Abstract
Magnetically actuated microrobot in a liquid media is faced with the problem of head-tilting reaction caused by its hydrodynamic structure and its speed while moving horizontally. When the instance microrobot starts a lateral motion, the drag force acting on it increases. Thus, the microrobot is unable to move parallel to the surface due to the existence of drag force that cannot be neglected, particularly at high speeds such as >5 mm/s. The effect of it scales exponentially at different speeds and the head-tilting angle of the microrobot changes relative to the reference surface. To the best of our knowledge, there is no prior study on this problem, and no solution has been proposed so far. In this study, we developed and experimented with 3 control models to stabilize microrobot motion characteristics in liquid media to achieve accurate lateral locomotion. The microrobot moves in an untethered manner, and its localization is carried out by a neodymium magnet (grade N48) placed inside its polymer body. This permanent magnet is called a carrier-magnet. The fabricated microrobot is levitated diamagnetically using a pyrolytic graphite placed under it and an external permanent magnet, called a lifter-magnet (grade N48), aligned above it. The lifter-magnet is attached to a servo motor mechanism which can control carrier-magnet orientation along with roll and pitch axes. Controlling the angle of this servo motor, together with the lifter-magnet, allowed us to cope with the head-tilting reaction instantly. Based on the finite element method (FEM), analyses that were designed according to this experimental setup, the equations giving the relation of microrobot speed with servo motor angle along with the microrobot head-tilting angle with servo motor angle, were derived. The control inputs were obtained by COMSOL® (version 5.3, COMSOL Inc., Stockholm, Sweden). Using these derived equations, the rule-based model, laser model, and hybrid model techniques were proposed in this study to decrease the head-tilting angle. Motion control algorithms were applied in di-ionized water medium. According to the results for these 3 control strategies, at higher speeds (>5 mm/s) and 5 mm horizontal motion trajectory, the average head-tilting angle was reduced to 2.7° with the ruled-based model, 1.1° with the laser model, and 0.7° with the hybrid model.
Highlights
Microrobot actuation studies have focused on electromagnetic methodologies associated with different control approaches
A levitated microrobot in liquid media cannot move parallel to the surface during horizontal movements due to their hydrodynamic structures
Previous studies were applied to various levitation techniques for the stabilization and control of the horizontal movements of microrobots [2,3,4,5]
Summary
Microrobot actuation studies have focused on electromagnetic methodologies associated with different control approaches. Khamesee and his team obtained similar results, even though they added drag force into their control model [5] Arai and his team applied high-frequency ultrasound vibrations on the surface upon which the microrobot moves and achieved better results [30]. The main purpose of the developed control techniques is the minimization of the drag force’s effect on the microrobot, which moves inside a fluidic environment in an untethered manner. They can be utilized in any application that requires complex trajectories tracking and precise transportation of micro and nano structures. All control techniques are compared to the uncontrolled head-tilting reaction
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