Abstract:
An obstacle traversing wheel assembly that rolls easily without dragging over electrical cords, trash and debris includes a primary wheel that is journaled on an axle which is attached to a load carrying frame. At least four independently rotatable secondary wheels are mounted around the circumference of the primary wheel at locations equidistant from each other and from the primary wheel axle. The secondary wheels are all of the same diameter and are spaced apart on the primary wheel at a distance that is less than the diameter of a secondary wheel. The wheel assembly finds use as the wheel members on luggage, as the leading wheel of an in-line skate board, and for supporting any other load carrying module that is rolled across a debris-strewn surface.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     This invention relates to a wheel assembly that can traverse rough surfaces and roll over small obstacles without dragging. 
     More particularly, this invention relates to a wheel assembly which comprises a wheel holder that is rotatable about a central axis, the wheel holder having mounted thereon at least four independently rotatable wheels. 
     2. Background Art 
     Hand trucks or dollies used to transport loads up and down stairways have long used a wheel arrangement consisting of a pair of star-shaped plates which rotate about a main axle and include a number of wheels, usually three or four, mounted on stub axles. Such a wheel arrangement is often referred to as a spider or star wheel. The plates and wheels are sized such that two of the stub axle mounted wheels can be in simultaneous contact with the lands of two adjacent steps. 
     A stair climbing hand truck equipped with a pair of star wheels, each having four radially projecting arms spaced at 90° one to another, is described in U.S. Pat. No. 2,706,640 to Marshall. Roller wheels are mounted at the arm ends. The star wheel used by Marshall is sized such that two adjacent roller wheels can simultaneously contact the lands of two adjacent steps when the hand truck ascends or descends a stairway. 
     Another hand truck having stair climbing capabilities is disclosed in the Boyd patent, U.S. Pat. No. 4,142,732. The Boyd truck employs a pair of star-like plates journaled on a main axle with each plate carrying three stub axles, one on each projecting plate leg. A wheel is mounted on each stub axle and the plate and wheels are sized such that wheels are in contact with the lands of two adjacent steps at all times while the truck is on a stairway. 
     A motorized wheel chair that is able to go up and down stairs and climb sidewalk or pavement curbs is shown in U.S. Pat. No. 4,709,772. The wheel chair uses a pair of wheel assemblies, each comprising three wheels mounted on a triangular support frame. Each frame and wheel assembly is rotated by a powered shaft that is fixed to the frame center. 
     Wheel assemblies for traversing obstacles and to climb stairs are shown in U.S. Pat. No. 3,326,563 to Whitacker, U.S. Pat. No. 4,457,526 to Persson, and U.S. Pat. No. 4,687,213 to Ridderstolpe. The wheel assemblies described in the three patents all use a star or spider wheel arrangement in which three wheels are mounted symmetrically on a plate or support member which in turn rotates about a main shaft or axle. 
     While the wheel assemblies of the type shown in the above listed prior art work well at climbing stairs and curbs, none of those designs can be successfully scaled down in size to use on items which require a relatively small diameter wheel such as luggage, in-line skates and skate boards, grocery carts, electronic test equipment carts and the like. The need for a simple and inexpensive wheel assembly that can traverse small obstructions such as hose lines, electrical cords, twigs and small branches, gravel, sidewalk irregularities and the like without wheel dragging has long been present. This invention fills that need. 
     SUMMARY OF THE INVENTION 
     This invention provides a wheel assembly that can freely roll or climb over small obstacles such as electrical cords, pavement irregularities, small stones and other trash without wheel drag. The assembly includes a primary wheel member that is rotatable about a central axis. At least four smaller secondary wheels are mounted on axles attached around the circumference of the primary wheel at locations equidistant from each other and from the central axis. Each secondary wheel has a diameter that is greater than is the distance between adjacent wheel locations, and is free to rotate about its axis. The wheel assemblies of this invention roll easily across electrical cords, pneumatic lines and small trash, and are particularly useful on rolling luggage, tool carts, electronic test equipment, skates, chairs, and the like. 
     Thus, the primary object of this invention is to provide a wheel assembly that rolls over obstacles without wheel drag. Other objects of the invention will be evident from the drawings and the description of preferred embodiments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a partially broken away side view of the wheel assembly of this invention showing the primary wheel member with six secondary wheels mounted thereon rolling on an obstructed surface; 
     FIG. 2 is an end-on view showing a first embodiment of the wheel assembly of FIG. 1; 
     FIG. 3 is a detail view of a secondary wheel used in the embodiment of FIG. 2; 
     FIG. 4 is an end-on view showing a second embodiment of the wheel assembly of FIG. 1; 
     FIG. 5 is an end-on view showing a third embodiment of the wheel assembly of FIG. 1; 
     FIG. 6 shows an element of the primary wheel member that may be used in either the FIG. 2 or the FIG. 4 embodiment; 
     FIG. 7 illustrates the wheel assembly of this invention mounted upon the frame of a carrier module which may be a piece of luggage, a tool holder, an electronic test device, or similar article; 
     FIG. 8 shows the wheel assembly of this invention in use with furniture, specifically an office chair; 
     FIG. 9 depicts the wheel assembly of this invention as used in a grocery cart; and 
     FIG. 10 shows the inventive wheel assembly used as the front, or lead, wheel of an in-line skate. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring first to FIGS. 1 and 2, there is shown a first preferred embodiment of the obstacle surmounting wheel assembly  10  of this invention. The assembly  10  includes a primary wheel comprising a pair of wheel holders  12  and  14  arranged to rotate about a central axis  15 . Wheel holders  12  and  14  preferably are formed as two parallel, spaced apart, circular, plate-like members having a central bore to accommodate an axle about which the primary wheel rotates. At least four secondary, equal diameter, wheels  18  are rotatably mounted between holders  12  and  14  by means of a journaled axle  20  extending between holders  12  and  14  and secured in place by a nut or other locking means  21 . Wheels  18  are spaced apart a distance that is less than one wheel diameter, and are located equidistant from each other and from axle  20 . 
     In this embodiment, secondary wheels  18  may be configured as shown in the view of FIG.  3 . Wheel  18  of FIG. 3 includes a circular disk-like portion  23  having a generally flat or textured edge bearing surface  24 . A cylindrical boss  26  projects coaxially outward from one side of disk portion  23  for a distance somewhat greater than the thickness of disk portion  23 . A bore  27 , to accept axle  20 , extends axially through both boss  26  and disk portion  23 . Wheels  18  are then arranged in assembly  10  with boss  26  of adjacent wheels alternating in direction as is shown to provide clearance for the overlap between the disk portion  23  of adjacent wheels. The wheels may be machined from circular stock of a suitable material or preferably may be molded from a construction plastic such as polyurethane. 
     FIG. 4 illustrates another embodiment of wheel assembly  10 . This embodiment may use the same wheel holders  12  and  14  as does the embodiment of FIG.  2 . However, in this embodiment the two wheel holders are secured one to the other in an held apart relationship by way of a cylindrical spacer and bearing member  31  disposed axially with the two wheel holders. Wheels  33  of this embodiment are disk shaped without the projecting boss of wheels  18 . The wheels are mounted on stub axles  35  which extend inwardly from the wheel holders  12  and  14  and are arranged so that adjacent wheels are journaled one from holder  12  and the next from holder  14 . Axles  35  may be secured to the wheel holders by means of locking nut  37 . As with the embodiment of FIG. 2, wheels  33  are located equidistant one from the other and from the center of bearing member  31  at a distance less than the diameter of the wheels. 
     A third embodiment of the wheel assembly is illustrated in FIG.  5 . This embodiment employs but a single wheel holder  41  that is provided with a central bore  43  journaled for rotation about a shaft or axle. At least four stub axles  45  are fixed to holder  41  and the disk-like wheels  33 . of the FIG. 4 embodiment are mounted on the axles alternating with the wheels  18  of FIG. 2 to obtain an overlapping arrangement as is shown. As in the embodiments of FIGS. 2 and 4, wheels  33  and  18  are all the same diameter and are equi-spaced, one from another, at a distance less than that of the wheel diameter. 
     FIG. 6 illustrates a wheel holder  50  that may be used in either the FIG. 2 or FIG. 4 embodiments. Holder  50  comprises a flat, generally circular plate  51  having a centered bore  53  to allow rotation of the wheel holder about an axle. Plate  51  is provided with a plurality of equi-spaced, grouped openings  55 ,  56 ,  57 ,  58 ,  59  and  60 , each opening adapted for the mounting of a stub axle therein. As shown in this figure each group of openings comprises a plurality, suitably three, of axle-accepting holes bored through plate  51  at differently spaced radial distances from the central bore. The outermost holes of each grouping are spaced apart an equal distance one from another, and from the central bore as well. A similar relationship holds among the center and innermost holes of each grouping. It is preferred that the holes of each grouping not be located along a common radial line of plate  51  in order to obtain maximum structural strength. This arrangement allows installation of different sized groups of secondary wheels onto the same wheel holders. 
     Referring once again to FIG. 1, there is shown a partially broken away side view of the wheel assembly  10  rolling along a surface  70  as it bumps into obstruction  72 . Obstruction  72  typically might be an electrical cord or pneumatic line lying on a workplace floor, a small stone or branch on a parking lot or pavement surface, or an irregularity in a sidewalk. As assembly  10  moves to the right along an unobstructed surface, only the lowermost two,  18   a  and  18   b , of the secondary wheels are in rolling contact with surface  70 . The remaining secondary wheels and the primary wheel are motionless. As secondary wheel  18   b  strikes obstruction  72  it stalls and causes a right-ward rotational tilt of the entire wheel assembly  10 , bringing secondary wheel  18   c  downward to roll over obstruction  72 . The force required to precipitate that rotational tilt is modest, amounting to little more than the force required to lift the wheel assembly (and the weight that it supports) a short distance. That distance comprises a span amounting to the difference in distance  77  between the centerpoint  75  of wheel assembly  10  and surface  70  and the longest distance  79  between centerpoint  75  and the circumference of the wheel,  18   b , in contact with the obstruction  72 . Distance  77  may be viewed as being the effective radius of the wheel assembly, and twice that distance then constitutes the effective diameter of the wheel assembly. As may be appreciated, the structure of the wheel assembly allows it to literally walk over small obstructions. 
     As has been set out before, the wheel assembly of this invention requires a minimum of four secondary wheels equi-spaced around the circumference of a primary wheel means. Because the diameter of each secondary wheel is greater than is the distance between wheels, adjacent wheels overlap and are offset one to another. Thus, when the wheel assembly traverses a surface, the two wheels in contact with that surface follow separate, parallel tracks, one wheel in each track. That geometry, separate and parallel tracking of adjacent wheels, tends to increase the stability of a wheel assembly that is pivotally attached to a load-supporting frame through a conventional yoke or horn arrangement. It can further be appreciated that the overlapping arrangement of adjacent secondary wheels can best be obtained through use of an even number of secondary wheels, preferably four, six, or eight and most preferably six. It is conceptually possible to utilize an odd number of secondary wheels, say five or seven, but an odd number of secondary wheels requires three, rather than two, parallel wheel tracks. Such an arrangement necessitates a wider wheel assembly to accommodate the three tracks, is more complicated in construction, and has less rolling stability than does a wheel assembly having an even number of secondary wheels. 
     FIGS. 7-10 illustrate a group of preferred applications for the wheel assembly of this invention. FIG. 7 depicts wheel assembly  10  in use with a carrier module  80  which may be any load carrying container, for example, a piece of luggage, medical or electronic test equipment, a tool chest, or items of a similar nature which are moved from place to place across obstructed surfaces. A plurality, typically three or four, of wheel assemblies  10  are mounted to a bottom load supporting member or frame  82  of carrier module  80 . The wheel assemblies may be fixedly or pivotally mounted to frame  82  as is desired. A handle means  84  may be attached to module  80  for ease of towing or pushing the module. 
     FIG. 8 illustrates wheel assemblies  10  in use with a piece of furniture, in this case an office chair  90 . One wheel assembly  10  is pivotally mounted to each chair leg member  92  by means of a conventional horn bracket  93 , thus allowing the chair to be freely rolled in any direction. 
     FIG. 9 shows the wheel assembly  10  of this invention used with a grocery or shopping cart  95 . In many parts of the country, purchased goods such as groceries are carried from the store to an automobile that may be parked in a lot some distance from the store with the same shopping cart that was used to gather goods in the store. Conventional wheels, particularly the two front, swiveled wheels, tend to stall and drag when the cart is pushed over debris, such as gravel and small branches, that is commonly found in parking lots. Wheel drag is substantially eliminated by replacing the two front cart wheels with the wheel assemblies  10  of this invention as is shown in the Figure. The two rear cart wheels  97  may be replaced as well, but the drag problem is not as severe with the rear wheels as it is with the front. 
     FIG. 10 depicts another preferred use for the wheel assembly of this invention. The Figure shows an in-line skate  101  comprising a boot  104  having a linear chassis  105  attached to the boot sole by means of brackets  107  and  108 . Chassis  105  supports a plurality of wheels  10 ,  111 ,  112 , and  113  arranged one behind the other to track in the same path. A drag brake  115  projects downwardly from the chassis at the rear thereof. The front, or lead, wheel  10  comprises the wheel assembly of this invention while the trailing three wheels  111 ,  112  and  113 , are conventional. The three trailing wheels are all the same diameter, and it is preferred that the effective diameter of wheel assembly  10  be equal to that of the other three wheels. Effective diameter here is defined as was set out earlier in the discussion of FIG.  6 . 
     Users of in-line skates risk falling when a skate hits an obstacle that the front or lead wheel cannot surmount or which causes that wheel to drag. Wheel assembly  10  easily rides over obstacles which cause an ordinary wheel to jam or drag, and the trailing wheels of the skate then tend to ride over the obstacle as well, thus enhancing skating safety. Similar advantages are obtained by the use of wheel assembly  10  on scooters. In this embodiment, frame  82  comprises a platform on which the scooter user stands. 
     The wheel assembly of this invention has been shown and described with respect to certain embodiments thereof and that description is for the purpose of illustration and not limitation. Other variations and modifications of the described invention will be apparent to those skilled in the art and are included within the scope of the invention as set out in the appended claims.