Abstract:
A trestle ladder includes adjustable leg extensions to accommodate uneven and irregular surfaces while maintaining the ladder in proper vertical and horizontal orientation. A binding clamp is employed to retain the extension in the desired position and auxiliary rungs are provided for use when the extension of the legs is sufficient to require them.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to ladders in general and particularly to trestle ladders which are generally recognized as two ladders interconnected in an inverted &#34;V&#34; configuration. The invention is concerned with providing a trestle ladder with the capability of accommodating irregular or uneven surfaces at each of its legs while maintaining the body of the ladder in proper horizontal and vertical orientation to safety support a workman and his equipment thereon. 
     SUMMARY OF THE INVENTION 
     In utilizing ladders in general, and trestle ladders in particular, workmen are frequently confronted with the need to support the individual legs or rails of the ladder on uneven or irregular surfaces. Painters&#39; ladders, for example, are frequently positioned on various types of staircases and these present particularly graphic examples of such uneven support surfaces. Staircases with landings and circular staircases present even more significant problems to the user of the ladder when access to vertical walls adjacent the staircases is desired. In some instances, it is necessary to provide adjustment for each of the four legs of a trestle ladder to accommodate a different elevation for a supporting surface. Accordingly, it is a primary object of the invention to provide and facilitate adjustment of the legs or rails of a trestle ladder to accommodate such uneven or irregular supporting surfaces upon which the ladder is positioned. 
     In those instances where substantial extension adjustment of the legs is necessary, it is also contemplated within the field of this invention that supplemental rungs may be provided in the extension area in order that the workman may climb the ladder without an inordinate long distance between the support surface and the first regular rung of the ladder. It is therefore a further object of the invention to provide supplementary or auxiliary rungs selectively securable to the ladder rails, rungs, or extensions thereof to effectively lengthen the operational range of the ladder. 
    
    
     Other objects and advantages will become obvious from a consideration of the following description and drawings wherein like numerals represent like element throughout the several views. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective illustration of the preferred embodiment of the trestle ladder of the invention; 
     FIG. 2 is an enlarged perspective illustration of the preferred embodiment of the binding device used with the invention; 
     FIG. 3 is a sectional fragmentary cross-sectional view of the binding mechanism of FIG. 2; 
     FIG. 4 is a fragmentary cross-sectional view of an alternative embodiment of the binding device; 
     FIG. 5 is a perspective view of the ladder with an auxiliary ladder in place; 
     FIG. 6 is a perspective view of a ladder with the extensions extended and auxiliary rungs carried therewith in place; 
     FIG. 7 is a fragmentary perspective view of a detail of the auxiliary rungs illustrated in FIG. 6; and 
     FIG. 8 is a perspective view of a trestle ladder having telescopic extensions and additional rungs in place in the extension area. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIG. 1 of the drawings, a preferred embodiment of a trestle ladder is illustrated as positioned on a circular staircase with each of the four legs supported on a surface of different elevation. As illustrated, the ladder includes conventional uprights or rails 10 separated by vertically spaced rungs 18. Two such ladders are shown with their rails intersecting at the upper extremity to define an inverted V-shaped trestle. Each rail 10 consists of a generally rectangular hollow tube within which is disposed a telescoping extension 12. The extension may be of any suitable length but generally should have sufficient extension capability to accommodate any reasonable need on the part of the user without rendering the ladder unstable or unsafe. Each rail includes a binding means generally illustrated at 14 which will be described more fully hereinafter. 
     Each extension element includes an elongated transverse slot generally illustrated at 16 extending substantially throughout the length of the extension element. 
     Referring now more specifically to FIGS. 3 and 4 of the drawings, the binding means shown generally at 14 for securing the extension element in the desired position is illustrated. A binding bolt 30 includes an enlarged head 32 and a threaded shank. The rail 10 is provided with a pair of aligned openings 22 and 24 extending through the walls thereof and the binding bolt is positioned within those openings and preferably with the enlarged head area 32 on the inside of the rail. The binding mechanism is operated by means of a binding wheel 46 threadably attached to the binding bolt 30 in a manner whereby compressive pressure may be applied to the rail 10 and the extension 12 to secure the extension element in the desired position. The binding bolt may include flat shoulders 34 to preclude rotation. 
     As illustrated in FIG. 2 of the drawings, the binding means contemplates an enlarged opening 22 on the outside face of the rail 10 within which a flexible binding disk 36 is positioned. The disk is of generally circular configuration with a central opening designed to encircle the shank of the binding bolt 30. A spring plate 38 is secured to the rail 10 by means of a pair of suitable fasteners 50 which also extend through the side walls of the rail 10 and a pair of washers 48. The spring plate includes a central opening through which the binding bolt passes and the plate is configured to overlie the binding disk 36 positioned within the enlarged opening 22. The plate retains the binding disk in position and simultaneously supports the outer shank of the binding bolt in correct axial alignment with the rail 10. 
     A washer assembly includes an enlarged washer 40, a spring or wave washer 42 and a compression washer 44 between the outer face of the spring plate 38 and the innermost extremity of the threaded binding wheel 46. In the assembled relationship, as illustrated in FIGS. 2 and 3, the binding bolt extends through the leg 10 and is arranged in registry through the slot 16 to permit the application of binding forces by manipulation of the binding wheel 46. 
     Thus, it may be seen that the various legs of the ladder may be extended by the selective manipulation of the binding means and the positioning of the extension elements to accommodate virtually any elevational situation with which each leg is confronted. 
     In order to provide for easy ascent and to avoid the extended rung distance illustrated in FIG. 1 between the bottom rung of the ladder per se and the surface or surfaces upon which the extension legs are mounted, auxiliary steps are provided. 
     As best seen in FIGS. 5, 6, 7 and 8 of the drawings, the auxiliary steps may take any suitable form and as illustrated in the FIG. 5 embodiment include a supplemental pair of uprights 60 provided with hook elements 70 at the upper end configured to engage and be supported by a convenient rung 18 in the ladder body. Any number of transverse auxiliary rungs 68 may be provided and a ledge rung 7 is positioned at the lowermost extremity of the auxiliary ladder portion. The ledge portion includes inwardly directed flanges 74 which are designed to embrace the outer faces of the extensions 12 in order to secure the auxiliary ladder against lateral displacement. 
     The rung spacing in the auxiliary ladder is generally equivalent to the rung spacing in the primary ladder, thus facilitating ascent and descent by the workman. 
     FIGS. 6, 7 and 8 of the drawings illustrate a modified embodiment of the auxiliary rung arrangement and in this example, the auxiliary rungs 18 are configured to extend between and through the extension elements 12 in vertically adjustable position within the slots 16. Retention pins 20 as seen best in FIG. 7 insure the lateral position of the auxiliary rungs 18. 
     Vertical positioning of the auxiliary rungs is controlled by a flexible support element in the form of a pair of chains 78. The rungs are secured in a predetermined spaced relationship along the chains 78 so that upon extension, as many rungs as may be needed may be employed to accommodate the extension elements. If desired, a third chain 80 may be utilized to secure the rungs in the collapsed condition as best seen in FIG. 6. An appropriate retention hook 82 on the lowermost rung 84 will enable the rungs to be moved into a stacked or storage position. As seen in FIG. 8, the chains 78 supporting the rungs are attached to the lowermost rung in the ladder 84 and are moved into a flaccid condition when the rungs are in the retained stacked condition seen in FIG. 6. 
     In operation, the workman will position the ladder for access to a wall or other object on which work is to be performed and by the manipulation of the binding wheels 46 on each of the several legs of the trestle ladder, adjustment of the extension elements 12 to whatever degree may be required in order to accommodate the irregular surface while maintaining the ladder in a stable vertically and horizontally oriented position. Upon achieving such extension, the binding wheel is tightened by rotating the same until sufficient compressive pressure is applied to the binding mechanism to support the extension element in the desired position. This procedure is repeated for each leg where adjustment is necessary. 
     The auxiliary legs may then be placed in position by hanging the hooks 70 over a convenient rung of the ladder to permit the embodiment illustrated in FIG. 5 to extend to a position near the supporting surface while simultaneously providing appropriate rung spacing for a safe ascent. 
     In the embodiment of FIGS. 6-8, the retention chain 80 is released and the several rungs are allowed to move vertically by gravity within the slots of the extension elements to a position where the chains are in a supporting position with the proper rung spacing determined by the number of links in each chain between successive rings. 
     It will be obvious that many variations of the binding means and the auxiliary rung arrangements may be employed within the scope of the appended claims and those arrangements illustrated in the drawings are to be considered as exemplary of operational embodiments and not of restriction.