Patent Publication Number: US-6336521-B1

Title: Ladder levelling device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of application Ser. No. 09/296,289 filed Apr. 22, 1999, which is abandoned. 
    
    
     TECHNICAL FIELD 
     The invention relates to devices which permit a ladder to stand level on an uneven surface. 
     BACKGROUND ART 
     Various devices are known to assist in supporting a ladder on an uneven or sloped surface. Hodson U.S. Pat. No. 4,456,095 issued Jun. 26, 1984 discloses one such device. It provides a frame for attachment to the legs of the ladder, with a support arc which is adjustable through the frame to raise or lower the feet of the support arc to accommodate irregularities in the supporting surface. This device however does not adapt to ladders of different widths. Hodson U.S. Pat. No. 4,591,023 issued May 27, 1986 discloses a levelling device for ladders which may be used on ladders of differing widths, but it is difficult to adjust this device, since it is necessary to lift the ladder to unweight the lugs which grip the arcuate support bar in order to adjust the support bar. There is therefore a need for a ladder levelling device which is easily adjustable to different surfaces. There is further a need for a ladder levelling device is easily adjustable to different surfaces and which adapts to ladders of differing widths. 
     DISCLOSURE OF INVENTION 
     The invention therefore provides a device for supporting in a level manner on an uneven surface a ladder having parallel side rails joined by rungs, the device comprising: i) an arcuate support member provided at either end thereof with ground-engaging feet; and ii) two opposed bracket means for adjustably and releasably securing the side rails of the ladder to the arcuate support member; wherein the bracket means each comprise: iii) securement means adapted for attaching to a side rail of a ladder; iv) a locking plate provided with an aperture for slidably receiving the arcuate support member, pivotally mounted in the securement means for pivotal movement between a first binding and locking position and a second releasing and adjusting position; and v) means for biasing the locking plates to bind against the arcuate support member and thereby secure the bracket member against movement relative to the arcuate support member in the biasing direction when the locking plate is in the locking position. 
     In a further aspect, the invention provides a device for supporting in a level manner on an uneven surface a ladder having parallel side rails joined by rungs, the device comprising: i) an arcuate support member provided at either end thereof with ground-engaging feet; and ii) opposed bracket means for adjustably and releasably securing the side rails of the ladder to the arcuate support member; wherein the bracket means each comprise: iii) a cylindrical housing releasably held in said bracket means and provided with apertures to receive said arcuate support member in a direction perpendicular to the central axis of said cylindrical housing; iv) a locking plate extending through and pivotally mounted in the cylindrical housing; and v) means for biasing the locking plates to bind against the arcuate support member and thereby secure the bracket member against movement relative to the arcuate support member in the biassing direction. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     In drawings which disclose a preferred embodiment of the invention: 
     FIG. 1 is a front elevation of the lower part of a ladder and the levelling device of the invention; 
     FIG. 2 is a side elevation of the lower part of a ladder and the levelling device shown in FIG. 1; 
     FIG. 3 is a top view of the levelling device of the invention; 
     FIG. 4 is an exploded front elevation of the lower part of a ladder in phantom outline and the levelling device of the invention showing the fastening means; 
     FIG. 5 is a detail view of the bracket assembly and lever lock plates partly in cross-section along lines A—A of FIG. 6; 
     FIG. 6 is a side elevation of the levelling device shown in FIG. 4; 
     FIG. 7 is a perspective view partially cut away of the attachment bracket for a second embodiment of the invention used for ladders of fixed width; 
     FIG. 8 is a front elevation of the attachment bracket shown in FIG. 7 with the lower part of the ladder and the support arc shown in dotted outline; 
     FIG. 9 is a top view of the attachment bracket shown in FIG. 7; 
     FIG. 10 is a cross-section taken along lines C—C of FIG. 9; 
     FIG. 11 is a side elevation of the attachment bracket shown in FIG. 7 with the lower part of the ladder and the support arc shown in dotted outline; 
     FIG. 12 is a cross-section taken along lines B—B of FIG. 10.; 
     FIG. 13 is a detail in perspective view of a further embodiment of the attachment bracket; and 
     FIG. 14 is a detail in perspective view of yet a further embodiment of the attachment bracket. 
    
    
     BEST MODE(S) FOR CARRYING OUT THE INVENTION 
     With reference to the drawings, a ladder indicated at  10  has parallel side rails  12 ,  14  separated by a distance D, which is typically from 10 inches to 20 inches, and equally spaced rungs  16 . Ground surface  18  is sloped and therefore unstable for a standard ladder. The ladder levelling device  20  is secured to the lower ends of side rails  12 ,  14  by bracket assemblies  22 ,  24  which are fastened to the ladder by bolts  26 . It has a tubular support arch  28  which is preferably rectangular in cross-section, but may be other shapes in cross-section such as square, triangular or circular. The ends of support arch  28  are provided with feet  30  having rubber pads  32 . Feet  30  are preferably fixed on the ends of arch  28  but could be made to pivot either in the plane of the arch or universally. As shown in FIG. 1, the support arch has been rotated in direction E, from the position shown in phantom outline to the actual position shown, to permit the rungs  16  of the ladder  10  to be horizontal while nonetheless both feet  30  are flat on the ground surface  18 . Lever lock plates  34 , described in further detail below, permit the support arch  28  to be selectively locked in place or released for adjustment. 
     As shown in FIGS. 4 through 6, bracket assemblies  22 ,  24  each have a cylindrical housing  36  which has apertures  38 ,  40  through which the support arch  28  slides, and slots  42 ,  44  through which the lever lock plates  34  extend. Bracket assemblies  22 ,  24  have face plate  46  and side plates  48 . Side plates  48  have rounded lower edges (FIG.  1  and FIG.  4 ). Through bolts  50  secure side plates  48  against cylindrical housing  36 . Releasing bolts  50  allows the brackets to be adjusted to ladders of different widths, as described below. Lever lock plates  34  have a central aperture  52  through which support arch  28  can slide when lever lock plate  34  is perpendicular to support arch  28 . A spring  54  presses against lever lock plate  34 , which pivots about the end of plate  34  in slot  44 , and has sufficient range of motion in slot  42  so that lever lock plate  34  binds against support arch  28  when the lever lock plate  34  is freely released, preventing motion along the support arch  28  in the direction away from spring  54  (the direction in which the lever lock plate is biassed by spring  54 ), but not in the direction towards spring  54 . 
     Bracket assemblies  22 ,  24  are installed in opposing directions, thus preventing rotation of support arch  28  when both lever lock plates  34  are released. To adjust the device with the ladder  10  placed on uneven ground as in FIG. 1, the operator pushes down with one foot against the lever lock on the side with the higher terrain (arrow B) to disengage the lock and allow the support arch  28  to slide in direction E until the feet  30  are firmly on the ground and rungs  16  are horizontal. Lever lock plate  34  is then released and spring  54  forces it into binding engagement with support arch  28  to prevent movement. When weight is applied to the ladder  10 , the binding force of lever locking plates  34  against the support arch  28  increases to further prevent slippage. 
     To adjust the device  20  to ladders of different widths, bolts  50  are loosened, permitting cylindrical housings  36  to rotate within brackets  22 ,  24 . Brackets  22 ,  24  are then moved apart, or closer together the necessary distance so that when face plates  46  are secured to the legs  12 ,  14  of ladder  10 , the radial portions  35  of lever lock plates  34  lie along the radius of support arch  28 . Bolts  50  are then re-tightened so that cylindrical housing  36  is secured within brackets  22 ,  24  and the lower edge of side plate  48  bears down against cylindrical housing  36  when weight is placed on ladder  10 . 
     FIGS. 7 through 12 illustrate an embodiment of the invention which is not adjustable to ladders of different widths. Levelling device  70  has support arch  72 , two brackets  74  and two lever lock plates  76 . Bracket  74  has a face plate  78  which is fastened to lower leg  14  of ladder  10 . Support arch  72  extends through opening  80  in bracket  74  and through opening  82  in lever lock plate  76 . The upper end  77  of lever lock plate  76  extends through and pivots in slot  84  in face plate  78 . Spring  90  is located around support arch  72  extending between bracket  74  and lever lock plate  76 . 
     In this embodiment the brackets  74  are configured so that when face plates  78  are secured to the legs  12 ,  14  of ladder  10 , the radial portions  75  of lever lock plates  76  lie along the radius of support arch  72 . Adjustment of the device to uneven surfaces is accomplished in the same way as the previous embodiment. Bracket assemblies  74  are installed in opposing directions, thus preventing rotation of support arch  72  when both lever lock plates  76  are released, since springs  90  cause lever lock plates to bind against support arch  72 . To adjust the device with the ladder  10  placed on uneven ground, the operator pushes down with one foot against the lever lock  76  on the side with the higher terrain to disengage the lock  76  from support arch  72  and allow the ladder to slide around the support arch  72  until the feet  30  are firmly on the ground and rungs  16  are horizontal. The lever lock plate  76  is then released and spring  90  forces it into binding engagement with support arch  72  to prevent movement in the direction in which the lever lock plate is biassed by spring  90 . When weight is applied to the ladder  10 , again the binding force of lever locking plates  76  against the support arch  72  increases to further prevent slippage. 
     FIGS. 13 and 14 illustrate alternative embodiments of brackets  22 ,  24  herein housing  36  is non-cylindrical. In FIG. 13, housing  136  is square or rectangular in cross-section. The ends of side rails  12 ,  14  are pivotally secured to housing  136  by pins  138 . The support arch  28  slides through aperture  140 . The lever lock plate  144  extends through slot  142 . A spring (not shown) presses against lever lock plate  144  as in the previous embodiment. In FIG. 14, housing  236  is a solid plastic block, hexagonal in cross-section. The ends of side rails  12 ,  14  are pivotally secured to housing  236  by pins  238  and are radiused at  112  to fit and slide in correspondingly radiused shoulders  114  in housing  236 . The support arch  28  slides through aperture  240 . The lever lock plate (not shown) extends through slot  242 . A spring to press against lever lock plate, as in the previous embodiments, is located in chamber  244 . 
     As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.