Note: Descriptions are shown in the official language in which they were submitted.
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WO 98/19597 PCT/GB97/03025
SENSOR ARRANGEMENT FOR MONITORING PHYSICAL ACTIVITY
The present invention relates to a sensor arrangement and monitor system for
monitoring
physical activity associated with a living being, without having to be fitted
to the living
being and without using fields or signals which might be perceived as harmful
to a living
being, in particular when the living being is a baby.
Systems have been developed for home and hospital use to monitor the presence
of a baby
in a cot or a pram. for example by monitoring physical activity such as a
heartbeat or
breathing of the baby, which set off an alarm when the baby is removed by an
unauthorised person.
Further, medical staff monitor the patients under their care for any change
relating to their
1 ~ well being. Monitoring the physical activity of a new born baby,
particularly heartbeat
and breathing, can alert staff immediately to medical problems, such as a
potential cot
death incident.
For hospital use such systems must be capable of being applied to a number of
cots
simultaneously, for instance in a hospital ward where a number of cots would
be present.
Monitoring systems have been developed which use various types of sensors
which are
connected to the body of the living being. The sensors are then typically
connected to a
suitable form of processing facility. However, in such systems it is
inconvenient to have
to attach and detach the living being from the sensors when they are moved.
Also, the
attachment of sensors to a baby invariably requires the use of wires which may
become
entangled with the baby's limbs or around a baby's neck.
GB 2.150,332 discloses a heartbeat monitor in which a sensor is fitted to the
chest of a
baby. for example by being secured in a pocket of a close fitting vest which
pocket lies
over the chest of the baby. The sensor comprises a microphone for picking up
cardiac
sounds and avoids the use of wires to connect the sensor to a processing
facility by using
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a radio link. However, this system has the inconvenience of having to
repeatedly fit the
sensor to the baby.
Equipment for monitoring a heartbeat has to be able to detect a signal having
a very short
S pulse duration and if the sensor is not directly fitted to the living being
will have to pick
out the heartbeat signal of very small amplitude from a lot of background
movement or
noise including movement or noises made by the living being, such as
breathing, vocal
noises and limb movements as well as movement or noises emanating from the
surroundings of the living being.
GB 2,16S,979 discloses a monitor apparatus which describes a system which
monitors the
breathing of a baby by sensing pressure changes in an air envelope on which
the baby
rests. The air envelope is designed to couple the signal of interest to a
transducer which
communicates with the air envelope. However, GB 2,165,979 does not disclose in
detail
1 S how the air envelope is designed to discriminate between the signal of
interest and other
movement or noises occurring in the Local environment.
GB 2,192,460 discloses a sensor arrangement for monitoring respiration of a
living being
comprising a sounding board which is located underneath a mattress or cushion
on which
the living bein~~ rests and which transmits movement to a transducer which is
fitted to the
board. The signals from the transducer are processed to signal an alarm if
respiration
movement stops. However, this sensor arrangement is not arranged to be
responsive to
the much smaller movements associated with a heartbeat movement.
2S Accordingly, the present invention provides a sensor arrangement for
monitoring physical
activity associated with a living being, comprising a flexible board which
distorts in
response to physical activity to which is fitted a transducer for converting a
distortion of
the board into an electrical signal, characterised in that the board comprises
discontinuities. The discontinuities enable parts of the board to distort
somewhat
independently of other parts of the board and so allows the board to distort
easily while
being yet strong enough to support a mattress on which a living being rests
and stiff
enough to convey the signal. The more flexible the board is the more sensitive
it is to
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movement. The sensor arrangement according to the present invention is able to
reliably
pick up heartbeat movements from a living being through a mattress.
The discontinuities may be in the form of a plurality of grooves or a
plurality of slots.
Good results are achieved if the discontinuities are linear and if at least
some of the
discontinuities terminate adjacent to the transducer. This makes the region in
which the
transducer is located flex more in response to movement. The flexible region
close to the
transducer causes the transducer to distort and generate an electrical signal.
Preferably, the discontinuities extend radially from the transducer which has
the effect of
focussing movement of the board towards the transducer and of increasing the
flexing of
the board adjacent to the transducer.
Alternatively, the discontinuities can comprise a plurality of ribs in a board
made out of a
more flexible material which without the ribs would not be able to support the
mattress
and living being.
For the board to be able to distort optimally it should be spaced from the
surface on which
it rests. Therefore, preferably the board comprises at least one support
member for
spacing the board away from the surface on which the board rests. For best
results at least
one support member should act as a fulcrum for the transducer so that it is
more
responsive to distortions of the board.
Preferably, the transducer is a piezo-electric device.
The board can be made of plastic) preferably ABS plastic, metal, fibre board
or hard
board.
Embodiments of the present invention will now be described, by way of example
only,
with reference to the accompanying figures in which:
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Figure 1 shows schematically an embodiment of a system for monitoring a
heartbeat of a living being; and
Figures 2a to 2e schematically illustrate embodiments of support boards on
which
a transducer is mounted.
Referring to Figure 1. there is shown a schematic embodiment of a monitor
system (10)
for detecting physical activity, including heartbeat, associated with a baby.
A cot (20) for
a baby has underneath the mattress (30) a transducer arrangement (40). The
transducer
arrangement is exited by one or more physical activities associated with a
baby, such as a
heartbeat. breathing or limb movement, and produces a signal having components
derived
from or related to any such physical activities.
The transducer arrangement (40) is coupled, via a suitable signal transmission
medium to
a cot unit (50). The cot unit (50) comprises circuitry for processing the
signals received
from the transducer arrangement (40) to distinguish between various forms of
physical
activity emanating from or associated with a baby in the cot (20).
The cot unit can comprise an alarm or can be, directly or indirectly,
connected to an alarm
and can trigger the activation of an alarm (60) in the event that the signal
from the
transducer arrangement (40) indicates that at least a selectable one of a
plurality of
physical activities associated with the baby has changed or terminated. For
example, the
cot unit (50) may activate an alarm if a determination is made to the effect
that the signal
no longer contains a component indicative of heartbeat. Various thresholds can
be set
which monitor not only the presence of a particular component of the signal
but also the
level or rate of that component.
The alarm (60) is typically located in a central location where it has a high
probability of
attracting the attention of a responsible adult during home use or nursing
staff for hospital
use. The alarm (60) may produce an audio output or a visual indication, for
example,
where it is undesirable to disturb other babies or patients in a hospital.
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In one embodiment. the transducer arrangement comprises a suitably flexible
support
board (70) (see Figures 2a to 2e) having a piezo-ceramic device (80) centrally
disposed
thereon which produces a voltage when stressed or flexed. The piezo-ceramic
device (80)
is in the form of a disc. Manufacturing the board from a suitable plastic can
increase the
~ ~ sensitivity of the transducer arrangement as a whole to the physical
activities of a baby.
Preferably the support board is made from ABS plastic due to the low cost and
ability to
shape and work the plastic. Alternative embodiments can be realised in which
the flexible
board is manufactured from other plastics, metal, fibre board or hard board.
Mechanical means are utilised which increase the sensitivity of the transducer
arrangement to the movement of the mattress or baby by locating a fulcrum for
the
support board (70) directly below the piezo-electric element.
The support board (70) is formed with a plurality of discontinuities, such as
slots (90) (see
Figures 2b to 2d). In a further embodiment (see Figure 2a) the support board
(70) utilises
an arrangement of U-shaped grooves (94) on at least one of either the top or
bottom
surfaces thereof. 'fhe discontinuities ensure that the board is flexible and
so will readily
distort in response to the physical activities of the baby while remaining
strong enough to
support the mattress (30) and a baby.
Alternatively, the discontinuities can be a plurality of ribs (92) (see Figure
2e) which
enable a more fle~cible board material to be used while the board is still
strong enough to
support a mattress and a baby.
In a preferred embodiment (see in Figures 2b to 2d) the slots (90) are
radially disposed
with respect to a central portion of the support (70) board where the piezo
device (80) is
located. .=1 further embodiment (Figure 2d) also comprises further slots (90)
disposed
~ around the periphery of the support board (70). In Figure 4d the support
board (70)
comprises a total of ei'1ht slots having at the ends thereof a hole which
reduces the
stresses conventionally associated with the slots.
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The support board (70) is generally rectangular although other shapes are also
possible,
for example square or circular
Preferably the lower surface of the support board (70) is held in an elevated
position
S above and not in contact with the bottom of the cot. This enables the
support board to
deform easily and so increases its sensitivity to physical activity.
In the embodiments shown in Figures 2a to 2e, the degree by which the plastic
support
board (70) can flex is increased by using strategically placed feet (95)
(shown in dotted
lines) arranged to support the support board (70) such that movement thereof
is not
impeded by, for example, the bottom of the cot. The feet (95) are regularly
disposed
around the periphery of the support board (70) and one foot is centrally
disposed so as to
provide a fulcrum support for the piezo device. Therefore, as the baby moves,
including
breathing and heartbeat movements, the board flexes which, in turn, causes the
piezo
device to produce a signal indicative of such movement.
The piezo device is situated at the position on the support board (70) which
flexes the
most and therefore stresses the piezo device the most. This position has been
found to be
typically the centre of the board, particularly if a fulcrum support is
provided at the centre
of the board.
An alternative embodiment can be realised in which the feet are omitted.
According to
this alternative embodiment, the plastic support board is supported at its
edges by the
frame of the cot such that the board if free to flex and such movement is not
impeded by
the bottom surface. if any, of the cot.
During deep sleep. the only physical activities which are present are the
breathing and the
heartbeat.
Optionally, the support board (70) comprises a removable protective covering
(not
shown) to guard a~~ainst damage, for example, by bodily or other fluids.
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The piezo-ceramic device (80) is connected to the cot unit (50) using a co-
axial cable
( 100). Co-axial cable is preferred as it is less susceptible to mains
interference than most
cables. However. as an alternative, suitable screened twisted pair may be
utilised.
The cot unit is suitably programmed to determine whether or not it is
necessary to sound
the alarm. The presence or absence of the signals relating to heartbeat,
breathing or limb
movement can be utilised for monitoring the health of the baby or simply for
monitoring
whether or not the baby is present in the cot. For example, the alarm may be
sounded as
soon as a determination has been made that the breathing/limb movement and/or
heartbeat
signals are not present.
A microprocessor or alternative electrical circuitry can be provided within
the cot unit
(50). However. other embodiments can be realised in which the processing is
performed
remotely by, for example, a computer.
With further reference to Figure 1, in this embodiment which is suitable for
monitoring a
number of cots in a hospital ward, each cot unit (50) is connected via
communication link
( 102) to a computer or a system control ler ( 107). Also, a relay output unit
( 110) is
provided under the control of the cot unit (50) and/or the system controller
(107) to
perform various functions. such as to lock the doors to a maternity ward to
prevent a baby
being stolen, send a si~~nal to a pager informing the holder of the pager of
the problem, or
to sound an alarm.
The system controller ( 107) receives and displays status information
associated with a
plurality of cots, each haV111g its own transducer arrangement (40) and
associated cot unit
(50).
The cot units (50) and the system controller ( 107) can operate an alarm
independently. If
the system controller ( l07) does not receive an appropriate response after
interrogating a
cot unit (50) via the communication link ( 102) it will go into alarm
immediately.
Likewise each cot unit (50) detects or monitors interrogation by the system
controller
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( 107) and will SOtllld an alarm if it fails to be interrogated regularly.
This will highlight
hardware failure and guard against leads being cut.
The cot unit can be arranged so that it can be deactivated by a security
system such as a
~ magnetic swipe card device ( 112) or a security key-pad device by an
authorised adult that
wishes to remove a baby from a cot without setting off an alarm.
In the version of the monitor for domestic use it is useful for the cot unit
to include an
audio-microphone to detect audible sounds made by the baby. The cot unit can
then also
incorporate a radio transmitter which transmits a radio signal carrying the
audible sounds
plus any alarm si~~nal to a remote radio receiving unit which incorporates a
loud speaker.
The receiving unit is mobile and can be carried by and located in the
neighbourhood of an
adult responsible for the baby. Therefore, if the baby cries, the crying noise
will be
transmitted by the receiving unit and the responsible adult can act
appropriately. Further,
1 ~ if the heartbeat, breathing and/or limb movement activity of the baby
ceases an audible
alarm signal will be emitted by the receiving unit to alert the responsible
adult to the
danger.
Although, the above embodiments have been described in relation to babies, it
will be
appreciated that the present invention can equally be applied to other living
mammals
such as adults, small children and even animals.
For example, in a hospital for patients suffering from senile dementia or
similar illnesses,
the monitor system could be used to warn nursing staff when such patients get
out of bed
during the night. In this case, it may be necessary to use two transducer
arrangements
spaced apart under the mattress in order to reliably detect the presence of an
adult patient.
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