Biomedical Engineering Reference
In-Depth Information
Figure 13.7
Schematic view of a paddling based microrobot for capsule endoscope. (Re-
produced according to Park
et al.
(2007).)
devices to ensure the unidirectional movement. The prototype was 13
mm
in
diameter and 33
mm
in total length, leaving a hollow space of 7.6
mm
in diameter
to hold other parts needed for endoscopy, such as a camera, an RF modules and
batteries. An average speed up to 14.7
mm
/
min
was measured on the surface
of porcine colons during in-vitro experiments. The characteristic of SMAs is
the ability of deformation according to temperature change; unfortunately, the
environment in the living body is hostile for heat dissipation of the SMA and will
lower the efficiency of in-vivo test. Moreover, the local temperature rise of the
intestinal wall at the contact point should be guaranteed to be of no harm.
Park and colleagues Park
et al.
(2007) proposed a paddling based locomotive
mechanism for the capsule endoscope. The 13
mm
30
mm
capsule-type micro-
robot achieved movement by the six legs driven by a stepper micromotor together
with two mobile cylinders inside.
Fig. 13.7
shows the structure of the design.
A moving speed up to 6.42 mm/s was obtained during in-vitro experiments in
porcine small intestine.
The internal locomotion mechanism is usually integrated on board the capsule
and may offer better flexibility and dexterity. However, power constraint and
size limitation are two bottlenecks in the development of a completely wireless
active capsule endoscope. At present, button batteries are not powerful enough to
supply energy for the locomotion mechanisms and all of the mechatronic designs
introduced above need a cord connected to the external power supply. Moreover,
the sizes of the active capsules need further miniaturization in order to be swal-
lowable. Another aspect need to mention is that the introduced mechanisms can
only make one-way movement due to the directional shapes of the clampers, e.g.,
the legs and hooks.
×
13.3.3 Magnetic actuation methods
Magnetic force is an appealing option for the actuation of an active capsule
endoscope wirelessly because it can avoid internal power consumption by using
