Parameters Modelling and Fuzzy Control System of Neonatal ...

SETIT2009
incubators have carried out numerical or experimental
techniques [5, 8, 9]. The major objectives of these
studies are heat losses of the neonate, temperature
distribution, air flow, humidity control and a better
insight of the thermal interactions between the neonate
and its surrounding environment. In this paper, the
problem of heat transfer modelling is tackled, in the
perspective of robust temperature control.
The rest of the paper is organized as follows. In the
next section, the description of the process with
relevant signals is presented. The thermal
characterisation of the neonate and its environment is
complex and not well understood. But, they determine
the actual temperature in the incubator. A
mathematical heat transfer model is presented in the
section two. Our model is combining passive heat
losses and active heat production both from internal
(infant) and external sources. A robust control system
is presented in the third section, followed in section
four by simulation results validating our approach. We
then present potential applications of our system.
Finally, conclusions are addressed with attention
paid to neurofuzzy control or energy efficiency as
future work.
1. Process description
1.1. Neonate’s room
It has been drawn in the figure 1 the simplified cross
section of the chamber where babies are laid down.
d
w
Figure 1. Room for babies. Arrows indicate heating
air flow.
Walls are in plexiglas or such kind of material. A
mattress is sketched inside the room. The room is not
hermetic. Many small holes are provided for air
admission and expelling. There are also holes to
connect other monitoring apparatus to the baby in the
incubator. Room dimensions are approximately:
Wall width d between 5 and 10 mm
Height h between 40 and 80 cm
Width w between 50 and 100 cm
Length l between 70 and 150 cm
The control system will be located at the bottom of
the room. Sensors are placed on air inlets and outlet or
tapped on the infant skin.
h
1.2. Signals description
1.2.1 Temperature
Temperature is kept on a fixed value that medical
staff can choose around values between 27 and 39°C.
The precision around a setpoint Ts is ±δ where δ≤0.5
°C. The temperature must be kept in these bounds
though air is being renewed. If the temperature falls
out of the bounds, an alarm should sound and/or
display. Temperature is considered as the most critical
parameter. Particularly, for preterm neonates, the
internal control mechanisms of temperature are not
well developed as in an adult and the survival depends
on external control. For improving reliability, heating
with resistors and redundant temperature sensing are
proposed. For more universality of our system, the
range of controlled temperature will be enlarged, as
air, skin and core temperature (to name a few) will be
controlled.
1.2.2 Humidity
The simplest way to moisten the room air is to
force (by a fan) the air flux passing above a water tank
before it goes through holes to babies’ room. The
adjustment of the air-water contact surface leads to the
hygrometric regulation. The value can be set to a point
between 44 and 95%. Levels recommended in the
literature are located between 65 and 90%. As till to
now, this parameter needs not high precision, its
adjustment is done sometimes manually. Humidity is
linked to temperature. But the important point is to
make sure that the fan is running. Otherwise, an alarm
must sound. The alarm sounds also if water level in
the tank is too low.
1.2.3 Oxygen
Oxygenation can be obtained without a particular
effort with the air circulation. And holes are on the
walls of the room. Oxygen consumption measurement
can also inform on the metabolic heat production.
1.2.4 Breathing signal
The matter is that it happens for baby to "forget"
breathing (apnoea). The outcome of this might be the
death. One must then be sure the baby is breathing
normally. Expelled and incoming air to lungs have
different temperatures: thus, as a simple and low cost
sensing system, current/potential difference variations
across a thermistance located at the baby nose can be
monitored. But the two temperatures can be very close
and their difference is a time varying phenomenon.
Moreover, baby’s movements constitute artifacts
sources that can be superimposed to the signal. Preprocessing
is useful to avoid false decision. An alarm
is also needed here if the breathing is going wrong.
1.2.5 Other signals
Miscellaneous other signals, particularly from the
baby body (weight, baby temperature,
electrophysiological signals as ECG or EMG…) are
now generally sensed and processed by powerful
external equipments. They are foreseen in our system,
but are not our concern for the moment
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