Seat cushion for wheelchairs

A seat cushion for use in a wheelchair comprises a shaped tray and a filled envelope. The envelope is filled with a fluid like material which is flowably displaceable under the weight of a user. The shaped tray comprises a recess for receiving the buttocks region of the user as well as a front edge over which the legs of the user extend. A back wedge is mounted along a back edge of the tray and keeps the filled envelope from sliding over the back edge of the tray. Further, side wings located at the sides of the shaped tray near its front edge help constrain the legs of the wheelchair user in a generally forward direction within the width of the wheelchair seat. Side wedges mounted on the underside of the seat are selectively removable to accommodate the presence of a cross brace mechanism, as is commonly used in drop seat wheelchairs.

BACKGROUND OF THE INVENTION 
I. Field of the Invention 
This invention relates to a seat cushion to be used with a wheelchair, and 
more specifically to a seat cushion incorporating a shaped tray and an 
envelope filled with a flowable gel-like material. 
II. Description of the Related Art 
Users of wheelchairs typically have little or no use of their lower 
extremities. As such, they sit in wheelchairs, or similar structures such 
as recliners or beds, for long periods of time. Persons sitting in 
conventional wheelchairs or seats for long periods of time are sometimes 
prone to develop pressure sores, such as bed sores, at different points in 
the person's body which bear the weight of his body. For example, a person 
sitting upright in a wheelchair distributes his body weight over a 
relatively small area. As such, users of wheelchairs are prone to develop 
pressure sores. 
In addressing this problem, related inventions have utilized envelopes 
filled with various cushioning media including air, elastomeric foams, and 
gels. In some embodiments, the gel has been mixed with lightening 
substance, such as hollow glass spheres, which tend to lighten the weight 
of the gel-filled envelope. 
Some prior art designs have provided segments within the envelopes to 
improve the lateral stability to the user. For example, U.S. Pat. No. 
4,588,229 to Jay discloses an envelope featuring a seam 39 separating the 
envelope into right and left hand portions. This seam prevents gel within 
the envelope from shifting from right to left within the envelope under 
the weight of the user, thereby enhancing the stability of the cushion. 
Also disclosed in U.S. Pat. No. 4,588,229 is a shaped tray designed to be 
used with the above-discussed envelope. The shaped tray is made of a 
lightweight material and has a depressed seat area 42 surrounded by rims 
44, 46 on each side and a rim 48 in the front. The envelope is designed to 
be attached to the top surface of the tray and for them to be used as a 
unit. 
The present invention contemplates a new and improved shaped tray which 
overcomes the foregoing difficulties and others while providing and more 
advantageous overall results. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, a new and improved shaped tray to 
be used with a filled envelope is provided. 
According to one aspect of the invention, a seat cushion comprises a shaped 
tray and a filled envelope. The shaped tray has front, back and side edges 
and top and bottom surfaces. A back wedge is aligned near the back edge of 
the tray. The filled envelope is filled with a fluid-like material which 
is flowably displaceable under the weight of the user. The back wedge of 
the shaped tray is effective to prevent the envelope from sliding over the 
back edge of the shaped tray. 
According to another aspect of the invention, the back wedge is made of 
polyurethane foam and comprises a bearing surface, a bottom surface and a 
back surface. The bearing surface is inclined to the bottom surface of the 
shaped tray at an angle greater than 5.degree.. 
The bottom surface of the back wedge has a slot to selectively receive 
attaching means for attaching the back wedge to the tray. The back wedge 
has a cross section generally resembling a right triangle. 
According to another aspect of the invention, a seat adapted to be used in 
an associated wheelchair and sat upon by a user comprises a shaped tray 
and a side wedge. The side wedge is selectively affixed to a bottom 
surface of the tray in either one of the side edges. The side wedge is 
selectively removable to accommodate a cross brace of an associated drop 
seat wheelchair. 
According to another aspect of the invention, a seat adapted to be used in 
an associated-wheelchair comprises a shaped tray and a first side wing. 
The first side wing rises upwardly from a top surface of the tray and is 
located on one of the side edges near the front edge of the tray. The side 
wing constrains the user's legs in a forward direction. 
In another aspect of the invention, an abductor is selectively affixed to 
the top surface of the shaped tray and cooperates with first and second 
side wings to form first and second channels. The channels selectively 
receive and orient the legs of the wheelchair user. 
One advantage of the present invention is the capability of retaining the 
fluid-filled envelope on the top surface of the shaped tray and preventing 
the fluid filled envelope from sliding over the back edge of the shaped 
tray. 
Another advantage of the present invention is the feature of side wedges. 
By selectively removing or adjusting the side wedges, the seat can be 
fitted around cross braces typically found in a drop seat wheelchair. 
Previously, a user had to cut slots out of the bottom surface of a shaped 
tray in order to accommodate such cross braces. 
Another advantage of the present invention is the capability of orienting 
the user's legs in a generally forward direction. Previously, it was not 
uncommon for the user's legs, which are typically uncontrollable due to 
injury or illness, to stray from a forward direction. Instead, the legs 
were prone to splay outwardly or to twist around one another. The use of 
side wings and the abductor creates first and second channels which can 
selectively receive legs of the wheelchair user and orient them in a 
forward direction. 
Another advantage of the invention is the increased stability to the user, 
especially side-to-side, due to the longitudinal separation of the 
envelope into halves. 
Still another advantage of the invention is the comfort and improved 
support offered to the user through the use of the filled envelope. 
Still other benefits and advantages of the invention will become apparent 
to those skilled in the art to which it pertains upon a reading and 
understanding of the following detailed specification.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings wherein the showings are for purposes of 
illustrating a preferred embodiment of the invention only and not for 
purposes of limiting the invention, FIG. 1 shows an exploded view of a 
seat cushion 10 according to the invention. The seat cushion is primarily 
comprised of shaped tray 12 and envelope 14. 
The envelope 14 is filled with a flowable fluid-like material which is 
flowably displaceable under the weight of the wheelchair user. With 
reference to FIG. 7, the preferred embodiment of the envelope is 
disclosed, although its specific structure is not a part of the invention, 
and any filled envelope used for such shaped tray wheelchair applications 
is suitably used with the invention. The envelope 14 is split into right 
and left portions via heat seams 38 and inner and outer portions via heat 
seams 39. Preferably, heat seams are made throughout the envelope 14 to 
prevent of the fluid-like material from flowing too far within the 
envelope 14 under the weight of the user. For example, if all of the fluid 
in the envelope 14 should flow to one side of the envelope 14, the user 
would be essentially sitting on an inclined plane and would tend to pitch 
to one side of the wheelchair. Since the user of the wheelchair typically 
has little or no control of the lower portions of their body, such lateral 
instability is of concern. The partitioning of the envelope 14 by the 
seams 38 and 39 tends to create a more stable envelope 14, thereby 
increasing not only the comfort, but also the stability, of the user. 
The preferred fill material is hollow glass spheres. In the preferred 
embodiment, these spheres are SCOTCHLITE.RTM. glass bubbles, available 
from 3M.RTM. Corporation. The type utilized in the preferred embodiment is 
3M.RTM. designation C15/250, having a nominal density of 0.15 grams/cc. 
and 9.4 lbs./cu.ft. Its range is 0.12-0.18 grams/cc., with a bulk density 
of 0.07-0.12 grams/cc. Their size is a maximum of 5% by weight +US 80 mesh 
(177 microns). 
The preferred fluid-like material is petrolatum. This petrolatum is mixture 
of a hydrocarbon oil and wax can be purchased from Pennzoil Products Co. 
under the tradename PENRECO.RTM. Amber. The petrolatum or petroleum jelly 
is a microcrystalline wax with a defined oil content. Microcrystalline 
waxes consist mainly of iso and cycloparaffins with some alkylated 
aromatic hydrocarbons. Petrolatums have consistencies at 77.degree. F. USP 
and ASTM D937 between 35 and 410 with a melting point between 95.degree. 
F. and 170.degree. F. Petrolatums are non-toxic and some petrolatums have 
been approved for food and medicinal use. It has a semi-solid appearance 
and is odorless. It melts at between 122.degree. F. and 135.degree. F. 
with a specific gravity of 0.86 at 60.degree. F. The density of the 
petrolatum ranges from 0.83 gm/cc-0.87 gm/cc. 
In the preferred embodiment, the fill material is produced by mixing four 
50 pound boxes of 3M.RTM. Scotchlite glass bubbles with three 55 gallon 
drums of the Penreco.RTM. Amber petrolatum. The resulting fill material is 
comprised of approximately 49.2% glass bubbles by volume and 50.8% 
petrolatum by volume. In such a case, the volume of petrolatum comprising 
the fill material is not substantially greater than the volume of the 
interstitial spaces of the quantity of glass beads alone which ranges from 
0% to 61% by volume depending upon the bulk density and average true 
density of the 3M.RTM. type C15/250 glass bubbles present in a specific 
batch. 
In the preferred embodiment, the envelope is filled via fill spouts 40. The 
fill spouts are then sealed via a heat sealing mechanism. With reference 
to FIGS. 1 and 8, hook and loop strips 44 are positioned on the tray 12 
and on the bottom portion of the envelope 14. Corresponding hook and loop 
strips on the tray 12 and envelope 14 secure the tray to the envelope in a 
selectively removable manner. 
With reference to FIGS. 1 and 8-10, the shaped tray 12 features several 
innovative features. Shaped trays in general, have been known in the art. 
They typically contain an upper surface 50 having a recess 52. The recess 
52 is designed to selectively receive the buttocks region of the user. As 
such, the shaped tray 12 comprises a back edge 54, a front edge 56 and 
side edges 58, 60 (FIG. 8). The legs of the user extend fully over the 
front edge 56 while the buttocks are received within recess 52. 
A common problem in prior art designs has been the tendency of the filled 
envelope 14 to slide backwards over the back edge 54 of the tray 12 due to 
movement or slumping by the user. 
With references to FIGS. 1, and 4-6, applicant has developed a back wedge 
20. The back wedge 20 is shaped to fit the lines of recess 52. The back 
wedge 20 contains hook and loop strips 44 which attach the back wedge 54 
to the shaped tray 12. The back wedge 20 is selectively removable in order 
to accommodate a user with an abnormally tilted pelvis. In such cases, a 
permanently affixed back wedge 20 would be unsuitable. As is most clearly 
seen by FIG. 4, the back wedge has a triangular cross section, with two 
angles preferably near 45.degree., which retains the fluid-filled envelope 
14 onto the surface of the tray 12 in a most advantageous manner. The 
angle of the wedge 20 must be sufficient to prevent the fluid-filled 
envelope 14 from sliding off the back of the tray 12. It is believed that 
even a small angle, such as 5.degree., could be sufficient although the 
45.degree. angle shown in FIG. 4 is preferred. In the preferred 
embodiment, the wedge 20 is approximately 1.3 inches by 1.3 inches on the 
non-hypotenuse sides of the triangle shown in FIG. 4. In one embodiment, 
the back wedge 20 was made of polyurethane foam. A slot 62 in the bottom 
surface 64 of the back wedge 20 receives hook and loop strips 44 mounted 
on the center of recess 52. Similarly, recesses 63 on the ends of the back 
wedge 20 also receives hook and loop strips 44. 
With reference to FIGS. 1-3, side wedges 22, 24, are selectively mounted to 
a bottom surface 66 of tray 12 near the side edges 58, 60. The upper 
surface 70 of the side wedges 22, 24 feature hook and loop strips 44 which 
cooperate with corresponding hook and loop strips 44 on the bottom surface 
66 of the tray 12. In another embodiment, the side wedges 22, 24 are 
mounted to the bottom surface 66 of tray 12 via an interference fit. The 
side wedges 22, 24 are selectively removable to accommodate cross braces 
such as are typically found in drop seat wheelchairs. For example, with 
reference to FIG. 11, such a typical drop seat wheelchair is disclosed. 
The cross braces 74 add support to the drop seat wheelchair while allowing 
it to be folded for easy storage. The upper surface of the cross braces 74 
can present problems to shaped trays of prior art designs. Typically, a 
user of a drop seat wheelchair featuring a cross brace would cut away 
portions of the underside of typical foam shaped trays with knives or 
razor blades, thereby providing a recess to receive the cross braces 74. 
In applicant's structure, the side wedges 22, 24 can be easily removed if 
the tray 12 is to be used in such a drop seat wheelchair. If the tray 12 
is to then be removed from the wheelchair and placed in a different style 
of wheelchair, having no cross braces, the side wedges 22, 24 are easily 
and repeatably replaced. 
With reference to FIGS. 1 and 8-10, the upper surface 50 of the shaped tray 
12 also features side wings 30, 32. The side wings 30, 32 are located near 
the front edge 56 of the upper surface 50 of the shaped tray 12. The side 
wings 30, 32, as is best seen in FIGS. 9 and 10, rise upwardly from the 
upper surface 50 of the shaped tray 12. Typically, the user of the 
wheelchair has little or control of or feeling in their lower extremities. 
As such, it is difficult for them to keep their legs oriented forwardly in 
the chair and within the outer edges of the chair and/or seat 10. 
Sometimes involuntary muscular contractions cause the legs of the user to 
splay outwardly or twist inwardly about each other. The side wings 30, 32 
help constrain the legs of the user in a forward direction. 
Consistent with this objective is the use of abductor 28. The abductor is 
mounted between the side wings 30, 32 on the upper surface 50 of shaped 
tray 12. The abductor, along with the side wings 30, 32, create first and 
second channels 78, 80 to receive the legs of the user. 
The invention has been described with reference to a preferred embodiment. 
Obviously, modifications and alterations will occur to others upon a 
reading and understanding of this specification. It is intended to include 
all such modifications and alterations insofar as they come within the 
scope of the appended claims or the equivalents thereof.