• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.12
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• pp.1573-1578
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• 2011

In this study, a novel electromagnetic microrobot system with locomotion and drilling functions in threedimensional space was developed. Because of size limitations, the microrobot does not have actuator, battery, and controller. Therefore, an electromagnetic actuation (EMA) system was used to drive the robot. The proposed EMA system consists of three rectangular Helmholtz coil pairs in x-, y- and z-axes and a Maxwell coil pair in the z-axis. The magnetic field generated in the EMA coil system could be controlled by the input current of the EMA coil. Finally, through various experiments, the locomotion and drilling performances of the proposed EMA microrobot system were verified.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.3
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• pp.217-224
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• 2020

The use of a high gain flight control system to achieve high bandwidth performance increase the instability of a helicopter. To investigate these phenomena numerically, high fidelity EC155B1 helicopter model and simplified flight control system that include actuator, digital processor and noise rejection filter was developed. A study conducts an analytical investigation of roll axis stability of the helicopter model as feedback gain increases. And this study analyzes roll-rate and roll-attitude feedback gains limited by rotor flap mode. The results indicate that the phase delays caused by the filter can severely limit the usable values of the roll-rate and roll-attitude feedback gains.

• Journal of the Korean Vacuum Society
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• v.12 no.2
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• pp.144-149
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• 2003

Carbon tips were grown on Si cantilevers by applying an electron beam to them directly with Scanning Electron Microscope. A carbon tip was fabricated by aligning the electron beam directly down the vertical axis of Si cantilever and then irradiating a single spot on the cantilever for a proper time in the dominant atmosphere of residual gases generated by the oil of the diffusion pump. A number of control parameters for SEM, including exposure time, acceleration voltage, emission current, and beam probe current, were allowed to make various aspect ratio feature. The growth of carbon tips was not affected by the surface morphology of substrates. We could acquired the tip whose effective length is 0.5 $\mu\textrm{m}$, bottom diameter is 90 nm and cone half angle $3.5^{\circ}$ The growth technique of the high aspect ratio carbon tips on the tip-free cantilevers is available to reduce the complexities of fabricating sub-micron scale tips on the PZT thin film actuator integrated AFM cantilevers.

• International Journal of Precision Engineering and Manufacturing
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• v.9 no.3
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• pp.27-32
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• 2008

This paper describes a contact atomic force microscope (AFM) that can be used for high-speed precision measurements of microstructured surfaces. The AFM is composed of an air-bearing X stage, an air-bearing spindle with the axis of rotation in the Z direction, and an AFM probe unit. The traversing distance and maximum speed of the X stage are 300 mm and 400 mm/s, respectively. The spindle has the ability to hold a sample in a vacuum chuck with a maximum diameter of 130 mm and has a maximum rotation speed of 300 rpm. The bandwidth of the AFM probe unit in an open loop control circuit is more than 40 kHz. To achieve precision measurements of microstructured surfaces with slopes, a scanning strategy combining constant height measurements with a slope compensation technique is proposed. In this scanning strategy, the Z direction PZT actuator of the AFM probe unit is employed to compensate for the slope of the sample surface while the microstructures are scanned by the AFM probe at a constant height. The precision of such a scanning strategy is demonstrated by obtaining profile measurements of a microstructure surface at a series of scanning speeds ranging from 0.1 to 20.0 mm/s.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.8
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• pp.639-651
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• 2018

An analytical solution to generate attitude command profile for agile spacecraft is proposed. In realistic environment, obtaining analytical minimum-time optimal solution is very difficult because of following constraints-: 1) actuator saturation, 2) flexible mode excitation, 3) uplink command bandwidth limit. For that reasons, this paper applies two simplifications, an eigen-axis rotation and a finite-jerk approximated profile, to derive the solution in an analytical manner. The resulting attitude profile can be used as a feedforward or reference input to on-board attitude controller, and it can enhance spacecraft agility. Equations of attitude command profile are derived in two general boundary conditions: rest-to-rest maneuver and spin-to-spin maneuver. Simulation results demonstrate that the initial and final boundary conditions, in terms of time, attitude, and angular velocities, are well satisfied with the proposed analytical solution. The derived attitude command generation algorithm may be used to minimize a number of parameters to be uploaded to spacecraft or to automate a sequence of attitude command generation on-board.