• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.474-478
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• 2004

A bushing is a device used in automotive suspension systems to reduce the load transmitted from the wheel to the frame of the vehicle. A bushing is a hollow cylinder, which is bonded to a solid steel shaft at its inner surface and a steel sleeve at its outer surface. The relation between the force applied to the shaft and the relative deformation of a bushing is nonlinear and exhibits features of viscoelasticity. A force-displacement relation for bushings is important for multibody dynamics numerical simulations. For the nonlinear viscoelastic axial response, Pipkin-Rogers model, the direct relation of force and displacement, has been derived from Lianis model and the sinusoidal input was used for Pipkin-Rogers model, and the affection of displacement with frequency change was studied with Pipkin-Rogers model.

• 대한기계학회논문집
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• 제12권6호
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• pp.1265-1272
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• 1988

본 연구에서는 속도변환을 이용하여 기본체(base body)가 움직이는 경우에 대 한 일반적인 운동방정식을 유도하고, 이를 적절히 변형시킴으로써 로봇분야에서 이미 유도된 식과 비슷한 반복형태의 식을 얻을 수 있음을 보임으로써, 기계의 동력학 분야 에서 사용하고 있는 속도변환의 방법이 기본체가 고정되어 있는 경우가 대부분인 로봇 분야에서도 적용될 수 있음을 보이고자 한다. 또한 유도된 반복형태식을 이용하여 개방연쇄계(open-loop system)로 이루어진 기계시스템의 동력학 시뮬레이션에 적합한 알고리즘을 만들고 자동차를 예제로 택하여 유도된 방법의 타당성과 효율성을 검토하 였다.

• 대한기계학회논문집
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• 제16권5호
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• pp.899-909
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• 1992

본 연구에서는 대수 미분 방정식을 풀기위한 새로운 방법을 소개한다. 본 작업에서는 Lagrange multiplier의 값이 사전에 주어졌다고 생각하여, 즉 대수 미분 방정식을 순수한 상미분 방정식으로 변환하여, 잘 알려진 시간 적분법을 적용한다. 또 정확한 Lagrange Multiplier값은 반복 계산법(iterative scheme)에 의하여 계산한 다. 시간 적분의 정확도와 제한 조건의 정확도는 모두 보장된다. 특히 제한 조건 의 경우, 위치, 속도 및 가속도의 제한 조건이 모두 만족된다. 또 정확한 Lagrange multiplier의 값을 계산 가속기법(acceleration technique)에 의하여 대단히 빨리 계 산한다. 독립 좌표를 구할 필요가 없으므로 거대한 행열을 decomposition하는 등의 복잡한 절차가 불필요하며 N-R 반복법 역시 불필요하다. 이러한 사항들 및 Jacobian 행열의 sparsity로 인하여 경제적인 계산이 가능하게 된다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.893-898
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• 2004

This research proposes an implementation method of linearized equations of motion for multibody systems with closed loops. The null space of the constraint Jacobian is first pre multiplied to the equations of motion to eliminate the Lagrange multiplier and the equations of motion are reduced down to a minimum set of ordinary differential equations. The resulting differential equations are functions of all relative coordinates, velocities, and accelerations. Since the coordinates, velocities, and accelerations are tightly coupled by the position, velocity, and acceleration level constraints, direct substitution of the relationships among these variables yields very complicated equations to be implemented. As a consequence, the reduced equations of motion are perturbed with respect to the variations of all coordinates, velocities, and accelerations, which are coupled by the constraints. The position, velocity and acceleration level constraints are also perturbed to obtain the relationships between the variations of all relative coordinates, velocities, and accelerations and variations of the independent ones. The perturbed constraint equations are then simultaneously solved for variations of all coordinates, velocities, and accelerations only in terms of the variations of the independent coordinates, velocities, and accelerations. Finally, the relationships between the variations of all coordinates, velocities, accelerations and these of the independent ones are substituted into the variational equations of motion to obtain the linearized equations of motion only in terms of the independent coordinate, velocity, and acceleration variations.

• 드라이브 ㆍ 컨트롤
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• 제19권2호
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• pp.1-10
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• 2022

Field robots operate in various areas, including construction, agriculture, forestry and manufacturing. Typical tasks of field robots used in various areas include excavation, flattening, and demolition. Such tasks are often accomplished in narrow alleys or indoors. In the case of field robots, there is a limit to working in a small space. Thus, to compensate for these shortcomings, many field robots equipped with Tiltrotators have recently been observed. The advantages of Tiltrotator are improved task efficiency and reduced operating time by reducing unnecessary behavior. We need simulation models that can improve the ability of new people to work and simulate tasks in advance. Thus, in this paper, we developed a simscape-based simulation model and modeling of 6DOF systems for field robots equipped with Tiltrotator. Dynamic modeling of field robot 3D models using Simcape multibody and hydraulic systems of field robots using Simcape Hydraulics were modeled. We applied a PID controller to create a control system that operates along the input angle. Simulation results show that errors occur when comparing input and output angles, but overall, they move along input angles.

• 한국소음진동공학회논문집
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• 제23권3호
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• pp.234-239
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• 2013

There are many types of speed reducer for industrial uses. However the cycloid speed reducer is widely used in manipulators based on excellent performance of low backlash, high reduction ratio and compact size. It is essential to use precision speed reducer for accuracy of position controls on robot systems and electric vehicles. The cycloid speed reducer has a eccentric rotating motion and offset to avoid some problem of assembly, so it has a disadvantage for vibration. In this paper, a multi-body dynamic model is developed for a cycloid speed reducer and the dynamic behaviors of the reducer are investigated. The cycloid speed reducer consists of cycloidal plate gears, housing gear, input shaft, output pin and shaft, and eccentric bearings. Using a CAD program, each component of cycloid reducer is modeled based on the offset and eccentric. Multi-body simulations using Recurdyn and test using a rig tester are performed. As a result, the pin reaction force and the amplitude of housing displacement are increased by the larger offset and smaller eccentric value of cycloid reducer.

• 대한기계학회논문집A
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• 제27권8호
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• pp.1303-1308
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• 2003

This research proposes an implementation method of linearized equations of motion for multibody systems with closed loops. The null space of the constraint Jacobian is first pre-multiplied to the equations of motion to eliminate the Lagrange multiplier and the equations of motion are reduced down to a minimum set of ordinary differential equations. The resulting differential equations are functions of ail relative coordinates, velocities, and accelerations. Since the coordinates, velocities, and accelerations are tightly coupled by the position, velocity, and acceleration level constraints, direct substitution of the relationships among these variables yields very complicated equations to be implemented. As a consequence, the reduced equations of motion are perturbed with respect to the variations of all coordinates, velocities, and accelerations, which are coupled by the constraints. The position, velocity and acceleration level constraints are also perturbed to obtain the relationships between the variations of all relative coordinates, velocities, and accelerations and variations of the independent ones. The perturbed constraint equations are then simultaneously solved for variations of all coordinates, velocities, and accelerations only in terms of the variations of the independent coordinates, velocities, and accelerations. Finally, the relationships between the variations of all coordinates, velocities, accelerations and these of the independent ones are substituted into the variational equations of motion to obtain the linearized equations of motion only in terms of the independent coordinate, velocity, and acceleration variations.

• 대한기계학회논문집A
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• 제32권10호
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• pp.882-889
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• 2008

A humanoid is a robot with its overall appearance based on that of the human body. When the humanoid moves or walks, dynamic forces act on the body structure. Although the humanoid keeps the balance by using a precise control, the dynamic forces generate unexpected deformation or vibration and cause difficulties on the control. Generally, the structure of the humanoid is designed by the designer's experience and intuition. Then the structure can be excessively heavy or fragile. A humanoid design scenario for a systematic design is proposed to reduce the weight of the structure while sufficient strength is kept. Lower parts of the humanoid are selected to apply the proposed design scenario. Multi-body dynamics is employed to calculate the external dynamic forces on the parts and structural optimization is carried out to design the lower parts. Because structural optimization using dynamic forces directly is fairly difficult, linear dynamic response structural optimization using equivalent static loads is utilized. Topology and shape optimizations are adopted for two steps of initial and detailed designs, respectively. Various commercial software systems are used for analysis and optimization. Improved designs are obtained and the design results are discussed.

• Elastomers and Composites
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• 제38권4호
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• pp.334-341
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• 2003

부싱은 차체로 전달되는 하중을 줄여주는 역할을 하는 자동차 현가장치의 부품으로 바깥쪽 슬리브와 안쪽의 축 사이에서 가운데가 비어있는 실린더의 형상을 가진다. 축에 작용되는 하중과 부싱의 상대 변위는 비선형 점탄성 성질을 나타내며, 부싱에서 힘과 변위의 관계는 다물체 동역학 시뮬레이션에 중요하다. 비선형 점탄성 축방향모드에 대하여 힘과 변위와의 직접관계식인 ??킨-라저스 모델을 리아니스 모델로부터 유도하였으며, 사인함수의 변위를 ??킨-라저스 모델에 적용하여 주파수와 변위의 변화가 비선형 점탄성 부싱 모델에 미치는 영향에 대하여 알아보았다.

• Structural Engineering and Mechanics
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• 제63권5호
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• pp.691-702
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• 2017

Clearances are essential for the assemblage of mechanisms to allow the relative motion between the joined bodies. This clearance exists due to machining tolerances, wear, material deformations, and imperfections, and it can worsen the mechanism performance when the precision and smoothly-working are intended. Energy is a subject which is less paid attention in the area of clearance. The effect of the clearance on the energy of a flexible slider-crank mechanism is investigated in this paper. A clearance exists in the joint between the slider and the coupler. The contact force model is based on the Lankarani and Nikravesh model and the friction force is calculated using the modified Coulomb's friction law. The hysteresis damping which has been included in the contact force model dissipates energy in clearance joints. The other source for the energy loss is the friction between the journal and the bearing. Initial configuration and crank angular velocity are changed to see their effects on the energy of the system. Energy diagrams are plotted for different coefficients of friction to see its influence. Finally, considering the coupler as a flexible body, the effect of flexibility on the energy of the system is investigated.