Abstract:
A collapsible hand truck for supporting large and heavy objects such as entrance way doors. The hand truck being able to adjust to varying load center of gravities, thereby allowing a single individual to handle extremely heavy loads. A tiltable main frame which can rotate about a fulcrum point allowing even the heaviest loads to be shifted from a vertical to a horizontal plane with minimal effort by the individual. The main frame is supported by a pair of struts and the length of the frame is adjustable to compensate for doors of various lengths and center of gravities. A front strut having a pair of loading wheels and a rear strut having auxiliary caster wheels for maneuverability. The struts being rotative to each other.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a hand-propelled truck for carrying relatively large and heavy objects such as doors, and more particularly to a hand truck capable of adapting to the center of gravity of the object. 
     2. Description of the Prior Art 
     Hand trucks or dollies have been used for many years to move a variety of heavy objects. Normally, the hand truck is used by one person. It is typically designed having a lip or nose section for supporting the load, a frame for resting the load, a handle, a pair of wheels located at the bottom of the frame and occasionally a smaller pair of caster wheels for support and manuevering of the load. Braking systems are well known and they serve to lock the wheels in place when tilting the hand truck rearwards to the horizontal position. 
     The present invention provides a hand truck with an improved means for adjusting to a shift in the center of gravity of the load. This is essential for enabling a single person to handle a very heavy load. 
     Some prior art patents teach improved hand trucks having means for achieving some of the above objects. For instance U.S. Pat. No. 5,277,439 issued to George R. Pipes et al. on Jan. 11, 1994, depicts a hand truck that uses a pair of auxiliary wheels that swing away from the main frame, thereby allowing the load to be tilted backwards to a generally horizontal and stable position. The load rests on all four wheels and shows a much improved method over other prior patents. This invention requires the operator to control the movement of the main frame by a pull member whereas in the present invention no such mechanism is needed. 
     U.S. Pat. No. 4,919,442 issued to Thomas F. Green on Apr. 24, 1990, teaches the use of a leverage method for shifting the weights of the object to be carried. This patent basically forms a cart but not a hand truck that can be utilized as a work bench as well. 
     U.S. Pat. No. 5,445,399 issued to Frank S. Salvucci, Sr. on Aug. 29, 1995, shows a collapsable hand truck having a positive leg locking arrangement for a retractable leg. It utilizes a slide means for tilting the load. This invention does not seek to teach the ability of the hand truck to swing away from the main frame to form a horizontal work bench as does the present invention. 
     U.S. Pat. No. 3,968,974 issued to Nelson Wetzel on Jul. 13, 1976, teaches the use of a hand truck with an elaborate braking system. The present invention uses a very simple braking means. 
     U.S. Pat. No. 4,284,286 issued to Charles D. Lewallen on Aug. 18, 1987, describes a hand truck that utilizes auxiliary castor wheels to form a work table from a conventional hand truck. The present invention also forms a work bench, however it is the actual load (door) that provides the bench surface. 
     It is appreciated that the prior art addresses the need to more efficiently handle long or heavy objects with a simple hand truck. Some hand trucks have devices which secure the object to the truck and others have means for making adjustments for a changing center of gravity. It is evident that the hand truck of the present invention may be improved upon to a significant degree, and it is to this end, that this invention as shown and described herein is directed. 
     SUMMARY OF THE INVENTION 
     The invention is a self-propelled hand truck that utilizes the center of gravity of the load itself to assist a single operator in handling loads upwards of 400 pounds or more with a minimum of effort. The most pressing need that the invention addresses is in transporting doors that are often bulky and extremely heavy. It is recognized that the invention will perform equally as well transporting other loads, but for this specification the load will be assumed to be a door. The invention utilizes the weight of the load pivoting about a fulcrum point. 
     The invention includes a relatively rectangular main frame, upon which the door is placed. A pair of rectangularly shaped strut members support the main frame and the load thereupon. A pair of main wheels are attached to the forward strut for the purpose that wheels serve and a pair of auxiliary wheels (caster) are attached to the rear strut member for support and manueverability. A fulcrum assembly connects the frame to the struts. The frame and both struts can be extended in length to compensate for variations in lengths of the doors handled. The truck is relatively lightweight and manufactured from common materials, such as steel or aluminum. The strut and frame members are made from metal stock having a tubular and flat shape respectively. 
     Accordingly, it is a principal object of this invention to provide a hand truck that can be adjusted to the center of gravity of the load carried, thereby allowing the operator to utilize the weight of the load to assist him in handling it. 
     It is another object to provide a hand truck that will form a work bench whereby immediate repairs can be made. 
     It is a further object to provide a hand truck that is manufactured from the minimum number of parts and relatively inexpensive parts. 
     It is still another object of the invention to provide a hand truck that is capable of turning 360 degrees in its own tracks for manueverability. 
     And yet another object of the invention is to provide a hand truck for removing rather heavy and large doors, wherein the length and thickness of the door is not a factor. 
     It is another object of the invention to provide a hand truck that is collapsible for ease in moving and storage. 
     It is still another object of the invention to have the frame and support struts be capable of extension for handling extremely long doors. 
     And finally it is an object of the invention to provide a hand truck that will exhibit a high level of stability regardless of whether the load is vertical, tilted or horizontal to the ground surface. 
     These and other objects of the present invention will become readily apparent upon further review of the following specification and drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a pictorial view of the frame. 
     FIG. 2 is a side elevational view of the hand truck in a relatively vertical position. 
     FIG. 3 is a side elevational view of the hand truck in a tilted position. 
     FIG. 4 is a side elevational view of the hand truck when the main frame is in a horizontal position relative to the ground. 
     FIG. 5 is a top view of the strut members being connected to each other by a fulcrum assembly. 
    
    
     Similar reference characters denote corresponding features consistently throughout the attached drawings. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawings, the invention provides for a hand truck  10  for loading and manuevering large and heavy objects such as doors. These doors are usually of the large type, found at the entrances of private and public buildings. FIGS. 1-4 show the hand truck  10  comprising of a support frame  11 , a front strut member  12 , a rear strut member  13  and a fulcrum assembly for connecting all of them together in a cooperating relationship to each other. These features will be discussed in detail below. 
     Support frame  11  is a relatively open rectangular lattice structure having a pair of elongated rectangularly shaped side beams  15  and a center beam  16  parallel to the side beams  15 , all integral with each other by means of braces  17  perpendicularly spaced relative to the beams  15 ,  16 . The connection of braces  17  to beams  15 ,  16  being by conventional means such as welding. Frame  11  having a top end  18 , a bottom end  19 , a top surface and a bottom surface  21 . Integral with the bottom end  19  a lip  22  extends outwardly from the top surface  20 . The lip  22  receives door members and other objects to be transported, as is well known and understood. In order to make the frame  11  adjustable for tall doors, both side beams  15  are capable of being extended. Telescopic extension beams  23  are located at both ends  18 ,  19  and they can be manually extended outward to a plurality of selectable positions. The side beams  15  have apertures  24  whereby retaining pegs  25  can be inserted through a number of selectable openings in the extensions  23 . A pair of locking bars  26  each having a circular opening  27  therein, are each mounted to the bottom end  19  of one of the side beams. When desired, the frame  11  can be secured to the front strut member  12  by passing a locking rod  28  through the two openings  27 . Eyelets  29  are mounted on the bottom surface  21  at top and bottom ends  18  and  19  of the center beam  16 . This will be discussed in greater detail further on in this disclosure. For purposes of clarity of the illustration, the elements which help to secure the lip  22  to the frame  11  have been omitted. 
     FIGS. 1,  3  and  5  describe the open lattice type strut members  12  and  13 , each having a pair of elongate tubular shaped legs  30  connected by conventional means to crossarms  31 . Arms  31  are made from relatively flat metal stock and are arranged perpendicularly to legs  30 . A middle strap  54  parallel to and equidistantly spaced within the legs  30  provides additional structural strength of the struts  12 ,  13 . Each strut member  12 ,  13  having an upper end  32  and a lower end  33 . Each strut member  12 ,  13  having an exterior side  34  and an interior side  35 . Front strut member  12  including an axle  40  connected to the interior side  35  of its lower end  33 , wherein a pair of main wheels  41  for moving hand truck  10  and load are mounted on each distal end of the axle  40 . Extending radially outward from the axle  40 , and appropriately journaled thereto for rotation, is a front bracket  42  which is stabilized by connection to the lower end  33  of the interior side  35  of the front strut member  12 . A protruding platform  43 , for supporting an article (door) to be moved, extends outwardly from the lower exterior side  26  of the front strut  12 . In addition to supporting the lip  21 , the platform  43  allows the user to slide under the desired load (door). The rear strut member  13  has a support bar  44  at the lower end  33  for integrally connecting the tubular legs  30  to each other. A rear bracket  45  has an upper portion connecting it to the interior side  35  of the rear strut  13  and a lower portion containing a pair of auxiliary wheels  46 , which allow the hand truck  10  360 of rotational manueverability. A chain  36  links together the two strut members  12 ,  13  to maintain a workable height relative to the load. A tension spring assembly  57  interconnects between the front strut member  12  and the chain  36  for controlling the amount of slack in the chain  36  at various positions of the hand truck  10 . The tension spring  57  is made up of inexpensive metal spring coil, having sufficient tension strength to support the weight of the chain  36 . The strut members  12 ,  13  are joined together at their upper ends  32  in a pivotable relationship to each other by the fulcrum assembly  14 , thereby allowing the members  12  and  13  to freely rotate with respect to each other. The chain  36  limits the spread of the struts from each other. When extremely elongated loads are encountered, the tubular legs  30  are extendable to cooperatively respond to the frame  11  which is extended. Each upper leg  30  can be telescopically extended by extension legs  37 . Slotted openings  38  located at the upper ends of the legs  30  allow for retention pegs  39  to contain the extension to the desired length. 
     As shown in FIG. 5, the means for connecting the frame  11  and the struts  12 ,  13  is a fulcrum assembly  14  having a pair of elongated rectangular shaped frame bars  50 . Each frame bar connected on one longitudinal side to the bottom surface  21 , approximately at the middle point of each of side beam  15  by conventional fastening means such as welding. Each bar  50  having a hole  51  therein, the hole  51  located at approximately the center of the bar  50 . A fulcrum pin  52  passes through the holes  51  and also through the slotted openings  38  in the upper ends of the legs  37  of the strut members  12  and  13 . Conventional retaining means of the pin  52  are employed at both ends. It is this fulcrum pin  52  that allows the strut members  12 ,  13  to rotate in relation to each other, and it also allows the main frame  11  to pivot from a vertical position as shown in FIG. 2 to the slanted position as shown on FIG.  3  and finally the horizontal position as described by FIG. 4. A stop bar  53  extends from the lower portion of each frame bar  50  across and beneath the bottom surface  21  of the frame  11 . This stop bar  53  insures that the frame  11 , when pivoted into the horizontal work bench position, will not pivot rearwardly beyond the horizontal plane. When in the horizontal plane the individual can prop support poles  48   a  and  48   b , both having eyelet connectors at their distal ends  55 , to be connected by means of support pegs  49  to eyelets  29  located on the center beam  16  of frame  11 . The proximal ends  56  of the support poles  48   a  and  48   b  have rotational members  47  connecting to the lower portions of the rear and front strut members  13  and  12  respectively. 
     It is necessary, that when the frame  11  is being put into the rearward position, that the main wheels  29  be in a locked position. The brake system employed by the invention uses a conventional system, whereby a spring released coil causes a bar to be biased against the main wheels  41 . A hand control lever, mounted on the interior surface  35  of the front strut member  12  can be activated thereby causing the spring to be tensioned and thus pulling the bar away from the wheels so that the brake will be released. The braking system used herein is similar to those brake systems found in most hand trucks, therefore for the sake of clarity the brake system used herein is not shown in the drawings. 
     The present invention is an improved hand truck that allows a single individual to handle exremely heavy loads. The frame  11  of the basic hand truck  10  is approximately 6′10″ which is the height of an average door. For doors of greater height, the operator merely adjusts the the length of the frame  11  and struts  12 ,  13  to accommodate them to the height of the door being moved. In tilting the door rearwards, little physical effort is required regardless of the weight of the door. The weight of the door pivoting about the fulcrum  14  provides most of the necessary momentum. The essential inventive concept is to utilize the center of gravity of the door (load) as it pivots about the fulcrum point. As long as the center of gravity of the door is approximately at the fulcrum point, the weight of the top portion of the door moving downwardly and rearwardly is compensated by the weight of the bottom of the door moving in an upward direction. The stop bar  53  insures that the frame  11  will not pivot beyond the horizontal plane. The individual merely has to manuever the hand truck so that the lip of the truck can slide under the door to be moved. The individual tilts the door rearwardly 30° to 45° in order to handle it efficiently. Often it is desirable to make repairs to the door right at the jobsite. This is facilitated by the present invention having the capability to be put into a horizontal plane and thus be used as a work bench. The support poles  48   a  and  48   b  are positionable with the corresponding eyelets  29  of the main frame  11  to provide an extra measure of stability when the frame and door are in this plane. 
     It is to be understood that the present invention is not limited to the sole embodiment described above, but encompasses any and all embodiments within the scope of the following claims.