Abstract:
An electric hand truck having positive and negative lift capability. The hand truck can lower objects from stairs, loading docks, or trucks. The hand truck can also lift objects from the floor upward and climb stairs. It has a platform with caster wheels for easy of mobility in tight places. It has brakes and an adjustable tilt with a dolly such that the cargo hauled can be wheeled on the hand trucks main wheels and on the dolly wheels which support the object at an angle. The objects are raised or lowered by an electric motor run on a battery. The switch for the motor is a strip switch running the length of the rail extrusions for ease of access. The hand truck is lightweight and maneuverable. The dolly tilts the rail extrusions are easily adjustable angles to suit the load. Handles attached to the rail extrusions make the hand truck easy to maneuver.

Description:
This application claims benefit of Provisional No. 60/137,832, filed Jun. 7, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     I. Field of the Invention 
     This invention relates generally to hand trucks for moving heavy loads, and more particularly, to an electric motor powered hand truck for raising and lowering heavy loads, that hand truck being designed to be highly maneuverable when either loaded or unloaded by a single operator. 
     II. Discussion of the Prior Art 
     The closest prior art which I am aware is my own earlier electric hand truck described in U.S. Pat. No. 4,034,878, the teachings of which are hereby incorporated by reference. The present invention is considered to be a marked improvement over the product corresponding to my &#39;878 patent. Specific features considered to be improvements include, but are not limited to: 
     1. My new hand truck provides for both negative and positive lifting of a load. That is to say, with the floor as a reference, the hand truck of the present invention is capable of not only lowering a load below floor level, for example, at a loading dock, but is also capable of elevating the load above the floor as with a fork lift. It also has the ability to climb stairs and get into a truck with a full load on it. 
     2. My new design is of lighter weight construction, without a sacrifice in strength or load carrying capability. This is achieved by utilizing inner and outer side rails comprising aluminum extrusions for the vertical frame members, where the extrusions are designed to interlock, yet slide relative to one another without binding. 
     3. Improved mobility of the unit is assured by providing a plurality of swivel casters on the underside of the main load plate which attaches to the inner side rail extrusions of the vertical frame members and with the hand cart&#39;s main wheels journaled for rotation on a main frame casting that is affixed to the outer side rails of the left and right interlocking extrusions forming the vertical frame members. 
     4. Load bearing forks are pivotally mounted on the main frame casting and when lowered parallel to the ground, they straddle the load plate. The pivotal load arms are deployed when taking advantage of the positive lift feature of the hand cart, but are swung up and out of the way when utilizing the negative drop feature. 
     5. A motor driven lead screw is operatively coupled between the main frame casting and a top member spanning and affixed to the outer side rail extrusions and the lead screw cooperates with a traveling nut mounted on a top plate spanning the inner side rail extrusions. Thus, as the electric motor drives the lead screw, the inner and outer side rail extrusions are longitudinally displaced relative to one another in a direction depending upon the direction of rotation of the motor. 
     6. The interlocking side rail extrusions include longitudinal grooves extending the length thereof for permitting the attachment of a stabilizing carriage frame that is supported in a cantilevered dolly fashion toward the rear of the hand truck and which also has swivel caster wheels affixed to the underside thereof for engaging the ground when the hand truck is tilted back at an angle to the vertical. The slots in the side rail extrusions also permit flexible cinch belts to be used to secure a load onto the handcart. 
     7. The use of elongated lineal contact electrical switch strips mounted on the outer one of each of the extruded side rails makes it easy for an operator to control energization of the motor from a point anywhere along the side rails, thus obviating the need to search for a small on/off switch as in the prior art. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     Other features, objects and advantages of the invention will become apparent to those skilled in the art from the following detailed description of a preferred embodiment, especially when considered in conjunction with the accompanying drawings in which: 
     FIG. 1 is an exploded view of the handcart constructed in accordance with the present invention; 
     FIG. 2 is an exploded, cross-sectional view of the inner and outer side rail extrusions; and 
     FIG. 3 is an exploded partial perspective view of the load arms showing how an optional dump plate may be attached. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, the motorized hand truck of the present invention is seen to comprise a main casting  10  which is preferably fabricated from aluminum or another lightweight, yet strong, material. The main casting has rearward projecting ears  12  on a opposed sides thereof and extending through each of the ears is a bore  14  for receiving an axle assembly therethrough. The axle assembly is seen to comprise a main wheel shaft  16  and fitted over the shaft  16  is a tubular axle member  18 . A pair of wheels, as at  20 , are journaled for rotation on the shaft  16  by means of sleeve bearings  22 . The main wheel casting  10  is bolted to the rear edge surfaces of outer side rail extrusions  24  and  26  which telescopingly fit about inner side rail extrusions  28  and  30 . Nylon pads  31  and  33  (FIG. 2) are positioned between mating surfaces of the interlocking side rails to provide a relatively low friction contact, thereby facilitating the ability of the inner and outer side rails to slide relative to one another. When assembled together, the surface  35  of the inner rails  28  and  30  abuts the pad  33  having a low coefficient of friction while surface  37  of the outer frame rail extrusions  24  and  26  rides on the Nylon paid  31 . 
     Pivotally joined to the main casting  10  is a pair of load arms  32  and  34 . More specifically, a hinge pin, as at  36 , passes through a bore  38  formed in each of the load arms  32  and  34  with the pin fitting into a threaded bore  40  formed in the main frame casting  10 . When the arms  32  and  34  are lowered parallel to the ground, a rear end portion  42  thereof engages a projection  44  on the casting to prevent further counterclockwise rotation past the horizontal. The arms  32  and  34 , however, can be rotated in the clockwise direction to a vertical orientation straddling the left and right side rails. 
     As seen in FIGS. 2 and 3, the outer ends  37  and  39  of the load arms  32  and  34  are bifurcated to define a slot  41  and  43  therein and a bore  45  and  47  extends across the notch as best seen in FIG.  3 . An optional dump plate  49  includes lugs  51  and  53  also having a transverse bore extending therethrough are adapted to fit between the tines defining the notches  41  and  43  to be held in place by clevis pins  55  and  57  and spring clips  59 . 
     Bolted to the inner rails  28  and  30  proximate the lower end thereof is a load plate member  46 , preferably formed from cast aluminum. Bolted to the undersurface of the plate  46  are front and rear caster pairs  48  and  50 . A further pair of wheels (not shown) are mounted on an axle that extend between gusset members  52  that are integral with the load plate  46 . These wheels, being of a relatively small diameter as compared to the main wheels  20 , function as a fulcrum dolly when the hand cart is tipped to a rearward disposition when the main wheels happen to be elevated, all as will be further explained. The lower rear edge  53  of the gussets  52  on the load plate member  46  are formed in a radius of about 3 inches over an arc of about 60°, which, as will be explained, comes into play when manipulating the hand truck to climb stairs. 
     An inner top plate  54  extends between and bolts to the inner pair of side rail extrusions  28  and  30  and formed through the thickness dimension of the top plate  54  is a bore  56  which is adapted to receive an upper portion of an elongated lead screw  58  therethrough. Affixed to the undersurface of the top plate  54  is a traveling ball screw  60 . The upper end  62  of the lead screw  58  is journaled for rotation in a bearing  64  that fits into a bore (not shown) formed on the undersurface of a top plate member  66  that spans between and attaches to the upper end of the outer side rail extrusions  24  and  26 . A lower end of the lead screw  58  is journaled for rotation in a bearing mounted centrally in a base portion  68  of the main frame casting  10 . 
     A DC drive motor  70  is coupled through a clutch assembly  72  to the lead screw  58 . The motor and clutch are of a type manufactured and sold by Warner Ballscrew Corporation of Chicago, Ill., and is designed to rotate the lead screw  58  when carrying a predetermined weight. The clutch will slip if the weight limit is exceeded, preventing the load from being raised or lowered. A two-speed motor may also be used. When a light load is involved, it can be in the high-speed mode, but when heavily loaded, the motor may run at a low speed, high torque mode. A battery, preferably a rechargeable lead-acid type battery (not shown) mounts on the platform  68  of the main frame member  10  and is connected through an elongated strip switch (not shown) snaps into a groove  73  that runs the length of the side rails  24  and  26 . 
     A front screen panel  74  has side flanges  76  on opposed side edges thereof that are adapted to fit into longitudinal grooves, as at  78 , formed in the front edge of the inner side rail extrusions to prevent accidental contact with the motor driven lead screw. 
     A handle assembly, indicated generally by numeral  80 , attaches to the rear edge surface of the outer side rail extrusions  24  and  26 , which handles can be readily grasped by the operator for tilting the hand truck to the rear and for steering the hand truck as it is being pushed along the ground. 
     A stabilizing platform assembly is pivotally mounted to the main frame casting  10  and includes a pair of arms  84  and  86  that are maintained in parallel, spaced-apart relationship by a transversely extending plate  88 . The arms  84  and  86  each include a bore as at  90  extending therethrough such that the main wheel shaft  16  may pass through the apertures  90 , allowing rotation of the stabilizer carriage assembly  82  about the shaft  16 . The stabilizer carriage assembly also includes a pair of swivel caster wheels  92  which fasten to the undersurface of the plate  88  to engage the ground when the stabilizer assembly  82  is in its lowered disposition. Completing the stabilizer carriage assembly  82  are a pair of guide rods  94  and  96  which are pivotally joined to the outer ends of the arms  84  and  86 , as illustrated, and the upper ends of the guide rods  94  and  96  have apertures therethrough for fitting about studs, as at  98  that project from locking plates  100  that cooperate with grooves  102  and  104  formed vertically in the outer guide rail extrusions  24  and  26 . A handle  106  when rotated clockwise rotates the studs  98  into engagement with the outer side rails to prevent the slidable locking plates  100  from moving vertically. When the locking  106  is rotated counterclockwise, the studs are loosened to the point where the plates  100  can slide in their associated T-slots, allowing the stabilizer assembly  82  to be raised or lowered relative to the ground. 
     To prevent unwanted movement of the handcart, a break assembly is provided that cooperates with the wheels  20  to prevent their rotation. Specifically, coupled to the handle bar assembly  80 , and passing through a guide bracket  116 , is a steel rod  108  whose upper end attaches to the handle assembly  80 . The lower end of the rod  108  normally rides above the rubber surface of the wheels  20 , but when the handle bar is lowered, the lower end of the rod  108  presses securely against the wheels  20  to prevent their rotation. While a particular brake arrangements illustrated, other such braking devices can be substituted without departing from my invention. 
     OPERATION 
     When making a delivery of a household appliance, such as a refrigerator, the deliveryman will first raise the load arms  32  and  34  so that they are out of the way and then the load will be tipped such that the load plate  46  can be slipped under the appliance or its box or container. A cinch strap is then placed about the load and its ends are locked into slots, as at  75 , formed in the extrusions  24  and  26 . By pulling rearward on the handle assembly  80 , the handcart and load becomes supported on the wheels  20 . Now, by lowering the stabilizer assembly  82  and retightening the studs  98 , further rotation of the handcart and load is prevented. The delivery person may now readily push the handcart with its load from a loading dock into a waiting delivery truck. It has been found expedient to locate a rearward-facing recessed, pop-up hook on the loading dock and in the delivery truck bed to act as a deployable stop to prevent the motorized hand truck from unintentionally going over the edge of the dock or truck tail gate. The hook is dimensioned to engage the plate  88  of the stabilizer assembly before the wheels of the handcart reach the dock&#39;s edge or the tailgate&#39;s edge. 
     If the delivery truck is heavily loaded, it may be necessary to position the handcart with the load attached into a confined space. This can readily be done by returning the handcart to its vertical orientation and then actuating the lead screw drive motor to raise the outer rails and the main frame casting  10  so that the wheels  20  no longer contact the ground. The load will then be supported on the caster wheels  48  and  50 , allowing the load to be readily translated and rotated until it fits within the confined space. 
     Upon reaching the home site where the appliance is to be delivered, the delivery person will maneuver the handcart until the guide rail extrusions extend beyond the end of the tailgate of the delivery vehicle. At this point, the handle  80  will be manipulated to bring the locking rods  108  into engagement with the tires on the wheels  20 . Now, by actuating one of the two switch strips, the lead screw can be driven in a direction to lower the load plate carrying the appliance until the caster wheels  48  and  50  on the underside of the load plate contact the ground. At this point, the main frame casting  10  supporting the wheels  20  will be still at the level of the delivery truck&#39;s tailgate. In a prototype machine built in accordance with the present invention, it is possible to displace the load plate  46 ,  52 ″ below the level of the wheels  20 . 
     Next, by releasing the brake and pushing the hand cart a few inches forward as it rides on the caster wheels  48  and  50 , the motor  70  can be made to rotate the screw  58  in a direction to lower the main frame casting  10  and the wheels  20  to ground level by pressing anywhere along the length of the other of the two lineal contact switch strips. 
     By pulling back on the handle assembly  80 , the load can again be tipped rearward and the stabilizing platform  88  may also be lowered to bring its caster wheels  92  into contact with the ground. Here, the delivery person may now push the cart and load to the entry steps of the home where the delivery is to be made. 
     By sequentially raising and lowering the wheels  20 , tipping back the hand cart, elevating the load, returning the hand cart to the vertical and repeating these maneuvers, the hand cart can be made to “climb” stairs leading to the home&#39;s entrance door. Once through the doors, the appliance on the handcart can be wheeled to the area of the home where the appliance is to be installed. In moving a load down a flight of stairs, the knurled radiused surface  53  of the load plate engages the steps as a load is being lowered on the motorized hand truck, preventing the handcart from sliding relative to the stairs. 
     In other applications, it may be desirable to elevate a load to a point above the ground. Here, the load arms  32  and  34  will be rotated to their horizontal position and the load placed on them. Again, by squeezing the appropriate switch strip that extends along the rear edge of the outer side frame extrusion, the motor will be energized to rotate the lead screw in a direction to raise the top plate  66  affixed to the outer side rails and thereby lifting the main frame casting  10  and the load bearing arms  32  and  34  vertically upwards. 
     This feature can advantageously be used by a workman installing sheetrock ceiling panels. A sheetrock panel may be placed horizontally atop the cover plate  66  and the workman may stand on the load arms  32  and  34 . Actuation of the motor then causes the lead screw to elevate both the sheetrock panel and the workmen until the sheetrock panel is at ceiling height. The workmen may now use conventional sheetrock screws to secure the ceiling panel in place on the undersurface of the ceiling joists of the building. 
     When using the electric hand truck of the present invention to transport baled waste from a compactor to a dumpster, the optional dump plate  49  shown in FIG. 3 can advantageously be used. Here, the plate  49  will be rotated about the clevis pins  55  and  57  so as to lay atop the load arms  32  and  34 . A box or a bale ejected from the compactor will sit on and be supported by the dump plate  49  when the load arms  32  and  34  rest on the ground. Once the load is in place on the dump plate, the lineal switch used to energize the motor to raise the load arms  32  and  34  is actuated and the hand truck may be tilted back with the stabilizer assembly deployed, allowing a person to easily push the hand cart to the location of a dumpster where the bale of waste is to be deposited. At this point, the hand cart will be returned to its vertical orientation supported by the caster wheels  48  and  50  on the bottom of the load plate close to a side of the dumpster. The motorized lead screw will again be actuated with the operation of the lineal switch associated with the raising of the load  32  and  34 , causing the bale of waste resting on the dump plate to be elevated to a level just above the upper rim of the dumpster. Now, the handcart can be moved on its caster wheels until the load is cantilevered over the open top of the dumpster. At this point, the operator will manually rotate the dump plate in a counterclockwise direction when viewed as in FIG. 3 until the load slides off of the dump plate into the open dumpster.