• Title/Summary/Keyword: Wheel Number

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Error Analysis of Reaction Wheel Speed Detection Methods (반작용휠 속도측정방법의 오차 분석)

  • Oh, Shi-Hwan;Lee, Hye-Jin;Lee, Seon-Ho;Yong, Ki-Lyuk
    • Journal of Astronomy and Space Sciences
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    • v.25 no.4
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    • pp.481-490
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    • 2008
  • Reaction wheel is one of the actuators for spacecraft attitude control, which generates torque by changing an inertial rotor speed inside of the wheel. In order to generate required torque accurately and estimate an accurate angular momentum, wheel speed should be measured as close to the actual speed as possible. In this study, two conventional speed detection methods for high speed motor with digital tacho pulse (Elapsed-time method and Pulse-count method) and their resolutions are analyzed. For satellite attitude maneuvering and control, reaction wheel shall be operated in bi directional and low speed operation is sometimes needed for emergency case. Thus the bias error at low speed with constant acceleration (or deceleration) is also analysed. As a result, the speed detection error of elapsed-time method is largely influenced upon the high-speed clock frequency at high speed and largely effected on the number of tacho pulses used in elapsed time calculation at low speed, respectively.

Analysis of Rail Wear Rate according to Wheel/Rail Contact Pressure on Curved Track (곡선부 차륜/레일 접촉압력에 따른 레일마모진전 경향 분석)

  • Sung, Deok-Yong
    • Journal of the Korean Society for Railway
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    • v.20 no.4
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    • pp.512-520
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    • 2017
  • On a typical railway, trains travel using the friction between the wheel and the rail. Contact pressure is generated between the wheel and the rail, and the magnitude of the contact pressure changes depending on the weight, speed, wheel-set hunting, and contact point of the vehicle. In this study, the contact characteristics were analyzed through the finite element analysis for the wheel/rail system on curved track, and fatigue damage and wear rate of wheel/rail according to contact pressure were analyzed through rolling contact fatigue test. Results indicate that, general and heat treated rails showed higher wear rate than wheels, and general and heat treated rail wear rate increased rapidly over a certain number of repetitions. In addition, the general rail wear rate was about 7 ~ 15% higher than that of the heat treated rail, and a regression equation for the rail wear rate with the contact pressure in the contact pressure range of 900 ~ 1,500 MPa was presented.

A Fundamental Study on the Internal Grinding of Tungste Carbide Materials for Metal Mould to Improve the Machining Performance (금형용 초경합금재의 내면연삭 가공능률향상에 관한 기초적 연구)

  • 허성중;이규천;김영일;김원일
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 1996.04a
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    • pp.39-43
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    • 1996
  • This paper described on the effect of residual stocks in internal grinding of tungsten carbide materials in order to improve the grinding efficiency as well as grinding accuracy. Though the fundamental investigation is carried out for tungsten carbide materials using electroplated diamond wheel, the residual stock after grinding process is effective to the grinding effciiency. The obtained results are as follows: (1) Under the depth of cut(t) is constant and decreasing the workpiece velocity(Vw), the resiudal stock after grinding is increased, but the difference is little less than the difference by table speed. (2) Increasing the wheel velocity, the residual stock after grinding is decreased. Therefore in order to minimize the residual stock, the wheel velocity should be increased as far as possible. (3) The surface foughness and out-of roundness increased with depth of cut and table speed, and decreased with wheel velocity, but it may as well adopt as much as polssible under the dimensional tolerance which is required for high efficiency grinding. (4) In order to remove residual stock, the spark-out grinding shoule be done, and it also can be improved about 20 .approx. 25% throughout spark-out grinding, and the number of optimal spark-out times were within 10 times.

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Research on Ultra-precision Grinding Work of Silicon Carbide (실리콘 카바이드의 초정밀 연삭 가공에 관한 연구)

  • Park, Soon-Sub;Won, Jong-Ho
    • Journal of the Korean Society for Precision Engineering
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    • v.26 no.9
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    • pp.58-63
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    • 2009
  • Silicon carbide (SiC) has been used for many engineering applications because of their high strength at high temperatures and high resistances to chemical degradation. SiC is very useful especially for a glass lens mold whose components demanded to the machining with good surface finish and low surface damage. The performance and reliability of optical components are strongly influenced by the surface damage of SiC during grinding process. Therefore, the severe process condition optimization shall be necessary for the highly qualified SiC glass lens mold. Usually the major form of damage in grinding of SiC is a crack occurs at surface and subsurface. The energy introduced in the layers close to the surface leads to the formation of these cracks. The experimental studies have been carried out to get optimum conditions for grinding of silicon carbide. To get the required qualified surface finish in grinding of SiC, the selection of type of the wheel is also important. Grinding processes of sintered SiC work-pieces is carried out with varying wheel type, depth of cut and feed using diamond wheel. The machining result of the surface roughness and the number of flaws, have been analyzed by use of surface profilers and SEM.

System Modeling and Simulation for an In-wheel Drive Type $6{\times}6$ Vehicle (인휠드라이브 타입 $6{\times}6$ 차량 플랫폼을 위한 시스템 모델링 및 시뮬레이션)

  • Lee, Jeong-Yeob;Suh, Seung-Whan;Shon, Woong-Hee;Kim, Chang-Jun;Han, Chang-Soo
    • Transactions of the Korean Society of Automotive Engineers
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    • v.19 no.2
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    • pp.1-11
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    • 2011
  • The skid-steering method that applied a number of mobile robot currently is extremely effective in narrow area. But it contains several problems such as its natural properties, slip, occurred by different direction between vehicle's driving and wheel's rotary. Through this paper, suitable control algorithm of $6{\times}6$ skid steering wheeled vehicle and its driving methods are proposed by analyzing the behavior $6{\times}6$ skid-steered wheeled vehicle model designed by engineering analysis strategy. To do this, based on a behavior of designed driving system, required torque and other performance of in-wheel type motor system are considered, and finally control algorithm for each wheel is proposed and simulated using this model. To test the proposed vehicle system, driver model is designed using PID closed loop system and included in the total driving control algorithm. The Performance of designed vehicle model is verified by using DYC (Direct Yaw Control) cornering mode and slip mode control to follow the steering input which are essential to evaluate the driving performance of $6{\times}6$ vehicle. Proposed modeling strategy and control method will be implemented to the real $6{\times}6$ in-wheel drive type vehicle.

Transfer System using Radial Electrodynamic Wheel over Conductive Track (래디얼 동전기 휠을 이용한 전도성 트랙 위에서의 이송 시스템)

  • Jung, Kwang Suk
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.18 no.11
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    • pp.794-801
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    • 2017
  • When a radial wheel is placed so as to partially overlap a conductive plate and rotated, a lift force is generated on the wheel, a thrust force along the edge, and a lateral force which tends to reduce the overlap region. When several of these wheels are combined, it is possible to realize a system in which the stability of the remaining axes is ensured, except in the traveling direction. To validate the overall characteristics of the multi-wheel system, we propose a transfer system levitated magnetically using radial electrodynamic wheels. The proposed system is floated and propelled by four wheels and arranged in a structure that allows the thrusts generated by the front and rear wheels to offset each other. The dynamic stability of the wheel and the effect of the pole number on the three-axial forces are analyzed by the finite element method. At this time, the thrust and levitation force are strongly coupled, and the only factor affecting them is the wheel rotation speed. Therefore, in order to control these two forces independently, we make use of the fact that the ratio of the thrust to the levitation force is proportional to the velocity and is independent of the size of the gap. The in-plane and out-of-plane motion control of the system is achieved by this control method and compared with the simulation results. The experimental results show that the coupled degrees of freedom can be effectively controlled by the wheel speed alone.

Measuring and Generation the speed of reaction wheel for Spacecraft Dynamic Simulator using the T-Method (위성동역학 시뮬레이터용 T-방식을 이용한 반작용휠 속도 측정 및 펄스 생성)

  • Kim, Yong-Bok;Oh, Si-Hwan;Lee, Seon-Ho;Yong, Ki-Lyok;Rhee, Seung-Wu
    • Aerospace Engineering and Technology
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    • v.6 no.1
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    • pp.74-82
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    • 2007
  • The M-Method that measures the speed of actuator with counting the number of Reaction wheel Tacho Pulse has the many advantages such that a realization is simple and measuring time is uniform, but it also has the disadvantage that measuring speed becomes worse as the wheel speed goes lower. On the contrary, the T-Method that measures the time duration between the pulses is more accurate at lower-speed and its time delay is smaller than M-Method, but its realization is more difficult than M-Method because measuring time is varying with wheel speed variation. Thought M/T Method mixing M-Method with T-Method is widely used in order to measure the speed in the motor industrial area, one of two methods has been used in the spacecraft design area. Therefore, we try to apply both methods together to measuring the speed of Reaction Wheel, the core actuator for low earth orbit satellite. This paper provides the Reaction Wheel simulation board located in the Spacecraft Dynamic Simulator, ground support test set.

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TOTAL DOMINATION NUMBER OF CENTRAL GRAPHS

  • Kazemnejad, Farshad;Moradi, Somayeh
    • Bulletin of the Korean Mathematical Society
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    • v.56 no.4
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    • pp.1059-1075
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    • 2019
  • Let G be a graph with no isolated vertex. A total dominating set, abbreviated TDS of G is a subset S of vertices of G such that every vertex of G is adjacent to a vertex in S. The total domination number of G is the minimum cardinality of a TDS of G. In this paper, we study the total domination number of central graphs. Indeed, we obtain some tight bounds for the total domination number of a central graph C(G) in terms of some invariants of the graph G. Also we characterize the total domination number of the central graph of some families of graphs such as path graphs, cycle graphs, wheel graphs, complete graphs and complete multipartite graphs, explicitly. Moreover, some Nordhaus-Gaddum-like relations are presented for the total domination number of central graphs.

k-PRIME CORDIAL GRAPHS

  • PONRAJ, R.;SINGH, RAJPAL;KALA, R.;NARAYANAN, S. SATHISH
    • Journal of applied mathematics & informatics
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    • v.34 no.3_4
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    • pp.227-237
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    • 2016
  • In this paper we introduce a new graph labeling called k-prime cordial labeling. Let G be a (p, q) graph and 2 ≤ p ≤ k. Let f : V (G) → {1, 2, . . . , k} be a map. For each edge uv, assign the label gcd (f(u), f(v)). f is called a k-prime cordial labeling of G if |vf (i) − vf (j)| ≤ 1, i, j ∈ {1, 2, . . . , k} and |ef (0) − ef (1)| ≤ 1 where vf (x) denotes the number of vertices labeled with x, ef (1) and ef (0) respectively denote the number of edges labeled with 1 and not labeled with 1. A graph with a k-prime cordial labeling is called a k-prime cordial graph. In this paper we investigate the k-prime cordial labeling behavior of a star and we have proved that every graph is a subgraph of a k-prime cordial graph. Also we investigate the 3-prime cordial labeling behavior of path, cycle, complete graph, wheel, comb and some more standard graphs.

Two Feature Points Based Laser Scanner for Mobile Robot Navigation (레이저 센서에서 두 개의 특징점을 이용한 이동로봇의 항법)

  • Kim, Joo-Wan;Shim, Duk-Sun
    • Journal of Advanced Navigation Technology
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    • v.18 no.2
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    • pp.134-141
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    • 2014
  • Mobile robots use various sensors for navigation such as wheel encoder, vision sensor, sonar, and laser sensors. Dead reckoning is used with wheel encoder, resulting in the accumulation of positioning errors. For that reason wheel encoder can not be used alone. Too much information of vision sensors leads to an increase in the number of features and complexity of perception scheme. Also Sonar sensor is not suitable for positioning because of its poor accuracy. On the other hand, laser sensor provides accurate distance information relatively. In this paper we propose to extract the angular information from the distance information of laser range finder and use the Kalman filter that match the heading and distance of the laser range finder and those of wheel encoder. For laser scanner with one feature point error may increase much when the feature point is variant or jumping to a new feature point. To solve the problem, we propose to use two feature points and show that the positioning error can be reduced much.