Abstract:
A tube with an external channel of a complex geometry. The channel does not distort or collapse when the tube is bent 90 degrees with a 4-inch radius. Fabric may be inserted into and securely held in the external channel. The tube is suitable for constructing frames of fabric structures, such as dodgers and biminis for boats, tents, chairs, etc.

Description:
BACKGROUND INFORMATION 
   1. Field of the Invention 
   The invention relates to the field of tubes or pipes. More particularly, the invention relates to a tube with an external channel. 
   2. Description of the Prior Art 
   Tubing, particularly aluminum tubing, is frequently used for building tube frames, such as the frames for biminis and dodgers on boats. Other common uses for such tube frames include collapsible beach chairs, tents, baby strollers, etc. Common to the types of frames just mentioned is that the frame is used to support a fabric structure, such as the dodger enclosure on a boat, the seat and back rest on the chair, etc. The tubing is a suitable material for the frame because it is lightweight, yet strong. It is also easily bendable with a pipe bender, so it can be used to construct and shape a frame to fit a particular substructure. Although it is understood that there are innumerable uses for such tube frames, for purposes of illustration, reference will be made hereinafter to a “dodger” and frame for a dodger, whereby the dodger is representative of any fabric structure supported on a tube frame. 
   One of the disadvantages of the tube frame is that the fabric has to be fitted over the frame. In the case of the beach chair, the two ends of the fabric seat are provided with a tube or sleeve that slides over the tubing. More complex structures comprise a number of panels, such as two side panels, a front panel, a top panel, and a back panel. Such a complex structure is a boat enclosure called a “dodger.” Because of the need to fit the fabric structure over the frame, the panels are stitched together to form a unitary construction that is fitted over the tube frame. Often, two adjacent panels are stitched together and a sleeve stitched over the seam, so that a section of the tube frame is insertable through the sleeve. This unitary construction creates difficulties because the fabric structure is bulky and heavy, making it difficult to handle. If one panel requires cleaning or repair, the entire structure has to be removed from the frame for delivery to a cleaning or repair facility. 
   Another disadvantage of the conventional tube frame is that the fabric often bunches up on the frame, providing an unaesthetic look. The bunching up may create folds in the fabric, which promote mildew and growth of mold, because moisture becomes trapped in the folds. 
   What is needed, therefore, is a bendable tube that enables individual panels of fabric to be secured to it, without requiring that the fabric be secured with a sleeve of fabric or that adjacent panels be stitched together. What is further needed is a tube frame made of such a tube and a means of securing fabric panels smoothly and evenly to the frame. What is yet further needed is such a tube frame that provides an aesthetically pleasing appearance. 
   BRIEF SUMMARY OF THE INVENTION 
   The invention is a metal tube with an external channel that does not distort or collapse when the tube is bent. The tube is extruded of anodized aluminum. The geometry of the channel is complex and allows the tube to be bent without collapsing, even when bent about a relatively small radius. The channel is not circular or rectangular, but of a curved, somewhat teardrop shape. The inner hollow core of the tube is somewhat oval in cross-section. The tube may have one, two, three or more external channels, depending on its intended use. A tongue forms a dividing wall between any two adjacent channels. 
   The sections of a frame to which fabric is to be attached are made of the tube according to the invention. Individual panels of the fabric are attached to the frame. The edge of the panel to be secured to the frame is provided with a contoured, flexible border that is slidingly insertable in and capturable within the channel. Suitable materials for providing the border include foam piping material, cord, rope or braid, or other firm materials that will bend around the contours of the frame but are firm enough to remain captured within the channel. Individual sliders, such as are used to attach drapes to channel track, may also be used. If two panels of fabric are attached to the same section of a two-channel tube, the edge of one panel is inserted into the first channel and the edge of the second panel into the second channel. 
   An example of a tube that is particularly well suited for a dodger frame is one that is extruded from 6061-T6 aluminum and anodized. This material provides a tube that is pleasing in appearance and has the desired light weight and high strength for securing heavy fabric on a straight or curved stretch of tube. The tube is 1″ in diameter, with the walls and bridge ⅛″ thick. A tube of these dimensions can be bent to a radius as small as four inches, without the channels collapsing or distorting. 
   The individual panels of fabric are secured to the frame by inserting the edge of the fabric into the external channel. The fabric is smoothly and evenly secured to the tube, along straight and curved sections and the finished look is smooth and elegant. When two panels are attached to the same section of tube, a portion of the tongue between the two channels remains visible, which provides a clean and contrasting look that is aesthetically appealing. 
   The tube according to the invention may also be provided as a telescoping tube. An inner or connector tube is slidingly inserted into the hollow tube core of the tube. A setscrew or other suitable means is used to secure the connector tube at a particular distance within the tube. 
   A feeder or endcap may be used to provide a finished end to the tube and also to help insert the fabric edge into the channel. The endcap has a hollow core with a threaded bore, and two external channels with end openings. The hollow core and threaded bore align with the hollow core of the tube. A screw-in eyeend may be threaded into the threaded bore, for attaching the frame to a boat deck, a wall, or other support structure. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention is described with reference to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements. 
       FIG. 1  is a cross-sectional view of the tube according to the invention, showing the geometry of the channels, the bridge and the tongue. 
       FIG. 2  is the cross-sectional view of the tube of  FIG. 1 , illustrating with greater detail the radii of the curves that form the channel and the inner hollow core. 
       FIG. 3A  illustrates a side bend on the tube of  FIG. 1 . 
       FIG. 3B  ilustrates an inside bend on the tube of  FIG. 1 . 
       FIG. 3C  illustrates an outside bend on the tube of  FIG. 1 . 
       FIG. 4  is a perspective view of a telesoping tube according to the invention. 
       FIG. 5A  is a frontal view of an end cap. 
       FIG. 5B  is a side view of the end cap. 
       FIG. 6  illustrates a reinforced fabric edge being inserted into a channel. 
       FIG. 7  is an illustration of a dodger for a boat, constructed of fabric panels that are individually attached to sections of the tube frame. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention will now be described more fully in detail with reference to the accompanying drawings, in which the preferred embodiments of the invention are shown. This invention should not, however, be construed as limited to the embodiments set forth herein; rather, they are provided so that this disclosure will be complete and will fully convey the scope of the invention to those skilled in the art. 
     FIG. 1  is a cross-sectional view of a tube  100  according to the invention, showing an inner hollow core  10  and a channel  20 . It is the shape and configuration of the channel  20  that is unique to the invention and it is understood that, depending on the particular intended use, one, two, three, or more channels  20  may be provided in the tube  100 . The tube  100  has a tube wall  12  that forms a bridge  14  in the area of the channel  20 . The inner hollow core  10  is delineated by a first inner wall section  10 A and a second inner wall  10 B. The channel  20  has a complex geometry that is delineated by a first curve  20 A, a second curve  20 B, a first channel arm  20 C and a second channel arm  20 D. In the embodiment shown, two channels  20  are provided in the tube wall  12  with a tongue  24  therebetween. The two channels  20  are in mirror-reverse juxtaposition to each other and the tongue  24  forms the second curve  20 B and the second channel arm  20 D for both of the channels  20 . The tube wall  12  and bridge  14  have a first thickness T 1 . The first channel arm  20 C has thickness T 1  at its base and tapers to a second thickness T 2 , which is ½ the first thickness T 1 . The radius of curvature of the first curve  20 A is significantly smaller than the radius of curvature of the second curve  20 B. 
     FIG. 2  shows the radii or diameters of the various curves. The diameters of a one-inch overall outside diameter tube will be given here for purposes of illustration only. It is understood that the tube  100  according to the invention is not limited to a one-inch outside diameter tube. A person skilled in the art understands that the radii of the various curves will be adapted proportionally to form tubes according to the invention of other diameters. D 10 A is the overall diameter of the tube: one inch overall outside diameter and ¾ inch overall inside diameter of the first inner wall section  10 A. D 10 B defines the curve of the second inner wall section  10 B, which is 1⅛ inch in diameter. D 10 C defines the transition curve  10 C between the first inner wall section  10 A and the second inner wall section  10 B. D 20 E defines the curvature  20 E of the first channel arm; D 20 A defines the diameter of the first curve  20 A; and D 20 B the diameter of the second curve  20 B. D 20 D defines the curvature of the outer end of the second channel arm  20 D. 
     FIGS. 3A-3C  show the tube  100  with a 90 degree bend in a 4-inch radius, with a side bend, an inside bend, and an outside bend. The channel  20  does not distort to any significant degree with any of these bends. 
     FIG. 4  is a perspective view of a telescoping tube  200  according to the invention, showing an inner tube  160 , also called a connector, slidably inserted into the hollow core  10  of the tube  100 . Setscrews are shown as a means  162  of fixing the telescoping distance of the connector  160  relative to the tube  100 . 
     FIGS. 5A and 5B  are views of an end cap  180  that is used to close the end of the tube  100 . The end cap  180  has a central throughbore  184 . A threaded bore  182  is provided at the beginning of the throughbore  184 . An external channel  186  is formed in the endcap  180 . The number of external channels  186  and their alignment on the endcap  180  correspond to the number of external channels  20  and their alignment on the tube  100  with which the endcap  180  is to be used. 
     FIG. 6  illustrates use of the endcap  180  as a feeder, showing a panel P of fabric being inserted into a tube  100  through the endcap  180 . The external channel  186  in the endcap  180  is preferably provided with a feeder opening, which facilitates insertion of the panel P. A fabric attachment means  170  is attached to an edge of the panel P as shown and slidingly inserted into the external channel  186  and then into the external channel  20 . In the embodiment shown, the fabric attachment means  170  is a foam piping enclosed within a sleeve of the fabric. Other suitable fabric attachment means include rope, chord, or braid, individual sliders, or other means that are attachable to the panel P and capturable by the channel arms  20 C and  20 D. As shown in  FIG. 6 , the fabric attachment means  170  is circular in diameter and does not correspond precisely to the shape of the channel  20 . Nevertheless, the diameter is great enough that it remains captured in the channel  20  by the first and second channel arms  20 C and  20 D. Also shown in  FIG. 6  is frame attachment means  190  which is threaded into the threaded bore  182  on the endcap  180 . Illustrative of a suitable frame attachment means  190  is the endeye shown in this embodiment. The frame attachment means  190  is any suitable device that enables the frame  300  to be attached to the deck of a boat, to a wall, or other structural support. 
     FIG. 7  is an illustration of a boat enclosure  300 , such as a dodger, constructed of a frame made of the multiple sections  100 A,  100 B, . . . of the tube  100 . Panels P of fabric are secured to the frame. A first panel P 1  and a second panel P 2  are secured in the channels on a first section  100 A. Only the tongue  24  of the tube section  100 A is visible on the outside of the enclosure  300 . 
   It is understood that the embodiments described herein are merely illustrative of the present invention. Variations in the construction of the tube, a frame constructed of the tube, and a fabric structure supported by the frame may be contemplated by one skilled in the art without limiting the intended scope of the invention herein disclosed and as defined by the following claims.