Abstract:
A lightweight, multifunctional, robotic construction aid capable of replacing heavy, dangerous, conventional construction equipment including cranes, manlifts, scissorlifts, scaffolds, and extension ladders. More particularly, the apparatus comprises a base, a lower ladder portion, an upper ladder portion, and a support. The lower ladder portion is pivotably connected to the base and extends therefrom in a first direction. The upper ladder portion is pivotably connected to the lower ladder portion and extends therefrom in a second direction opposite the first direction and includes an access therethrough from the lower ladder portion. The support is capable of bearing the weight of the first and second ladder portions and of fixing the relative positions of the upper ladder portion, the lower ladder portion, and the base.

Description:
This is a continuation of application Ser. No. 09/515,546 filed Feb. 29, 2000 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This application relates generally to construction equipment and, more particularly, to a versatile piece of construction equipment capable of performing a number of functions valuable at a construction site. 
     2. Description of the Related Art 
     The construction site is a very demanding work environment. Time is almost always a factor in every job, and there is usually a lot of pressure to meet certain schedules so that a construction project is finished “on time.” Efficient operation and organization of tasks and crew is therefore very important. However, no matter how efficiently organized, there is always a certain amount of otherwise productive time wasted for a variety of reasons. 
     One reason is the poor utility, availability and/or accessibility of equipment. Each piece of equipment is usually designed for one specific task. Consequently, as the construction continues, equipment must be switched out as tasks are completed and new tasks are begun. One may, for instance, need to break down a crane used to unload materials and retrieve a forklift to move materials to a desired point on the construction site. Such concerns might even be as mundane as a worker having to retrieve a tool stored in a vehicle at the edge of the site. Although each of these incidents is necessary and, in itself, consumes little time, they cumulatively consume a great deal of time that is not actually devoted to the construction project itself. The more workers there are, the greater this cumulative time loss becomes. 
     The construction site is also very dangerous. Many workers are typically found on a construction site, each of which is focused on the specific task to which they are assigned. If the proper tool or equipment is not handy, a worker may use a tool poorly suited or improperly deployed for a given task, and get injured. The more workers involved and the more inaccessible the tools are, the more likely this is to happen. Sometimes workers are simply too focused on their specific task and are unaware of unsafe conditions or events occurring around them. Again, the more workers on a given site, the more likely this is to happen. Thus, the number of workers and the convenient location of tools are significant factors that affect construction site safety. 
     The present invention is directed to resolving one or all of the problems mentioned above. 
     SUMMARY OF THE INVENTION 
     The invention is, in its various aspects and embodiments, a lightweight, multifunctional, construction aid capable of replacing heavy, dangerous, conventional construction equipment including cranes, manlifts, scissorlifts, scaffolds, and extension ladders. More particularly, the apparatus comprises a base, a lower ladder portion, an upper ladder portion, and a support. The lower ladder portion is pivotably connected to the base and extends therefrom in a first direction. The upper ladder portion is pivotably connected to the lower ladder portion and extends therefrom in a second direction opposite the first direction and includes an access therethrough from the lower ladder portion. The support is capable of bearing the weight of the upper and lower ladder portions and of fixing the relative positions of the upper ladder portion, the lower ladder portion, and the base. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and in which: 
     FIG. 1 is an isometric view of one embodiment of an extension ladder constructed in accordance with the present invention; 
     FIG. 2 details the access from the lower ladder portion to the upper ladder portion of the embodiment in FIG. 1; 
     FIGS. 3A-3E illustrate one particular embodiment of the base for the extension ladder in FIG. 1; 
     FIG. 4 depicts a gantry crane implemented with an embodiment of an extension ladder alternative to that in FIG. 1; 
     FIGS. 5A-5B illustrate the crane section of the gantry crane in FIG. 4 in an isometric, side view and a sectional view of a block and tackle and a track  504  along line  5 B— 5 B in FIG. 5A, respectively; 
     FIG. 6 depicts a man-lift implemented with the embodiment of the extension ladder in FIG. 4; 
     FIGS. 7A-7C illustrate a third particular embodiment of an extension ladder alternative to that in FIG.  1  and built in accordance with the present invention; 
     FIG. 8 depicts a man-lift similar to that in FIG. 6, but implemented with the extension ladder of FIGS. 7A-7C; 
     FIG. 9 depicts how several add-on features may be implemented with the extension ladder of FIGS. 7A-7C; and 
     FIG. 10 illustrates an alternative deployment of the extension ladder of FIGS.  7 A- 7 C. 
    
    
     While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will be appreciated that, in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort, even if complex and time-consuming, would be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. 
     Turning now to the drawings, FIG. 1 illustrates one particular embodiment of an extension ladder  100  constructed in accordance with the present invention. The extension ladder  100  generally comprises a base  102 ; a pair of struts  104 ; a lower ladder portion  106 ; and an upper ladder portion  108 . The extension ladder  100  also includes a plurality of cables  110  capable of offsetting the torque generated by gravity operating on the center of gravity for the upper ladder portion around the pair of pivots  114  by which the lower and upper ladder portions  106 ,  108  are pivotably joined. In the embodiment of FIG. 1, these cables  110  also fixing the relative positions of the upper ladder portion  108 , the lower ladder portion  106 , and the base  102 . The struts  104  are connected extend from the base  102  and are pivotably connected to the lower ladder potion  106  at the pivots  112 . In some embodiments, the struts may be pivotably joined to the base. The lower ladder portion  106  is also pivotably joined to the base  102  at a pair of pivots  111 . The base  102 , in this particular embodiment, includes a guide  105 . The guide  105  constrains the movement of the lower ladder portion  106  about the first and second pair of pivots  112 ,  111 . However, some alternative embodiments may omit the guide  105 . 
     The upper ladder portion  108  includes an access  124  therethrough from the lower ladder portion  106 . The access  124  may be a simple opening in some embodiments. Note that the size of the opening will be implementation specific. The opening for the access  124  must be large-enough for a worker and equipment to pass through, but not so large it impedes the worker&#39;s ascent of the upper ladder portion  108 . 
     However, other embodiments, such as the one illustrated in FIG. 1, may include more elaborate means for providing access from the lower portion  106  to the upper portion  108 . FIG. 2 details one particular embodiment  200  of the access  124  in FIG.  1 . In this embodiment, a removable door  205  covers an opening  210 . The removable door  205  includes a plurality of rollers  215  on either side  220  of the removable door  205 . The rollers are fitted into a track  225  mounted on, formed in, or defined by the top surface  230  of the risers  235  of the upper ladder portion  108 . A worker climbs the lower portion  106  until he reaches the access  124 , raises the removable door  205 , and climbs the lower portion  106  until he is through the access  124 , holding the removable door  205  open. Once through, the worker releases the removable door  205 , which closes by operation of gravity, and climbs the upper portion  108 . In the embodiment illustrated, the removable door  205  includes a plurality of treads  240  to facilitate the worker&#39;s ascent of the upper ladder portion  108  over the removable door  205 . The treads  240  are spaced roughly the same as the treads  255  of the upper ladder portion  108 . 
     Returning to FIG. 1, in the illustrated embodiment, the base  102  includes a plurality of outriggers  116  extending radially. Note that, in this embodiment, the cables  110  include a plurality of guys  118  running between the outriggers  116  and various points on the lower and upper ladder portions  106 ,  108 . Four guys  118  are shown, but the number will be implementation specific. Similarly, the number of outriggers  116 , where employed, will be implementation specific. Three outriggers  116 , for instance, would be sufficient for some embodiments. However, four outriggers  116  provide excellent support via the guys  118  for the lower and upper ladder portions  106 ,  108  and excellent stability. Note also that each of the outriggers  116  in the illustrated embodiments includes a foot  119  to provide additional stabilization, although these may be omitted in some embodiments. 
     The extension ladder  100  is shown erected in FIG.  1 . Note that the lower ladder portion  106  extends in a first direction, represented by the arrow  120 , and the upper ladder portion  108  extends in a second direction, represented by the arrow  122 . The second direction  122  is opposite the first direction  120 . Extending the lower and upper ladder portions  106 ,  108  in opposite directions permits the lower and upper portions  106 ,  108  to position the worker over the approximate center of gravity of the extension ladder  100 . Note also that the guys  118  are taut, because of the forces encountered in their support function and in fixing the relative positions of the upper ladder portion  108 , lower ladder portion  106 , and base  102 . 
     FIGS. 3A-3E illustrate one particular embodiment  300  for the base  102  in FIG. 1 in sectioned side, top, and rear plan views, respectively. In this particular embodiment, the base  300  includes a housing  302  (which may be omitted in some implementations) on a platform  304 . The housing  302  encloses a space  306  and is open at the top  308 . The base  300  houses an engine  310  that, in this particular embodiment, powers a plurality of wheels  312  and drives a hydraulic system comprising a hydraulic gear box  314  and a plurality of hydraulic pistons  316   a - 316   d . In one particular implementation, the engine  310  is a 40 Hp diesel engine. The base  300  also includes a plurality of jointed outriggers  116   a , only two of which are shown in any given view, that are pivotably mounted to the base  300  and articulate to extend radially outward. Note that this differs from the embodiment of the base  102  shown in FIG.  1 . The base  102  in FIG. 1 includes outriggers  116  that are not jointed. Returning to FIGS. 3A-3C, the base  300  also includes a compressor (not shown) in this particular implementation. 
     The hydraulic system adds several useful options to the extension ladder  100  of FIG.  1 . The wheels  312 , in this implementation, retract into the base  300  by operation of the hydraulic pistons  316   b - 316   d  through the hydraulic gear box  314 . The hydraulic piston  316   a  lifts the lower and upper ladder portions  106 ,  108  through the hydraulic gear box  314  and an auxiliary hydraulic system. Although the auxiliary hydraulic system is not shown, its implementation will become apparent to those skilled in the art having the benefit of this disclosure. The hydraulic system may also articulate the jointed outriggers  116   a  from the slots  320  in the platform  304  to extend them and then to return them to the slots  320 . 
     The engine  310  and the hydraulic system (i.e., the hydraulic gear box  314  and hydraulic pistons  316   a - 316   d ) consequently provide embodiments of the extension ladder  100  employing the base  300  with a useful mobility. The extension ladder  100  may be transported to a work site and unloaded in conventional fashion. Once unloaded, the engine  310  can be started to drive the hydraulic system, which can then be used to lower the wheels  312  from the base  300 . Using a steering mechanism not shown, the engine  310  is then operated to drive the extension ladder  100  to the place on the site at which it is to be used. The outriggers  116   a  are then extended, the wheels  112  retracted into the base  300 , and the upper and lower portions  108 ,  106  raised. Once the upper and lower portions  108 ,  106  are raised, the cables  110  are placed. The engine  310  may then be turned off or, if desired, left on to power the compressor  318 . The process may be reversed to move the extension ladder  100  to a new location. 
     Note, however, that the invention does not require this mobility in all embodiments. Some embodiments may omit the engine  310  and the hydraulic system. These embodiments may exhibit wide variation, including, but not limited to: 
     slots (not shown) in the platform  304  in the manner of a wooden pallet, so that the extension ladder  100  may be moved by, for instance, a forklift; 
     the wheels  312  not being retractable, and being mechanically held once the extension ladder  100  is positioned; 
     a hand crank by which the lower and upper ladder portions  106 ,  108  may be raised or by which the outriggers  116 ,  116   a  may be extended; and 
     “permanently” extended lower and upper ladder portions  106 ,  108  that do not collapse and, consequently, do not need to be raised. 
     However, the mobility exhibits great utility in the construction site by, among other things, not requiring additional equipment to move. 
     In the particular embodiment illustrated, however, the housing  302  and platform  304  also define a rectangular steel tool box approximately 8 ft.×4 ft.×4 ft. (_m×_m×_m) in size. The housing  302  and platform  304  are made of welded steel plate and angle. Certain features of the outriggers  116   a  are best shown in FIGS. 3D-3E. Although the outriggers  116  in FIG. 1 are solid, one-piece members, each outrigger  116   a  in FIGS. 3A-3C is a two part member extending at 90° from the platform  304  and swiveling. Each outrigger  116   a  includes three screw down locking devices  322 , one each at the comer  324 , the middle  326 , and at the end  328  of the outrigger  116   a , for mounting screw down or to hold removable counterweight system. 
     Various embodiments of the extension ladder  100  may also be combined or modified with alternative capabilities to provide additional utility on a worksite. For instance, a variety of hoisting frames can be attached to the ladders in different configurations allowing the unloading of material from the truck, raising and erecting the steel, loading material to the roof structure, etc. The extension ladder  100  may also be able to have an integrated automatic rising basket system. 
     FIG. 4 illustrates how one such variant embodiment may be used to implement a gantry crane  400 . The gantry crane  400  generally comprises two facing extension ladders  402  supporting a crane section  404 . Each extension ladder  402  includes a base  102 , a plurality of outriggers  116 , a lower ladder portion  106 , and an upper ladder portion  108  having an access  124  therethrough. Note, however, that the support  110  comprises a pair of braces  406  extending from one of the outriggers  116  to the pivots  114 . The braces  406  replace the struts  104  in the embodiment of FIG.  1 . Note also that the crane section  404  is supported and stabilized in this particular embodiment by a plurality of guys  408  running upwardly from the outriggers  116 . 
     FIGS. 5A-5B illustrate the crane section  404  in greater detail. FIG. 5A is an isometric, side view of the crane section  404 , which generally comprises a plurality of block and tackles  502  moving along a pair of tracks  504 . FIG. 5B is a sectional view of a block and tackle  502  and a track  504  along line  5 B— 5 B in FIG.  5 A. As shown in FIG. 5B, the block  506  translates along the rail  508  of the track  506  on a pair of opposed wheels  510  rotatably mounted to a spindle  512 . The block  506  and tackle  514  (in FIG. 5A) are suspended from the track  506  by the spindle  512 . Each block and tackle  502  traverses the rails  504  in the direction of the arrow  516 , shown also in FIG.  4 . 
     Returning to FIG. 4, the gantry crane  400  may be assembled by first positioning the extension ladders  402  facing each other, as shown. The extension ladders  402  are collapsed. The crane section  404  is fastened to the upper ladder portions  108  of the extension ladders  402 . In one implementation, the crane section  404  is fastened using nuts and bolts (not shown) threaded through co-aligned holes (also not shown) in the crane section and the upper ladder portions  108 . Note that the upper ladder portions  108  are pivotably connected to the brace  407  by the pivots  409  to permit relative movement as the extension ladders  402  are raised and lowered. 
     Each of the extension ladders  402  is implemented using the base  300  of FIGS. 3A-3C, and so provides power to the gantry crane  400  accordingly. The extension ladders  402 , with the crane section  404  fastened thereto, are then raised using the power provided by the base  300 . Once the extension ladders  402  are raised, the supports  110  are placed. Note that, in this particular embodiment, the weight of the crane section  404  loads the supports  110 . The block and tackles  502  can then traverse the crane section  404  powered by the base  300 . The base  300  also includes a winch (not shown) by which the block and tackles  502  may raise various loads. 
     FIG. 6 illustrates an alternative implementation  600  in which the crane section  404  is displaced by a lift including a personnel basket  602  suspended between the two extension ladders  402 . The personnel basket  602  in the particular implementation  600  illustrated may carry people, as well as equipment and supplies. Eight motors (not shown) are attached to the comers  606  of the personnel basket  602 . The motors can lift the basket  602  up two tracks (not shown) along the risers  605 . 
     Note that the implementation  600  includes multiple crane sections  404  such as are described above. One of the crane sections  404  structurally joins the two upper ladder portions  108  as in the gantry crane  400  in FIG.  4 . However, two of the crane sections  404  are fastened to only a single one of the lower ladder portions  106  and the upper ladder portions  108 , as opposed to being suspended between the two extension ladders  402  from the brace  409 . One or all of the crane sections  402  may be omitted in various alternative implementations. 
     The invention in its various aspects may also include a variety of screw down mounting systems, e.g., the screw downs  322  in FIGS. 3D-3E, as well as a removable counterweight system (not shown), whichever is needed at any given time. The screw down system may mount into pre-poured receptacles (not shown) within a slab (not shown). The base  102  may comprise a mobile toolbox  325 , as shown in FIGS. 3A-3C, acting as a counterweight. Welding leads, hoses, power cords, etc. can run in cable trays along either of the ladder portions  106 ,  108 . If so, they may be secured, readily available for visual inspection, and properly placed, thereby eliminating the need to roll out or roll up this equipment. 
     FIGS. 7A-7C illustrate a second particular embodiment  700 . The extension ladder  700  is an embodiment alternative to that in FIG.  1  and built in accordance with the present invention. The extension ladder  700  includes a base  300  such as is shown in FIGS. 3A-3E and discussed above. The extension ladder  700  also includes an enclosed platform, or “man basket,”  702  affixed to the uppermost end  704  of the upper ladder portion  108 . However, the support  110   b  comprises four gin poles  705 , instead of the guy wires in FIG. 1 or the braces in FIG.  4 . The supports  110   b  may be used to lift the extension ladder  700  from its collapsed position, shown in FIG. 7B, to its raised position, shown in FIG. 7A, and then to collapse it again. The relative positions of the lower ladder portion  106 , upper ladder portion  108 , and the support  110   b  as the extension ladder is moved from position to the other is shown in FIG.  7 C. 
     More particularly, the four gin poles  705  are pinned at each upper comer  706  of the toolbox  325  with a swiveling base  300 . The gin poles  705  are fabricated in three parts and extend in an A-frame type fashion to lift the lower and upper ladder portions  106 ,  108 . The lower and upper ladder portions  106 ,  108  are cross-braced by the braces  708 . The lower and upper ladder portions  106 ,  108  comprise two 20-foot extension ladders of welded tubular steel atop each other. The lower ladder portion  106  is pinned three feet past the end of the toolbox  325 , i.e., three feet from the foot  710  of the lower ladder portion  106 . The upper ladder portion  108  is pinned to the lower ladder portion  106  at the other end, four feet from the top. As mentioned, the upper and lower ladder portions  106 ,  108  are lifted into place by the gin poles  705  and pinned in position. 
     Because of the elbow-shaped configuration of the lower and upper ladder portions  106  and  108 , the fully extended manbasket  702  is 30 feet high and is very near the center of gravity, which stabilizes the ladder  100 ,  700 . The toolbox  325  and equipment it might store (not shown) add further stability, acting as a counterweight. The access  124  through the upper extension ladder  108  includes a five-foot sliding removable door  205 , discussed more fully above, at its bottom with spring weight and pins. A worker climbs the lower ladder portion  106 , passes through the removable door  205  at the bottom of the upper ladder portion  108 , slides the door  205  closed, and continues to the top of the upper ladder portion  108 . 
     FIG. 8 illustrates how two of the extension ladders  700  in FIGS. 7A-7C may be configured to implement a man-lift  800 . The man lift  800  is similar in structure and operation to the man lift  600  in FIG. 6, except it employs the extension ladders  700  instead of the extension ladders  100 . The extension ladders  700  may also be configured to implement a gantry crane (not shown) such as the gantry crane  400  in FIG.  4 . Two mobile, freestanding ladders  700  are pinned together to make up the base structure. A man lift system may be pinned within the base structure. Alternatively, an external extending-retracting twin gantry crane (not shown) system may be fastened to the base structure. The twin gantry crane can be used to off-load material from a truck, move such materials, load them onto a roof structure, and/or erect structural steel members, columns, and beams. 
     FIG. 9 depicts an embodiment  900  of the extension ladder  700  in FIG. 7A that demonstrates the versatility of the present invention. The extension ladder  900  in the illustrated implementation includes: 
     the enclosed platform  702 ; 
     a high chair  902  suspended from a lower leg extension  904  from the upper ladder portion  108 ; and 
     a slide around plank  906  hung from the top end  908  of the lower ladder portion  106 . 
     Note that each of the gin poles  705 , in this particular embodiment, includes an extension boot  910  to achieve additional height with the enclosed platform  702 . Additional bracing  912  is also included. As will be appreciated by those skilled in the art having the benefit of this disclosure, the need for and the location of such additional bracing will be implementation specific. 
     The extension ladders  100 ,  700  may also be stacked to achieve greater elevation for working platforms. FIG. 10 depicts one such stacked implementation  1000  using three extension ladders  700  first discussed in connection with FIGS. 7A-7C pinned together—two beneath and one atop the two below. The extended reach of this configuration with these dimensions is 100 ft. This configuration will also need an adapted outrigger set-up wherein outriggers  116   a  are pinned together to widen overall stance at its base. 
     In this particular implementation  1000 , the toolbox  325  has a canopy  1002  and fold-down bench  1004  for first-aid, lunch, breaks or getting out of the weather. The toolbox  325  may also have a urinal attachment, oxygen-acetylene tanks with sensor(s), and/or a fork truck attachment. The toolbox  325  may also include a small refrigerator-oven, heater-fan, personal storage area, a cell phone, and/or a computerized sensing system to record work done. In one particular implementation, the computer sensing system disallows unsafe practices outside the design parameters of the extension ladder  700 , e.g., unsafe configurations, loads, etc. 
     Among its many advantages and benefits, the present invention improves safety conditions and costs factors on practically any construction site. The present invention redesigns the way the work is accomplished and eliminates, or at least reduces, numerous known hazards. For instance, there typically will be no heavy equipment, no overhead loads, and no high work outside of a hand rail. The various embodiments also provide tie off without restriction or production loss. 
     Furthermore, the present invention will reduce the size of the erection crew from six workers to three and reduce the overall construction hazards under which they work. Note, however, that although designed to aid in the construction of commercial warehouse-type buildings, it may be employed in a wide range of environments including, but not limited to, utility work, industrial construction, ironwork, pipefitting, electrical work, etc. 
     The invention can therefore be used to implement a wide variety of construction tools to streamline and economize construction. For instance, the invention may first be deployed as the crane  400  in FIG.  4 . The crane  400  can off-load structural steel (not shown) from trucks (also not shown); load three to five columns and/or beams on each side (while resting vertically on the outriggers); roll over to a work position; and proceed to construct the steel putting up the pieces from one side. Note that, to be unloaded in this manner, the steel must be loaded in a particular order, and turned correctly and in order. Nevertheless, the crane  400  may then roll around 180° to erect the steel on the other side of the work position. This operation would be able to move and erect up to fourteen pieces of steel per trip between the truck and the work position. 
     More particularly, three pieces may be erected at any given time. First, the columns are set and those two workers proceed up each ladder. The third worker raises the beam for connection, then workers return to ground. The crane  400  moves down the column line erecting four more pieces, two columns, and two beams. It is then able to rotate 180° to erect the steel from the opposite side of the robot and return to the steel pile to reload. The number of pieces of steel loaded will depend upon the weight and/or size of the members. 
     Once the structural steel is up, the crane  400  may be broken down into two mobile extension ladders  100  so that miscellaneous steel operations and modifications can be performed in two separate locations. The weight of the loaded base  102  acts as a counterweight to stabilize the rest of the extension ladder  100 . Since the ladder&#39;s base may, in some embodiments, store a worker&#39;s tools, this also brings all the tools to the desired location as work progresses. All of the hoses, welding leads, and cords for equipment stored in the base  102  are fixed in place so the worker does not have to roll out or roll up equipment and tools. 
     Two extension ladders  100  may then even be implemented as the elevator  600  or to hoist materials to the roof of a structure. For the elevator  600 , the central elevator frame pins within the top hoist frame and to the inner base of each base  102 . The elevator carriage acts as a scissorlift or scaffolding, giving safe access to any variety of elevations. For use in hoisting materials to a roof (not shown). For instance, materials may be unloaded and moved parallel to the side of the building using the crane  400 . The outriggers  116  are extended and screwed down. The load is then attached and lifted up the wall to the roof elevation. The outside outrigger  116  may then roll up next to the building wall six inches away, then shift the crane  400  forward four feet, lower the load onto the roof parallel to the load-bearing external wall. 
     Thus, as set forth above, the invention is able to function as a crane, or as three manlifts, as a scaffold or personnel elevator in various embodiments. The rigging time between the various configurations, e.g., the extension ladder  100 , crane  400 , and elevator  600 , is designed to be minimal, allowing changeover and change-back to be as simple and safe as possible. The invention may also be a “home base” on a construction site, keeping the equipment secure and readily available. It saves time and effort in a variety of ways, allowing fewer men to work smarter, not harder, as well as safer and faster. This results in a lower bid and/or higher profit margins in the construction industry. Still other advantages and benefits may arise from the application of the present invention. 
     The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design shown herein, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.