Abstract:
A wheelchair or a vehicle for sand or loose soil comprises one or more skids, each equipped with a spring-loaded roller or roller plate. Examples of the vehicle include a wheelchair and a planetary rover. Preferably, a beach, shower or pool wheelchair comprises two front skids in place of front wheels. The skids provide a resistance-free, broad footprint in the sand and a low-resistance narrow footprint when used on hard, e.g. boardwalk, surfaces. A wheelchair may further comprise a lightweight, easy to fold frame, which closes like a pair of eyeglasses. Still further, a wheelchair may provide a removable and reclining lounge chair seat to allow the user to exit the wheelchair to enter the water or sit and recline on the sand. In addition, dog bone or dumbbell shaped wheels provide the wheelchair strong, lightweight support and a wide footprint and can be equipped with grip notches for user self-propulsion. The inventive wheelchair provides the user with a combination of improvements, which respect the user&#39;s grace and dignity.

Description:
This application claims priority to Provisional Patent Application No. 60/382,513 filed on May 22, 2002. 

   FIELD OF THE INVENTION 
   The present invention relates to a vehicle for sand, loose soil or soft terrain equipped with a skid comprising a spring-loaded roller. In particular, the present invention provides a foldable beach wheelchair having a removable seat and two front skids, each comprising a spring-loaded roller or a removable roller plate which provide a low-resistance, broad footprint on the sand and a narrow, low resistance footprint on pavement, boardwalk or hard ground. 
   BACKGROUND OF THE INVENTION 
   With very limited success, wheelchairs have been adapted to access areas requiring travel over soft terrain, such as sand, loose soil and gravel. Attempts at designing beach wheelchairs, in particular those described in U.S. Pat. No. 4,641,850, to Rice et al., provided removable wide metal bands surrounding the propulsion wheels of the wheelchair so as to keep the wheels from sinking in the sand. However, such beach wheelchairs and their additional parts would invariably sink into the sand and get fouled and the metal in such chairs would corrode in the salt air. Further, the front wheels or casters would sink into the sand anyway, dragging the user and her dignity down with them. Still further, once the user accessed the beach, she still had to negotiate her way into and out of the water by exiting and then re-entering the wheelchair. 
   Compounding the indignity caused by immobile, corrosable and easily fouled beach wheelchairs, existing beach wheelchairs fold like an accordion and their frames often start folding on their own during the user&#39;s struggle to travel on the sand. The wheelchairs thus fail to support the user properly and can thereby cause muscle and back strain. As if this were not enough indignity, the seating materials of existing beach wheelchairs do not breathe and can cause chafing and discomfort. 
   A recent low pressure tire design, described in U.S. Pat. No. 6,279,631, to Tuggle, provides a fairly inelastic low pressure tire material for a beach wheelchair that can flatten under load to ease movement over soft surfaces. However, the low pressure tire concept does not solve the problem of fouling or corrosion and does not address the problem caused when any tires, front or rear, sink in the sand. Further, the low-pressure tire concept does not address the need to provide an easy to fold wheelchair that does not fail to support the user when in use. Still further, no seat materials are taught or suggested which prevent chafing and irritation to the user. 
   There remains great and long felt demand for a wheelchair that allows easy travel over soft ground and sand and which will not corrode in the salt air. As well, wheelchair users continue to desire comfortable seat materials that breathe. Still further, an easy to fold, lightweight wheelchair frame would enhance ease of use in comparison to existing accordion-style folding beach wheelchairs. Finally, wheelchair users still lack for a beach wheelchair that allows easy exit and re-entry to permit them to get on the beach or enter the water. Accordingly, the present inventors have sought to provide a wheelchair that solves the aforementioned problems while respecting the user&#39;s dignity. 
   SUMMARY OF THE INVENTION 
   The present invention provides a wheelchair comprising a seat, two rear wheels, two front skids and a frame onto which each of the seat, wheels and skids are mounted. Each front skid on the wheelchair comprises a skid body having within it a spring-loaded roller or a removable roller plate on which the wheelchair rests, creating little resistance while the wheelchair rolls on pavement or hard ground. In addition, the skid body provides a broad footprint to decrease resistance and to prevent sinking in sand, soft terrain or loose soil. Spring tension keeps the roller tight in its socket to prevent sand or soil penetration into the roller and consequent fouling. The roller plate edge may or may not be flush with the bottom surface or the skid and the roller plate and roller may be interchangeable. Further, dumbbell or dog bone shaped rear wheels provide a wide footprint and the wheels and frame of the wheelchair are constructed of a lightweight, corrosion proof material. Still further, a removable, reclining seat supports the full length of the wheelchair user&#39;s legs with a comfortable porous film material and allows for easy exit and re-entry. Accordingly, the present invention provides a highly mobile and dignified beach wheelchair. 
   A wheelchair frame and wheels maybe made of lightweight hollow material, such as rotationally or hollow molded or cast polyvinyl chloride (PVC) or high density polyethylene (HDPE), with or without fiber or mesh reinforcement, wherein the hollow material may be foam filled to provide a floatable pool wheelchair. 
   The present invention further provides a wheelchair frame comprising side wings that fold inwardly against said back rest support, wherein each side wing may be equipped with one or more than one slidable ledger disposed horizontally under the seat, for example, under the seat at or above the user&#39;s knee, such as under the thigh above the knee, to support seats having variable widths. Further, by sliding outwardly as the side wings fold inwardly, the ledgers allow the side wings to fold without obstruction against the inside of the back of the wheelchair frame. The side wings may further have a hinge stop that causes the wings to lock against the back rest support and allows the wings to fold and unfold with a flipping action, like the arms of a pair of eyeglasses. 
   The present invention still further provides a skid comprising a spring-loaded roller or removable roller plate that may be used on soft terrain, loose soil, sand or mud, for example, in place of wheels on a planetary rover or any vehicle which should have a steady, wide footprint, such as a walker or a water walker for pool therapy. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1   a  depicts an exemplary use of a beach wheelchair in accordance with the present invention. 
       FIG. 1   b  depicts an embodiment of a seat attachment to a wheelchair frame and an exploded view of the spring support for a seat in accordance with the present invention. 
       FIG. 1   c  depicts another embodiment of a seat attachment to a wheelchair frame in accordance with the present invention. 
       FIG. 2   a  depicts a top view of an embodiment of a wheelchair comprising a frame having a contoured back rest support and pivotally mounted side wings in accordance with the present invention. 
       FIG. 2   b  depicts an embodiment of a skid in accordance with the present invention. 
       FIG. 3   a  depicts a rear view of an embodiment of a beach wheelchair in accordance with the present invention. 
       FIG. 3   b  depicts a front view of an embodiment of a beach wheelchair in accordance with the present invention. 
       FIG. 4  depicts a side view of an embodiment of a beach wheelchair in accordance with the present invention. 
       FIG. 5  depicts an embodiment of the seat of a beach wheelchair in accordance with the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   A broad footprint beach wheelchair in accordance with a preferred embodiment of the present invention includes several inventive improvements over the current state of the art. For example, a skid having a spring-loaded roller or removable roller plate comprises an improvement in wheelchair design, but is also inventive in its own right. The several drawing figures assist in describing some of the advantages of the present invention. 
   All ranges cited herein are inclusive and combinable. 
   As used herein, the term “roller plate” refers to a plate attachable to the bottom of a skid, as well as detachable therefrom, and providing a roller footprint. 
   Any off-the shelf beach seat that fits onto the wheelchair frame may be used, such as one having an aluminum tube frame. As the one or more than one slidable ledger in each side wing of the wheelchair frame can accommodate any size or width of commercially available beach seat, any such seat may be used and the seat may or may not comprise an adjustable leg rest. The adaptable wheelchair frame and the off-the shelf beach seat may therefore be used with a custom seat to provide a shower wheelchair. 
   A removable seat  53  that supports the full length of a wheelchair user&#39;s body is shown in  FIG. 1   a . The horizontal section of seat  53  extends all the way to a user&#39;s knee and supports the full upper portion of the user&#39;s leg, unlike previous seats which cut off above the knee. Seat  53  comprises leg rest  52  and back rest  51 . Leg rest  52  and back rest  51  may each be adjustable using a conventional ratcheting mechanism (not shown) found in beach chairs. Leg rest  52  provides support of the full length of a user&#39;s legs. Seat  53  may also have supports or legs (not shown) which fold under the horizontal section of seat so as not to interfere with frame  40 . 
   As shown in  FIGS. 1   b  and  1   c , seat back rest  51  conforms to and may attach removably to back rest support  54  of the frame  40  via the seat frame itself ( FIG. 1   b ) or via two vertical attachment members  55  ( FIG. 1   c ) which are part of the frame of the seat. The vertical attachment members  55  of back rest  51  may slide or key into female attachment slots  42  ( FIGS. 1   b  and  5 ) located in the front side of back rest support  54 . Members  55  and slots  42  preferably are shaped, respectively, like male and female right triangular prisms or cylinders of the same size, and can comprise other shapes. Preferably, as shown in  FIG. 1   c , back rest support  54  is angled so that back rest  51  and support  54  align in a parallel fashion to ease attachment. As shown in  FIG. 1   b , members  55  allow seat  53  to rest on high-K value springs  41  located in spring sockets  49  disposed at the bottom of each of slots  42 . The springs  41  cushion the user against shocks and are preferably constructed of vesconite (polyethylene terephthalate engineering thermoplastic, Vesco Plastics Sales (Pty.) Ltd.) to resist abrasion and wear. 
   Alternatively, a removable seat may attach to a wheelchair frame via two or more supports (not shown) attached on the inside of each side wing. Supports for seat should conform to the frame of a seat&#39;s leg rest, so that, for example, supports may comprise j-bends for round tubular, rod or cylindrical seat frames or L-bends for square tubular frames. Supports should be spaced apart so that one support is adjacent the back end of a seat leg rest and has a bullet catch or spring loaded catch to allow the seat to snap fittingly in place, i.e. a “snapfit.” 
   To make a fully static seat support, seat  53  may rest on one or more than one seating rail, rod, cylinder or contoured ledger (not shown), which is part of each of the side wings  43  ( FIG. 2   a ) of the wheelchair frame  40 . The ledger may be beveled to receive the round tubing of a seat frame, may have a squared upper surface to receive a square tube seat frame or may be equipped with a pinhole or pin which matches, respectively, to a corresponding pin or pinhole in a seat frame. Ledger may also be beveled to accommodate any legs or supports for seat  53  which fold underneath the seat. 
   In another embodiment, ledger should be slidable, for example, attached through an aperture in each side wing to allow each side wing to fold inwardly against back rest support, for example support  54  ( FIG. 1   b ) of frame  40 . A slidable ledger may have a flat circumferential lip or flange at each end to keep it attached with a side wing, so that the lip or flange closes flush with the surface of the side wing. 
   Because seat  53  supports the full length of a user&#39;s body and because the beach wheelchair  10  can be preferably made of a moisture resistant, non-corrosable material, such as hollow or rotationally molded or cast PVC or HDPE, with or without fiber or fiber mesh reinforcement and/or foam filing, a user can easily exit and re-enter wheelchair  10 . The user may do this, for example, by lowering leg support  52 , and slipping off and then back on the chair using the full length of seat  53 . In a floatable wheelchair, a user may enter the water prior to exiting the chair and then swim out of and back into the chair. 
   By virtue of a support system which relies on the force of gravity and weight, seat  53  can easily be removed by a user simply by lifting it out of attachment slots  42  or snap fits, for example, by lifting the two seat handles  11 . Once removed, seat  53  can recline just like an ordinary beach chair. 
   Seat  53  is preferably made from a porous film material like porous nylon, porous HDPE or porous Novex (LDPE or low density polyethylene, BP/Amoco), may include woven web materials such as polyesters, and may include polyurethane padding disposed between two layers of the film. “Film” as used herein includes single and multi-layer films as well as sized films. 
   As shown in  FIG. 2   b , a skid comprises a skid body  20  having a socket  23  for receiving a spring  21  and a roller  22  or a skid body may comprise a roller plate (not shown). Roller  22  is disposed within said socket  23  and beneath said spring  21  and preferably comprises a ball. Spring tension keeps a roller tight in the sockets to eliminate sand penetration and subsequent abrasion. In a roller plate (not shown), a roller may be spring loaded or may float on bearings housed inside a recess in a plate adapted to receive the roller. Socket  23  need not be absolutely vertical, however it should be disposed so that the weight of the wheelchair  10  creates sufficient spring tension to force roller  22  to protrude from beneath skid body  20  so as to bear the weight of wheelchair  10 . Preferably, socket  23  is disposed in skid body  20  in a wheelchair  10  or other vehicle at an angle within about 10 degrees of vertical. Socket  23  may have a lip at its flange to assist in cleaning off roller  22  as it passes into skid body  20  and should have an opening at the bottom of skid body  20  that is small enough in diameter that roller  22  cannot fall out of skid body  20 . 
   When a skid body has a roller plate, the roller plate may be interchangeable with a roller. The roller plate may screw in flush to the bottom of the skid body or may snap fit securely into a recess in the skid body adapted to receive the roller plate, such as via two or more than two spring loaded ball bearings, rollers or bullet catches in the roller plate. Similarly, the spring loaded catches, for example, may be a part of a recess in the skid body into which fits securely a lip, flange or tab of the roller plate. 
   As shown in  FIG. 1   a , skid body  20  provides the front footprint or footprints of wheelchair  10 . Roller  22  or a skid plate (not shown) may provide the front footprint of said wheelchair on improved or hard ground, such as on pavement, concrete, boardwalk and the like. The “footprint” of a skid is defined by the width of that portion of the skid that touches the ground. Skid body  20  itself bears the weight of the wheelchair on sand, loose soil and mud and provides a broad footprint that is from about 4 inches wide to about 10 inches wide so as to provide a broad footprint without interfering with a user&#39;s feet, for example, from 6 to 9 inches wide. A skid body may have a hemispherical bottom, an ellipsoid bottom or a continuously rounded bottom having a wide radius of curvature of about 2 feet to about 4 feet, as shown in  FIG. 2   b.    
   To insure proper weight distribution, the ratio of the width or diameter of skid body to the width or diameter of a roller plate should range from 6:1 to 1.1:1, and the ratio of the width or diameter of skid body to the width or diameter of a roller, including a roller in a roller plate should range from 12:1 to 1.2:1. 
   Each skid body  20  attaches to frame  40  ( FIG. 1   a ) via a front leg  47  of wheelchair  10 . Front leg  47  may be threaded to receive skid body  20  which may comprise female socket  48  ( FIG. 2   b ) for receiving each leg  47 . Alternatively, each front leg  47  may comprise a caster attachment, a circumferential lip extending sideways at its end, or spring loaded retractable bearings, wherein the attachment, lip or bearings snap securely into a recess in female socket  48 . Female socket  48  may itself be threaded, or may comprise a socket having a ring-shaped recess at its bottom to receive a snap ring or retractable bearings from front leg  47 . Similarly, skid body  20  may comprise a male member (not shown), like front leg  47 , which fits securely into a female socket (not shown) in front leg  47 . 
   Skid body  20  may be made from a friction resistant material chosen from polytetrafluoroethylene (PTFE), polyoxymethylene (POM), POM-co-(meth)acrylate, POM-(meth)acrylate block copolymers, PTFE coated aluminum, PTFE coated magnesium alloy, and PTFE-coated thermoplastic polymer, such as PTFE coated PVC. PTFE is the preferred material for skid body  20 . “Aluminum” as used herein includes cast and anodized aluminum. 
   Roller plates, rollers, springs, supports, ledgers, screws and hardware and any bushing or spring loaded catch may be constructed of, or may be coated or laminated with one or more film of vesconite (polyethylene terephthalate based engineering thermoplastic from Vesco Plastics Sales (Pty.) Ltd.), polyacetals, aromatic polycarbonates, and copolymers thereof, or stainless steel to resist abrasion and wear. 
   In another embodiment of the present invention, as shown in  FIG. 2   a , wheelchair frame  40  comprises a back rest support  54 , contours  46  on each side which circumscribe an arc of about 90 degrees, mounts or pivot attachments  44  for frame side wings  43 , mounts  45  ( FIG. 4 ) for rear wheels  30  and legs  47  having screw threads for attachment of each skid body  20  to frame  40 . Frame  40  preferably comprises a contoured back rest support  54  which fits the curve of a users back and hips. Frame side wings  43 , are hinged or pivotally attached at wing pivot  44  to back rest support  54 , and are adapted to fold inwardly against said back rest support once seat  53  and wheels  30  are removed from frame  40 . Wing pivot  44  may comprise a female hole in frame  40 , usually located in the top of contour  46  and adapted to receive a pin (not shown) contained in each side wing  43 . The pinhole may be offset slightly inboard or rearward from frame  40  along the top of frame contour  46  to prevent the frame from hindering the folding of side wings  43 . Preferably side wings  43  are mounted via an eccentric or hinge stop that allows them to fold into or away from back rest support  40  with a snap much in the same way as the two stems or arms of a pair of eyeglasses fold against and away from the lenses. 
   In another embodiment of the invention, as shown in  FIG. 2   a , pin  32  located on each wheel  30  mounts releasably into wheel mount holes  45  located on each side wing  43  of frame  40 . Holes  45  preferably are slightly widened at their base to accommodate bearings from pin  32  which is preferably a quick release pin. A preferred quick release attachment for wheels  30  to frame  40  comprises a mushroom capped pin which when pressed retracts bearings which are used to hold the pin in hole  45 . An example of a pin suitable for use in the present invention is a quick release axle made by Alco Sales &amp; Service Co, Burr Ridge, Ill. 
   As shown in  FIGS. 3   a  and  3   b , wheels  30  have a dog bone diametrical cross-section which allows for lightweight while providing a wide footprint in loose soil or sand. The width of the tire or that portion of the wheel or ball that touches the ground defines the “footprint” of a wheel or ball. The footprint of wheels  30  may range from about 3 ½ to about 6 inches wide, and is preferably about 5 inches wide. The footprint should not be so narrow as to allow the wheelchair to sink into loose soil or sand and should not be so wide as to make it difficult for the user to reach the wheel grip  31  located on the outside of wheel  30 . Wheels  30  can be cambered as shown in the figure, but are preferably disposed normal (90° angle) to the ground so that a wheelchair user may access stalls in public restrooms. 
   In a preferred embodiment of the present invention, wheels comprise conventional grip notches  31  for user self propulsion. Grip notches  31  may comprise a ring-shaped hand rail having finger-sized rounded indentations in it, or may comprise from about 3 to about 8 grip handles periodically spaced flush or nearly flush with the tread of the wheel on the outer portion of wheel  30 . Grip notches  31  may be mounted on each wheel  30 , for example, with sheet metal screws set into nylon split grommets which are placed in the wheel. 
   To maintain light weight and prevent corrosion, frame  40  and wheels  30  may be constructed of ¼″ hollow molded, rotationally molded or cast PVC or HDPE, optionally with fiber or fiber web or mesh reinforcement. Frame and wheels may also be foam filled to provide a floating wheelchair suitable for use as a pool wheelchair. Alternatively, frame  40  and wheels  30  may be constructed of cast aluminum or magnesium alloy. However, the aluminum may not be adequately moisture resistant. 
   Unless otherwise specified, in making the beach wheelchair of the present invention, conventional bearings, springs, bushings and hardware can be used in a conventional manner. All supports, ledgers, bearings, bushings and rollers which contact moving parts may be constructed of vesconite (engineering thermoplastic), polyacetals, aromatic polycarbonates, and copolymers thereof, as well as stainless steel to resist abrasion and wear. 
   In an alternative embodiment of the present invention, one or two or more spring-loaded roller skids may be provided in a vehicle other than a wheelchair. When used in other vehicles, the spring-loaded roller skids function much in the same way that they do in a wheelchair. The roller is disposed within a socket and beneath the spring such that the weight of the vehicle creates spring tension forcing the roller to protrude from beneath the body of the skid so as to bear the weight of the vehicle. The roller provides a footprint on improved or hard ground, whereas wherein said skid bears the weight of the vehicle on sand, loose soil and mud. 
   In use, the spring-loaded roller or roller plate skid may be attached to any vehicle in the place of any non-propulsion wheel, i.e. not propelled by pedaling, by hand or by attachment to a drive train, such as the front wheel or wheels of any rear-wheel drive vehicle. For added stability, one or two or more skids may also be used in addition to wheels, e.g. they may be used for training to ride a bicycle. A skid according to the present invention may be attached to a vehicle frame via a threaded socket, a quick release pin, an axle, or any means commonly used for attaching wheels that are not drive wheels to wheelchairs, bicycles and automobiles. The only limitation on the attachment of the skid to the frame of a vehicle is that the attachment must allow the skid to bear the weight of the vehicle on the roller or the roller plate. In accordance with this embodiment of the present invention, the vehicle may be a planetary rover or craft, an all terrain vehicle (ATV), including three wheel and four wheel ATV&#39;s, a mobile home, a trailer, such as a boat trailer, a mountain bike, a bicycle trailer, a walker or a water walker and a motorcycle side car.