• Title/Summary/Keyword: unstable performance

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Internal Model Control for Unstable Overactuated Systems with Time Delays

  • Mahmoud, Ines;Saidi, Imen
    • International Journal of Computer Science & Network Security
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    • v.21 no.1
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    • pp.64-69
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    • 2021
  • In this paper, we have proposed a new internal model control structure (IMC). It is aimed at unstable overactuated multivariable systems whose transfer matrices are singular and unstable. The model inversion problem is essential to understand this structure. Indeed, the precision between the output of the process and the setpoint is linked to the quality of the inversion. This property is preserved in the presence of an additive disturbance at the output. This inversion approach proposed in this article can be applied to multivariable systems with no minimum phase or minimum phase shift with or without delays in their transfer matrices. It is proven by an example of simulation through which we have shown its good performance as a guarantee of stability, precision as well as rapidity of system responses despite the presence of external disturbances and we have tested this control structure in the frequency domain hence the robustness of the IMC.

Design and Performance Evaluation of Controller for Unstable Motion of Underwater Vehicle after Water Entry (수중운동체 입수 초기의 불안정 거동에 대한 제어기 설계 및 성능평가)

  • Park, Yeong-Il;Ryu, Dong-Ki;Kim, Sam-Soo;Lee, Man-Hyung
    • Journal of the Korean Society for Precision Engineering
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    • v.16 no.6
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    • pp.166-175
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    • 1999
  • This paper describes a design and performance evaluation of robust controller which overrides unstable motion and pulls out quickly after water entry of underwater vehicle dropped from aircraft or surface ship. We use 6-DOF equation for model of motions and assume parameter uncertainty to reflect the difference of real motion from modelled motion equation. we represent a nonlinear system with uncertainty as Takagi and Sugeno's(T-S) fuzzy models and design controller stabilizing them. The fuzzy controller utilizes the concept of so-called parallel distributed compensation (PDC). Finally, we confirm stability and performance of the controller through computer simulation and hardware in the loop simulation (HILS).

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An Experimental Application of Observer/controller Identification Algorithm to the System Identification of Inherently Unstable Systems

  • Park, Mun-Soo;Yang, Dong-Hoon;Hong, Suk-Kyo
    • 제어로봇시스템학회:학술대회논문집
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    • 2002.10a
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    • pp.63.4-63
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    • 2002
  • $\textbullet$ Closed System Identification for inherently unstable systems $\textbullet$ Application of Observer/controller Identification (OCID) algorithm to those systems $\textbullet$ An open-loop system model with corresponding controller and observer gains are identified using OCID $\textbullet$ Experimental example of the OCID algorithm for an inverted pendulum system operating in closed-loop $\textbullet$ Modal analysis and time response to the added distrubance are presented to evaluate the performance of the OCID algorithm.

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Fuzzy Rule for Curve Path Tracking of a Unicycle Robot (유니사이클 로봇의 곡선경로 추종을 위한 퍼지규칙)

  • 김중완;정희균
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 1996.11a
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    • pp.425-429
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    • 1996
  • Our unicycle has simple mechanical structure. But unicycle's dynamic system is a very sensitive unstable nonlinear system. In this paper, a fuzzy inference control mechanism was established throughout an inquiry into human riding a unicycle, and we developed a direct fuzzy controller to control our unicycle robot. This proposed fuzzy controller is consisted with fuzzy logic controllers for attitude stability and wheel's velocity. Computer simulation results show that our fuzzy controller has very powerful performance to unstable nonlinear unicycle robot system.

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Effects of Dual Task Training on Balance and Functional Performance in High School Soccer Players with Functional Ankle Instability

  • Kwak, Kwang-Il;Choi, Bum-Jin
    • The Journal of Korean Physical Therapy
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    • v.28 no.4
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    • pp.254-258
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    • 2016
  • Purpose: This study was conducted to identify the effects of dual task training on balance and functional performance in high school soccer players with functional ankle instability. Methods: Twenty high school soccer players with functional ankle instability were randomly assigned to a single task training group and a dual task training group. One participant who did not participate regularly in the training was excluded. The single task training group (n=9) received balance training on an unstable surface. The dual task training group (n=10) received balance training on an unstable surface and had to catch thrown balls during the balance training. Both groups were trained for 4 weeks, 3 days a week. The balance and functional performance of both groups was measured before and after training. Balance was measured using an anterior-posterior and medio-lateral balance. Functional performance was measured based on a figure-of-8 hop test, up-down hop test, and a single hop test. All data were analyzed by repeated two-way ANOVA tests. Results: A time by group interaction effect was not observed in the medio-lateral balance test, figure-of-8 hop test, or single hop test (p>0.05). A time by group interaction effect was observed in the anterior-posterior balance and up-down hop test (p<0.05). Conclusion: These results suggest that dual task training improved balance and functional performance better than single task training for some items.

Autopilot gain adjustment for flight control system with limiter (제한기가 있는 비행제어시스템의 자동조종 알고리듬 이득 조정)

  • 최동균;유재종;김종환
    • 제어로봇시스템학회:학술대회논문집
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    • 1997.10a
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    • pp.1864-1866
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    • 1997
  • Uncertainties in the aerodynamic coefficients or time delay effects in implementing an autopilot algorithm can make a Flight Control System(FCS) unstable. When a FCS enters unstable state, the actuator or sensor limiters in FCS make the unstable system not diverge but be in the state of stable limit cycle. If an autopilot recognize the FCS to be in the stable limit cycle phenomenon, it woudl be better to adjust autopilot gains to stabilize the FCS. A novel method to stabilize a FCS using parameter estimation and maintenance of given phase margin is proposed. The method is applied to roll control loop and verified its performance.

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Visualization of Electro-osmotic Flow Instability in a T-shape Microchannel (T자형 마이크로 채널 내부 전기삼투 유동의 불안정성 가시화)

  • Han, Su-Dong;Lee, Sang-Joon
    • Journal of the Korean Society of Visualization
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    • v.3 no.2
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    • pp.45-50
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    • 2005
  • Electro-osmotic flow (EOF) instability in a microchannel has been experimentally investigated using a micro-PIV system. The micro-PIV system consisting of a two-head Nd:Yag laser and cooled CCD camera was used to measure instantaneous velocity fields and vorticity contours of the EOF instability in a T-shape glass microchannel. The electrokinetic flow instability occurs in the presence of electric conductivity gradients. Charge accumulation at the interface of conductivity gradients leads to electric body forces, driving the coupled flow and electric field into an unstable dynamics. The threshold electric field above which the flow becomes unstable and rapid mixing occurs is about 1000V/cm. As the electric field increases, the flow pattern becomes unstable and vortical motion is enhanced. This kind of instability is a key factor limiting the robust performance of complex electrokinetic bio-analytical devices, but can also be used for rapid mixing and effective flow control fer micro-scale bio-chips.

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CONSIDERATIONS CONCERNING IMPROVEMENT OF EMERGENCY EVASION PERFORMANCE

  • Nozaki, H.
    • International Journal of Automotive Technology
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    • v.7 no.2
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    • pp.187-193
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    • 2006
  • When emergency evasion during running is required, a driver sometimes causes a vehicle to drift, that is, a condition in which the rear wheels skid due to rapid steering. Under such conditions, the vehicle enters a very unstable state and often becomes uncontrollable. An unstable state of the vehicle induced by rapid steering was simulated and the effect of differential steering assistance was examined. Results indicate that, in emergency evasion while cornering and during which the vehicle begins to drift, unstable behavior like spins can be avoided by differential steering assistance and both the stability and control of the vehicle is improved remarkably. In addition, reduction of overshoot during spin evasion by the differential steering assistance has been shown to enable the vehicle to return to a state of stability in a short time in emergency evasion during straight-line running. Moreover, the effectiveness of differential steering assistance during emergency evasion was confirmed using a driving simulator.

A Study on Unsteady Flow and Movement around a Check Valve in a Scroll Compressor (스크롤 압축기 밸브주변의 비정상유동과 밸브거동에 관한 연구)

  • Lee, Jin-Kab;Rew, Ho-Seon
    • The KSFM Journal of Fluid Machinery
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    • v.2 no.1 s.2
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    • pp.108-113
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    • 1999
  • In a scroll compressor it is generally accepted that a check valve is necessary to prevent reverse rotation of the scrolls. The check valve is subjected to discharge pulsations and their resultant forces. The flow phenomena around the check valve may affect the efficiency and the noise level significantly. The motivation of this study is to understand the flow phenomena and the unstable motion of the check valve on operating conditions in order to identify reasons raising noise and improve the performance of the check valve. In this study, unsteady flow simulation was performed using CFD and the pressure distribution around the check valve was obtained. This paper also shows that unstable motion of the check valve on standard operating conditions through theoretical analysis and flow visualization.

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Stabilization Control Method Development for Single Axis Unstable System Using SGCMG (SGCMG를 이용한 단축 불안정 시스템의 안정화 제어 기법 개발)

  • Lee, Junsik;Yi, Junyong;Yoo, Jihoon;Kim, Jichul;Cheon, Dongik;Oh, Hwa-Suk
    • Journal of Aerospace System Engineering
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    • v.7 no.4
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    • pp.12-17
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    • 2013
  • Control Moment Gyroscope(CMG) is one of the most efficient momentum exchange devices for satellite attitude control and essential device for agile maneuver system. This paper presents the details of a designed Single Gimbal CMG with a constant speed momentum wheel and single axis attitude control unstable to stable. In order to keep the naturally unstable equivalent point, it should be controlling the gimbal constantly. The experimental data are compared with theoretical result and requirements are used to verify their performance specifications.