• 대한기계학회논문집
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• 제17권11호
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• pp.2730-2741
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• 1993

A mathematical model of the seeker scan-loop which is composed of a spin-stabilized gyroscope and its driving signal processors is derived. The derived model has a transmission zero pair on the imaginary axis near to the required bandwidth. The LQG/LTR design methodology is evolved for the derived scan-loop model. To implement the designed LQG/LTR compensator to the actual plant, the compensator order is reduced using the internally balanced realization method. The performances of the LQG/LTR compensator are tested and compared with those of the P-control. Especially, stability-robustnessexperiments for model uncertainties represented in the form of time-delays are performed. It is demonstrated that the LQG/STR compensator is actually very robust to model uncertainties.

• Smart Structures and Systems
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• 제20권4호
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• pp.483-498
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• 2017

Real-Time Hybrid Simulation (RTHS) is a powerful and cost-effective dynamic experimental technique. To implement a stable and accurate RTHS, time delay present in the experiment loop needs to be compensated. This delay is mostly introduced by servo-hydraulic actuator dynamics and can be reduced by applying appropriate compensators. Existing compensators have demonstrated effective performance in achieving good tracking performance. Most of them have been focused on their application in cases where the structure under investigation is subjected to inputs with relatively low frequency bandwidth such as earthquake excitations. To advance RTHS as an attractive technique for other engineering applications with broader excitation frequency, a discrete-time feedforward compensator is developed herein via various optimization techniques to enhance the performance of RTHS. The proposed compensator is unique as a discrete-time, model-based feedforward compensator. The feedforward control is chosen because it can substantially improve the reference tracking performance and speed when the plant dynamics is well-understood and modeled. The discrete-time formulation enables the use of inherently stable digital filters for compensator development, and avoids the error induced by continuous-time to discrete-time conversion during the compensator implementation in digital computer. This paper discusses the technical challenges in designing a discrete-time compensator, and proposes several optimal solutions to resolve these challenges. The effectiveness of compensators obtained via these optimal solutions is demonstrated through both numerical and experimental studies. Then, the proposed compensators have been successfully applied to RTHS tests. By comparing these results to results obtained using several existing feedforward compensators, the proposed compensator demonstrates superior performance in both time delay and Root-Mean-Square (RMS) error.

• 대한방사선치료학회지
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• 제8권1호
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• pp.55-61
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• 1996

A radiation beam incident on irregular or sloping surface produces an inhomogeneity of absorbed dose. The use of a tissue compensator can partially correct this dose inhomogeneity. The tissue compensator should be made based on experimentally measured thickness ratio. The thickness ratio depends on beam energy, distance from the tissue compensator to the surface of patient, field size, treatment depth, tissue deficit and other factors. In this study, the thickness ratio was measured for various field size of $5cm{\times}5cm,\;10cm{\times}10cm,\;15cm{\times}15cm,\;20cm{\times}20cm$ for 4MV X-ray beams. The distance to the compensator from the X-ray target was fixed, 49cm, and measurement depth was 3, 5, 7, 9 cm. For each measurement depth, the tissue deficit was changed from 0 to(measurement depth-1)cm by 1cm increment. As a result, thickness ratio was decreased according to field size and tissue deficit was increased. Use of a representative thickness ratio for tissue compensator, there was $10\%$ difference of absorbed dose but use of a experimentally measured thickness ratio for tissue compensator, there was $2\%$ difference of absorbed dose. Therefore, it can be concluded that the tissue compensator made by experimentally measured thickness ratio can produce good distribution with acceptable inhomogeneity and such tissue compensator can be effectively applied to clinical radiotherapy.

• Journal of Advanced Marine Engineering and Technology
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• 제34권2호
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• pp.267-274
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• 2010

중력보상기의 구조에 대해 연구하였고, 이를 적용하여 로봇 관절의 성능을 개선하기 위하여 새롭게 개발한 6축의 로봇 매니퓰레이터에 대해 설명한다. 로봇의 기구학 해석을 하였다. 또한, 다양한 스프링으로 구성된 중력보상기를 적용한 로봇 관절구동기의 성능에 대하여 시뮬레이션 하였다. 시뮬레이션 결과에 따르면, 중력보상기를 적용한 로봇 매니퓰레이터의 관절에 가해지는 외부부하는 중력보상기에 사용되는 스프링의 강도에 비례하여 줄어드는 것이 검증되었다.

• 한국정밀공학회지
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• 제28권4호
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• pp.455-462
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• 2011

This paper is about the design of a new gravity compensator for the lower body exo-skeleton device. The exo-skeleton devices is for increasing the torque of the human body joint for the purpose of helping the disabled, workers in the industry, and military soldiers. So far, most of studied exo-skeleton devices are actuated by the motors, but motors are limited in energy such that a short durability is always a big problem. In this paper, a new gravity compensator is proposed to reduce the torque load applied to human body joints due to gravity. The gravity compensator is designed using a tortional bar spring, and its structure and characteristics are studied through the test and computer simulation. A design concept on the exo-skeleton device using the gravity compensator is presented. An analysis and computer simulation on the torque reduction of the proposed exo-skeleton device that applies and non-applies the gravity compensator are performed.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제52권8호
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• pp.405-412
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• 2003

This paper presents a three-phase Line-Interactive uninterruptible power supply (UPS) system with series-parallel active power-line conditioning capabilities, using synchronous reference frame (SRF) based controller, which allows an effective power factor correction, source harmonic voltage compensation, load harmonic current suppression, and output voltage regulation. The three-phase UPS system consists of two active power compensator topologies. One is a series active compensator, which works as a voltage source in phase with the source voltage to have the sinusoidal source current and high power factor under the deviation and distortion of the source voltage. The other is a parallel active compensator which works as a conventional sinusoidal voltage source in phase with the source voltage, providing to the load a regulated and sinusoidal voltage with low THD (total harmonic distortion). The control algorithm using SRF method and the active power flow through the Line-interactive UPS systems are described and studied. The simulation and experimental results are depicted in this paper to show the effect of the proposed algorithm.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 학술대회 논문집 정보 및 제어부문
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• pp.751-753
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• 2004

In rotating systems, backlash imposed limitations on the quality of control. System with gear is an example where this is a well-known limitation. In order to increase the controller performance, we design a fuzzy system to compensate the backlash effect. We prove that under certain conditions the fuzzy compensator guarantees that the backlash output converges to the desired trajectory. Simulation results show that the fuzzy compensator is robust to the backlash parameter.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 A
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• pp.300-302
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• 1996

In this paper a new series-parallel compensated uninterruptible power supply is proposed. Its series compensator shapes input current to sinusoid. The power handled by series compensator is only a quarter of ratings. And parallel compensator delivers sinusoidal voltage to nonlinear load. The parallel compensator is backedup with battery. This system has capabilities of power line conditioner and backup power with reduced size.

• 전력전자학회:학술대회논문집
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• 전력전자학회 1999년도 전력전자학술대회 논문집
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• pp.448-451
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• 1999

This paper describes controller development for a dynamic voltage compensator using a shunt diode converter and series inverter. The control system was designed using 1/4 period integrator and vector relationship between the supply voltage and load voltage. A simulation model and scaled hardware model were developed for analyzing performance of the controller and the whole system. Both results confirm that the dynamic compensator can restore the load voltage under the fault of the distribution system.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1991년도 한국자동제어학술회의논문집(국내학술편); KOEX, Seoul; 22-24 Oct. 1991
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• pp.299-304
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• 1991

A novel approach based on a nonlinear compensator is proposed to prevent 'windup', which is caused by the saturation of the actuator and the integration action of the controller. The anti-windup compensator is located between the conventional linear controller, designed neglecting the saturation, and the actuator. It was proven based on the describing function method that, if the closed loop control systems are stable assuming no saturation, then there exist a range of compensator gain which prevents any limit-cycle and hence, guarantees the system stability. The computer simulation results show that the compensator proposed in the manuscript can eliminate unstable limit cycle and improve the transient response.