Abstract:
The pull-out sections of folding ladders must be locked on the guiding elements pertaining thereto for ladder use and should also be easily unlocked. A locking bolt used to fix the elements can be axially and manually moved inside a guide element against an adjustment spring to engage a hollow profile section of a rung on the pull-out sections. A lockable guide element with a bayonet fitting is included on the ladder element to enable easy locking and unlocking.

Description:
FIELD OF THE INVENTION 
     The invention relates to a folding ladder, the ladder elements of which can be telescopically extended by means of pull-out sections movable thereon, whereby the pull-out sections can be fixed by means of a locking mechanism in several positions on the respectively associated ladder element on one of its rungs—constructed as a hollow-profile section—which locking mechanism has a locking bolt, which can be guided into the hollow-profile section of the rung under the action of an adjusting spring and handle and can be locked in this position, and whereby furthermore the locking bolt fixed on the handle is axially movably supported in a guide element mounted on the ladder element. 
     BACKGROUND OF THE INVENTION 
     Such a folding ladder is already known from the Offenlegungsschrift DE 44 03 001 A1. The guide element for the locking bolt is in this design constructed on a flange piece, which is riveted or screwed to the respective ladder element. 
     The purpose of the invention is to design a folding ladder of the type described in detail above in such a manner that such a guide element can be secured in a simple manner on the provided ladder element without having to use an expensive rivet or screw connection. However, such a mounting is at the same time also supposed to offer suitable permanent security against a self-release of the connection. 
     SUMMARY OF THE INVENTION 
     The purpose is attained according to the invention in such a manner that the guide element can be fastened on the ladder element by means of a bayonet fitting. A mounting of the guide element designed in this manner can be created with one single manipulation. The elements of the bayonet fitting can be co-provided without any difficulties and additional expense during the manufacture of the guide element and of the ladder element, as will become apparent by the details identified more closely below. 
     Thus, it is for example advantageous when the bayonet fitting consists of a guide flange provided on the front side on the guide element and a counter flange, which concentrically surrounds in the ladder element a guide hold for the guide element, whereby the guide flange can have at least three holding element, which can be guided through surface-complementary holding recesses of the counter flange, and, after an axial rotation of the guide flange against the counter flange, rests on its front surface not facing the guide element, whereby an annular flange of the guide element, abutting the ladder element, determines the axial introduction of the guide flange into the ladder element. 
     The counter flange consists thus alone of the receiving recesses, which enlarge the guide hole in the ladder element radially outwardly, and it is thus not a separate structural part, but instead merely a defined surface section of the ladder element. During the introduction of the guide hole into the web of the ladder element, it is automatically and without additional input manufactured at the same time. 
     The guide flange does not present an obstacle during the movement of the pull-out section on the ladder element, when, as this is common, the web of the pull-out section is guided spaced from the web of the ladder element, which as a rule is already desired for different reasons. Thus, the ends of the rungs project at all times slightly over the web of the pull-out section, to which it is in most cases flanged or connected in a different manner so that this projection requires already a certain spacing between the webs. The ladder elements are therefore equipped with guide edges, which determine the spacing between the respective pull-out sections. 
     It is advantageous when a position-securing lock is available for the bayonet lock, for example, an eyelet piece with an axis-parallel first pin hole for a locking pin is provided on the circumference of the guide element, which locking pin is driven into a second pin hole in the ladder element, which second pin hole is axially aligned with the first one. The second pin hole is designed such that the locking pin can only be driven in when a secure bayonet fitting has been created, which means, when the guide element, after the introduction of the guide flange into the counter flange, has been rotated accordingly. 
     In detail, the locking bolt is best constructed pipe-shaped and connected, preferably pinned, to the handle so that it can be changed through a direct manual operation between its axial positions corresponding to locking or unlocking. Furthermore, it is possible to provide a lock against rotation between the guide element and the locking bolt (and thus also the handle). 
     However, it is particularly advantageous thereby when the lock against rotation is not complete and unreleasable but instead permits a—however, limited—rotation of the locking bolt (and this only in its position when it is removed from the rungs). It can thereby advantageously consist of a crosspin fastened in the guide element and an axis-parallel guide groove in the locking bolt, through which guide groove extends the crosspin. The guide groove has in a preferred embodiment a preferably acute-angled laterally bent section. Such an arrangement offers the advantage that the locking bolt, when it is unlocked, can be moved by a slight rotation into a stable unlocking position so that it need not be held during the adjustment of the respective pull-out section. 
     An arrangement has been created with the invention, in which the guide element can be mounted quickly and safely on the ladder element, and, moreover, in which care is taken in a simple manner that the unlocking of the locking bolt can be transitioned into a stable position ready for use so that the locking bolt loaded by the adjusting spring on the one hand does not hinder the adjustment of the associated pull-out section and on the other hand does not need to be manually held during such an adjustment. The folding ladder can therefore be manufactured expediently and can be handled comfortably. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be discussed in greater detail hereinafter in connection with one exemplary embodiment and the drawings, in which: 
     FIG. 1 shows a folding ladder in an isometric view in its position of use, 
     FIG. 2 shows an enlarged detail A of FIG. 1 with a locked pull-out section, and 
     FIG. 3 shows an exploded view of the detail A of the individual parts of the locking mechanism, all in a three-dimensional illustration, and 
     FIG. 4 a  is a side view (FIG. 4 a ) of the guide element of the invention, and 
     FIG. 4 b  is a cross-sectional view B—B of FIG. 4 a , and 
     FIGS. 5 and 6 are each a side view of a locking bolt and a handle according to the invention, all in schematically simplified and differently enlarged illustrations. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A folding ladder according to the invention consists in accordance with FIG. 1 first of all of ladder elements  1  with bases  11 . Pull-out sections  2  are movable on the ladder elements  1 , which pull-out sections  2  are connected with one another in pairs by joints  21  in the exemplary embodiment and form together with the ladder elements  1  a folding ladder. The ladder elements  1  and the pull-out sections  2  permit various operating lengths of the folding ladder due to their reciprocal telescopic movement. The pull-out sections  2  are connected with one another in pairs by rungs  22  to form extension pieces  20 ; also the ladder elements  1  are assembled in a similar manner in pairs by rungs  22  to form ladder sections  10 . The ladder sections  10  and extension pieces  20  of the folding ladder illustrated in the position of use in FIG. 1 are folded together and moved for transport and storage. 
     To secure the—extended—position of use of the folding ladder of FIG. 1, a locking mechanism  3  is provided on each pairing of a ladder element  1  and a pull-out section  2 , as it can be easily recognized in the enlarged illustration of FIG. 2; the details of such a locking mechanism are shown in FIG.  3 . 
     The pull-out sections  2  are thereby locked on the ladder element  1  by a manually axially movable locking bolt  31 , which can be moved into the cross section of a rung  22  designed with a hollow-profile section and can also again be pulled out of this position. Both the locked and also the unlocked position of the locking bolt  31  are designed as stable detained positions as will be shown later on. The details are shown in FIG.  3 . 
     The essentially pipe-shaped locking bolt  31  is axially and—to a limited degree—also rotationally movable in a guide element  32 . The guide element  32  has for this purpose (FIG. 4 b ) a bearing hole  32   a.  A crosspin  32   b  extends through axis-parallel guide grooves  31   a  (FIG. 5) in the locking bolt  31 , which crosspin, as indicated in FIG. 4 a,  is pinned together with the guide element  32  by means of pin holes  32   c,  after the locking bolt  31  has been introduced into said guide hole. The axial mobility of the locking bolt  31  is thus determined by the length of the guide grooves  31   a . In the place of one single cross pin  32   b  extending through the entire locking bolt  31  it is also possible to utilize one or two short crosspins  32   b , which are driven merely into the area of the guide groove  31   a . The guide groove  31   a  and the crosspin  32   b  thus form a lock against rotation  31   a ;  32   b  of the locking bolt  31 . 
     A front end of the locking bolt  31  is at least partially closed on its end directed into the rungs  22  by a front wall  32   c , which is flanged, for example, to its hollow-cylindrical body  31   b ; the front wall  32   c  is designed somewhat curved (FIG. 5) so that guiding the locking bolt  31  into the hollow-profile section of a rung  22  is made easier, and serves as an axial fixed bearing for an adjusting spring  33  sunk into the locking bolt  31  (FIG.  3 ), which adjusting spring loads the locking bolt  31  in the direction of a lock position of the pull-out section  2 ; this position is thus the position of the locking mechanism  3  which is the regular and stable position without interference. 
     The locking bolt  31  is furthermore fixedly connected to a handle  34 , here by means of a connecting pin  34   a  (FIG.  3 ). The adjusting spring  33  at the other end rests on a further fixed bearing of the handle  34 ; the handle  34  has for this purpose (FIG. 6) a spring bearing  34   b  for the adjusting spring  33  designed as a cylindrical pressure spring. The spring bearing  34   b  is designed as an axially fixed cylindrical stamped hub, which furthermore has, directed front-sidedly onto the adjusting spring  33 , an annular groove  34   c,  into which the locking bolt  31  can be axially received; a cross bore  34   d  (FIG. 6) provided in this area is used to drive in the connecting pin  34   a.  Thus, the locking bolt  31  can be moved with a handle piece  34   e  of the handle  34 . 
     The guide grooves  31   a  are at their end not facing the handle  34  bent at an acute angle each to form a short bent section  31   d.  When the locking bolt  31  is pulled back by means of the handle  34  into its position unlocked from the pull-out section  2 , it can be slightly rotated so that the crosspin  32   b  moves into the area of the bent section  31   d.  This unlocked position is stable under the influence of the adjusting spring  33  because the locking bolt  31  cannot “by itself” move back into the axis-parallel area of the guide groove  31   a  but only with the help of the handle  34  after a short movement opposite to the action of the adjusting spring  33 , by which the acute wedges  31   e  (FIG. 5) constructed by the bent sections  31   d  can be overcome. 
     The ladder element  1  (FIGS. 2,  3 ) is approximately U-shaped in cross section with a web  1   a  between two bent belts  1   b.  FIG. 3 easily shows that a guide hole  13  for the guide element  32 , which guide hole  13  is provided in the web  1   a  of the ladder element  1 , does not have a closed circular-cylindrical contour. Instead same is radially enlarged on its circumference around essentially rectangular holding recesses  14 . Thus,—in the exemplary embodiment, four—holding recesses  14  form (together with the surface sections  15  enclosed by them and edging the guide holes  13 ) a counter flange G for a guide flange F defining the guide element  32  on its front side, which guide flange (FIG. 4 a ) consists of a flange ring  32   d  and of several (here four) holding elements  32   e  radially following said flange ring. The holding elements  32   e  are approximately surface-congruent with the holding recesses  14  in such a manner that the guide flange F can be placed with its holding elements  32   e  comfortably through the counter flange G with its holding recesses  14 . It then rests on the inside of the web  1   a  approximately on the counter flange G and can be rotated such that its holding elements  32   e  move out of the area of the holding recesses  14  and rest on the surface pieces  15 . The bayonet fitting F, G formed out of the guide flange F and the counter flange G is locked in this position. 
     The guide flange F cannot extend at a random distance through the counter flange G because its axial mobility is limited in this direction by an annular flange  32   f  so that the surfaces of the holding elements  32   e  and of the surface sections  15 , which surfaces face one another, are closely adjacent. The bayonet fitting F, G can in this manner be realized with relatively little axial clearance, and the guide flange F remains spaced from the pull-out section  2  so that same, when the locking bolt  31  is released from the rungs  22 , is freely movable against the ladder element  1 . 
     The guide element  32  is secured in a simple manner against radial rotation. A radial eyelet piece  32   g  is for this purpose constructed on the guide element  32  (FIG. 4 a ), which eyelet piece has a first pin hole  32   h,  which is axis-parallel with respect to the guide element  32 . A second pin hole in the web  1   a  (not shown in the drawing) is arranged in such a manner that a locking pin can be driven into these two pin holes when the bayonet fitting F, G is rotated into its locking angular position. Thus, the bayonet fitting F, G cannot be released. In spite of this, it is possible to exchange or remove the guide element  32  without difficulty when needed.