Abstract:
A caster includes a mounting plate, a horn having a horn base and at least one leg, a wheel axle coupled to the at least one leg and defining a rolling axis, a caster wheel coupled to the wheel axle and rotatable about the rolling axis, and an eccentric bearing assembly coupling the horn with the mounting plate. In one embodiment, the bearing assembly includes first, second, and third rings of rolling elements, defining first, second, and third horizontal bearing planes, respectively. The second and third rings of rolling elements are positioned eccentrically within the first ring of rolling elements. In another embodiment, the first bearing plane extends between the second and third bearing planes. A transport vehicle includes a vehicle body and at least one swivel caster having an eccentric bearing assembly.

Description:
TECHNICAL FIELD 
     The present invention relates generally to casters. More particularly, the invention relates to bearing assemblies for swivel casters. 
     BACKGROUND 
     Casters are commonly attached to transport vehicles, such as carts, trailers, trucks, or dollies, and allow for rolling movement of the transport vehicle along a ground surface. Casters generally include a horn, also referred to as a yoke, having a pair of legs that extend downwardly and support a caster wheel that rolls along the ground surface. 
     Casters may be permitted to rotate about a vertical axis (termed “swivel”), or they may be fixed or restricted (termed “rigid”). Swivel casters generally include a horn base that is rotatably coupled with a mounting plate or a stem such that the horn and caster wheel may swivel about the vertical axis relative to the caster mounting plate or stem. This swiveling action allows for multi-directional rolling movement of the caster wheel, which enables steering and turning of the vehicle and thereby enhances vehicle maneuverability. In contrast, rigid casters include a horn that is rigidly attached to the mounting plate, such that the horn and caster wheel are fixed relative to the mounting plate and do not rotate about a vertical axis. Transport vehicles may be fitted with one or more swivel casters and one or more rigid casters depending on the application and transport design. In a common arrangement, a vehicle may include swivel casters on an rear, operator-end of the vehicle, and rigid casters on the front, opposing end of the vehicle. For improved vehicle maneuverability in tight spaces, the vehicle may be provided with swivel casters at both vehicle ends. An example of this is a common furniture dolly or a grocery cart. 
     A problem common to vehicles equipped with multiple swivel casters is the propensity of the swivel casters to “lock up” and thereby create significant resistance to rolling movement of the vehicle. Such “locking up” may occur when the vehicle is temporarily brought to rest and at least two casters are allowed to swivel to positions in which two or more caster wheels become substantially misaligned, such that the caster wheel of one caster is oriented in one direction of travel and the caster wheel of an opposing caster is oriented in a different direction of travel. Such “locking up” of the swivel casters may also occur upon attempts by the operator at sudden and substantial changes in direction of travel of the vehicle. For example, when a vehicle having four swivel casters is pushed toward a wall such that the cart abuts the wall, it may then become difficult to slide the cart along the wall to reposition it. In any such case, a substantial force by an operator may be required to “break” the locked condition of the swivel casters, thereby creating risk of injury to the operator. These problems are often magnified when the swivel casters are heavily loaded in a vertical direction, as is often the case with heavy-duty swivel casters used in industrial applications. 
     The “locking up” effect described above is due primarily to the concentric bearing design of conventional swivel casters, which defines a single vertical swivel axis. Prior attempts to remedy the above-described drawbacks have yielded swivel casters having two swivel axes defined by two separate, non-overlapping bearing assemblies spaced apart from each other, thereby presenting a bulky structural design. Accordingly, there is a need for an improved swivel caster that addresses the “locking up” difficulty of conventional swivel casters when mounted on a vehicle, while also presenting a compact structural design that is suitable for heavy-duty, industrial applications. 
     SUMMARY 
     An exemplary embodiment of a caster includes a mounting plate adapted to be mounted to a vehicle, a horn having a horn base and at least one leg extending away from the horn base, a wheel axle coupled to the at least one leg and defining a rolling axis, a caster wheel coupled to the wheel axle and rotatable about the rolling axis, and a bearing assembly coupling the horn with the mounting plate. The bearing assembly includes a first ring of rolling elements, a second ring or rolling elements, and a third ring or rolling elements. The second ring of rolling elements and the third ring of rolling elements are positioned eccentrically within the first ring of rolling elements. 
     A caster according to another embodiment includes a mounting plate adapted to be mounted to a vehicle, a horn having a horn base and at least one leg extending away from the horn base, a wheel axle coupled to the at least one leg and defining a rolling axis, a caster wheel coupled to the wheel axle and rotatable about the rolling axis, and a bearing assembly coupling the horn with the mounting plate. The bearing assembly includes a first ring of rolling elements and a second ring of rolling elements encircled by the first ring of rolling elements. The first ring of rolling elements defines a first bearing plane and the second ring of rolling elements defines a second bearing plane, and the second bearing plane extends between the first bearing plane and the mounting plate. 
     A transport vehicle configured to move along a ground surface includes a vehicle body and at least one swivel caster coupled to the vehicle body with a mounting plate. The at least one swivel caster includes an eccentric bearing assembly having a first ring of rolling elements and a second ring of rolling elements positioned eccentrically within the first ring of rolling elements. The first ring of rolling elements defines a first bearing plane and the second ring of rolling elements defines a second bearing plane, and the second bearing plane extends between the first bearing plane and the mounting plate. 
     Various additional features and advantages of the invention will become more apparent to those of ordinary skill in the art upon review of the following detailed description of the illustrative embodiments taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description of the embodiments given below, serve to explain the principles of the invention. 
         FIG. 1  is an isometric view of a transport vehicle fitted with two swivel casters and two rigid casters. 
         FIG. 1A  is an isometric view of a transport vehicle fitted with four swivel casters and two rigid load casters. 
         FIG. 2  is an isometric view of a swivel caster including an eccentric bearing assembly according to an embodiment of the invention. 
         FIG. 3  is a partially disassembled view of the caster and eccentric bearing assembly of  FIG. 2 . 
         FIG. 4  is a side cross-sectional view of the swivel caster and eccentric bearing assembly, taken along section line  4 - 4  of  FIG. 2 . 
         FIG. 5  is a top cross-sectional view of the swivel caster and eccentric bearing assembly taken along section line  5 - 5  of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the figures, and beginning with  FIG. 1 , a transport vehicle is shown in the form of a standard platform truck  10  having a front end  12 , a rear end  14 , a platform  16 , and a transport bar  18 . The platform truck  10  is provided at its front end  12  with a pair of rigid casters  20  and at its rear end  14  with a pair of swivel casters  22  having eccentric bearing assemblies  24 . One of the rigid casters  20  is hidden from view. The platform  16  is configured to receive a load of one or more objects for transportation by the truck  10  along a ground surface. The transport bar  18 , as shown, may be in the form of a pipe handle and an operator may exert a pushing or pulling force thereon for moving the truck  10  in a desired direction. 
     While the transport vehicle is shown in  FIG. 1  as a standard platform truck  10  having four casters, the transport vehicle may be any other suitable vehicle adapted to include any number of casters for providing rolling movement along a ground surface, such as any truck, cart, trailer, or dolly. For example,  FIG. 1A  shows a transport vehicle in the form of a tilt truck  30  having six casters. A front end  32  and rear end  34  of the tilt truck  30  each include two swivel casters  22  having eccentric bearing assemblies  24 , one of the swivel casters  22  at the front end  32  being hidden from view. A middle portion  36  of the tilt truck  30  includes two rigid load casters  40 , one being hidden from view. As shown, the rigid load casters  40  each include a load caster wheel  42  (referred to as a “load wheel”) having a diameter that is greater in dimension than that of a swivel caster wheel  26  of any of the swivel casters  22 . Accordingly, the load wheels  42  continuously contact the ground surface on which the tilt truck  30  sits, and the tilt truck  30  may pivot about a horizontal axis (not shown) defined by load wheel axles  44  such that the swivel caster wheels  26  provided at either the front end  32  or the rear end  34  of the tilt truck  30  also contact the ground surface. As such, ideally only four casters of the tilt truck  30  contact the ground surface at any one time. 
     Referring to  FIG. 2 , an exemplary embodiment of the swivel caster  22  including an eccentric bearing assembly  24  is shown. The caster  22  includes a mounting plate  50  and a horn  60  that is rotatably coupled to the mounting plate  50  with the eccentric bearing assembly  24 . The horn  60  may swivel relative to the mounting plate  50  about a primary swivel axis A 1  and secondary swivel axis A 2 , the swivel axes A 1 , A 2  being substantially vertical and parallel to each other. The mounting plate  50  includes a plurality of mounting slots  52  for mounting the swivel caster  22  to a transport vehicle, as shown in  FIGS. 1 and 1A . The horn  60  includes a horn base  62  and a pair of legs  64 ,  66  that are securely attached to the horn base  62 , for example by welds (not shown). The legs  64 ,  66  extend downwardly from the horn base  62  at an angle and include a pair of opposed axle holes (not shown) for receiving a wheel axle  70 . The wheel axle  70  is coupled to the legs  64 ,  66  with at least one axle nut  72  and defines a substantially horizontal axis (not shown). The caster wheel  26  is coupled to legs  64 ,  66  with the wheel axle  70  and is rotatable about the horizontal axis defined by the wheel axle  70 , thereby enabling rolling movement of the caster  22  in a direction in which the caster wheel  26  is aligned. 
     The caster wheel  26  may be of any size, shape, and material suitable for the application and the environment in which the caster  22  is operated. Suitable materials for the wheel  26  may include any metals or polymers of varying hardness, including plastics, polyurethanes, and rubbers. For example, the wheel  26  may include a cast iron center portion and a polyurethane tread applied to the outer circumference of the center portion. In other embodiments (not shown), the caster  22  may be provided with multiple caster wheels, such as caster wheel  26 , arranged beside each other. 
       FIG. 3  shows a partially disassembled view of the swivel caster  22  and its eccentric bearing assembly  24 . The eccentric bearing assembly  24  enables swiveling movement of the caster wheel  26  relative to the mounting plate  50  and the vehicle (not shown) to which the caster  22  is mounted. Starting from a radially outer position, the eccentric bearing assembly  24  includes an outer ring  80  that is positioned between the mounting plate  50  and the horn base  62 . A bottom surface (not shown) of the outer ring  80  overlies the horn base  62  and is separated therefrom by a bearing seal  82 . A top surface  84  of the outer ring  80  is coupled to the mounting plate  50  with any suitable mechanical fastening means, such as a plurality of screws  86 . As shown, the mounting plate  50  includes a plurality of through holes  88  arranged circularly and extending axially through a thickness of the mounting plate  50 . Each through hole  88  aligns with a corresponding threaded hole  90  that extends axially through the top surface  84  of the outer ring  80 , such that the screws  86  may be inserted downwardly through the through holes  88  and threaded into the threaded holes  90  to thereby rigidly couple the outer ring  80  to the mounting plate  50 . 
     An inner radial surface  92  of the outer ring  80  includes an outer primary ball race  94  for engaging and retaining a plurality of primary bearing balls  96  within the bearing assembly  24 . An outer radial surface  98  of the outer ring  80  includes a primary ball port  100  that extends radially through the outer ring  80  and opens to the outer primary ball race  94 . The primary ball port  100  is sized such that the primary bearing balls  96  may be inserted therethrough and passed into the outer primary ball race  94  when assembling the eccentric bearing assembly  24 . A primary plug  102  is inserted into and preferably threadedly engaged with the primary ball port  100  after the primary bearing balls  96  have been loaded into the bearing assembly  24 , as shown in  FIG. 3 . 
     A generally disk-shaped eccentric adapter  110  is positioned radially inward of the outer ring  80  and includes an outer radial surface  112  and an eccentrically positioned inner bore  114  that extends axially through the eccentric adapter  110  and defines an inner radial surface  116 . When assembled, the outer radial surface  112  of the eccentric adapter  110  sits adjacent to and opposes the inner radial surface  92  of the outer ring  80 . Furthermore, the outer radial surface  112  of the eccentric adapter  110  includes an inner primary ball race  118  that is aligned with and cooperates with the outer primary ball race  94  to thereby engage and retain the primary bearing balls  96  in the form of a ring within the bearing assembly  24 . The inner radial surface  116  of the eccentric adapter  110  is positioned eccentrically relative to the outer radial surface  112  and includes an upper outer secondary ball race  120  configured to engage and retain a plurality of upper secondary bearing balls  122 , and further includes a lower outer secondary ball race  124  configured to engage and retain a plurality of lower secondary bearing balls  126 . 
     An upper secondary ball port  128  and a lower secondary ball port  130  each extends radially through the outer radial surface  112  of the eccentric adapter  110  and opens to the upper and lower outer secondary ball races  120 ,  124 , respectively. The secondary ball ports  128 ,  130  are sized such that the upper and lower secondary bearing balls  122 ,  126 , respectively, may be inserted therethrough and passed into the upper and lower outer secondary ball races  120 ,  124 , respectively, when assembling the eccentric bearing assembly  24 . Inner and outer upper secondary plugs  132  and  134  are inserted into and preferably threadedly engaged with the upper secondary ball port  128  after the upper secondary bearing balls 122  have been loaded into the bearing assembly  24  through the upper secondary ball port  128 . In a similar manner, inner and outer lower secondary plugs  136  and  138  are inserted into and preferably threadedly engaged with the lower secondary ball port  130  after the lower secondary ball bearings  126  have been loaded into the bearing assembly  24 . Each of the outer secondary plugs  134 ,  138  is inserted after the corresponding inner secondary plug  132 ,  136  so as to radially abut the inner secondary plug  132 ,  136  in locking engagement. 
     A core column  140  extends axially from the horn base  62  toward the mounting plate  50 . During assembly, the core column  140  is positioned within the inner bore  114  of the eccentric adapter  110  such that a top surface  142  of the core column  140  sits substantially flush with a top surface  111  of the eccentric adapter  110 , and an outer radial surface  144  of the core column  140  sits adjacent to and opposes the inner radial surface  116  of the eccentric adapter  110 . The outer radial surface  144  of the core column  140  includes an upper inner secondary ball race  146  that is aligned with and cooperates with the upper outer secondary ball race  120  to thereby engage and retain the upper secondary bearing balls  122  in the form of a ring within the bearing assembly  24 . The core column  140  further includes a lower inner secondary ball race  148  that is aligned with and cooperates with the lower outer secondary ball race  124  to thereby engage and retain the lower secondary bearing balls  126  in the form of a ring within the bearing assembly  24 . 
     As shown in the figures, the upper and lower secondary bearing balls  122 ,  126  are of substantially the same diameter, though they may be of different diameters as preferred depending on the desired application. The secondary bearing balls  122 ,  126  are preferably of a smaller diameter than the primary bearing balls  96 , which allows for a compact overall design of the eccentric bearing assembly  24 . Moreover, including dual, upper and lower sets of secondary ball races  120 ,  124 ,  146 ,  148  provides for a better distribution of radial forces transmitted between the core column  140 , the eccentric adapter  110 , and the outer ring  80 , as compared to a bearing design including only a single set of secondary ball races. 
     As shown best in  FIG. 3 , each of the ball races  94 ,  118 ,  120 ,  124 ,  146 ,  148  defines a groove extending circumferentially about its corresponding radial surface  92 ,  112 ,  116 ,  144  and having a semi-circular cross-section with a radius corresponding to the radius of the respective bearing balls  96 ,  122 ,  126  being engaged and retained. Accordingly, the pluralities of bearing balls  96 ,  122 ,  126  are each formed into the shape of a ring when loaded into the bearing assembly  24  and retained by their respective ball races  94 ,  118 ,  120 ,  124 ,  146 ,  148 . While bearing balls  96 ,  122 ,  126  are shown and described herein, persons of ordinary skill in the art will appreciate that the eccentric bearing assembly  24  may be modified to incorporate any other type of rolling element desired, such as tapered cylindrical rollers, for example. 
       FIG. 4  shows a side cross-sectional view of the eccentric bearing assembly  24  in an assembled configuration. As shown, the outer ring  80  is fixed to the mounting plate  50  with screws  86 , the eccentric adapter  110  is received within the outer ring  80  and rotatably coupled thereto with primary bearing balls  96 , and the core column  140  of the horn  60  is received within the inner bore  114  of the eccentric adapter  110  and rotatably coupled thereto with upper and lower secondary bearing balls  122 , 126 . The ring of upper secondary bearing balls  122  is positioned coaxially with the ring of lower secondary bearing balls  126 . Accordingly, the eccentric adapter  110  is rotatable relative to the outer ring  80  about the substantially vertical, primary swivel axis A 1 , and the core column  140  and the horn  60  from which it extends are rotatable relative to the eccentric adapter  110  about the substantially vertical, secondary swivel axis A 2 . This configuration enables the caster wheel  26  to swivel about swivel axis A 1  and swivel axis A 2 , simultaneously or independently. As shown, the swivel axes A 1 , A 2  are offset from each other in an axial direction, and each swivel axis A 1 , A 2  is positioned radially inward of the inner secondary ball races  146 ,  148  such that they extend through the core column  140 . Accordingly, the eccentric bearing assembly  24  presents a structure that is compact in a radial direction. 
     As best shown in  FIG. 4 , a primary bearing plane P 1  is that which horizontally bisects the ring of primary bearing balls  96 . Similarly, an upper secondary bearing plane P 2  is that which horizontally bisects the ring of upper secondary bearing balls  122 , and a lower secondary bearing plane P 3  is that which horizontally bisects the ring of lower secondary bearing balls  126 . The rings of primary and secondary bearing balls  96 ,  122 ,  126  are positioned such that the primary bearing plane P 1  extends horizontally between the upper and lower secondary bearing planes P 2 , P 3  with equidistant spacing in an axial direction. Moreover, the upper secondary bearing plane P 2  extends horizontally between the primary bearing plane P 1  and the mounting plate  50 , and the lower secondary bearing plane P 3  extends horizontally between the primary bearing plane P 1  and the horn base  62 . Accordingly, the eccentric bearing assembly  24  presents a structure that is compact in an axial direction as well. 
     Also shown in  FIGS. 3 and 4 , the horn base  62  includes an annular shoulder  150  extending axially from the horn base  62  toward the eccentric adapter  110  and encircling the core column  140 . The shoulder  150  defines an annular gap  152  in which a bearing lubricant (not shown) may reside for lubricating the internal components of the bearing assembly  24 . The bearing seal  82  is positioned between the outer ring  80  and the horn base  62  and operates to retain lubricant within and block any external contaminants from entering the bearing assembly  24 . 
       FIG. 5  is a top cross-sectional view of the bearing assembly  24 , showing the components described above with the exception of the mounting plate  50 . As shown, the ring of upper secondary bearing balls  122  is positioned radially inward of and encircled by the ring of primary bearing balls  96  such that that they form eccentric circles. The ring of lower secondary bearing balls  126  is not seen in  FIG. 5  in view of its coaxial alignment with the ring of upper secondary bearing balls  122 . 
     While the present invention has been illustrated by the description of specific embodiments thereof, and while the embodiments have been described in considerable detail, it is not intended to restrict or in any way limit the scope of the appended claims to such detail. The various features discussed herein may be used alone or in any combination. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and methods and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the scope or spirit of the general inventive concept.