Page 337 - Control Theory in Biomedical Engineering

308 Control theory in biomedical engineering

Since an elevated temperature is a requirement before the actuation of
the SMA to return to its original shape, there have been some methods
developed to achieve this aim. The most popular is the usage of current
to increase the temperature via heat due to the resistance of the wire. In addi-
tion to allowing the SMA to keep its thin profile, it also facilitates even heat-
ing of the alloy. Some other methods of actuation also include using fluid, as
per US5645520A, where an insert regulates the temperature via the ratio of
hot and cold water as well as installed heating elements. The active endo-
scope invented by Ikuta et al. makes uses of a fluid cooling system as well.
The inclusion of such mechanisms is bound to increase the girth of the tube
significantly, which is not desirable considering that girth is a luxury when
designed for use in the respiratory tract.
In conventional bending applications, the most used mechanic of
bending is having the number of bending actuators be equal to that of
the number of directions that the device can pull in. However, this
hinders ability to reduce the diameter of the tube. A method to reduce
diameter is to reduce the total amount of actuators needed while retaining
the same amount of directions in which bending can occur. One such
example is patent US5897488A, where the number of actuators was
reduced from four to three. One notable mention is the mask that was
designed to facilitate the endoscopy process involving entry via orifices
in the upper half of the body (US 0100368). The mask, however, is
directed at subjects that are required to be sedated, with ports allowing
the insertion of an oxygen tube and to test for tidal carbon dioxide. This
design incorporates features that are redundant in a procedure that is to be
done without anesthesia. The proximity of the mask wall to the nostril is
also too long for accurate insertion of the device. Nasal dilators have also
been developed, for example patent 5895509. While they have potential
in terms of reducing the proximity of the scope to the orifice and the
widening of the airway, the lack of self-positioning mechanism may lead
to imprecise positioning of the scope. This leads to discomfort, which is
an unwanted outcome.
While there are many prior arts regarding endoscopes that have been
developed for medical use, there is little mention of a design that is catered
to home use. In addition, the insertion of the various control mechanisms
means that there is still a baseline on the minimum thickness achievable,
which makes it unfeasible for self-administering of the endoscopy process
because the girth of the tube might cause severe trauma to the surrounding
tissues if navigation is poorly done.