Abstract:
A twistable connecting structure for linking two wheeled assemblies (such as foot platforms) of a personal transportation device. This connecting structure has flexible elongated members linking the wheeled assemblies, and rigid support members bridging the gap between the elongated members. This configuration enables the connecting structure to twist without bending.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to land vehicles having tiltable segments, such as those steerable by a tiltable platform or platforms. In particular, it relates to personal transportation devices having wheeled assemblies linked by a connecting structure wherein the wheeled assemblies are independently tiltable. 
     In existing personal transportation devices having two wheeled assemblies linked by a connecting structure, independent tilting of the wheeled assemblies is achieved by pivoting of part of the connecting structure. An example of this is the connecting element (a “twist-pipe” in some embodiments) of the skateboard disclosed in U.S. Pat. No. 7,195,259. Twisting of the twist-pipe is possible because two or more pipe sections are pivotably coupled end-to-end. This method allows for effective twisting, but it necessarily involves moving contact between various parts, and these parts could wear out with use. 
     A need therefore exists for a connecting structure that can serve a function similar to that of the connecting element described in the &#39;259 patent, while avoiding fricative contact between its constituent parts. Such a connecting structure would not only be less prone to wearing out, but could also be manufactured more simply and at lower cost. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an embodiment of a personal transportation device comprising a torsionally flexible connecting structure in accordance with the present invention. 
         FIG. 2  is a perspective view of an embodiment of a personal transportation device comprising a torsionally flexible connecting structure wherein the connecting structure and the foot platforms are made from the same piece of material, in accordance with the present invention 
         FIG. 3  is another perspective view of the personal transportation device of  FIG. 2 . 
         FIG. 4  is a perspective view of another embodiment of a personal transportation device comprising a torsionally flexible connecting structure in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , a perspective view of one embodiment of a personal transportation device  100  comprising two wheeled assemblies (in this case foot platforms)  104  linked by a torsionally flexible connecting structure  101  in accordance with the present invention is shown. Connecting structure  101  comprises four elongated members  102  in an arrangement whose transverse cross-section is a trapezoid. Connecting structure  101  further comprises at least one support member  103 . (Preferably, there are several support members  103 .) Elongated members  102  are substantially parallel to each other. Elongated members  102  are furthermore flexible, the degree of flexibility depending on their thickness and on the material used. Support member(s)  103  are substantially perpendicular to elongated members  102 , rigidly connect elongated members  102  to each other, and are sufficiently thin at the points of connection such that elongated members  102  may be separate from each other throughout the large majority of their length. If more than one support member  103  are used, it is preferable, but not necessary, to space them at substantially equal intervals along the length of elongated members  102 . 
     Connecting structure  101  cannot substantially bend because bending of connecting structure  101  would require elongated members  102  to move closer together, which is substantially prevented by support member(s)  103 . However, connecting structure  101  does allow for torsional movement. When twisting force is applied to connecting structure  101 , each individual elongated member  102  bends into a helical shape, resulting in twisting of connecting structure  101 . Elongated members  102 , being elastically flexible, resist bending, and tend to straighten; connecting structure  101  is therefore inherently biased toward a non-twisted shape. The twisting capability of connecting structure  101  allows the foot platforms  104  of transportation device  100  to be tilted relative to each other, enabling turning as well as propulsion. (Propulsion can be achieved by means such as oscillatory motion of the feet, particularly if the wheels are inclined-axle casters.). 
     Referring to  FIGS. 2 and 3 , perspective views of another embodiment of a personal transportation device  200  are shown. Personal transportation device  200  comprises two wheeled assemblies (foot platforms)  204  linked by torsionally flexible connecting structure  201 , wherein said foot platforms  204  and connecting structure  201  are made from a single piece of material. This differs from personal transportation device  100  of  FIG. 1  in that it is simpler to manufacture; the configuration and function of the connecting structure are the same. Whereas  FIGS. 1 and 4  show embodiments having torsionally flexible connecting structures  101  and  401  each having four elongated members  102  and  402 , connecting structure  201  in  FIGS. 2 and 3  has three elongated members  202  in an arrangement whose transverse cross-section is a triangle. 
     Referring to  FIG. 4 , a perspective view of one embodiment of a personal transportation device  400  comprising two wheeled assemblies  404  linked by a torsionally flexible connecting structure  401  in accordance with the present invention is shown. Connecting structure  401  comprises four elongated members  402 , in an arrangement whose transverse cross-section is a trapezoid. In this embodiment the first wheeled assembly  405  is associated with the front wheel of personal transportation device  400 , and the second wheeled assembly  406  is associated with the two rear wheels. Connecting structure  401  allows the first wheeled assembly  405  to be tilted independently of the second wheel assembly  406 , thus providing, among other benefits, the ability to lean during turns for greater stability.