Wheel chair abstract
A self propelled wheel chair is adaptable to climbing and descending
stairs and steep slopes. The wheel chair is foldable for transporting
and storing. Operation on level ground is similar to the operation
of a conventional wheel chair. The wheel chair is supported by caster
wheels on the front corners and by spider wheels on the rear corners.
Skids are mounted to the caster forks for stabilizing the front
of the chair during climbing operations. The casters are mounted
to parallelogram linkages on the front of the wheel chair. The parallelogram
linkages move the casters down and forward for repositioning to
the climbing mode. The spider wheels are rotatably mounted to four
bar linkages on the wheel chair side frames. The spider wheels engage
the stairs to propel and stabilize the wheel chair during climbing
or descending of stairs. The four bar linkages sequence the repositioning
of the spider wheels and casters for climbing. Weight is shifted
to the spider wheels for climbing so that they can provide climbing
forces without slipping. Propulsion and transition control and power
are provided by individual hand wheels linked by chain drives to
the spider wheels and transition linkages. Propulsion power for
both conventional level operation and stair climbing operation is
transmitted through the same hand wheels and spider wheels. The
hand wheels are grounded to the wheel chair structure by no back
brakes to brake the wheel chair linkages and spider wheels in place
when the hand wheels are released by the passenger.
Wheel chair claims
What is claimed is:
1. A self propelled vehicle adaptable to climbing stairs comprising:
a cargo supporting frame, a pair of symmetrical rear suspension
frames with a spider wheel rotatably attached to each, and a pair
of symmetrical forward suspension frames with a sloped skid rigidly
attached; with the rear suspension frames attached to the cargo
supporting frame by a plurality of arms with ends rotatably attached
to the cargo frame and the rear suspension frames, with the forward
suspension frames attached to the cargo frame by a plurality of
arms with ends rotatably attached to the cargo frame and the forward
suspension frames; with rear frames and forward suspension frames
containing a common attachment arm causing said frames to move in
sequence with each other for respositioning the spider wheels in
a forward and upward direction and skids in a forward and downward
direction for traversing stairs with supporting loads carried primarily
by the spider wheels.
2. Vehicle in claim 1 with caster wheels attached to the forward
suspension frames.
3. Vehicle in claim 2 with mechanical means for locking the caster
wheels, said means comprising a slider rod attached to the frame
which is forced by a spring into a hole in a disk which is rigidly
attached to the caster wheels, when the rear and forward support
frames are in the position for traversing stairs and the caster
wheels swivel to the backing position by backing the vehicle and
with mechanical means for unlocking the casters when the rear and
forward suspension frames are in the position for traversing level
surfaces, said means comprising a lever and series linkage which
lift the sliding rod out of the hole in the disk.
4. Vehicle in claim 1 with an arm for each locking spider wheel
with only one minor wheel able to contact level surface per side
when said vehicle is being repositioned for level operation and
means for mechanically disengaging said aim for each locking spider
wheel when vehicle is being positioned for stair traversing.
5. Vehicle in claim 1 with seat and other accommodations for a
passenger.
6. Invalid vehicle in claim 5 with means for reclining seat back
to provide occupant comfort.
7. Vehicle in claim 1 with means for transmitting manual or motor
power to spider wheels.
8. Vehicle in claim 7 with means for preventing back driving of
spider wheel by vehicle and cargo weight.
9. Vehicle in claim 1 with means for transmitting manual or motor
power for repositioning the spider wheels.
10. Vehicle in claim 3 with means for preventing back driving of
vehicle transition inputs.
11. Vehicle in claim 1 with means for folding to reduce said vehicle
size for transporting or storing.
Wheel chair description
FIELD OF INVENTION
This invention relates to an improved occupant powered and controlled
vehicle which is adaptable to climbing steps or stairs, as well
as traversing surfaces with modest or steep slopes. More particularly,
it relates to vehicles of this type which are constructed to serve
as invalid wheel chairs.
DISCUSSION OF PRIOR ART
Heretofore, invalid wheel chairs have been restricted to level
surfaces, modest sloped ramps, elevators or negotiation of such
surfaces with the assistance of attendants. Many vehicles have been
proposed, but all have certain diadvantages which my invention is
intended to overcome. One class of such vehicles employs tracks
for climbing and separate large diameter wheels for propulsion on
level surfaces. This class of vehicles is penalized by the additional
weight and size required for two independent propulsion systems.
A second class of vehicles employs spider like wheels which engage
steps. One such vehicle is U.S. Pat. No. 2,931,449 patented by C.
A. King. The King patent requires passenger sequencing of two means
of driving the spider wheels and a seat leveling drive system as
it climbs each step. The three drive systems required by the King
invention makes it difficult to design as a lightweight occupant
powered folding wheel chair.
OBJECTS
Accordingly, a first object of my invention is to provide a wheel
chair suitable for negotiating steps and slopes without the assistance
of an attendant.
A further object of the invention is to provide a wheel chair as
described which is automatically adaptable to the negotiation of
stairs and slopes of varying dimensions.
A further still object of the invention is to provide a wheel chair
as described which automatically maintains the occupant seat substantially
level during climbing from one step to the next step.
A further object of the invention is to provide a wheel chair as
described which is occupant powered and controlled in a simple and
natural manner.
A further object of the invention is to provide a wheel chair as
described which receives all propulsion inputs in the same device
without passenger sequencing while climbing from step to step.
A still further object is to provide a wheel chair as described
which will traverse in a conventional manner on smooth level surfaces,
pass through normal doors and turn around in narrow hallways.
A further still object is to provide a wheel chair as described
which is lightweight, foldable and transportable.
A still further object is to provide a wheel chair as described
which operates with a minimum loss of mechanical power in the propulsion
and transition drive systems and in the vehicle interface with obstacle
surfaces.
A further object is to provide a wheel chair as described which
has means to prevent back driving of propulsion and transition power
inputs. Such means shall operate automatically without occupant
control input to prevent the wheel chair from rolling down stairs
or steep slopes.
A still further object is to provide a wheel chair as described
which is adaptable to powered operation.
Further objects and advantages of my invention will become apparent
from a consideration of the drawinges and ensuing description thereof.
DRAWINGS
FIG. 1 is a plan view of a wheel chair employing my invention and
shown in the conventional operating position.
FIG. 2 is a side elevation view of the wheel chair embodiment shown
in FIG. 1.
FIG. 3 is a rear elevation view of the wheel chair embodiment shown
in FIG. 1.
FIG. 4 is an exploded side elevation view of the wheel chair embodiment
shown in FIG. 1.
FIG. 5A is a side elevational view of the left hand caster and
its locking mechanism. FIG. 5B is a plan view of the left hand caster
and its locking mechanism.
FIG. 6 is a section view cut through the left side hand wheel rotation
axis.
FIG. 7A is a detail side elevation view of the spider wheel.
FIG. 7B is a cross section view cut through the spider wheel rotation
axis.
FIG. 8A through FIG. 8K is a series of schematic side elevation
views illustrating the manner in which the embodiment negotiates
a stairway.
FIG. 9A is a schematic freebody diagram of typical forces acting
on the wheel chair. FIG. 9B is a schematic freebody diagram of typical
forces acting on the spider wheel.
FIG. 10 is a schematic side elevation view of the path of the front
caster and skid traveling up or down typical stairs.
FIG. 11 is a schematic side elevation view of the path of the spider
wheel traveling up or down typical stairs.
FIG. 12 is a schematic side elevation view illustrating the moment
arms and the path of a four minor wheel spider wheel descending
stairs.
FIG. 13 is a schematic side elevation view of the moment arms and
the path of a three minor wheel spider wheel descending stairs.
DESCRIPTION
The embodiment of my invention consists of a seat frame with spider
like wheels attached at the rear on each side of the frame and with
castering wheels with angled skids attached on each side on the
front. The caster wheels and spider wheels are mounted on linkages
which allow them to be repositioned for stair climbing. Propulsion
power and transition inputs are applied through hand wheels mounted
on the transition linkages. Operation and appearance of the embodiment
of my invention are similar to those of a conventional wheel chair.
Referring to FIGS. 1,2,3 and 4; the seat frame 10 of my invention
has a well known scissor type folding mechanism 11. The seat frame
10 consists of a left side frame 21, a right side frame 22, forward
seat cross brace 12, rear seat cross brace 13 and two toggle links
14. Additionally, a flexible seat back 15, a flexible seat bottom
16, hand grips 17, left foot rest 23 and right foot rest 24 are
mounted to the seat frame 10.
Since the components which mount to the left side frame 21 and
right side frame 22 are constructed and mounted as mirror images
of each other with reference to plane 18, only the left side will
be described. Corresponding members on the right side will be denoted
by the next highest even number. On the left side the caster 25
is mounted to the parallelogram linkage 27. The parallelogram linkage
27 includes an upper link 29, a caster arm 31 and a lower caster
link 33. Skid 35 is rigidly attached at an angle to the caster fork
37 as shown in FIG. 5A. An upper skid 39 is rigidly attached to
the caster arm 31. The upper link 29 is pivotably mounted to both
the side frame 21 and caster arm 31. The lower caster link 33 is
also pivotably mounted to both the side frame 21 and the caster
arm 31.
The caster arm 31 includes a caster lock. Referring to FIG. 5A
and FIG. 5B, the lock incorporates a pawl 41 which is mounted to
a bellcrank 43. The bellcrank 43 is rotatably attached to the caster
arm 31. A slotted disk 45 is rigidly attached to the caster fork
37. The slot 47 on the slotted disk 45 is aligned with the pawl
41 when the caster 25 is in the vehicle backing position as shown
in FIG. 2. A compressible link 49 is pivotably attached to the bellcrank
43 and to a lug 19 on the end of lower caster link 33. The compressible
link 49, a well known funk spring, is a collapsible link with fixed
extended and compressed lengths and is normally held at its extended
length by a compression spring.
Referring to FIG. 4, the spider wheel 51 and drive systems are
mounted to a bogie 53 which is suspended from the side frame 21.
The forward end of the bogie 53 is pivotably attached to the lower
caster link 33. The lower aft end of the bogie 53 is pivotably mounted
to the side frame 21 with an idler link 55. The top of the bogie
53 is connected to the side frame 21 with two links in series: a
transition arm 57 and an arm rest link 59. The transition arm 57
is rotatably connected to the bogie 53. The arm rest link 59 is
pivotably attached to the transition arm 57 and the side frame 21.
A large diameter chain sprocket 61 is rigidly attached to the transition
arm 57. The sprocket 61 is connected to a small diameter chain sprocket
65 with an endless link chain 63. The small diameter sprocket 65
is rotatably attached to the bogie 53. Referring to FIG. 6, the
small diameter sprocket 65 is normally indexed to the bogie 53 by
a well known no back brake 67. The transition hand wheel 69, transition
no back brake 67 and small diameter sprocket 65 are rotatably mounted
about a common axis on the bogie 53. The transition hand wheel 69
is rigidly attached to the input side of the transition no back
brake 67. The small diameter sprocket 65 is torsionally connected
to the output side of the transition no back brake 67 by transition
drive shaft 71. The transition no back brake 67 is indexed to the
bogie 53 by the truss 73. The truss 73 is rigidly connected to the
bogie 53, as shown in FIG. 4, and to the transition no back brake
67.
Referring to FIG. 7A and 7B, the spider wheel 51 includes four
minor wheels 75 rotatably mounted to the spider wheel frame 77.
A small diameter chain sprocket 79 is torsionally connected to each
minor wheel 75 by a minor wheel axle 81. The four sprockets 79 are
mechanically coupled to each other and to a large diameter sprocket
83 by an endless link chain 85. Five sprocket idlers 87 are rotatably
mounted to the spider wheel frame 77 to provide suitable routing
for the endless link chain 85. The large diameter sprocket 83 is
coaxially and rotatably mounted to the spider wheel 51. The large
diameter sprocket 83 is rigidly attached to a second large diameter
sprocket 89. Referring to FIG. 4, the large diameter sprocket 89
is coupled to a small diameter sprocket 91 by an endless link chain
93. The small diameter sprocket 91 is rotatably attached to the
bogie 53. The small diameter sprocket 91 is rigidly attached to
the output side of the propulsion no back brake 95 as shown in FIG.
6. A disk 97 is rigidly attached to the outer diameter of the propulsion
no back brake 95. The propulsion hand wheel 99, propulsion no back
brake 95, and small diameter sprocket 91 are all coaxially and rotatably
mounted to the bogie 53. A screw actuated caliper brake 101 is attached
to the bogie 53 with friction surfaces 105 engaging each side of
the disk 97. A brake handle 103 is attached to the caliper nut 107.
The caliper nut 107 is threaded on to caliper screw 109 which is
rigidly attached to the bogie 53. Referring to FIG. 4, a rachet
pawl 111 is configured to engage the spider wheel frame 77. A tension
spring link 113 is pivotably attached to the transition arm 57 and
the rachet pawl 111. The tension spring link 113 consists of a conventional
tension spring surrounded by a hollow tube.
OPERATION
Normal level operation is similar to that of a conventional wheel
chair. The front caster wheels 25 and 26 caster to accommodate directional
changes. Manual hand power is applied to the propulsion hand wheels
99 and 100 to propel the wheel chair. Steering is accomplished by
stalling one side and propelling the other. The spider wheels 51
and 52 are restrained with the forward minor wheels 75 and 76 lifted
off the ground by the ratchet pawls 111 and 112 to prevent the minor
wheels 75 and 76 from scrubbing while turning during conventional
operation.
Folding for transporting or storing is accomplished in the same
manner as for a conventional wheel chair. The passenger dismounts
and the side frames 21 and 22 are pushed together, collapsing the
seat frame scissor folding mechanism 11.
The wheel chair passenger faces down the stairs during both climbing
and descending operations. To climb stairs, the wheel chair is backed
up to the stairs until the minor wheels 75 and 76 are stalled against
the first step as shown in FIG. 8A. Since the operation of both
sides of the wheel chair are similar, only the left side will be
described. The passenger engages the propulsion no back brake 95
by pushing down on the brake handle 103 until the caliper brake
101 grasp the disk 97, as shown in FIG. 6, to index the propulsion
no back brake 95 to the bogie frame 53. The propulsion no back brake
95 prevents the weight of the passenger and wheel chair from back
driving the wheel chair when climbing stairs or over running when
descending stairs. Torsion applied to the output side of the propulsion
no back brake 95 is grounded to the bogie 53 unless an opposing
torque is applied to the input side of the propulsion no back brake
95 by the passenger through the propulsion hand wheel 99. Torsion
applied to the input side of the propulsion no back brake 95 by
the passenger releases the propulsion no back brake 95 and is then
transferred to the output side of it. The propulsion no back brake
95 is automatically reset when the propulsion hand wheel 99 is released.
After manually engaging the propulsion no back brake 95, the passenger
continues rotating the propulsion hand wheel 99 to begin climbing.
The spider wheel 51 begins to rotate about the stalled supporting
minor wheel 75 and continues until a second minor wheel 75 contacts
the top of the first step as shown in FIG. 8B. Additional rotation
of the spider wheel 51 lifts the forward minor wheel 75 off the
ground as shown in FIG. 8C. The passenger seat frame 10 is tilted
forward as the spider wheel 51 climbs. Before the seat tilting reaches
an uncomfortable level, the passenger must stop climbing and begin
repositioning the wheel chair to the climbing position. The passenger
rotates the transition hand wheel 69 to drive the transition arm
57 to reposition the bogie 53 and parallelogram caster linkage 27
as shown in FIG. 8D. The transition arm 57 is grounded to the bogie
53 by the transition no back brake 67. Torsion applied to the input
side of the transition no back brake 67 by the transition hand wheel
69 releases the transition no back brake 67. The transition hand
wheel 69 torque is then transmitted to the transition arm 57 to
reposition it. Release of the transition hand wheel 69 allows the
transition no back brake 67 to reset. The parallelogram caster linkage
27 maintains the skids 35 and 39 in a constant pitch attitude relative
to the seat frame 10 as it moves the caster 25 and skids 35 and
39 in a forward and downward direction. The bogie 53 raises the
spider wheel 51 up and forward to near the composite passenger and
chair center of gravity during transition to the climbing position.
The passenger continues alternately climbing and repositioning
the bogie 53 and caster 25 until the wheel chair is repositioned
to match the stair angle as shown in FIG. 8E. As the passenger continues
to climb, the skids 35 and 39 contact the first step and are dragged
up the stairs as shown in FIG. 8F. Continued climbing is possible
since skid reactions are minimized by moment arm changes made during
transition. FIG. 9A and 9B show typical wheel chair climbing and
spider wheel freebody diagrams with balanced forces and moments.
The horizontal moment arm 121 of the reaction point on skids 35
or 39 or caster 25 about the center of gravity 123 has been increased
and the horizontal moment arm 125 of the spider wheel 51 rotation
axis about the center of gravity 123 has been reduced. The spider
wheel 51 shown in FIG. 7A results in the moment generated by loads
applied to the spider wheel 51 being grounded by the traction force
component 129 of the supporting minor wheel 131. The resulting minor
wheel 131 traction force 129 is reduced to a practical level by
the mechanical drive advantage between the large diameter sprocket
83 and the small diameter sprocket 79. In the example shown in FIG.
9A and 9B, the 669.8 in.lb moment grounded through a chain drive
ratio of 96 teeth on the large diameter sprocket 83 to 20 teeth
on the small diameter sprocket 79 and a 4.1 in. minor wheel 75 radius
results in a 34.0 lb traction load ((669.8 in.lb.times.20/96)/4.1
in.=34.0 lb.). This produces a vertical force 127 on the supporting
minor wheel 131 which is high enough, 90.8 lb., and a horizontal
force 129 component which is low enough, 34.0 lb., to require a
feasible coefficient of friction (coefficient of friction required=34.0
lb./90.8 lb.=0.374) to avoid slipping of the supporting minor wheel
131 and to maintain stability. Selection of the spider wheel 51
mechanical advantage is the key to the climbing ability of the spider
wheel 51. If the ratio of moment at the spider wheel 51 to moment
at the minor wheel 131 is too small, an excessive horizontal force
component 129 will be required at the supporting minor wheel 131
to develop the vertical climbing force required at the supporting
minor wheel 131. For example, 20 teeth on both sprockets 79 and
83 and the same 669.8 in.lb moment would require in a traction force
of 163.4 lb. for the same 4.1 in. minor wheel 75 radius ((669.8
in.lb..times.20/20)/4.1 in.=163.4 lb.). The friction coefficient
required would not be practical (friction coefficient required=163.4
lb./90.8 lb.=1.8). A friction coefficient requirement between the
minor wheel and stairs greater than 0.5 or 0.6 may allow slipping
and instability on the stairs.
The caster 25 with skid 35 and 39 follows a path 133 up the stairs
which is essentially straight as shown in FIG. 10. The spider wheel
51 rotation axis follows path 135 which is also essentially straight
as shown in FIG. 11. These straight paths permit the wheel chair
frame 10 to maintain a pitch attitude which is nearly constant and
is approximately level without repositioning the caster 25 and spider
wheel 51 during climbing from step to step.
When the spider wheel 51 reaches the top of the stairs as shown
in FIG. 8G, the wheel chair frame 10 begins to pitch backward as
the caster 25 continues to climb and the spider wheel 51 remains
level. The passenger must cease climbing and reposition the caster
25 and spider wheel 51 to relevel the seat frame 10 as shown in
FIG. 8H. The passenger continues alternately climbing and repositioning
until the caster 25 is on the top of the level of the stairs and
the seat is in the level position as shown in FIG. 8I through FIG.
8K.
As the wheel chair is repositioned to the level position, the caster
lock linkage unlocks the caster 25. Referring to FIGS. 5A and 5B,
rotation of the lower caster arm 33 operates the lock linkage to
disengage the pawl 41 from the slotted disk 45. Referring to FIG.
4, the spider wheel ratchet pawl 111 is activated by motion of the
transition arm 57 and tension link 113 as the wheel chair moves
to the level position. The ratchet pawl 111 engages the spider wheel
51 and lifts the forward minor wheel 75 off the ground as the bogie
53 is repositioned to the level position.
The passenger disengages the propulsion no back brake 95 by pulling
the brake handle 103 upward to release the caliper brake 101 from
the disk 97. Referring to FIG. 8K, the passenger is now free to
propel the wheel chair in the conventional manner at the top of
the stairs.
The wheel chair descends the stairs in a similar manner to climbing.
Again referring to FIG. 8K and describing only the left side, the
passenger approaches the stairs facing down them. The passenger
then backs away from the stairs to allow the caster 25 to reverse.
The passenger then rotates the transition hand wheel 69 to pitch
the seat frame 10 attitude backward to permit the caster lock linkage
to lock the caster 25, to lower the forward minor wheel 75 and to
deactivate the ratchet pawl 111. The passenger now verifies that
the caster 25 is locked by attempting to turn the wheel chair or
by visually observing the caster lock. The passenger then activates
the propulsion no back 95 by pushing down on the brake handle 103.
The passenger propels the wheel chair to approach the stairs and
allows the caster wheels to rest near the edge. The passenger rotates
the transition hand wheel 69 to reposition the caster 25 and spider
wheel 51 until the wheel chair reaches the limit of rearward seat
pitch attitude which is comfortable to the passenger. The passenger
then alternately repositions the wheel chair and descends until
the wheel chair is fully repositioned for descending as shown in
FIG. 8G. As the forward minor wheel 75 rolls over the edge of the
top of the stairs, the minor wheel 75 descends and the spider wheel
51 begins rotating in the same direction as the minor wheels 75.
The configuration of the spiderwheel 51 must be compatable with
stairs in both climbing and descending modes. Referring to FIG.
12, the distance 137 between minor wheels must be long enough to
permit stepping up during climbing. Then to insure that the supporting
minor wheels 75 will rest on level step surfaces during descending,
means is required to insure that one minor wheel 75 of the spider
wheel 51 hugs a step riser, as shown in FIG. 12. Means to insure
stepping of the spider wheel 51 down the stairs and to insure spider
wheel 51 hugging of the riser is provided by controlling the horizontal
position of the spider wheel rotation center 139 when the supporting
loads are transferred from one minor wheel 75 to another as shown
in FIG. 12. If the spider wheel 51 rotation axis is between the
horizontal limits 141 of the two minor wheels 75 on the stairs as
shown in FIG. 13, no moment at the rotation center of the spider
wheel 51 is produced by the minor wheel 75 reactions. Without a
moment at the spider wheel 51 rotation center, no spider wheel 51
rotation is available for stepping and no crowding force is available
to maintain hugging of the spider wheel 51 against a step riser.
If the spider wheel 51 rotation axis is not between the horizontal
limits 141 of the two minor wheels 75 resting on the steps as shown
in FIG. 12, a moment is produced at the spider wheel 51 rotation
axis. The moment then causes the spider wheel 51 to rotate as the
spider wheel 51 descends to produce stepping or transferring of
supporting loads from one minor wheel to the next. Also the moment
produced by the vertical reaction of the minor wheel about the spider
wheel rotation center is reacted through the spider wheel mechanical
drive system and grounded by minor wheel 75 horizontal traction
loads at the vertical surfaces of the next highest step riser. Thereby
providing the spider wheel 51 the means to hug the stair riser.
Means to insure that the horizontal position of the spider wheel
rotation axis 139 is not located between the horizontal limits 141
of the supporting minor wheels axis when two minor wheels rest on
two steps is insured by proper selection of the spider wheel 51
geometry. The sum of angle A and angle B as shown in FIG. 12 and
FIG. 13 must be greater than 90 degrees for the spider wheel rotation
axis 139 to be outside the horizontal position limits 141 of the
two minor wheels resting on the two steps. Angle A is defined as
the acute angle between a line 143 connecting the rotation axis
of the two minor wheels resting on the two steps and a horizontal
line 145 through the lower minor wheel 75. For equal radius minor
wheels 75, angle A is defined by the distance 137 between the two
minor wheel 75 axis and the step riser height 149. Angle B is the
acute angle between a line 147 connecting the spider wheel 51 rotation
axis and the lower minor wheel 75 rotation axis and a line 143 connecting
the rotation axis of the two minor wheels 75 resting on the two
steps. For radially symmetrical spider wheels, angle B is determined
by the number of minor wheels 75 per spider wheel 51. For the stair
geometry and minor wheel to minor wheel distances shown in FIG.
12 and FIG. 13, selection of a minumum of four minor wheels per
spider wheel insures that the spider wheel will step down the stairs.
Failure of the spider wheel to rotate the supporting loads from
one minor wheel to the next during descending may result in an unstably
positioned supporting minor wheel 131 as shown in FIG. 13. Referring
to FIGS. 8F through 8A, continued spider wheel 51 rotation lifts
the aft minor wheel 75 off the top step and lowers the next minor
wheel 75 to the next lower step. The wheel chair continues down
the steps and is repositioned back to the conventional level position
at the bottom of the stairs. As the wheel chair is repositioned
to the level position, the ratchet pawl 111 is reactivated and the
spider wheel 51 is rotated against it. The spider wheel 51 is then
restrained with the forward minor wheel 75 lifted off the ground
as shown in FIG. 2. The passenger lowers the brake handle 103 and
the wheel chair is ready for conventional operation at the bottom
of the stairs.
The wheel chair may be repositioned to recline for the comfort
and pleasure of the passenger by simply repositioning the spider
wheels 51 and 52 and caster wheels 25 and 26 by rotating the transition
hand wheels 69 and 70 as is done for transition to the stair climbing
position. The wheel chair may also be repositioned for negotiation
of steep slopes by rotating the transition hand wheels 69 and 70
as required to level the seat frame 10 with the casters 25 and 26
and the spider wheels 51 and 52 resting on a sloped surface.
A powered version may be provided by replacing or supplementing
the hand wheels with electric motors with suitable controls and
batteries or other suitable engines and power sources.
While the above description contains many specifities, these should
not be construed as limitations on the scope of the invention, but
rather as an exemplification of one preferred embodiment thereof.
Many variations are possible for, example a motorized invalid chair,
an appliance dolly version, a stair climbing robot, or life support
system carrier. Accordingly, the scope of the invention should not
be determined by the embodiment illustrated, but by the appended
claims and their legal equivalents. |