Abstract:
A caster system wherein a constant force is applied to the caster for load support purposes. A plurality of casters are interconnected by a fluid conduit system and each caster includes an expansible chamber motor for adjusting the vertical position of the caster. A fluid pressurizing unit communicates with the conduits and an adjustable force compression spring selectively varies the biasing force on the piston to adjust the equal force imposed upon each caster wheel.

Description:
FIELD OF THE INVENTION 
     The invention pertains to casters and caster systems wherein a constant biasing force is imposed upon the caster wheel for load supporting purposes. 
     DESCRIPTION OF THE RELATED ART 
     Casters are widely used to support material handling trucks, tables, bins, receptacles, pallet lift trucks, and the like. In some instances, it is desirable that the caster be spring mounted so that shocks may be absorbed, or the weight supported by a specific caster can be adjusted. Where a plurality of casters are simultaneously employed for support purposes, it is usually desirable that each caster exerts the same force upon the load in order to equalize wheel wear and produce uniform load support. 
     Where casters are individually spring supported, it is very difficult to individually adjust casters so that equal forces are supported by each caster when a plurality of casters are used together for load bearing purposes. 
     OBJECTS OF THE INVENTION 
     It is an object of the invention to provide a caster which is vertically adjustable, and wherein the caster load characteristics can be accurately adjusted. 
     A further object of the invention is to provide a vertically adjustable caster wherein the vertical position of the caster wheel is adjusted by fluid pressure, such as oil pressure, and wherein the pressure upon the fluid supporting the caster can be varied. 
     Yet another object of the invention is to provide a caster system wherein a plurality of casters are used for load bearing purposes, and wherein the load supporting force of each caster is identical. 
     An additional object of the invention is to provide a caster system utilizing a plurality of casters wherein a pressurized fluid is used to simultaneously vertically adjust all of the casters in the system, and wherein uniform pressure is employed in all casters for load bearing purposes, and such pressure can be easily adjusted. 
     SUMMARY OF THE INVENTION 
     Casters constructed in accord with the inventive concepts utilize a caster housing having a support plate mounted thereon for mounting the caster. The caster housing includes an internal cylindrical chamber defining an expansible chamber motor, and a piston is reciprocally mounted within the chamber. A lever mounted upon the caster housing pivotally supports the caster wheel for vertical adjustment, and the caster piston is affixed to the lever to apply the desired vertical force to the caster wheel. In the disclosed embodiment, one end of the lever is pivotally mounted to the caster housing, while the caster wheel is mounted upon the other end of the lever, and the lever center region is affixed to the caster piston. 
     The fluid pressure within the caster expansible chamber motor, preferably a hydraulic oil, is pressurized by a pressure unit comprising a cylindrical chamber having a piston reciprocally mounted therein. The pressure unit piston is biased toward the associated chamber by a compression spring whose degree of compressive force is adjustable by a compressing screw. 
     A plurality of casters constructed in accord with the invention may be interconnected by a common conduit system wherein the internal expansible chambers of each piston housing are in communication, and also in communication with the fluid pressurizing unit. In this instance, each of the caster levers, and caster wheel, is subjected to a common fluid pressurizing force from the pressurizing unit, and thereby a constant biasing force on the load may be imposed by the plurality of interconnected casters regardless of number. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The aforementioned objects and advantages of the invention will be appreciated from the following description and accompanying drawings wherein: 
     FIG. 1 is a plan view of a caster system using the invention wherein four casters are interconnected to a single pressurizing unit, 
     FIG. 2 is a side elevational view, partially broken away, of a single caster constructed in accord with the invention, 
     FIG. 3 is a diametrical, elevational, sectional view taken through a caster housing in accord with the invention, the caster wheel, wheel lever and pivot being omitted for clarity of illustration, and 
     FIG. 4 is a diametrical, elevational, sectional view of the type of pressurizing unit which may be employed with the caster of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A caster unit assembly is generally indicated at  10 . Four caster units  10  are illustrated in FIG. 1, while a single caster unit is shown in FIGS. 2 and 3. All of the caster units are identical. 
     The caster units each consist of a housing  12  having a support plate  14  attached thereto. The support plate  14  includes bolt holes for receiving fasteners wherein the caster unit may be mounted as desired. In the drawings, the caster units  10  are illustrated in a manner wherein the caster wheels are located above the housing  12  whereby a plurality of caster units can be used to support a large workpiece, table, or the like, which is to be moved upon the casters. Of course, the caster units  10  can be mounted in a more conventional manner, 180° from the orientation shown in the drawings, wherein the caster wheel is located below the housing  12 . Regardless of the mounting of the caster units to accommodate the particular caster application, the constant pressure imposed upon the caster wheel occurs. 
     Each housing  12  has a column  16  welded thereto as will be appreciated from FIG. 2, and the upper end of the column  16  includes a pivot shaft  18  for a purpose later described. Interiorly, the housing  12  includes a cylindrical chamber  20  communicating with a threaded port  22 . A cylindrical piston  24  is reciprocally received within the chamber  20  and is sealed at  26 . It will be appreciated that the chamber  20  and the piston  24  constitute a typical simple expansible chamber motor. A pivot shaft  28  is located at the outer end of the piston  24  as will be appreciated from FIGS. 2 and 3. 
     A pair of levers  30  are mounted in a spaced parallel relationship and support the rotatable caster wheel  32  at the levers&#39; outer end upon the caster axle  34 . The other end of the levers  30  are pivotally connected to the column  16  by pivot shaft  18 , FIG. 2, and elongated slots  36 , FIG. 2, are defined in the central region of the levers  30  for receiving the piston pivot shaft  28 . Accordingly, it will be appreciated that as the piston  24  reciprocates within the chamber  20 , the piston shaft  28  acting upon the levers  30  through elongated slots  36  will raise and lower the caster wheel  32  relative to the support plate  14 . The elongated configuration of the slots  36  will prevent binding as the levers  30  are operated by the piston. 
     The caster units  10  are pressurized by a fluid medium, usually hydraulic oil, by a pressure unit  37 , FIGS. 1 and 4. The pressure unit  37  is mounted upon support columns  38 , and will normally be located in relatively close proximity to the caster units  10  pressurized thereby. The columns  38  support plates  40  by a plurality of bolts  42  threaded into the upper ends of the columns  38 . 
     A cylindrical tube  44  is mounted upon the plates  40  having an open upper end, and a cylindrical chamber  46 . A port  48  is located in the lower region of the tube  44  in communication therewith. 
     A cylindrical piston  49  is reciprocally received within the chamber  46 , FIG. 4, and the piston includes an enlarged piston head  50  located above plates  40 . A tubular spring jacket  52  is mounted upon the upper plate  40  and includes a cover  54 . Centrally, the cover  54  is provided with a threaded hole through which the threaded screw  56  extends. Screw  56  includes hexagonal upper end  50  for application of a wrench thereto in order to rotate the screw  56 , and a lock nut  60  threaded upon screw  56  will lock the screw in its desired axial position. The lower of the end screw  56  includes a spring pad  62 , FIG. 4, whereby the compression spring  64  housed within the spring jacket  52  will be located between the piston head  50  and the spring pad  62 . The extent of compression of spring  64  is determined by the axial position of screw  56  within jacket cover  54 . The further the screw extends through the jacket cover, the greater the force imposed by the spring  64  on the piston  49 . 
     With reference to FIG. 1, each of the caster units  10  includes a supply conduit  66  which is attached to the port  22  of each caster unit chamber  20 . Each of the supply conduits  66  communicates with the manifold conduit  68 , and the pressure unit  73  communicates with the manifold conduit  68  through conduit  70  which is in communication with port  48 . Accordingly, it will be appreciated that the pressure imposed upon the fluid within pressure unit chamber  46  will simultaneously be imposed upon all of the caster unit pistons  24 , and hence, the caster wheel levers  30 . 
     From the above description, it will be appreciated that the fluid pressure within the chambers  20  of the caster units  10  will be the same in each caster unit as determined by the pressure of the fluid within the pressure unit chamber  46 . In this manner, a constant force is imposed on all of the caster unit pistons  24 , and hence, the caster wheels  32 . The interconnection of all of the caster units  10  by the conduit system assures constant supporting forces on each of the caster assemblies of the caster array, and regardless of whether the caster units  10  are oriented in the position shown in the drawings, reversed, or used in any other orientation, equal forces are created in each of the casters. Of course, it will be appreciated that a pumping movement of the piston  49  will simultaneously increase or decrease the pressure within the caster units  10 , and by utilizing various known means for positioning the piston  49 , such as by a hydraulic pump, manually operated lever arm, or the like, the casterwheels  32  may be used to simultaneously “jack up” a load, or lower the same. 
     It will be appreciated that various modifications to the inventive concepts may be apparent to those skilled in the art without departing from the spirit and scope of the invention.