Demands for high-performance vibration isolation and oscillation suppression systems have been increasing in various scientific and industrial fields such as high-precision control, semiconductor manufacturing and so on. There are two kinds of vibration to be reduced by a vibration isolation system. One is the vibration transmitted from ground or support point through the path of its post. The other is an impact caused by disturbance acting directly on the workspace. Lower stiffness of supporting suspension is better to reduce the former oscillation effects, such as automobile suspensions, while elimination of direct disturbance, later one, needs higher stiffness. Therefore, simultaneous suppression of both of base and direct disturbance effects on a workspace conflicts and requires a tradeoff between them. Conventional passive-type oscillation systems are composed of spring and dampers. Once, they are tuned, namely spring and damper parameters determined, their structure couldn't be changed anymore. This results degradation of suppression performance when the operation conditions are changed. In contrast to passive one, active-type oscillation suppression systems can modify their structure effectively when operation conditions are varied. Therefore, active type systems can easily break through this conflict.

Moreover, in the course of active vibration isolation, power consumption for control action and cost of sensors are significant problems to be solved effectively. Introduction of levitating electromagnets as actuators has some merits over the other candidate actuator types.

Contact free operation

No abrasion

Only electrical power source necessity

Suitability for some special applications such as clean room requirements.

Integration of permanent magnets into the magnet structure does not only decrease electrical power consumption but also brings about considerably reduced magnet size. From this point of views, in this study, an active vibration system utilizing hybrid electromagnets as actuators have been considered.

Prof. Mizuno proposed that controlling a hybrid electromagnet in zero power control mode could give naturally negative stiffness contrary to normal spring when external force applied to a hybrid electromagnet. Furthermore, his idea has been revealing that serial connection of negative stiffness element with mechanical spring can turn into infinite stiffness by which eliminates both of the disturbance effects on the workspace. This idea has some pitfalls in the sense of practical realization.

Perfect equalization of negative stiffness of electromagnet with a spring might not be easy and practical every time.

Additional dynamics such as damper and a second mass would be introduced to the system. So that the system performance degrades from ideal one.

Electromagnet's nonlinearly has dominant effect when the gap length of the electromagnet takes values far away from linearization point.

To cure these pitfalls and also guaranty the system stability, in this research, gap length type servo control has been proposed. Summary, if the gap clearance of electromagnet tracks displacement of passive elements, constraint of negative and positive stiffness is automatically obtained. Maglev based actuators have substantial nonlinear features; therefore, stability must be assured. To improve the stability of such a system fuzzy-based control design procedure has been proposed, accordingly. Furthermore, to satisfy full redundancy multiple-arrangement of the electromagnets has been investigated in the form of several configrations. Outline of the dissertation as follows.

Chapter one introduces the fundamental ideas and gives a brief sketch about current techniques of oscillation suppression.

Chapter two investigates some important topologies of active oscillation suppression systems employing electromagnets as actuator and develops a mathematical model for triple star configuration of electromagnets in conjunction with passive elements.

Chapter three explains fundamental controller and observer design approaches on the basis of linear control theory.

Chapter four outlines fuzzy control approach in order to eliminate the drawbacks of linear counterpart.

Chapter five confirms effectiveness of the proposed servo control based on fuzzy approach by simulation studies.

Chapter six describes basics of the experimental test bench and furthermore releases experimental results supporting that the proposed idea of oscillation suppression is experimentally effective and plausible.

Chapter seven draws some significant conclusion on the dissertation and shows future prospects.

本論文は，「Fuzzy-Based Nonlinear Stabilizing Levitation Control of Multiple Electromagnets as Servo Actuators for Active Oscillation Suppression of Mechanically Flexible Structure　（弾性構造物能動的振動抑制のサーボ駆動のための多自由度浮上電磁石のファジー理論を用いた非線形安定化制御）」と題し，機械的振動の磁気浮上を用いた能動的抑制制御を検討したもので，全体で7章からなる．

第1章は，振動抑制とその応用，およびそのための制御技術の先行研究を概観し，その中での磁気浮上制御技術の有用性を説明して，本研究の位置付けを行っている．

第2章では，受動的機械要素と多自由度磁気浮上系を組み合わせることで，振動抑制能動制御を行う方式を提案し，その原理，基本構成，運動方程式と先行研究の成果に基づく磁気浮上安定化制御の基本的考え方を説明している．

第3章では，磁気力特性の線形近似に基づく各種制御法とその得失，使用可能なセンサの種類や数が限定される際の可観測性と状態推定性能など，振動抑制のアクチュエータとして用いる磁気浮上系の制御に関する理論を述べている。そして，ゼロパワー磁気浮上を用いた振動抑制と，受動的機械要素の変位情報を用いた浮上ギャップ長のサーボ制御による振動抑制の比較を，数値計算に基づく性能評価を通じ詳しく論じている．

第4章では，前章の平衡点近傍における磁気浮上の基本的な安定化制御に加え，サーボアクチュエータとしてギャップを変化させて用いる目的では磁気力の非線形性を考慮した制御が必要となることを述べている．この磁気力の非線形性を少ない点数の同定結果から効率よくモデル化し，浮上安定化制御器のゲイン調整を系統的に行う手法としてTakagi-Sugeno-Kang形のファジー制御を用いることとし，その理論を概説すると同時に本論文の対象への適用方法を説明し，安定性判別の手法にも言及している．

第5章では，実験系の設計の予備検討および4章の理論の実証として動的な数値計算に基づきオブザーバとファジー制御を組み合わせる方法の記述と，その制御の性能，外乱抑制効果の評価を行っている．

第6章では，これまで述べてきた制御方式の実証のため，主要部の位置関係がセンサ情報として得られる条件で試験機を製作した．これを用いて、構造的に機械振動を容易に起こす系における浮上安定化制御を実現すると共に，磁気浮上系のギャップを積極的に変動させて振動抑制を能動的に行う提案方法の有効性を，測定を通じて実証している．

第7章は，「まとめ」であり，本論文で得られた成果をまとめると共に，今後の技術課題について述べている．

以上を要するに，本論文は，大きなギャップ変動を許容するため非線形特性が顕著に現れる磁気浮上系の安定化制御を，ファジー理論を応用して実現し，実現された磁気浮上系をアクチュエータとして用い，ギャップ長を受動的機械要素の変位情報に基づきサーボ制御することで能動的振動抑制を行う方法を提案し，弾性懸架支持された磁性体のテーブルに対向した三自由度浮上磁石への応用実験を通じてその実現可能性を示したもので，今後の電気工学の進展に寄与するところが少なくない．

よって本論文は博士（工学）の学位請求論文として合格と認められる．