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BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an improved extension ladder structure, and more particularly to an extension ladder apparatus, which is assembled and folded easily and securely, providing superior safety. 
         [0003]    2. Description of the Prior Art 
         [0004]    Accordingly, stepladders have become a requisite tool for casual use. For example, climbing tools such as a ladder or scaffolding enable people to readily process construction or obtain the objects at a high place. 
         [0005]    A conventional stepladder  800 , as shown in  FIG. 1 , is assembled by two side rails having a footpad respectively to prevent slippage, and is provided with parallel spaced step portions therein. The stepladder appears as an A-frame ladder during usage. 
         [0006]    Stepladders are typically large and bulky; therefore, it is uneasy and inconvenient to carry them. Moreover, the storage of a folded stepladder may occupy large space, which makes the use of a stepladder inflexible. 
         [0007]    Various extension ladder structures have been disclosed in U.S. Pat. Nos. 4,989,692, 5,492,430, 5,495,915, 2004/0195043A, 6,708,800, and 5,743,355 to improve the fixed stepladder as shown in  FIG. 1A . However, the extension ladders in those applications still require respective control during folding and cannot achieve the automatic folding, which is not ideal for use. 
         [0008]    To improve the shortcomings of existing extension ladders, the Chinese Patent No. 200620113407.6 named “Extension Ladder” has been issued on Apr. 29, 2006 and the Utility Model No. 899705 has been obtained. 
         [0009]    Referring to  FIG. 1B , which is the partial view of the extension stepladder in the Chinese patent No. 200620113407.6, after a locking mechanism within the first-length transverse step portion is pulled, with a tie rod plate  801  that can be held up and down, one end of the tie rod plate  801  extends to the upper end of the cross hole, the out-protruding part is inserted into the lower end cross hole  802  of the upper transverse step portion, and then the turning rod  803  disposed within the upper transverse step portion is pushed so that the locking bar withdraws from the upper transverse step portion to unlock. Accordingly, the locking mechanism above the second length can be unlocked in order and each length of the side rail sections will go down and be folded. 
         [0010]    However, after the Chinese Patent No. 200620113407.6 described above has been completed, through constantly tests, it is found that when an extension ladder is used in a dirty environment, the holes above or under the step portions may be filled with dust and other contaminants so that the tie rod plate cannot be moved smoothly, which will cause unlock failure or other problems. 
         [0011]    Also, unlocking requires the tie rod plate  801  to push the turning rod  803 . If a tie rod plate  801  gets stuck or cannot pass through the cross hole, the entire stepladder cannot be folded smoothly which causes inconvenience while using it. 
         [0012]    As to the side rail sections that can be fit in with each other, since there is no effective locking mechanism, the upper side rail section may depart from the lower side rail section when they are used erroneously, which causes unsafety. 
         [0013]    Accordingly, the present invention has been invented to solve the above-mentioned problems occurred in the prior art. 
       SUMMARY OF THE INVENTION 
       [0014]    Accordingly, the present invention aims at improving an extension ladder structure which comprises a plurality of rail side sections, connection kits, locking mechanism and transverse step portion, makes the structure simpler, safer, and more stable, and can solve the above-mentioned problems occurred in conventional extension ladders. Since transmission parts are largely decreased, the parts that need further process and technology are also reduced, which save costs and reduce manufacturing difficulties. Furthermore, the locking mechanism is completely hidden, which can reduce the risk of mistaken unlocking. Also, a confirmation window for the locking bolt is provided in the present invention, which facilitates the safety confirmation before using the extension ladder. 
         [0015]    In the improvement of an extension ladder structure in the present invention, a fixing ejection bar is provided at the upper end of the connection kit that is used to fit into the side rail section. A locking mechanism is provided within the connection kit. One end of the connection kit is covered by a transverse step portion. Accordingly, when the fixing ejection bar of the lower connection kit is inserted upward into the upper connection kit, the locking mechanism within the upper connection kit can be pushed to unlock. Since the ejection bar is a fixed device, any damage caused by external force or problems that lead to unable to perform operations can be avoided. This is another objective of the present invention. 
         [0016]    In the improvement of an extension ladder structure in the present invention, an unlocking bock that can be fit into the upper end of the fixing ejection bar is provided, and an partition ejection bar that is equal to the ejection bar is provided at the upper end of the unlocking bock. When the unlocking bock is fit into the upper end of said fixing ejection bar, a locking mechanism within the upper connection kit can be pushed by the ejection bar, so that a space between the upper step portion and lower step portion remain during the folding, which allows cables or wires to be passed through or allows operators who need to wear gloves in a long time to hold the ladder easily when the extension ladder is used in any specific location. This is another objective of the present invention. 
         [0017]    In the improvement of an extension ladder structure in the present invention, an elastic support set is disposed at the bottom of said extension ladder, which not only increases the basal area of said extension ladder and enhances the safety, but also suitable for adjustment in different places or uneven ground (step differences) to increase the applicable scope and locations and enhance the stability. This is another objective of the present invention. 
         [0018]    In the improvement of an extension ladder structure in the present invention, a locking mechanism that will not be skidded is disposed between the upper side rail section and lower side rail section. This is another objective of the present invention. 
         [0019]    The detailed structure, application principle, function, and effects of the present invention will be more apparent from the following descriptions taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1A  is a three-dimensional view of the conventional ladder; 
           [0021]      FIG. 1B  is a partial sectional view of the Patent No. 095108511; 
           [0022]      FIG. 2  is an illustration showing the folding of the extension ladder in the present invention; 
           [0023]      FIG. 3  is an illustration showing the extension of the extension ladder in the present invention; 
           [0024]      FIG. 4  is a three-dimensional exploded view of the first-length rung section and its locking mechanism; 
           [0025]      FIG. 5  is a partial sectional view of the embodiment in the present invention; 
           [0026]      FIG. 6  is an exterior view of the rung section in the embodiment of the present invention; 
           [0027]      FIG. 7  is a three-dimensional exploded view of the rung section above the second length and its locking mechanism in the embodiment of the present invention; 
           [0028]      FIG. 8  is a three-dimensional assembly view of the embodiment in the present invention; 
           [0029]      FIG. 9  is a three-dimensional view of the connection kits from another perspective in the embodiment of the present invention; 
           [0030]      FIG. 10  is a plan view of the unfolded ladder in the embodiment of the present invention; 
           [0031]      FIG. 11  is a plan view of the folded ladder in the embodiment of the present invention; 
           [0032]      FIG. 12  is a three-dimensional view of the second embodiment of the present invention; 
           [0033]      FIG. 13  is a plan view of the unfolded ladder in the second embodiment of the present invention; 
           [0034]      FIG. 14  is an enlarged view of the part AB of the  FIG. 13 . 
           [0035]      FIG. 15  is a plan view of the third embodiment of the present invention; 
           [0036]      FIG. 16  is a three-dimensional view of the elastic support set in the third embodiment of the present invention; 
           [0037]      FIG. 17  is a partial plan view of the elastic support set in the third embodiment of the present invention; 
           [0038]      FIG. 18  is a partial three-dimensional view of the elastic support set in the third embodiment of the present invention; 
           [0039]      FIG. 19  is a three-dimensional exploded view of the fourth embodiment of the present invention; 
           [0040]      FIG. 20  is an illustration showing the folding of the extension ladder in the present invention; 
           [0041]      FIG. 21A  is an enlarged view of the part A of the  FIG. 20 ; 
           [0042]      FIG. 21B  is an enlarged view of the part B of the  FIG. 20 . 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0043]    The present invention discloses the improvement of an extension ladder structure wherein the extension ladder  1  can be folded as shown in  FIG. 2  or unfolded as shown in FIG.  3 . Said extension ladder  1  comprises a plurality of side rail sections  2 , connection kits  3 , and transverse step portion  5 , which is present as a stepladder extending upward when it is unfolded and each of its side rail sections can be fit in with each other when it is folded. 
         [0044]    Referring to  FIG. 4 , each side rail section  2  of the extension ladder in the present invention is hollow and tubular-shaped and can be fit in with each other. That is, the second side rail section  2   a , which has a smaller diameter but the same shape with the first side rail section  2 , can be fit into the first side rail section  2 . The second side rail section  2   a  can be slid within the first side rail section. Other side rail sections can be fit in with each other accordingly. 
         [0045]    As shown in  FIG. 4 , a snap-fit hole  21  and an orientation hole  22  are provided above the first side rail section so that the connection kit  3  can fit through the holes. 
         [0046]    As shown in the figure, said connection kit  3  comprises a ringlike covering part  31  that can be fit through the upper end of a side rail section and a pivotal joint  32  extending toward from the ringlike covering part  31 ; after said ringlike covering part  31  is fit into the upper end of said side rail section by using a screw  33  to fix it, an orientation tenon  34  for embedding snap-fit hole  21  of the           side rail section is provided on the internal wall of said side rail section; an adhesive channel  35  is provided whose one end is provided with an adhesive-infusing hole  36  so that adhesive can be infused therein to stick the side rail section together; a via hole  30  is provided on the ringlike covering part  31 . The via hole  30  is interlinked with the orientation hole  22  of the side rail section after the ringlike covering part  31  is fit in with its upper end. 
         [0047]    Said pivotal joint  32  is formed with the ringlike covering part  31  and a channel  37  is formed therein which is interlinked with the via hole  30 . The two sides of said channel  37  are side plates  321  and  322 . A upright opening  38  is provided on the internal wall of said side plates  321  and  322 ; a transverse step portion  5  is fit in with the external part of the pivotal joint  32 ; a cross hole  51  is provided on the lower surface of the transverse step portion  5 . 
         [0048]    A first-length locking mechanism  4   a , is provided in the interior of the channel  37  of the first-length connection kit  3 , which includes a block plate  41 , a locking bar  42 , a spring  43 , a pull rod  44 , and a control pad  45 ; said block plate  41  is inserted and fixed within the upright opening  38  of the pivotal joint  32  and a cross hole  411  is formed in the center of said pivotal joint  32 . After the joint part  441  of the pull rod  44  passes through the cross hole  411 , it is jointed with the end connection  421  of the locking bar  42 . One end of the locking bar  42  passes through the via hole  3  of the connection kit  3  and the orientation hole  22  of the side rail section  2 . A narrow opening  422  is provided in the main body of the locking bar  42  for a C-shaped plate  46  to be inserted into the narrow opening  422  to restrain the spring  43 . Accordingly, when the locking bar  42  is pushed and shifted by the pull rod  44 , the spring  43  needs to be used to return the locking bar  42  to its original position. 
         [0049]    The block plate  41 , locking bar  2 , spring  43 , and pull rod  44  are disposed in the interior of the first-length locking mechanism  4   a  described above, and are covered by a transverse step portion  5 . One end of the pull rod  44  is connected with the control pad  45  disposed under the transverse step portion  5 , so that the movement of locking bar  42  can be controlled manually by the control pad  45 ; a guide plate  451  is disposed above the control pad  45 , and a horizontal groove  452  is formed under the guide plate  451 , which can push the guide plate  451  into the cross hole  51  of the transverse step portion  5 . With the horizontal groove  452 , sliding along the edge of the cross hole  51  is available. 
         [0050]    As shown in the figure, a through and fixing hole  23  is provided in the external part of the side rail section  2   a  above the second length; a out-protruding ring  24  is provided under the through and fixing hole  23 ; a corresponding in-protruding ring  25  (as shown in  FIG. 5 ) is provided in the interior of the first-length side rail section  2 . By way of the joint of the out-protruding ring  24  and in-protruding ring  25 , the side rail section  2   a  is moved upward and downward within the first-length side rail section  2  so that the through and fixing hole  23  can be oriented to the orientation hole  22  of the first-length side rail section  2  and the locking bar  42  can pass through the through and fixing hole  23 . Accordingly, the upper side rail section and lower side rail section can be extended and fixed to some extent. 
         [0051]    In addition, a buckle hole  26  is disposed at the lower end of the side rail section  2   a  above the second length so that a buffering device  6  can be hooked in the buckle hole  26  of the side rail section through a protruding part  61  and can be fixed in the lower end of the side rail section  2   a ; an elastic seal ring  62  is disposed outside the lower end of the buffering device  6  so that appropriate friction remains from the internal wall of the side rail section since the elastic seal ring  62  is shifted upward and downward within the side rail section, which reduces the noise occurred. Said elastic seal ring  62  also has the folding cushion function. Also, a film  63  is disposed within the buffering device  6 . A hole is formed on the film  63  so that air can get into the film  63  through the hole to achieve the cushion effect when the buffering device  6  is shifted upward and downward. 
         [0052]    As shown in  FIG. 6 , to avoid that two side rail sections depart from each other, an in-protruding encircling ring part  201  is provided at the upper tube opening of side rail section in the present invention; an out-protruding ring part  202  is provided at the lower tube opening of side rail section. Accordingly, after the upper side rail section passes upward through the lower side rail section, the encircling ring part  201  and protruding ring part  202  restrain from each other, which prevents the side rail sections from departing from each other and ensures the safety. 
         [0053]    Referring to  FIG. 7 , the upper locking mechanism  4   b , upper connection kit  3   a , and upper transverse step portion  5   a  of the side rail section  2   a  above the second length are different from those in the first length side rail section. A cross hole at the lower end of the upper transverse step portion  5   a  is not required. 
         [0054]    As shown in the figure, the upper connection kit  3   a  not only has the structure of first-length connection kit  3  but also has an axial opening  39  on the internal wall of the side plates  321  and  322 . Also, an opening  310  is provided at the bottom of the ringlike covering part  31  of connection kit  3   a  which is connected with the pivotal joint  32 . 
         [0055]    The upper locking mechanism  4   b  disposed within the upper connection kit  3   a  comprises a locking bar  410 , a spring  420 , a sleeve  430 , and a turning rod  440 . The sleeve  430  is provided with a upright plate  431 . The two sides of the upright plate  431  can be inserted and fixed within the upright opening  38  of the pivotal joint  32 . One end of the locking bar  410  can be fit into the sleeve  430 . A spring  420  is provided at one end of the sleeve  430  inserted with the locking bar  410  so that the locking bar  410  can be switched horizontally and return back to its original position. A rabbet  411  is provided in the main body of the locking bar  410  for disposing the turning rod  440 . 
         [0056]    As shown in the figure, the turning rod  440 , presented as V-shaped, has a yoke  441  at one end that can be inserted into the rabbet  411  of locking bar  410 , and has a base plate  442  at another end; a downward protruding bump  443  is formed at the lower end of said base plate  442 ; a pivot  444  is formed in the joint of the yoke  441  and base plate  442  so that the turning rod  440  can be embedded into an axial opening  39  of the upper connection kit  3   a  through the pivot  444  and the bump  443  can be exposed from the opening  310  (as shown in  FIG. 8 ). 
         [0057]    Referring to  FIG. 9 , regardless of the first-length connection kit  3  or upper connection kit  3   a , a upward protruding fixing ejection bar  300  is provided at the upper end of the ringlike covering part  31 . The fixing ejection bar  300  is formed with the connection kit  3  ( 3   a ). Since it is formed at upper end of the ringlike covering part  31 , it is not covered by the transverse step portion  5 . Said fixing ejection bar  300  is oriented to the opening  310  of the upper connection kit  3   a.    
         [0058]    During implementation, as shown in  FIGS. 10 and 11 , when the control pad  45  is switched toward the center of the stepladder, through the pull rod  44 , it drives the locking bar  42  to withdraw from the through and fixing hole  23  of the side rail section. The upper side rail section  2   a , upper connection kit  3   a , and upper transverse step portion  5   a  fall down after the locking bar  42  withdraws from the through and fixing hole  23 . When the upper connection kit  3   a  falls down and sticks on the first-length connection kit  3  (as shown in  FIG. 11 ), the fixing ejection bar  300  at the upper end of the first-length connection kit  3  enters into the opening  310  of the upper connection kit  3   a  while pushing the bump  443  of the turning rod  440  within the upper locking mechanism to rotate the turning rod  440  and then the locking bar  410  is pulled back through the yoke  441  of the turning rod  440 . When the locking bar  410  withdraws from the through and fixing hole of the third-length side rail section, the third-length side rail section, connection kit, and transverse step portion fall down simultaneously, and the fixing ejection bar  300  of the third-length connection kit will be pushed against the fourth-length turning rod, and then the fourth-length side rail section, connection kit, and transverse step portion will fall down; accordingly, once the first-length control pad  45  is pushed, each length of the side rail sections will go down and be folded; also, through the setup of the buffering device  6  and elastic seal ring  62 , each length of the side rail sections can cushion the extension or folding without any noise. 
         [0059]    With the construction described above, the extension ladder in the present invention not only decreases the part cost but also increases the using reliability through the simplified structure. Also, the locking mechanism is hidden in the internal part which can avoid danger of touching the turning rod carelessly during unlocking. 
         [0060]    Referring to  FIG. 12 , in another embodiment of the extension ladder in the present invention, an unlocking bock  7  is additionally provided. A partition ejection bar  71  that is equal to the ejection bar is provided at the upper end of the unlocking bock  7 ; a groove for the ejection bar  72  that is equal to the ejection bar is provided at the lower end of the unlocking bock. When the unlocking bock  7  is fit into the upper end of the fixing ejection bar  300 , the fixing ejection bar  300  is also pushed up. 
         [0061]    Referring to  FIGS. 13 and 14 , since the unlocking bock  7  can be fit into the upper end of the fixing ejection bar  300 , the turning rod  440  within the upper connection kit can be pushed through the partition ejection bar  71  to unlock, which not only will not impact the operation of the locking mechanism, but also renders a partition space  73  between the upper transverse step portion  5   a  and lower transverse step portion  5  during folding. The partition space  73  allows cables or wires to be passed through or allows operators who need to wear gloves in a long time to hold the ladder easily when the extension ladder is used in any specific location. 
         [0062]    Referring to  FIG. 15 , in another embodiment of the extension ladder in the present invention, an elastic support set  8  is provided at the lower end of extension ladder  1 , which not only increases the basal area of the extension ladder, enhances the safety, but also provides more applicable locations based on different, uneven ground or step differences, and enhances the reliability. 
         [0063]    Referring to  FIGS. 16 ,  17 , and  18 , said elastic support set  8  comprises two rail portions  81 ,  82  that can be fit in with the side rail section; a step portion  83  is disposed between the two rail portions  81 ,  82 ; a pedestal  84  is disposed at the lower end of the rail portions  81 ,  82 ; an extension bar  85  is disposed at the upper end of said pedestal  84 . A ball-shaped stand  86  is connected with a pedestal  84  at the lower end of the extension bar  85  so that the extension bar  85  can be rotated arbitrarily; a stable element  87  is disposed at the upper end of the extension bar  85  so that the extension bar  85  contacts with the internal wall of rail portions  81  and  82  through the stable element  87  without swaying. Said pedestal  84  comprises a rubber pad  841 , a middle cover  842 , and a upper cover  843 . The middle cover  842  and upper cover  843  are hooked up with each other and cover the ball-shaped stand  86  so that the extension bar  85  can be adjusted and rotated. 
         [0064]    In addition, a tensile control mechanism  88  is provided in the middle of the extension bar  85  which is formed through that a top inclined spring  882  is provided within a base  881 . The upper end of said top inclined spring  882  is pushed against a one-way snap-fit iron sheet  883 . The upper end of one-way snap-fit iron sheet  883  sticks on an inclined piece  884 ; a hole (not shown in the figure) is disposed at the center of the one-way snap-fit iron sheet  883  and inclined piece  884  so that the extension bar  85  can pass therethrough. Accordingly, when the one-way snap-fit iron sheet  883  is inclined, the extension bar  85  gets stuck through the inclined hole edge so that the extension bar  85  can only be pulled upward and cannot be pulled back, which ensures the safety of using the stepladder. Therefore, with the one-way snap-fit iron sheet  883 , extension bar  85  can adjust the height difference of the ladder foothold. 
         [0065]    A switch  885  is disposed in one end of the one-way snap-fit iron sheet  883 . When the switch  885  is pushed up, the one-way snap-fit iron sheet  883  is pulled back as horizontal. At this time, since the extension bar  85  no longer gets stuck with the hole edge, the extension bar  85  can be pulled back arbitrarily. 
         [0066]    Referring to  FIG. 19 , the extension ladder in the present invention is equipped with the locking display function. As shown in the figure, a window frame  323  or  324  is disposed respectively in the two sides of the pivotal joint  32  of connection kit  3 . Two display cards  91  and  92  showing two sections  9   a  and  9   b  on their external surface respectively are disposed with the window frames  323  and  324 , wherein a transverse bolt  93  is disposed at one end of the first display card  91 ; a transverse dowel hole  94  is disposed at one end of the second display card  92 ; a transverse hole  951  is disposed in the main body of the locking bar  95  so that the first display card  9  passes through the transverse hole  951  with the bolt  93 , and then the second display card  92  is inserted into the dowel hole  94 . A window opening  961  is provided at two sides of the transverse step portion  96  respectively for exposing the first section  9   a  or second section  9   b  of the display card. 
         [0067]    Accordingly, through observing whether the first section  9   a  or second section  9   b  is displayed in the window opening  961 , locking of the locking bar can be secured and application safety can be ensured. 
         [0068]    Therefore, referring to  FIGS. 20 ,  21 A, and  21 B, wherein  FIG. 21A  is an enlarged view of the part A of the  FIG. 20  showing that when the locking bar is inserted into the through and fixing hole of a side rail section, the second section  9   b  is displayed in the window opening  961 ;  FIG. 21B  is an enlarged view of the part B of  FIG. 20  showing that after the locking bar is withdrawn from the through and fixing hole of the side rail section, the first section  9   a  is exposed in the window opening  961 . Accordingly, whether the locking bar is locked and fixed can be confirmed from the outside of the window opening  961  and the safety can be enhanced. 
         [0069]    Therefore, in the improvement of an extension ladder structure in the present invention, since a fixing ejection bar is disposed at the upper end of the connection kit, an in-protruding encircling ring part is disposed at the upper tube opening of the side rail section, and a out-protruding protruding ring part is disposed at the lower end of the side rail section, which can prevent the side rail sections from departing from each other and enhance the fabrication convenience and controllability. With the setup of the unlocking bock and elastic support set, the applicable scope and reliability is increased. 
         [0070]    As described above, the extension ladder apparatus in the present invention certainly enhances appliance safety, and makes folding and using quick and convenient, which can improve the deficiencies of conventional ladders. Also, the present invention has not yet opened to public, it is then complied with the conditions of allowable patents. 
         [0071]    Although the above-mentioned embodiments of the present invention have been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Summary:
An extension ladder ( 1 ) comprises a plurality of ladder sections ( 2 ), connection kits ( 3 ) and transverse step beams ( 5 ). Each ladder section is a hollow rail having different caliber, which can be interconnected by telescoping with each other. A snap-fit mechanism is provided between the upper ladder section and the lower ladder section to make them not slip when the extension ladder is extended. The upper end of each ladder section is provided with a connection kit transverse provided. The upper end of the connection kit is provided with a fixed protuberant pin ( 300 ), an inside thereof is provided with a locking mechanism ( 4   b ). The locking mechanism ( 4   b ) is provided with a turning key ( 440 ). An outside of the connection kit is covered by the transverse step beam. When the upper connection kit and other lower connection kit are close to each other, the protuberant pin of the lower connection kit pushes the turning key in the connection kit so that the locking mechanism of the upper connection kit can be unlocked to make the upper ladder sections fall automatically in turn.