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Constrained Doubly Coprime Factorization for All Stabilizing $\mathfrak{H}_{\infty}$ Controllers
Kim, Junghoon,Yim, Jongguk,Choi, Youngjin 제어로봇시스템학회 2014 Transaction on control, automation and systems eng Vol.12 No.3
The conventional Youla parameterization (equivalently Q-Parameterization) approach to solve $\mathfrak{H}_{\infty}$ optimal control problems requires solving the well-known matrix dilation optimization as a method for satisfying the $\mathfrak{H}_{\infty}$-norm constraint of the closed-loop transfer matrix. As an alternative, this paper presents a constrained doubly coprime factorization so that the $\mathfrak{H}_{\infty}$-norm constraint of the closed-loop transfer matrix can be satisfied without the need for matrix dilation optimization. For a given $\mathfrak{H}_{\infty}$-norm constraint, a constrained plant is suggested from a state estimator that includes the worst-case disturbance and estimation effects. Then, the constrained doubly coprime factorization is derived from the constrained plant model. All the stabilizing $\mathfrak{H}_{\infty}$ controllers are expressed by using the constrained coprime factors. Finally, an application example is provided to demonstrate the effectiveness of the proposed method.
Robust control using recursive design method for flexible joint robot manipulators
Je Sung Yeon,Jongguk Yim,박종현 대한기계학회 2011 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.25 No.12
A flexible joint robot manipulator can be regarded as a cascade of two subsystems: link dynamics and the motor dynamics. Using this structural characteristic, we propose a robust nonlinear recursive control method for flexible manipulators. The recursive design is done in two steps. First, a fictitious robust control for the link dynamics is designed as if it has a direct control input. As the fictitious control, a nonlinear H∞ -control using energy dissipation is designed in the sense of L_2-gain attenuation from the disturbance caused by uncertainties to performance. In the process, Hamilton-Jacobi (HJ) inequality is solved by a more tractable nonlinear matrix inequality (NLMI) method. In the second step, the other fictitious and the actual robust control are designed recursively by using the Lyapunov’s second method. The proposed robust control is applied to a two-link robot manipulator with flexible joints in computer simulations. The simulation results show that the proposed robust control has robustness to the model uncertainty caused by changes in the link inertia and the joint stiffness.
Human Shoulder Motion Extraction Using EMG Signals
Jang, Giho,Kim, Junghoon,Choi, Youngjin,Yim, Jongguk Korean Society for Precision Engineering 2014 International Journal of Precision Engineering and Vol.15 No.10
This paper suggests a joint angle extraction method for shoulder flexion movement in a sagittal body plane. Surface electromyogram (EMG) signals measured at trapezius muscle are utilized for joint angle extraction in real-time. The relationship between the shoulder motion and the measured EMG signal can be modeled using a spring-damper pendulum model. In the suggested model, the EMG signal is described as the function of the shoulder flexion joint angle and its derivative with dynamic model parameters. In pre-processing procedures, the raw EMG signals are processed by taking root mean square (RMS) and filtering out noises with low-pass filter (LPF). Also, the model parameters are determined through an optimization for the measured EMG signals and their corresponding real joint angles measured from vision tracker system. A part of the model parameters are modified with two different slopes when the shoulder joint angle exceeds 90 degrees. For the main procedures, the moving average filter-based model dynamics is implemented to extract the shoulder angle, here, the moving average filtering is performed with the varying window size to reduce the oscillations of the EMG signals caused by the muscle fatigue. Finally, we show the effectiveness the suggested method through several experiments.