Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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FIELD OF THE INVENTION
This in~ention relates to inflatable supports, such
as air mattresses, and especially ripple beds.
BAC~GRO~D TO THE INVENTION
In a ripple bed, air is supplied under pressure to
two separate air passages in an inflatable mattress. m e
passages take the ~orm of a series of parallel tubes
supplied from common header tubes, one for each passage,
located on opposite sides of the mattress. Alternate
transverse tubes go to one header tube, and the intervening
transverse tube goes to the other header tube. The two
passages are inflated and deflated cyclicly, the cycles of
th¢ two passages being out of phase so that as one is beLng
inflated the other is being deflated. This creates a
ripple effect on the surface of the bed, which has been
- found particularly useful in helping to prevent bedsores in
bed-ridden patients. Leakage of air from the top surface
may also be provided ~o assist in cooling the patient and
evaporating moisture. Air beds of this type are for
example disclosed in U.S. Specifications Nos. 2998817 and
3653083 and U.K. Specification No. 949652.
S~IARY OF THE I~VENTION
The present invention provides an inflatable sup-
port for a patient comprising an upper and a lower infla-
table layer, the upper layer having a plurality of separate
air passages which are independently inflatable and de-
flatable and are distributed over the area of the layer
as a series of tubes such that the tubes of different
passages are juxtapoxed, and a lower separately inflatable
layer below the upper layer for continuous inflation so
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that substantially the entire upper layer is continuously
supported by the lower layer in use, the upper surface of
the upper inflatable layer being of air permeable material
or provided with air bleed apertures whereby escaping air
can issue directly over the body of a patient resting on
the upper surface. The function of the lower inflatable `
layer is particularly important during the changeover
perioa when one set of tubes is deflating and the other
set has not yet been fully inflated~ The lower infla-
table layer also provides a soft support to the upperlayer which has been found to be a desirable feature.
The upper inflatable layer preferably takes the form
of a series of transverse tubes supplied by common header
tubes, one for each passage, located at the sides of the
support, alternate transverse tubes communicating with one
header tube, and intervening transverse tubes communicating
with the other header tube. Preferably air bleed apertures
are arranged non-uniformly over the surface to provide
air bleeding from selected areas of the surface. The lower
inflatable layer may comprise a single inflatable envelope,
or alternatively it may be divided by partitions into a
number of separately inflatable compartments.
Inflation equipment may also be included with the
air bed, comprising a source of compressed gas, suitably
air (and referred to herein generally as air), supplying
separate conduits to the lower and upper inflatable layers,
the conduit to the upper layer branching to the separate
inlets of the different passages in the upper layer, and
switching device being provided to cyclicly switch the air
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supply between the branches. The compressed air supply is
preferably provided by a motor driven compressor. The
switching device preferably includes means for varying the
cycle length. The switching device may comprise a motor
driven valve. The motor speed of the valve or compressor
is preferably variable so that the air pressure to the
support, both the upper and lower layers, can be varied to
suit different weights of body supported thereby, and in
the case of a variable speed valve the ripple speed can
also be varied.
BRIEF DESCRIPTION OF THE ~RAWINGS AMD
DESCRIPTION OF PREFERRED EMBODIMENTS
In order that the invention may be more clearly
understood, one embodiment will now be described with
reference to the drawings, wherein:
Fig. 1 shows a perspective cut-away view of part of
~ mattress of the invention, and indicates diagrammatically
the arrangement of its inflation equipment,
- Fig. 2 shows diagrammatically one form of timing
valve for switching the air flow to alternate passages of
the upper inflatable layer,
Fig. 3 shows a cut-away portion of a modification to
the construction of Fig. 1,
Fig. 4 shows a perspective view of a motor-operated
valve, and
Fig. 5 shows the mating faces of the valve disc and
valve body.
Referring to Fig. 1; the mattress ~s constructed
~rom flexible air-impermeable sheet material, and comprises
an upper inflatable layer 10 and a lower inflatable layer
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12. The lower inflatable layer is defined by lower and
upper sheets 14,16 respectively, while the upper layer is
formed from a top sheet 18 peripherally sealed to the sheet
16. The sheets 16,18 are also sealed together within the
area defined by the peripheral seal, to provide two lateral
tubes 20,22 respec*ively running down opposite sides of the
mattress, and a series of transverse tubes extending
between the lateral tubes. The transverse tubes are in two ,
sets 24,26 respectively, the tubes 24 communicating with
the lateral tube 20 at one side of the mattress, while the
tubes 26 communicate w~th the lateral tube 22 at the
opposite side of the mattress. There are thus defined two
separate air passages in the upper inflatable layer between
the sheets 16,18, one passage comprising the lateral tube
20 and transverse tubes 24, and the other passage comprising
the lateral tubes 22 and the transverse tubes 26. Some at
least of the transverse tubes are provided with very small
apertures 28, which provide a control`led leak of air from
the upper inflatable layer. The lower inflatable layer is
provided with an air inlet 30 at a suitable point. If the
layer 12 should be constructed to provide a number of
separate compartments instead of a single inflatable
envelope, then it can be provided with a corresponding
number of air inlets. The two air passages of the upper
inflatable layer are provided with separate air inlets
32,34 respectively leading into the lateral tubes.
Flexible elongate members 36, such as p.v.c. tubing,may be
provided so as to extend along the lateral tubes 20,22 to
ensure that they are kept open to the passage of air.
For ease of manufacture each inflatable layer could
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be formed of two separate sheets, as shown in Fig. 3, thus
employing a total of four sheets of material. The sheet 16
is thus replaced by two sheets 1~,17, the sheet 15 being
sealed to the sheet 14 to form the lower inflatable layer
and the sheet 17 sealed to the sheet 1~ to form the upper
inflatable layer. These two intermediate sheets may be
interconnected so as to locate the upper layer on the lower
layer. However the upper layer may be detachable from the
lower layer so that either can be used separately.
The mattress is supplied with compressed air from an
electrically driven compressor 38. The compressor
preferably has a variable output, suitably by using a
variable speed drive motor, so that the air pressure to the
mattress can be adjusted to suit different weights of b~ y
supported thereon. The outlet from the pump branches, one
branch 40 going directly or via a pressure reduction valve,
to the inlet of the lower inflatable layer. The other
branch 4~ leads to a cyclic switch-over valve 46, from
which it emerges as further branches 42,44 going to the
inlets 32,34 respectively of the two air passages of the
upper inflatable layer.
In operation, the lower inflatable layer is kept
inflated to the outlet pressure of the compressor (although
this could be reduced by a suitable valve or controlled
leak if desired). The air from the compressor is supplied
to the upper inflatable layer through first one air passage
then the other on an endlessly cyclical basis, for example
with each passage being inflated for a period of twenty
seconds before switching to the other passage. This
switching of the air supply back and forth between the
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branches 42,44 is effected by the switch-over device 46
which incorporates a timer which periodically switches the
valve back and forth. The timer may be of any suitable
type. For example, the valve may be cyclicly operated by
an electric motor, preferably a variable speed motor so
that the cycle frequency can be altered. Electric motors
with electronic speed controls are known in the art.
Alternatively the switching may be effected electrically
by a solenoid or the like at intervals controlled by an
electronic timing device of known kind. Another
arrangement uses a fluidic astable device such as is shown
in Fig. 2.
Referring to Fig. 2, the fluidic astable device,
which is a device known in the fluidics art, comprises an
air inlet passage 54 which branches to two air outlet
passages 56,58, the passages being arranged in the form of
a Y. Inlet pnssage 54 is connected to the conduit 41 from
the compressor 38, while the outlet passages 56,58 are
connected to the branch conduits 42,44 respectively. From
the outlet passages 56,58 extend two air bleed tubes 60,62
respectively, each of which leads to a variable throttle
valve 64 and air chamber 66 in series (although they could
be in parallel). From the air chambers 66 extend
respective air tubes 68,70 which open into the opposite
sides of the inlet passage 54 at the junction with the
passages 56,58. In operation, air supplied through the
inlet passage 54 can be de*lected into one or other of the
passages 56,58, by a certain minimum rate of air flowing
from the opposite tube 68 or 70. Once air is flowing
through one of the outlet passages it will continue to do
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so until it is flipped over into the other outlet passage
by the application of a minimum rate of air issuing from
the other tube 70 or 68. The air for the tubes 70,68 is
obtained ~rom the bleed tubes 60,62 respectively, so that
air passing through one of the outlet passages will provide
the air bleed necessary to switch the air flow over to the
other passage. The switching process thus cycles
automatically, the cycle period being determined by the
resistance-capacitance of the throttle 64 and chamber 66 in
each air bleed passage. The throttle valves 64 are
variable so that the cycle times can be adjusted as
desired. Additionally or alternatively the chambers 66
could be adjustable. This type of switching device is
simple to construct, and has essentially no moving parts.
An example of a motor operated val~e for alternating
the supply of air is shown in Figs. 4 and 5. An electric
motor 72 operates through a step-down gear box 74 to rotate
a valve disc 76 which-is in sliding contact with a face 78
of a valve body 80 which is fixed to the gear box housing.
The valve body has radial inlet ports 81,82,84 for
connection to the branches 41, 42 and 44 respectively. The
inlet port 81 connects through a passage 85 with a central
chamber 86 which is open on the face 78 of the valve body.
The ports 82,84 connect through respective passages 87,88
with respective diametrically opposed openings 89,90 in
the face 78. In its face 91 which contacts the face 78,
the valve disc 76 has a semi-annular channel 92 which
registers with the openings 89,90, and a radial channel 93
which connects the channel 92 with the chamber 86 in the
valve body. Thus, on rotation of the disc 76, air
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supplied to the chamber 86 passes via the channels 93,92
to the openings 89 and 90 alternately. The disc speed is
varied by varying the motor speed (although a varisble
speed gear box could be used instead). ~or example, with
motor speed varying from 60 to 600 rpm and an appropriate
speed reduction in the gear box, a ripple period (i.e. the
period from maximum inflation of one set of tubes to
maximum inflation of the other set of tubes) of from about
seven seconds to about seventy seconds can be obtained.
When the air supply is switched to one of the
passages of the upper inflatable layer, the lateral and
transverse tubes of that air passage inflateto support a
body lying on the mattress. The lateral and transverse
tubes of the other passage, now that there is no longer
the air supply to that passage, gradually deflate through
the loss of air thr~ugh the apertures 28. This alternate
inflation and deflation of the two sets of transverse tubes
produces a rippling effect, and prevents continuous
pressure being applied to any one part of the body
supported on the mattress. Because the lower inflatable
layer remains inflated throughout, it will act to support a
body on the mattress in the area of either of the air
passages of the upper inflatable layer, if that layer
should deflate to such an extent that sheet 18 bears on the
sheet 16. A variable pressure reduction valve 45 can be
provided in the branch 40 to enable the firmness of the
underlying support to be varied independently of the
support provided by the upper layer.
Although the invention has been particularly
described in relation to a mattress, it could be applied to
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other inflatable supports, such as seat cushions. The
switch-over valve device may be capable of being placed in
a condition in which both air passages of the upper layer
are simultaneously inflated. This may be useful, for
example, in making a bed or mo~ing or treating a patient
on the bed.
