Patent Publication Number: US-7588042-B2

Title: Folding shaft for umbrellas

Description:
FIELD OF THE INVENTION 
   The present invention relates to a folding shaft for umbrellas and the sections of the shaft includes polygonal shape sections and circular shape sections which are be alternatively connected to the sections of polygonal shape. 
   BACKGROUND OF THE INVENTION 
   A conventional folding shaft of an umbrella generally includes three or four sections which are retractably connected to each other in a sequence such that when the umbrella is not in use, the shaft can be folded to be a short shaft. The foldable shaft is cooperated with an opening device which includes a spring arranged to be extended through the sections of the shaft. In order to smoothly extend or fold the shaft, the inner diameter of each section has to be controlled so as to ensure smooth operation while the opening device can be installed therein. However, a gap is defined between the sections and affects the operation of the folding shaft. Conventional folding shaft of umbrellas generally includes sections each have a circular cross section and the friction between the sections is significant. If the gaps between the circular sections are made large to reduce the friction and accommodate the spring of the opening device, the spring might not be installed in stable condition. 
   The present invention intends to provide a folding shaft for umbrellas and the sections of the folding shaft includes sections with polygonal shape and sections with circular section, the sections with polygonal shape and sections with circular section are retractably connected to each other in an alternative sequence so as to obtain minimum gap between sections. 
   SUMMARY OF THE INVENTION 
   The present invention relates to a folding shaft for umbrellas and the shaft comprises a first section having a circular cross section, a second section movably mounted to the first section and a third section movably mounted to the second section. The second section includes an enclosed cross section which includes a plurality of straight sides and a plurality of first curved portions connected between the straight sides. The third section includes an enclosed cross section which includes a plurality of inward curved sides and a plurality of second curved portions connected between the inward curved sides, and the inward curved sides of the third section are located corresponding to the straight sides of the second section. The second curved portions of the third section are located corresponding to the first curved portions. 
   The present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, a preferred embodiment in accordance with the present invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows the three sections of the first embodiment of the folding shaft are assembled; 
       FIG. 1   a  shows a cross section of the three sections in  FIG. 1 ; 
       FIG. 2   a  shows the cross section of the central section in  FIG. 1 ; 
       FIG. 2   b  shows the cross section of the intermediate section in  FIG. 1 ; 
       FIG. 2   c  shows the cross section of the external section in  FIG. 1 ; 
       FIG. 3  shows the five sections of the second embodiment of the folding shaft are assembled; 
       FIG. 3   a  shows a cross section of the five sections in  FIG. 3 ; 
       FIG. 4   a  shows the cross section of the central section in  FIG. 3 ; 
       FIG. 4   b  shows the cross section of the first intermediate section in  FIG. 3 ; 
       FIG. 4   c  shows the cross section of the second intermediate section in  FIG. 3 ; 
       FIG. 4   d  shows the cross section of the third intermediate section in  FIG. 3 ; 
       FIG. 4   e  shows the cross section of the external section in  FIG. 3 ; 
       FIG. 5  shows four sections of the third embodiment of the folding shaft of the present invention are assembled together; 
       FIG. 5   a  shows the sections of the shaft are in extended status, and 
       FIG. 5   b  shows the four sections of the third embodiment of the folding shaft of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIGS. 1 ,  1   a , and  2   a - 2   c , the first embodiment of the folding shaft of the present invention comprises a first section  10  having a circular cross section, a second section  20  movably mounted to the first section  10  and including an enclosed cross section which includes a plurality of straight sides  21  and a plurality of first curved portions  22  connected between the straight sides  21 , and a third section  30  movably mounted to the second section  20  and including an enclosed cross section which includes a plurality of inward curved sides  31  and a plurality of second curved portions  32  connected between the inward curved sides  31 . The inward curved sides  31  of the third section  30  are located corresponding to the straight sides  21  of the second section  20 , and the second curved portions  32  of the third section  30  are located corresponding to the first curved portions  22 . Preferably, the depth of each of the inward curved sides  31  is 1/10 to ⅕ of the length of the side. In this embodiment, the second section  20  includes five straight sides  21  and five first curved portions  22 , and the third section  30  includes five inward curved sides  31  and five second curved portions  32 . 
     FIGS. 3 ,  3   a  and  4   a - 4   e  show a second embodiment of the folding shaft of the present invention wherein five sections are involved and includes a first section  110  having a circular cross section, a second section  120  movably mounted to the first section  110  and including an enclosed cross section which includes a plurality of first straight sides and a plurality of first curved portions connected between the first straight sides. A third section  130  is movably mounted to the second section  120  and has a circular cross section. A fourth section  140  is movably mounted to the third section  130  and includes an enclosed cross section which includes a plurality of second straight sides  121  and a plurality of second curved portions  122  connected between the second straight sides  121 . The second straight sides  121  of the fourth section  140  are located corresponding to the first straight sides of the second section  120 , and the second curved portions  122  of the fourth section  140  are located corresponding to the first curved portion of the second section  120 . A fifth section  150  is movably mounted to the fourth section  140  and includes an enclosed cross section which includes a plurality of inward curved sides  131  and a plurality of third curved portions  132  connected between the inward curved sides  131 . The inward curved sides  131  of the fifth section  150  are located corresponding to the second straight sides  121  of the fourth section  140 , and the third curved portions  132  of the fifth section  150  are located corresponding to the second curved portions  122 . Preferably, the second section  120  includes five first straight sides and five first curved portions, and the fourth section  140  includes five second straight sides  121  and five second curved portions  122 . The fifth section  150  includes five inward sides  131  and five third curved portions  132 . 
     FIGS. 5 ,  5   a  and  5   b , a third embodiment of the folding shaft of the present invention four sections wherein a first section  1  has a circular cross section and a polygonal section  1   a  extending from a first end thereof, a notch defined longitudinally in a second end of the first section  1 . A second section  2  is retractably received in the first section  1  and includes an enclosed polygonal cross section. Two circular sections  2   a  are connected to two ends of the second section  2 . A third section  3  is retractably received in the second section  2  and includes a circular cross section, two polygonal sections  3   a  connected on two ends of the third section  3 . A fourth section  4  is retractably received in the third section  3  and includes an enclosed polygonal cross section. A circular section  4   a  is connected to a first end of the second section  2  and a second end of the second section  2  includes a longitudinal opening. 
   The gaps between the sections of the folding shaft is controlled to be the minimum so that the folding shaft can be made smaller, and the gaps also ensure that the spring can be well installed in the folding shaft to ensure the operation of the folding shaft. 
   While we have shown and described the embodiment in accordance with the present invention, it should be clear to those skilled in the art that further embodiments may be made without departing from the scope of the present invention.