Abstract:
A ladder having platform steps, the ladder being convertible between a deployed position for supporting a person or other load, to a storage, scaffold, or ramp position in which the steps lie in a generally planar arrangement. When deployed, the ladder steps remain parallel to each other and form a series of parallelograms with the rails of the ladder. The ladder is also capable of being locked or secured at various angles of deployment. The ladder further includes receivers to selectively receive accessories such as wheels, hooks, handles, or pads. The addition of accessories such as wheels allows the ladder in the storage position to be used as a creeper, dolly, or cart.

Description:
RELATED APPLICATION 
       [0001]    This application is a continuation-in-part of U.S. application Ser. No. PCT/US09/54630 filed on Aug. 21, 2009. This application also claims priority to U.S. Provisional Application No. 61/430,331 filed on Jan. 6, 2011. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to the field of ladders and scaffolding, particularly ladders with platform steps and accessories that attach thereto. The invention also relates to creepers and hand carts. 
       BACKGROUND OF THE INVENTION 
       [0003]    The ladder of the present invention is a platform step ladder designed to allow the ladder to be positioned at various inclinations, while allowing the platform steps to remain generally parallel to the ground. In another configuration, the platform steps of the ladder can align to form a generally or substantially continuous planar surface to allow the ladder to be used as a platform or as a ramp. In alternate embodiments, the ladder of the present invention can include mechanisms to allow the ladder to be locked or secured at a particular inclination. Additionally, the ladder can include a wheeled base to allow the ladder to be moved from place to place. In further embodiments of the invention, the ladder is constructed to accept accessory bars to permit the attachment of accessories such as wheels, to allow the ladder, when in the platform configuration, to be used as a creeper. Other accessory bars include wheels and a handle to allow the platform to be used as a cart. Other accessory bars include hooks or pads to be used on the top end of the ladder when the ladder is deployed. 
       SUMMARY OF THE INVENTION 
       [0004]    The ladder base consists of a rectangular frame with four forward attachment brackets and four rear brackets extending upwards from the base. The ladder frame includes a plurality of ladder frame rails and a plurality of steps located between the rails. Pairs of ladder frame rails are connected by support or pivot rods, similar in form to the rungs of a conventional ladder, to form a front frame and a rear frame. In the preferred embodiment, the support rods are welded to the frame rails. In alternate embodiments, the support rods fit through apertures in the rails and are secured to the rails by welds, mechanical fasteners such as threads and nuts, or cotter pins. While the support rods may be free to rotate with respect to the ladder rails, it is not necessary. The platform or steps of each ladder link the front frame and the rear frame. The ladder frame rails attach to the brackets of the base with pivot rods welded to the ladder frame rails. In other embodiments, other means of attachment, such as rivets, nuts and bolts, pins, or other fasteners can be used to pivotably attach the rails to the base. 
         [0005]    The steps or platforms of the ladder are free to rotate about or hinge around the support rods connecting the ladder rails. The pivot arrangement may be improved by means of fitted bushings. The steps are made of a center brace, two end brackets and three support brackets with a tread plate on the top side of the bracket weldment. The steps are secured to the frame with support or pivot rods inserted through the steps and welded to the frame rails. At the ends of the ladder frame are four locking brackets that engage the lock pins to secure the assembly in the ramp or scaffold function. 
         [0006]    When assembled, the ladder is adjustable so that it may be inclined at different angles with respect to the ground while allowing the platform steps to remain generally parallel to the base of the assembly, which is intended to be placed on the ground. As the ladder frame rails rotate with respect to the base, the steps and base act to keep the four rails parallel at any pitch angle. When the ladder is collapsed, the steps line up to form the surface of a scaffold or ramp. 
         [0007]    At or near the top end of the ladder frame, various attachments can be added for certain applications, allowing the ladder to attach to or interface with another object, such as a rail on the side of a farm implement or a receiver mounted on a flatbed trailer. Of course, the ladder can be deployed free-standing against a wall or other structure, or attachments such as hooks, a roller and track configuration or a bracket assembly for securing to a flatbed type semi trailer. Pneumatics or hydraulics could also be implemented to actuate one pair of the rails to quickly flatten the ladder to make a ramp or slide. In other embodiments, supports or jacks between the ladder rails and the ground or other reference surface can be used to secure the ladder at a particular inclination. 
         [0008]    The ladder is also constructed to receive accessory bars that allow features to be selectively attached and removed from the ladder. Specifically, the accessory bars equipped with a headrest and swivelable wheels, disclosed herein allow the ladder, when in the stowed or platform configuration, to be used as a creeper for accessing height restricted areas such as the underside of a trailer, car, or truck. Other accessory bars can include non swivelable wheels such as those mounted on an axel extending across the accessory bar or also included an upright handle that is selectively locked in an upright or first position, but allowed to pivot between the upright and horizontal position when unlocked. Providing the wheels and handle allow the ladder, when in the stowed or platform configuration, to be used a hand cart or trailer. 
         [0009]    The ladder of the present invention can be described as having three main components: 
         [0010]    1) Ladder frames 
         [0011]    2) Ladder base and steps 
         [0012]    3) application/attachment assembly 
       1) Ladder Frame: 
       [0013]    Components of ladder frames include a plurality of rails, and a plurality of support rods. In the preferred embodiment, four rails are used. The support rods connect pairs of rails, in a fashion similar to ladder rungs, to form what are akin to two normal ladders. The spacing of the support rods can vary depending upon the application of the ladder. The spacing of the support rods on each frame will be similar, so that the steps linking the two ladder frames will maintain the same angle with respect to each other. The two ladder frames are linked by the base and steps, the support rods pivotably or hingedly supporting the platform steps. Components of ladder frame can be assembled in a manner that when in an unfolded working position at a 45 degree pitch, ladder will give the appearance of a flight of stairs. 
         [0014]    In addition, when the ladder frame is in a folded position or storage position, it can be used as a ramp or scaffolding, as the steps of the ladder fold to lie in a generally planar arrangement between the rails. 
       2) Ladder Base and Steps: 
       [0015]    The bottom of the ladder frame pivotably attaches to brackets on the ladder base. The base includes brackets that are offset in height. The offset allows one set of frame rails to overlie another set of frame rails, allowing the ladder to fold and form a platform or scaffold surface. Once the frame is attached to base and steps are attached to the support rods, the ladder may be set at different angles, and the steps will remain parallel to the base. While the brackets may be placed at the corners of the base, it is advantageous to have the based extend some distance in front of the front set of brackets. The extension of the base provides leverage to resist the torque that may be generated by loads on the steps of the ladder when the ladder is in use. The base may also include handles on its periphery to allow ease of carrying. The handles can also provide the user a convenient handhold when deploying or stowing the ladder when the ladder is used in a track mounted configuration. 
         [0016]    The ladder base will also provide secure footing for the ladder assembly in addition to having a locking device to be used when ladder is in a folded down position for use as a ramp or for storage. The ladder base is optional, and a ladder consistent with the invention described herein can be constructed without a base. In such an embodiment, the locking mechanism to lock the two ladder frames together is located on the steps, or on the rails. 
         [0017]    In a ladder that does not have a base, the steps link the two ladder frames. In such an embodiment, the ends of the rails may include height adjustment devices to assist in leveling the ladder frames on uneven ground. 
         [0018]    The linkage provided by the base and steps allows the ladder of the present invention to be used at an infinite number of pitches between 0-90 degrees, since the angle formed by the rails with respect to the ground may change, although the platform steps remain parallel to the ground and to each other. When viewed from the side, the frame rails and the steps form a parallelogram. 
         [0019]    The ability to keep the steps parallel is of benefit if the top of the ladder is fixed to a piece of machinery, such as a farm implement or flatbed trailer. The ladder can be deployed to varying levels, such as the ground or a pickup truck bed, while the steps remain parallel to the ground in either instance. 
         [0020]    Additionally, the ladder, when in folded so that the ladder rails lie against one another, or so the base and the rails are parallel, the steps form a generally planar surface, so that the ladder can be uses as a platform or a ramp. 
       3) Application/Attachment Assembly: 
       [0021]    In some applications, the top end of ladder simply rests freely against the work area. However, the ladder of the present invention can accommodate optional attachments at the top end of ladder, allowing the ladder to be more securely fixed to an object or work area. Such attachments described herein allow mounting the ladder to all types of machinery, vehicles, and buildings etc. Application/attachment assemblies may consist of one or a combination of the following. 1) Hooks attached to top of ladder may be used to secure ladder to a rod on any given fixed point. 2) Square, rectangular, round tubing or post material or any combination may be pivotably attached to the ladder, allowing the post to be placed in a suitable receiver on the work area. An example of such a receiver would be a vertical hole, receiver, or stake pocket in the frame of a flatbed trailer; 3) Any other form of receiver that will firmly secure ladder to any fixed point; 4) pads to protect any surface that the ladder rests against; 5) wheels. 
         [0022]    The above assemblies may also be used on both of ladder ends so as when ladder is in a closed or folded position, it can be used as a form of scaffolding or ramp between two fixed points. In particular, the attachment of wheels and a headrest to the ladder in the folded configuration will allow the structure to be used as a creeper or dolly. The attachment of a handle would allow the structure to be used as a cart. 
         [0023]    The additional assemblies or accessories may be placed on accessory bars that are selectively attached and detached from receivers on the ends of the ladder. 
         [0024]    The ladder assembly may be made of one or more of the following materials; aluminum, steel, fiberglass, wood, composites, or any other material of suitable strength and durability. 
         [0025]    The length of ladder assembly can be as long as desired, but also remaining within an acceptable standard of safety. Lengths will be determined according to application. 
         [0026]    The width of ladder can also vary according to application and desire while remaining within a standard of safety. 
         [0027]    Step construction: standard placement of step assembly within ladder frame is preferred to be 12″ center to center as it is on conventional ladders from rung to rung. This can also deviate from standard if desired. Step assembly depth or length shall also be as desired. If ladder is to be used as a ramp it is preferred that the depth/length of the steps shall be great enough to allow steps to meet or nearly meet end to end while in folded position so as to form a generally planar, nearly continuous surface. Step assembly depth/length can be decreased if desired to allow more spacing between the steps or individual platforms when the ladder is folded. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]      FIG. 1  is a perspective view of the ladder in a deployed configuration. 
           [0029]      FIG. 2  is a perspective view of the ladder in a stowed or scaffold. configuration. 
           [0030]      FIG. 2   a  is a close-up partial perspective view of a portion of  FIG. 2 . 
           [0031]      FIG. 3  is an underside partial perspective view of a representative step assembled on the ladder. 
           [0032]      FIG. 4  is a top perspective view of a step. 
           [0033]      FIG. 5  is a top partial perspective view of the base and bottom step assembled on the ladder, the foot support surface of the step removed. 
           [0034]      FIG. 6  is a top perspective view of a base. 
           [0035]      FIG. 7  is a top partial perspective view of the top step assembled on the ladder. 
           [0036]      FIG. 8  is a top partial perspective view of the top of the ladder with a staker. 
           [0037]      FIG. 9  is a top partial perspective view of the top of the ladder attached to rollers and track. 
           [0038]      FIG. 10  is a top perspective view of a base having stability extensions and handles. 
           [0039]      FIG. 11  is a perspective view of a ladder with supports to adjust the inclination of the ladder. 
           [0040]      FIG. 12  is a perspective view of a ladder with supports to adjust the inclination of the ladder and a handrail. 
           [0041]      FIG. 13  is perspective view of a ladder with supports to adjust the inclination of the ladder, a handrail, and a wheeled base. 
           [0042]      FIG. 14  is a partial perspective view of a linkage for adjusting the inclination of the ladder. 
           [0043]      FIG. 15  is a top plan view of an infinitely adjustable linkage mounted on the ladder. 
           [0044]      FIG. 16  is a side elevational view of an infinitely adjustable linkage mounted on the ladder. 
           [0045]      FIG. 17  is a partial perspective view of a ladder fixed to an object and having adjustable actuators to adjust the level of the steps. 
           [0046]      FIG. 18  is a side view of a ladder rail having a height adjuster. 
           [0047]      FIG. 19  is a perspective view of a shortened ladder in the deployed position with the base side members having receivers for receiving accessory bars. 
           [0048]      FIG. 20  is a perspective view of a ladder in the stowed position with a first unmounted accessory bar including a headrest and swivelable wheels and a second unmounted accessory bar having swivelable wheels. 
           [0049]      FIG. 21  is a perspective view of a ladder in the stowed position with mounted accessory bars. 
           [0050]      FIG. 22  is a perspective view of a ladder in the stowed position with a first mounted accessory bar having a lockable and pivotable handle positioned in an upright position and wheels, and a second mounted accessory bar having wheels. 
           [0051]      FIG. 23  is a perspective view of a ladder in the stowed position with a first mounted accessory bar having a lockable and pivotable handle and wheels, and a second mounted accessory bar having wheels. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0052]    The ladder  10  includes four ladder rails  15   a - d , each having a top end  16   a - d  and a bottom end  17   a - d . Each rail  15   a - d  is pivotably connected at their bottom ends  17   a - d  to a base  18 . In the preferred embodiment, the rails  15   a - d  are square metal tube stock, although other materials, such as solid stock, I beams, angle iron, channel stock, fiberglass, composites, and lumber, could be utilized to form the rails. It is not necessary that the rails be of tube stock. While the rails are square in the preferred embodiment, they may also be of any convenient shape. The length of the rails can vary, although for flatbed trailer applications, it is preferred that the rails be at least  60  in length. It is preferred that at least two of the ladder rails extend  48  inches above the top most step, here step  20   a,  to provide for a hand grip when a person is on the top most step  20   a.    
         [0053]    Each rail  15   a - d  is pivotally attached to a plurality of steps  20   a - g  positioned at generally equal intervals between the rail top ends  16   a - d  and the rail bottom ends  17   a - d . The intervals closely match the length of the steps  20 , so that the steps form a nearly continuous surface when the ladder  10  is in the folded or ramp configuration shown in  FIG. 2 . In the preferred embodiment, the steps  20  are seven in number and are approximately 12 inches square. 
         [0054]    The steps  20   a - g  are pivotally attached to the rails  15   a - d  by support rods  25   a - n  that extend between pairs of rails, much like the rungs of a traditional ladder. So constructed, the ladder has a first frame  11  and a second frame  12  linked together by the plurality of steps  20   a - g . In the embodiments shown in the figures, support rods  25   h - n  connect rails  15   c  and  15   d  to form the first frame  11 . The support rods  25   a - g  connect rails  15   a  and  15   b  to form the second frame  12 . The support rods  25   a - n  fit through apertures in the rails  15   a - d  and are secured at their terminal ends by welding the support rod ends to the outside surface of the rail. It is also possible to weld the rods at any area in which the rod and the rail contact each other. In other embodiments, the support rods need not go through apertures in the rails, but may be attached to brackets attached to the exterior surface of the rails, or attached to the surface of the rails themselves without the need for brackets. One skilled in the art will recognize that there are may ways to attach the rods to the rails so that the rods will support the steps  20   a - g  and allow the steps to move relative to the rails as the angle of the rails with respect to the ground is changed. 
         [0055]    In other embodiments, the steps  20   a - g  are fastened to the rails  15   a - d  by fasteners, such as nuts and bolts, rivets, pins, or other fasteners known in the industry. In such embodiments, the steps  20   a - g  in conjunction with the fasteners act to connect the rails to each other. 
         [0056]    The steps  20   a - g  are shown in detail with reference to a single step in  FIGS. 3-5 . The steps  20  are generally  12  inches square, but one skilled in the art will recognize that the dimension of the steps may be change to suit the application. Each step includes a frame  21  formed by a pair of side members  22   a  and  22   b  spaced apart by cross members  23   a - c . The members are preferably joined by welding. A tread plate or other foot support surface  28  overlies the frame  21 . 
         [0057]    The side members  22   a  and  22  b include apertures to accept a support rod  25 . The side members  22   a  and  22   b  can be “L” shaped to allow pairs of apertures  26   a - b  and  27   a - b  to be offset vertically. The vertical offset is generally the same as the height of a rail, the offset allowing the rails to lie against or in close proximity to one another when the ladder  10  is in the folded, collapsed, storage, or ramp configuration shown in  FIG. 2 . In other embodiments, be side members can be straight, and include downwardly extending brackets to produce the offset. A bushing  121   a - d  may be placed in the apertures to allow the step  20  to rotate about the rod  25  in an improved fashion. The steps may be spaced apart form the rails by spacers that fit over the rods, the spacers having a diameter larger that the diameter of apertures in the brackets attaching the steps to the rods so as to keep distance between the rails and the steps. 
         [0058]    In alternate embodiments, the brackets are planar metal members with an aperture to accept the rods  25 , or other fastener, and thereby allow the step  20  to rotate with respect to the rod  25  or other fastener. In alternate embodiments, the bracket  30  may be fixed to the fastener, rod  25 , or other member, and the fastener allowed to rotate with respect to the rail  15 . The apertures in the brackets are offset vertically by a distance equal to the overall height of one rail. The bracket will also allow a surface for welding the support rod in a metal construction. 
         [0059]    The offset of the apertures  27   a - b  and  27   a - b  in the side members  22   a  and  22   b  is approximately the width of a side rail  15  from front to back. In the preferred embodiment, the offset is approximately 1.25 inches. This offset allows the ladder to form a platform when in the stowed configuration by allowing the rails  15   b  and  15   c  to lie in close proximity or against each other, as shown in  FIG. 2 . Thus, the offset is controlled somewhat by the width of the rails and the placement of the apertures in the rails. 
         [0060]    In other embodiments, a step  20  may be constructed out of a single piece of material. Such material may include metal, wood, plastic, composites, or any other material known to one skilled in the art. For instance, the step  20  may be made as a blow-molded piece of plastic. Such a step may include reinforcing ribs made of plastic or some other material such as metal, but may not necessarily need such reinforcement. The single piece step may include a first set of apertures and a second set of apertures vertically off-set from the first set of apertures. 
         [0061]    The base  18  of the preferred embodiment includes a frame composed of four side members  45   a - d  connected to form a rigid structure. The base  18  is preferably a welded fabrication consisting of two end tubes  45   b  and  45   d  and two side tubes  45   a  and  45   c  of the same stock size as the rails  15   a - d . One skilled in the art will recognize that other sizes and materials may be used to construct the base  18 . The end tubes  45   b  and  45   d  and the two side tubes  45   a  and  45   c  form a frame that is generally rectangular with dimensions allowing that the rails of the first frame  11  will be separated by at least the overall width of one step assembly, and is the foundation for the hinge brackets. 
         [0062]    The hinge brackets  50   a - d  connect the four rails  15   a - d  with a minimal amount of free-play, but to allow for free rotation. The hinge brackets holding the first frame  11  are preferably spaced apart on the base  18  from the brackets holding the second frame  12  at the same distance that horizontally separates the apertures on the side member  22 . The hinge brackets  50   a - d  are generally upstanding planar members that include apertures  56  to accept the connecting rods  25 . The apertures are vertically offset by approximately the same distance as the apertures  26   a  and  27   a  of the steps  20  in order to allow the ladder  10  to fold into a generally flat configuration. In such a folded configuration, the steps  20   a - g  form a support surface. When in a folded configuration the first frame  11  lies over the second frame  12 . In the folded configuration, the first frame  11  is displaced from the second frame  12  in the horizontal direction by the horizontal distance between the apertures  26  and  27  of the step  20  side member  22 . 
         [0063]    It is preferred that there is structure to secure the ladder  10  in the folded or platform position shown in  FIG. 2 . In the preferred embodiment, the locking structure secures the first frame  11  to the second frame  12 . On skilled in the art will recognize that other components can be secured together to maintain the ladder  10  in the platform or folded configuration. 
         [0064]    As shown in  FIG. 2   a , the locking structure includes a lock plate  60  with a slot  61  to engage a locking pin  62  and a hole to attach to one end of one support rod  25 . Such structure can be placed at or near the ends of the rails on both sides of the ladder  10 , as shown in  FIGS. 1 and 2 . The lock plate  60  is a generally planar member. The slot  61  is offset from the hole a distance equal to the overall height of one rail  15 , and is shaped so that the slot  61  is a small section of a circular arc of a radius that is equal to the overall height of one rail  61 . This will allow the lock plate  60  to engage the lock pin  62  smoothly over an angle of approximately 16 degrees. In this arrangement, the support rod  25   g  is not fastened to the bracket  50   a  or rail  15 , but directly to the lock plate  60  itself allowing for free rotation of the entire length of the support rod  25   g.    
         [0065]    The top end  16   a  and  16   b  of the rails  15   a  and  15   b  may include accessories to allow the ladder  10  to attach or interact with work surfaces or other objects. The top ends  16   a  and  16   b  need not be the extreme terminus of the rails  15 , but are generally beyond the midpoint of the rails. The top ends  16   a  and  16   b  may include hooks  70   a  and  70   b . The hooks  70   a  and  70   b  may be formed as an integral part of the rails  15   a  and  15   b,  or be separate components attached to the rails by welding, fasteners, or other means or structures known in the art to attach components together. 
         [0066]    The top end may also include brackets  72   a  and  72   b  to accept a generally “T” shaped stake or post  75 . The post  75  is a structure that allows the ladder to be fixed to another structure such as a flatbed trailer. The post  75  includes a portion that is affixed to the other structure and a second portion that is allowed to rotate with respect to the rails  15  of the ladder  10 . In the preferred embodiment the post  75  includes a horizontal portion that is free to rotate in the brackets  72 , thus allowing the post  75  to rotate with respect to the rails about an axis that is parallel to the plane of any one of the steps  20   a - g . The post  75  has a downwardly extending appendage  76  that can be accepted by a receiver  90 , such as a hole in the frame of a flatbed trailer. One skilled in the art will recognize that other receivers can be used to accept the post  75  and that other configurations can be used for the r post such that the post can be fixed to an object and allow the ladder to rotate about the post  75 . 
         [0067]    The top ends  16   a  and  16   b  may include wheels  80  or other rolling members. The wheels  80  can interact with track  78  mounted to a work surface such as a piece of heavy equipment or flatbed trailer. The track is preferably mounted in a horizontal position, with an end  79  presented or exposed to a user. The track has a length that is preferably equal to the length from the place on the rail that the wheel is mounted to the base of the ladder. This arrangement allows the ladder to be placed in its flat or stowed configuration and then slid along the tracks  78  to be stowed. In such a stowed configuration, the ladder  10  can also be used as a work platform, as the tread plates  28  of the steps  20   a;g  will form a generally planar surface. 
         [0068]    In an alternate embodiment shown in  FIG. 10 , the base  118  can include an extension  120  that extends in front of brackets  150   c  and  150   d.  Described another way, the brackets are not placed at the corners of the base  18 , but are instead displaced from the corners. The extension  120  may include handles  160   a  and  160   b.  Handles  160   a  and  160   b  may be placed on the sides of the base  118 . In other respects, the base  118  is similar to base  18 . 
         [0069]    In alternate embodiments as shown in  FIGS. 11-13 , the ladder  210  can be supported by supports  290   a  and  290   b.  The supports have one end pivotably attached to the ladder frame rails  215   a  and  215   b,  preferably at the rail top ends to improve leverage. However, they may be positioned anywhere along the length of the rails, or may be pivotably attached to any other members of the ladder frame. 
         [0070]    The supports  290   a  and  290   b  can be adjusted to vary the inclination of the ladder  210 . The supports  290   a  and  290   b  can be adjusted by allowing first support members  291   a  and  291   b  to slide within the second support members  292   a  and  292   b.  The sliding members may be fixed in place by a pin placed in apertures, locking collars, or other means known to secure sliding members. In other embodiments, the supports may be pneumatically or hydraulically operated. 
         [0071]    The alternate ladder may include a handrail assembly  280  shown in  FIGS. 12 and 13 . The handrail assembly  280  includes a first upright or stanchion  281  fixably mounted to the uppermost step, and a second upright or stanchion  282  fixably mounted to the base  210 . The stanchions are pivotably connected to a handrail  285  that extends there between. 
         [0072]    in other embodiments, the ladder, such as the ladder  210 , can be mounted on a wheeled frame  300 , to allow the ladder to easily be moved from place to place. The wheeled frame  300  includes wheels  310  mounted near the corners. The frame includes brackets  395  to pivotably mount the supports  290   a  and  290   b.    
         [0073]    In any of the ladder embodiments, the ladder may be locked in a particular inclination using a linkage  370  between the ladder side rails such as between  15   a  and  15   d  or  15   b  and  15   c.  Such linkage links the first frame  11  to the second frame  12 . As shown in  FIG. 13 , the linkage  370  is pivotably attached to side rail  15   c,  and extends to side rail  15   b,  where one of a plurality of slots  375  engages a pin  380  to selectively lock the ladder inclination. One skilled in the art will recognize that other mechanisms or structures can be used to lock or otherwise secure the inclination of the ladder. 
         [0074]    An alternative linkage that allows infinite adjustment is shown in  FIG. 15 . The alternate linkage includes a first slotted linking member  471  and a second slotted linking member  472 , each liking member having a slot to sunning the length of the linking member. The linking members  471  and  472  are arranged on either side of rails  15   a  and  15   d  so that the rails are between the linking members  471  and  472  and the slots of the linking members are aligned with each other. The linking members  471  and  472  are secured to the rails  15   a  and  15   d  by fasteners such as nuts  410  and bolts  420 . Other fasteners can be used so long as the linking members are allowed to pivot with respect to the rails  15   a  and  15   d.  In the preferred embodiment, the connection between the linking members  471  and  472  and rail  15   a  allows pivoting, but does not allow the fastener to move along the slot. Thus the ladder rail  15   a  is translationally fixed with respect to the linking members  471  and  472 . Rail  15   d  is not translationally fixed with respect to the liking members  471  and  472 , and the fastener is allowed to slide in the slots of the linking members  471  and  472 . In order to restrain or limit the translational movement, a stop  480  is placed in the slot. The stop  480  can be a nut and bolt. In the preferred embodiment, the stop  480  is a cam action lever clamp that allows the user to selectively secure and unsecure the stop at a position in the slot. The cam action lever clamp includes a stud or post  481  that is inserted in the slot and a cam action lever  482  that attaches to the post  481 . A spacer  484  is paced about the post  481  to allow the clamp to grasp the linking member  472  between the lever  482  and the spacer  484 , and linking member  471  between the post  481  and the spacer  484 . To improve friction, the inside surfaces of the linking members  471  or  472  or the spacer  484  may include surface features such as ridges, grooves  485 , or other structures to increase friction. 
         [0075]    In another embodiment, shown in  FIG. 17 , the second frame  12  is fixed or attached to another object so that the first frame is allowed to pivot about the attachment. In the embodiment shown in  FIG. 17 , the support rod  25   g  is fixed in place so that the second frame  12  can pivot with respect to it, but is fixed in other degrees of freedom of movement. The first frame is pivotably connected to adjustable actuators  700   a  and  700   b . The adjustable actuators  700   a  and  700   b  are fixed to an object such as the object fixed to the second frame  12 , or to yet another object such as the ground. The adjustable actuators are then used to adjust the angle of the steps  10  by moving the first frame  11  with respect to the fixed second frame  12 . 
         [0076]    The ladder  10  may be constructed without the base  18 . In such an embodiment, it may be useful to have the bottom ends  17   c  and  17   b  of the rails  15   c  and  15   d  of the first frame  11  be slightly longer than the bottom ends  17   a  and  17   b  of the rails  15   a  and  15   b  of the second frame. The extra length will depend upon the vertical offset used on the steps  20 . The additional length allows for the steps to be level when the ladder  10  without the base  18  is placed on level ground. The vertical off set is typically the height of one rail  15 , as previously discussed. 
         [0077]    The bottom ends  17   a - d  of the rails  15   a - d  may also include height adjusters. A representative height adjuster  750  is shown in  FIG. 17 . While only one adjuster is shown, it may be applied to any of the rails  15   a - d . The adjuster  750  operates by allowing an adjuster support member  751  to slide within the rail  15 . The support member is sized  751  to fit within the rail  15 . The support member  751  and the rail are fixed in place by a pin placed in an aperture  752  in the rail  15 , and in one of a plurality of apertures  755 . In other embodiments, locking collars, or other means known to secure sliding members may be used. In other embodiments, the supports may be pneumatically or hydraulically operated. When the ladder  10  is used without the base  18 , the adjuster support member  751  will contact the ground or other surface. When used with a base  18 , the adjuster support member  751  may include an additional aperture  760  for attachment to the base  18  in the place of the bottom ends  17   a - d  of the rails  15   a - d.    
         [0078]    With reference to  FIGS. 19  through.  24 , another embodiment of the ladder  10  is shown. In this embodiment, the ladder  10  includes structure to allow the ladder  10  to be converted into a creeper or a cart when in the platform configuration by the attachment of accessory bars  600  to the rails  15  and base  18  of the ladder  10 . With the use of accessory bars  600  placed in suitable receivers on the ladder  10 , wheels, pads, hooks, or other structures that may be used with the ladder in the ladder  10  or in the platform configuration can be selectively attached or removed from the ladder  10 . In other embodiments, the accessories, such as wheels, pads, hooks, or other structures may be placed on posts that connect to only one receiver. 
         [0079]    As shown in  FIG. 20 , the accessory bars  600  attach to the ends  16   a  and  16   b  of the ladder rails  15   a  and  15   b  or to the base  18 . When the ladder rails  15   a  and  15   b  and base  18  are made of tube stock, the ends of the ladder rails  16   a  and  16   b  are open to receive the accessory bars  600 . Being open, they form receivers to receive the accessory bars  600 . 
         [0080]    When the ladder rails  15   a  and  15   b  are used to receive the accessory bar  600 , they may only do so when the ladder  10  is in the platform configuration, thus exposing the first ends  16   a  and  16   b.  When the ladder is deployed, the base  18  prevents the first ends  16   a  and  16   b  from receiving the accessory bar  600 . 
         [0081]    When other materials are used for construction of the ladder  10  such that the ends are not open to form receivers the ends  16   a  and  16   b  and base  18  are equipped with receivers, such as lengths of open square tube stock attached to the ladder rail ends  16  or the base  18 . The accessory bars  600  are sized to fit into the open ends of the tube stock. The accessory bars  600  are preferably held in place on the ladder by removable locking pins  630  that fit into holes in the ends of the ladder rails  16   a  and  16   b  and base  18 . The accessory bars  600  have corresponding holes that align with the holes in the ladder rails  16   a  and  16   b  and base  18  when thee accessory bars  600  are in place, allowing the accessory bars  600  to be selectively secured. One skilled in the art will recognize that other structures can be used to selectively attach and remove the accessory bars  600 . 
         [0082]      FIGS. 19-24  show a ladder  10  of the present invention, but one that is shorter than the one shown in  FIGS. 1-17 . In this embodiment, which is merely an example, the ladder  10  has for steps  20   a - 20   d.  The base  18  of the ladder is also modified, but the ladder  10  is otherwise similar in construction and components. The base  18  of the ladder  10  of the embodiment shown in  FIGS. 19-24  also has the tube members  45  forming the base  18 , the end tubes  45   b  and  45   d  placed so that the open ends  640  of the end tubes  45   b  and  45   d _face towards the front of the ladder  10  rather than the sides. In such a position, the open ends  640  form receivers for the receipt of the ends or posts  620  of the accessory bars  630 . Such a base  18  configuration could also be used on the Ladder  10  shown in  FIGS. 1-17  as well. 
         [0083]    The accessory bars  600  in the basic form include a cross member  610  and two posts  620 . In the preferred embodiment, the cross member  610  and posts  620  span the width of the ladder  10  from ladder rail to ladder rail, or across the width of the base  18  for an accessory bar  600  that is attached to the base  18 . In the preferred embodiment, the ladder rails  15  are positioned at the same width as the base  18 , so an accessory bar  600  that fits the base  18  will also fit the ladder rails  15 . 
         [0084]    The posts  620  are positioned on the cross member  610  so that the posts  620  will fit into the ends of the ladder rails  16   a  and  16   b,  or into receivers on the ladder rails  15 . The posts  620  extend from the cross member  610  approximately 5 to 8 inches and are preferably positioned at right angles to the cross member  610 . One skilled in the art will recognize that the posts  620  can be of different lengths and need not be of the same length. The length of the post  620  also need not be 5 to 8 inches, and the length may be longer or shorter, although it is preferred that the posts  620  fit into the rails  15 , base  18 , or receiver for at least three inches so to provide stable and secure attachment. 
         [0085]    As shown in  FIGS. 20 and 21 , the accessory bars  600  include pivoting wheels or casters  645  to allow the ladder  10  to be used as a creeper. The wheels  645  preferably are low profile and are positioned near the corners of the accessory bar  600  to allow for a more stable platform. One of the accessory bars  600  includes a headrest  650 . The headrest  650  is preferably attached by a bracket  647  to the accessory bar  600  that attaches to the base  18 . In the preferred embodiment, the bracket  647  elevates the headrest  650  from the accessory bar  600  so that the headrest  650  is positioned above the step  20   d  when the accessory bar  600  is attached to the ladder  10 . In the preferred embodiment, the headrest  650  is thus displaced both vertically and horizontally from the position of the accessory bar cross member  610 . In such a case the headrest bracket  647  is “U” shaped. In other embodiments, the headrest bracket  674  is removable from the accessory bar  600 . In such a case, the accessory bar  600  is equipped with a receiver to receive the headrest bracket  647 . In other embodiments, the headrest bracket  647  is height adjustable to allow the height of the headrest  650  above the step  20   d  to be adjusted. This may be accomplished by providing the headrest bracket  647  with a plurality of spaced apart apertures, and providing the headrest bracket receiver with a corresponding aligning aperture for the insertion and removal of a locking pin, similar to the arrangement use for the height adjustment of the ladder  10  and shown in  FIG. 18 . 
         [0086]    While the headrest equipped accessory bar  600  has been shown as attached to the base  18 , the headrest equipped accessory bar  600  may also be attached to the ladder rails  15   a  and  15   b  at the opposite end of the ladder  10 . In such an instance, the non-headrest equipped accessory bar is attached to the base  18 . 
         [0087]    With reference to  FIGS. 22-24 , the accessory bars  600  may be equipped with an axel  652  and larger non swiveling wheels  653  to convert the ladder  10  into a cart. Such an example is shown with accessory bar  602 . In the preferred embodiment, the axel  652  extends away from the sides of the accessory bar  602 . In other embodiments, one or all of the accessory bars  600  includes swivelable wheels  645  to allow easy maneuverability of the cart. For instance a first accessory bar  602  will include non swiveling wheels  653  on an axel  652 , and the other accessory bar  601  will include swivelable wheels  654  such as casters. In any of the cart embodiments, one of the accessory bars  600  will include a handle  660 . In the figures shown, the handle  660  is attached to the accessory bar  601  that includes swivelable wheels  654 . The handle  660  is pivotably attached to be placed in a secured upright position, and also be allowed to pivot downward when the locking mechanism is released. It is preferred that the handle  660  freely be allowed to pivot in the unlocked position to allow the handle  660  to be placed a varying heights when connected to a hitch  662 , as shown in  FIG. 24 , for use of the ladder  10  as a cart that is towable by a tractor or other conveyance having a hitch  662  or other attachment point. 
         [0088]    The embodiments described herein are merely examples and are not meant to limit the scope of the invention.