• Journal of Advanced Marine Engineering and Technology
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• v.34 no.8
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• pp.1153-1158
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• 2010

In this paper, We make horizontal balancer (HB) and confirm a possibility of the technique that can be applied to ship through horizontal vibration reduction experiment. We use MATLAB as the simulator tool and experimental equipment consists of two induction motors shafts of which cam type unbalanced loads are fixed to, DSP and inverter circuit. Two induction motors perform roles as vibrator and balancer respectively, DSP control softwares such as speed, phase and vector control program. The simulation and experimental results show that the balancer characterizes good vibration reduction by phase control.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.1
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• pp.71-78
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• 2002

This paper is concerned with the design and implementation of magnetic damper system to reduce the vibration of suspension system actively. Cylindrical type electro-magnetic actuator with permanent magnet is analyzed and effective controller design is made. Magnetic force analyzed and transfer function for the total system is determined by experimental data using error minimization method. For experiments, simple suspension structure system is utilized, in which a magnetic damper composed of permanent magnet and digital controller is attached. In order to drive the system, bipolar power amplifier of voltage control type is utilized. Stable and high speed control board is used to perform digital control logic for the given system. This paper shows that the magnetic damper system using phase-lead controller excellently reduces vibration of 1-D.O.F (degree of freedom) suspension system.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.2
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• pp.170-178
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• 2012

This paper is concerned with the development of power amplifier and controller for piezoelectric actuator and sensor used in smart structures. Even though a high-voltage power amplifier is provided in the form of an operational amplifier, a very high DC voltage is still necessary as a power supply. In this study, we propose a low-cost design for the power amplifier including the DC power supply. We also need a controller on which a control algorithm will be mounted. In general, a digital signal processing chip is popularly used because of high speed. However, only commercial product is available for smart structure applications. In this paper, a controller consisting of a DSP and electronic circuits suitable for piezoelectric sensor and actuator pair is proposed. To validate the proposed controller with power amplifier, experiment on smart structure was carried out. The experimental results show that the proposed control system can be effectively used for smart structure applications with low cost.

• Journal of Power Electronics
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• v.16 no.3
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• pp.1076-1086
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• 2016

PI controllers are one of the most widely used controllers in industrial control systems due to their simple algorithms and stability. The parameters K_p and K_i determine the performance of the system response. The response is expected to improve by increasing the gain of the PI controller. However, too large a gain will accelerate the speed response and cause vibrations, which is not what is expected. This paper proposes a way to suppress vibrations by detecting the vibration frequency and extracting the vibration signal as a compensation to the speed feedback. Additionally, in order to improve its disturbance rejection ability, a low-order disturbance observer is proposed. This paper also explains the operation principle of the proposed method by analyzing the transfer function and it describes the design of the controller parameters in detail. Simulation and experimental results are provided to verify the merits of the proposed method. These results also show the good performance of the proposed method. It has a rapid response and suppresses vibrations.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.48 no.10
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• pp.562-570
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• 1999

In the industrial motor drive system which is composed of a motor and load connected with a flexible shaft, a torsional vibration is often generated because of the elastic elements in torque transmission. This vibration, which is generated in a two-mass mechanical system. To solve this problem, recently there has been a lot of researches for the robust control relevant to the $H_{\infty}$ control suppressing the torsional vibration and rejecting the torque disturbance. In the case of the $H_{\infty}$controller, however, the command tracking property becomes worse because of overshoot during transient response. For this reason the $H_{\infty}$ controller, which includes the two-degrees-of-freedom(TDOF) controller, is designed in order to improve command tracking property. However, it also includes complexity realizing this controller. In this paper, a new $H_{\infty}$ controller with partial state feedback is proposed. Proposed $H_{\infty}$controller has simple structure but satisfies with the fast command tracking property and the attenuation of disturbances and vibrations simultaneously, just like the complicated TDOF $H_{\infty}$ controller.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.11
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• pp.1042-1048
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• 2012

A 2-axis gimbal system is one of main disturbance sources affecting image jitter response of a satellite. The gimbal system comprises azimuth stage and elevation stage, and these pointing mechanism can be rotated by stepping motors about its azimuth and elevation axes simultaneously. Because of the complex and coupled dynamic motion of the gimbal system, its moment of inertia and structural modes can be changed according to the system configuration, and thus the gimbal system generates complicated and non-linear disturbance characteristics. In order to improve the jitter response of a spacecraft, it is an indispensable process to reduce the micro-vibration disturbance level of the antenna system. In the present research, a 2-axis gimbal system was manufactured and then its micro-vibration test was performed in terms of two types of stepping motors(2-phase and 5-phase). The test results show that the disturbance level of the gimbal system can be reduced by replacing the 2-phase stepping motor with the 5-phase one, and the average disturbance attenuation ratio is 56 % in peak level and 48 % in standard deviation level. The experimental results confirm that it is an efficient jitter reduction method to adopt a high-phase stepping motor.

• Design & Manufacturing
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• v.14 no.3
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• pp.44-49
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• 2020

One of display trends today is development of high pixel density. To get high PPI, a small size of pixel must be developed. RGB pixel is arranged by evaporation process which determines pixel size. Normally, a fine metal mask (FMM; Invar alloy) has been used for evaporation process and it has advantages such as good strength, and low thermal expansion coefficient at low temperature. A FMM has been manufactured by chemical etching which has limitation to controlling the pattern shape and size. One of alternative method for patterning FMM is laser micromachining. Femtosecond laser is normally considered to improve those disadvantages for laser micromachining process due to such short pulse duration. In this paper, a femtosecond laser drilling for thickness of 16 ㎛ FMM is examined. Additionally, we introduce experimental results for controlling taper angle of hole by vibration module adapted in laser system. We used Ti:Sapphire based femtosecond laser with attenuating optics, co-axial illumination, vision system, 3-axis linear stage and vibration module. By controlling vibration amplitude, entrance and exit diameters are controllable. Using vibrating objective lens, we can control taper angle when femtosecond laser hole drilling by moving focusing point. The larger amplitude of vibration we control, the smaller taper angle will be carried out.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.15 no.2
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• pp.51-56
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• 2016

High brittleness is a characteristic of glass, and in many cases it is broken during the process of machining due to processing problems, such as scratches, chipping, and notches. Machining defects occur due to the vibration of the equipment. Therefore, design techniques are needed that can control the vibration generated in the equipment to increase the strength of tempered glass. The natural frequency of the machine tool via vibration analysis (computer simulation) must be accurately understood to improve the design to ensure the stability of the machine. To accurately understand the natural frequency, 3D modeling, which is the same as actual apparatus, was used and a constraint condition was also applied that was the same as that of the actual apparatus. The maximum speeds of ultrasonic and high frequency, which are 15,000 rpm and 60,000 rpm, respectively, are considerably faster than those of typical machine tools. Therefore, an improved design is needed so that the natural frequency is formed at a lower region and the natural frequency does not increase through general design reinforcement. By restructuring the top frame of the glass processing, the natural frequency was not formed in the operating speed area with the improved design. The lower-order natural frequency is dominant for the effects that the natural frequency has on the vibration. Therefore, the design improvement in which the lower-order natural frequency is not formed in the operating speed area is an optimum design improvement. It is possible to effectively control the vibrations by avoiding resonance with simple design improvements.

• Physical Therapy Korea
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• v.26 no.1
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• pp.19-27
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• 2019

Background: Compared to healthy people, patients with chronic lower back pain have reduced balance abilities which may cause proprioception problems, patients with chronic lower back pain avoid physical activities due to pain, and reduced activity levels lead to muscle weakening, which can further exacerbate pain. Recently, there have been many studies on the use of sensory stimulation; and among these studies, interventions that use vibrational stimulation have shown functional improvements in the patients. Objects: This study examined the effects of a stabilization exercise with vibration stimulation on the balance ability and disability in patients with chronic back pain. Methods: The subjects of the study were 30 persons who were randomly assigned to the experimental group and the control group, with 15 subjects in each. The subjects were evaluated before and after intervention via a balance ability test, the Korean Oswestry disability index (KODI) test, a pain test, and a proprioceptive sensory test. Both groups received general physical therapy. The experimental group performed the stabilization exercise with vibration stimulation, and the control group performed a general stabilization exercise, three times a week for six weeks. Results: After the intervention, both groups showed significant improvements in the balance ability test, the KODI test, the pain test, and the proprioceptive sensory test. The experimental group showed statistically significant, higher improvements than the control group in the balance ability test, the KODI test, and the proprioceptive sensory test. Conclusions: The stabilization exercise with vibration stimulation for patients with chronic back pain has been reported to provide greater functional improvements than the conventional intervention method. Therefore, the stabilization exercise in a vibration stimulation environment could be a useful intervention for patients with chronic back pain.

• Journal of the Korea Institute of Military Science and Technology
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• v.24 no.4
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• pp.357-367
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• 2021

This paper studies the simulations of active airframe vibration controls for the Sikorsky X2 helicopter with a lift-offset coaxial rotor. The 4P hub vibratory loads of the X2TD rotor are obtained from the previous work using a rotorcraft comprehensive analysis code, CAMRAD II. The finite element analysis software, MSC.NASTRAN, is used to model the structural dynamics of the X2TD airframe and to analyze the 4P vibration responses of the airframe. A simulation study using Active Vibration Control System(AVCS) with Fx-LMS algorithm to reduce the airframe vibrations is conducted. The present AVCS is modeled using MATLAB Simulink. When AVCS is applied to the X2TD airframe at 250 knots, the 4P longitudinal and vertical vibration responses at the specified airframe positions, such as the pilot seat, co-pilot seat, engine deck, and prop gearbox, are reduced by 30.65 ~ 94.12 %.