• Proceedings of the KIEE Conference
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• 1999.07b
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• pp.894-896
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• 1999

PID 제어는 50년의 역사를 갖기 때문에 현장의 사용자는 이 제어방식에 익숙해져 있으며, 제어장치의 구성이 간단하며 제어기의 최적동조가 가능하므로 많은 분야에서 사용되고 있다[1]. 그러나 PID 제어기에 의해서 얻은 결과에 대하여 만족하기 위해서는 많은 시행착오를 겪어야 한다. 또한 만족하는 결과를 얻었다고 할지라도 외란, 플랜트의 동특성이 바뀌는 경우 시스템을 추종하지 못하기 때문에 파라미터를 재조정하여야 한다. 유전 알고리즘은 자연세계의 진화 현상에 기초한 계산모델로서 John Holland에 의해서 1975년에 개발된 전역적인 최적화 알고리즘이며[1][2], 비선형 고차원, 불연속, 다중모드, 노이즈 함수 등에 대하여 강건함을 보여주고, 복잡한 탐색 공간에서 최적 값을 스스로 발견하는 학습 능력을 갖는다. 이 방법은 재생산, 교배, 돌연변이를 통하여 최적해를 찾은 방법으로 1989년에 D. E. Goldgerg에 의해서 체계적으로 정리된 후 여러 분야에서 응용되고 있다[3][4]. 그러나 유전 알고리즘은 목적함수만을 이용하여 해집단을 탐색하기 때문에 숙련운전자가 원하는 제어 특성 명세인 상승시간, 정착시간, 초과량(oveshoot) 둥을 구체적으로 명시하여 제어에 반영할 수 없다. 또한, 유전 알고리즘은 입력 값이 크게 바뀔 경우 다른 시스템으로 인식하여 새로운 탐색을 수행하는 단점을 가지고 있다. 본 논문은 첫째, 기준모델을 도입하여 플랜트의 성능을 기준모델로 표현하여 플랜트가 요구하는 성능지표를 정량적으로 규정하는 것이 가능하였다. 또한, 이것은 미지 플랜트 동특성을 식별하기 위한 신호로 사용되어, 플랜트의 정보를 얻는데 이용되었다. 즉, 기준모델과 플랜트 출력사이의 추종 오차 정보가 적응기구인 PID 유전제어기의 입력으로 사용되며, 구형파 입력의 경우에도 기준모델과 플랜트의 출력차는 크게 변하지 않는다. 따라서, 유전 알고리즘의 목적함수에 기준 모델을 제안 적용하여 안정적이고, 세밀한 제어를 수행하였다. 둘째, PID의 간단하면서 확실한 제어가 가능하다는 점과 전역적인 최적값을 찾을 수 있는 유전 알고리즘을 적용하여 고속제어를 요하는 직류 서보 모터(DC Servo Motor) 운전 시 실시간 파라미터 동조에 적용하였다.

• Transactions on Electrical and Electronic Materials
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• v.11 no.5
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• pp.206-211
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• 2010

Piezoelectric energy harvesting uses piezoelectric, which is able to convert unused mechanical vibration energy to electrical energy, such as with motor and machinery. The piezoelectric energy harvester was constructed with a cantilever made of lead zirconate titanate with a metal plate. The primary material was soft lead zirconium titanate (PZT-5H) due to the large strain availability, acceptable mechanical strength and high piezoelectric constant. This technique's drawback is that the energy efficiency is lower than the other energy harvesting methods, but this study increases the output electric power efficiency by analyzing a finite element method for the structure of the piezoelectric energy harvester. We manufactured two cantilever types as follows: the L-60 and L-33 bimorph piezoelectric energy harvesters. Their resulting energy harvesters were able to obtain high voltage values as follows: 27.4 mV and 40.6 mV. Moreover, these results have a similar band of resonance frequency it comparison to the simulation. Consequently, this study was confirmed with validity. The output electric powers of the L-60 and L-33 types have 3.1 mW/s and 5.8 mW/s with 47 Hz and 148 Hz of resonance frequency and then, the load resistivities were $100k\Omega$ and $10k\Omega$, respectively.

• Journal of the Ergonomics Society of Korea
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• v.29 no.3
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• pp.347-356
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• 2010

The purpose of this study is to analyze the spine stability by comparing muscle activation in various scaffold working conditions. The independent working conditions were designed by two levels of working height, existence and absence of safety handrail, and the two levels of expertise. The corresponding activities of the agonist and antagonist muscles of spine were simultaneously recorded by using EMG. As results, novice worker showed increased muscle activity while doing the task on the 2nd floor, absence of handrail. And expert showed the increase of co-contraction while working on the 2nd floor without handrail. Such co-contraction was found to increase the spine stability when the working condition become risky. On the other hand, the co-contraction was prolonged, the spine muscle fatique and disc pressure could be increased, which would increase the risk of musculo-skeletal disorder. The results of co-contraction in this study indicates that the motor control system responds to maintain the stability of the spine particularly when workers cognitively recognize the danger of falling or imbalance. This study also quantitatively accounted for the biomechanical cause of LBP among workers who has to prevent themselves from falling. Therefore, if can be said that safe environment preventing falling can also prevent workers from MSDs as well. Such knowledge can be applied to design ergonomic workplace environment as well as movable scaffold.

• Journal of muscle and joint health
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• v.11 no.2
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• pp.136-152
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• 2004

Purpose: The purpose of this study was to summarize trends and status of nursing research utilizing experimental designs in the Journal of Rheumatology Health over the past 10 years. Method: The Journal of Rheumatology Health published 37 experimental research articles between 1994 and 2004. These articles were included in a retrospective descriptive analysis. A checklist was utilized for data collection. Results: Qoasi-experimental researches were more frequent than pre-experimental research, but there were 8 research studies which had no hypothesis. The most frequently used nursing interventions were exercise/movement, and cognitive, followed by sensitive, and social interventions. There were very few research studies that used random assignment for internal validity. The rate of effectiveness of self-help interventions was lower than socio-psychological, cognitive, or motor-physical interventions. There was no research regarding families of patients with rheumatoid disease. Conclusion: Rigorous experimental research design is needed for internal and external validity in future research. Generalizing the effects of nursing interventions that are the results of rigorous experimental designs will contribute to promote the quality of life of patients with rheumatism and their families.

• Transactions of the KSME C: Technology and Education
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• v.3 no.3
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• pp.183-191
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• 2015

In this study, the finite element analysis was carried out to investigate dynamic characteristics of the AGF(Active Gurney Flap) which is under development for reducing vibration and noise of the helicopter rotor system. The Gurney flap is a kind of small flat plate, mounted normal to the lower surface of the airfoil near to the trailing edge. An electric motor, L-shaped linkages and flap parts were integrated into a rotor bade, and 3~5/rev control was given to the AGF to reduce the vibration in the fixed frame. Thus, an explicit time integration method was adopted to investigate the dynamic response of the AGF with considering both centrifugal force due to the rotor rotation and active control input, and it can be seen that the vertical displacement of the AGF was satisfied to meet the design requirement.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.35S no.8
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• pp.106-112
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• 1998

Recently, the amount of image and audio data has been increasing dramatically for high performance. According to this trend, a high-density magnetic recording system is necessitated and the tracks of magnetic tapes are getting narrower. This, in turn, requires the capstan servo system of the magnetic recording system such as DVCR to control precisely the speed and position of the capstan motor. Especially, in case of play-back, the capstan servo system should be able to position and maintain the head on the desired place of the track. To meet this requirement, digital camcorders use ATF (Automatic Track Following). In this paper, a new ATF block using discrete Fourier transform is proposed. The proposed ATF block was designed and implemented in ALTERA FPGA chips and fully tested in a real DVCR system. It is shown through experiments that the new ATF block is more cost-effective than other existing ATF blocks using digital lowpass filters. In particular, the number of logic gates can be reduced by 20% in average, compared to the existing ATF's.

• Korean Journal of Agricultural Science
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• v.47 no.1
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• pp.43-58
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• 2020

Mulching plastic is used for the purpose of maintaining soil temperature, moisture, and weed and pest prevention in agriculture. Any remaining plastic after use may contaminate the soil and damage crop growth. To solve this problem, mulching plastic wrappers have been studied and developed, but the actual use rate is quite low due to their poor performance and frequent tearing of the plastic on the field. In this study, we developed a tractor attachable mulching plastic wrapper to minimize the tearing of the mulched plastic. The developed mulching plastic wrapper consists of hydraulic motors and pumps, valves, a microcontroller, and sensors. The collecting speed of the plastic mulch was calculated considering the tractor's travel speed and the radius of the collecting drum. A proportional controller was designed to control the rotating speed of the hydraulic motor as the plastic was wound around the collection drum and the radius increased. The performance of an indoor experiment was quite promising because the difference between the collecting speed predicted by the calculation and the actual collecting speed was 2.71 rpm. Based on a field verification test, the speed difference was max. 14.28 rpm; thus, the, proportional integral derivative (PID) controller needs to be considered to control the drum speed precisely. Another issue was found when the soil covered at the edge of the plastic was hardened or the road surface was uneven, the speed control was unstable, and the plastic was torn. In future research, vibrational plows will be equipped to break-up the harden soil for collecting the plastic smoothly.

• Journal of the Ergonomics Society of Korea
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• v.36 no.3
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• pp.213-219
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• 2017

Objective: The present study identified the minimum legible text size by an experiment for eight combinations of background and text colors, which will be used in designing visual information on group-view display (GVD). Background: Information on minimum legible text size is needed to design the visual information presented on GVD in a radioactive waste control room. Method: The experiment was conducted for 22 male participants (age: mean = 37, SD = 6.7; visual acuity: over 0.8) who were recruited by considering demographic characteristics of current control room operators. Eight combinations of background and text colors were considered and the minimum legible text size was determined for each combination by applying the method of limits, one of psychophysical methods. Results: The minimum legible text size was significantly different in accordance with the combination of background and text colors. Statistical analysis results showed that luminance contrast and color contrast between background and text influenced the minimum legible text sizes. Conclusion: This study concluded that the minimum legible text size is 8 minute of arc for various combinations of background and text colors. Application: The minimum legible text size identified in the present study can be utilized in designing visual information on GVD at the main control room in a radioactive waste facility.

• Physical Therapy Rehabilitation Science
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• v.5 no.3
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• pp.143-148
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• 2016

Objective: This study aimed to quantify one of the useful upper extremity movements to evaluate motor control abilities between the groups of people with mild and moderate arm impairments performing a door handling task. Design: Cross-sectional study. Methods: Twenty-one healthy participants and twenty-one persons with chronic stroke (9 mild stroke and 12 moderate stroke) were recruited for this study. Stroke participants were divided into 2 groups based on Fugle-Meyer Assessment scores of 58-65 (mild arm) and 38-57 (moderate arm). All they performed door handling task including the pronation and supination phases 3 times. We measured some movement factors which were reaction time, movement time, hand of peak velocity, hand of movement units to perform door handling task using the three-dimensional motion analysis. Results: The majority of kinematic variables showed significant differences among study groups (p<0.05). The reaction time, total and phase of movement time, hand of peak velocity, the number of movement units discriminated between healthy participants and persons with moderate upper limb stroke (p<0.05). In addition, reaction time, total and phase of movement time, the number of movement units discriminated between those with moderate and mild upper limbs of stroke patients (p<0.05). Conclusions: Three-dimensional kinematic motion analysis in this study was a useful tool for assessing the upper extremity function in different subgroups of people with stroke during the door handling task. These kinematic variables may help clinicians understand the arm movements in door handling task and consist of discriminative therapeutic interventions for stroke patients on upper extremity rehabilitation.

• Physical Therapy Rehabilitation Science
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• v.8 no.4
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• pp.175-186
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• 2019

Objective: Non-specific chronic low back pain (NS-CLBP) has been related to abnormal trunk muscle activations, but literature reported considerable variability in muscle amplitudes of NS-CLBP patients during prolonged sitting periods. Therefore, the purpose of this study was to examine the differences among homogenous NS-CLBP subgroups in muscle activity, using muscle co-contraction indices as a more objective approach, and their roles on pain development during a 1-hour period of prolonged sitting. Design: Cross-sectional study. Methods: Twenty NS-CLBP subjects with motor control impairment (MCI) [10 classified as having flexion pattern disorder, and 10 with active extension pattern disorder], and 10 healthy controls participated in the study. Subjects followed a 1-hour sitting protocol on a standard office chair. Four trunk muscle activities including amplitudes and co-contraction indices were recorded using electromyography over the 1-hour period. Perceived back pain intensity was recorded using a numeric pain rating scale every 10 minutes throughout the sitting period. Results: All study groups presented with no significantly distinctive trunk muscle activities at the beginning of sitting, nor did they change over time when pain increased to a significant level. Both MCI subgroups reported a similarly significant increase in pain behavior through mid-sitting (p<0.001). However, after mid-sitting, they significantly differed from each other in pain (p<0.01) but did not differ in the levels of muscle activation. Conclusions: This study was the first to highlight the similarities in trunk muscle activities among homogenous NS-CLBP patients related to MCI and compared them to healthy controls while sitting for an extended period of time, and the significant increase in pain over the 1-hour sitting might not be attributed to trunk muscle activation.