Abstract:
A castor assembly for supporting a load such as an article of furniture so that it can easily be moved in any desired direction. The assembly includes a load-bearing base member from which a vertical axle is projected. Pivoted on this axle is a swivel frame, while mounted below the frame on a horizontal axle is a ground-engaging caster wheel. Also mounted on the swivel frame is at least one support roller which engages the base member. The position of the roller on the swivel frame is such as to minimize the moment of force developed between the vertical axle and the caster wheel, thereby protecting the assembly from the adverse effects of excessive loads and impact forces.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates generally to caster assemblies for the support and movement of articles of furniture, as well as factory and baggage trucks, portable equipment and the like. In particular, the invention relates to a caster assembly which is capable of supporting heavy loads without becoming impaired and having a high resistance to shock forces.  
           [0003]    2. Status of Prior Art  
           [0004]    A caster assembly is composed of one or more wheels mounted on a swivel frame for the support and movement of the article such as a movable cart, trolley or gurney on which the assembly is installed, In a typical caster assembly such as one attached to the leg of a chair, a load-supporting base member secured to the base of the leg has projecting therefrom a vertical axle on which one end of a swivel frame is pivoted. Mounted below the other end of the frame is a ground-engaging caster wheel rotatable on a horizontal axle.  
           [0005]    When a chair which has attached to each of its legs a conventional caster assembly, each caster wheel swivels about a vertical axle projecting from the leg of the chair to assume an orientation in which the horizontal axis of rotation of the wheels is normal to the chosen direction of chair movement. Hence as the chair advances in the chosen direction, the caster wheels on the legs rotate freely.  
           [0006]    The quick angular re-alignment of the caster wheels with the direction of movement which takes place as the direction is changed not only makes possible swift transportation of the load but also prolongs the effective life of the caster wheels.  
           [0007]    As noted in U.S. Pat. No. 4,254,532 to Hager in which is disclosed a caster assembly, the axis of each caster wheel is necessarily offset horizontally from the swivel axis in order to cause the caster to trail properly. As a consequence, the caster-assembly is vulnerable to impact forces. Thus when the ground-engaging wheel of the assembly is traveling at a fast speed and it strikes an obstruction in its path, the resultant impact force may break the caster.  
           [0008]    In order to reduce stresses imposed on the caster bracket or swivel frame when the caster strikes an obstruction, and to avoid injury to the caster, Hager interposes a support roller between the swivel frame and the load at a point spaced radially outwardly from the swivel axis.  
           [0009]    A standard caster assembly is designed by its manufacturer to operate efficiently when the load it bears is no greater than a predetermined value. Hence a caster assembly is given a load rating by its manufacturer. Casters intended for a baggage truck are designed to safely support a load for which its wheels are rated. But as is often the case, when the truck in use is overloaded with baggage, the caster assembly may be incapable of surviving this excessive load.  
           [0010]    The concern of the present invention is with the ability of a caster assembly whose wheels are substantially the same as those in a standard caster assembly to withstand loads and impact forces that the standard assembly cannot tolerate.  
           [0011]    As noted in PCT Publication WO 01/38201, in a castor assembly in which a castor wheel is mounted on a swivel, the axle of the caster is horizontally offset with respect to the axis of the swivel. This creates a moment of force that may be of sufficient strength to break the vertical axle on which the castor swivel is pivoted.  
           [0012]    The moment of force is the result of the force produced by a load multiplied by its perpendicular distance from a point of turning. A moment of force is equivalent to a torque which gives rise to torsion. In the context of a caster assembly, this torsion may twist and break the swivel axle and, in doing so disable the assembly.  
           [0013]    When the load borne by a castor assembly is close to or exceeds its load rating, then with a conventional caster assembly the resultant high moment of force may be powerful enough to disable the assembly. To reduce the moment of force assembly disclosed in the above-identified PCT publication, includes at least one support roller that is interposed between the pivoted swivel on which a caster wheel is mounted and the load imposed on the swivel. While this PCT arrangement does reduce the moment of force, it does not fully cancel it out so that the caster assembly is capable of tolerating very heavy loads.  
           [0014]    Moreover, the support roller in the PCT publication interposed between the swivel and a base member supporting the load, lengthens the overall height of the assembly so that its height is significantly greater than that of a standard caster assembly which lacks a support wheel. The ideal caster assembly is one whose swivel is in close proximity to a base member supporting the load so as to raise the load above ground no more a necessary to accommodate the ground-engaging caster wheel.  
           [0015]    Also of prior art interest is U.S. Pat. No. 4,569,227 to Keane which discloses a swivel caster structure in which a caster wheel is carried on a base. A roller functioning as a force transfer agent is carried by the base for transmitting an overlying load (in this case a vacuum cleaner) vertically downward toward the caster wheel away from the swivel axis in order to improve the effective life of the structure.  
         SUMMARY OF THE INVENTION  
         [0016]    In view of the foregoing, the main object of this invention is to provide an improved caster assembly in which a caster which is swiveled from a vertical axle projecting below a base member supporting the load, the assembly including at least one support roller interposed between the swivel and the base member to protect the assembly from adverse effects resulting from an excessive load or impact forces.  
           [0017]    More particularly, an object of this invention is to provide a caster assembly in which a frame on which is mounted a caster wheel is pivoted from a vertical axle, the frame had mounted thereon a pair of support rollers which are symmetrically disposed with respect to the vertical axle and to the caster wheel, the arrangement being such as to cancel out the moment of force and to enhance the resistance of the assembly to the adverse effects of an excessive load and impact forces.  
           [0018]    A significant feature of the invention is that the overall height of the assembly is not much greater or no greater than that of a standard assembly having a like caster wheel, for in an assembly in accordance with the invention, the load-support rollers are nested in wells or recesses formed in the swivel frame so that only the uppermost segment of each roller is raised above the frame to engage the load.  
           [0019]    Briefly stated these objects are attained in a castor assembly for supporting a load such as an article of furniture so that it can easily be moved in any desired direction. The assembly includes a load-bearing base member from which a vertical axle is projected which pivots a swivel frame. Mounted on the fee is a ground-engaging caster wheel having a horizontal axle. Also mounted on the swivel frame is at least one support roller which engages the base member to support the load imposed therein. The position of the roller relative to the caster wheel is such as to cancel out the moment of force between the vertical axle and the caster wheel, thereby protecting the assembly from the adverse effects of an excessive load and of impact forces.  
           [0020]    In a preferred embodiment of the invention, the swivel frame is generally triangular in form and is pivoted at its apex on the vertical axle projecting below the load-bearing base member. The caster wheel is mounted below the frame adjacent its rear end midway between its corners on a central axis that extends to the pivot point. Hence when the frame is turned, the caster wheel is movable in a circular orbit whose center is the pivot point. A pair of load-supporting rollers are mounted adjacent the respective rear corners of the triangular frame on either side of its central axis and symmetrically with respect to the caster wheel. Hence, the rollers are movable in a circular orbit which is concentric with and adjacent to the main caster wheel orbit to provide a common line of action. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    For a better understanding of the invention as well as other objects and features thereof reference is made to the annexed drawings wherein:  
         [0022]    [0022]FIG. 1 is an isometric view of a caster assembly seen upside-down, having a pair of support rollers, in accordance with a first preferred embodiment of the invention;  
         [0023]    [0023]FIG. 2 is an elevated view of the assembly shown in FIG. 1 detached from the load-bearing member included in the assembly;  
         [0024]    [0024]FIG. 3 presents another isometric view of the caster wheel assembly;  
         [0025]    [0025]FIG. 4 is a plan view of a second embodiment of a caster assembly in accordance with the invention;  
         [0026]    [0026]FIG. 5 is a side view of the second embodiment;  
         [0027]    [0027]FIG. 6 illustrates the fork supporting the caster wheel in the second embodiment; and  
         [0028]    [0028]FIG. 7 is a perspective view of a third embodiment of a caster assembly in accordance with the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0029]    All embodiments of a caster assembly in accordance with the invention are adapted to support a load, such as a baggage truck, a chair or a desk so that it can easily be moved in any desired direction. The assembly includes a load bearing base member which is attachable to the load and has a vertical axle projecting therefrom. This axle functions as a pivot for a swivel frame having a caster wheel which swivels on the base member which bears the load. Thus as the load is pushed in a desired direction, the caster wheel is swiveled into alignment with this direction.  
         [0030]    First Embodiment: FIG. 1 illustrates a caster assembly in accordance with the invention in which the swivel frame is a horizontal bar  2  having top and bottom sides  15  and  16 , respectively. Horizontal bar  2  is provided at one end with an axle  20  which projects vertically from the top side of the bar and engages a load-supporting member  21  attachable to the load. The bar turns freely about axle  20  and is also free to a limited degree to vertically slide up and down, being prevented, however, from disengaging from the load-bearing member completely. The load-bearing member  21  is preferably provided with a cup-like protrusion  25 , so as to shorten the required length of vertical axle  20 , thus reducing the moment experienced by the axle.  
         [0031]    Supported at the other end of horizontal bar  2  is a caster wheel  3 . Wheel  3  is received within a cavity  33  formed in the bar and it partially protrudes downwardly from the bar to engage the ground. Axle  12  of caster wheel  3  is supported on its ends by matching carriers  30  on the bar.  
         [0032]    [0032]FIG. 2 is an elevated view of the caster assembly shown in FIG. 1, in which the swivel frame  2  is detached from the load-bearing member  2 . Bar  2  is provided with arcuate extensions or wings  31 . Each of these wings caries at its end a support roller  5 , which is partially sunken in a cavity  7  and protrude therefrom. The axis of rotation of each support roller  5  is aligned radially with respect to vertical axle  20 , this being the axis of rotation of the pivoted swivel frame.  
         [0033]    Axle  6  of each support roller  5  is snapped into position inside matching sockets  32  on the side walls of each cavity  7 . A protrusion  34 , which in fact is the wall of cavity  33  shown in FIG. 1, bulges out from bar  2 . But it does not interfere with the smooth operation of the swivel, for it is comfortably accommodated between the support rollers  5 . However this protrusion  34  must be below the support rollers  5  so that they can come in contact with the load-bearing surface.  
         [0034]    The arrangement of support rollers  5  is in an arcuate formation to allow swivel bar  2  to comfortably turn about vertical axle  20 , thereby facilitating a smooth ride. This is achieved because the axis of rotation of support rollers  5  is aligned radially to the vertical axis of rotation of the bar.  
         [0035]    Vertical axle  20  is provided with a pair of opposing resilient flaps  36 , each having a rim  37  so that they can be snapped into a bore provided on the load bearing member and remain engaged thereby. However, in practice, other methods of engagement of the vertical axle to the load-bearing surface may be used. And instead of the vertical axle being projected upwardly from the swivel frame to engage the load bearing member, it can be projected downwardly from the load bearing member to engage the swivel frame. In practice, vertical axle  20  may be provided with a double-action snap.  
         [0036]    [0036]FIG. 3 is another isometric view of the swivel frame, shown in FIG. 1. The bottom surface  21  of the load-bearing member is preferably a planar surface so that it presents no obstacle to swiveling of the swivel frame. It may also be provided with a clearly defined track to provide a circular path for the support rollers. An annular rim  22  surrounding this track provides protection against inadvertent jamming caused by external obstacles.  
         [0037]    A swivel assembly in accordance with the present invention is of particular appeal to the plastics industry in that its components may be molded from plastic materials, such as POM, polyamide, polypropylene, and the like. The caster assembly can therefore be fabricated to have a light weight, this being another advantage of the invention. In practice, however, die assembly may be made of lightweight aluminum or heavier steel or stainless steel.  
         [0038]    Load support rollers  5  provide supporting points for the load which release the vertical axle from the moment of force to which it is subjected by the load-bearing member. The support rollers are positioned so that the imaginary arc tangent to their planes of rotation is not tangential to the axis of rotation of the caster wheel, for this may cause the support rollers to flap and give rise to a jittery motion due to an unstable balance of the forces acting on the rollers. While only one caster wheel is included in this embodiment, it is possible to have two or more caster wheels supported below horizontal bar  2 , provided that they are in proper alignment.  
         [0039]    Second Embodiment: In the caster assembly shown in FIGS. 4, 5 and  6 , a swivel frame  50  is swingable on a vertical axle  51  functioning as a pivot. Axle  51  projects downwardly from a load-supporting member  52  attached to the base of a load  53  such as baggage truck or the leg of a desk. Obviously the dimensions of the caster assembly and its structural strength must be appropriate to the nature of the load.  
         [0040]    Swivel frame  50  which has a generally triangular form is provided at its apex with a socket for receiving vertical axle  51  which functions as the pivot on which the frame swivels. Supported on this triangular frame below its rear end is a caster wheel  55  mounted on a fork having parallel arms  54  which embrace opposite ends of the horizontal axle  56  of caster wheel  58 , as best seen in FIG. 6.  
         [0041]    Because in this fork arrangement, the parallel as projected from the frame are vertical and at right angles to the frame to which it is attached. The fork is therefore exposed mainly to compressive forces, for only a minor moment of force is applied to the arms of the fork.  
         [0042]    Integral with tae rear end of the triangular swivel frame  50  and coplanar therewith is a U-shaped extension  50 E whose parallel branches B 1  and B 2  are joined to the corners of the fame at its rear end. The central axis X of the frame which runs from the pivot point at the apex of the frame to a point midway between parallel branches B 1  and B 2 , acts as an axis of symmetry between a pair of load-support rollers  57  and  58  mounted for rotation on these branches. The horizontal axles on which rollers  57  and  58  are supported are in alignment with radial axes Y and Z extending from the pivot point on either side of the central axis X.  
         [0043]    Hence when the swivel frame  50  swings on its pivot, rollers  57  and  58  then travel in a circular orbit O 1  whose dead center is the pivot point. And when the load is pushed and the swivel frame swings to align its caster wheel with the direction of movement, the caster wheel then travels in a circular orbit O 2  which is concentric with orbit O 1  and close thereto. Thus the caster wheel is on a common line of action with the pair of support rollers symmetrically disposed with respect to the caster wheel. Hence the caster wheel and rollers are in a balanced, symmetrical arrangement on the fame.  
         [0044]    The benefit gained by this balanced arrangement on the swivel frame is that whereas in the assembly without support rollers, the resultant moment of force may be great enough to disable the caster assembly, with support rollers included in the assembly, the moment of forced is effectively cancelled out and the caster assembly is capable of handling heavier loads without becoming disabled. And the caster assembly is shock resistant, for should the caster wheel strike an obstruction, the resultant impact force, by way of the support rollers, would be absorbed by the load.  
         [0045]    Should the caster assembly lack the support rollers, then when the load is being pushed to move at a fast pace, the weight of the load may be such as to cause the caster assembly to collapse. This may have serious consequences should it cause the load to topple.  
         [0046]    Third Embodiment: The caster assembly illustrated in FIG. 7 is a small scale version of die assembly shown in FIG. 4 and is appropriate for attachment to relatively light weight articles such as chairs.  
         [0047]    The swivel frame  59  shown in FIG. 7 has the shape of an equilateral triangle having rounded corners which lends itself to being combined with a circular load-bearing member such as that shown in FIG. 3 having a circular rim which is swept by the corners of the frame as it is being swiveled. The rim in this case protects the swivel frame from impact forces.  
         [0048]    Swivel frame  59  is provided adjacent one corner with a socket  60  adapted to receive a vertical axle projecting from a load-support member which acts to pivot the frame. Nested in wells adjacent the other two corners of the frame are load-support rollers  61  and  62 , while attached to the underside of the frame is a caster wheel  63 .  
         [0049]    It will be seen that it is only the upper segment of the rollers that project above frame  59  to engage the load bearing member. Hence the overall height of the assembly is not much greater than that of an assembly without rollers.  
         [0050]    The balanced symmetry of this arrangement is the same as that of the caster assembly shown in FIG. 4 and has the same advantages, for it results in the cancellation of the moment of force.  
         [0051]    In practice rubber or polymer O-rings may be installed on the rollers and on the base member to reduce noise and shock. When, as in FIG. 3, the swivel frame is turnable within a cylindrical casing, the casing may be provided with a circular cover to prevent dust and water from entering the casing to contaminate the swivel assembly.  
         [0052]    Because of the balanced, symmetrical arrangement of the rollers and the caster wheel, the caster is resistant to shock forces imposed on its sides.  
         [0053]    While there have been shown preferred embodiments of the invention, it is to be understood that many changes may be made therein without departing from the spirit and concept underlying the invention. Thus, instead of support rollers nested in recesses in the swivel frame in the symmetrical arrangement shown in FIG. 7, arcuate slides may be used for the same purpose to slide rather than roll on the undersurface of the base member.