Abstract:
The ladder stand employs a pair of swivable caster wheels at the front and a pair at the rear which are used in cooperation with a pair of closely located non-swivable caster wheels, thereby providing a structure which has three modes of operation, one mode for climbing, a second mode which permits the stand to be pushed in a straight line with wide turns and a third mode of operation which permits the stand to be first pushed laterally and to provide sharp turns. A front wheel support is mounted on the front end and a retractable first pair of swivable caster wheels is mounted on the front support. A rear wheel support is mounted on the rear end, with a retractable second pair of swivable caster wheels mounted on the rear support. A third pair of non-swivable rigid caster wheels are mounted at the rear end.

Description:
BACKGROUND OF THE INFORMATION 
     1. Field of the Invention 
     The present invention relates to a safety mobile ladder stand and more particularly, to a large ladder stand which can be used in small spaces where mobility of a larger ladder stand is restricted. 
     2. Description of the Prior Art 
     Mobile or safety ladder stands are generally known in the industry and are used by workers and persons who need to reach products or materials stored on shelves in stores and warehouses. Such safety ladder stands also generally incorporate a rolling/locking mechanism so that the ladder stand can be moved easily to different locations in the warehouse or building when such a mechanism is actuated. With such a construction, the rolling/locking mechanism is deactivated when the mobile ladder stand is to be used such as when a person climbs on it to reach overhead shelves or spaces. The deactivation of the rolling/locking mechanism stabilizes the ladder stand in a fixed position thereby allowing for a safer and steadier use of the stand. 
     Some large mobile ladder stands with rolling/locking mechanisms are difficult or awkward to maneuver in small spaces such as in the aisleways of stores or warehouses. This is due to the fact that the length of the base must be increased to accommodate a taller ladder stand. Since such ladder stands are generally supported by wheel sets at all four corners of the base, a longer base makes turning of the stand difficult. 
     The problem stated previously was addressed in part in U.S. Pat. No. 5,941,341 entitled “Mobile Ladder Stand” which issued on Aug. 24, 1999. This patent discloses a safety ladder stand having a generally rectangular base having a front and rear and a center beam, with a plurality of stair treads extending upwards from the front of the base and means for supporting the stair treads secured to the base. Front wheels are mounted at the front of the base and beneath the top of the stair treads, with center wheels mounted on the center beam of the base and rear wheels mounted at the rear of the base. A set of feet are mounted at the front of the base. The ladder stand has an activated position and a deactivated position. In the activated position, the front and center wheel sets are in contact with the ground to enable the ladder stand to roll and the rear wheels and front support feet are out of contact with the ground. In the deactivated position of the ladder stand, the front and center wheel sets are not in contact with the ground and the rear wheels and the front wheels are in contact with the ground to prevent the ladder stand from being rolled. It includes means for moving the ladder stand from the deactivated position to the activated position. 
     The assignee of the present invention has manufactured for many years relatively small ladder stands with five to nine steps which are provided with a base having wheel supports at the front and rear of the stand. Each wheel support is provided with a safe-lock mechanism and a pair of swivable casters or wheels rotatable throughout 360°. The use of the safe-lock mechanism and swivable caster wheels at the rear end of the base allows the ladder stand to be more readily maneuverable in confined spaces. 
     The assignee of the present invention has also manufactured for many years relatively large ladder stands with six to nineteen steps, as an example, having a base with a safety lock mechanism and a pair of swivable caster wheels at the front and a pair of rigid caster wheels at the rear of the base. It is difficult with such a construction to maneuver the large ladder stands in confined spaces. 
     While a great variety of mobile ladder stands have been heretofore been proposed, nevertheless there remains a need for improved relatively large mobile ladder stands which are simple in construction, are relatively inexpensive to manufacturer and are convenient to use. 
     SUMMARY OF THE INVENTION 
     It is a feature of the present invention to provide an improved relatively large ladder stand which is stable when the ladder stand is in use and is mobile when it is required to move the ladder stand in confined spaces or areas. 
     It is a further feature of the present invention to provide an improved relatively large mobile ladder stand which employs a pair of swivable caster wheels at the front of the ladder and a pair of swivable caster wheels at the rear of the ladder which are used in cooperation with a pair of closely located non-swivable caster wheels, thereby providing a structure which has three modes of operation, one mode for climbing, a second mode which permits the ladder to be pushed in a straight line with wide turns and a third mode of operation which permits the ladder stand to be first pushed laterally and to provide sharp turns. 
     In the broader aspects of this invention, there is provided a ladder stand comprising a unitary base having a front end and a rear end, with a plurality of stair treads extending upwardly from the base and supported thereon. A front wheel support is mounted on and located approximate to the front end of the base and a retractable first pair of swivable caster wheels is mounted on the front wheel support. The ladder stand further has a rear wheel support mounted on and located inwardly from the rear end of the base, with a retractable second pair of swivable caster wheels mounted on the rear wheel support. A third pair of non-swivable rigid caster wheels are mounted at the rear end of the base outwardly from the retractable second pair of caster wheels. A plurality of foot pads are mounted on the front end of the base forward of the retractable first pair of swivable caster wheels. 
     A pair of laterally spaced apart independently operated foot pedals are mounted on the base at the front end thereof. Front and rear linkages are respectively carried by the front and rear wheel supports. A trip bar is located at the front end of the bottom stair tread. A trip tube is connected on one end to the front linkage and on the other end to the rear linkage. A reset tube is connected on one end to the front linkage and on the other end to the rear linkage. With such a construction, the trip bar of the present invention, when actuated, causes the trip tube to raise the front and rear wheel supports and the corresponding first and second pairs of swivable caster wheels from the ground thereby permitting the base to drop onto the foot pads at the front end and onto the rigid caster wheels at the rear end of the base thereby placing the ladder stand in a first mode of operation intended for a person climbing the ladder. 
     One of the pedals of the present invention, when actuated, causes the reset tube to lower the front wheel support and to bring the first pair of swivable caster wheels into contact with the ground thereby raising the front end of the base and the foot pads off the ground while maintaining the rigid caster wheels on the ground thereby placing the ladder stand in a second mode of operation intended for the ladder stand to be pushed to a new location either forward, backward or diagonally with straight tracking of the wheels. 
     The other of the pedals of the present invention, when actuated, lowers the rear wheel support and brings the second pair of swivable caster wheels into contact with the ground and raises the third pair of rigid caster wheels off the ground while maintaining the front caster wheels in contact with the ground thereby providing a third mode of operation intended for the ladder stand to be pushed or turned in confined spaces, with the four swivel caster wheels allowing for forward, backward, diagonal and lateral movement. 
     Other objects and distinctive features of the present invention which have not been referred to previously will appear from the following specification and claims and from the accompanying drawings wherein is shown a preferred embodiment of the present invention as described in the specification. The showing so made is not intended to be either exhaustive or as limiting the scope of the subject invention. The purpose here is to illustrate the invention so that others skilled in the art may so fully understand its principles and applications, that they may embody it and adapt it in any of various forms appropriate to the attainment of any particular or appropriate purpose in use. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the ladder stand or apparatus in accordance with the present invention. 
     FIG. 2 is a side elevation of the safety ladder stand showing the first and second pair of swivable wheels in contact with the ground and further illustrating the third set of wheels and the foot pads spaced from the ground. 
     FIG. 3 is a top view of the base of the ladder stand looking in the direction of arrows  3 — 3  of FIG.  2 . 
     FIG. 4 is a fragmentary side elevational view of the wheel base of the ladder stand, with parts broken away and with the first and second swivable wheels in contact with the ground. 
     FIG. 5 is a fragmentary side elevational view, with parts broken away of the wheeled base, after the trip bar has been actuated so as to raise the first and second swivable wheels and to bring the legs or feet at the front of the base and the rigid wheels at the end of the base into contact with the ground as in the first mode of operation. 
     FIG. 6 is a top view of the base of the ladder stand with parts broken away in order to show the construction of the front and rear wheel supports. 
     FIG. 7 is a fragmentary front elevational view of the ladder stand showing the front wheels in contact with the ground and the foot pads in an elevated position. 
     FIG. 8 is a perspective view of a prior art ladder stand employing a frame with front and rear wheel supports, each wheel support containing a pair of swivable caster wheels. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, the present invention is shown embodied in a safety mobile ladder stand or assembly  10  comprising a rigid structural frame  12  for supporting a plurality of horizontal stair treads or steps  20  including the lower stair tread  22  and the top stair tread  24 , with any number of intermediate treads or steps therebetween, as an example, from six to sixteen steps. The plurality of stair treads  20  are secured together at each of the sides thereof by a pair of straps  26  and  28 . In order to protect the person climbing the stairs or treads  20 , a pair of side hand rails  30  are provided. The hand rails  30  at the lower ends thereof are provided with inwardly turned extensions  32  which are connected to the inclined straps  26 ,  28 . The upper ends of the hand rails  30  are provided with rearwardly turned rail portions  34  which form part of the safety rail enclosure  35  provided at the top of the ladder stand  10  above the top tread  24 . The hand rails  30  are also connected to straps  26  and  28  by cross braces  31 . 
     The safety rail enclosure  35  is open at the front and includes the vertical rails  33  of varying heights which are interconnected by horizontal braces or struts  37  and the rail portions  34  as best illustrated in FIGS. 1 and 2. The safety rail enclosure  35  provides safety grips for a person when standing on the top tread or platform  24 . 
     The frame  12  includes a pair of vertical support beams  36  at the rear thereof which extends from the base  38  to beneath the top tread  24 . The upper part of the frame  12  at the rear thereof includes an upper diagonal member  39  which extends from the upper end of one rail  36  to an intermediate portion of the other rail  36  as best shown in FIG.  1 . The frame  12  further includes a pair of front support members  40  which are arranged generally vertically, with the upper ends of each member  40  connected to a horizontal support structure consisting of horizontal framing members  42 ,  44  which are interconnected by a laterally extending member  46 . The vertical members  40  are connected on the lower ends of the base  38  and the upper ends thereof are connected to the rear of the frame  12  by means of rearwardly and downwardly extending support members or braces  46  and  48 . The cross members, beams and support elements forming the ladder stand  10  may be manufactured from steel or from 1 inch, 16 gauge aluminum tubing which is standard in the industry. The framing members are connected by bolts and nuts or by other means such as rivets or welding, well known in the art. It should be appreciated that the design of the stair treads and the arrangement of the support means and cross members are well known in the art and are not therefore critical to the practicing of the present invention. 
     The base  38  of the mobile ladder stand  10  includes a pair of longitudinally extending members  50  which are appropriately secured to laterally extending member  52  at the rear of the frame  12  and to the intermediate or center beam  54 . The base also includes a brace  55  between center beam  54  and one of the longitudinally extending members  50 . 
     The base  38  further includes at the front there of a laterally extending front support means  60  including a laterally extending element  62  attached to the tread  22  with the element  62  terminating in a pair of downwardly turned legs  64  which are provided with foot pads or bumpers  66 . The longitudinal members  50  are secured to the legs  64  by suitable fasteners. The front support means  60  may also include a center leg and foot pad for larger ladder stands. 
     A front wheel support  70  is rotatably or movably mounted on and located adjacent or proximate to the front end of the base  38 . The front wheel support  70  includes a frame  72  which includes bearing plates  74  and  76 . The bearing plates  74 ,  76  provide support for the pair of front caster wheels  80  which are mounted in housings  82  and are rotatably carried by the bearing plates  74 ,  76  for rotation or swiveling throughout 360°. The construction of the caster wheels  80  and their respective housing are well known in the art. 
     The front wheel support  70  includes a safe-lock mechanism for rotatably raising and lowering the frame  72  to raise or lower the wheels  80  relative to the ground. Such mechanism includes a conventional trip bar  86  at the front of the lowest step or tread  22  which is coupled to the frame  72 . The frame  72  is provided with a pair of upstanding first and second front linkages  88  and  90 . 
     The front wheel support  70  also includes a left pedal  96  and a right pedal  94  as viewed in FIG.  1 . Pedal  94  includes a foot portion  100 , an upright portion  102  and a generally rectangular base portion  104  carried by the frame  72  as viewed in FIG.  5 . Pedal  94  controls the front linkage  90  and the trip tube as will be subsequently described. 
     The left pedal  96 , as shown in FIG. 4., includes a foot portion  106 , an upright portion  108  and a generally rectangular base portion  110  carried by the frame  72 . Pedal  96  controls the front linkage  88  and the reset tube as will be subsequently described. 
     A rear wheel support  114  is rotatably mounted on and located inwardly from the rear end of the base  38  as illustrated in FIG.  4 . The rear wheel support  114  includes a frame  116  attached to the longitudinal members  50 . The frame  116  includes a pair of horizontal bearing plates  120  which support a retractable second pair of swivable caster wheels mounted thereon. The second pair of swivable caster wheels  122  are each mounted in a housing  124  and are rotatably carried by the bearing plates  120  for rotation through 360°. 
     A third pair of non-swivable rigid caster wheels  128  are mounted on the rear end of the base  38 . The rigid caster wheels  128  are mounted in housings  130  and are rotatable only and are not swivable. The wheels  128  are located close to but outwardly from the retractable second pair of swivable caster wheels  122 . 
     The rear wheel support  114  is provided with a pair of rear brackets or linkages  132  and  134 . The rear linkage  132  is longitudinally aligned with front linkage  90 , while the rear linkage  134  is longitudinally aligned with the front linkage  88  as illustrated in FIG. 6. A trip tube  140  is connected on one end to the front bracket or linkage  90  and on the other end to the rear bracket or linkage  132 . A reset tube  144  is connected on one end to the front linkage  88  and on the other end to the rear linkage  134  as shown in FIG. 6. A spring  145  is carried by the rear wheel support  114  to assist in the resetting of the trip tube  140 . 
     Prior to installing the trip tube  140  and the reset tube  144 , it is advisable to place the ladder stand in an upright position. The first step is to reset the front and rear caster wheel assemblies  80  and  122  so that the ladder stand  10  is able to roll on the four swivable casters or wheels. The next step is to connect the trip tube  140  to the linkages  90  and  132 . The trip tube has an eye bolt end which is connected to the rear linkage  132  while the crimped end is connected to the front linkage  90 . It is necessary to tighten the bolts which connect the ends of the trip tube to the linkages. The bolts, when tightened, must still allow for the front and rear linkages to rotate. 
     The reset tube  144  is longer then the trip tube  140  although the tubes could be of the same length. The third step requires the eye bolt end of the reset tube  144  to be connected to the rear linkage  134  while the crimped end is connected to the front linkage  88 . When attaching the reset tube  144  to the rear linkage  134 , it is important that the eye bolt on the reset tube  144  and the lock nut are both on the outside of the rear linkage  134  as shown in FIG.  6 . Thereafter the bolts are tightened sufficiently to permit both the front and rear linkages to rotate. 
     In operation, a person steps on the trip bar  86  which causes the ladder to drop onto the bumpers or pads  66  located in the front of the ladder stand  10  and onto the rigid casters or wheels  128  located at the rear of the stand. To reset the front of the ladder to roll on the swivel casters or wheels  80 , it is necessary to step on the right pedal  94 . To reset the rear of the ladder  10  to roll on the swivel casters or wheels  122 , it is necessary to step down on the left pedal  92 . 
     The ladder stand  10  provides stability when climbing and advances the mobility thereof when moving. The ladder stand  10  has three modes of operation. The first mode is when a person steps on the trip bar  86  which is located along the front edge of the bottom step  22 . As a result thereof, the ladder stand  10  comes to rest on the front pads  66  and the rigid caster wheels  128  located in the rear. The rigid caster wheels  128  are in position to prevent movement of the ladder. This mode of operation is intended for climbing the ladder stand  10 . 
     The second mode of operation occurs by stepping on the right pedal  94  located near the floor in the front of the ladder stand  10 . At that time, the front legs  64  and the corresponding pads  66  are lifted from the floor. The swivel casters  80  located in the front and the rigid casters  128  located in the rear of the ladder stand  10  support the ladder. This allows or permits a person to push the ladder stand  10  to a new location. Such operation is beneficial when pushing the ladder stand  10  over relatively long distances. When rolling, the rigid casters or wheels  128  keep the tracking of the ladder straight. A ladder supported by four swivel casters, as in the prior art, tend to turn and drift off course, forcing the user to overcome this tendency. In mode number 2, the ladder stand  10  may only be pushed forward, backward or diagonally with straight tracking of the wheels. The turning radius is equal to the base length of the ladder stand. The first and second modes of operation just described are standard methods of operation in many conventional rolling ladders or ladder stands. 
     The third mode of operation distinguishes the present invention from the prior art. Once the ladder stand is in the second mode of operation, stepping on the left pedal  92  located near the floor near the front of the ladder stand  10  lifts the rear rigid caster wheels  128  from the floor. The swivable caster wheels  80  at the front and the swivable caster wheels  122  at the rear support the ladder stand  10 . This permits the ladder stand  10  to be pushed to a new location. The third mode of operation is beneficial when pushing or turning the ladder stand in confined spaces. The use of the four swivable caster wheels and  80  and  122  allow for forward, backward, diagonal and lateral movements. The turning radius is reduced to one half of the base length of the ladder stand  10 . The third mode of operation is new and unique to relatively large ladder stands. 
     PRIOR ART (FIG.  8 ) 
     One of the prior art ladder stands made and sold for many years by the assignee of record is partially illustrated in FIG.  8 . The ladder stand  160  has a rectangular base  162  including a pair of tubular longitudinally extending member  164  connected by a cross member  166  at the rear end thereof. A front wheel support  168  and a rear wheel support  170  are movably carried by the base  162 . The front wheel support  168  is provided with a pair of conventional swivable casters or wheels  172  while the rear wheels support  170  is provided with a pair of swivable casters or wheels  174 . The ladder stand  160  has a super structure above the base  160 , not shown, including the front vertical legs  180  and the rear vertical legs  182 . Each of the legs  180 ,  182  are provided with foot pads or bumpers  184 . The pedals  186  are provided for raising and lowering the front casters or wheels  172 , and the connecting rod  190  is used to raise and lower the rear casters or wheels  174 . The rear mounted swivel casters or wheels  174  allow the ladder stand, as an example, with five to eight steps, to be more readily maneuverable in confined spaces. When climbing the ladder stand  160 , the wheels are raised and the stand rests on the leg bumpers  184 . 
     While there have been described above the principals of this invention in connection with a specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of the invention.