Patent Publication Number: US-2005115766-A1

Title: Anti-slip attachment for ladders

Description:
RELATED APPLICATIONS  
      This application claims the benefit of U.S. Provisional Patent Application No. 60/524,134 filed on Nov. 20, 2003. 
    
    
     BACKGROUND  
      a. Field of the Invention  
      The present invention relates generally to safety devices for ladders, and, more particularly, to an attachment for preventing ladder from slipping laterally against a gutter during use.  
      b. Background  
      Ladders in general, and extension ladders in particular, present significant safety concerns. It is well documented that falls from ladders result in numerous injuries and deaths on an annual basis.  
      One particular hazard is the tendency of ladders to slip sideways when resting against gutters. As can been seen in  FIG. 1 , a person  10  when cleaning or repairing a gutter  12  tends to reach out to one side or the other when working, due to the inconvenience involving in descending and moving the ladder  14  to another location, with the result that this unbalances the ladder and tends to cause it to slide laterally on the gutter and possibly topple over. Even more dangerous is the tendency of the ladder to slip when attempting to step onto it from the roof in order to descend, when the user is facing backwards and feeling for a rung with his foot.  
      The frequency of this hazard is increasing due to the increasing use of aluminum (and other metal and slippery-surfaced materials) in the construction of both gutters and ladders. For example, when an aluminum extension ladder is placed against an aluminum gutter there is almost no frictional resistance to the ladder sliding laterally.  
      As a partial solution, some ladders have been fitted with various forms of stabilizing struts and braces which rest against the ground. These are at best only a partial solution, and become less effective as the ladder is extended to increased heights. Moreover, the struts and braces are cumbersome and make the ladder to difficult to store or transport, and also add significant cost.  
      Accordingly, there exists a need for an attachment for effectively preventing a ladder from slipping laterally when placed against a gutter or similar structure or surface. Furthermore, there exists a need for such an attachment that is effective regardless of the height to which the ladder is extended. Still further, there exists a need for such an attachment that does not encumber the transportation or storage of the ladder, or otherwise compromise its use. Still further, there exists a need for such an attachment that can be used with a wide variety of conventional ladders, both new and those already in use, without requiring significant modification thereof. Still further, there exists a need for such an attachment that is inexpensive and yet durable and long lasting in use.  
     SUMMARY OF THE INVENTION  
      The present invention has solved the problems cited above, and is an anti-slip attachment for a ladder that forms a frictional engagement between the ladder and the metal gutter or similar structure when the ladder is placed thereon.  
      Broadly, the invention comprises (a) a layer of resiliently compressible material having a comparatively high surface coefficiency of friction against smooth metal, and (b) means for mounting the layer of resiliently compressible material to a ladder so that the layer will bear against and be partially compressed by the edge of the gutter when the ladder is rested thereon.  
      The layer of resiliently compressible material may comprise a strip of the resiliently compressible material, and the means for mounting the material to the ladder may comprise an adhesive for being adhered to the forward faces of the side rails of the ladder. The strip may comprise a roll of the resiliently compressible material having an adhesive backing.  
      Alternatively, the means for mounting the layer of resiliently compressible material to the ladder may comprise a frame having the resiliently compressible material mounted to a face thereof, and means for mounting the frame to the ladder. The frame may comprise first and second clips that are mountable to the side rails of the ladder so that the faces having the layer of resiliently compressible material are directed towards the gutter when the ladder is placed thereon.  
      The resiliently compressible material may comprise a resiliently compressible foam material. The resiliently compressible foam material may be a PVC foam material.  
      The layer of resiliently compressible material may be configured so that the material will be only partially compressed when forced against the gutter under a predetermined maximum operating load of the ladder, so that the layer of resiliently compressible material will retain a reserve range of compression when the ladder is fully loaded. The reserve range of compression may be about 50% of the total range of compression of the layer of material.  
      The present invention also provides an anti-slip ladder assembly, comprising (a) a ladder, and (b) a layer of resiliently compressible material having a comparatively high surface coefficient of friction that is mounted to the ladder so as to bear against and engage an edge of a gutter when the ladder is placed thereon. The layer of resiliently compressible material may comprise first and second strips of resiliently compressible material that are adhered to the faces of first and second side rails of the ladder. The resiliently compressible material may comprise strips of resiliently compressible foam material having an adhesive backing. The resiliently compressible material may comprise resiliently compressible PVC foam material. The layer of resiliently compressible material may be configured so that the material will be only partially compressed when forced against the gutter under a predetermined maximum operating load of the ladder, so that the layer of resiliently compressible material will retain a reserve range of compression when the ladder is fully loaded. The reserve range of compression may be about 50% of the total range of compression of the layer of material.  
      The invention further provides a method for forming a frictional engagement between a ladder and a metal gutter, comprising the steps of mounting to a ladder a layer of resiliently compressible material having a high surface coefficient of friction against smooth metal, and resting the ladder against a metal gutter so that the layer of resiliently compressible material establishes a frictional engagement that prevents the ladder from slipping laterally along the edge of the gutter.  
      These and other features and advantages of the present invention will be apparent from a reading of the following detailed description with reference to the accompanying drawings.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is an elevational, environmental view of a ladder in accordance with the prior art, showing the manner in which this tends to slip along the gutter as the operator reaches to one side;  
       FIG. 2  is an elevational view of a ladder having an anti-slip attachment in accordance with the present invention adhered thereto, showing the manner in which the attachment engages the metal gutter of a house when placed thereon;  
       FIG. 3  is an enlarged, cross-sectional view of the area of contact between the ladder of  FIG. 2  and the gutter against which it is placed, showing the manner in which the compressible layer of the anti-slip attachment yields resiliently to conform to and engage the surface of the gutter;  
       FIG. 4  is an elevational, partial view of a ladder having a strip of compressible material being applied thereto from a roll of the material, so as to form the anti-slip attachment of  FIGS. 2-3 ;  
       FIG. 5  is an elevational view, similar to  FIG. 2 , showing an anti-slip attachment in accordance with a second embodiment of the present invention, in which the yieldingly compressible material is mounted to a pair of clips that are fitted over the side rails of the ladder, the ladder being shown in a cross-section taken along line  5 - 5  in  FIG. 6 ;  
       FIG. 6  is an elevational view of the ladder and anti-slip attachments of  FIG. 5 , showing the position of the clips on the side rails of the ladder; and  
       FIG. 7  is a cross-sectional view of the ladder and anti-slip attachments of  FIGS. 5-6 , taken along line  7 - 7  in  FIG. 6 , showing the manner in which the clips fit over and engage the side rails of the ladder;  
       FIG. 8  is an elevational view, similar to  FIG. 5 , showing an anti-slip attachment in accordance with a third embodiment of the present invention, in which the yieldingly compressible material is mounted to a pair of channel-shaped frames that are slipped over the side rails of the ladder;  
       FIG. 9  is a perspective view of one of the slip-on, channel-shaped frames of  FIG. 8 , showing the configuration of the frame and the strip of resiliently compressible material thereon in greater detail;  
       FIG. 10  is a first partial, elevational view of the ladder and one of the slip-on frames of  FIGS. 8-9 , showing the manner in which the upper end of a side rail enters and is received in the channel-shaped frame as the latter is slid onto the rail;  
       FIG. 11  is a second partial, elevational view of the side rail and slip-on frame of  FIG. 10 , showing the manner in which the side rail fits within and is engaged by the channel-shaped frame as the frame is slid onto the rail and into the desired position;  
       FIG. 12  is a cross-sectional view, taken along line  12 - 12  in  FIG. 11 , showing the relationship of the channel-shaped frame and strip of resiliently compressible material to the side rail of the ladder in greater detail; and  
       FIG. 13  is a cross-sectional view of an anti-slip attachment assembly in accordance with a fourth embodiment of the present invention, showing the manner in which the brackets thereof are mounted by a threaded rod which passes through one of the staves of the ladder.  
    
    
     DETAILED DESCRIPTION  
      The present invention is an anti-slip attachment for a ladder which frictionally engages the surface of a metal gutter or similar surface structure so as to prevent the ladder from sliding thereon.  FIGS. 2-7  illustrate two embodiments of the invention.  
      In the first preferred embodiment that is illustrated in  FIG. 2 , the attachment is formed of a strip of resiliently compressible material  20  that is adhered to the forward face  22  of each rail  24  of the ladder  26 . The surface of the resiliently compressible layer  20  will consequently bear against the lip  28  of the gutter  30  when the ladder is placed thereon, as shown in  FIG. 2 .  
      The pressure of the ladder against the gutter causes the lip  28  of the gutter to press into the resilient material of the anti-slip attachment, as shown in  FIG. 3 . This causes the resiliently compressible material to deform so that its surface follows the contour of the gutter lip, forming a contact patch  32  having an increased surface area. The compressible material is selected to have surface qualities similar to that of soft rubber, i.e., it has a high degree of “tackiness” and resistance to slipping when pressed against a smooth metal surface. The material thus has a high surface coefficient of friction, e.g., a static coefficient of friction (μ s ) well above 0.5 and preferably above about 0.9.  
      The large contact patches  32  consequently establish a firm frictional engagement with the lip of the gutter that prevents the ladder from sliding laterally thereon. Moreover, any tipping movement will cause the rail of the ladder on the side towards the direction of tipping to slide downwardly (as well as laterally) against the gutter (see  FIG. 1 ); as this happens, the material of the compressible strip in the area  34  just above the contact patch (see  FIG. 3 ) will tend to build or “mound” up so as to abut the upper surface  36  of the gutter lip, further acting to arrest the movement of the ladder.  
      In combination, these actions of the resiliently compressible strips (i.e., the frictional engagement of the contact patch in combination with the abutment of the material against the upper surface of the gutter lip) are extremely effective in preventing the ladder from developing any tipping or sliding motion during use; in prototype testing, using anti-slip strips in accordance with the preferred embodiment of the present invention, it has been found essentially impossible for a person to cause the ladder to slide laterally against an aluminum gutter, even when pulling forcefully in a sideways direction on the gutter itself.  
      Another particular advantage of the elongate configuration of the strips of resiliently compressible material is that this makes it very easy for the operator to position the anti-slip material against the edge of the gutter, regardless of differences in the height of the gutter above the ground. As is well know, the height of most extension ladders is adjustable only in increments (typically, by the distance between the individual staves of the ladder); the vertical length of the elongate strips avoids the problem of the anti-slip areas being positioned above or below the gutter when the ladder is adjusted to the nearest incremental height. The elongate dimension of the strips also prevents them from moving off of and losing contact with the edge of the gutter in the event that some movement occurs that changes the angle of the ladder relative to the gutter. For most conventional extension ladders, it is preferred that the length of the strips be at least as great as the spacing between the staves/rungs (e.g., about 10-16 inches), although much longer strips (e.g., 3-5 feet or more) may be advantageous from the standpoint of convenience. Moreover, it will be understood that in some embodiments the resiliently compressible, anti-slip material may be provided in other shapes besides elongate, rectangular strips, for example, in an oval or rounded configuration.  
      In order for the anti-slip strips to provide the above advantages, it is important that the resiliently compressible material be selected to have a durometer, or indentation hardness, in combination with its thickness such that it will significantly compress but will not “bottom out” against the ladder rails  22  under normal loads. In other words, the material is preferably selected so that, when the ladder with which it is used is at its maximum normally acceptable inclination and working load, with the rails of the ladder pressing against the edge of the gutter, the material will not be completely collapsed and will retain a degree of compressible travel. Thus, as is shown in  FIG. 3 , even when the ladder is bearing the full load of a user and associated tools, etc., the material of the strips  20  has not bottomed out, and an area  38  of reserve compression remains available between the gutter lip and the forward faces  22  of the ladder rails. The amount of reserve compression may vary depending on design factors, however, it is generally suitable that the material be selected to yield by about 50% of its total available compression when subjected to a maximum operating load of the ladder within a specified range of lean angles.  
      As can be seen with further reference to  FIG. 3 , each of the strips  20  of the anti-slip attachment of the preferred embodiment is formed by a layer of resiliently compressible foam material  40  backed by a layer of adhesive  42  that affixes the compressible material to the face  22  of the rail.  FIG. 4 , in turn, illustrates a method in which the anti-slip material is conveniently supplied in the form of a roll  34  of adhesive cushioning tape. This can be packaged and supplied to the purchaser, separately from or together with the ladder as desired, and is easily applied to the faces of the rails  24  by simply unrolling the tape in a conventional fashion and pressing it against the surface  22  so that the material adheres firmly thereto. It will be understood, however, that other forms of application may be employed, for example, the resiliently compressible material may be extruded or molded directly on the faces of the ladder rails in an OEM operation, or may be formed as an integral part of the faces of the rails themselves.  
      Suitable adhesive foam tape material is available from Saint-Gobain Performance Plastics, Granville, N.Y., with equivalent products being available from other manufacturers. Cellular PVC (polyvinyl chloride) foam material is generally preferred due to its comparatively high surface coefficient of friction and its ability to establish firm frictional engagement under both wet and dry conditions, plus its overall durability and resistance to abrasion; it will be understood, however, that other resilient materials may be used, such as urethane, polyurethane, silicone or rubber foams or various non-cellular rubber-like materials, for example. Using firm PVC foam material in readily available durometers, suitable dimensions for the adhesive tape are 1⅛ inches wide by ⅜ inch thick, which again may vary depending on design factors.  
      One example of an eminently suitable high-density, closed-cell PVC foam material, available from Saint-Gobain Performance Plastics, has the properties set forth in the following Table A:  
                       TABLE A                       Properties   Test Method   Value                  Thickness, inches (mm)       .375 (8.5)       Hardness   Shore OO   52       Density lbs./ft 3  (kg/m 3 )   ASTM D1667     15 (240)       Compression Force Deflection psi   ASTM D1667     9 (64)       (kPa) @ 30%       Force to Compress, psi (kPA) @   ASTM D1667     14 (94)       30%                  
 
      In the second embodiment, which is illustrated in  FIGS. 5-7 , there are first and second clips,  50   a,    50   b  that attach to the two rails  52   a,    52   b  of the ladder and which engage the lip  28  of the gutter  30  in substantially the same manner as described above. The clips consequently provide separate frames on which the tape is mounted, which are in turn mountable to the ladder.  
      As can be seen in  FIG. 7 , each of the clips is formed in the shape of semi-enclosed channel. In the illustrated embodiment the channel is constructed of steel-sheet metal, however, it will be understood that plastic or other suitable materials may be used. The channel includes a comparatively wide web  54  having a flange  56  along its forward edge, the strip of foam material  58  being adhered to the outer surface thereof. A second flange  58  along the opposite edge of the web  54  is bent back parallel to the web so as to form a return  60  that defines semi enclosed U-shaped channel area  26 . The inside angle between the web and the forward flange  56  is somewhat less than 90°, e.g., 80-85°.  
      To install one of the clips on a rail of the ladder, the U-shaped channel area  60  is first slipped over the rearward flange  64  of the ladder rail and the clip is then pulled/pushed forwardly. When the rearward flange of the ladder is fully seated against the rearward flange  58  of the clip, as is shown in  FIG. 7 , the forward flange  56  is bent forwardly to widen the spacing between the forward and rearward flanges of the clip sufficiently that the former can be slipped over the forward flange  66  of the ladder rail. When the clip has been pressed home, so that its web lies generally parallel to the web  68  of the ladder rail, the forward flange  56  snaps resiliently back to its initial orientation to lock the clip in place. The strip of resiliently compressible anti-slip material is thus positioned so that it will be compressed between the gutter and the rail of the ladder during use.  
      In a third embodiment, which is illustrated in  FIGS. 8-12 , there are two channel-shaped frames  70   a,    70   b  (only  70   a  being visible in  FIG. 8 ), that have a channel-shaped configuration and that slip over the two side rails  72   a,    72   b  of the ladder rather than clipping onto them in the manner shown in  FIGS. 5-7 .  
      As can be seen in  FIG. 9 , each of the slip-on frames has a generally channel-shaped configuration, with a side web  74  and forward and rearward flanges  76 ,  78  with returns  80 ,  82 , that in combination define a semi-enclosed, U-shaped channel area  84 ; the generally U-shaped configuration facilitates manufacture of the frames from stamped/bent sheet metal, however, it will be understood that in some embodiments that the channel areas may be fully enclosed. A strip  86  of the resiliently compressible material is mounted to the forwardly-directed face of each forward flange  76 , in a manner similar to the embodiment described with regard to  FIGS. 5-7 . However, at the upper and lower ends of the rearward flange  78  a pair of ramp-shaped biasing members  88   a,    88   b  protrude inwardly towards the channel area  84 . In the embodiment that is illustrated, the biasing members are formed of separate pieces of resiliently flexible material (e.g., metal or plastic), each having a mounting portion  90  that is spot welded, bonded or otherwise mounted to the inside surface  92  of the rearward flange  78  (see  FIG. 10 ), with a leaf portion  94  that bends forwardly from the mounting portion so as to extend into the channel area. This provides the advantage of being able to form the biasing members of a material having superior resiliency and wear characteristics as compared with the material of the frame; however, it will be understood that in some embodiments the biasing members may be formed integrally (e.g., stamped or molded) with and of the same material as the frame itself.  
      As can be seen in  FIG. 10 , the side web  74  and therefore the channel area  84  is sized somewhat wider than the side rail of the ladder. The leaf portions  94  of the biasing members  88   a,    88   b  include main ramp portions  96  that extend into the channel area to define a width that in turn is less than that of the side rails; distal ramp portions  98  at the ends of the main ramp portions are angled back outwardly towards the rearward side of the frame.  
      Accordingly, as can be seen in  FIG. 10 , the frame members  70   a,    70   b  can be slid onto the upper ends of the side rails  72   a,    72   b,  in the direction indicated by arrow  100 . As this is done, the distal ramp portion  98  contacts and rides over the upper, rearward corner of the side rail (which is typically radiussed as shown), so that the leaf portion of the biasing member is forced outwardly in the direction indicated by arrow  104 . As a result, the leaf portion develops an inward bias against the rearward surface  106  of the rail as the frame is slid thereover.  
      As a result, the upper and lower biasing members  88   a,    88   b  maintain a constant inward pressure towards rails, as indicated by arrow  110  in  FIG. 11 . This generates a sliding but comparatively high-friction engagement at the contact areas between the rearward surfaces  106  of the rails and the junctures/apexes  108  of the ramp portions of the biasing members. The frictional engagement is sufficiently high to hold the frames in place, but low enough to be overcome by simply grasping the frames and pushing them in one direction or the other. Consequently, the operator is able to conveniently slide the frames to the desired location along the rails, at which the strips of resiliently compressible material will contact the gutter, after which the frictional engagement will maintain the frames in position and prevent them from sliding until the operator next desires to adjust their positions. Furthermore, as can be seen in  FIG. 12 , the forward pressure exerted by the biasing members holds the forward flange of the frame firmly in place against the front surface  112  of the rail, so as to form a stable interfit in which the anti-slip strips  86  are properly positioned at the front edges of the ladder.  
       FIG. 13  shows a fourth embodiment of the invention, in which the frames  120   a,    120   b  have a somewhat simplified configuration, with the forward and rearward flanges  122 ,  124  extending at right angles to the webs  126 . As with the embodiments described above, the strips of resiliently compressible cushioning material  128  are adhered to the outer surfaces of the forward flanges  122 . In this embodiment, however, mounting is accomplished by means of a threaded rod  130  that passes through a hollow interior of one of the staves  132  of the ladder; conventionally, the staves of aluminum ladders are hollow and open at each end so that the rod can be readily passed therethrough. First and second wing nuts  134  are mounted on the ends of the rod  130  and secure the clips to the rails of the ladder when tightened; suitably, the rod is a 20-inch length of ¼-inch ready rod, with ¼-inch wing nuts on each end. However, it will be understood that in some embodiments a nut may be used on only one end of the rod, with the other end being a bolt head or fixed to the opposite clip; moreover, other attachment and tightening means may be used in other embodiments.  
      The embodiments which are shown in  FIGS. 5-13  illustrate just a few of many different structures that may be used to provide an anti-slip attachment in which the resiliently compressible material mounts to the ladder via a secondary structure or frame rather than being adhered directly to the ladder rails themselves. As a general rule, those embodiments which employ secondary structures that are faced with the non-slip compressible material may be somewhat more costly than the first embodiment described above (i.e., in which the compressible tape is adhered directly to the faces of the rails), however, they may offer certain advantages in terms of being able to provide contact patches that are wider (and therefore “grippier”) than those which are limited to the width of the individual rails of the ladder. It will be understood, however, that all such embodiments fall within the scope and spirit of the present invention, regardless of the whether the resiliently compressible material is mounted directly on the rails of the ladder or on a secondary frame or structure that in turn mounts to the rails and/or staves of the ladder.  
      It is to be recognized that various alterations, modifications, and/or additions may be introduced into the constructions and arrangements of parts described above without departing from the spirit or ambit of the present invention.