• 대한전기학회논문지:시스템및제어부문D
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• 제55권1호
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• pp.20-23
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• 2006

This paper presents a new approach to the problem of designing a cascaded three-parameters controller for a given linear time invariant (LTI) plant in unity feedback system. We consider a proportional-integral-derivative (PID) and a first-order controller with the specified overshoot and settling time. This problem is difficult to solve because there may be no analytical solution due to the use of low-order controller. Furthermore, the zeros of controller just appear in the zeros of feedback system. The key idea of our method is to impose a constraint on the controller parameters so that the zeros of resulting controller are distant from the dominant pole of closed-loop system to the left as far as the given interval. Two methods realizing the idea are suggested. We have employed the characteristic ratio assignment (CRA) in order to deal with the time response specifications. It is noted that the proposed methods are accomplished only in parameter space. Several illustrative examples are given.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1995년도 Proceedings of the Korea Automation Control Conference, 10th (KACC); Seoul, Korea; 23-25 Oct. 1995
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• pp.530-533
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• 1995

This paper deals with the problem of motion planning for a unicycle-like robot. We present a simple local planner for unicycle model, based on an approximation of the desired configuration generated by local holonomic planner that ignores motion constraints. To guarantee a collision avoidance, we propose an inequality constraint, based on the motion analysis with the constant control input and time interval. Consequently, we formulate our problem as the constrained optimization problem and a feedback scheme based on local sensor information is established by simply solving this problem. Through simulations, we confirm the validity and effectiveness of our algorithm.

• Journal of Ship and Ocean Technology
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• 제2권1호
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• pp.42-57
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• 1998

Genetic Algorithm (GA) is applied to obtain optimal Inspection plan for fatigue deteriorating structures. The optimization problem is defined so as to minimize inspection cost in the 1ifs-time of the structure under the constraint that the increment of failure probability in each inspection interval is maintained below a target value. Optimization parameters are the inspection timing and the inspection quality. The inspection timing is selected from the discrete intervals such as one year, two years, three years, etc. The inspection quality is selected from the followings; no inspection, normal inspection, sampling inspection or precise inspection. The applicability of the proposed GA approach is demonstrated through the numerical calculations assuming a structure consisting of four member sets. Influences of the level of target failure probability, initial defect condition and stress increase due to plate thickness reduction caused by corrosion on inspection planning are discussed.

• 한국멀티미디어학회논문지
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• 제9권12호
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• pp.1529-1541
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• 2006

Moving objects have been widely employed in traffic and logistic applications. Spatio-temporal aggregations mainly describe the moving object's behavior in the spatial data warehouse. The previous works usually express the object moving in some certain region, but ignore the object often moving along as the trajectory. Other researches focus on aggregation and comparison of trajectories. They divide the spatial region into units which records how many times the trajectories passed in the unit time. It not only makes the storage space quite ineffective, but also can not maintain spatial data property. In this paper, a spatio-temporal aggregation index structure for moving object trajectory in constrained network is proposed. An extended B-tree node contains the information of timestamp and the aggregation values of trajectories with two directions. The network is divided into segments and then the spatial index structure is constructed. There are the leaf node and the non leaf node. The leaf node contains the aggregation values of moving object's trajectory and the pointer to the extended B-tree. And the non leaf node contains the MBR(Minimum Bounding Rectangle), MSAV(Max Segment Aggregation Value) and its segment ID. The proposed technique overcomes previous problems efficiently and makes it practicable finding moving object trajectory in the time interval. It improves the shortcoming of R-tree, and makes some improvement to the spatio-temporal data in query processing and storage.

• 한국컴퓨터정보학회논문지
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• 제15권10호
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• pp.113-120
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• 2010

본 논문에서는 비디오 프록시 서버의 제한된 저장 공간을 효율적으로 활용하기 위한 시간 제약 다중 요청 기법을 제안한다. 제안하는 기법은 요청된 동영상 데이터를 전송받아 사용자에게 전송하고 비디오 프록시 서버에 일시적으로 저장한다. 이때 일시적으로 저장된 동영상 데이터는 설정된 시간 내에서 발생되는 사용자의 요청의 상태에 따라 저장장치에서 삭제되거나 저장된다. 또한 새롭게 요청된 동영상의 저장 공간을 확보하기 위해서 저장장치에 저장되어 있는 동영상 세그먼트 중 요청 가능성이 가장 낮은 세그먼트를 선정하고 제거한다. 이를 위해 사용자에 의해 주로 요청되는 동영상 세그먼트 부분인 전방 클래스와 요청되지 않았거나 요청될 가능성이 적은 세그먼트 부분인 후방 클래스로 분리한다. 분리된 클래스 중 후방 클래스에서 가장 오래전에 요청된 세그먼트를 선정하여 삭제함으로써 제한된 공간을 효율적으로 활용한다. 실험을 통해 제안하는 방법이 기존의 방법들 보다 높은 적중률을 보이는 동시에 보다 적은 삭제 횟수를 보인다는 것을 확인한다.

• 제어로봇시스템학회논문지
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• 제16권3호
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• pp.293-299
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• 2010

The multiple block localization method in a wide area for multiple robots using iGS is proposed in this paper. The iGS is developed for the indoor global localization using ultrasonic and RF sensors. To measure the distance between a mobile robot and a beacon, the tag on the mobile robot wakes up one beacon to send out the ultrasonic signal and measures the traveling time from the beacon to the mobile robot. As the number of robots is increased, the sampling time of localization also becomes longer. Note that only one robot can localize its own position calling beacons one by one during each of the sampling interval. This is a severe constraint for the localization of multiple robots in a wide area. This paper proposes an efficient localization algorithm for the multiple robots in a wide area which can be divided into multiple blocks. For a given block, a master beacon is designated to synchronize robots. By the access of the synchronization signal, each beacon in the selected group sends out an ultrasonic signal. When the robots in the block receive the ultrasonic signal, they can calculate their own locations based on the distances to the beacons, which are obtained by the multiplication of flight time and velocity of the ultrasonic signal. The efficiency of the algorithm is verified through the real experiments.

• International Journal of Aeronautical and Space Sciences
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• 제8권1호
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• pp.10-20
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• 2007

For spacecraft attitude control, reaction wheel (RW) steering laws with more than three wheels for three-axis attitude control can be derived by using a control allocation (CA) approach.1-2 The CA technique deals with a problem of distributing a given control demand to available sets of actuators.3-4 There are many references for CA with applications to aerospace systems. For spacecraft, the control torque command for three body-fixed reference frames can be constructed by a combination of multiple wheels, usually four-wheel pyramid sets. Multi-wheel configurations can be exploited to satisfy a body-axis control torque requirement while satisfying objectives such as minimum control energy.1-2 In general, the reaction wheel steering laws determine required torque command for each wheel in the form of matrix pseudo-inverse. In general, the attitude control command is generated in the form of a feedback control. The spacecraft body angular rate measured by gyros is used to estimate angular displacement also.⁵ Combination of the body angular rate and attitude parameters such as quaternion and MRPs(Modified Rodrigues Parameters) is typically used in synthesizing the control command which should be produced by RWs.¹ The attitude sensor signals are usually corrupted by noise; gyros tend to contain errors such as drift and random noise. The attitude determination system can estimate such errors, and provide best true signals for feedback control.⁶ Even if the attitude determination system, for instance, sophisticated algorithm such as the EKF(Extended Kalman Filter) algorithm⁶, can eliminate the errors efficiently, it is quite probable that the control command still contains noise sources. The noise and/or other high frequency components in the control command would cause the wheel speed to change in an undesirable manner. The closed-loop system, governed by the feedback control law, is also directly affected by the noise due to imperfect sensor characteristics. The noise components in the sensor signal should be mitigated so that the control command is isolated from the noise effect. This can be done by adding a filter to the sensor output or preventing rapid change in the control command. Dynamic control allocation(DCA), recently studied by Härkegård, is to distribute the control command in the sense of dynamics⁴: the allocation is made over a certain time interval, not a fixed time instant. The dynamic behavior of the control command is taken into account in the course of distributing the control command. Not only the control command requirement, but also variation of the control command over a sampling interval is included in the performance criterion to be optimized. The result is a control command in the form of a finite difference equation over the given time interval.⁴ It results in a filter dynamics by taking the previous control command into account for the synthesis of current control command. Stability of the proposed dynamic control allocation (CA) approach was proved to ensure the control command is bounded at the steady-state. In this study, we extended the results presented in Ref. 4 by adding a two-step dynamic CA term in deriving the control allocation law. Also, the strict equality constraint, between the virtual and actual control inputs, is relaxed in order to construct control command with a smooth profile. The proposed DCA technique is applied to a spacecraft attitude control problem. The sensor noise and/or irregular signals, which are existent in most of spacecraft attitude sensors, can be handled effectively by the proposed approach.

• 한국산학기술학회논문지
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• 제9권1호
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• pp.221-227
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• 2008

시간제한을 가지는 차량경로문제는 배송 및 물류에서 가장 중요한 문제 중의 하나이다. 현실적으로 고객의 서비스를 위하여 정해진 시간 안에 출발해서 배송을 끝마쳐야 한다. 그러므로 본 연구는 개선된 유전자 알고리즘을 이용하여 차량의 용량 및 운행시간을 초과하지 않으면서 고객의 서비스를 제공해주며 비용을 최소화하는 목적이 있다. 그리고 본 연구에서 제안한 개선된 유전자 알고리즘을 이용하면 다른 휴리스틱 기법보다 더욱 효율적인 시간제한을 가지는 차량경로문제에서 훌륭한 해를 도출할 수 있다. 따라서 차량경로문제의 해를 도출할 수 있는 개선된 유전자 알고리즘을 이용한 GUI 방식의 컴퓨터 프로그램을 개발하고 표준문제를 통하여 비교한 결과 본 연구에서 개발된 프로그램이 매우 유용한 결과를 보였다.

• 한국인터넷방송통신학회논문지
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• 제18권2호
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• pp.169-176
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• 2018

본 논문에서는 센서노드가 전력소모를 줄이기 위하여 주기적으로 휴면상태를 갖는 듀티사이클 기반 무선센서 네트워크를 고려한다. 이러한 네트워크에서는 듀티사이클 간격이 커진다면 전력소모는 감소하지만 종단간 지연시간은 늘어나게 된다. 무선센서네트워크의 많은 애플리케이션은 지연시간에 민감하며 패킷이 센서노드로부터 싱크노드에게 전달되는 데 있어서 지연시간제약 요구사항이 있다. 기존의 대부분의 연구는 종단간 지연시간을 줄이는 것에만 초점을 맞추고 지연시간제약에 대해 고려를 하지 않음으로써 종단간지연시간과 전력소모에 대한 균형을 맞추기 어려웠다. 지연시간제약을 고려하는 연구에서도 노드들간의 시각동기화를 요구하거나 노드들이 특정한 분포를 갖는다고 가정하였다. 기존 연구의 이러한 제약을 극복하기 위하여 본 논문에서는 지연시간제약조건을 충족시키면서 동시에 전력소모를 줄이기 위한 듀티사이클 스케쥴링 알고리즘을 제안한다. 먼저 종단간 지연시간의 확률분포를 추정하고 획득한 분포를 이용하여 지연시간제약조건을 만족하는 최대 듀티사이클 간격을 결정한다. 시뮬레이션 결과에 따르면 제안되는 알고리즘은 주어진 지연시간제약 요구사항을 만족하면서도 낮은 전력소모 성능을 보인다.

• 천문학회지
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• 제47권6호
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• pp.293-302
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• 2014

Simultaneous time monitoring observations of $H_2O$ $6_{16}-5_{23}$, SiO J = 1-0, 2-1, 3-2, and $^{29}SiO$ ${\upsilon}=0$, J = 1-0 lines are carried out in the direction of the Mira variable star TX Cam with the Korean VLBI Network single dish radio telescopes. For the first time, the $H_2O$ maser emission from TX Cam is detected near the stellar velocity at five epochs from April 10, 2013 (${\phi}=3.13$) to June 4, 2014 (${\phi}=3.89$) including minimum optical phases. The intensities of $H_2O$ masers are very weak compared to SiO masers. The variation of peak antenna temperature ratios among SiO ${\upsilon}=1$, J = 1-0, J = 2-1, and J = 3-2 masers is investigated according to their phases. The shift of peak velocities of $H_2O$ and SiO masers with respect to the stellar velocity is also investigated according to observed optical phases. The $H_2O$ maser emission occurs around the stellar velocity during our monitoring interval. On the other hand, the peak velocities of SiO masers show a spread compared to the stellar velocity. The peak velocities of SiO J = 2-1, and J = 3-2 masers show a smaller spread with respect to the stellar velocity than those of SiO J = 1-0 masers. These simultaneous observations of multi-frequencies will provide a good constraint for maser pumping models and a good probe for investigating the stellar atmosphere and envelope according to their different excitation conditions.