Abstract:
The invention comprises a cart for reducing and alleviating ergonomic stresses on the musculoskeletal system of workers in a variety of building trades, including tile setting and grouting, concrete staining, wood floor refinishing, finish carpentry, electrical finishing, plumbing, and others, that require workers to spend extended periods of the working day in compromising and unsupported kneeling positions. The cart is designed to distribute forces along the shinbone of the worker and redirect them from the back, pelvis, keens, ankles and other joints. A further advantage of the cart is the ability to maneuver around the work surface using pivoting shin supports and without the need for repeated standing and kneeling.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of PCT/US2014/023255 filed Mar. 11, 2014 which claims priority from U.S. Provisional Application 61/778,371 filed Mar. 12, 2013, the disclosures of which are hereby incorporated by reference in their entireties for all purposes. 
    
    
     FIELD OF THE INVENTION 
     The present invention is in the area of ergonomic apparatus to reduce and relieve stress on the musculoskeletal system, and to decrease overuse injuries to the joints, tendons and muscles of the feet, ankles, knees, sacral spine, lumbar spine, thoracic spine and cervical spine of workers who are required to spend extended time in a kneeling or squatting position. 
     BACKGROUND OF THE INVENTION 
     Many industrial trades such as tile setting and grouting, concrete staining, wood floor refinishing, finish carpentry, electrical finishing, plumbing, and others, require workers to spend extended periods of the working day in compromising and dangerously unsupported kneeling positions. Due to the nature of these jobs, there is associated repetitive stress and pressure on many parts of the body during the workday. The positions the workers must be in have both acute and chronic effects on the health and longevity of the laborer. The prolonged and unsupported stress required to perform these duties can lead to musculoskeletal system overuse injuries. The spectrum of injury can result from deterioration of any of the overused joints, tendons, ligaments and muscles of the feet, ankles, knees, hips, pelvis, sacral spine, lumbar spine, thoracic spine and cervical spine, and neck. 
     These workers also spend a large amount of time bent over while kneeling. Over a workers lifetime, this secondary prolonged stress only compounds the above musculoskeletal disorders including accelerated osteoarthritis, ligamental and muscular strain, and ligamental and muscle tear. This can be in all of the body parts mentioned above. 
     Current recommendations from the Occupational Safety and Health Administration (OSHA) call for the use of cushioned kneepads. Yet, cushioned kneepads only address one of the many stresses put on the body and do nothing to alleviate stress on the feet, ankles, hips, pelvis, and spine. They ultimately do little to alleviate anything but moderate to severe knee pain and gross deformation of the knees. 
     A number of apparatus have been proposed in the past to deal with the stresses on workers knees. U.S. Pat. No. 2,448,427 discloses a knee pad dolly. U.S. Pat. No. 3,976,155 discloses a cart that supports the worker&#39;s chest while laying tile. U.S. Pat. No. 5,380,021 and U.S. Pat. No. 5,427,391 disclose knee supports with attached wheels. U.S. Pat. No. 5,870,774, U.S. Pat. No. 5,937,440, U.S. Pat. No. 6,219,845, and U.S. Pat. No. 7,197,770 describe various configurations of strap-on knee pads with wheels. All of these inventions, however, ultimately fall short of alleviating the compounding stressors on the worker&#39;s body that can ultimately lead to injury of the unsupported body part directly or indirectly by compensatory overuse. 
     U.S. Pat. No. 6,302,413 describes a cart with a seat and knee supports. Yet as before, even this apparatus fails to fully alleviate the pressures applied to the worker&#39;s knees, Achilles tendon and lower back while working. Further, it does not facilitate stress-free movement around the work area, leading, in turn, to possible further injury. 
     The present invention seeks to mitigate the long-term risks of acute and chronic pain and arthritis associated with occupations requiring prolonged durations of kneeling, while improving job comfort and performance for workers in such occupations. This apparatus will lead to decreased immediate and long term disability claims and will lead to increased productivity, which is an investment for both labor and management. 
     SUMMARY OF THE INVENTION 
     The foregoing and further needs are satisfied by embodiments of the invention. 
     In some embodiments, the invention comprises a cart with pivotably-mounted shin supports. In other embodiments, the invention comprises a cart with casters and pivotably-mounted shin supports. In some embodiments of the invention the shin supports are capable of flexing to allow the proximal or knee ends to contact the ground or work surface. 
     In some embodiment, the user is able to reposition the cart on the work surface by alternately weighting and unweighting the proximal or knee ends of the shin supports and moving the shin supports in the direction of desired motion. 
     In other embodiments of the invention, the shin supports are secured to a rear base member of the cart with torsion mountings. In some embodiments, the torsion mountings allow the user to move the cart in a forward or reverse motion by alternately weighting and unweighting the proximal or knee ends of the shin supports while moving their legs in the direction of desired travel. 
     In some embodiments, the invention comprises a cart back support adjustable for height and position. 
     In other embodiments, the invention comprises a cart comprising pivoting casters that allow close approach to a work area. 
     In still other embodiments, the casters are replaced with stationary feet. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1 . Isometric view of an embodiment of the cart 
         FIG. 2 . Side view of an embodiment of the cart 
         FIG. 3 . Rear view of an embodiment of the cart 
         FIG. 4A . Detailed view of an embodiment for a shin support and mounting 
         FIG. 4B . Detailed view of an embodiment for a self-adjusting shin support 
         FIG. 5A . Side view of an embodiment for adjusting the height of the back support member 
         FIG. 5B . Cutaway view showing an embodiment for the back support height adjustment mechanism 
         FIG. 6 . A folded embodiment of the cart 
         FIG. 7 . Another folded embodiment of the cart 
         FIG. 8 . An embodiment for swiveling caster mounts 
         FIG. 9A . Exploded isometric view of an embodiment of the cart with torsion mounting of the shin supports 
         FIG. 9B . Bottom view of an embodiment of the cart with torsion mounting of the shin supports 
         FIG. 10A . Underside view of an embodiment of the cart enabling movement of the torsion mounts along an arc-shaped path 
         FIG. 10B . Detailed view of arc-shaped slot in an embodiment of the cart enabling movement of the torsion mounts along an arc-shaped path 
         FIG. 10C . Cross-sectional view of an embodiment of the cart enabling movement of the torsion mounts along an arc-shaped path 
         FIG. 11A . Underside view of an alternative embodiment of the cart with low profile using roller casters 
         FIG. 11B . Cross-sectional view of roller caster embodiment 
         FIG. 12A . Exploded isometric view of cart with an alternate embodiment for adjusting the back support member 
         FIG. 12B . Exploded isometric view of an alternate embodiment for back support adjustment mechanism 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows an isometric view of an embodiment of the cart. In some embodiments the cart comprises a basic frame comprising a rear base member  130  with casters  101  and  102  attached to the proximal and distal ends, respectively, and a central base member  140  attached perpendicularly to the rear base member  130  at the central portion of the rear base member  130 . As is well known in the art, casters comprise wheels, a frame and axle to hold the wheel, and a mounting pin to facilitate swivel motion. The central base member  140  has a front caster  100  at the proximal end. A back support member  150  is attached to the central portion of the central base member  140  and extends in a substantially vertical direction therefrom. The back support member  150  further comprises a padded back support element  160  attached thereto. There are two shin supports  110  and  120  pivotably mounted on the rear base member  130 . The back support member  150  may be hingeably attached to the central base member  140 . The hinge  170  allows the height of the back support element  160  to be adjusted as explained below and shown in  FIG. 5 . The hinge  170  may be further configured to allow the back support member  150  to fold forward, as shown in  FIG. 6 , facilitating transport and storage of the cart. An optional clamp  180  may be installed on the central base member  140  to hold the back support member  150  in place for storage. Alternatively, a pin to may be used in place of clamp  180  to fasten the back support member  150  in place for storage. 
     The base members  130  and  140  as well as the back support member  150  may be constructed of any durable material with sufficient strength to support a worker, including, but not limited to, solid or tubular metals, solid or tubular plastics, carbon fiber composites, or even wood or wood composite materials. These elements may be square, round, rectangular, or any cross-sectional shape that promotes adequate structural strength. The elements described may be produced separately and joined together. Alternatively, the base members may be injection molded or produced as a single unit. 
     The casters assemblies—comprising front caster assembly  100 , right-side caster assembly  101 , and left-side caster assembly  102 —are preferably fully pivoting casters with wheels made of a material appropriate for the surface on which the cart is to be used. Alternatively, a roller caster such that shown and described in  FIG. 11C  can be used for the front caster assembly  100 , the right-side caster assembly  101 , and the left-side caster assembly  102 . Suitable and desirable wheel materials may include rubber, polyurethane or other plastics, and polymeric materials such as fluoropolymers, acetal copolymers, Teflon®, Delrin®, and the like. The caster assemblies may be mounted for easy removal and replacement as needed due to wear or the desire to install a caster of a different size or material. 
     The proximal and distal ends of the rear base member  130  as well as the proximal end of the central base member  140  are preferably configured in an arcuate shape, rising in a vertical direction above the wheels or casters. An arcuate shape allows wheels or casters of nearly any size to be attached while maintaining a distance between the bottom of the shin supports  110  and  120  and the ground or work surface so as to allow the grip soles  124  on the under sides of, and at the proximal ends of shin supports  110  and  120  to contact the ground when a user&#39;s weight is applied to the knee region of the shin support. When a grip sole  124  on the proximal end of one or both shin supports  110  and  120  touches the ground, the cart is stabilized in position for working or pivoting from one position to another. 
     In some embodiments of the invention, the arcuate sections of the rear base member  130  and central base member  140  may be removable and replaceable to allow use of the base assembly with casters of different diameters by attaching sections with a greater or lesser arc diameter. This is accomplished by creating separable segments at the proximal and distal ends of the rear base member  130  and at the proximal end of the central base member  140 . 
       FIG. 2  shows the side view of an embodiment of the invention.  FIG. 2  shows, in particular, the front caster assembly  100  and the right caster assembly  101 . Each of the caster assemblies  100 ,  101 , and  102  may be mounted through holes in the central base member  140  and rear base member  130 . The holes may extend completely through the base members with the casters held in place by retaining rings, shown in the figure as  200  and  201 . External snap rings, or other mounting approaches such as threaded stem, welded, and flange-mounted with nuts and bolts may also be used. Alternatively, the caster mountings may be contained completely inside the respective base members. In some embodiments, a roller caster can be located in the central base member and held captive by a retainer, such as that show and described in  FIG. 11C . In still other embodiments, the casters may be replaced by feet mounted in the same positions, resulting in a cart that does not move yet still provides the same ergonomic stress relief for workers performing tasks in a kneeling position. The feet can be made from plastic, rubber or metal and can be mounted in place of the casters or directly at the ends of the arcuate portions of the base members. 
     In some embodiments, a kit containing a plurality of arcuate base member sections, casters of various sizes and materials, and feet for a variety of work surfaces is provided with or without a basic base frame comprising the rear base member  130 , the central base member  140  and the back support member  150  with a back support  160 . The kit may also include replacement back support members  160  of the same or alternate sizes and materials. 
     The back support  160  may be mounted in a fixed position or adjustably mounted to the back support member  150 . The position of the back support  160  may be adjusted along the back support member  150  by the back support adjustment  162 . This is further illustrated in  FIG. 5 . In other embodiments, the back support  160  maybe shaped ergonomically and may further comprise padding made from materials with appropriate shape and durometer to support even distribution of the user&#39;s mass. These materials may include, but are not limited to, silicones, rubbers, and polymeric foams. 
       FIG. 3  shows a rear view of an embodiment of the invention. The shin supports  110  and  120  are pivotably mounted on the rear base member  130 . The mounting interface may be made using externally bonded collars and mountings or internally to the rear base member  130  with holes in the rear base member  130 . While  FIG. 3  shows one mounting assembly for each shin support,  210  and  220  respectively, one of skill in the art will readily recognize that multiple mounting assemblies and mounting positions can be made along the rear base member  130  to accommodate users with various statures, and larger or smaller body sizes. 
     In some embodiments, the invention comprises a cart with a plurality of mounting assemblies for shin supports. 
       FIG. 4A  shows an exploded view of a single shin support assembly  400 .  FIG. 4A  also shows a shin support mounting assembly  500 . In some embodiments, the invention comprises a cart with two shin support assemblies. 
     A shin support assembly comprises a shin support  121 , optional padding  122 , a grip sole  124 . In some embodiments the shin support further comprises a grip sole mounting  125 . In other embodiments, the grip sole  124  is directly attached to the shin support  121 . In other embodiments, the grip sole  124  is an integral part of the shin support  121 . 
     One of skill in the art will no readily recognize that the shin support  121  may have varying geometry capable of supporting different users. Each shin support assembly  400  may further comprise padding  122  made from materials with appropriate shape and durometer to support even distribution of the user&#39;s mass. These materials may include, but are not limited to, silicones, rubbers, and polymeric foams. 
     A shin support assembly  400  further comprises a mounting assembly  500 , an exploded view shown in  FIG. 4A . Mounting of each shin support assembly  400  may be accomplished with mounting assembly  500  comprising a mounting rod, or pin,  123  affixed to the shin support  121 , a collar  211  externally connected to the rear base member  130 , and bushing  212  inserted in the collar. Alternatively, the bushing  212  may be mounted internal to the rear base member  130 , eliminating the need for the external collar  211 , or with a reinforcing collar inserted internally to the rear base member  130 . The mounting assembly  500  for the shin supports, whether internal or external to the rear base member  130 , allows the user to independently move each leg as needed and to contact the grip sole  124  on the under side of, and at the proximal end of each shin support assembly  400  with the work surface, floor, or ground as needed to stabilize the position of the cart or move from one location to another. The bushing  212  is preferably a T-bushing, however other bushing configurations may be employed. The bushing  212  can be made of rubber or other material sufficiently rigid to form an interference fit with the mounting rod  123  but with sufficient flexibility to allow the bushing  212  to compress when the user&#39;s weight is applied and to flex forward slightly to allow the grip sole  124  on the proximal end of a shin support assembly  400  to touch the ground when weight is applied to the knee region. 
     In some embodiments, the shin support mounting assembly  500  can be configured and installed within an arc-shaped slot as shown and described in  FIG. 10 . 
     The grip soles  124  may be made from materials such as polytetrafluoroethylene (also known as PTFE or Teflon®), rubber, or other plastics or materials appropriate to avoid marring work surface finishes. The grip soles  124  are preferably replaceable for wear or for use on a different work surface. 
     In some embodiments, the grip sole  124  is mounted in a grip sole mount  125  to allow rotation about its axis. This rotation allows the user to pivot the cart on the contact point of the grip sole  124  with the work surface, and makes it easier to move about the work area. 
     The right-side shin support  110  and left-side shin support  120 , collectively referred to as shin supports, are configured to individually cradle the legs of the user from just above the foot up to the knee region of the leg. A user, kneeling in the cart, will rest his or her lower back against the back support  160 . In doing so, the forces and stresses otherwise directed fully to the ankles and knees of a person kneeling on a hard surface or with kneepads, become distributed evenly along the nearly horizontal shinbone. When the user wishes to move the cart across the work area, he or she simply alternates weighting and unweighting of the knees, which in turn weights and unweights the proximal end of the shin supports, and moves their legs in the direction they wish to go. Contacting the grip soles mounted on the proximal ends of the shin supports  110  and  120  with the ground serves to stop movement and stabilize the cart in position for working. 
     In some embodiments of the invention, the shin supports assemblies  400  are not pivotably mounted. They are fixed in position and the user employs other means for moving about the work area, such as pushing the cart by hand. These embodiments still provide the user with the stress-relief benefits of the cart. 
     Each shin support  121  in a shin support assembly  400  can be made from a variety of materials, including but not limited to, molded plastics, composites, carbon fiber material, or shaped metal so as to form a cradle for the shin portion of the users&#39; legs. Additionally, the shin support  121  may be made in various geometries to specifically accommodate users of various sizes and statures. In some embodiments, padding is added to the shin supports to further cushion and relieve stress that may be exerted on the user&#39;s legs, ankles, and knees. In still other embodiments, the padding is removable for replacement for wear or for accommodating a different user. 
       FIG. 4B  shows another embodiment for the design and construction of a shin support  121  and the optional shin support padding  122 , respectively depicted as  121   b  and  122   a . The embodiments depicted in  FIG. 4B  are formed to be self-adjusting to the users shin. In these embodiments, the application of force by the users shin causes the sides of the shin support to contract or expand, there by adjusting more closely to the shape of the shin. The expansion or contraction function is accomplished by the scalloped design of the sidewalls of the support as shown in  FIG. 4B . This feature provides further comfort and thus stress relief. The self-forming shin supports may be incorporated into any of the embodiments disclosed herein. Materials such as metal or resilient plastics may be formed in the manner shown in  FIG. 4B . 
       FIG. 5A  shows an embodiment of the back support member  150 . A plurality of adjustment holes  151  serve as adjustment points for the height of the back support. One of skill in the art will readily realize that any number of holes, more or less than the three holes shown, may be employed to accommodate construction of carts of various sizes.  FIG. 5B  is a cross-sectional view of an embodiment an adjustment mechanism. A leaf spring  320  is configured with detents alignment pins  325  and  326  on each end. The detents alignment pins  325  and  326  engage with holes  151  as appropriate to adjust the height of the back support member  150 . A height adjusting element  330  rests between the leaf spring  320  and the rear base member  130 . Adjusting the leaf spring  320  changes the position of the height adjusting element  330  and causes the height of the back support member  150  to change as it pivots on the hinge  170 . One of skill in the art will readily recognize that other mechanisms may be employed to adjust the angle and height of the back support member  150 . Other methods known in the art that may be used to adjust the height of the back support member  150  include jackscrews, scissor hinge, and external adjustment pins, interlocking splines, ratcheting gear teeth, and the like. 
     In some embodiments of the invention, the back support member  150  is adjustable. In other embodiments, the back support member is in a fixed position. 
     In some embodiments the position of the back support  160  may be adjusted up or down to further accommodate users of varying size and stature. A variety of height adjustment mechanisms are possible, including a leaf spring and detent assembly similar to that shown for adjusting the position of the back support member  150 . Other mechanisms are known in the art such as quick pinning, set screws, and adjustable clamps. 
     In some embodiments, the back support  160  may be mounted to allow pivoting in the vertical direction about the adjustment point. In still other embodiments, the back support is configured to pivot in the horizontal direction, or in both the vertical and horizontal directions. 
       FIG. 6  shows an embodiment of the invention wherein the hinge assembly  170  allows the back support member  150  to be folded completely forward. This embodiment allows for easy carrying or storage of the cart. Any number of clamping mechanisms known in the art may be employed to retain the back support member  150  to the central base member  140 . 
       FIG. 7  depicts yet another embodiment of the cart wherein the rear base member  130  is constructed to fold when not in use. In some embodiments, a rear member hinge assembly  170  comprises detent holes  712  and  718  and rear base member pivots  714  and  716 . Spring-loaded detents  720  and  722  are arranged to engage and disengage with the detent holes  712  and  718  to allow the rear base member  130  to lock into an open position or fold closed as shown in  FIG. 7 . 
     In another embodiment of the invention the spring-loaded detents are replaced with removable pins or screws that protrude through the holes  714  and  720  on one side and through the holes  718  and  722  on the other side. One of skill in the art will readily appreciate other hinging and locking mechanisms known in the art to allow opening and closing of the rear base member  130 . 
       FIG. 8  shows an embodiment for the caster assemblies  101 ,  102 , and optionally  100  wherein the overall horizontal profile, or footprint, of the cart may be controlled or reduced. In some embodiments the casters  801  pivot away from the work area thus making it possible for the user to move closer to the work area. A swivel joint  810  is placed at the proximal and distal ends of the rear base member  130  before the arcuate section previously described. The motion of the swivel joint  810  is limited by a guide pin  815  that is held in place by a roll pin  805 . Roll pin  805  limits the travel of the guide pin  815 . Guide pin  815  can be retracted to allow the caster mounting arm  802  to rotate about it axis in guide slot  820  until engaging the pocket shoulders  822  of the swivel joint  810 . In some embodiments the guide pin  815  is fully inserted and penetrating thru both walls of the swivel joint  810  into two or more fixed positions  824 , to fix the caster swivel arm  802  in a fully open position or a fully closed position. The fully open position provides the cart with a larger footprint and the fully closed position reduces to footprint of the cart. One of skill in the art will now appreciate that additional fixed positions may be added to enable additional fixed caster positions and a number of fixed footprints for the cart. The caster mounting arm may be held in place by a flat head fastener  830  and a thrust washer  825 . Alternative mechanisms to the guide pin  815  include, but are not limited to, roll pins, screws, shoulder bolts. 
       FIGS. 9A and 9B  show an exploded isometric view and a bottom view, respectively, of yet another embodiment of the invention. In this embodiment, the shin support assemblies  400  are mounted to a rear base member  910  by torsion rods  920  secured in torsion-producing mounting joints. The torsion-producing mounting joints comprise a square torsion collar  925  on the end of the torsion rod  920 , a square rubber mounting collar  930  positioned in a mounting position  915  on the rear base member  910 . In some embodiments, the torsion collar and mounting collar are square. In other embodiments, the torsion collar and mounting collar are rectangular, and in still other embodiments, the torsion collar and mounting collar are any polygonal shape. 
     The rear base member is preferentially made from a rectangular tube or channel, however other shapes may be used, such as the cylindrical shape previously described. The rear base member may contain a plurality of mounting positions  915  as needed to accommodate users of various sizes and statures. The torsion producing joints may be retained in place by any of a number of fastening techniques to allow for secure but repositionable connections, including a screw and washer  950 . Caster assemblies as previously described may be used in this embodiment. The central base member  905  and the caster assemblies  940  may also be made as previously described. Alternatively, the rear and central base members may be injection molded or produced as a single unit. 
     In use, torsion is created by the torsion collar  925  as it twists in the square rubber mounting collar  930  positioned in the rear base member in mounting position  915 . Forward motion of the unweighted shin support produces torsion in the joint on the opposite side. When the user shifts his or her weight to the opposite shin support, the torsion causes the newly unweighted side of the cart to move in a forward direction, thus allowing the user to engage in a forward walking-like motion by alternately unweighting, advancing, and weighting the shin supports. 
     In some embodiments, the shin supports are pivotably mounted to the torsion rods as previously described. In other embodiments the shin supports are fixed in position on the torsion rods. 
     One of skill in the art will readily see other mechanisms to produce the torsion needed to move the cart as described. 
       FIGS. 10A, 10B, and 10C  show an embodiment with a unitized rear and central base member  955 . Such a portion may be made by injection molding of plastic or other polymeric materials or by cutting the shape from metal or other sufficiently strong material.  FIGS. 10A, 10B, and 10C  further depict an embodiment wherein the shin support assemblies  400  are mounted to a combined rear and central base member  955 . Slots in the base member allow each shin support to travel along an arc-shaped path at the distal end. The arc-shaped travel can be facilitated using methods such as T-bushing rollers  952  installed in arc-shaped guide slots contained in the base member as shown in  FIG. 10A . A thrust washer  954  and a T-roller bushing  952  are held captive, using an external snap ring  953  or similar fastening methodology. In use, the thrust washers and T-roller bushings rotate, guided by the arc-shaped slot in the base member. 
       FIG. 11A  shows yet another embodiment with a unitized rear and central base member  980 .  FIG. 11A  illustrates the underside view of the base member  980  and one of the three casters indicated as  981 .  FIG. 11B  illustrates a roller caster  981  held in place with a retaining ring  983 . Roller casters can advantageously provide a lower profile for the cart and allow the user to get closer to the work area. 
       FIGS. 12A and 12B  illustrate an alternative embodiment for adjusting the height of the back support member using a ratcheting mechanism. Seat arm  1006  engages with seat foot  1004  with mating gears or teeth. Adjustments may be made when the user applies a downward force to the seat foot  1004 . The downward force causes the seat foot  1004  to pivot on spacers  1001  compressing compression springs  1002  that are located in the seat foot pockets  1008 . The compressed springs allow separation of the matting gears in both the seat arm  1006  and the seat foot  1004  allowing the user to adjust the position of the back support member. The spacers  1001  ensure the guide rollers  1007  and the seat foot  1004  are free floating between the end caps  1000 . This allows the seat foot  1004  to travel smoothly along the seat arm  1006 . Solid rivets  1010  may be used to hold the seat foot adjustment mechanism together. A tab on torsion spring  1003  can be snapped onto the seat arm  1006  using “P slots” as shown. The torsion spring  1003  helps ensure that the seat adjustment foot  1004  does not drag on the surface of the floor when the user is in motion on the cart. One of skill in the art will now readily recognize other means to adjust the seat height and keep the seat foot from engaging work surface. 
     One of skill in the art will appreciate a variety of modifications that fall within the scope of these descriptions and claims. Further, one of skill in the art will appreciate that the various elements of the embodiments described herein may be interchanged to form other embodiments that fall within the scope of the invention.