Note: Descriptions are shown in the official language in which they were submitted.
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Title: RAISABLE LEG REST
FIELD OF THE INVENTION
This invention relates to the general field of wheelchairs, and more
particularly to wheelchairs which include leg rests to support the wheelchair
user's legs.
BACKGROUND OF THE INVENTION
Wheelchairs have been known and used for many years to assist
disabled people in moving about. Wheelchairs generally include a mobile
platform, which includes the base and wheels, a seat mounted to the base,
and legrests to comfortably secure and support the wheelchair user's legs.
Since most wheelchair users are confined to their chairs for extended
periods, wheelchairs are usually designed to provide a variety of sitting
positions. This enhances user comfort and enables the user to relieve
excessive pressure in any single area, which can cause sores. The need for
variety has given rise to wheelchairs with such features as seats that tilt or
recline, and raisable leg rests. Since individual wheelchair users vary
greatly
in size and body type, it is a challenge to construct a chair that is
sufficiently
versatile in providing a range of positions suitable for many people, while
using mechanisms that are safe, reliable, and preferably low cost.
Raisable legrests in particular present certain problems. Legrests are
designed to support a user's lower leg and move it between a lowered
position and a raised position. The lower leg range of motion may be from
a vertical (leg bent 90 degrees) to horizontal (leg straight, parallel to
ground).
Leg rests typically include a pivoting down tube with a footplate, a calf pad,
and an actuator to move the down tube between selected positions.
Generally the weight of the lower leg will be supported in any given position
by the footplate and the calf pad, with the calf pad taking on more weight as
the legrest is raised.
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A problem with this arrangement is that the user's lower leg is
typically longer than the down tube. As the leg rest is raised there is an
inward pressure created on the user's foot from the footplate. This will force
the user's knee to pop up, lifting the upper leg off the seat to some extent.
The upper leg will therefore lack support, and there will be localized
pressure
at the contact point with the seat. Attempted solutions in the prior art
usually
involve providing an extension mechanism to extend or retract the down tube
telescopically in accordance with the raising or lowering of the legrest.
These solutions however are generally complicated, prone to breakdown,
and costly. It is also difficult to provide a mechanism that works effectively
for users of varying size.
An example of such a structure is shown in U.S. Pat. 5,711,580 to
Barclay, which uses two down tubes to move the footplate. The second
down tube comprises two link arms connected at an unsupported, exposed
joint 36. Aside from the difficulty of making such a structure perform as
intended, it can be appreciated that the exposed link arms and joint structure
may be easily damaged in the course of daily use.
Other problems associated with raisable leg rests concern the support
provided by the calf pad as the legrest is raised. To begin with, the legrest
length problem described above may lead to the user's leg lifting off the
legrest. Another issue arises from the fact that most users need increasing
calf support as the legrest is raised, but minimal or no support when the
legrest is in the low end of its range. In fact, contact with an unneeded calf
pad can be uncomfortable when the leg rest is in a vertical position. Calf
pad support is related to the distance or spacing between the calf pad and
the down tube. However, most legrests require the user to select a single
predetermined setting for the calf pad spacing, which then remains fixed
over the whole range of motion. It can be difficult to find a single setting
that
is both close enough to provide adequate support while the legrest is being
raised, and at the same time far enough apart to be comfortable when the
legrest is in a substantially lowered position. As a result, most users are
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forced to tradeoff a preferred level of comfort in one position against a
lesser
level of comfort in another position.
A further issue, somewhat related to the above, is that users may
have very different preferences regarding the support provided by the calf
pad relative to the footplate. The wheelchair using population is as diverse
as the general population, and people will vary greatly in size, weight, leg
shape, individual areas of sensitivity or injury, as well as matters of
personal
comfort. For example, a person with heavy calves may be more comfortable
with greater calf support relative to the footplate, while another may prefer
the opposite, perhaps to relieve pressure from a skin condition at the calf.
These matters have not been adequately addressed by the prior art.
An attempt to address the issue of user comfort in a wheelchair legrest is
shown in U.S Pat. 3,189,384 to Bliss. This patent discloses a calf pad
mounted to the down tube through tubular rubber elements. As the legrest
rises, the calf pad can shift into a more comfortable angular postion for the
user due to the resiliency of the rubber. While Bliss may provide a marginal
improvement in comfort, it does not address any of the calf pad support
problems described above.
Besides reasons of comfort, having a calf pad retract as far as
possible when the legrest is in a fully lowered position is generally
desirable
because it shortens the overall length of the wheelchair, which enhances
manoeuvrability. Having a little extra space behind the calf may allow users
to push their feet back, shortening the effective chair length even further.
For some wheelchair users in cramped or small residential environments,
even a small improvement in this aspect can result in much improved
manoeuvrability and quality of life.
Yet another problem with raisable legrests is that they are susceptible
to damage from banging into walls, doors, and other structures, which can
occur frequently due to extensive daily use. The popular powered
wheelchairs can reach speeds of 8 m.p.h., exacerbating the problem. The
problem is most acute with respect to actuators, since they tend to get easily
damaged by sudden shocks and are costly to replace.
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Unless these and other practical problems associated with wheelchair
legrests are resolved, wheelchair users will continue to experience
discomfort from using legrests that are costly, ineffective, and unreliable.
Such considerations may affect user behaviour, leading to avoidance of
desired leg positions that have been rendered uncomfortable due to legrest
inadequacies. Some users may also become excessively cautious for fear
of an accidental bump that would incur costly damage to the actuator. For
people who are already compelled to spend the greater part of their lives
confined to a wheelchair, such loss of enjoyment is especially unfortunate.
SUMMARY OF THE INVENTION
What is desired is a raisable legrest which overcomes the problems
associated with the current devices used for raising the legs of wheelchair
users.
Most particularly, the legrest device should allow the user to raise his
or her lower leg over a full range of motion. Preferably, the lower leg should
be raisable from a lowered, generally vertical position where the lower leg
is approximately perpendicular to the ground to a raised, generally horizontal
position where the lower leg is approximately parallel to the ground.
Throughout the range of motion of the leg the legrest should comfortably
support the lower leg, without applying inward pressure on the user's foot,
which causes the knee to lift, raising the upper leg off the seat and the
lower
leg off the legrest. The legrest should preferably also provide adequate and
comfortable support at the user's calf for any legrest elevation, while at the
same time reducing or eliminating pressure on the calf when the legrest is
in the vertical or down position. There would also be the added benefit of
shortening the length of the chair, or providing more space behind the calf,
for enhanced manoeuverability. It would be advantageous as well to provide
the user with the means to adjust the legrest to suit his or her individual
needs. In this way, the user would experience an improved degree of
comfort and would thereby be encouraged to use the legrest without
hesitation in accordance with his or her personal inclination. Preferably the
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device would be relatively simple in construction to help keep the cost of the
device low and yet still have a high reliability. Lastly, it would be
desirable
if the legrest device were easy to install both on new wheelchairs and as an
easily attached upgrade to existing wheelchairs.
The raisable legrest device of the present invention includes a means
for adjusting the position of the legrest pivot point in at least a vertical
direction, so that the pivot point can be positioned close to the axis of
rotation of the user's knee. This allows the legrest down tube to match the
length of the user's lower leg. In this way the legrest down tube is adequate
to support the leg at any raised position, and a telescoping mechanism is not
needed. Calf support is improved by pivotally connecting the calf support to
the down tube, directing the actuator to act on the pivotable calf pad rather
than the down tube, and by installing a compressible element such as a
rubber pad between the calf pad and down tube. As the legrest is raised,
the calf pad accepts an increasing portion of the leg's weight, causing the
rubber pad to compress and bringing the calf pad closer to the down tube.
As the legrest is lowered, the rubber pad is less compressed, and it acts to
separate the calf pad from the down tube. In this way the legrest device of
the present invention varies support on the calf as the legrest moves through
its full range of motion. A stop on the down tube protects the actuator from
impact when the legrest is in the down position, and the rubber pad provides
similar protection when the legrest is in a raised position.
Accordingly, there is provided a raisable legrest for a wheelchair, the
legrest comprising:
a frame, to support a user's lower leg, said frame being attachable to
the wheelchair, said frame being movable between a lowered position
and a raised position about a pivot point when attached to said
wheelchair; and
a pivot point position adjustor, located between the pivot point and the
wheelchair, for adjusting the position of the pivot point in at least a
vertical direction;
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wherein the pivot point can be positioned by the pivot point position
adjustor to be coaxial with an approximate center of rotation of a knee of
the user.
According to another aspect ofthe invention, there is further provided:
a calf support to further support the user's lower leg, said calf support
being pivotally connected to the frame at a frame pivot point;
an actuator, to apply a force on the calf support, to move said frame
between the lowered position and the raised position; and
a compressible positioning element, positioned between the calf
support and the frame, for permitting the calf support position relative to
said frame to be varied as a moment about said frame pivot point
changes;
wherein, as said moment increases about said frame pivot point, said
compressible positioning element compresses, and said calf pad support
moves closer to said frame to provide support to the lower leg of the
user.
BRIEF DESCRIPTION OF THE DRAWINGS
Reference will now be made, by way of example only, to preferred
embodiments of the invention as illustrated in the attached figures.
Figure 1 is a perspective view of the raised legrest of the present
invention;
Figure 2a is a side view of a wheelchair equipped with a conventional
legrest device, with the legrest device in a lowered position;
Figure 2b is a view of the wheelchair of Fig. 2a, with the legrest
device in a raised position;
Figure 2c is a side view of a wheelchair equipped with the legrest
device of the present invention, with the legrest device in a lowered
position;
Figure 3a is a side view of a wheelchair equipped with the legrest
device of Fig. 1 of the present invention, with the legrest device in a fully
lowered or vertical position;
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Figure 3b is a view of the wheelchair of Fig. 3a, with the legrest
device in a raised position;
Figure 3c is a view of the wheelchair of Fig. 3a, with the legrest
device in a fully raised or horizontal position; and
Figure 4 is a schematic view of the legrest device of the present
invention, showing the forces acting on the device.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The raisable legrest apparatus or device of the present invention is
shown in Fig. 1. The apparatus is generally indicated with reference
numeral 10, and broadly comprises a frame or down tube 12, a pivot point
position adjustor 14, a calf support 16, an actuator 18, and a compressible
positioning element 20.
The present invention 10 attaches to a wheelchair and provides
support for a wheelchair user's lower leg as the leg is moved between a
lowered and a raised position. In Fig. 1 the device 10 is shown attached to
a wheelchair frame or seat frame 22 that is part of a wheelchair (not shown).
The seat frame 22 is a generally preferred point of attachment since it is
secure, conveniently located, and typically constructed of a hollow but high
strength material such as steel.
As shown in Fig. 1, a horizontal element 24 fits slidably within the seat
frame 22 and is adjustable in a forward and rearward direction as indicated
by arrow 25. Instead of being constructed as a straight element, the
horizontal element 24 can also be curved outwards to provide a wider space
for the user's leg. Not shown in the figure is a releasable holder which can
be set to hold element 24 in place at a desired horizontal position. The
releasable holder may be, for example, holes in the seat frame 22 and
element 24, though which a bolt may be inserted. Thus, upon initial
installation a preferred horizontal position can be selected to suit the user,
and the element 24 can be held or locked in place by said releasable holder.
Returning to Fig. 1, a legrest receiver or holder 26 in the general form
of a hollow cylinder is attached towards a forward end of horizontal element
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24. The receiver 26 has two notches 27 cut out of its upper surface. One
notch 27 is visible in Fig. 1, with the other one positioned on the exact
opposite side of the cylinder.
A vertical element 28 fits slidably within legrest receiver 26 at right
angles to the movement of horizontal element 24 as indicated by arrow 29.
This connection is facilitated by having at least one of the vertical element
28 or the holder 26 be hollow, so the other element can slidably fit within
the
hollow element. The vertical element 28 has a discrete number of
connection points or holes 31, shown in outline in Fig. 1. There is also a
dowel pin 30 built into the vertical element 28. It can be seen that the dowel
pin 30 is sized and shaped to slidably engage the notch 27, so that vertical
element 28 rests on and is connected to legrest receiver or holder 26. Once
inserted, vertical element 28 is prevented from rotating by the dowel pin 30
in the notch 27.
A pivot block 32 is adjustably connected towards a top end of vertical
element 28. The pivot block 32 is preferably a solid block with a hollow
section 33 sized and shaped to receive the vertical element 28, and a
carved-out section 34 having a back wall 35 and a pivot pin or pivot point 36.
It can be seen from Fig. 1 that the pivot block 32 can be adjustably
connected to vertical element 28 by inserting a fastener or bolt 37 through
a hole 38 in the hollow section 33 of the pivot block 32, and continuing
through one of holes 31 in vertical element 28. It can be appreciated that
other means of connection may also be used as long as the vertical element
28 and pivot block 32 can be adjustably and securely connected. This may
include, for example, a continuous type of connection that allows for more
incremental variations in vertical height.
It can now be appreciated that the pivot block 32, which supports
pivot point 36, can be raised to a desired vertical height in a direction
along
arrow 29 by selecting one of the holes 31 in the vertical element 28 to insert
the bolt 37. Upon bolting, the vertical element 28 and pivot block 32 will be
fixed together, and so the pivot point 36 will be located at a fixed vertical
height. In this way the pivot point 36 is adjustable in at least a vertical
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direction. It is preferred that the range of vertical height adjustment of
pivot
point 36 be at least 2 inches. Moreover, setting the position of horizontal
element 24 will set a horizontal position of pivot point 36.
The pivot point position adjustor 14 according to the present invention
is located between the pivot point and the wheelchair and comprehends a
means of adjusting the position of the pivot point 36 in at least a vertical
direction. The means of adjustment may be generally described by an
extendable vertical support element which supports the pivot point.
For example, in the preferred embodiment of Fig. 1 described above,
the extendable vertical support element may include the vertical element 28,
pivot block 32, and fastener or bolt 37 which adjust the position of the pivot
point 36 in a vertical direction by means of a rack and pin connection. The
fastener or bolt 37 holds the extendable vertical support element at a fixed
vertical height. The extendable vertical support element may alternatively
be considered to be the vertical element 28 and fastener 37 alone, without
the pivot block 32, because elements 28 and 37 are sufficient to adjust the
vertical position of the pivot point 36. The extendable vertical support
element therefore may be said to engage the holder at one end and the
pivot block at the other end, and is adjustably connected therebetween.
A feature of this embodiment is that the vertical adjustability function
is separate from the means of attachment to the wheelchair. As noted, the
extendable vertical support element or vertical element 28 and holder 26 fit
together in a dowel pin and notch arrangement. This arrangement therefore
has the advantage of providing a quick release coupling, since the legrest
10 can be easily and quickly attached to or removed from the wheelchair by
simply placing the vertical element 28 in the holder 26 or by lifting it out.
While the above arrangement is preferred because of the quick
release coupling feature, the present invention comprehends all
mechanically equivalent forms, such as threaded connections, releasably
clampable connections, or the like that permit a vertical adjustment of the
pivot point. For example, in an alternative embodiment the extendable
vertical support element may be a holder 26 in the form of a releasable
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clamp and a vertical element 28 having a pivot point 36. With the clamp
released, the vertical element 28 could be moved in a vertical direction. The
releasable clamp could then be clamped to set the vertical element 28, and
with it the pivot point 36, at a fixed vertical height. The releasable clamp
may also include a fastener such as a screw or bolt to hold the vertical
element 28 at a fixed vertical height.
It can be appreciated that in this embodiment the pivot point 36 could
be supported by a pivot block fixedly attached to vertical element 28, or as
noted the pivot point 36 could attach directly to the vertical element 28 and
no pivot block is needed. Thus while the pivot block 32 is a convenient
element to use to attach the pivot point 36, as long as there is an extendable
vertical support element present elsewhere in the pivot point position
adjustor to adjust the height of the pivot point in a vertical direction, a
separate pivot block 32 is not necessary. However, it can also be
appreciated that since the extendable vertical support element adjusts the
position of the pivot point in a vertical direction, the extendable vertical
support element will preferably have a top end and a bottom end, with the
pivot point being located towards the top end.
For additional flexibility the pivot point position adjustor 14 may
include a horizontal adjustor comprising means to position the pivot point in
a horizontal direction. The horizontal adjustor may include, for example, the
horizontal element 24 and releasable holder described above.
The frame or down tube 12 is attachable to the wheelchair through
the pivot point 36. It can be seen in Fig. 1 that the frame 12 is attached to
the pivot point 36 at a top of the frame 12. Accordingly, as the frame 12
pivots or swings about pivot point 36 in a downward direction it can be
appreciated that the frame is movable into a lowered position. Similarly, as
the frame 12 pivots or swings in an upward direction it can be appreciated
that the frame 12 is moveable into a raised position. Therefore the frame 12
is moveable between a lowered and a raised position.
At a bottom of the frame 12 there is a footplate 42 provided to serve
as a platform for the wheelchair user's foot. The footplate 42 is generally
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constructed of metal, plastic, or other durable material, and through its
mounting connection through footplate fastener 43 the footplate 42 is
generally free to pivot, flex, or flip up with respect to the frame 12.
The frame 12 is preferably in the form of a tubular metal element and
provides support for the user's lower leg. To perform this function the frame
12 has a length which is adjustable to accommodate the user's leg.
Accordingly, the frame 12 is preferably constructed in two parts as an upper
frame 39 slidably connected to a lower frame 40. Upper frame 39 is
attached to the pivot point 36 at the top and lower frame 40 is attached at
the bottom to footplate 42. Most conveniently at least one of the frames is
hollow, so that the other frame is slidable within the hollow core. In Fig. 1
the upper frame 39 is shown as hollow, and lower frame 40 is slidable within
the hollow interior of frame 39. The frame 12 may be set to a desired length
by placing a bolt (not shown) through frame extension holes 41 in the upper
frame 39 and a counterpart hole in the lower frame 40. It can be
appreciated that other means of locking the two frames together, such as a
releasable clamp, may also be used.
The length of the frame 12 may be conveniently measured as the
distance between the pivot point 36 and footplate 42. This length can be
adjusted as described above to be approximately equal to the leg-length, or
length of the user's lower leg. As will be discussed below, the frame 12
remains at this adjusted length as the frame 12 moves between the lowered
and raised position.
In the preferred embodiment of the invention shown in Fig. 1 there is
also included a frame-stop 44 to stop the frame 12 from being movable
beyond a predetermined lower position. The frame-stop 44 is located
towards a top of the frame 12 near the pivot point 36. The frame-stop 44
has an adjustable position and is interposed between the frame 12 and the
back wall 35 of the pivot block 32. As shown in Fig. 1 frame-stop 44 may be
conveniently implemented as a simple screw threaded into the underside of
frame 12. It can be appreciated however that frame-stop 44 could equally
be implemented as a screw threaded into the back wall 35 of the pivot point
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position adjustor. Therefore, frame-stop 44 is attachable to at least one of
the frame 12 or the pivot point position adjustor 14.
Upon retraction of frame 12 by the actuator or a rearward force
against frame 12, frame-stop 44 contacts the back wall 35 and stops any
further rearward movement of frame 12. The frame-stop position can be
adjusted by threading the screw the desired distance, since this will affect
where the screw hits the back wall 35. This in turn determines the amount
of rearward travel of frame 12 and the predetermined lowered position of the
frame. In the event that the frame 12 is forced backward, for example, by
the user banging the legrest 10 against a wall, frame-stop 44 stops the
frame 12 from moving too far backward and damaging actuator 18.
The calf support 16 further supports the user's lower leg and is
pivotally connected to the frame 12 at a frame pivot point 48. The calf
support 16 includes a push plate 45 and a calf pad 56 adjustably connected
to the push plate 45 through mounting plate 54. The calf pad 56 is a
cushion or pillow type article that supports the user's calf, and for clarity
is
shown in outline in Fig. 1 so that the portion of the push plate 45 hidden by
the calf pad 56 can be more clearly seen. More particularly, it can be seen
in Fig. 1 that the user's lower leg is supported by calf pad 56, and that push
plate 45 pivotally connects with the frame 12 at frame pivot point 48. A
portion of the push plate 45 extends rearwardly and attaches to the actuator
18 at pivotal connector 52, which is preferably a quick release type
connector.
Push plate 45 is a fabricated part sized and shaped to facilitate the
interconnection of several elements. It has been found that a suitable push
plate 45 may be constructed as a stamped metal plate, though it can be
appreciated that other forms of the push plate 45 may also be adequate.
As shown in Fig. 1, push plate 45 is pivotally connected to the frame
12 at an adjustable length along the frame 12. There are a plurality of holes
46 along frame 12 for connecting to the calf support 16, and a frame pivot
point or hole 48 in the push plate. The pivotal connection may be
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accomplished by inserting a pin (not shown) through the selected hole 46
and frame pivot point 48.
It can be further seen that there are a plurality of predetermined
locations or holes 50 on one of which a compressible positioning element 20
is positioned. The holes 50 are positioned so that the compressible
positioning element is between the frame 12 and the calf support 16, or in
particular the push plate 45 of calf support 16. In Fig. 1 the holes 50 are
shown on a surface of the push plate 45 but it can be appreciated that they
could equally be on the surface of the frame 12, as long as the compressible
positioning element 20 is between the frame 12 and push plate 45. In Fig.
1 there are a representative three holes 50, which may be designated for
convenient reference as upper hole 50a, middle hole 50b, and lower hole
50c. The compressible positioning element 20 is shown inserted in middle
hole 50b.
The compressible positioning element 20 is preferably formed from
a resilient material that can be formed in the shape of a pad or ball for
insertion into a predetermined location or hole 50. The material preferably
maintains some rigidity when in an uncompressed state and should be
sufficiently elastic or resilient to return to the fully uncompressed state
when
it is not compressed. It should also be durable, to withstand repeated
compression and decompression without cracking or loss of elasticity. It has
been found that a compressible positioning element 20 made of rubber
provides adequate results, though it can be appreciated that other materials
such as urethane, a conventional spring, or even an air or gas spring may
also be used. For convenience the compressible positioning element 20
may be referred to as a rubber pad or rubber 20.
The push plate also includes a stop 58. In Fig. 1 the stop 58 is shown
positioned at the top of the push plate 45 near the calf support hole 46, and
is formed as part of push plate 45 in the shape of a tab or projecting metal
piece, bent back slightly off the frame 12. In general, the stop 58 is
positioned so that as the portion of the push plate 45 attached to the
actuator 18 pivots away from the frame 12 the stop 58 will contact the frame
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12 and prevent further movement of the push plate 45. In this way the stop
restricts the pivot range of the calf support 16 or in particular, the push
plate
45 of the calf support 16. In the absence of stop 58 the push plate 45 would
be able to pivot much farther back, perhaps as far as 90 degrees away from
the frame 12.
It can be appreciated that the push plate 45 is a convenient element
to pivotally attach the calf pad 56 to the frame 12, connect to the actuator
18
so the actuator 18 can apply force on the calf support 16, and allow for the
positioning of a compressible positioning element or rubber 20. While the
preferred embodiment of the push plate 45 is a stamped metal plate that can
be sized and shaped to attach to the frame 12 and make the various
connections shown, it can be appreciated that other means of connecting
the calf pad to the frame, the actuator to the calf pad, and positioning the
rubber 20 may be used. For example, the rubber 20 may be positioned in
holes 50 located on the underside or part of frame 12 rather than on the
push plate 45.
The actuator 18 is preferably an electrically powered element that
moves a shaft within a housing. The actuator 18 is shown having its shaft
attached to the push plate 45 at pivotal connector 52. The origin of the
actuator 18 is whithin the attached wheelchair and is accordingly not shown
in Fig. 1. The actuator 18 represents any element that applies a force on the
calf support 16, or more particularly the push plate 45 and calf pad 56. The
actuator 18 will most commonly be electrically powered, particularly on
powered wheelchairs. However the actuator 18 could be a manual device,
for example, a ratcheted device movable into successively forward positions
by the user or an attendant, or a hydraulic device.
The movement of the actuator 18 is generally represented by arrow
60 and is generally in a forward and backward direction, where the forward
direction applies a force moving the calf pad 56 forward and the reverse
direction retracts the calf pad 56. In this way the actuator 18 moves the calf
support 16 and with it the frame 12 between a lowered and a raised position.
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It can be seen that as the actuator 18 moves forward, the push plate
45 will pivot so that the calf pad 56 moves forward and the stop 58 moves
rearward. The compressible positioning element or rubber 20 will engage
the underside of the frame 12, and cause the frame 12 and attached
footplate 42 to rise. It can be appreciated that since the rubber 20 is
between the push plate 45 and frame 12 it will compress, particularly if the
legrest 10 is being used and it is occupied by a wheelchair user's leg.
As the actuator 18 retracts the frame 12 will move from a raised to a
lowered position, and eventually to a fully lowered or down position. Several
factors govern the position of the elements of the legrest 10 of the present
invention in the fully lowered position. First, the frame 12 will stop
retracting
upon engagement of the frame-stop 44 with the back wall 35. The frame-
stop 44 is adjustable, and will preferably be adjusted to stop at a
predetermined lowered position that is comfortable for the user. While this
will often be 90 degrees or vertical, some users may prefer a less vertical
setting such as 80 or even 70 degrees from the horizontal.
In order to receive the shock protection benefit of the frame-stop 44
in the fully lowered position, the actuator will continue to retract past the
point where the frame-stop 44 engages. The amount of further retraction of
the actuator again may be adjusted in advance. Setting the actuator to
retract further has the benefit of pulling the calf pad back a greater
distance,
so it will be less likely to contact the user's calf. However, the actuator
has
a limited total range of travel. The more it is allowed to retract to reach
the
fully lowered position, the less it will advance when moving forward and
raising the frame. In practice therefore it is often preferable to set the
actuator to retract to just past the point where the frame-stop 44 engages.
This ensures that the frame-stop 44 is engaged, and preserves a maximum
degree of actuator range of motion for forward travel.
Yet another factor is that the resiliency of the compressible element
or rubber pad 20 will cause the calf support 16, or more particularly the calf
pad 56 of calf support 16, to separate from and form a predetermined pivot
angle with the frame 12 when the frame 12 is in the lowered position.
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Depending on the setting of the frame-stop 44 and amount of actuator
retraction, the rubber pad 20 may be in an uncompressed state or may still
be compressed. As will be discussed below, the degree of separation or
pivot angle will vary depending on the position of rubber pad 20, and will be
greater the closer the rubber pad 20 is to the frame pivot point 48.
Finally, the device 10 is further designed so that the stop 58 on push
plate 45 will generally not engage in the ordinary course of retraction by the
actuator to the fully lowered position. The stop 58 is available to further
protect the actuator by engaging the frame 12 in the event the calf pad 56
receives a further external mechanical force or push. Preferably stop 58 will
contact the frame 12 without the actuator 18 moving much further, to better
protect the actuator.
The operation of the raisable legrest 10 can now be described.
Turning to Fig. 2a there is a wheelchair user 62 sitting on a wheelchair 64.
The user 62 has an upper leg 66 supported by a seat cushion 68 and a
lower leg 67 supported by a conventional legrest device. For clarity, the
legrest device shown in Figs. 2a and 2b is a representative conventional
legrest device of the type well known in the prior art. It can be seen that
this
conventional device also includes an actuator 18, a calf pad 56 and a
footplate 42. There is a horizontal element 24 extending from the seat frame
22, and a frame 12 that connects with the element 24 at a representative
fixed pivot point 70.
In the conventional set-up the horizontal element 24 is used to extend
the seat frame 22 so that it fits the length of the user's upper leg 66. The
user's lower leg 67 is supported by the legrest, and in particular the frame
12, calf pad 56, and footplate 42. The user has a knee with an effective
center of rotation or knee pivot point 72. In Fig. 2a it can be seen that the
conventional legrest has a radius or length "x" extending from the pivot point
70 to the footplate 42, that pivots about the pivot point 70. It can also be
seen that the user's lower leg 67 has a length "y" extending from the
effective center of the knee 72 to the footplate 42. It is clear that in the
configuration shown the length "y" of the user's lower leg 67 is longer than
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the length "x" of the legrest frame 12, and that pivot points 70 and 72 are
not
co-axial.
In Fig. 2a the legrest device is shown in a lowered position, where the
legrest is approximately vertical, or perpendicular to the ground. Fig. 2b
shows the legrest in a raised position as a result of extension of actuator
18.
The result of this configuration associated with the conventional legrest can
now be seen. Due to the difference in length between the conventional
legrest "x" and the user's lower leg "y", and the non-coincident centers of
rotation 70 and 72 respectively, there is insufficient length in the frame 12
of the legrest to accommodate the user's lower leg 67. As a result there is
an inward pressure on the user's foot, which forces the knee to pop up off
the seat 68. This is unacceptable as it is uncomfortable and awkward forthe
user 62. As well, it forces the weight of the user to be uncomfortably
concentrated at a localized area 74 of the leg 66. As discussed above,
some prior art legrest devices use an extension mechanism (not shown) to
extend the legrest in the direction shown by "z" in Fig. 2a as the legrest
moves from a lowered to an elevated position. However, such extension
mechanism devices are invariably costly, complicated, and prone to
breakdown.
The wheelchair 64 equipped with the raisable legrest of the present
invention 10 is shown in Fig. 2c. The legrest 10 includes the additional
elements of the vertical element 28, legrest receiver 26, and pivot block 32
supporting a pivot point 36. The down tube or frame 12 connects to the
pivot block 32 at the pivot point 36. These elements permit the user to
adjust the position of the pivot point 36 in at least a vertical direction.
In the operation of the legrest device 10 of the present invention the
user or attendant would adjust the vertical element 28, along with the
horizontal position element 24 so that the pivot point 36 of the legrest
device
10 is co-axial with an effective center of rotation of a knee of the user 72.
Further, due to this arrangement it can be seen in Fig. 2c that the length "x"
of the frame 12 of the legrest device 10 is approximately equal to the length
"y" of the user's lower leg 67. While a complex knee joint does not have a
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precise center of rotation like a simple mechanical pivot, it has been found
that being able to position the pivot point close to the effective center of
rotation of the knee provides increased comfort for users.
The result of this configuration may be seen in Fig. 3, which shows
the legrest 10 of the present invention in a lowered vertical position in Fig.
3a, a raised position in Fig. 3b, and at a fully raised position or
approximately
a horizontal position, in Fig. 3c. It can be seen that as a result of the
legrest
being co-axial and equal in length to the lower leg 67, raising the legrest
does not produce inward pressure and there is simply no need for an
10 automatic extension mechanism to dynamically increase the length of the
down tube or frame 12. The user's lower leg 67 remains comfortably
supported by the legrest at all times and as there is no inward pressure the
user's knee is not forced up off the seat 68.
It can now be appreciated how the legrest device 10 of the present
invention achieves a full range of motion of the user's leg 67. The device 10
of the present invention has the additional benefit of simplicity since it
does
not require the extension mechanism required by the devices of the prior art.
The operation of the adjustable calf pad feature of the present
invention can now be described. With reference to Fig. 1, the push plate 45
of calf support 16 may be connected at frame pivot point 48 with one of the
holes 46 on frame 12. Generally, a particular hole 46 will be selected to
optimize the orientation of actuator 18. It is preferred that actuator 18 be
directed close to the horizontal rather than in an upward direction where it
could be obstructed by other parts of the legrest device 10. Then, the calf
pad 56 may be adjusted in position relative to the push plate 45 by
adjustment of the mounting plate 54. In this way the calf pad 56 may be
positioned to line up with the user's calf.
It can be appreciated that, given the pivot point adjustment feature of
the present invention, it can be expected that the calf pad 56 will reliably
remain behind the user's calf throughout the full range of motion between
the lowered and raised position, as shown in Fig. 3. Further, shear will not
develop between the calf pad and the calf if the pivot point is properly
CA 02359379 2001-10-19
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positioned. This aspect of the present invention is a significant improvement
over the prior art. Further, it can be appreciated that the adjustable calf
pad
feature of the present invention, to be described below, is enhanced in
effectiveness due to the reliable positioning of the calf pad.
Returning now to Figs. 2a and 2b, it may be seen that in the
conventional legrestthe calf pad 56 is set to a fixed separation distance "s1"
from the frame 12. While this fixed distance s1 may be adjustable by the
user, once it is set it does not change as the legrest 10 moves from the
lowered to the raised position. It may also be noted that in this arrangement
the actuator 18 can apply force to either the calf pad 56 or the frame 12.
Since the calf pad and frame are rigidly connected to maintain a fixed
spacing, the frame 12 will be raised the same regardless of whether the
actuator 18 connects with the frame 12 or calf pad 56.
In Fig. 2a the legrest is in a lowered position, close to vertical, and the
calf pad 56 is not needed. In this position it would be preferable to have a
large separation "s" so that the calf pad 56 does not make contact with the
user's calf. However, if s1 is set to a large value then when the legrest is
raised, as shown in Fig. 2b, the user's leg may be somewhat distant and not
naturally be supported by the calf pad. It is possible that the user's foot
may
slip slightly out of the footplate 42, to permit the calf pad 56 to take up
some
of the weight. The user's leg however will likely not be comfortably
supported when the legrest is being raised. In practice, users will often
choose to make s1 smaller, to get the calf pad support. However in that
case there will be pressure or contact from the calf pad 56 when the legrest
is in the almost fully lowered vertical position of Fig. 2a. Since no one
position of the calf pad 56 or s1 can satisfy the comfort settings of both
lowered and raised positions the result is a tradeoff which leaves the user
dissatisfied in both positions.
Accordingly, it can be appreciated that while the legrest 10 is rising,
it is generally desired to have the calf pad close to the frame 12, or a small
"s", to provide support and take up some of the weight of the lower leg 67.
It is also generally desirable that when the legrest is in a more lowered
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position, particularly when vertical, that the space "s" be larger so that the
calf pad ideally does not exert any pressure on the user's calf. Also as
noted, a larger "s" is desirable to allow for the possibility that the user's
feet
may be able to be drawn back and thereby shorten the effective overall chair
length.
Fig. 3 shows the action of the calf pad 56 of the legrest 10 of the
present invention, as the legrest 10 moves from a fully lowered or vertical
position in Fig. 3a to a fully raised or horizontal position in Fig. 3c. The
separation "s" between the calf pad 56 and the frame 12 in each position is
indicated. It can be seen that the separation "s" starts out relatively large
in
Fig. 3a, so that the calf pad is either not in contact with the user's calf,
or at
least exerting relatively less pressure. In the intermediate raised position
of
Fig. 3b it can be seen that the separation "s" has narrowed, thereby
providing more support for the user's calf. Finally, in the horizontal
position
of Fig. 3c the separation "s" has shrunk even further and the calf pad 36 is
directly under the user's lower leg. This profile, by contrast with the calf
pad
positioning "s1" shown from the conventional legrest of Figs. 2a and 2b, is
closer to that desired by most users.
This may be better understood by noting that in Fig. 3 the actuator 18
pushes on the push plate 45, which in turn pushes the calf pad 56. In the
fully lowered position of Fig. 3a the actuator is not active. The rubber 20
presses the push plate 45 and calf pad 56 away from the frame 12 to form
the predetermined pivot angle. When the rubber 20 is in upper hole 50a the
separation or predetermined pivot angle between the calf pad 56 and frame
12 is largest, for given settings of the frame-stop 44 and actuator 18, and
when in the lower hole 50c the separation is the smallest. In any event, "s"
is relatively large and the calf pad 56 is relatively far from the user's
calf,
which is desirable when the legrest is in the fully lowered position.
In Figs. 3b and 3c the actuator is activated and exerts a force raising
the push plate 45 and calf pad 56, as well as the frame 12. However the
weight of the lower leg 67 pushes the frame 12 downwards, which squeezes
the rubber 20. This reduces the separation "s", bringing the calf pad 56
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closer to the frame 12. The smaller "s" results in better support for the
user's calf, allowing the calf pad 56 to take on more weight than it would
under the conventional arrangement. Again, this resulting smaller "s" is
desirable when the legrest is in a raised position.
Essentially, the more weight that is placed on the footplate 42, the
more compression will occur of the rubber 20, leading the calf pad 56 to
become closer and more able to provide support. Accordingly, for any
position of the rubber 20, the rubber 20 provides a position adjustment
through the range of motion of the calf pad 56 by the actuator 18.
Therefore, the legrest 10 of the present invention is an improvement over
the conventional legrest in that it enables the separation between the calf
pad 56 and down tube 12 to vary over the range of movement of the legrest
10. The legrests of the prior art have only a fixed separation distance,
forcing the user to trade-off comfort in one position for less comfort in the
other. The present invention 10 transfers weight from the footplate 42 to the
calf as the footplate 42 is elevated. As well, the user can pre-select the
hole
50 in which to place the rubber 20 to achieve optimum comfort across the
range of movement.
Figure 4 provides a more graphical view of the operation of the
present invention. The figure shows the present invention 10 with the
legrest in a fully raised position, with a representation of the various
forces
at work. The weight of the user's lower leg 67 on the legrest 10 creates a
force F1 from the footplate 42, and a force F2 from the calf pad 56. There
is an equal upward counter-force F3 provided by the actuator 18. In this
case the frame 12 may be viewed as a lever having a distance equal to the
length of frame 12 and acting about the pivot point 36. There will be a
moment produced about the pivot point 36 by the downward force on the
frame 12. This is resisted by an opposite moment created by the actuator
about the frame pivot point 48 equal to the product of the force F1 and the
distance "d". This moment in effect is what causes the rubber 20 to
compress. As the rubber compresses the separation "s" gets smaller. This
however means that the calf pad will take up more of the weight of the lower
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leg 67, so F2 increases and F1 decreases, however slightly. The various
forces continue to adjust incrementally until an equilibrium is reached.
Thus it can be seen that the compressible positioning element or
rubber pad 20, positioned between the calf support 16 and the frame 12,
permits the calf support position relative to the frame, i.e. the separation
"s",
to be varied as the moment about frame pivot point 48 changes. As the
moment about frame pivot point 48 increases, the compressible positioning
element or rubber pad 20 compresses, and the calf pad 56 support moves
closer to the frame 12 to provide support to the lower leg 67 of the user.
The positioning of the rubber 20 may now be understood. Fig. 1
shows three predetermined locations or holes 50 to receive the
compressible positioning element 20. For illustration purposes the rubber
has been inserted into the middle hole 50b. It can be appreciated that
more than 3 holes could have been used. From the figure, it can be seen
15 that when the rubber 20 is in the upper hole 50a, the pivot angle of the
frame
12 relative to the push plate 45 will be larger and the calf pad 56 will be
spaced further from the down tube 12. This setting accordingly results in
more compression and travel by the calf pad 56. The converse will be true
as the rubber 20 is moved to positions 50b and 50c. For the lower positions
20 there is less compression, leverage, and travel. The lowest position is
closer
to that of the conventional legrest having a fixed separation s1.
The advantages of the present invention may be better understood
by considering certain practical issues. Many wheelchairs have items that
act as barriers that prevent the legrest from reaching a fully lowered or
vertical position. For example, wheelchairs often have a cowling, which is
a plastic covering that covers the top of the wheelchair to enhance the
chair's appearance. The cowling may block the calf pad from retracting to
the fully lowered or vertical position. Other items that may act as barriers
in
this way include the battery or battery cover. However, many users will want
to achieve a position as close to the vertical as possible, to obtain as much
of a true sitting position as possible and to enhance maneuverability.
Accordingly, these users of the present invention will most likely choose to
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insert the rubber 20 in the lowest available position. In this way they will
get
as close to the vertical position as possible. While there would be more calf
pressure in this setting, this would probably still be considered preferable
by
these users since at least the footrest will be closest to the vertical. While
this setting is closest to conventional legrest it can be appreciated that the
present invention at least offers the user a choice which would otherwise be
unavailable.
Another type of barrier might be castors that block the footplate. In
this case while the legrest still cannot retract fully, there may well be
nothing
blocking the calf pad. Therefore in this case it would be reasonable to set
the rubber 20 at a higher position. This would force the calf pad back while
the legrest is in the lowest possible position. While the legrest would not be
in a fully lowered vertical position, as before the user at least has the
benefit
of choice, and in addition the benefits of reduced or eliminated calf pressure
and the possibility to reduce the overall chair length and enhance
maneuverability.
In a conventional legrest, where there is a large fixed separation (s1)
the calf pad may well be comfortably off the calf at a fully lowered legrest
position. While this may be desirable to the user, due to the large
separation, as the legrest rises the calf pad will be unable to receive a
large
weight transfer and this may well be uncomfortable to the user. Where the
separation (s1) is small the user will likely have more comfortable calf
support as the legrest rises but uncomfortable calf pad contact when the
legrest is in a fully lowered position.
Each of the predetermined locations 50a, 50b, and 50c provide for a
separation "s" that is larger in the lowered position than in the raised
position, with the largest separation in the fully lowered or vertical
position,
and the smallest separation in the fully raised or horizontal position of the
legrest. The higher predetermined location such as 50a will have a generally
larger separation throughout the range of motion of the legrest. The user of
the present invention 10 has the opportunity to select the setting most
appropriate to his or her circumstances. This may include such
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considerations such as the presence or absence of a cowling and other
aspects of chair configuration, and the user's personal preferences
regarding calf support relative to foot support, and calf pad contact in the
fully lowered position.
It can now be appreciated how the legrest 10 of the present invention
better transfers weight from the foot to the calf, resulting in greater
comfort
for the user.
Wheelchair users commonly bump into walls, doors, and other
obstacles. Since the legrest is the most forward part of the chair, it is the
part most likely to be struck in a collision. While the legrest itself is
fairly
sturdy, it can happen that jarring of the frame 12 may cause the frame to be
pushed back, which in turn could jolt and damage the actuator. This is a
problem for users because the actuator is an expensive device to replace or
repair.
However, this matter is addressed by the present invention. The
rubber 20 used to affect calf pad separation also acts as a buffer or bumper
to receive unexpected jostling from the front without causing the actuator to
retract.
Yet another protection against jostling from the front is provided by
the frame-stop 44. If the legrest is jarred from the front, particularly when
in
the fully lowered position, the frame 12 will be driven back until the frame-
stop 44 engages the back wall 35. As noted, this is commonly set to occur
prior to the actuator retracting to its bottom position.
Accordingly, it can now be appreciated how the present invention is
more secure and less fragile than the legrests otherwise available. It can
also be appreciated how the present invention may be easily manufactured
or installed in pre-exising wheelchairs. All that is required is to secure the
device to the wheelchair at the seat frame 22 or similar location, and connect
the actuator from the wheelchair to the push plate 45.
It will be appreciated by those skilled in the art that the foregoing
description was in respect of preferred embodiments and that various
alterations and modifications are possible within the broad scope of the
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appended claims without departing from the spirit of the invention. For
example, while reference is made to adjusting the positioning of the
compressible element or rubber by inserting the rubber into one of a plurality
of positions, further variation is possible by threading the rubber into each
position. An even finer adjustment of calf pad positioning may be made
available by adjusting the degree of threading of the rubber into the selected
position of insertion. Further, the stop could also be made adjustable so that
the extent to which the push plate is allowed to pivot back could be set by
the user. Also, further shock absorbtion may be achieved by adding rubber
bushing to the pivot point 36 and a rubber bumper to the contact point of the
frame-stop 44. Various other modifications will be apparent to those skilled
in the art but are not described in any further detail herein.
