Abstract:
A cart for moving loads includes a frame supported on wheels, a source of electric power supported on the frame, a drive system including a traction motor connected to the power source for driving a wheel secured to the frame and contacting ground, and a controller for adjusting a rotary direction of the drive wheel in response to selected states of an input to the controller.

Description:
BACKGROUND OF INVENTION 
     The present invention relates generally to an apparatus for transporting heavy loads on the floor of a factory or assembly plant. More particularly, the invention relates to a cart controlled by a vehicle operator and powered by onboard electric energy. 
     Various techniques used to transport material and components between workstations on a factory floor include conveyors such as conventional belt conveyors, fork trucks and manned tuggers. However, when the transported load is heavy, in the range of about 2000 pounds, ergonometric guidelines frequently limit the ability to use conventional media to perform this function without exceeding the guidelines. 
     A preferable technique would provide a vehicle that operates under electric power and is guided by a vehicle operator to transport relatively heavy loads along any undefined path. The vehicle or cart would produce no noxious exhaust gas. The onboard power source, electric storage batteries, would be rechargeable easily and quickly at convenient locations in the factory or assembly plant. 
     Preferably a cart for this purpose would be manufactured at minimal cost and could carry its own power supply, traction drive and controller for selecting drive direction and speed. The cart would be steered manually on caster wheels. 
     SUMMARY OF INVENTION 
     A cart for moving loads includes a frame supported on wheels, a source of electric power supported on the frame, a drive system including a traction motor connected to the power source for driving a wheel secured to the frame and contacting ground, and a controller for adjusting a rotary direction of the drive wheel in response to selected states of an input to the controller. 
     The vehicle and its operating systems are assembled readily and installed easily on the cart&#39;s frame or vehicle&#39;s chassis at low cost and without a high degree of technical complexity or sophistication. 
     The truck provides a high level of capability and flexibility that surpasses that of alternative transportation techniques, and meets or exceeds safety specifications for a power assist device at a substantially lower cost that otherwise commercially available. 
     The truck is a relatively inexpensive device that assists production operators and material handling personnel to move loads of about one ton around a production plant. 
     The scope of applicability of the preferred embodiment will become apparent from the following detailed description, claims and drawings. It should be understood, that the description and specific examples, although indicating preferred embodiments of the invention, are given by way of illustration only. Various changes and modifications to the described embodiments and examples will become apparent to those skilled in the art. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of a cart supported on wheels and a system for driving the cart; 
         FIG. 2  is a perspective view showing the drive system installed on the frame of  FIG. 1 ; and 
         FIG. 3  is a schematic diagram showing a control box for controlling forward and reverse drive in response to the current state of switching devices such as push buttons. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings, illustrated in  FIG. 1  is a cart  10 , which includes a rectangular welded frame  12  formed preferably of rolled or extruded members, each member having a closed cross section in the form of a rectangular, preferably square, tube. The frame  12  is supported on a first set of caster wheels  14 ,  15 , each wheel bolted to a support  16 ,  17 , respectively, which is located at a corner of the frame  12  and welded to the lower surface of the frame  12 . A second set of wheels similarly mounted to the frame  12 , but located at the opposite end of the frame  12 , are on casters to facilitate steering the vehicle. A handle  19 , secured to the end of the frame where the caster wheels are located, is used to apply a lateral steering force manually to the cart. 
     A single drive wheel  20 , in traction contact with the floor is aligned with a central longitudinal axis of the frame  12 , evenly spaced between wheels  14 ,  15 . Drive wheel  20  is supported on a drive shaft  22 , whose axis is directed laterally and is located in a substantially horizontal plane. In one application of the cart  10 , the wheel  20  has an outer diameter of about eight inches, and the diameter of drive shaft  22  is ⅝ inches. 
       FIGS. 1 and 2  show that the drive wheel  20  and its drive system  24  are mounted on the underside of the frame  12 . A plate  26  is supported on bolts  28 , which are secured to the frame  12 . The length of rectangular steel tubing  30 , supported on the plate  26  and contacting the lower surface of frame  12 , establishes the vertical location of the plate  26 . A wheel housing  32 , formed by a length of rectangular steel tubing located at the underside of the plate  26 , is bolted to the plate  26 . A clutch housing  34 , formed by a length of rectangular steel tubing located at a lateral side of the wheel housing  32  is bolted to the wheel housing  32 . 
     The drive system includes a clutch unit  36 , located in clutch housing  34 ; a cart drive motor  38 ; a gear unit  40  for transmitting rotating power from the motor to the clutch unit; a flange bearing  42  bolted to the outer wall of wheel housing  32 ; a flange bearing  44  bolted to the inner walls of the clutch housing  34  and wheel housing  32 ; and bronze wheel bushing spacers  46 ,  47 , which enclose the drive shaft  22  between the bearings  42 ,  44 . Drive shaft  22  is secured to the drive wheel  20 , which extends downward through the lower wall of the wheel housing  32 . 
     Clutch unit  36  alternately opens and closes a drive connection between the drive wheel  20  and gear unit  40  in response the presence and absence of electric current supplied to a solenoid of the clutch unit. The cart  10  supports onboard electric storage batteries  52 , which supply the electric current to the clutch unit  36 . 
     A controller or control box  50  for controlling operation of the motor  38  and clutch unit  36  is supported on the frame  12 . Batteries  52 , interconnected to produce 24V output, are connected to the control box  50 . Electric current carried on line  54  (shown in  FIG. 3 ) from control box  50  is supplied to the clutch unit  36  and cart motor  38 . 
       FIG. 3  illustrates the control box and interconnections with it in more detail. The control circuit inside control box  50  is controlled manually from outside the box through two forward-drive push buttons  56 ,  58  and two reverse-drive push buttons  60 ,  62 . When both of the forward drive push buttons  56 ,  58  are depressed, two switches in the control circuit open an electrical connection between the terminals of batteries  52  and a motor controller, which causes the motor  38  to rotate the drive wheel  20  in the forward direction, thereby producing forward drive of the cart. When either of the forward drive push buttons  56 ,  58  is released from its depressed state, power to the drive wheel  20  is discontinued, thereby stopping the cart  10 . 
     When both of the reverse drive push buttons  60 ,  62  are depressed, two switches in the control circuit close an electrical connection between the terminals of batteries  52  and the motor controller, which causes the motor  38  to rotate drive wheel  20  in a reverse drive direction, thereby producing reverse drive of the cart. When either of the reverse drive push buttons  60 ,  62  is released from its depressed state, power to the drive wheel  20  is discontinued, thereby stopping the cart  10 . 
     The requirement that two push buttons be depressed concurrently to drive the cart in either direction is a safety precaution intended to avoid personal injury and property damage due to use of the cart. 
     A plug-in battery charger (not shown) is used to recharge the batteries  52  from a power source preferably connect to a public utility grid. 
     In operation, an operator standing near the cart  10  selects forward or rearward drive by depressing the appropriate push buttons. The drive system  24  responds to the operator&#39;s input by transmitting power to the drive wheel  20  in the selected direction. An operator, accompanying the cart along its travel to a desired location, steers the cart by applying a relatively low magnitude of laterally-directed manual steering force to handle  19 . 
     While certain embodiments of the present invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.