• The korean journal of orthodontics
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• v.43 no.3
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• pp.120-126
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• 2013

Objective: To gain basic information regarding the biologic stability of plasma ion-implanted miniscrews and their potential clinical applications. Methods: Sixteen plasma ion-implanted and 16 sandblasted and acid-etched (SLA) miniscrews were bilaterally inserted in the mandibles of 4 beagles (2 miniscrews of each type per quadrant). Then, 250 - 300 gm of force from Ni-Ti coil springs was applied for 2 different periods: 12 weeks on one side and 3 weeks contralaterally. Thereafter, the animals were sacrificed and mandibular specimens including the miniscrews were collected. The insertion torque and mobility were compared between the groups. The bone-implant contact and bone volume ratio were calculated within 800 mm of the miniscrews and compared between the loading periods. The number of osteoblasts was also quantified. The measurements were expressed as percentages and analyzed by independent t-tests (p < 0.05). Results: No significant differences in any of the analyzed parameters were noted between the groups. Conclusions: The preliminary findings indicate that plasma ion-implanted miniscrews have similar biologic characteristics to SLA miniscrews in terms of insertion torque, mobility, bone-implant contact rate, and bone volume rate.

• Bulletin of the Korean Space Science Society
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• 2008.10a
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• pp.36.1-36.1
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• 2008

An Unscented Kalman Filter(UKF) for estimation of attitude and rate of a spacecraft using only magnetometer vector measurement is presented. The dynamics used in the filter is nonlinear rotational equation which is augmented by the quaternion kinematics to construct a process model. The filter is designed for low Earth orbit satellite, so the disturbance torques include gravity-gradient torque, magnetic disturbance torque, and aerodynamic drag. The magnetometer measurements are simulated based on time-varying position of the spacecraft. The filter has been tested not only in the standby mode but also in the detumbling mode. To stabilize the attitude, linear PD controller is applied and the actuator is assumed to be thruster. A Monte-Carlo simulation has been done to guarantee the stability of the filter performance to the various initial conditions. The UKF performance is compared to that of EKF and it reveals that UKF outperforms EKF.

• Wind and Structures
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• v.30 no.3
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• pp.261-273
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• 2020

This paper deals with the design, wind tunnel testing, and performance analysis of small wind turbines targeting low-power applications. Three different small-size blade designs in terms of size, shape, and twisting angle are considered and tested. We conduct wind tunnel tests while measuring the angular speed of the rotating blades, the generated voltage, and the current under varying resistive loading and air flow conditions. An electromechanical model is also used to predict the measured voltage and power and verify their consistency and repeatability. The measurements are found in qualitative agreement with those reported in previously-published experimental works. We present a novel methodology to estimate the mechanical torque applied to the wind turbine without the deployment of a torque measuring device. This method can be used to determine the power coefficient at a given air speed, which constitutes an important performance indicator of wind turbines. The wind tunnel tests revealed the capability of the developed wind turbines to deliver more than 1225 mW when subject to an air flow with a speed of 7 m/s. The power coefficient is found ranging between 26% and 32%. This demonstrates the aerodynamic capability of the designed blades to extract power from the wind.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.26 no.4
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• pp.436-442
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• 2016

This paper presents the torsional vibration isolation performance evaluation of a centrifugal pendulum absorbers (CPAs) that has a continuously varying resonance frequencies proportional to engine firing (excitation) order. CPAs are commonly used to suppress torsional vibrations in rotating machinery and internal combustion engines. In this study, they are employed on the current spring type torsional damper inside a torque converter of automotive vehicle. To evaluate the effectiveness of designed resonance tuning order, the torsional vibration transmissibility based on torque measurements with respect to different engine firing orders is experimentally measured with a lower-inertia dynamometer. The torsional vibration transmissibility with respect to different frequencies with engine order of 2 is also evaluated. It has been demonstrated that the significant vibration reduction over operational frequency range of interest can be achieved by attaching simple pendulums. Future research direction includes the study on theoretical analysis, improved design of pendulum etc.

• The Journal of Korea Robotics Society
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• v.16 no.2
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• pp.147-154
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• 2021

One of the most challenging issues when robots interact with the environment is to establish contact quickly and avoid high impact force at the same time. The proposed method implements the passive suspension system using the redundancy of the torque-controlled robot. Instead of utilizing the actual mechanical compliance, the distal joints near the end-effector are controlled to act as a virtual spring-damper system with low feedback gains. The proximal joints are precisely controlled to push the mid-link, which is defined as the boundary link between the proximal and distal joints, towards the environment with high feedback gains. Compared to the active compliance methods, the contact force measurements or estimates are not required for contact establishment and the control time delay problems do not occur correspondingly. The proposed method was applied to the landing foot control of the 12-DoF biped robot DYROS-RED in the simulations. In the results, the impact force during landing was significantly reduced at the same collision speed.

• Journal of Institute of Control, Robotics and Systems
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• v.21 no.6
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• pp.538-546
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• 2015

This paper describes an intelligent ankle assistive robot which provides assistive power to reduce ankle torque based on an analysis of ankle motion and muscle patterns during walking on level and sloped floors. The developed robot can assist ankle muscle power by driving an electric geared motor at the exact timing through the use of an accelerometer that detects gait phase and period, and a potentiometer to measure floor slope angle. A simple muscle assistive link mechanism is proposed to convert the motor torque into the foot assistive force. In particular, this mechanism doesn't restrain the wearer's ankle joint; hence, there is no danger of injury if the motor malfunctions. During walking, the link mechanism pushes down the top of the foot to assist the ankle torque, and it can also lift the foot by inversely driving the linkage, so this robot is useful for foot drop patients. The developed robot and control algorithm are experimentally verified through walking experiments and EMG (Electromyography) measurements.

• Journal of the Korean Society for Precision Engineering
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• v.29 no.9
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• pp.1026-1034
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• 2012

The purpose of this study was to verify the validation of effect on improvement of muscle strength unbalance according to exercise load deviation during rowing exercise. We performed evaluation of muscular activity and joint torque before the test. We recruited twenty subjects who one side's muscle strength is bigger in more 20% than other side. Subjects divided two groups. One is dominant left side and the other was dominant right side. Subjects performed rowing exercise in electric load deviation rowing equipment (Robo.gym, Humonic Co., Ltd., Daegu, Korea). Exercise performed four sets a day including 25 times a set, and three days a week. Measurements consist of evaluation of muscular activity and joint torque. Exercise load deviation adapted that different value of muscle strength in both arms multiplied 1RM% and added 1RM 50%. The results in adapted load deviation showed that the differences of maximal peak torque in 22.75% were getting increase significantly during exercise in 5.72%. This interpreted that rowing exercise with loading deviation types could provide muscle strength and muscular endurance exercise in same time for balance. Our study found out that loading deviation could provide muscle strength and muscular endurance exercise for improving muscle unbalance.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.4
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• pp.291-299
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• 2021

This paper presents the control logic for the momentum wheel and gimbals in the CMG system. First, the design of the control logic for the momentum wheel is described in consideration of the power consumption and stability. Second, the design of the control logic for the gimbals considering the resonance of the vibration absorber and stability is explained. Third, the measurement configuration for the force and torque generated by the CMG is described. Fourth, the results of the frequency and time response test of the momentum wheel and gimbals are shown. Last, the measurements of the force and the torque generated through the CMG are explained.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.2
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• pp.71-76
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• 2017

The roll damping problem in the design of ships and offshore structures remains a challenge to many researchers due to the fluid viscosity and nonlinearity of the phenomenon itself. In this paper, the study on viscous roll damping of a circular cylinder was carried out using forced oscillations. The roll moment generated by forced oscillation using a torque sensor was measured for each forced oscillation period and compared with the empirical formula. Although the magnitude of the measured torque from the shear force was relatively small, the results were qualitatively similar to those obtained from the empirical formula, and showed good agreement with the quantitative results in some oscillation periods. In addition, the flow around the circular cylinder wall was observed closely through the PIV measurements. Owing to the fluid viscosity, a boundary layer was formed near the wall of the circular cylinder, and a minute wave was generated by periodical forced oscillations at the free surface through the PIV measurement. In this study, the suitability of the empirical formula for the roll moment caused by viscous roll damping was verified by model tests. The wave making phenomenon due to the fluid viscosity around the wall of a circular cylinder was testified by PIV measurements.

• The KSFM Journal of Fluid Machinery
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• v.19 no.6
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• pp.55-60
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• 2016

We present an experimental setup for measuring the mechanical performance of centrifugal blood pumps. Using a 3D printer to construct supporting parts and magnetic couplings, we developed the measurement setup that can be used for various types of blood pumps. The experimental setup is equipped with sensors to measure a variety of mechanical characteristics of blood pumps including pressure, flow rate, torque, temperature, and rotating speed. Our experimental measurements for two commercial blood pumps are consistent with data provided by manufacturers, which indicates that the our setup offers the accurate measurements of blood pump performance. Utilizing the experimental setup, we tested aqueous glycerin solutions mimicking the density and viscosity of blood, which enabled us to predict the difference in operations using water and blood.