• 소음진동
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• 제7권6호
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• pp.953-958
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• 1997

Corrugation of railway track can be caused by the various dynamic behaviors of traveling wheels and track. In this paper, the coupled vibrations of traveling wheel and railway track are analyzed as the cause of corrugations. To analyze the coupled vibration, the track supported by the sleepers and the traveling wheels are identified to the elastically supported infinite beam and the spring-mass system which runs at constant speed. The Hertzian contact spring is considered between the infinite beam and spring-mass system are calculated. The cause and development of rail corrugation are discussed in the view point of contact force fluctuation affected by the elastic supports and the corrugated surface profile on the track. By the obtained results, the possibilities of resonance are checked between the excitation by the corrugated surface profile and the natural frequency of contact spring-mass system. It may be thought to a development of railway corrugation.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.475-480
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• 2008

Hemming, especially curl hemming, is required along the wheel housing for safety. Robot roller hemming is suitable for it. In this paper, both the flat hemming and the curl hemming along either the straight profile or the curved profile are analyzed using finite element program MSC.Marc to verify the hemming test results. Both the inner panel and the outer panel are modeled using 3-D solid elements and the roler is modeled using rigid surface. In the curl hemming, there is a case that the curl is not formed if the pre-hemming force is not sufficient. It agrees with the test results.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1997년도 춘계학술대회논문집; 경주코오롱호텔; 22-23 May 1997
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• pp.241-246
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• 1997

Corrugation of railway track can be caused by the various dynamic behaviors of traveling wheels and track. In this paper, the coupled vibrations of traveling wheel and railway track are analyzed as the cause of corrugations. To analyze the coupled vibration, the track supported by the sleepers and the traveling wheels are identified to the elastically supported infinite beam and the spring-mass system which runs at constant speed. The Hertzian contact spring is considered between the infinite beam and spring-mass system. The dynamic responses of elastically supported infinite beam and spring-mass system are calculated. The cause and development of rail corrugation are discussed in the view point of contact force fluctuation affected by the elastic supports and the corrugated surface profile on the track. By the obtained results, the possibilities of resonance are checked between the excitation by the corrugated surface profile and the natural frequency of contact spring-mass system. It may be thought to a development of railway corrugation.

• 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.

• 한국기계가공학회지
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• 제15권3호
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• pp.79-85
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• 2016

Truing process is a very important process for recovering the shape of wheels worn by continuous grinding operation. In this study, the devices, controller, and spindle for electro-discharge truing were developed, and the electro-discharge truing method was applied to metal-bonded grinding wheels and compared with the conventional truing method. The shapes of the grinding wheels were measured by a surface profile measurement device. The protrusion of abrasives on the surface of the wheels was compared with the conventional truing method using an optic microscope measurement device. The experimental results showed that the performance of the electro-discharge truing method, in terms of the protrusion of abrasives on the surface of the wheels and the recovery of the shape of the worn wheels, was similar to that of the conventional truing method.

• International journal of advanced smart convergence
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• 제9권3호
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• pp.199-206
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• 2020

A wheelchair is an essential rehabilitation assistant device for the movement of paraplegia patients and generally paralyzed patients who cannot walk normally. In particular, the applicability of the manual/motorized wheelchair is gradually increasing. Until now, decelerators using belt, chain and worm gears, etc have been widely used. However, a decelerator takes a large space although it is a simple device and thus is not ideal for the driving part of manual/motorized wheelchair. For these reasons, in this study we developed a driving part producing a large driving force through a decelerator using planetary gears rather than conventional worm gear-based decelerator. We designed the tooth profile of the planetary gears for decelerator using Kisssoft program, In addition, we designed the driving part so as to apply it to the wheels of conventional wheelchairs, and then optimized the mechanism for the principles of manual/motorized transposition of the driving part and the operational principles. Based on the results of this study, we finally designed and manufactured a driving part for wheelchair decelerator in the form of planetary gears with 1 sun gear, 2 planetary gears and 1 ring gear.

• 대한금속재료학회지
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• 제48권12호
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• pp.1103-1108
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• 2010

We fabricated flanged outer races for wheel bearing units using 0.52%C clean steels, and then characterized and studied the transformation behavior. The outer races produced by hot forging and high frequency induction hardening in this study were analyzed through microstructural characterization using OM, SEM, TEM, and X-ray diffractometer and their microhardness depth profiles of the raceway contacted by balls were measured using MVH tester. The surface hardened layers with a uniform hardness profile in the raceway consisting of very fine martensite with sub-micron sized retained austenite could be formed for very short time during high frequency induction hardening after hot forging. The very fine martensite may be transformed on rapid cooling, from the inhomogeneous austenite nucleated on rapid heating in small particles of pearlitic cementite fragmentated by hot forging. On the other hand the sub-micron sized retained austenite may be chemically stabilized due to their extremely small size, from the small austenite nucleated at the grain boundaries.

• 한국자동차공학회논문집
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• 제7권9호
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• pp.195-202
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• 1999

The kinematic and complicance characteristics of torsion beam axle is structurally related to the location and section profile of torsion beam and the span from body mounting point to wheel center. This paper presents the effect of section properties in torsion beam on the structural characteristics and roll behavior of suspension. The structural characteristics is on the maximum stress on the welding area of torsion beam and the roll behavior is on roll steer and roll-camber of suspension which are important for controllability and stability in cornering. Four factors are used for the section design of torsion beam, which are thickness , midline length, are inner radius, and sector half angle . Through the structural and quasi-static analysis made for six torsion beam axle models, it can be noticed that roll steer and the structural durability of suspension are closely related to warping constant and shear center in section properties of torsion beam.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 추계학술대회 논문집 Vol.16
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• pp.539-542
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• 2003

Recently, the polymer insulators which are being used for high voltage applications have some advantages such as light weight, small size, vandalism resistance, hydrophobicity and easy making process. During outdoor service of polymer insulators, the surface of the insulating material is frequently subjected to moisture and contamination which lead to the well known phenomenon of dry band arcing. Their tracking resistance, erosion resistance, end sealing and shed design are very important because dry band arcing causes degradation of polymer surface. The shape design of porcelain insulator is formalized but design standard for polymer insulator is no standardized up to now, much research is necessary in real condition. In this paper, the aging property of polymer insulator with shed shape(regular, alternative type) is analyzed through numerical analysis, CEA(canadian electricity association) tracking wheel test and IEC 61109 Annex C.

• 문화기술의 융합
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• 제8권5호
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• pp.515-524
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• 2022

도시철도 침목플로팅궤도(STEDEF)의 분기기는 콘크리트 도상에 매입된 목침목과 침목 하부의 침목방진패드로 구성된 방진궤도로서 침목방진패드의 열화 및 이에 따른 스프링강성의 변화가 침목지지조건의 변화를 초래할 수 있다. 현재 약 21년의 공용기간 동안 발생된 망간크로싱의 손상수량은 전체 부설수량 대비 약 17%로 조사되었으며, 사용 기간 15년 이후(누적통과톤수 약 5.5억톤)부터 손상 물량이 증가하는 것으로 분석되었다. 본 연구에서는 실물 망간크로싱과 차륜의 형상을 모사한 3차원 수치모델을 이용한 매개변수 해석(차륜의 위치, 침목지지조건 및 동적 윤중의 크기)을 수행하여 실제 현장에서 발생된 망간크로싱의 손상유형 및 발생원인을 분석하였다. 연구결과, 노즈부 주변 침목에 뜬침목이 발생된 경우, 설계 궤도충격계수가 적용된 동적윤중 작용 시 노즈부 단면의 발생응력이 항복강도를 초과하였으며, 이는 실제 현장에서 발생된 손상위치와 비교적 잘 일치하는 것으로 분석되었다. 따라서 망간크로싱의 손상을 최소화하기 위해서는 노즈부 주변의 침목지지조건을 일정한 수준으로 유지하고, 손상된 망간크로싱 교체 시에는 침목 하부 경계조건의 균일성 확보를 위해 침목방진패드를 함께 교체하는 것이 바람직할 것으로 분석되었다.