Abstract:
A ski exercising machine has a set of at least two parallel rails joined to cross members at the ends, the cross members providing support on a horizontal support surface, and joined to a central frame structure extending from the horizontal surface near the center to the rails, the rails extending from each cross member at each end upward at an acute angle with the horizontal rising to a maximum height in the center. A wheeled carriage rides on the rails, and there is at least one articulated footpad mounted to the wheeled carriage. A first power band having two ends, anchored at both ends by a clamp to a bottom surface of the frame structure beneath the wheeled carriage, passes over first rollers fixed to the cross members, and is anchored to the wheeled carriage, such that the power band is extended and exerts a restraining force toward the center of the machine as the wheeled carriage translates on the rails to either side of center. The set of rails is characterized in that the rails have a central arcuate portion and straight portions extending from each cross member to the central arcuate portion. In preferred embodiments there may be two articulated footpads, and footpads of different sorts are provided as modular assemblies for quick changing. Various rail structures are taught, including structures having keeper apparatus for the wheeled carriage.

Description:
CROSS-REFERENCE TO RELATED DOCUMENTS 
     This application is related in part to U.S. Pat. No. 5,147,257 issued on Sep. 15, 1992 and filed on Sep. 4, 1990, which is a divisional of U.S. Pat. No. 4,953,853 issued on Sep. 4, 1990 and filed on Apr. 6, 1988, which is a continuation-in-part of U.S. Pat. No. 4,743,014 issued on May 10, 1998 and filed on Jul. 30, 1987. This application is also related to U.S. Pat. No. 5,020,793 issued on Jun. 4, 1991 filed on Oct. 24, 1989, which is also a continuation-in-part of U.S. Pat. No. 4,743,014. The related patents are included herein in their entirety by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to exercising apparatus for a user to simulate the motions, exertions and techniques involved in skiing, thereby increasing the user&#39;s strength and skill, and more particularly to improvements in such apparatus. 
     BACKGROUND OF THE INVENTION 
     Apparatus for use by skiers on which they may simulate the motions, exertions and techniques required in skiing has been built and sold for several years. In particular U.S. Pat. No. 3,524,641 was issued to Robert J. Ossenkop on Aug. 18, 1970, for a device comprising a movable carriage on a set of rails. The carriage of that device is constrained in its movement on the rails by flexible members attached to both the carriage and to transverse members between the rails near each end of the set of rails, and a user can move the carriage from side to side on the rails to simulate the Wedeln or “parallel” technique of skiing. 
     U.S. Pat. No. 3,547,434 was issued to the same inventor on Dec. 15, 1970. This later patent is for a device similar to the first device, but comprising a number of improvements, such as movable footrests on the carriage whereby a user may simulate turning and edging techniques in addition to parallel skiing; and, in some embodiments may also move the feet relative to one another. 
     The inventions referenced above each include a safety strap attached to a transverse member between the parallel rails and to the carriage on the rails in addition to the flexible member by which the carriage is constrained to travel on the rails. The purpose of the safety strap is to provide for a situation in which the aforementioned flexible member might rupture on one side of the carriage, providing a sudden force urging the carriage to the side where the flexible member remains unruptured, which sudden force could dislodge a user and perhaps cause serious injury. The safety strap in such instance provides a restoring force toward the center tending to lessen the amplitude of carriage displacement that might otherwise occur. 
     In U.S. Pat. No. 4,743,014, to which this case is related, and by the same inventor, an exerciser is disclosed having a pair of spaced-apart rails, a platform for riding on the rails, a first resilient element providing a first restoring force on the platform, and a second resilient element providing a second restoring force on the platform. The second resilient element has an adjustment element contacting the second resilient element in at least three points. 
     In the latter exerciser, the rails are held in a spaced-apart relationship by a brace element in the center, which is fastened to the rails by screw-type fasteners, and by transverse elements fastened at the ends of the rails. The transverse elements at the ends are tubular in form, and the rails pass through openings in the tubular transverse elements, fastening to a bracket internal to each tubular transverse element. This joining arrangement is illustrated by FIGS. 1A and 1B of the referenced patent. As shown in these figures rails  301  and  303  pass through holes  305  and  307  respectively into tubular transverse element  309 . Inside, the rails are fastened to a bracket  311  by screw fasteners  313  and  315 . Rubber-like end caps  317  and  319  close the ends of the tubular transverse element after assembly and act as non-skid pads in contact with the floor in operation. The end caps are of molded rubber-like material, and disk-like pieces carrying designs and lettering are added for identification and aesthetic effect. This particular method of joining and spacing the rails has not proved entirely satisfactory in terms of cost and ease of assembly, and in terms of strength and rigidity of assembly, and the multiple-piece construction of the end caps has also proved to be relatively expensive. 
     Although related U.S. patents issued to the inventor address the above problem and other problems related to construction and function of various components of the parent ski exerciser, there are. still non-obvious improvements desired in several areas related to construction or assembly techniques, profile, materials, and longevity of the apparatus. For example, in U.S. Pat. No. 5,147,257 (hereinafter &#39;257), in FIGS. 5A and 5B, a ski exerciser is illustrated both in an elevation view (FIG.  5 A), and in a plan view (overhead FIG.  5 B). Arcuate rails  15  comprise tubing structures having a continuous arc or bow over their entire length. 
     It has been discovered through empirical method that an even better action may be simulated with rails shaped somewhat differently than in the prior art. Firstly, the tubing material used in rails  15  can be changed to exhibit even more strength than previously. Secondly, the inventor has discovered that other shapes for the rails than fully arcuate provide better skiing feel than the fully arcuate rails in the referenced prior patents. 
     FIG. 5A in &#39;257 illustrates roller assemblies housing rollers such as rollers  25  and  27  which are identical in size and construction with other illustrated rollers which make rolling contact with resilient members  23  and  59 . The diameter of the aforementioned rollers is disclosed as approximately 1 inch, and the rollers are generally cylindrical. It has been discovered that larger rollers, also crowned have a beneficial effect in smoother power band operation. The crowned rollers keep the belts better centered on the rollers. 
     The present inventor has also determined that improvements may be made in the positioning of wheels for the wheeled carriage, and in the form of the rails and how the wheels interface to the rails. 
     What is clearly needed is a modularly enhanced ski-excising device that provides further distinct advantages for the expanding field of users. Such a device could be manufactured with fewer assembly parts, retain a lightweight characteristic, provide additional stability and rigidity, and require less work for a user to assemble and operate, as well as providing for a more realistic workout. 
     SUMMARY OF THE INVENTION 
     In a preferred embodiment of the present invention a ski exercising machine is provided, comprising a set of at least two parallel rails joined to cross members at the ends, the cross members providing support on a horizontal support surface, and joined to a central frame structure extending from the horizontal surface near the center to the rails, the rails extending from each cross member at each end upward at an acute angle with the horizontal rising to a maximum height in the center; a wheeled carriage riding on the rails; at least one articulated footpad mounted to the wheeled carriage; and a first power band having two ends, anchored at both ends by a clamp to a bottom surface of the frame structure beneath the wheeled carriage, passing over first rollers fixed to the cross members, and anchored to the wheeled carriage, such that the power band is extended and exerts a restraining force toward the center of the machine as the wheeled carriage translates on the rails to either side of center. The set of rails is characterized in that the rails have a central arcuate portion and straight portions extending from each cross member to the central arcuate portion. 
     In some embodiments the cross members are spaced apart more than 48 inches, and the arcuate portion extends for at least one third of the overall length. Also in some embodiments there are two articulated footpads mounted to the wheeled carriage, each footpad having a contact surface for a user&#39;s foot and pivoted to rotate about an axis orthogonal to the direction of the rails, the axis below the level of the contact surface. In some embodiments footpads mount to an upper tray assembly adapted to removably fasten to the wheeled carriage, forming thereby a quick-change module. 
     In a preferred embodiment the first power band is clamped to an undersurface of the wheeled carriage at two positions, one each at each end of the wheeled carriage, such that the first power band lies flat along the width of the wheeled carriage under the wheeled carriage. Also in a preferred embodiment the cross members at the ends are welded to the rails and the rails are welded to the central frame structure, and the bottom surface of the central frame structure is joined by welding to the cross members on each end by power band guides, the power band guides, the cross members, and the bottom surface of the central frame structure all lying parallel to and adjacent the horizontal surface. The first rollers fixed to the cross members are positioned such that the first power band anchored at the ends to the clamp at the bottom surface of the frame structure lies in the power band guides to each side of the central structure, passing under and over the rollers to the wheeled carriage, the power band guides acting as protective members preventing the first power band from contacting the horizontal support surface. 
     In most embodiments there is a second power band within the first power band, the second power band having ends both fastened at the clamp holding the ends of the first power band above the ends of the first power band, the second power band extending to second rollers rotatably mounted to a structure welded to the bottom surface of the central frame structure to each side of center, the second power band passing under and over the second rollers back toward center, and over a third roller rotatably mounted under the wheeled carriage. The third roller is mounted spaced apart from the first power band clamped to the undersurface of the wheeled carriage by about twice the thickness of the power band, such that the second power band passing over the roller contacts both the roller and the first power band. 
     In some embodiments the wheeled carriage has weight-bearing wheels positioned to ride on upper surfaces of the rails and keeper wheels opposite individual ones of the weight-bearing wheels, the keeper wheels contacting undersurfaces of the rails, such that the wheeled carriage so equipped is positively retained on the rails. Also in some embodiments two articulated footpad assemblies each comprises a foot contact area having front and back upward extensions pivotally joined to frame elements above the footpad area, forming swing-cradle footpads. In a special embodiment the two swing-cradle footpad assemblies each mount slidably by an interface to the upper tray, the interface including a lock-unlock mechanism whereby the footpad assemblies may be unlocked, adjusted in position on the upper tray, and relocked, so the center distance between the footpads may be readily adjusted. 
     The two articulated footpads may be joined by at least one link, such that the footpads are constrained to rotate together about their respective axes, and the footpads have a home position wherein the footpads are each canted inward, the degree of cant determined by the length of the link. In some cases the link is adjustable, such that the degree of cant at the home position may be adjusted. 
     In yet another embodiment there is a snowboard footpad simulating a snowboard mounted on an interchangeable upper tray assembly, the snowboard footpad being rotatable about an axis orthogonal to the direction of the rails, and having a length in the direction of the axis significantly more than the width of the wheeled carriage riding on the rails, and extending beyond the wheeled carriage on both sides. The snowboard footpad has a surface for a user&#39;s feet, and the axis for pivoting is above the level of the surface for the user&#39;s feet. 
     In several embodiments the rails are extruded each having a groove in an upward facing surface, and the wheeled carriage includes wheels that ride within the groove in the upward-facing surface. In some other embodiments there is also a groove in a downward-facing surface of each rail, and the wheeled carriage includes wheels engaging both the upward-facing and downward-facing grooves. In yet other embodiments each rail has a “C” cross-section comprising internally an upper, downward-facing track and a lower, upward-facing track, and wherein the wheeled carriage has two or more wheels guiding on the upper track and two or more wheels guiding on the lower track. 
     In yet another embodiment of the invention a ski exercising machine is provided, comprising a set of at least two parallel rails joined to cross members at the ends, the cross members providing support on a horizontal support surface, and joined to a central frame structure extending from the horizontal surface near the center to the rails, the rails extending from each cross member at each end upward at an acute angle with the horizontal rising to a maximum height in the center; a wheeled carriage riding on the rails; at least one articulated footpad mounted to the wheeled carriage; and a set of three power bands each anchored at both ends by a clamp to a bottom surface of the frame structure beneath the wheeled carriage, passing over separate roller sets, with one or more of the power bands anchored to the wheeled carriage and one or more passing over a roller anchored to the wheeled carriage. 
     In the many embodiments of the present invention significant improvements are provided over ski-exercise machines known in the art, the improvements making such equipment more durable, less expensive to build, and providing even more realistic operation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES 
     FIG. 1A is an elevation view of a frame structure of a ski-exercising device according to an embodiment of the present invention. 
     FIG. 1B is a cross section taken along line  1 B— 1 B of FIG.  1 A. 
     FIG. 2 is a plan view of the frame structure of FIG. 1 with added components illustrated according to an embodiment of the present invention. 
     FIG. 3 is a perspective view of a center portion of the structure of FIG. 1 with covering components removed. 
     FIG. 4 is a perspective view of a wheeled carriage-assembly shown without an upper carriage according to an embodiment of the present invention. 
     FIG. 5 is a perspective view of an upper carriage-assembly supporting a suspended footpad mounted according to an embodiment of the present invention. 
     FIG. 6 is an elevation view of a wheeled carriage-assembly and mounted foot platforms according to an embodiment of the present invention. 
     FIG. 7A is perspective broken-view of a portion of a rail, transverse end member, and end-cap according to an embodiment of the present invention. 
     FIG. 7B is an elevation view of an end-side of the end cap of FIG.  7 A. 
     FIG. 7C is an elevation view of a bottom-side of the end cap of FIG.  7 B. 
     FIG. 8 is a perspective view illustrating various components of a quick-release roller assembly according to an embodiment of the present invention. 
     FIG. 9A is a plan view of an elongated footpad and carriage-assembly according to an embodiment of the present invention. 
     FIG. 9B is an elevation view of the footpad and carriage assembly FIG.  9 A. 
     FIG. 10 is an elevation view of the frame structure of FIG. 1 illustrating roller-band tensioning hardware according to an embodiment of the present invention. 
     FIG. 11A is a broken view of a potion of toothed rails and a toothed gear of FIG. 10 according to an embodiment of the present invention. 
     FIG. 11B is an elevation view of the handle assembly of FIG.  10 . 
     FIG. 11C is an elevation view of the rail-guide bracket of FIG.  10 . 
     FIG. 11D is a right-side view of the bracket of FIG.  11 C. 
     FIG. 11E is a broken view of a portion of the bottom toothed-rail, roller, and bracketed roller-mount of FIG.  10 . 
     FIG. 11F is a broken view of the bottom toothed-rail, roller, and bracketed roller-mount of FIG. 10 as seen from an overhead vantage. 
     FIG. 12 is a perspective view of an adjustable double footpad module according to an embodiment of the preset invention. 
     FIG. 13A is a plan view and FIG. 13B is a side view of a slotted base-plate according to an embodiment of the present invention. 
     FIG. 13C is an end-view of the slotted cam-rod of FIG.  12 . 
     FIG. 14 is a cross-sectional view of a main wheel, a keeper wheel, and a semi-arcuate rail according to an alternate embodiment of the present invention. 
     FIG. 15 is a cross section of an integral captive rail and wheel arrangement in an embodiment of the present invention. 
     FIG. 16 is an elevation view of a ski-exercising device illustrating an optional third power band according to another embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     It is the object of the present invention to provide a ski exercising apparatus similar to that apparatus covered in cross-related documents above, that is modularly enhanced such that, among other improvements, changing applications on the apparatus may be performed with minimal effort. It is also an object of the present invention that the above apparatus be generally and innovatively improved to accomplish a goal of maintaining a lightweight while increasing strength and durability of the apparatus. A further object of the present invention is to provide such an apparatus as described above having a lower profile, improved safety features, and having fewer assembly parts with which to contend. Such a ski-exercising apparatus is described in enabling detail below. 
     FIG. 1 is an elevation view of a frame structure  11  of a ski-exercising apparatus  9  according to an embodiment of the present invention. Apparatus  9  is provided having a generally similar frame-architecture to previously described exercisers disclosed in related U.S. patents issued to the inventor except for novel improvements that are described below. For the purpose of clarification, only a frame structure  11  of apparatus  9  is described in this embodiment. Additional components not seen here are described later in this specification. 
     In a preferred embodiment of the present invention, frame structure  11  comprises a pair of semi-arcuate rails  22  that are held parallel to each other and are affixed at either end of each rail to a pair of transverse end-members  27 . As this is an elevation view, only one of the pair of rails is seen. The spacing and parallelism is seen in plan view FIG.  2 . This arrangement of rails  22  affixed to members  27  forms the basic frame-structure  11  of apparatus  9 . One notable difference between semi-arcuate rails  22  and the fully arcuate rails disclosed in related patents such as rails 15 of U.S. Pat. No. 5,147,257, is as the respective descriptors imply. That is, as in FIG. 1A, rails  22  are arced only in their center portions  23  and illustrated by a dimensional notation E. The dimension lines associated with portion  23  mark the locations where the arced portion of each rail  22  ends at positions sharing an equal distance from a theoretical vertical center of rails  22 . 
     The total distance E in a preferred embodiment is approximately 26 inches, defined as that portion of each rail  22  that is arced. The stated arc of arcuate portion  23  has a radius of approximately 76 inches although a slightly higher or lower radius may be used in other embodiments. Non-arcuate portions of rails  22  are witnessed by element numbers  19  and  21  on the left and right side of apparatus  9  as seen in this view. The lengths (taken horizontally) for rail portions  19  and  21  are approximately 15 inches respectively. Rail portions  19  and  21  are substantially straight from their junctures with arcuate portion  23 . The dimensions cited above are intended to be approximate only. When including an approximate 2.36-inch (6 cm) diameter for each transverse member  27 , the approximate overall length of frame structure  11  is about 61 inches. Semi-arcuate rails  22  may be manufactured from heavy-gauge steel tubing as described in U.S. Pat. No. 5,147,257. In one embodiment, rails  22  may be made of extruded steel or aluminum bars rather than steel tubing, and rails may be solid or hollow in different embodiments. Such rails may often also be formed in a forming die to manufacture tracks. 
     Solid aluminum bars may in some circumstances offer more strength than steel tubing in terms of flexing or bending while retaining a lightweight characteristic. Moreover, such bars may be extruded to comply with varied shapes as may be desired, and may also be produced in hollow configurations. In this particular embodiment, rails  22  are solid and round in cross-section (rods). The semi-arcuate design and solid structure of rails  22  adds considerable strength and durability causing less flex when rails are in use. It is not specifically required that rails  22  be of round cross-section in order to practice the present invention. The inventor intends merely that keeping a round cross-section consistent with previously used steel tubing is consistent with conventional wheels used on wheeled-carriage assemblies such as carriage 11 described in U.S. Pat. No. 5,147,257. 
     In another embodiment, rails  22  may be extruded and then die-formed to a shape that may conform to an alternate wheel design. Such an embodiment is described later in this specification. The size of rails  22  is approximately 2.5 cm. (1-inch) in diameter as is consistent with previous related embodiments. However, this should not be construed as a limitation in diameter but only a preference in balancing durability with lightweight characteristics. Other diameters for rails  22  are plausible. Transverse members used in an embodiment where rails are aluminum will also be made of aluminum tubing to facilitate welding. However, where rails are steel tubing or rods, transverse members will typically be manufactured from steel tubing. A durable polymer coating is applied to all visible parts and surfaces of apparatus  9  in order to provide a resistance to corrosion and for appearance purposes. 
     The straight portions of rails  22  to each side of arcuate portion  23  provide a carriage movement in operation that more nearly simulates an actual skiing-experience, as has been testified to by users of the apparatus. 
     In a preferred embodiment of the present invention, rails  22  are welded to transverse members  27  to form a one-piece truss-frame insuring long life and durability along with ease of assembly of associated elements. However, many fastening methods are known and practiced in the art and could also be used to affix rails  22  to transverse members  27 . The frame structure  11  of apparatus  9  also comprises belt guides  24  located in a substantially centered and parallel position in-between rails  22  and welded, at opposite ends, to transverse members  27  and to a support frame member  31  supporting the rails in the centered arcuate portion. Belt guides  24  allow a power band such as element 23 of FIG. 5A of &#39;257 to be separated from the floor or carpet during operation, thus contributing to longer life and sparing wear and discoloration of the floor or carpet. A belt guide of the type disclosed herein has not been previously taught. A pair of raised ribs  26  running the length of belt guides  24  on each side of member  31  are provided and adapted to allow a power band to avoid contact with the bottom of belt guide  24  further reducing wear and noise. 
     Support member  31  is provided for the purpose of lending additional support to the frame structure  11  of apparatus  9 , and for housing mechanisms associated with operation of the exerciser. A structure of the same name is illustrated in FIG. 5A (element 55) of &#39;257 and member  31  is analogous to that member, but improved in function. For example, support member  31  as illustrated herein, is longer in length than the aforementioned member 55 thereby supporting more area of rails  22 . Support member  31  may be provided as one piece or as a plurality of components welded together such that one single piece is formed. Support member  31  is made wider than previously disclosed support members such that it may be welded in some embodiments to the outside edges of rails  22  instead of having rail-inserted tabs as described with member 55 of FIG. 5A in &#39;257. Welding support member  31  to the outside edges of rails  22  increases the strength and durability of frame structure  11 , and allows further improvements described more fully below. 
     Support member  31  is further welded to belt guides  24  as previously described, effectively adding these components to frame structure  11  so as to form a single contiguous and integral frame, thereby lending strength, durability, and eliminating assembly requirements. Also welded to support member  31  is a tension-adjustment structure  25 . Structure  25  in this embodiment is a u-shaped structure welded to the bottom of member  31  such that two vertical planes are presented, one on each side of the power band path, with holes for positioning rollers for adjustment of power band tension. The length of structure  25  is such that it extends beyond each side of member  31 , as shown, and guides  24  weld to structure  25 . In this manner structure  25  becomes a part of the overall welded structure  11  adding durable strength to the structure as a whole. Additionally, two roller brackets  34  are illustrated, housing rollers  35  in this embodiment, and these are also welded to transverse members  27  and to belt guide  24 , and are part of frame structure  11  of apparatus  9 . Much assembly is avoided and much durability and strength is added by providing a multi-component but single piece welded frame architecture for apparatus  9  as will readily be appreciated by one with skill in the art. 
     A protective resilient, non-skid pad  29  is provided and mounted in a position beneath support member  31 . Pad  29  may be affixed to support member  31  by gluing, fastening such as by recessed screws, or other known methods. The purpose of pad  29  is to protect floor coverings from contact with support member  31  so as to avoid scratching and the like, as well as to keep apparatus  9  from skidding when in use. This pad also provides service in reducing vibration and noise. Four resilient end-caps  17  are provided to cover the ends of transverse members  27 . End-caps  17  provide non-skid contacts between apparatus  9  and a floor or other support surface. 
     Another component illustrated in this embodiment is an optional support frame  14  for a novice user to hold on to for stabilization while using apparatus  9 . Support frame  14 , termed an Assistant Coach by the inventor, comprises a tubing structure  16 , a cross member  13 , and padded gripping areas  15 . Tubing structure  16  may be a one-piece tube bent to form structure  16 , or a combination of straight and curved pieces, which are provided and assembled to form structure  16 . Steel or another form of durable tubing of an approximate 1-inch diameter may be used. Other sizes are also useful. 
     Gripping areas  15  (one on each side) may be formed of a durable synthetic material such as a dense polyurethane foam, vinyl, or other materials known for providing a gripping surface to tube handles and the like that are common in the field of exercise equipment. In one embodiment, gripping areas  15  may be removed such as by conventional methods known in the art. In another embodiment, gripping areas  15  are permanent such as sprayed on or glued. Cross member  13  may be manufactured from a durable plastic or other material such as sheet steel or aluminum. Cross member  13  may in some embodiments be welded to tube structure  16 . In other embodiments, other known fastening techniques such as nut and bolt, or metal screws may be used. There are many possibilities. 
     Support frame  14  is welded or fastened to two transverse members similar to members  27  but not seen here because of the direction of view (see FIG. 2 element  49 ). Such members act as an optional extension to transverse members  27  at the rear of apparatus  9 . By removing resilient end-caps  17  from the rear or front of apparatus  9 , support structure  14  may be connected to the transverse members  27  of frame structure  11 . In some embodiments an additional interface and support element is added between elements  11  and  27 . 
     FIG. 2 is a plan view of the frame structure  11  of apparatus  9  of FIG. 1 with added components illustrated according to an embodiment of the present invention. As previously described, support frame  14  is an optional extension to frame structure  11  of apparatus  9 . A user wishing to install support frame  14  simply removes two end caps  17  from the rear of frame structure  11  and connects the support frame. The point of connection for the two structures is illustrated as line  51  at either end of device  9 . 
     Transverse members  49  each have a fitting end  52  that is of a smaller diameter over a suitable length than the inside diameter of transverse members  27 . The diameter is small enough so that transverse members  49  may be easily fit into transverse members  27  such that when fully inserted lines  51  are formed representing the joining of each structure. Circular shims (not shown) that are once split through along a longitudinal edge of each shim are used to obtain a snug fit between transverse members  27  and  49 . Such shimming methods are well known in the art. Setscrews (not shown) or other known types of fasteners may be used to secure the installation. 
     As seen in this overhead view, power band guides  24  extend from each end of the structure (members  27 ) toward the center and are welded at opposite ends to structure  25 , which in turn welds to member  31  (FIG.  1 A). Roller brackets  34  are welded to transverse members  27  and to belt guide  24  as previously described above. Two rollers  47  and  45  are illustrated as mounted to tensioning structure  25 . Rollers  47  and  48  are provided and adapted to support a central power band  46 . Likewise, a power band  43  is supported by rollers  35  and  37 . An additional roller (not shown) is provided for further support of power band  46  and is centered in-line and in-between rollers  47  and  45  at a raised position such that a triangular configuration of the three rollers is formed. Power bands  43  and  46  are manufactured of a proprietary rubber compound or similar material as described in U.S. Pat. No. 5,147,257. Aforementioned rollers such as rollers  35  and  37  are manufactured of polypropylene or similar material in a preferred embodiment. 
     Tension-adjustment structure  25  acts as a rigid mounting location for rollers  47  and  45 . A plurality of openings provided in collinear arrangement through opposite-facing sides of structure  25  are used to mount rollers  47  and  45  via a quick-release pin-and-shaft mounting technique that is described in detail later in this specification. By removing and re-mounting rollers in different positions on structure  25 , tension adjustments to power band  46  may be affected. 
     A wheeled lower carriage assembly indicated as element  33  in FIG. 2, but best seen in FIG. 4, rides on rails  22 . This carriage is described in further detail below with reference to FIG.  4 . Foot platforms  39  and  41  are mounted to an upper platform unit  89 , which in turn mounts to the lower wheeled carriage assembly by fasteners  53 . The arrangement of an upper platform for footpads mounting as a unit to a lower wheeled carriage allows different footpad arrangements to be quickly and easily traded on a standard wheeled carriage. 
     Center fastener  54  is not used when installing and removing upper foot platforms, because it is a mounting fastener for a power-band roller beneath carriage  33 . A clearance hole is provided in the upper platform for this fastener. 
     Foot platforms  39  and  41 , in the arrangement shown, provide a parallel skiing simulation that is one option for mode of operation with apparatus  9 . By swapping upper platforms with different foot interface arrangements the overall apparatus can be quickly adapted to other applications, as will be clearer with following description. 
     In the embodiment shown, foot platforms  39  and  41  each have a footpad surface thereon. Footpad surface  38  is affixed to platform  39 , and footpad surface  42  is affixed to platform  41 . Footpad surfaces  38  and  42  are preferably made of a non-skid durable rubber material. Surfaces  38  and  42  may be installed using an adhesive, or other known methods such as screw fasteners or the like. Similarly, other materials may be used instead of rubber as long as a non-skid effect is maintained. 
     Rollers  35 ,  37 ,  47 ,  45 , and the previously described roller (not shown) that completes a triangular configuration with rollers  47  and  45  are now significantly larger in diameter than rollers previously disclosed in related applications. Whereas previously disclosed rollers were described as having about a 1-inch (2.5 cm) diameter, the rollers of the present invention have substantially a 2-inch (5 cm) diameter and are crowned. That is, the rollers are somewhat curved on the outer surface that meets the power band, so there is a marginally larger diameter at the center plane of the roller than at the roller edges. This improvement in design ensures that the power bands always remain centered on the rollers, which obviates contact with roller brackets and the like, reducing frictional wear to the power bands, and leads to smoother and quieter operation of apparatus  9 . 
     FIG. 3 is a perspective view of the center portion of frame structure  11  of FIG. 1 with covering components removed to show the elements beneath. As previously described, support member  31  is welded to rails  22 . In this example, a plurality of individual welds  55  is placed symmetrically along the length of support member  31 . There are three welds  55  shown in this example, however, there may be more or fewer such welds without departing from the spirit and scope of the present invention. In one embodiment, a continuous weld may run the entire length of support member  31 . Also in this example, welds  55  are illustrated as being placed from the outside edges (rear-edge welds not visible) of support member  31  to the outside of rails  22 . There are many possibilities regarding number of and location of welds  55 . 
     Tensioning structures  25 , as described with reference to FIGS. 1 and 2, are welded to belt guides  24  and to support member  31 . Brackets  25  are shown with rollers  47  and  45  mounted thereon. A suitable thickness for the material used to manufacture support member  31  and belt guide  24  is about 3 mm. or ⅛ of an inch. In one embodiment of the present invention, aircraft quality aluminum may replace sheet steel for such components where possible. Using high quality aluminum instead of materials such as steel cited in related applications helps to strengthen frame structure  11  as well as to reduce weight. 
     Yet another marked improvement over the prior art is in the method of clamping the ends of power bands. In related documents it is described that the central resilient element has it&#39;s ends clamped at one location while a second resilient element has its ends clamped at locations on either side of the central clamp. Therefore three clamping locations exist for securing the free ends of power bands. In this example, only one clamping location  57  is required. Clamp  57  secures both the ends of power band  43  and those of power band  46  of FIG.  2 . This method reduces work-steps required to install power bands. A single clamping location also ads considerable safety in that only one clamp must be checked for integrity therefore lessening the possibility of error in set-up. In this particular example, clamp  57  is a bar clamp utilizing two standard hex-head nuts and bolts to effect tightening. 
     FIG. 3 also illustrates the positioning of rollers  45  and  47  in structures  25 . The position of the rollers in this embodiment can be changed into any other of the holes in the sides of structures  25  to adjust the tension on the inner power band. 
     FIG. 4 is a perspective view of wheeled carriage-assembly  33  shown without an upper foot-platform  89  according to an embodiment of the present invention. As disclosed in related applications such as U.S. Pat. No. 5,147,257, for example, there are four main weight-bearing wheels that are mounted to the carriage body and adapted to make contact on the upper surfaces of rails  22  such that the carriage assembly may ride side-to-side on the rails as urged by a user. The wheels are approximately 2 cm wide and are machined using an ultra high molecular weight (UHMW) long-chain polymer material as described in U.S. Pat. No. 5,147,257. A standard button-head shoulder-bolt (not shown) forms the shaft of each wheel. Ball bearings, washers, a lock washer, and a castle nut complete the assembly components for mounting wheels to the carriage body as described in U.S. Pat. No. 5,147,257. 
     As in &#39;257, there are four main wheels that ride on upper surfaces of rails  22 . Two are visible in this embodiment and are represented by element numbers  67  and  68 . The remaining two main wheels are located toward the rear portion of carriage assembly  33  and are therefore hidden from view by carriage body  70 , and are not represented in FIG. 4 to avoid unnecessary detail. These main wheels are mounted rotationally to carriage body  70 . 
     Wheels  67  and  68  in a preferred embodiment are mounted at an approximate 12 degree angle from vertical with the angle toward the space in-between rails  22  such that they make contact with a more inwardly surface of each rail. The rolling surface of each wheel is concave such that the radius across the width of each wheel substantially matches the cross-sectional radius of rails  22 . Wheels  67  and  68  as well as two main wheels that are not visible here are mounted through provided openings strategically located on carriage body  70 . 
     In this embodiment, an additional set of four keeper wheels is provided of which two wheels  71  and  69  are visible in this view. Two other keeper wheels are located toward the rear of carriage assembly  33  and are hidden in this view by carriage body  70 . Components forming the shaft and mounting hardware for keeper-wheels  71  and  69  are the same as those already described for wheels  67  and  68 . 
     Keeper wheel  71  and  69  are strategically located beneath rails  22  at angled positions that are inverted from the angled positions of main wheels  67  and  68 , and directly below weight-bearing wheels. Two angled mounting brackets  75  and  73  are provided and adapted to secure keeper wheels  71  and  69  by being also mounted to upper wheels  67  and  68 . Wheels at the rear of carriage assembly  33  (not shown) are similarly secured as brackets  75  and  73  run the entire length of carriage assembly  33 , 
     In this embodiment brackets  73  and  75  are secured to the upper wheels and the lower wheels, so the lower keeper wheels are positioned by the upper wheels, which are mounted to the carriage body. In other embodiments brackets  73  and  75  may extend further upward and be fastened to the underside of the carriage, such as by rivets or welding. The brackets may, for example, be fastened by any convention joining means. Angled mounting-brackets  75  and  73  assume an inclusive angle of approximately 140 degrees such that each wing is substantially parallel to desired wheel positions when mounted. Ideally, carriage assembly  33  will remain resident on rails  22  when changing applications. This will allow for interchangeability of pre-assembled modules that are complete with selected foot platforms mounted. Upper platforms such as platform  89  of FIG. 2 may vary in physical appearance depending on the application; however, identical fastening locations allow interchangeability with carriage assemblies such as carriage assembly  33 . 
     There are yet additional improvements made to assembly  33  over the prior art. One such improvement is the provision of two clamping locations  63   a  and  65   a  located on the under-surface of carriage body  70  for the outer power band. A clamp bar  63  is illustrated as one of two such clamp bars that are used to secure resilient element  43 . A second clamp bar for clamping location  65   a  is not shown, but may be assumed to be present. Previous embodiments disclosed in related documents describe only one clamping location located directly beneath the center of the carriage assembly. An advantage of having power band  43  clamped in two locations is that noise caused by a resilient element flapping against the underside of the carriage body is eliminated, and the carriage is stabilized even further. 
     Roller  59  is a third roller previously described to form a triangular configuration of rollers to support power band  46  of FIG.  2 . Like all rollers described in this specification, roller  59  is crowned for the purpose of guiding resilient member  46  such that it remains centered on the rollers. 
     In this embodiment, roller  59  assumes a position much nearer in proximity to the underside of carriage body  70  than in the cross-referenced patents. This is due in part to the larger diameter (2 inch) attributed to rollers of the present invention as opposed to previously disclosed 1 inch diameter rollers in related documents. In addition, roller  59  is simply mounted in a position that is nearer the underside of carriage body  70  by means of a roller bracket  61 . This is done to reduce wear caused by resilient members rubbing and slapping against each other, and also, to reduce associated noise. The clearance is carefully designed as well so that, as the roller carriage moves to each side and back on the rails, the slack portion of the outer power band is carried to the side in the direction of carriage motion, which also reduces noise and sudden engagement. 
     It will be apparent to one with skill in the art that there are other possible wheel arrangements that may be used with carriage assembly  33  than the one illustrated herein without departing from the spirit and scope of the present invention. For example, the tilt angle of main and keeper wheels may be more or less than 20 degrees as mentioned in this embodiment. There may also be more or fewer main and or keeper wheels than is illustrated here. 
     In one embodiment, independent wheel pairs comprising one main wheel and an associated keeper wheel may be bracketed independently such that there are four independently movable wheel sets. 
     FIG. 5 is a perspective view of an upper platform assembly  90  supporting a suspended footpad  79  mounted to a carriage assembly  33  (wheels and brackets not shown) according to an embodiment of the present invention. 
     In this example, a single suspended footpad  79  is provided and adapted to be pivotally suspended over upper platform assembly  90 , termed a cradle in related U.S. Pat. No. 5,020,793, by means of two pivot points  85  and  87 . Each pivot point  85  and  87 , in a preferred embodiment, comprises a journal bearing, a spacer bushing, and a threaded stud with suitable lock washers and a nut fastener. There are equivalent ways known in the art to accomplish such a pivot. A suitable rubber cover is provided and adapted to fit over pivot points  85  and  87  to protect components from corrosion and general exposure. Pivot points  85  and  87  are arraigned in collinear fashion on opposite facing support wings represented by element number  81 . The pivots are fixedly mounted in vertical structures  83 , which are a part of the platform that mounts to carriage  33 . As described in U.S. Pat. No. 5,020,793, footpad  79  may swing freely about pivot points  85  and  87  as illustrated by double arcs that represent direction of swing. 
     The general application illustrated in this example is as stated in the aforementioned related document whereas a user places only one foot in footpad  79  after it is installed on apparatus  9  of FIG.  1 . By traversing back and forth over rails  22  of FIG. 1, he or she experiences a benefit of simulated edging. As the length of traversing approaches maximum length of rails  22 , footpad  79  pivots maximally about pivot ends  85  and  87 . 
     Also noted herein is a no-skid surface  93  provided in the same fashion as previously disclosed in FIG. 2 (elements  38  and  42 ). The fasteners for mounting the upper platform to carriage  33  are not seen in this view, but are the same as previously described for upper platforms in this disclosure. 
     According to a preferred embodiment of the present invention, footpad  79  with upper platform assembly  90  may be removed as one unit from and installed as one unit onto any wheeled carriage-assembly having suitable mounting locations. In this way, a carriage assembly such as assembly  33  of FIG. 2 may be kept resident on apparatus  9  of FIG. 2 with the loosening, removing, and re-tightening of only two hex-head nuts being required to change applications. This method reflects the modular nature of accessories such as footpad  79  mounted to upper platforms according to a preferred embodiment. Loosening and tightening bolts may be performed with the aid of a convenient T-handle socket tool (not shown) adapted to fit hex-head nuts  53 . In a preferred embodiment, all hex-head nuts subject to requirements of being removed and replaced due to the change of applications are the same size fitting the T-handle socket tool. 
     Carriage assembly  33  is shown in this example to illustrate orientation of footpad  79 . Carriage assembly  33  may be of a different overall length than assembly  33  of FIG.  2 . For example, a single footpad such as footpad  79  does not require a longer carriage assembly whereas a dual footpad installation would require a longer carriage assembly. In a preferred embodiment, carriage assembly  33  of FIG. 2 has a maximum length such that all modular accessories are supported. That is not to say, however, that a modular accessory cannot have it&#39;s own carriage of a different overall length. 
     Carriage assembly  33  of FIG. 2 would preferably remain resident on rails  22  of apparatus  9  (FIG. 2 ), especially if keeper wheels are used as previously described. However, in an alternate embodiment where keeper wheels are not used, the carriage assembly illustrated in this example may have main wheels installed and may be thought of as one module comprising assembly  33 , upper platform  90 , and footpad  79 . In this embodiment, a roller such as roller  59  of FIG. 4 may be shared between different applications. A quick release of roller  59  and removal of bar clamps such as clamp  63   a  of FIG. 4 will also allow removal and replacement of different modules. However, removing bar clamps entails much more effort on the part of a user. The added effort may be offset by the fact that different applications may require different tensioning adjustment with respect to a resilient member such as member  46  of FIG.  2 . 
     In addition to providing a single footpad in modular fashion as illustrated herein, in a further embodiment an upper platform is provided having two such single suspended footpads may be mounted in spaced-apart fashion. In yet another embodiment an upper platform assembly is provided wherein the spacing between suspended footpads is adjustable, and the adjustment apparatus is described further below with reference to FIG.  12 . Also, because of added keeper wheels such as wheels  69  and  71  of FIG. 4, retaining a wheeled carriage on rails  22 , footpad(s)  79  may be significantly extended in length without the risk of tipping carriage  33  off of rails when in use. 
     FIG. 6 is an elevation view of wheeled carriage-assembly  33 , upper platform  89 , and mounted foot platforms  39  and  41  of FIG. 2 according to an embodiment of the present invention. Part of the upper carriage walls are broken out in this figure for the purpose of enabling a view of inner components, and the bottom plate of upper platform  89  is therefore shown partially in cross-section. 
     As with previously disclosed embodiments described in related documents, footpads  39  and  41  are pivotally mounted to pivot supports  103  and  105  respectively. Supports  103  and  105  are part of the upper-platform assembly not removed in this example. There are four pivot supports such as supports  103  and  105  with the remaining two identical supports positioned directly behind and to the backside of assembly  33  and therefore not seen in this view. Pivot pins  102  and  111  form a pivotal connection between depended ears  109  and  110  and an identical set of depended ears (not shown) located at the backside of footpads  39  and  41  respectively. A section-view of this relationship is detailed and described in &#39;257 FIG. 6. Footpads  39  and  41  are die-cast in one embodiment to include the described depended ears. 
     A link-rod  115  is provided and attached to pivot points  104  and  113 . The above-described configuration including components is duplicated at the backside of the assembly. 
     The connected link-rod assembly enables footpads  39  and  41  to pivot in unison during operation of apparatus  9  of FIG.  2 . Resilient blocks  97  and  95  are provided as shock absorbers and are made of rubber or other suitable resilient materials. 
     Link-rod  115  is of a length such that when attatched to pivot points  104  and  113  with footpads  39  and  41  brought to their center-most position about pivot rods  102  and  111 , that each footpad is canted, in some embodiments, somewhat toward the center (canted positions not specifically shown). However, in other embodiments it is desired that footpads  39  and  41  may be adjusted to assume a more level profile to facilitate use by more experienced users. 
     There are two ways to accomplish this task. In one embodiment, a second set of link-rods (not shown) is provided of a shorter overall length than the set represented by link-rod  115 . By replacing link-rods  115  with the shorter rods, footpads  39  and  41  may be canted to a more level position. This, of course assumes that footpads  39  and  41  as used, in this embodiment, with link-rod  115  are canted in as described above. This method requires that four link-rods be provided with the modular footpad-assembly, two for the canted-in configuration, and two for the more level configuration. 
     In another embodiment link rods are provided that are themselves adjustable, so the effective length of the rods, and therefore the degree of cant of the footpads may be adjusted within certain limits. 
     FIG. 7A is perspective broken-view of a portion of a rail  22 , transverse end-member  27 , and end-cap  17  according to an embodiment of the present invention. In a preferred embodiment, rails  22  are welded to a location (W) above the longitudinal centerline of transverse end-members  27 . The higher location allows keeper wheels such as wheels  71  and  69  of FIG. 4 from coming in contact with the floor at maximally traversed locations on rails  22 . End-cap  17  now has a corrugated bottom for shock absorption as well as additional no-skid protection. 
     FIG. 7B is an elevation view of an end-side of end cap  17  of FIG.  7 A. End-cap  17  is molded of rubber-like material as described in previous embodiments. In order to improve over previous designs, a series of alternating raised portions  119  and grooves  117  are provided to form a corrugation feature extending across the bottom surface of cap  17 . As described above, this adds a no-skid enhancement and a shock absorption enhancement. 
     FIG. 7C is a plan view of a bottom-side of end cap  17  of FIG.  7 B. In addition to a corrugation formed by hills  119  and valleys  117 , a pattern containing a plurality of through openings is provided generally through the bottom surface of end cap  17  and extending into the inner space reserved for housing the circular end of transverse member  27  of FIG.  7 A. These openings are also illustrated in FIG. 7B as vertical dotted lines but are not described or witnessed. Openings  121  provide additional shock absorption capability. There are nine such openings in this example, however, it will be apparent to one with skill in the art that more or fewer openings  121  may be provided. Moreover, differing patterns may be used as well. 
     FIG. 8 is a perspective view illustrating components of a quick-release roller-assembly according to an embodiment of the present invention. As previously described in FIGS. 2 and 4 above, rollers supporting power bands such as roller  47  illustrated here, are crowned. Such a crowned area is labeled and illustrated by an accompanying witness arrow. A dimension C represents the diameter of roller  47  at the crowned area. It has been described above that a preferred diameter is 2-inches for rollers, which is assumed to be taken at the crowned area leaving the end diameters of each roller less than two inches in diameter. However, in some embodiments, the crowned area of a roller such as roller  47  may be larger than 2-inches. 
     A roller shaft or pin  123  is provided and adapted to be an axle for roller  47  between elements of structure  25  of which broken portions are represented here. Pin  123  has a spring-loaded detent  125  in one end and a pull ring  124  through a hole in the other end. Through-openings in elements  25 , each having a polymer bushing  127 , are provided to receive pin  123 . By placing a roller in position between brackets  25 , pin  123  may be placed through selected collinear bracket-holes with bushings  127  and roller  47 . Pin  123  is of sufficient length such that it protrudes past the outer surfaces of structure  25  on both sides, and when in place detent  125  prevents accidental withdrawal. The quick-release pins for rollers provide a means of quickly re-positioning rollers in structure  25  for tensioning adjustment. In an alternative embodiment later described, the rollers may be adjustably spaced even more simply using a dialed adjustment mechanism. 
     FIG. 9A is a plan view of an elongated footpad  133  and carriage-assembly  33  according to an embodiment of the present invention. A single footpad  133  is provided and adapted as a snowboard simulator presented as an option for apparatus  9  of FIG.  2 . Footpad  133  is pivotally mounted to an upper platform assembly  89  in much the same fashion as footpads  39  and  41  of FIG. 6 except that footpad  133  is centrally mounted and there is no link-rod assembly required. Carriage assembly  33  is also illustrated in this example to show orientation only. A non-slip surface  135 , preferably made of rubber-like material, is provided as in other embodiments previously described. Raised edges  131  are provided around the outer edges of footpad  133  for added protection from slipping. 
     A dimension L (length) is provided to be sufficient for allowing a user to place both feet on footpad  133  in positions similar to those used in snowboarding. A standard example would be standing sideways one foot spaced apart from the other about shoulder width. The exact dimension may vary according to application, however 25 inches should be sufficient for most users. A dimension W (width) is provided to be sufficient for covering the length of a users shoe or boot, about 15 inches. 
     In some embodiments not shown, there may be molded or otherwise formed positions to engage a user&#39;s feet, and fastening arrangements are also possible. 
     In another preferred embodiment of the invention the mounting of the single footpad for simulating operation of a snowboard is as shown for the footpads of FIG. 5, with the footpad suspended from pivots higher than the foot position. 
     The application presented here is only possible in an embodiment wherein keeper wheels are used such as wheel  71  and  69  of FIG.  4 . Footpad  133  and upper platform  89  is a modular accessory and may be easily mounted to carriage assembly  33  of FIG. 2 by removing two hex-head nuts  132 , placing the unit over carriage assembly  33  of FIG.  2  and then replacing and re-tightening the nuts. Clearance holes  134  are provided through footpad  133  to allow access for a T-handle socket-tool such as the one previously described in FIG.  5 . 
     FIG. 9B is an elevation view of mounted footpad  133  of FIG.  9 A. As described in previous embodiments, footpad  133  is die-cast. However, other suitable materials and forming methods may also be used. Depended ears  137  are provided at either end on the underside of footpad  133  for the purpose of accepting a pivot rod  141  through collinear and opposite facing openings. Pivot rod  141  also extends through collinear openings provided in support wings  142  arranged in similar opposite facing fashion as depended ears  137 . When mounted, pivot rod  141  extends through all four collinear openings in depended ears  137  and support wings  142 . Pivot rod  141  also extends through both walls of the upper platform assembly  89  of FIG. 9A (not shown). Pivot rod  141  may be secured to the above mentioned carriage walls by castle nuts or other types of fastening nuts (not shown) as described in U.S. Pat. No. 5,147,257. 
     In this example, there are no link-rods or other required hardware to direct rotation of footpad  141 . Rather, a resilient stop is provided and adapted to stabilize the rotation of footpad  133  while in use. Stop  139  is analogous to resilient blocks  97  and  95  of FIG. 6 in that it acts to impede and direct rotation. However, resilient stop  139  is provided as one piece rather than two pieces in this example. Stop  139  also extends the length of carriage assembly  89  such that maximum support is afforded. When not in use, footpad  133  rests against stop  139  in a centered and level position. 
     In one embodiment, stop  139  has two areas within it&#39;s molded architecture that are hollow or perhaps filled with a less dense material than rubber. These areas are shown here by dotted polygonal shapes. The respective areas lie, one beneath the left side of footpad  133 , and one beneath the right of footpad  133 . When footpad  133  is in use such as on apparatus  9  of FIG. 2, the areas within stop  139  are caused to collapse under pressure of a respective side of footpad  133  during normal rotation. For example, each time a user traverses to one side of apparatus  9 , the opposite-side area is caused to collapse. Several factors dictate the amount of collapse. These factors include a user&#39;s weight, speed of traverse, and any hard motions urged on footpad  133  by the user. Preferably, resilient stop  139  is manufactured to withstand sudden shock, and be strong enough to support a considerable stress without complete collapse. Advanced users may simulate back and forth movements experienced in snowboarding. 
     FIG. 10 is an elevation view of frame structure  11  of FIG. 1 illustrating an optional roller/band tensioning hardware  143  according to an embodiment of the present invention. According to this embodiment of the present invention, an optional apparatus and method is provided for tensioning a central power band such as band  46  of FIG.  2 . Instead of a quick-release method for rollers as described in FIG. 5, whereby rollers are removed and then re-mounted in different positions, structure  25  on each side now has an elongated slot  153  for enabling a mounted roller such as roller  45  to be loosened and slidably positioned. Each structure  25  has opposite slots  153  on either side of belt-guide  24  such that a pair of slots  153  may accept a roller assembly such as for rollers  45  and  47 . 
     Rollers  47  and  45  are, in this embodiment, held by an upper toothed-rail  145  for roller  45 , and a lower toothed-rail  147  for roller  47 , further illustrated in following FIG.  11 A. Bracketed roller mounts (not detailed) on the roller side of each toothed rail form a rigid connection between the roller shafts of respective rollers to respective toothed rails. Toothed rail  145  is rectangular in cross-section and has a plurality of gear-teeth (not shown) arraigned along it&#39;s length in the manner of a gear rack. In some embodiments a standard gear rack may be used. 
     When positioned properly, toothed rail  145  presents it&#39;s gear teeth in a downward direction or along it&#39;s bottom surface. Toothed rail  147  is identical to toothed rail  145  and they are, in fact, interchangeable. An inverse positional relationship exists with toothed rails  145  (top rail) and  147  (bottom rail) such that respective gear tracks will face each other. Toothed rails  145  and  147  are held parallel and in position by a rail guide  150 , as shown in FIG. 10 and 11C and D. Rail guide  150  has two rail-keepers installed thereon and adapted to hold toothed rails  145  and  147  in a parallel relationship and at the required distance apart. These are a rail keeper  149  positioned left of center, and a rail keeper  151  positioned right of center. The above-mentioned components of hardware  143  are manufactured of a durable material to provide wear resistance, for example, and there are several suitable materials for such applications. 
     A gear (pinion)  159 , as shown in FIGS. 11A and B, is provided and adapted to mesh with opposite-facing gear tracks as presented on toothed rails  145  and  147 . In this example, the gear is positioned directly behind of and forms a part of a gear-handle assembly  155 . Hardware  143  may be conveniently mounted to the inside front surface of U-shaped support member  31  with conventional fasteners as known in the art. A cutout opening  157  is provided through the front wall of U-shaped support structure  31  to enable user access to a gear-handle assembly  155  for the purpose of adjusting tension. In some embodiments there is an access door. 
     In operation, a user adjusts power band tension to a greater or lesser amount by turning gear-handle assembly  155  clockwise (more tension) or counterclockwise (less tension). When the desired tension is achieved, he or she then releases a spring-loaded handle, and the positions are maintained. It may be assumed, of course, that a power band such as band  46  of FIG. 2 is in place during this operation. An incremental scale is preferably provided as a stamped or otherwise marked convention on the front face of support member  31 , or along surfaces of the guides for the adjustment assembly. This will allow a user to return to known tension amounts without experimentation. 
     It will be apparent to one with skill in the art that a method for mounting hardware  143  to frame structure  11  may differ from the specific apparatus illustrated here without departing from the spirit and scope of the present invention. For example, U-shaped support member  31  may have a suitable slot running along its length for hardware  143  to fit into. There are other possibilities. 
     FIG. 11A is a broken view of a portion of toothed rails (racks)  145  and  147  and a toothed gear (pinion)  159  of FIG. 10 according to an embodiment of the present invention. Gear  159 , as previously described in FIG. 10, is positioned between and meshes with toothed rails  145  and  147 . 
     FIG. 11B is an elevation view of the handle assembly  155  of FIG. 10, and its integration with gear  159  and its mounting and operation. In this embodiment gear  159  is fixedly mounted to a shaft  173  that extends through opposite frame members  167  and  175  carried by bearings  177 . A serrated wheel  165  is slidably mounted to shaft  173  outside the area of gear  159  by a spline on the shaft and the wheel. Shaft  173  has an end  161  and a compression spring which urges wheel  165  toward frame member  167 . Pins  169  fit into matching holes in frame member  167 , urged by spring  165 . A user may grasp wheel  165 , pull it toward end  161  against spring  165 , whereby pins  169  are withdrawn from the matching holes in frame member  167 , and the wheel is free to turn the gear. By turning the gear in either direction the user can then move rollers  47  and  45  either closer together or further apart, thus adjusting the tension on the power band. When the user releases the wheel, the spring causes the pins to re-engage, and the rollers are then retained in the new positions. 
     It will be apparent to one with skill in the art that there are many other mechanisms that may be employed to create a spring-loaded engagement handle for gear  159  without departing from the spirit and scope of the present invention. Other handle functions and assembly requirements may differ from the example shown here. The inventor intends the above-described handle assembly to be only one example. 
     The skilled artisan will understand that supporting guide  150 , as shown in FIGS. 11C and 11D, and other supporting elements for the rack-and-pinion mechanism described above may be accomplished in a number of different ways, and is within the skill of engineering practitioners. Detailed description of this portion of the mechanism is therefore not undertaken here. 
     FIG. 11E is a broken view of a portion of lower rack  147 , roller  47 , and a bracketed roller-mount  187  of FIG.  10 . As previously described, a roller such as roller  47  is mounted to a rack such as rack  147  by means of a bracketed roller mount shown here as element  187 . Roller mount  187  is adapted to fit over the ends of a roller axle by virtue of a forked construction, similar in some respects to a mount for a paint roller, for example. 
     FIG. 11F is a plan view of the assembly of FIG.  11 E. As can be seen in this view, roller mount  187  is a simple forked bracket structure fastened to the end of rack  147 . Guide ends  188  are provided for guiding in slots of the rail guides  150  to constrain the translation direction in operation. In a preferred embodiment these guides are of a UHMW material for low-friction and for noise and vibration reduction. 
     FIG. 12 is a perspective view of an adjustable double-footpad upper module  195  according to a further embodiment of the present invention. This model is termed the Double Black Diamond model by the inventor. As previously noted in FIG. 5, a suspended footpad assembly such as footpad  79  may be double mounted in an adjustable manner. Two suspended footpads  79  are illustrated in this embodiment mounted in a locked position on an adjustable plate assembly  189 . Footpads  79  are similar in construction to footpad  79  of FIG. 5; hence they retain the same element number here. 
     Plate assembly  189  is an intermediary base that bolts on to a wheeled carriage such as carriage  33  of FIG.  4 . Plate  189  has two opposite facing edges that provide guide channels  193  and  194  for movable suspended footpad assemblies. Channel  193  on one side is best illustrated in FIG.  12 . Channel  193  is adapted to house a slotted cam-rod  191 , which is adapted to lock the movable footpad assemblies in place. 
     Cam-rod  191  has a plurality of slots  192  arranged in equally spaced and collinear fashion, and presented over the entire length of channel  193  along one side of the plate assembly. The purpose of slots  192  is to engage a plurality of equally spaced teeth provided on one edge each of two toothed base-plates (not shown here but illustrated below), one each affixed to the bottoms of footpad assemblies  79 . 
     A spring-loaded lever  197  is provided on one end of cam-rod  191  and is adapted to cause rotation of cam-rod  191  within channel  193  enabling slots  192  to be presented inward as shown or rotated back into channel  193  as directed by a user. Spring lever  197  in this embodiment fastens to channel  193  such that a wound spring engages a fixed location in the channel while the opposite end of the spring is retained by lever  197  creating a spring tension. There are several ways known in the art for a spring lever to be mounted such that a shaft or other part is put under spring tension. The spring-loaded arrangement provides for the cam rod to be always urged into the locked position for the footpad assemblies, so these assemblies may only be moved to adjust center distance under positive direction of the user. 
     By manually rotating spring lever  197  a user can unlock the footpad assemblies and manually move each to a new position as desired. In this way, footpads may be slidably inserted from either end of adjuster-plate  189 , as indicated by directional arrows, and adjusted to any desired spacing related to center distance. When desired positions are attained, letting go of spring lever  197  locks the footpads in place on plate assembly  189 . In one embodiment, a safety lock is provided to give added assurance that the footpad assemblies will stay in position during operation. Channel  194  on the opposite side is adapted to house non-toothed edges of the aforementioned toothed base-plates. 
     FIG. 13A is a plan view of a toothed base-plate  199  according to an embodiment of the present invention, and FIG. 13B is a side view of the base plate of FIG.  13 A. As previously described, footpads  79  of FIG. 12 each have a toothed base-plate  199  installed on the bottom surfaces of associated footpad assemblies  79  (FIG.  12 ). Each base-plate  199  has a row of equally spaced teeth  205  presented along one edge for the purpose of engaging slots  192  of FIG. 12 in cam  191 . In this embodiment, base-plate  199  has two spacer bars  201  and  203  adapted to space it from the underside of the outer frame member of a footpad assembly when mounted. 
     Bars  201  and  203  are, in this example, formed of one piece with base-plate  199 , however, in other embodiments, they may be separate mounted structures. There are four threaded holes  207  (two for each spacer bar) provided through base-plate  199  and spacer bars  201 , and  203  for mounting purposes. Machine screws or the like may be used for mounting plate  199  to the outer frame member of each footpad assembly. As seen in FIG. 13B, bolt holes  207  are chamfered on the side making contact with carriage assembly  33  such that they lay flat and may slide without scratching or marring the surface. 
     FIG. 13C is an end-view of the slotted cam-rod  191  of FIG. 12 in this embodiment. Cam-rod  191  has a slotted portion  192  as previously described, a radiused back-grind  209 , and a flat portion  207 . As slots  192  are rotated in the direction of the arrow, engaging teeth  205  on base-plate  199  of FIG. 13A are released at the beginning point of back-grind  209 . As flat  207  rotates so as to face teeth  205 , a small amount of space is created between the top land portions of teeth  205  and the surface of flat  207  enabling footpad assemblies such as footpads  79  to be moved to a different position or removed altogether. 
     It will be apparent to one with skill in the art that there may be more than one general configuration of slots and teeth than is illustrated here without departing from the spirit and scope of the present invention. For example, a base-plate such as plate  199  may be slotted while a cam-rod such as rod  191  is toothed. There may be more or fewer slots and teeth presented, and so on. In an alternate embodiment, footpad assemblies may be lowered in from the top with teeth and slots remaining in a rigid configuration on both sides of a base-plate and on opposite facing structures mounted to an adjuster-plate wide enough to support this type of fitting. Clamps could be used to secure the footpad assemblies after lowering them into place. 
     In another embodiment of the present invention an alternative adjustment mechanism for footpads may be used comprising one or more spring-loaded pop-up detents. A first footpad assembly may be mounted to the plate assembly separately, allowing for individual adjustment, or with a second footpad as an assembly. A pop-up detent can be mounted on an edge of a footpad assembly in a position so that when a user manually pulls back and then releases a spring-loaded pin within the detent assembly, the pin slides in and out of a slot or hole on the face or edge of the plate assembly, the pin and slot or hole being in-line when the desired footpad position is attained. The plate assembly can have a plurality of such slots or holes arranged in equally spaced and collinear fashion. A spring-loaded detent assembly could comprise a cylindrically shaped casing open on the end facing the hole or slot and containing a pin that slides in and out in both directions. A protrusion or attachment to the pin serves as a handle enabling a user to manually pull the pin back within the casing. Within the casing and located behind the pin a spring of roughly the same diameter of the pin provides outward tension to the pin when a user manually pulls it back using the handle. When a user manually releases the pin in the mounted detent assembly the spring tension behind the pin pushes the pin into the aligned slot or hole and locks the footpad assembly into the desired position. Once locked into the desired position by the pin assembly, the footpad assembly may be otherwise mainly secured to the plate assembly by utilizing many different methods. By again pulling back the pin a user can unlock the footpad assembly and adjust to another position as desired. This manner of spring-loaded pin arrangement within the detent assembly provides for the locking pin to be always urged into the outer or locked position. In addition to the footpad adjustment functionality of the pop-up detent assembly, in various alternative embodiments the detent assembly may have more or less of an integral role of securing the footpad assembly to the plate assembly. 
     It will be apparent to the skilled artisan that there are alternative arrangements and mechanisms that might be used to allow the footpads to be spaced and secured with the new spacing. The mechanisms described above are but a few of the possibilities. There are many others. For example, an intermediate plate assembly could be provided wherein there are two plates with one telescoping into the other, and having a locking apparatus to fix the relative positions when the desired separation is achieved. In this embodiment one footpad would be mounted to one of the telescoping plates and the other footpad to the other. 
     FIG. 14 is a cross-sectional view of a semi-arcuate rail  217  with a main wheel  213 , and a keeper wheel  215  in position according to an alternate embodiment of the present invention. As previously described in FIG. 1 above, semi-arcuate rails, shown round in FIG.  1  and other FIGS. in embodiments described above, may also be extruded to provide opposite channels for wheels, and then die-formed to obtain a desired semi-arcuate shape. This embodiment is especially useful for applications having footpads or platforms of exceptionally large dimensional features (length and width) than standard assemblies. Keeper-wheels such as wheels  215  and wheels  71  and  69  of FIG. 4 provided added restraint in order to prevent an assembly from tipping or otherwise being lifted from rails during operation. 
     Rail  217  is shown welded in this illustration to frame member  31 , and in embodiments of the overall apparatus using such extruded rails, the rails would also be welded to end rails  27  as described previously for rails  22 . Wheels  213  and  215  are not shown as assembled to a wheeled carriage in this illustration, but would in practice be mounted to such carriages in much the same manner as already described for wheels used with round rails. 
     FIG. 15 is a cross-section view through a rail  219  in yet another embodiment of the invention, showing a wheel assembly  221  having a shaft  223 , with the wheel engaged in rail  219 . In this embodiment rails  219  replace rails  22  or  217  shown in other embodiments, and are formed in an arc or an arc with straight-leg portions as taught elsewhere in this disclosure. Rails  219  may be extruded from suitable material, or may be formed by bending a plate and then forming the necessary arc using a die or other suitable tool. In preferred embodiments rails  219  are welded to structure  31  as shown, and also to end rails  27  (not shown). 
     In this embodiment Wheels  221  are mounted to a wheeled carriage by shafts  223  in various positions to support the carriage in its to-and-fro movements on (in) rails  219 . Some wheels are mounted to contact the upper portion of rails  219  as shown in FIG. 15, and others are mounted to contact the lower portion of rails  219 , thus accomplishing the functions of the wheeled carriage taught with reference to FIG. 4 having keeper wheels. It will be apparent to the skilled artisan that there are a variety of positions wheels may be mounted to accomplish the purpose. 
     FIG. 16 is an elevation view of a ski-exercising apparatus  301  according to an embodiment of the invention illustrating an optional third power band. Apparatus  301  is provided having elements similar to those of exercisers previously described herein except for novel improvements described below. For this reason only the improvements are described. To better illustrate elements within, additional roller-mount openings similar to those of tensioning structure  25  of FIG. 1A are not shown but may be assumed to be present, and cut-away views are shown of the wheeled carriage and support member. 
     Apparatus  301  provides a third power band  302  assembled between the first, or outer, power band and the second, or inner, power band. In this embodiment the free ends of third power band  302  are illustrated as fastened at clamp  306 , having one end clamped between the free ends of the outer band and the other end in between the ends of the outer and inner bands. It will be apparent that the clamping locations of power bands and positions of clamped free ends may vary. A tensioning structure  303  is provided, illustrated as a modification to a tensioning structure such as that of FIG. 1A, having a longer length and properties to support a third power band and hardware. Tensioning structure  303  is welded in this embodiment to the bottom surface of the central frame structure similarly to embodiments previously described. Rollers  304  and  305  are rotatably mounted to the outer positions of tensioning structure  303  providing support to third power band  302 , third power band  302  extending from clamp  306  passing under the inner rollers mounted between rollers  304  and  305  and passing under and over rollers  304  and  305  back toward center, over a third roller rotatably mounted under the wheeled carriage and fastened with the outer power band to the underside of the wheeled carriage by clamps  307  and  308 . 
     It will be apparent to one with skill in the art that the many improvements to existing ski-exercising equipment described as separate embodiments herein add durability, safety, improved operating characteristics, manufacturability, and convenience over apparatus of the prior art. The improvements also enable implementation of new apparatus such as the previously described snowboard application of FIGS. 9A and 9B, and the Double Diamond application (double-suspended Footpads) application of FIG.  12 . Moreover, future applications may now be implemented by developing new upper platform assemblies, and still be integrated easily with the improved rail and carriage apparatus as taught herein. Therefore, the present invention should be afforded the broadest scope possible. The spirit and scope of the present invention is limited only by the claims that follow.