen is interposed between the first and second lock bars and a lock bar casing surrounding the first and second lock bars. 
     In one implementation, the apparatus further includes a cassette housing into which the screen is retractable. 
     In another implementation, the lock bar casing has a generally U-shape profile, having a first end and a second end. 
     In another implementation, the apparatus further includes an end cap affixed to each of the first and second ends. 
     In another implementation, the end caps each include a cap head and a blade extension connected to a lower surface of the cap head. 
     In another implementation, the blade extension mates with a cavity formed between an inner wall of the lock-bar casing and an outer surface of one of the first and second lock bars. 
     In still another implementation, the lock bars each comprise an inner an outer surface, the inner and outer surfaces being inverted mirror images of each other. 
     In yet another implementation, the inner surfaces each comprise a series of elongated rods forming a corrugated surface for mating with a respective corrugated surface. 
     In another implementation, the outer surfaces each comprise an elongate channel offset and parallel to a respective elongate channel on a respective outer surface. 
     In another implementation, the interposition of the screen between the first and second lock bars create a friction lock. 
     In another aspect, the invention features a pull-bar screen system, including a screen for retraction into and extension from a cassette housing, a lock-bar casing connected to a lower end of the screen, the pull-bar providing a means for retracting and extending the screen into and out of the cassette housing, lock bars positioned on either side of the lower end of the screen and within the lock bar casing, wherein the lock-bar casing and the lock bars form a pull-bar and end caps connected to either end of the lock bar casing. 
     In one implementation, the system further includes a bottom rail for interconnection with the pull-bar when the pull-bar is pulled into a retracted position, thereby holding the retracted screen in an open position. 
     In another implementation, the system further includes a female indentation located on an outer end of the pull bar for mating with a male protrusion on the bottom rail. 
     In another implementation, the system further includes means for receiving the pull-bar into the bottom rail. 
     In another implementation, the system further includes a frame having an upper end and a lower end, the cassette housing being connected adjacent the upper and the bottom rail being connected adjacent the lower end. 
     In another aspect, the invention features a pull-bar screen system, including a sheet of screen material, a pull bar located on one end of the screen material, the pull-bar having a first end and a second end, means for creating a mechanical friction lock on an end of the screen material and located within the pull-bar and an end cap positioned on both ends of the pull bar. 
     In one implementation, the end caps include blade extensions for interconnection with the means for creating a friction lock. 
     In another implementation, the system further includes a lock bar casing surrounding the means for creating a friction lock. 
     In another implementation, the lock bar casing includes an opening through which the sheet of screen material protrudes and is pinched by the means for creating a friction lock, the pinching occurring adjacent the opening. 
     In another implementation, the means for creating a friction lock is a mated set of corrugated surfaces placed in opposition to one another and holding the screen therein. 
     One advantage of the invention is that screen material is connected directly to a pull bar. 
     Another advantage of the invention is that the pull bar of the pull bar screen is connected directly to the screen through frictional lock bars. 
     Another advantage of the invention is that the need for high frequency welding is eliminated. 
     Another advantage of the invention is that it eliminates the need for vinyl strip extrusion. 
     Another advantage of the invention is that the pultruded pull-bar can take place of presently available pull-bars without necessitating modification of the existing pull-bar system, thereby allowing retrofitting of existing systems. 
     Another advantage of the invention is that it can be implemented as a new system. 
     Another advantage of the invention is that the screen material is not deformed when it is connected to the pull bar, thereby being held in place by frictional contact. 
     Another advantage of the invention is that the structural integrity of the screen is increased. 
     Other objects, advantages and capabilities of the invention are apparent from the following description taken in conjunction with the accompanying drawings showing the preferred embodiment of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a top exploded view the constituent components of a prior art pull bar apparatus; 
         FIG. 2  illustrates a perspective exploded view of the constituent components of an embodiment of a pull bar screen apparatus; 
         FIG. 3  illustrates an end view of an embodiment of an assembled pull bar; 
         FIG. 4  illustrates an end view of an embodiment of a friction lock bar; 
         FIG. 5  illustrates a side view of an embodiment of a lock bar casing; 
         FIG. 6  illustrates a side view of an embodiment of a pull bar end cap; 
         FIG. 7  illustrates a bottom view of an embodiment of a pull bar end cap; 
         FIG. 8  illustrates an end view of an embodiment of a pull bar end cap; 
         FIG. 9  illustrates an embodiment of a bottom rail for a pull bar apparatus; and 
         FIG. 10  illustrates an alternate embodiment of a bottom rail for a pull bar apparatus. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the drawings wherein like reference numerals designate corresponding parts throughout the several figures, reference is made first to  FIG. 2  that illustrates a perspective exploded view of the constituent components of an embodiment of a pull bar screen apparatus  100 . In general, the apparatus  100  includes a sheet of screen  105  material that can be formed from a variety of materials, but typically is formed of a suitable mesh material such as vinyl. The apparatus  100  further includes two opposing lock bars  120  that are typically inverted mirror images of one another. The lock bars  120  typically include an inner corrugated surface  125 , the corrugated inner surface being generally formed from elongated parallel ridges  130 . The corresponding elongated ridges  130  of the inverted mirror image lock bar  120  are placed together in mated engagement when the opposing lock bars  120  are placed together with the inner corrugated surfaces  125  in mechanical contact. A lower edge  106  of the screen  105  is placed in between the inner corrugated surfaces  125  such that the lower edge  106  is held between the ridges  130  of the inner corrugated surfaces  125  and retained by frictional contact. The lock bars  120  further include an outer surface  140  that each include an elongated channel  145 . 
     The apparatus  100  further includes an outer lock bar casing  150  that is placed around the lock bars  120  after placement of the lower edge  106  of the screen  105  between the lock bars  120 . As discussed further in the description below, the lock bar casing  150  has a generally U-shape profile that is biased toward a closed position such that a force must be asserted against the bias in order to place the engaged lock bars  120  within the lock bar casing  150 . 
     The apparatus  100  further includes end caps  180  that are placed on the open ends of the lock bar casing  150  after placement of the lock bars  120  and the screen  105  is achieved as immediately described above. In general, the end caps  180  each include blade extensions  185  that are discussed further in the description below. 
     In general, it is appreciated that the apparatus  100  described above can advantageously include a cassette housing  200  into which the screen  105  can retract. Those skilled in the art appreciate that the cassette housing can include a spring loaded roll bar  205  onto which the screen  105  can retract as needed. It is understood that there are a variety of additional devices that can retract the screen into cassette housing  200 . 
       FIG. 3  illustrates an end view of an embodiment of an assembled pull bar formed by the lock bars  120  and the lock bar casing  150 . As described above, the apparatus  100  includes a sheet of screen  105  material having a lower edge  106  that is interposed and held in frictional contact between and with the two opposing lock bars  120 . The inner corrugated surfaces  125 , being generally formed from elongated parallel ridges  130 , are in mated engagement with one another. The lock bars  120  further include an outer surface  140  that each include an elongated channel  145 . The apparatus  100  further includes an outer lock bar casing  150  that is placed around the lock bars  120  after placement of the lower edge  106  of the screen  105  between the lock bars  120 . As mentioned above, the lock bar casing  150  has a generally U-shape profile that is biased toward a closed position. The open end of the U-shape includes lips  151  that are positioned in opposition to one another thereby forming an opening  152  through which the screen  105  protrudes from the lock bar casing  150 . The lock bars  120  further include rounded ends  141  that when brought together with corresponding rounded ends  141 , a set of lips is formed adjacent and pinched within the opening  152  thereby providing an additional pinching and thus increased frictional contact of the lower edge  106  of the screen  105  between the lock bars  120 . The lock bar casing  150  generally further includes a closed end  154 . 
     The lock bar casing  150  further generally includes an inner surface  153  that is in mechanical contact with the outer surface  140  of the lock bars  120 . However, a cavity  160  is formed in the assembled state due to the presence of the channel  145  on the outer surface  140  of the lock bars  120 . 
       FIG. 4  illustrates a end view of an embodiment of a friction lock bar  120 . AS described above, the lock bars  120  are typically inverted mirror images of one another. The lock bars  120  typically include an inner corrugated surface  125 , the corrugated inner surface being generally formed from elongated parallel ridges  130 , which include corresponding troughs  131  thereby creating the corrugated surface  125 . The corresponding elongated ridges  130  of the inverted mirror image lock bar  120  are placed together in mated engagement when the opposing lock bars  120  are placed together with the inner corrugated surfaces  125  in mechanical contact. The lock bars  120  further include an outer surface  140  that each include an elongated channel  145 . The lock bars  120  further include rounded ends  141 . 
       FIG. 5  illustrates a side view of an embodiment of a lock bar casing  150 . As described above, the outer lock bar casing  150  is placed around the lock bars  120  after placement of the lower edge  106  of the screen  105  between the lock bars  120 . The lock bar casing  150  has a generally U-shape profile that is biased toward a closed position such that a force must be asserted against the bias in order to place the engaged lock bars  120  within the lock bar casing  150 . The lock bar casing  150  further generally includes an inner surface  153 . 
     The open end of the U-shape includes lips  151  that are positioned in opposition to one another thereby forming an opening  152  through which the screen  105  protrudes from the lock bar casing  150 . The lock bar casing  150  generally further includes a closed end  154 . The closed end  154  can further include claws  156  that are described further below. 
       FIG. 6  illustrates a side view of an embodiment of a pull bar end cap  180 .  FIG. 7  illustrates a bottom view of an embodiment of a pull bar end cap  180 .  FIG. 8  illustrates an end view of an embodiment of a pull bar end cap  180 . In general, the end cap  180  includes blade extension  185  that are connected to a lower surface  191  of a cap head  190 . In general, the lower surface  191  comes into contact with the ends of the pull bar that includes the lock bar casing  150  and lock bars  120  in between. The outer surface  192  can be rounded for an aesthetic appearance. Referring again to  FIG. 3 , it is appreciated that blade extensions advantageously fit into the cavities  160  created from bringing the channels  145  into proximity to the inner surface  153  of the lock bar casing  150 . It is further appreciated that since the lock bars  120  are inverted mirror images of each other, the corresponding channels are positioned parallel but offset from one another. Therefore, the blade extensions  185  are correspondingly positioned on the cap head  190  in a parallel but offset orientation. With the cavities  160  and blade extensions  185  being in corresponding positions, the blade extensions  185  can easily mate with the cavities  160  to create a snug fit of the end caps  180  on the ends of the lock bar casing  150 . 
     In general, the apparatus  100  in conjunction with the cassette housing  200  as well as additional devices can form a pull bar screen system and kit, which can be used as a new installation into existing door and window frames or as a retrofit to existing pull bar screen systems. 
       FIG. 9  illustrates an embodiment of a bottom rail  300  for a pull bar apparatus  100 , thereby forming a pull bar screen system  400 . In general, the bottom rail can include a U-shape channel or bottom guide pultrusion  305  into which the pull bar (formed by lock bars  120 , lock bar casing  150  and end caps  180 ) can be fitted and retained. The lock bar casing  150  can be fitted to a corresponding protrusions  310  located within the channel  305  that aids in closing any gaps created by the lack screen on the pull bar. Alternatively, the channel  305  can include side claws  315  that can create a frictional connection with the sides of the lock bar casing as shown in  FIG. 10  that illustrates an alternate embodiment of a bottom rail for a pull bar apparatus  100 . The bottom rail  300  can further include an outer ramp  320 . 
     The foregoing is considered as illustrative only of the principles of the invention. Further, various modifications may be made of the invention without departing from the scope thereof and it is desired, therefore, that only such limitations shall be placed thereon as are imposed by the prior art and which are set forth in the appended claims.