Biomedical Engineering Reference
In-Depth Information
Fig. 7
Model for the second sensing ring built using Solid Works
The bigger holes on the outside of the ring are 120
ı
away from each other. These
holes are used to connect two N
2
O sensors and an air inlet to avoid creating a
vacuum in the system. Also, the main groove, coloured in blue, is bigger and now
round in section, instead of rectangular, as in the first model. This new format of
groove increases the volume were the gas will be circulating. On each side of it there
is a smaller and thinner groove where 'O' Rings can be fitted to seal the device, in
case there is a need to perform experiments with a completely sealed environment.
With the sensors connections placed 120
ı
apart it does not matter which
connector is attached to which hole as the relative angle between them will be
maintained. This would make the device much easier to use in a surgical situation
and also makes it easier to develop a control/recording measuring system.
The two thinner outer grooves in the testing ring were considered inappropriate
for further measurements due to the fact that, in the real situation there will always
be some gaps between the ring device and the real colon. This is because the colon
is a flexible surface, making it very difficult for a perfect attachment with a rigid
surface. In order words, it would be very difficult to avoid any leakage between the
device and colon during an actual surgical procedure. Therefore, a third model of
testing ring was created and a change was also made to the colon analogue. Figure
8
shows the third design in Solid Works (Fig.
9
).
The other change with this sensor ring is that the locating holes are now at 45
ı
intervals. This corresponds to the angles that it was decided should be studied.
Because the O-rings helped locate the “colon” centrally in the sensor ring, changes
were also made to the tube to ensure that the tube was centrally located. Some small
pads were fitted around the tube with gaps between them. The reason for the gaps
is due to the fact that in real life the sensing ring would not be perfectly attached
to the colon, and there would be always a certain amount of leakage between both
(Fig.
10
).
Lastly and one of the most important changes, was the introduction of two flow
control valves in the sensing inlet pipes. They are used to balance the volume of gas
