Abstract:
A vehicle including a load frame, a drive assembly, and a pivot link assembly. The load frame includes castor wheels to rollingly support the load frame on a support surface. The drive assembly includes a drive frame, a drive wheel, and a rigid castor wheel wherein the drive wheel and rigid castor wheel are each mounted to the drive frame. The pivot link assembly couples the drive frame to the load frame and permits the drive frame to move vertically and angularly relative to the load frame.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention is generally directed to material handling vehicles and, more particularly, to a vehicle having a vertically floating drive assembly.  
           [0002]    Automatic guided vehicles (AGVs) are used throughout the material handling industry to transport loads. The term AGV is commonly used to refer to robust vehicle designs having any of a number of available automated guidance systems. Automatic guided carts (AGCs) is a term commonly used to refer to a less robust vehicle used for similar but smaller-scale applications. Current AGC designs generally include a frame with swivel castors located at the four corners of the frame. Other features may include a drive wheel assembly and rigid castors for directional control of the cart. In one current design, two rigid castors are fixed to the frame and located approximately midway between the swivel castors on each side of the cart frame. The two pair of swivel castor axes and the rigid castor axis are generally parallel to each other. The steerable driving unit is attached to the cart frame, generally by way of a plate that is hinged and spring loaded from the cart frame to ensure that the steerable drive wheel maintains adequate traction with the support surface.  
           [0003]    While this arrangement is generally acceptable for uniform support surfaces, situations where the floor is not level and flat may give rise to losses in the directional control of the cart. More particularly, when the cart encounters an uneven surface, the direct mounting of the swivel and rigid castors to the cart frame may cause one or more of the three sets of castors to become disengaged from the support surface. Since the rigid castors are used for direction control of the cart, loss of contact between the rigid castors and the floor may cause loss of directional control of the cart. The only wheel that has significantly uniform contact with the floor is the hinged and spring loaded steerable drive wheel.  
         SUMMARY OF THE INVENTION  
         [0004]    In view of the above, a need exists for a AGC design that more effectively maintains directional control for the cart or AGV. More particularly, a need exists to maintain both the steerable drive wheel and at least one rigid castor in contact with the floor surface at all times.  
           [0005]    To meet these and other needs that will be apparent to those skilled in the art based upon this description and the appended drawings, the present invention is directed to a material handling vehicle having a load bearing support frame with wheels to rollingly engage a support surface as well as a drive assembly having a drive frame supporting a drive wheel and a rigid castor. A pivot link assembly rotationally coupled to the load frame and the drive frame permits the drive frame to vertically float and change angular orientation relative to the drive frame thereby ensuring that the drive wheel and rigid castor maintain operative contact with the support surface even on uneven contours.  
           [0006]    Further scope of applicability of the present invention will become apparent from the following detailed description, claims, and drawings. 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. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    The present invention will become more fully understood from the detailed description given here below, the appended claims, and the accompanying drawings in which:  
         [0008]    [0008]FIG. 1 is an underside perspective view of an AGC according to the present invention;  
         [0009]    [0009]FIG. 2 is an upper perspective view of the drive assembly and float coupling assembly illustrated in FIG. 1;  
         [0010]    [0010]FIG. 3 is a perspective view of the drive assembly;  
         [0011]    [0011]FIG. 4 is a perspective view of the pivot link assembly;  
         [0012]    [0012]FIG. 5 is a side perspective view of the AGC shown in FIG. 1 with a side load frame tube removed for clarity;  
         [0013]    [0013]FIG. 6 is a side elevational view of the cart shown in FIG. 5 with the drive assembly in its centered position;  
         [0014]    [0014]FIG. 7 is a side elevational view of the cart shown in FIG. 5 with the drive assembly in its fall up position and rotated counterclockwise;  
         [0015]    [0015]FIG. 8 is a side elevational view of the cart shown in FIG. 5 with the drive assembly in its fall down position and rotated clockwise; and  
         [0016]    [0016]FIG. 9 is a sectional view take along the line  9 - 9  shown in FIG. 6. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]    An automated guided cart  10  according to the present invention is illustrated and described with reference to FIGS.  1 - 5 . It should be appreciated that the applications for the vertically floating drive unit according to the present invention may be used in a variety of applications beyond the illustrated AGC. For example, the present invention may be used with automated guided vehicles of a variety of configurations as well as other material handling vehicles permitting the vehicles to function with greater precision along unevenly contoured surfaces.  
         [0018]    The AGC  10  includes a load frame  12  supported at each of its corners by swivel castors  14 . A drive assembly  16  includes a drive frame  18 , a drive wheel  20 , and a pair of rigid castors  22 . The drive wheel  20  and rigid castors  22  are each fixed for movement with the drive frame  18 . As is conventionally known, the drive wheel  20  is rotatable about a drive axis  24  and a steering axis  26 . Each of the rigid castors  22  are rotatable only about a single axis  28  oriented perpendicular to the AGC&#39;s longitudinal axis  30 . Accordingly, when the rigid castors are engaged with the cart support surface, the castors tend to maintain the directional control of the cart in its axial direction.  
         [0019]    A pivot link assembly  36  interconnects the drive assembly  16  with the load frame  12  through two pivot axes thereby permitting the drive assembly to vertically float relative to the load frame. The pivot link assembly  36  also is configured to permit the angular orientation of the drive assembly  16  to vary within a predetermined range relative to the load frame  12 . These vertical and angular degrees of freedom maintain the drive wheel unit  20  and rigid castors  22  in contact with the cart support surface, even when the support surface has an uneven contour.  
         [0020]    In the illustrated embodiment, the pivot link assembly  36  includes first and second side rails  38  and  40  (FIG. 4) interconnected by a support plate  42 . The rails are pivotally coupled at each of their respective ends to the load frame  12  via frame bearing blocks  44  and to the drive frame  18  via drive unit bearing blocks  46 . A first pivot shaft  50  rotatably connects the rearward end of the rails  38  and  40  and support plate  42  to the frame bearing blocks  44 . In a similar manner, the forward ends of the rails  38  and  40  are rotatably coupled to the respective drive unit bearing blocks  46 . The pivot shafts  50  and  52  are preferably oriented parallel to one another and parallel to the rigid castor axis  28 .  
         [0021]    While the pivot link assembly  36  may have a variety of configurations, the illustrated embodiment includes cut-outs  56  in the plate  42  to receive the rigid castors  22 . The vertical float and angular reorientation capability of the drive assembly, as well as the tricycle configuration of the drive wheel and rigid castors, maintain the steerable drive wheel and at least one rigid castor in contact with floor surfaces having uneven contours. As a result, the drive/directional control integrity of the AGC is superior to previous cart designs. An illustration of the float and angular reorientation capability of the present invention is provided in FIGS.  6 - 8 . Specifically, FIG. 6 is a side elevation view of the cart  10  with the drive assembly  16  in its centered position, i.e., with the bearing surfaces of the drive wheel  20 , rigid castors  22 , and swivel castors  14  at the same elevation. When the cart encounters an uneven surface, the drive assembly  16  is pivotable relative to the load frame  12  about axes  50  and  52  to provide vertical float and angular reorientation. For example, the drive assembly  16  is illustrated in FIG. 7 in its full up position and rotated counterclockwise and in FIG. 8 in its full down position and rotated clockwise. It should be appreciated that these orientations are illustrated for exemplary purposes and that the range of movement of the drive assembly is not necessarily limited to the specific orientations or ranges illustrated and described herein.  
         [0022]    The range of vertical float and pivoting movement permitted by the pivot link assembly  36  is preferably limited by appropriately configured and positioned pivot stops. In the illustrated embodiment, the range of vertical float is limited to one inch, with one-half inch of float being provided above and below the centered position shown in FIG. 6. Additionally, a biasing mechanism is preferably operatively positioned between the load frame and the drive frame to apply a downward spring loading on the tricycle drive assembly  16 . This additional loading enhances the traction of the drive wheel  20  and rigid castors  22  with the support surface. Finally, it is also desirable to include one or more rotation stops to prevent over-rotation of the drive frame  18 . As most clearly illustrated in FIG. 2, the drive wheel  20 , and its associated limit switches and actuators  59 , are generally positioned at the forward end of the frame  18 . A power source, such as the illustrated pair of batteries  58 , are in a center compartment and a rear compartment accommodates the control electronics for the cart. In this configuration, the loading on the drive frame  18  tends to rotate the drive assembly in a counterclockwise direction about axis  52  as indicated by arrow  54 . The rotation stops are used to limit this rotation.  
         [0023]    One skilled in the art will appreciate that numerous pivot and rotation stop configurations, such as brackets, bolts, and the like, may be used to limit the vertical float and rotation of the drive assembly and that a variety of springs or other biasing mechanism may serve to maintain drive traction. For example, the illustrated embodiment includes stop assemblies  60  that are positioned proximate the drive unit bearing blocks  46  (FIGS.  5 - 9 ) and that serve as the pivot stops and bias mechanism for the drive assembly  16 . Each stop assembly  60  includes a spring bracket  62  fixed to the load frame  12  and a coil spring  64  disposed about a bolt  65 . The spring  64  is compressed between the bracket  62  and pivot plate  42  to exert a downward bias on the plate. A down stop washer  66  is normally spaced a predetermined distance from the bracket  62  by a spacer tube  68 . Thus, the drive assembly  16  is able to pivot downward from its centered position (FIG. 6) until the washer is displaced the predetermined distance and abuts the bracket  62  (FIG. 8). The upward pivot stop is provided by a stop flange  70  (FIGS. 5 and 9) that is fixed to the drive frame  18  and that includes a leg  72  positioned to abut the load frame  12  or bracket  62  when the drive assembly  16  is in its full up position (FIG. 7).  
         [0024]    Finally, in the illustrated embodiment, a rotation stop assembly  76  is positioned proximate the forward end of the drive assembly  16 . The rotation stop (FIG. 5) includes a rotation bracket  78  having a slot  80  within which a stop pin  82  is disposed for movement. The bracket  78  and pin  82  are each fixed to one of the drive frame  18  and load frame  12  so that relative frame movement is limited by bracket/pin abutment. Notwithstanding the above description of the stop assemblies  60 , spring  64 , and stop assembly  76 , those skilled in the art will appreciate that a variety of equivalent mechanisms known in the art may be used to provide the stop and bias functions without departing from the scope of the invention defined by the appended claims.  
         [0025]    A further benefit of the use of the floating drive unit is that the load frame  12  and drive frame  18  are independently loaded. Thus, the payload supported by the load frame  12  and swivel castors  14  may be varied based upon operational goals whereas the loading on the drive unit is dependent principally upon the weight of the drive unit and any bias provided by the coil spring  62 . Also, by including on-board power, control, and mechanical components necessary for autonomous movement, the drive assembly may be disconnected from the load frame  12  and pivot link assembly  36  if it is desired to use the drive assembly as an autonomous vehicle. Possible applications for such autonomous use would include use as a small towing device or lightweight cart where space constraints prevented the effective movement of the larger load frame  12 .  
         [0026]    The foregoing discussion discloses and describes an exemplary embodiment of the present invention. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims that various changes, modifications and variations can be made therein without departing from the true spirit and fair scope of the invention as defined by the following claims.