• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2001년도 ICCAS
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• pp.47.2-47
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• 2001

This paper is concerned with the limiting zeros, as the sampling period tends to zero, of a multivariable discrete-time system composed of an approximate fractional-order hold (AFROH), a continuous-time plant and a sampler in cascade. An approximate fractional-order hold is proposed to implement fractional-order hold (FROH) and is applied to instead of the zero-order hold (ZOH). The implementing problem of the fractional-order hold is overcome. The properties of the limiting zeros are studied and the location problem of them is solved. In addition, a stability condition of the zeros for sufficiently small sampling period is derived ...

• 한국산학기술학회논문지
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• 제19권1호
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• pp.12-17
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• 2018

가상환경에 대한 현실감을 증강시키기 위해서는 햅틱 시스템의 안정성을 유지하면서 가상환경 모델의 강성을 최대한 크게 할 수 있는 방법이 필요하다. 이에 기존 연구에서 영차홀드 대신 일차홀드를 적용하는 방법이 제시되었고, 영차홀드를 이용할 때보다 가상 스프링의 안정성 영역을 더 크게 확보할 수 있음을 시뮬레이션을 통해 제시했다. 그렇지만 실제로 시스템을 구현하는 측면에서 보면, 영차홀드가 일반적이고 손쉬운 방법이다. 이에 본 논문에서는 영차홀드를 사용하지만, 일차홀드와 동등한 안정성 영역을 확보하기 위한 방법으로 외삽법과 고주파 영차홀드 출력 방법을 제안한다. 제안된 방법에 대한 시뮬레이션을 통해 고주파 영차홀드의 샘플링 주기가 작아질수록 가상 스프링의 안정성 영역이 일차홀드를 적용한 경우와 거의 같아짐을 보였고, 기존 연구에서 제시된 영차홀드만을 적용한 경우보다는 수 배에서 수십 배 안정성 영역이 더 커질수 있음을 보였다. 따라서 제안된 방법을 통해 가상 환경 속 강체에 대한 현실감을 증강시킬 수 있을 것으로 기대된다.

• 융복합기술연구소 논문집
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• 제10권1호
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• pp.41-45
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• 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.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1997년도 한국자동제어학술회의논문집; 한국전력공사 서울연수원; 17-18 Oct. 1997
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• pp.593-596
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• 1997

This paper is concerned with the properties of zeros of discrete-time systems which are composed of a hold, a continuous-time plant and a sampler in cascade. Here the signal reconstruction is based on the fractional order hold. In order to overcome the implementing problem of the fractional order hold, the piecewise constant reconstruction method by use of the zero order hold is introduced. The properties of the zeros are explored in the limiting cases when the sampling period tends to zero. The stability conditions of the zeros for sufficiently small sampling periods are also presented.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 심포지엄 논문집 정보 및 제어부문
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• pp.152-154
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• 2007

Anew discretization method for the input-driven nonlinear continuous-time system with time delay is proposed. It is based on the combination of Taylor series expansion and first-order hold assumption. The mathematical structure of the new discretization scheme is explored. The performance of the proposed discretization procedure is evaluated by case studies. The results demonstrate that the proposed discretization scheme can assure the system requirements even though under a large sampling period. A comparison between first order hold and zero-order hold is simulated also.

• 한국산학기술학회논문지
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• 제18권1호
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• pp.572-578
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• 2017

사용자가 원격으로 가상환경에 접속하여 가상물체를 조작할 때 현실감을 증강시키기 위해서 햅틱 시스템이 사용된다. 그러나 원격 시스템 환경에는 통신시간지연이 발생하며, 발생된 통신시간지연은 햅틱 시스템을 불안정하게 만들 수 있다. 본 논문에서는 종래의 샘플-홀드 방식인 영차홀드 (ZOH; Zero-Order-Hold)가 아닌 일차홀드 (FOH; First-Order-Hold)를 포함하는 햅틱 시스템에서 시뮬레이션을 통해 통신시간지연과 햅틱 장치의 물성치 변화에 따른 가상 스프링상수의 안정성 영역을 분석하고 이를 통해 안정적인 햅틱 시스템을 구현하고자 한다. 통신시간지연이 없으면 일차홀드 (FOH) 방식이 영차홀드(ZOH) 방식보다 가상 스프링상수의 안정성 영역을 증가시킬 수 있었다. 그러나 통신시간지연이 증가하면, 샘플-홀드 방식보다 통신시간지연이 시스템 안정성에 더 큰 영향을 끼치므로, 샘플-홀드 방식에 따른 가상 스프링상수의 안정성 영역 크기에는 차이가 없어진다. 또한 통신시간지연과 일차홀드 방식이 포함되면 가상 스프링상수의 안정성 영역은 통신시간지연 크기에 반비례하고, 햅틱 장치의 댐핑상수 ($B_d$)에 정비례하여 증가하지만, 햅틱 장치의 질량 ($M_d$)에는 영향받지 않음을 알 수 있었다.

• 제어로봇시스템학회논문지
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• 제20권4호
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• pp.389-394
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• 2014

This paper presents the effect of a reflective force computed from a first-order-hold method on the stability of a haptic system. A haptic system is composed of a haptic device with a mass and a damper, a virtual spring, a sampler and a sample-and-hold. The boundary condition of the maximum virtual stiffness is analytically derived by using the Routh-Hurwitz criterion and the condition shows that the maximum virtual stiffness is proportional to the square root of the mass and the damper of a haptic device and also is inversely proportional to the sampling time to the power of three over two. The effectiveness of the derived condition is evaluated by the simulation. When the reflective forces are computed by using the first-order-hold method, the maximum available stiffness to guarantee the stability is increased several hundred times as large as when the zero-order-hold method is applied.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2003년도 ICCAS
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• pp.2765-2770
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• 2003

This paper introduces a novel control algorithm, energy bounding algorithm, for stable haptic interaction. The energy bounding algorithm restricts energy generated by zero-order hold within consumable energy by physical damping that is energy consumption element in the haptic interface. The passivity condition can always be guaranteed by the energy bounding algorithm. The virtual coupling algorithm restricts the actuator force with respect to the penetration depth and restricts generated energy. In contrast, energy bounding algorithm restricts the change of actuator force with respect to time and restricts generated energy by zero-order hold. Therefore, much stiffer contact simulation can be implemented by the energy bounding algorithm. Moreover, the energy bounding algorithm doesn’t is not computationally intensive and the implementation of it is very simple.

• 융복합기술연구소 논문집
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• 제2권2호
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• pp.35-39
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• 2012

This paper presents the effect of data-hold methods on stability of haptic system with a virtual wall. When a human operator interacts with virtual wall, the lager the stiffness of the virtual wall is, the more realistic the operator feels that the virtual wall is. However, if the stiffness of the virtual wall becomes extremely large, the system may be unstable. When a virtual wall is designed, it is necessary to analyze the maximum available stiffness to guarantee a stable haptic interaction. The simulation model in this paper is developed based on the haptic device model, sampler, a virtual wall model, and data hold methods to compute the maximum stiffness for stability. The effectiveness of the simulation is evaluated through comparing the results of previous studies with the results of this simulation. In addition, the effects of two data hold methods, that is, zero-order hold (ZOH) and first-order hold (FOH) on the stability are analyzed and the values of the maximum available stiffness are compared through the simulation.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2002년도 ICCAS
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• pp.44.4-44
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• 2002

This paper investigates some conditions such that zeros are added to the system with a monotone nondecreasing step response in order to hold the monotonicity as before. Two conditions are presented for the cases that a real zero and complex conjugate zeros are added to the system satisfying the monotonicity condition, respectively. To exemplify the proposed results, some simple examples via computer simulation are shown in this paper. Proposed conditions can be easily used in the control system design since they are only formulated in terms of pole-zero configurations.