Abstract:
The invention is embodied in a modular system for making structural frameworks in which crystal-like hubs are used to connect lightweight struts in a variety of configurations. The hubs are comprised of uniform nodes and cylindrical trunnions, several embodiments of which be used in a structural configuration to create irregular shapes. The struts are equipped with end grips which snap into engagement with the trunnions and nodes of the crystal-like hubs. The end grips have C-shaped gripping sections and stems which fit into a hollow tube which forms the body of the strut. The end grips are free to rotate about the axis of the strut, and the end grips can rotate about the axis of the trunnions to which it is attached. Such freedom of rotation allows complete flexibility of design.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     The present invention relates to a system for constructing space frames and, more particularly, to a modular system including hubs in combination with cylindrical tubes or struts which can be used to make simple, lightweight structures which are easily assembled. 
     Space grid and frame structures have long been used in architectural and engineering projects. Such structures are popular because of the repetitive nature of the design, wherein a basic geometric configuration is used. A base module is used repeatedly simply by adding more joints and connecting members to create a structure of a particular shape. The traditional space frame and grid structure comprises a grid of intersecting members forming a pattern of triangles which imparts rigidity and structural integrity to the grid. The use of rigid hubs, usually in the form of a ball with axial tapped holes in rectangular, orthoganal and hexagonal directions, is a consequence of the commitment to mathematical modeling and geometric regularity. Using the minimum number of triangular patterns minimizes the number of different angular relationships and tube lengths, so that the same type of hub may be used repeatedly throughout the structure. For example, the German &#34;Mero&#34; and &#34;Meroform&#34;, and the American &#34;Unistruct&#34; are well known systems in which the cylindrical tubes or struts are rigidly connected at a particular angle relative to a static joint. Such systems are limited in that they provide no flexibility for adjusting the central converging angle of the struts in bridging of a static joint. As a result, the possibilities of forming geometrical patterns are limited. 
     An object of the present invention is to provide a universal static hub which ha maximum flexibility in joining and securing cylindrical tubes or struts to such a hub in constructing decorative frameworks. 
     Another object of the invention is to provide a flexible joint in a structural framework which has the ability to generate all forms of geometric configuration, both curved and planar. 
     Yet another object of the invention is to provide an assembly which is neat and simple, and to provide an assembly in which bolts are not required. 
     Still another object of the invention is to provide a static hub in which up to 18 struts may be connected. 
     A further object of the invention is to provide a decorative framework in which the geometric patterns may differ and which, therefore, is usable to enclose irregular spaces. 
     These and other objects and advantages of the invention are achieved with a modular system which includes a crystal-like static hub which may have one or more planar arrays of interconnected trunnions. In one embodiment, the trunnions are arranged to form a generally octahedral-hexagonal prism. The prism is formed by joining two hexagonal planar arrays of trunnions, each array having six nodes. The trunnions of the crystal-like hub are engaged by end grips which are attached to opposite ends of tubular members or struts. The end grips have a C-shaped section which clips into engagement with a trunnion. The C-shaped section has flat end surfaces which abut the nodes at the opposite ends of the trunnion to which the end grip is attached. The end grip is axially fixed to the strut, but free to rotate about the axis of the strut. The crystal-like hub can be used to attached up to 18 such end grips. Since the end grips are free to rotate about the trunnion, and since the struts are free to rotate about the end grips, a wide variety of angular relationships can be used to create structures of a nearly infinite variety of configurations. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The objects and advantages of the invention will become apparent upon a reading of the following specifications, read in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a plan schematic view of a structural configuration in accordance with the present invention; and 
     FIG. 2 is a side elevational schematic view of the arrangement shown in FIG. 1; and 
     FIG. 3 is a perspective schematic view of an alternative arched structural arrangement in accordance with the present invention; and 
     FIG. 4 is a plan view of a crystal-like hub made in accordance with the present invention; and 
     FIG. 5 is a side elevational view of the crystal-like hub shown in FIG. 4; and 
     FIG. 6 is a schematic perspective view showing the manner in which the hub of FIGS. 4 and 5 is made; and 
     FIG. 7 is a side elevational view of a first alternative embodiment of a crystal-like hub made in accordance with the present invention; and 
     FIG. 8 is a perspective view of an end grip made in accordance with the present invention; and 
     FIG. 9 is a plan view of a second alternative embodiment of a crystal-like hub of the present invention; and 
     FIG. 10 is a sectional view taken along line 10--10 of FIG. 9; and 
     FIG. 11 is a schematic perspective view of the manner in which the crystal-like hub of FIGS. 9 and 10 is made; and 
     FIG. 12 is a plan view of a crystal-like hub in accordance with the present invention with end grips and struts attached thereto; and 
     FIGS. 13 and 14 are sectional views which show the engagement of an end grip and a crystal-like hub in accordance with the present invention; and 
     FIG. 15 is a sectional view which shows an alternative embodiment of the engagement between a strut and an end grip in accordance with the present invention; and 
     FIG. 16 is a sectional view taken along line 16--16 of FIG. 15. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1, 2 and 3 show two embodiments of the present invention in assembled form. FIGS. 1 and 2 show an example of a framework which is generally planar. The crystal-like hubs 10 shown in FIGS. 1 and 2 are used to connect upper struts 12, lower struts 14, and diagonal struts 16. The means by which such framework as is shown in FIGS. 1 and 2 can be attached to a building are not shown. However, means by which the framework can be attached to a building include a combination of fasteners and wire, such as those which are typically used to hang suspended ceilings. Alternatively, the framework shown in FIGS. 1 and 2 could be freestanding if placed on vertical supports, which may or may not be made of the strut/hub arrangement of the present invention. 
     As will be discussed later, the crystal-like hubs of the present invention allow a variety of structural configurations. FIG. 3 shows an arched array of struts in which hubs (not shown in FIG. 3) are used to connect longitudinal struts 18 and diagonal struts 16. The arcuate configuration is held in place with long struts 19. 
     FIGS. 4 and 5 are bottom and side views, respectively, of an octahedral hexagonal hub which is comprised of twelve nodes, six upper nodes 22, and six lower nodes 23. Each of the nodes receives three trunnions. The upper trunnions 20 link the upper nodes 22, and the lower trunnions 21 link the lower nodes 23. The vertical trunnions 24 each join an upper and a lower node. FIG. 6 shows schematically the manner in which the orthogonal hexagonal hub 10 is put together. An upper half-hub 26 which includes the upper nodes 22, the upper trunnions 20 and three vertical trunnions 24, is molded as a single unit in a two plate mold. A lower half-hub 28 which is identical in shape and which can be made from the same mold as the upper half-hub 26 includes the lower nodes 23 the lower trunnions 21, and three vertical trunnions. The vertical trunnions of each of the half-hubs 26 and 28 are alternating so that when the half-hubs are aligned as shown in FIG. 6, they can be joined to form the completed crystal-like hub 10 shown in FIGS. 4 and 5. Similarly, three alternating nodes on each half-hub have bores 25 (See 20 FIG. 4) to receive the trunnions carried by mating half-hub. The preferred method of joining the upper and lower half-hubs is by sonic welding, but other techniques such as solvent welding, etc., may be used. 
     FIG. 7 shows a first alternative embodiment of a crystal-like hub 10a. The crystal-like hub 10a is similar to the upper portion of the crystal-like hub 10. The hub 10a does not have vertical trunnions. Nor does it have lower nodes or lower trunnions. The hub 10a is a hexagonal generally planar ring which can connect up to six struts. 
     FIG. 8 shows an end grip 30 which is used to connect a strut to a hub in accordance with the present invention. The end grip 30 includes a C-shaped section 32 which projects from a stem 50. The C-shaped section is connected to the stem by a neck 44. The end grip 30 further includes a collar 46. The C-shaped section has an inner cylindrical surface 38 and an outer cylindrical surface 40 which are generally concentric and spaced from each other to form flat sides 42. The inner and outer ends 34 and 36 are resilient so that the C-shaped section can open slightly to snappingly engage the trunnions 20, 21 and 24. The inner cylindrical surface 38 is shaped to closely match the cylindrical surface of the trunnions. Similarly, the width of the C-shaped section 32 is substantially equal to the distance between the various nodes 22 and 23, so that the annular side surfaces 41 of the nodes abut and guide the flat side 42 of the end grips. Further-more, the radius of the outer cylindrical surface 40 is generally equal to the radius associated with the outer surfaces of the nodes. The relationship between the outer surfaces of the C-shaped section and the nodes provides the end grip/hub assembly with a neat appearance, as can be seen in FIG. 12. 
     FIGS. 9, 10 and 11 show a second alternative of a crystal-like hub 10b of the present invention. The hub 10b is generally cubical in configuration and includes a set of four upper nodes 22b, four upper trunnions 20b, four vertical trunnions 24b, four lower nodes 23b, and four lower trunnions 21b. Thus, the hub 10b provides a total of 12 attachment locations for end grips of the present invention. It should be noted that the spacing between the nodes of the various hubs 10, 10a and 10b is made to be the same, so that a combination of hubs will be usable in a given structure so that a user of the system can design a structure with complete flexibility. 
     Similar to the manner in which the octahedral hexagonal hub 10 is assembled (as shown in FIG. 6), FIG. 11 shows the manner in which the cubical hub 10b is assembled. The upper and lower half-hubs 26b and 28b are identical, and each has two vertical trunnions 24b. The two half-hubs are brought together in the manner shown in FIG. 11 and are sonically welded or otherwise connected to form the cubical hub shown in FIGS. 9 and 10. 
     FIGS. 13, 14 and 15 are sectional views which show the manner in which a tubular strut 52 is connected to an end grip 30, and these figures show the manner in which the end grip is attached to a hub 10. FIG. 13 shows an end grip 30 with its stem 50 inserted into the end 52 of the tubular strut 11. The wall of the tubular strut 11 has been deformed inwardly to form an annular ring 54 which engages a complementary annular recess 58 formed in the end grip 30. The collar 46 is adjacent to the end 52 of the tubular strut 11. The engagement between the annular ring 54 and the annular recess 58 allows rotation of the strut 11 relative to the end grip 30. Thus, the grip 30 is free to rotate within the end of the strut 11 about the longitudinal axis of the strut 11. However, axial movement between the strut 11 and the end grip 30 is limited both by the engagement of the ring 54 and the recess 58 and by the abutment of the end 52 and the collar 46. FIG. 14 shows a larger sized end grip 30c in which the stem 50c is connected to the C-shaped section 32c by a tapered collar section 48. The end grip 30c and the larger diameter strut 11c are connected to one another in the same manner as is described with reference to the embodiment shown in FIG. 13. 
     FIG. 15 shows an alternative method of attaching a strut 11d to an end grip 30d. The tubular strut 11d has been modified to include an annular interior recess 56. A resilient retaining ring 54d is disposed between the annular recess 58d, which is formed in the stem 50d. As can be seen in FIG. 16, the depth of the annular recess 58 is sufficient to allow resilient deformation of the ring 54d so that the stem may be inserted into the end 52d of the strut 11d. When the annular ring is in alignment with the internal annular recess 56d, the ring 54d will expand into engagement with the recess 56d and will prevent relative axial movement of the stem 50d and the strut 11d while allowing relative rotation between the stem 50d and the strut 11d. 
     As can be seen in FIG. 12, tubular struts of various diameters are attached to a crystal-like hub. The C-shaped sections of each end grip are identical. The need for tubular struts of larger or smaller diameter will depend upon the structural function of the strut. For longer spans, larger diameters will provide larger moments of inertia and greater resistance to bending. In contrast, when a strut is entirely in tension, a smaller diameter tubular strut may suffice. However, when a strut is in compression, a larger diameter may be required to resist buckling. The universal nature of the crystal-like hub and end grip configurations enable a designer to accommodate all of the structural requirements which may arise in designing an irregular framework. 
     The materials used in the various components include plastic and metal. The crystal-like hub 10 is preferably made of an injection molded ABS plastic. Similarly, the end grips 30 are also preferably made of ABS plastic. Alternatively, PVC plastic may be used. However, the tubular struts 11 are preferably made of aluminum. The combination of plastic and aluminum makes the resulting framework as light weight as possible. The nature of the components makes them easy to assemble, transport and support. The resilient retaining ring 54d can be made of either plastic or metal, but is preferably steel. 
     While the invention has been described with respect to particular embodiments shown and discussed above, numerous alternatives, modifications and variations will occur to those who read and understand this specification. It is intended that all such alternatives, modifications and variations be included within the spirit and scope of the following claims: