Wheel chair abstract
The electric wheel-chair comprises drive wheels on one axle group,
and swivel wheels on a second axle group, with the swivel wheels
being either freely pivotable or positively steerable by an engageable
steering drive. The positive steering system may have either a purely
electric configuration in the form of a pair of electric steering
drives, or an electro-mechanical configuration in the form of a
common steering drive and a mechanical steering mechanism with electro-mechanical
disengagement of the positive steering system. Switch-over from
pivoting to steering operation is monitored by position sensors
provided on the swivel wheels. As the seat assembly is adapted to
be rotated to a corresponding position, the swivel wheels may be
operated alternatively as the front wheels or the rear wheels of
the wheel-chair. Owing to the engageable steering drive, the wheel-chair
is well adapted for both indoor operation and outdoor operation,
thereby considerably enhancing the mobility of a disabled person.
Wheel chair claims
We claim:
1. An electric wheel-chair comprising:
a chassis;
a first axle having drive wheels, which is connected to the chassis;
a pair of second axles which are connected to the chassis, each
having a swivel wheel that is pivotable about an axis perpendicular
to movement direction of the wheel-chair, so that the swivel wheels
change steering radius in response to change in running direction
of the wheel-chair;
an actuator independently coupled to each swivel wheel for steering
the wheel in response to steering control signals;
a seat assembly mounted on the chassis;
a drive unit coupled to each drive wheel for driving the wheel
in response to maneuvering control signals indicative of desired
wheel-chair maneuvers to be executed by the drive unit;
an operating unit coupled to the drive units and the actuators
for causing generation of the control signals; and
means for selectively disengaging coupling of at least one of the
swivel wheels from the actuator.
2. The wheel-chair of claim 1, wherein the actuators are positioning
motors and wherein the steering control signals are generated by
a computer coupled to the positioning motors and the control unit.
3. The wheel-chair of claim 1, wherein the control unit has means
for selectively activating drive unit performance of wheel-chair
steering maneuvers when steering actuators are coupled to the swivel
wheels.
4. The wheel-chair of any one of claim 1-3, wherein the control
unit generates maneuvering and steering control signals which coordinate
interaction of the actuators and drive units for steering the wheel-chair.
5. The wheel-chair of any one of claims 1-3, wherein the means
for selectively disengaging coupling is operable only above a selected
swivel wheel pivot angle deviation from a straight line running
position.
6. The wheel-chair of any one of claim 1-3, wherein the means for
selectively disengaging coupling is a means for mechanical coupling.
7. The wheel-chair of claim 6, wherein the means for mechanical
coupling is a friction clutch.
8. The wheel-chair of claim 6, wherein the means for mechanical
coupling has positive interlocking engagement between mechanical
components.
9. The wheel-chair of any one of claim 1-3, wherein the means for
selectively disengaging coupling is an electric motor which steers
the swivel wheel in response to steering control signals when the
motor is energized and which allows unrestrained rotation of the
swivel wheel when the motor is de-energized.
10. The wheel-chair of any one of claims 1-3, further comprising
a swivel angular position detector proximal to each swivel wheel
that is coupled to the corresponding swivel wheel actuator.
11. The wheel-chair of claim 10, wherein the angular position detector
is a mechanical, sensors.
12. The wheel-chair of any one of claims 1-3, wherein the control
unit is coupled to a computer which generates the actuator control
signals in response to signals generated by the control unit.
13. The wheel-chair of claim 12, further comprising a speed selector
coupled to the computer so that the computer monitors selected speed
and generates actuator control signals in response to the monitored
speed.
14. The wheel-chair of any one of claims 1-3, wherein the means
for selectively disengaging coupling of the actuators is manually
disengageable.
15. The wheel-chair of claim 1, wherein the actuators are positioning
motors, the steering control signals are generated by a computer
coupled to the positioning motors and the control unit, and the
control unit has means for selectively activating drive unit performance
of wheel-chair steering maneuvers when the steering actuators are
coupled to the swivel wheels.
16. The wheel-chair of claim 26, wherein the angular position detector
is an optical sensor.
17. The wheel-chair of claim 26, wherein the angular position detector
is an electronic sensor.
Wheel chair description
The present invention relates to an electric wheel-chair comprising
a chassis which has large drive wheels mounted on a first axle group
and smaller swivel wheels mounted on a second axle group, and which
further includes a seat assembly, a drive unit for the drive wheels,
and an operating unit for controlling the drive unit. In electric
wheel-chairs of this type, the larger drive wheels are normally
use not only for propulsion, but also for steering purposes, because
the (turning) direction is determined by the difference in speed
of rotation of the drive wheels.
Generally, wheel-chairs serve to improve the mobility of people
who lost their capability to walk or other body functions. Depending
on the degree of handicap, different systems and constructions of
wheel-chairs are employed. In the case of a severe reduction in
one or more body functions, the use of a power-operated wheel chair,
normally of an electric wheel-chair, becomes necessary in general.
In order to provide for as high as possible a mobility of a disabled
person when using an electric wheel-chair, the latter must satify
requirements which may be inconsistent with each other depending
on the kind of use and place of use.
For use of an electric wheel-chair within closed rooms --this constituting
normally the major part of use--maximum manoeuvrability of the wheel-chair
in combination with easy handling and minimum weight thereof is
desirable. When the same wheel-chair is used outside of closed rooms
under different conditions, for greater distances, etc., other requirements
are imposed on this wheel-chair, e.g. with respect to good reaction,
good directional stability, capability of easily travelling across
obstacles, good shock absorption, etc.
In the past, these different requirements also resulted in different
(constructional) concepts of wheel-chairs, which may be roughly
classified into two categories:
(1) Electric wheel-chairs for indoor use:
In general, these are wheel-chairs having small swivel casters
or swivel wheels in the front and large drive wheels at the rear
end, with the swivel wheels normally not having any auxiliary steering
means. Change of direction of the electric wheel-chair is obtained
solely through the difference in speed of rotation of the pair of
drive wheels.
(2) Electric wheel-chairs for outdoor use:
In general, these are electric wheel-chairs having large drive
wheels in the front to permit easy travel across obstacles, and
swivel wheels or steerable wheels in the rear portion, with these
steerable wheels frequently being provided with a positive steering
system. Here, the positive steering action and the difference in
speeds of rotation of the drive wheels are usually coordinated with
each other.
These conventional wheel-chairs designed for one specific field
of use each, are useful for the other field of use to a limited
degree only. For example, a wheel-chair designed for outdoor use
and provided with positive steering of the swivel wheels through
a mechanical steering linkage, is not expedient for indoor use since
the positive steering system permits a limited angle of traverse
only. On the other hand, wheel-chairs designed for indoor use and
having freely pivotable steerable wheels are not very suited for
outdoor use, because the pair of pivotable (swivelling) wheels result
in a certain instability in the travel direction. For these reasons,
a disabled person would always need two wheel-chairs, this being
not possible in most instances for financial reasons and reasons
of storing space.
It is the object of the invention to provide an electric wheel-chair
which is designed so that it may be used with advantages for both
indoor use and outdoor use, and which equally satisfies the various
above-mentioned requirements.
In an electric wheel-chair of the type as outlined above, according
to the invention this object is solved in that the swivel wheels
are freely pivotable selectively, and that at least one of said
swivel wheels is adapted to be positively steered through engageable
steering actuator means.
Owing to the selective engagement of steering actuator means with
the swivel wheels as according to the invention, use can be made
of the advantages of both the free pivotability and the positive
steering, as required. As the swivel wheels are expediently operated
as front or rear wheels as required, the seat assembly, too, is
expediently designed to be pivotable or rotatable, so that it may
be rotated to the respective direction of travel depending on the
orientation of the drive wheels and swivel wheels.
Preferably, the selectively engageable positive steering system
is coordinated with the difference in speed of rotation of the drive
wheels. Further, the arrangement may be made so that the steering
drive means is engageable manually or automatically in accordance
with the speed (of travel) of the wheel-chair.
Special embodiments and further developments of the invention are
disclosed in the subclaims.
Below, the invention is explained in greater detail with reference
to exemplary embodiments. These embodiments relate to a combination
electric wheel-chair in which the seat assembly may be rotated by
180.degree. as required, depending on whether the drive wheels are
to be used as the front or the rear wheels. However, the wheel-chair
may be designed differently with respect to the seat assembly and
its other structure.
In the drawings:
FIG. 1 is a side elevational view of a combination electric wheel-chair;
FIG. 2 is a schematical front elevational view of a swivel wheel
assembly;
FIG. 3 is a plan view of a modified swivel wheel assembly;
FIG. 4 is a simplified functional diagram of a positive steering
system comprising one common steering drive means for both swivel
wheels with mechanical turning circle adjusting means;
FIG. 5 is a simplified functional diagram of a positive steering
system comprising steering drive means for one swivel wheel only;
and
FIG. 6 is a simplified functional diagram of a positive steering
system comprising independent steering drive means for each swivel
wheel.
FIG. 1 shows in side elevational view a combination electric wheel-chair.
A chassis 1 comprises large drive wheels 3 mounted on an axle 2,
and pivotally mounted swivel wheels 5 suspended from wheel forks
4. A seat assembly (or group) 6 is rotatably mounted on the chassis
1 through a central column 7. In a conventional manner, the seat
assembly includes foot rests 8 and a back rest 9 as well as a laterally
positioned operating unit 10 provided with a control stick 11. By
tilting the control stick 11 from the zero (neutral) position to
the front or rear, a signal being proportional to the desired speed
of travel is input to the drive system; the electric wheel-chair
responds with a corresponding forward or reverse speed. By lateral
tilting of the control stick 11 to the left or right, a corresponding
desired change of direction is set for the electric wheel-chair.
As mentioned above, in the wheel-chair shown in FIG. 1 the seat
assembly 6 is mounted for rotation on the chassis 1. In the position
shown, the back rest 9 is positioned above the drive wheels 3, while
the foot rests 8 are located above the swivel wheels 5. Thus, the
drive wheels are positioned at the rear end relative to the seating
direction or direction of travel, respectively. This configuration
is particularly favorable for indoor use because of the high manoeuvrability
of the electric wheel-chair. When the seat assembly is rotated by
180.degree., the back rest 9 comes to be located above the swivel
wheels 5, and the foot rests 8 assume a position above the drive
wheels 3. Then, the drive wheels are at the front end as seen in
the direction of travel. This configuration provides special advantages
for outdoor use, because larger obstacles are easier to be overcome
by the large front wheels. In both configurations (or modes of operation)
of the combination electric wheel-chair, or with a fixedly mounted
seat assembly for each wheel-chair, it holds that changes of direction
are brought about by different speeds of rotation of the drive wheels
3, whereas the swivel wheels 5 follow the direction determined by
the drive wheels 3 due to the rolling friction on the ground and
the trail or caster angle.
In the electric wheel-chair according to the invention, these swivel
wheels 5 are positively steerable or powersteerable by (selectively)
connectible or engageable steering actuator 12, such that these
swivel wheels become steerable wheels. Various embodiments of this
engageable steering drive means can be seen from FIGS. 2 to 5.
As shown in FIG. 2, each of the pair of swivel wheels 5 may be
provided with an associated steering actuator 13; in this structure,
a transmission element of any suitable type, e.g. one toothed belt
14 for each wheel, transmits the rotary motion of the steering drive
means to shaft 15 of the respective wheel fork 16. In the wheel
5 shown at the right in FIG. 2, it is indicated in what a manner
the steering drive means 13, in a special embodiment, is connected
to shaft 15 through a--schematically illustrated--clutch or coupling
17. The clutch or coupling 17 is or any conventional deign known
in the art, including for example friction clutches or mechanical
coupling devices with positive mechanical interlocking engagement
between mechanical compenents. When the coupling 17 is disengaged,
the swivel wheel 5 is free to pivot. The free pivotability of the
rear wheels imparts a high manoeuvrability to the electric wheel-chair;
namely, the wheel-chair may turn substantially on the point. Owing
to the instability of the vehicle with rear-mounted swivel wheels,
however, this configuration must be limited to lower speeds of travel
only, and it should therefore be chosen preferably for indoor use
only.
In order to obtain safety or stability of the electric wheel-chair
within a wide range of travelling speeds, automatic engagement of
the power steering system at a given speed of travel is possible.
FIG. 3 illustrates the principle of a positive (or power) steering
system through one single steering actuator 18 for both swivel wheels.
This steering actuator 18 is mounted to the chassis through a schematically
illustrated suspension 19, and it acts on both swivel wheels 5 through
a (steering) tie rod 20. As a positive steering system of this type
permits a limited pivot angle only, in this case a coupling (not
shown in detail) is provided which may be disengaged, if necessary,
in order to regain the full freedom of movement of the swivel wheels
(for indoor use of the wheel-chair). For operation of the steering
unit, the position of the swivel wheels is monitored or detected
by position sensors (not illustrated, either). Engagement of the
positive steering system is possible only in a proper relative position
of the swivel wheels and steering actuator.
FIG. 4 illustrates the functional principle of a positive steering
system comprising a steering actuator 18 according to FIG. 3. The
setting of a turning circle of the swivel wheels is performed through
a mechanical steering mechanism, and the pair of swivel wheels are
interconnected through a schematically shown tie rod 20.
The direction of travel is selected through the operating unit
10 by means of the control stick 11. Engagement of the positive
steering system through couplings 17 may be selected via the switching
unit 26. Depending on the position of the switch provided in the
switching unit 26, said engagement is performed manually (left hand
position) or automatically within a permissible pivoting range,
and/or in accordance with the speed of travel of the wheel-chair.
In the example shown, the speed v.sub.s set on the operating unit
10 is signalled to the speed threshold unit 28, and the selected
direction r.sub.s is signalled to the direction range setting unit
27. These units 27 and 28 generate a signal within a predetermined
range of direction or when a given speed of travel is exceeded,
respectively, and such signal is supplied to said switching unit
26 either directly or through an AND gate 29. A comparator 30 provides
a directional signal for defining a specific turning circle to the
positioning (or actuator) element 31 in accordance with the position
of the control stick 11. Accordingly, the swivel wheels 5, with
the couplings engaged, are turned to the set or selected position
through the steering actuator 18.
The angular position is monitored or detected by a position detecting
unit. In this instance, the position of the steering actuator is
detected by a sensor 32, and the position of the swivel wheels is
detected by sensors 33. The swivel wheel angular position detecting
sensors 33 may be any conventional design known in the art, such
as mechanical, optical or inductive, capacitive or magnetic types
of electronic sensors. Comparator units 34 and control units 35
control the relative position between the steering system and the
swivel wheels. The output signal from these control units 35 is
supplied to an AND gate 36 together with the signal provided by
the switching unit 26. When both these signals are applied, the
respective couplings 17 are operated, and the swivel wheels 5 are
accordingly engaged with the steering actuator 18. Sensor 32 feeds
back the position of the steering drive means to the comparator
30, and readjustment is performed by the positioning element 31
and the steering actuator 18 in the case of deviations.
FIG. 5 illustrates a comparable functional principle of a positive
steering system comprising a steering actuator 18 which acts upon
one swivel wheel 5 only. In this structure, the second wheel 5 is
freely rotatable (turnable) and not used for positive steering purposes.
In any other respect, the functional principle is the same as that
of FIG. 4, except that the mechanical connection to the second swivel
wheel 5 is missing and, accordingly, the coupling 17 and the position
detecting unit 32 or 33, respectively, are provided only for the
positively steered swivel wheel 5.
A further modification of the same functional principle is illustrated
in FIG. 6. This Figure shows a positive steering system comprising
an independent steering actuator 18 for each swivel wheel 5. The
turning circle of the swivel wheels is selected (or set) via the
respective steering actuator 18, with a steering angle computer
37 performing control of both steering drive means. In other respects,
the function of the various elements is the same as described in
conjunction with FIG. 4. Unlike FIG. 4, this system includes, in
addition to a pair of steering actuators 18, also separate positioning
elements 31 and comparators 30. Engagement of the positive steering
system through couplings 17 takes place in the same manner as in
FIG. 4. When the positive steering system is deactivated, both wheels
5 are freely pivotable.
If load-responsive steering actuators 18 are chosen which allow
the wheels to pivot freely in a load-free operation, the couplings
17 could be omitted. For example, a low-friction electric steering
drive means would allow free pivoting of the steerable (swivel)
wheels in a currentless state of operation.
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