BACKGROUND 
     The following background information may present examples of specific aspects of the prior art (e.g., without limitation, approaches, facts, or common wisdom) that, while expected to be helpful to further educate the reader as to additional aspects of the prior art, is not to be construed as limiting the present invention, or any embodiments thereof, to anything stated or implied therein or inferred thereupon. 
     The following is an example of a specific aspect in the prior art that, while expected to be helpful to further educate the reader as to additional aspects of the prior art, is not to be construed as limiting the present invention, or any embodiments thereof, to anything stated or implied therein or inferred thereupon. 
     The present invention is directed to an elevator that traverses a double ladder in a smooth continuous path. The elevator uses specially oriented and aligned rollers and wheels to engage the side rails. The rollers and wheels can selectively engage either ladder, or the overlap portion between the ladders, depending on the position of the elevator on the double ladder. 
     It is well known that ladders have been commonly used in order to carry a person or worker up or down along a building wall or other structure. Ladders can include a rigid pair of side rails connected by horizontal rungs. Sometimes, two or more ladders can be joined to extend the potential height of the ladder. 
     It can sometimes be problematic to carry heavy objects to the top of a house, to a second or higher story of a building, or onto a roof. For example, carrying heavy materials like shingles up a ladder with hands is a dangerous proposition in that carrying such materials may require the use of both hands. Furthermore, manually carrying multiple packages of shingles, tools, or perhaps beverages is likely to require multiple trips up and down the ladder, which creates a more dangerous climbing scenario. 
     Often, the lifting can be accomplished with a crane, but the expense of using a crane is often prohibitive. The manpower to operate the crane might not be available. In addition, it would be difficult and expensive to transport a large piece of equipment such as a crane to a job site. 
     Often, a specially configured elevator is used to automatically climb the ladder. The elevator is a motorized platform that rides the side rails of the ladder to move up and down the ladder. However, if the ladder is a double or triple ladder having more than one individual sections, the junction between the ladders is generally wider and less stable than at the single ladder sections. The elevator may not be able to cross these junctions where the ladders overlap. 
     For the foregoing reasons, there is an elevator that traverses a double ladder in a smooth, continuous path through the use of strategically placed guides and rollers that engage specific surfaces and flanges on the double ladder. 
     Elevators for ladders have been utilized in the past; yet none with the present double ladder climbing capacity of the present invention. See U.S. Pat. Nos. 2,499,975; 3,215,254; and 6,782,972. 
     For the foregoing reasons, there is a double ladder elevator that traverses double ladders in a first position, a second position, and an overlap position. 
     SUMMARY 
     The present invention is directed to an elevator that is effective for lifting loads along the length of a double ladder. The elevator utilizes guiding mechanisms having different orientations and designs to smoothly cross over misalignments, instabilities, and wide sections on the double ladder. In some embodiments, the double ladder comprises a first ladder and a second ladder that join together to form an overlap portion. The overlap portion is wider and generally less stable than the individual ladders. The present invention helps overcome the physical barriers imposed at the overlap portion. 
     For better understanding the elevator, the first ladder is oriented to engage a ground surface for support, while the second ladder is oriented above the first ladder. The first and second ladders join at an overlap portion that is wider than the individual ladders, and can often form a staggered, misaligned section of the double ladder for the elevator to traverse. The elevator moves between each ladder and the overlap portion in a smooth, continuous path. The guiding mechanisms on the underside of the elevator move between engagement and disengagement of each ladder and the overlap portion based on the movement and location of the elevator relative to the double ladder. 
     The elevator includes four guide units that guide the elevator along a longitudinal axis of the double ladder. Each guide unit includes three spaced wheels joined together by a guide axis. The outer wheels engages one of the ladders and the overlap portion. The central wheel straddles both ladders. The guide units create stability, yet have sufficient flexibility to allow for play between the elevator and the double ladders. 
     The elevator further includes eight rollers that roll along the outer side rails of each ladder. The rollers exert an inward pressure from the elevator towards the double ladder. Four of the rollers engage the first ladder and the overlap portion, and four oppositely positioned rollers engage the second ladder and the overlap portion. The rollers may include rubber rollers sized to straddle along the side rails. 
     The elevator also utilizes notched rollers that orient perpendicularly to each other and form tight fittings with different surfaces on the side rails. The notched rollers suppress vibrations and slippage between the elevator and the ladders. All of the guiding mechanisms work together to create a synergy that enables a smooth continuous path of travel across the individual ladders and the overlap portion. 
     One objective of the present invention is to provide a ladder elevator that crosses over a double ladder. 
     Another objective is to carry heavy loads up a double ladder. 
     Another objective is to provide relatively inexpensive wheels and rollers in a strategically aligned configuration to overcome the physical barriers at the junction of a first ladder and a second ladder. 
     Another objective is to maintain inward pressure from the elevator towards the side rails to increase friction and provide a smooth conveyance of the elevator. 
     Another objective is to suppress vibrations on the elevator while traversing the double ladder. 
     Another objective is to regulate operation of the elevator with a foot pedal. 
     Another objective is to manufacture an elevator for a double ladder that is easy to use and economical to manufacture. 
    
    
     
       DRAWINGS 
       These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and drawings where: 
         FIGS. 1A, 1B, and 1C  are detailed perspective views of an exemplary elevator traversing an exemplary double ladder, where  FIG. 1A  is the elevator in a first position,  FIG. 1B  is the elevator in an overlap position, and  FIG. 1C  is the elevator in a second position; 
         FIGS. 2A and 2B  are side views of exemplary double ladders and various wheels and rollers from the inner surface of the housing, where  FIG. 2A  is a detailed perspective view, and  FIG. 2B  is an elevated side view, and 
         FIG. 3  is a sectioned top view of an exemplary platform projecting out from the elevator and the wheels and rollers in the housing. 
     
    
    
     DESCRIPTION 
       FIGS. 1A-3  illustrate one embodiment of an elevator  100  engaged with a double ladder  182 . The present invention is directed to an elevator  100  that traverses a double ladder  182  in a smooth continuous path. The elevator  100  uses specially oriented and aligned rollers and wheels to engage the side rails of the two separate ladders. The rollers and wheels can selectively engage either ladder, or the overlapping between the two ladders, depending on the position of the elevator  100  on the double ladder  182 . 
     As referenced in  FIG. 1A , the elevator  100  utilizes guiding mechanisms having different orientations and designs to smoothly cross overlapping ladders, misalignments, and lateral instability in the double ladder  182 . Those skilled in the art will recognize that the double ladder  182  comprises a first ladder  108  and a second ladder  110  that join together to slidably overlap or move in different directions relative to each other. The guiding mechanisms utilized by the elevator  100  are aligned and oriented in such a manner as to facilitate movement between the ladders  108 ,  110  and bring the elevator  100  into closer engagement with the double ladder  182 . 
     To better understand the elevator  100 , it is significant to note that the double ladder  182  comprises a first ladder  108  and a second ladder  110  that slidably engage each other. The first ladder  108  is oriented to engage a ground surface for support, while the second ladder  110  is oriented above the first ladder  108 . The first and second ladders  108 ,  110  align and fasten together. 
     The first and second ladders  108 ,  110  can be a staggered, slightly misaligned configuration. The double ladder  182  may be formed from a separate first ladder  108  and second ladder  110  joined together, or as an extendable first ladder  108  with the extension being the second ladder  110 . The first ladder  108  includes a pair of first side rails  160 . The second ladder  110  includes a pair of second side rails  162 . Both side rails  160 ,  162  work together to carry the elevator  100  along the double ladder  182 . 
     As shown in  FIGS. 1B and 1C , the first ladder  108  includes a plurality of first rungs  130  spanning and cross-connecting the pair of first side rails  160 . Likewise, the second ladder  110  includes a plurality of second rungs  128  spanning and cross-connecting the pair of second side rails  162 . In some embodiments, each first side rail  160  carries a pair of inturned flanges  164 . The pair of inturned flanges  164  define a first channel  166  that faces outwardly from the first rungs  130 . The outer periphery of each first side rail  160  forms a generally L-shaped first outer edge  168 . The opposite end forms a first inner edge  170 . In one embodiment, the pair of second side rails  162  can include hooks for latching upon the first rungs  130  to support the two ladders  108 ,  110  at selected telescopic positions. In one alternative embodiment, more than two ladders could join together. The elevator  100  could perform in substantially the same manner in this case. 
     The second side rails  162  carry a pair of outturned flanges  172 . The first channel  166  is configured to receive the pair of outturned flanges  172 , thereby holding the ladders  108 ,  110  together. The pair of outturned flanges  172  define a second channel  174  that faces inwardly towards the second rungs  128 . The slidable engagement between the inturned flanges  164  and the outturned flanges  172  telescopically supports the first ladder  108  and the second ladder  110  together. Each second side rail  162  includes a second inner edge  178  that engages the first channel  166 . Each second rail  162  also includes a second outer edge  176  facing opposite the second inner edge  178 . The surfaces and angles formed by the aforementioned edges  168 ,  170 ,  176 ,  178  and flanges  164 ,  172  help support the various guiding mechanisms on the elevator  100 . 
     The elevator  100  is configured to slidably traverse the double ladder  182  in a smooth, continuous path. The elevator  100  is supported on the ladder by the side rails  160 ,  162 , which guide the elevator  100  along the length of each ladder  108 ,  110 . 
     The elevator  100  forms different contact points with the double ladder  182 , depending on the position on the double ladder  182 . For example,  FIG. 1A  illustrates the elevator  100  in a first position  102  while engaging only with the first ladder  108 .  FIG. 1C  illustrates the elevator  100  in the second position  106  while engaging only the second ladder  110 .  FIG. 1B  illustrates the elevator  100  is in an overlap position  104  while engaging both ladders  108 ,  110 . 
     The elevator  100  comprises a housing  112  defined by a housing outer surface  132 , a housing inner surface  150 , a housing first end  114 , and a housing second end  116 . The housing inner surface  150  forms the underside of the elevator  100 . The housing outer surface  132  forms a protective shell for the inner components of the elevator  100 . The housing first end  114  orients towards the first ladder  108 , while the housing second end  116  orients towards the second ladder  110 . In some embodiments, a platform  120  extends normal to the housing first end  114  to support objects as the elevator  100  traverses the double ladder  182 . 
       FIGS. 2A and 2B  illustrate four guide units  132  that mount on the housing inner surface  150 . The four guide units  132  help guide the elevator  100  along the length of the double ladder  182 . The four guide units  132  are effective for aligning the elevator  100  with the double ladder  182 , and preventing excessive lateral movement by the elevator  100  and the double ladder  182  as the elevator  100  traverses between the first position  102  and the second position  106 . The guide units  132  also bridge both ladders  108 ,  110 , where slight misalignments between the first ladder  108  and the second ladder  110  may occur. Specifically, the guide units  132  traverse across the first side rails  160  and/or the second side rails  162 , depending on the position of the elevator  100  relative to the ladders  108 ,  110 . In one alternative embodiment, more or less guide units  132  may be utilized. 
     Each guide unit  184  includes guide wheels that are rotatably connected around a guide axis  138 . Together, the guide wheels create a synergy that enables the elevator  100  to slidably traverse between the first and second ladders  108 ,  110  while maintaining an efficient contact point between the elevator  100  and each ladder  108 ,  110 . In some embodiments, the three guide wheels may include a large guide wheel  140 , a middle guide wheel  142 , and a small guide wheel  144 . All the guide wheels  140 ,  142 ,  144  rotate freely on a guide axis  138 . The guide wheels  140 ,  142 ,  144  are spaced apart by the proper distance along the guide axis  138  to permit simultaneous engagement with the first and second side rails  160 ,  162 . 
     The large guide wheel  140  helps guide the elevator  100  along the first side rail  160 . The large guide wheel  140  comprises a large disc  152  engaged with a concentrically positioned small disc  154 . The large disc  152  includes a large disc inner surface (not shown) that engages a first outer edge  168  of the first side rail  160 . A groove  156  forms between the large disc  152  and the small disc  154 . The large guide wheel  140  is operable to provide guidance from the first position  102  and the overlap position  104 . At the second position  106 , the large guide wheel  140  is free from engagement. 
     The small guide wheel  144  helps guide the elevator  100  along the second side rail  162 . The small guide wheel  144  engages a second outer edge  176  on the second side rail  162 . The small guide wheel  144  is grooved to ride the outturned flanges  172  that extend from the second outer edge  176 . The small guide wheel  144  is operable as a guiding mechanism from the second position  106  and the overlap position  104 . At the first position  102 , the small guide wheel  144  is free from engagement. 
     The middle guide wheel  142  straddles between the first ladder  108  and the second ladder  110 . The middle guide wheel  142  creates a stabilizing effect between the large guide wheel  140  and the small guide wheel  144 . The middle guide wheel  142  rides through the first channel  166  and engages a second inner edge  178  formed by the second side rail  162 . The middle guide wheel  142  further rotatably engages an outer surface of the second side rails  162 . 
     Each guide unit  184 , comprises of the large guide wheel  140 , the small guide wheel  144 , and the middle guide wheel  142 , joined through the common guide axis  138  to form a structured linear extension across the first and second ladders  108 ,  110 , such that excessive lateral movement is inhibited. However, the guide units  184  maintain sufficient play to compensate for undesirable lateral movement between the elevator  100  and the double ladder  182 , and misalignments that may form in the overlap position  104 . 
     The housing inner surface  150  further mounts four first ladder rollers  134  and four second ladder rollers  136  near opposed corners in the housing  112 . The eight total rollers  134 ,  136  orient perpendicularly to the four guide units  184 , rolling on the first outer edge  168  and the second outer edge  176  on the flanges  164 ,  172 . The rollers  134 ,  136  chiefly serve to press the elevator  100  against the side rails  162 . In this manner, a normal inward pressure is provided that works with the pressure applied by the four guide units  184  to create stability for the double ladder  182 . The inwardly directed pressure from the rollers  134 ,  136  restricts forward and backward swaying by the double ladder  182 . The pressure from the rollers  134 ,  136  also increases traction between the elevator  100  and the ladders  108 ,  110  for creating more efficient movement by the elevator  100 . In some embodiments, the rollers  134 ,  136  may include rubber rollers sized to roll and balance on the first outer edge  168  and the second outer edge  176  on the flanges  164 ,  172 . 
     Four of the first ladder rollers  134  rotatably engage the first ladder  108 . The first ladder rollers  134  rotatably engage the first outer edge  168 . Out of these four first ladder rollers  134 , two are proximal to opposed outer corners on the housing first end  114 , and two position near opposed outer corners of the housing second end  116 . The first ladder rollers  134  are operable from the first position  102  and the overlap position  104 . At the second position  106 , the first ladder rollers  134  are free from engagement. In one alternative embodiment, more or less of the first ladder rollers  134  may be utilized. 
     Four of the second ladder rollers  136  engage from the opposite end of the double ladder  182 , rolling across the second outer edge  176  of the second side rails  162 . Out of these four second ladder rollers  136 , two are proximal opposed outer corners on the housing first end  114 , and two position near opposed outer corners of the housing second end  116 . The second ladder rollers  136  are operable from the second position  106  and the overlap position  104 . At the first position  102 , the second ladder rollers  136  are free from engagement. In one alternative embodiment, more or less of the second ladder rollers  136  may be utilized. 
     The housing inner surface  150  further comprises two pairs of first ladder notched rollers  146 . Each pair of first ladder notched rollers  146  is oriented perpendicularly to each other at opposed outer corners of the housing first end  114 . In this manner, the two pairs of first ladder notchod rollers  146  buttress each other, and at least partially suppress vibrations and slippage between the elevator  100  and the first ladder  108 . Each first ladder notched roller  146  also enhances alignment between the elevator  100  and the first ladder  108 . The two pairs of first ladder notched rollers  146  are operable from the first position  102  and the overlap position  104 . At the second position  106 , the two pairs of first ladder notched rollers  146  are free from engagement. In one alternative embodiment, more or less of the first ladder notched rollers  146  may be utilized. 
     In some embodiments, the housing inner surface  150  comprises two second ladder notched rollers  148 . The notched configuration of the second ladder notched rollers  148  is efficacious for suppressing vibrations and slippage between the elevator  100  and the second ladder  110 . In one embodiment, the notch may include a generally V-shape. The second ladder notched rollers  148  also force a more precise alignment between the elevator  100  and the second ladder  110 . The second ladder notched rollers  148  are disposed on opposed outer corners of the housing first end  114 . Each second ladder notched roller  148  is arranged opposite a second ladder roller  136 , creating a frictional force on the second outer edge  176 . Each second ladder notched roller  148  traverses along the second side rail  162 , in alignment with a corresponding second ladder roller  136 . Like the second ladder roller  136 , the two second ladder notched rollers  148  engage the second ladder  110  from the second position  106  and the overlap position  104 , yet remains free in the first position  102 . The two second ladder notched rollers  148  are operable from the second position  106  and the overlap position  104 . At the first position  102 , the two second ladder notched rollers  148  are free from engagement. In one alternative embodiment, more or less of the second ladder notched rollers  148  may be utilized. 
     Turning now to  FIG. 3 , a platform  120  extends normal to the housing first end  114  to support objects as the elevator  100  traverses the double ladder  182 . The platform  120  may carry a variety of object, including, without limitation, people, paint buckets, construction material, and electrical material. In some embodiments, the platform  120  may include a plurality of ridged apertures for enabling fluids to pass through and providing enhanced traction. Those skilled in the art will recognize that the platform  120  forms a necessary large surface area to carry objects. For example, the double ladder  182  requires two hands to climb, thereby making the carrying of objects up the double ladder  182  difficult. The elevator  100  enables object to be carried up the double ladder  182  hands free. 
     In some embodiments, the platform  120  overlays a motorized and reversible winch  122  that is powered by means of a reversible motor  124 ; whereby the elevator  100  may be readily raised and lowered by means of simple electrical control switches for the motor  124 . A pedal  180  selectively controls the direction of movement for the elevator  100 . A cable  126  extends from the winch  122  upwardly towards a rung on the second ladder  110 . The winch  122  draws in the cable  126  to pull the elevator  100  up towards the second ladder  110 , and pays out the cable  126  to move the elevator  100  down towards the first ladder  108 . 
     While the inventor&#39;s above description contains many specificities, these should not be construed as limitations on the scope, but rather as an exemplification of several preferred embodiments thereof. Many other variations are possible. For example, the elevator  100  could be utilized for multiple ladders of more than two individual ladders. Accordingly, the scope should be determined not by the embodiments illustrated, but by the appended claims and their legal equivalents.
An elevator climbs and lifts loads along the length of a double ladder. The double ladder comprises a first ladder and a second ladder that join together to form an overlap portion. The overlap portion is wider and generally less stable than the individual ladders. The elevator helps overcome the physical barriers imposed at the overlap portion. The elevator utilizes guiding mechanisms having different orientations and designs to smoothly cross over misalignments and instable structures in the double ladder. The elevator includes a housing. The underside of the housing includes guide units that ride the side rails to align a first ladder and a second ladder. Rollers press the housing in contact to the ladders. Notched rollers suppress vibrations on the housing. The guide mechanisms selectively engage the ladders and the overlap portion based on the position of the elevator. A motorized platform extends from the housing.