• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.19 no.1
• /
• pp.12-17
• /
• 2018

In order to enhance the realism of a virtual environment, a method of maximizing the stiffness of the virtual environment model is needed, which maintains the stability of the haptic system. In our previous research, we proposed a haptic system with a first order hold, instead of a zero order hold, and showed that the maximum available stiffness of a virtual spring with the first-order hold is larger than that with the zero-order hold. However, in terms of real system implementation, the zero order hold is a more common and easy method. In this paper, we propose an extrapolation method and a high frequency zero-order-hold output method in order to obtain the stability region using a zero order hold, which is equivalent to the method using the first-order-hold. The simulation results shows that the stability range of the virtual spring becomes almost the same as that of the method using the first order hold when the sampling period of the high frequency zero-order-hold method is decreased. Moreover, the stability range of the proposed method is several times to several tens of times greater than that of the method using the zero order hold only. Therefore, it is expected that the proposed method can enhance the realism of rigid bodies in a virtual environment.

• Proceedings of the Korea Information Processing Society Conference
• /
• 2001.10a
• /
• pp.631-634
• /
• 2001

가상 현실이나 게임 제작 분야에서는 움지임에 따른 변형을 실시간으로 처리하는 것이 요구되고 있다. 변형 처리를 위한 일반적인 모델은 질량-스프링(mass-spring) 방법을 이용한 것으로, 그 구현이 쉽고 처리 속도가 빨라 대화형 시스템(interactive system)에서 실시간 처리를 위한 모델로 주목되고 있다. 반면에, 이 모델은 외부의 제어에 대하여 super-elastic한 문제를 내포하여 그 적용이 제한되어 있다. 본 논문에서는 스프링 모델의 근본적인 문제인 super-elastic 문제를 극복하기 위한 근사 방법을 제안한다. 제안하는 방법은 하이브리드 접근 방식으로, 이산 점 사이의 내부 힘들을 선처리(pre-processing)하여 elastic한 성분을 나누어 처리한다. 선처리 과정에서는 변형 물체의 물리적 속성에 따라 늘어나는(elongation) 성분과 굽어지는(bending) 성분을 따로 처리함으로써, 극심히 늘어나는(super-elongation) 문제를 극소화할 수 있다. 본 논문의 결과로는 빈번한 제어에 대응되는 움직임을 빠르게 생성할 수 있음을 보이며, 안정적이면서 그럴 듯한 움직임을 생성할 수 있음을 보인다.

• Proceedings of the Korean Information Science Society Conference
• /
• 2003.04c
• /
• pp.630-632
• /
• 2003

컴퓨터 가상현실 기술은 반복적인 교육과 훈련을 필요로 하는 의료 시뮬레이션 분야에 도입되어 시술 훈련, 수술 계획 및 수술 시뮬레이션 등의 영역에 응용되고 있다. 3차원적 가시화나 네비게이션에 치중하던 기존의 의료 시뮬레이션에 보다 현실감을 증진시키기 위해서는 인체 해부학적 기관의 변형성과 사용자와 대상 기관 사이의 물리적인 상호작용이 반영되어야 한다. 본 연구에서는 기존의 2차원 및 3차원 마우스만을 사용하던 상호작용 환경을 개선하여 시술 동작시 물리적인 역감을 전달받을 수 있는 햅틱 인터페이스를 도입하고. 보다 현실감 있는 시각적 디스플레이를 위해 햅틱 워크벤치를 사용하였다. 사용자의 햅틱 인터페이스 조작에 따른 가상 인체 기관의 물리적 변형 및 이에 따른 물리적 역감은 삼각메쉬를 이용한 매스-스프링 모델을 사용하여 구현하였고. 가상 시술 도구와 가상 인체 기관와의 빠른 충들 감지를 위해서는 OBBTree를 적용하였다.

• Journal of Institute of Convergence Technology
• /
• v.6 no.2
• /
• pp.15-20
• /
• 2016

This paper presents the effects of a virtual mass on the stability boundary of a virtual spring in the haptic system. A haptic system consists of a haptic device, a sampler, a virtual rigid body and zero-order-hold. The virtual rigid body is modeled as a virtual spring and a virtual mass. According to the virtual mass and the sampling time, the stability boundary of the virtual spring is analyzed through the simulation. As the virtual mass increases, the value of the virtual spring to guarantee the stability gradually increases and then decreases after reaching the maximum value. These simulation results show that the addition of the virtual mass enables to expand the stability boundary of the virtual spring.

• Journal of Institute of Convergence Technology
• /
• v.3 no.2
• /
• pp.23-29
• /
• 2013

When a human operator interacts with a virtual wall that is modeled as a virtual spring model, the lager the stiffness of the virtual spring is, the more realistic the operator feels that the virtual wall is. In the previous studies, it is shown that the maximum available stiffness of a virtual spring to guarantee the stability can be increased when the first-order-hold method is applied, however the effects of a human impedance on the stability are not considered. This paper presents the effects of a human impedance on stability of haptic system with a virtual spring and a first-order-hold (FOH) method. The human impedance model is modeled as a linear second-order system model. The relations between the maximum available stiffness of a virtual spring and the human impedance such as a mass, a damping and a stiffness are analyzed through the MATLAB simulation. It is shown that the maximum available stiffness is proportional to the square root of the human mass or damping respectively.

• Journal of the Korea Computer Graphics Society
• /
• v.25 no.3
• /
• pp.55-63
• /
• 2019

Recently, the GPU computing method has been utilized to improve the performance of the physics simulation field. In particular, in the case of a deformed object simulation requiring a large amount of computation, a GPU-based parallel processing algorithm is required to guarantee real-time performance. We have studied the parallel structure design method to improve the performance of the mass spring simulation method which is one of the methods of implementing the deformation object simulation. We used OpenGL's GLSL, a graphics library that allows direct access to the GPU, and implemented the GPGPU environment using an independent pipeline, the compute shader. In order to verify the effectiveness of the parallel structure design method, the mass - spring system was implemented based on CPU and GPU. Experimental results show that the proposed method improves computation speed by about 6,000% compared to the CPU Environment. It is expected that the lightweight simulation technology can be effectively applied to the augmented reality and the virtual reality field by using the design method proposed later in this research.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.7 no.1
• /
• pp.108-115
• /
• 1995

An efficient model for the dynamic analysis of caisson breakwaters under impulsive wave loadings is presented. The caisson structure is. regarded as a rigid body, and the rubble mound foundation is idealized as virtual added masses, springs, and dampers using the elastic half-space theory. The frequency-dependent hydrodynamic added mass and damping coefficients are considered by using the time memory functions and added mass at infinite frequency. To simulate the permanent sliding phenomenon of the caisson, the horizontal spring is modeled as a nonlinear spring with plastic behaviors. Comparisons with experimental results show that the present model gives fairly good results. Sensitivity analysis is performed for the relevant parameters affecting the dynamic responses of a caisson breakwater. Numerical experiments are also carried out to investigate the applicability to the prediction of permanent sliding distance and critical weight of the caisson.

• Journal of the korean Society of Automotive Engineers
• /
• v.16 no.3
• /
• pp.19-29
• /
• 1994

본 연구에서는 상태방정식과 출력방정식에 외란항을 포함하게 된다. 최적조건을 이용하여 외란항을 포함한 리카티 방정식을 유도하고 그로부터 제어로직을 얻을 수 있다. 본 연구에서의 차량 모델링은 스프링 위 질량 3자유도와 스프링 아래 질량 4자유도 운전석의 연직방향 1자유도를 포함한 총 자유도의 선형모델로 하였다. 또 본 연구에서는 예견제어를 이용하였는데 차량앞에 미리 도로면의 정보를 인식할 수 있는 가상적인 측정장치가 있다고 가정하였다. 결과에서는 기존의 수동형 현가장치와 최적제어를 이용한 능동형 현가장치를 구분하고, 예견시간에 따른 차량의 성능을 비교 분석하였다.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.24 no.1
• /
• pp.33-41
• /
• 2011

This study presents modeling technologies applicable to an unbonded post-tension system using a finite element software package. In this study, both direct modeling method and multiple spring method were used. The direct modeling method adopts tube-to-tube contact elements to represent the physical feature of a post-tension system. The multiple spring method uses virtual tendons attached to the real tendons using a number of rigid axial springs that freely rotate at the ends. Both modeling technologies provide accurate predictions. However, only the multiple spring method provides numerically stable and reliable responses with a consideration of concrete tension stiffening effects. Therefore, the multiple spring method turned out to be a generally applicable modeling technology for the unbonded post-tension system. Comparisons were made for the analytical and experimental results for the verification of the selected method, and parameter studies were carried out to confirm the appropriateness of the modeling assumptions and parameters adopted in the analysis.

• Journal of Institute of Convergence Technology
• /
• v.10 no.1
• /
• pp.41-45
• /
• 2020

This paper presents the effects of a virtual mass on the stability boundary of a virtual spring in the haptic system with first-order-hold. The virtual rigid body is modeled as a virtual spring and a virtual mass. When first-order-hold is applied, we analyze the stability boundary of the virtual spring through the simulation according to the virtual mass and the sampling time. As the virtual mass increases, the stability boundary of the virtual spring gradually increases and then decreases after reaching the maximum value. The results are compared with the stability boundary in the haptic system with zero-order-hold. When a virtual mass is small, the stability boundary of a virtual spring in the system with first-order-hold is larger than that in the system with zero-order-hold.