Jongho Choi

Two-dimensional actuation of a microrobot with a stationary two-pair coil?system

This paper proposes a new two-dimensional (2D) actuation method for a microrobot that uses a stationary two-pair coil system. The coil system actuates the microrobot by controlling the magnitude and direction of the external magnetic flux. The actuation of the microrobot consists of an alignment to the desired direction and a linear movement of the microrobot by non-contact electromagnetic actuation. Firstly, the actuation mechanism of the stationary coil system is theoretically derived and analyzed. Secondly, the tendency of the magnetic flux in the coil system are analyzed and compared by preliminary theoretical analysis. Through various locomotive experiments of the microrobot, the performance of the electromagnetic actuation by the proposed stationary two-pair coil system is evaluated. Using the proposed 2D actuation method, the microrobot is aligned to the desired direction by Helmholtz coils and is driven to the aligned direction by Maxwell coils. By the successive current control of the coil system, the microrobot can move along a desired path, such as a rectangular-shaped or a diamond-shaped path.

Two-dimensional locomotive permanent magnet using electromagnetic actuation system with two pairs stationary coils

Two-dimensional electromagnetic actuation system (EMA) was developed to manipulate microrobot for the intravascular therapy. This system consists of two pairs of Helmholtz coils and Maxwell coils and a cylindrical type permanent magnet is used as a microrobot. It is verified that the microrobot can move without power line using electromagnetic field. We analyzed this locomotive mechanism of the microrobot using two-dimensional EMA system theoretically and validated the performance of the mechanism by various experiments. The position of the microrobot which is inside of region of interest (ROI) could be recognized by CCD camera. This position information is used for feedback signal, a simple proportional (P) controller is used for this EMA system. The final goal of this paper is to control the micro robot position precisely. Firstly, we demonstrate the autonomous locomotion of the microrobot along a predefined desired path. Secondly, we adopt an applicable joystick system as a master which the operators can use in a real operation and realize the path control of the microrobot.

Positioning of microrobot in a pulsating flow using EMA system

The purpose of this paper is the positioning control of the microrobot in a pulsating flow using electromagnetic actuation (EMA) System. Several types of EMA systems which are 2-dimensional and 3-dimensional locomotion control of microrobot were proposed and studied. Generally, these conventional researches of EMA systems showed the results of locomotion of microrobot in a fluid without flow. However, in the case of test of microrobot in a blood vessel, it is required that the experiments of locomotion should be performed in a pulsating flow like bloodstream. For that reason, we carried out basic locomotion research of the microrobot in the pulsating flow. For this experiment, we used simple 1-dimensional EMA system which consists of a pair of Helmholtz and Maxwell coils, and we set up a vascular simulator which can generate pulsating flow in the vessel phantom. The magnetized microrobot was inserted in the vascular simulator. The electromagnetic force which affects the motion of the microrobot was controlled by regulating input current to EMA system. The input current regulation was performed by considering the magnitude of flow rate and drag force of fluid to the microrobot. To measure the pressure variance of a pulsating flow in the vascular phantom, the pressure transducer was placed in front of the region of interest (ROI) and the control input which compensates the drag force to microrobot was generated by using the transducer signal. In addition, the position of microrobot was acquired through the CMOS camera and the feedback control loop was also implemented for accurate positioning control. The performance of the positioning control was evaluated by in-vitro experiments using vascular simulator. In addition, the feasibility of the position control of the microrobot was also evaluated by in-vivo animal experiments.

Position stabilization of microrobot using pressure signal in pulsating flow of blood vessel

The target of this paper is the pressure sensor based positioning control of the microrobot in a pulsating flow of blood vessel using an electromagnetic actuation (EMA) system. For treatment of these coronary arterial diseases, various type microrobots with a wireless locomotive actuating power using EMA were proposed. However, because the intravascular blood flows have pulsate fluctuating and high pressurized waves, it is estimated that the stable positioning control of the microrobot in the blood vessel was very difficult. In detail, the pulsating blood flow generates the pulse type drag force on the microrobot and the drag force makes the microrobots oscillating motion in the blood vessel. For the accurate positioning control of the microrobot, the pulse type drag force on the microrobot should be compensated. Therefore, for the compensation of the drag force on the microrobot, the pressure transducer in the blood vessel was introduced and the pressure signal of the blood flow was used. Through the pressure sensor based compensation of the drag force, the stabilization of the position of the microrobot could be tested and evaluated.

Position-based compensation of electromagnetic fields interference for electromagnetic locomotive microrobot

Recently, the locomotion of a microrobot wirelessly actuated by electromagnetic actuation systems has been studied in many ways. Because of the inherent characteristics of an electromagnetic field, however, the magnetic field of each coil in the electromagnetic actuation system induces magnetic field interferences, which can distort the desired electromagnetic field, preventing the microrobot from following the desired path. In this article, we used two pairs of Helmholtz coils and two pairs of Maxwell coils in a two-dimensional electromagnetic actuation system. Generally, the two pairs of Helmholtz coils generate the torque for the rotation of the microrobot and the two pairs of Maxwell coils generate the propulsion force of the microrobot. Both pairs of Helmholtz and Maxwell coils have to work to simultaneously align and propel the microrobot in a desired direction. In this situation, however, the electromagnetic fields produced by the Helmholtz coils can interfere with those produced by the Maxwell coils. This interference is closely dependent on the position of the microrobot in the region of interest inside the electromagnetic coils system. This means that the alignment direction and propulsion force of the microrobot can be distorted according to the position of the microrobot. Therefore, we propose a compensation algorithm for the electromagnetic field interference using the position information of the microrobot to correct the magnetic field interferences. First, the interference of an electromagnetic field obeying the Biot–Savart law is analyzed by numerical analysis. Second, a position-based compensation algorithm for the locomotion of a microrobot is proposed. Various locomotion tests of a microrobot verified that the proposed compensation algorithm could reduce the normalized average tracking error from 5.25% to 1.92%.

Fabrication of a High-Aspect-Ratio Nano Tip Integrated Micro Cantilever with a ZnO Piezoelectric Actuator

This paper reports on the high-aspect-ratio (HAR) nano tip integrated micro cantilever with the ZnO piezoelectric actuator. The cantilever is proposed for the ferroelectric material investigation using the conductive AFM tip, which uses the interaction between the nano tip and the material. The HAR nano tip integrated cantilever is needed to suppress the undesirable effects caused by the interaction between a cantilever and a material. The fabricated device consists of two parts, the cantilever part and the supporting glass part. The HAR nano tip integrated cantilever part is fabricated using the trench refilling process. For the size reduction and the high resonance frequency, the rf-magnetron sputtered ZnO layer is also integrated on the cantilever. The anodic bonded glass supports the cantilever, and the indirect contact between the glass and the electrodes prevents the ZnO breakdown during the bonding process. The HAR nano tip has 6μm side length, over 18μm height, which is built on the 85μm-wide, 300μm-long, and 1.2μm-thick cantilever. The aspect ratio of the tip is three or more and the tip radius is less than 15nm. The simulated spring constant and the resonance frequency are 1.4N/m and 27.81kHz, respectively.

Electromagnetic actuation methods for intravascular locomotive microrobot

Heart diseases such as angina pectoris and myocardial infarction have been becoming the leading causes of death all over the world in recent years. The pharmacotherapy and the surgical operations have been executed for treating heart problems. The percutaneous coronary intervention (PCI) with catheter is frequently used for the treatment of coronary artery diseases, but the treatment of chronic total occlusion (CTO) is very difficult and challenging operation, since there is no efficient alternative therapy until now. For this reason, the microrobot to improve the intravascular treatment is one of the growing research areas. In this paper, various electromagnetic actuation (EMA) systems to supply driving power for the microrobot were proposed. The performance of the locomotion of microrobot in the 2D and 3D space were validated with in-vitro experiments and also the in-vivo tests were performed for demonstrating the movement of microrobot in the living rabbit.