Lateral sliding roller board

A roller board allowing the rider to slide laterally in a manner similar to a snowboard. The roller board is comprised of a platform having four fixed wheels, and two pivoting rollers positioned along the platform's longitudinal axis. The fixed wheels function similarly to conventional skateboard trucks. The pivoting rollers rotate to align themselves with the direction of force exerted on the platform. The pivoting rollers are spring biased to align themselves with the longitudinal axis of the platform. A height differential between the two types of rollers enables the rider to transfer weight from one type of roller to the other, alternating between the carving and sliding characteristics of a snowboard.

BACKGROUND--FIELD OF THE INVENTION 
This invention relates to skateboards, specifically to a skateboard that 
can transition in and out of a mode of controlled omnidirectional motion 
in a manner similar to the behavior of a snowboard. 
BACKGROUND--DESCRIPTION OF PRIOR ART 
Throughout skateboarding's history, the basic configuration of equipment 
has been consistent: deck, trucks, wheels. Product advances have always 
occurred in the context of this basic configuration. In the 1970's, 
urethane wheels replaced clay wheels. Later developments included 
kicktails, laminated wood decks for strength, precision housed bearings, 
and griptape and concave decks for better control. These advances have not 
changed the essential functionality of the board nor its motion 
characteristics. Meanwhile, riders have pushed the existing equipment to 
absurd new limits, performing tricks unimaginable several years ago. 
During this period, snowboarding has arrived and is now rapidly growing in 
popularity. Much of this popularity results from snowboarding's seductive 
freedoms of movement. While these movements result from complex 
interactions between the board, rider and snow conditions, at least two 
general motion characteristics can be readily identified and these are 
described below. Many aspects of these motions are common to several snow 
and water sports such as skiing, wakeboarding and body boarding. The 
discussion below limits itself to snowboarding because of its direct 
similarities to skateboarding. 
First, a snowboard rider can turn by leaning her weight towards the 
intended direction of travel. This effect results from the presence of 
sidecut and flex in the board design. As the board leans onto its edge, it 
turns an arc equivalent to the radius of the board's edge. If this type of 
turn is executed cleanly, it is referred to as "carving" and involves 
little or no lateral slippage of the board and rider. The rider can 
control the severity of the turn radius by leaning more or less weight. 
Skateboards have long replicated this carving behavior through the 
mechanical design of skateboard trucks. The truck's simple design turns 
the skateboard through gentle or severe turns depending on the amount of 
lean by the skateboarder. 
The other general motion characteristic of a snowboard is its ability to 
offer a second direction of travel, other than the forward/backward 
direction. The rider can adjust her weight such that the board can slip 
forward, backward, sideways or some amount in each direction. Given that 
pure carving is limited to a forward component of motion, full 
omnidirectional motion can be achieved by the introduction of lateral 
motion. Lateral motion frequently is represented in the form of skidding, 
as when a car skids while turning on a slick surface. A snowboard rider 
can engage this second direction of travel with a velocity that is as 
great or greater than the forward motion component. 
It should be noted that a second direction of travel has never been 
available to the general skateboarder. During the late 1970's and early 
1980's, a number of expert skateboarders engaged in a technique referred 
to as "powersliding", where, through brute force alone, a rider would 
drive their skateboard to slide sideways. This maneuver never gained 
widespread popularity for several compelling reasons: (1) it was very 
difficult to learn and execute and thus potentially dangerous; (2) it 
required considerable momentum best generated only by high speeds on a 
steep hill; and (3) overcoming the considerable friction of the wheels 
required the riders to push their boards far out in front of their bodies, 
often necessitating the use of very heavily padded gloves to protect their 
hands while leaning and dragging on the passing pavement. Finally, 
powersliding generally required the rider to be traveling either fully 
sideways or not at all. All of the subtle mixtures of forward and sideways 
motion components, so compelling on a snowboard, were virtually impossible 
to engage during a powerslide. 
These determined attempts by skateboarders to achieve a second direction of 
travel are not surprising given the novel feeling of motion that it 
provides. Lateral sliding enables the rider to perform a wide variety of 
tricks and maneuvers. A snowboard rider can rotate 180.degree., 
360.degree. or more, slowly or quickly, while already in motion down a 
hill. A rider can land a jump in any orientation--backwards, forwards, 
sideways or anywhere in between--and ride away successfully. In 
combination with carving, lateral motion lets a rider transition in and 
out of skidding in a highly controlled manner to maneuver skillfully down 
a mountain. 
Because of the great appeal of snow sports, many attempts have been made to 
replicate them on land or pavement. Not surprisingly, almost all of the 
prior art represents attempts to simulate skiing. Most of these devices 
ignore the omnidirectional mode. U.S. Pat. Nos. 4,134,598 to Urisaka 
(1979) and 4,805,936 to Krantz (1989) describe wheeled skis that contain a 
caster in conjunction with other fixed wheels. A wheeled grass ski is 
described in U.S. Pat. 5,195,781 to Osawa (1993) that simulates sidecut, 
theoretically enabling the device to turn when leaned to the side. U.S. 
Pat. No. 4,744,576 to Scollan (1988) details a device that lets the skier 
slide back and forth, while the device itself does not move laterally. 
None of these examples allow true lateral sliding with respect to the 
terrain being traveled over. 
Amongst the prior art examples attempting to offer true lateral motion, 
U.S. Pat. No. 5,312,258 to Giorgio (1994) uses an array of ball-type 
roller bearings. Unlike a ski or snowboard, this device includes no means 
for controlling the omnidirectional motion. Also, while perhaps functional 
on a constructed half pipe, it would be undermined by dirt and the rougher 
surface of pavement on a street or playground. U.S. Pat. No. 3,827,706 to 
Milliman (1974) uses a combination of pivoting casters and fixed casters 
where the fixed casters are slightly closer to the ground than the fixed 
wheels. This would potentially allow the skier to angle the ski in and out 
of a sliding mode. No means is provided to stabilize the casters or to 
smooth the transitions as weight is transferred from a pivoting caster to 
a fixed caster. U.S. Pat. No. 4,886,298 to Shols (1989) employs a complex 
twisting ski design that combines four casters with normal skateboard 
trucks. 
Three patents in this area show the use of a biased, pivoting caster. U.S. 
Pat. No. 4,460,187 to Shimizu (1984) describes two skis and U.S. Pat. No. 
5,125,687 to Hwang (1992) describes a single board for simulating the 
parallel skiing body position. Both inventions have a single caster 
towards the front, with an extension spring tensioning the caster to point 
straight ahead. These inventions do not allow lateral sliding; they do not 
permit the caster to rotate through 180.degree. or 360.degree.; they do 
not allow for the possibility of multiple locations of bias on the caster; 
and they do not permit the characteristics of the bias force to be 
optimized. 
The skis described in U.S. Pat. No. 4,886,298 to Shols (1989) incorporate a 
bias via a hinge and a compliant mounting surface. As weight is applied to 
the ski, the caster tilts along the hinge axis, biasing the caster in the 
forward direction. This configuration satisfies only the ability to rotate 
360.degree. unimpeded. It does not permit more than one direction of bias; 
its force profile starts low and grows gradually, allowing wobbling and 
doing little to help the rider back into the straight ahead position; and 
the force profile can not be modified. 
Biased casters that allow unimpeded 360.degree. rotation and specific force 
profiles are described by U.S. Pat. Nos. 4,246,677 to Downing and Williams 
(1981) and 4,280,246 to Christensen (1981). These inventions relate to 
semi-automated cart delivery systems typically used in hospitals for 
transporting food and medication. When the carts are lifted, the pivoting 
casters rotate to a predetermined angle, allowing them to move through an 
automated system. When the casters are touching the ground, the inventions 
function only to lessen wheel flutter. They are not intended to augment 
the cart's motion and steering characteristics. 
SUMMARY OF THE INVENTION 
Accordingly, it is the objective of the present invention to bring a new 
freedom of movement to skateboarding. This freedom is best represented by 
the motion and balance characteristics of snowboarding. Specifically, the 
objects and advantages are: 
(a) to provide the ability to "carve," as a conventional skateboard can, 
where leaning weight to one side causes the device to turn in that 
direction; 
(b) to provide the ability to shift into a mode of omnidirectional 
behavior, where the device can easily travel forwards, backwards, sideways 
or any combination thereof; 
(c) to provide the ability to transition smoothly and controllably between 
carving and the omnidirectional mode; 
(d) to provide a user interface that simulates the balance characteristics 
of snowboarding and other board sports, where the omnidirectional mode is 
engaged when weight is relatively evenly distributed across the board and 
this mode can be exited by transferring significant weight to the board's 
edge; 
(e) to provide the ability to rotate the board 1 80.degree., 360.degree., 
or more, repeatedly, without lifting or unweighting the board, while in 
motion over terrain; 
(f) to provide a means such that the relative ease of entering the 
omnidirectional mode can be increased or decreased according to the user's 
preference; 
(g) to provide the ability to ride on different types of terrain, including 
paved surfaces, grass and dirt; 
(h) to provide a means for speed control; and 
(i) to create a device that is economical to produce and sell. Further 
objects and advantages of my invention will become apparent from a 
consideration of the drawings and ensuing description.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
A typical embodiment of the present invention is shown in FIG. 1. A 
platform 20 has a center base 21, two sides 22, a front tip 23, and a rear 
tail 24. Front tip 23 is sufficiently different in shape from rear tail 24 
that the user can easily distinguish one from the other. Sides 22 are 
roughly identical to each other. Platform 20 is wider and longer than a 
normal skateboard deck. Typical skateboard decks measure between 7.5" to 
8.5" wide and 31" to 34" long. Platform 20 measures 10.5" wide and 40" 
long. As will be shown later, this additional size makes the roller board 
easier to ride and control. 
A rider 28 positions herself on platform 20 in a stance similar to that 
used for snowboarding, surfing or conventional skateboarding. Rider 28 
stands sideways with a rear foot 27 roughly perpendicular to a 
longitudinal center line 29. A front foot 26 is typically angled somewhat 
towards tip 23. This stance allows rider 28 to easily shift her weight 
onto her toes or onto her heels. Rider 28 can also move freely about the 
surface of platform 20, assuming different stances for different 
maneuvers. As with a conventional skateboard, front tip 23 and rear tail 
24 angle upwards from base 21. By transferring weight to tip 23 or tail 
24, rider 28 can perform numerous tricks and maneuvers where part or all 
of the roller board becomes elevated from the ground. 
FIG. 2 shows a cross-section of platform 20, cut perpendicular to 
longitudinal center line 29. To assist rider 28 in transferring lateral 
and rotational force to platform 20, the shape of platform 20 is concave, 
with sides 22 gently angled upwards from base 21. Angled sides 22 create a 
surface that rider 28 can push sideways against. In addition, a high 
friction surface such as grip tape can be applied to the topside of 
platform 20. This also enhances the ability of rider 28 to apply lateral 
and rotational force to the roller board. 
As shown in FIG. 3, two basic types of mechanical components are mounted to 
the underside of platform 20. Fixed wheel assemblies 30, 31 are positioned 
along longitudinal center line 29, roughly towards tip 23 and tail 24, 
mirroring one another. Biased pivoting roller assemblies 50, 51 are 
positioned just inside of fixed wheel assemblies 30, 31, also along 
longitudinal center line 29. The fixed wheel assemblies 30, 31 provide a 
different functional characteristic and a different effect on maneuvering 
than do the biased pivoting roller assemblies 50, 51. Combining the 
assemblies 30, 31, 50, 51 together in the unique manner of this invention 
simulates snowboarding very effectively. 
FIG. 3 also shows the considerable distance between fixed wheel assemblies 
30, 31. As measured from a transverse axis 46 of fixed wheel assembly 30 
to transverse axis 46 of fixed wheel assembly 31, the distance measures 
28", compared to an equivalent distance of 20" on a conventional 
skateboard. This distance creates a much longer wheel base than found on a 
conventional skateboard. This longer wheel base makes the roller board 
more stable and easier to ride. By comparison, surf boards, snowboards and 
skis all become more stable as the length of their base is increased. 
FIG. 3 also shows the close proximity between fixed wheel assemblies 30, 31 
and biased pivoting roller assemblies 50, 5 1, respectively. Biased 
pivoting roller assembly 50 is positioned as close as possible to fixed 
wheel assembly 30 but not so close that they mechanically interfere with 
each other. Likewise, biased pivoting roller assembly 51 is positioned as 
close as possible to fixed wheel assembly 31 but not so close that they 
mechanically interfere with each other. Increasing the distance between 
biased pivoting roller assemblies 50, 51 contributes to the overall 
stability of the roller board in the same manner as increasing the 
distance between fixed wheel assemblies 30, 31. 
Referring now to FIG. 4, fixed wheel assemblies 30, 31 are similar in many 
respects to conventional skateboard trucks, but with unusually wide axles. 
At their widest dimension (along a transverse axis 46), fixed wheel 
assemblies 30,31 greatly 20". The widest conventional skateboard trucks 
measured along this same dimension are less than 10" wide. The unusual 
width of fixed wheel assemblies 30, 31 greatly increases the roller 
board's overall stability. It also greatly lessens the possibility of the 
roller board "catching an edge," where the roller board stops abruptly 
while sliding laterally. Finally, the unusual width helps give the roller 
board a wide range of speed control. This is explained in greater detail 
further on. 
Still referring to FIG. 4, a fixed wheel base 32 sandwiches a height 
adjustment riser 44 when attached to platform 20. The assembly has an axle 
mount 34 with transverse axis 46 to which a fixed wheel 40 is attached. A 
flexible connection is made between a collar 39 attached to axle mount 34 
and base 32 with a bolt 36 housed in an elastomeric sleeve 37. 
Referring now to FIG. 5, bolt 36 is held fixed by a press fit 42 into base 
32 at an acute angle with respect to base 32. Fixed wheel assemblies 30, 
31 provide limited pivotal movement of fixed wheels 40 when platform 20 is 
tilted. Because fixed wheel assemblies 30, 31 are oriented symmetrically 
such that collars 39 face towards the center of platform 20, this pivotal 
movement of fixed wheels 40 causes platform 20 to turn. Thus, when the 
rider leans to one side, platform 20 turns in that direction. A threaded 
nut 38 allows the compression of elastomeric sleeve 37 so that the force 
necessary for the pivotal movement can be raised or lowered. 
Referring now to FIG. 6, biased pivoting roller assemblies 50, 51 provide 
the means for omnidirectional motion. A pivoting roller 52 stays in 
constant contact with the ground and can rotate to align itself with the 
direction of force exerted on platform 20 while the user is turning or 
sliding. The assembly is spring biased to align itself along longitudinal 
center line 29 of platform 20, pointed either forward or backwards. This 
bias simulates the natural tracking tendency of a ski or snowboard and 
greatly enhances the user's control. The bias is gauged to be strong 
enough to add control, but not so strong that the rider is impeded from 
rotating platform 20 into sideways travel. 
This spring bias is implemented as follows. Pivoting roller 52 is attached 
to a caster 54 and rotates around a horizontal axis 58. In turn, a base 
plate 56 is attached to the underside of platform 20. A cam follower 60 is 
pivotally attached to caster 54 and includes a torsion spring 64. Cam 
follower 60 includes a bearing 62 and is forced by spring 64 against a cam 
66 that is fixed relative to base plate 56. This causes caster 54 to 
rotate to a position of least force between cam 66 and cam follower 60. By 
adjusting the shape of cam 66 and the spring force on cam follower 60, a 
variety of bias profiles can be obtained. FIG. 7 shows a cross sectional 
view of biased pivoting roller assemblies 50, 51. 
A preferred embodiment of cam 66 is shown in FIG. 8. The shape is 
symmetrical along a major axis 74 and a minor axis 76. Two notches 68 
create positions of least resistance where a sizable threshold of force 
must be surpassed to allow rotation of caster 54. The radius of notch 68 
corresponds to the radius of bearing 62 so that a snug, stable fit is 
engaged when pivoting roller assembly 50, 51 is aligned with longitudinal 
center line 29 of platform 20. On either side of notches 68, the radial 
distance to the edge of cam 66 increases as rotation continues until it 
reaches an apex 72. Apex 72 is gently pointed to prevent cam follower 60 
from sticking at the transition from one side of cam 66 to the other. In 
other words, caster 54 will always be biased to return to one of two 
stable positions. 
FIG. 9 shows a graph of the forces acting on pivoting roller 52 via caster 
54 when in different orientations. The x-axis represents the orientation 
of pivoting roller 52 with respect to the front of the board. The y-axis 
represents the amount of force acting to return the pivoting roller to the 
position of 0.degree. or 180.degree.. When aligned with the longitudinal 
center line 29 of platform 20, pivoting roller 52 rests in a stable 
position. As the orientation is rotated away from this position, force 
rises sharply to a "threshold level," then levels off. The use of cam 66 
permits great control over the type of force being applied to caster 54. 
The shape of cam 66 can be modified in an infinite number of ways to 
change the characteristic of the bias. 
The roller board succeeds because of the unique interactive effect between 
fixed wheel assembly 30, 31 and biased pivoting roller assembly 50, 51. 
Together, the assemblies 30, 31, 50, 51 allow the rider to control the 
amount of friction between fixed wheels 40 and the surface being traveled 
over, whether that surface is pavement, grass, dirt or rock. When this 
friction is increased, fixed wheels 40 allow the rider to carve turns. 
When this friction is decreased, fixed wheels 40 can slide laterally 
enabling the rider to engage a mode of omnidirectional motion. Friction is 
generally a function of force and material. While the material of fixed 
wheels 40 does not change, the amount of force acting on them can be 
varied greatly. This occurs through the unique interaction of fixed wheels 
40 and pivoting rollers 52 as demonstrated in FIGS. 10-12. 
Pivoting rollers 52 extend slightly closer to the ground than fixed wheels 
40. FIG. 10 shows the positions of the different rollers relative to the 
ground when the rider places her weight towards one edge of platform 20. 
In this position, sufficient force can be applied to fixed wheels 40 on 
one side of platform 20 to allow them to frictionally engage the ground. 
As a result, fixed wheels 40 prevent platform 20 from sliding sideways. 
They also allow the rider to carve as on a conventional skateboard. A 
height differential .DELTA.h can be measured between elevated fixed wheel 
40 (on one side of platform 20) and the ground. The greater the size of 
.DELTA.h, the easier it is for the rider to enter into a mode of 
omnidirectional motion. By changing the thickness of height adjustment 
riser 34, .DELTA.h can be increased or decreased. The value of Ah would 
typically range from 1/16" (difficult to slide laterally) to 1/2" (easy to 
slide laterally). 
FIG. 11 shows the roller board when the rider's weight is perfectly 
centered over platform 20. Ideally, both fixed wheels 40 are slightly 
above the ground and the rider's weight rests solely on pivoting rollers 
52. In this configuration, the roller board is free to travel in any 
direction, constrained only by the spring bias acting on pivoting rollers 
52. It is important to note that entering the omnidirectional mode of 
travel does not depend on fixed wheels 40 being elevated from the ground. 
The important factor is the amount of force being applied to them. As long 
as the rider is generally centered over platform 20, her weight will rest 
predominantly on pivoting rollers 52. This reduces the friction between 
fixed wheels 40 and the ground to a level where the device can easily 
slide sideways. 
FIG. 12 shows the position of the various rollers as weight is shifted to 
the opposite side. The effect is the same as described for FIG. 10. By 
shifting weight from one side to another, rider 28 can use the roller 
board to carve without entering into a sliding mode. This behavior is 
equivalent to a snowboarder shifting from one edge of the snowboard to the 
other. While fixed wheels 40 frequently lose contact with the ground, the 
rider does not feel these transitions. They are cushioned by elastomeric 
sleeve 37 in fixed wheel assembly 30, 31. 
FIGS. 10-12 help to demonstrate the value of the unusual width of fixed 
wheel assembly 30, 31. First, the wider the axle mount 34, the smaller the 
proportion of weight borne by fixed wheels 40 when the rider is roughly 
centered on platform 20. This minimizes friction between the fixed wheels 
40 and the surface traveled over. Yet if platform 20 is also very wide, 
the rider can still transfer considerable weight onto fixed wheels 40 by 
moving to the platform's edge. A configuration of fixed wheels 40 
positioned wide apart and a wide platform 20 gives the rider a smooth and 
controllable transition between the carving mode and the omnidirectional 
mode. 
FIGS. 10-12 also show how the rider can implement variable speed control. 
When the device is traveling fully sideways with the rider's weight 
centered over platform 20, the travel is almost as efficient as traveling 
with platform 20 pointed forward. To slow down, the rider can shift her 
weight from base 21 to side 22. This weight transfer vastly increases the 
friction acting on two of fixed wheels 40, effectively slowing the board. 
The rider can vary the speed control by varying the amount of weight 
transfer. 
As the rider transitions her weight on and off of fixed wheels 40, the 
design of biased pivoting roller assembly 50, 51 has many compelling 
advantages. First, the roller board engages a stable position when 
traveling straight forward and also when traveling straight backwards. 
This makes it symmetrical in performance, allowing 180.degree. rotations, 
just like a real snowboard. Second, the bias force holding pivoting roller 
52 aligned straight increases rapidly at first, then levels off (see FIG. 
9). This bias force profile limits wobbling of pivoting roller 52 and 
enables the rider to easily track a straight line when desired. Yet the 
rider can also easily rotate the board sideways by deliberately applying 
the "threshold force" (see FIG. 9). Third, this bias force profile is 
especially effective at returning the rider to a straight ahead position 
after executing a slide or a rotation. As the rider brings the device 
close to straight ahead, there is a very subtle but reassuring feeling of 
it locking into place. Fourth, while the caster is stable at two 
positions, it is free to rotate an infinite number of times unimpeded. 
This is especially important as snowboarders frequently rotate 
successively in one direction. Fifth, this bias profile can easily be 
modified by changing the shape of cam 66 and the stiffness of spring 64. 
Thus, numerous custom force profiles are possible. In addition, the force 
profile of the front pivoting roller assembly 50 might be configured 
differently from the back pivoting roller assembly 51. 
Accordingly, it can be seen that the roller board brings a new freedom of 
movement to skateboarding, approximating many of the movements found in 
snowboarding. The roller board provides the ability to "carve," as a 
conventional skateboard can, where leaning weight to one side causes the 
device to turn in that direction. It permits a mode of omnidirectional 
motion, where the device can easily travel forwards, backwards, sideways 
or any combination thereof. It provides the ability to transition smoothly 
and controllably between the carving mode and the omnidirectional mode. 
The roller board also provides a user interface that simulates the balance 
characteristics of snowboarding and other board sports, where the 
omnidirectional mode is engaged when the rider's weight is relatively 
evenly distributed across the board and this mode can be exited by 
transferring weight to the board's edge. It allows rotations of 
180.degree., 360.degree., or more, repeatedly, without lifting or 
unweighting the board, while in motion over terrain. It includes a height 
adjustment means such that the relative ease of entering the 
omnidirectional mode can be increased or decreased according to the user's 
preference. It provides the ability to ride on a variety of terrains, 
including paved surfaces, grass and dirt. It enables the rider to slow 
down when necessary, by increasing the friction between fixed wheels 40 
and the surface traveled over. Finally the roller board is relatively 
simple in its design and would be economical to produce and sell. 
Although the description above contains many specificities, these should 
not be construed as limiting the scope of the invention but as merely 
providing illustrations of some of the presently preferred embodiments of 
this invention. Thus the scope of the invention should be determined by 
the appended claims and their legal equivalents, rather than by examples 
given.