Abstract:
A non-self-supporting ladder having an anti-slide-out device which enables a user to set up the ladder at the specified minimum ladder set-up angle θ or greater angles for precluding the base of the ladder from sliding away from a structure against which the ladder is leaning upon application of a weight on the ladder, but prevents the ladder to be set up at angles smaller than θ. The device includes an inboard roller assembly having a bracket connected to each side rail of the ladder and a roller connected to each bracket oriented and disposed so as to impose a specified ladder inclination angle θ, when the lower end of the ladder and the rollers simultaneously rest on a substantially flat horizontal surface. At set-up angles smaller than the specified minimum angle θ, only the rollers rest on the horizontal surface, preventing the ladder from being set up.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to a straight or extension ladder comprising anti-slide-out means for determining the minimum ladder set-up angle whereby the base of the ladder is precluded from sliding away from the wall or other structure against which the ladder is leaning upon application of a weight on the ladder.  
           [0003]    2. Description of Prior Art  
           [0004]    A straight or extension ladder maintains its equilibrium when placed against a wall or other structure by the friction resistance against sliding that is created between the side rail feet and the ground surface. When this friction force is not sufficient, the base of the ladder slides away from the wall dropping its climber. Over one-third of all ladder accidents are caused by ladder slide-out.  
           [0005]    The equations of equilibrium for straight or extension ladders indicate that the resistance against slide-out increases with the steepness of the ladder. The steepness of the ladder is normally characterized by the acute angle formed between the ground surface and the center line of the ladder. In the United States, ladders are designed and tested using an angle of 75.52°, which is also used as the limiting ladder set-up angle to avoid slide-out. The safety factor against ladder slide-out falls off very quickly as the ladder angle becomes shallower.  
           [0006]    There are a number of popular techniques for establishing the 75.52° ladder angle. The first of these is the one-in-four method by which the angle is set by arranging the geometry such that the base-to-wall distance is one-forth of the active ladder length.  
           [0007]    Another method involves the mounting of an “L” on the side rail of the ladder in a special orientation. When the ladder is correctly set up, the L achieves a natural orientation with its legs in a vertical and horizontal direction.  
           [0008]    Yet a third method involves anthropometric set-up in which four instructional steps are placed on ladder labels to achieve a ladder angle of approximately 75°. These instructional steps are—1) place toes against bottom of ladder side rails; 2) stand erect; 3) extend arms straight out; and 4) palms of hands should touch top of rung at shoulder level.  
           [0009]    A further means for achieving proper set-up of a ladder is taught by U.S. Pat. No. 2,845,719 wherein a bubble level is attached to the outside of the ladder side rail at eye level to disclose any chosen set-up angle. U.S. Pat. No. 3,118,234 teaches a pendulum device attached to the outside of the ladder side rail whereby, when the ladder is set up at a ladder angle of 75°, a mark on the pendulum housing lines up with the pendulum. If the ladder base is too far in or out, the pendulum housing is marked appropriately “move in” or “move out” so that the user will move the ladder base in the correct direction.  
           [0010]    U.S. Pat. No. 5,740,881 teaches yet another approach in which an electronic circuit and alarm are attached to a ladder with two sensors. One of the sensors determines the side-to-side orientation of the ladder while the other determines the ladder inclination angle. When incorrectly set up, the alarm sounds and the actual angles are displayed.  
           [0011]    Yet another device for determining proper inclination of a ladder is a “monster eye”, named after a toy, which is mounted under the sixth base section rung at eye level. The monster eye consists of two concentric spheres, the inner sphere of which is opaque and weighted on one side and the outer sphere of which is transparent. Between the spheres, the space is filled with liquid that allows the inner sphere to rotate freely so that its weighted side can remain in a downward-facing orientation. When an equator line on the inner sphere falls between two closely spaced parallel lines painted around the equator of the outer sphere, the ladder has achieved an inclination angle of 75.5°.  
           [0012]    One problem associated with each of the above described methods and devices is that the set-up protocol may be completely ignored by the users, who may adopt any arbitrary inclination angle that suits their immediate fancy, risking thereby a non-safe ladder set-up.  
           [0013]    It will also be appreciated that there are numerous devices known in the art for stabilizing a ladder. U.S. Pat. No. 5,341,899 teaches an anti-skid hand leveling device for ladders which includes a pair of devices consisting of a guide rail along which an upper carriage and a lower carriage slide independently. The upper carriage provides a mounting platform onto which a brace is rotatably mounted. The lower carriage provides a mounting platform onto which an outrigger-type foot is mounted. When pivoted to a specified angle and lowered so as to contact the ground, the brace prevents the ladder from skidding in a direction away from the object against which the ladder is resting. Similar devices are taught by U.S. Pat. No. 4,723,629 and U.S. Pat. No. 4,130,181. See also U.S. Pat. No. 5,918,698; U.S. Pat. No. 4,632,220; U.S. Pat. No. 3,059,723; U.S. Pat. No. 2,868,427; U.S. Pat. No. 1,710,026; U.S. Pat. No. 1,352,566; U.S. Pat. No. 840,365; U.S. Pat. No. 776,446; and U.S. Pat. No. 530,374. Although providing stabilization for straight and extension ladders, none of these prior art references provides any means for ensuring proper set-up of the ladder so as to preclude ladder inclination angles below a specified limiting ladder set-up angle.  
         SUMMARY OF THE INVENTION  
         [0014]    Accordingly, it is one object of this invention to provide an apparatus for ensuring proper ladder inclination angles which preclude slide-out of the base of the ladders upon application of a weight to the ladder.  
           [0015]    It is another object of this invention to provide a method and apparatus for proper ladder set-up which passively rejects any ladder inclination angle below a specified limiting ladder set-up angle θ, for example 75.5°.  
           [0016]    These and other objects of this invention are addressed by a non-self-supporting ladder comprising two substantially parallel, elongated, spaced apart side rails having an upper and a lower end and a plurality of substantially parallel, spaced apart rung elements joining the spaced apart side rails. An inboard roller assembly comprising a bracket and a roller rotatable over its central axis is connected to each of the spaced apart side rails, whereby the central axes of the rollers are oriented so as to be essentially parallel to the spaced apart rung elements joining the spaced apart side rails. The inboard roller assemblies are disposed so as to impose a specified ladder inclination angle θ when the lower end of the spaced apart side rails and the rollers rest on a substantially flat horizontal surface. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    These and other objects and features of this invention will be better understood from the following detailed description taken in conjunction with the drawings wherein:  
         [0018]    [0018]FIG. 1 is a side view of the lower portion of a rigid ladder system at different inclination angles having an anti-slide-out device in accordance with one embodiment of this invention;  
         [0019]    [0019]FIG. 2 is a side view of a ladder having an anti-slide-out device in accordance with one embodiment of this invention showing equilibrium and non-equilibrium states for the ladder;  
         [0020]    [0020]FIG. 3 is a side view of an anti-slide-out device for a ladder employing an eccentric mechanism in accordance with one embodiment of this invention;  
         [0021]    [0021]FIG. 4 is a side view of the anti-slide-out device shown in FIG. 3 with the eccentric mechanism at a shallow inclination angle after loading;  
         [0022]    [0022]FIGS. 5 a - 5   e  are side views of an anti-slide-out device at various load conditions and inclination angles in accordance with one embodiment of this invention;  
         [0023]    [0023]FIGS. 6 a - 6   e  show side views of an anti-slide-out device for a straight or extension ladder in accordance with one embodiment of this invention;  
         [0024]    [0024]FIG. 7 is a side view of an anti-slide-out device for a straight or extension ladder in accordance with yet another embodiment of this invention;  
         [0025]    [0025]FIG. 8 is a side view of a ladder comprising an anti-slide-out device in accordance with one embodiment of this invention;  
         [0026]    [0026]FIG. 9 is a side view of a ladder comprising an anti-slide-out device comprising a preloaded spring suspension in accordance with one embodiment of this invention;  
         [0027]    [0027]FIG. 10 is a side view of an anti-slide-out device comprising a preloaded flat spring suspension in accordance with one embodiment of this invention; and  
         [0028]    [0028]FIG. 11 is a side view of an anti-slide-out device comprising a detented slider in accordance with one embodiment of this invention. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0029]    If frictionless wheels are fixed to the base of a ladder to act as its feet, the ladder cannot support either itself or a live load. For any angle of inclination, the ladder will slide out away from the vertical wall or structure against which it is leaning. FIG. 1 shows the bottom portion of a ladder comprising side rail  12  and rungs  14  and a device for determining the proper set-up inclination angle for the ladder in accordance with one embodiment of this invention comprising outrigger or bracket  13  attached to the base of the ladder, which bracket  13  supports roller  11 . Roller  11  in accordance with one embodiment of this invention is a pneumatic tire wheel. One such device is attached to each side rail  12 . Three dispositions of the ladder are shown in FIG. 1. As illustrated in the center disposition, rollers  11  are located so that the ladder base  16  and rollers  11  simultaneously touch horizontal surface or ground  15  when the ladder inclination angle achieves the desired set-up angle, θ. At angles steeper than θ, as shown in the right-most disposition, rollers  11  are lifted above surface  15  leaving the ladder base  16  in contact with the support surface  15 . It should be noted that steeper set-up angles, such as that shown in the right-most disposition, are more difficult from which to slide out. By contrast, the left-most disposition of the ladder shown in FIG. 1 depicts a ladder inclination that is shallower than the desired set-up angle θ. In this case, ladder base  16  is above the surface  15  and the ladder is supported only by rollers  11 . Consequently, the ladder will start falling because the ladder base will propel itself in the direction away from the support wall or structure. If the user does not oppose this motion, the ladder will fall against the ground.  
         [0030]    An examination of the “too shallow” case shown in FIG. 1 reveals three feed-back mechanisms that indicate to the user an improper inclination angle. First, ladder base  16  can be seen not touching the ground  15 . Second, the ladder will push against a user standing in front of the ladder or it will accelerate in the direction indicated by arrow  17 . Finally, if the ladder is not too heavy, attempts to mount the lowest of the rungs  14  will lift the top of the ladder up off the support structure. There is a seesaw action that gives rise to a fulcrum rotation about the axles of rollers  11 . The seesaw action is associated with rollers  11  positioned inboard of the bottom rung as illustrated in FIG. 1.  
         [0031]    In a rigid world, a climber would adjust the ladder to achieve simultaneous contact of the ladder base  16  and rollers  11 . Then, a slight additional rearward movement would permanently elevate the rollers  11  and allow climbing to proceed. In the real world of flexibility, the ladder will sag when supporting a climber. Unfortunately, this sag will always rotate the ladder base  16  in a direction which moves rollers  11  downward. It is possible for this downward movement to jack up the ladder base  16  causing the ladder base  16  to leave the ground  15  and remove all resistance to slide-out. The climber and the ladder collapse together as rollers  11  run away from the supporting wall or structure. This fail-to-danger scenario may be actively averted by instructing the user to leave a specified ground clearance beneath the rollers during set-up. On the other hand, a passive system may be used to preclude the roll out phenomenon entirely.  
         [0032]    Such a system is shown, for example, in FIG. 2 in which rollers  11  are spring loaded. At shallow angles less than the desired set-up angle θ, the left-most illustration of FIG. 2, spring  20  carries the weight of ladder  10  and any extension sections thereof with a safety factor, for example 1.5 times the ladder weight. In this state, the ladder base  16  is elevated from the ground surface and the ladder  10  will accelerate away from the support wall or structure in the direction of arrow  17 . This state provides both visual and tactile feedback relative to the improper set-up angle. At any shallow angle less than θ, the user may stabilize the ladder with his hands while he mounts a rung. This live load, indicated by arrow  21 , on ladder  10  will overcome the pre-load in spring  20  and allow ladder base  16  to push against the ground with sufficient force to develop almost the full frictional resistance to slide-out associated with the specific ladder inclination. This situation is shown in the center illustration of FIG. 2 using conventional spring loaded rollers often found in self-supported ladder stands. The set-up shown in the right-most illustration of FIG. 2 shows a ladder at the exact inclination angle θ desired or specified by standards or codes. Currently, this angle is 75.52°. Theoretically, an infinitesimally larger angle than θ will completely lift rollers  11  from the ground surface allowing side rails  12  to develop their full resistance to slide-out. If ladder sag under live load should force rollers  11  into the ground, they cannot cause the side rails to lift because their lifting or jacking capability is limited to the spring force. The spring force is always small; it is somewhat larger than the self weight of the ladder. The anti-slide-out device in accordance with the embodiment shown in FIG. 2 comprises a passive spring system. Bracket  13  is connected to side rail  12  of ladder  10  and roller  11  is attached to rod  22  which is slidably connected to bracket  13 . That portion of rod  22  between roller  11  and bracket  13  is surrounded by preloaded spring  20 . This passive spring system adds robustness to the anti-slide-out safety system of this invention. It should be noted that rollers  11  enable ladder  10  to be moved in the same manner as a wheelbarrow.  
         [0033]    In accordance with other embodiments of this invention, spring loaded rollers such as those shown in FIG. 2 are automatically removable from active participation once a live load is imposed on the ladder. Some embodiments of this property are shown in FIGS. 3, 4,  5   a - 5   e ,  6   a - 6   e  and  7 .  
         [0034]    [0034]FIG. 3 shows one embodiment of the anti-slide-out device of this invention oriented so as to provide the desired angle of inclination θ. The device comprises fixed bracket  30  attached to side rail  12  of ladder  10 . Roller  11  is disposed at one end of square rod  32  around which is disposed compression spring  31 . The opposite end of square rod  32  is connected to hinged fitting  35 , which, in turn, is hingedly connected to fixed bracket  30 . Hinged fitting  35  comprises torsion spring  33  which tends to rotate hinged fitting  35  against stop  34 . Any loads transferred to roller  11  in an upward direction will also hold hinged fitting  35  against stop  34 . The eccentricity of roller  11  relative to hinged fitting  35 , together with the spring constant of torsion spring  33  and compression spring  31  may be combined with the preloading of the two springs to maintain contact of hinged fitting  35  with stop  34  under the self weight of ladder  10 . On the other hand, if the inclination of ladder  10  is shallow, and if a live load is placed on ladder  10 , the mechanism assumes the geometry shown in FIG. 4. In this configuration, almost no upward force is exerted on ladder  10  by the roller mechanism. Even when the live load is removed, a ladder  10  will not be lifted by the mechanism and the original configuration shown in FIG. 3 will not be recovered. To restore the original/initial geometry of FIG. 3, the user must lift the ladder and allow torsion spring  33  to recock the system.  
         [0035]    It can, thus, be seen that the eccentric mechanism of FIGS. 3 and 4 provides two additional safety features. First, when the ladder is misused, that is set up at shallow angles, the spring system will not reduce the force on the side rail feet which might compromise the frictional resistance to slide-out. Second, when the user dismounts a ladder set up at a shallow angle, compared to the desired angle of inclination, the ladder will remain in equilibrium and not push back from the vertical support structure.  
         [0036]    In accordance with the embodiment of FIGS. 3 and 4, the roller suspension system is unloaded when the self weight and live load on the ladder exceed a preset limit. The user can reset or reactivate the suspension system merely by lifting the ladder of the ground surface.  
         [0037]    Another embodiment of the anti-slide-out device of this invention is shown in FIGS. 5 a - 5   e . The device, detailed in FIG. 5 e  comprises roller mechanism support bracket  85  which is fixedly connected to the ladder  10 . Roller  11  is disposed at one end of roller arm  80 , the opposite end of which is pivotably connected by means of pivot shaft  87  to roller mechanism support bracket  85 . Roller arm  80  forms a longitudinally oriented detent slot  81  in which is disposed a detent pin  82 . One end of over-the-center pretensioned detent spring  88  is connected to detent pin  82  and the other end of over-the-center pretensioned detent spring  88  is connected to spring support pin  89  extending outwardly from roller mechanism support bracket  85 . Roller mechanism support bracket  85  further comprises roller arm stops  83 ,  84  disposed on either side of roller arm  80 . An edge portion of roller mechanism support bracket  85  disposed between roller arm stop  83  and roller arm stop  84  forms a detent cam  86 . In operation, detent pin  82  is held against the cam profile  86  by means of over-the-center pretension spring  88 , which is designed to carry the weight of the ladder, and any extension sections, with a small safety factor, in a manner similar to that of FIG. 2 previously described. At shallow angles less than the desired angle of inclination θ, as shown in FIG. 5 a , the anti-slide-out device in accordance with this embodiment carries the weight of the ladder but the side rail feet are elevated from the ground surface resulting in acceleration of the ladder away from the support wall or structure. This state provides both visual and tactile feedback relative to the improper set-up angle. At any shallow angle less than θ, the user may stabilize the ladder with his hands while mounting a rung  14 . This live load on the ladder acts through roller  11  on roller arm  80 , pushing detent pin  82  over the cam hump of detent cam  86 . The action by the over center pretensioned detent spring  88  moves roller  11  together with roller arm  80  out of the way toward the ladder as shown in FIG. 5 b . This roller state provides the user with an immediate visual feedback that the set-up angle was improper. However, the feet of side rails  12  will now be in contact with the ground, pushing against it with sufficient force to develop the full frictional resistance to slide-out associated with the specific ladder inclination.  
         [0038]    [0038]FIG. 5 c  shows ladder  10  employing the anti-slide-out cam and detent mechanism of FIG. 5 e  at the exact inclination angle θ desired or specified by standards or codes. A larger angle than θ will lift the rollers  11  from the ground surface allowing the side rails  12  to develop their full resistance to slide-out. If ladder sag under live loads should happen to push rollers  11  against the ground, rollers  11  will not cause side rails  12  to lift. Instead, as shown in FIG. 5 d , the sag will act through roller  11  on roller arm  80 , pushing detent pin  82  over the cam hump of detent cam  86  resulting in action by the over center pretensioned detent spring  88  moving roller  11  with roller arm  80  out of the way, in a direction away from ladder  10  leaving only the feet of side rails  12  to contact the ground and to develop their full resistance to slideout. This roller state provides the user with an immediate visual feedback that the setup angle was proper in contrast to that of FIG. 5 b . After using the ladder, the user can restore roller  11  to its neutral position by hand by moving roller arm  80  to the position shown in FIG. 5 e , or for storing purposes by moving roller arm  80  to the position shown in FIG. 5 b.    
         [0039]    A further embodiment of the anti-slide-out device of this invention is shown in FIGS. 6 a - 6   e , which embodiment employs the roller support device detailed in FIG. 6 e . The device comprises roller mechanism support bracket  100  attached to ladder  10  and roller arm  107  having one end pivotally connected by means of roller arm pivot shaft  101  to roller mechanism support bracket  100  and having an opposite end connected to roller  11 . Roller arm  107  forms detent slot  106  in which is disposed a detent pin  105 . The device further comprises pretensioned spring  109  having one end connected to detent pin  105  and having an opposite end connected to spring support pin  108  connected to and extending from one face of roller mechanism support bracket  100 . Roller mechanism support bracket  100  further comprises roller arm stops  102  and  103  disposed on either side of roller arm  107 . The edge region of roller mechanism support bracket  100  disposed between roller arm stops  102  and  103  forms a detent cam  104 .  
         [0040]    In operation, the embodiment of the anti-slide-out device of this invention shown in FIGS. 6 a - 6   e  acts in a manner analogous to that of the embodiment of FIGS. 5 a - 5   e  as described hereinabove, except that it has been modified to preclude ladder  10  from being set up at an angle shallower than the desired inclination angle θ, even under action of a live load W as indicated by arrow  111 , as shown in FIGS. 6 a  and  6   b . The transition from the embodiment of FIG. 5 to that of FIG. 6 is accomplished by removing the cam hump of detent cam  104  closest to ladder  10 , repositioning roller arm stop  103  closest to ladder  10 , and repositioning spring support pin  108  so as to no longer be disposed along the longitudinal axis of roller arm  107 . As shown in FIGS. 6 c  and  6   d , when ladder  10  is positioned with the desired set-up angle θ, there is no slide-out of the ladder under either the unloaded condition of FIG. 6 c  or the loaded condition with sag due to the load of  6   d . As in the case of the embodiment shown in FIGS. 5 a - 5   e , after using the ladder, the user can restore roller  11  to its neutral position by hand by moving roller arm  107  to the position shown in FIG. 6 e.    
         [0041]    [0041]FIG. 7 shows yet another embodiment of the anti-slide-out device of this invention utilizing the roller support device substantially as shown in FIG. 6 e . The device and its mechanism, when utilized on a ladder, cause the ladder to act in a manner analogous to the ladder of FIGS. 6 a - 6   e  except that it has been modified in a manner which eliminates the snap-out retraction of roller  11  and roller arm  107  to an out-of-the-way position. This is achieved by removing the cam hump of the embodiment shown in FIG. 6 e  and eliminating detent slot  106 , which is no longer necessary. This modification enables roller  11  and roller arm  107  to give under sag due to the presence of a live load at the set-up angle θ, but does not retract them to an out-of-the-way position as shown in FIG. 6 d . In this case, when the live load is removed from the ladder, or if the ladder is lifted up, roller arm  107  and roller  11  automatically return to their neutral position with respect to roller mechanism support bracket  100  as shown in FIG. 7.  
         [0042]    In accordance with one embodiment of the anti-slide-out device of this invention, rollers  11  are elastically mounted without preloading as shown in FIG. 8. Roller  11  is connected to one end of flat spring  40 , the opposite end of which is connected to side rails  12  of ladder  10 . Due to the extreme simplicity of this embodiment, the device has high reliability, high robustness and the potential for minimum cost. In addition, to satisfy horizontal storage requirements, the device can be deflected flat against side rails  12  when not in use.  
         [0043]    [0043]FIG. 9 is a side view of an anti-slide-out device similar to the device shown in FIG. 2 utilizing a preloaded spring system. The device comprises roller  11  connected to an underside of an elongated pivotal bracket  51  having one end pivotally connected to side rails  12  by means of hinge pin  56 . A first angle bracket  52  is connected to side rail  12  at a position above hinge pin  56  and a second angle bracket  53  is attached to the end of elongated pivotal bracket  51  opposite to the end connected to side rail  12 . A rod  54  is slidably connected to first angle bracket  52  and second angle bracket  53 . Preloaded spring  50  surrounds rod  54  between first angle bracket  52  and second angle bracket  53 . Preloaded compression spring  50  pretensions rod  54 , as a result of which the suspension will act rigidly until sufficient roller reaction force, indicated by arrow  55 , overcomes the preload whereupon preloaded compression spring  50  will exhibit elastic behavior.  
         [0044]    In accordance with one embodiment of this invention shown in FIG. 10, the elastically mounted roller system of FIG. 8 is preloaded. The device comprises flat spring  40  connected at one end by attachment means  63  to side rail  12  and having roller  11  connected at an opposite end thereof. Threaded rod  60  has one end extending through flat spring  40  and an opposite end connected by pin  62  to side rail  12 . Surrounding threaded rod  60  in the area between flat spring  40  and pin  62  is preloaded spring  61 .  
         [0045]    In accordance with one embodiment of this invention as shown in FIG. 11, the anti-slide-out device incorporates a mechanism that acts as a mechanical fuse to unload the springs when their compression force reaches a preset limit. The device comprises fixed bracket  30  connected to side rails  12 . Roller  11  is connected to one end of vertically oriented threaded rods  72 , the other end of which extends through fixed bracket  30  and is held in place by nut  73 . Connected to threaded rod  72  proximate to roller  11  is detented force limiter  70 . Disposed between detented force limiter  70  and fixed bracket  30 , and surrounding threaded rod  72  is preloaded spring  71 . As shown in FIG. 11, detented force limiter  70  is merely a detented slider. It should be noted that the detented slider must be manually reset or repositioned after it has acted to unload the spring by sliding downward.  
         [0046]    While in the foregoing specification this invention has been described in relation to certain preferred embodiments thereof, and many details have been set forth for purpose of illustration, it will be apparent to those skilled in the art that the invention is susceptible to additional embodiments and that certain of the details described herein can be varied considerably without departing from the basic principles of the invention.