Patent Abstract:
An extension ladder with improved mechanism includes a plurality of ladder sections, connection kits, locking mechanism, and transverse step portions; wherein each ladder section is a hollow rung, and the caliber of the rung becomes smaller when it is in a higher location. The upper ladder section and lower ladder section can be interconnected and fit each other; said connection kits are horizontally provided in the upper end of said ladder section. The internal part of said connection kit is provided with a locking mechanism to snap-fit into the through hole of said ladder section to secure the extension between each ladder section. The outside of said locking mechanism is covered by the transverse step portion, by the improved locking mechanism, the extension ladder can be assembled easily and firmly for providing superior safety to people, even when an external force is applied.

Full Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an extension ladder, and more particularly to an extension ladder, which can be assembled easily and firmly for providing superior safety to people. 
     2. Description of the Prior Art 
     It is noticed that 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. 
     A conventional stepladder  800 , as shown in  FIG. 1 , is assembled by two ladder units having a pair of footpads respectively installed at the lower end of the ladder section 811 to prevent slippage, and is provided with parallel spaced step plates 821 therein. The stepladder appears as an A-frame ladder during usage. 
     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. 
     Accordingly, the present invention has been invented to solve the above-mentioned problems occurred in the prior art. 
     SUMMARY OF THE INVENTION 
     Therefore, an object of the present invention is to provide an extension ladder with improved structure, which is composed of multi-segment ladder sections, connection kits, locking mechanism, and transverse step portions, providing ease and convenience to fold and take along, store, or unfold and use. 
     According to the extension ladder of present invention, the locking mechanism has further improvements, such that after the extension ladder is extended for people&#39;s uses, the ladder would not loose and cause danger. So as to confirm user&#39;s security, this is the second object of present invention. 
     In the extension ladder of the present invention, the connection kits and hollow rungs are locked in place, and then stuck and fastened. This prevents these components from loose and disattachment, which serves as another object of the present invention. 
     According to the extension ladder of present invention, the locking mechanism provided inside the connection kits are wrapped by transverse step beams, and can avoid the damage of rust, which serves as further object of the present invention. 
     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 
         FIG. 1  is a three-dimensional view of the conventional extension ladder; 
         FIG. 2  is a front view showing the present invention before use; 
         FIG. 3  is a front view showing the present invention has been extended for use; 
         FIG. 3A  is a sectional view showing the magnified “A” portion of  FIG. 3 . 
         FIG. 4  is a three-dimensional exploded view showing the first ladder section and transverse step beam of the present invention; 
         FIG. 5  is a three-dimensional exploded view showing the ladder section and transverse step beam in the present invention except the first ladder section; 
         FIG. 6  is a three-dimensional assembly view showing the assembly of the construction of ladder section and transverse step beam of the present invention; 
         FIG. 7  is a sectional view showing the assembly of the construction of the ladder section and transverse step beam of the present invention; 
         FIG. 8  is a sectional view showing the embodiment of present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The extension ladder with improved structure of the present invention, as shown in  FIG. 2 , wherein the extension ladder  1  is foldable, or unfoldable as shown in  FIG. 3 , includes a plurality of ladder sections, connection kits  3 , and transverse step beams  5 . The stepladder appears as a rising ladder when it is unfolded and used, and can be folded by fitting the ladder sections with different calibers one another. 
     Referring to  FIGS. 4 ,  5 , and  6 , such ladder section  2  fits each other by providing similar-shaped but smaller internal ladder section  2   a . Said cannular-shaped ladder section  2  is provided with a snap-fit hole  21  and an orientation hole  22  on its upper end, and provided with a through hole  23  on its lower end. Also, an outward extruded blocking ring  25  is provided on the upper end of said through hole  23  at proper height, and on the surface of said ladder section  2 , an inward protruding furrow ring  26  which is extruded inward to the interior of ladder section  2  is formed at a position properly apart from said outward blocking ring  25 . (Please refer to  FIG. 3 .). 
     The connection kit  3  has a ringlike covering part  31  and a pivotal joint  32 . Said ringlike covering part  31  is horizontally provided on the upper end of the ladder section, and affixed to the ladder section by fastening a screw therein. A plurality of orientation tenons  34  are provided on the inside of said connection kit for engaging with the snap-fit hole  21  of said ladder section, so that the connection kit can be assembled with the ladder section quickly. Also, the inside wall of said connection kit is provided with an adhesive channel  35 , wherein the adhesive are infused into the adhesive-infusing hole  36  on its one end so that the connection kit can be firmly adhered to the ladder section  2 . Moreover, a via hole  30  is provided on the connection kit for interconnection with the internal channel  37  of said pivotal joint  32 . 
     Said pivotal joint  32  is integrally molded with the ringlike covering part  31 , and comprises two vertical side plates  321 ,  322  having a channel  37  between them, so as to hold a locking mechanism  4 ; on the inner surface of vertical side plates  321 ,  322 , there are a pair of opposite vertical grooves  38  and two concaves  391 ,  392 , wherein, said vertical grooves  38  are formed at the position near the end of side plates  321 ,  322 ; and one of said concave  391  is formed on each of the upper edge of said side plates  321 ,  322 , while the other concave  392  is formed on each of the lower edge of said side plates  321 ,  322 . 
     The locking mechanism  4  comprises a base locking construction  4   a  and a plurality of upper locking constructions  4   b . As shown in  FIG. 5 , each of the upper locking construction  4   b  includes a locking gate  41 , a locking bar  42 , a spring  43 , a turning key  44  and a passive key  45 ; wherein, said locking gate  41  has a fixing plate  410  for inserting into the vertical grooves  38  formed on said plates  321 ,  322 , at the center of the fixing plate  410 , there is a sleeve  413  having an open end facing said via hole  30 . 
     Said locking bar  42  is a cylindric rod, its one end passes through said via hole  30  and said orientation hole  22  formed in said ladder section  2 , while the other end can be inserted into said sleeve  413 . There is a spring  43  installed between said locking bar  42  and said sleeve  413 , then said locking bar  42  would return to its original position by the force of spring  43 . On the locking bar  42 , there are two mounting grooves to form sectional axes  421 ,  422  having radius smaller than that of locking bar  42 . 
     Said turning key  44  is formed with a first panel  441  and a second panel being connected in V shape. The upper end of the first panel  441  is formed with a pair of separate arms  443 , the space between the separate arms  443  can be used for mounting with the sectional axis  422  of said locking bar  42 . the connection portion of said first panel  441  and second panel  442  then is formed with a pair of locking pawl  444  extruded outward from side surfaces. By mounting the locking pawl  444  into said concave  392  formed on the side plates  321 ,  322  of said ringlike covering part  31 , then when the second panel  442  of said turning rod  44  is pushed upward from the lower position, then the locking bar  42  can be moved back and fro by using the locking pawl  444  as axis. 
     Said passive key  45  has a pushing plate  451  having locking pawls  452  extruded outward from its side ends. Similarly, the locking pawl  452  can be mounted into said concave  391  formed on the side plates  321 ,  322  of said ringlike covering part  31 , in addition, the lower end of said pushing plate  451  is formed with a pair of separate feet  453 , the space between the separate feet  453  can be used for mounting with the section axis  421  of said locking bar  42 . When the locking bar  42  is horizontally removed, the passive key  45  then can swing to 90 degrees, such that the pushing plate  451  becomes perpendicular to the side plates  321 ,  322 . 
     When the upper locking construction  4   b  is installed in the pivotal joint  32 , the transverse step beam  5  is then provided onto the outside of said pivotal joint  32 , on lower face of said transverse step beam  5 , there is a hole  51  formed at a position opposite to the second panel  442  of said turning key  44 , while a second hole  52  is formed at a position opposite to the said passive key  45 , so as to let said pushing plate  451  to extrude upward. 
     Please refer to  FIG. 4 , the base locking construction  4   a  has a spring  43 , a turning key  44  and a passive key  45  which are identical in structure of the same elements of said upper locking construction  4   b . The structures of the spring  43 , the turning key  44  and the passive key  45  are not repeated herewith. While the structural differences between the base locking construction  4   a  and the upper locking construction  4   b  are then stated as follows: 
     As shown in  FIG. 4  and  FIG. 5 , the locking bar  42  of the base locking construction  4   a  not only has a pair of section axes  421 ,  422  for mounting the corresponding elements of said turning key  44  and passive key  45 , but also has a narrow sleeve  423  formed at the section for mounting spring  43  such that a C-shaped clamp  424  can be fixed inside the sleeve  423 . And there is a clamping part  425  formed at one end of the locking bar  42 . At the position of upper locking construction  4   b  for locating locking gate  41 , there is a vertical fixing plate  46  having a via hole  461  at its center part to be inserted into the vertical  38  formed on said plates  321 ,  322  of said pivotal joint  32 . 
     In addition, there is installed with a manual control button  47  and a connection rod  48 . At the upper end of said manual control button  47 , there is a guiding plate  471  having horizontal groove  472  formed at its lower end, such that the guiding plate  471  can be pushed into the shifting hole  53  formed on the lower side of transverse step beam  5 , and the manual control button  47  cab be mounted onto the shifting hole  53  to move to and fro on the shifting hole  53 . 
     Furthermore, the central part of manual control button  47  has a furrow  473 , so as to connect the manual control button  47  with one end of said connection rod  48  by a pin  474 . Said connection rod  48  has the front end penetrates the via hole  461  of said fixing plate  46 , and then connect to the clamping part  425  of locking bar  42  by a pin  426 . The other end of said connection rod is bent downward, so as to penetrate the shifting hole  53  of said transverse step beam  5  and extend into the furrow  473  of said manual control button  47  to connect together with it. 
     In addition, the lower end of the ladder section  2   a  is provided with a conical sleeve-shaped buffering device  6 . The upper end of said buffering device, by means of a hooked tip  61  provided thereon, is affixed to the opening  24  of said ladder section  2   a . The lower-end outside of said buffering device is provided with an elastic seal ring  62  to increase friction when it contacts with the inside of said rail and reduce noise. When the ladder section  2   a  is pulled upward, the ladder can be pull extensively, and when the ladder section  2   a  is pushed downward, the elastic seal ring  62  then shall generate a force against the ladder section  2  to slow down the downward movement of ladder. Also, the internal part of said buffering device  6  can be provided with a mylar with its surface having a hole, which allows airs to enter the cavity of said mylar when the buffering device  6  moves upward and downward, and thus enhances the cushion effect. 
     When the assembling has been completed, as shown in the figures, the bottom of the ladder section  2  is provided with a buffering device  6  and an elastic seal ring  62  to increase the friction between the ladder section and the inside wall of internal ladder section, so that the purpose of slowing down the descending can be achieved. Also, the connection kit and the upper end of said ladder section are provided with adhesive channel  35  to infuse the adhesive therein, so that the connection kit and the ladder section can be adhered to each other. Accordingly, the present extension ladder is assembled integrally and securely. Moreover, the provided locking mechanism  4  is fully covered by the connection kit  3  and the transverse step portion  5 , which not only makes it easy and convenient to control the locking mechanism, but also prevents the damage caused by any foreign object. 
     When the internal ladder section  2   a  and ladder section  2  are relatively extended, the blocking ring  25  having a larger caliber on the outside of said internal ladder section  2   a  is firmly against the inwardly protruding furrow ring  26  and to be fixed at its position (as shown in  FIG. 3A ) in the external ladder section  2 . Meanwhile, the through hole on the lower end of said internal ladder section  2   a  is directly located in a route having the orientation hole  22  of said external ladder section, via hole  30  of said connection kit, and locking bar  42 , which enables the locking bar  42  to be inserted in the fixed position smoothly when it is moved forward. 
     In using the present invention, as shown in  FIG. 7  and  FIG. 8 , the manual control button  47  of said base locking construction  4   a  is moved to the central part of said transverse step beam  5 , then the connection rod  48  pulls the locking bar  42  out of the orientation hole  22  of said ladder section  2 , when the locking bar  42  is moving, said turning key  44  then is pushed to rotate in clockwise direction and said passive key  45  is pushed to rotate in counter-clockwise direction, finally, the pushing plate  451  of said passive key  45  extends outward from the second via hole  52  of said transverse step beam  5 . 
     Then, the pushing plate  451  of said passive key  45  passes through the via hole  51   a  of second transverse step beam  5   a , and then pushes the second panel  442   a  of the turning key  44   a  inside the second transverse step beam  5   a , then the turning key  44   a  rotates clockwisely. At the same time, the turning key  44   a  pushes the locking bar  42   a  inside the second transverse step beam  5   a  moves out of the orientation hole  22   a  of said second ladder section  2 . The ladder becomes unlocked and the second ladder  2   a  then can be pulled upward until the passing hole  23   a  of said second ladder section  2   a  is opposite to the via hole  30  of said base ladder section  2   a , and then the locking bar  42   a  will be inserted into said passing hole  23   a  by the action of spring  43   a , the second ladder section  2   a  therefore obtains an extended condition. In addition, when the locking bar  42   a  moves out of the orientation hole  22   a  of said second ladder section  2   a , the passive key  45   a  installed on the second transverse step beam  5   a  then rotates counter-clockwisely, its pushing plate  451   a  then extends outward and continuously pushes the turning key inside the third transverse step beam, such that the locking constructions of other levels are unlocked. 
     When the locking bar  42  returns to locking position, and the pushing plate  451  of passive key  45  does not completely return to horizontal locking position. If the transverse step beam  5  is mistakenly stepped or pressed downward, the locking bar  42  will be pushed into the ladder section and rigidly locking the construction. Therefore, the present invention has very good functions of security. 
     Accordingly, the extension ladder with improved structure in the present invention are integrally assembled securely by providing a snap-fit hole  21 , orientation tenon  34 , and blocking ring  25  between the connection kit  3  and ladder section  2  for quick and correct orientation. Also, the ladder assembly can be securely by providing with the adhesive channel  35 . Furthermore, the locking mechanism  4  is provided on the connection kit  3  for making the assembling more convenient, the control of the ladder easier, and prolonging ladder life. 
     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. 
     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.

Technology Classification (CPC): 4