Collapsible tubular frame
BACKGROUND OF THE INVENTION 
     Common collapsible frames for tents, sunshades, etc. used nowadays are not so convenient in collapsing them, generally taking time in extending and assembling them. 
     SUMMARY OF THE INVENTION 
     This invention has been devised to offer a kind of collapsible tubular frame for tents, sunshades, etc., having a simpler structure than conventional ones for shrinking and extending in a short time and becoming a minimum size as best as possible when shrunk. 
     The shrinkable tubular frame in this invention is composed of a plurality of curved tubes of the same length and curvature but different diameter so that the curved tubes can be shrunk in a largest-diameter one and finally become very short after all tubes except the largest one are all shrunk in the largest one. 
     A fixing unit is provided to lock two neighboring curved tubes when extended out and to loosen the two tubes when they are to be shrunk. 
     A winding unit is provided in a left largest-diameter curved tube to wind a rope adapted to extend from an outer end of the left curved tube to an outer end of the right curved tube when this frame is to be shrunk to pull the other curved tubes except the left largest one to shrink into the left largest one. 
     A coil spring is provided to extend inside the frame from the outer end of the left largest tube to the outer end of the right smallest tube to assist the tubes to be shrunk by its elasticity. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     The invention will be better understood by reference to the accompanying drawings, wherein: 
     FIG. 1 is a cross-sectional view of a shrinkable tubular frame in the present invention; 
     FIG. 2 is a cross-sectional view of the shrinkable tubular frame in a shrunk position in the present invention; 
     FIG. 3 is a perspective view of two shrinkable tubular frames utilized for a tent frame in the present invention; and, 
     FIG. 4 is a magnified view of a fixing unit in the shrinkable tubular frame in the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A shrinkable tubular frame in the present invention, as shown in FIG. 1, includes a plurality of hollow curved tubes 1, a plurality of fixing units 3, and a winding unit 4 combined together. For example, it is made up of three tubes 1, a left largest diameter one 6, an intermediate larger-diameter one 8 and a right smallest-diameter one 7, a coil spring 2 extending inside the three tubes from an outer end of the left tube 6 to an outer end of the right tube 7, and two fixing units 3, 3 respectively fixing each two tubes 6 and 8, 8 and 7 together. The three tubes 6, 7, 8, have the same length and curvature but different diameter so that the right smallest-diameter tube 7 can be shrunk inside the intermediate larger-diameter tube 8, and the tube 8 can be shrunk inside the largest-diameter tube 6 so that the shrunk frame has only a third length of the whole tubular frame extended out as shown in FIG. 2. 
     The fixing unit 3 has a projecting plate 11, as shown in FIG. 4, fixed on an outer surface of an inner end of the tube 6, a threaded hole 12 provided in the plate 11, a tapered hole 13 in a left end of the intermediate tube 8 corresponding to the threaded hole 12, a steel bead 31 to fit nearly half in the tapered hole 13 urged by a coil spring 32 pushed by an adjusting bolt 33 engaging the threaded hole 12 and urging one end of the coil spring 32. After the tubes 8 and 7 are pulled to extend out fully, the two fixing units 3, 3 lock the three tubes 6, 7, 8, securely in an extended position with a proper tightness. 
     The winding unit 4 is mounted in a chamber 14 provided in the outer end of the tube 6, having a worm gear 42, a worm 41 meshing with the worm gear 42, a shaft 43 of a motor 5, a gear shaft 44 of the worm gear 42 and a rope 45 wound on the worm gear 42 and extending through the three tubes to be bound at the outer end of the tube 7. The motor 5 can be substituted by a handle (not shown in the Figures) connected with the worm 42 so as to manually winding the rope in shrinking the tubes 9 and 8 in the tube 6 instead of using electricity to rotate the motor 5. 
     This shrinkable tubular frame is applicable to a tent, a sunshade, etc. as shown in FIG. 3. First, the left end of the tube 6 of the shrinkable tubular frame is to be secured on the ground, then the tube 7 is manually pulled out of the tube 9 and then the tube 9 out of the tube 6. Next, the two fixing units 3, 3 are manipulated to fix the three tubes 6, 7, 8 securely and finally the outer end of the tube 7 is secured on the ground. When a plurality of this shrinkable tubular frames are prepared on the ground in the extended position, a tent 9 can be extended to cover on them. 
     In collapsing the extended tubular frame, after the tent 9 is taken down, the outer end of the tube 7 is released from the ground. Then the two fixing units 3, 3 are loosened by screwing the bolts 33, 33, and the motor 5 is started to wind the rope 45 of the winding unit 4, pulling the tube 7 to shrink in the tube 8, then the tube 8 in the tube 6. Or the handle instead of the motor is used to perform the same work. And the long coil spring 2 has elasticity to assist shrinking action. 
     While the preferred embodiments of the invention have been described above, it will be recognized and understood that various modifications may be made therein and the appended claims are intended to cover all such modifications which may fall within the spirit and scope of the invention.