• Structural Engineering and Mechanics
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• v.30 no.1
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• pp.1-20
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• 2008

The dynamic characteristics of the passive, semi-active, and active tuned-liquidcolumn dampers (or TLCDs) are studied in this paper. The design of the latter two are based on the first one. A water-head difference (or simply named as water head in this paper) of a passive TLCD is pre-set to form the so-called semi-active one in this paper. The pre-set of water head is released at a proper time instant during an earthquake excitation in order to enhance the vibration reduction of a structure. Two propellers are installed along a shaft inside and at the center of a passive TLCD to form an active one. These two propellers are driven by a servo-motor controlled by a computer to provide the control force. The seismic responses of a five-story shear building with a passive, semiactive, and active TLCDs are computed for demonstration and discussion. The responses of this building with a tuned mass damper (or TMD) are also included for comparison. The small-scale shaking-table experiments of a pendulum-like system with a passive or active TLCD to harmonic and seismic excitations are conducted for verification.

• Transactions of Materials Processing
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• v.17 no.1
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• pp.27-34
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• 2008

In order to manufacture a doubly curved sheet metal, the incremental roll forming process which adopts advantages such as the flexibility of the incremental forming process and continuous bending deformation of the roll forming process has been experimentally investigated. An experimental equipment was developed which was named as unit roll set (URS) consisting of two pairs of support rolls and an upper center roll. The upper roll equipped with the servo control unit is motor-driven and can be positioned in the vertical direction according to the user's commands. Four support rolls are idle, and they freely rotate only along the axis so as to transfer the plate more stably in the tangential direction of the rotation of the driving roll. In the process, the plate is deformed incrementally as deformation proceeds simultaneously in longitudinal and transverse directions. Through the experiments using URS, information regarding to forming schedules is found out to fabricate curved hull plates. This study demonstrates the further application of the incremental roll forming process in shipbuilding industries.

• Journal of the Korean Society of Visualization
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• v.7 no.2
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• pp.64-71
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• 2010

The flow and noise characteristics of wake behind wind-turbine blades have been investigated experimentally using a two-frame particle image velocimetry (PIV) technique. Experiments were carried out in a POSTECH subsonic large wind-tunnel ($1.8^W{\times}1.5^H{\times}4.3^L\;m^3$) with KBP-750D (3-blade type) wind-turbine model at a freestream velocity of $U_o\;=\;15\;m/s$ and a tip speed ratio $\lambda\;=\;6.14$ (2933 rpm). The wind-turbine blades are connected to an AC servo motor, brake, encoder and torque meter to control the rotational speed and to extract a synchronization signal for PIV measurements. The wake flow was measured at four azimuth angles ($\phi\;=\;0^{\circ}$, $30^{\circ}$, $60^{\circ}$ and $90^{\circ}$) of the wind-turbine blade. The dominant flow structure of the wake is large-scale tip vortices. The turbulent statistics such as turbulent intensity are weakened as the flow goes downstream due to turbulent dissipation. The dominant peak frequency of the noise signal is identical to the rotation frequency of blades. The noise seems to be mainly induced by the tip vortices.

• Journal of Biomedical Engineering Research
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• v.24 no.5
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• pp.435-442
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• 2003

In this paper, biomechanical aspects of dynamic대학교postural responses against forward perturbations were experimentally determined simultaneous measurements of joint angles, accelerations. EMG activations, center of pressure(CoP) movements and ground reaction forces(GRF), Thirteen young healthy volunteers, stood on a flat platform, were translated into the forward direction by an AC servo-motor at two separate velocities(0.1m and 0.2m/s). In order to recover postural balance against the forward perturbation, joint motions were observed in the sequence of the ankle dorsiflexion, the knee flexion and then the hip flexion during the later acceleration phase. Both acceleration patterns at the heel and the sacrum were shown the forward acceleration pattern during the later acceleration phase and early of constant velocity phase as increasing platform velocity, respectively. Tibialis anterior(TA) for the ankle dorsiflexion and biceps femoris(BF) for the knee flexion. the primary muscle to recover the forward perturbation, was activated during the half of acceleration phase. Ankle strategy was used for slow-velocity perturbation, but mixed strategy of both ankle and hip used for the fast-velocity perturbation. In addition, parameters of perturbation such as timing and magnitude influenced the postural response against the perturbation.

• Proceedings of the KIEE Conference
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• 1996.07b
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• pp.1027-1030
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• 1996

The purpose of this study was to develop systematic diagnostic system testing easily, rapidly vestibular function of patients suffered from vestibular syndrome such as nausea vomiting, dizzness, ataxia. Diagnostic system composed of rotatory chair system which rotated sinusoidally patients against their vertical axis for purpose of invoking eye movement by vestibulo-ocular reflex and the softwares which storaged eye movement into computer and analyzed eye movement. Rotatory chair system consisted of comfortable chair and DC servomotor with reducer(1:80) by controlled servo in field of nonlinear motor control, double feedback loops system containing velocity feedback loop and position feedback loop was applied to this sever controlled rotatory chair system. Maximum rotatory velocity of rotatory chair was upto 60 degree per second and frequency range was 0.01 to 0.64 Hz. These above results suggest that clinical rotatory chair system may test easily, rapidly vestibular function and diagnose etiology of dizziness, thus giving effective assistance on the treatment of dizziness patients.

• The Transactions of the Korean Institute of Power Electronics
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• v.9 no.5
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• pp.485-490
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• 2004

This paper presents a new interpolation algorithm for measuring high resolution position information which is prepared to a nino servo control motor using analog quadrature encoder. In the past, there are large capacity of memory(ROM or RAM) and two high price and resolution A/D(Analog-to-Digital Converter) for sensing two quadrature signals from a analog sinusoidal encoder interpolation. But high resolution of position from sinusoidal encoder can be obtained by using only small capacity of memory, one A/D converter and comparator. Experimental results show that the proposed algorithm is useful for measuring high resolution position.

• Journal of the Institute of Convergence Signal Processing
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• v.19 no.2
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• pp.54-60
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• 2018

In this paper, we propose an efficient automatic control method for the collision avoidance of drones. In general, the drones are controlled by transmitting to the flight control (FC) module the received PWM signals transmitted from a RC controller which transduce movements of the knob into PWM signal. We implemented the collision avoidance module in-between receiver and FC module to monitor and change the throttle, pitch and roll control signals to avoid drone collision. In order to avoid the collision, a LiDAR distance sensor and a servo-motor are installed and periodically measure the obstacle distance within -45 degrees from 45 degrees in flight direction. If the collision is predicted, the received PWM signal is changed and transmitted to the FC module to prevent the collision. We applied our proposed method to a hexacopter and the experimental results show that the safety is improved because it can prevent the collision caused by the inadvertency or inexperienced maneuver.

• Journal of Electrical Engineering and Technology
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• v.9 no.2
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• pp.514-522
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• 2014

A new type of high precision electromagnetic suspension (EMS) which can support heavy tray along long stroke rail is proposed in this paper. Compared with the conventional EMS, the suggested moving-core typed EMS has the levitation electromagnets (EMs) on the fixed rail. This scheme has high load capability caused by iron-core and enables simple tray structure. Also it does not have precision degradation caused by heat generation from EMs, which is a drawback of conventional EMS. With these merits, the proposed EMS can be an optimal contactless linear bearing in next generation flat panel display (FPD) manufacturing process if the ability of long stroke movement is proved. So a special Section Switching Algorithm (SSA) is derived from the resultant force and moment equations of the levitated tray which enables long stroke movement of the tray. In order to verify the feasibility of the suggested SSA, a simple test-setup of the EMS with 2 Section-changes is made up and servo-controlled in the simulation and experiment. The simulation shows the perfect changeover the EMs, and the experiment shows overall control performance of under ${\pm}40{\mu}m$ gap deviations. These results reveal that the newly suggested contactless linear bearing can simultaneously achieve high load capability and precision gap control as well as long stroke.

• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.2
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• pp.166-174
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• 2014

Fuel injection pressure has steadily increased in diesel engines for the purpose of improving fuel efficiency and cleaning exhaust gas, but it has now reached a point, where the cost for higher pressure does not warrant additional gains. Common rail systems on modern diesel engines have fuel pumps that are mechanically driven by crankshaft. The pumps actually house two pumping module inside: a low pressure pump component and a high pressure pump component. Part of the fuel compressed by the low pressure component returns to the tank in the process of maintaining the pressure in the common rail. Since the returning fuel represents pumping loss, fuel economy improves if the returned fuel can be eliminated by using a properly controled electrical fuel pump. As the first step in developing an electrical fuel pump the fuel supply system on a 6 liter diesel engine was modeled with AMESim to analyze the workload and the fuel feed rate of the injection pump, and the results served as basis for selecting a suitable servo motor and a reducer to drive the pump. A motor controller was built using a DSP and a program which controls the common rail pressure using a proportional control method based on the target fuel pressure information from the engine ECU. A test rig to evaluate performance of the fuel pump is implemented and used to show that the newly developed electrically driven fuel pump can satisfy the fuel flow demand of the engine under various operating conditions when the rotational speed of the pump is adequately controlled.

• Journal of The Korean Astronomical Society
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• v.51 no.6
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• pp.207-214
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• 2018

A coelostat is often used for solar observations, because it corrects the image rotation automatically by guiding sunlight into a fixed telescope with two plane mirrors. For the purposes of education and spectroscopic observation, the solar group at Seoul National University (SNU) plans to develop the SNU coelostat (SNUC) and install it in the SNU Astronomical Observatory (SAO). Requirements of the SNUC are < 1" positioning accuracy with 30 cm beam size on the entrance pupil in the compact dome. To allow for installation in the small dome, we design a compact slope type coelostat with a 45 cm primary plane mirror and a 39 cm secondary plane mirror. The motion of the SNUC is minimized by fixing the position of the slope frame. Numerical simulations of the available observational time of the designed coelostat shows that the sun can be observed ay all times from June to early August and at least three hours in other months. Since the high accuracy driving motors installed in the SNUC can be affected by external environment factors such as humidity and temperature variations, we design a prototype to test the significance of these effects. The prototype consists of a 20 cm primary plane mirror, a 1 m slope rail, a direct drive motor, a ballscrew, a linear motion guide, an AC servo motor, a reduction gear and a linear encoder. We plan to control and test the accuracy of the prototype with varying atmospheric conditions in early 2019. After testing the prototype, the SNUC will be manufactured and installed in SAO by 2020.