Abstract:
A novel lockstep mechanism for a rolling ladder is described. The weight-releasing ladder lockstep allows a ladder to be relocated on wheels but when a person climbs the ladder, the front wheels are automatically retracted and the ladder rests firmly with its front feet on the floor. When in the climbing (stationary) position the front wheels of the lockstep are retracted and the ladder rests on the lockstep&#39;s feet. When in the rolling position, the ladder is tilted slightly back on its rear wheels and the wheels of the lockstep are pushed down to allow the ladder to roll. When in the rolling position, the lockstep wheels are held in place via a latch which is isolated from rolling vibrations through pivoting shock links and springs.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims the benefit of U.S. Provisional Application No. 60/661,955 filed on Mar. 15, 2005, which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Lockstep ladders were first introduced over fifty years ago. A lockstep is used to raise a rolling ladder, also commonly know as a rolling staircase, into its rolling position and when stepped on, drops the ladder&#39;s feet to the ground thereby locking it in the climbing position. 
     Since their inception all locksteps have functioned basically the same way. A lever is used to raise the ladder into the rolling position and it is held in place by a hook which is generally kept in place by a tension spring. The original design of the lockstep uses the bottom step as a lever. The step pivots on its rear edge and the front of the step is raised when the ladder is in the rolling position. When the user steps on the first step of the ladder the front of the step is rotated down by the weight of user, releasing the lockstep and dropping the feet to the floor putting the ladder in the climbing position. 
     This design worked well for many years but had significant functional and safety problems. Functionally, the ladder was difficult to put in the rolling position for taller, heavier ladders. The step needed to be lifted up with the top of the foot to put the ladder in the rolling position, the heavier the ladder the more difficult this was to do. The safety problem came into play primarily when the ladder was left on a retail store floor unattended and in the rolling position. In this position the front of the step was up. Shoppers, often children, would sit on the lowest step and generally grab the step as they were sitting. The ladder was released by their body weight as they were sitting and would severely pinch and in some cases sever shoppers&#39; fingers. 
     In the late 1990&#39;s ladder manufactures all became painfully aware of this problem as accident victims sued the manufacturers. Since that time most manufactures changed to a new design which involves two separate levers, a pedal to lift the ladder into the rolling position and a trip bar to release the ladder, dropping it to the floor. In this prior art design the step does not move. The trip bar is positioned in front of the step so that when the user steps on the bottom step his foot pushes the trip bar down releasing the lockstep and the ladder feet drop to the ground for climbing. This design eliminates the safety problem and works well, however this prior art lockstep has two areas where improvement would be desirable. First, it has two levers: the pedal and the trip bar. Users get confused and try to lift the ladder by pushing on the trip bar breaking the lockstep. Second, the trip bar can be easily stepped over or bent out of position from stepping on it as described above. This action allows the ladder to be climbed in the rolling position a violation of OSHA and ANSI safety regulations. This also creates a durability problem since the lockstep is designed to support the weight of the ladder in the rolling position not a ladder and person. 
     BRIEF DESCRIPTION OF THE INVENTION 
     A novel lockstep mechanism for a rolling ladder is described. The weight-releasing ladder lockstep allows a ladder to be relocated on wheels but when a person climbs the ladder, the front wheels are automatically retracted and the ladder rests firmly with its front feet on the floor. When in the climbing (stationary) position the front wheels of the lockstep are retracted and the ladder rests on the lockstep&#39;s feet. When in the rolling position, the ladder is tilted slightly back on its rear wheels and the wheels of the lockstep are pushed down to allow the ladder to roll. When in the rolling position, the lockstep wheels are held in place via a latch which is isolated from rolling vibrations through pivoting shock links and springs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of the lockstep in the rolling position. 
         FIG. 2  is a perspective view of the lockstep from underneath in the rolling position. 
         FIG. 3  is a side view of the lockstep in the rolling position. 
         FIG. 4  is a side view of a rolling ladder incorporating the lockstep. 
         FIG. 5  is a perspective view of the lockstep base. 
         FIG. 6  is a perspective view of the lockstep frame. 
         FIG. 7  is a perspective view of a shock link. 
         FIG. 8  is a series of side views of the lockstep showing the stages of movement of the lockstep invention from rolling position to stationary position. 
         FIG. 9  is a series of side views of the lockstep showing the stages of movement of the lockstep invention from stationary position to rolling position. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The improved lockstep  2  is shown in  FIGS. 1 ,  2  and  3 . In this preferred embodiment, the ladder  1  (shown in  FIG. 4 ) is put in the latched or rolling position using a single pedal  3 . While in the stationary position (wheels retracted) the base step  22  is supported through legs  16  and feet  17 . Preferably, there is no trip bar in this improved design. The ladder stairs  18  are moved into rolling position using a foot pedal  3  and rollers  6  to provide leverage, thereby lifting even the largest ladders easily. In the rolling position, compression springs  5  in combination with shock links  12  are used to support the weight of the ladder  1  and to function as shock absorbers allowing the ladder  1  to be rolled over rough surfaces without activating the release of the lockstep  2 . As a user steps on the base step  22  his weight tilts the ladder stairs  18  forward and towards the ground. The compression springs  5  are calibrated using spacers in such a way that as soon as the user applies a predetermined amount weight (in one preferred embodiment seventy pounds) to the base step  22 , the shock link  12  pivots up causing the release bar  27  to mechanically release a latch  25  allowing the lockstep frame  20  to swing free dropping the feet  17  to the floor and making the ladder  1  ready for climbing. This prevents anyone from being on the ladder  1  without the ladder dropping into a safe climbing position. 
     This invention is a major improvement over existing weight actuated locksteps which all tend to fall into the stationary position when rolled across floors due to vibration. In prior art designs, it was difficult to adjust latch or spring tension so that it would be tense enough not to release from rolling vibrations yet sufficiently relaxed so that the weight of a smaller person or child (about seventy pounds) would cause it to release. If the tension was set too high, lighter users could step on the ladder without it falling into non-moveable position, thus creating a safety hazard. If the tension was set too low, the ladder feet would fall to the ground while the ladder was being moved thus creating a major nuisance and making the ladder impractical for many environments. The present invention overcomes this limitation. 
     With reference to  FIGS. 1 ,  2  and  3 , a lockstep base  14  is made up of legs  16 , feet  17  and lockstep base frame  15 , all rigidly attached to the bottom ladder step  22  (also referred to herein as a base step).  FIG. 5  shows a perspective view of the lockstep base  14  (base step  22  not shown). A caster wheel frame  8  supports caster wheels  4  and is pivotally attached to the lockstep base frame  15  at the caster pivots  30  on the base frame extension arms  13 , said base frame extension arms  13  forming a portion of the lockstep base frame  15 . A lockstep frame  20  with a pedal  3  (preferably shaped to easily allow a user to apply pressure through his foot) moves across the caster frame  8  on rollers  6  and is pivotally attached to two shock links  12  (one on each side of the lockstep base  14 ) at the lockstep frame pivots  31 .  FIG. 6  shows lockstep frame alone. Two rollers  6  (not shown in  FIG. 6 ) are mounted through the roller pivots  33  viewable in  FIG. 6 . Preferably, the two shock links  12  are attached by a cross bar  9  to stabilize the shock links  12 , as shown in  FIG. 1 .  FIG. 7  shows one of the two shock links alone. 
     The lockstep frame  20  further has a latch mount  23  to which a latch arm  26  is attached for engaging into a latch catch  24  underneath the caster frame  8 . The latch mount  23 , latch arm  26 , latch catch  24  and latch spring  28 , together form a latch  25 . 
     The shock links  12  are pivotally connected to the lockstep base frame  15  at the shock link pivots  32 . The shock links  12  are held in place against the lockstep base frame  15  by springs  5  that press the two together via a bolt  7  that passes through the lockstep base frame  15  and the shock links  12 . In this manner as the shock links  12  pivot up, the bolt  7  pulls the bottom of the spring  5  up and compresses it against the lockstep base frame  15 . The result is that as the shock links  12  pivot upwards, the springs  5  apply a downward force to pull the shock links  12  back towards the lockstep base frame  15 . 
     In order to show the working of the invention,  FIGS. 8   a  through  8   d  show the lockstep moving from the rolling (wheels down) position to the stationary (feet down) position, and  FIGS. 9   a  through  9   d  show the lockstep moving back to the rolling position. To more clearly describe the invention, certain stages have been repeated so that  FIGS. 8   a  and  9   d  (and  FIG. 3 ) are the same and  FIGS. 8   d  and  9   a  are the same. 
     In the wheels-down rolling position ( FIGS. 1 ,  2 ,  3 ,  4 ,  8   a  and  9   d ), the latch  25  is engaged and holds the caster wheel frame  8  to keep the wheels  4  in the down position. The weight of the ladder  1  is supported by the caster wheels  4  on the caster frame  8  which is held down by the lockstep frame  20  through the rollers  6 . In this position the ladder stairs  18  and ladder frame  40  are rotated slightly back on the rear wheels  41  of the ladder  1 . While the ladder  1  is being relocated on its wheels  4 ,  41 , the ladder  1  might encounter bumps in the floor surface. The bumps cause the caster wheels to “push up” on the ladder. The “pushing up” is absorbed to a great extent by the shock link springs  5 , thus preventing the latch  25  from decoupling from the caster wheel frame  8  and lowering the lockstep base  14  onto its feet  17 . In all known prior art weight releasing locksteps, the combination of heavy stairs and rough surfaces would often cause the latching mechanism to release thus raising the front wheels and preventing further rolling of the ladder. By isolating the caster wheel frame  8  from the lockstep base  14  through shock links  12  and springs  5 , the ladder  1  can be rolled across bumpy surfaces without the vibrations causing the latch  25  to release. 
     When a user steps on the ladder  1  (usually on the base step  22 ), his weight causes the shock link springs  5  to compress and shock links  12  to pivot up at the shock link pivots  32  ( FIG. 8   b ). As the shock links  12  pivot up, they pull up the lockstep frame  20  with them which in turn pulls the caster frame  8  upwards. During this upward movement of the lockstep frame  20  and the caster frame  8 , the latch arm  26  is forced against the latch release bar  27  causing the latch arm  27  to disengage from the latch catch  24 , releasing it from the caster frame  8  ( FIG. 8   c ). At this point, the lockstep frame  20  is free to move on its rollers  6  across the caster frame  8  and the lockstep frame  20  pivots up allowing the caster frame  8  to freely pivot up via the caster pivots  30 . With the casters  4  unable to support the weight of the ladder  1 , the ladder rests firmly on the feet  17  and legs  16  of the lockstep base  14  ( FIG. 8   d ). It should be noted that the same disengagement would occur if a user skipped the base step  22  and tried to stand on any of the lower stairs  18  of the ladder  1 . 
     As shown in  FIG. 9 , to put the ladder  1  back into the rolling position a user presses, preferably with his foot, on the lockstep frame pedal  3 . This causes the lockstep frame  20  to pivot, via the lockstep frame pivots  31 , causing a downward force on the caster frame  8  through the rollers  6  as the lockstep frame  20  moves down and towards the back (the lockstep base feet  17  being the front) rolling across the caster frame  8  ( FIG. 9   a ). This downward force causes the caster frame  8  to pivot down, via the caster pivots  30 , forcing the caster wheels  4  onto the ground and the lockstep base  2  up (along with the ladder stairs  18 ). The caster wheels  4  then support the weight of the ladder  1  ( FIG. 9   b ). The latch arm  26  extending from the lockstep frame  20  to the caster frame  8  is forced down (by the downward movement of the lockstep frame  20 ) as the lockstep arm passes over latch catch  24 , thereby compressing the latch spring  28  ( FIG. 9   c ). Eventually the latch arm  26  slides over the latch catch  24  and into the locked position ( FIG. 9   d ). With the latch  25  closed, the lockstep frame  20  is prevented from pivoting back to the up position. The latch  25  is held in place by the latch spring  28  pressing the latch arm  26  against the latch catch  24 . Engaging the caster wheels  4  as described involves lifting the ladder stairs  18  by rotating the ladder stairs  18  and ladder frame  40  about the rear wheels  41 . This lifting task is made easier by the rollers  6  and the leverage created by the lockstep frame  20  and foot pedal  3 . 
     In one embodiment, the compression springs  5  are calibrated so that when in the rolling position they support the weight of the ladder plus seventy pounds, but remain essentially decompressed thus allowing the shock link to function. 
     The lockstep  2  is attached, preferably rigidly, to the ladder stairs  18  and the ladder frame  40  as shown in  FIG. 4  to form the rolling ladder  1 . The rear wheels  41  are connected rotationally to the ladder frame  40 . 
     The terms wheels and casters are used interchangeably herein and the use of either term herein is not meant to exclude the other term and is meant to include any rolling mechanism. Likewise the latch is not meant to be limited to the spring loaded latch described but may be any type of latching mechanism, including mechanical or magnetic. 
     The particularly embodiment described herein is provided by way of example and is not meant in any way to limit the scope of the claimed invention. It is understood that the invention is not limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. Without further elaboration, the foregoing will so fully illustrate the invention, that others may by current or future knowledge, readily adapt the same for use under the various conditions of service