You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to devices for attaching to a ladder, and to ladders in combination with such devices. More specifically, the present invention relates to a wheeled attachment for a ladder, to allow the ladder to function as a hand truck. 
     2. Description of the Relevant Art 
     Service persons, such as electricians, plumbers, and heating and air conditioning mechanics, often work at sites remote from their shops or offices. Typically, tools and materials are transported to the work site using a service truck. Also, it is common that many jobs require the use of a stepladder. 
     Once the service truck is driven and parked close to the work site, the stepladder, tools and materials for the specific job must be carried from the service truck to the work site. When working in a location remote from the parking area, significant time is consumed carrying the stepladder, tools and materials to the work site. For example, one trip between an upper floor of a high rise building and a remote parking location can take more than half an hour. If several trips are required to bring the step ladder and all the necessary tools and materials to the work site, the total cost of the work is greatly increased. Therefore, the fewer trips required between the service truck and the work site, the more cost effectively the work can be performed. 
     One solution to carrying a stepladder, tools and materials between the service truck and the work site would be to use a hand truck. A hand truck offers a great conveyance, and eases the burden of the service person. However, if a service person were to use a hand truck, this would require that a hand truck be carried in the service truck. It is well known that space inside a service truck is limited, and often completely accounted for in accommodating the necessary stepladder, tools and materials. 
     To this end, a piece of equipment consolidating a stepladder and a hand truck has been proposed in the background art. U.S. Pat. No. 5,382,032, issued on Jan. 17, 1995 to James R. Wilson, and U.S. Pat. No. 3,954,155, issued on May 4, 1976 to Orlando Guidara, both illustrate a stepladder with wheels, which can function as a hand truck. Unfortunately, the devices of the background art suffer drawbacks. 
     Both references disclose fixed wheels, which protrude away from a top portion of the ladder. When a person uses the stepladder, the placement of the wheels encroaches on the user&#39;s upward movement. The encroachment forces the user to lean away from, rather than into the stepladder, especially as the user ascends higher on the ladder. Good safety practices recommend that a user should lean into, rather than away from, the ladder. 
     Another drawback is that the protruding, fixed wheels can be an obstacle to the user, and push against a user&#39;s body, when standing on the ladder and trying to reach to the sides of the ladder. If the wheels protrude above the top of the ladder, the wheels will interfere with placing and balancing a flat object, such as a board or a saw, on the flat top surface platform of the ladder. 
     Yet, another drawback is that the wheels are exposed in a prominent location at the top of the ladder, when the ladder is in use. If a user lost their balance, the user might grasp for the wheels to regain their balance. Since the wheels are rotatable, they would not lend themselves well for grasping in an emergency. 
     Another significant drawback is the positioning of the fixed wheels outside the limits of the side rails. In other words, the outer profile, or footprint, of the ladder is altered by the wheels when the ladder is folded up for storage. This arrangement requires additional space for storing the background art&#39;s device in a service truck. Further, the background art&#39;s device may not fit into a standard ladder rail, often provided on the top or side of a service truck. 
     SUMMARY OF THE INVENTION 
     The present invention has as a primary object to solve one or more of the drawbacks associated with the background art. 
     It is an object of the present invention to provide a device for attachment to a ladder, which allows the ladder to function as a hand truck, wherein a wheel assembly is located so as to be remote from a person on the ladder in order to not interfere with the person&#39;s use of the ladder. 
     It is a further object of the present invention to provide a device for attachment to a ladder, which allows the ladder to function as a hand truck, wherein a wheel assembly is located so to be remote from a top of the ladder in order to not interfere with the use of the top of the ladder. 
     It is an even further object of the present invention to provide a device for attachment to a ladder, which allows the ladder to function as a hand truck, wherein the device does not significantly change an outer profile of the ladder when the ladder is in a storage condition. 
     Moreover, it is an object of the present invention to provide a device for attachment to a ladder, which allows the ladder to function as a hand truck, wherein the device attaches to the ladder without structurally altering the ladder. 
     These and other objects are accomplished by a combination comprising: a ladder including a plurality of steps; and an assembly attached proximate an end of said ladder, said assembly including: a pivotable linkage, said pivotable linkage being pivotable between a first position and a second position relative to said ladder; and at least one wheel mounted to said pivotable linkage. 
     Further, these and other objects are accomplished by an assembly for attachment to a ladder, said assembly comprising: a base for fixing proximate an end of the ladder; a pivotable linkage attached to said base, said pivotable linkage being pivotable between a first position and a second position relative to said base; and at least one wheel mounted to said pivotable linkage. 
     Moreover, these and other objects are accomplished by an assembly for attachment to a ladder, said assembly comprising: a base for fixing proximate an end of the ladder, said base including a first bracket and a second bracket, said first bracket for abutting one side of a first rail of the ladder, said second bracket for abutting another side of the first rail of the ladder, and at least one first fastener for connecting said first bracket to said second bracket in order to frictionally fix said first bracket and said second bracket to the first rail of the ladder; a linkage attached to said first bracket; and at least one wheel mounted to said linkage. 
     Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitative of the present invention, and wherein: 
     FIG. 1 is a perspective view of ladder in a hand truck mode, in accordance with the present invention; 
     FIG. 2 is a side view of a ladder in a ready-for-use mode; 
     FIG. 3 is an exploded view of a landing gear assembly; 
     FIG. 4 is a close-up view of the landing gear assembly in a deployed condition; 
     FIG. 5 is a cross sectional view taken along line  5 — 5  in FIG. 2; 
     FIG. 6 is a cross sectional view, similar to FIG. 5, illustrating an alternative embodiment for attaching the landing gear assembly to the ladder; 
     FIG. 7 is an exploded view of a carry plate assembly; 
     FIG. 8 is a close-up view of the carry plate assembly in a deployed condition; 
     FIG. 9 is a cross sectional view taken along line  9 — 9  in FIG. 2; and 
     FIG. 10 is a cross sectional view, similar to FIG. 9, illustrating an alternative embodiment for attaching the carry plate assembly to the ladder. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a perspective view of an A-frame type stepladder C in a closed and inverted position. The ladder C includes a landing gear assembly A and a carry plate assembly B. The landing gear assembly A and the carry plate assembly B are illustrated in deployed conditions. When the landing gear assembly A and the carry plate assembly B are in the deployed conditions, and the ladder C is closed and inverted, the ladder C is considered to be in a hand truck mode. In the hand truck mode, the ladder C can be used for carrying items on the carry plate assembly B. 
     FIG. 2 is a side view of the ladder C in an open and upright position. The landing gear assembly A and the carry plate assembly B are illustrated in retracted conditions. When the landing gear assembly A and the carrying plate assembly B are in the retracted conditions, and the ladder C is opened and upright, the ladder C is considered to be in a ready-for-use mode. In the ready-for-use mode, the ladder C can be used as a conventional ladder, such that a user can climb on the ladder C. When the landing gear assembly A and the carrying plate assembly B are in the retracted conditions, and the ladder is folded together, the ladder is in a storage mode. 
     The ladder C includes such conventional ladder structural elements as: a first step side rail  101 ; a second step side rail  102 ; a first brace side rail  103 ; a second brace side rail  104 ; a plurality of steps  110  connected between the first and second step side rails  101  and  102 ; a plurality of cross braces  111  connected between the first and second brace side rails  103  and  104 , a top cap  120  connecting the first and second step side rails  101  and  102  and the first and second brace side rails  103  and  104  together; and a couple of locking braces  100  connected between the first step side rail  101  and the first brace side rail  103  and between the second step side rail  102  and the second brace side rail  104 , respectively. Although several specific structural elements of one type of conventional ladder have been illustrated, it should be noted that the landing gear assembly A and carry plate assembly B, of the present invention, can be applied to any type of conventional or inventive ladder. 
     With reference to FIGS. 3-5, the component parts of the landing gear assembly A will be disclosed. The landing gear assembly A includes a first arm  13  and a second arm  14 . The first arm  13  is connected to the second arm  14  by an axle  15 . The first arm  13  is connected to the axle  15  via a first screw  16 . The second arm  14  is connected to the axle  15  via a second screw  17 . Although screws have been illustrated, it should be noted that bolts, rivets, welds, nails, or other types of known fasteners could be used instead of the first and second screws  16  and  17 . Alternatively, the first arm  13 , the second arm  14  and the axle  15  could be integrally formed as a single unit. 
     A first wheel  18  and a second wheel  19  are mounted on the axle  15 . The first wheel  18  and the second wheel  19  are freely rotatable about the axle  15  and may contain bearings, bushings, or the like to facilitate their rotation about the axle  15 . The first wheel  18  is prevented from sliding along the axle  15  toward the second wheel  19  by a first retaining washer  20 . Likewise, the second wheel  19  is prevented from sliding along the axle  15  toward the first wheel  18  by a second retaining washer  21 . Third and fourth retaining washers (not shown) may be included to keep the first and second wheels  18  and  19  from sliding along the axle  15  in directions away from each other. Alternatively, an inner hub of the first and second wheels  18  and  19  may be allowed to abut against the first and second arms  13  and  14 , respectively. 
     With reference to FIGS. 3 and 5, a first retaining pin  22  is inserted though a hole in the first arm  13 , adjacent an end of the first arm  13 . The first retaining pin  22  may be constructed in various manners. For example, the first retaining pin  22  may be a threaded cylindrical member, such as a machine screw or a bolt. A head of the first retaining pin  22  abuts the first arm  13  and prevents the first retaining pin  22  from passing through the hole in the first arm  13 . 
     A portion of the first retaining pin  22 , projecting from the first arm  13 , is inserted through a hole in a first bracket. The first bracket may take the form of a substantially planar first plate  24 . A first spring  26  encircles a portion of the first retaining pin  22 , projecting from the first plate  24 . A first nut  28  is threaded onto an end of the first retaining pin  22 , in order to secure the first arm  13  to the first plate  24 , in a manner which allows pivoting of the first arm  13  relative to the first plate  24 . Of course, other types of pivot-allowing attachments could be used to attach the first arm  13  to the first plate  24 . 
     In order to attach the first plate  24  to the ladder C, the first plate  24  is abutted against an inside portion of the first step side rail  101 , above the uppermost step  110  and just below the top cap  120 . The first spring  26  and first nut  28  connected to the first retaining pin  22  are positioned inside an inward facing U-shaped channel of the first step side rail  101 . Next, a second bracket in the form of a C-shaped first member  30  is placed around an outer periphery of the first step side rail  101 . Finally, a plurality of first fasteners  60 , such as bolt/nut combinations, are inserted through an aligned first plurality of through first holes  61  formed around the edges of the first member  30  and the first plate  24 . The first member  30 , the first plate  24 , and the plurality of first fasteners  60  constitute a first base, about which the first arm pivots. 
     The plurality of first fasteners  60  attach the first plate  24  to the first step side rail  101  in a secure manner, via a clamping friction. In order to improve the frictional attachment, it is possible to insert a friction-increasing pad, such as a rubber mat, between the first plate  24  and/or the first member  30  and the first step side rail  101 . In order to improve the pivoting action of the first arm  13  relative to the first plate  24 , it is possible insert a first bearing  64  between the first arm  13  and the first plate  24 , as illustrated in FIG. 5, 
     The ladder C illustrated has the inward facing U-shaped channel formed in the first step side rail  101 , as is common with ladders constructed of fiberglass or aluminum. However, it is important to note that it would also be possible to attach the first plate  24  to ladders with other configurations. For example, a wooden ladder could have a recess bored into it, or a hole drilled though it, in order to accommodate the first spring  26  and the first nut  28  connected to the first retaining pin  22 . 
     However, in a preferred alternative embodiment, as illustrated in FIG. 6, the first plate  24  could include a first open ended box  82 . The first open ended box  82  would provide an offset from the solid first step side rail  101 ′ for accommodating the first spring  26  and the first nut  28  connected to the first retaining pin  22 . 
     The second arm  14  is attached to a second base and to the second step side rail  102  in a manner analogous to the attachment of the first arm  13  to the first base and the first step side rail  101 . In other words, the attachment of the second arm  14  involves a third bracket in the form of a second plate  25 , a second retaining pin  23 , a second spring  27 , a second nut  29 , a fourth bracket in the form of a second U-shaped member  31 , a plurality of second fasteners  62 , a plurality of second through holes  63 , and a second bearing  65 . Further, in the case of a solid second step side rail  102 ′, the second plate  25  could include a second open ended box  83 , as illustrated in FIG.  6 . 
     With reference to FIGS. 7-9, the component parts of the carry plate assembly B will be disclosed. The carry plate assembly B includes a platform  40 . The platform  40  is a generally planar member with upper and lower surfaces. One or both of the upper and lower surfaces may include pleating, or other forms of anti-slip surfacing or anti-slip coatings. 
     The platform  40  is bordered on a forward edge by a first lip  37 , on a rearward edge by a second lip  41 , on a first side edge by a third lip  39 , and on a second side edge by a fourth lip  38 . The first, second, third and fourth lips  37 ,  41 ,  39 ,  38  extend away from the upper surface of the platform  40  at an angle of approximately ninety degrees, and serve to keep items placed on the platform  40  from sliding off an edge of the platform  40 . In a preferred embodiment, the second lip  41  extends furthest away from the platform  40 . Also, in the preferred embodiment, the third lip  39  and the fourth lip  38  are angled or slopping from the relatively higher second lip  41  to the relatively lower first lip  37 . 
     With reference to FIGS. 7 and 9, a third retaining pin  43  is inserted through a hole in the third lip  39 , adjacent an end of the third lip  39 . The third retaining pin  43  may be constructed in various manners, as suggested in reference to the first retaining pin  22 , discussed above. A head of the third retaining pin  43  abuts the third lip  39  and prevents the third retaining pin  43  from passing through the hole in the third lip  39 . 
     A portion of the third retaining pin  43 , projecting from the third lip  39 , is attached to a first foundation by insertion through a hole in a third plate  45 . A third spring  49  encircles a portion of the third retaining pin  43 , projecting from the third plate  45 . A third nut  51  is threaded onto an end of the third retaining pin  43 , in order to secure the third lip  39  to the third plate  45 , in a manner which allows pivoting of the third lip  39  relative to the third plate  45 . Of course, other types of pivot-allowing attachments could be used to attach the third lip  39  to the third plate  45 . 
     In order to attach the third plate  45  to the ladder C, the third plate  45  is abutted against an inside portion of the first brace side rail  103  above the uppermost cross brace  111  and just below the top cap  120 . The third spring  49  and third nut  51  connected to the third retaining pin  43  are positioned inside an inward facing U-shaped channel of the first brace side rail  103 . Next, a third member  47 , having a substantially C-shaped profile, is placed around an outer periphery of the first brace side rail  103 . Finally, a plurality of third fasteners  66 , such as bolt/nut combinations, are inserted through an aligned plurality of through holes  67  formed around the edges of the third member  47  and the third plate  45 . 
     The plurality of third fasteners  66  attach the third plate  45  to the first brace side rail  103  in a secure manner, via a clamping friction. In order to improve the frictional attachment, it is possible to insert a friction-increasing pad, such as a rubber mat, between the third plate  45  and/or the third member  47  and the first brace side rail  103 . In order to improve the pivoting action of the third lip  39  relative to the third plate  45 , it is possible insert a third bearing  69  between the third lip  39  and the third plate  45 , as illustrated in FIG.  9 . 
     The ladder C has an inward facing U-shaped channel formed in the first brace side rail  103 , as is common with ladders constructed of fiberglass or aluminum. However, it is important to note that it would also be possible to attach the third plate  45  to ladders with other configurations. For example, a wooden ladder could have a recess bored into it, or a hole drilled though it, in order to accommodate the third spring  49  and the third nut  51  connected to the third retaining pin  43 . 
     However, in a preferred alternative embodiment, as illustrated in FIG. 10, the third plate  45  could include a third open ended box  98 . The third open ended box  98  would provide an offset from the solid first brace side rail  103 ′ for accommodating the third spring  49  and the third nut  51  connected to the third retaining pin  43 . 
     The fourth lip  38  is attached to a second foundation and to the second brace side rail  104  in a manner analogous to the attachment of the third lip  39  to the first foundation and the first brace side rail  103 . In other words, the attachment of the fourth lip  38  involves a fourth plate  44 , a fourth retaining pin  42 , a fourth spring  48 , a fourth nut  50 , a fourth member  46 , a plurality of fourth fasteners  70 , a plurality of fourth through holes  71 , and a fourth bearing  68 . Further, in the case of a solid second brace side rail  104 ′, the fourth plate  44  could include a fourth open ended box  99 , as illustrated in FIG.  10 . 
     Although the present invention has been illustrated in conjunction with an A-frame type stepladder, it would be possible to apply the present invention to other types of ladders. For example, in the case of a telescoping ladder, the landing gear assembly A could be attached to one telescoping section of the ladder, while the carry plate assembly B could be applied to another telescoping section of the ladder. 
     One advantage of the present invention can be seen in that a pivotable linkage, formed by the first and second arms  13  and  14 , has the ability to place the first and second wheels  18  and  19  into one of two positions. In a first position, the first and second wheels  18  and  19  are located between an uppermost step of the plurality of steps  110  and the top cap  120 . In a second position, the first and second wheels extend away from the ladder C, and are spaced from a side edge of the top cap  120 . 
     In the first position, the first and second wheels  18  and  19  do not interfere with use of the ladder C when the ladder is in the ready-for-use mode. Also, in the first position, the first and second wheels  18  and  19  do not change the outer profile of the ladder C when the ladder C is folded together in the storage mode. 
     To achieve the second position, the first and second wheels  18  and  19  are rotated in an outward fashion approximately 110 degrees from the first position. In the second position, the first and second wheels  18  and  19  sufficiently clear an outer edge of the top cap  120  so that an inverted and closed ladder C may be tilted back and the weight of the ladder, and any items on the carry plate assembly B, are born by the first and second wheels  18  and  19 . 
     Of course, it would be possible to have the first and second wheels  18 ,  19  locatable in a third position. For example, the third position might overextend the first and second wheels  18  and  19 , putting them beyond the plane of the top cap  120 . For example, the first and second wheels  18  and  19  might be rotated 140 degrees from the first position to achieve the third position. Such a third position might be useful when pushing or pulling the ladder C in the hand truck mode over rough terrain or through high grass. 
     Although the landing gear assembly A and carry plate assembly B have been illustrated as having no bias toward any given position, it would be possible to bias one or both to a particular position. For example, the first and second wheels  18  and  19  could be spring biased to stay in the first position. In order to place the first and second wheels  18  and  19  into the second position, one would need to move the first and second wheels  18  and  19  against the spring bias and lock them in place using a locking device. A spring-loaded pin assembly, as will be later discussed, is utilized in order to lock the landing gear assembly A into one of the first or second positions. 
     Likewise, as illustrated in FIG. 2, the platform  40  could be spring biased to a position X adjacent to the first and second brace side rails  103  and  104 . In order to place the platform  40  into a position Y, one would need to move the platform  40  against the spring bias and then lock it into place using a locking device. The position Y could correspond to an angle of approximately ninety degrees relative to the first and second brace side rails  103  and  104 . The position Y would be suitable for use of the carry plate assembly B when the ladder C is in the hand truck mode. 
     It would also be possible to lock the platform  40  into a position Z. The position Z could correspond to an angle of approximately seventy-five degrees relative to the first and second brace side rails  103  and  104 . The position Z would be suitable for use of a reverse side of the platform  40  as a paint bucket stand or work stand when the ladder C is in the ready-to-use mode. Again, a spring-loaded pin assembly, as discussed below, is utilized in order to lock the carry plate assembly B into one of the X, Y or Z positions. 
     As illustrated in FIGS. 3 and 4, a first spring-load pin  91  is threaded into a threaded into a through hole in the first arm  13 . The first spring-loaded pin  91  includes a gripping head fixed to a shaft. The shaft is slideably mounted into a sleeve. The sleeve includes external threading, which is threaded into the through hole in the first arm  13 . 
     The shaft is spring biased and tends to pull the gripping head towards the first arm  13 , and tends to extend the shaft out of the through hole on a back side of the first arm  13 , facing the first plate  24 . The spring-load pin  91  is a commercially available, staple product. 
     The tip end of the shaft extending from the back side of the first arm  13  presses against the first plate  24 . When the landing gear assembly A is located in the first position, the end of the shaft snaps into one of a pair of first locking holes  130 . When the landing gear assembly A is located in the second position, the end of the shaft snaps into one of a pair of second locking holes  132 . When the landing gear assembly A is transitioning between the first and second positions, the tip end of the shaft rides on, and traces an arc path across, a surface of the first plate  24 , facing the first arm  13 . 
     In order to disengage the shaft of the first spring-loaded pin  91  from within one of the first or second locking holes  130 ,  132 , a user grips the gripping head. The gripping head is pulled away from the first arm  13 , against the spring bias, until the shaft withdraws from the locking hole  130  or  132 . 
     FIGS. 3 and 4 illustrate a second spring-loaded pin  92  threaded into the second arm  14 . The second spring-loaded pin  92  functions in a manner analogous to the first spring-loaded pin  91 . A shaft of the second spring-loaded pin  92  protrudes into the other of the pair of first locking holes  130 , when the landing gear assembly A is in the first position. Further, the shaft of the second spring-loaded pin  92  protrudes into the other of the pair of second locking holes  132 , when the landing gear assembly A is in the second position. Although first and second spring-loaded pins  91  and  92  have been illustrated, a single spring-loaded pin  91  or  92  could be provided to lock the landing gear assembly A into the first or second positions. 
     FIGS. 7 and 8 illustrate third and fourth spring-loaded pins  88  and  87 . The third and fourth spring-loaded pins  88  and  87  are constructed in the same manner as the first and second spring-loaded pins  91  and  92 . The third and fourth spring-loaded pins  88  and  87  are threaded into the third and fourth lips  39  and  38 , respectively. 
     A pair of locking holes  84 ,  85  is provided for each of the three positions X, Y, and Z of the carrying plate assembly B. When the carry plate assembly B is located at one of the positions X, Y, or Z, the shafts of the third and fourth spring-loaded pins  88  and  87  will snap into one of the pairs of locking holes  84 ,  85 . In order to move the carry plate assembly B from one of the positions X, Y or Z, the user pulls the gripping heads, of the third and fourth spring-loaded pins  88  and  87 , toward each other. Pulling the gripping heads, releases the shafts from within the locking holes  84 ,  85 . 
     A particular advantage of the present invention resides in the mounting system employed to attach the landing gear assembly A and the carry plate assembly B to the ladder C. Both are attached via frictional engagement. There is no need to drill holes or cut access guides into the ladder C. This attachment form is particularly advantageous, since removing material from the ladder could weaken the structural integrity of the ladder C, and alter the weight limits or ratings associated with the ladder C. 
     The frictional engagement also allows the landing gear assembly A and the carry plate assembly B to be easily removed from the ladder C. After the assemblies A and B are removed, the ladder C is restored to its original state. Therefore, a user can transfer the assemblies A and B to a new or different ladder. 
     No materials for construction have been assigned to the various component parts of the invention. It is envisioned by the inventor that practically any known material, or combination of materials, could be used in the fabrications of various ones of the component parts. For example, the first and second arms  13  and  14  could be formed of cast or forge metals, non-metallic composites, or even wood, such as plywood. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

Summary:
A device for attaching to a ladder allows the ladder to function as a hand truck. The device includes a pair of retractable wheels. The retractable wheels can be stored away inside an outer profile of an opened or closed stepladder, so that the wheels do not interfere with a user when the ladder is opened and do not take up space when the ladder is closed. The device may also include a retractable carry platform for holding loads when the ladder is used as a hand truck. A reverse side of the carry platform can serve as a paint bucket support or work surface when the ladder is in use. Both the retractable wheels and the retractable carry platform are attached to the ladder by a frictional engagement which does not violate the structural integrity of the ladder.