Abstract:
Afoot sanding disc includes a hub; a concentric abrasive disc having a diameter smaller than the hub diameter. A shaft concentrically attached to the bottom surface of the hub has a free end and a central cavity of a determined shape extending from the free end to a determined depth into the shaft. The shaft is shaped, sized and configured to matingly receive within the cavity a portion of a mandrel attached to an output shaft of a motorized rotary tool, thereby operably coupling the disc to an output shaft of the motarized rotary tool. A circular recess concentrically formed in a top surface of the hub receives the abrasive disc. The abrasive disc is devoid of a central aperture. The hub may include a thermochromic material in a concentration effective to cause a change in color when the hub reaches a predetermined temperature. The hub may also be rigid or flexible.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention generally relates to a pedicure device, and more particularly, to a foot sanding disc with a flat abrasive surface, smooth periphery, and slip-on shaft that facilitates manual installation on a motorized rotary tool.  
       BACKGROUND  
       [0002]     During a pedicure, calluses and dry, flaky skin are abraded or scraped from the bottom of the feet. Typically, the feet are soaked in a warm bath. Once the warm water has softened the skin on the feet, the bottoms of the feet are scrubbed with a pedicure sander  110  comprised of an abrasive sanding pad attached to a durable plastic handle, a callus rasp  120 , a pumice stone  130 , and/or a similar abrasive article, as shown in  FIG. 1 . Additionally, some technicians will use a corn and callus plane  140  comprised of a stainless steel head with a raised shaving blade to slice thick, tough callus from the feet.  
         [0003]     Unfortunately, pedicures performed using such conventional instruments are strenuous, tedious tasks. A technician performing the pedicure must maintain a hunched position while exerting appreciable force in performing a repetitive sanding motion for several minutes. In the course of a workday, a technician may require several breaks to recover from fatigue. Over the long term, the repetitive strain leads to a high rate of attrition as well as costly workplace related injuries such as carpal tunnel syndrome.  
         [0004]     Additionally, some of the conventional instruments present hazards. In particular, a callus plane may cause serious injury if used improperly.  
         [0005]     To reduce the risks and deleterious effects of the manual process, several rotary and belt sanders have been devised for grooming feet. While such known devices obviate a repetitive sanding motion and reduce the risk of severe injury, they suffer certain shortcomings. For example, the known disc-shaped sanding elements of such devices are recessed slightly, reducing the effectiveness of abrasion. Additionally, the sanding elements of such devices are often difficult and time consuming to replace. Furthermore, the sanding elements of such devices are not suitable for use on conventional rotary machines. Instead, they must be used on proprietary motorized devices.  
         [0006]     Concomitantly, sanding elements for conventional motorized sanding tools are not well suited for pedicures. Such sanding elements typically require tools for installation and removal, making these tasks inconvenient. Additionally, disc-shaped sanding elements typically have an exposed screw head for fastening the disc to a pad, which poses a serious risk of injury to sensitive feet. Furthermore, many disc-shaped sanding elements have exposed peripheries, which may cut into and seriously injure feet.  
         [0007]     The invention is directed to overcoming one or more of the problems and solving one or more of the needs as set forth above.  
       SUMMARY OF THE INVENTION  
       [0008]     To solve one or more of the problems set forth above, in an exemplary implementation of the invention, a foot sanding disc is provided. The foot sanding disc includes a hub having a top surface, a bottom surface, and a hub diameter; an abrasive disc having a disc diameter smaller than the hub diameter, the abrasive disc being concentrically mounted to the top surface of the hub; and a shaft concentrically attached to the bottom surface of the hub, the shaft having a free end and a central cavity of a determined shape extending from the free end to a determined depth into the shaft, the shaft being configured to matingly receive within the cavity a portion of a mandrel attached to an output shaft of a motorized rotary tool, thereby operably coupling the disc to an output shaft of the motarized rotary tool. The central cavity has a cross sectional shape (e.g., circular, oval, elliptical, triangular, square, pentagonal or octagonal) and size compatible with the mandrel, and may include a roughened surface or a tapered configuration.  
         [0009]     In another aspect of the invention, a circular recess concentrically formed in the top surface of the hub is configured to concentrically receive the abrasive disc. The abrasive disc has a determined disc thickness, and the circular recess has a depth approximately the same as or slightly less than the disc thickness. The circular recess has a planar surface for engaging the abrasive disc, and the abrasive disc is either bonded to the planar surface or integrally formed on the planar surface. The abrasive disc is devoid of a central aperture.  
         [0010]     In yet another aspect of the invention, the hub and shaft are comprised of polyvinyl chloride (PVC), polyethylene, polypropylene, polystyrene, acrylics, cellulosics, acrylonitrile-butadiene-styrene terpolymers, urethanes, thermo-plastic resins, thermo-plastic elastomers (TPE), acetal resins, polyamides, polycarbonates and/or polyesters. The hub may also include a thermochromic material in a concentration effective to cause a change in color when the hub reaches a predetermined temperature. The hub may be rigid or flexible. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The foregoing and other aspects, objects, features and advantages of the invention will become better understood with reference to the following description, appended claims, and accompanying drawings, where:  
         [0012]      FIG. 1  conceptually illustrates prior art pedicure devices to illustrate principles of the invention; and  
         [0013]      FIG. 2  provides a top perspective view of an exemplary foot sanding disc with an abrasive disc in accordance with principles of the invention; and  
         [0014]      FIG. 2A  provides a top perspective view of an exemplary foot sanding disc without an abrasive disc in accordance with principles of the invention; and  
         [0015]      FIG. 3  provides a bottom view of an exemplary foot sanding disc in accordance with principles of the invention; and  
         [0016]      FIG. 4  provides a side view of an exemplary foot sanding disc in accordance with principles of the invention; and  
         [0017]      FIG. 5  provides another side view of an exemplary foot sanding disc in accordance with principles of the invention; and  
         [0018]      FIG. 6  provides a detail view of encircled portion B-B from  FIG. 4  in accordance with principles of the invention; and  
         [0019]      FIG. 7  provides a bottom perspective view of an exemplary foot sanding disc in accordance with principles of the invention; and  
         [0020]      FIG. 8  provides a side view of an exemplary mandrel for use with a foot sanding disc in accordance with principles of the invention; and  
         [0021]      FIGS. 9A through 9D  conceptually illustrate dimensioned views of an exemplary foot sanding disc in accordance with principles of the invention. 
     
    
       [0022]     Those skilled in the art will appreciate that  FIGS. 1 through 8  are not intended to be drawn to any particular scale; the invention is not limited to the dimensions or proportions shown in  FIGS. 9A through 9D ; and the Figures are not intended to illustrate every embodiment of the invention. The invention is not limited to the exemplary embodiments depicted in the Figures or the shapes, relative sizes, ornamental aspects, dimensions or proportions shown in the Figures.  
       DETAILED DESCRIPTION  
       [0023]     In an exemplary implementation of the invention, a foot sanding disc according to principles of the invention includes a flat abrasive sanding surface, smooth periphery and slip-on shaft for manual attachment to a rotary tool without the need for special tools. Referring now to  FIG. 2 , a top perspective view of an exemplary foot sanding disc in accordance with principles of the invention is shown. A disc-shaped hub  210  supports a concentric abrasive disc  250 . The hub  210  includes a top surface  212  upon which the abrasive disc  250  is mounted, and a bottom surface  208  from which a shaft  230  stems.  
         [0024]     The diameter of the hub  210  is larger than the diameter of the concentric abrasive disc  250 . Thus, the periphery of the abrasive disc  250  does not extend beyond the periphery of the hub  210 . This reduces the risk of cutting injuries caused by exposed edges of the abrasive disc  250 . By way of example and not limitation, the hub  210  may have a diameter of approximately 1.55 inches, while the concentric abrasive disc may have a diameter of approximately 1.45 inches, as conceptually shown in  FIGS. 9A-9D .  
         [0025]     As shown in  FIGS. 2A and 4  through  6 , a circular recess  255  is concentrically formed in the top surface  212  of the hub  210  to receive the concentric abrasive disc  250 . The diameter of the circular recess  255  is slightly larger than the diameter of the concentric abrasive disc  250 . The depth of circular recess  255  is the same as or slightly less than the thickness of the concentric abrasive disc  250 . Thus, the periphery of the abrasive disc  250  does not extend beyond the periphery of the circular recess  255 . By way of example and not limitation, the circular recess may have a diameter of approximately 1.46 inches, while the concentric abrasive disc may have a diameter of approximately 1.45 inches. The depth of the circular recess may be approximately 0.01 to 0.05 inches, while the thickness of the concentric abrasive disc may be approximately 0.01 to 0.05 inches. The abrasive surface of the concentric abrasive disc  250  is exposed and level with or slightly above the top surface of the hub  210  to facilitate abrasive contact with calluses and dry, flaky skin.  
         [0026]     The concentric abrasive disc  250  is preferably comprised of a substrate, such as paper or fabric, coated with an abrasive material such as a silica, garnet, silicon carbide, or aluminum oxide, suitable for smoothing and polishing. The disc  250  is devoid of a central aperture. The grit of the abrasive face could be calibrated based on the foot surface to be sanded and the type of finish desired. The disc may have a very fine, fine, medium, coarse, or very coarse abrasive surface grit.  
         [0027]     In an alternative implementation, the concentric abrasive disc  250  may be integrally formed with the foot sanding disc. In such an embodiment, abrasive material such as a silica, garnet, silicon carbide, or aluminum oxide, may be bonded directly to the surface of the circular recess  255 , with the abrasive surface being approximately level with or slightly above the top surface  212  of the hub  210  to facilitate abrasive contact with calluses and dry, flaky skin.  
         [0028]     The circular recess  255  of the top surface of the hub  210  has a planar surface  257  for engaging the abrasive disc. The concentric abrasive disc  250  is preferably bonded to the planar surface  257  of the circular recess  255  of the top surface of the hub  210 . A layer of glue, adhesive, or other bonding agent may be disposed over substantially the entire side of the concentric abrasive disc  250  which will contact the circular recess  255  of the top surface of the hub  210 . Thus, the concentric abrasive disc  250  can be affixed to the hub  210  without use of a screw or other mechanical fastener that may interfere with a pedicure or harm feet.  
         [0029]     As shown in  FIGS. 3 through 7 , the bottom surface  208  of the hub  210  may optionally include a recessed area  220  or may be flat or feature some other configuration. Advantageously, a recessed area conserves material and reduces overall weight. Advantageously, a lightweight hub requires less rotational force to spin and reduces the weight borne by the technician, thereby reducing worker fatigue. Finally, thinner hubs require less material to produce, and are inherently less expensive. Strengthening ribs and similar structures may be added to a thin hub, to the extent necessary to maintain structural integrity.  
         [0030]     Referring now to  FIGS. 3, 4 ,  5  and  7 , the shaft  230  of the foot sanding disc has free end  232  with a cavity  240  of a determined interior depth and an inner circumference that is configured to matingly receive the distal end  820  of a mandrel  800 , as described below. The cavity  240  may include a roughened surface (i.e., textured cavity surfaces with a high coefficient of friction) and/or a tapered configuration to frictionally engage the mandrel. While the cavity  240  shown in  FIGS. 3-5 ,  7  and  8  is generally circular in cross section, other shapes may be used provided that they are compatible with the shape of the mandrel  800 . For example, the cavity  240  may be keyed (i.e., shaped) to securely engage the mandrel  800  without slippage during rotation. By way of example and not limitation, a cavity with an oval, elliptical, triangular, square, pentagonal or octagonal cross section may be used to securely engage a mandrel with an oval, elliptical, triangular, square, pentagonal or octagonal cross section, respectively.  
         [0031]     Advantageously, the shaft  230  enables manual installation and removal of the foot sanding disc without any tools. A user may manually slide the shaft  230  of the foot sanding disc onto and off of a mandrel  800  coupled to a rotary tool. Such installation and removal requires relatively little effort and time to accomplish.  
         [0032]     An exemplary mandrel  800  as conceptually illustrated in  FIG. 8 , includes a distal end  820 , a flange  815  and a proximal end  810 . The distal end  820  includes a cross-sectional shape that is compatible with the cavity  240  of the shaft  230 . The proximal end  810  is configured (i.e., sized and shaped) for coupling to a conventional rotary hand tool equipped with a collet and a collet nut, which are coupled to the output shaft of the rotary tool. The flange  815 , which is optional, provides a backstop and a structure for distributing stress along the free end of shaft  230 . By way of example and not limitation, the proximal end  810  may feature a generally circular cross section. Likewise, the distal end  820  is configured (i.e., sized and shaped) to securely fit within the cavity  240  of the shaft  230 . Various shapes may be used for the distal end  820 , provided that the shape is compatible with the cavity  240  of the shaft  230 . For example, the distal end  820  may be keyed (i.e., shaped) to securely engage the cavity  240  of the shaft  230  without slippage during rotation. By way of example and not limitation, a distal end  820  with a square, pentagonal or octagonal cross section may be used to securely engage a cavity  240  of a shaft  230  with a square, pentagonal or octagonal cross section, respectively. The mandrel may be comprised of any materials suitable for drill bits and the like, such as metals, alloys and composites.  
         [0033]     The hub  210  and shaft  230  are preferably comprised of a rigid plastic or polymeric material, such as polyvinyl chloride (PVC), polyethylene, polypropylene, polystyrene, acrylics, cellulosics, acrylonitrile-butadiene-styrene terpolymers, urethanes, thermo-plastic resins, thermo-plastic elastomers (TPE), acetal resins, polyamides, polycarbonates and polyesters. While many other materials may be used alone or in combination with the aforementioned materials and/or other materials, without departing from the scope of the present invention, preferably the material is relatively inexpensive and durable, easy to use in manufacturing operations and results in an aesthetically acceptable product. The material may further include additives to provide desired properties such as desired colors, structural characteristics, glow-in-the dark properties and thermal reactivity (e.g., color changes according to heat).  
         [0034]     By way of example and not limitation, the hub  210  and shaft  230  may optionally be formulated to change color when they reach a predetermined or higher temperature. High temperatures attained during extended periods of use may serve as a safety indicator. This can be accomplished by mixing a thermochromic additive to the base material in an amount that is sufficient to achieve a desired color changing range. As an example, a mixture of approximately 10% to 25% (pbw) of Matsui Interantional Co., Inc.&#39;s Chromicolor® concentrate may be introduced to the base material, to provide a plastic structure that visibly changes color at a determined elevated temperature, such as approximately 105, 110 or 120 degrees Fahrenheit. A color change will alert a technician to the possibility of excessive friction and risk of possible injury.  
         [0035]     The hub  210  is preferably sufficiently strong and heat resistant such that the hub does not structurally fail from the stresses and heat generated during use. Within these parameters, the hub  210  may be either rigid or somewhat flexible. Illustratively, certain embodiments of the invention may utilize a hub that is formulated to exhibit flexibility and resiliency such that the hub can conform somewhat to the contours of a foot and return to its original shape without appreciable permanent deformation during normal use.  
         [0036]     The hub  210  and shaft  230  may be produced using any suitable manufacturing techniques known in the art for the chosen material, such as (for example) injection, compression, structural foam, blow, or transfer molding; polyurethane foam processing techniques; vacuum forming; and casting. Preferably the manufacturing technique is suitable for mass production at relatively low cost per unit, and results in an aesthetically acceptable product with a consistent acceptable quality.  
         [0037]     In use, the foot sanding disc is operably coupled to a rotary hand tool. The rotary hand tool contains a motor with a rotary output shaft. The mandrel  800  is mounted to the rotary hand tool by a collet and a collet nut, which are coupled to the output shaft of the rotary tool. The shaft  230  of the foot sanding disc has a cavity of a determined interior depth and an inner circumference that is configured to matingly receive the distal end  820  of the mandrel  800 . Rotation of the output shat of the rotary tool induces a rotation of the mandrel  800 , which induces a rotation of shaft  230 , which induces rotation of the hub  210  and the attached abrasive disc  250 , thereby allowing sanding of a foot by applying the abrasive face of the disc  250  thereto.  
         [0038]     For illustrative purposes,  FIGS. 9A through 9D  conceptually illustrate dimensioned views of a preferred foot sanding disc in accordance with principles of the invention. Those skilled in the art will appreciate that the invention is not limited to the dimensions or proportions shown in  FIGS. 9A through 9D , and that the Figures are not intended to illustrate every embodiment of the invention.  
         [0039]     While the invention has been described in terms of various embodiments, implementations and examples, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the appended claims including equivalents thereof. The foregoing is not intended to limit the invention to the exact construction and operation shown and described. Alternative embodiments of the invention, including variations in size, materials, components, shape, form, function, manner of operation, assembly and use that are obvious to one skilled in the art are intended to be encompassed by the invention. Accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.