Abstract:
An apparatus that fits onto a ladder for securing the ladder safely to a circular pole. The apparatus has a pair of curved arms that are each rotatable about a pivot so that they will close onto a pole. The arms are caused to rotate by a lever portion that contacts the pole as the ladder is forced toward the pole such as when it is set up and when a climber begins to climb the ladder. As the lever portion is forced against the pole the curved arm rotates to enclose the pole. The arms have a symmetrical control element in the form of meshed gears so that they act symmetrically as they are set up initially and as they rotated into the enclosing position.

Description:
PRIORITY CLAIM 
       [0001]    Priority is claimed from U.S. Provisional Application Ser. No. 61/129,817 filed on Jul. 22, 2008 the content of which is incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    Ladder safety has been a long standing and is an important consideration. It is addressed in OSHA Standard 1926.1053. 
         [0003]    One important aspect of ladder safety is the placement of ladders against circular structures such as utility poles, electrical poles, tree trunks, etc. 
         [0004]    The problem is that the straight rung of a ladder, when placed on a circular, or any curved surface creates instability. Also, even if both ladder rails can contact the pole, if only one does, the ladder erection is unstable; and then also, even if both rails contact the pole, it can be unstable 
         [0005]    While the problem is well known, solutions have been few and inadequate. There is a need for a reliable way to place a ladder against a round pole or the like in a secure manner. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0006]      FIGS. 1   a  and  1   b  and  1   c  show how a ladder can be positioned on a pole in unstable positions. 
           [0007]      FIG. 2  shows a side view of an embodiment of the invention. 
           [0008]      FIG. 3  shows a top view of an embodiment of the invention. 
           [0009]      FIG. 4  shows a perspective view of an embodiment of the invention. 
           [0010]      FIG. 5  shows a front partial exploded view of an embodiment of the invention. 
           [0011]      FIG. 6  shows a perspective exploded view of an embodiment of the invention. 
           [0012]      FIG. 7  shows a close-up view of an embodiment of the invention 
           [0013]      FIG. 8  shows a view of an embodiment of the invention in the open position relative to a pole. 
           [0014]      FIG. 9  shows a view of an embodiment of the invention in the closed position. 
           [0015]      FIG. 10  shows an embodiment of the invention in use. 
           [0016]      FIG. 11  shows an embodiment of the invention in use. 
       
    
    
     DETAILED DESCRIPTION  
       [0017]    The invention resides in an apparatus that can be attached to a ladder and that has gripping arms as part of a mechanism in which the gripping arms move into a position engaging around a pole as the ladder is set up. One feature of the invention is a pair of gripping arms that have a concave curved portion for engaging around a pole and each gripping arm having a lever portion that will engage the pole upon erecting the ladder and will cause the gripping arms to pivot into an enclosing position. Another feature of the invention is a mechanism that places the gripping arms in a symmetrical position and also places the levers in a symmetrical position and then causes the levers and consequently the gripping arms to move in unison from an open position to a closed position around a pole and maintaining the correct symmetry of the ladder and the pole for stability, with the gripping arms enclosing the pole. The mechanism also has a mounting structure that enables placement of the apparatus in a correct position on the ladder. It is designed to attach to any extension ladder and allows the ladder user to climb any kind of pole (i.e. electric pole, light pole, tree trunk, etc.) and be able to securely climb the pole, or circular structure. 
         [0018]    Embodiments of the invention will now be described in conjunction with the figures. 
         [0019]    The term pole adequately defines most applications of the invention. Examples are utility poles and other upstanding structures that have an exterior curvature that can be secured by enclosing engagement of a pair of gripping arms. Typical of such poles are those of circumference that will fall inside the rails of a ladder; that is in which the curvature is such that the pole can contact the ladder&#39;s uppermost rung but not the ladder rails resulting in undesired instability. If the curvature is slight enough that the ladder rails will make contact and not the rung, then instability may still be present, for example if the ladder is erected with only one rail in contact initially (the ladder can twist as the user climbs so that both rails touch, but it is still unstable). 
         [0020]    For cases in which the pole contacts the rung, there are two possible configurations. A pole may have its entire circumference (assuming circular) inside the width of the ladder rails, or the circumference may extend beyond the rails.  FIGS. 1   a  and  1   b  illustrate typical arrangements of that type of configuration that the present invention is intended to avoid. In  FIG. 1   a  the pole is fully inside the ladder rails. In  FIG. 1   b  the curvature extends outside the ladder rails, but does not touch either rail (although it could touch one rail, which would be a very unstable ladder set-up).  FIG. 1   c  is a configuration in which the pole curvature is so slight that it will not touch the rung, but only one or both rails. This is also an undesirable ladder set-up if only one rail is in contact, the ladder will twist as the user climbs, making it unstable. 
         [0021]    The following description is with reference to  FIGS. 2-7 . It will be seen that the numbering system uses an “a” designation for one side and a “b” designation for the other side when there is parity of the parts described. However when both are referred to, the “a” and “b” distinction may be omitted. The safety device  10  can be described as having two general portions, a frame portion  12  and an operating portion  14 . The frame portion  12  has two elements, a support beam  16  which as shown has a reversed Z shape including a plate called a lower mounting plate  18   a.  The frame portion also has an upper mounting plate  18   b.  The support beam  16  serves to locate ladder mounting members, upper ladder mounting member  20  and lower ladder mounting member  22  and the operating portion  14 . The upper mounting plate  18   b  is parallel to the lower mounting plate  18   a.  The operating portion  14  is mounted on the plates  18   a  and  18   b.  All of the upper and lower ladder mounting members  20  and  22 , the support beam  16  and the upper plate  18   b  are welded together and as will be seen, locate the parts for correct mounting on a ladder and operation. 
         [0022]    The upper and lower ladder mounting members  20  and  22  are elongated U-shaped channel channels  20  and  22 , attached to the support beam  16  and adapted to that fit over adjacent ladder rungs. They are each equipped with a pair of positive lock pins  24  such as Positive Lock Pins made by Pivot Point, Inc of Hustisford, Wis.. 
         [0023]    The operating portion  14  is attached to the frame portion  12  on the parallel plates  18   a  and  18   b.  The operating portion  14  has a pair of inwardly (concave) curved claws or calipers  28 . The calipers  28  are identical and are mounted as mirror images in vertically staggered relationship. Each caliper  28  has a pivot point  30  which defines, “outside the pivot point”, an outer or gripping portion  32   a  which has a concave curve  34  and which also defines, “inside the pivot point” a lever portion  36 . The lever portion  36  has a curved camming surface  38 . Each caliper  28  also has a slot  40  which is shaped on a radius R from the pivot point  30  of the other caliper which is also the distance between the pivot points. 
         [0024]    The calipers  28  are mounted between the plates  18   a  and  18   b.  They are mounted on shoulder bolts  44   a  and  44   b  extending through holes  46   a  and  46   b  in the plate  18   b  and holes  48   a  and  48   b  in plate  18   a,  which holes are centered at the pivot points  30  of the calipers  28  and which are separated by the distance R. Each caliper has a gear  50   a  and  50   b  attached to it at its pivot point, the gears  50   a  and  50   b  being meshed. There is a Nylon hat washer  52   a  and  52   b  at each pivot point  30  mounted on the respective shoulder bolt  44   a  and  44   b  and serving as a bearing in the slot  40  through which it passes. Other Nylon washers  47   a  and  47   b  are fitted for normal bearing and spacing purposes. The shoulder bolts  44   a  and  44   b  are secured by nuts and washers as shown in  FIGS. 5 and 6 . 
         [0025]    Mounting of the gear  50   a  on caliper  28   a  and gear  50   b  on caliper  28   b  is not detailed, but they can be screwed on by tapping holes in them and with countersunk screws. In installing the gears  50   a  and  50   b , their mesh placement must be set or “clocked” to put the calipers into symmetry as described below. 
         [0026]    With assembly the calipers will rotate together on their respective pivot points  30 , as will be described in more detail below. For the best and safest operation, the calibers must be mounted for symmetrical movement and symmetrical position relative to the ladder and the prospective pole. That movement is obtained by the gears  50   a  and  50   b  being fitted to their respective calipers  28  for meshing symmetrically with respect to a center line also called a line of symmetry, LS (see  FIGS. 3 and 7 ). That is, the calipers  28   a  and  28   b  are set for symmetrical placement and pivoting with respect to the line of symmetry LS and the gears  50   a  and  50   b  are meshed to establish maintain the symmetry of the calipers. The line of symmetry LS passes through the gears&#39; pitch circles where they mesh (see  FIG. 7 ). Therefore, the gears  50   a  and  50   b  will control the calipers  28   a  and  28   b  to move symmetrically together, toward and away from the line of symmetry LS. The line of symmetry LS should also be perpendicular to a length axis defined by the U-shaped channels  20  and  22 , which renders line of symmetry perpendicular (see  FIG. 3 ) to a length axis of ladder rungs when the device is set onto a ladder. With this structure the positioning and the movement of the calipers will be symmetrical with each other and with ladder rungs. That will result in the pole being gripped centrally of the device and symmetrically relative to the axis of the ladder rungs 
         [0027]    There is another mechanical feature that requires that the outermost point on the camming surfaces  38   a  and  38   b  that is, the point in contact with the pole must always remain on its side (the inside) of its pivot point, that is it must never go “overcenter”, in order to provide the pivoting force needed to rotate the calipers. The overcenter position could occur if the calipers are spread too far apart, causing the camming surfaces to rotate too far. 
         [0028]    In order to accommodate correct use of ladders according to OSHA standard 1926.1053, the device  10  is made so that the calipers will extend with respect to the U-shaped channel channels  20  and  22  at an angle of 75.5°, which is shown on  FIG. 2 . This will put the calipers in the best horizontal position relative to a vertical pole. 
         [0029]      FIGS. 8 and 9  show the device set initially in position ( FIG. 8 ) and then in its installed position ( FIG. 9 ). In  FIG. 8 , the calipers are open and the camming surfaces  38   a  and  b  are in contact with a pole. As the ladder is forced against the pole the calipers will rotate as shown by the arrows, into the position shown in  FIG. 9 . 
         [0030]    After a ladder is erected on a pole it should be secured in place. This is provided by a line and a retaining assembly that attaches to each caliper and has a line extending around the pole. It can be tightened on one or both sides. An exemplary embodiment is shown in  FIGS. 8 and 9  in which lugs  52   a  and  b  are welded to the calipers  28   a  and  b  at a selected point that will give a good amount of contact with the pole by a securing line. Mounted on the lugs are tensioners  54   a  and  b . A line is attached in a fixed manner to one tensioner and in a selectable manner to the other tensioners. The tensioners can be tightened. In the embodiment shown, the line is a chain  56 . The tensioners are a threaded knob and one tensioner has an open hook  58  while the other one has an eye bolt  60 . The chain  56  is fixed at one end on the eye bolt  60 . In use, before the ladder is erected, the tensioners should be set in their most loose position. After the ladder is set up and the user has climbed up, the chain  60  is wrapped around the pole and a link inserted in the open hook  58 , as tightly as is practical. Then the tensionsers are tightened to fully secure the chain. 
         [0031]      FIG. 12  shows a gripping arm  64  which is configured for a square pole. This arm in a left and right placement as in the configuration above will work the same way the curved arms do. 
         [0032]    In use the ladder safety device  10  is mounted on a ladder as shown in  FIGS. 10 and 11 . It can be mounted on either the first and second ladder rungs, or on a lower pair such as the second and third, or the third and fourth. In  FIG. 10  it is shown mounted on the third and fourth rungs and in  FIG. 10  it is shown mounted on the first and second rungs. It attaches to the rungs of the ladder in seconds by way of hanging the U-shaped channels over the rungs. Then the positive lock pins are inserted to keep the device in place while standing up the ladder for use. For the most stable set up the device should be installed on a ladder mid-way of the length of the rungs. That is the U-shaped channels should be centered on the rungs. 
         [0033]    As the ladder is tilted toward the pole the camming surfaces  38  contact the pole surface and as force is placed on the ladder the lever portions  36  will rotate around the pivot points  30 , which rotation is symmetrical due to the operation of the gears  50   a  and  50   b,  which in turn will cause the calipers  28  to symmetrically enclose the pole. 
         [0034]    The symmetrical operation of the embodiment described above has been found to be important to avoid instability in the enclosing process by ensuring that the pole is centered on the device and at right angles to the ladder rungs. Absent this symmetry the ladder can slip and be unstable during the enclosing operation and after the ladder is erected. 
         [0035]    The mechanism for symmetrical rotation of the calipers can be any mechanism that causes controlled contra-rotation of the calipers by a symmetrical engagement and contra-rotational movement on the inside of the pivot point. 
         [0036]    However, the unit can be constructed without the gears in which case the calipers  28  will still pivot, but they will function independently, and at a greater risk of instability in the ladder being put in place as well as in the final position. 
         [0037]    The foregoing Detailed Description of exemplary and preferred embodiments is presented for purposes of illustration and disclosure in accordance with the requirements of the law. It is not intended to be exhaustive nor to limit the invention to the precise form or forms described, but only to enable others skilled in the art to understand how the invention may be suited for a particular use or implementation. The possibility of modifications and variations will be apparent to practitioners skilled in the art. No limitation is intended by the description of exemplary embodiments which may have included tolerances, feature dimensions, specific operating conditions, engineering specifications, or the like, and which may vary between implementations or with changes to the state of the art, and no limitation should be implied therefrom. This disclosure has been made with respect to the current state of the art, but also contemplates advancements and that adaptations in the future may take into consideration of those advancements, namely in accordance with the then current state of the art. It is intended that the scope of the invention be defined by the Claims as written and equivalents as applicable. Reference to a claim element in the singular is not intended to mean “one and only one” unless explicitly so stated. Moreover, no element, component, nor method or process step in this disclosure is intended to be dedicated to the public regardless of whether the element, component, or step is explicitly recited in the Claims. No claim element herein is to be construed under the provisions of 35 U.S.C. Sec. 112, sixth paragraph, unless the element is expressly recited using the phrase “means for . . . ” and no method or process step herein is to be construed under those provisions unless the step, or steps, are expressly recited using the phrase “comprising step(s) for . . . ”