Published papers

In this paper, we study a consensus control problem for resilient multi-agent systems considering leader failure. We present cooperative control to solve the formation problem, enabling the agents to maintain relative positions even if any agent, including the leader, malfunctions. To accomplish this goal, we designed an algorithm that implements distributed observers for fault detection to assess each agent's reliability. The algorithm reduces the effect of faults by limiting information exchange with low-reliability agents. Next, we extended the adjacency matrix so that any follower can replace the leader in response to the leader's failure. Finally, we verify the proposed method through simulations.

This paper deals with μ-synthesis of an electromagnetic suspension system. First, an issue of modeling a real physical electromagnetic suspension system is discussed. We derive a nominal model as well as a set of models in which the real system is assumed to reside. Different model structures and possible model parameter values are fully employed to determine unstructured additive plant perturbations, which directly yield uncertainty frequency weighting function. Second, based on the set of plant models, we setup robust performance control objectives. Third, we make use of the D-K iteration approach for the controller design. Finally, implementing the controller with a digital signal processor, experiments are carried out. With these experimental results, we show robust performance of the designed control system.

An active magnetic bearing (AMB) is a bearing used to suspend a rotor by magnetic forces without any contact. Feedback control is indispensable for a magnetic bearing, because it is essentially an unstable system. To design a feedback control system, a linear mathematical model of the plant is convenient; however, the force of the electromagnet is highly nonlinear. Thus, usually a linear approximation around the operating point is employed, but the obtained linearized model cannot express the exact behavior of the system at any other operating points. In this paper, we discuss the wide area stabilization of magnetic bearings using the exact linearization approach. First, we derive a nonlinear mathematical model for a magnetic bearing, then we show that this nonlinear system belongs to a class of exactly linearizable nonlinear systems. Next, by using the exact linearization method, we transfer the nonlinear model of a magnetic bearing to a linear time-invariant state model in spite of change of the operating point and the rotational speed of the rotor. Then we construct the state feedback control system by the conventional LQ method. Finally, we evaluate the validity of our proposed method by experiments.

This paper deals with uncertain model structures, model validation and robust performance analysis of active magnetic bearing systems. The dynamics of active magnetic bearing systems are characterized by their instability and complex dynamics of rotor and electromagnets. One of the most critical problems of AMBs is a description of a complex behavior of the dynamics of electromagnets and their forces. The exact description of them is almost hopeless, some approximations and assumptions must be employed, and consequently a discrepancy between the real physical system and the nominal design model cannot be avoided. This discrepancy of the magnetic bearing systems is a serious problem of stability and performance. Hence feedback control is indispensable to stabilize the system, further the closed-loop systems of AMBs should have robustness for stability and performance against model uncertainties. First we derive a nominal mathematical model of AMBs as a linear state-space model under some assumption and idealization, then we consider the discrepancy between the real physical systems and the obtained nominal design model. This discrepancy can be expressed as the structured uncertainties by Linear Fractional Transformation. These uncertainties include linearization error, parametric uncertainties, unmodeled dynamics, and gyroscopic effect. Then we set the interconnection structure which contains the above structurally represented uncertainties. Next we design a robust controller which achieves robust performance condition. Finally, we validate the interconnection structure with the nominal model and uncertainties, and analyze the robustness of stability and performance of the closed-loop system via the mixed structured singular value.

This paper deals with an H-infinity control attenuating initial-state uncertainties, and its application to a magnetic suspension system. An H-infinity control problem, which treats a mixed attenuation of disturbance and initial-state uncertainty for linear time-invariant systems in the infinite-horizon case, is examined. The mixed attenuation supplies H-infinity controls with good transients or assures H-infinity controls of robustness against initial-state uncertainty. We apply this method to a magnetic suspension system, and evaluate attenuation property of the proposed disturbance and initial-state uncertainty via simulations and experiments.

本論文はフォードバック線形化を用いた非線形磁気浮上系のH∞制御のロバスト性と脆弱性に関して議論している．モデリング検証のため，まず２つの仮定に基づいて２つの非線形モデルを導出し，それぞれにフィードバック線形化H∞コントローラを設計した．つぎにこれらのコントローラを用いてステップ状の力外乱が浮上体に加わった場合の浮上体の位置情報を計測し，ロバスト性，さらにモデル構造に起因する脆弱性に関して検証と考察を行った．

This paper deals with uncertain model structures, model validation and robust performance analysis of active magnetic bearings. The dynamics of active magnetic bearing systems are characterized by their instability and complex dynamics of rotor and electromagnets. The feedback control is indispensable to stabilize the system, further the closed-loop systems of magnetic bearings should have robustness for stability and performance against model uncertainties. First we derive a nominal mathematical model of AMBs as a linear state-space model under some assumption and idealization, then we consider the discrepancy between the real physical systems and the obtained nominal design model. This discrepancy can be expressed as the structured uncertainties by Linear Fractional Transformation. These uncertainties include linearization error, parametric uncertainties, unmodeled dynamics, and gyroscopic effect. Then we set the interconnection structure which contains the above structurally represented uncertainties. Next we design a robust controller which achieves robust performance condition. Finally, we validate the interconnection structure with the nominal model and uncertainties, and analyze the robustness of stability and performance of the closed-loop system via the mixed structured singular value.

This paper deals With a generalized H-infinity control attenuating initial-state uncertainties. An H-infinity control problem, which treats a mixed attenuation of disturbance and initial-state uncertainty for linear time-invariant systems in the infinite-horizon case, is examined. The mixed attenuation supplies H-infinity controls with good-transients and assures H-infinity controls of robustness against initial-state uncertainty. We derive a necessary and sufficient condition of the generalized mixed attenuation problem. Furthermore we apply this proposed method to a magnetic suspension system, and evaluate attenuation property of the proposed generalized H (infinity) control approach.

This paper deals with H∞ control attenuating initial-state uncertainties, and its application to a magnetic suspension system. H∞ control problem, which treats as a mixed attenuation of disturbance and initial-state uncertainty for linear time-invariant systems in the infinite-horizon case, is examined. The mixed attenuation supplies H∞ controls with good transients and assures H∞ controls of robustness against initial-state uncertainty. We apply this method to a magnetic suspension system, and evaluate attenuation property of the proposed disturbance and initial-state uncertainty via simulations and experiments. © 2003, The Institute of Electrical Engineers of Japan. All rights reserved.

本稿では従来の結果から直交条件を外して，外乱と初期状態の不確かさの混合減衰無限時間区間H∞制御問題を定式化し，解の存在のための必要十分条件を導出する．さらに，可解条件だけでなく，補償器の1つの厳密な構成法も導出する．また提案手法を実際に磁気浮上システムに適用し，制御系の設計，および数値シミュレーションを行った．結果を従来法と比較することにより，過渡応答特性に関する提案手法の有用性を示した．

This paper deals with robust control of a master-slave teleoperation robotic system considering environmental uncertainties. We construct a master-slave system by using two 2-DOF Direct Drive robot manipulators and design a robust control system via impedance shaping and mu-Synthesis considering various uncertainties; e.g., environment and operator dynamics, perturbation of impedance model and time delay in telecommunications. The proposed control methodology can guarantee the robust stability and the robust performance for all these uncertainties of the master-slave robotic system. Several experimental results show the effectiveness of our proposed approach for various environmental uncertainties.

This paper deals with an H(infinity) DIA control system design of a magnetic bearing considering periodic disturbance. R. control problem which treats a mixed Disturbance and an Initial state uncertainty Attenuation (DIA) control is expected to provide a good transient property, and we confirmed that DIA control has a good rotational performance by some experiments. On the other hand, active magnetic bearings allow contact free suspension of rotors and they are used for various industrial purposes. We derive a mathematical model of the magnetic bearing which has complicated rotor dynamics and nonlinear magnetic property. In this paper, we propose a modified control system design of R DIA control in order to consider the periodic disturbance for the magnetic bearings. In fact, we get a controller taken a peak at specified frequency by adding a frequency weighting function in generalized plant. Experimental results show that the proposed robust control approach is effective for improving rotational performance.

本研究では初期状態の不確かさのもとで良好な過渡応答特性とロバスト制御性能を達成するために，H∞DIA制御にロバスト制御性 能を付加するμ-シンセシスの適用を提案する．具体的にはD-KイテレーションにH∞DIA制御を適用したμ-シンセシスを構築することにより所望の性能を有する制御系の設計が期待できる．従来法と比較することにより提案手法が良好な過渡応答特性とロバスト制御性能を示すことを制御実験により確認する．

This paper deals with the passivity-based synchronized control of teleoperation considering position tracking and power scaling. In the proposed method, the motion and the force relation between the master and slave robots can be specified freely. Using a passivity of the systems and Lyapunov stability methods, the asymptotic stability of teleoperation with communication delay and power scaling is proven. Several experimental results show the effectiveness of our proposed method.

This paper deals with a high performance and robust control scheme based on Generalized Internal Model Control(GIMC) Structure. We apply the GIMC structure to the unstable magnetic suspension system and construct a high performance and robust control system. GIMC structure can switch two controllers which have high performance and high robustness respectively. The two controllers using in GIMC structure are designed via H-infinity mixed sensitivity problem. The experimental results show the effectiveness of GIMC structure.

This paper deals with a passivity-based approach to wide area stabilization of magnetic suspension systems. It is well known that the magnetic suspension systems have strong nonlinearity. In order to realize wide area stabilization of magnetic suspension systems, we design the passivity-based feedback controller considering a nonlinear dynamics of the magnetic suspension systems and a leakage inductance of the electromagnet especially. The systems can be decomposed two subsystems; an electrical subsystem and a mechanical subsystem. We design nonlinear passivity-based controllers for both two subsystems. Steady-state and transient time responses results for some operating points show the effectiveness of the proposed controller experimentally.

本研究では二輪車を静止状態に限定し，この状態で安定化できる自立走行二輪車を提案する．ライダの重心移動に相当する台車系とハンドル操作系を備えた小型の二輪車を構成する．制御系設計に必要なモデルの運動方程式は，Lagrange 法により導出する．得られた線形モデルに対する安定化制御器をH∞ループ整形設計手法を用いて設計し，姿勢制御実験を行うことにより提案する自立走行二輪車のモデリングとロバスト姿勢制御系について検証を行なう．