Page 484 - Handbook of Biomechatronics

478 Ahmet Fatih Tabak

Fig. 5 Depiction of motion control incorporated with gravity compensation. The
electromagnetic coils, which are separately driven by a decision making and controller
unit. The controller unit accepts visual servoing data relayed by the camera. Depending
on the position of the micro-swimmer, the digital, that is, discrete, a control signal is
generated by the decision-making code. Then, the signal passes through a digital to
analog converter (DAC) so a continuous signal is obtained which will be amplified to
adequate power before entering the coils. Coils effectively generate the magnetic field
and field gradient superimposed to induce magnetic torque, T m (Nm), and magnetic
force, F m (N), respectively. The magnetic force counteracts the gravitational attraction,
2
g (m/s ), hence keeping the position along the vertical lab coordinate fixed. In the
meantime, as the magnetic field rotates, the helical micro-swimmer follows that rotation
harnessing the forward thrust (Mahoney et al., 2011).

there was an unquestionable advantage of in vitro, performing in a physical
simulation rather than in an actual living tissue, experimentation where a
camera was able to capture images in real time. The micro-robotic system
should be able to sense their environment, as all robotic systems are expected
to. However, being very small in dimensions and being immersed in living
tissue, that is, in vivo, present certain problems in that regard. For instance,
because of size constraints and energy consumption, the artificial end-
effector itself will probably not be able to accommodate the necessary hard-
ware onboard to relay all the relevant information on the basic physical and
geometric conditions of the ever-changing surroundings. Therefore, the
computer, that is, the autonomous controller, or the user, that is, the pilot,
is expected to infer to a certain degree based on what is available at any
instant. In such cases, one type of most valuable data comes from various
versions of visual-servoing methods.
Fluorescence imaging is one of those methods (Servant et al., 2015):
a number of magnetically actuated helical swimmers are coated with