Download attached - Robotics and Mechatronics

Abstract
Minimal invasive surgery (MIS) aims to reduce patient trauma and recovery time. One
field of research within MIS is the utilization of microrobots to diagnose and deliver
drugs at hard-to-reach regions within the human body. These microrobots could have
magnetic properties which allow us to control them by applying magnetic fields. The
goal of this Master0 s thesis project is to develop a testbed to perform three-dimensional
(3D) closed loop control of microrobots.
Control of microrobots in 3D space is implemented using the developed MagneticallyActuated Robotic System (MARS). MARS has eight electromagnets which are used to
generate almost uniform magnetic fields of 64.5 mT in magnitude, magnetic field gradients of 1.52 Tm−1 , and gradient of the squared magnetic fields of 127.1 mT2 mm−1 .
These magnetic fields and gradients allow us to control paramagnetic microparticles,
microjets and magnetotactic bacteria within a 3D space of maximum 2.4 mm3 . Feedback for the position controllers is provided by two microscopes with attached cameras
which provide images at 50 frames per second. The images provided by the cameras
are used by feature tracking algorithms to determine the position of the microrobot.
Furthermore, MARS is equipped with an autofocusing system. The position and autofocusing controllers, and feature tracking algorithms are implemented on a real-time
control platform.
It is experimentally demonstrated that MARS is capable of achieving point-to-point
position control of paramagnetic microparticles in 3D space. The position accuracy
during the experiment is approximately 5.3 µm, the average velocity is 367 µms−1 , and
the maximum velocity is 2 mms−1 . Also a self-propelled microjet is position controlled
in 3D space. The position accuracy during this experiment is approximately 157 µm
and the average velocity is 121 µms−1 . To our knowledge, we have for the first time
demonstrated the closed loop control of microjets in 3D space.
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