Kazuya Edamura

Dielectric fluid motors

On the application of high electric fields to a dielectric fluid, a convective motion of the fluid is induced. By controlling the fluid motion in nonuniform dc fields, a new type of fluid motor is developed. An angular velocity of more than 15 s−1 (150 rpm) can be achieved at a dc voltage of 5 kV for a motor with a rotor radius of 10 mm. The efficiency of energy transformation from electric to kinetic energy is about 4%. Since magnetic fields and switching circuits are not required, the advantage of the fluid motor will be enhanced by size reduction. The dielectric fluid motor is attractive as a source of mechanical energy in a micromachine.

A Micro Artificial Muscle Actuator using Electro-conjugate Fluid

Soft robots inspired from natural systems are one of the main research topics in the robotic field since the last decade. Accordingly, artificial muscles were widely investigated due to their potentials in soft machines or soft robots. Many types of artificial muscles have been developed, including pneumatic actuators, ion-exchange polymer composite actuators, polymer gels, shape memory alloys, and so on. However, these artificial muscles are not used as practical actuators. In this study, the authors propose a new type of micro artificial muscle actuator (< 1 cm3) utilizing an electro-conjugate fluid (ECF) which generates a powerful jet flow when subjected to a high voltage (~ kV). The actuator basically consists of a fiber-reinforced silicone rubber tube and a micro pressure source using the ECF. The inner pressure of the silicone rubber tube is increased by the jet flow generated at the pressure source. The silicone rubber tube contracts along the actuator axis with the increasing pressure. The driving characteristics of the micro artificial muscle actuator were experimentally investigated. The experimental results show that this new actuation technology yields great potentials for driving soft robots.

Electrorheology of dilute suspensions induced by hydrodynamic instability

Abstract The viscosity behavior in electric fields was measured for dilute suspensions of p-[perfluoro(2-isopropyl-1,3-dimethyl-1-butenyl)oxy]benzoic acid particles (PFNA) in silicone oils. The application of electric fields causes a viscosity increase in a wide range of shear rates. Since the electrorheological (ER) effect is much stronger at low shear rates, the flow becomes shear-thinning. However, contrary to conventional ER suspensions which are reversibly converted between Newtonian fluids and Bingham solids, the PFNA suspensions are fluids even in electric fields. When the particle concentration is increased to 5 wt.%, the ER effect reaches saturation. Further increase does not contribute to additional viscosity enhancement. These results cannot be explained through the chain formation mechanism established for conventional systems. After the ER experiments, the bob surface of the rheometer is covered with several stripes of aggregated particles. Although the strength of electric and shear fields is constant in the rheometer, the periodic structure may be formed in the flow of electrified suspensions. When a dielectric liquid is subjected to high electric fields, the secondary motion of liquid can be induced by the Coulomb force acting on free charge. The electrohydrodynamic (EHD) convection is responsible for the periodic distribution of particles concentration. The ER effect of PFNA suspensions may be generated by a combined effect of EHD convection and external shear.

Relation between yield stress and column thickness in electrorheological fluids

Creep and recovery were measured for very dilute suspensions in electric fields using a stress-controlled rheometer. The creep curve comprises instantaneous and retardation regions at low stresses. Although the constant-rate strain due to viscous flow is negligibly small, the strain is not recovered after the removal of stress. The behavior is plastic. When the stress is increased beyond some critical value, the strain increases linearly with time and the responses are characterized as purely viscous. Therefore, the suspension has a static yield stress as a transition point from a solid to a liquid. The yield stress increases exponentially with particle concentration. In electric fields, the particles all align into chains spanning the electrode gap. It can be seen from microscopic observation that the system consists of a collection of thick columns constructed by the aggregates of many primary chains. The strength of an individual column increases rapidly with column thickness due to multichain interactions. The intrinsic mechanism of plastic responses in electrorheological fluids is attributed to the deformation of thick columns.

Electro-Conjugate Fluid Jet-Driven Micro Artificial Antagonistic Muscle Actuators and their Integration

An electro-conjugate fluid (ECF) is a type of dielectric and functional fluid that generates a powerful jet flow when subjected to high DC voltage. Although a high voltage is needed to generate the jet flow, the current is quite low at several microamperes, resulting in a total power consumption of several milliwatts. Using this smart fluid, we can develop micro fluid-driven mechanical components without any bulky pumps. Also, it is clarified that the power density of the ECF jet is higher when the electrode pair is miniaturized; therefore, it is suitable for micro actuators. Here, we propose and fabricate three types of soft actuators with an antagonistic configuration: (i) micro artificial muscle cells, (ii) a McKibben-type micro artificial muscle actuator using the ECF effect and (iii) a micro finger actuator with two chambers to bend. The actuators basically consist of a silicone rubber tube covered with a fiber sleeve and a micro pressure source using the ECF effect. Next, we apply and integrate these actuators into a micro robot hand, driven with ECF jets. The driving characteristics of the micro artificial muscle actuator and the integrated micro ECF hand with ECF fingers were fabricated and experimentally investigated. The experimental results show that this ECF jet actuation is effective for driving soft micro hands.

Magneto-rheological valve-integrated cylinder and its application:

Abstract This paper presents a novel magneto-rheological (MR) valve-integrated cylinder and its use in manipulator operations. Conventional MR valves are flow channels that have magnetic poles and control MR fluid flow by using the apparent viscosity change created by the application of a magnetic field. The proposed MR cylinder consists of an electromagnet-mounted piston with an annular gap, a cylinder made of magnetic material, and an upstream restriction. The MR valve has an electromagnet which controls the differential pressure of a piston and the output force. The MR cylinder features a simple, compact, and low-cost structure, a long stroke, robustness against dispersed particles, a high output force that is sufficient to drive mechanical systems, and easy force control. Furthermore, in this study, to decrease fluid power loss in pipelines, a novel low base viscosity MR fluid is created by the use of low-density ferrite particles. The basic characteristics of an MR cylinder using the new MR fluid are experimentally evaluated utilizing a fabricated MR cylinder mounted onto a manipulator. Based on these results, optimally designed MR cylinders are mounted onto a manipulator and the basic validity of the system is experimentally confirmed.

Concept of a liquid rate gyroscope using an electro-conjugate fluid

We propose a novel liquid rate gyroscope using an electro-conjugate fluid in this study. The electro-conjugate fluid (ECF) is a dielectric fluid that works here as a functional/smart fluid generating a powerful jet flow (ECF jet) when subjected to high DC voltage. Using the ECF jet, we developed a liquid rate gyroscope based on the principle of a conventional gas rate sensor operated by Coriolis force. Because the ECF jet is generated only with a tiny electrode pair, the pumping part of proposed ECF gyroscope needs no mechanically moving parts, resulting in making the ECF gyroscope suitable for micro sensor compared to the gas rate sensor having a pumping mechanism inside. We fabricated a prototype of liquid rate gyroscope (40 mm times 60 mm times t7 mm) and confirmed its characteristics by experiment. The experimental results confirm the effectiveness of the proposed liquid rate gyroscope. The scale factor of -29 mV/(deg/s) is obtained with applied voltage of 4.5 kV.

Practical design of a liquid rate gyroscope using an electro-conjugate fluid

Abstract 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/(°/s), ±400°/s, 0.04°/s, and 2 per cent of full scale (with a range of ±60°/s), respectively. These results show that the ECF liquid rate gyroscope could possibly become the next generation standard of micro gyroscopes.

Rheological Changes of Suspensions Induced by Electrohydrodynamic Instability

A new type of ER suspension is invented with a fluorinated organic compound. The suspensions show a viscosity increase without yield stress on the application of electric fields. The results cannot be explained by the chain formation mechanism. After the ER experiments, the plate surface of rheometer is covered with stripes of aggregated particles. The periodic structure may be formed in the electrified suspensions. When a dielectric liquid is subjected to high electric fields, the secondary motion of liquid can be induced. The electrohydrodynamic convection is responsible for the periodic distribution of particles. The ER effect of the suspensions may be generated by a combined effect of electrohydrodynamic convection and external shear.

ECF Micropump-Integrated Micro Hand by MEMS Technology

On purpose to realize a novel flexible micro-hand for biological and medical applications, this paper presents a major step forward in this direction by directly integrating micropumps into eccentric tube type micro-fingers driven by the ECF (Electro-Conjugate Fluid) jet. ECF is a functional fluid which can generate the strong jet by applying high DC voltage between the electrodes. The ECF eccentric tube type micro-hand (ECF-ETMH) comprises three elastic PDMS micro-fingers with eccentric void and their corresponding MEMS-fabricated ECF micropumps. Because of the geometrical asymmetry created by an eccentric void in a cylindrical elastic body, this micro-finger acts bending motion upon the pressurization of the eccentric void by the ECF jet. Each ECF micropump has 41 pairs of a triangular prism and slit electrodes (TPSEs) that are designed to generate maximum pressures of 300kPa at the applied voltage of 3.5kV. We successfully fabricated eccentric tube type micro-fingers (ETMF) by high aspect ratio micromolding. Although we could not succeed in integrating the ECF micropumps and ETMFs due to the leakage, we experimentally proved the feasibility of this micro-hand system by investigating the characteristics of them separately.Copyright