• International Journal of Precision Engineering and Manufacturing
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• v.1 no.2
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• pp.24-34
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• 2000

In this paper we propose a controller design method, called Quasi-LQG/$H_{\infty}$/LTR for nonlinear servo systems with hard nonlinearities such as Coulomb friction, dead-zone. Introducing the RIDF method to model Coulomb friction and dead-zone, the statistically linearized system is built. Then, we consider $H_{\infty}$ performance constraint for the optimization of statistically linearized systems, by replacing a covariance Lyapunov equation into a modified Riccati equation of which solution leads to an upper bound of the LQG performance. As a result, the nonlinear correction term is included in coupled Riccati equation, which is generally very difficult to thave a numerical solution. To solve this problem, we use the modified loop shaping technique and show some analytic proofs on LTR condition. Finally, the Quasi-LQG/$H_{\infty}$/LTR controller for a nonlinear system is synthesized by inverse random input describing function techniques (ITIDF). It is shown that the proposed design method has a better performance robustness to the hard nonlinearity than LQG/$H_{\infty}$/LTR method via simulations and experiments for the timing-belt driving servo system that contains the Coulomb friction and dead-zone.

• Journal of Institute of Control, Robotics and Systems
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• v.20 no.12
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• pp.1209-1216
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• 2014

This paper copes with control design for unmanned aerial vehicle transportation system. Moving pendulum dynamics of slung-load system is derived using two methods: Udwadia-Kalaba equation and Newtonian approach. PID controller is applied to Udwadia-Kalaba equation model for structural consistency and linear quadratic Gaussian / Loop Transfer Recovery (LQG/LTR) technique is employed for Newtonian model with minimal state-space realization. Characteristics of PID and LQG/LTR controller are compared, and two controllers are combined to compensate the drawbacks of each other. Numerical simulation is set for two cases and conducted to evaluate performance of designed controllers. The result proves that combination of LQG/LTR and PID control performs stable and robust.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.24 no.4
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• pp.414-420
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• 2015

In this study, the linear quadratic Guassian loop transfer recovery (LQG/LTR) control technique was combined with an integrator and applied to an inchworm having piezoelectric actuators for precise motion tracking. The piezoelectric actuator showed nonlinear response characteristics, including hysteresis, due to its ferroelectric characteristics and the residual displacement phenomenon. This paper proposes a feedback control scheme using the LQG/LTR controller with an integrator to improve the ability to track the response to complex input signals and to suppress the phenomenon of hysteresis and residual vibration. Experimental results show that the developed feedback control system for an inchworm can track the various motion contours quickly without residual vibration or overshoot.

• 제어로봇시스템학회:학술대회논문집
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• 1986.10a
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• pp.503-505
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• 1986

주어진 제어대상 모델에 대하여 제어기를 구성하여 실제로 적용하는 경우 모델의 불일치, 모델링에서 고려하지 않은 외란(disturbance), 측정잡음등에 의하여 성능이 설계시와 달라진다. 실제적용에서도 성능을 계속 유지하기 위하여 제어기는 안정성, 계수변화(parameter variation)에 대한 강인성(robustness), 외란상쇄(disturbance rejection) 및 측정잡음에 둔감함등의 특성을 가져야 한다. 귀환(feedback)을 사용하여 제어기를 구성하는 경우 위의 모든 조건을 만족 시킬 수 없으므로 제어목적에 따라 적당한 조건을 선정하여 중요한 특성을 주로 갖게 한다. 본 논문에서는 쌍동선(small waterplane area twin hull ship-SWATHS)에 대하여 PID, LQ, LQG 제어기를 구성하여 안정성, 계수 변화에 대한 강인성, 외란 상쇄 및 측정잡음의 영향을 비교하였다. 쌍동선의 경우 다른 단동선(mono hull ship)에 비하여 접수면(waterplane)이 적으므로 무게증변을 흡수할 수 있는 복원력이 약하여 적은 외력에도 상하동요(heave)와 종동요(pitch)가 심하게 일어난다. 이러한 동요를 줄이는 것이 쌍동선의 제어목적이다. 본 연구에서는 먼저 선형화된 수직축 운동방정식을 이용하여 선체운동의 모델을 구했으며 중첩의 원리(super-position theorem)에 의하여 주파수 응답의 합으로 파도입력을 모델링 하였으며 제어를 위하여 필요한 측정치는 IMU(Inertial Measurement Unit)에서 제공된다고 가정하였다. 쌍동선의 동요의 원인은 파도, 바람, 조류 등이 있으나 파도에 의한 영향이 가장 크므로 본 논문에서는 파도에 의한 영향만을 고려하였다. 파도는 쌍동선에 외란으로 작용하며 측정할 수 없는 양이므로 PID, LQ 제어에서는 제어모델에 포함되지 않지만 LQG 제어에서는 제어모델에 포함된다. LQG 제어의 경우 제어모델에 파도를 백색잡음으로 가정하고 제어기를 구성한 것 (LQG1)과 2차의 쉐이핑필터(shaping filter)를 사용하여 구성한 것(LQG2)으로 나누었다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.5
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• pp.65-73
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• 2008

Retaining large stability margin is essential in designing a feedback control system to deal with the uncertainties inherently existing in the mathematical model and the control apparatus. The LQG controller in general loses the stability margin due to the embed Kalman filter. The performance of a control system called LTR with a DUOX structure(LTR/DOUX) to overcome the demerit of LQG controller is to be investigated from the responses in both the time and the frequency domain. The results indicated that the LTR/DOUX recovered the gain margin of 30dB approximately 20 times more than that of LQG/DOUX, resulting in a robust stable control system.

• Structural Engineering and Mechanics
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• v.83 no.1
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• pp.93-108
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• 2022

Real-time hybrid simulation (RTHS) was applied to investigate the train-bridge interaction of a high-speed railway system, where the railway bridge was selected as the numerical substructure, and the train was physically tested. The interaction between the two substructures was reproduced by a servo-hydraulic shaking table. To accurately reproduce the high-frequency interaction responses ranging from 10-25Hz using the hydraulic shaking table with an inherent delay of 6-50ms, an adaptive time series (ATS) compensation algorithm combined with the linear quadratic Gaussian (LQG) was proposed and implemented in the RTHS. Testing cases considering different train speeds, track irregularities, bridge girder cross-sections, and track settlements featuring a wide range of frequency contents were conducted. The performance of the proposed ATS+LQG delay compensation method was compared to the ATS method and RTHS without any compensation in terms of residual time delays and root mean square errors between commands and responses. The effectiveness of the ATS+LQG method to compensate time delay in RTHS with high-frequency responses was demonstrated and the proposed ATS+LQG method outperformed the ATS method in yielding more accurate responses with less residual time delays.

• 제어로봇시스템학회:학술대회논문집
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• 1993.10a
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• pp.491-497
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• 1993

In MIMO design, input and output units are different from each other. By this reason, the effect of larger units to smaller one is not trivial and there is no method of proper scaling, optimal scaling. In this paper, robust stability of MIMO LQG/LTR design are analised when the plnat inputs and outputs are scalled. The upper bound of model error to guarantee the robust stability is obtained, and gain margin and phase margins are computed with respect to scalling matrices.

• Proceedings of the KIEE Conference
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• 1989.07a
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• pp.121-124
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• 1989

In this thesis, a decomposed LQG/LTR controller is designed for an undersea vehicle. The modellig error which results from decomposition of the original model is considered to the design specification for maintaining the robust stability. The LQG/LTR controller designed with new specification is simulated.

• Proceedings of the KIEE Conference
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• 1992.07a
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• pp.279-281
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• 1992

In this paper, an LQG/LTR procedure for stable nonminimum phase systems is suggested using predictor scheme. In the method, the performance of the target feedback loop can be easily adjusted and the recovery error is less dependent on the location of NMP zeros than previous methods. The gain and phase margin and the robust ness for modeluncertainty of the suggested control system are obtained.

• 제어로봇시스템학회:학술대회논문집
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• 1991.10a
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• pp.191-196
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• 1991

LQG/LTR method have a theoretical constraint that it cannot applied to nonminimum phase plant. In this paper, we suggest two methods of approximation of minimum phase plant for a given nonminimum phase plant to solve this constraint. Error is described by additive form which can reduce its magnitude in broad frequency range. A optimal approximation method was suggesetd by using Hankel operator theory and Nehari theory. It is showen by example that the methods suggested can resolve the frequency domain constraint arised in Stein and Athans approximation.