Patent Publication Number: US-6711780-B2

Title: Hinge for collapsible ladders

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a hinge for collapsible ladders, and more particularly, to a hinge for collapsible ladders having an improved structure in which a hinge spring for the collapsible ladders is not exposed externally. 
     Korean Utility Model Registration No. 1991-303 discloses a common hinge for collapsible ladders. As shown in FIGS. 1A and 1B, this conventional invention discloses the hinge having an auxiliary round plate  3 ″ disposed between a pair of round plates  3  and  3 ′. A rotary plate  11  contacts one side of the auxiliary round plate  3 ″ by a flange  11 ′ formed around the auxiliary round plate  3 ″ and can be rotated. Center apertures,  4 ,  4 ′ and  4 ″ which mate with a center aperture  4 ″′ of the rotary plate  11  are locked with a bushing  5 , and a gap formed between portions A and B positioned in one direction of the flange  11 ′ is used with an operating part  13  of the rotary plate  11 . One end of a tension spring  14  is mounted in an aperture  13 ′ of the operating part  13 . Locking rods  8  and  8 ′ of a locking handle  7  extend into apertures  15  and  16  and locking apertures  9  and  9 ′ by pressure from a press part  18  having a press axle  6  with a spring  17  surrounding press axle  6 . At the same time, the operating part  13  which is rotatably biased in the direction of portion A, provides that the locking rods  8  and  8 ′ smoothly enter along inclined planes  16 ′ of the apertures  16 . 
     Since an operation of the hinge for the collapsible ladders disclosed in the above Korean Utility Model Registration has been already known, and also its structure does not include a characterized portion of the present invention, a detailed description thereof shall be omitted. 
     The hinge for the collapsible ladders described above has problems that may cause damage or breakdown of the spring due to its external exposure, and further, hands or gloves of an operator may be jammed in the spring when the press part is pressed. 
     SUMMARY OF THE INVENTION 
     In order to solve the above problems, it is an object of the present invention to provide a hinge for collapsible ladders having a safety structure which can inwardly house a hinge spring for the collapsible ladders, prevent any damage or breakdown of the spring, and keep an operator safe during use of the ladder. 
     To accomplish the above object of the present invention, a hinge for collapsible ladders, includes an external frame including a center aperture and a pair of locking apertures; an inner frame including a center aperture and a plurality of pairs of locking apertures, the inner frame being rotatably movable relative to the external frame around the center apertures; a rotary plate rotatably disposed between the inner frame and the external frame and having locking apertures therein; a substantially flat rotary spring having one end mounted to the inner frame and an opposite end mounted to the rotary plate to impart a turning force to the rotary plate; a hub member rotatably connecting the inner frame and the external frame about the center apertures, and supporting the frames, the hub member including a locking end at one side thereof; a locking part having a locking end for extension into the locking apertures of the external and inner frames to fix an angle of the inner frame and the external frame relative to each other; a press axle connected with the locking part and passing through the hub member, the press axle including a spring bearing end; and a spring positioned between the locking end of the hub member and the bearing end of the press axle. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 a  is a front view showing a conventional hinge for collapsible ladders; 
     FIG. 1 b  is an exploded perspective view showing the conventional hinge for collapsible ladders; 
     FIG. 2 is a perspective view showing a hinge for collapsible ladders according to the present invention; 
     FIG. 3 is an exploded perspective view showing the hinge for collapsible ladders according to the present invention; 
     FIG. 4 is a sectional view of the hinge for collapsible ladders according to the present invention; and 
     FIG. 5 is a sectional view illustrating an operation state of the hinge for collapsible ladders according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A preferred embodiment of the present invention will be described below in more detail with reference to the accompanying drawings. 
     FIGS. 2 and 3 are a perspective view and an exploded perspective view showing the hinge for collapsible ladders according to the present invention. 
     As illustrated, an external frame  200  comprises  2  center aperture  206  for locking formed at the center thereof, and a pair of locking apertures  204  positioned in the periphery of the center aperture  206 . An inner frame  300  which is connected into the inside of the external frame  200 , comprises a center aperture  306  for locking formed at the center thereof, and pairs of locking apertures  304  positioned in the periphery of the center aperture  306 , for adjusting a connection angle. Inner frame  300 , as shown beet in FIG. 3 includes, two opposing circular disks  302  in spaced apart relation to form a hollow area therein, and opposing stringers extending therefrom. Aligned openings  308  are provided in circular disks  302 . A rotary round plate  400  is disposed to rotatably move between the external frame  200  and the inner frame  300 . The rotary round plate  400  comprises locking apertures  404  at the same position as those of the locking apertures  304  of the inner frame  300 . In order to impart a turning force to the rotary round plate  400 , one side of a substantially flat rotary spring  410  is locked to the inner frame  300 , and the other side thereof is fitted with a bent part  402  of the rotary round plate  400  that extends through openings  308  in circular disks  302 . The external and inner frames  200  and  300  and the rotary round plate  400  are rotatably assembled together in a center relation by an annular hub member  550 . One side of the annular hub member  560  forms a locking end  564  and the other side thereof forms an unlocking end  566 . It is preferable that the locking end  564  includes a frame bearing flange, and a side end of the unlocking end  566  is locked with a locking ring  540  by riveting. 
     A spring  520  is inserted between a press axle  500  and the locking end  564  of the annular hub member  560 . The press axle  500  is locked with a nut  510  by extending a screw part  502  of the press axle  500  into a locking handle  580  through the annular hub member  560 . Since the press axle  500  has a locking portion, it is tightly locked with the locking handle  580  with only the nut  510 . After locking the press axle  500  and the locking handle  580  with the nut  510 , it is preferable to fit a protection cap  512  over screw part  502  and nut  510  in order to prevent loosening of the nut  510 . 
     Also, it is preferable that the spring  520  has a cone shape to guide the press axle  500 . 
     FIG. 4 is a sectional view taken along the line  4 — 4  of FIG.  2 . 
     As shown, the annular hub member  560  has one locking end and another unlocking end. At the center of the locking end, there are provided a press axle aperture  568  through which the press axle  500  is passed, and a flange  562  for supporting the external frame  200 . The annular hub member  560  passes through the center apertures of the locked frames, and is locked by riveting through a joint with the locking ring  540 . 
     The press axle  500  comprises a screw part  502  positioned at the end thereof for connection with the locking handle  580 , a locking pin  504  for supporting the locking handle  580 , and a spring bearing end  506  for bearing the spring  520 . As illustrated, one side of the spring  520  is supported by the spring bearing end  506 , and the other side thereof is supported by the locking end  564  of the annular hub member  560 . 
     The spring  520  is not exposed externally because it is housed between the locking end of the annular hub member  560  and the spring bearing end  506  of the press axle  500 . 
     FIG. 5 is a sectional view showing a state where the press part  508  is pressed in to vary the connection angle of the frames. 
     As shown, even though the press part  508  is pressed, the spring is still disposed between the locking end  564  of the annular hub member  560  and the spring bearing end  506  of the press axle  500  to thereby avoid its exposure. 
     As described above, the hinge for the collapsible ladders having a safety structure according to the present invention can provide effects that prevent breakdown and damage of the spring and keep an operator safe during use of the ladder since the spring is housed within the annular hub member. 
     Having described a specific preferred embodiment of the invention with reference to the accompanying drawings, it will be appreciated that the present invention is not limited to that precise embodiment and that various changes and modifications can be effected therein by one of ordinary skill in the art without departing from the scope or spirit of the invention defined by the appended claims.