Kinji Asaka

A new type of fish-like underwater microrobot

This paper presents a new prototype model of an underwater fish-like microrobot utilizing ionic conducting polymer film (ICPF) actuator as the servo actuator to realize swimming motion with three degrees of freedom. A biomimetic fish-like microrobot using ICPF actuator as a propulsion tail fin and a buoyancy adjuster for the swimming structure in water or aqueous medium is developed. The overall size of the underwater prototype fish shaped microrobot is 45 mm in length, 10 mm in width, and 4 mm in thickness. It has two tails with a fin driven respectively, a body posture adjuster, and a buoyancy adjuster. The moving characteristic of the underwater microrobot is measured by changing the frequency of input voltage from 0.1-5 Hz in water and the amplitude of input voltage from 0.5-10 V. The experimental results indicate that changing the amplitude and frequency of input voltage can control the swimming speed of proposed underwater microrobot.

Bending of polyelectrolyte membrane platinum composites by electric stimuli: Part II. Response kinetics

In previous papers, it was reported that a solid polymer electrolyte membrane-platinum (SPM-Pt) composite bent in response to electric stimuli. In this paper, a model, in which electric fields can induce mechanical deformation in the SPM via electrokinetically induced pressure gradients, was applied to the kinetics of the bending response. In order to compare the theoretical model with the experimental result, simultaneous measurement was carried out with the displacement and the electrochemical properties for the composites prepared from membranes of different thickness in various kinds of salt solution. The curvature response was simulated by the empirical equations having one characteristic time. The characteristic time was linearly proportional to the square of the thickness of the membrane. The parameter which means curvature per unit charge was linearly proportional to the reciprocal of the square of the membrane thickness, and the water transference coefficient of the membrane of various ionic forms. The results support the theoretical model. In addition to the electrokinetic effect, the model includes the effect of the interfacial stress between the Pt electrode and the SPM. The bending behavior after the characteristic time can be explained successfully by the model including the interfacial effect.

Sheet-Type Braille Displays by Integrating Organic Field-Effect Transistors and Polymeric Actuators

A large-area, flexible, and lightweight sheet-type Braille display has been successfully fabricated on a plastic film by integrating high-quality organic transistors and soft actuators. An array of rectangular plastic actuators is mechanically processed from a perfluorinated polymer electrolyte membrane. A small semisphere, which projects upward from the rubberlike surface of the display, is attached to the tip of each rectangular actuator. The effective display size is 4times4 cm2. Each Braille letter consists of 3times2 dots and 24 letters; in other words, 6 letters times 4 lines can be displayed. Pentacene field-effect transistors with top-contact geometry have a channel length of 20 mum and a mobility of 1 cm2/Vmiddots. The Braille dots on one line are driven for 0.9 s. The total thickness and weight of the entire device are 1 mm and 5.3 g, respectively. The present scheme will enable people with visual impairments to carry the Braille sheet display in their pockets and read Braille e-books at any time. Since all the device components are manufactured on plastic films, these sheet-type Braille displays are mechanically flexible, lightweight, shock resistant, and potentially inexpensive to manufacture; therefore, they are suitable for mobile electronics

The effects of counter ions on characterization and performance of a solid polymer electrolyte actuator

Abstract A perfluorocarboxylic acid membrane was chemically plated with gold bends under electric stimuli in water. When exchanged with alkali metal ions as counter ions, the displacement is rapid, though charge-specific displacement, or ‘pumping’ efficiency, is small. The fast response is thought to be linked with the small radius of the hydrated ion relative to the hydrophilic channel size in the membrane. In contrast, the charge-specific displacement with alkyl ammonium ions increases, while the rate decreases, systematically with molecular size. The effects are interpreted in terms of an ‘ion-pumping’ model, in which the size of the hydrated ion relative to that of the hydrophilic channel is of paramount importance. A good ‘pumping’ ion inevitably effects only a slow displacement.

Fish-like underwater microrobot with 3 DOF

It is our purpose to develop an underwater microrobot that has the characteristics of flexibility, driven by a low voltage, good response and safety in body. We propose a prototype model of an underwater microrobot utilizing an ICPF (ionic conducting polymer film) actuator as the servo actuator to realize swimming motion with 3 DOF. A biomimetic fish-like microrobot using an ICPF actuator as a propulsion tail fin and a buoyancy adjuster for a microrobot swimming structure in water or aqueous medium has been developed. The overall size of the underwater microrobot prototype shaped as a fish is 45mm in length, 10 mm in width and 4 mm in thickness. There is a pair of fins and a buoyancy adjuster. The characteristics of the underwater microrobot is measured by changing the frequency and amplitude of input voltage. The experimental results indicate that the swimming speed of the proposed underwater micro robot can be controlled by changing the frequency of input voltage; the moving direction (upward or downward) can be controlled by changing the amplitude and the frequency of input voltage.

A snake-like swimming robot using IPMC actuator/sensor

We constructed a snake-like swimming robot using IPMC actuator, and verified swimming motion based on numerical simulation and experiments. In applying periodic inputs with appropriate frequency and phase shift, the snake-like robot is capable of smooth propulsion. It is known that IPMC has a sensor function that IPMC films generate electromotive voltage when bending or being deformed. By using the sensor function into the snake-like robot, it is considered that autonomous propulsive motion can be realized by feedback of the sensor signal. In this paper, we consider the autonomous locomotion of the snakelike swimming robot with IPMC actuator/sensor, and verify the realization of swimming motion by feedback of the sensor signal. Furthermore, the efficiency of the autonomous locomotion is investigated

Effect on bending behavior of counter cation species in perfluorinated sulfonate membrane–platinum composite

The perfluorinated sulfonate membrane (Nafion ®117)–platinum composites having H+, mono- and bivalent metal ions as counter cations in the membranes were prepared and the bending behaviors of the composites actuated by the step voltage were investigated in deionized water. The bending behaviors of all composites have the same tendency as the composites to bend quickly to the anode side just after applying the step voltage and gradually to bend back to the cathode side in spite of keeping on the application. However, they show differences in the bending rate and the maximum displacement to the anode side just after applying the step voltage, which are influenced by counter cation species in the membrane. In particular, the composite having Li+ has the largest maximum displacement (about 1.1 mm) to the anode side. The relationship between the maximum displacements of the composites and water states in the membranes were studied. The maximum displacements of the composites depend on the water content in the membranes. In both series of the composites having mono- and bivalent metal ions, the maximum displacements increase with increasing water content, except the composites having Rb+ and Sr2+ which belong to fifth period in the periodic table. In spite of the result that the water content in the membrane having H+, which is about 20wt%, is nearly equal to that in the membrane having Naa, the maximum displacement of the composite having H+ is only about one-third as large as that of the composite having Na+. The water structures in the membranes were investigated by using differential scanning calorimetry (DSC). The DSC endothermograms obtained indicate that the freezing water in the membrane having H+ has a much stronger interaction with sulfonate groups and counter cations than that in the membrane having Na+. It is concluded that the content and structure of the freezing water in the membrane have a profound effect on the bending behavior of the composite.

State of water and ionic conductivity of solid polymer electrolyte membranes in relation to polymer actuators

This paper studies the state of the water and the ionic conductivity of solid polymer electrolyte membranes (SPM) of various ionic forms relating to polymer actuators. Perfluorinated polymers in both sulfonic and carboxylic forms were studied. From differential scanning calorimetry (DSC) measurements, the freezable water content in the SPM was estimated. From impedance measurements, the membrane conductivity of the SPM was estimated by equivalent circuit analysis. The counter cation in the SPM can be categorized in three groups from the freezable water content and the ionic conductivity of the membrane. Group A includes small hydrophilic cations such as those of the alkali and alkaline earth metals, for which the membrane conductivity increases with an increase in the freezable water content of the membrane. Group B includes hydrophobic cations such as alkyl ammonium ions except tetrapropyl- and tetrabutyl-ammonium ions in the perfluorosulfonic acid membrane. The ionic conductivity depends on the size of the ion and the membrane has a relatively large freezable water content. Group C includes the large hydrophobic cations such as TPrA and TBA in perfluorosulfonic acid membrane, which have a low conductivity and low freezable water content. In the light of these results, the deformation properties of the SPM/metal composites are discussed.

Electrolytes in porous electrodes: Effects of the pore size and the dielectric constant of the medium

Monte Carlo simulations in the constant voltage ensemble were performed for electrolytes in porous electrodes. It was found that the electrical and mechanical properties in porous electrodes dramatically change depending on the pore size and the dielectric constant of the medium. For a low dielectric constant of the medium, the capacitance of porous electrodes tends to increase as the pore size decreases and the pressure in the porous electrodes is positive or negative depending on the pore size. For a high dielectric constant of the medium, on the contrary, the capacitance tends to decrease as the pore size decreases and the pressure is positive for all the conditions studied here. Such pore size dependencies are explained in terms of the balance between the electrostatic interaction and the volume exclusion interaction in the porous electrode.

Development of a Rajiform Swimming Robot using Ionic Polymer Artificial Muscles

Ionic polymer-metal composite (IPMC), which is one of the electro-active polymer actuators, is expected as artificial muscles for robots. An interesting property of IPMC is that it requires water to work, therefore it is suitable for underwater robots. In this paper, we developed an underwater robot which mimics rajiform swimming, that is the swimming form of a ray fish. Fins are designed using sixteen IPMCs. For autonomous operation, miniaturization of the electrical devices such as a micro controllers and small amplifiers are performed. A simple traveling wave control input is employed to generate moment on the fin. In the experiment, propulsion speed is measured under various control parameters. Furthermore, incremental wave of the fin is observed although the amplitude of the control input is spatially uniform. We also discuss this phenomenon from the point of view of interaction between elasticity of the actuator and fluid dynamics