Tae-Kyu Kwon

Control of Self-Excited Vibration of a Rotor System With Active Gas Bearings

This paper presents an experimental study on the active control of self-excited vibrations in a rotor-bearing system supported on a pair of externally pressurized thrust bearings in the axial direction and on actively controlled journal gas bearings in the radial direction. The active journal gas bearings used are of the tilting-pad type with one traditional passive pad and two active pads with embedded piezoelectric actuators. Feedback control systems are constructed with gap sensors for measuring the vibration of the rotor, embedded piezoelectric actuators, and PID controllers. The experimental results show that the self-excited vibration can be effectively suppressed with the designed feedback control system, if the gains of the PID controllers are properly tuned.

Characteristics of the Muscle Activities of the Elderly wearing the Lower limb Orthosis during Gait on the Treadmill

We have developed a lower limb orthosis with a pneumatic rubber actuator, which is intended for the assistance and the enhancement of lower limb muscular activities of the elderly. For this purpose, we investigated the characteristics of the muscular activities with and without the orthosis in gait motion on treadmill. To find out the characteristics of the muscle activities, we analyzed the gait motion of the subject and flexing and extending motion of the knees and measured muscular power in the lower limb. The subjects wearing the lower limb orthosis were instructed to perform gait on the treadmill and flexing and extending motion of the knees in sitting position for monitoring of electromyogram and muscular activities. We used the C8051F Target Board (SILICON LABORATORIES, Inc., USA) for the orthosis control. The air pressure of the pneumatic actuator was varied from one kgf/cm2 to four kgf/cm2 to find the most suitable air pressure. Through this study, we expect to find the effect of the lower limb orthosis in the gait motion and muscular activities along with the most suitable air pressure in the pneumatic actuator of the orthosis for the enhancement of muscular power for the elderly

Design of an intravenous oxygenator.

The aim of this study was to design a new intravenous blood–gas exchange device and to estimate the design characteristics of the device with a dimensionless function by using a substance that can be used instead of bovine blood. In addition, the characteristics of oxygen transfer were estimated using empirical formulas and the reliability of the equations was ascertained by comparing their output with an experiment performed using bovine blood. The dimensionless function was derived using distilled water and bovine blood to estimate the oxygen transfer rate. Using the derived equations, the calculated oxygen transfer rates for bovine blood and distilled water were similar for Reynolds numbers ranging from 0.7 to 7.0. Therefore, it is possible to estimate the oxygen transfer rate in bovine blood, which is a non-Newtonian fluid, using distilled water, which is a Newtonian fluid. Moreover, it was possible to verify the related equations because the oxygen transfer rate could be estimated using the derived equations, according to the diameters of the various device modules.

Enhancement of oxygen transfer in hollow fiber membrane by the vibration method

The purpose of this study was to assess and quantify the beneficial effects of gas exchange according to the various frequencies of the sinusoidal wave that are excited by a PZT actuator, on patients suffering from acute respiratory distress syndrome (ARDS). In this study, an experimental method for the flow hydrodynamics was developed through a bundle of sinusoidally vibrated hollow fibers to observe how well vibrations might enhance the performance of the VIVLAD. We measured the effect of the various excitation frequencies of the PZT actuator on the gas transfer rates and hemolysis from the maximum gas transfer rate. As a result, the maximum oxygen transfer rate was reached at the maximum amplitude and through the transfer of vibrations to the hollow fiber membranes. The device was maximum excited by a frequency band of 7 Hz at various water flow rates, as this frequency was the 2nd mode resonance frequency of the flexible beam. 675 hollow fiber membranes were also bundled, within the blood flow, into the device.

Vibration Characteristics of Piezoelectric Lead Zirconate Titanate by Fluid Flow in Intravascular Oxygenator

In this paper, we describe the enhancement in oxygen transfer rate in hollow-fiber-membrane (HFM) modules using a plumbum piezoelectric lead zirconate titanate (PZT) actuator and a piezoelectric poly vinylidene fluoride (PVDF) sensor. We developed a vibrating intravascular lung assist device (VIVLAD) for patients having chronic respiratory problems and performed experiments on hydrodynamic flow through a bundle of sinusoidal vibrating hollow fibers. These modules were used to provide some insight into how wall vibrations might enhance the performance of an intravascular lung assist device. The experimental design and procedure are then applied to the fabrication of a device used to assess the effectiveness of membrane vibrations. The test section was a cylindrical duct with an inner diameter of 30 mm. The flow rate was controlled by a pump and monitored by a built-in flowmeter. The vibration apparatus was composed of a piezovibrator, a function generator, and a power amplifier. The direction of vibration was radial to the fluid flow. Gas flow rates of up to 6 L/min through 120-cm-long hollow fibers were achieved by exciting the piezovibrator. The time and frequency responses of PVDF sensors were investigated through various frequencies in VIVLAD. In these devices, the flow of blood and the source of oxygen were separated by a semipermeable membrane that allows oxygen and carbon dioxide to diffuse into and out of the fluid, respectively. Results of the experiments have shown that a vibrating intravascular lung assist device performs effectively.

Analysis of the assistance characteristics for the plantarflexion torque in elderly adults wearing the powered ankle exoskeleton

Ankle exoskeleton with an artificial pneumatic actuator, which is intended for the assistance and enhancement of muscular activity, was developed. In this study, the effectiveness of the system was investigated during plantarflexion motion of ankle joint. To find an effectiveness of the system, the subjects performed maximal voluntary isokinetic plantarflexion contraction on a Biodex-dynamometer. Plantarfexion torque of the ankle joint is assisted by subjects soleus muscle that is generated when ankle joint do plantarflexion motion. We used the muscular stiffness signal of a soleus muscle for feed-forward control of ankle-foot orthosis as physiological signal. For measurement of this signal, we made the muscular stiffness force sensor. We compared a muscular stiffness force of a soleus muscle between with feed-forward control and without it and a maximal plantarflexion torque between not wearing a ankle-foot orthosis, without feed-forward control wearing it and with feed-forward control wearing it in each ten elderly adults. The experimental result showed that a muscular stiffness force of a soleus muscle with feed-forward control was reduced and plantarflexion torque of an ankle joint only wearing ankle-foot orthosis was reduced but a plantarflexion torque with feed-forward control was increased. The amount of a increasing with feed-forward control is higher than the amount of a decreasing only wearing it. Therefore, we confirmed the effectiveness of the developed ankle-foot orthosis with feed-forward control.

Development of portable ECG measurement device and PC software for automatic ST analysis

ECG is used on purpose to keep good health or monitor cardiac function of aged person as well as on purpose to diagnose the disease of heart patients. The ambulatory ECG monitoring system under guarantee of safety and accuracy is very efficient to prevent the progress of heart disease and sudden death. These systems can detect the temporary change of ECG that is very significant to diagnose heart disease such as myocardial ischemia, arrhythmia and cardiac infarction. In this paper, we describe the ECG signal analysis algorithm and measurement system for ECG monitoring. The designed small-size portable ECG device consisted of instrumentation amplifier, micro-controller, filter and RF module. The developed device measures ECG with four electrodes in the body and detects QRS complex and ST level change in real-time. Also it transmits the measured signal to the personal computer. The developed software for ECG analysis in personal computer has the function to detect the feature points and ST level change.

Evaluation of Bio-Mechanical Character istics According to Loading Deviation Methods dur ing Rowing Exercise

The purpose of this study was to verify the validation of exercise effect with loading deviation during rowing exercise. We performed evaluation of based physical fitness and joint torque before the experiment for finding muscle unbalance. So we recruited twenty four subjects who have bigger muscle strength in more 20% than average one. Subjects divided two groups. One is dominant upper limbs(DU) and the other was dominant lower limbs(DL). Subjects performed rowing exercise using electric equipment (Robo.gym.Humonic.korea). Exercise is performed four sets a day including 25 times a set, and three days a week. Measurement consist of evaluation of based physical fitness and joint torque using biodex(biodex system3.USA). Evaluation of exercise effect performed each week in joint torque of shoulder, lumbar and knee joint and each month in based physical fitness. Also we adapted 30% of 1RM for muscular endurance and 70% of 1RM for muscle strength as exercise load. The results showed that the difference of maximal peak torque were getting increase significantly during exercise. Also difference of various factor in based physical fitness were getting increase significantly except flexibility and agility. This interpreted that rowing exercise with loading deviation types could provide muscle strength and muscular endurance exercise in same time. These results could be interpret to two ways. One is effect of improving physical fitness for rowing exercise and the other meaned validation of loading deviation in rowing exercise. Our study is going to verify the validation of loading deviation during rowing and we found out that loading deviation could provide muscle strength and muscular endurance exercise for improving muscle unbalance. Our study can be used development of exercise equipment and program for normal people with muscle unbalance. Also that provide effect of whole body exercise to anybody.

Basic Study to Develop Biosensors Using Surface Acoustic Waves

In this paper, we present a study of the bonding between piezoelectric substrates and semiconductor materials. We have studied [O. S. Wolfbesis: Fiber Optic Chemical Sensors and Biosensors, 1st ed. (CRC Press, Boca Raton, 1991) p. 21.] the surface state (hydrophilic) of GaAs, LiNbO3 and quartz substrates after different treatments methods [R. Hughes, A. Ricco, M. Butler and S. Martin: Science 254 (1991) 74.], the effects of migration of water molecules out of bonding surfaces induced by microwave and laser radiation. When Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) is used as a piezoelectric material, we have evaluated if PMN-PT can be made practically available for a new surface acoustic wave (SAW) biosensor detecting protein. The experimental results clarified that improvements in the bonding process are effective in obtaining a stronger bonding interface between the piezoelectric substrate and semiconductor materials. The frequency filtering of the central frequency of the PMN-PT substrate is also superior to that of the LiTaO3 substrate, but the result was not completely satisfactory. However, the electromechanical coupling coefficient of the PMN-PT substrate is excellent, therefore it will be used as a SAW sensor, in the near future, provided that new interdigital transducer (IDT) design will also be available to increase the frequency of filtering.

Effect on Improvement of Muscle Strength Imbalance according to Load Deviation Pattern of Left and Right Arms in Upper Limbs

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.