You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No.: 60/142,441, filed Jul. 6, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a roll-up or curtain type modular security door system and, more particularly, to an improved adjustable tensioning arrangement for torsion springs utilized with modular, roll-up or curtain type security door systems. 
     This application relates to an improvement of U.S. Pat. No. 4,930,563, issued to Finch, et al., the disclosure of which is incorporated herein by reference as though set forth herein in haec verba. 
     2. Description of the Related Art 
     With ever-increasing urban crowding, the demand for storage space for infrequently used personal property has grown sharply. Such storage space, which used to be in a garage or basement, is not available in most apartments and condominiums, resulting in the development of the mini-warehouse or mini-storage facility. This type of facility features a secure, lockable storage space which is rented mainly to individuals. Since a wide variety of property may be stored in such facilities, including furniture and other large items, it is desirable to provide a large sealable door to provide access to individual storage areas. This eliminates conventional doors for the most part, since they are either too small or too unwieldy to be acceptable to the public. 
     Roll-up or curtain doors represent a convenient way to provide an easily operable closure, and they do so in a fairly limited space. Roll-up doors are typically constructed using a sheet of relatively thin metal which is formed by stamping or rolling to provide a plurality of horizontal corrugations extending the entire width of the door. This construction allows the door to be rolled up as it is raised for opening, thereby allowing the door to be stored in a cylindrical configuration at the top of the door opening., Vertical guide tracks, which may be made of extruded aluminum or formed galvanized steel, are typically mounted at opposite sides of the door opening and serve to guide the door as it moves up and down. 
     The top of the formed metal sheet is fastened to a barrel assembly which is constructed with a heavy wall, steel tube axle which supports thereon two or more galvanized steel drums or wheels. The barrel assembly is rotatably mounted between two brackets located slightly above the upper corners of the door opening. The barrel assembly is biased by one or two tempered steel torsion springs to balance the weight of the roll-up door, thereby allowing the door to be easily raised or lowered in a simple one-hand operation. Adhesively affixed tapes extend along the inner face of the door where contact is made with the galvanized steel drums or wheels to protect the door against wear by the galvanized steel drums or wheels, and to avoid rubbing of the successive layers of the roll-up door against each other. 
     The door also has a locking mechanism mounted thereon, which may be a simple sliding bolt type lock. With this mechanism, when the door is closed the bolt slides into a locking engagement with the guide track or with other metal means which prevents the door from being opened unless the bolt is opened. A simple padlock owned by the storage user may then be used to lock the bolt assembly. 
     This type of roll-up door is easy to operate, and will provide years of dependable service with virtually no maintenance. Such doors are relatively inexpensive, particularly when compared to similar roll-up doors which are made of a plurality of interlocking slats or panels. 
     Roll-up or curtain type doors represent a convenient way to provide an easily operable and secure closure. Spring arrangements, often involving torsion springs, are frequently used to ease the task of raising or lowering such doors. 
     In order to provide the desired reduction in force required to raise or lower a door, a spring arrangement must be properly tensioned. Frequently, this tensioning is performed during the construction or installation of the security door assembly. Because of this fact, the tensioning arrangement is fixed, and not easily adjustable to suit the particular needs of individual users. The degree of tensioning preferred by individual users varies over a wide range, and spring tensions set by a manufacturer during construction or unit assembly cannot accommodate this variability. 
     From the preceding description, it will be appreciated that such doors are relatively easy to manufacture, and the business of manufacturing them is quite competitive. Accordingly it is desirable to minimize the cost of manufacturing the doors as much as possible while still retaining a high degree of quality and reliability. The minimization of the number of different parts required is an objective which reduces the cost of manufacturing, and also reduces the number of different parts which must be stocked. 
     Minimizing the quantity of hardware components such as nuts and bolts is also desirable, from two standpoints. First, the cost factor mandates using the smallest number of hardware items necessary. Secondly, and even more importantly, since such doors are sold in complete kits, it is desirable to minimize the number of parts and by so doing the amount of assembly required. Owners of storage facilities must either install the doors themselves, or pay to have the doors installed. It is apparent that a door which is simple, easy, and quick to install will have a significant competitive advantage over doors that are not. 
     It will be appreciated that providing an easily adjustable tensioning arrangement for modular security door systems is desirable. Given that the business of manufacturing modular security door systems is quite competitive, it is also desirable to minimize the cost of manufacturing such an adjustable tensioning arrangement while still retaining a high degree of product quality and reliability. The minimization of the number of different parts required to be designed and fabricated serves to reduce the costs of manufacturing. 
     Accordingly, it is an objective of the present invention to develop a design minimizing the number of parts needed in fabricating a curtain type door, thereby reducing the cost and the amount of work necessary to install the door. To the greatest degree possible, the door should be of a modular design which further facilitates both kitting and installation. The door must be installable using only simple hand tools, and it must be simple to install. The tensioning arrangement must be capable of accommodating the tensions desired by individual users. Finally, the door must accomplish all of the aforesaid advantages while maintaining the highest degree of quality, durability, and dependability, and presenting no relative disadvantage. 
     SUMMARY OF THE INVENTION 
     The advantages discussed above are realized by the present invention. With this invention, the number of parts necessary for assembly of the door is reduced in two ways. First, and most significantly, the main components of the door are modular in design, and may be used on either side of the door. In other words, there are no longer right side and left side components; rather, the various parts are usable on either side of the door. This presents several advantages. The number of different parts which must be fabricated and stocked by the manufacturer is reduced significantly, since previously a number of the major components of the door were required to be manufactured in right side and left side versions, which were not interchangeable. In addition, the installer of the door need not worry about which side a particular part is designed to fit; instead, the part will fit either side interchangeably. 
     The second reduction in the number of parts required is obtained by minimizing the number of hardware items required. Insofar as possible, the assembly of the door is accomplished without hardware items such as bolts, nuts, and screws. This reduces the cost of the door, and also makes the assembly much easier and quicker. For example, the brackets used to secure the door guide tracks to the sides of the door opening slideably engage with the guide tracks instead of requiring bolts, nuts, and washers to secure them. The brackets used to carry the barrel assembly are similarly engaged onto the guide tracks, and require only a single bolt to retain them in place. 
     The reduction in parts is obtained at no cost in quality, durability, or long term dependability whatsoever. The roll-up doors of the present invention may be manufactured at lower cost and sold at reduced prices, giving them a tremendous competitive advantage over prior art roll-up doors. The installation of the doors is quicker and easier, and the door is just as secure. It will therefore be appreciated that the roll-up door of the present invention offers significant advantages over the art while incurring no relative disadvantage whatsoever. 
     With this invention, an easily adjustable tensioning arrangement for modular security door systems is provided. The adjustable tensioning arrangement may be produced with a minimal number of required parts, and at very low cost. 
     The use of readily fabricated steel or other metal components for construction of the present invention serves to reduce the cost of manufacture. Alternately, the present invention may incorporate components made from injection molded or other plastic type materials. Furthermore, the incorporation by the present invention of unitary construction methods aids in reducing both the number of required parts and costs of manufacturing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other advantages of the present invention are best understood with reference to the drawings, in which: 
     FIG. 1 is a side view of the interchangeable guide track used to support a roll-up door of the type described on the left or right side thereof, illustrating the notches formed on the side thereof; 
     FIG. 2 is a back view of the interchangeable guide track shown in FIG. 1; 
     FIG. 3 is an end view of the interchangeable guide track shown in FIGS. 1 and 2, illustrating the bends therein; 
     FIG. 4 is a perspective view of the brackets used to support the guide track shown in FIG. 1-3; 
     FIG. 5 is a side view of one of the barrel assembly U-shaped support brackets; 
     FIG. 6 is a top view of the U-shaped support bracket shown in FIG. 5; 
     FIG. 7 is an exploded perspective view of the interchangeable guide track of FIGS. 1-3, the U-shaped support bracket of FIGS. 5 and 6, the main barrel assembly support plate, and the plate support bracket; 
     FIG. 8 is a perspective view of the main barrel assembly support plate being installed onto the plate support bracket; 
     FIG. 9 is a perspective view of the assembled main barrel assembly support plate and plate support bracket being installed at the top of the guide track; 
     FIG. 10 is a perspective view of the assembled main barrel assembly support plate and plate support bracket fully installed at the top of the guide track; 
     FIG. 11 is an exploded perspective view of the entire roll-up door of the present invention illustrating the construction thereof; 
     FIG. 12 is a side view of the bottom edge of the door, which bottom edge is made of a formed metal sheet and fastened to the lower edge of the door in a double re-entrant joint; 
     FIG. 13 is a side view of an alternate bottom edge of the door, which alternate bottom edge is made of extruded aluminum; 
     FIG. 14 is a perspective view of a security storage shelf unit using the roll-up door of the present invention; 
     FIG. 15 is an exploded perspective view of the improvement combination of the present invention, showing the torsion spring assembly, the adjustable tensioning arrangement, the axle, and the support plate illustrating the construction thereof; 
     FIG. 16 is a perspective view of an alternate adjustable tensioning arrangement, which alternate tensioning arrangement is fabricated of steel or other suitable material; 
     FIG. 17 is an exploded perspective View of a second embodiment of the present invention, showing the torsion spring assembly, the adjustable tensioning arrangement, the axle, and the support plate illustrating the construction thereof; 
     FIG. 18 is an exploded perspective view of the positioning pin and the support plate illustrating the detail thereof; 
     FIG. 19 is a perspective view of another embodiment of the positioning pin of FIG. 18; and 
     FIG. 20 is a perspective view of still another embodiment of the positioning pin of FIG.  18 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The guide tracks used in previously known roll-up doors are typically made for either the right side or the left side of the door, and are not generally interchangeable. FIGS. 1 to  3  illustrate a guide track  20  which is used in the present invention interchangeably for either the right or left track. The guide track  20  of the preferred embodiment is formed of galvanized steel sheet stock bent as best shown in FIG.  3 . 
     The guide track  20  has a plurality of pairs of retaining slots  22  formed therein to receive tabs, which will be described below in conjunction with FIG.  4 . The retaining slots  22  are stamped into the guide track  20  at the time it is manufactured. One pair of the retaining slots  22  is located at each end of the guide track  20 . The spacing between the retaining slots  22  is identical at each end of the guide track  20 . Additional pairs of the retaining slots  22  may be located between the pairs of retaining slots  22  at either end of the guide track  20 , depending on the length of the guide track  20 . The guide track  20  shown in the FIGS. have one such additional pair of retaining slots  22 . 
     Referring next to FIG. 4, a mounting bracket  24  which may be used to mount the guide track  20  in position on the side of the opening into which the door is to be installed is illustrated. The mounting bracket  24 , which is preferably made of stamped steel stock, has a tab  26  designed to precisely engage one of the retaining slots  22 . When the mounting bracket  24  is installed into one of the retaining slots  22 , it may be slid into the retaining slot  22  from the left of the guide track  20  as shown in FIG.  2 . When the tab  26  is fully inserted into the retaining slot  22 , a portion  28  of the mounting bracket  24  bent 90 degrees from the portion of the mounting bracket  24  containing the tab  26  will be flat against back side of the guide track  20  shown in FIG.  1 . 
     A mounting portion  30  of the mounting bracket  24  is also bent 90 degrees from the portion of the mounting bracket  24  containing the tab  26 . The mounting portion  30  is maintained in its 90 degree relationship by two stiffener protrusions  32  which are stamped into the mounting bracket  24 . A first slot  34  and a second slot  36  are located on the mounting bracket  24 . The first and second slots  34 ,  36  are of different sizes to allow different size mounting hardware to be used to attach the mounting brackets to the side of the opening into which the door is to be installed. Only one of the two slots  34 ,  36  will generally be used in the installation of the door; having two different sizes of slots allows different sizes of hardware to be used as available or at the option of the installer. 
     It should also be noted that only one mounting bracket  24  will generally be used in each pair of retaining slots  22 . The installer will have the option of deciding which of the pair of retaining slots  22  the mounting bracket  24  is installed into. The purpose of having the retaining slots  22  in pairs will become evident later, in conjunction with the discussion of FIGS. 9 and 10. It will be appreciated that in accordance with the principles of the present invention, the mounting bracket  24  is installed into the retaining slot  22  without needing additional hardware, thereby saving both the cost of such hardware and the time needed to install such hardware. 
     Referring now to FIGS. 5-7, and also to FIG. 10, for example, a U-shaped support bracket  40  is illustrated, which U-shaped support bracket  40  will be used to support the barrel assembly, to be discussed later in conjunction with FIG.  11 . The U-shaped support bracket  40  has a notch  42  therein, the notch  42  extending throughout the curved section of the U-shaped support bracket  40  and up much of the length of the legs of the U-shaped support bracket  40 . The notch  42  has narrowed portions  44  at the ends of the notch  42  near the tops of the legs of the U-shaped support bracket  40 . The notch  42  also has a narrowed portion  46  at the bottom of the curved portion of the notch  42 . 
     Referring now to FIG. 7, a main barrel assembly support plate  50  is shown. At one end of the support plate  50 , there are two notches in the support plate  50 , one above the other. The upper notch is a rectangular notch  52 , and the lower notch is an L-shaped notch  54 . Located roughly between the rectangular notch  52  and the L-shaped notch  54  is an aperture  56 . 
     Near the other end and at the top of the support plate  50  is an irregularly shaped notch  58 . Directly under the irregularly shaped notch  58  is a large circular aperture  60 . Surrounding the large circular aperture  60  at approximately 90 degree intervals are two apertures  62 ,  64  and two notches  66 ,  68 . The irregularly shaped notch  58  has a first deeper portion  70 , and a second deeper portion  72 . The first deeper portion  70  is nearer the end on the support plate  50  not having the rectangular notch  52  and the L-shaped notch  54  therein, while the second deeper portion  72  is nearer the end on the support plate  50  having the rectangular notch  52  and the L-shaped notch  54  therein. The first deeper portion  70  is also deeper than the second deeper portion  72 , for reasons which will become evident later. 
     The irregularly shaped notch  58  has at the end nearer the end on the support plate  50  not having the rectangular notch  52  and the L-shaped notch  54  therein a retaining projection  74 , which retaining projection  74  is located approximately half way down the first deeper portion  70 . The irregularly shaped notch  58  also has at the end nearer the end on the support plate  50  having the rectangular notch  52  and the L-shaped notch  54  therein a second retaining projection  76 , which retaining projection  76  is located near the top of the first deeper portion  70 . 
     When the U-shaped support bracket  40  is placed into the irregularly shaped notch  58  with the rounded portion of the U downward, the top of the U-shaped support bracket  40  immediately above the narrowed portions  44  is forced past the retaining projections  74 ,  76 . The retaining projections  74 ,  76  then act to retain the U-shaped support bracket  40  in the position shown, for example, in FIGS. 9 and 10. 
     The narrowed portions  44  of the U-shaped support bracket  40  will grip the portions of the support plate  50  located immediately below the deeper portions  70 ,  72 . Likewise, the narrowed portion  46  at the bottom of the U-shaped support bracket  40  will grip the portion of the support plate at the bottom of the large circular aperture  60 . It should be noted that the U-shaped support bracket  40  fits onto the support plate  50  so a shaft supported within the rounded portion of the U-shaped support bracket  40  will not contact the large circular aperture  60 , which has a slightly larger diameter than the diameter of the rounded portion of the U-shaped support bracket  40 . The bottom of the U-shaped support bracket  40  will also be directed slightly toward the end on the support plate  50  having the rectangular notch  52  and the L-shaped notch  54  therein a second retaining projection  76 , since when the barrel assembly and the door are installed the force will help to retain the U-shaped support bracket  40  in the irregularly shaped notch  58 . 
     Referring to FIG. 8, the installation of the support plate  50  onto a plate support bracket  80  is shown. The plate support bracket  80  is made from a piece of flat stock bent to have a 90 degree bend therein, as shown. The entire portions of the plate support bracket  80  on each side of the bend are mirror images. Two tabs are located on each side of the bend and on the top portion of the plate support bracket  80 , with each tab being parallel to and spaced away from the surface of the plate support bracket  80 . A first tab  82  is near the top of the plate support bracket  80  on each side of the bend, and the open end of the first tab  82  faces upwardly. A second tab  84  is below the first tab  82  on the plate support bracket  80  on each side of the bend, and the open end of the second tab  84  faces away from the bend on the plate support bracket  80 . 
     Two additional tabs are located on each side of the bend and on the bottom portion of the plate support bracket  80 , with each of these tabs being formed by material cut away from the plate support bracket  80 . A third tab  86  is located at the bottom of the plate support bracket  80  on each side of the bend, and the third tab  86  faces toward the line defined by the bend. A fourth tab  88  is located above the third tab  86  on each side of the bend, and faces away from the line defined by the bend. The fourth tabs  88  are directly above the respective third tabs  86 , and it will be appreciated that the third and fourth tabs  86 ,  88  will fit into two slots located one above the other, as will become evident as described below in conjunction with FIGS. 9 and 10. 
     Also located on the plate support bracket  80  on each side of the bend therein are two slots. A first slot  90  between the first tab  82  and the second tab  84  and a second slot  92  between the second tab  84  and the fourth tab  88  are of different sizes to allow different size mounting hardware to be used therein. One side of the plate support bracket  80  will be fastened to the side of the opening into which the door is to be installed; the other side is used to hold the support plate  50 . Only one of the two slots  90 ,  92  will generally be used in the installation of the door. Located between the second tab  84  and the first slot  90  on each side of the bend is an aperture  94 . 
     The installation of the support plate  50  onto the plate support bracket  80  may now be described. As shown in FIG. 8, the second tab  84  is inserted into the bottom portion of the L-shaped notch  54 . The support plate  50  is then pushed toward the bend in the plate support bracket  80 , causing the second tab  84  to move to engage the surface of the support plate  50  around the L-shaped notch  54 , and also causing the first tab  82  to fit through the rectangular notch  52 . The support plate  50  is then moved downwardly with respect to the plate support bracket  80 , causing the second tab  84  to move upward into the top of the L-shaped notch  54 , and also causing the first tab  82  to engage the surface of the support plate  50  above the rectangular notch  52 , as shown in FIGS. 9 and 10, for example. A bolt (not shown in FIG. 7) may be inserted through the aperture  56  and the aperture  94  to secure the support plate  50  to the plate support bracket  80 . 
     Referring now to FIG. 9, the installation of the plate support bracket  80  onto the top of the guide track  20  is illustrated. The top two retaining slots  22  in the guide track  20  are used to support the plate support bracket  80 . The fourth tab  88  is inserted into the top one of the retaining slots  22 , and the third tab  86  is inserted into the next lower one of the retaining slots  22  with the plate support bracket  80  at an angle to the guide track  20  as shown in FIG.  9 . 
     The plate support bracket  80  is then brought to an upright position bringing it in line with the guide track  20 , causing the fourth tab  88  to be fully inserted into the top one of the retaining slots  22 , and the third tab  86  to be fully inserted into the next lower one of the retaining slots  22 . It will be appreciated that the weight of the barrel assembly (not shown in FIGS. 9 and 10, but suspended from the U-shaped support bracket  40 ) will maintain the fourth tab  88  in a fully inserted position in the top one of the retaining slots  22 , and the third tab  86  in a fully inserted position in the next lower one of the retaining slots  22 . 
     Moving now to FIG. 11, the complete assembly of the present invention may be explained and understood. It will be immediately understood by those skilled in the art that the components described up to this point herein are universal; in other words, the same component may be used and will fit on either side of the roll-up door. The guide track  20  is the first such component, and may be used on opposite sides by merely turning it end-for-end. The retaining slots  22  are located equidistant from each end, and therefore only one guide track  20  need be manufactured instead of distinct left and right guide tracks. The mounting bracket  24  may also be used in any of the multiple retaining slots  22  on a guide track  20  on either side of the door. 
     As discussed above, the plate support bracket  80  is made of two portions on each side of the bend therein which are mirror images of each other. This enables the plate support bracket  80  to be used on either side of the door. One face of the plate support bracket  80  will be directed inwardly with respect to the opening in which the door is situated. The other face of the plate support bracket  80  will be directed directly away from the opening, and as such will lie flat against the wall adjacent the opening. Again, since the plate support bracket  80  will fit on either side of the door, only one plate support bracket  80  need be manufactured. 
     The support plate  50  is entirely of flat construction, and it will be appreciated that the first tab  82  and the second tab  84  may fit into the rectangular notch  52  and the L-shaped notch  54 , respectively, from either side. Accordingly, only a single support plate  50  must be manufactured. Likewise, the U-shaped support bracket  40  will fit onto a support plate  50  on either side of the door, so only a single U-shaped support bracket  40  need be manufactured. 
     The guide tracks  20  have a plastic door slide  100  having a C-shaped or U-shaped cross sectional configuration mounted on each of the two longitudinal edges (FIG. 3) thereof, with the plastic door slides  100  functioning to guide the door when it is raised or lowered. A guide track  20  is installed on each side of the opening immediately inside the edge of the opening, with the side of the guide track  20  on the right as the guide track  20  is shown in FIG. 3 facing the outside of the wall having the opening in which the door is to be installed. A plate support bracket  80  is attached to the top pair of retaining slots  22  on each on the guide tracks  20 , with one face of the plate support bracket  80  being directed inwardly with respect to the opening in which the door is situated, and the other face of the plate support bracket  80  being directed directly away from the opening and flat against the walls adjacent the opening therein. 
     A mounting bracket  24  is mounted in one of each pair of retaining slots  22  in the guide tracks  20 , except for the top pair of retaining slots  22  in each guide track  20 , which has the plate support bracket  80  mounted therein. The mounting brackets  24  are placed in the one of each pair of the retaining slots  24  which in the opinion of the installer best facilitates attachment of the mounting bracket  24  to the wall surrounding the opening in which the door is being installed. It should also be noted again that the guide tracks  20  may have more pairs of retaining slots  22  therein if the guide tracks are very long. 
     The guide tracks  20  are retained in place by lag screws or other such hardware (not shown) inserted through at least one of the first and second slots  34 ,  36  in each of the mounting brackets  24 , and through at least one of the first and second slots  90 ,  92  in each of the plate support brackets  80 . As mentioned previously, the different sizes of the first and second slots  34 ,  36  and the first and second slots  90 ,  92  enable the use of different sizes of lag bolts or other mounting hardware. Also, only one lag bolt is required to secure each of the mounting brackets  24  and the plate support brackets  80 . 
     The U-shaped support brackets  40  are mounted as previously described onto the support plates  50 . The barrel assembly, which is supported by the U-shaped support brackets  40 , may now be described. An axle  102  has a pair of support wheels  104 ,  106  mounted thereon, which support wheels  104 ,  106  will both support the door and provide a means around which the door may be rolled as it is raised. The axle  102  has a pair of retaining sleeves  108 ,  110  mounted near the ends thereof. When the ends of the axle  102  are inserted into and supported by the U-shaped support brackets  40 , the retaining sleeves  108 ,  110  prevent lateral movement of the axle  102  in the U-shaped support brackets  40 . The ends of the axle  102  preferably extend slightly through the U-shaped support brackets  40 , to allow a frictional retaining ring  112  to be slipped over the ends of the axle  102 , thereby also retaining the ends of the axle  102  in the U-shaped support brackets  40 . 
     A torsion spring  114  is attached at one end of the axle  102 . The torsion spring  114  has at its ends provisions for securing the ends with bolts. One end of the torsion spring  114  is secured to an aperture  116  in the support wheel  104  by a bolt, and the other end of the torsion spring  114  is secured to one of the two apertures  62 ,  64  or the two notches  66 ,  68  by a bolt. Although only one torsion spring  114  is shown in FIG. 11, a second torsion spring could be used at the other end of the axle  110 . If a second torsion spring is used, it would be secured at one end to the support wheel  106 , and at the other end to the support plate  50  at that end of the axle  110 . 
     A formed metal curtain type door  120  is attached to and suspended from the support wheels  104 ,  106  at the top thereof, as is conventional in the art. The door  120  has on the inside thereof two flexible spacer/runners  122 ,  124 , which are adhesively affixed to the door  120  in line with the positions of the support wheels  104 ,  106  to absorb the wear occasioned by the door  120  bearing against the support wheels  104 ,  106 , and to prevent abrasion between adjacent rolls when the door  120  is being raised or lowered. 
     The door  120  has mounted thereon a slide bolt assembly consisting of a slide bolt support member  130  which is mounted to the outside of the door  120  with bolts. Slideably mounted in the slide bolt support member  130  is a slide bolt  132 . The slide bolt  132  has a tongue  134  which extends toward the side of the door  120 . When the slide bolt  132  is in the open position, the tongue  134  is retracted into the slide bolt support member  130 , allowing the door  120  to be opened or closed freely. When the slide bolt  132  is in the closed position, the tongue  134  extends out from the slide bolt support member  130  beyond the edge of the door  120 . By having an aperture (not shown) in the guide track  20  to receive the tongue  134 , the door  120  may be locked in its fully closed (down) position. The slide bolt support member  130  and the slide bolt  132  have cooperating apertures therein to allow a lock to retain the slide bolt  132  in either a fully closed or a fully opened position. 
     The bottom edge of the door  120  is reinforced by using a reinforcing beam  140 , which is preferably fastened to the bottom of the door  120  by using a double re-entrant joint. The reinforcing beam  140  is preferably made of formed sheet stock, as shown in the cross-sectional illustration of FIG. 12. A double re-entrant joint  142  is formed by inserting a bent portion on the bottom of the door  120  into a cooperating bent portion on the top of the reinforcing beam  140 . The bent portions of the door  120  and the reinforcing beam  140  are then pressed together to form a secure joint therebetween. A sealing strip  144  is retained in the bottom of the reinforcing beam  140  to provide a water resistant seal between the bottom of the door  120  and the floor or ground. 
     Alternately, the reinforcing beam  140  may be made using a metal molding, as shown in the reinforcing beam  140 A shown in FIG.  13 . The reinforcing beam  140 A has a hook portion  146  at the top thereof which hook  146  engages the bent portion on the bottom of the door  120 . A cooperating planar surface  148  retains the bent portion on the bottom of the door  120  in engagement with the hook  146  when the hook  146  and the planar portion  148  are pressed together, thereby forming a secure joint between the door  120  and the reinforcing beam  140 A. A sealing strip  144 A is retained in the bottom of the reinforcing beam  140 A to provide a water resistant seal on the bottom of the door  120 . 
     Referring again to FIG. 11, a segment of angle iron  150  is shown mounted onto the reinforcing beam  140  on the inside of the door  120 . Similarly, on the opposite side of the reinforcing beam  140  two angle segments  152  are mounted, preferably using the same mounting hardware as used to mount the segment of angle iron  150 . The angle segments  152  may be used to allow the door  120  to be closed using a foot. 
     The segment of angle iron  150  is used to restrain the door  120  from being opened too far. A retaining segment  154  is mounted onto one of the guide tracks  20  at the top thereof and on the inside thereof. When the door  120  is fully opened, the segment of angle iron  150  will contact the retaining segment  154 , thereby preventing the door  120  from opening further. An additional retaining segment  154  may be similarly mounted on the other guide track  20 . Completing the construction of the system, a rope  156  may be attached to the center of the segment of angle iron  150 , thereby allowing the door  120  to be easily pulled down. This is particularly useful if the door  120  is too high to allow a user to reach the bottom of the door when it is fully opened. 
     Referring now to FIG. 14, an alternate embodiment of arrangement of FIGS. 1-3 is shown which uses the door assembly described above to make a secure storage unit  160 . By attaching a door such as that described above to the front of a metal shelf unit  162  having a plurality of shelves  164  therein, the storage unit  160  with shelves is made securable. The roll-up door  120  is mounted on guide tracks  20  which are mounted onto the front edges of the sides of the storage unit  162 . The barrel assembly (not shown in FIG. 14) is thereby mounted over the top of the shelf unit  162 . It will be appreciated that this innovation is highly useful in an industrial setting to store goods or equipment which must be locked up to prevent theft. 
     Referring now to FIG. 15, there is shown an adjustable tensioning arrangement for modular security door systems which may be applied to improve the door assembly described above. A tensioning body  200  has a mounting plate  202  adjacent shoulder  204 . Sleeve  206  is formed adjacent shoulder  204  opposite mounting plate  202 . Sleeve  206  is provided with multiple planar surfaces (“flats”) for engaging an adjustment tool (not shown). Tensioning body  200  defines an axle bore  208  centrally aligned and extending through sleeve  206 , shoulder  204  and mounting plate  202 . Axle bore  208  is sized to receive axle  102  and is provided with a number of lubrication grooves  209  to permit lubrication of the axle  102  within the bore  208 . Support plate  50 , corresponding to plate  50  shown in FIG. 7, for example, defines a large circular aperture  60  and smaller circular apertures  62 ,  64 ,  66  and  68  surrounding large circular aperture  60  and positioned at approximately 90° intervals surrounding large circular aperture  60 . Large circular aperture  60  is adapted to receive sleeve  206  and shoulder  204 , providing a bearing surface for shoulder  204 . 
     When assembled, axle  102  extends through torsion spring  114  with optional retaining ring  112  providing a bearing surface between retaining sleeve  108  and the back side (not visible in FIG. 15) of mounting plate  202 . Axle  102  extends through axle bore  208  of the tensioning body  200  which is supported by shoulder  204  within circular aperture  60 . Axle  102  is retained in place by washer  113  and cotter pin  111 . Tensioning body  200  is rotatable within aperture  60  by application of a wrench or similar tool in engagement with the flats on sleeve  206 . 
     Mounting plate  202  has apertures  214  positioned at approximately 90° intervals. The positions of the apertures  214  correspond to the positions of apertures  62 ,  64 ,  66 , and  68  in support plate  50 . 
     One of the apertures  214  is provided with a recessed portion  210  adapted to receive spring retaining pin  212  in flush cooperation with the face of mounting plate  202 . Recessed portion  210  is set into mounting plate  202  on the same side of mounting plate  202  as shoulder  204 . When assembled, spring retaining pin  212  extends through the corresponding aperture  214  to engage one end of torsion spring  114  and is retained by washer  211  and nut  213 . 
     To provide adjustment of the tension of torsion spring  114 , tensioning body  200  may be rotated by tooled engagement with sleeve  206  until the desired tension adjustment of torsion spring  114  has been achieved. When the tension of torsion spring  114  has been adjusted to the desired setting, apertures  62 ,  64 ,  66  and  68  are brought into alignment with apertures  214 . Positioning pin  216  is inserted through one of the apertures  214  and a selected one of the apertures  62 ,  64 ,  66  or  68  in order to fix the adjustment of the tension of torsion spring  114  at the desired setting. 
     FIG. 16 depicts an alternative embodiment of the tensioning body  200 , designated by the reference numeral  200 ′. All other reference numerals are the same as in FIG.  15 . In this embodiment, sleeve  206  provides bearing engagement with large circular aperture  60  of support plate  50 , such that shoulder  204  may be eliminated. Sleeve  206  has a cylindrical configuration providing for adjustment by way of a pipe wrench or similar means (not shown). The tensioning body  200 ′ is preferably made of metal, whereas the tensioning body  200  of FIG. 15 is designed to be fabricated from a suitable plastic material. 
     Referring now to FIG. 17, another alternative embodiment of the adjustable tensioning arrangement of FIG. 15 is shown, designated by the reference numeral  200 ″. For other elements corresponding to the structure depicted in FIG. 15, the same reference numerals are used in FIG.  17 . In this embodiment, support plate  50  defines a plurality of keyhole-shaped apertures  70  surrounding large circular aperture  60  and positioned radially outward about large circular aperture  60 . Keyhole-shaped apertures  214  consist of a generally circular portion with a generally rectangular “slot” portion extending therefrom. 
     Keyhole-shaped apertures  70  are positioned such that the generally rectangular slot portion of each aperture is aligned about the circumference of a circle axially aligned with and surrounding large circular aperture  60 . 
     Mounting plate  202  of tensioning body  200 ″ has a plurality of apertures  214  extending therethrough. Apertures  214  are axially aligned with and circumferentially spaced about axle bore  208 . 
     In this embodiment, positioning pin  216  may comprise a carriage bolt, as shown in further detail in FIG.  18 . Circular portion  70   a  of keyhole-shaped aperture  70  is adapted to receive the cylindrical threaded portion of positioning pin  216 . Generally rectangular slot portion  70   b  of keyhole-shaped aperture  70  is adapted to receive the unthreaded, square cross-sectioned shoulder portion of positioning pin  216 . 
     The embodiment of FIG. 17 has the advantage that manipulation of the positioning pin  216  in the aperture  70  is easier. In this embodiment there is no need to hold the positioning pin  216  against rotation when tightening or loosening the pin retaining element, such as the nut  218 , as in other embodiments. The generally circular portion  70   a  of keyhole-shaped aperture  70  permits the insertion of positioning pin  216 . After positioning pin  216  is passed through the generally circular portion  70   a  of one of keyhole-shaped apertures  70  and one of apertures  214  of mounting plate  202 , to be retained by threaded engagement with nut  218 , tensioning body  200 ″ may be rotated to bring the square cross-sectioned portion of positioning pin  216  into secure engagement with the slot portion  70   b  of keyhole-shaped aperture  70 . In so doing, undesired rotation of positioning pin  216  is precluded and the safety and ease in securing of the torsion spring tensioning arrangement is greatly enhanced. 
     FIG. 19 shows an alternative configuration of positioning pin  216 . A thumb turn head is provided for increased ease of use. 
     In FIG. 20, still another alternative configuration of positioning pin  216  is shown. A hex head is provided for engagement by a wrench or pliers for ease of assembly and use. 
     Although there have been described hereinabove various specific arrangements of an ADJUSTABLE TENSIONING ARRANGEMENT FOR MODULAR SECURITY DOOR SYSTEM in accordance with the invention for the purpose of illustrating the manner in which the invention may be used to advantage, it will be appreciated that the invention is not limited thereto. Accordingly, any and all modifications, variations or equivalent arrangements which may occur to those skilled in the art should be considered to be within the scope of the invention as defined in the annexed claims.

Summary:
An adjustable tensioning arrangement for modular security door systems has modular components interchangeable for use on either side of the door system, thereby reducing significantly the number of parts which must be manufactured for the door. The adjustable tensioning arrangement is capable of accommodating a variety of tensions desired by individual users. The adjustable tensioning arrangement may be produced with a minimal number of required parts, and at very low cost. Construction of the adjustable tensioning arrangement may incorporate readily fabricated steel components, or utilize injection molded or other plastic type materials.