Published papers

In surgical robots, compact manipulators with multi-degree-of-freedom (DOF) are essential owing to a small work volume in the patient body. Conventional single-DOF actuators such as electromagnetic motors require a multiple number of actuators to generate multi-DOF motion, which in turn results in bulky mechanism combined with transmission device. Our previous work has developed a compact ultrasonic motor capable of generating a multi-DOF rotation of a spherical rotor utilizing three natural vibration modes of a bar-shaped stator. The present study designs and builds a novel multi-DOF master-slave system for laparoscopic surgical procedures, using a single ultrasonic actuator. The system consists of surgical forceps on multi-DOF wrist with joystick controller. Experimental results have confirmed high responsiveness and precise position control of the master-slave system.

従来の多自由度超音波モータの多くは，複数の固有振動モードの固有振動数を縮退させ，これらの組み合わせによって回転子の多自由度運動を実現していた．しかし，振動設計が複雑となるため，実用上問題が多かった．本研究では，複数の振動子をマトリクス状に配置し，固有振動数が異なる複数の固有振動モードを選択的に組み合わせることによって振動子マトリクス上に置かれた移動子に多自由度運動を生成する新たな多自由度超音波モータを開発した．

マイクロロボットハンドなどの微小な機械システムでは，スケール効果によって摺動部などでの損失の影響が増大するため，一般的な機能要素を用いた設計には限界がある．このため，本研究では関節に弾性ヒンジを用いた5指マイクロロボットハンドを開発した．本ハンドはワイヤ駆動によってヒト指と同様にMP，PIP，DIP関節を駆動する構成である．弾性ヒンジの利用によって，摺動損失の低減およびスペース効率の向上を実現した．

A robot finger is developed for five-fingered robot hand having equal number of DOF to human hand. The robot hand is driven by a new method proposed by authors using ultrasonic motors and elastic elements. The method utilizes restoring force of elastic element as driving power for grasping an object, so that the hand can perform the soft and stable grasping motion with no power supply. In addition, all the components are placed inside the hand thanks to the ultrasonic motors with compact size and high torque at low speed. Applying the driving method to multi-DOF mechanism, a robot index finger is designed and implemented It has equal number of joints and DOF to human index finger, and it is also equal in size to the finger of average adult male. The performance of the robot finger is confirmed by fundamental driving test.

A novel multi-fingered exoskeleton haptic device using passive force feedback has been proposed by the authors. The haptic device solves the conventional problems of previously developed master-slave systems with force feedback, such as oscillations, complex structures and complicated control algorithm. However some problems still remain in the conventional passive elements. In the present paper an ultrasonic clutch for multi-fingered exoskeleton haptic device with passive force feedback function is developed. The ultrasonic clutch can solve problems of conventional passive elements, such as time delay, instability, and large size, by using unique characteristics of ultrasonic motor as fast response, silent motion, and non-magnetic feature. It can also be designed to be smaller than conventional elements due to its simple structure. The clutch locks or releases the rotor by use of ultrasonic levitation phenomenon. First, we have designed the structure of the ultrasonic clutch using an equation of ultrasonic levitation phenomenon, results from structural analysis and finite element (FE) analysis of piezoelectric material of the vibrator Then we have manufactured the ultrasonic clutch and have conducted a driving experiment. Finally, we have demonstrated that the maximum levitation force is around 20 N and the static friction torque of the ultrasonic clutch is up to 0.14 Nm.

In this paper we analyze the mechanical characteristics of the single-phase-drive type ultrasonic motors. Though single-phase-drive type ultrasonic motors (USMs) has many merits against the multi-phase-drive type USMs, the research of them are not popular and the design method is not established yet. We simulated the static driving characteristics of the single-phase-drive type USM and cleared up the relationship between design parameters and T-N curve, output power and frictional efficiency. Finally we will show the adequacy of the simulations by conducting the driving tests.

In the present paper, a newly developed ultrasonic clutch is proposed. The ultrasonic clutch can solve problems of conventional passive elements, such as time delay, instability, and large size, by using unique characteristics of ultrasonic motor, as fast response, silent motion, and non-magnetic feature. It can also be designed to be smaller than conventional elements due to its simple structure. The clutch locks or releases the rotor by use of ultrasonic levitation phenomenon. First, we have designed the structure of the ultrasonic clutch using an equation of ultrasonic levitation phenomenon, results from structural analysis and finite element (FE) analysis of piezoelectric material of the vibrator. Then we have manufactured the ultrasonic clutch and have conducted a driving experiment. Finally, we have demonstrated that the maximum levitation force is around 20 N and the static friction torque of the ultrasonic clutch is up to 0.14 Nm.

腹腔鏡下手術は腹部にあけた直径10mm以下の穴を介して鉗子および腹腔鏡を体内に挿入し腹腔鏡画像下で手術する低侵襲手術である．患者への負担が少ない代わりに術者には高いスキルが要求される．本研究では，球状回転子に直交3軸回りの多自由度回転を生成し得る多自由度超音波モータを用いて，鉗子先端に手首のような多自由度運動を実現する多自由度鉗子のプロトタイプを実現した．

Multi-DOF actuators have become more useful in the field of robotics, thanks to the increasing number of DOFs of systems. General features of ultrasonic motor are suitable for constructing a direct-drive multi-DOF actuator. However, those previously developed do not have advantages in volume and weight against the multi-DOF motion unit composed of several electromagnetic motors. In the present study authors develop a novel multi-DOF ultrasonic motor with a plate stator and a spherical rotor. First, a new driving principle of the motor is proposed. Next, the stator geometry is designed in detail using finite element method, and the prototype of the multi-DOF ultrasonic motor with plate stator is produced. The stator is relatively compact against the rotor. Then, vibration characteristics of the stator and driving characteristics of the motor have been measured respectively. The result confirms that the motor successfully provides the multi-DOF motion of rotor around orthogonal axes by single plate stator. Finally, self-oscillation driving circuit for the motor is proposed.

多自由度超音波モータは振動方向が互いに直交する3つの固有振動モードを組み合わせて球状回転子に任意軸回りの回転運動を生成する．すなわち，入力パラメータ7つに対して出力3つとなる冗長非線形性を有している．したがって，所望の駆動状態を実現するための入力の組み合わせは複数存在するため，超音波モータに対する経験的所見とニューラルネットワークによる非線形写像を組み合わせて，所望の駆動状態に対して唯一の入力を決定する逆モデルを提案し，これを用いて多自由度超音波モータの駆動制御を実現した．

機能性流体の一つである電界共役流体（ECF）に生じるジェット流の圧力により駆動される新たな駆動原理のマイクロアクチュエータを提案，試作し，この駆動特性を実験的に検討した．ブルドン管と同様の原理により駆動される本アクチュエータは，6 kV印加時に設計仕様1.8 mmの178 %の出力変位および2 mNの発生力を得た．このマイクロアクチュエータは，発生力は微小であるが，印加電圧により出力変位を制御できることから，マイクロミラーの微小位置決めなどへの応用が期待できる．

電界共役流体は直流高電圧の印加によって活発なジェット流を発生する．本流体を用いると，複数の微小な電極対を円筒チャンバ内に配置するだけで回転流を発生できる．本研究では，これに円盤を封入すると回転流によって浮揚，回転することを利用して，円盤とチャンバの相対角度から角速度を検出する新たなジャイロスコープを提案した．また，上記ジャイロスコープのプロトタイプを試作し，基礎的特性を明らかにした．

As a man-machine interaction increases its importance in robotics and mechatronics fields, a soft robot inspired from natural systems becomes one of the research trends. There are several research topics related to soft robots such as soft structures or artificial skins, compliance control, soft actuators or artificial muscles, and so on. For the natural muscle potentially has great flexibility, the authors believe the artificial muscle actuator must have a great potential in soft robots. Hence in this study we develop a new type of micro artificial muscle cell, which is an element of an integrated artificial muscle, using electro-conjugate fluid and measure its driving performances. In addition, position control characteristics are also clarified by experiments. As a result, the micro artificial muscle cell using electro-conjugate fluid shows quite good control performances.

本研究は，高電圧の印加によって活発なジェット流が生じる電界共役流体（ECF）を利用したECFマイクロジャイロスコープの実現を目的とした．はじめに，液体中の円盤を回転軸なしで浮揚，回転できるロータ径3mmおよび1.5mmのマイクロモータを実現し，回転特性を実験的に明らかにした．つぎに，上記のモータ全体に角速度が加わると浮揚円盤が傾くことを利用した新たなジャイロスコープを提案，試作した．

本研究では微小電極対によって高電圧を印加すると活発なジェット流を発生する電界共役流体（ECF）を利用したマイクロモータの微小化および作動流体の相違に伴う性能向上について検討した．すなわち，表面に放射状電極対を持つディスクプレート(DP)ロータを積層した内径5mmのDP形ECFマイクロモータを設計，試作し，駆動特性を実験により明らかにした．この結果，小型化により出力パワー密度が向上し，作動流体の違いにより出力パワー密度が約4.5倍に向上することが確認された．

This paper presents a novel type of multi degree-of-freedom ultrasonic motors. Today, in various fields, actuators having multi degrees-of-freedom is needed. In the past, many multi-degree-of-freedom actuators have been developed. However, they are all still large and heavy. Thus, we propose a miniature multi-degree-of-freedom actuator using plural single-phase-driven ultrasonic vibrators. A single-phase-driven ultrasonic motor is known for its miniaturizing facility. On the other hand, it is also known for its lack of output force. Therefore, we proposed to use plural single-phase-driven vibrators and also tried to make one vibrator generate great force. This motor has many small vibrators; each one having four patterns in the thrust direction. By controlling the frequency of each vibrator, we can obtain multiple movements of a movable object. First, we proposed the principles of this motor. Next, we selected vibration modes and designed the size of a vibrator to be 10 x 7.5 x 0.9 mm(3) using finite element analysis. Finally, we measured frequency, vibration, and driving characteristics of the vibrators. The maximum thrust was about 3.14 N and the maximum torque was about 6 mN-m.

We proposed a novel micro hand in which three kinds of soft actuators driven by ECF jet. The electro-conjugate fluid (ECF) Is, a dielectric fluid that works as a functional fluid, generating a powerful jet flow (ECF jet) when Subjected to high DC voltage. First, we have proposed an ECF micro artificial muscle Cell using ECF and integrated the cells. Second, we newly proposed and fabricated an ECF micro artificial antagonistic muscle, which consist of a pair of sleeve-type artificial muscles like. a McKibben type and a common tube. Finally, we proposed an ECF micro finger which is composed of two Fiber-reinforced soft tubes. The main advantage of the ECF soft actuator is tank and power source built-in.

An electro-conjugate fluid (ECF) is a kind of dielectric fluid that works as a functional/smart fluid generating a powerful jet flow (ECF jet) when subjected to a high d.c. voltage. The authors previously proposed the first liquid rate gyroscope in the world using ECF. The ECF liquid rate gyroscope proposed uses the drift of the ECF jet due to the Coriolis force when an angular motion is applied. The contribution of the proposed concept to gyroscope technology is that it provides the possibility of a low-cost micro gyroscope with inherent robustness to external impact. To move beyond a mere laboratory curiosity, the present paper describes the practical design of an ECF liquid rate gyroscope and characterizes the prototype. The ECF liquid rate gyroscope developed in this study has a scale factor, range of detection, resolution, and linearity of 32 mV/(degrees/s), +/-400 degrees/s, 0.04 degrees/s, and 2 per cent of full scale (with a range of +/-60 degrees/s), respectively. These results show that the ECF liquid rate gyroscope could possibly become the next generation standard of micro gyroscopes.