Abstract:
A method of personal locomotion including stepping onto first and second wheeled shoe accessories and engaging the first wheeled shoe accessory against a support surface to roll on the second wheeled shoe accessory in a desired direction at an angle to a normal walking direction. The wheeled shoe accessory includes a rigid board having a length sufficient to span a width of a shoe placed sideways across the board, with the board supporting at least an arch region of the shoe. At least one axle assembly is secured to a lower surface of the board. The user experience is similar to that of a skateboard, but with decoupled feet for individual maneuverability of each wheeled shoe accessory.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This U.S. patent application claims priority under 35 U.S.C. §120 to U.S. application Ser. No. 11/202,957, filed Aug. 12, 2005, which is a continuation-in-part of U.S. application Ser. No. 10/847,242, filed May 17, 2004, which is a continuation of U.S. application Ser. No. 10/081,388, filed Feb. 20, 2002, now U.S. Pat. No. 6,764,082. The entire contents of the above prior applications are hereby incorporated by reference. 
     
    
     TECHNICAL FIELD  
       [0002]     This invention relates to personal locomotion on wheeled devices.  
       BACKGROUND  
       [0003]     There have been several proposals over the last century, and earlier, for walking shoes that can be readily converted to function temporarily as roller skates. A principal advantage to such shoes is the enhanced flexibility in transportation modes that they afford. Most are familiar with the rigid skate frames from several years ago that strapped to the underside of practically any normal walking shoe to permit the wearer to roll upon four wheels arranged two forward, two rear, in a forward or normal walking direction as in a standard roller skate. There is at least one walking shoe on the market that contains wheels that can be retracted into the sole of the shoe for walking, and then extended for rolling. Of course, such shoes require soles with thicknesses sufficient to fully contain such rollers when retracted, but have the advantage of not requiring their rolling parts to be carried separately while walking.  
         [0004]     In a rolling mode with these and standard roller skates, the wearer generally is able to propel himself along with alternating forward thrusts with each foot, in a motion similar to ice skating. The direction of travel is generally determined by the fore-aft or toe-heel axis of the foot. In-line skates have their wheels aligned along the fore-aft center line of the shoe, and can provide some directional control by tilting the skate to change the camber of the wheels. Some in-line skates have been employed for sliding down railings in a direction perpendicular to the fore-aft shoe centerline, either by sliding down the railing with the railing positioned between a middle pair of rollers, or on skid plates between the wheels.  
         [0005]     There is another shoe that has a removable roller mounted in a cavity the heel of the sole. For walking, the roller can be completely removed from its cavity. In a rolling mode, the wearer can, with practice and balance, roll in a forward direction upon the cylindrical roller with ankle locked and shin flexed. To obtain forward momentum, the wearer is instructed to run on the forward portions of the soles, and then lean back to engage only the heel rollers of both shoes with the ground for sustained rolling in the fore-aft direction as determined by the roller geometry and orientation.  
         [0006]     Skateboarding is yet another mode of transportation and sport popular with young people. Skateboards are generally characterized as boards supported by forward and rear “trucks,” each having a pair of wheels mounted upon a tiltable axle. While rolling forward on the board, side-to-side weight fluctuations tilt the board and cause a shift in the rolling direction of the wheels to provide controllable steering of the board. The rolling direction is thus determined by the orientation of the wheel axles, although the normal rolling direction is along a major fore-aft axis of the board. It is common for the skateboarder to place her feet at an angle with respect to the major board axis, with one foot behind the other, similar to the stance of a surfer on a surfboard.  
       SUMMARY  
       [0007]     In one aspect, s method of personal locomotion includes supporting oneself on a pair of separately movable wheeled devices to roll along a rolling direction at an angle to a normal walking direction defined by a user. Each wheeled device supports a respective foot and includes a device body and at least one roller secured to the device body. The roller is mounted to rotate about an axle defining a primary axis of rotation extending at an angle to the walking direction, as viewed from above the wheeled device. The method includes accelerating in a desired direction corresponding to the normal walking direction by engaging the wheeled devices against a support surface, repositioning the wheeled devices to engage the rollers against the support surface, and then rolling in the desired direction, at an angle to the normal walking direction, supported by the rollers.  
         [0008]     In some implementations, accelerating in the desired direction includes walking or running upon a forward region of the device body. Repositioning of the wheeled devices may include lifting each wheeled device from the support surface, rotating the wheeled device away from the direction of acceleration, and then engaging the roller upon the support surface. In some instances, repositioning the wheeled devices includes moving the wheeled devices along the support surface while rotating the wheeled devices away from the direction of acceleration, where the wheeled devices continuously maintain contact with the support surface. In some examples, repositioning the wheeled devices includes repeatedly moving the wheeled devices in opposite directions along the normal walking direction to continue rolling in a desired direction at an angle to the normal walking direction.  
         [0009]     The wheeled devices are repositioned to roll in a direction substantially perpendicular to the normal walking direction defined by a user. The wheeled device may be a shoe including a sole defining a forward region positioned beneath toes and at least part of a ball of a foot received within the shoe and having a lower surface exposed across the forward region to engage a supporting surface for walking thereon, and at least one roller secured to the sole and disposed rearward of the forward region. The roller is mounted to rotate about an axle defining a primary axis of rotation extending at an angle to the walking direction, as viewed from above the shoe. The shoes may include at least two rollers laterally spaced across the sole. The centers of the two rollers have a lateral spacing of about 20 percent of an overall length of the sole. The shoes may include at least two rollers spaced apart along the walking direction. The mid-planes of the two rollers are spaced apart along the walking direction by a distance of about 30 percent of an overall length of the sole. The axle is secured to the sole through a compliant mount that resiliently deforms as the axle is rotated about its kingpin axis. The axle carries two rollers, one disposed on either side of the kingpin axis. The rollers are mounted for rotation about the axle through separate bearings containing rolling elements.  
         [0010]     In some implementations, the wheeled device includes a rigid board having upper and lower surfaces and defining a longitudinal axis configured to be oriented along the rolling direction of the wheeled device. The upper surface of the board has a length along the longitudinal axis sufficient to span a width of a piece of footwear placed sideways across the board, with the board supporting at least an arch region of a piece of footwear. At least one axle assembly is secured to the lower surface of the board and includes an axle and at least one roller rotatably mounted on the axle for rolling in the rolling direction. The board is sized to fit entirely under the piece of footwear. The wheeled device may also include at least one releasable fastener configured to secure the board to an underside of the piece of footwear to retain the wheeled device to the piece of footwear during use. The releasable fastener includes a projection extending upwardly from the upper surface of the board. The projection is configured to be received by a receptacle defined by a sole of the piece of footwear. The releasable fastener is configured to permit the piece of footwear to be selectively positionable on the board in either of two positions, each with the piece of footwear angled with respect to the rolling direction. The axle assembly of the wheeled device includes a compliant mount resiliently deformable and secured to the lower surface of the board. The compliant mount defines a canted kingpin axis. The axle is secured to the compliant mount and rotatable about the canted kingpin axis for inducing yaw with respect to the rolling direction. The method may include first and second axle assemblies with the compliant mounts secured to the lower surface of the board such that their canted kingpin axes are in opposing directions to one another.  
         [0011]     In another aspect, a personal locomotion device includes a pair of separately movable wheeled devices to roll along a rolling direction at an angle to a normal walking direction defined by a user. Each wheeled device supports a respective foot and includes a device body and at least one roller secured to the device body. The roller is mounted to rotate about an axle defining a primary axis of rotation extending at an angle to the walking direction, as viewed from above the wheeled device.  
         [0012]     In yet another aspect, a personal locomotion device includes a pair of separately movable wheeled devices to roll along a rolling direction at an angle to a normal walking direction defined by a user. Each wheeled device supports a respective foot and includes a device body and at least one roller pivotally secured to the device body to swivel among multiple positions under the device body. The roller is mounted to rotate about an axle defining a primary axis of rotation extending at an angle to the walking direction in each swivel position, as viewed from above the wheeled device.  
         [0013]     In another aspect, a method of personal locomotion includes supporting oneself on a pair of separately movable wheeled devices to roll along a rolling direction at an angle to a normal walking direction defined by a user. Each wheeled device supports a respective foot and includes a device body defining a grinding portion on an underside of the device body for sliding along surface edges and at least one roller secured to the device body. The roller is mounted to rotate about an axle defining a primary axis of rotation extending at an angle to the walking direction, as viewed from above the wheeled device. The method includes positioning the grinding portion of at least one wheeled device on a surface edge so that the corresponding foot of the user is substantially parallel with the walking direction, as viewed from above the wheeled device, and a longitudinal axis of the surface edge, and then allowing the grinding portion of the wheeled device to slide along the surface edge.  
         [0014]     In another aspect, a method of personal locomotion includes supporting oneself on a pair of separately movable wheeled devices to roll along a rolling direction at an angle to a normal walking direction defined by a user. Each wheeled device supports a respective foot and includes a device body defining a grinding portion on an underside of the device body for sliding along surface edges and at least one roller secured to the device body. The roller is mounted to rotate about an axle defining a primary axis of rotation extending at an angle to the walking direction, as viewed from above the wheeled device. The method includes positioning the grinding portion of at least one wheeled device on a surface edge, the rolling direction of the wheeled device being at an angle with a longitudinal axis of the surface edge, and then allowing the grinding portion of the wheeled device to slide along the surface edge.  
         [0015]     According to another aspect of the invention, a wheeled shoe accessory includes a rigid board having upper and lower surfaces and defining a longitudinal axis configured to be oriented along a rolling direction of the wheeled shoe accessory, the upper surface of the board having a length along the longitudinal axis sufficient to span a width of a piece of footwear placed sideways across the board, with the board supporting an arch region of the piece of footwear. In some implementations, the board is sized to fit entirely under the piece of footwear. Preferably, the board is of a length, measured along the longitudinal axis, of between about 8 and 14 inches, and is of a width, perpendicular to its longitudinal axis, of between about 2½ and 4 inches.  
         [0016]     At least one axle assembly is secured to the lower surface of the board. The axle assembly includes an axle and at least one roller rotatably mounted on the axle for rolling in the rolling direction. Preferably, the axle assembly includes a compliant mount resiliently deformable and secured to the lower surface of the board, the compliant mount defining a canted kingpin axis. The axle is secured to the compliant mount and rotatable about the canted kingpin axis for inducing yaw with respect to the rolling direction. In some configurations, the wheeled shoe accessory includes first and second axle assemblies with their compliant mounts secured to the lower surface of the board such that their canted kingpin axes are in opposing directions to one another.  
         [0017]     The wheeled shoe accessory also has at least one releasable fastener configured to secure the board to an underside of the piece of footwear to retain the wheeled shoe accessory to the piece of footwear during use. In some implementations, the releasable fastener is a projection extending upwardly from the upper surface of the board and configured to be received by a receptacle defined by a sole of the piece of footwear. In one example, the projection is of a shape selected to prevent rotation of the board about an axis normal to the board with the projection received in the piece of footwear. Preferably, the projection is elongated with its length extending along the longitudinal axis of the board. In a presently preferred implementation, the releasable fastener is a substantially rectangular mounting boss having a height of about ¾ inch, a length of about 1⅛ inch, and a width of about ¾ inch. Preferably, the releasable fastener is configured to permit the piece of footwear to be selectively positionable on the board in either of two positions, each with the piece of footwear angled with respect to the rolling direction. For example, the releasable fastener may be securable to the board in either of at least two angular orientations. In one example, the releasable fastener defines a center axis and opposing undercuts on either side of the center axis for receiving an attachment mechanism embedded in an underside of the piece of footwear. Preferably, the undercuts defined by the releasable fastener are of an elongated shape spanning the width of the releasable fastener and have a height of about ⅛ inch and a depth of about 3/16 inch.  
         [0018]     In some implementations, the wheeled shoe accessory also includes an orientation plate secured to the upper surface of the board and configured to receive the releasable fastener. The orientation plate defines a protrusion along its upper surface to align the received releasable fastener in a particular orientation with respect to the board&#39;s longitudinal axis.  
         [0019]     In another aspect, an article of footwear includes a sole, an upper portion joined to the sole, and an attachment mechanism embedded in the sole for securing a wheeled shoe accessory to the sole. The attachment mechanism includes a body defining an elongated receptacle and a longitudinal axis, the receptacle defining a center axis and configured to receive a mounting boss of a wheeled shoe accessory. In some implementations, the receptacle defines a substantially rectangular opening. The attachment mechanism also includes at least one manually operable lock control device configured to engage and retain the received mounting boss within the receptacle. For example, in some implementations, the lock control device includes a button actuator disposed in the body along the longitudinal axis of the body and accessible from the side of the sole. A retainer arm is disposed in the body and joined to the button actuator, the retainer arm configured to engage and retain the received mounting boss in the receptacle with the retainer am in an engagement position. A spring is disposed in the body and biases the retainer arm toward its engagement position. Preferably, the lock control device includes two oppositely directed buttons joined to respective retainer arms configured to engage the mounting boss from opposite directions.  
         [0020]     Some other aspects of the invention feature a rigid board for a wheeled shoe accessory, the board having upper and lower surfaces and defines a longitudinal axis configured to extend along a rolling direction of the wheeled shoe accessory. The upper surface of the board has a length along the longitudinal axis sufficient to span a width of a piece of footwear placed sideways across the board, with the board supporting an arch region of the piece of footwear.  
         [0021]     According to one such aspect, the board defines mounting holes arranged to mount at least one axle assembly on the lower surface of the board, and includes a projection extending from its upper surface and configured to selectively secure a releasable fastener in either of two selectable orientations with respect to the longitudinal axis of the board. In some implementations, the projection his two elongated ribs oriented at different angles with respect to the longitudinal axis of the board, and a central post defining a threaded hole therein for receiving a threaded fastener to secure the releasable fastener to the board.  
         [0022]     According to another such aspect, the board defines a generally square recess in the upper surface along the longitudinal axis for receiving an orientation plate for selectively positioning a releasable fastener secured to the upper surface of the board in a particular orientation with respect to the board&#39;s longitudinal axis. Preferably, the recess has a side length of about 1¼ inches and a depth of about 0.2 inch. In some implementations, the board further defines a hole therethrough at a center of the recess of about ¼ inch in diameter.  
         [0023]     Various implementations of the concepts disclosed herein enable an enhanced user experience resulting from rolling in a direction other than a walking direction, while allowing individual foot maneuverability. Unlike skateboarding and surfing, the user&#39;s feet are decoupled to permit individual foot angulations and travel paths, while allowing the user to face at an angle to the general direction of motion. As a result, wheeled shoe accessory users can perform complex foot movements while rolling sideways. In addition, the disclosed wheeled show accessories can be employed for other purposes when not secured to footwear, such as by serving as hand-held toys for play. For example, decorative covers may be placed over the releasable fasteners, such as to simulate miniature characters “riding” the boards. Alternatively, the releasable fastener may be replaced with a flat plate that enables the board to be ridden by smaller children, or by larger children on only one foot in standard footwear. Hand grips may also be releasably secured to the fasteners, enabling a user to roll on either one or two pairs of such wheeled shoe accessories, at least partially supported on his or her arm or arms.  
         [0024]     The details of one or more implementations of the disclosure are set fourth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.  
     
    
     DESCRIPTION OF DRAWINGS  
       [0025]      FIGS. 1 and 2  illustrate sidewalk “surfing” and grinding, respectively, with shoes having rollers in their soles.  
         [0026]      FIGS. 3-5  are side, back and bottom views, respectively, of a first shoe.  
         [0027]      FIGS. 5A and 5B  are alternate bottom views of the first shoe.  
         [0028]      FIGS. 6 and 7  are side and bottom views, respectively, of a second shoe.  
         [0029]      FIG. 8  is a partial bottom view of a third shoe.  
         [0030]      FIG. 9  is a back view of the third shoe.  
         [0031]      FIGS. 10-12  are side, back and bottom views, respectively, of a fourth shoe.  
         [0032]      FIGS. 13 and 14  are side and bottom views, respectively, of a fifth shoe.  
         [0033]      FIGS. 15 and 16  are partial side and bottom views, respectively, of a sixth shoe.  
         [0034]      FIGS. 17 and 18  are partial side and bottom views, respectively, of a seventh shoe.  
         [0035]      FIGS. 19 and 20  are side and bottom views, respectively, of an eighth shoe.  
         [0036]      FIGS. 21-23  are side, bottom and back views, respectively, of a right shoe equipped with a steerable truck assembly.  
         [0037]      FIG. 24  is a back view of a left shoe equipped with a steerable truck assembly.  
         [0038]      FIG. 25  is a bottom view of a second shoe with a truck assembly.  
         [0039]      FIG. 26  is a cross-sectional view, taken along line  26 - 26  in  FIG. 25 .  
         [0040]      FIG. 27  is a side view of the truck assembly of the shoe of  FIG. 25 .  
         [0041]      FIGS. 28-29  are bottom and back views, respectively, of a third shoe with a truck assembly.  
         [0042]      FIG. 30  is a side view of the truck assembly of the shoe of  FIG. 28 .  
         [0043]      FIGS. 31-32  are side and bottom views, respectively, of a shoe equipped with a double truck assembly.  
         [0044]      FIG. 33  is a rear view of the shoe of  FIG. 31 , with the double truck assembly shown in cross-section.  
         [0045]      FIGS. 34 and 35  are back views of a shoe with a retractable wheel assembly in the arch region of the sole, with the wheel assembly shown in its extended and retracted positions, respectively, and the sole shown in cross-section.  
         [0046]      FIG. 36  is a side view of a two-wheeled truck assembly, with the wheels shown in dashed outline.  
         [0047]      FIG. 37  is an exploded view of the truck assembly of  FIG. 36 , without the wheels.  
         [0048]      FIGS. 38 and 39  are perspective views of the axle and mounting bracket, respectively, of the truck assembly of  FIG. 36 .  
         [0049]      FIGS. 40 and 41  are back views of left and right shoes, respectively, equipped with both steerable truck assemblies and non-steerable wheels.  
         [0050]      FIG. 42  is a bottom view of the shoe of  FIG. 41 .  
         [0051]      FIG. 43  is a perspective view of a wheeled shoe accessory secured to a shoe.  
         [0052]      FIG. 44  is an exploded view of the components of  FIG. 43 .  
         [0053]      FIG. 45  is an exploded view of the board with assembled releasable fastener, with the fastener oriented to place the heel-toe shoe axis perpendicular to the rolling direction.  
         [0054]      FIG. 46  is a bottom perspective view of the portion of the fastener embedded in the footwear.  
         [0055]      FIG. 47  is a perspective view of an axle assembly.  
         [0056]      FIG. 48  is a perspective view of the board of the accessory.  
         [0057]      FIG. 49  is a perspective view of the board with assembled releasable fastener. 
     
    
       [0058]     Like reference symbols in the various drawings indicate like elements.  
       DETAILED DESCRIPTION  
       [0059]      FIGS. 1 and 2  illustrate that many of the attitudes or stances assumed by surfers and skateboarders may also be obtained with shoes having rollers in their soles, with the rollers specifically adapted to roll along in a direction other than the walking direction, in accordance with several aspects of the present invention. For example,  FIG. 1  shows a user  10  rolling along a concrete sidewalk  12  with his feet oriented generally perpendicular to his direction of motion. Shoes  14  have rolling elements  16  in the arch region of their soles, enabling the user to balance his or her weight directly on the rolling elements for lateral motion. Preferably, there is sufficient room in the toe region of the flexible shoe soles, beyond the rolling elements  16 , to allow the user to run or walk on the toe regions without engaging the rollers. This can be useful for obtaining a running start before jumping into a surfing position on the rollers for continued motion. In some instances, the rollers may enable surfing along an edge  18  of a curbstone, as shown in  FIG. 2 , or an inclined railing or hand rail.  
         [0060]     Referring first to the implementation illustrated in  FIGS. 3-5 , shoe  20  has an upper portion  22  and a sole  24 . Not much detail is shown on upper  22 , as the shoe upper may be in any suitable form known in the art. Upper  22  may extend upward to cover the wearer&#39;s ankle, as illustrated, or may be of a lower cut. Alternatively, upper  22  may extend up the wearer&#39;s calf in the form of a boot. Upper  22  may be of a flexible material or may be of rigid form, as employed in ski and skate boot shells, for example. Likewise, sole  24  may be flexible or rigid, depending on the application. In one preferred implementation, sole  24  is molded of a flexible elastomer with a forward region  26 , an arch region  28  and a heel region  30 . The flexibility of forward region  26 , which covers the toe and ball portions of the foot, and the flexibility of the transition between forward region  26  and arch region  28 , enable sole  24  to flex during normal walking and during “toe-walking,” in which the wearer walks only upon the forward portions of their feet, as called “tip-toeing” by children.  
         [0061]     A cylindrical roller  32  is mounted within a cavity  34  in arch region  28 . Roller  32  is mounted for rotation about an axle pin  36  that extends in the fore-aft direction of the shoe, such that roller  32  is free to rotate as indicated by arrows in  FIG. 4 . In this illustration, roller  32  is only about 1.0 inch (25 millimeters) long and about 1.25 inches (32 millimeters) in diameter, with a cylindrical outer surface. Examples of other roller configurations are discussed below. A rigid axle mount cup  38 , or other support, is insert-molded into sole  24  to provide the mounting structure to which axle pin  36  is releasably secured. The ends of axle pin  36  snap into corresponding recesses at the forward and aft edges of cup  38 , and can be released from their recesses manually by pulling roller  32  from its cavity. Thus, roller  32  can be easily removed by the wearer, without the use of hand tools and without having to remove the shoes.  
         [0062]     As can be seen in  FIGS. 3 and 4 , the outer surface of roller  32  extends below the lowermost part of sole  24 , so that the wearer can engage roller  32  against a flat supporting surface, such as a sidewalk, without engaging any other portion of the sole. Additionally, as seen in  FIG. 4 , the lateral edges of sole  24  are chamfered or otherwise relieved to provide ground clearance when the shoe is tipped to either side on roller  32 . Preferably, the sole is relieved give a tilt clearance θ of at least about 10 degrees in at least one direction, with the roller sufficiently embedded to only have an exposed height ‘h’, below the lowest surrounding sole surface, of no more than about 0.5 inch (13 millimeters).  
         [0063]     In the implementation of  FIGS. 5A and 5B , axle pin mounting cup  38   a  defines four axle pin mounting recesses  40 , one set in its fore and aft edges for mounting roller  32  in the side-rolling orientation of  FIG. 5A , and another set in its side edges for mounting roller  32  in a forward rolling direction as shown in  FIG. 5B . Again, roller  32  is conveniently removed for normal walking, but can be quickly snapped into place in either illustrated orientation, enabling the wearer to selectively configure the shoes for skating or surfing modes.  
         [0064]     In the implementation of  FIGS. 6 and 7 , shoe  20   a  has an hourglass-shaped roller  42  positioned in its arch region, with a maximum outer diameter of about 2.0 inches (51 millimeters) and a central diameter of about 1.0 inch (25 millimeters). By its shape, roller  42  defines a central channel  44  for receiving a laterally extending support surface feature, such as an edge of a curbstone (see  FIG. 2 ), or a stair railing for extreme sports maneuvers. When rolling along a flat supporting surface, roller  42  engages the surface only on its two, spaced-apart maximum diameter regions  46 , providing low rolling contact area and corresponding rolling resistance, while also providing a relatively long extent “L” of contact for stability. In this case, longitudinal rolling extent “L” is about 2.75 inches (70 millimeters), or about 25 percent of the overall length of the sole  24   a.  The curvature shown in these views of the rolling surface of roller  42  at its two ends, beyond rolling extent “L”, gives some steering effect when the shoe is tilted fore-aft to place only one end of the roller in contact with the ground.  
         [0065]     Another feature of this implementation is that the axle pin supporting structure  38   a  embedded in sole  24   a  defines multiple sets of axle pin receivers  40  defining axle axes arranged at different angles, allowing roller  42  to be inserted in any of three distinct positions. In the center position, as shown, roller  42  rolls only about a fore-aft axis  170  aligned with the normal walking direction “D”, such that the user may roll exactly sideways. At other times, the user may wish to roll in a direction slightly angled from the sideways direction. If such is the case, the user may quickly snap roller  42  from its central position and reinsert it in one of the other two positions, with rolling axes displaced from the fore-aft direction by an angle α of about 15 degrees. For surfing stability, it may be desired to place the roller  42  of a forward shoe in a skewed position while leaving the roller of a rearward shoe in a centered position.  
         [0066]     For even more stability, one or both shoes may be equipped with twin rollers spaced apart along the width of the shoe. For example,  FIGS. 8 and 9  illustrate a shoe with two rollers  42  mounted in parallel in the arch region of the shoe sole. In this case, both rollers  42  roll about parallel axes running fore-aft along the shoe, with their central channels  44  aligned. As with the above-described implementations, rollers  42  are removable for walking or running. The rollers contact the ground at points separated a distance “X” along the direction of rolling travel, giving enhanced stability for each shoe. This can be particularly important for reducing inner thigh stress during prolonged use. Preferably, distance “X” is at least about 2.0 inches (51 millimeters).  
         [0067]     The shoe illustrated in  FIGS. 10-12  has four rolling elements  48  arranged at four corners of a rectangle. Two rollers  48  are arranged in parallel in the heel region of the shoe, while the other two rollers  48  are arranged in parallel just forward of the arch region of the shoe, such that the pattern of rollers encompasses the arch region. This arrangement of rollers provides excellent stability as the ground contact points define and encompass a broad planar area of length L 1  of about 3.0 inches (76 millimeters) and width W 1  of about 2.0 inches (51 millimeters). Each roller  48  rolls about a fore-aft axis and is of barrel shape, with the barrel curvature enabling some steering by tilting the shoe forward or aft for rolling contact on only either the rear wheels or the front wheels.  
         [0068]     Other side-rolling roller arrangements are also envisioned. For example,  FIGS. 13 and 14  shoe a shoe with four rollers  48  arranged in an offset pattern, with their ground contact points defining corners of a planar parallelogram. This enables the use of rollers with large rolling diameters while keeping their lateral separation W 2  narrower than if the rollers were placed side-by-side. Rollers  48  may be mounted for easy removal for walking, as discussed above, or securely mounted in the sole for use only as a rolling shoe, as shown. Preferably, the forward rollers  48  are mounted far enough from the toe of the shoe to enable toe-walking.  
         [0069]     Side-rolling elements  48  may also be combined with arch rollers or skid plates for both side-rolling and grinding.  FIGS. 15 and 16  show a shoe with the four-roller arrangement of the shoe of  FIG. 10 , but with the addition of a grinding roller  50  in the arch region of the shoe sole, between the fore and rear rollers  48 . Rollers  48  project farther from the sole than does grinding roller  50 , such that for side-rolling, only rollers  48  engage the ground. However, the user may jump from a side-rolling mode onto a railing to grind on arch roller  50 , with the railing received in the central reduced diameter portion  51  of the grinding roller. Each of the rollers  48 ,  50  in this implementation may be removed for walking mode or for replacement, by snapping the forward end of each roller axle out of a corresponding recess in supporting structure  38   b,  and then tilting the axle away from the sole and pulling the other end of the axle out of a corresponding socket in the supporting structure.  
         [0070]     As an alternative to a grinding roller, a grinding plate  52  can be employed, embedded in the sole along the centerline of the shoe, as shown in  FIGS. 17 and 18 . Grind plate  52  has a concave central portion for receiving and sliding along a railing or such. In this particular implementation, the shoe is also equipped with slide plates  54  overlaying the sides of the sole in the arch region of the shoe, for engaging a rail in combination with grind plate  52  for certain maneuvers.  
         [0071]     In another quad roller arrangement shown in  FIGS. 19 and 20 , four elongated, concave rollers  50  are arranged in two parallel rows, with two rollers in the heel region and two rollers forward of the arch region. Together, the rollers provide eight discrete ground contact points upon which the shoe can roll in sideways manner, and define two separate grinding channels.  
         [0072]     Steering control may also be accomplished by mounting the rolling members to the sole with compliant mounts, such as by incorporating a desired amount of compliance in the axle-pin mounting structure within the shoe sole.  
         [0073]     More aggressive maneuverability is provided with a roller or wheel mount that induces a change in the wheel axle orientation in response to a steering input. For example, the shoe  82  in  FIGS. 21-23  is equipped with a full axle truck assembly  84 , of a similar type to those commonly employed in pairs on skateboards. The base  86  of truck assembly  84  is securely attached to the sole of the shoe in its arch region. Truck assembly  84  carries an axle  88  about which two generally cylindrical rollers  90  rotate independently, of a construction similar to skateboard wheels. As shown in  FIG. 23 , axle  88  has a pin  92  that is received in a socket of base  86  and can freely rotate within the socket. Axle  88  is also secured to base  86  by canted shoulder bolt  94 , between two compliant bushings  96   a  and  96   b . This arrangement causes axle  88  to slightly rotate in a steering sense (i.e., in the plane of  FIG. 22 ) when it is tilted in the plane of  FIG. 21  by compression of bushings  96   a  and  96   b , providing intuitive directional (i.e., yaw) control.  
         [0074]     Looking in combination at  FIGS. 23 and 24 , both of a pair of shoes can each be equipped with a truck assembly  84 , for independent turning control of each foot in a sideways rolling, “surfing” mode. In the illustrated arrangement, the left foot truck axle  88  has its pin  92  extending to the left, while the right foot truck axle  88  has its pin  92  extending to the right, such that the truck axles pivot in opposite sense when their respective shoes are tilted in the same sense, for turning the truck axles out of phase with one another.  
         [0075]     Truck assemblies  84  can be mounted to the shoe sole for quick removal to transition to a walking or running mode. In  FIGS. 25-27 , truck assembly  84   a  has four quick release fasteners  98  for releasably securing the base of the truck assembly to the shoe sole. In  FIGS. 28-30 , on the other hand, the entire truck assembly  84   b  is secured to the shoe sole with a single quick release pin  100  that is readily grasped and pulled from the shoe sole by ring  102 . When in place, pin  100  extends through a hole  104  in a mounting boss  106  extending from the base of truck assembly  84   b,  enabling the truck assembly to be mounted in either of two opposite orientations as desired for particular rolling directions and steering modes.  
         [0076]     Referring to  FIGS. 31-33 , shoe  108  has a double truck assembly  110  mounted beneath in the arch region of the sole. Truck assembly  110  supports two independently tiltable wheel axles  112 , each with a corresponding pivot pin  92  rotatable within a corresponding socket of the joint truck assembly base  114 . Truck axles  112  are arranged in opposition for more aggressive steering sensitivity, giving shoe  108  all of the steering capability of a traditional skateboard, all within the width W 2  of the shoe sole rather than requiring a long board on which both feet are placed. Preferably, the overall wheelbase WB of double truck assembly  110  is about 2.0 inches (51 millimeters) or less. In one preferred implementation, the wheelbase WB is about 2.0 inches (51 millimeters), and the fore-aft distance T B  between wheel midplanes is about 3.0 inches (76 millimeters), in a men&#39;s size 9 shoe with an overall sole length L S  of about 12 inches (30.5 centimeters). Thus, the wheel center track width T B  and wheelbase WB were about 30 percent and 20 percent of the shoe length, respectively. With two such shoes  108 , a wearer can relatively position his or her feet in any number of positions while rolling sideways and steering, enabling maneuvers impossible with skateboards. As with some of the other implementations described above, the toe and ball region  113  of the sole of shoe  108  is unobstructed by the truck assembly and its wheels  90 , enabling the wearer to toe-walk on the front portion of the sole when not rolling. Heel-walking is also possible on the exposed heel surface  111  of the sole. Preferably, the sole is flexible forward of the arch region, for more comfortable walking. As with the above truck implementations, double truck assembly  110  can be releasably mounted to the shoe sole.  
         [0077]     The shoe  116  of  FIGS. 34 and 35  has a two-wheeled roller assembly  118  mounted in its arch region for rolling in a sideways direction (similar to the shoe of  FIG. 31 ), but configured to be readily retractable into the sole of the shoe for walking. In its extended position ( FIG. 34 ), wheels  90  are partially disposed below the lower surface  120  of the shoe sole, and held in that position by a manually operable latch  122 . When retracted ( FIG. 35 ), the entire roller assembly  118  is contained within the recess  124  defined in the shoe sole. Latch  122  and axle  126  are both mounted to the shoe to pivot about respective pins  128  and  130 , and biased by torsion springs (not shown) toward the positions shown in  FIG. 35 . It will be understood that such retractability is readily incorporated into several of the above-described roller configurations.  
         [0078]      FIGS. 36-39  illustrate a steerable roller truck assembly  132  for use in skates, skateboards, or the like. The illustrated example can be constructed with an advantageously low overall height “H T ” of less than about 1.0 inch (25 millimeters), for example, for incorporation into the sideways-rolling shoe implementations shown above. The three primary components of the assembly are a rigid mounting bracket  134 , two compliant wedge-shaped bushings  136 , and an axle  138  that carries two wheels  90 . To assemble the truck assembly, the two wedge-shaped bushings are first placed into corresponding compartments on either side of a central web  140  of bracket  134 . Next, axle  138  is slid over a rigidly mounted pin  142  of bracket  134  until it contacts the angled front surfaces of the bushings. In place, axle  138  cooperates to retain bushings  136  in their compartments. Axle  138  is axially retained on pin  142  by a retaining clip  144  or other fastener means. An adjustable locknut (not shown) at the distal end of pin  142 , for example, may be employed to maintain a bushing preload over time, if the axle is configured to leave a gap between the axle and bracket at inner end of the axle as shown. This arrangement also allows bushing compliance to slightly cushion normal wheel loads, as well, and a secondary bushing washer (not shown) may be placed between the axle and the bracket at the inner end of pin  142  if desired. Alternatively, axle  138  may be configured to slide along pin  142  until it contacts a rigid stop surface of bracket  134 . During use, torque applied to axle  138  about bracket pin  142  resiliently compresses one or the other of the bushings to enable steering of the axle about pin  142 . Bushings  136  can be molded of polyurethane, with a hardness of about 50 to 95 shore A, for example.  
         [0079]     Referring to  FIG. 38 , axle  138  has a central body  146  that defines an open circular slot  148  for receiving the pin of the bracket. Slot  148  encompasses, in cross-section, more than 180 degrees of a defined circle, so as to radially retain the pin. The open side of slot  148  accommodates the central web of the bracket. Surfaces  150  adjacent slot  148  bear against the angled surfaces of the bushings in use. An axle pin  152  of about 0.25 inch (6 millimeters) in diameter is rigidly secured within a bore of body  146 , and is configured as known in the art to carry the wheels.  
         [0080]      FIG. 39  illustrates the structure of mounting bracket  134 . Pin  142  is of about 0.25 inch (6 millimeters) in diameter, pressed into a hole in the lower portion of the bracket and soldered to central web  140  for added support. A rear wall  154  of the bracket extends from the central web around the rear corners of the bracket, to define the cushion compartments  156 . A groove  158  at the distal end of pin  142  receives the retaining clip.  
         [0081]      FIGS. 40-42  show a pair of shoes  160 L and  160 R, each with a steerable truck assembly  84  as well as a non-steerable wheel  162 . In each shoe, the non-steerable wheels are shown inboard of the truck assemblies  84  and provide a third contact wheel for added stability of each shoe, as compared with the implementation of  FIGS. 23 and 24 . Wheels  162  are each mounted about for rotation about their own axle  164 , laterally spaced from the truck assemblies  84  and supported between rigid flanges  166  extending from a common base  168  of the truck assembly.  
         [0082]     FIGS.  43  illustrates one implementation of a wheeled shoe accessory  200  attached to the sole  210  of an article of footwear  220 . Referring to  FIGS. 44-45 , wheeled shoe accessory  200  includes a board  300 , at least one axle assembly  370  secured to the lower surface of board  300 , an orientation plate  310  secured to board  300 , and a releasable fastener  320  configured to secure board  300  to the sole of the article of footwear. Board  300  is generally rigid and defines a center axis  302  and a longitudinal axis  304  along a rolling direction. In one aspect, board  300  has a length along the longitudinal axis  304  of 11 inches and a width of 2.75 inches. Board  300  also defines a mounting portion  306  for mounting orientation plate  310  and is located along the longitudinal axis  304 . In one aspect, mounting portion  306  defines a generally square recess in the upper surface of board  300  and centered on the center axis  302 , the recess having a width of 1.25 inches and a depth of 0.2 inches. Mounting portion  306  also defines a hole  308  of 0.3 inch diameter through the center of the recess along the center axis  302  for securing orientation plate  310 . Finally, board  300  defines a plurality of holes  309  (eight shown) for mounting at least one axle assembly  370  on the lower surface of board  300 . In one aspect, board  300  defines two sets of four holes  309 , positioned on either side of the center axis  302  for mounting two axle assemblies  370  centered on the longitudinal axis  304  and equal distances from the center axis  302 .  
         [0083]      FIG. 45  illustrates one implementation of a board assembly  201  of a wheeled shoe accessory. Orientation plate  310  is received by the recess defined by mounting portion  306  and is secured to board  300  by a fastener  318  inserted from the lower side of board  300  through the hole  308  defined by mounting portion  306 . Orientation plate  310  is configured to receive releasable fastener  320  in two or more orientations and defines a center axis  312 . In the illustrated implementation, orientation plate  310  is configured to receive releasable fastener  320  such that their center axes  312  are co-linear and the longitudinal axis  324  defined by releasable fastener  320  is selectively oriented at 0, +45 or −45 degrees with respect to the center axis  304  of board  300 . In other implementations, orientation plate  310  is configured to receive releasable fastener  320  at other desired angles. In this example, orientation plate  310  defines two aligned, parallel half-round protrusions  316  along its upper surface to align releasable fastener  320  in one orientation, and two other sets of protrusions  316   a  and  316   b  that are received in common, linear slots defined in the lower end of the releasable fastener, for mounting the fastener in two other respective angular orientations about the center axis of the board.  
         [0084]     Referring to  FIGS. 44 and 46 , releasable fastener  320  is received by an attachment mechanism  340  embedded in the sole  220  of an article of footwear  210 . As shown in  FIGS. 46 , attachment mechanism  340  includes a body  350  defining a center axis  342  and a longitudinal axis  344 . Attachment mechanism  340  is embedded in the sole of the article of footwear such that the longitudinal axis  344  of body  350  is perpendicular to a direction of walking (i.e., perpendicular to the longitudinal, heel-toe axis of the footwear). Body  350  defines along the center axis  342  a cavity  360  configured to receive releasable fastener  320 . As shown, two buttons  352  are disposed in the body along the longitudinal axis  344  and biased by springs  354  such that the buttons  352  are accessible for actuation on either side of the sole of the shoe. The buttons  352  actuate respective retainer arms  356  disposed in body  350  to operate in opposing directions along the longitudinal axis  344 . Each retainer arm  356  is configured to engage a corresponding retention feature of the releasable fastener as the fastener inserted into the cavity  360 . The springs  354  also bias the retainer arms  356  to engage and retain the inserted releasable fastener. A cover  358  encloses the retainer arms  356  in the body  350 .  
         [0085]      FIG. 47  illustrates one implementation of an axle assembly  370 . The axle assembly  370  includes a compliant mount  376  resiliently deformable and defining a canted kingpin axis  372 . An axle  378  is secured to the compliant mount  376  and rotatable about the canted kingpin axis  372  for inducing yaw with respect to the rolling direction. At least one roller  380  is rotatably mounted on the axle  378  for rolling in the rolling direction.  
         [0086]     The wheeled board assembly described above is convertible into a miniature skateboard-like toy, by replacing the releasable fastener and orientation plate with a flat plate  390 , as shown in  FIGS. 48 and 49 . Plate  390  fits flush inside recess  306 , and is retained by the same threaded fastener  318  that is shown securing orientation plate  310  in  FIG. 41 . With plate  390  in place ( FIG. 49 ), the upper surface of plate  390  is coplanar with the upper surface of board  300 . For at least smaller children, board  300  so configured is of ample size to enable at least portions of both feet to be placed upon the upper board surface for play.  
         [0087]     A number of implementations of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other implementations are within the scope of the following claims.